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Faulkner RA, Yang Y, Tsien J, Qin T, DeBose-Boyd RA. Direct binding to sterols accelerates endoplasmic reticulum-associated degradation of HMG CoA reductase. Proc Natl Acad Sci U S A 2024; 121:e2318822121. [PMID: 38319967 PMCID: PMC10873557 DOI: 10.1073/pnas.2318822121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Accepted: 01/09/2024] [Indexed: 02/08/2024] Open
Abstract
The maintenance of cholesterol homeostasis is crucial for normal function at both the cellular and organismal levels. Two integral membrane proteins, 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) and Scap, are key targets of a complex feedback regulatory system that operates to ensure cholesterol homeostasis. HMGCR catalyzes the rate-limiting step in the transformation of the 2-carbon precursor acetate to 27-carbon cholesterol. Scap mediates proteolytic activation of sterol regulatory element-binding protein-2 (SREBP-2), a membrane-bound transcription factor that controls expression of genes involved in the synthesis and uptake of cholesterol. Sterol accumulation triggers binding of HMGCR to endoplasmic reticulum (ER)-localized Insig proteins, leading to the enzyme's ubiquitination and proteasome-mediated ER-associated degradation (ERAD). Sterols also induce binding of Insigs to Scap, which leads to sequestration of Scap and its bound SREBP-2 in the ER, thereby preventing proteolytic activation of SREBP-2 in the Golgi. The oxygenated cholesterol derivative 25-hydroxycholesterol (25HC) and the methylated cholesterol synthesis intermediate 24,25-dihydrolanosterol (DHL) differentially modulate HMGCR and Scap. While both sterols promote binding of HMGCR to Insigs for ubiquitination and subsequent ERAD, only 25HC inhibits the Scap-mediated proteolytic activation of SREBP-2. We showed previously that 1,1-bisphosphonate esters mimic DHL, accelerating ERAD of HMGCR while sparing SREBP-2 activation. Building on these results, our current studies reveal specific, Insig-independent photoaffinity labeling of HMGCR by photoactivatable derivatives of the 1,1-bisphosphonate ester SRP-3042 and 25HC. These findings disclose a direct sterol binding mechanism as the trigger that initiates the HMGCR ERAD pathway, providing valuable insights into the intricate mechanisms that govern cholesterol homeostasis.
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Affiliation(s)
- Rebecca A. Faulkner
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX75390-9046
| | - Yangyan Yang
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX75390-9046
| | - Jet Tsien
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX75390-9046
| | - Tian Qin
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX75390-9046
| | - Russell A. DeBose-Boyd
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX75390-9046
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2
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Zhou X, Wu X, Wang R, Han L, Li H, Zhao W. Mechanisms of 3-Hydroxyl 3-Methylglutaryl CoA Reductase in Alzheimer's Disease. Int J Mol Sci 2023; 25:170. [PMID: 38203341 PMCID: PMC10778631 DOI: 10.3390/ijms25010170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Revised: 12/16/2023] [Accepted: 12/19/2023] [Indexed: 01/12/2024] Open
Abstract
Alzheimer's disease (AD) is the most common neurodegenerative disease worldwide and has a high incidence in the elderly. Unfortunately, there is no effective therapy for AD owing to its complicated pathogenesis. However, the development of lipid-lowering anti-inflammatory drugs has heralded a new era in the treatment of Alzheimer's disease. Several studies in recent years have shown that lipid metabolic dysregulation and neuroinflammation are associated with the pathogenesis of AD. 3-Hydroxyl 3-methylglutaryl CoA reductase (HMGCR) is a rate-limiting enzyme in cholesterol synthesis that plays a key role in cholesterol metabolism. HMGCR inhibitors, known as statins, have changed from being solely lipid-lowering agents to neuroprotective compounds because of their effects on lipid levels and inflammation. In this review, we first summarize the main regulatory mechanism of HMGCR affecting cholesterol biosynthesis. We also discuss the pathogenesis of AD induced by HMGCR, including disordered lipid metabolism, oxidative stress, inflammation, microglial proliferation, and amyloid-β (Aβ) deposition. Subsequently, we explain the possibility of HMGCR as a potential target for AD treatment. Statins-based AD treatment is an ascent field and currently quite controversial; therefore, we also elaborate on the current application prospects and limitations of statins in AD treatment.
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Affiliation(s)
- Xun Zhou
- Science and Technology Innovation Center, Guangzhou University of Chinese Medicine, Guangzhou 510405, China; (X.Z.); (X.W.); (R.W.); (L.H.)
- Department of Endocrinology, The Fourth Clinical Medical College of Guangzhou University of Chinese Medicine, Shenzhen 518033, China;
| | - Xiaolang Wu
- Science and Technology Innovation Center, Guangzhou University of Chinese Medicine, Guangzhou 510405, China; (X.Z.); (X.W.); (R.W.); (L.H.)
| | - Rui Wang
- Science and Technology Innovation Center, Guangzhou University of Chinese Medicine, Guangzhou 510405, China; (X.Z.); (X.W.); (R.W.); (L.H.)
| | - Lu Han
- Science and Technology Innovation Center, Guangzhou University of Chinese Medicine, Guangzhou 510405, China; (X.Z.); (X.W.); (R.W.); (L.H.)
| | - Huilin Li
- Department of Endocrinology, The Fourth Clinical Medical College of Guangzhou University of Chinese Medicine, Shenzhen 518033, China;
| | - Wei Zhao
- Science and Technology Innovation Center, Guangzhou University of Chinese Medicine, Guangzhou 510405, China; (X.Z.); (X.W.); (R.W.); (L.H.)
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3
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Chu S, Xie X, Payan C, Stochaj U. Valosin containing protein (VCP): initiator, modifier, and potential drug target for neurodegenerative diseases. Mol Neurodegener 2023; 18:52. [PMID: 37545006 PMCID: PMC10405438 DOI: 10.1186/s13024-023-00639-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Accepted: 06/27/2023] [Indexed: 08/08/2023] Open
Abstract
The AAA+ ATPase valosin containing protein (VCP) is essential for cell and organ homeostasis, especially in cells of the nervous system. As part of a large network, VCP collaborates with many cofactors to ensure proteostasis under normal, stress, and disease conditions. A large number of mutations have revealed the importance of VCP for human health. In particular, VCP facilitates the dismantling of protein aggregates and the removal of dysfunctional organelles. These are critical events to prevent malfunction of the brain and other parts of the nervous system. In line with this idea, VCP mutants are linked to the onset and progression of neurodegeneration and other diseases. The intricate molecular mechanisms that connect VCP mutations to distinct brain pathologies continue to be uncovered. Emerging evidence supports the model that VCP controls cellular functions on multiple levels and in a cell type specific fashion. Accordingly, VCP mutants derail cellular homeostasis through several mechanisms that can instigate disease. Our review focuses on the association between VCP malfunction and neurodegeneration. We discuss the latest insights in the field, emphasize open questions, and speculate on the potential of VCP as a drug target for some of the most devastating forms of neurodegeneration.
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Affiliation(s)
- Siwei Chu
- Department of Physiology, McGill University, Montreal, HG3 1Y6, Canada
| | - Xinyi Xie
- Department of Physiology, McGill University, Montreal, HG3 1Y6, Canada
| | - Carla Payan
- Department of Physiology, McGill University, Montreal, HG3 1Y6, Canada
| | - Ursula Stochaj
- Department of Physiology, McGill University, Montreal, HG3 1Y6, Canada.
- Quantitative Life Sciences Program, McGill University, Montreal, Canada.
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4
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Wu DG, Wang YN, Zhou Y, Gao H, Zhao B. Inhibition of the Proteasome Regulator PA28 Aggravates Oxidized Protein Overload in the Diabetic Rat Brain. Cell Mol Neurobiol 2023; 43:2857-2869. [PMID: 36715894 DOI: 10.1007/s10571-023-01322-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2022] [Accepted: 01/19/2023] [Indexed: 01/31/2023]
Abstract
Oxidized protein overloading caused by diabetes is one accelerating pathological pathway in diabetic encephalopathy development. To determine whether the PA28-regulated function of the proteasome plays a role in diabetes-induced oxidative damaged protein degradation, brain PA28α and PA28β interference experiments were performed in a high-fat diet (HFD) and streptozotocin (STZ)-induced rat model. The present results showed that proteasome activity was changed in the brains of diabetic rats, but the constitutive subunits were not. In vivo PA28α and PA28β inhibition via adeno-associated virus (AAV) shRNA infection successfully decreased PA28 protein levels and further exacerbated oxidized proteins load by regulating proteasome catalytic activity. These findings suggest that the proteasome plays a role in the elimination of oxidized proteins and that PA28 is functionally involved in the regulation of proteasome activity in vivo. This study suggests that abnormal protein turbulence occurring in the diabetic brain could be explained by the proteasome-mediated degradation pathway. Changes in proteasome activity regulator PA28 could be a reason to induce oxidative aggregation in diabetic brain. Proteasome regulator PA28 inhibition in vivo by AAV vector injection could aggravate oxidized proteins abundance in brain of HFD-STZ diabetic rat model.
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Affiliation(s)
- Dong-Gui Wu
- School of Basic Medicine Sciences, Dali University, 6th Snowman Road, Dali, 671000, Yunnan, People's Republic of China
- Zhuhai People's Hospital, 79th Kangning Road, Zhuhai, 519000, Guangdong, People's Republic of China
| | - Yu-Na Wang
- School of Basic Medicine Sciences, Dali University, 6th Snowman Road, Dali, 671000, Yunnan, People's Republic of China
| | - Ye Zhou
- School of Basic Medicine Sciences, Dali University, 6th Snowman Road, Dali, 671000, Yunnan, People's Republic of China
| | - Han Gao
- School of Basic Medicine Sciences, Dali University, 6th Snowman Road, Dali, 671000, Yunnan, People's Republic of China
| | - Bei Zhao
- School of Basic Medicine Sciences, Dali University, 6th Snowman Road, Dali, 671000, Yunnan, People's Republic of China.
- Li Yun-Qing Expert Workstation of Yunnan Province (No. 202005AF150014) based in Dali University, 6th Snowman Road, Dali, 671000, Yunnan, People's Republic of China.
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5
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Morimoto S, Takahashi S, Ito D, Daté Y, Okada K, Kato C, Nakamura S, Ozawa F, Chyi CM, Nishiyama A, Suzuki N, Fujimori K, Kondo T, Takao M, Hirai M, Kabe Y, Suematsu M, Jinzaki M, Aoki M, Fujiki Y, Sato Y, Suzuki N, Nakahara J, Okano H. Phase 1/2a clinical trial in ALS with ropinirole, a drug candidate identified by iPSC drug discovery. Cell Stem Cell 2023; 30:766-780.e9. [PMID: 37267913 DOI: 10.1016/j.stem.2023.04.017] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2022] [Revised: 01/12/2023] [Accepted: 04/24/2023] [Indexed: 06/04/2023]
Abstract
iPSC-based drug discovery led to a phase 1/2a trial of ropinirole in ALS. 20 participants with sporadic ALS received ropinirole or placebo for 24 weeks in the double-blind period to evaluate safety, tolerability, and therapeutic effects. Adverse events were similar in both groups. During the double-blind period, muscle strength and daily activity were maintained, but a decline in the ALSFRS-R, which assesses the functional status of ALS patients, was not different from that in the placebo group. However, in the open-label extension period, the ropinirole group showed significant suppression of ALSFRS-R decline and an additional 27.9 weeks of disease-progression-free survival. iPSC-derived motor neurons from participants showed dopamine D2 receptor expression and a potential involvement of the SREBP2-cholesterol pathway in therapeutic effects. Lipid peroxide represents a clinical surrogate marker to assess disease progression and drug efficacy. Limitations include small sample sizes and high attrition rates in the open-label extension period, requiring further validation.
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Affiliation(s)
- Satoru Morimoto
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan; Department of Neurology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Shinichi Takahashi
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan; Department of Neurology, Keio University School of Medicine, Tokyo 160-8582, Japan; Department of Neurology and Stroke, Saitama Medical University International Medical Center, Saitama 350-1298, Japan
| | - Daisuke Ito
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan; Department of Neurology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Yugaku Daté
- Department of Neurology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Kensuke Okada
- Department of Neurology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Chris Kato
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Shiho Nakamura
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Fumiko Ozawa
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Chai Muh Chyi
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan; Keio University Global Research Institute, Tokyo 108-8345, Japan
| | - Ayumi Nishiyama
- Department of Neurology, Tohoku University Graduate School of Medicine, Sendai, Miyagi 980-8575, Japan
| | - Naoki Suzuki
- Department of Neurology, Tohoku University Graduate School of Medicine, Sendai, Miyagi 980-8575, Japan
| | - Koki Fujimori
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Tosho Kondo
- Research Center of Neurology, ONO Pharmaceutical Co., Ltd., Osaka 541-8564, Japan
| | - Masaki Takao
- Department of Clinical Laboratory, National Center of Neurology and Psychiatry (NCNP), Tokyo 187-0031, Japan; Department of Neurology, Mihara Memorial Hospital, Isesaki, Gunmma 372-0006, Japan
| | - Miwa Hirai
- Department of Biochemistry, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Yasuaki Kabe
- Department of Biochemistry, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Makoto Suematsu
- Department of Biochemistry, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Masahiro Jinzaki
- Department of Radiology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Masashi Aoki
- Department of Neurology, Tohoku University Graduate School of Medicine, Sendai, Miyagi 980-8575, Japan
| | - Yuto Fujiki
- Keio University Hospital Clinical and Translational Research Center, Tokyo 160-8582, Japan
| | - Yasunori Sato
- Department of Preventive Medicine and Public Health, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Norihiro Suzuki
- Department of Neurology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Jin Nakahara
- Department of Neurology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Hideyuki Okano
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan.
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6
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Kilgas S, Ramadan K. Inhibitors of the ATPase p97/VCP: From basic research to clinical applications. Cell Chem Biol 2023; 30:3-21. [PMID: 36640759 DOI: 10.1016/j.chembiol.2022.12.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2022] [Revised: 11/13/2022] [Accepted: 12/21/2022] [Indexed: 01/15/2023]
Abstract
Protein homeostasis deficiencies underlie various cancers and neurodegenerative diseases. The ubiquitin-proteasome system (UPS) and autophagy are responsible for most of the protein degradation in mammalian cells and, therefore, represent attractive targets for cancer therapy and that of neurodegenerative diseases. The ATPase p97, also known as VCP, is a central component of the UPS that extracts and disassembles its substrates from various cellular locations and also regulates different steps in autophagy. Several UPS- and autophagy-targeting drugs are in clinical trials. In this review, we focus on the development of various p97 inhibitors, including the ATPase inhibitors CB-5083 and CB-5339, which reached clinical trials by demonstrating effective anti-tumor activity across various tumor models, providing an effective alternative to targeting protein degradation for cancer therapy. Here, we provide an overview of how different p97 inhibitors have evolved over time both as basic research tools and effective UPS-targeting cancer therapies in the clinic.
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Affiliation(s)
- Susan Kilgas
- Medical Research Council Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK.
| | - Kristijan Ramadan
- Medical Research Council Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK.
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7
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Hartmann H, Ho WY, Chang JC, Ling SC. Cholesterol dyshomeostasis in amyotrophic lateral sclerosis: cause, consequence, or epiphenomenon? FEBS J 2022; 289:7688-7709. [PMID: 34469619 DOI: 10.1111/febs.16175] [Citation(s) in RCA: 25] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Revised: 08/10/2021] [Accepted: 08/31/2021] [Indexed: 01/14/2023]
Abstract
Amyotrophic lateral sclerosis (ALS), the most common adult-onset motor neuron disease, is characterized by the selective degeneration of motor neurons leading to paralysis and eventual death. Multiple pathogenic mechanisms, including systemic dysmetabolism, have been proposed to contribute to ALS. Among them, dyslipidemia, i.e., abnormal level of cholesterol and other lipids in the circulation and central nervous system (CNS), has been reported in ALS patients, but without a consensus. Cholesterol is a constituent of cellular membranes and a precursor of steroid hormones, oxysterols, and bile acids. Consequently, optimal cholesterol levels are essential for health. Due to the blood-brain barrier (BBB), cholesterol cannot move between the CNS and the rest of the body. As such, cholesterol metabolism in the CNS is proposed to operate autonomously. Despite its importance, it remains elusive how cholesterol dyshomeostasis may contribute to ALS. In this review, we aim to describe the current state of cholesterol metabolism research in ALS, identify unresolved issues, and provide potential directions.
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Affiliation(s)
- Hannelore Hartmann
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Wan Yun Ho
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Jer-Cherng Chang
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Shuo-Chien Ling
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.,Healthy Longevity Translational Research Programme, National University Health System, Singapore, Singapore.,Program in Neuroscience and Behavior Disorders, Duke-NUS Medical School, Singapore, Singapore
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8
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Chen H, Qi X, Faulkner RA, Schumacher MM, Donnelly LM, DeBose-Boyd RA, Li X. Regulated degradation of HMG CoA reductase requires conformational changes in sterol-sensing domain. Nat Commun 2022; 13:4273. [PMID: 35879350 PMCID: PMC9314443 DOI: 10.1038/s41467-022-32025-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2022] [Accepted: 07/12/2022] [Indexed: 01/20/2023] Open
Abstract
3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) is the rate-limiting enzyme in cholesterol synthesis and target of cholesterol-lowering statin drugs. Accumulation of sterols in endoplasmic reticulum (ER) membranes accelerates degradation of HMGCR, slowing the synthesis of cholesterol. Degradation of HMGCR is inhibited by its binding to UBIAD1 (UbiA prenyltransferase domain-containing protein-1). This inhibition contributes to statin-induced accumulation of HMGCR, which limits their cholesterol-lowering effects. Here, we report cryo-electron microscopy structures of the HMGCR-UBIAD1 complex, which is maintained by interactions between transmembrane helix (TM) 7 of HMGCR and TMs 2-4 of UBIAD1. Disrupting this interface by mutagenesis prevents complex formation, enhancing HMGCR degradation. TMs 2-6 of HMGCR contain a 170-amino acid sterol sensing domain (SSD), which exists in two conformations-one of which is essential for degradation. Thus, our data supports a model that rearrangement of the TMs in the SSD permits recruitment of proteins that initate HMGCR degradation, a key reaction in the regulatory system that governs cholesterol synthesis.
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Affiliation(s)
- Hongwen Chen
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Xiaofeng Qi
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Rebecca A Faulkner
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Marc M Schumacher
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Linda M Donnelly
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Russell A DeBose-Boyd
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
| | - Xiaochun Li
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
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9
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Elsabrouty R, Jo Y, Hwang S, Jun DJ, DeBose-Boyd RA. Type 1 polyisoprenoid diphosphate phosphatase modulates geranylgeranyl-mediated control of HMG CoA reductase and UBIAD1. eLife 2021; 10:64688. [PMID: 34842525 PMCID: PMC8641950 DOI: 10.7554/elife.64688] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2020] [Accepted: 11/28/2021] [Indexed: 11/18/2022] Open
Abstract
UbiA prenyltransferase domain-containing protein-1 (UBIAD1) utilizes geranylgeranyl pyrophosphate (GGpp) to synthesize the vitamin K2 subtype menaquinone-4. The prenyltransferase has emerged as a key regulator of sterol-accelerated, endoplasmic reticulum (ER)-associated degradation (ERAD) of HMG CoA reductase, the rate-limiting enzyme in synthesis of cholesterol and nonsterol isoprenoids including GGpp. Sterols induce binding of UBIAD1 to reductase, inhibiting its ERAD. Geranylgeraniol (GGOH), the alcohol derivative of GGpp, disrupts this binding and thereby stimulates ERAD of reductase and translocation of UBIAD1 to Golgi. We now show that overexpression of Type 1 polyisoprenoid diphosphate phosphatase (PDP1), which dephosphorylates GGpp and other isoprenyl pyrophosphates to corresponding isoprenols, abolishes protein geranylgeranylation as well as GGOH-induced ERAD of reductase and Golgi transport of UBIAD1. Conversely, these reactions are enhanced in the absence of PDP1. Our findings indicate PDP1-mediated hydrolysis of GGpp significantly contributes to a feedback mechanism that maintains optimal intracellular levels of the nonsterol isoprenoid.
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Affiliation(s)
- Rania Elsabrouty
- Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, United States
| | - Youngah Jo
- Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, United States
| | - Seonghwan Hwang
- Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, United States
| | - Dong-Jae Jun
- Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, United States
| | - Russell A DeBose-Boyd
- Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, United States
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10
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Schumacher MM, DeBose-Boyd RA. Posttranslational Regulation of HMG CoA Reductase, the Rate-Limiting Enzyme in Synthesis of Cholesterol. Annu Rev Biochem 2021; 90:659-679. [PMID: 34153214 DOI: 10.1146/annurev-biochem-081820-101010] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The polytopic, endoplasmic reticulum (ER) membrane protein 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase produces mevalonate, the key intermediate in the synthesis of cholesterol and many nonsterol isoprenoids including geranylgeranyl pyrophosphate (GGpp). Transcriptional, translational, and posttranslational feedback mechanisms converge on this reductase to ensure cells maintain a sufficient supply of essential nonsterol isoprenoids but avoid overaccumulation of cholesterol and other sterols. The focus of this review is mechanisms for the posttranslational regulation of HMG CoA reductase, which include sterol-accelerated ubiquitination and ER-associated degradation (ERAD) that is augmented by GGpp. We discuss how GGpp-induced ER-to-Golgi trafficking of the vitamin K2 synthetic enzyme UbiA prenyltransferase domain-containing protein-1 (UBIAD1) modulates HMG CoA reductase ERAD to balance the synthesis of sterol and nonsterol isoprenoids. We also summarize the characterization of genetically manipulated mice, which established that sterol-accelerated, UBIAD1-modulated ERAD plays a major role in regulation of HMG CoA reductase and cholesterol metabolism in vivo.
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Affiliation(s)
- Marc M Schumacher
- Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA;
| | - Russell A DeBose-Boyd
- Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA;
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11
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Li H, Yu XH, Ou X, Ouyang XP, Tang CK. Hepatic cholesterol transport and its role in non-alcoholic fatty liver disease and atherosclerosis. Prog Lipid Res 2021; 83:101109. [PMID: 34097928 DOI: 10.1016/j.plipres.2021.101109] [Citation(s) in RCA: 74] [Impact Index Per Article: 24.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 05/31/2021] [Accepted: 06/02/2021] [Indexed: 12/12/2022]
Abstract
Non-alcoholic fatty liver disease (NAFLD) is a quickly emerging global health problem representing the most common chronic liver disease in the world. Atherosclerotic cardiovascular disease represents the leading cause of mortality in NAFLD patients. Cholesterol metabolism has a crucial role in the pathogenesis of both NAFLD and atherosclerosis. The liver is the major organ for cholesterol metabolism. Abnormal hepatic cholesterol metabolism not only leads to NAFLD but also drives the development of atherosclerotic dyslipidemia. The cholesterol level in hepatocytes reflects the dynamic balance between endogenous synthesis, uptake, esterification, and export, a process in which cholesterol is converted to neutral cholesteryl esters either for storage in cytosolic lipid droplets or for secretion as a major constituent of plasma lipoproteins, including very-low-density lipoproteins, chylomicrons, high-density lipoproteins, and low-density lipoproteins. In this review, we describe decades of research aimed at identifying key molecules and cellular players involved in each main aspect of hepatic cholesterol metabolism. Furthermore, we summarize the recent advances regarding the biological processes of hepatic cholesterol transport and its role in NAFLD and atherosclerosis.
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Affiliation(s)
- Heng Li
- Institute of Cardiovascular Disease, Key Laboratory for Arteriosclerology of Hunan Province, Hunan International Scientific and Technological Cooperation Base of Arteriosclerotic Disease, Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, Hengyang Medical College, University of South China, Hengyang, Hunan 421001, China
| | - Xiao-Hua Yu
- Institute of Clinical Medicine, The Second Affiliated Hospital of Hainan Medical University, Haikou, Hainan 460106, China
| | - Xiang Ou
- Department of Endocrinology, the First Hospital of Changsha, Changsha, Hunan 410005, China
| | - Xin-Ping Ouyang
- Department of Physiology, Institute of Neuroscience Research, Hengyang Key Laboratory of Neurodegeneration and Cognitive Impairment, Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, Hengyang Medical College, University of South China, Hengyang, Hunan 421001, China.
| | - Chao-Ke Tang
- Institute of Cardiovascular Disease, Key Laboratory for Arteriosclerology of Hunan Province, Hunan International Scientific and Technological Cooperation Base of Arteriosclerotic Disease, Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, Hengyang Medical College, University of South China, Hengyang, Hunan 421001, China.
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12
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Coates HW, Capell-Hattam IM, Brown AJ. The mammalian cholesterol synthesis enzyme squalene monooxygenase is proteasomally truncated to a constitutively active form. J Biol Chem 2021; 296:100731. [PMID: 33933449 PMCID: PMC8166775 DOI: 10.1016/j.jbc.2021.100731] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Revised: 04/24/2021] [Accepted: 04/28/2021] [Indexed: 02/06/2023] Open
Abstract
Squalene monooxygenase (SM, also known as squalene epoxidase) is a rate-limiting enzyme of cholesterol synthesis that converts squalene to monooxidosqualene and is oncogenic in numerous cancer types. SM is subject to feedback regulation via cholesterol-induced proteasomal degradation, which depends on its lipid-sensing N-terminal regulatory domain. We previously identified an endogenous truncated form of SM with a similar abundance to full-length SM, but whether this truncated form is functional or subject to the same regulatory mechanisms as full-length SM is not known. Here, we show that truncated SM differs from full-length SM in two major ways: it is cholesterol resistant and adopts a peripheral rather than integral association with the endoplasmic reticulum membrane. However, truncated SM retains full SM activity and is therefore constitutively active. Truncation of SM occurs during its endoplasmic reticulum–associated degradation and requires the proteasome, which partially degrades the SM N-terminus and disrupts cholesterol-sensing elements within the regulatory domain. Furthermore, truncation relies on a ubiquitin signal that is distinct from that required for cholesterol-induced degradation. Using mutagenesis, we demonstrate that partial proteasomal degradation of SM depends on both an intrinsically disordered region near the truncation site and the stability of the adjacent catalytic domain, which escapes degradation. These findings uncover an additional layer of complexity in the post-translational regulation of cholesterol synthesis and establish SM as the first eukaryotic enzyme found to undergo proteasomal truncation.
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Affiliation(s)
- Hudson W Coates
- School of Biotechnology and Biomolecular Sciences, UNSW Sydney, Sydney, NSW, Australia
| | | | - Andrew J Brown
- School of Biotechnology and Biomolecular Sciences, UNSW Sydney, Sydney, NSW, Australia.
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13
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Sharpe LJ, Coates HW, Brown AJ. Post-translational control of the long and winding road to cholesterol. J Biol Chem 2021; 295:17549-17559. [PMID: 33453997 DOI: 10.1074/jbc.rev120.010723] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 10/12/2020] [Indexed: 01/19/2023] Open
Abstract
The synthesis of cholesterol requires more than 20 enzymes, many of which are intricately regulated. Post-translational control of these enzymes provides a rapid means for modifying flux through the pathway. So far, several enzymes have been shown to be rapidly degraded through the ubiquitin-proteasome pathway in response to cholesterol and other sterol intermediates. Additionally, several enzymes have their activity altered through phosphorylation mechanisms. Most work has focused on the two rate-limiting enzymes: 3-hydroxy-3-methylglutaryl CoA reductase and squalene monooxygenase. Here, we review current literature in the area to define some common themes in the regulation of the entire cholesterol synthesis pathway. We highlight the rich variety of inputs controlling each enzyme, discuss the interplay that exists between regulatory mechanisms, and summarize findings that reveal an intricately coordinated network of regulation along the cholesterol synthesis pathway. We provide a roadmap for future research into the post-translational control of cholesterol synthesis, and no doubt the road ahead will reveal further twists and turns for this fascinating pathway crucial for human health and disease.
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Affiliation(s)
- Laura J Sharpe
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | - Hudson W Coates
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | - Andrew J Brown
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, New South Wales, Australia.
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14
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Dodge JC, Yu J, Sardi SP, Shihabuddin LS. Sterol auto-oxidation adversely affects human motor neuron viability and is a neuropathological feature of amyotrophic lateral sclerosis. Sci Rep 2021; 11:803. [PMID: 33436868 PMCID: PMC7804278 DOI: 10.1038/s41598-020-80378-y] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Accepted: 12/16/2020] [Indexed: 12/12/2022] Open
Abstract
Aberrant cholesterol homeostasis is implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS), a fatal neuromuscular disease that is due to motor neuron (MN) death. Cellular toxicity from excess cholesterol is averted when it is enzymatically oxidized to oxysterols and bile acids (BAs) to promote its removal. In contrast, the auto oxidation of excess cholesterol is often detrimental to cellular survival. Although oxidized metabolites of cholesterol are altered in the blood and CSF of ALS patients, it is unknown if increased cholesterol oxidation occurs in the SC during ALS, and if exposure to oxidized cholesterol metabolites affects human MN viability. Here, we show that in the SOD1G93A mouse model of ALS that several oxysterols, BAs and auto oxidized sterols are increased in the lumbar SC, plasma, and feces during disease. Similar changes in cholesterol oxidation were found in the cervical SC of sporadic ALS patients. Notably, auto-oxidized sterols, but not oxysterols and BAs, were toxic to iPSC derived human MNs. Thus, increased cholesterol oxidation is a manifestation of ALS and non-regulated sterol oxidation likely contributes to MN death. Developing therapeutic approaches to restore cholesterol homeostasis in the SC may lead to a treatment for ALS.
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Affiliation(s)
- James C Dodge
- Rare and Neurological Diseases Therapeutic Area, Sanofi R+D, 49 New York Avenue, Framingham, MA, 01701, USA.
| | - Jinlong Yu
- Rare and Neurological Diseases Therapeutic Area, Sanofi R+D, 49 New York Avenue, Framingham, MA, 01701, USA
| | - S Pablo Sardi
- Rare and Neurological Diseases Therapeutic Area, Sanofi R+D, 49 New York Avenue, Framingham, MA, 01701, USA
| | - Lamya S Shihabuddin
- Rare and Neurological Diseases Therapeutic Area, Sanofi R+D, 49 New York Avenue, Framingham, MA, 01701, USA
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15
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Neutral Lipid Cacostasis Contributes to Disease Pathogenesis in Amyotrophic Lateral Sclerosis. J Neurosci 2020; 40:9137-9147. [PMID: 33051352 DOI: 10.1523/jneurosci.1388-20.2020] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Revised: 07/31/2020] [Accepted: 08/28/2020] [Indexed: 12/14/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a fatal neuromuscular disease characterized by motor neuron (MN) death. Lipid dysregulation manifests during disease; however, it is unclear whether lipid homeostasis is adversely affected in the in the spinal cord gray matter (GM), and if so, whether it is because of an aberrant increase in lipid synthesis. Moreover, it is unknown whether lipid dysregulation contributes to MN death. Here, we show that cholesterol ester (CE) and triacylglycerol levels are elevated several-fold in the spinal cord GM of male sporadic ALS patients. Interestingly, HMG-CoA reductase, the rate-limiting enzyme in cholesterol synthesis, was reduced in the spinal cord GM of ALS patients. Increased cytosolic phospholipase A2 activity and lyso-phosphatidylcholine (Lyso-PC) levels in ALS patients suggest that CE accumulation was driven by acyl group transfer from PC to cholesterol. Notably, Lyso-PC, a byproduct of CE synthesis, was toxic to human MNs in vitro Elevations in CE, triacylglycerol, and Lyso-PC were also found in the spinal cord of SOD1G93A mice, a model of ALS. Similar to ALS patients, a compensatory downregulation of cholesterol synthesis occurred in the spinal cord of SOD1G93A mice; levels of sterol regulatory element binding protein 2, a transcriptional regulator of cholesterol synthesis, progressively declined. Remarkably, overexpressing sterol regulatory element binding protein 2 in the spinal cord of normal mice to model CE accumulation led to ALS-like lipid pathology, MN death, astrogliosis, paralysis, and reduced survival. Thus, spinal cord lipid dysregulation in ALS likely contributes to neurodegeneration and developing therapies to restore lipid homeostasis may lead to a treatment for ALS.SIGNIFICANCE STATEMENT Neurons that control muscular function progressively degenerate in patients with amyotrophic lateral sclerosis (ALS). Lipid dysregulation is a feature of ALS; however, it is unclear whether disrupted lipid homeostasis (i.e., lipid cacostasis) occurs proximal to degenerating neurons in the spinal cord, what causes it, and whether it contributes to neurodegeneration. Here we show that lipid cacostasis occurs in the spinal cord gray matter of ALS patients. Lipid accumulation was not associated with an aberrant increase in synthesis or reduced hydrolysis, as enzymatic and transcriptional regulators of lipid synthesis were downregulated during disease. Last, we demonstrated that genetic induction of lipid cacostasis in the CNS of normal mice was associated with ALS-like lipid pathology, astrogliosis, neurodegeneration, and clinical features of ALS.
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16
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Li MX, Yang Y, Zhao Q, Wu Y, Song L, Yang H, He M, Gao H, Song BL, Luo J, Rao Y. Degradation versus Inhibition: Development of Proteolysis-Targeting Chimeras for Overcoming Statin-Induced Compensatory Upregulation of 3-Hydroxy-3-methylglutaryl Coenzyme A Reductase. J Med Chem 2020; 63:4908-4928. [DOI: 10.1021/acs.jmedchem.0c00339] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Mei-Xin Li
- Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Wuhan University, Wuhan 430072, P.R. China
| | - Yiqing Yang
- MOE Key Laboratory of Protein Sciences, School of Pharmaceutical Sciences, MOE Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Tsinghua University, Beijing 100084, P.R. China
| | - Qiuye Zhao
- MOE Key Laboratory of Protein Sciences, School of Pharmaceutical Sciences, MOE Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Tsinghua University, Beijing 100084, P.R. China
| | - Yue Wu
- MOE Key Laboratory of Protein Sciences, School of Pharmaceutical Sciences, MOE Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Tsinghua University, Beijing 100084, P.R. China
| | - Lei Song
- State Key Laboratory of Proteomics, Beijing Proteome Research Center, National Center for Protein Sciences PHOENIX Center, Beijing Institute of LifeOmics, Beijing 102206, P.R. China
| | - Haiyan Yang
- School of Life Sciences, Tsinghua University, Beijing 100084, P.R. China
| | - Ming He
- MOE Key Laboratory of Protein Sciences, School of Pharmaceutical Sciences, MOE Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Tsinghua University, Beijing 100084, P.R. China
| | - Hongying Gao
- MOE Key Laboratory of Protein Sciences, School of Pharmaceutical Sciences, MOE Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Tsinghua University, Beijing 100084, P.R. China
| | - Bao-Liang Song
- Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Wuhan University, Wuhan 430072, P.R. China
| | - Jie Luo
- Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Wuhan University, Wuhan 430072, P.R. China
| | - Yu Rao
- MOE Key Laboratory of Protein Sciences, School of Pharmaceutical Sciences, MOE Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Tsinghua University, Beijing 100084, P.R. China
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17
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Jun DJ, Schumacher MM, Hwang S, Kinch LN, Grishin NV, DeBose-Boyd RA. Schnyder corneal dystrophy-associated UBIAD1 is defective in MK-4 synthesis and resists autophagy-mediated degradation. J Lipid Res 2020; 61:746-757. [PMID: 32188638 DOI: 10.1194/jlr.ra119000551] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 02/21/2020] [Indexed: 12/15/2022] Open
Abstract
The autosomal dominant disorder Schnyder corneal dystrophy (SCD) is caused by mutations in UbiA prenyltransferase domain-containing protein-1 (UBIAD1), which uses geranylgeranyl pyrophosphate (GGpp) to synthesize the vitamin K2 subtype menaquinone-4 (MK-4). SCD is characterized by opacification of the cornea, owing to aberrant build-up of cholesterol in the tissue. We previously discovered that sterols stimulate association of UBIAD1 with ER-localized HMG-CoA reductase, which catalyzes a rate-limiting step in the synthesis of cholesterol and nonsterol isoprenoids, including GGpp. Binding to UBIAD1 inhibits sterol-accelerated ER-associated degradation (ERAD) of reductase and permits continued synthesis of GGpp in cholesterol-replete cells. GGpp disrupts UBIAD1-reductase binding and thereby allows for maximal ERAD of reductase as well as ER-to-Golgi translocation of UBIAD1. SCD-associated UBIAD1 is refractory to GGpp-mediated dissociation from reductase and remains sequestered in the ER to inhibit ERAD. Here, we report development of a biochemical assay for UBIAD1-mediated synthesis of MK-4 in isolated membranes and intact cells. Using this assay, we compared enzymatic activity of WT UBIAD1 with that of SCD-associated variants. Our studies revealed that SCD-associated UBIAD1 exhibited reduced MK-4 synthetic activity, which may result from its reduced affinity for GGpp. Sequestration in the ER protects SCD-associated UBIAD1 from autophagy and allows intracellular accumulation of the mutant protein, which amplifies the inhibitory effect on reductase ERAD. These findings have important implications not only for the understanding of SCD etiology but also for the efficacy of cholesterol-lowering statin therapy, which becomes limited, in part, because of UBIAD1-mediated inhibition of reductase ERAD.
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Affiliation(s)
- Dong-Jae Jun
- Departments of Molecular Genetics,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Marc M Schumacher
- Departments of Molecular Genetics,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Seonghwan Hwang
- Departments of Molecular Genetics,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Lisa N Kinch
- Biophysics,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Nick V Grishin
- Biophysics,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046; Howard Hughes Medical Institute,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Russell A DeBose-Boyd
- Departments of Molecular Genetics,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046. mailto:
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18
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Jo Y, Kim SS, Garland K, Fuentes I, DiCarlo LM, Ellis JL, Fu X, Booth SL, Evers BM, DeBose-Boyd RA. Enhanced ER-associated degradation of HMG CoA reductase causes embryonic lethality associated with Ubiad1 deficiency. eLife 2020; 9:54841. [PMID: 32118581 PMCID: PMC7069719 DOI: 10.7554/elife.54841] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Accepted: 03/02/2020] [Indexed: 12/15/2022] Open
Abstract
UbiA prenyltransferase domain-containing protein-1 (UBIAD1) synthesizes the vitamin K subtype menaquinone-4 (MK-4). Previous studies in cultured cells (Schumacher et al., 2015) revealed that UBIAD1 also inhibits endoplasmic reticulum (ER)-associated degradation (ERAD) of ubiquitinated HMG CoA reductase (HMGCR), the rate-limiting enzyme of the mevalonate pathway that produces cholesterol and essential nonsterol isoprenoids. Gene knockout studies were previously attempted to explore the function of UBIAD1 in mice; however, homozygous germ-line elimination of the Ubiad1 gene caused embryonic lethality. We now report that homozygous deletion of Ubiad1 is produced in knockin mice expressing ubiquitination/ERAD-resistant HMGCR. Thus, embryonic lethality of Ubiad1 deficiency results from depletion of mevalonate-derived products owing to enhanced ERAD of HMGCR rather than from reduced synthesis of MK-4. These findings provide genetic evidence for the significance of UBIAD1 in regulation of cholesterol synthesis and offer the opportunity in future studies for the discovery of new physiological roles of MK-4.
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Affiliation(s)
- Youngah Jo
- Department of Molecular Genetics, University of Texas Southwestern Medical, Dallas, United States
| | - Steven S Kim
- Department of Molecular Genetics, University of Texas Southwestern Medical, Dallas, United States
| | - Kristina Garland
- Department of Molecular Genetics, University of Texas Southwestern Medical, Dallas, United States
| | - Iris Fuentes
- Department of Molecular Genetics, University of Texas Southwestern Medical, Dallas, United States
| | - Lisa M DiCarlo
- Department of Molecular Genetics, University of Texas Southwestern Medical, Dallas, United States
| | - Jessie L Ellis
- Center at Dallas and Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Somerville, United States
| | - Xueyan Fu
- Center at Dallas and Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Somerville, United States
| | - Sarah L Booth
- Center at Dallas and Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Somerville, United States
| | - Bret M Evers
- Department of Pathology, University of Texas Southwestern Medical, Dallas, United States
| | - Russell A DeBose-Boyd
- Department of Molecular Genetics, University of Texas Southwestern Medical, Dallas, United States
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19
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Kwon D, Kim SM, Correia MA. Cytochrome P450 endoplasmic reticulum-associated degradation (ERAD): therapeutic and pathophysiological implications. Acta Pharm Sin B 2020; 10:42-60. [PMID: 31993306 PMCID: PMC6976991 DOI: 10.1016/j.apsb.2019.11.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 10/30/2019] [Accepted: 10/31/2019] [Indexed: 02/07/2023] Open
Abstract
The hepatic endoplasmic reticulum (ER)-anchored cytochromes P450 (P450s) are mixed-function oxidases engaged in the biotransformation of physiologically relevant endobiotics as well as of myriad xenobiotics of therapeutic and environmental relevance. P450 ER-content and hence function is regulated by their coordinated hemoprotein syntheses and proteolytic turnover. Such P450 proteolytic turnover occurs through a process known as ER-associated degradation (ERAD) that involves ubiquitin-dependent proteasomal degradation (UPD) and/or autophagic-lysosomal degradation (ALD). Herein, on the basis of available literature reports and our own recent findings of in vitro as well as in vivo experimental studies, we discuss the therapeutic and pathophysiological implications of altered P450 ERAD and its plausible clinical relevance. We specifically (i) describe the P450 ERAD-machinery and how it may be repurposed for the generation of antigenic P450 peptides involved in P450 autoantibody pathogenesis in drug-induced acute hypersensitivity reactions and liver injury, or viral hepatitis; (ii) discuss the relevance of accelerated or disrupted P450-ERAD to the pharmacological and/or toxicological effects of clinically relevant P450 drug substrates; and (iii) detail the pathophysiological consequences of disrupted P450 ERAD, contributing to non-alcoholic fatty liver disease (NAFLD)/non-alcoholic steatohepatitis (NASH) under certain synergistic cellular conditions.
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Key Words
- 3MA, 3-methyladenine
- AAA, ATPases associated with various cellular activities
- ACC1, acetyl-CoA carboxylase 1
- ACC2, acetyl-CoA carboxylase 2
- ACHE, acetylcholinesterase
- ACOX1, acyl-CoA oxidase 1
- ALD, autophagic-lysosomal degradation
- AMPK1
- AP-1, activator protein 1
- ASK1, apoptosis signal-regulating kinase
- ATF2, activating transcription factor 2
- AdipoR1, gene of adiponectin receptor 1
- Atg14, autophagy-related 14
- CBZ, carbamazepine
- CHIP E3 ubiquitin ligase
- CHIP, carboxy-terminus of Hsc70-interacting protein
- Cytochromes P450
- Endoplasmic reticulum-associated degradation
- FOXO, forkhead box O
- Fas, fatty acid synthase
- GAPDH, glyceraldehyde 3-phosphate dehydrogenase
- INH, isoniazid
- IRS1, insulin receptor substrate 1
- Il-1β, interleukin 1 β
- Il-6, interleukin 6
- Insig1, insulin-induced gene 1
- JNK1
- Lpl, lipoprotein lipase
- Mcp1, chemokine (C–C motif) ligand 1
- Non-alcoholic fatty liver disease
- Non-alcoholic steatohepatitis
- Pgc1, peroxisome proliferator-activated receptor coactivator 1
- SREBP1c, sterol regulatory element binding transcription factor 1c
- Scd1, stearoyl-coenzyme A desaturase
- Tnf, tumor necrosis factor
- UPD, ubiquitin (Ub)-dependent proteasomal degradation
- Ub, ubiquitin
- gp78/AMFR E3 ubiquitin ligase
- gp78/AMFR, autocrine motility factor receptor
- shRNAi, shRNA interference
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Abstract
Endoplasmic reticulum-associated degradation (ERAD) is an essential process that removes misfolded proteins from the ER, preventing cellular dysfunction and disease. While most of the key components of ERAD are known, their specific localization remains a mystery. This study uses in situ cryo-electron tomography to directly visualize the ERAD machinery within the native cellular environment. Proteasomes and Cdc48, the complexes that extract and degrade ER proteins, cluster together in non–membrane-bound cytosolic microcompartments that contact ribosome-free patches on the ER membrane. This discrete molecular organization may facilitate efficient ERAD. Structural analysis reveals that proteasomes directly engage ER-localized substrates, providing evidence for a noncanonical “direct ERAD” pathway. In addition, live-cell fluorescence microscopy suggests that these ER-associated proteasome clusters form by liquid–liquid phase separation. To promote the biochemical reactions of life, cells can compartmentalize molecular interaction partners together within separated non–membrane-bound regions. It is unknown whether this strategy is used to facilitate protein degradation at specific locations within the cell. Leveraging in situ cryo-electron tomography to image the native molecular landscape of the unicellular alga Chlamydomonas reinhardtii, we discovered that the cytosolic protein degradation machinery is concentrated within ∼200-nm foci that contact specialized patches of endoplasmic reticulum (ER) membrane away from the ER–Golgi interface. These non–membrane-bound microcompartments exclude ribosomes and consist of a core of densely clustered 26S proteasomes surrounded by a loose cloud of Cdc48. Active proteasomes in the microcompartments directly engage with putative substrate at the ER membrane, a function canonically assigned to Cdc48. Live-cell fluorescence microscopy revealed that the proteasome clusters are dynamic, with frequent assembly and fusion events. We propose that the microcompartments perform ER-associated degradation, colocalizing the degradation machinery at specific ER hot spots to enable efficient protein quality control.
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21
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Mechanisms and regulation of cholesterol homeostasis. Nat Rev Mol Cell Biol 2019; 21:225-245. [DOI: 10.1038/s41580-019-0190-7] [Citation(s) in RCA: 450] [Impact Index Per Article: 90.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/24/2019] [Indexed: 12/14/2022]
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22
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Valosin-containing protein mediates the ERAD of squalene monooxygenase and its cholesterol-responsive degron. Biochem J 2019; 476:2545-2560. [DOI: 10.1042/bcj20190418] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Revised: 08/27/2019] [Accepted: 08/29/2019] [Indexed: 12/17/2022]
Abstract
AbstractSqualene monooxygenase (SM) is an essential rate-limiting enzyme in cholesterol synthesis. SM degradation is accelerated by excess cholesterol, and this requires the first 100 amino acids of SM (SM N100). This process is part of a protein quality control pathway called endoplasmic reticulum-associated degradation (ERAD). In ERAD, SM is ubiquitinated by MARCH6, an E3 ubiquitin ligase located in the endoplasmic reticulum (ER). However, several details of the ERAD process for SM remain elusive, such as the extraction mechanism from the ER membrane. Here, we used SM N100 fused to GFP (SM N100-GFP) as a model degron to investigate the extraction process of SM in ERAD. We showed that valosin-containing protein (VCP) is important for the cholesterol-accelerated degradation of SM N100-GFP and SM. In addition, we revealed that VCP acts following ubiquitination of SM N100-GFP by MARCH6. We demonstrated that the amphipathic helix (Gln62–Leu73) of SM N100-GFP is critical for regulation by VCP and MARCH6. Replacing this amphipathic helix with hydrophobic re-entrant loops promoted degradation in a VCP-dependent manner. Finally, we showed that inhibiting VCP increases cellular squalene and cholesterol levels, indicating a functional consequence for VCP in regulating the cholesterol synthesis pathway. Collectively, we established VCP plays a key role in ERAD that contributes to the cholesterol-mediated regulation of SM.
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23
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Scheffer J, Hasenjäger S, Taxis C. Degradation of integral membrane proteins modified with the photosensitive degron module requires the cytosolic endoplasmic reticulum-associated degradation pathway. Mol Biol Cell 2019; 30:2558-2570. [PMID: 31411939 PMCID: PMC6740197 DOI: 10.1091/mbc.e18-12-0754] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Protein quality mechanisms are fundamental for proteostasis of eukaryotic cells. Endoplasmic reticulum–associated degradation (ERAD) is a well-studied pathway that ensures quality control of secretory and endoplasmic reticulum (ER)–resident proteins. Different branches of ERAD are involved in degradation of malfolded secretory proteins, depending on the localization of the misfolded part, the ER lumen (ERAD-L), the ER membrane (ERAD-M), and the cytosol (ERAD-C). Here we report that modification of several ER transmembrane proteins with the photosensitive degron (psd) module resulted in light-dependent degradation of the membrane proteins via the ERAD-C pathway. We found dependency on the ubiquitylation machinery including the ubiquitin-activating enzyme Uba1, the ubiquitin-conjugating enzymes Ubc6 and Ubc7, and the ubiquitin–protein ligase Doa10. Moreover, we found involvement of the Cdc48 AAA-ATPase complex members Ufd1 and Npl4, as well as the proteasome, in degradation of Sec62-myc-psd. Thus, our work shows that ERAD-C substrates can be systematically generated via synthetic degron constructs, which facilitates future investigations of the ERAD-C pathway.
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Affiliation(s)
- Johannes Scheffer
- Department of Chemistry/Biochemistry, Philipps-University Marburg, 35043 Marburg, Germany
| | - Sophia Hasenjäger
- Department of Biology/Genetics, Philipps-University Marburg, 35043 Marburg, Germany
| | - Christof Taxis
- Department of Biology/Genetics, Philipps-University Marburg, 35043 Marburg, Germany
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24
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Jo Y, Hamilton JS, Hwang S, Garland K, Smith GA, Su S, Fuentes I, Neelam S, Thompson BM, McDonald JG, DeBose-Boyd RA. Schnyder corneal dystrophy-associated UBIAD1 inhibits ER-associated degradation of HMG CoA reductase in mice. eLife 2019; 8:44396. [PMID: 30785396 PMCID: PMC6402834 DOI: 10.7554/elife.44396] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Accepted: 02/19/2019] [Indexed: 12/14/2022] Open
Abstract
Autosomal-dominant Schnyder corneal dystrophy (SCD) is characterized by corneal opacification owing to overaccumulation of cholesterol. SCD is caused by mutations in UBIAD1, which utilizes geranylgeranyl pyrophosphate (GGpp) to synthesize vitamin K2. Using cultured cells, we previously showed that sterols trigger binding of UBIAD1 to the cholesterol biosynthetic enzyme HMG CoA reductase (HMGCR), thereby inhibiting its endoplasmic reticulum (ER)-associated degradation (ERAD) (Schumacher et al. 2015). GGpp triggers release of UBIAD1 from HMGCR, allowing maximal ERAD and ER-to-Golgi transport of UBIAD1. SCD-associated UBIAD1 resists GGpp-induced release and is sequestered in ER to inhibit ERAD. We now report knockin mice expressing SCD-associated UBIAD1 accumulate HMGCR in several tissues resulting from ER sequestration of mutant UBIAD1 and inhibition of HMGCR ERAD. Corneas from aged knockin mice exhibit signs of opacification and sterol overaccumulation. These results establish the physiological significance of UBIAD1 in cholesterol homeostasis and indicate inhibition of HMGCR ERAD contributes to SCD pathogenesis.
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Affiliation(s)
- Youngah Jo
- Departments of Molecular Genetics, Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, United States
| | - Jason S Hamilton
- Departments of Molecular Genetics, Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, United States
| | - Seonghwan Hwang
- Departments of Molecular Genetics, Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, United States
| | - Kristina Garland
- Departments of Molecular Genetics, Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, United States
| | - Gennipher A Smith
- Departments of Molecular Genetics, Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, United States
| | - Shan Su
- Departments of Molecular Genetics, Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, United States
| | - Iris Fuentes
- Departments of Molecular Genetics, Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, United States
| | - Sudha Neelam
- Department of Ophthalmology, Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, United States
| | - Bonne M Thompson
- Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, United States
| | - Jeffrey G McDonald
- Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, United States
| | - Russell A DeBose-Boyd
- Departments of Molecular Genetics, Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, United States
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25
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Ma S, Sun W, Gao L, Liu S. Therapeutic targets of hypercholesterolemia: HMGCR and LDLR. Diabetes Metab Syndr Obes 2019; 12:1543-1553. [PMID: 31686875 PMCID: PMC6709517 DOI: 10.2147/dmso.s219013] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Accepted: 07/25/2019] [Indexed: 12/14/2022] Open
Abstract
Cholesterol homeostasis is critical and necessary for the body's functions. Hypercholesterolemia can lead to significant clinical problems, such as cardiovascular disease (CVD). 3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) and low-density lipoprotein cholesterol receptor (LDLR) are major points of control in cholesterol homeostasis. We summarize the regulatory mechanisms of HMGCR and LDLR, which may provide insight for new drug design and development.
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Affiliation(s)
- Shizhan Ma
- Department of Endocrinology and Metabolism, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan250021, People’s Republic of China
- Department of Endocrinology and Metabolism, Shandong Provincial Hospital Affiliated to Shandong University, Jinan250021, People’s Republic of China
| | - Wenxiu Sun
- Department of Pharmacy, Taishan Vocational College of Nursing, Taian271000, People’s Republic of China
| | - Ling Gao
- Department of Endocrinology and Metabolism, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan250021, People’s Republic of China
- Scientific Center, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan250021, People’s Republic of China
- Scientific Center, Shandong Provincial Hospital Affiliated to Shandong University, Jinan250021, People’s Republic of China
- Correspondence: Ling GaoScientific Center, Shandong Provincial Hospital Affiliated to Shandong University, 324 Jing 5 Road, Jinan, Shandong Province250021, People’s Republic of ChinaTel +86 531 6877 6910Email
| | - Shudong Liu
- Department of Endocrinology, Shandong Rongjun General Hospital, Jinan250013, People’s Republic of China
- Shudong LiuDepartment of Endocrinology, Shandong Rongjun General Hospital, 23 Jiefang Road, Jinan, Shandong Province250013, People’s Republic of ChinaTel +86 531 8238 2351Email
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26
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Schumacher MM, Jun DJ, Johnson BM, DeBose-Boyd RA. UbiA prenyltransferase domain-containing protein-1 modulates HMG-CoA reductase degradation to coordinate synthesis of sterol and nonsterol isoprenoids. J Biol Chem 2017; 293:312-323. [PMID: 29167270 DOI: 10.1074/jbc.ra117.000423] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Revised: 11/20/2017] [Indexed: 12/17/2022] Open
Abstract
UBIAD1 (UbiA prenyltransferase domain-containing protein-1) utilizes geranylgeranyl pyrophosphate (GGpp) to synthesize vitamin K2 We previously reported that sterols stimulate binding of UBIAD1 to endoplasmic reticulum (ER)-localized 3-hydroxy-3-methylglutaryl (HMG) CoA reductase. UBIAD1 binding inhibits sterol-accelerated, ER-associated degradation (ERAD) of reductase, one of several mechanisms for feedback control of this rate-limiting enzyme in the branched pathway that produces cholesterol and nonsterol isoprenoids such as GGpp. Accumulation of GGpp in ER membranes triggers release of UBIAD1 from reductase, permitting its maximal ERAD and ER-to-Golgi transport of UBIAD1. Mutant UBIAD1 variants associated with Schnyder corneal dystrophy (SCD), a human disorder characterized by corneal accumulation of cholesterol, resist GGpp-induced release from reductase and remain sequestered in the ER to block reductase ERAD. Using lines of genetically manipulated cells, we now examine consequences of UBIAD1 deficiency and SCD-associated UBIAD1 on reductase ERAD and cholesterol synthesis. Our results indicated that reductase becomes destabilized in the absence of UBIAD1, resulting in reduced cholesterol synthesis and intracellular accumulation. In contrast, an SCD-associated UBIAD1 variant inhibited reductase ERAD, thereby stabilizing the enzyme and contributing to enhanced synthesis and intracellular accumulation of cholesterol. Finally, we present evidence that GGpp-regulated, ER-to-Golgi transport enables UBIAD1 to modulate reductase ERAD such that synthesis of nonsterol isoprenoids is maintained in sterol-replete cells. These findings further establish UBIAD1 as a central player in the reductase ERAD pathway and regulation of isoprenoid synthesis. They also indicate that UBIAD1-mediated inhibition of reductase ERAD underlies cholesterol accumulation associated with SCD.
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Affiliation(s)
- Marc M Schumacher
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046
| | - Dong-Jae Jun
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046
| | - Brittany M Johnson
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046
| | - Russell A DeBose-Boyd
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046.
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27
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Johnson BM, DeBose-Boyd RA. Underlying mechanisms for sterol-induced ubiquitination and ER-associated degradation of HMG CoA reductase. Semin Cell Dev Biol 2017; 81:121-128. [PMID: 29107682 DOI: 10.1016/j.semcdb.2017.10.019] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 10/19/2017] [Indexed: 11/30/2022]
Abstract
Accelerated ubiquitination and subsequent endoplasmic reticulum (ER)-associated degradation (ERAD) constitute one of several mechanisms for feedback control of HMG CoA reductase, the rate-limiting enzyme in synthesis of cholesterol and nonsterol isoprenoids. This ERAD is initiated by the accumulation of certain sterols in ER membranes, which trigger binding of reductase to ER membrane proteins called Insigs. Insig-associated ubiquitin ligases facilitate ubiquitination of reductase, marking the enzyme for extraction across the ER membrane through a reaction that is augmented by nonsterol isoprenoids. Once extracted, ubiquitinated reductase becomes dislocated into the cytosol for degradation by 26S proteasomes. In this review, we will highlight several advances in the understanding of reductase ERAD, which includes the discovery for a role of the vitamin K2 synthetic enzyme UBIAD1 in the reaction and demonstration that sterol-accelerated ERAD significantly contributes to feedback regulation of reductase and cholesterol metabolism in livers of whole animals.
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Affiliation(s)
- Brittany M Johnson
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, United States
| | - Russell A DeBose-Boyd
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, United States.
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28
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Loregger A, Raaben M, Tan J, Scheij S, Moeton M, van den Berg M, Gelberg-Etel H, Stickel E, Roitelman J, Brummelkamp T, Zelcer N. Haploid Mammalian Genetic Screen Identifies UBXD8 as a Key Determinant of HMGCR Degradation and Cholesterol Biosynthesis. Arterioscler Thromb Vasc Biol 2017; 37:2064-2074. [PMID: 28882874 PMCID: PMC5671778 DOI: 10.1161/atvbaha.117.310002] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Accepted: 08/29/2017] [Indexed: 01/23/2023]
Abstract
Supplemental Digital Content is available in the text. Objective— The cellular demand for cholesterol requires control of its biosynthesis by the mevalonate pathway. Regulation of HMGCR (3-hydroxy-3-methylglutaryl coenzyme A reductase), a rate-limiting enzyme in this pathway and the target of statins, is a key control point herein. Accordingly, HMGCR is subject to negative and positive regulation. In particular, the ability of oxysterols and intermediates of the mevalonate pathway to stimulate its proteasomal degradation is an exquisite example of metabolically controlled feedback regulation. To define the genetic determinants that govern this process, we conducted an unbiased haploid mammalian genetic screen. Approach and Results— We generated human haploid cells with mNeon fused to endogenous HMGCR using CRISPR/Cas9 and used these cells to interrogate regulation of HMGCR abundance in live cells. This resulted in identification of known and new regulators of HMGCR, and among the latter, UBXD8 (ubiquitin regulatory X domain-containing protein 8), a gene that has not been previously implicated in this process. We demonstrate that UBXD8 is an essential determinant of metabolically stimulated degradation of HMGCR and of cholesterol biosynthesis in multiple cell types. Accordingly, UBXD8 ablation leads to aberrant cholesterol synthesis due to loss of feedback control. Mechanistically, we show that UBXD8 is necessary for sterol-stimulated dislocation of ubiquitylated HMGCR from the endoplasmic reticulum membrane en route to proteasomal degradation, a function dependent on its UBX domain. Conclusions— We establish UBXD8 as a previously unrecognized determinant that couples flux across the mevalonate pathway to control of cholesterol synthesis and demonstrate the feasibility of applying mammalian haploid genetics to study metabolic traits.
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Affiliation(s)
- Anke Loregger
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Matthijs Raaben
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Josephine Tan
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Saskia Scheij
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Martina Moeton
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Marlene van den Berg
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Hila Gelberg-Etel
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Elmer Stickel
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Joseph Roitelman
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Thijn Brummelkamp
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Noam Zelcer
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.).
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29
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Guerriero CJ, Reutter KR, Augustine AA, Preston GM, Weiberth KF, Mackie TD, Cleveland-Rubeor HC, Bethel NP, Callenberg KM, Nakatsukasa K, Grabe M, Brodsky JL. Transmembrane helix hydrophobicity is an energetic barrier during the retrotranslocation of integral membrane ERAD substrates. Mol Biol Cell 2017; 28:2076-2090. [PMID: 28539401 PMCID: PMC5509421 DOI: 10.1091/mbc.e17-03-0184] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Revised: 05/12/2017] [Accepted: 05/16/2017] [Indexed: 12/25/2022] Open
Abstract
Integral membrane proteins fold inefficiently and are susceptible to turnover via the endoplasmic reticulum-associated degradation (ERAD) pathway. During ERAD, misfolded proteins are recognized by molecular chaperones, polyubiquitinated, and retrotranslocated to the cytoplasm for proteasomal degradation. Although many aspects of this pathway are defined, how transmembrane helices (TMHs) are removed from the membrane and into the cytoplasm before degradation is poorly understood. In this study, we asked whether the hydrophobic character of a TMH acts as an energetic barrier to retrotranslocation. To this end, we designed a dual-pass model ERAD substrate, Chimera A*, which contains the cytoplasmic misfolded domain from a characterized ERAD substrate, Sterile 6* (Ste6p*). We found that the degradation requirements for Chimera A* and Ste6p* are similar, but Chimera A* was retrotranslocated more efficiently than Ste6p* in an in vitro assay in which retrotranslocation can be quantified. We then constructed a series of Chimera A* variants containing synthetic TMHs with a range of ΔG values for membrane insertion. TMH hydrophobicity correlated inversely with retrotranslocation efficiency, and in all cases, retrotranslocation remained Cdc48p dependent. These findings provide insight into the energetic restrictions on the retrotranslocation reaction, as well as a new computational approach to predict retrotranslocation efficiency.
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Affiliation(s)
| | - Karl-Richard Reutter
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
| | - Andrew A Augustine
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
| | - G Michael Preston
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
| | - Kurt F Weiberth
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
| | - Timothy D Mackie
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
| | | | - Neville P Bethel
- Cardiovascular Research Institute, Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, CA 94158
| | - Keith M Callenberg
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
| | - Kunio Nakatsukasa
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260.,Division of Biological Science, Graduate School of Natural Sciences, Nagoya City University, Nagoya, Aichi 467-8501, Japan
| | - Michael Grabe
- Cardiovascular Research Institute, Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, CA 94158
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
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30
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Hwang S, Nguyen AD, Jo Y, Engelking LJ, Brugarolas J, DeBose-Boyd RA. Hypoxia-inducible factor 1α activates insulin-induced gene 2 (Insig-2) transcription for degradation of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase in the liver. J Biol Chem 2017; 292:9382-9393. [PMID: 28416613 DOI: 10.1074/jbc.m117.788562] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Revised: 04/14/2017] [Indexed: 12/15/2022] Open
Abstract
Cholesterol synthesis is a highly oxygen-consuming process. As such, oxygen deprivation (hypoxia) limits cholesterol synthesis through incompletely understood mechanisms mediated by the oxygen-sensitive transcription factor hypoxia-inducible factor 1α (HIF-1α). We show here that HIF-1α links pathways for oxygen sensing and feedback control of cholesterol synthesis in human fibroblasts by directly activating transcription of the INSIG-2 gene. Insig-2 is one of two endoplasmic reticulum membrane proteins that inhibit cholesterol synthesis by mediating sterol-induced ubiquitination and subsequent endoplasmic reticulum-associated degradation of the rate-limiting enzyme in the pathway, HMG-CoA reductase (HMGCR). Consistent with the results in cultured cells, hepatic levels of Insig-2 mRNA were enhanced in mouse models of hypoxia. Moreover, pharmacologic stabilization of HIF-1α in the liver stimulated HMGCR degradation via a reaction that requires the protein's prior ubiquitination and the presence of the Insig-2 protein. In summary, our results show that HIF-1α activates INSIG-2 transcription, leading to accumulation of Insig-2 protein, which binds to HMGCR and triggers its accelerated ubiquitination and degradation. These results indicate that HIF-mediated induction of Insig-2 and degradation of HMGCR are physiologically relevant events that guard against wasteful oxygen consumption and inappropriate cell growth during hypoxia.
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Affiliation(s)
| | | | - Youngah Jo
- From the Department of Molecular Genetics and
| | | | - James Brugarolas
- Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046
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31
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Scott Kiss R, Sniderman A. Shunts, channels and lipoprotein endosomal traffic: a new model of cholesterol homeostasis in the hepatocyte. J Biomed Res 2017; 31:95-107. [PMID: 28808191 PMCID: PMC5445212 DOI: 10.7555/jbr.31.20160139] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The liver directs cholesterol metabolism in the organism. All the major fluxes of cholesterol within the body involve the liver: dietary cholesterol is directed to the liver; cholesterol from peripheral cells goes to the liver; the liver is a major site of cholesterol synthesis for the organism; cholesterol is secreted from the liver within the bile, within apoB lipoproteins and translocated to nascent HDL. The conventional model of cholesterol homeostasis posits that cholesterol from any source enters a common, rapidly exchangeable pool within the cell, which is in equilibrium with a regulatory pool. Increased influx of cholesterol leads rapidly to decreased synthesis of cholesterol. This model was developed based on in vitro studies in the fibroblast and validated only for LDL particles. The challenges the liver must meet in vivo to achieve cholesterol homeostasis are far more complex. Our model posits that the cholesterol derived from three different lipoproteins endosomes has three different fates: LDL-derived cholesterol is largely recycled within VLDL with most of the cholesterol shunted through the hepatocyte without entering the exchangeable pool of cholesterol; high density lipoprotein-derived CE is transcytosed into bile; and chylomicron remnant-derived cholesterol primarily enters the regulatory pool within the hepatocyte. These endosomal channels represent distinct physiological pathways and hepatic homeostasis represents the net result of the outcomes of these distinct channels. Our model takes into account the distinct physiological challenges the hepatocyte must meet, underlie the pathophysiology of many of the apoB dyslipoproteinemias and account for the sustained effectiveness of therapeutic agents such as statins.
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Affiliation(s)
- Robert Scott Kiss
- Research Institute of the McGill University Health Centre, Montreal, Quebec H4A 3J1, Canada.,Department of Medicine, McGill University, Montreal, Quebec H4A 3J1, Canada
| | - Allan Sniderman
- Research Institute of the McGill University Health Centre, Montreal, Quebec H4A 3J1, Canada.,Department of Medicine, McGill University, Montreal, Quebec H4A 3J1, Canada
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32
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Römisch K. A Case for Sec61 Channel Involvement in ERAD. Trends Biochem Sci 2016; 42:171-179. [PMID: 27932072 DOI: 10.1016/j.tibs.2016.10.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 10/19/2016] [Accepted: 10/20/2016] [Indexed: 11/25/2022]
Abstract
Proteins that misfold in the endoplasmic reticulum (ER) need to be transported back to the cytosol for degradation by proteasomes, a process known as ER-associated degradation (ERAD). The first candidate discussed as a retrograde protein transport conduit was the Sec61 channel which is responsible for secretory protein transport into the ER during biogenesis. The Sec61 channel binds the proteasome 19S regulatory particle which can extract an ERAD substrate from the ER. Nevertheless its role as a general export channel has been dismissed, and Hrd1 and Der1 have been proposed as alternatives. The discovery of export-specific sec61 mutants and of mammalian ERAD substrates whose export is dependent on the 19S regulatory particle suggest that dismissal of a role of Sec61 in export may have been premature.
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Affiliation(s)
- Karin Römisch
- Department of Biology, Naturwissenschaftlich-technische Fakultät 8, Saarland University, 66123 Saarbruecken, Germany.
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33
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Baldridge RD, Rapoport TA. Autoubiquitination of the Hrd1 Ligase Triggers Protein Retrotranslocation in ERAD. Cell 2016; 166:394-407. [PMID: 27321670 DOI: 10.1016/j.cell.2016.05.048] [Citation(s) in RCA: 144] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Revised: 04/19/2016] [Accepted: 05/13/2016] [Indexed: 12/16/2022]
Abstract
Misfolded proteins of the ER are retrotranslocated to the cytosol, where they are polyubiquitinated, extracted from the membrane, and degraded by the proteasome. To investigate how the ER-associated Degradation (ERAD) machinery can accomplish retrotranslocation of a misfolded luminal protein domain across a lipid bilayer, we have reconstituted retrotranslocation with purified S. cerevisiae proteins, using proteoliposomes containing the multi-spanning ubiquitin ligase Hrd1. Retrotranslocation of the luminal domain of a membrane-spanning substrate is triggered by autoubiquitination of Hrd1. Substrate ubiquitination is a subsequent event, and the Cdc48 ATPase that completes substrate extraction from the membrane is not required for retrotranslocation. Ubiquitination of lysines in Hrd1's RING-finger domain is required for substrate retrotranslocation in vitro and for ERAD in vivo. Our results suggest that Hrd1 forms a ubiquitin-gated protein-conducting channel.
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Affiliation(s)
- Ryan D Baldridge
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.
| | - Tom A Rapoport
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.
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34
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Abstract
The endoplasmic reticulum is the port of entry for proteins into the secretory pathway and the site of synthesis for several important lipids, including cholesterol, triacylglycerol, and phospholipids. Protein production within the endoplasmic reticulum is tightly regulated by a cohort of resident machinery that coordinates the folding, modification, and deployment of secreted and integral membrane proteins. Proteins failing to attain their native conformation are degraded through the endoplasmic reticulum-associated degradation (ERAD) pathway via a series of tightly coupled steps: substrate recognition, dislocation, and ubiquitin-dependent proteasomal destruction. The same ERAD machinery also controls the flux through various metabolic pathways by coupling the turnover of metabolic enzymes to the levels of key metabolites. We review the current understanding and biological significance of ERAD-mediated regulation of lipid metabolism in mammalian cells.
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Affiliation(s)
- Julian Stevenson
- Program in Metabolic Biology, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720;
| | - Edmond Y Huang
- Program in Metabolic Biology, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720;
| | - James A Olzmann
- Program in Metabolic Biology, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720;
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35
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Hwang S, Hartman IZ, Calhoun LN, Garland K, Young GA, Mitsche MA, McDonald J, Xu F, Engelking L, DeBose-Boyd RA. Contribution of Accelerated Degradation to Feedback Regulation of 3-Hydroxy-3-methylglutaryl Coenzyme A Reductase and Cholesterol Metabolism in the Liver. J Biol Chem 2016; 291:13479-94. [PMID: 27129778 DOI: 10.1074/jbc.m116.728469] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Indexed: 11/06/2022] Open
Abstract
Accumulation of sterols in endoplasmic reticulum membranes stimulates the ubiquitination of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), which catalyzes a rate-limiting step in synthesis of cholesterol. This ubiquitination marks HMGCR for proteasome-mediated degradation and constitutes one of several mechanisms for feedback control of cholesterol synthesis. Mechanisms for sterol-accelerated ubiquitination and degradation of HMGCR have been elucidated through the study of cultured mammalian cells. However, the extent to which these reactions modulate HMGCR and contribute to control of cholesterol metabolism in whole animals is unknown. Here, we examine transgenic mice expressing in the liver the membrane domain of HMGCR (HMGCR (TM1-8)), a region necessary and sufficient for sterol-accelerated degradation, and knock-in mice in which endogenous HMGCR harbors mutations that prevent sterol-induced ubiquitination. Characterization of transgenic mice revealed that HMGCR (TM1-8) is appropriately regulated in the liver of mice fed a high cholesterol diet or chow diet supplemented with the HMGCR inhibitor lovastatin. Ubiquitination-resistant HMGCR protein accumulates in the liver and other tissues disproportionately to its mRNA, indicating that sterol-accelerated degradation significantly contributes to feedback regulation of HMGCR in vivo Results of these studies demonstrate that HMGCR is subjected to sterol-accelerated degradation in the liver through mechanisms similar to those established in cultured cells. Moreover, these studies designate sterol-accelerated degradation of HMGCR as a potential therapeutic target for prevention of atherosclerosis and associated cardiovascular disease.
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Affiliation(s)
- Seonghwan Hwang
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Isamu Z Hartman
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Leona N Calhoun
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Kristina Garland
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Gennipher A Young
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Matthew A Mitsche
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Jeffrey McDonald
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Fang Xu
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Luke Engelking
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Russell A DeBose-Boyd
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
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36
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Schumacher MM, Jun DJ, Jo Y, Seemann J, DeBose-Boyd RA. Geranylgeranyl-regulated transport of the prenyltransferase UBIAD1 between membranes of the ER and Golgi. J Lipid Res 2016; 57:1286-99. [PMID: 27121042 DOI: 10.1194/jlr.m068759] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Indexed: 11/20/2022] Open
Abstract
UbiA prenyltransferase domain-containing protein-1 (UBIAD1) utilizes geranylgeranyl pyrophosphate (GGpp) to synthesize the vitamin K2 subtype menaquinone-4. Previously, we found that sterols trigger binding of UBIAD1 to endoplasmic reticulum (ER)-localized HMG-CoA reductase, the rate-limiting enzyme in synthesis of cholesterol and nonsterol isoprenoids, including GGpp. This binding inhibits sterol-accelerated degradation of reductase, which contributes to feedback regulation of the enzyme. The addition to cells of geranylgeraniol (GGOH), which can become converted to GGpp, triggers release of UBIAD1 from reductase, allowing for its maximal degradation and permitting ER-to-Golgi transport of UBIAD1. Here, we further characterize geranylgeranyl-regulated transport of UBIAD1. Results of this characterization support a model in which UBIAD1 continuously cycles between the ER and medial-trans Golgi of isoprenoid-replete cells. Upon sensing a decline of GGpp in ER membranes, UBIAD1 becomes trapped in the organelle where it inhibits reductase degradation. Mutant forms of UBIAD1 associated with Schnyder corneal dystrophy (SCD), a human eye disease characterized by corneal accumulation of cholesterol, are sequestered in the ER and block reductase degradation. Collectively, these findings disclose a novel sensing mechanism that allows for stringent metabolic control of intracellular trafficking of UBIAD1, which directly modulates reductase degradation and becomes disrupted in SCD.
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Affiliation(s)
- Marc M Schumacher
- Departments of Molecular Genetics University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Dong-Jae Jun
- Departments of Molecular Genetics University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Youngah Jo
- Departments of Molecular Genetics University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Joachim Seemann
- Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Russell A DeBose-Boyd
- Departments of Molecular Genetics University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
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37
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Wright FA, Wojcikiewicz RJH. Chapter 4 - Inositol 1,4,5-Trisphosphate Receptor Ubiquitination. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2016; 141:141-59. [PMID: 27378757 DOI: 10.1016/bs.pmbts.2016.02.004] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Inositol 1,4,5-trisphosphate receptors (IP3Rs) are large (∼300kDa) proteins that associate into tetrameric ion channels in the endoplasmic reticulum (ER) membrane. Activation and opening of the channel upon binding of IP3 and Ca(2+) allows the flow of Ca(2+) ions from stores within the ER lumen to the cytosol, thereby promoting a number of Ca(2+)-dependent cellular events, such as secretion, neurotransmitter release, and cell division. Intriguingly, it appears that the same conformational change that IP3Rs undergo during activation makes them a target for degradation by the ubiquitin-proteasome pathway and that this mode of processing allows the cell to tune its internal Ca(2+) response to extracellular signals. Here, we review recent studies showing that activated IP3Rs interact with an array of proteins that mediate their degradation, that IP3Rs are modified by a complex array of ubiquitin conjugates, that this ubiquitination and degradation functions to regulate IP3-mediated Ca(2+) responses in the cell, and that mutations to different proteins involved in IP3R degradation result in a set of similar diseases.
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Affiliation(s)
- F A Wright
- Department of Pharmacology, SUNY Upstate Medical University, Syracuse, NY, United States
| | - R J H Wojcikiewicz
- Department of Pharmacology, SUNY Upstate Medical University, Syracuse, NY, United States.
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Anderson DJ, Le Moigne R, Djakovic S, Kumar B, Rice J, Wong S, Wang J, Yao B, Valle E, Kiss von Soly S, Madriaga A, Soriano F, Menon MK, Wu ZY, Kampmann M, Chen Y, Weissman JS, Aftab BT, Yakes FM, Shawver L, Zhou HJ, Wustrow D, Rolfe M. Targeting the AAA ATPase p97 as an Approach to Treat Cancer through Disruption of Protein Homeostasis. Cancer Cell 2015; 28:653-665. [PMID: 26555175 PMCID: PMC4941640 DOI: 10.1016/j.ccell.2015.10.002] [Citation(s) in RCA: 271] [Impact Index Per Article: 30.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Revised: 08/04/2015] [Accepted: 10/06/2015] [Indexed: 02/06/2023]
Abstract
p97 is a AAA-ATPase with multiple cellular functions, one of which is critical regulation of protein homeostasis pathways. We describe the characterization of CB-5083, a potent, selective, and orally bioavailable inhibitor of p97. Treatment of tumor cells with CB-5083 leads to accumulation of poly-ubiquitinated proteins, retention of endoplasmic reticulum-associated degradation (ERAD) substrates, and generation of irresolvable proteotoxic stress, leading to activation of the apoptotic arm of the unfolded protein response. In xenograft models, CB-5083 causes modulation of key p97-related pathways, induces apoptosis, and has antitumor activity in a broad range of both hematological and solid tumor models. Molecular determinants of CB-5083 activity include expression of genes in the ERAD pathway, providing a potential strategy for patient selection.
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Affiliation(s)
| | | | | | | | - Julie Rice
- Cleave Biosciences, Inc., Burlingame, CA 94010, USA
| | - Steve Wong
- Cleave Biosciences, Inc., Burlingame, CA 94010, USA
| | - Jinhai Wang
- Cleave Biosciences, Inc., Burlingame, CA 94010, USA
| | - Bing Yao
- Cleave Biosciences, Inc., Burlingame, CA 94010, USA
| | | | | | | | | | | | - Zhi Yong Wu
- Cleave Biosciences, Inc., Burlingame, CA 94010, USA
| | - Martin Kampmann
- Department of Cellular and Molecular Pharmacology and Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Yuwen Chen
- Department of Cellular and Molecular Pharmacology and Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Jonathan S Weissman
- Department of Cellular and Molecular Pharmacology and Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Blake T Aftab
- Division of Hematology & Oncology, Department of Medicine, Helen Diller Family Cancer Center, University of California, San Francisco, San Francisco, CA 94158, USA
| | | | | | - Han-Jie Zhou
- Cleave Biosciences, Inc., Burlingame, CA 94010, USA
| | | | - Mark Rolfe
- Cleave Biosciences, Inc., Burlingame, CA 94010, USA
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Acosta-Alvear D, Cho MY, Wild T, Buchholz TJ, Lerner AG, Simakova O, Hahn J, Korde N, Landgren O, Maric I, Choudhary C, Walter P, Weissman JS, Kampmann M. Paradoxical resistance of multiple myeloma to proteasome inhibitors by decreased levels of 19S proteasomal subunits. eLife 2015; 4:e08153. [PMID: 26327694 PMCID: PMC4602331 DOI: 10.7554/elife.08153] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Accepted: 08/31/2015] [Indexed: 01/06/2023] Open
Abstract
Hallmarks of cancer, including rapid growth and aneuploidy, can result in non-oncogene addiction to the proteostasis network that can be exploited clinically. The defining example is the exquisite sensitivity of multiple myeloma (MM) to 20S proteasome inhibitors, such as carfilzomib. However, MM patients invariably acquire resistance to these drugs. Using a next-generation shRNA platform, we found that proteostasis factors, including chaperones and stress-response regulators, controlled the response to carfilzomib. Paradoxically, 19S proteasome regulator knockdown induced resistance to carfilzomib in MM and non-MM cells. 19S subunit knockdown did not affect the activity of the 20S subunits targeted by carfilzomib nor their inhibition by the drug, suggesting an alternative mechanism, such as the selective accumulation of protective factors. In MM patients, lower 19S levels predicted a diminished response to carfilzomib-based therapies. Together, our findings suggest that an understanding of network rewiring can inform development of new combination therapies to overcome drug resistance. DOI:http://dx.doi.org/10.7554/eLife.08153.001 Cells have several mechanisms for removing proteins that have been damaged or are no longer needed. One of these mechanisms is carried out by a large protein complex called the proteasome. Drugs that block the proteasome are toxic to all cells, and a type of blood cancer called multiple myeloma is particularly sensitive to these ‘proteasome inhibitors’. However, tumors in patients with multiple myeloma can also become resistant to these drugs. Using a genetic approach, Acosta-Alvear et al. identified the factors that control the sensitivity of cells to proteasome inhibitors. In particular, reducing the levels of other factors that contribute to protein balance made the cells more sensitive. Using a combination of proteasome inhibitors and drugs that target these other factors could prove to be useful in the fight against multiple myeloma. The proteasome complex contains two types of subunits: regulatory subunits that recognize the proteins that need to be degraded, and catalytic subunits that degrade the proteins. The results of Acosta-Alvear et al. revealed how varying the levels of these two subunits influenced the sensitivity of cells to inhibitors. While decreasing the levels of catalytic subunits made the cells more sensitive, as expected, decreasing the level of regulatory subunits surprisingly made the cells resistant to the inhibitors. A possible explanation for this paradoxical result is that certain proteins are less effectively degraded by the proteasome in these cells, and that the buildup of these proteins protects the cells against the drugs. Acosta-Alvear et al. also found that lower levels of regulatory subunits desensitized multiple myeloma patients to therapy based on proteasome inhibition, suggesting that results from the genetic screen carried out in cells can predict clinical resistance mechanisms and guide the development of future therapies to increase patient survival. DOI:http://dx.doi.org/10.7554/eLife.08153.002
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Affiliation(s)
- Diego Acosta-Alvear
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States.,Howard Hughes Medical Institute, San Francisco, United States
| | - Min Y Cho
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States.,Howard Hughes Medical Institute, San Francisco, United States.,Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, United States
| | - Thomas Wild
- The Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Copenhagen, Denmark
| | - Tonia J Buchholz
- Onyx Pharmaceuticals, Inc. an Amgen subsidiary, South San Francisco, United States
| | - Alana G Lerner
- Onyx Pharmaceuticals, Inc. an Amgen subsidiary, South San Francisco, United States
| | - Olga Simakova
- Department of Laboratory Medicine, Clinical Center, National Institutes of Health, Bethesda, United States
| | - Jamie Hahn
- Department of Laboratory Medicine, Clinical Center, National Institutes of Health, Bethesda, United States
| | - Neha Korde
- Multiple Myeloma Section, Lymphoid Malignancies Branch, National Cancer Institute, Bethesda, United States.,Myeloma Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York, United States
| | - Ola Landgren
- Multiple Myeloma Section, Lymphoid Malignancies Branch, National Cancer Institute, Bethesda, United States.,Myeloma Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York, United States
| | - Irina Maric
- Department of Laboratory Medicine, Clinical Center, National Institutes of Health, Bethesda, United States
| | - Chunaram Choudhary
- The Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Copenhagen, Denmark
| | - Peter Walter
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States.,Howard Hughes Medical Institute, San Francisco, United States
| | - Jonathan S Weissman
- Howard Hughes Medical Institute, San Francisco, United States.,Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, United States
| | - Martin Kampmann
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, United States.,Howard Hughes Medical Institute, San Francisco, United States
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40
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Singaravelu R, Srinivasan P, Pezacki JP. Armand-Frappier Outstanding Student Award--The emerging role of 25-hydroxycholesterol in innate immunity. Can J Microbiol 2015; 61:521-30. [PMID: 26182401 DOI: 10.1139/cjm-2015-0292] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The metabolic interplay between hosts and viruses plays a crucial role in determining the outcome of viral infection. Viruses reorchestrate the host's primary metabolic gene networks, including genes associated with mevalonate and isoprenoid synthesis, to acquire the necessary energy and structural components for their viral life cycles. Recent work has demonstrated that the interferon-mediated antiviral response suppresses the sterol pathway through production of a signalling molecule, 25-hydroxycholesterol (25HC). This oxysterol has been shown to exert multiple effects, both through incorporation into host cellular membranes as well as through transcriptional control. Herein, we summarize our current understanding of the multifunctional roles of 25HC in the mammalian innate antiviral response.
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Affiliation(s)
- Ragunath Singaravelu
- a Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ottawa, ON K1N 6N5, Canada.,b Life Sciences Division, National Research Council Canada, Ottawa, ON K1A 0R6, Canada
| | - Prashanth Srinivasan
- a Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ottawa, ON K1N 6N5, Canada.,b Life Sciences Division, National Research Council Canada, Ottawa, ON K1A 0R6, Canada
| | - John Paul Pezacki
- a Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ottawa, ON K1N 6N5, Canada.,b Life Sciences Division, National Research Council Canada, Ottawa, ON K1A 0R6, Canada.,c Department of Chemistry, University of Ottawa, Ottawa, ON K1N 6N5, Canada
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41
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Schumacher MM, Elsabrouty R, Seemann J, Jo Y, DeBose-Boyd RA. The prenyltransferase UBIAD1 is the target of geranylgeraniol in degradation of HMG CoA reductase. eLife 2015; 4. [PMID: 25742604 PMCID: PMC4374513 DOI: 10.7554/elife.05560] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2014] [Accepted: 03/04/2015] [Indexed: 01/18/2023] Open
Abstract
Schnyder corneal dystrophy (SCD) is an autosomal dominant disorder in humans characterized by abnormal accumulation of cholesterol in the cornea. SCD-associated mutations have been identified in the gene encoding UBIAD1, a prenyltransferase that synthesizes vitamin K2. Here, we show that sterols stimulate binding of UBIAD1 to the cholesterol biosynthetic enzyme HMG CoA reductase, which is subject to sterol-accelerated, endoplasmic reticulum (ER)-associated degradation augmented by the nonsterol isoprenoid geranylgeraniol through an unknown mechanism. Geranylgeraniol inhibits binding of UBIAD1 to reductase, allowing its degradation and promoting transport of UBIAD1 from the ER to the Golgi. CRISPR-CAS9-mediated knockout of UBIAD1 relieves the geranylgeraniol requirement for reductase degradation. SCD-associated mutations in UBIAD1 block its displacement from reductase in the presence of geranylgeraniol, thereby preventing degradation of reductase. The current results identify UBIAD1 as the elusive target of geranylgeraniol in reductase degradation, the inhibition of which may contribute to accumulation of cholesterol in SCD. DOI:http://dx.doi.org/10.7554/eLife.05560.001 People with a rare genetic disorder called ‘Schnyder corneal dystrophy’ gradually lose their vision, because their corneas become increasingly cloudy. This cloudiness is caused by a build-up of excessive amounts of cholesterol, and the disorder itself is caused by mutations in a gene that encodes a protein called UBIAD1. Researchers have previously discovered that the UBIAD1 protein is involved in making vitamin K2, but it is not clear how this protein also helps to control cholesterol levels in the cornea. An enzyme called HMG CoA reductase makes a molecule that is used to make cholesterol and many other similar sterol molecules. A ‘feedback loop’ operates in cells to control the amount of the reductase and prevent cholesterol from becoming too high or too low. Sterol molecules, together with another molecule called geranylgeraniol, participate in this feedback loop by promoting the destruction of the reductase enzyme. Here, Schumacher et al. reveal a link between UBIAD1 and the reductase that may explain how UBIAD1 contributes to the production of excess cholesterol in patients with Schnyder corneal dystrophy. The experiments show that, in the presence of sterol molecules, UBIAD1 can bind to HMG CoA reductase to protect the reductase from being destroyed by other proteins. Geranylgeraniol—which stops the UBIAD1 protein from binding to the enzyme—is required to completely destroy the reductase enzyme. However, when UBIAD1 is missing, the reductase enzyme is destroyed even in the absence of geranylgeraniol. Furthermore, the experiments show that the genetic mutations linked to Schnyder corneal dystrophy lead to the production of versions of the UBIAD1 protein that bind to the reductase enzyme even when geranylgeraniol molecules are present. This prevents the normal breakdown of the reductase enzyme, which could lead to the build up of cholesterol in the cornea of individuals with the disorder. Schumacher et al.'s findings show that the UBIAD1 protein helps to control the levels of cholesterol in cells by protecting the HMG CoA reductase enzyme from destruction. These findings may aid the development of new therapies to lower cholesterol levels in cells, which may help patients with Schnyder's corneal dystrophy and other conditions caused by high cholesterol levels. DOI:http://dx.doi.org/10.7554/eLife.05560.002
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Affiliation(s)
- Marc M Schumacher
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States
| | - Rania Elsabrouty
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States
| | - Joachim Seemann
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Youngah Jo
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States
| | - Russell A DeBose-Boyd
- Department of Molecular Genetics, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, United States
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42
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Kaiser ML, Römisch K. Proteasome 19S RP binding to the Sec61 channel plays a key role in ERAD. PLoS One 2015; 10:e0117260. [PMID: 25658429 PMCID: PMC4319758 DOI: 10.1371/journal.pone.0117260] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2014] [Accepted: 12/20/2014] [Indexed: 11/24/2022] Open
Abstract
Import of secretory proteins into the Endoplasmic Reticulum (ER) is an established function of the Sec61 channel. The contribution of the Sec61 channel to export of misfolded proteins from the ER for degradation by proteasomes is still controversial, but the proteasome 19S regulatory particle (RP) is necessary and sufficient for extraction of specific misfolded proteins from the ER, and binds directly to the Sec61 channel. In this work we have identified an import-competent sec61 mutant, S353C, carrying a point mutation in ER-lumenal loop 7 which reduces affinity of the cytoplasmic face of the Sec61 channel for the 19S RP. This indicates that the interaction between the 19S RP and the Sec61 channel is dependent on conformational changes in Sec61p hinging on loop 7. The sec61-S353C mutant had no measurable ER import defects and did not cause ER stress in intact cells, but reduced ER-export of a 19S RP-dependent misfolded protein when proteasomes were limiting in a cell-free assay. Our data suggest that the interaction between the 19S RP and the Sec61 channel is essential for the export of specific substrates from the ER to the cytosol for proteasomal degradation.
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Affiliation(s)
- Marie-Luise Kaiser
- Department of Microbiology, Faculty of Natural Sciences and Technology VIII, Saarland University, 66123, Saarbrücken, Germany
| | - Karin Römisch
- Department of Microbiology, Faculty of Natural Sciences and Technology VIII, Saarland University, 66123, Saarbrücken, Germany
- * E-mail:
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43
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Zattas D, Hochstrasser M. Ubiquitin-dependent protein degradation at the yeast endoplasmic reticulum and nuclear envelope. Crit Rev Biochem Mol Biol 2014; 50:1-17. [PMID: 25231236 DOI: 10.3109/10409238.2014.959889] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The endoplasmic reticulum (ER) is the primary organelle in eukaryotic cells where membrane and secreted proteins are inserted into or across cell membranes. Its membrane bilayer and luminal compartments provide a favorable environment for the folding and assembly of thousands of newly synthesized proteins. However, protein folding is intrinsically error-prone, and various stress conditions can further increase levels of protein misfolding and damage, particularly in the ER, which can lead to cellular dysfunction and disease. The ubiquitin-proteasome system (UPS) is responsible for the selective destruction of a vast array of protein substrates, either for protein quality control or to allow rapid changes in the levels of specific regulatory proteins. In this review, we will focus on the components and mechanisms of ER-associated protein degradation (ERAD), an important branch of the UPS. ER membranes extend from subcortical regions of the cell to the nuclear envelope, with its continuous outer and inner membranes; the nuclear envelope is a specialized subdomain of the ER. ERAD presents additional challenges to the UPS beyond those faced with soluble substrates of the cytoplasm and nucleus. These include recognition of sugar modifications that occur in the ER, retrotranslocation of proteins across the membrane bilayer, and transfer of substrates from the ER extraction machinery to the proteasome. Here, we review characteristics of ERAD substrate degradation signals (degrons), mechanisms underlying substrate recognition and processing by the ERAD machinery, and ideas on the still unresolved problem of how substrate proteins are moved across and extracted from the ER membrane.
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Affiliation(s)
- Dimitrios Zattas
- Department of Molecular Biophysics & Biochemistry, Yale University , New Haven, CT , USA
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