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Voss CM, Arildsen L, Nissen JD, Waagepetersen HS, Schousboe A, Maechler P, Ott P, Vilstrup H, Walls AB. Glutamate Dehydrogenase Is Important for Ammonia Fixation and Amino Acid Homeostasis in Brain During Hyperammonemia. Front Neurosci 2021; 15:646291. [PMID: 34220417 PMCID: PMC8244593 DOI: 10.3389/fnins.2021.646291] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2020] [Accepted: 04/19/2021] [Indexed: 01/06/2023] Open
Abstract
Impaired liver function may lead to hyperammonemia and risk for hepatic encephalopathy. In brain, detoxification of ammonia is mediated mainly by glutamine synthetase (GS) in astrocytes. This requires a continuous de novo synthesis of glutamate, likely involving the action of both pyruvate carboxylase (PC) and glutamate dehydrogenase (GDH). An increased PC activity upon ammonia exposure and the importance of PC activity for glutamine synthesis has previously been demonstrated while the importance of GDH for generation of glutamate as precursor for glutamine synthesis has received little attention. We therefore investigated the functional importance of GDH for brain metabolism during hyperammonemia. To this end, brain slices were acutely isolated from transgenic CNS-specific GDH null or litter mate control mice and incubated in aCSF containing [U-13C]glucose in the absence or presence of 1 or 5 mM ammonia. In another set of experiments, brain slices were incubated in aCSF containing 1 or 5 mM 15N-labeled NH4Cl and 5 mM unlabeled glucose. Tissue extracts were analyzed for isotopic labeling in metabolites and for total amounts of amino acids. As a novel finding, we reveal a central importance of GDH function for cerebral ammonia fixation and as a prerequisite for de novo synthesis of glutamate and glutamine during hyperammonemia. Moreover, we demonstrated an important role of the concerted action of GDH and alanine aminotransferase in hyperammonemia; the products alanine and α-ketoglutarate serve as an ammonia sink and as a substrate for ammonia fixation via GDH, respectively. The role of this mechanism in human hyperammonemic states remains to be studied.
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Affiliation(s)
- Caroline M Voss
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lene Arildsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jakob D Nissen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Pierre Maechler
- Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Medical Centre, Geneva, Switzerland
| | - Peter Ott
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
| | - Hendrik Vilstrup
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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2
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Proteins moonlighting in tumor metabolism and epigenetics. Front Med 2021; 15:383-403. [PMID: 33387254 DOI: 10.1007/s11684-020-0818-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 07/27/2020] [Indexed: 02/07/2023]
Abstract
Cancer development is a complicated process controlled by the interplay of multiple signaling pathways and restrained by oxygen and nutrient accessibility in the tumor microenvironment. High plasticity in using diverse nutrients to adapt to metabolic stress is one of the hallmarks of cancer cells. To respond to nutrient stress and to meet the requirements for rapid cell proliferation, cancer cells reprogram metabolic pathways to take up more glucose and coordinate the production of energy and intermediates for biosynthesis. Such actions involve gene expression and activity regulation by the moonlighting function of oncoproteins and metabolic enzymes. The signal - moonlighting protein - metabolism axis facilitates the adaptation of tumor cells under varying environment conditions and can be therapeutically targeted for cancer treatment.
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3
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Wang X, Liu R, Qu X, Yu H, Chu H, Zhang Y, Zhu W, Wu X, Gao H, Tao B, Li W, Liang J, Li G, Yang W. α-Ketoglutarate-Activated NF-κB Signaling Promotes Compensatory Glucose Uptake and Brain Tumor Development. Mol Cell 2019; 76:148-162.e7. [PMID: 31447391 DOI: 10.1016/j.molcel.2019.07.007] [Citation(s) in RCA: 83] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Revised: 05/25/2019] [Accepted: 07/08/2019] [Indexed: 12/12/2022]
Abstract
The rapid proliferation of cancer cells and dysregulated vasculature within the tumor leads to limited nutrient accessibility. Cancer cells often rewire their metabolic pathways for adaption to nutrient stress, and the underlying mechanism remains largely unknown. Glutamate dehydrogenase 1 (GDH1) is a key enzyme in glutaminolysis that converts glutamate to α-ketoglutarate (α-KG). Here, we show that, under low glucose, GDH1 is phosphorylated at serine (S) 384 and interacts with RelA and IKKβ. GDH1-produced α-KG directly binds to and activates IKKβ and nuclear factor κB (NF-κB) signaling, which promotes glucose uptake and tumor cell survival by upregulating GLUT1, thereby accelerating gliomagenesis. In addition, GDH1 S384 phosphorylation correlates with the malignancy and prognosis of human glioblastoma. Our finding reveals a unique role of α-KG to directly regulate signal pathway, uncovers a distinct mechanism of metabolite-mediated NF-κB activation, and also establishes the critical role of α-KG-activated NF-κB in brain tumor development.
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Affiliation(s)
- Xiongjun Wang
- State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Innovation Center for Cell Signaling Network, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China; Shanghai Key Laboratory of Molecular Andrology, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China; Precise Genome Engineering Center, School of Life Sciences, Guangzhou University, Guangzhou 510006, China
| | - Ruilong Liu
- State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Innovation Center for Cell Signaling Network, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China; Shanghai Key Laboratory of Molecular Andrology, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China
| | - Xiujuan Qu
- Department of Medical Oncology, the First Hospital of China Medical University, Shenyang 110001, China
| | - Hua Yu
- State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Innovation Center for Cell Signaling Network, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China; Shanghai Key Laboratory of Molecular Andrology, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China
| | - Huiying Chu
- Laboratory of Molecular Modeling, State Key Lab of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - Yajuan Zhang
- State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Innovation Center for Cell Signaling Network, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China; Shanghai Key Laboratory of Molecular Andrology, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China
| | - Wencheng Zhu
- State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Innovation Center for Cell Signaling Network, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China
| | - Xueyuan Wu
- Department of Radiation Oncology, First Affiliated Hospital of Wenzhou Medical College, Wenzhou, Zhejiang 325000, China
| | - Hong Gao
- State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Innovation Center for Cell Signaling Network, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China; Shanghai Key Laboratory of Molecular Andrology, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China
| | - Bangbao Tao
- Department of Neurosurgery, XinHua Hospital School of Medicine, Shanghai Jiaotong University, Shanghai 200092, China
| | - Wenfeng Li
- Department of Radiation Oncology, First Affiliated Hospital of Wenzhou Medical College, Wenzhou, Zhejiang 325000, China
| | - Ji Liang
- State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Innovation Center for Cell Signaling Network, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China; Shanghai Key Laboratory of Molecular Andrology, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China
| | - Guohui Li
- Laboratory of Molecular Modeling, State Key Lab of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
| | - Weiwei Yang
- State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Innovation Center for Cell Signaling Network, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China; Shanghai Key Laboratory of Molecular Andrology, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China.
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4
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Nassar OM, Li C, Stanley CA, Pettitt BM, Smith TJ. Glutamate dehydrogenase: Structure of a hyperinsulinism mutant, corrections to the atomic model, and insights into a regulatory site. Proteins 2018; 87:41-50. [PMID: 30367518 DOI: 10.1002/prot.25620] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 10/10/2018] [Accepted: 10/16/2018] [Indexed: 11/06/2022]
Abstract
Mammalian glutamate dehydrogenase (GDH) has complex allosteric regulation and the loss of GTP inhibition causes the hyperinsulinism/hyperammonemia syndrome (HHS) where insulin is hypersecreted upon consumption of protein. The archetypical HHS lesion is H454Y and lies in the GTP binding pocket. To better understand the mechanism of HHS, we determined the crystal structure of H454Y. When the bovine GDH crystal structures were minimized to prepare for further computational analysis, unusually large deviations were found at the allosteric NADH binding site due to chemical sequence errors. Notably, 387 lies in an allosteric where several activators and inhibitors bind and should be lysine rather than asparagine. All structures were re-refined and the consequence of this sequence error on NADH binding was calculated using free energy perturbation. The binding free energy penalty going from the correct to incorrect sequence found is +5 kcal/mol per site and therefore has a significant impact on drug development. BROADER AUDIENCE ABSTRACT: Glutamate dehydrogenase is a key enzyme involved in amino acid catabolism. As such, it is heavily regulated in animals by a wide array of metabolites. The importance of this regulation is most apparent in a genetic disorder called hyperinsulinism/hyperammonemia (HHS) where patients hypersecrete insulin upon the consumption of protein. We determined the atomic structure of one of these HHS mutants to better understand the disease and also analyzed an allosteric regulatory site.
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Affiliation(s)
- Omneya M Nassar
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas
| | - Changhong Li
- Division of Endocrinology, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - Charles A Stanley
- Division of Endocrinology, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - B Montgomery Pettitt
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas.,Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas
| | - Thomas J Smith
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas
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5
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Gaspar C, Silva-Marrero JI, Salgado MC, Baanante IV, Metón I. Role of upstream stimulatory factor 2 in glutamate dehydrogenase gene transcription. J Mol Endocrinol 2018; 60:247-259. [PMID: 29438976 DOI: 10.1530/jme-17-0142] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Accepted: 02/08/2018] [Indexed: 12/18/2022]
Abstract
Glutamate dehydrogenase (Gdh) plays a central role in ammonia detoxification by catalysing reversible oxidative deamination of l-glutamate into α-ketoglutarate using NAD+ or NADP+ as cofactor. To gain insight into transcriptional regulation of glud, the gene that codes for Gdh, we isolated and characterised the 5' flanking region of glud from gilthead sea bream (Sparus aurata). In addition, tissue distribution, the effect of starvation as well as short- and long-term refeeding on Gdh mRNA levels in the liver of S. aurata were also addressed. 5'-Deletion analysis of glud promoter in transiently transfected HepG2 cells, electrophoretic mobility shift assays, chromatin immunoprecipitation (ChIP) and site-directed mutagenesis allowed us to identify upstream stimulatory factor 2 (Usf2) as a novel factor involved in the transcriptional regulation of glud Analysis of tissue distribution of Gdh and Usf2 mRNA levels by reverse transcriptase-coupled quantitative real-time PCR (RT-qPCR) showed that Gdh is mainly expressed in the liver of S. aurata, while Usf2 displayed ubiquitous distribution. RT-qPCR and ChIP assays revealed that long-term starvation down-regulated the hepatic expression of Gdh and Usf2 to similar levels and reduced Usf2 binding to glud promoter, while refeeding resulted in a slow but gradual restoration of both Gdh and Usf2 mRNA abundance. Herein, we demonstrate that Usf2 transactivates S. aurata glud by binding to an E-box located in the proximal region of glud promoter. In addition, our findings provide evidence for a new regulatory mechanism involving Usf2 as a key factor in the nutritional regulation of glud transcription in the fish liver.
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Affiliation(s)
- Carlos Gaspar
- Secció de Bioquímica i Biologia Molecular, Departament de Bioquímica i Fisiologia, Facultat de Farmàcia i Ciències de l'Alimentació, Universitat de Barcelona, Barcelona, Spain
| | - Jonás I Silva-Marrero
- Secció de Bioquímica i Biologia Molecular, Departament de Bioquímica i Fisiologia, Facultat de Farmàcia i Ciències de l'Alimentació, Universitat de Barcelona, Barcelona, Spain
| | - María C Salgado
- Servei de Bioquímica Clínica, Hospital Sant Joan de Déu, Barcelona, Spain
| | - Isabel V Baanante
- Secció de Bioquímica i Biologia Molecular, Departament de Bioquímica i Fisiologia, Facultat de Farmàcia i Ciències de l'Alimentació, Universitat de Barcelona, Barcelona, Spain
| | - Isidoro Metón
- Secció de Bioquímica i Biologia Molecular, Departament de Bioquímica i Fisiologia, Facultat de Farmàcia i Ciències de l'Alimentació, Universitat de Barcelona, Barcelona, Spain
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6
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Grimaldi M, Karaca M, Latini L, Brioudes E, Schalch T, Maechler P. Identification of the molecular dysfunction caused by glutamate dehydrogenase S445L mutation responsible for hyperinsulinism/hyperammonemia. Hum Mol Genet 2018; 26:3453-3465. [PMID: 28911206 DOI: 10.1093/hmg/ddx213] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2017] [Accepted: 06/01/2017] [Indexed: 01/14/2023] Open
Abstract
Congenital hyperinsulinism/hyperammonemia (HI/HA) syndrome gives rise to unregulated protein-induced insulin secretion from pancreatic beta-cells, fasting hypoglycemia and elevated plasma ammonia levels. Mutations associated with HI/HA were identified in the Glud1 gene, encoding for glutamate dehydrogenase (GDH). We aimed at identifying the molecular causes of dysregulation in insulin secretion and ammonia production conferred by the most frequent HI/HA mutation Ser445Leu. Following transduction with adenoviruses carrying the human GDH-wild type or GDH-S445L-mutant gene, immunoblotting showed efficient expression of the transgenes in all the investigated cell types. Enzymatic activity tested in INS-1E beta-cells revealed that the mutant was much more sensitive to the allosteric activator ADP, rendering it highly responsive to substrates. INS-1E cells expressing either the wild type or mutant GDH responded similarly to glucose stimulation regarding mitochondrial activation and insulin secretion. However, at basal glucose glutamine stimulation increased mitochondrial activity and insulin release only in the mutant cells. In mouse and human islets, expression of mutant GDH resulted in robust elevation of insulin secretion upon glutamine stimulation, not observed in control islets. Hepatocytes expressing either the wild type or mutant GDH produced similar levels of ammonia when exposed to glutamine, although alanine response was strongly elevated with the mutant form. In conclusion, the GDH-S445L mutation confers hyperactivity to this enzyme due to higher sensitivity to ADP allosteric activation. This renders beta-cells responsive to amino acid stimulation, explaining protein-induced hypoglycemia secondary to non-physiological insulin release. Hepatocytes carrying mutant GDH produced more ammonia upon alanine exposure, which underscores hyperammonemia developed by the patients.
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Affiliation(s)
- Mariagrazia Grimaldi
- Department of Cell Physiology and Metabolism.,Faculty Diabetes Center, University of Geneva Medical Center, 1206 Geneva, Switzerland
| | - Melis Karaca
- Department of Cell Physiology and Metabolism.,Faculty Diabetes Center, University of Geneva Medical Center, 1206 Geneva, Switzerland
| | - Livia Latini
- Department of Cell Physiology and Metabolism.,Faculty Diabetes Center, University of Geneva Medical Center, 1206 Geneva, Switzerland
| | - Estelle Brioudes
- Faculty Diabetes Center, University of Geneva Medical Center, 1206 Geneva, Switzerland.,Department of Surgery, Cell Isolation and Transplantation Center, Geneva University Hospital, Geneva, Switzerland
| | - Thomas Schalch
- Department of Molecular Biology, Faculty of Science, Institute of Genetics and Genomics of Geneva (iGE3), Sciences III, University of Geneva, 1211 Geneva 4, Switzerland
| | - Pierre Maechler
- Department of Cell Physiology and Metabolism.,Faculty Diabetes Center, University of Geneva Medical Center, 1206 Geneva, Switzerland
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7
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Kim AY, Jeong KH, Lee JH, Kang Y, Lee SH, Baik EJ. Glutamate dehydrogenase as a neuroprotective target against brain ischemia and reperfusion. Neuroscience 2016; 340:487-500. [PMID: 27845178 DOI: 10.1016/j.neuroscience.2016.11.007] [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: 06/17/2016] [Revised: 11/02/2016] [Accepted: 11/06/2016] [Indexed: 01/13/2023]
Abstract
Deregulation of glutamate homeostasis is associated with degenerative neurological disorders. Glutamate dehydrogenase (GDH) is important for glutamate metabolism and plays a central role in expanding the pool of tricarboxylic acid (TCA) cycle intermediate alpha-ketoglutarate (α-KG), which improves overall bioenergetics. Under high energy demand, maintenance of ATP production results in functionally active mitochondria. Here, we tested whether the modulation of GDH activity can rescue ischemia/reperfusion-induced neuronal death in an in vivo mouse model of middle artery occlusion and an in vitro oxygen/glucose depletion model. Iodoacetate, an inhibitor of glycolysis, was also used in a model of energy failure, remarkably depleting ATP and α-KG. To stimulate GDH activity, the GDH activator 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid and potential activator beta-lapachone were used. The GDH activators restored α-KG and ATP levels in the injury models and provided potent neuroprotection. We also found that beta-lapachone increased glutamate utilization, accompanied by a reduction in extracellular glutamate. Thus, our hypothesis that mitochondrial GDH activators increase α-KG production as an alternative energy source for use in the TCA cycle under energy-depleted conditions was confirmed. Our results suggest that increasing GDH-mediated glutamate oxidation represents a new therapeutic intervention for neurodegenerative disorders, including stoke.
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Affiliation(s)
- A Young Kim
- Department of Physiology, Ajou University School of Medicine, Suwon 16499, Republic of Korea; Chronic Inflammatory Disease Research Center, Ajou University School of Medicine, Suwon 16499, Republic of Korea
| | - Kyeong-Hoon Jeong
- Gachon University of Medicine and Science, Incheon 406-840, Republic of Korea
| | - Jae Ho Lee
- Department of Biochemistry, Ajou University School of Medicine, Suwon 16499, Republic of Korea
| | - Yup Kang
- Chronic Inflammatory Disease Research Center, Ajou University School of Medicine, Suwon 16499, Republic of Korea
| | - Soo Hwan Lee
- Department of Physiology, Ajou University School of Medicine, Suwon 16499, Republic of Korea
| | - Eun Joo Baik
- Department of Physiology, Ajou University School of Medicine, Suwon 16499, Republic of Korea; Chronic Inflammatory Disease Research Center, Ajou University School of Medicine, Suwon 16499, Republic of Korea.
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8
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Shafi AA, Putluri V, Arnold JM, Tsouko E, Maity S, Roberts JM, Coarfa C, Frigo DE, Putluri N, Sreekumar A, Weigel NL. Differential regulation of metabolic pathways by androgen receptor (AR) and its constitutively active splice variant, AR-V7, in prostate cancer cells. Oncotarget 2016; 6:31997-2012. [PMID: 26378018 PMCID: PMC4741655 DOI: 10.18632/oncotarget.5585] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Accepted: 08/19/2015] [Indexed: 11/25/2022] Open
Abstract
Metastatic prostate cancer (PCa) is primarily an androgen-dependent disease, which is treated with androgen deprivation therapy (ADT). Tumors usually develop resistance (castration-resistant PCa [CRPC]), but remain androgen receptor (AR) dependent. Numerous mechanisms for AR-dependent resistance have been identified including expression of constitutively active AR splice variants lacking the hormone-binding domain. Recent clinical studies show that expression of the best-characterized AR variant, AR-V7, correlates with resistance to ADT and poor outcome. Whether AR-V7 is simply a constitutively active substitute for AR or has novel gene targets that cause unique downstream changes is unresolved. Several studies have shown that AR activation alters cell metabolism. Using LNCaP cells with inducible expression of AR-V7 as a model system, we found that AR-V7 stimulated growth, migration, and glycolysis measured by ECAR (extracellular acidification rate) similar to AR. However, further analyses using metabolomics and metabolic flux assays revealed several differences. Whereas AR increased citrate levels, AR-V7 reduced citrate mirroring metabolic shifts observed in CRPC patients. Flux analyses indicate that the low citrate is a result of enhanced utilization rather than a failure to synthesize citrate. Moreover, flux assays suggested that compared to AR, AR-V7 exhibits increased dependence on glutaminolysis and reductive carboxylation to produce some of the TCA (tricarboxylic acid cycle) metabolites. These findings suggest that these unique actions represent potential therapeutic targets.
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Affiliation(s)
- Ayesha A Shafi
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - Vasanta Putluri
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA.,Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, TX, USA.,Alkek Center for Molecular Discovery, Baylor College of Medicine, Houston, TX, USA
| | - James M Arnold
- Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, TX, USA
| | - Efrosini Tsouko
- Center for Nuclear Receptors and Cell Signaling, Department of Biology and Biochemistry, University of Houston, Houston, TX, USA
| | - Suman Maity
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA.,Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, TX, USA.,Alkek Center for Molecular Discovery, Baylor College of Medicine, Houston, TX, USA
| | - Justin M Roberts
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - Cristian Coarfa
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA.,Alkek Center for Molecular Discovery, Baylor College of Medicine, Houston, TX, USA
| | - Daniel E Frigo
- Center for Nuclear Receptors and Cell Signaling, Department of Biology and Biochemistry, University of Houston, Houston, TX, USA.,Genomic Medicine Program, Houston Methodist Research Institute, Houston, TX, USA
| | - Nagireddy Putluri
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA.,Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, TX, USA.,Alkek Center for Molecular Discovery, Baylor College of Medicine, Houston, TX, USA
| | - Arun Sreekumar
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA.,Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, TX, USA.,Alkek Center for Molecular Discovery, Baylor College of Medicine, Houston, TX, USA
| | - Nancy L Weigel
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA.,Scott Department of Urology, Baylor College of Medicine, Houston, TX, USA
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9
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Vetterli L, Carobbio S, Frigerio F, Karaca M, Maechler P. The Amplifying Pathway of the β-Cell Contributes to Diet-induced Obesity. J Biol Chem 2016; 291:13063-75. [PMID: 27137930 DOI: 10.1074/jbc.m115.707448] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Indexed: 12/24/2022] Open
Abstract
Efficient energy storage in adipose tissues requires optimal function of the insulin-producing β-cell, whereas its dysfunction promotes diabetes. The associated paradox related to β-cell efficiency is that excessive accumulation of fat in adipose tissue predisposes for type 2 diabetes. Insulin exocytosis is regulated by intracellular metabolic signal transduction, with glutamate dehydrogenase playing a key role in the amplification of the secretory response. Here, we used mice with β-cell-selective glutamate dehydrogenase deletion (βGlud1(-/-)), lacking an amplifying pathway of insulin secretion. As opposed to control mice, βGlud1(-/-) animals fed a high calorie diet maintained glucose tolerance and did not develop diet-induced obesity. Islets of βGlud1(-/-) mice did not increase their secretory response upon high calorie feeding, as did islets of control mice. Inhibited adipose tissue expansion observed in knock-out mice correlated with lower expression of genes responsible for adipogenesis. Rather than being efficiently stored, lipids were consumed at a higher rate in βGlud1(-/-) mice compared with controls, in particular during food intake periods. These results show that reduced β-cell function prior to high calorie feeding prevented diet-induced obesity.
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Affiliation(s)
- Laurène Vetterli
- From the Department of Cell Physiology and Metabolism and Faculty Diabetes Center, Geneva University Medical Centre, 1211 Geneva 4, Switzerland
| | - Stefania Carobbio
- From the Department of Cell Physiology and Metabolism and Faculty Diabetes Center, Geneva University Medical Centre, 1211 Geneva 4, Switzerland
| | - Francesca Frigerio
- From the Department of Cell Physiology and Metabolism and Faculty Diabetes Center, Geneva University Medical Centre, 1211 Geneva 4, Switzerland
| | - Melis Karaca
- From the Department of Cell Physiology and Metabolism and Faculty Diabetes Center, Geneva University Medical Centre, 1211 Geneva 4, Switzerland
| | - Pierre Maechler
- From the Department of Cell Physiology and Metabolism and Faculty Diabetes Center, Geneva University Medical Centre, 1211 Geneva 4, Switzerland
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10
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GDH-Dependent Glutamate Oxidation in the Brain Dictates Peripheral Energy Substrate Distribution. Cell Rep 2015; 13:365-75. [PMID: 26440896 DOI: 10.1016/j.celrep.2015.09.003] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Revised: 08/17/2015] [Accepted: 09/01/2015] [Indexed: 12/27/2022] Open
Abstract
Glucose, the main energy substrate used in the CNS, is continuously supplied by the periphery. Glutamate, the major excitatory neurotransmitter, is foreseen as a complementary energy contributor in the brain. In particular, astrocytes actively take up glutamate and may use it through oxidative glutamate dehydrogenase (GDH) activity. Here, we investigated the significance of glutamate as energy substrate for the brain. Upon glutamate exposure, astrocytes generated ATP in a GDH-dependent way. The observed lack of glutamate oxidation in brain-specific GDH null CnsGlud1(-/-) mice resulted in a central energy-deprivation state with increased ADP/ATP ratios and phospho-AMPK in the hypothalamus. This induced changes in the autonomous nervous system balance, with increased sympathetic activity promoting hepatic glucose production and mobilization of substrates reshaping peripheral energy stores. Our data reveal the importance of glutamate as necessary energy substrate for the brain and the role of central GDH in the regulation of whole-body energy homeostasis.
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11
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Glutamate Dehydrogenase Deficiency in Cerebellar Degenerations: Clinical, Biochemical and Molecular Genetic Aspects. Can J Neurol Sci 2015. [DOI: 10.1017/s0317167100048617] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
ABSTRACT:Glutamate dehydrogenase (GDH), an enzyme central to glutamate metabolism, is significantly reduced in patients with heterogenous neurological disorders characterized by multiple system atrophy (MSA) and predominant involvement of the cerebellum and its connections. In human brain, GDH exists in multiple isoforms differing in their isoelectric point and molecular mass. These are differentially reduced in quantity and altered in catalytic activity in patients with clinically distinct forms of MSA, thus suggesting that these GDH isoproteins are under different genetic control. Dysregulation of glutamate metabolism occurs in patients with GDH deficiency and is thought to mediate the disease’s neurodegeneration via neuroexcitotoxic mechanisms. This possibility is supported by additional data showing that glutamate binding sites are significantly decreased in cerebellar tissue obtained at autopsy from MSA patients. At the molecular biological level, several cDNAs specific for human GDH have been isolated recently and cloned. Northern blot analysis of various human tissues, including brain, has revealed the presence of multiple GDH-specific mRNAs. In addition, multiple GDH-specific genes are present in humans and these data are consistent with the possibility that the various GDH isoproteins are encoded by different genes. These advances have laid the groundwork for characterizing the human GDH genes and their products in health and disease.
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Botman D, Tigchelaar W, Van Noorden CJF. Determination of glutamate dehydrogenase activity and its kinetics in mouse tissues using metabolic mapping (quantitative enzyme histochemistry). J Histochem Cytochem 2014; 62:802-12. [PMID: 25124006 PMCID: PMC4230541 DOI: 10.1369/0022155414549071] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Glutamate dehydrogenase (GDH) catalyses the reversible conversion of glutamate into α-ketoglutarate with the concomitant reduction of NAD(P)(+) to NAD(P)H or vice versa. GDH activity is subject to complex allosteric regulation including substrate inhibition. To determine GDH kinetics in situ, we assessed the effects of various glutamate concentrations in combination with either the coenzyme NAD(+) or NADP(+) on GDH activity in mouse liver cryostat sections using metabolic mapping. NAD(+)-dependent GDH V(max) was 2.5-fold higher than NADP(+)-dependent V(max), whereas the K(m) was similar, 1.92 mM versus 1.66 mM, when NAD(+) or NADP(+) was used, respectively. With either coenzyme, V(max) was determined at 10 mM glutamate and substrate inhibition was observed at higher glutamate concentrations with a K(i) of 12.2 and 3.95 for NAD(+) and NADP(+) used as coenzyme, respectively. NAD(+)- and NADP(+)-dependent GDH activities were examined in various mouse tissues. GDH activity was highest in liver and much lower in other tissues. In all tissues, the highest activity was found when NAD(+) was used as a coenzyme. In conclusion, GDH activity in mice is highest in the liver with NAD(+) as a coenzyme and highest GDH activity was determined at a glutamate concentration of 10 mM.
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Affiliation(s)
- Dennis Botman
- Department of Cell Biology and Histology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands (DB, WT, CJFVN)
| | - Wikky Tigchelaar
- Department of Cell Biology and Histology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands (DB, WT, CJFVN)
| | - Cornelis J F Van Noorden
- Department of Cell Biology and Histology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands (DB, WT, CJFVN)
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The discovery of human of GLUD2 glutamate dehydrogenase and its implications for cell function in health and disease. Neurochem Res 2013; 39:460-70. [PMID: 24352816 DOI: 10.1007/s11064-013-1227-5] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2013] [Revised: 12/07/2013] [Accepted: 12/11/2013] [Indexed: 10/25/2022]
Abstract
While the evolutionary changes that led to traits unique to humans remain unclear, there is increasing evidence that enrichment of the human genome through DNA duplication processes may have contributed to traits such as bipedal locomotion, higher cognitive abilities and language. Among the genes that arose through duplication in primates during the period of increased brain development was GLUD2, which encodes the hGDH2 isoform of glutamate dehydrogenase expressed in neural and other tissues. Glutamate dehydrogenase GDH is an enzyme central to the metabolism of glutamate, the main excitatory neurotransmitter in mammalian brain involved in a multitude of CNS functions, including cognitive processes. In nerve tissue GDH is expressed in astrocytes that wrap excitatory synapses, where it is thought to play a role in the metabolic fate of glutamate removed from the synaptic cleft during excitatory transmission. Expression of GDH rises sharply during postnatal brain development, coinciding with nerve terminal sprouting and synaptogenesis. Compared to the original hGDH1 (encoded by the GLUD1 gene), which is potently inhibited by GTP generated by the Krebs cycle, hGDH2 can function independently of this energy switch. In addition, hGDH2 can operate efficiently in the relatively acidic environment that prevails in astrocytes following glutamate uptake. This adaptation is thought to provide a biological advantage by enabling enhanced enzyme catalysis under intense excitatory neurotransmission. While the novel protein may help astrocytes to handle increased loads of transmitter glutamate, dissociation of hGDH2 from GTP control may render humans vulnerable to deregulation of this enzyme's function. Here we will retrace the cloning and characterization of the novel GLUD2 gene and the potential implications of this discovery in the understanding of mechanisms that permitted the brain and other organs that express hGDH2 to fine-tune their functions in order to meet new challenging demands. In addition, the potential role of gain-of-function of hGDH2 variants in human neurodegenerative processes will be considered.
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Karaca M, Maechler P. Development of Mice with Brain-Specific Deletion of Floxed Glud1 (Glutamate Dehydrogenase 1) Using Cre Recombinase Driven by the Nestin Promoter. Neurochem Res 2013; 39:456-9. [DOI: 10.1007/s11064-013-1041-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Revised: 04/08/2013] [Accepted: 04/09/2013] [Indexed: 12/20/2022]
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Frigerio F, Karaca M, De Roo M, Mlynárik V, Skytt DM, Carobbio S, Pajęcka K, Waagepetersen HS, Gruetter R, Muller D, Maechler P. Deletion of glutamate dehydrogenase 1 (Glud1) in the central nervous system affects glutamate handling without altering synaptic transmission. J Neurochem 2012; 123:342-8. [PMID: 22924626 DOI: 10.1111/j.1471-4159.2012.07933.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2012] [Revised: 07/30/2012] [Accepted: 08/15/2012] [Indexed: 12/11/2022]
Abstract
Glutamate dehydrogenase (GDH), encoded by GLUD1, participates in the breakdown and synthesis of glutamate, the main excitatory neurotransmitter. In the CNS, besides its primary signaling function, glutamate is also at the crossroad of metabolic and neurotransmitter pathways. Importance of brain GDH was questioned here by generation of CNS-specific GDH-null mice (CnsGlud1(-/-)); which were viable, fertile and without apparent behavioral problems. GDH immunoreactivity as well as enzymatic activity were absent in Cns-Glud1(-/-) brains. Immunohistochemical analyses on brain sections revealed that the pyramidal cells of control animals were positive for GDH, whereas the labeling was absent in hippocampal sections of Cns-Glud1(-/-) mice. Electrophysiological recordings showed that deletion of GDH within the CNS did not alter synaptic transmission in standard conditions. Cns-Glud1(-/-) mice exhibited deficient oxidative catabolism of glutamate in astrocytes, showing that GDH is required for Krebs cycle pathway. As revealed by NMR studies, brain glutamate levels remained unchanged, whereas glutamine levels were increased. This pattern was favored by up-regulation of astrocyte-type glutamate and glutamine transporters and of glutamine synthetase. Present data show that the lack of GDH in the CNS modifies the metabolic handling of glutamate without altering synaptic transmission.
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Affiliation(s)
- Francesca Frigerio
- Department of Cell Physiology and Metabolism, University of Geneva Medical Centre, Geneva, Switzerland
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Vetterli L, Carobbio S, Pournourmohammadi S, Martin-Del-Rio R, Skytt DM, Waagepetersen HS, Tamarit-Rodriguez J, Maechler P. Delineation of glutamate pathways and secretory responses in pancreatic islets with β-cell-specific abrogation of the glutamate dehydrogenase. Mol Biol Cell 2012; 23:3851-62. [PMID: 22875990 PMCID: PMC3459861 DOI: 10.1091/mbc.e11-08-0676] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The amino acid profile and the secretory responses of glutamate dehydrogenase (GDH)-deficient β-cells are characterized. This study shows that GDH is essential for both insulin release and net glutamate synthesis evoked by glucose. Adding cellular glutamate restored the full development of glucose-stimulated insulin secretion, showing the requirement for permissive glutamate levels. In pancreatic β-cells, glutamate dehydrogenase (GDH) modulates insulin secretion, although its function regarding specific secretagogues is unclear. This study investigated the role of GDH using a β-cell–specific GDH knockout mouse model, called βGlud1−/−. The absence of GDH in islets isolated from βGlud1–/– mice resulted in abrogation of insulin release evoked by glutamine combined with 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid or l-leucine. Reintroduction of GDH in βGlud1–/– islets fully restored the secretory response. Regarding glucose stimulation, insulin secretion in islets isolated from βGlud1–/– mice exhibited half of the response measured in control islets. The amplifying pathway, tested at stimulatory glucose concentrations in the presence of KCl and diazoxide, was markedly inhibited in βGlud1–/– islets. On glucose stimulation, net synthesis of glutamate from α-ketoglutarate was impaired in GDH-deficient islets. Accordingly, glucose-induced elevation of glutamate levels observed in control islets was absent in βGlud1–/– islets. Parallel biochemical pathways, namely alanine and aspartate aminotransferases, could not compensate for the lack of GDH. However, the secretory response to glucose was fully restored by the provision of cellular glutamate when βGlud1–/– islets were exposed to dimethyl glutamate. This shows that permissive levels of glutamate are required for the full development of glucose-stimulated insulin secretion and that GDH plays an indispensable role in this process.
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Affiliation(s)
- Laurène Vetterli
- Department of Cell Physiology and Metabolism, University of Geneva Medical Center, Geneva, Switzerland
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Karaca M, Frigerio F, Maechler P. From pancreatic islets to central nervous system, the importance of glutamate dehydrogenase for the control of energy homeostasis. Neurochem Int 2011; 59:510-7. [DOI: 10.1016/j.neuint.2011.03.024] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Revised: 03/21/2011] [Accepted: 03/23/2011] [Indexed: 11/25/2022]
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Mariotti V, Melissari E, Amar S, Conte A, Belmaker RH, Agam G, Pellegrini S. Effect of prolonged phenytoin administration on rat brain gene expression assessed by DNA microarrays. Exp Biol Med (Maywood) 2010; 235:300-10. [PMID: 20404047 DOI: 10.1258/ebm.2009.009225] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Preliminary clinical trials have recently shown that phenytoin, an antiepileptic drug, may also be beneficial for treatment of bipolar disorder. To examine molecular mechanisms of action of phenytoin as a potential mood stabilizer, DNA microarrays were used to study the effect of phenytoin on gene expression in the hippocampus and frontal cortex of Sprague-Dawley rats. While our particular interest is in bipolar disorder, this is the first DNA microarray study on the effect of phenytoin in brain tissue, in general. As compared with control rats, treated rats had 508 differentially expressed genes in the hippocampus and 62 in the frontal cortex. Phenytoin modulated the expression of genes which may affect neurotransmission, e.g. glutamate decarboxylase 1 (Gad1) and gamma-aminobutyric acid A receptor, alpha 5 (Gabra5). Phenytoin also exerted an effect on neuroprotection-related genes, namely the survival-promoting and antioxidant genes v-akt murine thymoma viral oncogene homolog 1 (Akt1), FK506 binding protein 12-rapamycin associated protein 1 (Frap1), glutathione reductase (Gsr) and glutamate cysteine ligase catalytic subunit (Gclc). The expression of genes potentially associated with mechanisms of mood regulation such as adenylate cyclase-associated protein 1 (Cap1), Glial Fibrillary Acidic Protein (Gfap) and prodynorphin (Pdyn) was also altered. Some of the above genes are regarded as targets of classical mood stabilizers and their modulation supports the clinical observation that phenytoin may have mood-stabilizing effects. The results may provide new insights regarding the mechanism of action of phenytoin and genes found differentially expressed following phenytoin administration may play a role in the pathophysiology of either bipolar disorder or epilepsy.
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Affiliation(s)
- Veronica Mariotti
- Department of Experimental Pathology, Medical Biotechnology, Infectious Diseases and Epidemiology, University of Pisa, Italy
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Lee JY, Lee JH, Moon YW, Chun BG, Jahng JW. Proteomic analysis of lithium-induced gene expression in the rat hypothalamus. Int J Neurosci 2010; 119:1267-81. [PMID: 19922355 DOI: 10.1080/00207450902889201] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
The hypothalamic proteomes were analyzed 1 and 6 hr after an intraperitoneal injection of lithium chloride or sodium chloride (0.15 M, 12 ml/kg). Results showed that expression of 14 and 32 proteomes was increased consistently by 1 hr and 6 hr of lithium treatment, respectively. Among them, tentative implications of glial fibrillary acidic protein, receptor-type protein tyrosine phosphatase, spectrin, and glutamate dehydrogenase in the lithium-induced activation of the hypothalamic-pituitary-adrenal axis, and conditioned taste aversion have been discussed. The proteomes listed in this study will provide, at least, a new insight to understand the molecular mechanism of lithium's action in the brain.
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Affiliation(s)
- Joo Young Lee
- Department of Pharmacology, Korea University College of Medicine, Seoul, Korea
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20
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The human GLUD2 glutamate dehydrogenase: localization and functional aspects. Neurochem Int 2009; 55:52-63. [PMID: 19428807 DOI: 10.1016/j.neuint.2009.03.001] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2008] [Revised: 03/02/2009] [Accepted: 03/04/2009] [Indexed: 10/21/2022]
Abstract
In all mammals, glutamate dehydrogenase (GDH), an enzyme central to the metabolism of glutamate, is encoded by a single gene (GLUD1 in humans) which is expressed widely (housekeeping). Humans and other primates also possess a second gene, GLUD2, which encodes a highly homologous GDH isoenzyme (hGDH2) expressed predominantly in retina, brain and testis. There is evidence that GLUD1 was retro-posed <23 million years ago to the X chromosome, where it gave rise to GLUD2 through random mutations and natural selection. These mutations provided the novel enzyme with unique properties thought to facilitate its function in the particular milieu of the nervous system. hGDH2, having been dissociated from GTP control (through the Gly456Ala change), is mainly regulated by rising levels of ADP/l-leucine. To achieve full-range regulation by these activators, hGDH2 needs to set its basal activity at low levels (<10% of full capacity), a property largely conferred by the evolutionary Arg443Ser change. Studies of structure/function relationships have identified residues in the regulatory domain of hGDH2 that modify basal catalytic activity and regulation. In addition, enzyme concentration and buffer ionic strength can influence basal enzyme activity. While mature hGDH1 and hGDH2 isoproteins are highly homologous, their predicted leader peptide sequences show a greater degree of divergence. Study of the subcellular sites targeted by hGDH2 in three different cultured cell lines using a GLUD2/EGFP construct revealed that hGDH2 localizes mainly to mitochondria and to a lesser extent to the endoplasmic reticulum of these cells. The implications of these findings for the potential role of this enzyme in the biology of the nervous system in health and disease are discussed.
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Carobbio S, Frigerio F, Rubi B, Vetterli L, Bloksgaard M, Gjinovci A, Pournourmohammadi S, Herrera PL, Reith W, Mandrup S, Maechler P. Deletion of glutamate dehydrogenase in beta-cells abolishes part of the insulin secretory response not required for glucose homeostasis. J Biol Chem 2008; 284:921-9. [PMID: 19015267 DOI: 10.1074/jbc.m806295200] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insulin exocytosis is regulated in pancreatic ss-cells by a cascade of intracellular signals translating glucose levels into corresponding secretory responses. The mitochondrial enzyme glutamate dehydrogenase (GDH) is regarded as a major player in this process, although its abrogation has not been tested yet in animal models. Here, we generated transgenic mice, named betaGlud1(-/-), with ss-cell-specific GDH deletion. Our results show that GDH plays an essential role in the full development of the insulin secretory response. In situ pancreatic perfusion revealed that glucose-stimulated insulin secretion was reduced by 37% in betaGlud1(-/-). Furthermore, isolated islets with either constitutive or acute adenovirus-mediated knock-out of GDH showed a 49 and 38% reduction in glucose-induced insulin release, respectively. Adenovirus-mediated re-expression of GDH in betaGlud1(-/-) islets fully restored glucose-induced insulin release. Thus, GDH appears to account for about 40% of glucose-stimulated insulin secretion and to lack redundant mechanisms. In betaGlud1(-/-) mice, the reduced secretory capacity resulted in lower plasma insulin levels in response to both feeding and glucose load, while body weight gain was preserved. The results demonstrate that GDH is essential for the full development of the secretory response in beta-cells. However, maximal secretory capacity is not required for maintenance of glucose homeostasis in normo-caloric conditions.
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Tissue specificity of mitochondrial glutamate pathways and the control of metabolic homeostasis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:965-72. [PMID: 18486589 DOI: 10.1016/j.bbabio.2008.04.031] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Revised: 04/11/2008] [Accepted: 04/22/2008] [Indexed: 11/24/2022]
Abstract
Glutamate is implicated in numerous metabolic and signalling functions that vary according to specific tissues. Glutamate metabolism is tightly controlled by activities of mitochondrial enzymes and transmembrane carriers, in particular glutamate dehydrogenase and mitochondrial glutamate carriers that have been identified in recent years. It is remarkable that, although glutamate-specific enzymes and transporters share similar properties in most tissues, their regulation varies greatly according to particular organs in order to achieve tissue specific functions. This is illustrated in this review when comparing glutamate handling in liver, brain, and pancreatic beta-cells. We describe the main cellular glutamate pathways and their specific functions in different tissues, ultimately contributing to the control of metabolic homeostasis at the organism level.
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Choi MM, Kim EA, Choi SY, Kim TU, Cho SW, Yang SJ. Inhibitory properties of nerve-specific human glutamate dehydrogenase isozyme by chloroquine. BMB Rep 2008; 40:1077-82. [PMID: 18047806 DOI: 10.5483/bmbrep.2007.40.6.1077] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Human glutamate dehydrogenase exists in hGDH1 (housekeeping isozyme) and in hGDH2 (nerve-specific isozyme), which differ markedly in their allosteric regulation. In the nervous system, GDH is enriched in astrocytes and is important for recycling glutamate, a major excitatory neurotransmitter during neurotransmission. Chloroquine has been known to be a potent inhibitor of house-keeping GDH1 in permeabilized liver and kidney-cortex of rabbit. However, the effects of chloroquine on nerve-specific GDH2 have not been reported yet. In the present study, we have investigated the effects of chloroquine on hGDH2 at various conditions and showed that chloroquine could inhibit the activity of hGDH2 at dose-dependent manner. Studies of the chloroquine inhibition on enzyme activity revealed that hGDH2 was relatively less sensitive to chloroquine inhibition than house-keeping hGDH1. Incubation of hGDH2 was uncompetitive with respect of NADH and non-competitive with respect of 2-oxoglutarate. The inhibitory effect of chloroquine on hGDH2 was abolished, although in part, by the presence of ADP and L-leucine, whereas GTP did not change the sensitivity to chloroquine inhibition. Our results show a possibility that chloroquine may be used in regulating GDH activity and subsequently glutamate concentration in the central nervous system.
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Affiliation(s)
- Myung-Min Choi
- Department of Biomedical Laboratory Science, Konyang University, Daejeon 320-718, Korea
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Maechler P, Carobbio S, Rubi B. In beta-cells, mitochondria integrate and generate metabolic signals controlling insulin secretion. Int J Biochem Cell Biol 2006; 38:696-709. [PMID: 16443386 DOI: 10.1016/j.biocel.2005.12.006] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2005] [Revised: 12/08/2005] [Accepted: 12/12/2005] [Indexed: 12/14/2022]
Abstract
Pancreatic beta-cells are unique neuroendocrine cells displaying the peculiar feature of responding to nutrients, principally glucose, as primary stimulus. This requires translation of a metabolic substrate into intracellular messengers recognized by the exocytotic machinery. Central to this signal transduction mechanism, mitochondria integrate and generate metabolic signals, thereby coupling glucose recognition to insulin secretion. In response to a glucose rise, nucleotides and metabolites are generated by mitochondria and participate, together with cytosolic calcium, to the stimulation of insulin exocytosis. This review describes the mitochondrion-dependent pathways of regulated insulin secretion. In particular, importance of cataplerotic and anaplerotic processes is discussed, with special attention to the mitochondrial enzyme glutamate dehydrogenase. Mitochondrial defects, such as mutations and reactive oxygen species production, are presented in the context of beta-cell failure in the course of type 2 diabetes.
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Affiliation(s)
- Pierre Maechler
- Department of Cell Physiology and Metabolism, University Medical Centre, Geneva, Switzerland.
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Choi MM, Huh JW, Yang SJ, Cho EH, Choi SY, Cho SW. Identification of ADP-ribosylation site in human glutamate dehydrogenase isozymes. FEBS Lett 2005; 579:4125-30. [PMID: 16023112 DOI: 10.1016/j.febslet.2005.06.041] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2005] [Revised: 06/11/2005] [Accepted: 06/16/2005] [Indexed: 11/25/2022]
Abstract
When the influence of ADP-ribosylation on the activities of the purified human glutamate dehydrogenase isozymes (hGDH1 and hGDH2) was measured in the presence of 100 microM NAD+ for 60 min, hGDH isozymes were inhibited by up to 75%. If incubations were performed for longer time periods up to 3 h, the inhibition of hGDH isozymes did not increased further. This phenomenon may be related to the reversibility of ADP-ribosylation in mitochondria. ADP-ribosylated hDGH isozymes were reactivated by Mg2+-dependent mitochondrial ADP-ribosylcysteine hydrolase. The stoichiometry between incorporated ADP-ribose and GDH subunits shows a modification of one subunit per catalytically active homohexamer. Since ADP and GTP had no effects on the extent of modification, it would appear that the ADP-ribosylation is unlikely to occur in allosteric sites. It has been proposed that Cys residue may be involved in the ADP-ribosylation of GDH, although identification of the reactive Cys residue has not been reported. To identify the reactive Cys residue involved in the ADP-ribosylation, we performed cassette mutagenesis at three different positions (Cys59, Cys119, and Cys274) using synthetic genes of hGDH isozymes. Among the Cys residues tested, only Cys119 mutants showed a significant reduction in the ADP-ribosylation. These results suggest a possibility that the Cys119 residue has an important role in the regulation of hGDH isozymes by ADP-ribosylation.
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Affiliation(s)
- Myung-Min Choi
- Department of Biochemistry and Molecular Biology, University of Ulsan College of Medicine, 388-1 Poongnap-2dong, Songpa-gu, Seoul 138-736, South Korea
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Iida T, Kamo M, Uozumi N, Inui T, Imai K. Further application of a two-step heparin affinity chromatography method using divalent cations as eluents: Purification and identification of membrane-bound heparin binding proteins from the mitochondrial fraction of HL-60 cells. J Chromatogr B Analyt Technol Biomed Life Sci 2005; 823:209-12. [PMID: 16019269 DOI: 10.1016/j.jchromb.2005.06.025] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2004] [Revised: 06/07/2005] [Accepted: 06/09/2005] [Indexed: 10/25/2022]
Abstract
Membrane proteins were obtained from the mitochondrial fraction of HL-60 cells by solubilization with octyl glucoside and bound to heparin-gels. Bound proteins were successively eluted with solutions containing increasing concentrations of Mg(2+) in the first and increasing concentrations of Ca(2+) in the second chromatography. After SDS-PAGE and subsequent N-terminal amino acid analysis of proteins on each band, 13 proteins were identified. Fifteen out of the 37 proteins analysed were modified at their N-termini. These results show that this two-step affinity chromatography method using divalent cations as eluents can be applied to a variety of membranes for the isolation of specific proteins.
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Affiliation(s)
- Tsukimi Iida
- Department of Science of Human Life, City College of Mie, 157, Ishinnden-nakano, Tsu, Mie 514-0112, Japan.
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Yang SJ, Huh JW, Hong HN, Kim TU, Cho SW. Important role of Ser443 in different thermal stability of human glutamate dehydrogenase isozymes1. FEBS Lett 2004; 562:59-64. [PMID: 15044002 DOI: 10.1016/s0014-5793(04)00183-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2004] [Revised: 02/16/2004] [Accepted: 02/16/2004] [Indexed: 10/26/2022]
Abstract
Molecular biological studies confirmed that two glutamate dehydrogenase isozymes (hGDH1 and hGDH2) of distinct genetic origin are expressed in human tissues. hGDH1 is heat-stable and expressed widely, whereas hGDH2 is heat-labile and specific for neural and testicular tissues. A selective deficiency of hGDH2 has been reported in patients with spinocerebellar ataxia. We have identified an amino acid residue involved in the different thermal stability of human GDH isozymes. At 45 degrees C (pH 7.0), heat inactivation proceeded faster for hGDH2 (half life=45 min) than for hGDH1 (half-life=310 min) in the absence of allosteric regulators. Both hGDH1 and hGDH2, however, showed much slower heat inactivation processes in the presence of 1 mM ADP or 3 mM L-Leu. Virtually most of the enzyme activity remained up to 100 min at 45 degrees C after treatment with ADP and L-Leu in combination. In contrast to ADP and L-Leu, the thermal stabilities of the hGDH isozymes were not affected by addition of substrates or coenzymes. In human GDH isozymes, the 443 site is Arg in hGDH1 and Ser in hGDH2. Replacement of Ser by Arg at the 443 site by cassette mutagenesis abolished the heat lability of hGDH2 with a similar half-life of hGDH1. The mutagenesis at several other sites (L415M, A456G, and H470R) having differences in amino acid sequence between the two GDH isozymes did not show any change in the thermal stability. These results suggest that the Ser443 residue plays an important role in the different thermal stability of human GDH isozymes.
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Affiliation(s)
- Seung-Ju Yang
- Department of Biochemistry and Molecular Biology, University of Ulsan College of Medicine, 388-1 Poongnap-2dong, Songpa-gu, Seoul 138-736, South Korea
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Denaxa M, Pavlou O, Tsiotra P, Papadopoulos GC, Liapaki K, Theodorakis K, Papadaki C, Karagogeos D, Papamatheakis J. The upstream regulatory region of the gene for the human homologue of the adhesion molecule TAG-1 contains elements driving neural specific expression in vivo. ACTA ACUST UNITED AC 2004; 118:91-101. [PMID: 14559358 DOI: 10.1016/j.molbrainres.2003.07.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Cell adhesion molecules (CAMs) of the immunoglobulin superfamily (IgSF) exhibit restricted spatial and temporal expression profiles requiring a tight regulatory program during development. The rodent glycoprotein TAG-1 and its orthologs TAX-1 in the human and axonin-1 in chick are cell adhesion molecules belonging to the contactin/F3 subgroup of the IgSF. TAG-1 is expressed in restricted subsets of central and peripheral neurons, not only during development but also in adulthood, and is implicated in neurite outgrowth, axon guidance and fasciculation, as well as neuronal migration. In an attempt to identify the regulatory elements that guide the neuronal expression of TAG-1, we have isolated genomic clones containing 4 kb of the TAX-1 upstream sequence and used them to drive the expression of the LacZ reporter gene in transgenic mice. We demonstrate that this sequence includes elements not only sufficient to restrict expression to the nervous system, but also to recapitulate to a great extent the endogenous pattern of the TAG-1 expression in the developing CNS.
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Affiliation(s)
- Myrto Denaxa
- Department of Basic Science, University of Crete Medical School and Institute of Molecular Biology and Biotechnology, PO Box 1527, Vassilika Vouton, Heraklion 711 10, Crete, Greece
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Carobbio S, Ishihara H, Fernandez-Pascual S, Bartley C, Martin-Del-Rio R, Maechler P. Insulin secretion profiles are modified by overexpression of glutamate dehydrogenase in pancreatic islets. Diabetologia 2004; 47:266-76. [PMID: 14689183 DOI: 10.1007/s00125-003-1306-2] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/28/2003] [Revised: 10/27/2003] [Indexed: 11/26/2022]
Abstract
AIMS/HYPOTHESIS Glutamate dehydrogenase (GDH) is a mitochondrial enzyme playing a key role in the control of insulin secretion. However, it is not known whether GDH expression levels in beta cells are rate-limiting for the secretory response to glucose. GDH also controls glutamine and glutamate oxidative metabolism, which is only weak in islets if GDH is not allosterically activated by L-leucine or (+/-)-2-aminobicyclo-[2,2,1]heptane-2-carboxylic acid (BCH). METHODS We constructed an adenovirus encoding for GDH to overexpress the enzyme in the beta-cell line INS-1E, as well as in isolated rat and mouse pancreatic islets. The secretory responses to glucose and glutamine were studied in static and perifusion experiments. Amino acid concentrations and metabolic parameters were measured in parallel. RESULTS GDH overexpression in rat islets did not change insulin release at basal or intermediate glucose (2.8 and 8.3 mmol/l respectively), but potentiated the secretory response at high glucose concentrations (16.7 mmol/l) compared to controls (+35%). Control islets exposed to 5 mmol/l glutamine at basal glucose did not increase insulin release, unless BCH was added with a resulting 2.5-fold response. In islets overexpressing GDH glutamine alone stimulated insulin secretion (2.7-fold), which was potentiated 2.2-fold by adding BCH. The secretory responses evoked by glutamine under these conditions correlated with enhanced cellular metabolism. CONCLUSIONS/INTERPRETATION GDH could be rate-limiting in glucose-induced insulin secretion, as GDH overexpression enhanced secretory responses. Moreover, GDH overexpression made islets responsive to glutamine, indicating that under physiological conditions this enzyme acts as a gatekeeper to prevent amino acids from being inappropriate efficient secretagogues.
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Affiliation(s)
- S Carobbio
- Division of Clinical Biochemistry, University Medical Center, Geneva, Switzerland
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Zaganas I, Plaitakis A. Single amino acid substitution (G456A) in the vicinity of the GTP binding domain of human housekeeping glutamate dehydrogenase markedly attenuates GTP inhibition and abolishes the cooperative behavior of the enzyme. J Biol Chem 2002; 277:26422-8. [PMID: 11950837 DOI: 10.1074/jbc.m200022200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human glutamate dehydrogenase (GDH) exists in two isoforms encoded by the GLUD1 and GLUD2 genes, respectively. Although the two enzymes share in their mature form all but 15 of their 505 amino acids, they differ markedly in their allosteric regulation. To identify the structural basis for these allosteric characteristics, we performed site-directed mutagenesis on the human GLUD1 gene at sites that differ from the GLUD2 gene using a cloned GLUD1 cDNA. Results showed that substitution of Ala for Gly-456, but not substitution of His for Arg-470 or Ser for Asn-498, renders the enzyme markedly resistant to GTP inhibition (IC(50) = 2.80 microm) as compared with the wild type GLUD1-derived GDH (IC(50) = 0.19 microm). The G456A mutation abolished the cooperative behavior of the enzyme, as revealed by the GTP inhibitory curves. The catalytic and kinetic properties of the G456A mutant and its activation by ADP were comparable with those of the wild type GDH. Gly-456 lies in a very tightly packed region of the GDH molecule, and its replacement by Ala may lead to steric clashes with neighboring amino acids. These, in turn, may affect the conformational state of the protein that is essential for the allosteric regulation of the enzyme by GTP.
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Affiliation(s)
- Ioannis Zaganas
- Department of Neurology, University of Crete, School of Health Sciences, Section of Medicine, Heraklion, 71500 Crete, Greece
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Burbaeva GS, Turishcheva MS, Vorobyeva EA, Savushkina OK, Tereshkina EB, Boksha IS. Diversity of glutamate dehydrogenase in human brain. Prog Neuropsychopharmacol Biol Psychiatry 2002; 26:427-35. [PMID: 11999891 DOI: 10.1016/s0278-5846(01)00273-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Three forms of glutamate dehydrogenase (GDH, EC 1.4.1.3) are purified from human brain tissue. Two of them, named GDH I (consisting of 58+/-1-kDa subunit) and GDH II (consisting of 56+/-1 -kDa subunit), are readily solubilized and the third one, GDH III (consisting of 56+/-1-kDa subunit), is a membrane-associated (particulate bound) isoform. Kinetic constants were determined for GDH III. These GDH forms were found to differ in hydrophobicity as indicated by different affinity to Phenyl-Sepharose. All three GDH forms showed microheterogeneity on two-dimensional (2-D) gel electrophoresis. Specific polyclonal antibodies, which enable to determine the levels of immunoreactivities of all the GDH forms in human brain extracts by enzyme-chemiluminescent amplified (ECL)-Western immunoblotting, were obtained.
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Affiliation(s)
- Gulnur Sh Burbaeva
- Laboratory of Neurochemistry, Mental Health Research Center RAMS, Moscow, Russia.
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Kelly A, Stanley CA. Disorders of glutamate metabolism. MENTAL RETARDATION AND DEVELOPMENTAL DISABILITIES RESEARCH REVIEWS 2002; 7:287-95. [PMID: 11754524 DOI: 10.1002/mrdd.1040] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The significant role the amino acid glutamate assumes in a number of fundamental metabolic pathways is becoming better understood. As a central junction for interchange of amino nitrogen, glutamate facilitates both amino acid synthesis and degradation. In the liver, glutamate is the terminus for release of ammonia from amino acids, and the intrahepatic concentration of glutamate modulates the rate of ammonia detoxification into urea. In pancreatic beta-cells, oxidation of glutamate mediates amino acid-stimulated insulin secretion. In the central nervous system, glutamate serves as an excitatory neurotransmittor. Glutamate is also the precursor of the inhibitory neurotransmittor GABA, as well as glutamine, a potential mediator of hyperammonemic neurotoxicity. The recent identification of a novel form of congenital hyperinsulinism associated with asymptomatic hyperammonemia assigns glutamate oxidation by glutamate dehydrogenase a more important role than previously recognized in beta-cell insulin secretion and hepatic and CNS ammonia detoxification. Disruptions of glutamate metabolism have been implicated in other clinical disorders, such as pyridoxine-dependent seizures, confirming the importance of intact glutamate metabolism. This article will review glutamate metabolism and clinical disorders associated with disrupted glutamate metabolism.
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Affiliation(s)
- A Kelly
- Division of Endocrinology, Department of Pediatrics, The Children's Hospital of Philadelphia, University of Pennsylvania Medical School, 19104, USA
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Tanizawa Y, Nakai K, Sasaki T, Anno T, Ohta Y, Inoue H, Matsuo K, Koga M, Furukawa S, Oka Y. Unregulated elevation of glutamate dehydrogenase activity induces glutamine-stimulated insulin secretion: identification and characterization of a GLUD1 gene mutation and insulin secretion studies with MIN6 cells overexpressing the mutant glutamate dehydrogenase. Diabetes 2002; 51:712-7. [PMID: 11872671 DOI: 10.2337/diabetes.51.3.712] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Glutamate dehydrogenase (GDH) is important in normal glucose homeostasis. Mutations of GDH result in hyperinsulinism/hyperammonemia syndrome. Using PCR/single-strand conformation polymorphism analysis of the gene encoding GDH in 12 Japanese patients with persistent hyperinsulinemic hypoglycemia of infancy (PHHI), we found a mutation (Y266C) in one PHHI patient. This mutation was not found in any of the control or type 2 diabetic subjects. The activity of the mutant GDH (GDH266C), expressed in COS-7 cells, was constitutively elevated, and allosteric regulations by ADP and GTP were severely impaired. The effect of the unregulated increase in GDH activity on insulin secretion was examined by overexpressing GDH266C in an insulinoma cell line, MIN6. Although glutamine alone did not stimulate insulin secretion from control MIN6-lacZ, it remarkably stimulated insulin secretion from MIN6-GDH266C. This finding suggests that constitutively activated GDH enhances oxidation of glutamate, which is intracellularly converted from glutamine to alpha-ketoglutarate, a tricarboxylic acid cycle substrate, which thereby stimulates insulin secretion. Interestingly, insulin secretion is also exaggerated significantly at low glucose concentrations (2 and 5 mmol/l) but not at higher glucose concentrations (8--25 mmol/l). Our results directly illustrate the importance of GDH in the regulation of insulin secretion from pancreatic beta-cells.
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Affiliation(s)
- Yukio Tanizawa
- Department of Bio-Signal Analysis, Yamaguchi University Graduate School of Medicine, Ube, Japan.
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Fujioka H, Okano Y, Inada H, Asada M, Kawamura T, Hase Y, Yamano T. Molecular characterisation of glutamate dehydrogenase gene defects in Japanese patients with congenital hyperinsulinism/hyperammonaemia. Eur J Hum Genet 2001; 9:931-7. [PMID: 11840195 DOI: 10.1038/sj.ejhg.5200749] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2001] [Revised: 10/18/2001] [Accepted: 10/22/2001] [Indexed: 11/09/2022] Open
Abstract
Congenital hyperinsulinism and hyperammonaemia (CHH) is caused by dysregulation of glutamate dehydrogenase (GDH). We characterised the GDH gene in two Japanese patients with CHH. Patient 1 showed late-onset and mild hypoglycaemic episodes and mild hyperammonaemia, compared with patient 2. In GDH activity of lymphoblasts, patient 1 showed twofold higher basal GDH activity than control subjects and mild insensitivity for GTP inhibition. Patient 2 showed severe insensitivity for GTP inhibition, and similar allosteric stimulation by ADP in the controls. Genetic studies identified heterozygous and de novo L413V and G446D mutations in patients 1 and 2, respectively. COS cell expression study confirmed that both mutations were disease-causing gene. The insensitivity for GTP inhibition in L413V and G446D was emphasised in COS cell expression system as a result of the dosage effect of mutant GDH gene. L413V showed less impairment of GDH than G446D based on biochemical and genetic results, which was consistent with the clinical phenotype. Based on the structure of bovine GDH, G446D was located in GTP binding site of pivot helix and its surroundings, while L413V was located in alpha-helix of antenna-like structure. These different locations of mutations gave different effects on GDH enzyme. The antenna-like structure plays an important role in GDH activity.
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Affiliation(s)
- H Fujioka
- Department of Pediatrics, Osaka City University Graduate School of Medicine, Osaka, Japan
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Plaitakis A, Zaganas I. Regulation of human glutamate dehydrogenases: implications for glutamate, ammonia and energy metabolism in brain. J Neurosci Res 2001; 66:899-908. [PMID: 11746417 DOI: 10.1002/jnr.10054] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Glutamate dehydrogenase (GDH) catalyzes the oxidative deamination of glutamate to alpha-ketoglutarate using NAD or NADP as cofactors. In mammalian brain, GDH is located predominantly in astrocytes, where it is probably involved in the metabolism of transmitter glutamate. The exact mechanisms that regulate glutamate fluxes through this pathway, however, have not been fully understood. In the human, GDH exists in heat-resistant and heat-labile isoforms, encoded by the GLUD1 (housekeeping) and GLUD2 (nerve tissue-specific) genes, respectively. These forms differ in their catalytic and allosteric properties. Kinetic studies showed that the K(m) value for glutamate for the nerve tissue GDH is within the range of glutamate levels in astrocytes (2.43 mM), whereas for the housekeeping enzyme, this value is significantly higher (7.64 mM; P < 0.01). The allosteric activators ADP (0.1-1.0 mM) and L-leucine (1.0-10.0 mM) induce a concentration-dependent enzyme stimulation that is proportionally greater for the nerve tissue-specific GDH (up to 1,600%) than for the housekeeping enzyme (up to 150%). When used together at lower concentrations, ADP (10-50 mM) and L-leucine (75-200 microM) act synergistically in stimulating GDH activity. GTP exerts a powerful inhibitory effect (IC(50) = 0.20 mM) on the housekeeping GDH; in contrast, the nerve tissue isoenzyme is resistant to GTP inhibition. Thus, although the housekeeping GDH is regulated primarily by GTP, the nerve tissue GDH activity depends largely on available ADP or L-leucine levels. Conditions associated with enhanced hydrolysis of ATP to ADP (e.g., intense glutamatergic transmission) are likely to activate nerve tissue-specific GDH leading to an increased glutamate flux through this pathway.
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Affiliation(s)
- A Plaitakis
- Department of Neurology, School of Health Sciences, Section of Medicine, University of Crete, Heraklion, Crete, Greece.
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Yoon HY, Hwang SH, Lee EY, Kim TU, Cho EH, Cho SW. Effects of ADP on different inhibitory properties of brain glutamate dehydrogenase isoproteins by perphenazine. Biochimie 2001; 83:907-13. [PMID: 11698113 DOI: 10.1016/s0300-9084(01)01325-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Incubation of glutamate dehydrogenase isoproteins (GDH I and GDH II) from bovine brains with perphenazine resulted in a time-dependent loss of enzyme activity. 2-Oxoglutarate and NADH, separately or together, gave partial but not complete protection against the inhibition. Although there were no detectable differences between GDH I and GDH II in inhibition by perphenazine in the absence of ADP, the sensitivities to the inhibition by the drug were significantly distinct for the two isoproteins in the presence of ADP. Low concentrations of ADP (0.05-0.20 mM) did not interfere with the inhibition of GDH I and GDH II by perphenazine. However, in the presence of high concentrations of ADP (0.5-1.0 mM), inhibitory effects of perphenazine on GDH isoproteins were significantly diminished as determined by enzyme kinetics and quantitative affinity chromatography on perphenazine-Sepharose. GDH I was more sensitively reacted with ADP than GDH II on the inhibition by perphenazine. Since physiological ADP levels can vary from 0.05 to > 1.0 mM depending on the rate of oxidative phosphorylation, our results suggest a possibility that two types of GDHs are differently regulated by the antipsychotic actions of perphenazine depending on the physiological concentrations of ADP. GTP and L-leucine, other well-known allosteric regulators, did not affect the inhibitory actions of perphenazine on bovine brain GDH isoproteins.
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Affiliation(s)
- H Y Yoon
- Department of Biochemistry, University of Ulsan College of Medicine, 388-1 Poongnap-dong, Songpa-ku, Seoul 138-736, South Korea
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Plaitakis A, Metaxari M, Shashidharan P. Nerve tissue-specific (GLUD2) and housekeeping (GLUD1) human glutamate dehydrogenases are regulated by distinct allosteric mechanisms: implications for biologic function. J Neurochem 2000; 75:1862-9. [PMID: 11032875 DOI: 10.1046/j.1471-4159.2000.0751862.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Human glutamate dehydrogenase (GDH), an enzyme central to the metabolism of glutamate, is known to exist in housekeeping and nerve tissue-specific isoforms encoded by the GLUD1 and GLUD2 genes, respectively. As there is evidence that GDH function in vivo is regulated, and that regulatory mutations of human GDH are associated with metabolic abnormalities, we sought here to characterize further the functional properties of the two human isoenzymes. Each was obtained in recombinant form by expressing the corresponding cDNAs in Sf9 cells and studied with respect to its regulation by endogenous allosteric effectors, such as purine nucleotides and branched chain amino acids. Results showed that L-leucine, at 1.0 mM:, enhanced the activity of the nerve tissue-specific (GLUD2-derived) enzyme by approximately 1,600% and that of the GLUD1-derived GDH by approximately 75%. Concentrations of L-leucine similar to those present in human tissues ( approximately 0.1 mM:) had little effect on either isoenzyme. However, the presence of ADP (10-50 microM:) sensitized the two isoenzymes to L-leucine, permitting substantial enzyme activation at physiologically relevant concentrations of this amino acid. Nonactivated GLUD1 GDH was markedly inhibited by GTP (IC(50) = 0.20 microM:), whereas nonactivated GLUD2 GDH was totally insensitive to this compound (IC(50) > 5,000 microM:). In contrast, GLUD2 GDH activated by ADP and/or L-leucine was amenable to this inhibition, although at substantially higher GTP concentrations than the GLUD1 enzyme. ADP and L-leucine, acting synergistically, modified the cooperativity curves of the two isoenzymes. Kinetic studies revealed significant differences in the K:(m) values obtained for alpha-ketoglutarate and glutamate for the GLUD1- and the GLUD2-derived GDH, with the allosteric activators differentially altering these values. Hence, the activity of the two human GDH is regulated by distinct allosteric mechanisms, and these findings may have implications for the biologic functions of these isoenzymes.
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Affiliation(s)
- A Plaitakis
- Department of Neurology, University of Crete, School of Health Sciences, Section of Medicine, Heraklion, Crete, Greece.
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Abstract
Congenital hyperinsulinism (CHI) is a disease phenotype characterized by increased, usually irregular, insulin secretion leading to hypoglycemia, coma, and severe brain damage, left untreated. Hyperinsulinism may be caused by a range of biochemical disturbances and molecular defects. In pancreatic beta cells, insulin secretion is stimulated by closure of the ATP-dependent potassium channel (K(ATP) channel). K(ATP) channel is a complex composed of at least two subunits: the sulfonylurea receptor SUR1 and Kir6.2, an inward rectifier K+ channel member. Mutations in both subunits have been identified in patients with the autosomal recessive form of hyperinsulinism, including 28 different mutations in the SUR1 gene and two mutations in the Kir6.2 gene. These mutations co-segregated with disease phenotype, also known as persistent hyperinsulinemic hypoglycemia of infancy (PHHI), and with attenuated K(ATP) channel function. Inadequately high insulin secretion in one family with an autosomal dominant mode of inheritance is caused by a mutation in the glucokinase gene, resulting in increased affinity of the enzyme for glucose. Five different mutations have been identified in the glutamate dehydrogenase gene, resulting in overactivity of this enzyme and causing a syndrome of hyperinsulinism and hyperammonemia. In 13 cases, hyperinsulinism was caused by one or more focal pancreatic lesions with specific loss of maternal alleles of the imprinted chromosome region 11p15. In five patients, this loss of heterozygosity unmasked a paternally inherited recessive SUR1 mutation. The new molecular approaches in PHHI give further insight into the mechanism of pancreatic beta cell insulin secretion. The heterogeneous group of patients with CHI may now be classified according to their basic defects in the four different genes, with potential implications for a more specific treatment.
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Affiliation(s)
- T Meissner
- Division of Metabolic Diseases, University Children's Hospital, Heidelberg, Germany
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Choi SY, Hong JW, Song MS, Jeon SG, Bahn JH, Lee BR, Ahn JY, Cho SW. Different antigenic reactivities of bovine brain glutamate dehydrogenase isoproteins. J Neurochem 1999; 72:2162-9. [PMID: 10217298 DOI: 10.1046/j.1471-4159.1999.0722162.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The structural differences between two types of glutamate dehydrogenase (GDH) isoproteins (GDH I and GDH II), homogeneously isolated from bovine brain, were investigated using a biosensor technology and monoclonal antibodies. A total of seven monoclonal antibodies raised against GDH II were produced, and the antibodies recognized a single protein band that comigrates with purified GDH II on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot. Of seven anti-GDH II monoclonal antibodies tested in the immunoblot analysis, all seven antibodies interacted with GDH II, whereas only four antibodies recognized the protein band of the other GDH isoprotein, GDH I. When inhibition tests of the GDH isoproteins were performed with the seven anti-GDH II monoclonal antibodies, three antibodies inhibited GDH II activity, whereas only one antibody inhibited GDH I activity. The binding affinity of anti-GDH II monoclonal antibodies for GDH II (K(D) = 1.0 nM) determined using a biosensor technology (Pharmacia BIAcore) was fivefold higher than for GDH I (K(D) = 5.3 nM). These results, together with epitope mapping analysis, suggest that there may be structural differences between the two GDH isoproteins, in addition to their different biochemical properties. Using the anti-GDH II antibodies as probes, we also investigated the cross-reactivities of brain GDHs from some mammalian and an avian species, showing that the mammalian brain GDH enzymes are related immunologically to each other.
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Affiliation(s)
- S Y Choi
- Department of Genetic Engineering, Hallym University, Chunchon, Korea
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Wan M, Francke U. Evaluation of two X chromosomal candidate genes for Rett syndrome: Glutamate dehydrogenase-2 (GLUD2) and rab GDP-dissociation inhibitor (GDI1). ACTA ACUST UNITED AC 1998. [DOI: 10.1002/(sici)1096-8628(19980630)78:2<169::aid-ajmg14>3.0.co;2-l] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Stanley CA, Lieu YK, Hsu BY, Burlina AB, Greenberg CR, Hopwood NJ, Perlman K, Rich BH, Zammarchi E, Poncz M. Hyperinsulinism and hyperammonemia in infants with regulatory mutations of the glutamate dehydrogenase gene. N Engl J Med 1998; 338:1352-7. [PMID: 9571255 DOI: 10.1056/nejm199805073381904] [Citation(s) in RCA: 443] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND A new form of congenital hyperinsulinism characterized by hypoglycemia and hyperammonemia was described recently. We hypothesized that this syndrome of hyperinsulinism and hyperammonemia was caused by excessive activity of glutamate dehydrogenase, which oxidizes glutamate to alpha-ketoglutarate and which is a potential regulator of insulin secretion in pancreatic beta cells and of ureagenesis in the liver. METHODS We measured glutamate dehydrogenase activity in lymphoblasts from eight unrelated children with the hyperinsulinism-hyperammonemia syndrome: six with sporadic cases and two with familial cases. We identified mutations in the glutamate dehydrogenase gene by sequencing glutamate dehydrogenase complementary DNA prepared from lymphoblast messenger RNA. Site-directed mutagenesis was used to express the mutations in COS-7 cells. RESULTS The sensitivity of glutamate dehydrogenase to inhibition by guanosine 5'-triphosphate was a quarter of the normal level in the patients with sporadic hyperinsulinism-hyperammonemia syndrome and half the normal level in patients with familial cases and their affected relatives, findings consistent with overactivity of the enzyme. These differences in enzyme insensitivity correlated with differences in the severity of hypoglycemia in the two groups. All eight children were heterozygous for the wild-type allele and had a mutation in the proposed allosteric domain of the enzyme. Four different mutations were identified in the six patients with sporadic cases; the two patients with familial cases shared a fifth mutation. In two clones of COS-7 cells transfected with the mutant sequence from one patient, the sensitivity of the enzyme to guanosine 5'-triphosphate was reduced, findings similar to those in the child's lymphoblasts. CONCLUSIONS The hyperinsulinism-hyperammonemia syndrome is caused by mutations in the glutamate dehydrogenase gene that impair the control of enzyme activity.
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Affiliation(s)
- C A Stanley
- Division of Endocrinology, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, 19104, USA
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Frattini A, Faranda S, Bagnasco L, Patrosso C, Nulli P, Zucchi I, Vezzoni P. Identification of a new member (ZNF183) of the Ring finger gene family in Xq24-25. Gene 1997; 192:291-8. [PMID: 9224902 DOI: 10.1016/s0378-1119(97)00108-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Four genes were mapped to the Xq24-25 region by searching the EST and the non-redundant database with short tracts of genomic sequences. These were random STSs present in the STS database or sequences derived from CpG islands (EagI-based STSs). One of the four matches corresponded to the full length transcript from the intronless glutamate dehydrogenase gene. The second was the human homolog of the bovine NADH ubiquinone oxidoreductase MWFE subunit gene (GDB symbol: NDUFA1). The other two, ZNF183 and ITBA4, were novel genes whose function cannot directly be inferred from their sequence analysis. However, a known motif, the C3HC4 Ring finger domain, shared by various tumor suppressors, DNA repair genes and cytokine receptor-associated molecules, is present at the C terminus of the ubiquitously expressed ZNF183 gene. ITBA4 is expressed at various levels in different tissues and is alternatively processed in brain. Similarity search did not detect any significant match in databases. These results, together with others previously reported by our laboratory, suggest that comparison of genomic and transcribed sequences which are continuously accumulating in databases, can provide 'virtual' mapping of a substantial number of ESTs to the specific genomic region which the STSs have been derived from.
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Affiliation(s)
- A Frattini
- Istituto di Tecnologie Biomediche Avanzate, Consiglio Nazionale delle Ricerche, Milan, Italy.
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Cho SW, Lee J, Choi SY. Two soluble forms of glutamate dehydrogenase isoproteins from bovine brain. EUROPEAN JOURNAL OF BIOCHEMISTRY 1995; 233:340-6. [PMID: 7588764 DOI: 10.1111/j.1432-1033.1995.340_1.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Two soluble forms of novel glutamate dehydrogenase isoproteins, designated GDH I and GDH II, have been purified from bovine brain. GDH I and GDH II were separated on a hydroxyapatite column and eluted by a step gradient at different phosphate concentrations (30 mM and 50 mM for GDH I and GDH II, respectively). The preparations were homogeneous on SDS/PAGE. GDH I and GDH II showed similarity in their molecular sizes and are composed of six identical subunits having a molecular size of 57,500 Da. Differences between the biochemical properties of GDH I and GDH II, such as N-terminal amino acid sequences of intact and tryptic-digested enzymes, kinetic parameters, optimum pH and heat stability, were extensively examined in both reductive amination of alpha-oxoglutarate and oxidative deamination of glutamate. The different effects of ADP on GDH isoproteins were also studied under various conditions. These results indicate that GDH I and GDH II, isolated from bovine brain, are novel and distinct polypeptides.
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Affiliation(s)
- S W Cho
- Department of Biochemistry, College of Medicine, University of Ulsan, Seoul, Korea
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Grigoriou M, Kastrinaki MC, Modi WS, Theodorakis K, Mankoo B, Pachnis V, Karagogeos D. Isolation of the human MOX2 homeobox gene and localization to chromosome 7p22.1-p21.3. Genomics 1995; 26:550-5. [PMID: 7607679 DOI: 10.1016/0888-7543(95)80174-k] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We have isolated and characterized cDNA clones encoding a novel human homeobox gene, MOX2, the homologue of the murine mox-2 gene. The MOX2 protein contains all of the characteristic features of Mox-2 proteins of other vertebrate species, namely the homeobox, the polyhistidine stretch, and a number of potential serine/threonine phosphorylation sites. The homeodomain of MOX2 protein is identical to all other vertebrate species reported so far (rodents and amphibians). Outside the homeodomain, Mox-2 proteins share a high degree of identity, except for a few amino acid differences encountered between the human and the rodent polypeptides. A polyhistidine stretch of 12 amino acids in the N terminal region of the protein is also conserved among humans, rodents, and (only partly) amphibians. The chromosomal position of MOX2 was assigned to 7p22.1-p21.3.
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Affiliation(s)
- M Grigoriou
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology, Heraklion, Crete, Greece
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Teller JK, Baker PJ, Britton KL, Engel PC, Rice DW, Stillman TJ. Correlation of intron-exon organisation with the three-dimensional structure in glutamate dehydrogenase. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1247:231-8. [PMID: 7696313 DOI: 10.1016/0167-4838(94)00240-h] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The positions of the intron-exon boundaries in the genes for glutamate dehydrogenase from Chlorella sorokiniana rat, and human have been located on the three-dimensional structure of the highly homologous enzyme from Clostridium symbiosum and analysed for their position in the protein structure. This analysis shows no correlation between the positions of these boundaries in the mammalian and Chlorella glutamate dehydrogenase genes and no correlation with units of function in the enzyme and suggests that the present day exons do not represent the protein modules of an ancestral glutamate dehydrogenase. There appears to be no clear preference for the residues at the splice junctions to be either buried or exposed to solvent. However, the frequency with which the introns appear in the loops linking elements of secondary structure, rather than in either the alpha-helical or beta-sheet segments, is higher than predicted on the basis of the proportion of residues in the loops. This is consistent with but not proof of a role for exon modification/exchange in protein evolution since changes at these positions are less likely to disturb the structure and hence maintain function.
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Affiliation(s)
- J K Teller
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, UK
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Rothe F, Brosz M, Storm-Mathisen J. Quantitative ultrastructural localization of glutamate dehydrogenase in the rat cerebellar cortex. Neuroscience 1995; 64:iii-xvi. [PMID: 7753371 DOI: 10.1016/0306-4522(94)e0200-n] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Glutamate dehydrogenase is one of the main enzymes involved in the formation and metabolism of the neurotransmitter glutamate. In the present study we investigated the enzyme ultrastructurally in the cerebellar cortex, a region rich in well defined glutamatergic neurons, by pre-embedding immunocytochemical staining (peroxidase-antiperoxidase), as well as by post-embedding immunogold labelling employing a new system for quantitation and for specificity testing under the conditions of the immunocytochemical procedure. A new antiserum against immunologically purified bovine liver glutamate dehydrogenase or antibodies isolated from this by affinity chromatography were used in rats fixed by perfusion with aldehydes. The pre-embedding method displayed peroxidase reaction preferentially in mitochondria of astroglial cells (including the Bergmann glia). Mitochondria of neuronal tissue elements were usually free of peroxidase-reaction product. Extra-mitochondrial staining was not observed. The post-embedding immunogold method was employed to overcome penetration problems and allow semiquantitative analysis of localization and specificity. The highest densities of gold particles were found over the mitochondria in astroglial cell elements (including the Bergmann glia). Mitochondria in cell bodies of Bergmann glia had a lower particle density than those in astrocytic processes. In the latter, analysis of frequency distribution revealed no evidence of a population of mitochondria lacking glutamate dehydrogenase, but suggested the presence of populations with different levels of immunoreactivity. Comparison with the labelling of embedded bovine liver glutamate dehydrogenase indicated that the enzyme constitutes a high proportion (10%) of the total matrix protein of these mitochondria. A weaker but significant labelling was found in oligodendrocytes of the white matter. The labelling of mitochondria in neuronal elements including glutamatergic mossy fibre terminals was of the order of 15% of that in astroglial mitochondria. No difference was detected between glutamatergic neurons (mossy and parallel fibres, granular cells) and non-glutamatergic neurons (Purkinje cells). The particle density over non-mitochondrial areas was very close to background over empty resin. The results, obtained with different methods of tissue and antibody preparation, agree to show that the present form of glutamate dehydrogenase is restricted to mitochondria and preferentially localized in astrocytes.
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Affiliation(s)
- F Rothe
- Institute of Medical Neurobiology, Medical Faculty, University of Magdeburg, Germany
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Rothe F, Brosz M, Storm-Mathisen J. Quantitative ultrastructural localization of glutamate dehydrogenase in the rat cerebellar cortex. Neuroscience 1994; 62:1133-46. [PMID: 7531302 DOI: 10.1016/0306-4522(94)90349-2] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Glutamate dehydrogenase is one of the main enzymes involved in the formation and metabolism of the neurotransmitter glutamate. In the present study we investigated the enzyme ultrastructurally in the cerebellar cortex, a region rich in well defined glutamatergic neurons, by pre-embedding immunocytochemical staining (peroxidase-antiperoxidase), as well as by post-embedding immunogold labelling employing a new system for quantitation and for specificity testing under the conditions of the immunocytochemical procedure. A new antiserum against immunologically purified bovine liver glutamate dehydrogenase or antibodies isolated from this by affinity chromatography were used in rats fixed by perfusion with aldehydes. The pre-embedding method displayed peroxidase reaction preferentially in mitochondria of astroglial cells (including the Bergmann glia). Mitochondria of neuronal tissue elements were usually free of peroxidase-reaction product. Extra-mitochondrial staining was not observed. The post-embedding immunogold method was employed to overcome penetration problems and allow semiquantitative analysis of localization and specificity. The highest densities of gold particles were found over the mitochondria in astroglial cell elements (including the Bergmann glia). Mitochondria in cell bodies of Bergmann glia had a lower particle density than those in astrocytic processes. In the latter, analysis of frequency distribution revealed no evidence of a population of mitochondria lacking glutamate dehydrogenase, but suggested the presence of populations with different levels of immunoreactivity. Comparison with the labelling of embedded bovine liver glutamate dehydrogenase indicated that the enzyme constitutes a high proportion (10%) of the total matrix protein of these mitochondria. A weaker but significant labelling was found in oligodendrocytes of the white matter. The labelling of mitochondria in neuronal elements including glutamatergic mossy fibre terminals was of the order of 15% of that in astroglial mitochondria. No difference was detected between glutamatergic neurons (mossy and parallel fibres, granular cells) and non-glutamatergic neurons (Purkinje cells). The particle density over non-mitochondrial areas was very close to background over empty resin. The results, obtained with different methods of tissue and antibody preparation, agree to show that the present form of glutamate dehydrogenase is restricted to mitochondria and preferentially localized in astrocytes.
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Affiliation(s)
- F Rothe
- Institute of Medical Neurobiology, Medical Faculty, University of Magdeburg, Germany
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Shashidharan P, Michaelidis T, Robakis N, Kresovali A, Papamatheakis J, Plaitakis A. Novel human glutamate dehydrogenase expressed in neural and testicular tissues and encoded by an X-linked intronless gene. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(19)89484-x] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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