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PKCε contributes to lipid-induced insulin resistance through cross talk with p70S6K and through previously unknown regulators of insulin signaling. Proc Natl Acad Sci U S A 2018; 115:E8996-E9005. [PMID: 30181290 DOI: 10.1073/pnas.1804379115] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Insulin resistance drives the development of type 2 diabetes (T2D). In liver, diacylglycerol (DAG) is a key mediator of lipid-induced insulin resistance. DAG activates protein kinase C ε (PKCε), which phosphorylates and inhibits the insulin receptor. In rats, a 3-day high-fat diet produces hepatic insulin resistance through this mechanism, and knockdown of hepatic PKCε protects against high-fat diet-induced hepatic insulin resistance. Here, we employed a systems-level approach to uncover additional signaling pathways involved in high-fat diet-induced hepatic insulin resistance. We used quantitative phosphoproteomics to map global in vivo changes in hepatic protein phosphorylation in chow-fed, high-fat-fed, and high-fat-fed with PKCε knockdown rats to distinguish the impact of lipid- and PKCε-induced protein phosphorylation. This was followed by a functional siRNA-based screen to determine which dynamically regulated phosphoproteins may be involved in canonical insulin signaling. Direct PKCε substrates were identified by motif analysis of phosphoproteomics data and validated using a large-scale in vitro kinase assay. These substrates included the p70S6K substrates RPS6 and IRS1, which suggested cross talk between PKCε and p70S6K in high-fat diet-induced hepatic insulin resistance. These results identify an expanded set of proteins through which PKCε may drive high-fat diet-induced hepatic insulin resistance that may direct new therapeutic approaches for T2D.
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Wang Y, Li L, Wang Y, Zhu X, Jiang M, Song E, Song Y. New application of the commercial sweetener rebaudioside a as a hepatoprotective candidate: Induction of the Nrf2 signaling pathway. Eur J Pharmacol 2018; 822:128-137. [PMID: 29355553 DOI: 10.1016/j.ejphar.2018.01.020] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Revised: 01/10/2018] [Accepted: 01/15/2018] [Indexed: 10/18/2022]
Abstract
A large population of drug candidates have failed "from bench to bed" due to unwanted toxicities. We intend to develop an alternative approach for drug discovery, that is, to seek candidates from "safe" compounds. Rebaudioside A (Reb-A) is an approved commercial sweetener from Stevia rebaudiana Bertoni. We found that Reb-A protects against carbon tetrachloride (CCl4)-induced oxidative injury in human liver hepatocellular carcinoma (HepG2) cells. Reb-A showed antioxidant activity on reducing cellular reactive oxygen species and malondialdehyde levels while increasing glutathione levels and superoxide dismutase and catalase activities. Reb-A treatment induced nuclear factor erythroid-derived 2-like 2 (Nrf2) activation and antioxidant response element activity, as well as the expression of heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoreductase 1 (NQO1). Further mechanistic studies indicated that c-Jun N-terminal kinase (JNK), extracellular signal-regulated protein kinase (ERK), mitogen-active protein kinase (MAPK) and protein kinase C epsilon (PKCε) signaling was upregulated. Thus, the present in vitro study conclusively demonstrated that Reb-A is an activator of Nrf2 and is a potential candidate hepatoprotective agent. More importantly, the present study illustrated that seeking drug candidates from "safe" compounds is a promising strategy.
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Affiliation(s)
- Yuxin Wang
- Key Laboratory of Luminescence and Real-Time Analytical Chemistry (Southwest University), Ministry of Education, College of Pharmaceutical Sciences, Southwest University, Chongqing 400715, People's Republic of China
| | - Linyao Li
- Key Laboratory of Luminescence and Real-Time Analytical Chemistry (Southwest University), Ministry of Education, College of Pharmaceutical Sciences, Southwest University, Chongqing 400715, People's Republic of China
| | - Yawen Wang
- Key Laboratory of Luminescence and Real-Time Analytical Chemistry (Southwest University), Ministry of Education, College of Pharmaceutical Sciences, Southwest University, Chongqing 400715, People's Republic of China
| | - Xiaokang Zhu
- Key Laboratory of Luminescence and Real-Time Analytical Chemistry (Southwest University), Ministry of Education, College of Pharmaceutical Sciences, Southwest University, Chongqing 400715, People's Republic of China
| | - Mingdong Jiang
- Department of Radiation Oncology, The Ninth People's Hospital of Chongqing, Chongqing 400700, People's Republic of China.
| | - Erqun Song
- Key Laboratory of Luminescence and Real-Time Analytical Chemistry (Southwest University), Ministry of Education, College of Pharmaceutical Sciences, Southwest University, Chongqing 400715, People's Republic of China
| | - Yang Song
- Key Laboratory of Luminescence and Real-Time Analytical Chemistry (Southwest University), Ministry of Education, College of Pharmaceutical Sciences, Southwest University, Chongqing 400715, People's Republic of China.
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Metformin Induces Cell Cycle Arrest and Apoptosis in Drug-Resistant Leukemia Cells. LEUKEMIA RESEARCH AND TREATMENT 2015; 2015:516460. [PMID: 26688757 PMCID: PMC4673355 DOI: 10.1155/2015/516460] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Revised: 06/18/2015] [Accepted: 09/20/2015] [Indexed: 12/25/2022]
Abstract
Recent epidemiological studies indicate that the antidiabetic drug metformin has chemosensitizing and chemopreventive effects against carcinogenesis. Here, we demonstrate that metformin exerts varying degrees of antitumor activity against human leukemia cells, as reflected by differences in growth inhibition, apoptosis, and alterations to metabolic enzymes. In metformin-sensitive cells, autophagy was not induced but rather it blocked proliferation by means of arresting cells in the S and G2/M phases which was associated with the downregulation of cyclin A, cyclin B1, and cdc2, but not that of cyclin E. In 10E1-CEM cells that overexpress Bcl-2 and are drug-resistant, the effect of metformin on proliferation was more pronounced, also inducing the activation of the caspases 3/7 and hence apoptosis. In all sensitive cells, metformin decreased the Δψm and it modified the expression of enzymes involved in energy metabolism: PKCε (PKCepsilon) and PKCδ (PKCdelta). In sensitive cells, metformin altered PKCε and PKCδ expression leading to a predominance of PKCε over PKCδ which implies a more glycolytic state. The opposite occurs in the nonresponsive cells. In conclusion, we provide new insights into the activity of metformin as an antitumoral agent in leukemia cells that could be related to its capability to modulate energy metabolism.
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Mylroie H, Dumont O, Bauer A, Thornton CC, Mackey J, Calay D, Hamdulay SS, Choo JR, Boyle JJ, Samarel AM, Randi AM, Evans PC, Mason JC. PKCε-CREB-Nrf2 signalling induces HO-1 in the vascular endothelium and enhances resistance to inflammation and apoptosis. Cardiovasc Res 2015; 106:509-19. [PMID: 25883219 PMCID: PMC4431664 DOI: 10.1093/cvr/cvv131] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/06/2014] [Accepted: 04/03/2015] [Indexed: 12/25/2022] Open
Abstract
AIMS Vascular injury leading to endothelial dysfunction is a characteristic feature of chronic renal disease, diabetes mellitus, and systemic inflammatory conditions, and predisposes to apoptosis and atherogenesis. Thus, endothelial dysfunction represents a potential therapeutic target for atherosclerosis prevention. The observation that activity of either protein kinase C epsilon (PKCε) or haem oxygenase-1 (HO-1) enhances endothelial cell (EC) resistance to inflammation and apoptosis led us to test the hypothesis that HO-1 is a downstream target of PKCε. METHODS AND RESULTS Expression of constitutively active PKCε in human EC significantly increased HO-1 mRNA and protein, whereas conversely aortas or cardiac EC from PKCε-deficient mice exhibited reduced HO-1 when compared with wild-type littermates. Angiotensin II activated PKCε and induced HO-1 via a PKCε-dependent pathway. PKCε activation significantly attenuated TNFα-induced intercellular adhesion molecule-1, and increased resistance to serum starvation-induced apoptosis. These responses were reversed by the HO antagonist zinc protoporphyrin IX. Phosphokinase antibody array analysis identified CREB1((Ser133)) phosphorylation as a PKCε signalling intermediary, and cAMP response element-binding protein 1 (CREB1) siRNA abrogated PKCε-induced HO-1 up-regulation. Likewise, nuclear factor (erythroid-derived 2)-like 2 (Nrf2) was identified as a PKCε target using nuclear translocation and DNA-binding assays, and Nrf2 siRNA prevented PKCε-mediated HO-1 induction. Moreover, depletion of CREB1 inhibited PKCε-induced Nrf2 DNA binding, suggestive of transcriptional co-operation between CREB1 and Nrf2. CONCLUSIONS PKCε activity in the vascular endothelium regulates HO-1 via a pathway requiring CREB1 and Nrf2. Given the potent protective actions of HO-1, we propose that this mechanism is an important contributor to the emerging role of PKCε in the maintenance of endothelial homeostasis and resistance to injury.
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Affiliation(s)
- Hayley Mylroie
- Vascular Sciences, Imperial Centre for Translational and Experimental Medicine, National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK
| | - Odile Dumont
- Vascular Sciences, Imperial Centre for Translational and Experimental Medicine, National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK
| | - Andrea Bauer
- Vascular Sciences, Imperial Centre for Translational and Experimental Medicine, National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK
| | - Clare C Thornton
- Vascular Sciences, Imperial Centre for Translational and Experimental Medicine, National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK
| | - John Mackey
- Vascular Sciences, Imperial Centre for Translational and Experimental Medicine, National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK
| | - Damien Calay
- Vascular Sciences, Imperial Centre for Translational and Experimental Medicine, National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK
| | - Shahir S Hamdulay
- Vascular Sciences, Imperial Centre for Translational and Experimental Medicine, National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK
| | - Joan R Choo
- Vascular Sciences, Imperial Centre for Translational and Experimental Medicine, National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK
| | - Joseph J Boyle
- Vascular Sciences, Imperial Centre for Translational and Experimental Medicine, National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK
| | - Allen M Samarel
- The Cardiovascular Institute, Loyola University Chicago Stritch School of Medicine, Maywood, IL, USA
| | - Anna M Randi
- Vascular Sciences, Imperial Centre for Translational and Experimental Medicine, National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK
| | - Paul C Evans
- Department of Cardiovascular Sciences, University of Sheffield, Sheffield, UK
| | - Justin C Mason
- Vascular Sciences, Imperial Centre for Translational and Experimental Medicine, National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK
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Smith KP, Gifford KM, Waitzman JS, Rice SE. Survey of phosphorylation near drug binding sites in the Protein Data Bank (PDB) and their effects. Proteins 2015; 83:25-36. [PMID: 24833420 PMCID: PMC4233198 DOI: 10.1002/prot.24605] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Revised: 04/28/2014] [Accepted: 05/09/2014] [Indexed: 12/21/2022]
Abstract
While it is currently estimated that 40 to 50% of eukaryotic proteins are phosphorylated, little is known about the frequency and local effects of phosphorylation near pharmaceutical inhibitor binding sites. In this study, we investigated how frequently phosphorylation may affect the binding of drug inhibitors to target proteins. We examined the 453 non-redundant structures of soluble mammalian drug target proteins bound to inhibitors currently available in the Protein Data Bank (PDB). We cross-referenced these structures with phosphorylation data available from the PhosphoSitePlus database. Three hundred twenty-two of 453 (71%) of drug targets have evidence of phosphorylation that has been validated by multiple methods or labs. For 132 of 453 (29%) of those, the phosphorylation site is within 12 Å of the small molecule-binding site, where it would likely alter small molecule binding affinity. We propose a framework for distinguishing between drug-phosphorylation site interactions that are likely to alter the efficacy of drugs versus those that are not. In addition we highlight examples of well-established drug targets, such as estrogen receptor alpha, for which phosphorylation may affect drug affinity and clinical efficacy. Our data suggest that phosphorylation may affect drug binding and efficacy for a significant fraction of drug target proteins.
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Affiliation(s)
- Kyle P Smith
- Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, 60611
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