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Jung D, Bachmann HS. Regulation of protein prenylation. Biomed Pharmacother 2023; 164:114915. [PMID: 37236024 DOI: 10.1016/j.biopha.2023.114915] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 05/17/2023] [Accepted: 05/18/2023] [Indexed: 05/28/2023] Open
Abstract
Prenyltransferases (PTases) are known to play a role in embryonic development, normal tissue homeostasis and cancer by posttranslationally modifying proteins involved in these processes. They are being discussed as potential drug targets in an increasing number of diseases, ranging from Alzheimer's disease to malaria. Protein prenylation and the development of specific PTase inhibitors (PTIs) have been subject to intense research in recent decades. Recently, the FDA approved lonafarnib, a specific farnesyltransferase inhibitor that acts directly on protein prenylation; and bempedoic acid, an ATP citrate lyase inhibitor that might alter intracellular isoprenoid composition, the relative concentrations of which can exert a decisive influence on protein prenylation. Both drugs represent the first approved agent in their respective substance class. Furthermore, an overwhelming number of processes and proteins that regulate protein prenylation have been identified over the years, many of which have been proposed as molecular targets for pharmacotherapy in their own right. However, certain aspects of protein prenylation, such as the regulation of PTase gene expression or the modulation of PTase activity by phosphorylation, have attracted less attention, despite their reported influence on tumor cell proliferation. Here, we want to summarize the advances regarding our understanding of the regulation of protein prenylation and the potential implications for drug development. Additionally, we want to suggest new lines of investigation that encompass the search for regulatory elements for PTases, especially at the genetic and epigenetic levels.
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Affiliation(s)
- Dominik Jung
- Institute of Pharmacology and Toxicology, Center for Biomedical Education and Research (ZBAF), School of Medicine, Faculty of Health, Witten/Herdecke University, Witten, Germany
| | - Hagen S Bachmann
- Institute of Pharmacology and Toxicology, Center for Biomedical Education and Research (ZBAF), School of Medicine, Faculty of Health, Witten/Herdecke University, Witten, Germany.
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2
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Cao Y, Wang W, Zhan X, Zhang Y. PRDX6: A protein bridging S-palmitoylation and diabetic neuropathy. Front Endocrinol (Lausanne) 2022; 13:992875. [PMID: 36120430 PMCID: PMC9478578 DOI: 10.3389/fendo.2022.992875] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Accepted: 08/11/2022] [Indexed: 11/13/2022] Open
Abstract
Diabetic neuropathy is regarded as one of the most debilitating outcomes of diabetes. It can affect both the peripheral and central nervous systems, leading to pain, decreased motility, cognitive decline, and dementia. S-palmitoylation is a reversible posttranslational lipid modification, and its dysregulation has been implicated in metabolic syndrome, cancers, neurological disorders, and infections. However, the role of S-palmitoylation in diabetic neuropathy remains unclear. Here we demonstrate a potential association between activating protein palmitoylation and diabetic neuropathy. We compared the proteomic data of lumbar dorsal root ganglia (DRG) of diabetes mice and palmitoylome profiling data of the HUVEC cell line. The mapping results identified peroxiredoxin-6 (PRDX6) as a novel target in diabetic neuropathy, whose biological mechanism was associated with S-palmitoylation. Bioinformatic prediction revealed that PRDX6 had two palmitoylation sites, Cys47 and Cys91. Immunofluorescence results indicated PRDX6 translocating between the cytoplasm and cell membrane. Protein function analysis proposed that increased palmitoylation could competitively inhibit the formation of disulfide-bond between Cys47 and Cys91 and change the spatial topology of PRDX6 protein. Cl-HCO3- anion exchanger 3 (AE3) was one of the AE family members, which was proved to express in DRG. AE3 activity evoked Cl- influx in neurons which was generally associated with increased excitability and susceptibility to pain. We demonstrated that the S-palmitoylation status of Cys47 could affect the interaction between PRDX6 and the C-terminal domain of AE3, thereby regulating the activity of AE3 anion exchanger enzyme in the nervous system. The results highlight a central role for PRDX6 palmitoylation in protection against diabetic neuropathy.
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Affiliation(s)
- Yan Cao
- Department of Anesthesiology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou, China
| | - Wantao Wang
- Department of Spine Surgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
| | - Xiaorong Zhan
- Department of Endocrinology, Southern University of Science and Technology Hospital, Shenzhen, China
| | - Yitong Zhang
- School of Life Science, Beijing Institute of Technology, Beijing, China
- *Correspondence: Yitong Zhang,
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Aryal P, Syed I, Lee J, Patel R, Nelson AT, Siegel D, Saghatelian A, Kahn BB. Distinct biological activities of isomers from several families of branched fatty acid esters of hydroxy fatty acids (FAHFAs). J Lipid Res 2021; 62:100108. [PMID: 34418413 PMCID: PMC8479484 DOI: 10.1016/j.jlr.2021.100108] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 08/09/2021] [Accepted: 08/13/2021] [Indexed: 12/24/2022] Open
Abstract
Branched fatty acid esters of hydroxy fatty acids (FAHFAs) are endogenous lipids with antidiabetic and anti-inflammatory effects. Each FAHFA family consists of esters with different acyl chains and multiple isomers with branch points at different carbons. Some FAHFAs, including palmitic acid hydroxy stearic acids (PAHSAs), improve insulin sensitivity and glucose tolerance in mice by enhancing glucose-stimulated insulin secretion (GSIS), insulin-stimulated glucose transport, and insulin action to suppress hepatic glucose production and reducing adipose tissue inflammation. However, little is known about the biological effects of other FAHFAs. Here, we investigated whether PAHSAs, oleic acid hydroxy stearic acid, palmitoleic acid hydroxy stearic acid, and stearic acid hydroxy stearic acid potentiate GSIS in β-cells and human islets, insulin-stimulated glucose uptake in adipocytes, and anti-inflammatory effects in immune cells. We also investigated whether they activate G protein-coupled receptor 40, which mediates the effects of PAHSAs on insulin secretion and sensitivity in vivo. We show that many FAHFAs potentiate GSIS, activate G protein-coupled receptor 40, and attenuate LPS-induced chemokine and cytokine expression and secretion and phagocytosis in immune cells. However, fewer FAHFAs augment insulin-stimulated glucose uptake in adipocytes. S-9-PAHSA, but not R-9-PAHSA, potentiated GSIS and glucose uptake, while both stereoisomers had anti-inflammatory effects. FAHFAs containing unsaturated acyl chains with higher branching from the carboxylate head group are more likely to potentiate GSIS, whereas FAHFAs with lower branching are more likely to be anti-inflammatory. This study provides insight into the specificity of the biological actions of different FAHFAs and could lead to the development of FAHFAs to treat metabolic and immune-mediated diseases.
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Affiliation(s)
- Pratik Aryal
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA
| | - Ismail Syed
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA
| | - Jennifer Lee
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA
| | - Rucha Patel
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA
| | - Andrew T Nelson
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, California, USA
| | - Dionicio Siegel
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, California, USA
| | - Alan Saghatelian
- Clayton Foundation Laboratories for Peptide Biology, Salk Institute for Biological Studies, La Jolla, California, USA
| | - Barbara B Kahn
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA.
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Gamage S, Hali M, Kowluru A. CARD9 mediates glucose-stimulated insulin secretion in pancreatic beta cells. Biochem Pharmacol 2021; 192:114670. [PMID: 34233162 DOI: 10.1016/j.bcp.2021.114670] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Revised: 06/30/2021] [Accepted: 07/01/2021] [Indexed: 11/15/2022]
Abstract
Caspase recruitment domain containing protein 9 (CARD9) plays key regulatory role(s) in innate and adaptive immune responses. Recent evidence implicates CARD9 in the onset of metabolic diseases including insulin resistance. However, potential contributory roles of CARD9 in glucose-stimulated insulin secretion (GSIS) remain unknown. Herein, we report that CARD9 is expressed in human islets, rat islets, mouse islets and clonal INS-1 832/13 cells. Subcellularly, CARD9 is predominantly cytosolic (~75%) in INS-1 832/13 cells. siRNA-mediated depletion of CARD9 expression significantly (~50%) suppressed GSIS in INS-1 832/13 cells. Interestingly, glucose-induced activation of Rac1, a small G-protein, which is a requisite for GSIS to occur, is unaffected in CARD9-si transfected cells, suggesting that CARD9-mediates GSIS in a Rac1-independent fashion. Furthermore, insulin secretion promoted by KCl or mastoparan (a global G protein activator), remained resistant to CARD9 depletion in INS-1 832/13 cells. In addition, pharmacological inhibition (BRD5529) of interaction between CARD9 and TRIM62, its ubiquitin ligase, exerted no significant effects on GSIS. Lastly, depletion of CARD9 prevented glucose-induced p38, not ERK1/2 phosphorylation in beta cells. Based on these observations, we propose that CARD9 might regulate GSIS via a Rac1-independent and p38-dependent signaling module.
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Affiliation(s)
- Suhadinie Gamage
- Biomedical Research Service, John D. Dingell VA Medical Center, and Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI 48201, United States
| | - Mirabela Hali
- Biomedical Research Service, John D. Dingell VA Medical Center, and Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI 48201, United States
| | - Anjaneyulu Kowluru
- Biomedical Research Service, John D. Dingell VA Medical Center, and Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI 48201, United States.
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Ahn M, Oh E, McCown EM, Wang X, Veluthakal R, Thurmond DC. A requirement for PAK1 to support mitochondrial function and maintain cellular redox balance via electron transport chain proteins to prevent β-cell apoptosis. Metabolism 2021; 115:154431. [PMID: 33181191 PMCID: PMC8123936 DOI: 10.1016/j.metabol.2020.154431] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 11/04/2020] [Accepted: 11/07/2020] [Indexed: 01/05/2023]
Abstract
OBJECTIVE p21 (Cdc42/Rac1) activated Kinase 1 (PAK1) is a candidate susceptibility factor for type 2 diabetes (T2D). PAK1 is depleted in the islets from T2D donors, compared to control individuals. In addition, whole-body PAK1 knock out (PAK1-KO) in mice worsens the T2D-like effects of high-fat diet. The current study tested the effects of modulating PAK1 levels only in β-cells. MATERIALS/METHODS β-cell-specific inducible PAK1 KO (βPAK1-iKO) mice were generated and used with human β-cells and T2D islets to evaluate β-cell function. RESULTS βPAK1-iKO mice exhibited glucose intolerance and elevated β-cell apoptosis, but without peripheral insulin resistance. β-cells from βPAK-iKO mice also contained fewer mitochondria per cell. At the cellular level, human PAK1-deficient β-cells showed blunted glucose-stimulated insulin secretion and reduced mitochondrial function. Mitochondria from human PAK1-deficient β-cells were deficient in the electron transport chain (ETC) subunits CI, CIII, and CIV; NDUFA12, a CI complex protein, was identified as a novel PAK1 binding partner, and was significantly reduced with PAK1 knockdown. PAK1 knockdown disrupted the NAD+/NADH and NADP+/NADPH ratios, and elevated ROS. An imbalance of the redox state due to mitochondrial dysfunction leads to ER stress in β-cells. PAK1 replenishment in the β-cells of T2D human islets ameliorated levels of ER stress markers. CONCLUSIONS These findings support a protective function for PAK1 in β-cells. The results support a new model whereby the PAK1 in the β-cell plays a required role upstream of mitochondrial function, via maintaining ETC protein levels and averting stress-induced β-cell apoptosis to retain healthy functional β-cell mass.
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Affiliation(s)
- Miwon Ahn
- Department of Molecular and Cellular Endocrinology, Diabetes and Metabolism Research Institute and Beckman Research Institute at the City of Hope, Duarte, CA 91010, United States of America
| | - Eunjin Oh
- Department of Molecular and Cellular Endocrinology, Diabetes and Metabolism Research Institute and Beckman Research Institute at the City of Hope, Duarte, CA 91010, United States of America
| | - Erika M McCown
- Department of Molecular and Cellular Endocrinology, Diabetes and Metabolism Research Institute and Beckman Research Institute at the City of Hope, Duarte, CA 91010, United States of America
| | - Xin Wang
- Faculty of Biology, Medicine and Health, University of Manchester, UK
| | - Rajakrishnan Veluthakal
- Department of Molecular and Cellular Endocrinology, Diabetes and Metabolism Research Institute and Beckman Research Institute at the City of Hope, Duarte, CA 91010, United States of America
| | - Debbie C Thurmond
- Department of Molecular and Cellular Endocrinology, Diabetes and Metabolism Research Institute and Beckman Research Institute at the City of Hope, Duarte, CA 91010, United States of America.
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Kowluru A. Roles of GTP and Rho GTPases in pancreatic islet beta cell function and dysfunction. Small GTPases 2020; 12:323-335. [PMID: 32867592 DOI: 10.1080/21541248.2020.1815508] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
A growing body of evidence implicates requisite roles for GTP and its binding proteins (Rho GTPases) in the cascade of events leading to physiological insulin secretion from the islet beta cell. Interestingly, chronic exposure of these cells to hyperglycaemic conditions appears to result in sustained activation of specific Rho GTPases (e.g. Rac1) leading to significant alterations in cellular functions including defects in mitochondrial function and nuclear collapse culminating in beta cell demise. One of the objectives of this review is to highlight our current understanding of the regulatory roles of GTP and Rho GTPases in normal islet function (e.g. proliferation and insulin secretion) as well potential defects in these signalling molecules and metabolic pathways that could contribute islet beta cell dysfunction and loss of functional beta cell mass leading to the onset of diabetes. Potential knowledge gaps in this field and possible avenues for future research are also highlighted. ABBREVIATIONS ARNO: ADP-ribosylation factor nucleotide binding site opener; CML: carboxyl methylation; Epac: exchange protein directly activated by cAMP; ER stress: endoplasmic reticulum stress; FTase: farnesyltransferase; GAP: GTPase activating protein; GDI: GDP dissociation inhibitor; GEF: guanine nucleotide exchange factor; GGTase: geranylgeranyltransferase; GGpp: geranylgeranylpyrophosphate; GGPPS: geranylgeranyl pyrophosphate synthase; GSIS: glucose-stimulated insulin secretion; HGPRTase: hypoxanthine-guanine phosphoribosyltransferase; IMPDH: inosine monophosphate dehydrogenase; α-KIC: α-ketoisocaproic acid; MPA: mycophenolic acid; MVA: mevalonic acid; NDPK: nucleoside diphosphate kinase; NMPK: nucleoside monophosphate kinase; Nox2: phagocyte-like NADPH oxidase; PAK-I: p21-activated kinase-I; β-PIX: β-Pak-interacting exchange factor; PRMT: protein arginine methyltransferase; Rac1: ras-related C3 botulinum toxin substrate 1; Tiam1: T-cell lymphoma invasion and metastasis-inducing protein 1; Trx-1: thioredoxin-1; Vav2: vav guanine nucleotide exchange factor 2.
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Affiliation(s)
- Anjaneyulu Kowluru
- Biomedical Research Service, John D. Dingell VA Medical Center and Department of Pharmaceutical Sciences and Medicine, Wayne State University, Detroit, MI, USA
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Abstract
Glucose-induced (physiological) insulin secretion from the islet β-cell involves interplay between cationic (i.e., changes in intracellular calcium) and metabolic (i.e., generation of hydrophobic and hydrophilic second messengers) events. A large body of evidence affirms support for novel regulation, by G proteins, of specific intracellular signaling events, including actin cytoskeletal remodeling, transport of insulin-containing granules to the plasma membrane for fusion, and secretion of insulin into the circulation. This article highlights the following aspects of GPCR-G protein biology of the islet. First, it overviews our current understanding of the identity of a wide variety of G protein regulators and their modulatory roles in GPCR-G protein-effector coupling, which is requisite for optimal β-cell function under physiological conditions. Second, it describes evidence in support of novel, noncanonical, GPCR-independent mechanisms of activation of G proteins in the islet. Third, it highlights the evidence indicating that abnormalities in G protein function lead to islet β-cell dysregulation and demise under the duress of metabolic stress and diabetes. Fourth, it summarizes observations of potential beneficial effects of GPCR agonists in preventing/halting metabolic defects in the islet β-cell under various pathological conditions (e.g., metabolic stress and inflammation). Lastly, it identifies knowledge gaps and potential avenues for future research in this evolving field of translational islet biology. Published 2020. Compr Physiol 10:453-490, 2020.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Center for Translational Research in Diabetes, Biomedical Research Service, John D. Dingell VA Medical Center, Wayne State University, Detroit, Michigan, USA
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Syed I, Rubin de Celis MF, Mohan JF, Moraes-Vieira PM, Vijayakumar A, Nelson AT, Siegel D, Saghatelian A, Mathis D, Kahn BB. PAHSAs attenuate immune responses and promote β cell survival in autoimmune diabetic mice. J Clin Invest 2019; 129:3717-3731. [PMID: 31380811 PMCID: PMC6715391 DOI: 10.1172/jci122445] [Citation(s) in RCA: 52] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Accepted: 06/04/2019] [Indexed: 12/15/2022] Open
Abstract
Palmitic acid esters of hydroxy stearic acids (PAHSAs) are endogenous antidiabetic and antiinflammatory lipids. Here, we show that PAHSAs protect against type 1 diabetes (T1D) and promote β cell survival and function. Daily oral PAHSA administration to nonobese diabetic (NOD) mice delayed the onset of T1D and markedly reduced the incidence of T1D, whether PAHSAs were started before or after insulitis was established. PAHSAs reduced T and B cell infiltration and CD4+ and CD8+ T cell activation, while increasing Treg activation in pancreata of NOD mice. PAHSAs promoted β cell proliferation in both NOD mice and MIN6 cells and increased the number of β cells in NOD mice. PAHSAs attenuated cytokine-induced apoptotic and necrotic β cell death and increased β cell viability. The mechanism appears to involve a reduction of ER stress and MAPK signaling, since PAHSAs lowered ER stress in NOD mice, suppressed thapsigargin-induced PARP cleavage in human islets, and attenuated ERK1/2 and JNK1/2 activation in MIN6 cells. This appeared to be mediated in part by glucagon-like peptide 1 receptor (GLP-1R) and not the G protein-coupled receptor GPR40. PAHSAs also prevented impairment of glucose-stimulated insulin secretion and improved glucose tolerance in NOD mice. Thus, PAHSAs delayed the onset of T1D and reduced its incidence by attenuating immune responses and exerting direct protective effects on β cell survival and function.
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Affiliation(s)
- Ismail Syed
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA
| | - Maria F. Rubin de Celis
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA
| | - James F. Mohan
- Division of Immunology, Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA
| | - Pedro M. Moraes-Vieira
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA
| | - Archana Vijayakumar
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA
| | - Andrew T. Nelson
- Skaggs School of Pharmacy and Pharmaceutical Sciences, UCSD, La Jolla, California, USA
| | - Dionicio Siegel
- Skaggs School of Pharmacy and Pharmaceutical Sciences, UCSD, La Jolla, California, USA
| | - Alan Saghatelian
- Clayton Foundation Laboratories for Peptide Biology, Helmsley Center for Genomic Medicine, Salk Institute for Biological Studies, La Jolla, California, USA
| | - Diane Mathis
- Division of Immunology, Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA
| | - Barbara B. Kahn
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA
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Hwang HJ, Park KS, Choi JH, Cocco L, Jang HJ, Suh PG. Zafirlukast promotes insulin secretion by increasing calcium influx through L-type calcium channels. J Cell Physiol 2018; 233:8701-8710. [PMID: 29797580 DOI: 10.1002/jcp.26750] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Accepted: 04/18/2018] [Indexed: 01/08/2023]
Abstract
The zafirlukast has been reported to be anti-inflammatory and widely used to alleviate the symptoms of asthma. However, its influence on insulin secretion in pancreatic β-cells has not been investigated. Herein, we examined the effects of zafirlukast on insulin secretion and the potential underlying mechanisms. Among the cysteinyl leukotriene receptor 1 antagonists, zafirlukast, pranlukast, and montelukast, only zafirlukast enhanced insulin secretion in a concentration-dependent manner in both low and high glucose conditions and elevated the level of [Ca2+ ]i , further activating Ca2+ /calmodulin-dependent protein kinase II (CaMKII), protein kinase B (AKT), and extracellular signal-regulated kinase (ERK) signaling. These effects were nearly abolished by the L-type Ca2+ channel antagonist nifedipine, while treatment with thapsigargin, a sarco/endoplasmic reticulum Ca2+ ATPase inhibitor, did not have the same effect, suggesting that zafirlukast primarily induces the entry of extracellular Ca2+ rather than intracellular Ca2+ from the endoplasmic reticulum. Zafirlukast treatment resulting in a significant drop in glucose levels and increased insulin secretion in C57BL/6J mice. These findings will contribute to an improved understanding of the side effects of zafirlukast and potential candidate for a therapeutic intervention in diabetes.
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Affiliation(s)
- Hyeon-Jeong Hwang
- School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea
| | - Kyoung-Su Park
- In Vivo Research Center, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea
| | - Jang Hyun Choi
- School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea.,Korea Mouse Phenotyping Center, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea
| | - Lucio Cocco
- Cellular Signaling Laboratory, Department of Biomedical Sciences, University of Bologna, Bologna, Italy
| | - Hyun-Jun Jang
- School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea
| | - Pann-Ghill Suh
- School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea
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10
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Syed I, Lee J, Moraes-Vieira PM, Donaldson CJ, Sontheimer A, Aryal P, Wellenstein K, Kolar MJ, Nelson AT, Siegel D, Mokrosinski J, Farooqi IS, Zhao JJ, Yore MM, Peroni OD, Saghatelian A, Kahn BB. Palmitic Acid Hydroxystearic Acids Activate GPR40, Which Is Involved in Their Beneficial Effects on Glucose Homeostasis. Cell Metab 2018; 27:419-427.e4. [PMID: 29414687 PMCID: PMC5807007 DOI: 10.1016/j.cmet.2018.01.001] [Citation(s) in RCA: 120] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Revised: 08/24/2017] [Accepted: 01/03/2018] [Indexed: 12/28/2022]
Abstract
Palmitic acid hydroxystearic acids (PAHSAs) are endogenous lipids with anti-diabetic and anti-inflammatory effects. PAHSA levels are reduced in serum and adipose tissue of insulin-resistant people and high-fat diet (HFD)-fed mice. Here, we investigated whether chronic PAHSA treatment enhances insulin sensitivity and which receptors mediate PAHSA effects. Chronic PAHSA administration in chow- and HFD-fed mice raises serum and tissue PAHSA levels ∼1.4- to 3-fold. This improves insulin sensitivity and glucose tolerance without altering body weight. PAHSA administration in chow-fed, but not HFD-fed, mice augments insulin and glucagon-like peptide (GLP-1) secretion. PAHSAs are selective agonists for GPR40, increasing Ca+2 flux, but not intracellular cyclic AMP. Blocking GPR40 reverses improvements in glucose tolerance and insulin sensitivity in PAHSA-treated chow- and HFD-fed mice and directly inhibits PAHSA augmentation of glucose-stimulated insulin secretion in human islets. In contrast, GLP-1 receptor blockade in PAHSA-treated chow-fed mice reduces PAHSA effects on glucose tolerance, but not on insulin sensitivity. Thus, PAHSAs activate GPR40, which is involved in their beneficial metabolic effects.
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Affiliation(s)
- Ismail Syed
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Center for Life Sciences, Room 747, 330 Brookline Avenue, Boston, MA 02215, USA
| | - Jennifer Lee
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Center for Life Sciences, Room 747, 330 Brookline Avenue, Boston, MA 02215, USA
| | - Pedro M Moraes-Vieira
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Center for Life Sciences, Room 747, 330 Brookline Avenue, Boston, MA 02215, USA
| | - Cynthia J Donaldson
- Clayton Foundation Laboratories for Peptide Biology, Helmsley Center for Genomic Medicine, Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Alexandra Sontheimer
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Center for Life Sciences, Room 747, 330 Brookline Avenue, Boston, MA 02215, USA
| | - Pratik Aryal
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Center for Life Sciences, Room 747, 330 Brookline Avenue, Boston, MA 02215, USA
| | - Kerry Wellenstein
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Center for Life Sciences, Room 747, 330 Brookline Avenue, Boston, MA 02215, USA
| | - Matthew J Kolar
- Clayton Foundation Laboratories for Peptide Biology, Helmsley Center for Genomic Medicine, Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Andrew T Nelson
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
| | - Dionicio Siegel
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
| | - Jacek Mokrosinski
- University of Cambridge Metabolic Research Laboratories and NIHR Cambridge Biomedical Research Centre, Wellcome Trust-MRC Institute of Metabolic Science, Cambridge CB2 0QQ, UK
| | - I Sadaf Farooqi
- University of Cambridge Metabolic Research Laboratories and NIHR Cambridge Biomedical Research Centre, Wellcome Trust-MRC Institute of Metabolic Science, Cambridge CB2 0QQ, UK
| | - Juan Juan Zhao
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Center for Life Sciences, Room 747, 330 Brookline Avenue, Boston, MA 02215, USA
| | - Mark M Yore
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Center for Life Sciences, Room 747, 330 Brookline Avenue, Boston, MA 02215, USA
| | - Odile D Peroni
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Center for Life Sciences, Room 747, 330 Brookline Avenue, Boston, MA 02215, USA
| | - Alan Saghatelian
- Clayton Foundation Laboratories for Peptide Biology, Helmsley Center for Genomic Medicine, Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Barbara B Kahn
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Center for Life Sciences, Room 747, 330 Brookline Avenue, Boston, MA 02215, USA.
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11
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Li Y, Wu H, Liu N, Cao X, Yang Z, Lu B, Hu R, Wang X, Wen J. Melatonin exerts an inhibitory effect on insulin gene transcription via MTNR1B and the downstream Raf‑1/ERK signaling pathway. Int J Mol Med 2017; 41:955-961. [PMID: 29207116 DOI: 10.3892/ijmm.2017.3305] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 11/03/2017] [Indexed: 11/06/2022] Open
Abstract
The pineal hormone melatonin influences the secretion of insulin by pancreatic islets via the G‑protein‑coupled melatonin receptors 1 and 2 that are expressed in pancreatic β‑cells. Genome‑wide association studies indicate that melatonin receptor 1B (MTNR1B) single nucleotide polymorphisms are tightly associated with type 2 diabetes mellitus (T2DM). However, the underlying mechanism is unclear. Raf‑1 serves a critical role in the mitogen‑activated protein kinase (MAPK) pathways in β‑cell survival and proliferation and, therefore, may be involved in the mechanism by which melatonin impacts on T2DM through MTNR1B. In the present study, the mRNA expression of the two mouse insulin genes Ins1 and Ins2 was investigated in MIN6 cells treated with different concentrations of melatonin, and insulin secretion was detected under the same conditions. Following the overexpression or silencing of MTNR1B, the activities of components of the MAPK signaling pathway, including Raf‑1 and ERK, were evaluated. The impact of MTNR1B knockdown on the melatonin‑regulated insulin gene expression and insulin secretion were also investigated. The results demonstrated that exogenous melatonin inhibited the expression of insulin mRNA in the MIN6 cells. Insulin secretion by the MIN6 cells, however, was not affected by melatonin. The MAPK signaling pathway was inhibited in MIN6 cells by treatment with melatonin or the overexpression of MTNR1B. The knockdown of MTNR1B totally attenuated the regulating effect of melatonin on insulin gene expression. Additionally, the inductive effect of melatonin on the expression of insulin mRNA was attenuated when the activities of Raf‑1 or ERK were blocked using the chemical inhibitors GW5074 and U0126, respectively. It may be concluded that melatonin exerts an inhibitory effect on insulin transcription via MTNR1B and the downstream MAPK signaling pathway.
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Affiliation(s)
- Yanliang Li
- Department of Endocrinology and Metabolism, Huashan Hospital, Fudan University, Shanghai 200040, P.R. China
| | - Huihui Wu
- Department of Endocrinology and Metabolism, Huashan Hospital, Fudan University, Shanghai 200040, P.R. China
| | - Naijia Liu
- Department of Endocrinology and Metabolism, Huashan Hospital, Fudan University, Shanghai 200040, P.R. China
| | - Xinyi Cao
- Department of Endocrinology and Metabolism, Huashan Hospital, Fudan University, Shanghai 200040, P.R. China
| | - Zhen Yang
- Department of Endocrinology, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200092, P.R. China
| | - Bin Lu
- Department of Endocrinology and Metabolism, Huashan Hospital, Fudan University, Shanghai 200040, P.R. China
| | - Renming Hu
- Department of Endocrinology and Metabolism, Huashan Hospital, Fudan University, Shanghai 200040, P.R. China
| | - Xuanchun Wang
- Department of Endocrinology and Metabolism, Huashan Hospital, Fudan University, Shanghai 200040, P.R. China
| | - Jie Wen
- Department of Endocrinology and Metabolism, Huashan Hospital, Fudan University, Shanghai 200040, P.R. China
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Leduc M, Richard J, Costes S, Muller D, Varrault A, Compan V, Mathieu J, Tanti JF, Pagès G, Pouyssegur J, Bertrand G, Dalle S, Ravier MA. ERK1 is dispensable for mouse pancreatic beta cell function but is necessary for glucose-induced full activation of MSK1 and CREB. Diabetologia 2017; 60:1999-2010. [PMID: 28721437 DOI: 10.1007/s00125-017-4356-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Accepted: 06/02/2017] [Indexed: 11/24/2022]
Abstract
AIMS/HYPOTHESIS Insufficient insulin secretion from pancreatic beta cells, which is associated with a decrease in beta cell mass, is a characteristic of type 2 diabetes. Extracellular signal-related kinase 1 and 2 (ERK1/2) inhibition in beta cells has been reported to affect insulin secretion, gene transcription and survival, although whether ERK1 and ERK2 play distinct roles is unknown. The aim of this study was to assess the individual roles of ERK1 and ERK2 in beta cells using ERK1 (also known as Mapk3)-knockout mice (Erk1 -/- mice) and pharmacological approaches. METHODS NAD(P)H, free cytosolic Ca2+ concentration and insulin secretion were determined in islets. ERK1 and ERK2 subplasmalemmal translocation and activity was monitored using total internal reflection fluorescence microscopy. ERK1/2, mitogen and stress-activated kinase1 (MSK1) and cAMP-responsive element-binding protein (CREB) activation were evaluated by western blot and/or immunocytochemistry. The islet mass was determined from pancreatic sections. RESULTS Glucose induced rapid subplasmalemmal recruitment of ERK1 and ERK2. When both ERK1 and ERK2 were inhibited simultaneously, the rapid transient peak of the first phase of glucose-induced insulin secretion was reduced by 40% (p < 0.01), although ERK1 did not appear to be involved in this process. By contrast, ERK1 was required for glucose-induced full activation of several targets involved in beta cell survival; MSK1 and CREB were less active in Erk1 -/- mouse beta cells (p < 0.01) compared with Erk1 +/+ mouse beta cells, and their phosphorylation could only be restored when ERK1 was re-expressed and not when ERK2 was overexpressed. Finally, the islet mass of Erk1 -/- mice was slightly increased in young animals (4-month-old mice) vs Erk1 +/+ mice (section occupied by islets [mean ± SEM]: 0.74% ± 0.03% vs 0.62% ± 0.04%; p < 0.05), while older mice (10 months old) were less prone to age-associated pancreatic peri-insulitis (infiltrated islets [mean ± SEM]: 7.51% ± 1.34% vs 2.03% ± 0.51%; p < 0.001). CONCLUSIONS/INTERPRETATION ERK1 and ERK2 play specific roles in beta cells. ERK2 cannot always compensate for the lack of ERK1 but the absence of a clear-cut phenotype in Erk1 -/- mice shows that ERK1 is dispensable in normal conditions.
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Affiliation(s)
- Michele Leduc
- Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique (CNRS), Inserm, Université de Montpellier, 141 Rue de la Cardonille, 34094, Montpellier CEDEX 5, France
| | - Joy Richard
- Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique (CNRS), Inserm, Université de Montpellier, 141 Rue de la Cardonille, 34094, Montpellier CEDEX 5, France
| | - Safia Costes
- Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique (CNRS), Inserm, Université de Montpellier, 141 Rue de la Cardonille, 34094, Montpellier CEDEX 5, France
| | - Dany Muller
- Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique (CNRS), Inserm, Université de Montpellier, 141 Rue de la Cardonille, 34094, Montpellier CEDEX 5, France
| | - Annie Varrault
- Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique (CNRS), Inserm, Université de Montpellier, 141 Rue de la Cardonille, 34094, Montpellier CEDEX 5, France
| | - Vincent Compan
- Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique (CNRS), Inserm, Université de Montpellier, 141 Rue de la Cardonille, 34094, Montpellier CEDEX 5, France
| | - Julia Mathieu
- Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique (CNRS), Inserm, Université de Montpellier, 141 Rue de la Cardonille, 34094, Montpellier CEDEX 5, France
| | - Jean-François Tanti
- Faculté de Médecine, Centre Méditerranéen de Médecine Moléculaire, Inserm U1065, Université de Nice Sophia Antipolis, Nice, France
| | - Gilles Pagès
- Institute for Research on Cancer and Aging, Nice (IRCAN), Centre Antoine Lacassagne, Université de Nice Sophia Antipolis, Nice, France
| | - Jacques Pouyssegur
- Institute for Research on Cancer and Aging, Nice (IRCAN), Centre Antoine Lacassagne, Université de Nice Sophia Antipolis, Nice, France
- Medical Biology Department, Centre Scientifique de Monaco (CSM), Monaco, Principality of Monaco
| | - Gyslaine Bertrand
- Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique (CNRS), Inserm, Université de Montpellier, 141 Rue de la Cardonille, 34094, Montpellier CEDEX 5, France
| | - Stéphane Dalle
- Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique (CNRS), Inserm, Université de Montpellier, 141 Rue de la Cardonille, 34094, Montpellier CEDEX 5, France
| | - Magalie A Ravier
- Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique (CNRS), Inserm, Université de Montpellier, 141 Rue de la Cardonille, 34094, Montpellier CEDEX 5, France.
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Kowluru A. Role of G-proteins in islet function in health and diabetes. Diabetes Obes Metab 2017; 19 Suppl 1:63-75. [PMID: 28880478 PMCID: PMC5657296 DOI: 10.1111/dom.13011] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Revised: 05/03/2017] [Accepted: 05/12/2017] [Indexed: 12/17/2022]
Abstract
Glucose-stimulated insulin secretion (GSIS) involves interplay between metabolic and cationic events. Seminal contributions from multiple laboratories affirm essential roles for small G-proteins (Rac1, Cdc42, Arf6, Rab27A) in GSIS. Activation of these signalling proteins promotes cytoskeletal remodeling, transport and docking of insulin granules on the plasma membrane for exocytotic secretion of insulin. Evidence in rodent and human islets suggests key roles for lipidation (farnesylation and geranylgeranylation) of these G-proteins for their targeting to appropriate cellular compartments for optimal regulation of effectors leading to GSIS. Interestingly, however, inhibition of prenylation appears to cause mislocalization of non-prenylated, but (paradoxically) activated G-proteins, in "inappropriate" compartments leading to activation of stress kinases and onset of mitochondrial defects, loss in GSIS and apoptosis of the islet β-cell. This review highlights our current understanding of roles of G-proteins and their post-translational lipidation (prenylation) signalling networks in islet function in normal health, metabolic stress (glucolipotoxicity and ER stress) and diabetes. Critical knowledge gaps that need to be addressed for the development of therapeutics to halt defects in these signalling steps in β-cells in models of impaired insulin secretion and diabetes are also highlighted and discussed.
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Affiliation(s)
- Anjaneyulu Kowluru
- β-Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, and Department of Pharmaceutical Sciences, Wayne State University, Detroit, Michigan
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Safi SZ, Qvist R, Ong G, Karimian H, Imran M, Shah I. Stimulation of β-adrenergic receptors plays a protective role via increased expression of RAF-1 and PDX-1 in hyperglycemic rat pancreatic islet (RIN-m5F) cells. Arch Med Sci 2017; 13:470-480. [PMID: 28261303 PMCID: PMC5332455 DOI: 10.5114/aoms.2016.64131] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2014] [Accepted: 07/14/2015] [Indexed: 12/31/2022] Open
Abstract
INTRODUCTION It is a widely held view that a progressive reduction of beta-cell mass occurs in the progression of diabetes. RAF-1 kinase and pancreas duodenal homeobox 1 (PDX-1) are major factors that promote survival of cells and maintain normal insulin functions. In this study we investigated the effect of a β-adrenergic receptor agonist and antagonist on RAF-1 and PDX-1, and their respective effects on apoptosis and insulin release in RIN-m5F cells. MATERIAL AND METHODS RIN-m5F cells were cultured in normal (5 mM) and high (25 mM) glucose to mimic diabetic conditions, followed by treatment with 5 µM, 10 µM and 20 µM of isoproterenol and isoproterenol + propranolol for 6, 12 and 24 h. Western blotting and reverse transcription analysis were performed to examine the expression of RAF-1 and PDX-1. Annexin-V-FITC and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assays were used to investigate apoptosis. ELISA was used to measure insulin levels. Reverse transcription polymerase chain reaction was conducted to investigate the expression of genes. RESULTS Stimulation of β-adrenergic receptors with isoproterenol significantly induced RAF-1 and PDX-1 genes in a concentration-dependent and time-independent manner. Changes were significant both at protein and mRNA levels. Up-regulation of RAF-1 and PDX-1 was accompanied by improved insulin levels and reduced apoptosis. Concentrations of 10 µM and 20 µM for 12 and 24 h were more effective in achieving significant differences in the experimental and control groups. Propranolol reversed the effect of isoproterenol mostly at maximum concentrations and time periods. CONCLUSIONS A positive effect of a β-adrenergic agonist on RAF-1 and PDX-1, reduction in β-cell apoptosis and improved insulin contents can help to understand the pathogenesis of diabetes and to develop novel approaches for the β-cell dysfunction in diabetes.
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Affiliation(s)
- Sher Zaman Safi
- Department of Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
- Interdisciplinary Research Center in Biomedical Materials (IRCBM), COMSATS Institute of Information Technology, Lahore, Pakistan
| | - Rajes Qvist
- Department of Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
| | - Gracie Ong
- Department of Anesthesiology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
| | - Hamed Karimian
- Department of Pharmacy, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
| | - Muhammad Imran
- Biochemistry Section, Institute of Chemical Sciences, University of Peshawar, Peshawar, Pakistan
| | - Ikram Shah
- Department of Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
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Veluthakal R, Arora DK, Goalstone ML, Kowluru RA, Kowluru A. Metabolic Stress Induces Caspase-3 Mediated Degradation and Inactivation of Farnesyl and Geranylgeranyl Transferase Activities in Pancreatic β-Cells. Cell Physiol Biochem 2016; 39:2110-2120. [PMID: 27802439 DOI: 10.1159/000447907] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/30/2016] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND/AIMS At least 300 prenylated proteins are identified in the human genome; the majority of which partake in a variety of cellular processes including growth, differentiation, cytoskeletal organization/dynamics and vesicle trafficking. Aberrant prenylation of proteins is implicated in human pathologies including cancer; neurodegenerative diseases, retinitis pigmentosa, and premature ageing syndromes. Original observations from our laboratory have demonstrated that prenylation of proteins [small G-proteins and γ-subunits of trimeric G-proteins] is requisite for physiological insulin secretion. Herein, we assessed the impact of metabolic stress [gluco-, lipotoxicity and ER-stress] on the functional status of protein prenylation pathway in pancreatic β-cells. METHODS Farnesyltransferase [FTase] and geranylgeranyltransferase [GGTase] activities were quantified by radioisotopic methods. Caspase-3 activation and FTase/GGTase-α subunit degradation were determined by Western blotting. RESULTS We observed that metabolic stress activates caspase-3 and induces degradation of the common α-subunit of FTase and GGTase-I in INS-1 832/13 cells, normal rodent islets and human islets leading to functional defects [inactivation] in FTase and GGTase activities. Caspase-3 activation and FTase/GGTase-α degradation were also seen in islets from the Zucker diabetic fatty [ZDF] rat, a model for Type 2 diabetes. Consequential to defects in FTase/GGTase-α signaling, we observed significant accumulation of unprenylated proteins [Rap1] in β-cells exposed to glucotoxic conditions. These findings were replicated in β-cells following pharmacological inhibition of generation of prenylpyrophosphate substrates [Simvastatin] or catalytic activity of prenylating enzymes [GGTI-2147]. CONCLUSIONS Our findings provide the first evidence to suggest that metabolic stress induced dysfunction of the islet β-cell may, in part, be due to defective protein prenylation signaling pathway.
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Affiliation(s)
- Rajakrishnan Veluthakal
- Department of Molecular and Cellular Endocrinology, Diabetes and Metabolic Research Institute, City of Hope/BRI, Duarte, USA
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16
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Veluthakal R, Tunduguru R, Arora DK, Sidarala V, Syeda K, Vlaar CP, Thurmond DC, Kowluru A. VAV2, a guanine nucleotide exchange factor for Rac1, regulates glucose-stimulated insulin secretion in pancreatic beta cells. Diabetologia 2015. [PMID: 26224100 PMCID: PMC4591202 DOI: 10.1007/s00125-015-3707-4] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
AIMS/HYPOTHESIS Rho GTPases (Ras-related C3 botulinum toxin substrate 1 [Rac1] and cell division cycle 42 [Cdc42]) have been shown to regulate glucose-stimulated insulin secretion (GSIS) via cytoskeletal remodelling, trafficking and fusion of insulin-secretory granules with the plasma membrane. GTP loading of these G proteins, which is facilitated by GDP/GTP exchange factors, is a requisite step in the regulation of downstream effector proteins. Guanine nucleotide exchange factor VAV2 (VAV2), a member of the Dbl family of proteins, has been identified as one of the GDP/GTP exchange factors for Rac1. Despite recent evidence on the regulatory roles of VAV2 in different cell types, roles of this guanine nucleotide exchange factor in the signalling events leading to GSIS remain undefined. Using immunological, short interfering RNA (siRNA), pharmacological and microscopic approaches we investigated the role of VAV2 in GSIS from islet beta cells. METHODS Co-localisation of Rac1 and VAV2 was determined by Triton X-114 phase partition and confocal microscopy. Glucose-induced actin remodelling was quantified by live cell imaging using the LifeAct-GFP fluorescent biosensor. Rac1 activation was determined by G protein linked immunosorbent assay (G-LISA). RESULTS Western blotting indicated that VAV2 is expressed in INS-1 832/13 beta cells, normal rat islets and human islets. Vav2 siRNA markedly attenuated GSIS in INS-1 832/13 cells. Ehop-016, a newly discovered small molecule inhibitor of the VAV2-Rac1 interaction, or siRNA-mediated knockdown of VAV2 markedly attenuated glucose-induced Rac1 activation and GSIS in INS-1 832/13 cells. Pharmacological findings were recapitulated in primary rat islets. A high glucose concentration promoted co-localisation of Rac1 and VAV2. Real-time imaging in live cells indicated a significant inhibition of glucose-induced cortical actin remodelling by Ehop-016. CONCLUSIONS/INTERPRETATION Our data provide the first evidence to implicate VAV2 in glucose-induced Rac1 activation, actin remodelling and GSIS in pancreatic beta cells.
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Affiliation(s)
- Rajakrishnan Veluthakal
- Beta Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, 4646 John R, Detroit, MI, 48201, USA
- Department of Pediatrics, Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Ragadeepthi Tunduguru
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Daleep Kumar Arora
- Immunobiology and Cancer Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
| | - Vaibhav Sidarala
- Beta Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, 4646 John R, Detroit, MI, 48201, USA
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy, Wayne State University, Detroit, MI, USA
| | - Khadija Syeda
- Beta Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, 4646 John R, Detroit, MI, 48201, USA
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy, Wayne State University, Detroit, MI, USA
| | - Cornelis P Vlaar
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Puerto Rico, Medical Sciences Campus, San Juan, Puerto Rico
| | - Debbie C Thurmond
- Department of Pediatrics, Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN, USA
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Anjaneyulu Kowluru
- Beta Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, 4646 John R, Detroit, MI, 48201, USA.
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy, Wayne State University, Detroit, MI, USA.
- B-4237 Research Service, John D. Dingell VA Medical Center, 4646 John R, Detroit, MI, 48201, USA.
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Kowluru A, Kowluru RA. Protein prenylation in islet β-cell function in health and diabetes: Putting the pieces of the puzzle together. Biochem Pharmacol 2015. [PMID: 26215874 DOI: 10.1016/j.bcp.2015.07.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Post-translational prenylation involves incorporation of 15-(farnesyl) or 20-(geranylgeranyl) carbon derivatives of mevalonic acid into highly conserved C-terminal cysteines of proteins. The farnesyl transferase (FTase) and the geranylgeranyl transferase (GGTase) mediate incorporation of farnesyl and geranylgeranyl groups, respectively. At least 300 proteins are prenylated in the human genome; the majority of these are implicated in cellular processes including growth, differentiation, cytoskeletal function and vesicle trafficking. From a functional standpoint, isoprenylation is requisite for targeting of modified proteins to relevant cellular compartments for regulation of effector proteins. Pharmacological and molecular biological studies have provided compelling evidence for key roles of this signaling pathway in physiological insulin secretion in normal rodent and human islets. Recent evidence indicates that inhibition of prenylation results in mislocalization of unprenylated proteins, and surprisingly, they remain in active (GTP-bound) conformation. Sustained activation of G proteins has been reported in mice lacking GGTase, suggesting alternate mechanisms for the activation of non-prenylated G proteins. These findings further raise an interesting question if mislocalized, non-prenylated and functionally active G proteins cause cellular pathology since aberrant protein prenylation has been implicated in the onset of cardiovascular disease and diabetes. Herein, we overview the existing evidence to implicate prenylation in islet function and potential defects in this signaling pathways in the diabetic β-cell. We will also identify critical knowledge gaps that need to be addressed for the development of therapeutics to halt defects in these signaling steps in β cells in models of impaired insulin secretion, metabolic stress and diabetes.
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Affiliation(s)
- Anjaneyulu Kowluru
- John D. Dingell VA Medical Center, Detroit, MI 48201, United States; Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI 48201, United States.
| | - Renu A Kowluru
- Kresge Eye Institute, Wayne State University, Detroit, MI 48201, United States
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18
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Metabolomics applied to the pancreatic islet. Arch Biochem Biophys 2015; 589:120-30. [PMID: 26116790 DOI: 10.1016/j.abb.2015.06.013] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Revised: 06/19/2015] [Accepted: 06/21/2015] [Indexed: 01/18/2023]
Abstract
Metabolomics, the characterization of the set of small molecules in a biological system, is advancing research in multiple areas of islet biology. Measuring a breadth of metabolites simultaneously provides a broad perspective on metabolic changes as the islets respond dynamically to metabolic fuels, hormones, or environmental stressors. As a result, metabolomics has the potential to provide new mechanistic insights into islet physiology and pathophysiology. Here we summarize advances in our understanding of islet physiology and the etiologies of type-1 and type-2 diabetes gained from metabolomics studies.
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19
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ElAzzouny MA, Evans CR, Burant CF, Kennedy RT. Metabolomics Analysis Reveals that AICAR Affects Glycerolipid, Ceramide and Nucleotide Synthesis Pathways in INS-1 Cells. PLoS One 2015; 10:e0129029. [PMID: 26107620 PMCID: PMC4480354 DOI: 10.1371/journal.pone.0129029] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2014] [Accepted: 05/03/2015] [Indexed: 12/31/2022] Open
Abstract
AMPK regulates many metabolic pathways including fatty acid and glucose metabolism, both of which are closely associated with insulin secretion in pancreatic β-cells. Insulin secretion is regulated by metabolic coupling factors such as ATP/ADP ratio and other metabolites generated by the metabolism of nutrients such as glucose, fatty acid and amino acids. However, the connection between AMPK activation and insulin secretion in β-cells has not yet been fully elucidated at a metabolic level. To study the effect of AMPK activation on glucose stimulated insulin secretion, we applied the pharmacological activator 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) to an INS-1 (832/13) β-cell line. We measured the change in 66 metabolites in the presence or absence of AICAR using different stable isotopic labeled nutrients to probe selected pathways. AMPK activation by AICAR increased basal insulin secretion and reduced the glucose stimulation index. Although ATP/ADP ratios were not strongly affected by AICAR, several other metabolites and pathways important for insulin secretion were affected by AICAR treatment including long-chain CoAs, malonyl-CoA, 3-hydroxy-3 methylglutaryl CoA, diacylglycerol, and farnesyl pyrophosphate. Tracer studies using 13C-glucose revealed lower glucose flux in the purine and pyrimidine pathway and in the glycerolipid synthesis pathway. Untargeted metabolomics revealed reduction in ceramides caused by AICAR that may explain the beneficial role of AMPK in protecting β-cells from lipotoxicity. Taken together, the results provide an overall picture of the metabolic changes associated with AICAR treatment and how it modulates insulin secretion and β-cell survival.
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Affiliation(s)
- Mahmoud A. ElAzzouny
- The Department of Chemistry, University of Michigan, Ann Arbor, United States of America
- The Department of Internal Medicine, University of Michigan, Ann Arbor, United States of America
| | - Charles R. Evans
- The Department of Internal Medicine, University of Michigan, Ann Arbor, United States of America
| | - Charles F Burant
- The Department of Internal Medicine, University of Michigan, Ann Arbor, United States of America
| | - Robert T. Kennedy
- The Department of Chemistry, University of Michigan, Ann Arbor, United States of America
- The Department of Pharmacology, University of Michigan, Ann Arbor, United States of America
- * E-mail:
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Yore MM, Syed I, Moraes-Vieira PM, Zhang T, Herman MA, Homan EA, Patel RT, Lee J, Chen S, Peroni OD, Dhaneshwar AS, Hammarstedt A, Smith U, McGraw TE, Saghatelian A, Kahn BB. Discovery of a class of endogenous mammalian lipids with anti-diabetic and anti-inflammatory effects. Cell 2015; 159:318-32. [PMID: 25303528 DOI: 10.1016/j.cell.2014.09.035] [Citation(s) in RCA: 573] [Impact Index Per Article: 63.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2014] [Revised: 07/15/2014] [Accepted: 09/18/2014] [Indexed: 01/21/2023]
Abstract
Increased adipose tissue lipogenesis is associated with enhanced insulin sensitivity. Mice overexpressing the Glut4 glucose transporter in adipocytes have elevated lipogenesis and increased glucose tolerance despite being obese with elevated circulating fatty acids. Lipidomic analysis of adipose tissue revealed the existence of branched fatty acid esters of hydroxy fatty acids (FAHFAs) that were elevated 16- to 18-fold in these mice. FAHFA isomers differ by the branched ester position on the hydroxy fatty acid (e.g., palmitic-acid-9-hydroxy-stearic-acid, 9-PAHSA). PAHSAs are synthesized in vivo and regulated by fasting and high-fat feeding. PAHSA levels correlate highly with insulin sensitivity and are reduced in adipose tissue and serum of insulin-resistant humans. PAHSA administration in mice lowers ambient glycemia and improves glucose tolerance while stimulating GLP-1 and insulin secretion. PAHSAs also reduce adipose tissue inflammation. In adipocytes, PAHSAs signal through GPR120 to enhance insulin-stimulated glucose uptake. Thus, FAHFAs are endogenous lipids with the potential to treat type 2 diabetes.
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Affiliation(s)
- Mark M Yore
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA
| | - Ismail Syed
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA
| | - Pedro M Moraes-Vieira
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA
| | - Tejia Zhang
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA
| | - Mark A Herman
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA
| | - Edwin A Homan
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA
| | - Rajesh T Patel
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
| | - Jennifer Lee
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA
| | - Shili Chen
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA
| | - Odile D Peroni
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA
| | - Abha S Dhaneshwar
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA
| | - Ann Hammarstedt
- Department of Molecular and Clinical Medicine, the Sahlgrenska Academy, University of Gothenburg, Gothenburg 41345, Sweden
| | - Ulf Smith
- Department of Molecular and Clinical Medicine, the Sahlgrenska Academy, University of Gothenburg, Gothenburg 41345, Sweden
| | - Timothy E McGraw
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
| | - Alan Saghatelian
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
| | - Barbara B Kahn
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA.
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Sidarala V, Veluthakal R, Syeda K, Kowluru A. EHT 1864, a small molecule inhibitor of Ras-related C3 botulinum toxin substrate 1 (Rac1), attenuates glucose-stimulated insulin secretion in pancreatic β-cells. Cell Signal 2015; 27:1159-67. [PMID: 25725286 DOI: 10.1016/j.cellsig.2015.02.020] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 02/04/2015] [Accepted: 02/22/2015] [Indexed: 01/05/2023]
Abstract
Glucose-stimulated insulin secretion (GSIS) in the pancreatic β-cells entails a variety of signaling mechanisms including activation of small GTP-binding proteins (G-proteins). Previous studies from our laboratory in human islets, rodent islets and clonal β-cells have demonstrated that G-proteins (e.g., Arf6, Cdc42 and Rac1) play novel roles in cytoskeletal remodeling, which is a critical step in the trafficking of insulin-laden secretory granules for fusion with plasma membrane and release of insulin. To further understand regulatory roles of Rac1 in GSIS, we utilized, herein, EHT 1864, a small molecule inhibitor, which attenuates Rac1 activation by retaining the G-protein in an inert/inactive state, thereby preventing activation of its downstream effector proteins. We demonstrate that EHT 1864 markedly attenuated GSIS in INS-1 832/13 cells. In addition, EHT 1864 significantly reduced glucose-induced activation and membrane targeting of Rac1 in INS-1 832/13 cells. This Rac1 inhibitor also suppressed glucose-induced activation of ERK1/2 and p53, but not Akt. Lastly, unlike the inhibitors of protein prenylation (simvastatin), EHT 1864 did not exert any significant effects on cell morphology (cell rounding) under the conditions it attenuated Rac1-sensitive signaling steps leading to GSIS. Based on these findings, we conclude that EHT 1864 specifically inhibits glucose-induced Rac1 activation and membrane association and associated downstream signaling events culminating in inhibition of GSIS.
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Affiliation(s)
- Vaibhav Sidarala
- John D. Dingell VA Medical Center, Detroit, MI 48201, USA; Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI 48201, USA
| | - Rajakrishnan Veluthakal
- John D. Dingell VA Medical Center, Detroit, MI 48201, USA; Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI 48201, USA
| | - Khadija Syeda
- John D. Dingell VA Medical Center, Detroit, MI 48201, USA; Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI 48201, USA
| | - Anjaneyulu Kowluru
- John D. Dingell VA Medical Center, Detroit, MI 48201, USA; Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI 48201, USA.
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Phagocyte-like NADPH oxidase [Nox2] in cellular dysfunction in models of glucolipotoxicity and diabetes. Biochem Pharmacol 2014; 88:275-83. [DOI: 10.1016/j.bcp.2014.01.017] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Revised: 01/10/2014] [Accepted: 01/13/2014] [Indexed: 02/01/2023]
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Arora DK, Machhadieh B, Matti A, Wadzinski BE, Ramanadham S, Kowluru A. High glucose exposure promotes activation of protein phosphatase 2A in rodent islets and INS-1 832/13 β-cells by increasing the posttranslational carboxylmethylation of its catalytic subunit. Endocrinology 2014; 155:380-91. [PMID: 24265448 PMCID: PMC3891936 DOI: 10.1210/en.2013-1773] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Existing evidence implicates regulatory roles for protein phosphatase 2A (PP2A) in a variety of cellular functions, including cytoskeletal remodeling, hormone secretion, and apoptosis. We report here activation of PP2A in normal rat islets and insulin-secreting INS-1 832/13 cells under the duress of hyperglycemic (HG) conditions. Small interfering RNA-mediated knockdown of the catalytic subunit of PP2A (PP2Ac) markedly attenuated glucose-induced activation of PP2A. HG, but not nonmetabolizable 3-O-methyl glucose or mannitol (osmotic control), significantly stimulated the methylation of PP2Ac at its C-terminal Leu-309, suggesting a novel role for this posttranslational modification in glucose-induced activation of PP2A. Moreover, knockdown of the cytosolic leucine carboxymethyl transferase 1 (LCMT1), which carboxymethylates PP2Ac, significantly attenuated PP2A activation under HG conditions. In addition, HG conditions, but not 3-O-methyl glucose or mannitol, markedly increased the expression of LCMT1. Furthermore, HG conditions significantly increased the expression of B55α, a regulatory subunit of PP2A, which has been implicated in islet dysfunction under conditions of oxidative stress and diabetes. Thapsigargin, a known inducer of endoplasmic reticulum stress, failed to exert any discernible effects on the carboxymethylation of PP2Ac, expression of LCMT1 and B55α, or PP2A activity, suggesting no clear role for endoplasmic reticulum stress in HG-induced activation of PP2A. Based on these findings, we conclude that exposure of the islet β-cell to HG leads to accelerated PP2A signaling pathway, leading to loss in glucose-induced insulin secretion.
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Affiliation(s)
- Daleep K Arora
- Beta-Cell Biochemistry Laboratory (D.K.A., A.K.), John D. Dingell Veterans Affairs Medical Center, and Department of Pharmaceutical Sciences (D.K.A., A.K.), Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, Michigan 48201; Section of Endocrinology, Diabetes and Metabolism (B.M.), University of Illinois at Chicago, Chicago, Illinois 60612; Department of Engineering and Science (A.M.), University of Detroit Mercy, Detroit, Michigan 48221; Department of Pharmacology (B.E.W.), Vanderbilt University Medical Center, Nashville, Tennessee 37232; and Department of Cell, Developmental, and Integrative Biology (S.R.), University of Alabama at Birmingham, Birmingham, Alabama 35294
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Arora DK, Mohammed AM, Kowluru A. Nifedipine prevents etoposide-induced caspase-3 activation, prenyl transferase degradation and loss in cell viability in pancreatic β-cells. Apoptosis 2013; 18:1-8. [PMID: 23054080 DOI: 10.1007/s10495-012-0763-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Emerging evidence implicates novel roles for post-translational prenylation (i.e., farnesylation and geranylgeranylation) of various signaling proteins in a variety of cellular functions including hormone secretion, survival and apoptosis. In the context of cellular apoptosis, it has been shown previously that caspase-3 activation, a hallmark of mitochondrial dysregulation, promotes hydrolysis of several key cellular proteins. We report herein that exposure of insulin-secreting INS 832/13 cells or normal rat islets to etoposide leads to significant activation of caspase-3 and subsequent degradation of the common α-subunit of farnesyl/geranylgeranyl transferases (FTase/GGTase). Furthermore, the above stated signaling steps were prevented by Z-DEVD-FMK, a known inhibitor of caspase-3. In addition, treatment of cell lysates with recombinant caspase-3 also caused FTase/GGTase α-subunit degradation. Moreover, nifedipine, a calcium channel blocker, markedly attenuated etoposide-induced caspase-3 activation, FTase/GGTase α-subunit degradation in INS 832/13 cells and normal rat islets. Further, nifedipine significantly restored etoposide-induced loss in metabolic cell viability in INS 832/13 cells. Based on these findings, we conclude that etoposide induces loss in cell viability by inducing mitochondrial dysfunction, caspase-3 activation and degradation of FTase/GGTase α-subunit. Potential significance of these findings in the context of protein prenylation and β-cell survival are discussed.
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Affiliation(s)
- Daleep K Arora
- Beta-Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, Detroit, MI 48201, USA
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Signaling mechanisms of glucose-induced F-actin remodeling in pancreatic islet β cells. Exp Mol Med 2013; 45:e37. [PMID: 23969997 PMCID: PMC3789261 DOI: 10.1038/emm.2013.73] [Citation(s) in RCA: 103] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 06/24/2013] [Indexed: 12/12/2022] Open
Abstract
The maintenance of whole-body glucose homeostasis is critical for survival, and is controlled by the coordination of multiple organs and endocrine systems. Pancreatic islet β cells secrete insulin in response to nutrient stimuli, and insulin then travels through the circulation promoting glucose uptake into insulin-responsive tissues such as liver, skeletal muscle and adipose. Many of the genes identified in human genome-wide association studies of diabetic individuals are directly associated with β cell survival and function, giving credence to the idea that β-cell dysfunction is central to the development of type 2 diabetes. As such, investigations into the mechanisms by which β cells sense glucose and secrete insulin in a regulated manner are a major focus of current diabetes research. In particular, recent discoveries of the detailed role and requirements for reorganization/remodeling of filamentous actin (F-actin) in the regulation of insulin release from the β cell have appeared at the forefront of islet function research, having lapsed in prior years due to technical limitations. Recent advances in live-cell imaging and specialized reagents have revealed localized F-actin remodeling to be a requisite for the normal biphasic pattern of nutrient-stimulated insulin secretion. This review will provide an historical look at the emergent focus on the role of the actin cytoskeleton and its regulation of insulin secretion, leading up to the cutting-edge research in progress in the field today.
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van Lummel M, Zaldumbide A, Roep BO. Changing faces, unmasking the beta-cell: post-translational modification of antigens in type 1 diabetes. Curr Opin Endocrinol Diabetes Obes 2013; 20:299-306. [PMID: 23770733 DOI: 10.1097/med.0b013e3283631417] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
PURPOSE OF REVIEW Description on post-translational modification of islet-autoantigens in type 1 diabetes (T1D). RECENT FINDINGS T1D is an autoimmune disease characterized by progressive destruction of the insulin-producing beta-cells. It is a complex disease process that results from the loss of tolerance to beta-cell autoantigens. This loss of tolerance can be caused by modification of beta-cell autoantigens, generating 'neo-autoantigens', and inducing T-cell responses. Post-translational modifications (PTMs) within the endoplasmic reticulum of stressed beta-cells might impact on the autoantigen T-cell epitope repertoire and on T1D pathogenesis progression. This review summarizes the processes involved in beta-cell stress and PTM of beta-cell autoantigens in T1D. SUMMARY PTMs of beta-cell autoantigens provide a novel hypothesis to understand how autoreactive T-cells can escape immune tolerance and cause destruction of beta-cells ('beta-cell homicide'). Additionally, aberrant proteins produced by stressed beta-cells can cause their own destruction ('beta-cell suicide'). Upon endoplasmic reticulum-stress, proteins are misfolded or modified changing the protein structure. In T1D, this may generate new beta-cell (neo)autoantigens. PTM of islet-autoantigens provides a mechanism by which pathogenic T-cells can escape thymic deletion. This amplifies the immune response when encountering a modified beta-cell neo-autoantigen bound to T1D predisposing human leucocyte antigen molecules in the periphery.
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Affiliation(s)
- Menno van Lummel
- Department of Immunohematology and Blood Transfusion, Leiden University Medical Center, Leiden, The Netherlands
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Lorenz MA, El Azzouny MA, Kennedy RT, Burant CF. Metabolome response to glucose in the β-cell line INS-1 832/13. J Biol Chem 2013; 288:10923-35. [PMID: 23426361 PMCID: PMC3624472 DOI: 10.1074/jbc.m112.414961] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells is triggered by metabolism of the sugar to increase ATP/ADP ratio that blocks the KATP channel leading to membrane depolarization and insulin exocytosis. Other metabolic pathways believed to augment insulin secretion have yet to be fully elucidated. To study metabolic changes during GSIS, liquid chromatography with mass spectrometry was used to determine levels of 87 metabolites temporally following a change in glucose from 3 to 10 mM glucose and in response to increasing concentrations of glucose in the INS-1 832/13 β-cell line. U-[(13)C]Glucose was used to probe flux in specific metabolic pathways. Results include a rapid increase in ATP/ADP, anaplerotic tricarboxylic acid cycle flux, and increases in the malonyl CoA pathway, support prevailing theories of GSIS. Novel findings include that aspartate used for anaplerosis does not derive from the glucose fuel added to stimulate insulin secretion, glucose flux into glycerol-3-phosphate, and esterification of long chain CoAs resulting in rapid consumption of long chain CoAs and de novo generation of phosphatidic acid and diacylglycerol. Further, novel metabolites with potential roles in GSIS such as 5-aminoimidazole-4-carboxamide ribotide (ZMP), GDP-mannose, and farnesyl pyrophosphate were found to be rapidly altered following glucose exposure.
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Affiliation(s)
- Matthew A Lorenz
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48105, USA
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Chiang YA, Shao W, Xu XX, Chernoff J, Jin T. P21-activated protein kinase 1 (Pak1) mediates the cross talk between insulin and β-catenin on proglucagon gene expression and its ablation affects glucose homeostasis in male C57BL/6 mice. Endocrinology 2013. [PMID: 23183186 DOI: 10.1210/en.2012-1781] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
In gut endocrine L cells, the Wnt signaling pathway effector β-catenin (β-cat)/transcription factor 7-like 2 mediates the stimulatory effect of insulin on proglucagon (gcg) expression and glucagon-like peptide-1 (GLP-1) production. In several other cell lineages, insulin is able to stimulate p21-activated protein kinase 1 (Pak1). Here we determined the role of Pak1 in gcg expression and the effect of Pak1 deletion on glucose homeostasis. Insulin stimulated Pak1 activation through increasing its Thr423 phosphorylation in gut gcg-expressing cell lines, associated with increased gcg mRNA levels. This stimulation was attenuated by the Pak inhibitor 2,2'-dihydroxy-1,1'-dinaphthyldisulfide (IPA3) or dominant-negative Pak1. Both insulin and cAMP-promoting agents activated β-cat Ser675 phosphorylation, which was attenuated by IPA3 or protein kinase A inhibition, respectively. Gut gcg levels were reduced in male Pak1(-/-) mice, associated with impaired glucose tolerance after an ip or oral glucose challenge. These mice had lower circulating active GLP-1 levels after a glucose challenge as well as reduced distal ileum GLP-1 content after insulin treatment. Finally, the Pak1(-/-) mice exhibited reduced brainstem gcg level and abolished β-cat Ser675 phosphorylation in brain neurons after insulin treatment. We suggest that Pak1 mediates the cross talk between insulin and Wnt signaling pathways on gut and brain gcg expression, and its ablation impairs glucose homeostasis.
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Affiliation(s)
- Yuting Alex Chiang
- Departments of Physiology, University of Toronto, Ontario, Canada M5S 1A8
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29
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A p21-activated kinase (PAK1) signaling cascade coordinately regulates F-actin remodeling and insulin granule exocytosis in pancreatic β cells. Biochem Pharmacol 2012; 85:808-16. [PMID: 23246867 DOI: 10.1016/j.bcp.2012.12.003] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2012] [Revised: 12/04/2012] [Accepted: 12/06/2012] [Indexed: 12/21/2022]
Abstract
Human islet studies implicate an important signaling role for the Cdc42 effector protein p21-activated kinase (PAK1) in the sustained/second-phase of insulin secretion. Because human islets from type 2 diabetic donors lack ∼80% of normal PAK1 protein levels, the mechanistic requirement for PAK1 signaling in islet function was interrogated. Similar to MIN6 β cells, human islets elicited glucose-stimulated PAK1 activation that was sensitive to the PAK1 inhibitor, IPA3. Given that sustained insulin secretion has been correlated with glucose-induced filamentous actin (F-actin) remodeling, we tested the hypothesis that a Cdc42-activated PAK1 signaling cascade is required to elicit F-actin remodeling to mobilize granules to the cell surface. Live-cell imaging captured the glucose-induced cortical F-actin remodeling in MIN6 β cells; IPA3-mediated inhibition of PAK1 abolished this remodeling. IPA3 also ablated glucose-stimulated insulin granule accumulation at the plasma membrane, consistent with its role in sustained/second-phase insulin release. Both IPA3 and a selective inhibitor of the Cdc42 GTPase, ML-141, blunted the glucose-stimulated activation of Raf-1, suggesting Raf-1 to be downstream of Cdc42→PAK1. IPA3 also inhibited MEK1/2 activation, implicating the MEK1/2→ERK1/2 cascade to occur downstream of PAK1. Importantly, PD0325901, a new selective inhibitor of MEK1/2→ERK1/2 activation, impaired F-actin remodeling and the sustained/amplification pathway of insulin release. Taken together, these data suggest that glucose-mediated activation of Cdc42 leads to activation of PAK1 and prompts activation of its downstream targets Raf-1, MEK1/2 and ERK1/2 to elicit F-actin remodeling and recruitment of insulin granules to the plasma membrane to support the sustained phase of insulin release.
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Pardo FN, Altirriba J, Pradas-Juni M, García A, Ahlgren U, Barberà A, Slebe JC, Yáñez AJ, Gomis R, Gasa R. The role of Raf-1 kinase inhibitor protein in the regulation of pancreatic beta cell proliferation in mice. Diabetologia 2012; 55:3331-40. [PMID: 22926403 DOI: 10.1007/s00125-012-2696-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Accepted: 07/27/2012] [Indexed: 01/01/2023]
Abstract
AIMS/HYPOTHESIS Manoeuvres aimed at increasing beta cell mass have been proposed as regenerative medicine strategies for diabetes treatment. Raf-1 kinase inhibitor protein 1 (RKIP1) is a common regulatory node of the mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) pathways and therefore may be involved in regulation of beta cell homeostasis. The aim of this study was to investigate the involvement of RKIP1 in the control of beta cell mass and function. METHODS Rkip1 (also known as Pebp1) knockout (Rkip1 (-/-)) mice were characterised in terms of pancreatic and glucose homeostasis, including morphological and functional analysis. Glucose tolerance and insulin sensitivity were examined, followed by assessment of glucose-induced insulin secretion in isolated islets and beta cell mass quantification through morphometry. Further characterisation included determination of endocrine and exocrine proliferation, apoptosis, MAPK activation and whole genome gene expression assays. Capacity to reverse a diabetic phenotype was assessed in adult Rkip1 (-/-) mice after streptozotocin treatment. RESULTS Rkip1 (-/-) mice exhibit a moderately larger pancreas and increased beta cell mass and pancreatic insulin content, which correlate with an overall improvement in whole body glucose tolerance. This phenotype is established in young postnatal stages and involves enhanced cellular proliferation without significant alterations in cell death. Importantly, adult Rkip1 (-/-) mice exhibit rapid reversal of streptozotocin-induced diabetes compared with control mice. CONCLUSIONS/INTERPRETATION These data implicate RKIP1 in the regulation of pancreatic growth and beta cell expansion, thus revealing RKIP1 as a potential pharmacological target to promote beta cell regeneration.
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Affiliation(s)
- F N Pardo
- Laboratory of Diabetes and Obesity, IDIBAPS, Centre Esther Koplowitz, Rosselló 153, Barcelona, Spain
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Jayaram B, Kowluru A. Phagocytic NADPH oxidase links ARNO-Arf6 signaling pathway in glucose-stimulated insulin secretion from the pancreatic β-cell. Cell Physiol Biochem 2012; 30:1351-62. [PMID: 23095975 DOI: 10.1159/000343324] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/09/2012] [Indexed: 01/29/2023] Open
Abstract
BACKGROUND Recent findings from our laboratory have demonstrated that glucose-stimulated insulin secretion (GSIS) involves interplay between a variety of small G proteins belonging to the Rho (e.g., Cdc42 and Rac1) and ADP-ribosylation factor (e.g., Arf6) subfamilies. Using immunological, pharmacological and molecular biological approaches, we have also identified guanine nucleotide exchange factors (GEFs) for Rac1 (e.g., Tiam1) and Arf6 (e.g., ARNO) in clonal INS-1 832/13 cells, normal rat islets and human islets. As a logical extension to these studies, we investigated, herein, potential downstream signaling steps involved in Arf6/ARNO-mediated GSIS. METHODS Using a selective pharmacological inhibitor of ARNO/Arf6 signaling axis (e.g., secinH3) we assessed regulatory roles for Arf6/ARNO in promoting phospholipase D (PLD), phagocytic NADPH oxidase (Nox2), reactive oxygen species (ROS), extracellular-regulated kinases (ERK 1/2) and cofilin (actin-severing protein] signaling steps in clonal INS-1 832/13 cells. RESULTS Our data suggested a marked inhibition by secinH3 of glucose-induced PLD activation, ERK1/2 phosphorylation and dephosphorylation of cofilin, suggesting that Arf6/ ARNO signaling mediates PLD, ERK1/2 and cofilin activation in beta-cells. In addition, secinH3 blocked glucose-induced Nox2 activation and associated ROS generation, thus placing Nox downstream to Arf6/ARNO signaling step. Lastly, we also demonstrate a significantly higher cofilin phosphorylation (inactive) in islets derived from type 2 diabetic human donors as well as the Zucker Diabetic Fatty (ZDF) rat, a model for type 2 diabetes. CONCLUSION Together, our current findings identify signaling steps downstream to ARNO/Arf6 axis leading to insulin secretion.
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Affiliation(s)
- Bhavaani Jayaram
- Beta-Cell Biochemistry Laboratory, John D. Dingell VA Medical Center and Pharmaceutical Sciences, Wayne State University, Detroit, MI 48201, USA
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Yeo RWY, Yang K, Li G, Lim SK. High glucose predisposes gene expression and ERK phosphorylation to apoptosis and impaired glucose-stimulated insulin secretion via the cytoskeleton. PLoS One 2012; 7:e44988. [PMID: 23024780 PMCID: PMC3443235 DOI: 10.1371/journal.pone.0044988] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Accepted: 08/11/2012] [Indexed: 01/09/2023] Open
Abstract
Chronic high glucose (HG) inflicts glucotoxicity on vulnerable cell types such as pancreatic β cells and contributes to insulin resistance and impaired insulin secretion in diabetic patients. To identify HG-induced cellular aberrations that are candidate mediators of glucotoxicity in pancreatic β cells, we analyzed gene expression in ERoSHK6, a mouse insulin-secreting cell line after chronic HG exposure (six-day exposure to 33.3 mM glucose). Chronic HG exposure which reduced glucose-stimulated insulin secretion (GSIS) increased transcript levels of 185 genes that clustered primarily in 5 processes namely cellular growth and proliferation; cell death; cellular assembly and organization; cell morphology; and cell-to-cell signaling and interaction. The former two were validated by increased apoptosis of ERoSHK6 cells after chronic HG exposure and reaffirmed the vulnerability of β cells to glucotoxicity. The three remaining processes were partially substantiated by changes in cellular morphology and structure, and instigated an investigation of the cytoskeleton and cell-cell adhesion. These studies revealed a depolymerized actin cytoskeleton that lacked actin stress fibers anchored at vinculin-containing focal adhesion sites as well as loss of E-cadherin-mediated cell-cell adherence after exposure to chronic HG, and were concomitant with constitutive ERK1/2 phosphorylation that was refractory to serum and glucose deprivation. Although inhibition of ERK phosphorylation by PD98059 promoted actin polymerization, it increased apoptosis and GSIS impairment. These findings suggest that ERK phosphorylation is a proximate regulator of cellular processes targeted by chronic HG-induced gene expression and that dynamic actin polymerization and depolymerization is important in β cell survival and function. Therefore, chronic HG alters gene expression and signal transduction to predispose the cytoskeleton towards apoptosis and GSIS impairment.
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Affiliation(s)
- Ronne Wee Yeh Yeo
- Institute of Medical Biology, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
- Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, Singapore
| | | | - GuoDong Li
- Department of Clinical Research, Singapore General Hospital, Singapore, Singapore
| | - Sai Kiang Lim
- Institute of Medical Biology, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
- Department of Surgery, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
- * E-mail:
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Arora DK, Syed I, Machhadieh B, McKenna CE, Kowluru A. Rab-geranylgeranyl transferase regulates glucose-stimulated insulin secretion from pancreatic β cells. Islets 2012; 4:354-8. [PMID: 23114750 PMCID: PMC3524143 DOI: 10.4161/isl.22538] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
A growing body of evidence implicates essential roles for small molecular weight G-proteins (e.g., Cdc42, Rac1, Arf6 and Rab3A and Rab27A) in islet β-cell function including glucose-stimulated insulin secretion (GSIS). One of the known mechanisms for optimal activation of small G-proteins involves post-translational prenylation, which is mediated by farnesyltransferase (FTase) and geranylgeranyl transferases (GGTases I and II). The FTase catalyzes incorporation of a 15-carbon farnesyl group while the GGTase mediates incorporation of a 20-carbon geranylgeranyl group into the C-terminal cysteines of G-proteins. The FTase, GGTase I and GGTase II prenylate Ras, Cdc42/Rac1, and Rab G-proteins, respectively. While considerable evidence exists on FTase/GGTase I-mediated regulation of GSIS, very little is known about GGTase II (also referred to as Rab GGTase; RGGT) and its regulatory proteins in the cascade of events leading to GSIS. Herein, we provide the first immunological evidence to suggest expression of α- and β-subunits of RGGT in clonal INS 832/13 β-cells, normal rat islets and human islets. Furthermore, Rab escort protein1 (REP1), which has been shown to be critical for prenylation of Rab G-proteins, is also expressed in these cells. Furthermore, evidence is presented to suggest that siRNA-mediated knockdown of α- or β-subunits of RGGT and REP1 markedly attenuates GSIS in INS 832/13 cells. These findings provide the first evidence in support of key roles for RGGT and its regulatory proteins in GSIS.
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Affiliation(s)
- Daleep K. Arora
- Department of Pharmaceutical Sciences; Wayne State University; Detroit, MI USA
| | - Ismail Syed
- Division of Endocrinology; Diabetes and Metabolism; Department of Medicine; Beth Israel Deaconess Medical Center and Harvard Medical School; Boston, MA USA
| | - Baker Machhadieh
- Division of Endocrinology; Wayne State University; Detroit, MI USA
| | - Charles E. McKenna
- Department of Chemistry; University of Southern California; Los Angeles, CA USA
| | - Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences; Wayne State University; Detroit, MI USA
- Division of Endocrinology; Wayne State University; Detroit, MI USA
- Beta-Cell Biochemistry Laboratory; John D. Dingell VA Medical Center; Detroit, MI USA
- Correspondence to: Anjan Kowluru;
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Matti A, Kyathanahalli C, Kowluru A. Protein farnesylation is requisite for mitochondrial fuel-induced insulin release: further evidence to link reactive oxygen species generation to insulin secretion in pancreatic β-cells. Islets 2012; 4:74-7. [PMID: 22504835 PMCID: PMC3365803 DOI: 10.4161/isl.19121] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Several lines of recent evidence implicate regulatory roles for reactive oxygen species (ROS) in islet function and insulin secretion. The phagocyte-like NADPH oxidase (Nox2) has recently been shown to be one of the sources of ROS in the signaling events leading to glucose stimulated insulin secretion (GSIS). We recently reported inhibition of glucose- or mitochondrial fuel-induced Nox2-derived ROS by a specific inhibitor of protein farnesyl transferse (FTase; FTI-277), suggesting that activation of FTase might represent one of the upstream signaling events to Nox2 activation. Furthermore, FTase inhibitors (FTI-277 and FTI-2628) have also been shown to attenuate GSIS in INS 832/13 cells and normal rodent islets. Herein, we provide further evidence to suggest that inhibition of FTase either by pharmacological (e.g., FTI-277) or gene silencing (siRNA-FTase) approaches markedly attenuates mitochondrial fuel-stimulated insulin secretion (MSIS) in INS 832/13 cells. Together, our findings further establish a link between nutrient-induced Nox2 activation, ROS generation and insulin secretion in the pancreatic β-cell.
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Affiliation(s)
- Andrea Matti
- Department of Pharmaceutical Sciences; Eugene Applebaum College of Pharmacy and Health Sciences; Wayne State University; Detroit, MI USA
| | | | - Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences; Eugene Applebaum College of Pharmacy and Health Sciences; Wayne State University; Detroit, MI USA
- Beta-Cell Biochemistry Research Laboratory; John D. Dingell VA Medical Center; Detroit, MI USA
- Correspondence to: Anjaneyulu Kowluru,
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Syed I, Kyathanahalli CN, Jayaram B, Govind S, Rhodes CJ, Kowluru RA, Kowluru A. Increased phagocyte-like NADPH oxidase and ROS generation in type 2 diabetic ZDF rat and human islets: role of Rac1-JNK1/2 signaling pathway in mitochondrial dysregulation in the diabetic islet. Diabetes 2011; 60:2843-52. [PMID: 21911753 PMCID: PMC3198065 DOI: 10.2337/db11-0809] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
OBJECTIVE To determine the subunit expression and functional activation of phagocyte-like NADPH oxidase (Nox), reactive oxygen species (ROS) generation and caspase-3 activation in the Zucker diabetic fatty (ZDF) rat and diabetic human islets. RESEARCH DESIGN AND METHODS Expression of core components of Nox was quantitated by Western blotting and densitometry. ROS levels were quantitated by the 2',7'-dichlorofluorescein diacetate method. Rac1 activation was quantitated using the gold-labeled immunosorbent assay kit. RESULTS Levels of phosphorylated p47(phox), active Rac1, Nox activity, ROS generation, Jun NH(2)-terminal kinase (JNK) 1/2 phosphorylation, and caspase-3 activity were significantly higher in the ZDF islets than the lean control rat islets. Chronic exposure of INS 832/13 cells to glucolipotoxic conditions resulted in increased JNK1/2 phosphorylation and caspase-3 activity; such effects were largely reversed by SP600125, a selective inhibitor of JNK. Incubation of normal human islets with high glucose also increased the activation of Rac1 and Nox. Lastly, in a manner akin to the ZDF diabetic rat islets, Rac1 expression, JNK1/2, and caspase-3 activation were also significantly increased in diabetic human islets. CONCLUSIONS We provide the first in vitro and in vivo evidence in support of an accelerated Rac1-Nox-ROS-JNK1/2 signaling pathway in the islet β-cell leading to the onset of mitochondrial dysregulation in diabetes.
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Affiliation(s)
- Ismail Syed
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Detroit, Michigan
| | | | - Bhavaani Jayaram
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Detroit, Michigan
| | - Sudha Govind
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Detroit, Michigan
| | - Christopher J. Rhodes
- Kovler Diabetes Center, Department of Medicine, Section of Endocrinology, Diabetes, and Metabolism, University of Chicago, Chicago, Illinois
| | - Renu A. Kowluru
- Kresge Eye Institute, Wayne State University, Detroit, Michigan
| | - Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Detroit, Michigan
- β-Cell Biochemistry Laboratory, John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan
- Corresponding author: Anjaneyulu Kowluru,
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Watson ML, Macrae K, Marley AE, Hundal HS. Chronic effects of palmitate overload on nutrient-induced insulin secretion and autocrine signalling in pancreatic MIN6 beta cells. PLoS One 2011; 6:e25975. [PMID: 21998735 PMCID: PMC3187833 DOI: 10.1371/journal.pone.0025975] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Accepted: 09/14/2011] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Sustained exposure of pancreatic β cells to an increase in saturated fatty acids induces pleiotropic effects on β-cell function, including a reduction in stimulus-induced insulin secretion. The objective of this study was to investigate the effects of chronic over supply of palmitate upon glucose- and amino acid-stimulated insulin secretion (GSIS and AASIS, respectively) and autocrine-dependent insulin signalling with particular focus on the importance of ceramide, ERK and CaMKII signalling. PRINCIPAL FINDINGS GSIS and AASIS were both stimulated by >7-fold resulting in autocrine-dependent activation of protein kinase B (PKB, also known as Akt). Insulin release was dependent upon nutrient-induced activation of calcium/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) as their pharmacological inhibition suppressed GSIS/AASIS significantly. Chronic (48 h, 0.4 mM) palmitate treatment blunted glucose/AA-induced activation of CaMKII and ERK and caused a concomitant reduction (~75%) in GSIS/AASIS and autocrine-dependent activation of PKB. This inhibition could not be attributed to enhanced mitochondrial fatty acid uptake/oxidation or ceramide synthesis, which were unaffected by palmitate. In contrast, diacylglycerol synthesis was elevated suggesting increased palmitate esterification rather than oxidation may contribute to impaired stimulus-secretion coupling. Consistent with this, 2-bromopalmitate, a non-oxidisable palmitate analogue, inhibited GSIS as effectively as palmitate. CONCLUSIONS Our results exclude changes in ceramide content or mitochondrial fatty acid handling as factors initiating palmitate-induced defects in insulin release from MIN6 β cells, but suggest that reduced CaMKII and ERK activation associated with palmitate overload may contribute to impaired stimulus-induced insulin secretion.
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Affiliation(s)
- Maria L. Watson
- Division of Cell Signalling and Immunology, Sir James Black Centre, College of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Katherine Macrae
- Division of Cell Signalling and Immunology, Sir James Black Centre, College of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Anna E. Marley
- AstraZeneca, CVGI, Alderley Park, Macclesfield, Cheshire, United Kingdom
| | - Harinder S. Hundal
- Division of Cell Signalling and Immunology, Sir James Black Centre, College of Life Sciences, University of Dundee, Dundee, United Kingdom
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Wang Z, Oh E, Clapp DW, Chernoff J, Thurmond DC. Inhibition or ablation of p21-activated kinase (PAK1) disrupts glucose homeostatic mechanisms in vivo. J Biol Chem 2011; 286:41359-41367. [PMID: 21969371 DOI: 10.1074/jbc.m111.291500] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The p21-activated kinase PAK1 is implicated in tumorigenesis, and efforts to inhibit PAK1 signaling as a means to induce tumor cell apoptosis are underway. However, PAK1 has also been implicated as a positive effector of mechanisms in clonal pancreatic beta cells and skeletal myotubes that would be crucial to maintaining glucose homeostasis in vivo. Of relevance, human islets of Type 2 diabetic donors contained ~80% less PAK1 protein compared with non-diabetics, implicating PAK1 in islet signaling/scaffolding functions. Mimicking this, islets from PAK1(-/-) knock-out mice exhibited profound defects in the second/sustained-phase of insulin secretion. Reiteration of this specific defect by human islets treated with the PAK1 signaling inhibitor IPA3 revealed PAK1 signaling to be of primary functional importance. Analyses of human and mouse islet beta cell signaling revealed PAK1 activation to be 1) dependent upon Cdc42 abundance, 2) crucial for signaling downstream to activate ERK1/2, but 3) dispensable for cofilin phosphorylation. Importantly, the PAK1(-/-) knock-out mice were found to exhibit whole body glucose intolerance in vivo. Exacerbating this, the PAK1(-/-) knock-out mice also exhibited peripheral insulin resistance. Insulin resistance was coupled to ablation of insulin-stimulated GLUT4 translocation in skeletal muscle from PAK1(-/-) knock-out mice, and in sharp contrast to islet beta cells, skeletal muscle PAK1 loss was underscored by defective cofilin phosphorylation but normal ERK1/2 activation. Taken together, these data provide the first human islet and mammalian in vivo data unveiling the key and crucial roles for differential PAK1 signaling in the multi-tissue regulation of whole body glucose homeostasis.
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Affiliation(s)
- Zhanxiang Wang
- Basic Diabetes Group, Department of Pediatrics, Herman B. Wells Center for Pediatric Research, Indianapolis, Indiana 46202
| | - Eunjin Oh
- Basic Diabetes Group, Department of Pediatrics, Herman B. Wells Center for Pediatric Research, Indianapolis, Indiana 46202
| | - D Wade Clapp
- Basic Diabetes Group, Department of Pediatrics, Herman B. Wells Center for Pediatric Research, Indianapolis, Indiana 46202
| | | | - Debbie C Thurmond
- Basic Diabetes Group, Department of Pediatrics, Herman B. Wells Center for Pediatric Research, Indianapolis, Indiana 46202.
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Alejandro EU, Lim GE, Mehran AE, Hu X, Taghizadeh F, Pelipeychenko D, Baccarini M, Johnson JD. Pancreatic β-cell Raf-1 is required for glucose tolerance, insulin secretion, and insulin 2 transcription. FASEB J 2011; 25:3884-95. [PMID: 21817126 DOI: 10.1096/fj.10-180349] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Regulation of glucose homeostasis by insulin depends on pancreatic β-cell growth, survival, and function. Raf-1 kinase is a major downstream target of several growth factors that promote proliferation and survival of many cell types, including the pancreatic β cells. We have previously reported that insulin protects β cells from apoptosis and promotes proliferation by activating Raf-1 signaling in cultured human islets, mouse islets, and MIN6 cells. As Raf-1 activity is critical for basal apoptosis and insulin secretion in vitro, we hypothesized that Raf-1 may play an important role in glucose homeostasis in vivo. To test this hypothesis, we utilized the Cre-loxP recombination system to obtain a pancreatic β-cell-specific ablation of Raf-1 kinase gene (RIPCre(+/+):Raf-1(flox/flox)) and a complete set of littermate controls (RIPCre(+/+):Raf-1(wt/wt)). RIPCre(+/+):Raf-1(flox/flox) mice were viable, and no effects on weight gain were observed. RIPCre(+/+):Raf-1(flox/flox) mice had increased fasting blood glucose levels and impaired glucose tolerance but normal insulin tolerance compared to littermate controls. Insulin secretion in vivo and in isolated islets was markedly impaired, but there was no apparent effect on the exocytosis machinery. However, islet insulin protein and insulin 2 mRNA, but not insulin 1 mRNA, were dramatically reduced in Raf-1-knockout mice. Analysis of insulin 2 knockout mice demonstrated that this reduction in mRNA was sufficient to impair in vivo insulin secretion. Our data further indicate that Raf-1 specifically and acutely regulates insulin 2 mRNA via negative action on Foxo1, which has been shown to selectively control the insulin 2 gene. This work provides the first direct evidence that Raf-1 signaling is essential for the regulation of basal insulin transcription and the supply of releasable insulin in vivo.
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Affiliation(s)
- Emilyn U Alejandro
- Laboratory of Molecular Signalling in Diabetes, Diabetes Research Group, Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
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Kyathanahalli CN, Kowluru A. A farnesylated G-protein suppresses Akt phosphorylation in INS 832/13 cells and normal rat islets: regulation by pertussis toxin and PGE₂. Biochem Pharmacol 2011; 81:1237-47. [PMID: 21406184 DOI: 10.1016/j.bcp.2011.03.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2010] [Revised: 03/01/2011] [Accepted: 03/03/2011] [Indexed: 12/31/2022]
Abstract
Protein isoprenylation constitutes incorporation of either 15-carbon farnesyl or 20-carbon geranylgeranyl derivative of mevalonic acid onto the C-terminal cysteine, culminating in increased hydrophobicity of the modified proteins for optimal membrane anchoring and interaction with their respective effectors. Emerging evidence confirms the participatory role of prenylated proteins in pancreatic β-cell function including insulin secretion. Herein, we investigated the putative regulatory roles of protein farnesylation in cell survival signaling pathways in insulin-secreting INS 832/13 cells and normal rodent islets, specifically at the level of protein kinase-B/Akt phosphorylation induced by insulin-like growth factor [IGF-1]. Selective inhibitors of farnesylation [e.g., FTI-277 or FTI-2628] or knockdown of the β-subunit of farnesyl transferase by siRNA significantly increased Akt activation under basal and IGF-1-stimulated conditions. Consequentially, the relative abundance of phosphorylated FoxO1 and Bad were increased implicating inactivation of critical components of the cell death machinery. In addition, FTI-induced Akt activation was attenuated by the PI3-kinase inhibitor, LY294002. Exposure of INS 832/13 cells to pertussis toxin [PTx] markedly potentiated Akt phosphorylation suggesting involvement of a PTx-sensitive G-protein in this signaling axis. Furthermore, prostaglandin E₂, a known agonist of inhibitory G-proteins, significantly attenuated FTI-induced Akt phosphorylation. Taken together, our findings suggest expression of a farnesylated G-protein in INS 832/13 cells and normal rat islets, which appear to suppress Akt activation and subsequent cell survival signaling steps. Potential regulatory roles of the islet endogenous protein kinase-B inhibitory protein [Probin] in islet function are discussed.
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Affiliation(s)
- Chandrashekara N Kyathanahalli
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, 259 Mack Avenue, Detroit, MI 48202, USA
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Dalle S, Ravier MA, Bertrand G. Emerging roles for β-arrestin-1 in the control of the pancreatic β-cell function and mass: New therapeutic strategies and consequences for drug screening. Cell Signal 2011; 23:522-8. [DOI: 10.1016/j.cellsig.2010.09.014] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2010] [Accepted: 09/06/2010] [Indexed: 01/09/2023]
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Abstract
Many metabolic pathways, including oxidative stress, PKC and the polyol pathway have been implicated in the development of diabetic retinopathy, but despite extensive research, its pathogenesis remains unclear. Recent studies have shown the role of a low-molecular-weight GTP-binding protein (H-Ras)-mediated signaling pathway in its development. The key effector protein of Ras function is a threonine/serine kinase-Raf kinase, and this kinase is involved in a variety of functions, including the cell cycle and proliferation and apoptosis. In animal models of diabetic retinopathy, Raf kinase is activated in the retina and its microvasculature. Activated Raf kinase is associated with increased apoptosis of retinal capillary cells, the process that precedes the development of retinal histopathology, and inhibition of Raf kinase ameliorates apoptosis. In clinical settings, inhibitors of Raf kinase have shown promising results in cancer treatment, and Raf kinase antisense oligonucleotides, iCo 007, is now in Phase II trial for macular edema, a chronic ocular disease associated with retinal neovascularization. Further elucidating the role of Raf kinase in diabetic retinopathy, and advances in the generation of antisense therapy for chronic diseases, should help test Raf antisense oligonucleotides for the treatment of this blinding complication that diabetic patients fear the most.
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Syed I, Kyathanahalli CN, Kowluru A. Phagocyte-like NADPH oxidase generates ROS in INS 832/13 cells and rat islets: role of protein prenylation. Am J Physiol Regul Integr Comp Physiol 2011; 300:R756-62. [PMID: 21228337 DOI: 10.1152/ajpregu.00786.2010] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recent evidence suggests that an acute increase in the generation of phagocyte-like NADPH-oxidase (Nox)-mediated reactive oxygen species (ROS) may be necessary for glucose-stimulated insulin secretion. Using rat islets and INS 832/13 cells, we tested the hypothesis that activation of specific G proteins is necessary for nutrient-mediated intracellular generation of ROS. Stimulation of β-cells with glucose or a mixture of mitochondrial fuels (mono-methylsuccinate plus α-ketoisocaproic acid) markedly elevated intracellular accumulation of ROS, which was attenuated by selective inhibitors of Nox (e.g., apocynin or diphenyleneiodonium chloride) or short interfering RNA-mediated knockdown of p47(phox), one of the subunits of Nox. Selective inhibitors of protein prenylation (FTI-277 or GGTI-2147) markedly inhibited nutrient-induced ROS generation, suggesting that activation of one (or more) prenylated small G proteins and/or γ-subunits of trimeric G proteins is involved in this signaling axis. Depletion of endogenous GTP levels with mycophenolic acid significantly reduced glucose-induced activation of Rac1 and ROS generation in these cells. Other immunosuppressants, like cyclosporine A or rapamycin, which do not deplete endogenous GTP levels, failed to affect glucose-induced ROS generation, suggesting that endogenous GTP is necessary for glucose-induced Nox activation and ROS generation. Treatment of INS 832/13 cells or rat islets with pertussis toxin (Ptx), which ADP ribosylates and inhibits inhibitory class of trimeric G proteins (i.e., G(i) or G(o)), significantly attenuated glucose-induced ROS generation in these cells, implicating activation of a Ptx-sensitive G protein in these signaling cascade. Together, our findings suggest a prenylated Ptx-sensitive signaling step couples Rac1 activation in the signaling steps necessary for glucose-mediated generation of ROS in the pancreatic β-cells.
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Affiliation(s)
- Ismail Syed
- Dept. of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State Univ., Detroit, MI 48201, USA
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He K, Aizenman E. ERK signaling leads to mitochondrial dysfunction in extracellular zinc-induced neurotoxicity. J Neurochem 2010; 114:452-61. [PMID: 20412391 DOI: 10.1111/j.1471-4159.2010.06762.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A zinc-induced signaling pathway leading to extracellular signal-regulated kinase 1/2 (ERK1/2) activation and subsequent neuronal death has been investigated. We find that an extracellular zinc application stimulates biphasic phosphorylation of ERK1/2 and p38 MAPK in rat cultured neurons. The activation of ERK1/2, but not p38, is responsible for zinc neurotoxicity as only U0126, a MEK inhibitor that blocks ERK1/2 phosphorylation, significantly protects cortical neurons from zinc exposure. Over-expression of a dominant negative Ras mutant blocks zinc-induced Elk1-dependent gene expression in neurons, indicating the involvement of Ras activation in the zinc pathway leading to ERK phosphorylation and Elk1 signaling. We also find that zinc treatment results in neuronal mitochondrial hyperpolarization. Importantly, both U0126 and bongkrekic acid, an inhibitor of the mitochondrial adenine nucleotide translocase, effectively reduce zinc-triggered mitochondrial changes. As bongkrekic acid also prevents zinc-triggered neuronal death but not ERK1/2 phosphorylation, activation of MAPK signaling precedes and is required for mitochondrial dysfunction and cell death. These results provide new insight on the mechanism of extracellular zinc-induced toxicity in which the regulation of mitochondrial function by the Ras/MEK/ERK pathway is closely associated with neuronal viability.
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Affiliation(s)
- Kai He
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
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