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Habibe JJ, Clemente-Olivo MP, Scheithauer TPM, Rampanelli E, Herrema H, Vos M, Mieremet A, Nieuwdorp M, van Raalte DH, Eringa EC, de Vries CJM. Glucose-mediated insulin secretion is improved in FHL2-deficient mice and elevated FHL2 expression in humans is associated with type 2 diabetes. Diabetologia 2022; 65:1721-1733. [PMID: 35802167 PMCID: PMC9477948 DOI: 10.1007/s00125-022-05750-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Accepted: 05/09/2022] [Indexed: 02/05/2023]
Abstract
AIMS/HYPOTHESIS The general population is ageing, involving an enhanced incidence of chronic diseases such as type 2 diabetes. With ageing, DNA methylation of FHL2 increases, as well as expression of the four and a half LIM domains 2 (FHL2) protein in human pancreatic islets. We hypothesised that FHL2 is actively involved in glucose metabolism. METHODS Publicly available microarray datasets from human pancreatic islets were analysed for FHL2 expression. In FHL2-deficient mice, we studied glucose clearance and insulin secretion. Gene expression analysis and glucose-stimulated insulin secretion (GSIS) were determined in isolated murine FHL2-deficient islets to evaluate insulin-secretory capacity. Moreover, knockdown and overexpression of FHL2 were accomplished in MIN6 cells to delineate the underlying mechanism of FHL2 function. RESULTS Transcriptomics of human pancreatic islets revealed that individuals with elevated levels of HbA1c displayed increased FHL2 expression, which correlated negatively with insulin secretion pathways. In line with this observation, FHL2-deficient mice cleared glucose more efficiently than wild-type littermates through increased plasma insulin levels. Insulin sensitivity was comparable between these genotypes. Interestingly, pancreatic islets isolated from FHL2-deficient mice secreted more insulin in GSIS assays than wild-type mouse islets even though insulin content and islet size was similar. To support this observation, we demonstrated increased expression of the transcription factor crucial in insulin secretion, MAF BZIP transcription factor A (MafA), higher expression of GLUT2 and reduced expression of the adverse factor c-Jun in FHL2-deficient islets. The underlying mechanism of FHL2 was further delineated in MIN6 cells. FHL2-knockdown led to enhanced activation of forkhead box protein O1 (FOXO1) and its downstream genes such as Mafa and Pdx1 (encoding pancreatic and duodenal homeobox 1), as well as increased glucose uptake. On the other hand, FHL2 overexpression in MIN6 cells blocked GSIS, increased the formation of reactive oxygen species and increased c-Jun activity. CONCLUSIONS/INTERPRETATION Our data demonstrate that FHL2 deficiency improves insulin secretion from beta cells and improves glucose tolerance in mice. Given that FHL2 expression in humans increases with age and that high expression levels of FHL2 are associated with beta cell dysfunction, we propose that enhanced FHL2 expression in elderly individuals contributes to glucose intolerance and the development of type 2 diabetes. DATA AVAILABILITY The human islet microarray datasets used are publicly available and can be found on https://www.ncbi.nlm.nih.gov/geo/ .
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Affiliation(s)
- Jayron J Habibe
- Department of Medical Biochemistry, Amsterdam UMC, location University of Amsterdam, Amsterdam, the Netherlands
- Amsterdam Cardiovascular Sciences, Diabetes and Metabolism, University of Amsterdam, Amsterdam, the Netherlands
- Amsterdam Gastroenterology, Endocrinology and Metabolism, University of Amsterdam, Amsterdam, the Netherlands
- Department of Physiology, Amsterdam UMC, location Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
| | - Maria P Clemente-Olivo
- Department of Medical Biochemistry, Amsterdam UMC, location University of Amsterdam, Amsterdam, the Netherlands
- Amsterdam Cardiovascular Sciences, Diabetes and Metabolism, University of Amsterdam, Amsterdam, the Netherlands
- Amsterdam Gastroenterology, Endocrinology and Metabolism, University of Amsterdam, Amsterdam, the Netherlands
| | - Torsten P M Scheithauer
- Department of Experimental Vascular Medicine, Amsterdam UMC, location University of Amsterdam, Amsterdam, the Netherlands
| | - Elena Rampanelli
- Department of Experimental Vascular Medicine, Amsterdam UMC, location University of Amsterdam, Amsterdam, the Netherlands
| | - Hilde Herrema
- Department of Experimental Vascular Medicine, Amsterdam UMC, location University of Amsterdam, Amsterdam, the Netherlands
| | - Mariska Vos
- Department of Medical Biochemistry, Amsterdam UMC, location University of Amsterdam, Amsterdam, the Netherlands
- Amsterdam Cardiovascular Sciences, Diabetes and Metabolism, University of Amsterdam, Amsterdam, the Netherlands
- Amsterdam Gastroenterology, Endocrinology and Metabolism, University of Amsterdam, Amsterdam, the Netherlands
| | - Arnout Mieremet
- Department of Medical Biochemistry, Amsterdam UMC, location University of Amsterdam, Amsterdam, the Netherlands
- Amsterdam Cardiovascular Sciences, Diabetes and Metabolism, University of Amsterdam, Amsterdam, the Netherlands
- Amsterdam Gastroenterology, Endocrinology and Metabolism, University of Amsterdam, Amsterdam, the Netherlands
| | - Max Nieuwdorp
- Department of Experimental Vascular Medicine, Amsterdam UMC, location University of Amsterdam, Amsterdam, the Netherlands
| | - Daniel H van Raalte
- Department of Internal Medicine, Diabetes Center, Amsterdam UMC, location Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
| | - Etto C Eringa
- Department of Physiology, Amsterdam UMC, location Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
- Department of Physiology, Cardiovascular Institute Maastricht, Maastricht, the Netherlands
| | - Carlie J M de Vries
- Department of Medical Biochemistry, Amsterdam UMC, location University of Amsterdam, Amsterdam, the Netherlands.
- Amsterdam Cardiovascular Sciences, Diabetes and Metabolism, University of Amsterdam, Amsterdam, the Netherlands.
- Amsterdam Gastroenterology, Endocrinology and Metabolism, University of Amsterdam, Amsterdam, the Netherlands.
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Role of c-Jun N-terminal Kinase (JNK) in Obesity and Type 2 Diabetes. Cells 2020; 9:cells9030706. [PMID: 32183037 PMCID: PMC7140703 DOI: 10.3390/cells9030706] [Citation(s) in RCA: 95] [Impact Index Per Article: 23.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Revised: 02/16/2020] [Accepted: 03/11/2020] [Indexed: 12/13/2022] Open
Abstract
Obesity has been described as a global epidemic and is a low-grade chronic inflammatory disease that arises as a consequence of energy imbalance. Obesity increases the risk of type 2 diabetes (T2D), by mechanisms that are not entirely clarified. Elevated circulating pro-inflammatory cytokines and free fatty acids (FFA) during obesity cause insulin resistance and ß-cell dysfunction, the two main features of T2D, which are both aggravated with the progressive development of hyperglycemia. The inflammatory kinase c-jun N-terminal kinase (JNK) responds to various cellular stress signals activated by cytokines, free fatty acids and hyperglycemia, and is a key mediator in the transition between obesity and T2D. Specifically, JNK mediates both insulin resistance and ß-cell dysfunction, and is therefore a potential target for T2D therapy.
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Tang C, Yeung LSN, Koulajian K, Zhang L, Tai K, Volchuk A, Giacca A. Glucose-Induced β-Cell Dysfunction In Vivo: Evidence for a Causal Role of C-jun N-terminal Kinase Pathway. Endocrinology 2018; 159:3643-3654. [PMID: 30215691 PMCID: PMC6195676 DOI: 10.1210/en.2018-00566] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Accepted: 08/26/2018] [Indexed: 11/19/2022]
Abstract
Prolonged elevation of glucose can adversely affect β-cell function. Oxidative stress, which has been implicated in glucose-induced β-cell dysfunction, can activate c-jun N-terminal kinase (JNK). However, whether JNK is causal in glucose-induced β-cell dysfunction in vivo is unclear. Therefore, we aimed at investigating the causal role of JNK activation in in vivo models of glucose-induced β-cell dysfunction. Glucose-induced β-cell dysfunction was investigated in the presence or absence of JNK inhibition. JNK inhibition was achieved using either (i) the JNK-specific inhibitor SP600125 or (ii) JNK-1-null mice. (i) Rats or mice were infused intravenously with saline or glucose with or without SP600125. (ii) JNK-1 null mice and their littermate wild-type controls were infused intravenously with saline or glucose. Following the glucose infusion periods in rats and mice, β-cell function was assessed in isolated islets or in vivo using hyperglycemic clamps. Forty-eight-hour hyperglycemia at ~20 mM in rats or 96-hour hyperglycemia at ~13 mM in mice impaired β-cell function in isolated islets and in vivo. Inhibition of JNK using either SP600125 or JNK-1-null mice prevented glucose-induced β-cell dysfunction in isolated islets and in vivo. Islets of JNK-1-null mice exposed to hyperglycemia in vivo showed an increase in Pdx-1 and insulin 2 mRNA, whereas islets of wild-type mice did not. Together, these data show that JNK pathway is involved in glucose-induced β-cell dysfunction in vivo and is thus a potential therapeutic target for type 2 diabetes.
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Affiliation(s)
- Christine Tang
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Lucy Shu Nga Yeung
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Khajag Koulajian
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Liling Zhang
- Division of Cellular and Molecular Biology, Toronto General Research Institute, University Health Network, Toronto, Ontario, Canada
| | - Kevin Tai
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Allen Volchuk
- Keenan Research Centre for Biomedical Science, St. Michael Hospital, Toronto, Ontario, Canada
| | - Adria Giacca
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
- Institute of Medical Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
- Banting and Best Diabetes Centre, University of Toronto, Toronto, Ontario, Canada
- Correspondence: Adria Giacca, MD, Medical Sciences Building, 3336-1 King’s College Circle, Toronto, Ontario M5S 1A8, Canada. E-mail:
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Kaneto H, Matsuoka TA. Role of pancreatic transcription factors in maintenance of mature β-cell function. Int J Mol Sci 2015; 16:6281-97. [PMID: 25794287 PMCID: PMC4394532 DOI: 10.3390/ijms16036281] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Revised: 02/10/2015] [Accepted: 02/16/2015] [Indexed: 12/12/2022] Open
Abstract
A variety of pancreatic transcription factors including PDX-1 and MafA play crucial roles in the pancreas and function for the maintenance of mature β-cell function. However, when β-cells are chronically exposed to hyperglycemia, expression and/or activities of such transcription factors are reduced, which leads to deterioration of β-cell function. These phenomena are well known as β-cell glucose toxicity in practical medicine as well as in the islet biology research area. Here we describe the possible mechanism for β-cell glucose toxicity found in type 2 diabetes. It is likely that reduced expression levels of PDX-1 and MafA lead to suppression of insulin biosynthesis and secretion. In addition, expression levels of incretin receptors (GLP-1 and GIP receptors) in β-cells are decreased, which likely contributes to the impaired incretin effects found in diabetes. Taken together, down-regulation of insulin gene transcription factors and incretin receptors explains, at least in part, the molecular mechanism for β-cell glucose toxicity.
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Affiliation(s)
- Hideaki Kaneto
- Department of Diabetes, Endocrinology and Metabolism, Kawasaki Medical School, 577, Matsushima, Kurashiki 701-0192, Japan.
| | - Taka-aki Matsuoka
- Department of Metabolic Medicine, Osaka University Graduate School of Medicine, Osaka 565-0871, Japan.
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Role of ceramide in diabetes mellitus: evidence and mechanisms. Lipids Health Dis 2013; 12:98. [PMID: 23835113 PMCID: PMC3716967 DOI: 10.1186/1476-511x-12-98] [Citation(s) in RCA: 129] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2013] [Accepted: 06/28/2013] [Indexed: 02/06/2023] Open
Abstract
Diabetes mellitus is a metabolic disease with multiple complications that causes serious diseases over the years. The condition leads to severe economic consequences and is reaching pandemic level globally. Much research is being carried out to address this disease and its underlying molecular mechanism. This review focuses on the diverse role and mechanism of ceramide, a prime sphingolipid signaling molecule, in the pathogenesis of type 1 and type 2 diabetes and its complications. Studies using cultured cells, animal models, and human subjects demonstrate that ceramide is a key player in the induction of β-cell apoptosis, insulin resistance, and reduction of insulin gene expression. Ceramide induces β-cell apoptosis by multiple mechanisms namely; activation of extrinsic apoptotic pathway, increasing cytochrome c release, free radical generation, induction of endoplasmic reticulum stress and inhibition of Akt. Ceramide also modulates many of the insulin signaling intermediates such as insulin receptor substrate, Akt, Glut-4, and it causes insulin resistance. Ceramide reduces the synthesis of insulin hormone by attenuation of insulin gene expression. Better understanding of this area will increase our understanding of the contribution of ceramide to the pathogenesis of diabetes, and further help in identifying potential therapeutic targets for the management of diabetes mellitus and its complications.
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Zhang H, Yu C, Dai J, Keller JM, Hua A, Sottnik JL, Shelley G, Hall CL, Park SI, Yao Z, Zhang J, McCauley LK, Keller ET. Parathyroid hormone-related protein inhibits DKK1 expression through c-Jun-mediated inhibition of β-catenin activation of the DKK1 promoter in prostate cancer. Oncogene 2013; 33:2464-77. [PMID: 23752183 DOI: 10.1038/onc.2013.203] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2012] [Revised: 03/26/2013] [Accepted: 04/19/2013] [Indexed: 12/17/2022]
Abstract
Prostate cancer (PCa)bone metastases are unique in that majority of them induce excessive mineralized bone matrix, through undefined mechanisms, as opposed to most other cancers that induce bone resorption. Parathyroid hormone-related protein (PTHrP) is produced by PCa cells and intermittent PTHrP exposure has bone anabolic effects, suggesting that PTHrP could contribute to the excess bone mineralization. Wnts are bone-productive factors produced by PCa cells, and the Wnt inhibitor Dickkopfs-1 (DKK1) has been shown to promote PCa progression. These findings, in conjunction with the observation that PTHrP expression increases and DKK1 expression decreases as PCa progresses, led to the hypothesis that PTHrP could be a negative regulator of DKK1 expression in PCa cells and, hence, allow the osteoblastic activity of Wnts to be realized. To test this, we first demonstrated that PTHrP downregulated DKK1 mRNA and protein expression. We then found through multiple mutated DKK1 promoter assays that PTHrP, through c-Jun activation, downregulated the DKK1 promoter through a transcription factor (TCF) response element site. Furthermore, chromatin immunoprecipitation (ChIP) and re-ChIP assays revealed that PTHrP mediated this effect through inducing c-Jun to bind to a transcriptional activator complex consisting of β-catenin, which binds the most proximal DKK1 promoter, the TCF response element. Together, these results demonstrate a novel signaling linkage between PTHrP and Wnt signaling pathways that results in downregulation of a Wnt inhibitor allowing for Wnt activity that could contribute the osteoblastic nature of PCa.
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Affiliation(s)
- H Zhang
- Department of Urology, School of Medicine, University of Michigan, Ann Arbor, MI, USA
| | - C Yu
- 1] Department of Urology, School of Medicine, University of Michigan, Ann Arbor, MI, USA [2] Department of Immunology, Tianjin Key Laboratory of Cellular and Molecular Immunology, Key Laboratory of Educational Ministry, Tianjin Medical University, Tianjin, China
| | - J Dai
- Department of Urology, School of Medicine, University of Michigan, Ann Arbor, MI, USA
| | - J M Keller
- Department of Urology, School of Medicine, University of Michigan, Ann Arbor, MI, USA
| | - A Hua
- Department of Urology, School of Medicine, University of Michigan, Ann Arbor, MI, USA
| | - J L Sottnik
- Department of Urology, School of Medicine, University of Michigan, Ann Arbor, MI, USA
| | - G Shelley
- Department of Urology, School of Medicine, University of Michigan, Ann Arbor, MI, USA
| | - C L Hall
- Department of Urology, School of Medicine, University of Michigan, Ann Arbor, MI, USA
| | - S I Park
- Department of Periodontics and Oral Medicine, School of Dentistry, University of Michigan, Ann Arbor, MI, USA
| | - Z Yao
- Department of Immunology, Tianjin Key Laboratory of Cellular and Molecular Immunology, Key Laboratory of Educational Ministry, Tianjin Medical University, Tianjin, China
| | - J Zhang
- Center for Translational Medical Research, Guangxi Medical University, Guangxi, China
| | - L K McCauley
- 1] Department of Periodontics and Oral Medicine, School of Dentistry, University of Michigan, Ann Arbor, MI, USA [2] Department of Pathology, School of Medicine, University of Michigan, Ann Arbor, MI, USA
| | - E T Keller
- 1] Department of Urology, School of Medicine, University of Michigan, Ann Arbor, MI, USA [2] Department of Pathology, School of Medicine, University of Michigan, Ann Arbor, MI, USA
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Abstract
Type 2 diabetes is characterized by pancreatic β-cell dysfunction and insulin resistance, and the number of patients has markedly increased worldwide. In the diabetic state, hyperglycemia per se and subsequent induction of oxidative stress decrease insulin biosynthesis and secretion, leading to the aggravation of Type 2 diabetes. In addition, there is substantial reduction in expression and/or activities of several insulin gene transcription factors. This process is known as β-cell glucose toxicity, which is often observed under diabetic conditions. Taken together, it is likely that oxidative stress explains, at least in part, the molecular mechanism for β-cell glucose toxicity, which is often observed in Type 2 diabetes.
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Nlend RN, Aït-Lounis A, Allagnat F, Cigliola V, Charollais A, Reith W, Haefliger JA, Meda P. Cx36 is a target of Beta2/NeuroD1, which associates with prenatal differentiation of insulin-producing β cells. J Membr Biol 2012; 245:263-73. [PMID: 22729650 DOI: 10.1007/s00232-012-9447-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2012] [Accepted: 06/01/2012] [Indexed: 10/28/2022]
Abstract
The insulin-producing β cells of pancreatic islets are coupled by connexin36 (Cx36) channels. To investigate what controls the expression of this connexin, we have investigated its pattern during mouse pancreas development, and the influence of three transcription factors that are critical for β-cell development and differentiation. We show that (1) the Cx36 gene (Gjd2) is activated early in pancreas development and is markedly induced at the time of the surge of the transcription factors that determine β-cell differentiation; (2) the cognate protein is detected about a week later and is selectively expressed by β cells throughout the prenatal development of mouse pancreas; (3) a 2-kbp fragment of the Gjd2 promoter, which contains three E boxes for the binding of the bHLH factor Beta2/NeuroD1, ensures the expression of Cx36 by β cells; and (4) Beta2/NeuroD1 binds to these E boxes and, in the presence of the E47 ubiquitous cofactor, transactivates the Gjd2 promoter. The data identify Cx36 as a novel early marker of β cells and as a target of Beta2/NeuroD1, which is essential for β-cell development and differentiation.
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Affiliation(s)
- Rachel Nlend Nlend
- Department of Cell Physiology and Metabolism, University of Geneva, CMU, 1 Rue Michel Servet CH- 1211, Geneva 4, Switzerland
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Matsuoka TA, Kaneto H, Miyatsuka T, Yamamoto T, Yamamoto K, Kato K, Shimomura I, Stein R, Matsuhisa M. Regulation of MafA expression in pancreatic beta-cells in db/db mice with diabetes. Diabetes 2010; 59:1709-20. [PMID: 20424231 PMCID: PMC2889771 DOI: 10.2337/db08-0693] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE Islet beta-cells loose their ability to synthesize insulin under diabetic conditions, which is at least partially due to the decreased activity of insulin transcription factors such as MafA. Although an in vitro study showed that reactive oxygen species (ROS) decrease MafA expression, the underlying mechanism still remains unclear. In this study, we examined the effects of c-Jun, which is known to be upregulated by ROS, on the expression of MafA under diabetic conditions. RESEARCH DESIGN AND METHODS To examine the protein levels of MafA and c-Jun, we performed histological analysis and Western blotting using diabetic db/db mice. In addition, to evaluate the possible effects of c-Jun on MafA expression, we performed adenoviral overexpression of c-Jun in the MIN6 beta-cell line and freshly isolated islets. RESULTS MafA expression was markedly decreased in the islets of db/db mice, while in contrast c-Jun expression was increased. Costaining of these factors in the islets of db/db mice clearly showed that MafA and insulin levels are decreased in c-Jun-positive cells. Consistent with these results, overexpression of c-Jun significantly decreased MafA expression, accompanied by suppression of insulin expression. Importantly, MafA overexpression restored the insulin promoter activity and protein levels that were suppressed by c-Jun. These results indicate that the decreased insulin biosynthesis induced by c-Jun is principally mediated by the suppression of MafA activity. CONCLUSIONS It is likely that the augmented expression of c-Jun in diabetic islets decreases MafA expression and thereby reduces insulin biosynthesis, which is often observed in type 2 diabetes.
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Affiliation(s)
- Taka-aki Matsuoka
- Department of Metabolic Medicine, Osaka University Graduate School of Medicine, Osaka, Japan.
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Poitout V, Amyot J, Semache M, Zarrouki B, Hagman D, Fontés G. Glucolipotoxicity of the pancreatic beta cell. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1801:289-98. [PMID: 19715772 DOI: 10.1016/j.bbalip.2009.08.006] [Citation(s) in RCA: 269] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2009] [Revised: 08/13/2009] [Accepted: 08/13/2009] [Indexed: 02/07/2023]
Abstract
The concept of glucolipotoxicity refers to the combined, deleterious effects of elevated glucose and fatty acid levels on pancreatic beta-cell function and survival. Significant progress has been made in recent years towards a better understanding of the cellular and molecular basis of glucolipotoxicity in the beta cell. The permissive effect of elevated glucose on the detrimental actions of fatty acids stems from the influence of glucose on intracellular fatty acid metabolism, promoting the synthesis of cellular lipids. The combination of excessive levels of fatty acids and glucose therefore leads to decreased insulin secretion, impaired insulin gene expression, and beta-cell death by apoptosis, all of which probably have distinct underlying mechanisms. Recent studies from our laboratory have identified several pathways implicated in fatty acid inhibition of insulin gene expression, including the extracellular-regulated kinase (ERK1/2) pathway, the metabolic sensor Per-Arnt-Sim kinase (PASK), and the ATF6 branch of the unfolded protein response. We have also confirmed in vivo in rats that the decrease in insulin gene expression is an early defect which precedes any detectable abnormality in insulin secretion. While the role of glucolipotoxicity in humans is still debated, the inhibitory effects of chronically elevated fatty acid levels has been clearly demonstrated in several studies, at least in individuals genetically predisposed to developing type 2 diabetes. It is therefore likely that glucolipotoxicity contributes to beta-cell failure in type 2 diabetes as well as to the decline in beta-cell function observed after the onset of the disease.
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Affiliation(s)
- Vincent Poitout
- Montreal Diabetes Research Center, CRCHUM, Department of Medicine, University of Montreal, Montreal, QC, Canada.
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Nino-Fong R, Collins T, Chan C. Nutrigenomics, beta-cell function and type 2 diabetes. Curr Genomics 2008; 8:1-29. [PMID: 18645625 PMCID: PMC2474685 DOI: 10.2174/138920207780076947] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2006] [Revised: 08/12/2006] [Accepted: 10/13/2006] [Indexed: 01/15/2023] Open
Abstract
INTRODUCTION The present investigation was designed to investigate the accuracy and precision of lactate measurement obtained with contemporary biosensors (Chiron Diagnostics, Nova Biomedical) and standard enzymatic photometric procedures (Sigma Diagnostics, Abbott Laboratories, Analyticon). MATERIALS AND METHODS Measurements were performed in vitro before and after the stepwise addition of 1 molar sodium lactate solution to samples of fresh frozen plasma to systematically achieve lactate concentrations of up to 20 mmol/l. RESULTS Precision of the methods investigated varied between 1% and 7%, accuracy ranged between 2% and -33% with the variability being lowest in the Sigma photometric procedure (6%) and more than 13% in both biosensor methods. CONCLUSION Biosensors for lactate measurement provide adequate accuracy in mean with the limitation of highly variable results. A true lactate value of 6 mmol/l was found to be presented between 4.4 and 7.6 mmol/l or even with higher difference. Biosensors and standard enzymatic photometric procedures are only limited comparable because the differences between paired determinations presented to be several mmol. The advantage of biosensors is the complete lack of preanalytical sample preparation which appeared to be the major limitation of standard photometry methods.
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Affiliation(s)
- R Nino-Fong
- Department of Biomedical Sciences, University of Prince Edward Island, Charlottetown, PE C1A 4P3 Canada
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Abstract
Glucotoxicity, lipotoxicity, and glucolipotoxicity are secondary phenomena that are proposed to play a role in all forms of type 2 diabetes. The underlying concept is that once the primary pathogenesis of diabetes is established, probably involving both genetic and environmental forces, hyperglycemia and very commonly hyperlipidemia ensue and thereafter exert additional damaging or toxic effects on the beta-cell. In addition to their contribution to the deterioration of beta-cell function after the onset of the disease, elevations of plasma fatty acid levels that often accompany insulin resistance may, as glucose levels begin to rise outside of the normal range, also play a pathogenic role in the early stages of the disease. Because hyperglycemia is a prerequisite for lipotoxicity to occur, the term glucolipotoxicity, rather than lipotoxicity, is more appropriate to describe deleterious effects of lipids on beta-cell function. In vitro and in vivo evidence supporting the concept of glucotoxicity is presented first, as well as a description of the underlying mechanisms with an emphasis on the role of oxidative stress. Second, we discuss the functional manifestations of glucolipotoxicity on insulin secretion, insulin gene expression, and beta-cell death, and the role of glucose in the mechanisms of glucolipotoxicity. Finally, we attempt to define the role of these phenomena in the natural history of beta-cell compensation, decompensation, and failure during the course of type 2 diabetes.
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Affiliation(s)
- Vincent Poitout
- Montreal Diabetes Research Center, CR-CHUM, Technopole Angus, 2901 Rachel Est, Montreal, Quebec, Canada H1W 4A4.
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Abderrahmani A, Niederhauser G, Favre D, Abdelli S, Ferdaoussi M, Yang JY, Regazzi R, Widmann C, Waeber G. Human high-density lipoprotein particles prevent activation of the JNK pathway induced by human oxidised low-density lipoprotein particles in pancreatic beta cells. Diabetologia 2007; 50:1304-14. [PMID: 17437081 DOI: 10.1007/s00125-007-0642-z] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/30/2006] [Accepted: 01/15/2007] [Indexed: 12/17/2022]
Abstract
AIMS/HYPOTHESIS We explored the potential adverse effects of pro-atherogenic oxidised LDL-cholesterol particles on beta cell function. MATERIALS AND METHODS Isolated human and rat islets and different insulin-secreting cell lines were incubated with human oxidised LDL with or without HDL particles. The insulin level was monitored by ELISA, real-time PCR and a rat insulin promoter construct linked to luciferase gene reporter. Cell apoptosis was determined by scoring cells displaying pycnotic nuclei. RESULTS Prolonged incubation with human oxidised LDL particles led to a reduction in preproinsulin expression levels, whereas the insulin level was preserved in the presence of native LDL-cholesterol. The loss of insulin production occurred at the transcriptional levels and was associated with an increase in activator protein-1 transcriptional activity. The rise in activator protein-1 activity resulted from activation of c-Jun N-terminal kinases (JNK, now known as mitogen-activated protein kinase 8 [MAPK8]) due to a subsequent decrease in islet-brain 1 (IB1; now known as MAPK8 interacting protein 1) levels. Consistent with the pro-apoptotic role of the JNK pathway, oxidised LDL also induced a twofold increase in the rate of beta cell apoptosis. Treatment of the cells with JNK inhibitor peptides or HDL countered the effects mediated by oxidised LDL. CONCLUSIONS/INTERPRETATION These data provide strong evidence that oxidised LDL particles exert deleterious effects in the progression of beta cell failure in diabetes and that these effects can be countered by HDL particles.
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Affiliation(s)
- A Abderrahmani
- Service of Internal Medicine, CHUV-Hospital, Rue du Bugnon 9, 1005 Lausanne, Switzerland.
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Poitout V, Hagman D, Stein R, Artner I, Robertson RP, Harmon JS. Regulation of the insulin gene by glucose and fatty acids. J Nutr 2006; 136:873-6. [PMID: 16549443 PMCID: PMC1853259 DOI: 10.1093/jn/136.4.873] [Citation(s) in RCA: 147] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The insulin gene is expressed almost exclusively in pancreatic beta-cells. Metabolic regulation of insulin gene expression enables the beta-cell to maintain adequate stores of intracellular insulin to sustain the secretory demand. Glucose is the major physiologic regulator of insulin gene expression; it coordinately controls the recruitment of transcription factors [e.g., pancreatic/duodenal homeobox-1 (PDX-1), mammalian homologue of avian MafA/L-Maf (MafA), Beta2/Neuro D (B2), the rate of transcription, and the stability of insulin mRNA. However, chronically elevated levels of glucose (glucotoxicity) and lipids (lipotoxicity) also contribute to the worsening of beta-cell function in type 2 diabetes, in part via inhibition of insulin gene expression. The mechanisms of glucotoxicity, which involve decreased binding activities of PDX-1 and MafA and increased activity of C/EBPbeta, are mediated by high-glucose-induced generation of oxidative stress. On the other hand, lipotoxicity is mediated by de novo ceramide synthesis and involves inhibition of PDX-1 nuclear translocation and MafA gene expression. Glucotoxicity and lipotoxicity have common targets, which makes their combination particularly harmful to insulin gene expression and beta-cell function in type 2 diabetes.
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Affiliation(s)
- Vincent Poitout
- Department of Medicine, University of Montréal, Montréal, QC, Canada.
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Qiu Y, Sharma A, Stein R. p300 mediates transcriptional stimulation by the basic helix-loop-helix activators of the insulin gene. Mol Cell Biol 1998; 18:2957-64. [PMID: 9566915 PMCID: PMC110675 DOI: 10.1128/mcb.18.5.2957] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/1997] [Accepted: 02/17/1998] [Indexed: 02/07/2023] Open
Abstract
Pancreatic beta-cell-type-specific and glucose-inducible transcription of the insulin gene is mediated by the basic helix-loop-helix factors that bind to and activate expression from an E-box element within its enhancer. The E-box activator is a heteromeric complex composed of a beta-cell-enriched factor, BETA2/NeuroD, and ubiquitously distributed proteins encoded by the E2A and HEB genes. Previously, we demonstrated that the adenovirus type 5 E1A proteins repressed stimulation by the E-box activator in beta cells. In this study, our objective was to determine how E1A repressed activator function. The results indicate that E1A reduces activation by binding to and sequestering the p300 cellular coactivator protein. Thus, we show that expression of p300 in beta cells can relieve inhibition by E1A, as well as potentiate activation by the endogenous insulin E-box transcription factors. p300 stimulated activation from GAL4 (amino acids 1 to 147) fusion constructs of either BETA2/NeuroD or the E2A-encoded E47 protein. The sequences spanning the activation domains of BETA2/NeuroD (amino acids 156 to 355) and E47 (amino acids 1 to 99 and 325 to 432) were required for this response. The same region of BETA2/NeuroD was shown to be important for binding to p300 in vitro. The sequences of p300 involved in E47 and BETA2/NeuroD association resided between amino acids 1 and 1257 and 1945 and 2377, respectively. A mutation in p300 that abolished binding to BETA2/NeuroD also destroyed the ability of p300 to activate insulin E-box-directed transcription in beta cells. Our results indicate that physical and functional interactions between p300 and the E-box activator factors play an important role in insulin gene transcription.
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Affiliation(s)
- Y Qiu
- Department of Molecular Physiology and Biophysics, Vanderbilt Medical Center, Nashville, Tennessee 37232, USA
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16
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Ptasznik A, Beattie GM, Mally MI, Cirulli V, Lopez A, Hayek A. Phosphatidylinositol 3-kinase is a negative regulator of cellular differentiation. J Cell Biol 1997; 137:1127-36. [PMID: 9166412 PMCID: PMC2136228 DOI: 10.1083/jcb.137.5.1127] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/1997] [Revised: 03/21/1997] [Indexed: 02/04/2023] Open
Abstract
Phosphatidylinositol 3-kinase (PI3K) has been shown to be an important mediator of intracellular signal transduction in mammalian cells. We show here, for the first time, that the blockade of PI3K activity in human fetal undifferentiated cells induced morphological and functional endocrine differentiation. This was associated with an increase in mRNA levels of insulin, glucagon, and somatostatin, as well as an increase in the insulin protein content and secretion in response to secretagogues. Blockade of PI3K also increased the proportion of pluripotent precursor cells coexpressing multiple hormones and the total number of terminally differentiated cells originating from these precursor cells. We examined whether any of the recently described modulators of endocrine differentiation could participate in regulating PI3K activity in fetal islet cells. The activity of PI3K was inversely correlated with the hepatocyte growth factor/scatter factor-induced downregulation or nicotinamideinduced upregulation of islet-specific gene expression, giving support to the role of PI3K, as a negative regulator of endocrine differentiation. In conclusion, our results provide a mechanism for the regulation of hormone-specific gene expression during human fetal neogenesis. They also suggest a novel function for PI3K, as a negative regulator of cellular differentiation.
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Affiliation(s)
- A Ptasznik
- The Whittier Institute for Diabetes and Endocrinology, Department of Pediatrics, University of California at San Diego, School of Medicine, La Jolla, California 92037, USA
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Robinson GL, Henderson E, Massari ME, Murre C, Stein R. c-jun inhibits insulin control element-mediated transcription by affecting the transactivation potential of the E2A gene products. Mol Cell Biol 1995; 15:1398-404. [PMID: 7862133 PMCID: PMC230364 DOI: 10.1128/mcb.15.3.1398] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Pancreatic beta-cell-type-specific transcription of the insulin gene is principally controlled by trans-acting factors which influence insulin control element (ICE)-mediated expression. The ICE activator is composed, in part, of the basic helix-loop-helix proteins E12, E47, and E2-5 encoded by the E2A gene. Previous experiments showed that ICE activation in beta cells was repressed in vivo by the c-jun proto-oncogene (E. Henderson and R. Stein, Mol. Cell. Biol. 14:655-662, 1994). Here we focus on the mechanism by which c-Jun inhibits ICE-mediated activation. c-Jun was shown to specifically repress the transactivation potential of the E2A proteins. Thus, we found that the activity of GAL4:E2A fusion constructs was inhibited by c-Jun. The transrepression capabilities of c-Jun were detected only in pancreatic islet cell lines that contained a functional ICE activator. Repression of GAL4:E2A was mediated by the basic leucine zipper regions of c-Jun, which are also the essential regions of this protein necessary for controlling ICE activator-stimulated expression in vivo. The specific target of c-Jun repression was the transactivation domain (located between amino acids 345 and 408 in E12 and E47) conserved in E12, E47, and E2-5. In contrast, the activation domain unique to the E12 and E47 proteins (located between amino acids 1 and 99) was unresponsive to c-Jun. Our results indicate that c-Jun inhibits insulin gene transcription in beta cells by reducing the transactivation potential of the E2A proteins present in the ICE activator complex.
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Affiliation(s)
- G L Robinson
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232
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Sollerbrant K, Akusjärvi G, Linder S, Svensson C. The DNA binding domains of the yeast Gal4 and human c-Jun transcription factors interact through the zinc-finger and bZIP motifs. Nucleic Acids Res 1995; 23:588-94. [PMID: 7899077 PMCID: PMC306724 DOI: 10.1093/nar/23.4.588] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Different Gal4 fusion proteins, expressing unrelated transcription activator domains, were found to activate transcription from promoters containing dimerized AP1 DNA binding sites. Transactivation was dependent on the first 74 amino acids of Gal4. A direct interaction between Gal4 and c-Jun was demonstrated using a GSTGal4 fusion protein and in vitro translated human c-Jun. The interaction required the zinc finger containing DNA binding domain of Gal4 and the basic-leucine zipper region of c-Jun. These results demonstrated that the specificity of Gal4 fusion proteins in transient transfection experiments in mammalian cells is not restricted to reporters containing Gal4 binding sites, but also includes promoters containing AP1 binding sites. Furthermore, the Gal4 fusion proteins also activated transcription from a pUC18 vector fragment containing several putative AP1 binding sites. Finally, our results indicate that Gal4 activator proteins binding to Gal4 binding sites and to DNA bound AP1 factors can co-operatively activate transcription.
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Affiliation(s)
- K Sollerbrant
- Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institute, Stockholm, Sweden
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Isolation and characterization of a novel transcription factor that binds to and activates insulin control element-mediated expression. Mol Cell Biol 1994. [PMID: 7935390 DOI: 10.1128/mcb.14.10.6704] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pancreatic beta-cell-type-specific transcription of the insulin gene is principally regulated by a single cis-acting DNA sequence element, termed the insulin control element (ICE), which is found within the 5'-flanking region of the gene. The ICE activator is a heteromeric complex composed of an islet alpha/beta-cell-specific factor associated with the ubiquitously distributed E2A-encoded proteins (E12, E47, and E2-5). We describe the isolation and characterization of a cDNA for a protein present in alpha and beta cells, termed INSAF for insulin activator factor, which binds to and activates ICE-mediated expression. INSAF was isolated from a human insulinoma cDNA library. Transfection experiments demonstrated that INSAF activates ICE expression in insulin-expressing cells but not in non-insulin-expressing cells. Cotransfection experiments showed that activation by INSAF was inhibited by Id, a negative regulator of basic helix-loop-helix (bHLH) protein function. INSAF was also shown to associate in vitro with the bHLH protein E12. In addition, affinity-purified INSAF antiserum abolished the formation of the activator-specific ICE-binding complex. Immunohistochemical studies indicate that INSAF is restricted in terms of its expression pattern, in that INSAF appears to be detected only within the nuclei of islet pancreatic alpha and beta cells. All of these data are consistent with the proposal that INSAF is either part of the ICE activator or is antigenically related to the specific activator required for insulin gene transcription.
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Robinson GL, Cordle SR, Henderson E, Weil PA, Teitelman G, Stein R. Isolation and characterization of a novel transcription factor that binds to and activates insulin control element-mediated expression. Mol Cell Biol 1994; 14:6704-14. [PMID: 7935390 PMCID: PMC359201 DOI: 10.1128/mcb.14.10.6704-6714.1994] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Pancreatic beta-cell-type-specific transcription of the insulin gene is principally regulated by a single cis-acting DNA sequence element, termed the insulin control element (ICE), which is found within the 5'-flanking region of the gene. The ICE activator is a heteromeric complex composed of an islet alpha/beta-cell-specific factor associated with the ubiquitously distributed E2A-encoded proteins (E12, E47, and E2-5). We describe the isolation and characterization of a cDNA for a protein present in alpha and beta cells, termed INSAF for insulin activator factor, which binds to and activates ICE-mediated expression. INSAF was isolated from a human insulinoma cDNA library. Transfection experiments demonstrated that INSAF activates ICE expression in insulin-expressing cells but not in non-insulin-expressing cells. Cotransfection experiments showed that activation by INSAF was inhibited by Id, a negative regulator of basic helix-loop-helix (bHLH) protein function. INSAF was also shown to associate in vitro with the bHLH protein E12. In addition, affinity-purified INSAF antiserum abolished the formation of the activator-specific ICE-binding complex. Immunohistochemical studies indicate that INSAF is restricted in terms of its expression pattern, in that INSAF appears to be detected only within the nuclei of islet pancreatic alpha and beta cells. All of these data are consistent with the proposal that INSAF is either part of the ICE activator or is antigenically related to the specific activator required for insulin gene transcription.
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Affiliation(s)
- G L Robinson
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232
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21
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Glucose-induced transcription of the insulin gene is mediated by factors required for beta-cell-type-specific expression. Mol Cell Biol 1994. [PMID: 8289826 DOI: 10.1128/mcb.14.2.871] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The insulin gene is expressed exclusively in pancreatic islet beta cells. The principal regulator of insulin gene transcription in the islet is the concentration of circulating glucose. Previous studies have demonstrated that transcription is regulated by the binding of trans-acting factors to specific cis-acting sequences within the 5'-flanking region of the insulin gene. To identify the cis-acting control elements within the rat insulin II gene that are responsible for regulating glucose-stimulated expression in the beta cell, we analyzed the effect of glucose on the in vivo expression of a series of transfected 5'-flanking deletion mutant constructs. We demonstrate that glucose-induced transcription of the rat insulin II gene is mediated by sequences located between -126 and -91 bp relative to the transcription start site. This region contains two cis-acting elements that are essential for directing pancreatic beta-cell-type-specific expression of the rat insulin II gene, the insulin control element (ICE; -100 to -91 bp) and RIPE3b1 (-115 to -107 bp). The gel mobility shift assay was used to determine whether the formation of the ICE- and RIPE3b1-specific factor-DNA element complexes were affected in glucose-treated beta-cell extracts. We found that RIPE3b1 binding activity was selectively induced by about eightfold. In contrast, binding to other insulin cis-acting element sequences like the ICE and RIPE3a2 (-108 to -99 bp) were unaffected by these conditions. The RIPE3b1 binding complex was shown to be distinct from the glucose-inducible factor that binds to an element located between -227 to -206 bp of the human and rat insulin I genes (D. Melloul, Y. Ben-Neriah, and E. Cerasi, Proc. Natl. Acad. Sci. USA 90:3865-3869, 1993). We have also shown that mannose, a sugar that can be metabolized by the beta cell, mimics the effects of glucose in the in vivo transfection assays and the in vitro RIPE3b1 binding assays. These results suggested that the RIPE3b1 transcription factor is a primary regulator of glucose-mediated transcription of the insulin gene. However, we found that mutations in either the ICE or the RIPE3b1 element reduced glucose-responsive expression from transfected 5'-flanking rat insulin II gene constructs. We therefore conclude that glucose-regulated transcription of the insulin gene is mediated by cis-acting elements required for beta-cell-type-specific expression.
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Sharma A, Stein R. Glucose-induced transcription of the insulin gene is mediated by factors required for beta-cell-type-specific expression. Mol Cell Biol 1994; 14:871-9. [PMID: 8289826 PMCID: PMC358441 DOI: 10.1128/mcb.14.2.871-879.1994] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The insulin gene is expressed exclusively in pancreatic islet beta cells. The principal regulator of insulin gene transcription in the islet is the concentration of circulating glucose. Previous studies have demonstrated that transcription is regulated by the binding of trans-acting factors to specific cis-acting sequences within the 5'-flanking region of the insulin gene. To identify the cis-acting control elements within the rat insulin II gene that are responsible for regulating glucose-stimulated expression in the beta cell, we analyzed the effect of glucose on the in vivo expression of a series of transfected 5'-flanking deletion mutant constructs. We demonstrate that glucose-induced transcription of the rat insulin II gene is mediated by sequences located between -126 and -91 bp relative to the transcription start site. This region contains two cis-acting elements that are essential for directing pancreatic beta-cell-type-specific expression of the rat insulin II gene, the insulin control element (ICE; -100 to -91 bp) and RIPE3b1 (-115 to -107 bp). The gel mobility shift assay was used to determine whether the formation of the ICE- and RIPE3b1-specific factor-DNA element complexes were affected in glucose-treated beta-cell extracts. We found that RIPE3b1 binding activity was selectively induced by about eightfold. In contrast, binding to other insulin cis-acting element sequences like the ICE and RIPE3a2 (-108 to -99 bp) were unaffected by these conditions. The RIPE3b1 binding complex was shown to be distinct from the glucose-inducible factor that binds to an element located between -227 to -206 bp of the human and rat insulin I genes (D. Melloul, Y. Ben-Neriah, and E. Cerasi, Proc. Natl. Acad. Sci. USA 90:3865-3869, 1993). We have also shown that mannose, a sugar that can be metabolized by the beta cell, mimics the effects of glucose in the in vivo transfection assays and the in vitro RIPE3b1 binding assays. These results suggested that the RIPE3b1 transcription factor is a primary regulator of glucose-mediated transcription of the insulin gene. However, we found that mutations in either the ICE or the RIPE3b1 element reduced glucose-responsive expression from transfected 5'-flanking rat insulin II gene constructs. We therefore conclude that glucose-regulated transcription of the insulin gene is mediated by cis-acting elements required for beta-cell-type-specific expression.
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Affiliation(s)
- A Sharma
- Department of Molecular Physiology and Biophysics, Vanderbilt Medical Center, Nashville, Tennessee 37232
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