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Keller MP, Hawes EM, Schueler KL, Stapleton DS, Mitok KA, Simonett SP, Oeser JK, Sampson LL, Attie AD, Magnuson MA, O’Brien RM. An Enhancer Within Abcb11 Regulates G6pc2 in C57BL/6 Mouse Pancreatic Islets. Diabetes 2023; 72:1621-1628. [PMID: 37552875 PMCID: PMC10588275 DOI: 10.2337/db23-0215] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Accepted: 08/01/2023] [Indexed: 08/10/2023]
Abstract
G6PC2 is predominantly expressed in pancreatic islet β-cells where it encodes a glucose-6-phosphatase catalytic subunit that modulates the sensitivity of insulin secretion to glucose by opposing the action of glucokinase, thereby regulating fasting blood glucose (FBG). Prior studies have shown that the G6pc2 promoter alone is unable to confer sustained islet-specific gene expression in mice, suggesting the existence of distal enhancers that regulate G6pc2 expression. Using information from both mice and humans and knowledge that single nucleotide polymorphisms (SNPs) both within and near G6PC2 are associated with variations in FBG in humans, we identified several putative enhancers 3' of G6pc2. One region, herein referred to as enhancer I, resides in the 25th intron of Abcb11 and binds multiple islet-enriched transcription factors. CRISPR-mediated deletion of enhancer I in C57BL/6 mice had selective effects on the expression of genes near the G6pc2 locus. In isolated islets, G6pc2 and Spc25 expression were reduced ∼50%, and Gm13613 expression was abolished, whereas Cers6 and nostrin expression were unaffected. This partial reduction in G6pc2 expression enhanced islet insulin secretion at basal glucose concentrations but did not affect FBG or glucose tolerance in vivo, consistent with the absence of a phenotype in G6pc2 heterozygous C57BL/6 mice. ARTICLE HIGHLIGHTS
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Affiliation(s)
- Mark P. Keller
- Department of Biochemistry, University of Wisconsin–Madison, Madison, WI
| | - Emily M. Hawes
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
| | | | | | - Kelly A. Mitok
- Department of Biochemistry, University of Wisconsin–Madison, Madison, WI
| | - Shane P. Simonett
- Department of Biochemistry, University of Wisconsin–Madison, Madison, WI
| | - James K. Oeser
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
| | - Leesa L. Sampson
- Center for Stem Cell Biology, Vanderbilt University School of Medicine, Nashville, TN
| | - Alan D. Attie
- Department of Biochemistry, University of Wisconsin–Madison, Madison, WI
- Department of Chemistry, University of Wisconsin–Madison, Madison, WI
- Department of Medicine, University of Wisconsin–Madison, Madison, WI
| | - Mark A. Magnuson
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
- Center for Stem Cell Biology, Vanderbilt University School of Medicine, Nashville, TN
| | - Richard M. O’Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
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Yoshihara E. Adapting Physiology in Functional Human Islet Organogenesis. Front Cell Dev Biol 2022; 10:854604. [PMID: 35557947 PMCID: PMC9086403 DOI: 10.3389/fcell.2022.854604] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2022] [Accepted: 03/22/2022] [Indexed: 01/07/2023] Open
Abstract
Generation of three-dimensional (3D)-structured functional human islets is expected to be an alternative cell source for cadaveric human islet transplantation for the treatment of insulin-dependent diabetes. Human pluripotent stem cells (hPSCs), such as human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), offer infinite resources for newly synthesized human islets. Recent advancements in hPSCs technology have enabled direct differentiation to human islet-like clusters, which can sense glucose and secrete insulin, and those islet clusters can ameliorate diabetes when transplanted into rodents or non-human primates (NHPs). However, the generated hPSC-derived human islet-like clusters are functionally immature compared with primary human islets. There remains a challenge to establish a technology to create fully functional human islets in vitro, which are functionally and transcriptionally indistinguishable from cadaveric human islets. Understanding the complex differentiation and maturation pathway is necessary to generate fully functional human islets for a tremendous supply of high-quality human islets with less batch-to-batch difference for millions of patients. In this review, I summarized the current progress in the generation of 3D-structured human islets from pluripotent stem cells and discussed the importance of adapting physiology for in vitro functional human islet organogenesis and possible improvements with environmental cues.
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Affiliation(s)
- Eiji Yoshihara
- Lundquist Institute for Biomedical Innovation at Harbor-UCLA Medical Center, Torrance, CA, United States.,David Geffen School of Medicine at University of California, Los Angeles, CA, United States
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Liang J, Chirikjian M, Pajvani UB, Bartolomé A. MafA Regulation in β-Cells: From Transcriptional to Post-Translational Mechanisms. Biomolecules 2022; 12:biom12040535. [PMID: 35454124 PMCID: PMC9033020 DOI: 10.3390/biom12040535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Revised: 03/29/2022] [Accepted: 03/30/2022] [Indexed: 11/17/2022] Open
Abstract
β-cells are insulin-producing cells in the pancreas that maintain euglycemic conditions. Pancreatic β-cell maturity and function are regulated by a variety of transcription factors that enable the adequate expression of the cellular machinery involved in nutrient sensing and commensurate insulin secretion. One of the key factors in this regulation is MAF bZIP transcription factor A (MafA). MafA expression is decreased in type 2 diabetes, contributing to β-cell dysfunction and disease progression. The molecular biology underlying MafA is complex, with numerous transcriptional and post-translational regulatory nodes. Understanding these complexities may uncover potential therapeutic targets to ameliorate β-cell dysfunction. This article will summarize the role of MafA in normal β-cell function and disease, with a special focus on known transcriptional and post-translational regulators of MafA expression.
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Affiliation(s)
- Jiani Liang
- Department of Medicine, Columbia University, New York, NY 10032, USA; (J.L.); (M.C.); (U.B.P.)
| | - Margot Chirikjian
- Department of Medicine, Columbia University, New York, NY 10032, USA; (J.L.); (M.C.); (U.B.P.)
| | - Utpal B. Pajvani
- Department of Medicine, Columbia University, New York, NY 10032, USA; (J.L.); (M.C.); (U.B.P.)
| | - Alberto Bartolomé
- Instituto de Investigaciones Biomédicas Alberto Sols, CSIC-UAM, 28029 Madrid, Spain
- Correspondence:
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Tahbaz M, Yoshihara E. Immune Protection of Stem Cell-Derived Islet Cell Therapy for Treating Diabetes. Front Endocrinol (Lausanne) 2021; 12:716625. [PMID: 34447354 PMCID: PMC8382875 DOI: 10.3389/fendo.2021.716625] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Accepted: 07/19/2021] [Indexed: 12/14/2022] Open
Abstract
Insulin injection is currently the main therapy for type 1 diabetes (T1D) or late stage of severe type 2 diabetes (T2D). Human pancreatic islet transplantation confers a significant improvement in glycemic control and prevents life-threatening severe hypoglycemia in T1D patients. However, the shortage of cadaveric human islets limits their therapeutic potential. In addition, chronic immunosuppression, which is required to avoid rejection of transplanted islets, is associated with severe complications, such as an increased risk of malignancies and infections. Thus, there is a significant need for novel approaches to the large-scale generation of functional human islets protected from autoimmune rejection in order to ensure durable graft acceptance without immunosuppression. An important step in addressing this need is to strengthen our understanding of transplant immune tolerance mechanisms for both graft rejection and autoimmune rejection. Engineering of functional human pancreatic islets that can avoid attacks from host immune cells would provide an alternative safe resource for transplantation therapy. Human pluripotent stem cells (hPSCs) offer a potentially limitless supply of cells because of their self-renewal ability and pluripotency. Therefore, studying immune tolerance induction in hPSC-derived human pancreatic islets will directly contribute toward the goal of generating a functional cure for insulin-dependent diabetes. In this review, we will discuss the current progress in the immune protection of stem cell-derived islet cell therapy for treating diabetes.
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Affiliation(s)
- Meghan Tahbaz
- Lundquist Institute for Biomedical Innovation at Harbor-UCLA Medical Center, Torrance, CA, United States
| | - Eiji Yoshihara
- Lundquist Institute for Biomedical Innovation at Harbor-UCLA Medical Center, Torrance, CA, United States
- David Geffen School of Medicine at University of California, Los Angeles, CA, United States
- *Correspondence: Eiji Yoshihara,
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Hu L, He F, Luo Y, Luo H, Hai L, Li Y, Zhou Z, Liu F, Dai YS. Reduced Compensatory β-Cell Proliferation in Nfatc3-Deficient Mice Fed on High-Fat Diet. Exp Clin Endocrinol Diabetes 2019; 129:651-660. [PMID: 31546271 DOI: 10.1055/a-1008-9110] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
BACKGROUND High-fat-diet induces pancreatic β-cell compensatory proliferation, and impairments in pancreatic β-cell proliferation and function can lead to defects in insulin secretion and diabetes. NFATc3 is important for HFD-induced adipose tissue inflammation. But it is unknown whether NFATc3 is required for β cell compensatory growth in mice fed with HFD. METHODS NFATc3 mRNA and protein expression levels were quantified by RT-qPCR and Western blotting, respectively, in pancreatic islets of WT mice fed on HFD for 12-20 weeks. Adenoviral-mediated overexpression of NFATc3 were conducted in Min6 cells and cultured primary mouse islets. NFATc3-/- mice and WT control mice were fed with HFD and metabolic and functional parameters were measured. RESULTS We observed that the NFATc3 expression level was reduced in the islets of high-fat-diet (HFD)-fed mice. Adenovirus-mediated overexpression of NFATc3 enhanced glucose-stimulated insulin secretion and β-cell gene expression in cultured primary mouse islets. Nfatc3-/- mice initially developed similar glucose tolerance at 2-4 weeks after HFD feeding than HFD-fed WT mice, but Nfatc3-/- mice developed improved glucose tolerance and insulin sensitivity after 8 weeks of HFD feeding compared to Nfatc3+/+fed with HFD. Furthermore, Nfatc3-/- mice on HFD exhibited decreased β-cell mass and reduced expression of genes important for β-cell proliferation and function compared to Nfatc3+/+mice on HFD. CONCLUSIONS The findings suggested that NFATc3 plays a role in maintaining the pancreatic β-cell compensatory growth and gene expression in response to obesity.
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Affiliation(s)
- Li Hu
- Department of Metabolism and Endocrinology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,National Clinical Research Center for Metabolic Disease, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, Ministry of Education, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Fengli He
- Department of Metabolism and Endocrinology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,National Clinical Research Center for Metabolic Disease, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, Ministry of Education, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Yan Luo
- Department of Metabolism and Endocrinology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,National Clinical Research Center for Metabolic Disease, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, Ministry of Education, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Hairong Luo
- Department of Metabolism and Endocrinology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,National Clinical Research Center for Metabolic Disease, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, Ministry of Education, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Luo Hai
- Department of Metabolism and Endocrinology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,National Clinical Research Center for Metabolic Disease, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, Ministry of Education, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Yabin Li
- Department of Metabolism and Endocrinology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,National Clinical Research Center for Metabolic Disease, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, Ministry of Education, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Zhiguang Zhou
- Department of Metabolism and Endocrinology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,National Clinical Research Center for Metabolic Disease, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, Ministry of Education, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Feng Liu
- Department of Metabolism and Endocrinology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,National Clinical Research Center for Metabolic Disease, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, Ministry of Education, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Yan-Shan Dai
- Department of Metabolism and Endocrinology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,National Clinical Research Center for Metabolic Disease, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, Ministry of Education, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.,Bristol-Myers Squibb Company, Princeton, NJ 08540, United States
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6
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Boortz KA, Syring KE, Lee RA, Dai C, Oeser JK, McGuinness OP, Wang JC, O'Brien RM. G6PC2 Modulates the Effects of Dexamethasone on Fasting Blood Glucose and Glucose Tolerance. Endocrinology 2016; 157:4133-4145. [PMID: 27653037 PMCID: PMC5086534 DOI: 10.1210/en.2016-1678] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The glucose-6-phosphatase catalytic subunit 2 (G6PC2) gene encodes an islet-specific glucose-6-phosphatase catalytic subunit. G6PC2 forms a substrate cycle with glucokinase that determines the glucose sensitivity of insulin secretion. Consequently, deletion of G6pc2 lowers fasting blood glucose (FBG) without affecting fasting plasma insulin. Although chronic elevation of FBG is detrimental to health, glucocorticoids induce G6PC2 expression, suggesting that G6PC2 evolved to transiently modulate FBG under conditions of glucocorticoid-related stress. We show, using competition and mutagenesis experiments, that the synthetic glucocorticoid dexamethasone (Dex) induces G6PC2 promoter activity through a mechanism involving displacement of the islet-enriched transcription factor MafA by the glucocorticoid receptor. The induction of G6PC2 promoter activity by Dex is modulated by a single nucleotide polymorphism, previously linked to altered FBG in humans, that affects FOXA2 binding. A 5-day repeated injection paradigm was used to examine the chronic effect of Dex on FBG and glucose tolerance in wild-type (WT) and G6pc2 knockout mice. Acute Dex treatment only induces G6pc2 expression in 129SvEv but not C57BL/6J mice, but this chronic treatment induced G6pc2 expression in both. In 6-hour fasted C57BL/6J WT mice, Dex treatment lowered FBG and improved glucose tolerance, with G6pc2 deletion exacerbating the decrease in FBG and enhancing the improvement in glucose tolerance. In contrast, in 24-hour fasted C57BL/6J WT mice, Dex treatment raised FBG but still improved glucose tolerance, with G6pc2 deletion limiting the increase in FBG and enhancing the improvement in glucose tolerance. These observations demonstrate that G6pc2 modulates the complex effects of Dex on both FBG and glucose tolerance.
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Affiliation(s)
- Kayla A Boortz
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - Kristen E Syring
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - Rebecca A Lee
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - Chunhua Dai
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - James K Oeser
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - Owen P McGuinness
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - Jen-Chywan Wang
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - Richard M O'Brien
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
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Boortz KA, Syring KE, Dai C, Pound LD, Oeser JK, Jacobson DA, Wang JC, McGuinness OP, Powers AC, O'Brien RM. G6PC2 Modulates Fasting Blood Glucose In Male Mice in Response to Stress. Endocrinology 2016; 157:3002-8. [PMID: 27300767 PMCID: PMC4967123 DOI: 10.1210/en.2016-1245] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The glucose-6-phosphatase catalytic 2 (G6PC2) gene is expressed specifically in pancreatic islet beta cells. Genome-wide association studies have shown that single nucleotide polymorphisms in the G6PC2 gene are associated with variations in fasting blood glucose (FBG) but not fasting plasma insulin. Molecular analyses examining the functional effects of these single nucleotide polymorphisms demonstrate that elevated G6PC2 expression is associated with elevated FBG. Studies in mice complement these genome-wide association data and show that deletion of the G6pc2 gene lowers FBG without affecting fasting plasma insulin. This suggests that, together with glucokinase, G6PC2 forms a substrate cycle that determines the glucose sensitivity of insulin secretion. Because genome-wide association studies and mouse studies demonstrate that elevated G6PC2 expression raises FBG and because chronically elevated FBG is detrimental to human health, increasing the risk of type 2 diabetes, it is unclear why G6PC2 evolved. We show here that the synthetic glucocorticoid dexamethasone strongly induces human G6PC2 promoter activity and endogenous G6PC2 expression in isolated human islets. Acute treatment with dexamethasone selectively induces endogenous G6pc2 expression in 129SvEv but not C57BL/6J mouse pancreas and isolated islets. The difference is due to a single nucleotide polymorphism in the C57BL/6J G6pc2 promoter that abolishes glucocorticoid receptor binding. In 6-hour fasted, nonstressed 129SvEv mice, deletion of G6pc2 lowers FBG. In response to the stress of repeated physical restraint, which is associated with elevated plasma glucocorticoid levels, G6pc2 gene expression is induced and the difference in FBG between wild-type and knockout mice is enhanced. These data suggest that G6PC2 may have evolved to modulate FBG in response to stress.
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Affiliation(s)
- Kayla A Boortz
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., L.D.P., J.K.O., D.A.J., O.P.M., R.M.O.) and Medicine (C.D., A.C.P.), Vanderbilt University School of Medicine, and VA Tennessee Valley Healthcare System (A.C.P.), Nashville, Tennessee 37232-0615; and Department of Nutritional Sciences and Toxicology (J.-C.W.), University of California, Berkeley, Berkeley, California 94720-3104
| | - Kristen E Syring
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., L.D.P., J.K.O., D.A.J., O.P.M., R.M.O.) and Medicine (C.D., A.C.P.), Vanderbilt University School of Medicine, and VA Tennessee Valley Healthcare System (A.C.P.), Nashville, Tennessee 37232-0615; and Department of Nutritional Sciences and Toxicology (J.-C.W.), University of California, Berkeley, Berkeley, California 94720-3104
| | - Chunhua Dai
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., L.D.P., J.K.O., D.A.J., O.P.M., R.M.O.) and Medicine (C.D., A.C.P.), Vanderbilt University School of Medicine, and VA Tennessee Valley Healthcare System (A.C.P.), Nashville, Tennessee 37232-0615; and Department of Nutritional Sciences and Toxicology (J.-C.W.), University of California, Berkeley, Berkeley, California 94720-3104
| | - Lynley D Pound
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., L.D.P., J.K.O., D.A.J., O.P.M., R.M.O.) and Medicine (C.D., A.C.P.), Vanderbilt University School of Medicine, and VA Tennessee Valley Healthcare System (A.C.P.), Nashville, Tennessee 37232-0615; and Department of Nutritional Sciences and Toxicology (J.-C.W.), University of California, Berkeley, Berkeley, California 94720-3104
| | - James K Oeser
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., L.D.P., J.K.O., D.A.J., O.P.M., R.M.O.) and Medicine (C.D., A.C.P.), Vanderbilt University School of Medicine, and VA Tennessee Valley Healthcare System (A.C.P.), Nashville, Tennessee 37232-0615; and Department of Nutritional Sciences and Toxicology (J.-C.W.), University of California, Berkeley, Berkeley, California 94720-3104
| | - David A Jacobson
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., L.D.P., J.K.O., D.A.J., O.P.M., R.M.O.) and Medicine (C.D., A.C.P.), Vanderbilt University School of Medicine, and VA Tennessee Valley Healthcare System (A.C.P.), Nashville, Tennessee 37232-0615; and Department of Nutritional Sciences and Toxicology (J.-C.W.), University of California, Berkeley, Berkeley, California 94720-3104
| | - Jen-Chywan Wang
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., L.D.P., J.K.O., D.A.J., O.P.M., R.M.O.) and Medicine (C.D., A.C.P.), Vanderbilt University School of Medicine, and VA Tennessee Valley Healthcare System (A.C.P.), Nashville, Tennessee 37232-0615; and Department of Nutritional Sciences and Toxicology (J.-C.W.), University of California, Berkeley, Berkeley, California 94720-3104
| | - Owen P McGuinness
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., L.D.P., J.K.O., D.A.J., O.P.M., R.M.O.) and Medicine (C.D., A.C.P.), Vanderbilt University School of Medicine, and VA Tennessee Valley Healthcare System (A.C.P.), Nashville, Tennessee 37232-0615; and Department of Nutritional Sciences and Toxicology (J.-C.W.), University of California, Berkeley, Berkeley, California 94720-3104
| | - Alvin C Powers
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., L.D.P., J.K.O., D.A.J., O.P.M., R.M.O.) and Medicine (C.D., A.C.P.), Vanderbilt University School of Medicine, and VA Tennessee Valley Healthcare System (A.C.P.), Nashville, Tennessee 37232-0615; and Department of Nutritional Sciences and Toxicology (J.-C.W.), University of California, Berkeley, Berkeley, California 94720-3104
| | - Richard M O'Brien
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., L.D.P., J.K.O., D.A.J., O.P.M., R.M.O.) and Medicine (C.D., A.C.P.), Vanderbilt University School of Medicine, and VA Tennessee Valley Healthcare System (A.C.P.), Nashville, Tennessee 37232-0615; and Department of Nutritional Sciences and Toxicology (J.-C.W.), University of California, Berkeley, Berkeley, California 94720-3104
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Baerenwald DA, Bonnefond A, Bouatia-Naji N, Flemming BP, Umunakwe OC, Oeser JK, Pound LD, Conley NL, Cauchi S, Lobbens S, Eury E, Balkau B, Lantieri O, Dadi PK, Jacobson DA, Froguel P, O’Brien RM. Multiple functional polymorphisms in the G6PC2 gene contribute to the association with higher fasting plasma glucose levels. Diabetologia 2013; 56:1306-16. [PMID: 23508304 PMCID: PMC4106008 DOI: 10.1007/s00125-013-2875-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Accepted: 01/28/2013] [Indexed: 01/14/2023]
Abstract
AIMS/HYPOTHESIS We previously identified the G6PC2 locus as a strong determinant of fasting plasma glucose (FPG) and showed that a common G6PC2 intronic single nucleotide polymorphism (SNP) (rs560887) and two common G6PC2 promoter SNPs (rs573225 and rs13431652) are highly associated with FPG. However, these promoter SNPs have complex effects on G6PC2 fusion gene expression, and our data suggested that only rs13431652 is a potentially causative SNP. Here we examine the effect of rs560887 on G6PC2 pre-mRNA splicing and the contribution of an additional common G6PC2 promoter SNP, rs2232316, to the association signal. METHODS Minigene analyses were used to characterise the effect of rs560887 on G6PC2 pre-mRNA splicing. Fusion gene and gel retardation analyses characterised the effect of rs2232316 on G6PC2 promoter activity and transcription factor binding. The genetic association of rs2232316 with FPG variation was assessed using regression adjusted for age, sex and BMI in 4,220 Europeans with normal FPG. RESULTS The rs560887-G allele was shown to enhance G6PC2 pre-mRNA splicing, whereas the rs2232316-A allele enhanced G6PC2 transcription by promoting Foxa2 binding. Genetic analyses provide evidence for association of the rs2232316-A allele with increased FPG (β = 0.04 mmol/l; p = 4.3 × 10(-3)) as part of the same signal as rs560887, rs573225 and rs13431652. CONCLUSIONS/INTERPRETATION As with rs13431652, the in situ functional data with rs560887 and rs2232316 are in accord with the putative function of G6PC2 in pancreatic islets, and suggest that all three are potentially causative SNPs that contribute to the association between G6PC2 and FPG.
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Affiliation(s)
- D. A. Baerenwald
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 37232 Nashville, Tennessee, USA
| | - A. Bonnefond
- CNRS-UMR-8199, Institut Pasteur de Lille, F-59019, Lille, France
- University Lille Nord de France, F-59019 Lille, France
| | - N. Bouatia-Naji
- CNRS-UMR-8199, Institut Pasteur de Lille, F-59019, Lille, France
- University Lille Nord de France, F-59019 Lille, France
- INSERM U970, Paris Cardiovascular Research Center PARCC, 56 rue Leblanc, F-75015 Paris, France
| | - B. P. Flemming
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 37232 Nashville, Tennessee, USA
| | - O. C. Umunakwe
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 37232 Nashville, Tennessee, USA
| | - J. K. Oeser
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 37232 Nashville, Tennessee, USA
| | - L. D. Pound
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 37232 Nashville, Tennessee, USA
| | - N. L. Conley
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 37232 Nashville, Tennessee, USA
| | - S. Cauchi
- CNRS-UMR-8199, Institut Pasteur de Lille, F-59019, Lille, France
- University Lille Nord de France, F-59019 Lille, France
| | - S. Lobbens
- CNRS-UMR-8199, Institut Pasteur de Lille, F-59019, Lille, France
- University Lille Nord de France, F-59019 Lille, France
| | - E. Eury
- CNRS-UMR-8199, Institut Pasteur de Lille, F-59019, Lille, France
- University Lille Nord de France, F-59019 Lille, France
| | - B. Balkau
- INSERM, Centre for research in Epidemiology and Population Health (CESP), U1018, Epidemiology of diabetes, obesity and chronic renal disease over the lifecourse, F-94807, Villejuif, France
- Université Paris-Sud 11, UMRS 1018, F-94807 Villejuif, France
| | - O. Lantieri
- Institut inter-régional pour la santé (IRSA), F-37521 La Riche, France
| | - MAGIC Investigators
- Meta-Analysis of Glucose and Insulin related traits Consortium Investigators (http://www.magicinvestigators.org/)
| | - P. K. Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 37232 Nashville, Tennessee, USA
| | - D. A. Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 37232 Nashville, Tennessee, USA
| | - P. Froguel
- CNRS-UMR-8199, Institut Pasteur de Lille, F-59019, Lille, France
- University Lille Nord de France, F-59019 Lille, France
- Department of Genomics of Common Disease, School of Public Health, Imperial College London, W12 0NN London, UK
| | - R. M. O’Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 37232 Nashville, Tennessee, USA
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Bennett KA, Forsyth L, Burchell A. Functional analysis of the 5' flanking region of the human G6PC3 gene: regulation of promoter activity by glucose, pyruvate, AMP kinase and the pentose phosphate pathway. Mol Genet Metab 2011; 103:254-61. [PMID: 21474354 DOI: 10.1016/j.ymgme.2011.03.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/06/2011] [Revised: 03/11/2011] [Accepted: 03/11/2011] [Indexed: 10/18/2022]
Abstract
G6PC3 is a widely expressed isoform of glucose-6-phosphatase, found in many foetal and adult tissues. Mutations in this gene cause developmental abnormalities and severe neutropenia due to abolition of glucose recycling between the cytoplasm and endoplasmic reticulum. Low G6PC3 expression as a result of promoter polymorphisms or dysregulation could produce similar outcomes. Here we investigated the regulation of human G6PC3 promoter activity. HeLa and H4IIE cells were transiently transfected with G6PC3 promoter coupled to the firefly luciferase gene, and promoter activity was measured by dual luciferase assay. Activity was highest in a 453 bp segment of the G6PC3 promoter, from -455 to -3 relative to the transcriptional start site. This promoter was unresponsive to glucostatic hormones. Its activity increased significantly between 1 and 5.5 mM glucose, and was not elevated further by glucose concentrations up to 25 mM. Pyruvate increased its activity, but β-hydroxybutyrate and sodium acetate did not. Promoter activity was reduced by inhibitors of hexokinase, glyceraldehyde phosphate dehydrogenase and the oxidative branch of the pentose phosphate pathway, but not by a transketolase inhibitor. Deletion of two adjacent Enhancer-boxes (-274 to -279 and -299 to -304) reduced promoter activity and abolished the glucose effect, suggesting they could function as a glucose response element. Deletion of an additional downstream 140 bp (-140 to -306) restored activity, but not the glucose response, suggesting the presence of repressor elements in this region. 5-Aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR) reduced promoter activity, showing dependence on AMP-kinase. Regulation of the G6PC3 promoter is thus radically different to that of the hepatic isoform, G6PC. It is sensitive to carbohydrate, but not to fatty acid metabolites, and at much lower physiological concentrations. Based on these findings, we speculate that reduced G6PC3 expression could occur during hypoglycemic episodes in vivo, which are common in utero and in the postnatal period. If such episodes lower G6PC3 expression they could place the foetus or infant at risk of impaired immune function and development, and this possibility requires further examination both in vitro and in vivo.
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Affiliation(s)
- Kimberley Ann Bennett
- Maternal and Child Health Sciences, Ninewells Hospital and Medical School, University of Dundee, Dundee, DD1 9SY, UK.
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10
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The pancreatic islet β-cell-enriched transcription factor Pdx-1 regulates Slc30a8 gene transcription through an intronic enhancer. Biochem J 2011; 433:95-105. [PMID: 20942803 DOI: 10.1042/bj20101488] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The SLC30A8 gene encodes the zinc transporter ZnT-8, which provides zinc for insulin-hexamer formation. Genome-wide association studies have shown that a polymorphic variant in SLC30A8 is associated with altered susceptibility to Type 2 diabetes and we recently reported that glucose-stimulated insulin secretion is decreased in islets isolated from Slc30a8-knockout mice. The present study examines the molecular basis for the islet-specific expression of Slc30a8. VISTA analyses identified two conserved regions in Slc30a8 introns 2 and 3, designated enhancers A and B respectively. Transfection experiments demonstrated that enhancer B confers elevated fusion gene expression in both βTC-3 cells and αTC-6 cells. In contrast, enhancer A confers elevated fusion gene expression selectively in βTC-3 and not αTC-6 cells. These data suggest that enhancer A is an islet β-cell-specific enhancer and that the mechanisms controlling Slc30a8 expression in α- and β-cells are overlapping, but distinct. Gel retardation and ChIP (chromatin immunoprecipitation) assays revealed that the islet-enriched transcription factor Pdx-1 binds enhancer A in vitro and in situ respectively. Mutation of two Pdx-1-binding sites in enhancer A markedly reduces fusion gene expression suggesting that this factor contributes to Slc30a8 expression in β-cells, a conclusion consistent with developmental studies showing that restriction of Pdx-1 to pancreatic islet β-cells correlates with the induction of Slc30a8 gene expression and ZnT-8 protein expression in vivo.
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Artner I, Hang Y, Mazur M, Yamamoto T, Guo M, Lindner J, Magnuson MA, Stein R. MafA and MafB regulate genes critical to beta-cells in a unique temporal manner. Diabetes 2010; 59:2530-9. [PMID: 20627934 PMCID: PMC3279542 DOI: 10.2337/db10-0190] [Citation(s) in RCA: 182] [Impact Index Per Article: 13.0] [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 Several transcription factors are essential to pancreatic islet β-cell development, proliferation, and activity, including MafA and MafB. However, MafA and MafB are distinct from others in regard to temporal and islet cell expression pattern, with β-cells affected by MafB only during development and exclusively by MafA in the adult. Our aim was to define the functional relationship between these closely related activators to the β-cell. RESEARCH DESIGN AND METHODS The distribution of MafA and MafB in the β-cell population was determined immunohistochemically at various developmental and perinatal stages in mice. To identify genes regulated by MafB, microarray profiling was performed on wild-type and MafB(-/-) pancreata at embryonic day 18.5, with candidates evaluated by quantitative RT-PCR and in situ hybridization. The potential role of MafA in the expression of verified targets was next analyzed in adult islets of a pancreas-wide MafA mutant (termed MafA(ΔPanc)). RESULTS MafB was produced in a larger fraction of β-cells than MafA during development and found to regulate potential effectors of glucose sensing, hormone processing, vesicle formation, and insulin secretion. Notably, expression from many of these genes was compromised in MafA(ΔPanc) islets, suggesting that MafA is required to sustain expression in adults. CONCLUSIONS Our results provide insight into the sequential manner by which MafA and MafB regulate islet β-cell formation and maturation.
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Affiliation(s)
- Isabella Artner
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
- Lund Center for Stem Cell Biology and Cell Therapy, Lund University, Lund, Sweden
- Corresponding authors: Roland Stein, , and Isabella Artner,
| | - Yan Hang
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Magdalena Mazur
- Lund Center for Stem Cell Biology and Cell Therapy, Lund University, Lund, Sweden
| | - Tsunehiko Yamamoto
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Min Guo
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Jill Lindner
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
- Center for Stem Cell Biology, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Mark A. Magnuson
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
- Center for Stem Cell Biology, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Roland Stein
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
- Corresponding authors: Roland Stein, , and Isabella Artner,
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12
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Bouatia-Naji N, Bonnefond A, Baerenwald DA, Marchand M, Bugliani M, Marchetti P, Pattou F, Printz RL, Flemming BP, Umunakwe OC, Conley NL, Vaxillaire M, Lantieri O, Balkau B, Marre M, Lévy-Marchal C, Elliott P, Jarvelin MR, Meyre D, Dina C, Oeser JK, Froguel P, O'Brien RM. Genetic and functional assessment of the role of the rs13431652-A and rs573225-A alleles in the G6PC2 promoter that are strongly associated with elevated fasting glucose levels. Diabetes 2010; 59:2662-71. [PMID: 20622168 PMCID: PMC3279535 DOI: 10.2337/db10-0389] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
OBJECTIVE Genome-wide association studies have identified a single nucleotide polymorphism (SNP), rs560887, located in a G6PC2 intron that is highly correlated with variations in fasting plasma glucose (FPG). G6PC2 encodes an islet-specific glucose-6-phosphatase catalytic subunit. This study examines the contribution of two G6PC2 promoter SNPs, rs13431652 and rs573225, to the association signal. RESEARCH DESIGN AND METHODS We genotyped 9,532 normal FPG participants (FPG <6.1 mmol/l) for three G6PC2 SNPs, rs13431652 (distal promoter), rs573225 (proximal promoter), rs560887 (3rd intron). We used regression analyses adjusted for age, sex, and BMI to assess the association with FPG and haplotype analyses to assess comparative SNP contributions. Fusion gene and gel retardation analyses characterized the effect of rs13431652 and rs573225 on G6PC2 promoter activity and transcription factor binding. RESULTS Genetic analyses provide evidence for a strong contribution of the promoter SNPs to FPG variability at the G6PC2 locus (rs13431652: β = 0.075, P = 3.6 × 10(-35); rs573225 β = 0.073 P = 3.6 × 10(-34)), in addition to rs560887 (β = 0.071, P = 1.2 × 10(-31)). The rs13431652-A and rs573225-A alleles promote increased NF-Y and Foxa2 binding, respectively. The rs13431652-A allele is associated with increased FPG and elevated promoter activity, consistent with the function of G6PC2 in pancreatic islets. In contrast, the rs573225-A allele is associated with elevated FPG but reduced promoter activity. CONCLUSIONS Genetic and in situ functional data support a potential role for rs13431652, but not rs573225, as a causative SNP linking G6PC2 to variations in FPG, though a causative role for rs573225 in vivo cannot be ruled out.
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Affiliation(s)
- Nabila Bouatia-Naji
- CNRS-UMR-8199, Institut Pasteur de Lille, Lille, France
- University Lille Nord de France, Lille, France
| | - Amélie Bonnefond
- CNRS-UMR-8199, Institut Pasteur de Lille, Lille, France
- University Lille Nord de France, Lille, France
| | - Devin A. Baerenwald
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Marion Marchand
- CNRS-UMR-8199, Institut Pasteur de Lille, Lille, France
- University Lille Nord de France, Lille, France
| | - Marco Bugliani
- Department of Endocrinology and Metabolism, University of Pisa, Pisa, Italy
| | - Piero Marchetti
- Department of Endocrinology and Metabolism, University of Pisa, Pisa, Italy
| | - François Pattou
- INSERM U859, Université de Lille-Nord de France, Centre Hospitalier Regional et Universitaire de Lille, Lille, France
| | - Richard L. Printz
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Brian P. Flemming
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Obi C. Umunakwe
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Nicholas L. Conley
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Martine Vaxillaire
- CNRS-UMR-8199, Institut Pasteur de Lille, Lille, France
- University Lille Nord de France, Lille, France
| | | | | | - Michel Marre
- Department of Endocrinology, Diabetology and Nutrition, Bichat-Claude Bernard University Hospital, Assistance Publique des Hôpitaux de Paris, Paris, France; INSERM U695, Université Paris 7, Paris, France
| | - Claire Lévy-Marchal
- INSERM U690, Robert Debré Hospital, Paris; Paris Diderot University, Paris, France
| | - Paul Elliott
- Department of Epidemiology and Public Health, Imperial College London, London, U.K
| | - Marjo-Riitta Jarvelin
- Department of Epidemiology and Public Health, Imperial College London, London, U.K
- Institute of Health Sciences, University of Oulu, Department of Child and Adolescent Health, National Public Health Institute, Biocenter Oulu, University of Oulu, Oulu, Finland
| | - David Meyre
- CNRS-UMR-8199, Institut Pasteur de Lille, Lille, France
- University Lille Nord de France, Lille, France
| | - Christian Dina
- CNRS-UMR-8199, Institut Pasteur de Lille, Lille, France
- University Lille Nord de France, Lille, France
| | - James K. Oeser
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Philippe Froguel
- CNRS-UMR-8199, Institut Pasteur de Lille, Lille, France
- University Lille Nord de France, Lille, France
- Department of Genomics of Common Disease, School of Public Health, Imperial College London, London, U.K
| | - Richard M. O'Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
- Corresponding author: Richard M. O'Brien,
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A retrospective review of the roles of multifunctional glucose-6-phosphatase in blood glucose homeostasis: Genesis of the tuning/retuning hypothesis. Life Sci 2010; 87:339-49. [PMID: 20603134 DOI: 10.1016/j.lfs.2010.06.021] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2010] [Revised: 05/20/2010] [Accepted: 06/29/2010] [Indexed: 01/30/2023]
Abstract
In a scientific career spanning from 1955 to 2000, my research focused on phosphoenolpyruvate carboxykinase and glucose-6-phosphatase. Grounded in basic enzymology, and initially pursuing the steady-state rate behavior of isolated preparations of these critically important gluconeogenic enzymes, our key findings were confirmed and extended by in situ enzyme rate experiments exploiting isolated liver perfusions. These efforts culminated in the discovery of the liver cytosolic isozyme of carboxykinase, known today as (GTP)PEPCK-C (EC4.1.1.32) and also revealed a biosynthetic function and multicomponent nature of glucose-6-phosphatase (EC3.1.3.9). Discovery that glucose-6-phosphatase possessed an intrinsically biosynthetic activity, now known as carbamyl-P:glucose phosphotransferase - along with a deeper consideration of the enzyme's hydrolytic activity as well as the action of liver glucokinase resulted in the evolution of Tuning/Retuning Hypothesis for blood glucose homeostasis in health and disease. This THEN & NOW review shares with the reader the joy and exhilaration of major scientific discovery and also contrasts the methodologies and approaches on which I relied with those currently in use.
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14
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Abstract
Glucose-6-phosphatase catalyzes the hydrolysis of glucose 6-phosphate (G6P) to glucose and inorganic phosphate. It is a multicomponent system located in the endoplasmic reticulum that comprises several integral membrane proteins, namely a catalytic subunit (G6PC) and transporters for G6P, inorganic phosphate, and glucose. The G6PC gene family contains three members, designated G6PC, G6PC2, and G6PC3. The tissue-specific expression patterns of these genes differ, and mutations in all three genes have been linked to distinct diseases in humans. This minireview discusses the disease association and transcriptional regulation of the G6PC genes as well as the biological functions of the encoded proteins.
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Affiliation(s)
- John C Hutton
- Barbara Davis Center for Childhood Diabetes, University of Colorado at Denver, Aurora, Colorado 80045, USA
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15
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Dos Santos C, Bougnères P, Fradin D. A single-nucleotide polymorphism in a methylatable Foxa2 binding site of the G6PC2 promoter is associated with insulin secretion in vivo and increased promoter activity in vitro. Diabetes 2009; 58:489-92. [PMID: 18984742 PMCID: PMC2628624 DOI: 10.2337/db08-0587] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
OBJECTIVE The G6PC2 gene encoding islet-specific glucose-6-phosphatase related protein (IGRP) has a common promoter variant, rs573225 (-231G/A), located within a Foxa binding site. We tested the cis-regulatory effects of rs573225 on promoter activity and its association with insulin response to oral glucose. RESEARCH DESIGN AND METHODS Functional effects of rs573225 were explored in transfected INS-1 and HIT-T beta-cell lines. A total of 734 young obese subjects of European ancestry were genotyped for rs573225. Insulin and glucose levels were measured in response to oral glucose, and the insulinogenic index (IGI) of insulin secretion was calculated. RESULTS In vitro, the G allele showed a higher affinity for binding Foxa2 transcription factor and increased G6PC2 promoter activity. Foxa2 binding is modified if the C adjacent to the G allele is methylated. IGI was associated with rs573225 by linear regression analysis and was 30% greater in AA or AG than in GG obese children. rs573225 was also associated with fasting glucose. CONCLUSIONS rs573225 is a functional cis-regulatory (epi)-single-nucleotide polymorphism (SNP) of G6PC2 associated with glucose-insulin homeostasis in obese children, likely to explain the results of recent genome-wide association studies in nondiabetic adults.
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Affiliation(s)
- Christine Dos Santos
- Department of Pediatric Endocrinology and U561 Institut National de Santé et de Recherche Médicale, Hôpital Saint-Vincent de Paul, Paris, France
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