scholarly journals Regulation of Insulin Gene Transcription by the Immediate-Early Growth Response Gene Egr-1

Endocrinology ◽  
2006 ◽  
Vol 147 (6) ◽  
pp. 2923-2935 ◽  
Author(s):  
Kazuhiro Eto ◽  
Varinderpal Kaur ◽  
Melissa K. Thomas
Keyword(s):  
Transcriptional Activation ◽  
Growth Response ◽  
Insulin Gene ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Expression Levels ◽  
Promoter Sequences ◽  
Early Growth Response ◽  
Insulin Promoter ◽  
Insulin Gene Expression

Abstract Changes in extracellular glucose levels regulate the expression of the immediate-early response gene and zinc finger transcription factor early growth response-1 (Egr-1) in insulin-producing pancreatic β-cells, but key target genes of Egr-1 in the endocrine pancreas have not been identified. We found that overexpression of Egr-1 in clonal (INS-1) β-cells increased transcriptional activation of the rat insulin I promoter. In contrast, reductions in Egr-1 expression levels or function with the introduction of either small interfering RNA targeted to Egr-1 (siEgr-1) or a dominant-negative form of Egr-1 decreased insulin promoter activation, and siEgr-1 suppressed insulin gene expression. Egr-1 did not directly interact with insulin promoter sequences, and mutagenesis of a potential G box recognition sequence for Egr-1 did not impair the Egr-1 responsiveness of the insulin promoter, suggesting that regulation of insulin gene expression by Egr-1 is probably mediated through additional transcription factors. Overexpression of Egr-1 increased, and reduction of Egr-1 expression decreased, transcriptional activation of the glucose-responsive FarFlat minienhancer within the rat insulin I promoter despite the absence of demonstrable Egr-1-binding activity to FarFlat sequences. Notably, augmenting Egr-1 expression levels in insulin-producing cells increased the mRNA and protein expression levels of pancreas duodenum homeobox-1 (PDX-1), a major transcriptional regulator of glucose-responsive activation of the insulin gene. Increasing Egr-1 expression levels enhanced PDX-1 binding to insulin promoter sequences, whereas mutagenesis of PDX-1-binding sites reduced the capacity of Egr-1 to activate the insulin promoter. We propose that changes in Egr-1 expression levels in response to extracellular signals, including glucose, can regulate PDX-1 expression and insulin production in pancreatic β-cells.

scholarly journals Hedgehog Signaling Regulation of Homeodomain Protein Islet Duodenum Homeobox-1 Expression in Pancreatic β-Cells*

Endocrinology ◽  
2001 ◽  
Vol 142 (3) ◽  
pp. 1033-1040 ◽  
Author(s):  
Melissa K. Thomas ◽  
Jee H. Lee ◽  
Naina Rastalsky ◽  
Joel F. Habener
Keyword(s):  
Gene Expression ◽  
Transcriptional Activation ◽  
Gene Promoter ◽  
Insulin Gene ◽  
Reporter Construct ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Insulin Promoter ◽  
Insulin Gene Expression ◽  
Hh Signaling

Abstract Insulin gene expression in pancreatic β-cells is regulated by signals from developmental morphogen proteins known as hedgehogs (Hhs). By analyzing 5′-deletion insulin promoter-reporter constructs in transient transfections of clonal INS-1 β-cells, we located activating Hh-responsive regions within the rat insulin I promoter that include the glucose-response elements Far (E2) and Flat (A2/A3). Activation of Hh signaling in INS-1 cells by ectopic Hh expression increased (and inhibition of Hh signaling with the Hh-specific inhibitor cyclopamine decreased) transcriptional activation of a multimerized FarFlat enhancer-reporter construct. In DNA-binding studies, nuclear extracts from INS-1 cells activated by ectopic Hh expression increased (and extracts from INS-1 cells treated with cyclopamine decreased) protein binding to a radiolabeled FarFlat oligonucleotide probe. An antiserum directed against the transcription factor islet duodenum homeobox-1 (IDX-1), a regulator of pancreas development and activator of the insulin gene promoter, attenuated the binding activity of Hh-responsive protein complexes. Nuclear IDX-1 protein levels on Western blots were increased by ectopic Hh expression, thereby providing a mechanism for Hh-mediated regulation of the insulin promoter. Addition of cyclopamine to INS-1 cells decreased IDX-1 messenger RNA expression. In transient transfections of a− 4.5-kb mouse IDX-1 promoter-reporter construct, ectopic Hh expression increased (and cyclopamine administration decreased) transcriptional activation of the IDX-1 promoter in a dose-dependent manner. Thus, the IDX-1 gene is a direct regulatory target of Hh signaling in insulin-producing pancreatic β-cells. We propose that Hh signaling activates the insulin gene promoter indirectly via the direct activation of IDX-1 expression. Because IDX-1 gene expression is essential for insulin gene expression, pancreatic β-cell development, and normal glucose homeostasis, our findings that Hh signaling regulates IDX-1 expression in the endocrine pancreas suggest possible novel therapeutic approaches for diabetes mellitus.

scholarly journals MafA Stability in Pancreatic β Cells Is Regulated by Glucose and Is Dependent on Its Constitutive Phosphorylation at Multiple Sites by Glycogen Synthase Kinase 3

2007 ◽  
Vol 27 (19) ◽  
pp. 6593-6605 ◽  
Author(s):  
Song-iee Han ◽  
Shinsaku Aramata ◽  
Kunio Yasuda ◽  
Kohsuke Kataoka
Keyword(s):  
Gene Expression ◽  
Glycogen Synthase ◽  
Glucose Sensing ◽  
Insulin Gene ◽  
Glycogen Synthase Kinase ◽  
Glycogen Synthase Kinase 3 ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Amino Terminal ◽  
Insulin Gene Expression

ABSTRACT Regulation of insulin gene expression by glucose in pancreatic β cells is largely dependent on a cis-regulatory element, termed RIPE3b/C1, in the insulin gene promoter. MafA, a member of the Maf family of basic leucine zipper (bZip) proteins, is a β-cell-specific transcriptional activator that binds to the C1 element. Based on increased C1-binding activity, MafA protein levels appear to be up-regulated in response to glucose, but the underlying molecular mechanism for this is not well understood. In this study, we show evidence supporting that the amino-terminal region of MafA is phosphorylated at multiple sites by glycogen synthase kinase 3 (GSK3) in β cells. Mutational analysis of MafA and pharmacological inhibition of GSK3 in MIN6 β cells strongly suggest that the rate of MafA protein degradation is regulated by glucose, that MafA is constitutively phosphorylated by GSK3, and that phosphorylation is a prerequisite for rapid degradation of MafA under low-glucose conditions. Our data suggest a new glucose-sensing signaling pathway in islet β cells that regulates insulin gene expression through the regulation of MafA protein stability.

Blockage of ceramide metabolism exacerbates palmitate inhibition of pro-insulin gene expression in pancreatic β-cells

2010 ◽  
Vol 338 (1-2) ◽  
pp. 283-290 ◽  
Author(s):  
Jun Guo ◽  
YingYing Qian ◽  
XiaoXue Xi ◽  
XiaoHan Hu ◽  
JianXi Zhu ◽  
...  
Keyword(s):  
Gene Expression ◽  
Insulin Gene ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Insulin Gene Expression

Serum response factor expression is enriched in pancreatic β cells and regulates insulin gene expression

2011 ◽  
Vol 25 (8) ◽  
pp. 2592-2603 ◽  
Author(s):  
Aloke Sarkar ◽  
Mao Zhang ◽  
Shi‐He Liu ◽  
Swapna Sarkar ◽  
F. Charles Brunicardi ◽  
...  
Keyword(s):  
Gene Expression ◽  
Serum Response Factor ◽  
Insulin Gene ◽  
Response Factor ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Factor Expression ◽  
Insulin Gene Expression ◽  
Serum Response

scholarly journals Glucagon-like peptide-1 stimulates human insulin promoter activity in part through cAMP-responsive elements that lie upstream and downstream of the transcription start site

2005 ◽  
Vol 186 (2) ◽  
pp. 353-365 ◽  
Author(s):  
Colin W Hay ◽  
Elaine M Sinclair ◽  
Giovanna Bermano ◽  
Elaine Durward ◽  
Mohammad Tadayyon ◽  
...  
Keyword(s):  
Protein Binding ◽  
Human Insulin ◽  
Insulin Gene ◽  
Start Site ◽  
Β Cells ◽  
Transcription Start ◽  
Pancreatic Β Cells ◽  
Insulin Promoter ◽  
Glucagon Like Peptide ◽  
Glucagon Like Peptide 1

Glucagon-like peptide-1 (GLP-1) is a peptide hormone secreted from the enteroendocrine L-cells of the gut and which acts primarily to potentiate the effects of glucose on insulin secretion from pancreatic β-cells. It also stimulates insulin gene expression, proinsulin biosynthesis and affects the growth and differentiation of the islets of Langerhans. Previous studies on the mechanisms whereby GLP-1 regulates insulin gene transcription have focused on the rat insulin promoter. The aim of this study was to determine whether the human insulin promoter was also responsive to GLP-1, and if so to investigate the possible role of cAMP-responsive elements (CREs) that lie upstream (CRE1 and CRE2) and downstream (CRE3 and CRE4) of the transcription start site. INS-1 pancreatic β-cells were transfected with promoter constructs containing fragments of the insulin gene promoter placed upstream of the firefly luciferase reporter gene. GLP-1 was found to stimulate the human insulin promoter, albeit to a lesser degree than the rat insulin promoter. Mutagenesis of CRE2, CRE3 and CRE4 blocked the stimulatory effect of GLP-1 while mutagenesis of CRE1 had no effect. Analysis of nuclear protein binding to the four CREs showed that, while they share some proteins, each CRE site is unique. Stimulation of transcription by GLP-1 through CRE2, CRE3 and CRE4 resulted in altered protein binding that was different for each of the CRE sites involved. Collectively, these data show that the four human CREs are not simply multiple copies of the rat CRE site and further emphasise that the human insulin promoter is distinct from the rodent promoter.

scholarly journals PRMT4 is involved in insulin secretion via the methylation of histone H3 in pancreatic β cells

2015 ◽  
Vol 54 (3) ◽  
pp. 315-324 ◽  
Author(s):  
Joong Kwan Kim ◽  
Yongchul Lim ◽  
Jung Ok Lee ◽  
Young-Sun Lee ◽  
Nam Hee Won ◽  
...  
Keyword(s):  
Gene Expression ◽  
Insulin Secretion ◽  
High Glucose ◽  
Histone H3 ◽  
Insulin Gene ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Protein Arginine Methyltransferases ◽  
Insulin Synthesis ◽  
Insulin Gene Expression

The relationship between protein arginine methyltransferases (PRMTs) and insulin synthesis in β cells is not yet well understood. In the present study, we showed that PRMT4 expression was increased in INS-1 and HIT-T15 pancreatic β cells under high-glucose conditions. In addition, asymmetric dimethylation of Arg17 in histone H3 was significantly increased in both cell lines in the presence of glucose. The inhibition or knockdown of PRMT4 suppressed glucose-induced insulin gene expression in INS-1 cells by 81.6 and 79% respectively. Additionally, the overexpression of mutant PRMT4 also significantly repressed insulin gene expression. Consistently, insulin secretion induced in response to high levels of glucose was decreased by both PRMT4 inhibition and knockdown. Moreover, the inhibition of PRMT4 blocked high-glucose-induced insulin gene expression and insulin secretion in primary pancreatic islets. These results indicate that PRMT4 might be a key regulator of high-glucose-induced insulin secretion from pancreatic β cells via H3R17 methylation.

scholarly journals The Homeodomain of PDX-1 Mediates Multiple Protein-Protein Interactions in the Formation of a Transcriptional Activation Complex on the Insulin Promoter

2000 ◽  
Vol 20 (3) ◽  
pp. 900-911 ◽  
Author(s):  
Kinuko Ohneda ◽  
Raghavendra G. Mirmira ◽  
Juehu Wang ◽  
Jeffrey D. Johnson ◽  
Michael S. German
Keyword(s):  
Gene Transcription ◽  
Transcriptional Activation ◽  
Insulin Gene ◽  
Nuclear Proteins ◽  
Bhlh Protein ◽  
Homeodomain Protein ◽  
Β Cells ◽  
Activation Domains ◽  
Insulin Promoter ◽  
Insulin Gene Transcription

ABSTRACT Activation of insulin gene transcription specifically in the pancreatic β cells depends on multiple nuclear proteins that interact with each other and with sequences on the insulin gene promoter to build a transcriptional activation complex. The homeodomain protein PDX-1 exemplifies such interactions by binding to the A3/4 region of the rat insulin I promoter and activating insulin gene transcription by cooperating with the basic-helix-loop-helix (bHLH) protein E47/Pan1, which binds to the adjacent E2 site. The present study provides evidence that the homeodomain of PDX-1 acts as a protein-protein interaction domain to recruit multiple proteins, including E47/Pan1, BETA2/NeuroD1, and high-mobility group protein I(Y), to an activation complex on the E2A3/4 minienhancer. The transcriptional activity of this complex results from the clustering of multiple activation domains capable of interacting with coactivators and the basal transcriptional machinery. These interactions are not common to all homeodomain proteins: the LIM homeodomain protein Lmx1.1 can also activate the E2A3/4 minienhancer in cooperation with E47/Pan1 but does so through different interactions. Cooperation between Lmx1.1 and E47/Pan1 results not only in the aggregation of multiple activation domains but also in the unmasking of a potent activation domain on E47/Pan1 that is normally silent in non-β cells. While more than one activation complex may be capable of activating insulin gene transcription through the E2A3/4 minienhancer, each is dependent on multiple specific interactions among a unique set of nuclear proteins.

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