Glucose induces early growth response gene (Egr-1) expression in pancreatic beta cells

Abstract

Glucose homeostasis is maintained by beta cells of pancreatic islets through precisely regulated release of insulin from preformed granules. To maintain constant intracellular insulin stores while meeting wide physiological variations in demand, insulin synthesis is modulated in parallel with secretion rates [1]. Immediately following glucose stimulation, synthesis is primarily augmented through enhanced translation [2] and decreased degradation of existing insulin mRNAs [3]. Glucose also induces delayed responses that are manifested several hours after stimulation [4] by increasing insulin gene transcription [5] and expression of other genes involved in beta-cell function. Increased gene expression of glucose transporter 2 (GLUT-2) [6], pyruvate kinase [7], acetyl-coenzyme A-carboxylase [8], and 64 kDa glutamic acid decarboxylase (GAD65) [9] have been observed in primary rat islets in vitro and in rodent insulin-producing tumour cell lines following exposure to glucose. Together these changes comprise a delayed adaptive response that could be necessary to meet increased metabolic and secretory demands during extended or repeated periods of hyperglycaemia. Diabetologia (1999) Summary A copy deoxyribonucleic acid (cDNA) clone of the immediate early growth response gene, egr-1 (Krox-24, Zif268, NGFI-1), was isolated through subtractive hybridization screening to identify glucose-induced genes in pancreatic beta cells. Glucose rapidly and transiently induced egr-1 mRNA in the SV40-transformed murine beta-cell line, MIN6. Glucose also increased egr-1 mRNA expression in INS-1, bTC3 and RINm5F beta-cell lines, although with different kinetics. Expression of the 82 kDa Egr-1 protein was induced both in MIN6 cells stimulated with glucose in vitro and in primary rat islet cells stimulated in vivo or in vitro. This response is unique to beta cells since glucose did not affect egr-1 expression in NIH-3T3 fibroblasts or glucosesensitive hepatocytes. In beta cells egr-1 induction is specifically associated with insulin secretion, as it was not observed after stimulation with serum or insulin but was elicited by insulin secretagogues, including membrane depolarizing agents and cAMP agonists. Moreover, induction of egr-1 by glucose was inhibited by EDTA, indicating dependence on influx of extracellular Ca 2+. Other immediate early response genes, c-fos and junB, were also induced following glucose stimulation with kinetics similar to egr-1, whereas c-jun and junD expression were not affected. Since the zinc-finger protein encoded by egr-1 is highly homologous to transcription factors that control expression of glucose-regulated genes in yeast, Egr-1 could mediate delayed adaptive responses of beta cells to sustained glucose stimulation through transcriptional regulation. [Diabetologia (1999) 42: 195±203]

Upregulation of rat Ccnd1 gene by exendin-4 in pancreatic beta cell line INS-1: interaction of early growth response-1 with cis-regulatory element

“…In our experiments, the rapid and transient induction of EGR1 protein in response to exendin-4 ( Fig. 8a) was consistent with previous studies [9,34]. In addition, the time course of EGR1 protein induction was consistent with that of EGR1 binding to the radiolabelled oligo 5′ probe (Fig.…”

“…In pancreatic beta cells, the activator protein-1 (AP1) transcription factor consists of c-fos and c-Jun and is involved in the mitogenic signal for insulin receptor substrate [8]. Zif268, also known as EGR1, has been suggested to mediate beta cell growth as well as adaptive responses to sustained glucose stimulation [9]. Moreover, GLP-1 activates PI3-K and extracellular regulated kinase to induce target genes such as Fos (c-fos) Jun (c-Jun) and Egr1 (zif268), leading to beta cell proliferation [6,10].…”

Insulin expressed from endogenously active glucose-responsive EGR1 promoter in bone marrow mesenchymal stromal cells as diabetes therapy

“…There are similarities between our data and earlier data of Josefsen et al 9 of glucose-induced EGR1 mRNA in b-cells. These authors reported maximum glucosestimulated EGR1 expression within 30 min and a return to baseline 3 h after stimulation.…”

“…28,29 Indeed, high glucose upregulates EGR1 expression within minutes. 9 Overexpression of EGR1 activates insulin synthesis in b-cells indirectly by turning on PDX-1 expression, an effect mediated by EGR1 binding to the PDX-1 promoter. EGR1 thus lies upstream of PDX-1 in controlling insulin transcription.…”

Differential gene expression between Zucker Fatty rats and Zucker Diabetic Fatty rats: a potential role for the immediate-early gene Egr-1 in regulation of beta cell proliferation

“…We performed further studies on the immediate-early gene, Egr-1, which was down-regulated in ZDF islets, because other studies suggest it plays a role in the regulation of cell proliferation, differentiation and survival (Perez-Castillo et al 1993, Dinkel et al 1998, Thiel & Cibelli 2002, Pignatelli et al 2003 and it is induced by several insulin secretagogues in a calciumdependent manner (Josefsen et al 1999, Bernal-Mizrachi et al 2001. We show here that Egr-1 expression is strikingly enriched in islets and that its small interfering RNA (siRNA)-mediated silencing inhibits -cell proliferation.…”