Regulation of Pancreas Duodenum Homeobox-1 Expression by Early Growth Response-1

Kazuhiro Eto,Varinderpal Kaur,Melissa K Thomas

doi:10.1074/jbc.m607288200

Kazuhiro Eto, Varinderpal Kaur + Show 1 more

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https://doi.org/10.1074/jbc.m607288200

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Abstract

The homeodomain transcription factor pancreas duodenum homeobox-1 (PDX-1) is a key regulator of pancreatic beta-cell development, function, and survival. Deficits in PDX-1 expression result in insulin deficiency and hyperglycemia. We previously found that the glucose-responsive transcription factor early growth response-1 (Egr-1) activates the insulin promoter in part by increasing expression levels of PDX-1. We now report that Egr-1 binds and activates multiple regulatory sites within the pdx-1 promoter. We identified consensus Egr-1 recognition sequences within proximal and distal regions of the mouse pdx-1 promoter and demonstrated specific binding of Egr-1 by chromatin immunoprecipitation and electrophoretic mobility shift assays. Overexpression of Egr-1 increased transcriptional activation of the -4500 proximal pdx-1 promoter and of the highly conserved regulatory Areas I, II, and III. Mutagenesis of a specific Egr-1 binding site within Area III substantially decreased Egr-1-mediated activation. Egr-1 increased the transcriptional activation of Areas I and II, despite the absence of Egr-1 recognition sequences within this promoter segment, suggesting that Egr-1 also can regulate the pdx-1 promoter indirectly. Egr-1 increased, and a dominant-negative Egr-1 mutant repressed, the transcriptional activation of distal pdx-1 promoter sequences. Mutagenesis of a specific Egr-1 binding site within regulatory Area IV reduced basal and Egr-1-mediated transcriptional activation. Our data indicate that Egr-1 regulates expression of PDX-1 in pancreatic beta-cells by both direct and indirect activation of the pdx-1 promoter. We propose that Egr-1 expression levels may act as a sensor in pancreatic beta-cells to translate extracellular signals into changes in PDX-1 expression levels and pancreatic beta-cell function.

Highlights

MARCH 2, 2007 VOLUME 282 NUMBER 9 ment of the pancreas in the embryo and of insulin production and glucose homeostasis in the adult
We recently demonstrated that early growth response-1 (Egr-1), a zinc finger transcription factor that is known as zif268, NGFI-A, Krox24, and TIS8, regulates pancreas duodenum homeobox-1 (PDX-1) expression levels in clonal pancreatic ␤-cells [31]
Our results indicate that changes in Egr-1 expression levels influence the transcriptional activation of both proximal and distal regulatory segments of the mouse pdx-1 promoter

Summary

Introduction

MARCH 2, 2007 VOLUME 282 NUMBER 9 ment of the pancreas in the embryo and of insulin production and glucose homeostasis in the adult. In ChIP assays, we immunoprecipitated proximal pdx-1 promoter regulatory segments encompassing Area III within mouse genomic DNA derived from MIN6 cells with anti-Egr1 antibodies but not with negative control immunoglobulin IgG (Fig. 2D, upper panel).

Results

Conclusion