Regulation of pancreas duodenum homeobox-1 expression by early growth response-1.
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.
Eto
Kazuhiro
K
Laboratory of Molecular Endocrinology and Diabetes Unit, Massachusetts General Hospital, and Harvard Medical School, Boston, Massachusetts 02114, USA.
Kaur
Varinderpal
V
Thomas
Melissa K
MK
D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D004386:Duodenum / Q000378:metabolism; D051766:Early Growth Response Protein 1 / Q000378:metabolism / Q000502:physiology*; D005786:Gene Expression Regulation; D005801:Genes, Homeobox; D018398:Homeodomain Proteins / Q000235:genetics*; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D051379:Mice; D016296:Mutagenesis; D010179:Pancreas / Q000378:metabolism; D011401:Promoter Regions, Genetic; D051381:Rats; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics; D015533:Transcriptional Activation; D014162:Transfection
D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; D018398:Homeodomain Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C084010:pancreatic and duodenal homeobox 1 protein