Upstream stimulatory factor regulates Pdx-1 gene expression in differentiated pancreatic beta-cells.
The homeobox gene Pdx-1 plays a key role in the development of the pancreas. In the adult, however, expression of the Pdx-1 gene is restricted to pancreatic beta-cells and endocrine cells of duodenal epithelium. Recently, the transcription factor, upstream stimulatory factor (USF), has been shown to bind in vitro to a mutationally sensitive E-box motif within the 5'-flanking region of the Pdx-1 gene [Sharma, Leonard, Lee, Chapman, Leiter and Montminy (1996) J. Biol. Chem. 271, 2294-2299]. In the present study, we show that USF not only binds to the Pdx-1 gene promoter but also functionally regulates the expression of the Pdx-1 gene in differentiated pancreatic beta-cells. Adenovirus-mediated overexpression of a dominant negative form of USF2 decreased binding of endogenous USF to the E-box element by approximately 90%. This reduction in endogenous USF binding led to a greater than 50% decrease in Pdx-1 gene promoter activity, which, in turn, resulted in marked reductions in Pdx-1 mRNA and protein levels. Importantly, the lower Pdx-1 protein levels led to a greater than 50% reduction in Pdx-1 binding activity to the A3 element on the insulin gene promoter, and a significant reduction in insulin mRNA levels. Overall, our results show that USF functionally regulates Pdx-1 gene expression in differentiated pancreatic beta-cells and provide the first functional data for a role of USF in the regulation of a normal cellular gene.
Qian
J
J
Department of Physiology, Michigan State University, 214 Giltner Hall, East Lansing, MI 48824, USA.
Kaytor
E N
EN
Towle
H C
HC
Olson
L K
LK
D000818:Animals; D002478:Cells, Cultured; D004268:DNA-Binding Proteins; D005786:Gene Expression Regulation; D018398:Homeodomain Proteins; D006801:Humans; D007328:Insulin / Q000502:physiology*; D007515:Islets of Langerhans / Q000502:physiology*; D011401:Promoter Regions, Genetic; D015534:Trans-Activators / Q000096:biosynthesis / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*; D014162:Transfection; D051720:Upstream Stimulatory Factors
D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D007328:Insulin; D015534:Trans-Activators; D014157:Transcription Factors; C497181:USF1 protein, human; C497184:USF2 protein, human; D051720:Upstream Stimulatory Factors; C084010:pancreatic and duodenal homeobox 1 protein