An indirect role for upstream stimulatory factor in glucose-mediated induction of pyruvate kinase and S14 gene expression.
Transcription of the L-type pyruvate kinase (L-PK) and S14 genes is induced in hepatocytes in response to increased glucose metabolism. The regulatory sequences of these genes responsible for induction by glucose have been mapped to related E-box containing motifs in the promoters. Similarly, L-PK promoter activity is stimulated in a differentiated pancreatic beta-cell line, INS-1, in response to elevated glucose. By mutational analysis, we demonstrate that the sequence requirements for glucose induction in the INS-1 cell are identical to those observed in the hepatocyte, suggesting that the same transcriptional factor(s) is responsible for regulation of L-PK expression in the two cell types. One nuclear factor that binds to the glucose regulatory sequences of both of these genes is the Upstream Stimulatory Factor (USF), a ubiquitous E-box binding protein. Mice deleted for the USF2 gene display a severely delayed response to carbohydrate feeding (Vallet et al. [26]). This observation, however, does not differentiate between a direct and an indirect role for USF in the process. To gain further insight into the possible involvement of USF in glucose signaling, we have used a recombinant adenoviral construct that expresses a dominant negative form of USF. This dominant negative can dimerize with endogenous USF and is shown to inhibit DNA binding of USF in hepatocytes and INS-1 cells. However, expression of the dominant negative USF did not block the ability of glucose to stimulate L-PK or S14 gene expression in hepatocytes or L-PK promoter activity in INS-1 cells. We conclude that USF does not act by binding to the glucose regulatory sequences of the S14 or L-PK genes and the role of USF in the process of glucose induction is indirect.
Kaytor
E N
EN
Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis 55455, USA.
Qian
J
J
Towle
H C
HC
Olson
L K
LK
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D002458:Cell Fractionation; D002460:Cell Line; D004268:DNA-Binding Proteins; D004790:Enzyme Induction; D005786:Gene Expression Regulation; D005822:Genetic Vectors; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology*; D007340:Insulinoma; D008297:Male; D009154:Mutation; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic / Q000235:genetics; D011506:Proteins / Q000235:genetics*; D011770:Pyruvate Kinase / Q000235:genetics* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020218:Response Elements / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured; D051720:Upstream Stimulatory Factors
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011506:Proteins; C051065:THRSP protein, human; C501478:Thrsp protein, rat; D014157:Transcription Factors; D051720:Upstream Stimulatory Factors; C497182:Usf1 protein, rat; C497187:Usf2 protein, rat; D011770:Pyruvate Kinase; D005947:Glucose