HEPATOCYTE NUCLEAR FACTOR-1α INHIBITS INSULIN PROMOTER FACTOR 1-DEPENDENT TRANSACTIVATION OF THE HUMAN INSULIN GENE

To investigate the regulational interaction of hepatocyte nuclear factor-1α (HNF-1α) and insulin promoter factor 1 (IPF1) on insulin gene expression, either or both of the expression vectors carrying each transcription factor were transiently transfected into HeLa cells, RINm5F cells and MIN6 cells together with the luciferase reporter construct driven by a human preproinsulin gene promoter (−1998 to +237) designated as pINS-1998/luc. IPF1-transfection into HeLa cells strongly stimulated the luciferase activity to 725 fold that of the basal level. In contrast, HNF-1α-transfection resulted in only a 6.7 fold increase. In co-transfection experiments, increasing the amount of HNF-1α resulted in an 84.5% and 74.4% decrease in IPF1-stimulated luciferase activity in HeLa and RINm5F cells, respectively. Deletion constructs designated as pINS-248/luc, pINS-213/luc and pINS-185/luc were transfected into RINm5F cells to determine the role of the A3 element and its 5′ flanking sequence in the inhibitory effect of HN...