Identification of upstream stimulatory factor as an activator of the human dipeptidyl peptidase IV gene in Caco-2 cells.

The 5' upstream region (-448/-443) of the human dipeptidyl peptidase IV gene promoter containing a consensus E-box (CACGTG) was shown to bind upstream stimulatory factor using nuclear extracts from mouse (3T3) fibroblasts and the human intestinal and hepatic epithelial cell lines Caco-2 and HepG2. Supershift analysis with specific antibodies to USF-1 and USF-2 indicates that USF-1 is the primary isoform binding to the E-box in nuclear extracts from these cells. Using cell culture, transient cotransfection of USF expression vectors with dipeptidyl peptidase IV promoter constructs revealed that both USF-1 and USF-2 caused an approximately tenfold increase in reporter gene expression in Caco-2 cells. Mutant forms of USF-1 and -2 lacking the DNA binding or transcriptional activation domains were unable to stimulate reporter gene expression. Mutation of the E-box prevented binding of USF, although stimulation of reporter gene expression by cotransfection with USF was reduced by only 50%. By using a series of deletion constructs in cotransfection experiments, a second possible site of USF interaction with the dipeptidyl peptidase IV promoter was localized to the -119/-88 region.