Mutant HNF-1α and mutant HNF-1β identified in MODY3 and MODY5 downregulate DPP-IV gene expression in Caco-2 cells

Dipeptidylpeptidase IV (DPP-IV) is a well-documented drug target for the treatment of type 2 diabetes. Hepatocyte nuclear factors (HNF)-1α and HNF-1β, known as the causal genes of MODY3 and MODY5, respectively, have been reported to be involved in regulation of DPP-IV gene expression. But, it is not completely clear (i) that they play roles in regulation of DPP-IV gene expression, and (ii) whether DPP-IV gene activity is changed by mutant HNF-1α and mutant HNF-1β in MODY3 and MODY5. To explore these questions, we investigated transactivation effects of wild HNF-1α and 13 mutant HNF-1α, as well as wild HNF-1β and 2 mutant HNF-1β, on DPP-IV promoter luciferase gene in Caco-2 cells by means of a transient experiment. Both wild HNF-1α and wild HNF-1β significantly transactivated DPP-IV promoter, but mutant HNF-1α and mutant HNF-1β exhibited low transactivation activity. Moreover, to study whether mutant HNF-1α and mutant HNF-1β change endogenous DPP-IV enzyme activity, we produced four stable cell lines from Caco-2 cells, in which wild HNF-1α or wild HNF-1β, or else respective dominant-negative mutant HNF-1αT539fsdelC or dominant-negative mutant HNF-1βR177X, was stably expressed. We found that DPP-IV gene expression and enzyme activity were significantly increased in wild HNF-1α cells and wild HNF-1β cells, whereas they decreased in HNF-1αT539fsdelC cells and HNF-1βR177X cells, compared with DPP-IV gene expression and enzyme activity in Caco-2 cells. These results suggest that both wild HNF-1α and wild HNF-1β have a stimulatory effect on DPP-IV gene expression, but that mutant HNF-1α and mutant HNF-1β attenuate the stimulatory effect.