Effect of mutations in HNF-1α and HNF-1β on the transcriptional regulation of human sucrase–isomaltase in Caco-2 cells

Mutations in transcription factors hepatocyte nuclear factors (HNF)-1α and HNF-1β cause maturity-onset diabetes of the young (MODY) types 3 and 5, respectively. HNF-1α and HNF-1β mutations are well studied in some tissues, but the mechanism by which HNF-1α and HNF-1β mutations affect sucrase–isomaltase (SI) transcription in the small intestine is unclear. We studied the effects of 13 HNF-1α mutants and 2 HNF-1β mutants on human SI gene transcription, which were identified in subjects with MODY3 and MODY5, respectively. Transactivation activity of 11 HNF-1α and 2 HNF-1β mutants was significantly lower than that of wild (wt)-HNF-1α and wt-HNF-1β. Furthermore, in co-expression studies with mutant (mu)-HNF-1α/ wt-HNF-1β and wt-HNF-1α/mu-HNF-1β, the combination of mu-HNF-1α (P379fsdelCT and T539fsdelC)/wt-HNF-1β impaired SI transcription, but the others were not remarkably different from wt-HNF-1α/wt-HNF-1β. Although wt-HNF-1β inhibited the transactivation activity of wt-HNF-1α on SI transcription, the inhibitory effect was reduced by 2 HNF-1β mutants. These results suggest that SI transcription might tend to be unchanged or lower in MODY3, while occurring more in MODY5.