Two HNF-1 binding sites govern the glucose repression of the human sucrase-isomaltase promoter

We have previously shown, using the Caco-2 clone PF11, that glucose repress es transcription of the human sucrase-isomaltase (SI) gene and that the -37 0/+30 fragment of the SI gene conferred glucose-regulated expression on a h eterologous gene. Different fragments beginning at the already characterize d SI footprint (SIF) 1 (-53/-37), SIFR (-153/-129) or SIF3 (-176/-156) elem ents [Wu, Chen, Forslund and Traber (1994) J. Biol. Chem. 269, 17080-17085] were tested, in comparison with the -370/+30 fragment, for their capacity tcs inhibit reporter gene expression under high-glucose (25 mM) conditions. Unlike SIF1 and SIFR, the addition of the HNF (hepatocyte nuclear factor)- 1-binding element SIF3 to the promoter fragment was required for repression under high-glucose conditions. This effect was enhanced when the SI promot er was extended to position - 370, indicating that the - 370/ - 176 region contains elements that may co-operate with SIF3 to increase the metabolic c ontrol of the SI promoter. We have characterized an additional HNF-1-bindin g site near to and upstream from SIF3; SIF4. By mutagenesis of the three HN F-1-binding elements we show that the two distal HNF-1-recognition sites ar e the most important for the glucose regulation of the SI gene. Moreover, t his glucose regulation was abolished in PF11 cells overexpressing vHNF-1C ( variant HNF, an isoform of the HNF-1 family). We thus propose that the diff erential binding of HNF-1-family proteins to their DNA targets on the SI pr omoter constitutes the molecular mechanism that controls the glucose regula tion of the SI gene transcription.