A distant upstream promoter of the HNF-4 alpha gene connects the transcription factors involved in maturity-onset diabetes of the young

Maturity-onset diabetes of the young (MODY) is a monogenic, autosomal domin ant subtype of early-onset diabetes mellitus due to defective insulin secre tion by the pancreatic beta3-cell in humans. Five different genes have been identified including those encoding the tissue-specific transcription fact ors expressed in pancreatic beta -cells, i.e. HNF-4 alpha, (MODY1), HNF-1 a lpha (MODY3), IPF-1 (also known as PDX-1, MODY4) and HNF-1 beta (MODY5). An alyzing the transcription of the HNF-4 alpha gene, we now identify an alter native promoter, P2, which is 46 kb 5' to the previously identified P1 prom oter of the human gene. Based on RT-PCR this distant upstream P2 promoter r epresents the major transcription site in pancreatic beta -cells, but is al so used in hepatic cells. Transfection assays with various deletions and mu tants of the P2 promoter reveal functional binding sites for HNF-1 alpha, H NF-1 beta and IPF-1, the other transcription factors known to encode MODY g enes. We demonstrate the significance of this alternative promoter in a lar ge MODY family where a mutated IPF-1 binding site in the P2 promoter of the HNF-4 alpha gene co-segregates with diabetes (LOD score 3.25). These data suggest a regulatory network of the four MODY transcription factors interco nnected at the distant upstream P2 promoter of the HNF-4 alpha gene.