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

Abstract

Maturity-onset diabetes of the young (MODY) is a monogenic, autosomal dominant subtype of early-onset diabetes mellitus due to defective insulin secretion by the pancreatic β-cell in humans. Five different genes have been identified including those encoding the tissue-specific transcription factors expressed in pancreatic β-cells, i.e. HNF-4α (MODY1), HNF-1α (MODY3), IPF-1 (also known as PDX-1, MODY4) and HNF-1β (MODY5). Analyzing the transcription of the HNF-4α gene, we now identify an alternative promoter, P2, which is 46 kb 5′ to the previously identified P1 promoter of the human gene. Based on RT-PCR this distant upstream P2 promoter represents the major transcription site in pancreatic β-cells, but is also used in hepatic cells. Transfection assays with various deletions and mutants of the P2 promoter reveal functional binding sites for HNF-1α, HNF-1β and IPF-1, the other transcription factors known to encode MODY genes. We demonstrate the significance of this alternative promoter in a large MODY family where a mutated IPF-1 binding site in the P2 promoter of the HNF-4α gene co-segregates with diabetes (LOD score 3.25). These data suggest a regulatory network of the four MODY transcription factors interconnected at the distant upstream P2 promoter of the HNF-4α gene.