Mutations in the genes encoding hepatocyte nuclear factor 4α (HNF-4α) and HNF-1α impair insulin secretion and cause maturity onset diabetes of the young (MODY). HNF-4α is known to be an essential positive regulator of HNF-1α. More recent data demonstrates that HNF-4α expression is dependent on HNF-1α in mouse pancreatic islets and exocrine cells. This effect is mediated by binding of HNF-1α to a tissue-specific promoter (P2) located 45.6 kb upstream from the previously characterized Hnf4α promoter (P1). Here we report that the expression of HNF-4α in human islets and exocrine cells is primarily mediated by the P2 promoter. Furthermore, we describe a G → A mutation in a conserved nucleotide position of the HNF-1α binding site of the P2 promoter, which cosegregates with MODY. The mutation results in decreased affinity for HNF-1α, and consequently in reduced HNF-1α–dependent activation. These findings provide genetic evidence that HNF-1α serves as an upstream regulator of HNF-4α and interacts directly with the P2 promoter in human pancreatic cells. Furthermore, they indicate that this regulation is essential to maintain normal pancreatic function.
Sara K. Hansen, Marcelina Párrizas, Maria L. Jensen, Stepanka Pruhova, Jakob Ek, Sylvia F. Boj, Anders Johansen, Miguel A. Maestro, Francisca Rivera, Hans Eiberg, Michal Andel, Jan Lebl, Oluf Pedersen, Jorge Ferrer, Torben Hansen