Distinct Regulation of Hepatic Nuclear Factor 1α by NKX6.1 in Pancreatic Beta Cells

Hepatic nuclear factor 1 alpha (HNF1 alpha) is a key regulator of development and function in pancreatic beta cells and is specifically involved in regulation of glycolysis and glucose-stimulated insulin secretion. Abnormal expression of HNF1 alpha leads to development of MODY3 (maturity-onset diabetes of the young 3). We report that NK6 homeodomain 1 (NKX6.1) binds to a cis-regulatory element in the HNF1 alpha promoter and is a major regulator of this gene in beta cells. We identified an NKX6.1 recognition sequence in the distal region of the HNF1 alpha promoter and demonstrated specific binding of NKX6.1 in beta cells by electrophoretic mobility shift and chromatin immunoprecipitation assays. Site-directed mutagenesis of the NKX6.1 core-binding sequence eliminated NKX6.1-mediated activation and substantially decreased activity of the HNF1 alpha promoter in beta cells. Overexpression or small interfering RNA-mediated knockdown of the Nkx6.1 gene resulted in increased or diminished HNF1 alpha gene expression, respectively, in beta cells. We conclude that NKX6.1 is a novel regulator of HNF1 alpha in pancreatic beta cells. This novel regulatory mechanism for HNF1 alpha in beta cells may provide new molecular targets for the diagnosis of MODY3.