Dominant-negative suppression of HNF-1 alpha function results in defectiveinsulin gene transcription and impaired metabolism-secretion coupling in apancreatic beta-cell line

Mutations in the hepatocyte nuclear factor-1 alpha (HNF-1 alpha) have been linked to subtype 3 of maturity-onset diabetes of the young (MODY3), which is characterized by a primary defect in insulin secretion. The role of HNF- 1 alpha in the regulation of pancreatic beta-cell function was investigated . Gene manipulation allowed graded overexpression of HNF-1 alpha and contro lled dominant-negative suppression of HNF-1 alpha function in insulinoma IN S-1 cells. We show that HNF-1 alpha is essential for insulin gene transcrip tion, as demonstrated by a pronounced decrease in insulin mRNA expression a nd in insulin promoter activity under dominant-negative conditions, The exp ression of genes involved in glucose transport and metabolism including glu cose transporter-2 and L-type pyruvate kinase is also regulated by HNF-1 al pha. Loss of HNF-1 alpha function leads to severe defects in insulin secret ory responses to glucose and leucine, resulting from impaired glucose utili zation and mitochondrial oxidation, The nutrient-evoked ATP production and subsequent changes in plasma membrane potential and intracellular Ca2+ were diminished by suppression of HNF-1 alpha function. These results suggest t hat HNF-1 alpha function is essential for maintaining insulin storage and n utrient-evoked release. The defective mitochondrial oxidation of metabolic substrates causes impaired insulin secretion, indicating a molecular basis for the diabetic phenotype of MODY3 patients.