Dominant‐negative suppression of HNF‐1α function results in defective insulin gene transcription and impaired metabolism‐secretion coupling in a pancreatic β‐cell line

Mutations in the hepatocyte nuclear factor‐1α (HNF‐1α) 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‐1α in the regulation of pancreatic β‐cell function was investigated. Gene manipulation allowed graded overexpression of HNF‐1α and controlled dominant‐negative suppression of HNF‐1α function in insulinoma INS‐1 cells. We show that HNF‐1α is essential for insulin gene transcription, as demonstrated by a pronounced decrease in insulin mRNA expression and in insulin promoter activity under dominant‐negative conditions. The expression of genes involved in glucose transport and metabolism including glucose transporter‐2 and L‐type pyruvate kinase is also regulated by HNF‐1α. Loss of HNF‐1α function leads to severe defects in insulin secretory responses to glucose and leucine, resulting from impaired glucose utilization and mitochondrial oxidation. The nutrient‐evoked ATP production and subsequent changes in plasma membrane potential and intracellular Ca 2+ were diminished by suppression of HNF‐1α function. These results suggest that HNF‐1α function is essential for maintaining insulin storage and nutrient‐evoked release. The defective mitochondrial oxidation of metabolic substrates causes impaired insulin secretion, indicating a molecular basis for the diabetic phenotype of MODY3 patients.