A novel dominant-negative mutation of the hepatocyte nuclear factor-1 alpha gene in Japanese early-onset type 2 diabetes

We investigated the presence and the function of hepatocyte nuclear factor- 1 alpha (HNF-1 alpha) mutations in 26 Japanese subjects with type 2 diabete s. The subjects were between 20 and 39 years of age on diagnosis and had di abetic first-degree relatives. Two different frameshift mutations were foun d in 2 subjects (8 %). One novel mutation, T539fsdelC (deletion of C in cod on 539 for Thr), is predicted to generate a protein of normal 539 residues at the N-terminus followed by an abnormal 119 amino acid protein. The mutat ion, P291fsinsC (insertion of C in codon 291 for Pro) should lead to produc tion of a truncated protein of 315 amino acids. Transfection reporter assay using MIN6 and HepG2 cells revealed both mutations to have null function i n the transactivation of reporter gene expression. When transfected with wi ld-type gene, these mutations behaved as dominant-negative regulators in bo th cells. An equimolar amount of T539fsdelC reduced wild-type activity by s imilar to 80% in MIN6 cells, while the same concentration of P291fsinsc red uced it by 30%. The sequences responsible for the transactivation activity of HNF-1 alpha are confined largely to amino acids 547-628, so that the T53 9fsdelC mutation,which affects this entire region, replacing amino acids 54 0-631 with an abnormal 119 amino acid protein, may acquire a potent dominan t-negative function.