We investigated the presence and the function of hepatocyte nuclear factor-1α (HNF-1α)
mutations in 26 Japanese subjects with type 2 diabetes. The subjects were between
20 and 39 years of age on diagnosis and had diabetic first-degree relatives. Two different
frameshift mutations were found in 2 subjects (8%). One novel mutation, T539fsdelC
(deletion of C in codon 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
mutation, P291fsinsC (insertion of C in codon 291 for Pro) should lead to production
of a truncated protein of 315 amino acids. Transfection reporter assay using MIN6
and HepG2 cells revealed both mutations to have null function in the transactivation
of reporter gene expression. When transfected with wild-type gene, these mutations
behaved as dominant-negative regulators in both cells. An equimolar amount of T539fsdelC
reduced wild-type activity by ∼ 80% in MIN6 cells, while the same concentration of
P291fsinsc reduced it by 30%. The sequences responsible for the transactivation activity
of HNF-1α are confined largely to amino acids 547-628, so that the T539fsdelC mutation,
which affects this entire region, replacing amino acids 540-631 with an abnormal 119
amino acid protein, may acquire a potent dominant-negative function.
Key words
Maturity-Onset Diabetes of the Young - Luciferase Assay - Frameshift Mutation - Insulin
Secretion - Transcription Factor
