Aims/hypothesis. After screening 16 Korean families with early onset Type 2 diabetes in search for hepatocyte nuclear factor (HNF)-1α gene mutation, we identified a novel missense mutation (R263L) associated with MODY phenotype. We studied the biological characteristics of the mutation and the potential functional consequences based on the crystallographic structure of HNF-1α in complex with DNA.

Methods. DNA from subjects with a familial form of early onset diabetes was isolated and HNF-1α was sequenced. The R263L substitution was generated by PCR-based sited-directed mutagenesis. Functional and biochemical studies were conducted by reporter assay using glucose-transporter type 2 (GLUT2) or insulin promoters and electrophoretic mobility shift assay, respectively.

Results. Transfection of wild-type HNF-1α increased the reporter activities of GLUT2 and insulin promoters in NIH3T3 and SK-Hep1 cells, while R263L mutant was defective in transactivation of those promoters. Both wild-type HNF-1α and R263L mutant could not transactivate GLUT2 and insulin promoters in MIN6N8 insulinoma cells. R263L mutant had a defective cooperation with its heterodimeric partner HNF-1β or coactivator p300. R263L mutant protein displayed greatly reduced DNA binding ability, despite its comparable protein stability to the wild-type HNF-1α.

Conclusion/interpretation. These results suggest that the mutation of HNF-1α at codon 263 from arginine to leucine leads to the development of MODY3 through decreased insulin production and defective glucose sensing. These findings are in good agreement with the crystal structure in which R263 makes hydrogen bonds with phosphorus atoms of DNA backbone to mediate the stable binding of HNF-1α homeodomain to the promoter.