Overexpression of dominant negative mutant hepatocyte nuclear factor (HNF)-1 alpha inhibits arginine-induced insulin secretion in MIN6 cells

Aims/hypothesis. To explain the mechanisms whereby mutations in the HNF-1 a lpha gene cause insulin secretory defects. Methods. A truncated mutant HNF-1 alpha (HNF-1 alpha 288t) was overexpresse d in hepatoma cells (HepG2) and murine insulinoma cells (MING) using a reco mbinant adenovirus system and expression of the HNF-1 alpha target genes an d insulin secretion were examined. Results. Expression of phenylalanine hydroxylase and alpha 1-antitrypsin ge nes, the target genes of HNF-1 alpha, was suppressed in HepG2 cells by over expression of HNF-1 alpha 288t. In MIN6 cells, overexpression of HNF-1 alph a 288t did not change insulin secretion stimulated by glucose (5 mmol/l and 25 mmol/l) or leucine (20 mmol/l). Potentiation of insulin secretion by ar ginine (20 mmol/l, in the presence of 5 mmol/l or 25 mmol/l glucose) was, h owever, reduced (p < 0.0001 and p = 0.027, respectively). Similarly reduced responses were observed when stimulated with homoarginine. Expression of t he cationic amino acid transporter-2 was not reduced and insulin secretory response to membrane depolarization by 50 mmol/l KCl was intact. Conclusion /interpretation. The HNF-1 alpha 288t, which is structurally similar to the mutant HNF-1 alpha expressed from the common MODY3 allele, P291fsinsC, exe rts a dominant negative effect. Suppression of HNF-1 alpha in MIN6 cells se verely impaired potentiation of insulin secretion by arginine, whereas gluc ose-stimulated and leucine-stimulated insulin secretion was intact. Our fin dings delineate the complex nature of beta-cell failure in patients with MO DY3. This cell model will be useful for further investigation of the mechan ism of insulin secretory defects in these patients.