The G115S mutation associated with maturity-onset diabetes of the young impairs hepatocyte nuclear factor 4 alpha activities and introduces a PKA phosphorylation site in its DNA-binding domain

摘要

HNF4alpha (hepatocyte nuclear factor4alpha) belongs to a complex transcription factor network that is crucial for the function of hepatocytes and pancreatic P-cells. In these cells, it activates the expression of a very large number of genes, including genes involved in the transport and metabolism of glucose and lipids. Mutations in the HNF4a gene correlate with MODY1 (maturity-onset diabetes of the young 1), a for-m of type II diabetes characterized by an impaired glucose-induced insulin secretion. The MODY1 G115S (Gly(115) --> Ser) HNF4a mutation is located in the DNA-binding domain of this nuclear receptor. We show here that the G115S mutation failed to affect HNF4alpha-mediated transcription on apolipoprotein promoters in HepG2 cells. Conversely, in pancreatic P-cell lines, this mutation resulted in strong impairments of HNF4a transcriptional activity on the promoters of LPK (liver pyruvate kinase) and HNF1alpha, with this transcription factor playing a key role in endocrine pancreas. We show as well that the G115S mutation creates a PKA (protein kinase A) phosphorylation site, and that PKA-mediated phosphorylation results in a decreased transcriptional activity of the mutant. Moreover, the G115E (Gly(115) --> Glu) mutation mimicking phosphorylation reduced HNF4alpha DNA-binding and transcriptional activities. Our results may account for the 100% penetrance of diabetes in human carriers of this mutation. In addition, they suggest that introduction of a phosphorylation site in the DNA-binding domain may represent a new mechanism by which a MODY1 mutation leads to loss of HNF4alpha function.