The G115S mutation associated with maturity-onset diabetes of the young impairs hepatocyte nuclear factor 4alpha activities and introduces a PKA phosphorylation site in its DNA-binding domain.
HNF4alpha (hepatocyte nuclear factor 4alpha) belongs to a complex transcription factor network that is crucial for the function of hepatocytes and pancreatic beta-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 HNF4alpha gene correlate with MODY1 (maturity-onset diabetes of the young 1), a form of type II diabetes characterized by an impaired glucose-induced insulin secretion. The MODY1 G115S (Gly115-->Ser) HNF4alpha 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 beta-cell lines, this mutation resulted in strong impairments of HNF4alpha 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 (Gly115-->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.
Oxombre
Bénédicte
B
INSERM U459, Faculté de Médecine Henri Warembourg, 1 Place de Verdun, 59045 Lille Cedex, France.
Kouach
Mostafa
M
Moerman
Ericka
E
Formstecher
Pierre
P
Laine
Bernard
B
D017668:Age of Onset; D019943:Amino Acid Substitution / Q000235:genetics; D001665:Binding Sites / Q000235:genetics; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000473:pathology; D045744:Cell Line, Tumor; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D003920:Diabetes Mellitus / Q000235:genetics*; D005998:Glycine / Q000235:genetics*; D006367:HeLa Cells / Q000737:chemistry / Q000378:metabolism / Q000473:pathology; D051557:Hepatocyte Nuclear Factor 4; D006639:Histidine / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000473:pathology; D020125:Mutation, Missense / Q000235:genetics*; D010750:Phosphoproteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D010766:Phosphorylation; D012694:Serine / Q000235:genetics* / Q000378:metabolism; D013379:Substrate Specificity; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology
D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C496592:HNF4A protein, human; D051557:Hepatocyte Nuclear Factor 4; D010750:Phosphoproteins; D014157:Transcription Factors; D012694:Serine; D006639:Histidine; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases; D005998:Glycine