title: Functional characterization of the HNF4alpha isoform (HNF4alpha8) expressed in pancreatic beta-cells.
abstract: Mutations in the hepatocyte nuclear factor (HNF) 4alpha gene cause a form of maturity-onset diabetes of the young (MODY1), which is a monogenic form of type 2 diabetes characterized by impaired insulin secretion by pancreatic beta-cells. HNF4alpha is a transcription factor expressed in the liver, kidney, intestine, and pancreatic islet. Multiple splice variants of the HNF4alpha gene have been identified and an isoform of HNF4alpha8, an N-terminal splice variant, is expressed in pancreatic beta-cells. However, expression levels of HNF4alpha protein in pancreatic beta-cells and the transcriptional activity of HNF4alpha8 are not yet understood. In the present study, we investigated the expression of HNF4alpha in beta-cells and examined its functional properties. Western blotting and immunohistochemical analysis revealed that the expression of HNF4alpha protein in pancreatic islets and INS-1 cells was much lower than in the liver. A reporter gene assay showed that the transactivation potential of HNF4alpha8 was significantly weaker than that of HNF4alpha2, which is a major isoform in the liver, suggesting that the total level of HNF4alpha activity is very weak in pancreatic beta-cells. We also showed that the N-terminal A/B region of HNF4alpha8 possessed no activation function and C-terminal F region negatively regulated the transcriptional activity of HNF4alpha8. The information presented here would be helpful for the better understanding of MODY1/HNF4alpha diabetes.
authors.affiliation: Department of Internal Medicine and Molecular Science, Graduate School of Medicine, Osaka University, Osaka, Japan.
authors.forename: Arisa
authors.initials: A
authors.lastname: Ihara
authors.forename: Kazuya
authors.initials: K
authors.lastname: Yamagata
authors.forename: Takao
authors.initials: T
authors.lastname: Nammo
authors.forename: Atsuko
authors.initials: A
authors.lastname: Miura
authors.forename: Ming
authors.initials: M
authors.lastname: Yuan
authors.forename: Toshiya
authors.initials: T
authors.lastname: Tanaka
authors.forename: Frances M
authors.initials: FM
authors.lastname: Sladek
authors.forename: Yuji
authors.initials: Y
authors.lastname: Matsuzawa
authors.forename: Jun-ichiro
authors.initials: J
authors.lastname: Miyagawa
authors.forename: Iichiro
authors.initials: I
authors.lastname: Shimomura
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D007515:Islets of Langerhans / Q000378:metabolism*; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; C496592:HNF4A protein, human; D051557:Hepatocyte Nuclear Factor 4; C496593:Hnf4a protein, mouse; C496594:Hnf4a protein, rat; D010750:Phosphoproteins; D020033:Protein Isoforms; D014157:Transcription Factors