title: Discovery of novel vitamin D-regulated proteins in INS-1 cells: a proteomic approach.
abstract: BACKGROUND
  Experimental evidence indicates that vitamin D may have a beneficial role in pancreatic β-cell function. Global gene expression studies have shown that the active metabolite 1,25-dihydroxyvitamin D3 [1,25-(OH)2 D3 ] modulates genes involved in ion transport, lipid metabolism and insulin secretion.
  
  
  METHODS
  We employed stable isotope labelling by amino acids in cell culture in combination with liquid chromatography-tandem mass spectrometry to quantitatively assess the impact of two vitamin D metabolites, 1,25-(OH)2 D3 and 25-hydroxyvitamin D3 [25-(OH)D3 ], on global protein expression on a model rat β-cell line, insulinoma-derived INS-1 cells.
  
  
  RESULTS
  Although treatment with 1,25-(OH)2 D3 resulted in 31 differentially expressed proteins, 25-(OH)D3 had no impact on protein expression. Of these 31 proteins, 29 were upregulated, whereas two showed a decrease in abundance. Proteins whose expression levels markedly increased in the presence of 1,25-(OH)2 D3 included Crat, Hmgn2, Protein Tmsbl1 and Gdap1. One of the most important findings in this study is upregulation of proteins implicated in insulin granule motility and insulin exocytosis, suggesting a positive effect on insulin secretion. Moreover, modulation of several membrane transport proteins suggests that 1,25-(OH)2 D3 has an impact on the homeostatic regulation of ions, which is critical for most functions in the β-cell.
  
  
  CONCLUSIONS
  In this study, we discovered a number of novel 1,25-(OH)2 D3 -regulated proteins, which may contribute to a better understanding of the reported beneficial effects of vitamin D on pancreatic β-cells. All in all, our findings should pave the way for future studies providing insights into molecular mechanisms by which 1,25-(OH)2 D3 regulates protein expression in pancreatic β-cells.
authors.affiliation: Hormone Laboratory, Department of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Milaim
authors.initials: M
authors.lastname: Pepaj
authors.affiliation: Hormone Laboratory, Department of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: May K
authors.initials: MK
authors.lastname: Bredahl
authors.affiliation: Hormone Laboratory, Department of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Nina
authors.initials: N
authors.lastname: Gjerlaugsen
authors.affiliation: Hormone Laboratory, Department of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Mette E
authors.initials: ME
authors.lastname: Bornstedt
authors.affiliation: Hormone Laboratory, Department of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Per M
authors.initials: PM
authors.lastname: Thorsby
mesh_terms: D000818:Animals; D002112:Calcifediol / Q000494:pharmacology*; D002117:Calcitriol / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002853:Chromatography, Liquid; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism; D040901:Proteomics; D012333:RNA, Messenger / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D053719:Tandem Mass Spectrometry; D059467:Transcriptome / Q000187:drug effects; D014815:Vitamins / Q000494:pharmacology*
chemical_list: D012333:RNA, Messenger; D014815:Vitamins; D002117:Calcitriol; D002112:Calcifediol
keywords: 1,25-dihydroxyvitamin D3; INS-1; SILAC; insulin exocytosis; proteomics