Discovery of novel vitamin D-regulated proteins in INS-1 cells: A proteomic approach

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)2D3] 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)2D3 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)2D3 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)2D3 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)2D3 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)2D3-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)2D3 regulates protein expression in pancreatic β-cells. Copyright © 2014 John Wiley & Sons, Ltd.