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)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.