Tmem27 is upregulated by vitamin D in INS-1 cells and its serum concentrations are low in patients with autoimmune diabetes.

Transmembrane protein 27 (Tmem27), which is expressed in pancreatic β-cells, plays an important role in insulin secretion and pancreatic β-cell proliferation. Analysis of the INS-1 cell proteome using stable isotope labeling by amino acids in cell culture (SILAC) in combination with LC-MS identified Tmem27 as the one of most robustly (up to seven-fold) upregulated proteins after treatment with the active metabolite of vitamin D, 1,25-(OH)2D3. Furthermore, we report that Tmem27 which is cleaved and released from, i.e. pancreatic β-cells, is present in human serum and its levels are significantly lower in subjects with autoimmune diabetes as compared to healthy individuals (13% of the levels). Additionally, Tmem27 correlated positively (0.70) with C-peptide serum levels in healthy subjects. Our data indicate that Tmem27 could be of potential value as a serum marker for the pathogenesis of diabetes and as such may warrant the development of measurement methods with lower limit of detection for its further validation.