A single nucleotide polymorphism in the gene encoding the protein phosphatase m1K (PPm1K) is associated with increased risk for the development of type 2 diabetes but not insulin resistance in humans. We recently discovered that expression of the PPM1K gene in liver is suppressed by the carbohydrate response element binding protein (ChREBP) which controls transcriptional responses to changes in carbohydrate availability. Taken together these findings suggest that PPM1K might play an important role in the glucose responsive pancreatic β cell; however, little is known about the role of PPm1K in this cell type. Here we studied how changes in glucose concentration affect PPm1K expression in β cells and explored the effect of modulating PPM1K expression on β cell proliferation, insulin content and glucose stimulated insulin secretion. Studies were carried out in INS1-832/13 β cells in culture and key findings were validated in isolated rat islets. In line with our previous observations in liver, we found that increasing glucose concentrations in INS1 cells results in elevated ChREBP activity, measured by expression of the ChREBP β isoform, and lower PPM1K mRNA expression (P<0.01). Treatment of INS-1 cells with adenovirus expressing recombinant human PPM1K for 96h increased β cell proliferation (P<0.05) but robustly lowered GSIS (P<0.001). This effect was due to substantially lower insulin content in the Ad-PPm1K treated cells (P<0.01). Importantly, there was no effect of the control GFP adenovirus compared to non-transfected cells for any of these measures. Moreover, siRNA mediated knock down of PPM1K resulted in increased expression of INS1 and INS2 mRNA suggesting that altered transcription of the insulin gene likely accounts for the effect of PPm1K on β cell insulin content and release.
In conclusion, our data clearly demonstrate that PPM1K plays an important role in the regulation of β cell insulin production and proliferation.
Y. Deleye: None. J. Herring: None. K.H. Hess: None. B.R. Leininger: None. S.A. Hannou: None. I. Astapova: None. M.A. Herman: None. J.S. Tessem: None. P.J. White: None.
American Diabetes Association/Pathway to Stop Diabetes (1-16-INI-17 to P.J.W.)