FIGURE 5.

PS reduces but vanadate increases insulin secretion in response to glucose in human islets. A, PS decreased insulin secretion in response to glucose (11 mm) in human islets. B, in MIN6 cells transfected with WT-Nephrin, PS (30 and 300 μg/ml) increased Nephrin phosphorylation (Tyr(P)-1176/Tyr-1193/Tyr-1217) in a dose-dependent manner, but this was accompanied by increased Nephrin degradation. *, p < 0.05; **, p < 0.01. C, in MIN6 cells transfected with Y1217F-Nephrin, PS (30 and 300 μg/ml) increased Nephrin phosphorylation (Tyr(P)-1176/Tyr-1193) in a dose-dependent manner without affecting phosphorylation of Nephrin at Tyr-1217, and this was accompanied by stable total Nephrin levels. **, p < 0.01; ***, p < 0.001. D, PS decreased GSIR in WT-Nephrin-transfected MIN6 cells, similar to what was observed with PP2. ***, p < 0.001. However, PS increased GSIR in Y1217F-transfected MIN6 cells. **, p < 0.01. E, a dose-dependent increase in insulin secretion was observed in human islets pretreated with vanadate prior to glucose stimulation. F, Western blot analysis of phosphorylated and total Nephrin revealed that vanadate induced Nephrin phosphorylation (Tyr(P)-1176/Tyr-1193) in a dose-dependent manner (0.1 and 1 mm) without affecting total Nephrin levels. *, p < 0.05; ***, p < 0.001. G, vanadate (1 mm) also improved GSIR in MIN6 cells, a phenomenon that was partially prevented in Nephrin siRNA-treated cells. Islets from three independent donors were utilized for each experiment. *, p < 0.05; **, p < 0.01. CTRL, control. NT siRNA is a pool of non-targeting siRNA as a control.