In contrast, as further shown in Figure 2, no significant effect of CHF5074 tre

EGFR signaling leads to the activation of several Maraviroc CCR5 阻害剤 downstream cascades, with the two major pathways including PI3 kinase AKT and Ras Raf 1 ERK, Although much of the work studying these pathways has been performed in cancer cells, it has recently been demonstrated that endogenous Raf 1 signaling is required to suppress basal b cell apoptosis and that Raf 1 also participates in b cell proliferation, Further, low concentrations of insulin rescued human and rodent islets from serum withdrawal induced apoptosis through Raf 1 activation and islets isolated from mice with a 50% reduc tion in glucose stimulated insulin secretion had a 50% loss of ERK activation in response to glucose, Glu cose and insulin stimulate nuclear translocation of ERK, an event that has been proposed to promote b cell survival and growth via ERK dependent transcription, Our finding that EGF mediated signaling through the Raf 1 ERK pathway prolongs the survivin protein half life suggests another mechanism by which ERK signaling may promote the survival and growth of pancreatic b cells.<br><br> The EGF dependent early increase in survivin protein is not significantly regulated at the level of transcription, as there is no significant EGF dependent increase in sur vivin mRNA observed during these early time periods, MK-2206 nor is the survivin promoter activated. By contrast, experiments conducted in the presence of the protein synthesis inhibitor cyclohexamide support a post trans lational mechanism of EGF dependent regulation, with a decrease in protein degradation rate observed in the presence of EGF.<br><br> In contrast to the 30 minute half life of survivin in the absence of EGF, the survivin half life is increased to 90 minutes in the presence of EGF. The ubiquitin proteosome pathway plays a central role in the regulation of multiple proteins involved in cellular homeostasis, Many short lived, key regula tor proteins including the cyclins, cyclin kinase inhibitors mtorc2 阻害剤 CKI, and tran scription factors are regulated by this pathway, Ubi quitin proteasomes also regulate programmed proteolysis of pro and anti apoptotic proteins, includ ing Bcl 2 family proteins and IAPs, Previous work demonstrated that the ubiquitin proteasome pathway regulates survivin degradation in a cell cycle dependent manner, Deubiquitination of survivin is also required for the proper targeting of survivin and its partner chromosomal passenger proteins to centromeres, enabling accurate cell division to take place.<br><br> Our data suggest that EGF can inhibit ubiquitination of sur vivin in pancreatic b cells, thereby prolonging its pro tein half life. EGF is currently in human clinical trials to treat insu lin deficient diabetes, with preliminary results showing a decrease in exogen ous insulin requirements. It is unclear if this observed effect is due to improved b cell function or to increases in b cell proliferation of the remaining b cells. Our results show that EGF enhances survivin stability through activation of the Raf 1 ERK pathway in the pancreatic b cell lines MIN6 and INS 1 and support future work in exploring this pathway in vivo. Methods Cell culture MIN6 and INS 1 cells were grown under proliferating conditions in DMEM 10% FBS. Cells were serum deprived overnight prior to the addition of EGF or IGF 1 for 2 to 4 hours prior to adding glucose or insulin. To inhibit the EGF signaling pathways, cells were treated with the follow ing compounds: LY 249002, UO126, SP600125 and AG490 30 minutes prior to EGF treatment then harvested for Western blot at the times indicated.