Conversely, signal transduction via IRS1 is less www.selleckchem.com/products/BI6727-Volasertib.html critical for beta-cell growth and survival as mice lacking Irs1 did not become diabetic because of an adequate expansion of beta cell mass in presence of IRS2 [53]. In our conditions, reducing JNK3 did not show a significant decrease of IRS1 protein which indicates specific regulation of IRS2 by the JNK3 isoform. In contrast, we observed a slight increase in IRS1 expression levels when silencing JNK1. As expected from the loss of IRS2 expression, our study shows that JNK3 suppression further inhibits Akt2 phosphorylation (phospho-Ser474) by insulin. Akt2 (which lays immediately downstream of IRS2 in the insulin signaling cascade) has been shown to control beta-cell growth and survival as well; it distinctively regulates glucose metabolism as Akt2-null mice develop severe diabetes with high loss of beta-cell mass, a phenotype clearly similar to the one observed with Irs2-null mice [28], [29], [53].

Hence, we may link the protective action of JNK3 in insulin secreting cells to its preservative role on the IRS2/Akt2 signaling pathway. Akts may affect survival directly by regulating the activity (post-translational regulation) of their target substrates or indirectly by eliciting gene expression (transcriptional regulation). In beta-cells, GSK3�� is a direct substrate of the PI3K-Akt pathway and its down regulation (increased phosphorylation) can protect cells from death [44], [56], [57]. Akts also modulate (by phosphorylation) the activity of the FoxO1 and FoxO3A transcription factors and block their translocation into the nucleus [46].

In beta-cells, the exact role of the FoxO proteins is not fully characterized [58]. It has been shown that decreasing levels of FoxO1 restore Pancreatic and Duodenal homeobox1 (PDX1) expression and nuclear localization and rescue the loss of beta-cells in Irs2-deficient mice, suggesting that FoxO1 and PDX1 can mediate proliferative signals induced by Akts [47], [59]. Alternatively FoxO3A but not FoxO1 has been shown to regulate Irs2 expression [49]. In our conditions, JNKs silencing reduced FoxO3A activity (enhanced phosphorylation) particularly after JNK3 silencing. On the other hand, silencing JNK1 or JNK2 decreased FoxO1 activity, while its activity increased Batimastat when JNK3 is silenced (data not shown). Activated FoxO1 may trigger the transcriptional machinery to induce the expression of relevant genes to inhibit beta-cell survival [47]. The decrease in FoxO3A activity while Akts activities are low (because of reduced JNK3 in presence of cytokines) may participate to the observed defect in IRS2 expression. We have published previously that silencing of JNK3 aggravates the down-regulation of insulin mRNA levels caused by cytokines.