S7). p38α may inactivate GSK3β by direct phosphorylation of Ser389 or indirectly through phosphorylation of Thr9 by Akt, leading to β-catenin accumulation.20 Thus, p38 modulates canonical Wnt-β-catenin signaling, which is critical for normal cell proliferation and homeostasis.21 Inactivation of GSK3β produces embryonic lethality caused by severe liver degeneration associated with hypersensitivity to TNF-α and reduced NF-κB function.22 Inhibition of GSK3β may sensitize rat hepatocytes to apoptosis by reducing p65 phosphorylation and down-regulating NF-κB transactivation.23 In p38α-deficient

livers, activation of GSK3β due to reduced phosphorylation (Fig. 3B) does not seem to be associated with changes in apoptosis or p65 phosphorylation upon

BDL (Fig. EX 527 concentration S4). The p38α pathway is also involved in the up-regulation of inflammatory cytokines. p38 may positively regulate NF-κB activity by different mechanisms, including chromatin remodeling through Ser10 phosphorylation of histone H3 at NF-κB-dependent promoters or by impinging on IκB kinase (IKK) or the p65 subunit.20 However, in chronic cholestasis p38α deficiency did not significantly affect NF-κB activation (Supporting Fig. RG7204 order S4) or the expression of TNF-α and interleukin-6 (see Fig. 4). Nevertheless, RANTES and receptor 1 of TNF-α Bay 11-7085 were up-regulated in the liver of p38α-deficient mice under basal conditions and remained high during the first 12 days after cholestasis (Fig. 4B). RANTES is one of the major adjacent cysteines motif (CC) chemokines that is produced by T-lymphocytes, monocytes, endothelial cells, and fibroblasts. It is worth noting that expression of antiinflammatory IL-10 was markedly up-regulated at 12 days after cholestasis induction only in p38α KO mice, which should provide protection restraining the inflammatory response,

but this protection was lost in the long term (i.e., at 28 days) leading to up-regulation of Icam-1 and chemokine (C-C motif) ligand 2 (Ccl2) (Fig. 4B). Although previous reports have associated p38α with the regulation of apoptosis and fibrogenesis, liver-specific p38α-deficient mice did not show a higher degree of apoptosis or fibrosis upon chronic cholestasis compared with WT mice (see Fig. 4 and Supporting Fig. S5). Hence, neither apoptosis nor fibrosis would contribute to the increased mortality of these animals. p38α controls the differentiation and proliferation of many cell types, including hepatocytes.4, 24, 25 p38α may negatively regulate cell cycle progression at the G1/S and the G2/M transitions triggering cell cycle arrest by down-regulation of cyclins, up-regulation of cyclin-dependent kinase inhibitors, and by inducing p53 phosphorylation and the up-regulation of p16.