Multiple pluripotent cell populations, which together comprise the pluripotent cell lineage, have been identified. The mechanisms that control the progression between these populations are still poorly understood. The formation of early primitive ectoderm-like (EPL) cells from mouse embryonic stem (mES) cells provides a model to understand how one such transition is regulated. EPL cells form from mES cells in response to l-proline uptake through the transporter Slc38a2. Using inhibitors of cell signaling we have shown that Src family kinases, p38 MAPK, ERK1/2 and GSK3β are required for the transition between mES and EPL cells. ERK1/2, c-Src and GSK3β are likely to be enforcing a receptive, primed state in mES cells, while Src family kinases and p38 MAPK are involved in the establishment of EPL cells. Inhibition of these pathways prevented the acquisition of most, but not all, features of EPL cells, suggesting that other pathways are required. L-proline activation of differentiation is mediated through metabolism and changes to intracellular metabolite levels, specifically reactive oxygen species. The implication of multiple signaling pathways in the process suggests a model in which the context of Src family kinase activation determines the outcomes of pluripotent cell differentiation.

Heat shock factor 1 (HSF1) monitors the structural integrity of the proteome. Phosphorylation at S326 is a hallmark for HSF1 activation, but the identity of the kinase(s) phosphorylating this site has remained elusive. We show here that the dietary agent phenethyl isothiocyanate (PEITC) inhibits heat shock protein 90 (Hsp90), the main negative regulator of HSF1; activates p38 mitogen-activated protein kinase (MAPK); and increases S326 phosphorylation, trimerization, and nuclear translocation of HSF1, and the transcription of a luciferase reporter, as well as the endogenous prototypic HSF1 target Hsp70. In vitro, all members of the p38 MAPK family rapidly and stoichiometrically catalyze the S326 phosphorylation. The use of stable knockdown cell lines and inhibitors indicated that among the p38 MAPKs, p38γ is the principal isoform responsible for the phosphorylation of HSF1 at S326 in cells. A protease-mass spectrometry approach confirmed S326 phosphorylation and unexpectedly revealed that p38 MAPK also catalyzes the phosphorylation of HSF1 at S303/307, previously known repressive posttranslational modifications. Thus, we have identified p38 MAPKs as highly efficient catalysts for the phosphorylation of HSF1. Furthermore, our findings suggest that the magnitude and persistence of activation of p38 MAPK are important determinants of the extent and duration of the heat shock response.

Mitogen-activated protein (MAP) kinases bind tightly to many of their physiologically relevant substrates. We have identified a new subfamily of murine serine/threonine kinases, whose members, MAP kinase-interacting kinase 1 (Mnk1) and Mnk2, bind tightly to the growth factor-regulated MAP kinases, Erk1 and Erk2. MNK1, but not Mnk2, also binds strongly to the stress-activated kinase, p38. MNK1 complexes more strongly with inactive than active Erk, implying that Mnk and Erk may dissociate after mitogen stimulation. Erk and p38 phosphorylate MNK1 and Mnk2, which stimulates their in vitro kinase activity toward a substrate, eukaryotic initiation factor-4E (eIF-4E). Initiation factor eIF-4E is a regulatory phosphoprotein whose phosphorylation is increased by insulin in an Erk-dependent manner. In vitro, MNK1 rapidly phosphorylates eIF-4E at the physiologically relevant site, Ser209. In cells, Mnk1 is post-translationally modified and enzymatically activated in response to treatment with either peptide growth factors, phorbol esters, anisomycin or UV. Mitogen- and stress-mediated MNK1 activation is blocked by inhibitors of MAP kinase kinase 1 (Mkk1) and p38, demonstrating that Mnk1 is downstream of multiple MAP kinases. MNK1 may define a convergence point between the growth factor-activated and one of the stress-activated protein kinase cascades and is a candidate to phosphorylate eIF-4E in cells.

BACKGROUND Hyperbilirubinemia is associated with central nervous system damage in preterm neonates due to the neurotoxicity of bilirubin. This study explored the possible mechanisms of bilirubin's neurotoxicity, and the protective effect of baicalin (BAI) was also investigated. MATERIAL AND METHODS Isolated neonatal rat hippocampal neurons were exposed to free bilirubin (Bf). BAI was used to treat these neurons. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to evaluate the cell viability. Terminal deoxynucleotidyl transferase-dUTP nick-end labeling (TUNEL) assay was used to detect apoptosis. Contents of inflammatory cytokines were determined by enzyme-linked immunosorbent assay (ELISA). Protein expression and phosphorylation levels were assessed by Western blotting. Nuclear translocation was observed by immunofluorescent staining. RESULTS Bf incubation significantly induced apoptosis and decreased viabilities of neurons. The phosphorylation levels of MAP kinase kinase (MKK)3, MKK6, p38 mitogen- activated protein kinases (MAPK), nuclear translocation level of p65, and the expression levels of cleaved caspase3 and tumor necrosis factor (TNF)alpha were found to be dramatically higher in Bf-incubated neurons. BAI pre-treatment, however, increased cell viability by reducing cell apoptosis. BAI pre-treatment also reduced phosphorylation levels of MKK3, MKK6, p38 MAPK, and nuclear translocation level of p65, as well as the expression levels of cleaved caspase3 and TNFalpha, in Bf- incubated neurons. CONCLUSIONS BAI suppressed bilirubin-induced neuron apoptosis and inflammation by deactivating p38 MAPK signaling.

The p38 mitogen-activated protein kinases (MAPKs) are essential cytoplasmic signal molecules of innate immune pathways that play a vital role in host immune defense responses to pathogenic challenges. In this study, two fish p38 genes (Cip38α and Cip38β) were characterized for the first time from the grass carp Ctenopharyngodon idella. Similar to other reported p38MAPKs, both Cip38α and Cip38β contained a conserved phosphorylation motif (Thr-Gly-Tyr, TGY) and a substrate binding site (Ala-Thr-Arg-Trp, ATRW) in the serine/threonine protein kinase (S_TKc) domain. Expression profile analysis showed that Cip38α and Cip38β mRNAs were broadly expressed in all of the examined tissues and developmental stages of C. idella. In addition, in vivo injection experiments directly revealed that Cip38α and Cip38β showed strong responsiveness to Aeromonas hydrophila and muramyl dipeptide (MDP) challenges, and their expression levels were significantly upregulated in the intestine of grass carp. Additionally, the MDP-induced expression levels of intestinal inflammatory cytokines (TNF-α and IL-15) and an antimicrobial peptide (β-defensin) were significantly inhibited by the p38MAPK-specific inhibitor SB203580. Moreover, the nutritional dipeptide carnosine and Ala-Gln were found to significantly suppress the bacterial MDP-induced expression of p38MAPK pathway genes and inflammatory cytokines in the intestine of grass carp. Finally, overexpression analysis demonstrated that Cip38α and Cip38β could act as efficient activators in the regulation of AP-1 signaling pathways through interaction with CiMKK6. Altogether, this study provided experimental evidence of the presence of a functional p38 pathway in grass carp, which revealed its involvement in the intestinal immune response to bacterial challenges in bony fish.

Mitogen-activated protein (MAP) kinases are critical for cell signaling goals such as cellular proliferation and induction of apoptosis. We examined whether MAP kinases, as a point of convergence for multiple extracellular stimuli, are activated in proliferative glomerulonephritis (GN) in vivo. Accelerated crescentic anti-glomerular basement membrane (GBM) GN was induced in rats preimmunized with rabbit IgG by administration of rabbit anti-rat GBM serum. Whole cortical tissue and isolated glomeruli were then subjected to kinase activity assays and Western blot analysis. Cortical activity of the archetypal MAP kinase, extracellular signal-regulated kinase (ERK), was increased significantly one, three, and seven days after induction of GN. In contrast, activation of MAP kinases with antiproliferative actions, stress-activated protein kinase, and p38 MAP kinase was detectable only in the early stages of proliferative GN (days one and three), implying that different MAP kinases serve distinct roles in the pathogenesis of GN.

Mechanical ventilation causes ventilator-induced lung injury in animals and humans. Mitogen-activated protein kinases have been implicated in ventilator-induced lung injury though their functional significance remains incomplete. We characterize the role of p38 mitogen-activated protein kinase/mitogen activated protein kinase kinase-3 and c-Jun-NH(2)-terminal kinase-1 in ventilator-induced lung injury and investigate novel independent mechanisms contributing to lung injury during mechanical ventilation.

Zinc is an essential nutrient with remarkable importance for immunity, in particular for T-cell function. This is, at least in part, based on an involvement of zinc ions in immune cell signal transduction; dynamic changes of the intracellular free zinc concentration have recently been recognized as signaling events. Because the molecular targets of zinc signals remain incompletely understood, we investigated the impact of elevated intracellular free zinc on mitogen-activated protein kinase (MAPK) activity and MAPK-dependent cytokine production in human T-cells. p38 was activated by treatment with zinc and the ionophore pyrithione, whereas ERK1/2 and c-Jun N-terminal kinases were unaffected. In contrast, after T-cell receptor stimulation with antibodies against CD3, ERK1/2-phosphorylation was selectively suppressed by intracellular zinc. Mechanisms that had been shown to mediate zinc-effects in other cells, such as activation of the Src kinase Lck, inhibition of the protein tyrosine phosphatase CD45 or MAPK phosphatases and cyclic nucleotide/protein kinase A signaling were not involved. This indicates that the differential impact of zinc on the MAPK families in T-cells is mediated by mechanisms that differ from the ones observed in other cell types. Further investigation of the activation of p38 by zinc demonstrated that this MAPK is responsible for the zinc-mediated activation of CREB and mRNA expression of the Th1 cytokines interferon-gamma and interleukin-2. In conclusion, regulation of MAPK activity contributes to the impact of zinc on T-cell function.

Cleft lip repair surgery always results in visible scarring. It has been proved that scar formation can be reduced by inhibiting the p38 mitogen-activated protein kinases (p38MAPKs) signaling pathway. However, the interaction between p38MAPK and Smads in scar formation is still controversial.

Anopheles gambiae is the primary mosquito vector of human malaria parasites in sub-Saharan Africa. To date, three innate immune signaling pathways, including the nuclear factor (NF)-kappaB-dependent Toll and immune deficient (IMD) pathways and the Janus kinase/signal transducers and activators of transcription (Jak-STAT) pathway, have been extensively characterized in An. gambiae. However, in addition to NF-kappaB-dependent signaling, three mitogen-activated protein kinase (MAPK) pathways regulated by JNK, ERK and p38 MAPK are critical mediators of innate immunity in other invertebrates and in mammals. Our understanding of the roles of the MAPK signaling cascades in anopheline innate immunity is limited, so identification of the encoded complement of these proteins, their upstream activators, and phosphorylation profiles in response to relevant immune signals was warranted.

Chikungunya virus (CHIKV), a mosquito-borne Alphavirus, is endemic in different parts of the globe. The host macrophages are identified as the major cellular reservoirs of CHIKV during infection and this virus triggers robust TNF production in the host macrophages, which might be a key mediator of virus induced inflammation. However, the molecular mechanism underneath TNF induction is not understood yet. Accordingly, the Raw264.7 cells, a mouse macrophage cell line, were infected with CHIKV to address the above-mentioned question. It was observed that CHIKV induces both p38 and JNK phosphorylation in macrophages in a time-dependent manner and p-p38 inhibitor, SB203580 is effective in reducing infection even at lower concentration as compared to the p-JNK inhibitor, SP600125. However, inhibition of p-p38 and p-JNK decreased CHIKV induced TNF production in the host macrophages. Moreover, CHIKV induced macrophage derived TNF was found to facilitate TCR driven T cell activation. Additionally, it was noticed that the expressions of key transcription factors involved mainly in antiviral responses (p-IRF3) and TNF production (p-c-jun) were induced significantly in the CHIKV infected macrophages as compared to the corresponding mock cells. Further, it was demonstrated that CHIKV mediated TNF production in the macrophages is dependent on p38 and JNK MAPK pathways linking p-c-jun transcription factor. Interestingly, it was found that CHIKV nsP2 interacts with both p-p38 and p-JNK MAPKs in the macrophages. This observation was supported by the in silico protein-protein docking analysis which illustrates the specific amino acids responsible for the nsP2-MAPKs interactions. A strong polar interaction was predicted between Thr-180 (within the phosphorylation lip) of p38 and Gln-273 of nsP2, whereas, no such polar interaction was predicted for the phosphorylation lip of JNK which indicates the differential roles of p-p38 and p-JNK during CHIKV infection in the host macrophages. In summary, for the first time it has been shown that CHIKV triggers robust TNF production in the host macrophages via both p-p38 and p-JNK/p-c-jun pathways and the interaction of viral protein, nsP2 with these MAPKs during infection. Hence, this information might shed light in rationale-based drug designing strategies toward a possible control measure of CHIKV infection in future.

p38 mitogen-activated protein kinase (MAPK) signalling is critical in the pathophysiology of a variety of inflammatory processes. Leukocyte recruitment to the site of inflammation is a multistep process governed by specific signalling cascades. After adhesion in the lumen, many leukocytes crawl to optimal sites at endothelial junctions and transmigrate to extravascular tissue in a Mac-1-dependent manner. The signalling mechanisms that regulate postadhesion steps of intraluminal crawling, transmigration, and chemotaxis in tissue remain incompletely understood. The present study explored the effect of p38 MAPK inhibitor SB203580 on various parameters of neutrophil recruitment triggered by chemokine KC (CXCL1) gradient. Neutrophil-endothelial interactions in microvasculature of murine cremaster muscle were determined using intravital microscopy and time-lapsed video analysis. SB203580 (100 nM) did not change leukocyte rolling but significantly attenuated neutrophil adhesion, emigration, and transmigration and impaired the initiation of neutrophil crawling and transmigration. In response to KC chemotactic gradient, SB203580 significantly reduced the velocity of migration and chemotaxis index of neutrophils in tissue. The upregulation of Mac-1 expression in neutrophils stimulated by KC was significantly blunted by SB203580 in vitro. Collectively, our findings demonstrate that pharmacological suppression of p38 MAPK significantly impairs multiple steps of neutrophil recruitment in vivo.

The catechol metabolites of 17β-oestradiol (E2 β), 2-hydroxyoestradiol (2-OHE2 ) and 4-hydroxyoestradiol (4-OHE2 ), stimulate proliferation of pregnancy-derived ovine uterine artery endothelial cells (P-UAECs) through β-adrenoceptors (β-ARs) and independently of the classic oestrogen receptors (ERs). Herein we show that activation of ERK1/2, p38 and JNK mitogen activated protein kinases (MAPKs) is necessary for 2-OHE2 - and 4-OHE2 -induced P-UAEC proliferation, as well as proliferation induced by the parent hormone E2 β and other β-AR signalling hormones (i.e. catecholamines). Conversely, although 2-OHE2 and 4-OHE2 rapidly activate phosphatidylinositol 3-kinase (PI3K), its activation is not involved in catecholoestradiol-induced P-UAEC proliferation. We also show for the first time the signalling mechanisms involved in catecholoestradiol-induced P-UAEC proliferation; which converge at the level of MAPKs with the signalling mechanisms mediating E2 β- and catecholamine-induced proliferation. The present study advances our understanding of the complex signalling mechanisms involved in regulating uterine endothelial cell proliferation during pregnancy.

Thy-1 (CD90) crosslinking by monoclonal antibodies (mAb) in the context of costimulation causes the activation of mouse T-lymphocytes; however, the associated signal transduction processes have not been studied in detail. In this study we investigated the role of mitogen-activated protein kinases (MAPKs) in Thy-1-mediated T-lymphocyte activation using mAb-coated polystyrene microspheres to crosslink Thy-1 and costimulatory CD28 on murine T-lymphocytes. Concurrent Thy-1 and CD28 crosslinking induced DNA synthesis by T-lymphocytes, as well as interleukin (IL)-2 and IL-2 receptor (IL-2R) alpha chain (CD25) expression. Increased phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, p38 MAPK, and c-Jun N-terminal protein kinase (JNK) was also observed. Pharmacologic inhibition of ERK1/2 or JNK activation inhibited Thy-1-induced DNA synthesis and IL-2 production by T-lymphocytes. p38 MAPK inhibition also decreased DNA synthesis in Thy-1-stimulated T-lymphocytes; however, IL-2 production was increased in these cells. Inhibition of JNK, but not ERK1/2 or p38 MAPK, caused a marked reduction in Thy-1-induced CD25 expression. In addition, inhibition of p38 MAPK or JNK, but not ERK1/2, impaired the growth of IL-2-dependent CTLL-2 T-lymphocytes but did not substantially affect CD25 expression. Finally, exogenous IL-2 reversed the inhibitory effect of ERK1/2 or JNK inhibition on Thy-1-stimulated DNA synthesis by T-lymphocytes but did not substantially reverse JNK inhibition of CD25 expression. Collectively, these results suggest that during Thy-1-induced T-lymphocyte activation, ERK1/2 and JNK promoted IL-2 production whereas p38 MAPK negatively regulated IL-2 expression. JNK signalling was also required for CD25 expression. IL-2R signalling involved both p38 MAPK and JNK in CTLL-2 cells, whereas p38 MAPK was most important for IL-2R signalling in primary T-lymphocytes. MAPKs are therefore essential signalling intermediates for the Thy-1-driven proliferation of mouse T-lymphocytes.

We previously demonstrated that Group B Streptococcus (GBS), a pathogen that causes serious neonatal infections, induces macrophage apoptosis by beta-hemolysin to avoid the host immune response. GBS-induced macrophage apoptosis is characterized by a calcium increase and is caspase-independent. This study reports the involvement of c-Jun NH(2)-terminal kinase (JNK), p38 and extracellular signal-regulated kinase (ERK), three members of mitogen-activated protein kinases (MAPKs) family, in GBS-induced macrophage apoptosis. Our data indicate that during induction of apoptosis live GBS stimulates a strong persistent activation of JNK and p38 with concomitant inhibition of ERK. The time courses of MAPKs activation strongly correlate with GBS-induced macrophage apoptosis and are macrophage:GBS ratio-dependent. In fact, when GBS does not cause macrophage apoptosis, e.g. low macrophage:GBS ratio or non hemolytic GBS (gGBS), it induces a transient activation of JNK, p38, and ERK MAPKs. These latter results indicate that sustained and persistent activation of JNK and p38 and inhibition of ERK are involved in the GBS-induced macrophage apoptotic process and suggest that the time course and balance of MAPKs activation are critical for different macrophage responses to GBS (apoptosis versus antimicrobicidal activity). This study indicates a correlation between MAPKs activation and GBS-induced macrophage apoptosis. However, since neither ERK nor p38 inhibitors had an effect on GBS-induced apoptosis, their role in the complex signal network leading to GBS-induced macrophage apoptosis remains to be defined.

Inducible prostaglandin synthase (cyclooxygenase-2, COX-2) is expressed in rheumatoid and osteoarthritic cartilage and produces high amounts of proinflammatory prostanoids in the joint. In the present study we investigated the effects of the inhibitors of mitogen-activated protein kinase (MAPK) pathways Erk1/2, p38, and JNK on COX-2 expression and prostaglandin E2 (PGE2) production in human chondrocytes. Proinflammatory cytokine IL-1beta caused a transient activation of Erk1/2, p38, and JNK in immortalized human T/C28a2 chondrocytes and that was followed by enhanced COX-2 expression and PGE2 production. PD98059 (an inhibitor of Erk1/2 pathway) suppressed IL-1-induced COX-2 expression and PGE2 production in a dose-dependent manner, and seemed to have an inhibitory effect on COX-2 activity. SB203580 (an inhibitor of p38 pathway) but not its negative control compound SB202474 inhibited COX-2 protein and mRNA expression and subsequent PGE2 synthesis at micromolar drug concentrations. SP600125 (a recently developed JNK inhibitor) but not its negative control compound N1-methyl-1,9-pyrazolanthrone downregulated COX-2 expression and PGE2 formation in a dose-dependent manner. SP600125 did not downregulate IL-1-induced COX-2 mRNA expression when measured 2 h after addition of IL-1beta but suppressed mRNA levels in the later time points suggesting post-transcriptional regulation. Our results suggest that activation of Erk1/2, p38, and JNK pathways belongs to the signaling cascades that mediate the upregulation of COX-2 expression and PGE2 production in human chondrocytes exposed to proinflammatory cytokine IL-1beta.

We have previously reported that platelet-derived growth factor (PDGF)-BB stimulates synthesis of interleukin-6 (IL-6), a potent bone resorptive agent, in osteoblast-like MC3T3-E1 cells, and that the activation of p44/p42 mitogen-activated protein (MAP) kinase, p38MAP kinase and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) is implicated in the IL-6 synthesis. In the present study,we investigated the involvement of AMP-activated protein kinase (AMPK), a regulator of energy metabolism, in the PDGF-BB-stimulated IL-6 synthesis in MC3T3-E1 cells.

Endocytic trafficking plays an important role in the regulation of the epidermal growth factor receptor (EGFR). To address if cellular kinases regulate EGFR internalization, we used anisomycin, a potent activator of kinase cascades in mammalian cells, especially the stress-activated mitogen-activated protein (MAP) kinase subtypes. Here, we report that activation of p38 MAP kinase by anisomycin is sufficient to induce internalization of EGFR. Anisomycin and EGF employ different mechanisms to promote EGFR endocytosis as anisomycin-induced internalization does not require tyrosine kinase activity or ubiquitination of the receptor. In addition, anisomycin treatment did not result in delivery and degradation of EGFR at lysosomes. Incubation with a specific inhibitor of p38, or depletion of endogenous p38 by small interfering RNAs, abolished anisomycin-induced internalization of EGFR while having no effect on transferrin endocytosis, indicating that the effect of p38 activation on EGFR endocytosis is specific. Interestingly, inhibition of p38 activation also abolished endocytosis of EGFR induced by UV radiation. Our results reveal a novel role for p38 in the regulation of EGFR endocytosis and suggest that stimulation of EGFR internalization by p38 might represent a general mechanism to prevent generation of proliferative or anti-apoptotic signals under stress conditions.

Extracellular signal-regulated kinase and p38 have been shown to be cleaved in human neutrophils undergoing apoptosis induced by tumor necrosis factor-alpha and cycloheximide. However, the cleavage products of these molecules were undetected when apoptotic neutrophils were pretreated with phenylmethylsulfonyl fluoride or disrupted by nitrogen cavitation before preparation of cell lysates. The electron microscopy revealed that granules in apoptotic neutrophils were significantly swollen than those in control cells. These findings suggest that granule membrane may become destabilized during neutrophil apoptosis, leading to rapid proteolysis of these molecules by granule-derived serine proteases during preparation of cell lysates with the conventional lysis buffer.

Osteosarcoma (OS) is the most common malignant bone tumor in children and adolescents. Accumulating evidence has revealed that microRNAs (miRNAs) play a crucial role in the progression of OS. In this study, we found that miR-744-5p was the least expressed miRNA in patients with OS by analyzing GSE65071 from the GENE EXPRESSION OMNIBUS (GEO) database. Through real-time quantitative PCR (qRT-PCR), western blotting, colony formation assay, 5-Ethynyl-2-Deoxyuridine (EdU) incorporation assay, transwell migration, and invasion assays, we demonstrated its ability to inhibit the proliferation, migration, and invasion of OS cells in vitro. According to the luciferase reporter assay, transforming growth factor-β1 (TGFB1) was negatively regulated by miR-744-5p and reversed the effects of miR-744-5p on OS. Subcutaneous tumor-forming animal models and tail vein injection lung metastatic models were used in animal experiments, and it was found that miR-744-5p negatively regulated tumor growth and metastasis in vivo. Furthermore, rescue assays verified that miR-744-5p regulates TGFB1 expression in OS. Further experiments revealed that the p38 MAPK signaling pathway is involved in the miR-744-5p/TGFB1 axis. Generally, this study suggests that miR-744-5p is a negative regulator of TGFB1 and suppresses OS progression and metastasis via the p38 MAPK signaling pathway.