Activation and signaling of the p38 MAP kinase pathway

The family members of the mitogen-activated protein (MAP) kinases mediate a wide variety of cellular behaviors in response to extracellular stimuli. One of the four main sub-groups, the p38 group of MAP kinases, serve as a nexus for signal transduction and play a vital role in numerous biological processes. In this review, we highlight the known characteristics and components of the p38 pathway along with the mechanism and consequences of p38 activation. We focus on the role of p38 as a signal transduction mediator and examine the evidence linking p38 to inflammation, cell cycle, cell death, development, cell differentiation, senescence and tumorigenesis in specific cell types. Upstream and downstream components of p38 are described and questions remaining to be answered are posed. Finally, we propose several directions for future research on p38.     

Schistosoma mansoni excretory-secretory products stimulate a p38 signalling pathway in Biomphalaria glabrata embryonic cells

Following infection with Schistosoma mansoni larvae, haemocytes of resistant Biomphalaria glabrata snails execute a rapid defence during which they migrate towards and encapsulate the parasites. Such immediate and precise responses are thought to depend on signal transduction cascades though the signalling components involved remain largely unknown. It is proposed that mitogen-activated protein kinases may play a role in B. glabrata immune signalling, in particular p38 mitogen-activated protein kinases, which are known to be associated with stress and inflammatory signalling. Using degenerate PCR followed by Rapid Amplification of cDNA Ends a full-length p38 mitogen-activated protein kinase-like cDNA was cloned from both the B. glabrata embryonic (Bge) cell line (Bge-p38) and haemocytes (Bgh-p38). In addition, B. glabrata p38 mitogen-activated protein kinase activation was examined at the protein level in Western blot analyses using an antibody that specifically recognises activated/diphosphorylated p38 mitogen-activated protein kinase. Results showed that Bge cell p38 mitogen-activated protein kinase was activated/phosphorylated following 30 min incubation with anisomycin, an established p38 mitogen-activated protein kinase activator. Furthermore, p38 mitogen-activated protein kinase was also activated after only 5 min exposure to either the beta-glucan polymer laminarin or S. mansoni larval excretory-secretory products. In a comparative study, activated haemocyte p38 mitogen-activated protein kinase could also be detected using the anti-phosphorylated p38 antibody following cell treatment with anisomycin. However, in contrast with Bge cells, haemocyte p38 was not activated by either excretory-secretory products or laminarin treatments, suggesting fundamental differences in the role of p38 mitogen-activated protein kinase in signal transduction pathways between haemocytes and Bge cells.     

p38 MAPK信号转导途径在关节软骨细胞中的激活和作用

p38信号转导途径是MAPK途径的一种,软骨细胞是关节软骨中唯一的细胞成分。软骨细胞中的p38 MAPK可以被多种细胞因子、机械因素等所激活,它与软骨细胞表型的保持和分化、软骨细胞的肥大化和钙化、凋亡、软骨基质金属蛋白酶的合成、软骨炎性细胞因子的产生等有密切关系,可能在关节炎的发生发展中发挥了重要作用。     

ATR (ataxia telangiectasia mutated- and Rad3-related kinase) is activated by mild hypothermia in mammalian cells and subsequently activates p53

In vitro cultured mammalian cells respond to mild hypothermia (27-33?°C) by attenuating cellular processes and slowing and arresting the cell cycle. The slowing of the cell cycle at the upper range (31-33?°C) and its complete arrest at the lower range (27-28?°C) of mild hypothermia is effected by the activation of p53 and subsequent expression of p21. However, the mechanism by which cold is perceived in mammalian cells with the subsequent activation of p53 has remained undetermined. In the present paper, we report that the exposure of Chinese-hamster ovary-K1 cells to mildly hypothermic conditions activates the ATR (ataxia telangiectasia mutated- and Rad3-related kinase)-p53-p21 signalling pathway and is thus a key pathway involved in p53 activation upon mild hypothermia. In addition, we show that although p38MAPK (p38 mitogen-activated protein kinase) is also involved in activation of p53 upon mild hypothermia, this is probably the result of activation of p38MAPK by ATR. Furthermore, we show that cold-induced changes in cell membrane lipid composition are correlated with the activation of the ATR-p53-p21 pathway. Therefore we provide the first mechanistic detail of cell sensing and signalling upon mild hypothermia in mammalian cells leading to p53 and p21 activation, which is known to lead to cell cycle arrest.     

Oleoylethanolamide,a natural ligand for PPAR-alpha,inhibits insulin receptor signalling in HTC rat hepatoma cells

Oleoylethanolamide (OEA) is a lipid mediator belonging to the fatty acid ethanolamides family. It is produced by intestine and adipose tissue. It inhibits food intake and body weight gain, and has hypolipemiant action in vivo, as well as a lipolytic effect in vitro. OEA is a PPAR-alpha agonist, and recently it has been found that OEA is an endogenous ligand of an orphan receptor. Previously, we have shown that OEA inhibits insulin-stimulated glucose uptake in isolated adipocytes, and produces glucose intolerance in rats. In the present work, we have studied another insulin target cell, the hepatocyte using a rat hepatoma cell line (HTC), and we have studied the cross-talk of OEA signalling with metabolic and mitotic signal transduction of insulin receptor. OEA dose-dependently activates JNK and p38 MAPK, and inhibits insulin receptor phosphorylation. OEA inhibits insulin receptor activation, blunting insulin signalling in the downstream PI3K pathway, decreasing phosphorylation of PKB and its target GSK-3. OEA also inhibits insulin-dependent MAPK pathway, as assessed by immunoblot of phosphorylated MEK and MAPK. These effects were reversed by blocking JNK or p38 MAPK using pharmacological inhibitors (SP 600125, and SB 203580). Since OEA is an endogenous PPAR-alpha agonist, we investigated whether a pharmacologic agonist (WY 14643) may mimic the OEA effect on insulin receptor signalling. Activation of PPAR-alpha by the pharmacological agonist WY14643 in HTC hepatoma cells is sufficient to inhibit insulin signalling and this effect is also dependent on p38 MAPK but not JNK kinase. In summary, OEA inhibits insulin metabolic and mitogenic signalling by activation of JNK and p38 MAPK via PPAR-alpha.     

Phosphorylation of RSK2 at Tyr529 by FGFR2-p38 enhances human mammary epithelial cells migration

The members of p90 ribosomal S6 kinase (RSK) family of Ser/Thr kinases are downstream effectors of MAPK/ERK pathway that regulate diverse cellular processes including cell growth, proliferation and survival. In carcinogenesis, RSKs are thought to modulate cell motility, invasion and metastasis. Herein, we have studied an involvement of RSKs in FGF2/FGFR2-driven behaviours of mammary epithelial and breast cancer cells. We found that both silencing and inhibiting of FGFR2 attenuated phosphorylation of RSKs, whereas FGFR2 overexpression and/or its stimulation with FGF2 enhanced RSKs activity. Moreover, treatment with ERK, Src and p38 inhibitors revealed that p38 kinase acts as an upstream RSK2 regulator. We demonstrate for the first time that in FGF2/FGFR2 signalling, p38 but not MEK/ERK, indirectly activated RSK2 at Tyr529, which facilitated phosphorylation of its other residues (Thr359/Ser363, Thr573 and Ser380). In contrast to FGF2-triggered signalling, inhibition of p38 in the EGF pathway affected only RSK2-Tyr529, without any impact on the remaining RSK phosphorylation sites. p38-mediated phosphorylation of RSK2-Tyr529 was crucial for the transactivation of residues located at kinase C-terminal domain and linker-region, specifically, in the FGF2/FGFR2 signalling pathway. Furthermore, we show that FGF2 promoted anchorage-independent cell proliferation, formation of focal adhesions and cell migration, which was effectively abolished by treatment with RSKs inhibitor (FMK). These indicate that RSK2 activity is indispensable for FGF2/FGFR2-mediated cellular effects. Our findings identified a new FGF2/FGFR2-p38-RSK2 pathway, which may play a significant role in the pathogenesis and progression of breast cancer and, hence, may present a novel therapeutic target in the treatment of FGFR2-expressing tumours.     

Robustness and fragility in the yeast high osmolarity glycerol (HOG) signal‐transduction pathway

Cellular signalling networks integrate environmental stimuli with the information on cellular status. These networks must be robust against stochastic fluctuations in stimuli as well as in the amounts of signalling components. Here, we challenge the yeast HOG signal‐transduction pathway with systematic perturbations in components’ expression levels under various external conditions in search for nodes of fragility. We observe a substantially higher frequency of fragile nodes in this signal‐transduction pathway than that has been observed for other cellular processes. These fragilities disperse without any clear pattern over biochemical functions or location in pathway topology and they are largely independent of pathway activation by external stimuli. However, the strongest toxicities are caused by pathway hyperactivation. In silico analysis highlights the impact of model structure on in silico robustness, and suggests complex formation and scaffolding as important contributors to the observed fragility patterns. Thus, in vivo robustness data can be used to discriminate and improve mathematical models.     

Emerging MAP kinase pathways in plant stress signalling

Mitogen-activated protein kinase (MAPK) pathways transfer information from sensors to cellular responses in all eukaryotes. A surprisingly large number of genes encoding MAPK pathway components have been uncovered by analysing model plant genomes, suggesting that MAPK cascades are abundant players of signal transduction. Recent investigations have confirmed major roles of defined MAPK pathways in development, cell proliferation and hormone physiology, as well as in biotic and abiotic stress signalling. Latest insights and findings are discussed in the context of novel MAPK pathways in plant stress signalling.     

The pathways to tumor suppression via route p38

Besides its well-known functions in inflammation and other stresses, the p38 mitogen-activated protein kinase pathway also negatively regulates cell proliferation and tumorigenesis. Inactivation of the p38 pathway enhances cellular transformation and renders mice prone to tumor development with concurrent disruption of the induction of senescence. Conversely, persistent activation of p38 inhibits tumorigenesis. Mechanistic insights into this additional p38 function are starting to emerge. For example, p38 has been shown to have a crucial role in oncogene-induced senescence, replicative senescence, DNA-damage responses and contact-inhibition. In addition, the role of the p38 pathway in proliferative control and tumor suppression is mediated by its impact on several cell-cycle regulators. These findings reveal a tumor-suppressing function of the p38 pathway, and indicate that components of the p38 pathway are potential targets for novel cancer therapies.     

CK2 is acting upstream of MEK3/6 as a part of the signal control of ERK1/2 and p38 MAPK during keratinocytes autocrine differentiation

Protein kinase CK2 (formerly termed "casein kinase II") is a ubiquitously in mammalian cells distributed Ser/Thr kinase, with global role in cell regulation. Although, the involvement of CK2 in cell signalling is vast-investigated, virtually nothing is known about its contribution to signal control of keratinocytes differentiation. Here we show that, in autocrine differentiating keratinocytes, inhibition of the CK2 activity induced by 4,5,6,7-tetrabromobenzotriazole (TBB) causes reciprocal changes in the activities of major signal transduction regulators of keratinocytes differentiation, i.e. ERK1/2 and p38 MAPK, without affecting their protein levels. The ERK1/2 activity is strongly suppressed, while the activity of p38 is increased. We have also found that the activity of upstream and specific for p38 MAPK kinase MEK3/6 is also stimulated by TBB. These original results clearly demonstrate the participation of CK2 in the signal transduction pathway controlling MEK3/6, p38 MAPK, and ERK1/2 in the used model system.     

p38 Mitogen-activated protein kinase regulation of endothelial cell migration depends on urokinase plasminogen activator expression

The migration of endothelial cells in response to various stimulating factors plays an essential role in angiogenesis. The p38 MAPK pathway has been implicated to play an important role in endothelial cell migration because inhibiting p38 MAPK activity down-regulates vascular endothelial growth factor (VEGF)-stimulated migration. Currently, the signaling components in the p38 MAPK activation pathway and especially the mechanisms responsible for p38 MAPK-regulated endothelial cell migration are not well understood. In the present study, we found that p38 MAPK activity is required for endothelial cell migration stimulated by both VEGF and nongrowth factor stimulants, sphingosine 1-phosphate and soluble vascular cell adhesion molecule. By using dominant negative forms of signaling components in the p38 MAPK pathway, we identified that a regulatory pathway consisting of MKK3-p38alpha/gamma-MAPK-activated protein kinase 2 participated in VEGF-stimulated migration. In further studies, we showed that a minimum of a 10-h treatment with SB203580 (specific p38 MAPK inhibitor) was needed to block VEGF-stimulated migration, suggesting an indirect role of p38 MAPK in this cellular event. Most interestingly, the occurrence of SB203580-induced migratory inhibition coincided with a reduction of urokinase plasminogen activator (uPA) expression. Furthermore, agents disrupting uPA and uPA receptor interaction abrogated VEGF-stimulated cell migration. These results suggest a possible association between cell migration and uPA expression. Indeed, VEGF-stimulated migration was not compromised by SB203580 in endothelial cells expressing the uPA transgene; however, VEGF-stimulated migration was inhibited by agents disrupting uPA-uPA receptor interaction. These results thus suggest that the p38 MAPK pathway participates in endothelial cell migration by regulating uPA expression.     

Rho/ROCK-dependent pseudopodial protrusion and cellular blebbing are regulated by p38 MAPK in tumour cells exhibiting autocrine c-Met activation

BACKGROUND INFORMATION: The c-Met-dependent, beta-actin-rich, blebbed pseudopodia of MSV-MDCK-INV (invasive Moloney-sarcoma-virus-transformed Madin-Darby canine kidney) cells are induced by Rho/ROCK (Rho kinase) activation, and are morphologically distinct from flat extended lamellipodia. RESULTS: Microtubules were shown to extend to these actin-rich pseudopodial domains, and microtubule depolymerization by nocodazole treatment resulted in progressive cellular blebbing, initiating in the pseudopodial domains and resulting in transient cellular rounding and blebbing after 30 min. The blebbing response was dependent on autocrine HGF (hepatocyte growth factor) activation of c-Met and prevented by inhibition of RhoA, ROCK and p38 MAPK (p38 mitogen-activated protein kinase), but not ERK (extracellular-signal-regulated kinase) or PI3K (phosphoinositide 3-kinase). Phospho-p38 MAPK was present in pseudopodia, localizing activation of this signalling pathway to this protrusive membrane structure. In serum-starved cells, LPA (lysophosphatidic acid) activation of RhoA induced p38 MAPK-dependent pseudopodial protrusions, and inhibition of p38 MAPK prevented pseudopodial protrusion and displacement of MSV-MDCK-INV cells. MSV-MDCK-INV cells exhibited intermittent blebbing and rounding, which may represent an integral part of their motile behaviour. CONCLUSIONS: The localized activation of an autocrine HGF/c-Met loop regulates Rho/ROCK activation of p38 MAPK signalling to stimulate both membrane blebbing and pseudopod formation.     

Contribution of circulating leukocytes to cytokine production in pancreatic duct obstruction-induced acute pancreatitis in rats

p38 MAPK was originally characterized as a stress-induced kinase, along with JNK. Subsequently, p38 MAPK was found to be activated by stimuli other than cellular stress, such as growth factors and mitogens, like interleukin (IL)-2, IL-7 and IL-3. A notable exception was IL-4, as studies in mast cells showed no activation of p38 MAPK by this cytokine. In this study we show that the regulation of p38 MAPK is cell type dependent. Like other cytokines that signal through the gamma (gamma)(c), IL-4 can activate p38 MAPK in the CT6 T-cell line and BA/F3 pro-B-cells. However, IL-4 was unable to activate p38 MAPK in the murine macrophage cell line, RAW 264.7 and, indeed, prolonged exposure of cells to IL-4 results in suppression of LPS-induced MAPK activation. This result correlates with the well defined inhibitory effect of IL-4 on tumour necrosis factor alpha (TNFalpha) production. In contrast, studies in primary human monocytes showed that prolonged exposure to IL-4 resulted in enhanced activation of LPS-stimulated p38 MAPK; this correlated with an enhanced TNFalpha production. These data highlight the complexity of IL-4 signalling mechanisms, the diversity that can exist in the regulation of a given signalling pathway by a given cytokine and, furthermore, indicate the problems that can arise from extrapolation between different cell systems.