Characterization of the structure and function of the fourth member of p38 group mitogen-activated protein kinases, p38delta

The p38 mitogen-activated protein kinase (MAPK) pathway in rheumatoid arthritis

Chronic inflammatory processes are based on a sustained and tightly regulated communication network among different cells types. This network comprises extracellular mediators such as cytokines, chemokines and matrix-degrading proteases, which orchestrate the participation of cells in the chronic inflammatory process. The mirrors of this outside communication world are intracellular transcription factor pathways, which shuttle information about inflammatory stimuli to the cell nucleus. This review examines the function of one key signal transduction pathway of inflammation--the p38 mitogen-activated protein kinases (p38MAPK). The signalling pathway is considered as crucial for the induction and maintenance of chronic inflammation, and its components thus emerge as interesting molecular targets of small molecule inhibitors for controlling inflammation. This review not only summarises the current knowledge of activation, regulation and function of the p38MAPK pathway but also examines the role of this pathway in clinical disease. It gives an overview of current evidence of p38MAPK activation in inflammatory arthritis and elaborates the key molecular determinants which contribute to p38MAPK activation in joint disease.

MKP-1 inhibits high NaCl-induced activation of p38 but does not inhibit the activation of TonEBP/OREBP: opposite roles of p38alpha and p38delta

High NaCl rapidly activates p38 MAPK by phosphorylating it, the phosphorylation presumably being regulated by a balance of kinases and phosphatases. Kinases are known, but the phosphatases are uncertain. Our initial purpose was to identify the phosphatases. We find that in HEK293 cells transient overexpression of MAPK phosphatase-1 (MKP-1), a dual-specificity phosphatase, inhibits high NaCl-induced phosphorylation of p38, and that overexpression of a dominant negative mutant of MKP-1 does the opposite. High NaCl lowers MKP-1 activity by increasing reactive oxygen species, which directly inhibit MKP-1, and by reducing binding of MKP-1 to p38. Because inhibition of p38 is reported to reduce hypertonicity-induced activation of the osmoprotective transcription factor, TonEBP/OREBP, we anticipated that MKP-1 expression might also. However, overexpression of MKP-1 has no significant effect on Ton EBP/OREBP activity. This paradox is explained by opposing effects of p38alpha and p38delta, both of which are activated by high NaCl and inhibited by MKP-1. Thus, we find that overexpression of p38alpha increases high NaCl-induced TonEBP/OREBP activity, but overexpression of p38delta reduces it. Also, siRNA-mediated knockdown of p38delta enhances the activation of TonEBP/OREBP. We conclude that high NaCl inhibits MKP-1, which contributes to the activation of p38. However, opposing actions of p38alpha and p38delta negate any effect on TonEBP/OREBP activity. Thus, activation of p38 isoforms by hypertonicity does not contribute to activation of TonEBP/OREBP because of opposing effects of p38alpha and p38delta, and effects of inhibitors of p38 depend on which isoform is affected, which can be misleading.

Pharmacological properties of SD-282 - an alpha-isoform selective inhibitor for p38 MAP kinase

The effects of small-molecule p38 inhibitors in numerous models of different disease states have been published, including those of SD-282, an indole-5-carboxamide inhibitor. The aim of the present study was to evaluate the pharmacological activity of SD-282 on cytokine production in vitro as well as in 2 in vivo models of inflammation in order to illuminate the role of this particular inhibitor in diverse disease states. The results presented here provide further characterization of SD-282 and provide a context in which to interpret the activity of this p38 inhibitor in models of arthritis, pain, myocardial injury, sepsis and asthma; all of which have an inflammatory component. SD-282 represents a valuable tool to elucidate the role of p38 MAP kinase in multiple models of inflammation.

p38 mitogen-activated protein kinase is required for central nervous system myelination

The p38 MAPKs are a family of kinases that regulate a number of cellular functions including cell migration, proliferation, and differentiation. Here, we report that p38 regulates oligodendrocyte differentiation. Inhibition of p38 with PD169316 and SB203580 prevented accumulation of protein and mRNA of cell-stage specific markers characteristic of differentiated oligodendrocytes, including myelin basic protein, myelin-associated glycoprotein, and the glycosphingolipids, galactosylceramide and sulfatide. In addition, the cell cycle regulator p27(kip1) and the transcription factor Sox10 were also significantly reduced. Most significantly, p38 inhibitors completely and irreversibly blocked myelination of dorsal root ganglion neurons by oligodendrocytes and prevented the axolemmal organization of the axo-glial adhesion molecule Caspr. Our results suggest a role(s) for this kinase in key regulatory steps in the maturation of OLGs and initiation of myelination.

Involvement of p38alpha in kainate-induced seizure and neuronal cell damage

We investigated how p38alpha mitogen-activated protein kinase (p38) is related to kainate-induced epilepsy and neuronal damages, by using the mice with a single copy disruption of the p38 alpha gene (p38alpha(+/-)). Mortality rate and seizure score of p38alpha(+/-) mice administered with kainate were significantly reduced compared with the case of wild-type (WT) mice. This was clearly supported by the electroencephalography data in which kainate-induced seizure duration and frequency in the brain of p38alpha(+/-) mice were significantly suppressed compared to those of WT mice. As a consequence of seizure, kainate induced delayed neuronal damages in parallel with astrocytic growth in the hippocampus and ectopic innervation of the mossy fibers into the stratum oriens in the CA3 region of hippocampus in WT mice, whose changes were moderate in p38alpha(+/-) mice. Likewise, kainate-induced phosphorylation of calcium/calmodulin-dependent kinase II in the hippocampus of p38alpha (+/-) mice was significantly decreased compared to that of WT mice. These results suggest that p38alpha signaling pathway plays an important role in epileptic seizure and excitotoxicity.

p38 MAP-kinases pathway regulation, function and role in human diseases

Mammalian p38 mitogen-activated protein kinases (MAPKs) are activated by a wide range of cellular stresses as well as in response to inflammatory cytokines. There are four members of the p38MAPK family (p38alpha, p38beta, p38gamma and p38delta) which are about 60% identical in their amino acid sequence but differ in their expression patterns, substrate specificities and sensitivities to chemical inhibitors such as SB203580. A large body of evidences indicates that p38MAPK activity is critical for normal immune and inflammatory response. The p38MAPK pathway is a key regulator of pro-inflammatory cytokines biosynthesis at the transcriptional and translational levels, which makes different components of this pathway potential targets for the treatment of autoimmune and inflammatory diseases. However, recent studies have shed light on the broad effect of p38MAPK activation in the control of many other aspects of the physiology of the cell, such as control of cell cycle or cytoskeleton remodelling. Here we focus on these emergent roles of p38MAPKs and their implication in different pathologies.

Transfection of antisense p38α gene ameliorates myocardial cell injury mediated by hypoxia and burn serum

BACKGROUND

Myocardial damage occurs immediately following severe burns even before significant reduction in blood volume. This phenomenon is called postburn "shock heart" ("cardiac shock"), the pathogenesis of which is unclear. This study was designed to investigate the role of antisense p38 alpha gene transfection in ameliorating hypoxia and burn serum-mediated myocardial cell injury.

METHODS

A model of myocardial cells cultured under hypoxia and with burn serum was established. The cells were divided into control group (group C), the group cultured under hypoxia plus burn serum (group HS), and the group treated with antisense p38 alpha gene transfection (group A-p38 alpha) and cultured under hypoxia plus burn serum. Burn serum was collected from Wistar rats with 40% TBSA III degree burns. Hypoxia was produced using a mixed gas with 1% O(2). Antisense p38 alpha gene recombinants were constructed and expression of p38 alpha kinase, and NF-kappaB subunits p50, p65 and I kappa B alpha in myocardial cells were detected by Western blot. Myocardial viability was determined by tetrazolium colorimetry (MTT). Apoptosis was detected by flow cytometry. Lactate dehydrogenase (LDH) activity in cell culture supernatants was determined. Changes in TNFalpha and IL-1 beta mRNA expression were detected by RT-PCR.

RESULTS

Activation of p38 alpha kinase, expression of NF-kappaB p50, NF-kappaB p65 and I kappa B protein, and TNFalpha and IL-1 beta were downregulated significantly following antisense p38 alpha gene transfection into myocardial cells treated with hypoxia plus burn serum. Myocardial apoptosis and LDH activity in cell culture supernatants decreased markedly and myocardial viability increased significantly in the antisense p38 alpha gene treated group.

CONCLUSIONS

Results demonstrated that transfection of antisense p38 alpha gene diminishes myocardial cell injury mediated by hypoxia and burn serum, suggesting a new target for the prevention and treatment of myocardial damage after burn.

The role of p38 mitogen-activated kinase (MAPK) in the mechanism regulating cyclooxygenase gene expression in equine leukocytes

The goal of this study was to define the role for p38 mitogen-activated kinase (MAPK) in the signaling mechanism regulating pro-inflammatory cyclooxygenase (COX) gene expression in lipopolysaccharide (LPS)-activated equine leukocytes for the purposes of identifying novel targets for anti-inflammatory therapy in endotoxemic horses. The p38 MAPK has been shown to positively regulate inflammatory gene expression in human leukocytes and can be activated by a variety of stimuli including LPS, TNF-alpha, and IL-1. Activation-associated phosphorylated p38 MAPK has been implicated in the up-regulation of several inflammatory genes, including COX-2 which ultimately results in the production of prostanoids that are responsible for the pathophysiology associated with endotoxemia. Our hypothesis is that activation of p38 MAPK is essential for LPS-induced COX-2 expression in equine peripheral blood leukocytes. We tested our hypothesis by investigating the effects of the specific p38 MAPK inhibitors SB203580 and SB202190 on LPS-induced COX-2 protein expression and PGE(2) production in equine leukocytes. LPS stimulation activated p38 MAPK and increased COX-2 expression in a dose-dependent manner with maximal activation observed after 30min and 4h, respectively, at a concentration of 10 ng/ml LPS. In contrast, LPS stimulation did not affect COX-1 protein expression. Pretreatment with SB203580 or SB202190 significantly inhibited LPS-induced activation-associated p38 MAPK phosphorylation, COX-2 mRNA and protein levels, and PGE(2) production in equine leukocytes. Maximal inhibition of LPS-induced COX-2 protein expression was achieved at a concentration of 10 microM SB203580. We concluded that p38 MAPK is essential for LPS-induced COX-2 expression suggesting that p38 MAPK is a potential target for anti-inflammatory therapy during equine endotoxemia.

Exercise, MAPK, and NF-κB signaling in skeletal muscle

Mitogen-activated protein kinases (MAPKs) and NF-κB are two major regulators of gene transcription and metabolism in response to oxidative, energetic, and mechanical stress in skeletal muscle. Chronic activation of these signaling pathways has been implicated in the development and perpetuation of various pathologies, such as diabetes and cachexia. However, both MAPK and NF-κB are also stimulated by exercise, which promotes improvements in fuel homeostasis and can prevent skeletal muscle atrophy. This review will first discuss the major MAPK signaling modules in skeletal muscle, their differential activation by exercise, and speculated functions on acute substrate metabolism and exercise-induced gene expression. Focus will then shift to examination of the NF-κB pathway, including its mechanism of activation by cellular stress and its putative mediation of exercise-stimulated adaptations in antioxidant status, tissue regeneration, and metabolism. Although limited, there is additional evidence to suggest cross talk between MAPK and NF-κB signals with exercise. The objectives herein are twofold: 1) to determine how and why exercise activates MAPK and NF-κB; and 2) to resolve their paradoxical activation during diseased and healthy conditions.

Lysophosphatidic acid induces prostate cancer PC3 cell migration via activation of LPA(1), p42 and p38alpha

Prostate cancer cell migration is an essential event both in the progression of prostate cancer and in the steps leading to metastasis. We report here that lysophosphatidic acid (LPA), a potent bioactive phospholipid, induces prostate cancer PC3 cell migration via the activation of the LPA(1) receptor, which is linked to a PTX-sensitive activation mechanism of the mitogen-activated protein kinases (MAPK). Our results demonstrate that parallel activation of ERK1/2 and p38, but not JNK, is responsible for LPA-stimulated PC3 cell migration. Furthermore, using small interfering RNA (siRNA) technology, and overexpressing dominant-negative mutants of p38 MAPK isotypes of alpha, beta, gamma and delta, we have identified that the activation of ERK2 (p42) and p38alpha, but not of ERK1 and the other isoforms of p38 MAPK, is required for LPA-induced migration. Our study provides the first evidence for a functional role of p42 and p38alpha in LPA-induced mammalian cell migration, and also demonstrates, for the first time, that the receptor LPA(1) mediates prostate cancer cell migration. The results of the present study suggest that LPA, the receptor LPA(1), ERK2 and p38alpha are important regulators for prostate cancer cell invasion and thus could play a significant role in the development of metastasis.

Suppression of c-Src activity stimulates muscle differentiation via p38 MAPK activation

Role of c-Src in muscle differentiation has been controversial. Here, we investigated if c-Src positively or negatively regulates muscle differentiation, using H9c2 and C2C12 cell lines. Inhibition of c-Src by treatment with PP1 and SU6656, pharmacologic inhibitors of Src family kinases, or by expression of a dominant negative c-Src, all induced muscle differentiation in proliferation medium (PM). In differentiating cells in differentiation medium (DM), c-Src activity gradually decreased and reached basal level 3 days after induction of differentiation. Inhibition of c-Src suppressed Raf/MEK/ERK pathway but activated p38 MAPK. Inhibition of p38 MAPK did not affect c-Src activity in PM. However, it reactivated Raf/MEK/ERK pathway in c-Src-inhibited cells regardless of PM or DM. Concomitant inhibition of c-Src and p38 MAPK activities blocked muscle differentiation in both media. In conclusion, suppression of c-Src activity stimulates muscle differentiation by activating p38 MAPK uni-directionally.

Cloning and characterisation of p38 MAP kinase from Atlantic salmon A kinase important for regulating salmon TNF-2 and IL-1beta expression

p38 mitogen-activated protein kinase is activated by environmental stress and cytokines and plays a role in transcriptional regulation and inflammatory responses. In this study, three distinct Atlantic salmon p38 (As-p38) cDNAs were cloned, which all translated into 361 amino acid proteins. The As-p38 protein sequences possessed showed >85% identity to the mammalian homolog, p38alpha. All three contained the conserved phosphorylation motif TGY located in the activation loop of the kinase. Salmon p38 showed ubiquitous tissue distribution, including expression in the immune organs head kidney and spleen. A higher p38 mRNA expression was detected in the ovary compared to other organs suggesting that p38 may perform specific functions within this organ. Western blot analysis with an antibody specific for phosphorylated p38 showed that ectopically expressed As-p38 variants were activated in CHSE-214 cells in response to chemical stress. Furthermore, lipopolysaccharide, CpG oligonucleotides and recombinant trout IL-1beta induced endogenous phosphorylation of p38 in salmon head kidney macrophages in a dose-dependent manner. The importance of p38 for regulation of salmon innate immunity was further demonstrated by the ability of the p38 specific inhibitor SB203580 to completely abolish LPS-stimulated TNF-2 and IL-1beta mRNA expression in the macrophages.

Intrinsically active variants of all human p38 isoforms

The p38 mitogen-activated protein kinases are activated in response to various extracellular signals in eukaryotic cells and play a critical role in the cellular responses to these signals. The four mammalian isoforms (p38alpha, p38beta, p38gamma, and p38delta) are coexpressed and coactivated in the same cells. The exact role of each p38 isoform has not been entirely identified, in part due to the inability to activate each member individually. This could be resolved by the use of intrinsically active mutants. Based on previous studies on yeast p38/Hog1 [Bell M, Capone R, Pashtan I, Levitzki A & Engelberg D (2001) J Biol Chem276, 25351-2538] and human p38alpha[Diskin R, Askari N, Capone R, Engelberg D & Livnah O (2004) J Biol Chem279, 47040-47049] we have generated intrinsically active p38beta, p38gamma and p38delta mutants. In addition, we have identified a new activating mutation site in p38alpha. Most of the activating mutations are located in the L16 loop, in which conformational changes were shown to induce activation. We show that these changes impose substantial autophosphorylation activity, providing a mechanistic explanation for the intrinsic activity of the mutants. The new active variants maintain specificity towards substrates and inhibitors similar to that of the parental wild-type proteins, and are phosphorylated by mitogen-activated protein kinase kinase 6, their upstream activator. Thus, we have completed the development of a series of intrinsically active mutants of all p38 isoforms. These active variants could now become powerful tools for the elucidating the activation mechanism and specific biological roles of each p38 isoform.

Mouse preimplantation embryo responses to culture medium osmolarity include increased expression of CCM2 and p38 MAPK activation

Background

Mechanisms that confer an ability to respond positively to environmental osmolarity are fundamental to ensuring embryo survival during the preimplantation period. Activation of p38 mitogen-activated protein kinase (MAPK) occurs following exposure to hyperosmotic treatment. Recently, a novel scaffolding protein called Osmosensing Scaffold for MEKK3 (OSM) was linked to p38 MAPK activation in response to sorbitol-induced hypertonicity. The human ortholog of OSM is cerebral cavernous malformation 2 (CCM2). The present study was conducted to investigate whether CCM2 is expressed during mouse preimplantation development and to determine whether this scaffolding protein is associated with p38 MAPK activation following exposure of preimplantation embryos to hyperosmotic environments.

Results

Our results indicate that Ccm2 along with upstream p38 MAPK pathway constituents (Map3k3, Map2k3, Map2k6, and Map2k4) are expressed throughout mouse preimplantation development. CCM2, MAP3K3 and the phosphorylated forms of MAP2K3/MAP2K6 and MAP2K4 were also detected throughout preimplantation development. Embryo culture in hyperosmotic media increased p38 MAPK activity in conjunction with elevated CCM2 levels.

Conclusion

These results define the expression of upstream activators of p38 MAPK during preimplantation development and indicate that embryo responses to hyperosmotic environments include elevation of CCM2 and activation of p38 MAPK.

Strategies to design pyrazolyl urea derivatives for p38 kinase inhibition: a molecular modeling study

The p38 protein kinase is a serine-threonine mitogen activated protein kinase, which plays an important role in inflammation and arthritis. A combined study of 3D-QSAR and molecular docking has been undertaken to explore the structural insights of pyrazolyl urea p38 kinase inhibitors. The 3D-QSAR studies involved comparative molecular field analysis (CoMFA) and comparative molecular similarity indices (CoMSIA). The best CoMFA model was derived from the atom fit alignment with a cross-validated r (2 )(q (2)) value of 0.516 and conventional r (2) of 0.950, while the best CoMSIA model yielded a q (2) of 0.455 and r (2) of 0.979 (39 molecules in training set, 9 molecules in test set). The CoMFA and CoMSIA contour maps generated from these models provided inklings about the influence of interactive molecular fields in the space on the activity. GOLD, Sybyl (FlexX) and AutoDock docking protocols were exercised to explore the protein-inhibitor interactions. The integration of 3D-QSAR and molecular docking has proffered essential structural features of pyrazolyl urea inhibitors and also strategies to design new potent analogues with enhanced activity.

Apoptosis induced by the monomers HEMA and TEGDMA involves formation of ROS and differential activation of the MAP-kinases p38, JNK and ERK

OBJECTIVES

Cytotoxic methacrylate monomers have been identified in aqueous extracts of freshly cured compomers. Some of these compounds, including HEMA and TEGDMA, induce apoptosis and necrosis in vitro. The aim of the present study was to elucidate possible signaling pathways involved in apoptosis following exposure to HEMA or TEGDMA in a salivary gland cell line.

METHODS

The cells were exposed to various concentrations of HEMA or TEGDMA. ROS formation was determined by dichlorofluorescein assay. Phosphorylated MAP-kinases ERK1/2, p38 and JNK, as well as specific caspases were identified by Western blotting. Apoptosis was assayed by fluorescence microscopy.

RESULTS

HEMA or TEGDMA exposure resulted in ROS formation and concentration-dependent apoptosis as well as phosphorylation of ERK. Phosphorylation of JNK and p38 was induced by HEMA. Selective inhibitors of ERK and JNK modified the apoptotic response after HEMA and TEGDMA exposure, whereas p38 inhibition modified the apoptotic response only after HEMA exposure. Vitamin C reduced HEMA-induced apoptosis.

SIGNIFICANCE

ROS formation and differential MAP kinase activation appear to be involved in the apoptotic response following exposure to HEMA and TEGDMA.

PP2Cδ (Ppm1d, WIP1), an endogenous inhibitor of p38 MAPK, is regulated along WithTrp53 andCdkn2a following p38 MAPK inhibition during mouse preimplantation development

Preimplantation embryos utilize mitogen-activated protein kinase signaling (MAPK) pathways to relay signals from the external environment to prepare appropriate responses and adaptations to a changing milieu. It is therefore important to investigate how MAPK pathways are regulated during preimplantation development. This study was conducted to investigate whether PP2Cdelta (Ppm1d, WIP1) is expressed during mouse preimplantation development and to determine the influences of p38 MAPK inhibition on expression of Trp53 (p53), Ppm1d, (WIP1), and Cdkn2a (p16) during mouse preimplantation development. Our results indicate that Trp53, Ppm1d, and Cdkn2a mRNAs and TRP53 and PP2Cdelta proteins are expressed throughout mouse preimplantation development. Treatment of 2-cell embryos with SB220025 (potent inhibitor of p38 MAPK alpha/beta/MAPK 14/11) significantly increased Trp53, Ppm1d and Cdkn2a and Mapk14 mRNA levels at 12 and 24 hr. Treatment of 8-cell embryos with SB220025 for 12 hr increased Trp53, Ppm1d, and Cdkn2a mRNA levels, but not Mapk14 mRNA levels. Treatment of 8-cell embryos for 24 hr increased Trp53, and Ppm1d mRNA levels, but decreased Cdkn2a and Mapk14 mRNA levels. Therefore, blockade of p38 MAPK activity is associated with embryo stage specific influences on Trp53, Ppm1d, Cdkn2a, and Mapk14 expression during mouse preimplantation development. These results define downstream targets of p38 MAPK during preimplantation development and indicate that the p38 MAPK pathway regulates Trp53, Ppm1d, and Cdkn2a expression. This study increases our understanding of the mechanisms controlling preimplantation development and of the interactions between preimplantation embryos and their culture environments.

Diazoxide prevents diabetes through inhibiting pancreatic beta-cells from apoptosis via Bcl-2/Bax rate and p38-beta mitogen-activated protein kinase

Increased apoptosis of pancreatic beta-cells plays an important role in the occurrence and development of type 2 diabetes. We examined the effect of diazoxide on pancreatic beta-cell apoptosis and its potential mechanism in Otsuka Long Evans Tokushima Fatty (OLETF) rats, an established animal model of human type 2 diabetes, at the prediabetic and diabetic stages. We found a significant increase with age in the frequency of apoptosis, the sequential enlargement of islets, and the proliferation of the connective tissue surrounding islets, accompanied with defective insulin secretory capacity and increased blood glucose in untreated OLETF rats. In contrast, diazoxide treatment (25 mg.kg(-1).d(-1), administered ip) inhibited beta-cell apoptosis, ameliorated changes of islet morphology and insulin secretory function, and increased insulin stores significantly in islet beta-cells whether diazoxide was used at the prediabetic or diabetic stage. Linear regression showed the close correlation between the frequency of apoptosis and hyperglycemia (r = 0.913; P < 0.0001). Further study demonstrated that diazoxide up-regulated Bcl-2 expression and p38beta MAPK, which expressed at very low levels due to the high glucose, but not c-jun N-terminal kinase and ERK. Hence, diazoxide may play a critical role in protection from apoptosis. In this study, we demonstrate that diazoxide prevents the onset and development of diabetes in OLETF rats by inhibiting beta-cell apoptosis via increasing p38beta MAPK, elevating Bcl-2/Bax ratio, and ameliorating insulin secretory capacity and action.

Immunomodulatory effects of statins and autoimmune rheumatic diseases: novel intracellular mechanism involved

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, known as statins, are the most commonly prescribed agents for the treatment of hypercholesterolemia. However, the effects of statins may extend beyond their influences on serum cholesterol levels resulting in cholesterol-independent or pleiotropic effects. Clinical, animal and in vitro studies suggest that statins have additional clinical uses because of their anti-inflammatory and immunomodulatory effects, in part due to their capacity to interfere with the mevalonate pathway and inhibit prenylation of Rho family GTPases. This review focuses on the molecular mechanisms of the anti-inflammatory and immunomodulatory effects of statins. In base to all these information, we suggest that statins could have similar inhibitory effects on MAPKs pathways in cells from RA patients, including osteoclasts and fibroblasts.

Differential tissue expression and activation of p38 MAPK alpha, beta, gamma, and delta isoforms in rheumatoid arthritis

OBJECTIVE

Activation of p38 MAPK is a key signaling step in chronic inflammation. Inhibition of p38 MAPK is considered to be a promising future strategy to control inflammatory diseases, but studies of compounds to inhibit this kinase have so far been limited to investigation of their side effects. We undertook the present study to investigate which specific molecule, among 4 different isoforms of p38 MAPK (alpha, beta, gamma, and delta), is predominantly expressed and activated in inflammation. Such knowledge could allow more specific targeting of p38 MAPK in inflammatory disease.

METHODS

Studies were performed on inflamed tissue from patients with rheumatoid arthritis, as a prototype of inflammatory disease. The expression and activation of the alpha, beta, gamma, and delta isoforms of p38 MAPK were examined by immunoblotting, immunoprecipitation, and immunohistochemistry.

RESULTS

Immunoblot analysis revealed that alpha and gamma were the predominantly expressed p38 MAPK isoforms, whereas the other 2 isoforms were less frequently present. By immunohistochemistry, the expression of all p38 MAPK isoforms was localized to the synovial lining layer as well as to blood vessels. Colabeling with cell-specific markers revealed that macrophages expressed the alpha and gamma isoforms, synovial fibroblasts the beta and gamma isoforms, and granulocytes the delta isoform, whereas T lymphocytes were rarely positive for any p38 MAPK isoform. Double-labeling with isoform-specific antibody and pan-p38 antibody against the phosphorylated form of p38 MAPK showed activation of the alpha and gamma isoforms. Occasional activation of the beta isoform was also noted in the synovial lining and the endothelium, whereas the delta isoform, although expressed in pericytes around blood vessels, was not phosphorylated. This phosphorylation pattern was confirmed in immunoprecipitation studies in which activated p38 MAPK from synovial tissue extracts was identified as p38 MAPKalpha and -gamma but not p38 MAPKbeta or -delta.

CONCLUSION

These data show that the alpha and gamma isoforms of p38 MAPK dominate in chronic inflammation. Effective strategies to inhibit p38 MAPK should therefore aim to specifically target either or both of these isoforms.

Selective inhibition of p38α MAPK improves cardiac function and reduces myocardial apoptosis in rat model of myocardial injury

p38 MAPK is activated during heart diseases that might associate with myocardial damage and deterioration of cardiac function. In a rat model of myocardial injury, we have investigated cardioprotective effects of the inhibition of p38 MAPK using a novel, orally available p38α MAPK inhibitor. Rats were treated with Nω-nitro-l-arginine methyl ester (l-NAME, 40 mg·kg−1·day−1) in drinking water plus 1% salt for 14 days and ANG II (0.5 mg·kg−1·day−1) for 3 days. A selective p38α MAPK inhibitor, SD-282 (60 mg/kg), was administrated orally, twice a day for 4 days, starting 1 day before ANG II administration. The cardioprotective effects of p38α MAPK inhibition were evaluated by improvement of cardiac function, reduction of inflammatory cell infiltration, and cardiomyocyte apoptosis. SD-282 significantly improved cardiac function indicated by increasing stroke volume, cardiac output, ejection fraction, and stroke work and significantly decreasing arterial elastance. SD-282 also significantly reduced macrophage infiltration as judged by reduction of a specific marker, ED-1-positive staining cells ( P < 0.05) in the myocardium. Furthermore, cardiomyocyte apoptosis as indicated by caspase-3 immunohistochemical staining was abolished by SD-282, and this effect may contribute to the reduction of myocardial damage evaluated by imaging analysis ( P < 0.05 in both cases). Data suggest that p38α MAPK may play a critical role in the pathogenesis of cardiac dysfunction. Inhibition of p38α MAPK may be used as a novel cardioprotective strategy in attenuation of inflammatory response and deterioration of cardiac function that occurs in acute cardiovascular disease such as myocardial infarction.

Downregulation of human endothelial nitric oxide synthase promoter activity by p38 mitogen-activated protein kinase activation

Human endothelial nitric oxide synthase (eNOS) plays a crucial role in maintaining blood pressure homeostasis and vascular integrity. eNOS gene expression may be upregulated by a signaling pathway, including PI-3Kgamma--> Jak2--> MEK1 --> ERK1/2--> PP2A. It remains unclear whether other mitogen-activated protein kinase (MAPK) family members, such as JNK, p38 kinase, and ERK5/BMK1, also modulate eNOS gene expression. Our purpose, therefore, is to shed light on the effect of the p38 MAPK signaling pathway on the regulation of eNOS promoter activity. The results showed that a red fluorescent protein reporter gene vector containing the full length of the human eNOS promoter was first successfully constructed, expressing efficiently in ECV304 cells with the characteristics of real time observation. The wild-types of p38alpha, p38beta, p38gamma, and p38delta signal molecules all markedly downregulated promoter activity, which could be reversed by their negative mutants, including p38alpha (AF), p38beta (AF), p38gamma (AF), and p38delta (AF). Promoter activity was also significantly downregulated by MKK6b (E), an active mutant of an upstream kinase of p38 MAPK. The reduction in promoter activity by p38 MAPK could be blocked by treatment with a p38 MAPK specific inhibitor, SB203580. Moreover, the activation of endogenous p38 MAPK induced by lipopolysaccharide resulted in a prominent reduction in promoter activity. These findings strongly suggest that the activation of the p38 MAPK signaling pathway may be implicated in the downregulation of human eNOS promoter activity.

Activation of p38 mitogen-activated protein kinase promotes epidermal growth factor receptor internalization

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.

Role of MAPKs in development and differentiation: lessons from knockout mice

The ERK, p38MAPK, JNK mitogen-activated protein kinases (MAPKs) are intracellular signaling pathways that play a pivotal role in many essential cellular processes such as proliferation and differentiation. These cascades are activated by a large variety of stimuli and display a high degree of homology. So far, seven MAPK isoforms have been invalidated in mice leading to the discovery of their important functions in development and differentiation. As we could expect because of their multiple and specific properties in vitro, knockout (KO) of MAPK pathways leads to distinct phenotypes in mice. Surprisingly, into a given cascade, KOs of the various isoforms assign specific non-redundant biological functions to each isoform, without compensation by the others. These results emphasize the notion that, although initiated by the same external stimuli, these intracellular cascades activate kinase isoforms each with its own specific role.

Over-expression of interleukin-6 enhances cell survival and transformed cell growth in human malignant cholangiocytes

BACKGROUND/AIMS

Over-expression of IL-6 has been implicated in cholangiocarcinoma growth but the cellular mechanisms involved are unknown. Our aims were to assess the mechanisms by which over-expression of IL-6 promotes transformed cell growth in malignant cholangiocytes.

METHODS

Stably transfected cell lines over-expressing IL-6 were derived from malignant human cholangiocytes. Transformed cell growth was assessed by anchorage independent growth in vitro and by xenograft growth in nude mice. Expression of the anti-apoptotic protein Mcl-1 was quantitated by immunoblot analysis and by real-time PCR. Gene silencing was performed using siRNA. Dominant negative upstream kinase activators and isoform-specific constructs were used to evaluate the involvement of p38 MAP kinase signaling pathways.

RESULTS

Over-expression of IL-6 increased xenograft growth, anchorage independent growth and cell survival but did not significantly alter cell proliferation. The basal expression of Mcl-1 was increased in IL-6 over-expressing cells. Selective knockdown of Mcl-1 by siRNA increased gemcitabine-induced cytotoxicity. Moreover, IL-6 increased Mcl-1 mRNA and protein expression via a p38 MAPK dependent mechanism.

CONCLUSIONS

These data demonstrate a major role of survival signaling pathways in mediating the effects of IL-6 over-expression in cholangiocarcinoma growth. Mcl-1 is identified as a mediator of IL-6-induced tumor cell survival and shown to be transcriptionally regulated by IL-6 via a p38 MAPK dependent pathway. We conclude that modulation of IL-6 mediated survival signaling pathways involving the p38 MAPK or downstream targets such as Mcl-1 may prove useful therapeutic strategies for human cholangiocarcinoma.

Over-expression of interleukin-6 enhances cell survival and transformed cell growth in human malignant cholangiocytes

BACKGROUND/AIMS

Over-expression of IL-6 has been implicated in cholangiocarcinoma growth but the cellular mechanisms involved are unknown. Our aims were to assess the mechanisms by which over-expression of IL-6 promotes transformed cell growth in malignant cholangiocytes.

METHODS

Stably transfected cell lines over-expressing IL-6 were derived from malignant human cholangiocytes. Transformed cell growth was assessed by anchorage independent growth in vitro and by xenograft growth in nude mice. Expression of the anti-apoptotic protein Mcl-1 was quantitated by immunoblot analysis and by real-time PCR. Gene silencing was performed using siRNA. Dominant negative upstream kinase activators and isoform-specific constructs were used to evaluate the involvement of p38 MAP kinase signaling pathways.

RESULTS

Over-expression of IL-6 increased xenograft growth, anchorage independent growth and cell survival but did not significantly alter cell proliferation. The basal expression of Mcl-1 was increased in IL-6 over-expressing cells. Selective knockdown of Mcl-1 by siRNA increased gemcitabine-induced cytotoxicity. Moreover, IL-6 increased Mcl-1 mRNA and protein expression via a p38 MAPK dependent mechanism.

CONCLUSIONS

These data demonstrate a major role of survival signaling pathways in mediating the effects of IL-6 over-expression in cholangiocarcinoma growth. Mcl-1 is identified as a mediator of IL-6-induced tumor cell survival and shown to be transcriptionally regulated by IL-6 via a p38 MAPK dependent pathway. We conclude that modulation of IL-6 mediated survival signaling pathways involving the p38 MAPK or downstream targets such as Mcl-1 may prove useful therapeutic strategies for human cholangiocarcinoma.

MEKK3-mediated signaling to p38 kinase and TonE in hypertonically stressed kidney cells

Mitogen-activated protein kinase (MAPK) cascades contain a trio of kinases, MAPK kinase kinase (MKKK) --> MAPK kinase (MKK) --> MAPK, that mediate a variety of cellular responses to different signals including hypertonicity. The signaling response to hypertonicity is conserved across evolution from yeast to mammals in that it involves activation of p38/SAPK. However, very little is known about which upstream protein kinases mediate activation of p38 by hypertonicity in mammals. The MKKKs, MEKK3 and MEKK4, are upstream regulators of p38 in many cells. To investigate these signaling proteins as potential activators of p38 in the hypertonicity response, we generated stably transfected MDCK cells that express activated versions of MEKK3 or MEKK4, utilized RNA interference to deplete MEKK3, and employed pharmacological inhibition of p38 kinase. MEKK3-transfected cells demonstrated increased betaine transporter (BGT1) mRNA levels and upregulated tonicity enhancer (TonE)-driven luciferase activity under isotonic (basal) and hypertonic conditions compared with empty vector-transfected controls; small-interference RNA-mediated depletion of MEKK3 downregulated the activity of p38 kinase and decreased the expression of BGT1 mRNA. p38 Kinase inhibition abolished the effects of MEKK3 activation on BGT1 induction. In contrast, the response to hypertonicity in MEKK4-kA-transfected cells was similar to that observed in empty vector-transfected controls. Our data are consistent with the existence of an input from MEKK3 -->--> p38 kinase -->--> TonE.

CO as a cellular signaling molecule

Many biological functions of heme oxygenase (HO), such as cytoprotection against oxidative stress, vasodilation, neurotransmission in the central or peripheral nervous systems, and anti-inflammatory, anti-apoptotic, or anti-proliferative potential, have been attributed to its enzymatic byproduct carbon monoxide (CO), although roles for biliverdin/bilirubin and iron have also been proposed. In addition to these well-characterized effects, recent findings reveal that HO-derived CO may act as an oxygen sensor and circadian modulator of heme biosynthesis. In lymphocytes, CO may participate in regulatory T cell function. A number of the known signaling effects of CO depend on stimulation of soluble guanylate cyclase and/or activation of mitogen-activated protein kinases (MAPK). Furthermore, modulation of caveolin-1 status may serve as an essential component of certain aspects of CO action, such as growth control. In this review, we summarize recent findings of the beneficial or detrimental effects of endogenous CO with an emphasis on the signaling pathways and downstream targets that trigger the action of this gas.

Voltage-gated sodium channel Nav1.6 is modulated by p38 mitogen-activated protein kinase

Nav1.6 is the major sodium channel isoform at nodes of Ranvier in myelinated axons and, additionally, is distributed along unmyelinated C-fibers of sensory neurons. Thus, modulation of the sodium current produced by Nav1.6 might significantly impact axonal conduction. Mitogen-activated protein kinases (MAPKs) are expressed in neurons and are activated after injury, for example, after sciatic nerve transection and hypoxia. Although the role of MAPK in signal transduction and in injury-induced regulation of gene expression is well established, the ability of these kinases to phosphorylate and modulate voltage-gated sodium channels has not been reported. Sequence analysis shows that Nav1.6 contains a putative MAP kinase-recognition module in the cytoplasmic loop (L1), which joins domains 1 and 2. We show in this study that sodium channels and p38 MAP kinase colocalize in rat brain tissue and that activated p38alpha phosphorylates L1 of Nav1.6, specifically at serine 553 (S553), in vitro. None of the other cytoplasmic loops and termini of the channel are phosphorylated by activated p38alpha in these assays. Activation of p38 in the neuronal ND7/23 cell line transfected with Nav1.6 leads to a significant reduction in the peak Nav1.6 current amplitude, without a detectable effect on gating properties. The substitution of S553 with alanine within L1 of the Nav1.6 channel prevents p38-mediated reduction of Nav1.6 current density. This is the first demonstration of MAPK phosphorylation and modulation of a voltage-gated sodium channel, and this modulation may represent an additional role for MAPK in regulating the neuronal response to injury.

Multiple signaling pathways are involved in endothelin-1-induced brain endothelial cell migration

We have observed that the vasoactive peptide endothelin-1 is a potent inducer of migration of primary human brain-derived microvascular endothelial cells. By blocking signal transduction pathways with specific inhibitors, and using dominant negative mutant infections, we have demonstrated that multiple pathways are involved in endothelin-1-induced migration. Absolutely required for migration are protein tyrosine kinase Src, Ras, protein kinase C (PKC), phosphatidylinositol 3-kinase, ERK, and JNK; partial requirements were exhibited by cAMP-activated protein kinase and p38 kinase. Partial elucidation of the signal transduction sequences showed that the MAPKs ERK, JNK, and p38 are positioned downstream of both PKC and cAMP-activated protein kinase in the signal transduction scheme. The results show that human brain endothelial cell migration has distinct characteristics, different from cells derived from other vascular beds, or from other species, often used as model systems. Furthermore, the results indicate that endothelin-1, secreted by many tumors, is an important contributor to tumor-produced proangiogenic microenvironment. This growth factor has been associated with increased microvessel density in tumors and is responsible for endothelial cell proliferation, migration, invasion, and tubule formation. Because many signal transduction pathways investigated in this study are potential or current targets for anti-angiogenesis therapy, these results are of critical importance for designing physiological antiangiogenic protocols.

Activation of Bak and Bax through c-abl-protein kinase Cdelta-p38 MAPK signaling in response to ionizing radiation in human non-small cell lung cancer cells

Intracellular signaling molecules and apoptotic factors seem to play an important role in determining the radiation response of tumor cells. However, the basis for the link between signaling pathway and apoptotic cell death machinery after ionizing irradiation remains still largely unclear. In this study, we showed that c-Abl-PKCdelta-Rac1-p38 MAPK signaling is required for the conformational changes of Bak and Bax during ionizing radiation-induced apoptotic cell death in human non-small cell lung cancer cells. Ionizing radiation induced conformational changes and subsequent oligomerizations of Bak and Bax, dissipation of mitochondrial membrane potential, and cytochrome c release from mitochondria. Small interference (siRNA) targeting of Bak and Bax effectively protected cells from radiation-induced mitochondrial membrane potential loss and apoptotic cell death. p38 MAPK was found to be selectively activated in response to radiation treatment. Inhibition of p38 MAPK completely suppressed radiation-induced Bak and Bax activations, dissipation of mitochondrial membrane potential, and cell death. Moreover, expression of a dominant negative form of protein kinase Cdelta (PKCdelta) or siRNA targeting of PKCdelta attenuated p38 MAPK activation and conformational changes of Bak and Bax. In addition, ectopic expression of RacN17, a dominant negative form of Rac1, markedly inhibited p38 MAPK activation but did not affect PKCdelta activation. Upon stimulation of cells with radiation, PKCdelta was phosphorylated dramatically on tyrosine. c-Abl-PKCdelta complex formation was also increased in response to radiation. Moreover, siRNA targeting of c-Abl attenuated radiation-induced PKCdelta and p38 MAPK activations, and Bak and Bax modulations. These data support a notion that activation of the c-Abl-PKCdelta-Rac1-p38 MAPK pathway in response to ionizing radiation signals conformational changes of Bak and Bax, resulting in mitochondrial activation-mediated apoptotic cell death in human non-small cell lung cancer cells.

Rin GTPase couples nerve growth factor signaling to p38 and b-Raf/ERK pathways to promote neuronal differentiation

In neuronal precursor cells, the magnitude and longevity of mitogen-activated protein (MAP) kinase cascade activation contribute to the nature of the cellular response, differentiation, or proliferation. However, the mechanisms by which neurotrophins promote prolonged MAP kinase signaling are not well understood. Here we defined the Rin GTPase as a novel component of the regulatory machinery contributing to the selective integration of MAP kinase signaling and neuronal development. Rin is expressed exclusively in neurons and is activated by neurotrophin signaling, and loss-of-function analysis demonstrates that Rin makes an essential contribution to nerve growth factor (NGF)-mediated neuronal differentiation. Most surprisingly, although Rin was unable to stimulate MAP kinase activity in NIH 3T3 cells, it potently activated isoform-specific p38alpha MAP kinase signaling and weakly stimulated ERK signaling in pheochromocytoma (PC6) cells. This cell-type specificity is explained in part by the finding that Rin binds and stimulates b-Raf but does not activate c-Raf. Accordingly, selective down-regulation of Rin in PC6 cells suppressed neurotrophin-elicited activation of b-Raf and p38, without obvious effects on NGF-induced ERK activation. Moreover, the ability of NGF to promote neurite outgrowth was inhibited by Rin knockdown. Together, these observations establish Rin as a neuronal specific regulator of neurotrophin signaling, required to couple NGF stimulation to sustain activation of p38 MAP kinase and b-Raf signaling cascades required for neuronal development.

Priming effect of lipopolysaccharide on acetyl-coenzyme A:lyso-platelet-activating factor acetyltransferase is MyD88 and TRIF independent

LPS has a priming effect on various stimuli. For instance, LPS priming enhances the production of platelet-activating factor (PAF), a proinflammatory lipid mediator that is induced by PAF itself. Among various enzymes responsible for PAF biosynthesis, acetyl-coenzyme A:1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine acetyltransferase is one of the enzymes activated by PAF receptor stimulation. In this study we investigated the priming effect of LPS on the acetyltransferase activation by PAF in TLR4-knockout (KO) mice, MyD88-KO mice, and Toll/IL-1R domain-containing adaptor inducing IFN-beta (TRIF)-KO mice. This enzyme was biphasically activated by LPS. Although the first peak occurred within 30 min in wild-type (WT), but not TLR4-KO or MyD88-KO, macrophages, the second phase reached a maximum within hours in WT, MyD88-KO, and TRIF-KO, but not in TLR4-KO, macrophages. Only in the second phase was the increase in acetyltransferase activity upon PAF receptor activation remarkably enhanced in WT, MyD88-KO, and TRIF-KO cells, but not in TLR4-KO cells. These data demonstrated that LPS exerted a priming effect on PAF receptor-mediated acetyltransferase activation through the TLR4-dependent, but MyD88- and TRIF-independent, pathway.

Different pathways leading to activation of extracellular signal-regulated kinase and p38 MAP kinase by formyl-methionyl-leucyl-phenylalanine or platelet activating factor in human neutrophils

The signaling pathways leading to extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) activation by N-formyl-Met-Leu-Phe (fMLP) or platelet activating factor (PAF) in human neutrophils were examined. Previously, we found that changes of intracellular Ca2+ ([Ca2+]i) stimulated by PAF and fMLP were due to Ca2+ influx and internal Ca2+ release, respectively. To further determine the mechanism of MAPK activation and its relation with Ca2+ influx, blood from healthy human volunteers was taken by venous puncture. Human polymorphonuclear cells (PMNs) were isolated and incubated with protein kinase C (PKC) inhibitor Calphostin C, PKC-gamma isoform inhibitor GF109203X, phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002, phospholipase C (PLC) inhibitor U73122, phospholipase A2 (PLA2) inhibitor Aristolochic acid, store-operated calcium (SOC) channel inhibitor SKF96365, or extracellular calcium chelator EGTA followed by fMLP or PAF treatment. Phosphorylation of ERK p38 was determined by immunoblotting analysis. Our data indicate that neutrophil MAPK signaling pathways mediated by fMLP and PAF are different. PAF-induced ERK phosphorylation is mediated by PI3K, PKC, PLA2, PLC, and extracellular calcium, whereas fMLP-induced ERK phosphorylation does not involve the PKC-gamma isoform and extracellular calcium. PAF-induced p38 phosphorylation involves PLA2, whereas fMLP-induced p38 activation is PLC dependent.

Reduction of insulin-stimulated glucose uptake in L6 myotubes by the protein kinase inhibitor SB203580 is independent of p38MAPK activity

Insulin increases glucose uptake through translocation of the glucose transporter GLUT4 to the plasma membrane. We previously showed that insulin activates p38MAPK, and inhibitors of p38MAPKalpha and p38MAPKbeta (e.g. SB203580) reduce insulin-stimulated glucose uptake without affecting GLUT4 translocation. This observation suggested that insulin may increase GLUT4 activity via p38alpha and/or p38beta. Here we further explore the possible participation of p38MAPK through a combination of molecular strategies. SB203580 reduced insulin stimulation of glucose uptake in L6 myotubes overexpressing an SB203580-resistant p38alpha (drug-resistant p38alpha) but barely affected phosphorylation of the p38 substrate MAPK-activated protein kinase-2. Expression of dominant-negative p38alpha or p38beta reduced p38MAPK phosphorylation by 70% but had no effect on insulin-stimulated glucose uptake. Gene silencing via isoform-specific small interfering RNAs reduced expression of p38alpha or p38beta by 60-70% without diminishing insulin-stimulated glucose uptake. SB203580 reduced photoaffinity labeling of GLUT4 by bio-LC-ATB-BMPA only in the insulin-stimulated state. Unless low levels of p38MAPK suffice to regulate glucose uptake, these results suggest that the inhibition of insulin-stimulated glucose transport by SB203580 is likely not mediated by p38MAPK. Instead, changes experienced by insulin-stimulated GLUT4 make it susceptible to inhibition by SB203580.

Disparate expression of IL-12 by SJL/J and B10.S macrophages during Theiler's virus infection is associated with activity of TLR7 and mitogen-activated protein kinases

Differences in components of innate anti-viral immune responses may account for the contrast in susceptibility to Theiler's murine encephalomyelitis virus (TMEV) between SJL/J and B10.S mice. Herein, the expression of IL-12, interferon (IFN)-beta, Toll-like receptors 3 (TLR3), TLR7, and mitogen-activated protein (MAP)-kinases was evaluated in SJL/J and B10.S macrophages infected with TMEV. Twenty-four hours after infection, SJL/J macrophages exhibited higher levels of TMEV RNA, IL-12 p40, and TLR3 but lower levels of IL-12 p70 and the IL-12 p35 subunit compared with B10.S macrophages. Addition of exogenous IL-12 p70 or IFN-beta increased the resistance of SJL/J macrophages to TMEV infection. To assess MAP-kinases, macrophages were pretreated with the p38 MAP-kinase inhibitor SB203580 or extracellular signal-regulated kinases (ERK) MAP-kinase inhibitor U0126 before TMEV infection. U0126 reduced SJL/J but increased B10.S macrophage expression of IL-12 p40 and p70 in response to TMEV. U0126 decreased the IL-12 p35 response of SJL/J macrophages. To assess TLR7, SJL/J and B10.S macrophages were stimulated with loxoribine, a TLR7 ligand. Loxoribine induced more IL-12 p70 production and p35 expression in B10.S than SJL/J macrophages. U0126 increased loxoribine-induced expression of IL-12 p40 and IL-12 p70 in B10.S but not SJL/J macrophages. Thus, differences in production of IL-12 p70 due to expression of the p35 subunit and in activity of TLR7, as well as activation of factors downstream of ERK MAP-kinases likely underlie the disparity in innate immunity between SJL/J and B10.S macrophages to TMEV.

Reduced p38 mitogen-activated protein kinase in donor grafts accelerates acute intestinal graft-versus-host disease in mice

The gastrointestinal tract is a major target of graft-versus-host disease (GVHD), which constitutes a life-threatening complication of bone marrow transplantation. GVHD is mainly caused by the activation of donor-derived lymphocytes, in which cytokine cascades play essential roles. Since p38 MAPK (p38) has been identified as a regulator of cytokine reactions and proposed as a molecular target for anti-inflammatory therapy, we investigated the contribution of p38 to the severity of murine intestinal GVHD. Unexpectedly, p38alpha(+/-) donor graft induced more acute GVHD-related mortality and more severe gut injury. The survival of p38alpha(+/-) donor-derived intestinal intraepithelial lymphocytes (IEL) was prolonged in vitro and in vivo, and TNF-alpha expression in the p38alpha(+/-) donor-derived IEL was also increased compared with wild-type cells. In contrast, the p38alpha(+/-) grafted mice resulted in decreased expansion of donor lymphocytes in mesenteric lymph nodes, and the up-regulation of IL-12p40 and IL-18 was diminished. These findings suggest that p38 has dichotomous effects for inflammatory response in vivo; not only regulates inflammatory cytokine expression and lymphocyte expansion, but also has distinct regulatory functions for IEL in intestinal GVHD. In conclusion, the inhibition of p38 may not be a suitable anti-inflammatory strategy for GVHD due to the associated intestinal injury.

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.

Temporary blockade of contractility during reperfusion elicits a cardioprotective effect of the p38 MAP kinase inhibitor SB-203580

p38 MAP kinase activation is known to be deleterious not only to mitochondria but also to contractile function. Therefore, p38 MAP kinase inhibition therapy represents a promising approach in preventing reperfusion injury in the heart. However, reversal of p38 MAP kinase-mediated contractile dysfunction may disrupt the fragile sarcolemma of ischemic-reperfused myocytes. We, therefore, hypothesized that the beneficial effect of p38 MAP kinase inhibition during reperfusion can be enhanced when contractility is simultaneously blocked. Isolated and perfused rat hearts were paced at 330 rpm and subjected to 20 min of ischemia followed by reperfusion. p38 MAP kinase was activated after ischemia and early during reperfusion (<30 min). Treatment with the p38 MAP kinase inhibitor SB-203580 (10 μM) for 30 min during reperfusion, but not the c-Jun NH2-terminal kinase inhibitor SP-600125 (10 μM), improved contractility but increased creatine kinase release and infarct size. Cotreatment with SB-203580 and the contractile blocker 2,3-butanedione monoxime (BDM, 20 mM) or the ultra-short-acting β-blocker esmorol (0.15 mM) for the first 30 min during reperfusion significantly reduced creatine kinase release and infarct size. In vitro mitochondrial ATP generation and myocardial ATP content were significantly increased in the heart cotreated with SB-203580 and BDM during reperfusion. Dystrophin was translocated from the sarcolemma during ischemia and reperfusion. SB-203580 increased accumulation of Evans blue dye in myocytes depleted of sarcolemmal dystrophin during reperfusion, whereas cotreatment with BDM facilitated restoration of sarcolemmal dystrophin and mitigated sarcolemmal damage after withdrawal of BDM. These results suggest that treatment with SB-203580 during reperfusion aggravates myocyte necrosis but concomitant blockade of contractile force unmasks cardioprotective effects of SB-203580.

IL-6 activates serum and glucocorticoid kinase via p38alpha mitogen-activated protein kinase pathway

Interleukin-6 (IL-6) has been implicated as an autocrine factor involved in growth of several human cancers, such as tumors arising from the biliary tract or cholangiocarcinoma. In malignant biliary tract epithelia, IL-6 activates the p38 MAPK pathway, which mediates a dominant survival signaling pathway. Serum and glucocorticoid-stimulated kinase (SGK) has been implicated as a survival kinase, but its role in survival signaling by IL-6 is unknown. After IL-6 stimulation, p38 MAPK activation preceded phosphorylation of SGK at Ser78. Pretreatment with the pharmacological inhibitors of p38 MAPK SB-203580 or SB-202190 blocked IL-6-induced SGK phosphorylation at Ser78 and SGK activation. Overexpression of p38alpha increased constitutive SGK phosphorylation at Ser78, whereas dominant negative p38alpha MAPK blocked IL-6-induced SGK phosphorylation and nuclear translocation. Interestingly, in addition to stimulating SGK phosphorylation, both IL-6 stimulation and p38alpha MAPK overexpression increased SGK mRNA and protein expression. An increase in p38 MAPK and SGK occurred following enforced expression of IL-6 in vivo. Furthermore, inhibition of SGK expression by siRNA increased toxicity due to chemotherapeutic drugs. Taken together, these data identify SGK as both a downstream kinase substrate as well as a transcriptionally regulated gene target of p38 MAPK in response to IL-6 and support a role of SGK during survival signaling by IL-6 in human cancers, such as cholangiocarcinoma.

Activation of p38 MAPKalpha by extracellular pressure mediates the stimulation of macrophage phagocytosis by pressure

We have previously demonstrated that constant 20 mmHg extracellular pressure increases serum-opsonized latex bead phagocytosis by phorbol 12-myristate 13-acetate (PMA)- differentiated THP-1 macrophages in part by inhibiting focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK). Because p38 MAPK is activated by physical forces in other cells, we hypothesized that modulation of p38 MAPK might also contribute to the stimulation of macrophage phagocytosis by pressure. We studied phagocytosis in PMA-differentiated THP-1 macrophages, primary human monocytes, and human monocyte-derived macrophages (MDM). p38 MAPK activation was inhibited using SB-203580 or by p38 MAPKalpha small interfering RNA (siRNA). Pressure increased phagocytosis in primary monocytes and MDM as in THP-1 cells. Increased extracellular pressure for 30 min increased phosphorylated p38 MAPK by 46.4 +/- 20.5% in DMSO-treated THP-1 macrophages and by 20.9 +/- 9% in primary monocytes (P < 0.05 each). SB-203580 (20 microM) reduced basal p38 MAPK phosphorylation by 34.7 +/- 2.1% in THP-1 macrophages and prevented pressure activation of p38. p38 MAPKalpha siRNA reduced total p38 MAPK protein by 50-60%. Neither SB-203580 in THP-1 cells and peripheral monocytes nor p38 MAPK siRNA in THP-1 cells affected basal phagocytosis, but each abolished pressure-stimulated phagocytosis. SB-203580 did not affect basal or pressure-reduced FAK activation in THP-1 macrophages, but significantly attenuated the reduction in ERK phosphorylation associated with pressure. p38 MAPKalpha siRNA reduced total FAK protein by 40-50%, and total ERK by 10-15%, but increased phosphorylated ERK 1.4 +/- 0.1-fold. p38 MAPKalpha siRNA transfection did not affect the inhibition of FAK-Y397 phosphorylation by pressure but prevented inhibition of ERK phosphorylation. Changes in extracellular pressure during infection or inflammation regulate macrophage phagocytosis by a FAK-dependent inverse effect on p38 MAPKalpha that might subsequently downregulate ERK.

Spinal p38beta isoform mediates tissue injury-induced hyperalgesia and spinal sensitization

Antagonist studies show that spinal p38 mitogen-activated protein kinase plays a crucial role in spinal sensitization. However, there are two p38 isoforms found in spinal cord and the relative contribution of these two to hyperalgesia is not known. Here we demonstrate that the isoforms are distinctly expressed in spinal dorsal horn: p38alpha in neurons and p38beta in microglia. In lieu of isoform selective inhibitors, we examined the functional role of these two individual isoforms in nociception by using intrathecal isoform-specific antisense oligonucleotides to selectively block the expression of the respective isoform. In these rats, down-regulation of spinal p38beta, but not p38alpha, prevented nocifensive flinching evoked by intraplantar injection of formalin and hyperalgesia induced by activation of spinal neurokinin-1 receptors through intrathecal injection of substance P. Both intraplantar formalin and intrathecal substance P produced an increase in spinal p38 phosphorylation and this phosphorylation (activation) was prevented when spinal p38beta, but not p38alpha, was down-regulated. Thus, spinal p38beta, probably in microglia, plays a significant role in spinal nociceptive processing and represents a potential target for pain therapy.

Significance of cyclooxygenase-2 induced via p38 mitogen-activated protein kinase in mechanical stimulus-induced peritoneal adhesion in mice

Postoperative peritoneal adhesion represents a major complication of surgery, but the molecular mechanism underlying pathogenesis of adhesion is not fully understood. The present study investigated the roles of cyclooxygenase (COX)-1 and COX-2 in peritoneal adhesion induced by scraping the surface of the cecum and abdominal wall in mice. Slight, but macroscopically observable, peritoneal adhesion was induced even on day 1, and the extent of adhesion reached a maximum on day 7 and beyond. COX-1 mRNA was constitutively expressed in the intact cecum, and its expression level was not altered after the mechanical stimulus. In contrast, expression of the COX-2 gene was markedly increased after the stimulus, and maximum expression was observed on days 3 to 7. Mofezolac, a specific COX-1 inhibitor, had no effect on peritoneal adhesion at 30 mg/kg and had only marginal effects on prostaglandin (PG)E2 levels in the cecum or peritoneal fluid. On the other hand, two highly selective inhibitors for COX-2, NS-398 (N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide) and CAY10404 [3-(4-methylsulphonylphenyl)-4-phenyl-5-trifluoromethylisoxazole], dose-dependently inhibited both adhesion formation and the increase in PGE2 levels (3-30 mg/kg). The effects of NS-398 were eliminated when PGE2 or (R)-butaprost was administered exogenously. A COX-2 antisense oligonucleotide also attenuated adhesion formation. Activation of p38 mitogen-activated protein (MAP) kinase was observed in the traumatized cecum, and an MAP kinase inhibitor, SB202190 [4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)-1H-imidazole], inhibited adhesion formation (54% inhibition at 15 microM) and also reduced the COX-2 mRNA level and PGE2 levels. In conclusion, COX-2, but not COX-1, plays a significant role in mechanical stimulus-induced peritoneal formation in the mouse cecum.

Activation of p38 MAP kinase enhances sensitivity of muscle glucose transport to insulin

Muscle contractile activity is followed by an increase in the sensitivity of glucose transport to insulin. There is evidence suggesting that activation of p38 MAP kinase (p38) is involved in the stimulation of glucose transport by insulin and contractions. Exercise results in an increase in p38 phosphorylation that lasts for hours. In this context, we tested the hypothesis that activation of p38 results in an increase in insulin sensitivity. Muscles were exposed to anisomycin for 30 min to activate p38. Anisomycin increased p38 phosphorylation approximately 2.5-fold and glucose transport activity 2- to 3-fold. Three hours after anisomycin treatment, by which time the acute effect on glucose transport had partially worn off, sensitivity of muscle glucose transport to 60 microU/ml insulin was markedly increased. Both the activation of p38 and the increase in insulin sensitivity induced by anisomycin were completely prevented by pretreatment of muscles with the p38 inhibitor SB-202190. However, in contrast to the finding with anisomycin, inhibition of p38 activation did not prevent the contraction-induced increase in insulin sensitivity. Thus our results show that activation of p38 is followed by an increase in insulin sensitivity of muscle glucose transport. However, activation of p38 is not necessary for induction of an increase in muscle insulin sensitivity by contractions. This finding provides evidence that contractions have an additional effect that makes p38 activation unnecessary for enhancement of insulin sensitivity by contractile activity.

The p38 MAP kinase pathway and its biological function

p38 is a mitogen-activated protein (MAP) kinase with structural and functional characteristics that distinguish it from JNK and ERK MAP kinases. p38 activity is upregulated when cells are exposed to a variety of stimuli including bacterial pathogens, proinflammatory cytokines, certain growth factors, and other forms of environmental stress. By regulating downstream substrates that include protein kinases and transcription factors, p38 participates in transmission, amplification, and diversification of the extracellular signal, initiating several different cellular responses. Studies have revealed that activation of p38 pathway is related to many pathological changes that occur in the course of inflammatory/immunologic and cardiovascular diseases.

MAP kinases and the adaptive response to hypertonicity: functional preservation from yeast to mammals

The adaptation to hypertonicity in mammalian cells is driven by multiple signaling pathways that include p38 kinase, Fyn, the catalytic subunit of PKA, ATM, and JNK2. In addition to the well-characterized tonicity enhancer (TonE)-TonE binding protein interaction, other transcription factors (and their respective cis elements) can potentially respond to hypertonicity. This review summarizes the current knowledge about the signaling pathways that regulate the adaptive response to osmotic stress and discusses new insights from yeast that could be relevant to the osmostress response in mammals.

Overexpression of mitogen-activated protein kinase kinase 6 in the heart improves functional recovery from ischemia in vitro and protects against myocardial infarction in vivo

The mitogen-activated protein kinases (MAPK) have been the subject of many studies to identify signaling pathways that promote cell survival or death. In cultured cardiac myocytes, p38 MAPK promotes cell survival or death depending on whether it is activated by mitogen-activated protein kinase kinase 6 (MKK6) or MKK3, respectively. The objectives of the current study were to examine the effects of MKK6-mediated p38 activation in the heart in vivo. Accordingly, we generated transgenic (TG) mice that overexpress wild type MKK6 in a cardiac-restricted manner. Although p38 was about 17-fold more active in TG than non-transgenic (NTG) mouse hearts, TG mouse hearts were morphologically and functionally similar to those of NTG littermates. However, upon transient ischemia followed by reperfusion, the MKK6 TG mouse hearts exhibited significantly better functional recovery and less injury than NTG mouse hearts. Because MKK6 increases levels of the protective small heat shock protein, alpha B-crystallin (alpha BC), in cultured cardiac myocytes, we examined alpha BC levels in the mouse hearts. The level of alpha BC was 2-fold higher in MKK6 TG than NTG mouse hearts. Moreover, ischemia followed by reperfusion induced a 6.4-fold increase in alpha BC levels in the mitochondrial fractions of TG mouse hearts but no increase in alpha BC levels in any of the other fractions analyzed. These alterations in alpha BC expression and localization suggest possible mechanisms of cardioprotection in MKK6 TG mouse hearts.

p38α Mitogen-Activated Protein Kinase Inhibition Improves Cardiac Function and Reduces Myocardial Damage in Isoproterenol-Induced Acute Myocardial Injury in Rats

p38 mitogen-activated protein (MAP) kinase is activated during ischemic/hypoxic myocardial injury. However, the role of activated p38 MAP kinase on cardiac function after myocardial injury is not well understood. In the present study, we investigated the cardioprotective effects of p38 MAP kinase inhibition in a rat model of acute myocardial injury, induced by subcutaneous injection of isoproterenol (ISO, 20 mg/kg/d for 3 days). A synthetic p38 alpha MAP kinase inhibitor, SD-282 (40 mg/kg) or vehicle (0.25% Tween 80 in saline) was given intraperitoneally twice a day for 3 days, concomitant with ISO treatment. Cardiac function, systolic blood pressure, gene expression including collagen I and III, fibronectin and COX-2, and the myocardial injury were analyzed. Results showed that administration of SD-282 remarkably improved ISO-induced reduction of cardiac function with increases in ejection fraction (P < 0.001), cardiac output (P < 0.05), stroke volume (P < 0.001), and cardiac index (P < 0.01). SD-282 abolished ISO-induced reduction of systolic blood pressure (106.7 +/- 2.2 versus 123.1 +/- 5.3 mm Hg, P < 0.05). The ISO-induced expression of COX-2, collagen I and III, and fibronectin genes was reduced significantly (P < 0.05 in all cases) by administration of SD-282. The myocardial injury induced by ISO was significantly reduced by the treatment of SD-282 as judged by the reduction of myocardial necrosis. Data suggest that p38 alpha MAP kinase may be involved in the pathogenesis of cardiac dysfunction in ischemic myocardial injury. Inhibition of this enzyme may improve cardiac function and protect myocardium from ischemic/hypoxic injury that occurs during ischemic heart disease.

The L1 retroelement-related p40 protein induces p38delta MAP kinase

We characterized a full length L1 mRNA in a rheumatoid arthritis (RA) synovial tissue and determined the degree of methylation of its 5'-UTR. We asked whether not only intact but also altered L1s can exert biological activities by transfecting RA synovial fibroblasts (SF) with either retrotransposition-competent or incompetent L1s and examined their capacity to induce p38delta. Total RNA was isolated from the synovial tissue of a 35-year-old woman with highly destructive RA. A complete L1 sequence was obtained by 3'/5'-RACE. Methylation of the genomic 5'-UTR was determined by the sodium-disulfide/PCR method. RA-SF were transfected by lipofection with either a functional L1 or an ORF2-mutated L1 element. The expression of p38delta was measured by RT-PCR and Western blot. The full length L1 mRNA included a 5'-UTR, an ORF1 and an ORF2. Three of five CpG islands (60%) of the genomic L1 5'-UTR were hypomethylated and the ORF2 was deactivated by the insertion of stop codons. Both, intact and ORF2-mutated L1 vectors, induced the expression of p38delta. Thus, even an ORF2-mutated L1 element, as expressed in RA, is biologically active and both L1 ORF1 and p38delta transcripts may appear as a consequence of genomic hypomethylation. The induction of p38delta appears to be mediated by an ORF1/p40-dependent process. This is the first indication of a p40 mediated transactivation.