Coordinate activation of endogenous p38alpha, beta, gamma, and delta by inflammatory stimuli

B Cell Development and T-Dependent Antibody Response Are Regulated by p38γ and p38δ

p38MAP kinase (MAPK) signal transduction pathways are important regulators of inflammation and the immune response; their involvement in immune cell development and function is still largely unknown. Here we analysed the role of the p38 MAPK isoforms p38γ and p38δ in B cell differentiation in bone marrow (BM) and spleen, using mice lacking p38γ and p38δ, or conditional knockout mice that lack both p38γ and p38δ specifically in the B cell compartment. We found that the B cell differentiation programme in the BM was not affected in p38γ/δ-deficient mice. Moreover, these mice had reduced numbers of peripheral B cells as well as altered marginal zone B cell differentiation in the spleen. Expression of co-stimulatory proteins and activation markers in p38γ/δ-deficient B cells are diminished in response to B cell receptor (BCR) and CD40 stimulation; p38γ and p38δ were necessary for B cell proliferation induced by BCR and CD40 but not by TLR4 signaling. Furthermore, p38γ/δ-null mice produced significantly lower antibody responses to T-dependent antigens. Our results identify unreported functions for p38γ and p38δ in B cells and in the T-dependent humoral response; and show that the combined activity of these kinases is needed for peripheral B cell differentiation and function.

Molecular characterization and function of a p38 MAPK gene from Litopenaeus vannamei

p38 mitogen-activated protein kinases (MAPKs) are broadly expressed from yeasts to mammals, and are involved in the regulation of cells responsible to various extracellular stimuli. In this study, a p38 MAPK gene (designated as Lvp38) from Litopenaeus vannamei, was cloned and characterized. It contained the conserved structures of a Thr-Gly-Tyr (TGY) motif and a substrate-binding site, Ala-Thr-Arg-Trp (ATRW). The tissue distribution patterns showed that Lvp38 was widely expressed in all examined tissues, with the highest expression in hemocytes, nerves, and intestines. Quantitative real-time PCR revealed that Lvp38 was upregulated in gills and hemocytes after infection with the Gram-negative Vibrio alginolyticus and the Gram-positive Staphylococcus aureus. Reporter gene assays indicated that Lvp38 activated the expression of antimicrobial peptides (AMPs) of Drosophila and shrimp. Knockdown of Lvp38 by RNA interference (RNAi) resulted in a higher mortality of L. vannamei under V. alginolyticus and S. aureus infection, as well as a reduction in the expression of three shrimp AMP genes, namely, PEN4, crustin, and ALF2. Taken together, our data indicated that Lvp38 played a role in defending against bacterial infections.

p38γ and p38δ kinases regulate the Toll-like receptor 4 (TLR4)-induced cytokine production by controlling ERK1/2 protein kinase pathway activation

On the basis mainly of pharmacological experiments, the p38α MAP kinase isoform has been established as an important regulator of immune and inflammatory responses. However, the role of the related p38γ and p38δ kinases has remained unclear. Here, we show that deletion of p38γ and p38δ impaired the innate immune response to lipopolysaccharide (LPS), a Toll-like receptor 4 (TLR4) ligand, by blocking the extracellular signal-regulated kinase 1/2 (ERK1/2) activation in macrophages and dendritic cells. p38γ and p38δ were necessary to maintain steady-state levels of tumor progression locus 2 (TPL2), the MKK kinase that mediates ERK1/2 activation after TLR4 stimulation. TNFα, IL-1β, and IL-10 production were reduced in LPS-stimulated macrophages from p38γ/δ-null mice, whereas IL-12 and IFNβ production increased, in accordance with the known effects of TPL2/ERK1/2 signaling on the induction of these cytokines. Furthermore, p38γ/δ-deficient mice were less sensitive than controls to LPS-induced septic shock, showing lower TNFα and IL-1β levels after challenge. Together, our results establish p38γ and p38δ as key components in innate immune responses.

MAPK-activated protein kinase 2 is required for mouse meiotic spindle assembly and kinetochore-microtubule attachment

MAPK-activated protein kinase 2 (MK2), a direct substrate of p38 MAPK, plays key roles in multiple physiological functions in mitosis. Here, we show for the first time the unique distribution pattern of MK2 in meiosis. Phospho-MK2 was localized on bipolar spindle minus ends and along the interstitial axes of homologous chromosomes extending over centromere regions and arm regions at metaphase of first meiosis (MI stage) in mouse oocytes. At metaphase of second meiosis (MII stage), p-MK2 was localized on the bipolar spindle minus ends and at the inner centromere region of sister chromatids as dots. Knockdown or inhibition of MK2 resulted in spindle defects. Spindles were surrounded by irregular nondisjunction chromosomes, which were arranged in an amphitelic or syntelic/monotelic manner, or chromosomes detached from the spindles. Kinetochore-microtubule attachments were impaired in MK2-deficient oocytes because spindle microtubules became unstable in response to cold treatment. In addition, homologous chromosome segregation and meiosis progression were inhibited in these oocytes. Our data suggest that MK2 may be essential for functional meiotic bipolar spindle formation, chromosome segregation and proper kinetochore-microtubule attachments.

Studies of chirality effect of 4-(phenylamino)-pyrrolo[2,1-f][1,2,4]triazine on p38alpha by molecular dynamics simulations and free energy calculations

4-(Phenylamino)-pyrrolo[2,1-f][1,2,4]triazines have been discovered as inhibitors of p38alpha. Experimental assays have proven that the configuration of alpha-Me-benzyl connected with amide at C6 is essential for the binding affinity. The S-configured inhibitor (11j) displays 80 times more potency than the R-configured one (11k). Here we investigated the mechanism how different configurations influence the binding affinity using molecular dynamics simulations, free energy calculations and free energy decomposition analysis. We found that the van der Waals interactions play the most important role in differentiating the activities between 11j and 11k with p38alpha. The difference of the van der Waals interactions is primarily determined by two residues, LEU108 and LEU167. Consequently stabilization of pyrrolo[2,1-f][1,2,4]triazine ring is important for the activities of inhibitors. Meanwhile we observed that the different configuration of the alpha-Me-benzyl group leads to the difference of binding between 11j and 11k. In conclusion, our work shows that it is feasible to analyze the chirality effect of inhibitors with different configurations by molecular dynamics simulations and free energy calculations, and provides useful information for drug design.

Acid beta-glucosidase 1 counteracts p38delta-dependent induction of interleukin-6: possible role for ceramide as an anti-inflammatory lipid

Activation of protein kinase C (PKC) by the phorbol ester (phorbol 12-myristate 13-acetate) induces ceramide formation through the salvage pathway involving, in part, acid beta-glucosidase 1 (GBA1), which cleaves glucosylceramide to ceramide. Here, we examine the role of the GBA1-ceramide pathway, in regulating a pro-inflammatory pathway initiated by PKC and leading to activation of p38 and induction of interleukin 6 (IL-6). Inhibition of ceramide formation by fumonisin B1 or down-regulation of PKCdelta potentiated PMA-induced activation of p38 in human breast cancer MCF-7 cells. Similarly, knockdown of GBA1 by small interfering RNAs or pharmacological inhibition of GBA1 promoted further activation of p38 after PMA treatment, implicating the GBA1-ceramide pathway in the termination of p38 activation. Knockdown of GBA1 also evoked the hyperproduction of IL-6 in response to 4beta phorbol 12-myristate 13-acetate. On the other hand, increasing cellular ceramide with cell-permeable ceramide treatment resulted in attenuation of the IL-6 response. Importantly, silencing the delta isoform of the p38 family significantly attenuated the hyperproduction of IL-6. Reciprocally, p38delta overexpression induced IL-6 biosynthesis. Thus, the GBA1-ceramide pathway is suggested to play an important role in terminating p38delta activation responsible for IL-6 biosynthesis. Furthermore, the p38delta isoform was identified as a novel and predominant target of ceramide signaling as well as a regulator of IL-6 biosynthesis.

Pyrazolo-pyrimidines: a novel heterocyclic scaffold for potent and selective p38 alpha inhibitors

The synthesis and structure-activity relationships (SAR) of p38 alpha MAP kinase inhibitors based on a pyrazolo-pyrimidine scaffold are described. These studies led to the identification of compound 2x as a potent and selective inhibitor of p38 alpha MAP kinase with excellent cellular potency toward the inhibition of TNFalpha production. Compound 2x was highly efficacious in vivo in inhibiting TNFalpha production in an acute murine model of TNFalpha production. X-ray co-crystallography of a pyrazolo-pyrimidine analog 2b bound to unphosphorylated p38 alpha is also disclosed.

Synthesis and SAR of new pyrrolo[2,1-f][1,2,4]triazines as potent p38 alpha MAP kinase inhibitors

A novel series of compounds based on the pyrrolo[2,1-f][1,2,4]triazine ring system have been identified as potent p38 alpha MAP kinase inhibitors. The synthesis, structure-activity relationships (SAR), and in vivo activity of selected analogs from this class of inhibitors are reported. Additional studies based on X-ray co-crystallography have revealed that one of the potent inhibitors from this series binds to the DFG-out conformation of the p38 alpha enzyme.

The discovery of (R)-2-(sec-butylamino)-N-(2-methyl-5-(methylcarbamoyl)phenyl) thiazole-5-carboxamide (BMS-640994)-A potent and efficacious p38alpha MAP kinase inhibitor

A novel structural class of p38alpha MAP kinase inhibitors has been identified via iterative SAR studies of a focused deck screen hit. Optimization of the lead series generated 6e, BMS-640994, a potent and selective p38alpha inhibitor that is orally efficacious in rodent models of acute and chronic inflammation.

MAPK and heat shock protein 27 activation are associated with respiratory syncytial virus induction of human bronchial epithelial monolayer disruption

Respiratory syncytial virus (RSV) is the major cause of bronchiolitis in infants, and a common feature of RSV infections is increased lung permeability. The accumulation of fluid in the infected lungs is caused by changes in the endothelial and epithelial membrane integrity. However, the exact mechanisms of viral-induced fluid extravasation remain unclear. Here, we report that infection of human epithelial cells with RSV results in significant epithelial membrane barrier disruption as assessed by a decrease in transepithelial electrical resistance (TEpR). This decrease in TEpR, which indicates changes in paracellular permeability, was mediated by marked cellular cytoskeletal rearrangement. Importantly, the decrease in TEpR was attenuated by using p38 MAPK inhibitors (SB-203580) but was partially affected by JNK inhibitor SP-600125. Interestingly, treatment of A549 cells with MEK1/2 inhibitor (U-0126) led to a decrease in TEpR in the absence of RSV infection. The changes in TEpR were concomitant with an increase in heat shock protein 27 (Hsp27) phosphorylation and with actin microfilament rearrangement. Thus our data suggest that p38 MAPK and Hsp27 are required for RSV induction of human epithelial membrane permeability.

Novel therapies for rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, systemic inflammatory disease that causes significant morbidity and mortality. The pathogenesis outlined to date in RA consists of a cascade of pro-inflammatory cytokines and chemokines leading to the recruitment of inflammatory cells and the self perpetuation of inflammation, ultimately leading to cartilage and bone destruction. The dramatic progress in understanding the molecular immunology in RA has led to a transition from conventional treatment with aggressive immune suppression to targeted biological-based therapies that control the inflammatory pathways associated with RA. This article reviews the current biological and small-molecule therapies approved for the treatment of RA and those in development, including antibodies, tolerising agents and vaccines.

Bluetongue virus and double-stranded RNA increase human vascular permeability: role of p38 MAPK

Endothelial cell (EC) involvement in viral hemorrhagic fevers has been clearly established. However, virally activated mechanisms leading to endothelial activation and dysfunction are not well understood. Several different potential mechanisms such as direct viral infection, alterations in procoagulant/anticoagulant balance, and increased cytokine production have been suggested. We utilized a model of EC barrier dysfunction and vascular endothelial leakage to explore the effect of bluetongue virus (BTV), a hemorrhagic fever virus of ruminants, on human lung endothelial cell barrier properties. Infection of human lung EC with BTV induced a significant and dose-dependent decrease in trans-endothelial electrical resistance (TER). Furthermore, decreases in TER occurred in conjunction with cytoskeletal rearrangement, suggesting a direct mechanism for viral infection-mediated endothelial barrier disruption. Interestingly, double-stranded RNA (dsRNA) mimicked the effects of BTV on endothelial barrier properties. Both BTV- and dsRNA-induced endothelial barrier dysfunction was blocked by treatment with a pharmacological inhibitor of p38 MAPK. The induction of vascular permeability by dsRNA treatment or BTV infection was concomitent with induction of inflammatory cytokines. Taken together, our data suggest that the presence of dsRNA during viral infections and subsequent activation of p38 MAPK is a potential molecular pathway for viral induction of hemorrhagic fevers. Collectively, our data suggest that inhibition of p38 MAPK may be a possible therapeutic approach to alter viral-induced acute hemorrhagic diseases.

c-Jun N-terminal kinase negatively regulates dsRNA and RSV induction of tumor necrosis factor- alpha transcription in human epithelial cells

Secretion of inflammatory cytokines is the initial step of the immune response to viral infections. This innate immune response is mediated by the expression of a variety of cytokines, exemplified by tumor necrosis factor- alpha (TNF-alpha). The presence of dsRNA during viral infections is a key step in activation of several signaling pathways, including protein kinase R (PKR), toll-like receptor 3 (TLR3), mitogen-activated protein kinase (MAPK), activator protein-1 (AP-1), interferon regulatory factors (IRFs), and NF-kappaB pathways, which are all relevant in the expression of inflammatory cytokines. We previously reported that PKR and p38 MAPK were required for dsRNA and viral induction of inflammatory cytokines in epithelial cells. Here, we report that activation of c-Jun N-terminal kinase (JNK) during dsRNA treatment or respiratory syncytial viral (RSV) infection negatively regulates the induction of TNF-alpha in human epithelial cells. Inhibition of JNK by a pharmacologic inhibitor showed that expression of TNF-alpha increased following both dsRNA treatment and infection with RSV. Importantly, transfection of epithelial cells with a dominant-negative mutant of JNK significantly increased dsRNA induction of TNF-alpha. The mechanism by which JNK inhibition increases TNF-alpha induction appears to be through p38 MAPK activation. Our data show that JNK is a negative regulator of dsRNA and RSV induction of TNF-alpha expression and, thus, may act as a counterbalance to proinflammatory signals generated during viral infections.

The antiapoptotic effect of heme oxygenase-1 in endothelial cells involves the degradation of p38 alpha MAPK isoform

Heme oxygenase-1 (HO-1) protects endothelial cells (EC) from undergoing apoptosis. This effect is mimicked by CO, generated via the catabolism of heme by HO-1. The antiapoptotic effect of CO in EC was abrogated when activation of the p38alpha and p38beta MAPKs was inhibited by the pyridinyl imidazole SB202190. Using small interfering RNA, p38beta was found to be cytoprotective in EC, whereas p38alpha was not. When overexpressed in EC, HO-1 targeted specifically the p38alpha but not the p38beta MAPK isoform for degradation by the 26S proteasome, an effect reversed by the 26S proteasome inhibitors MG-132 or lactacystin. Inhibition of p38alpha expression was also observed when HO-1 was induced physiologically by iron protoporphyrin IX (hemin). Inhibition of p38alpha no longer occurred when HO activity was inhibited by tin protoporphyrin IX, suggesting that p38alpha degradation was mediated by an end product of heme catabolism. Exogenous CO inhibited p38alpha expression in EC, suggesting that CO is the end product that mediates this effect. The antiapoptotic effect of HO-1 was impaired when p38alpha expression was restored ectopically or when its degradation by the 26S proteasome was inhibited by MG-132. Furthermore, the antiapoptotic effect of HO-1 was lost when p38beta expression was targeted by a specific p38beta small interfering RNA. In conclusion, the antiapoptotic effect of HO-1 in EC is dependent on the degradation of p38alpha by the 26S proteasome and on the expression of p38beta.

Infectious bursal disease virus infection induces macrophage activation via p38 MAPK and NF-κB pathways

In the present study, we show that infection with infectious bursal disease virus (IBDV) causes activation of macrophages, the key cells involved in inflammatory and immune-regulatory functions. Exposure of cultured spleen macrophages (SM) from SPF chickens to IBDV resulted in the production of nitric oxide (NO). In addition, there was upregulation of mRNA expression of inducible nitric oxide synthase (iNOS), IL-8 and cyclooxygenase-2 (COX-2). The signal transduction pathways involved in macrophage activation were examined. The role of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappaB (NF-kappaB) was tested by using specific pharmacological inhibitors. Addition of p38 MAPK inhibitor, SB-203580 and NF-kappaB inhibitor Bay 11-7082, suppressed IBDV-induced NO production and mRNA expression of iNOS, IL-8 and COX-2. The results suggest that IBDV uses cellular signal transduction machinery, in particular the p38 MAPK and NF-kappaB pathways, to elicit macrophage activation. The increased production of NO, IL-8 and COX-2 by macrophages may contribute to bursa inflammatory responses commonly seen during the acute IBDV infection.

Bordetella type III secretion and adenylate cyclase toxin synergize to drive dendritic cells into a semimature state

Bordetella bronchiseptica establishes persistent infection of the murine respiratory tract. We hypothesize that long-term colonization is mediated in part by bacteria-driven modulation of dendritic cells (DCs) leading to altered adaptive immune responses. Bone marrow-derived DCs (BMDCs) from C57BL/6 mice infected with live B. bronchiseptica exhibited high surface expression of MHCII, CD86, and CD80. However, B. bronchiseptica-infected BMDCs did not exhibit significant increases in CD40 surface expression and IL-12 secretion compared with BMDCs treated with heat-killed B. bronchiseptica. The B. bronchiseptica type III secretion system (TTSS) mediated the increase in MHCII, CD86, and CD80 surface expression, while the inhibition of CD40 and IL-12 expression was mediated by adenylate cyclase toxin (ACT). IL-6 secretion was independent of the TTSS and ACT. These phenotypic changes may result from differential regulation of MAPK signaling in DCs. Wild-type B. bronchiseptica activated the ERK 1/2 signaling pathway in a TTSS-dependent manner. Additionally, ACT was found to inhibit p38 signaling. These data suggest that B. bronchiseptica drive DC into a semimature phenotype by altering MAPK signaling. These semimature DCs may induce tolerogenic immune responses that allow the persistent colonization of B. bronchiseptica in the host respiratory tract.

MKK3 mitogen-activated protein kinase pathway mediates carbon monoxide-induced protection against oxidant-induced lung injury

The stress-inducible gene heme oxygenase (HO-1) has previously been shown to provide cytoprotection against oxidative stress. The mechanism(s) by which HO-1 provides this cytoprotection is poorly understood. We demonstrate here that carbon monoxide (CO), a byproduct released during the degradation of heme by HO, plays a major role in mediating the cytoprotection against oxidant-induced lung injury. We show in vitro that CO protects cultured epithelial cells from hyperoxic damage. By using dominant negative mutants and mice deficient in the genes for the various MAP kinases, we demonstrate that the cytoprotective effects of CO are mediated by selective activation of the MKK3/p38 beta protein MAP kinase pathway. In vivo, our experiments demonstrate that CO at a low concentration protects the lungs, extends the survival of the animals, and exerts potent anti-inflammatory effects with reduced inflammatory cell influx into the lungs and marked attenuation in the expression of pro-inflammatory cytokines.

Viral induction of inflammatory cytokines in human epithelial cells follows a p38 mitogen-activated protein kinase-dependent but NF-kappa B-independent pathway

The initial step in an immune response toward a viral infection is the induction of inflammatory cytokines. This innate immune response is mediated by expression of a variety of cytokines exemplified by TNF-alpha and IL-1beta. A key signal for the recognition of intracellular viral infections is the presence of dsRNA. Viral infections and dsRNA treatment can activate several signaling pathways including the protein kinase R pathway, mitogen-activated protein kinase (MAPK) pathways, and NF-kappaB, which are important in the expression of inflammatory cytokines. We previously reported that activation of protein kinase R was required for dsRNA induction of TNF-alpha, but not for IL-1beta. In this study, we report that activation of the p38 MAPK pathway by respiratory viral infections is necessary for induction of inflammatory cytokines in human bronchial epithelial cells. Inhibition of p38 MAPK by two different pharmacological inhibitors showed that expression of both TNF-alpha and IL-1beta required activation of this signaling pathway. Interestingly, inhibition of NF-kappaB did not significantly reduce viral induction of either cytokine. Our data show that, during the initial infections of epithelial cells with respiratory viruses, activation of the p38 MAPK pathway is associated with induction of inflammation, and NF-kappaB activation may be less important than previously suggested.

p38 MAP kinases: key signalling molecules as therapeutic targets for inflammatory diseases

The p38 MAP kinases are a family of serine/threonine protein kinases that play important roles in cellular responses to external stress signals. Since their identification about 10 years ago, much has been learned of the activation and regulation of the p38 MAP kinase pathways. Inhibitors of two members of the p38 family have been shown to have anti-inflammatory effects in preclinical disease models, primarily through the inhibition of the expression of inflammatory mediators. Several promising compounds have also progressed to clinical trials. In this review, we provide an overview of the role of p38 MAP kinases in stress-activated pathways and the progress towards clinical development of p38 MAP kinase inhibitors in the treatment of inflammatory diseases.

Ribotoxic stress activates p38 and JNK kinases and modulates the antigen-presenting activity of dendritic cells

Initiation of adaptive immunity requires activation of dendritic cells (DC) by "danger" signals. This study examines the functional consequences of activating a cellular stress response in human DC. Anisomycin, a potent inducer of this "stress" response, selectively activates p38 kinase in DC at low concentrations, and both p38 kinases and JNKs at higher concentrations. Activation of p38, was accompanied by an increase in the potency of dendritic cells to activate T cells. In contrast to LPS, anisomycin had no effect on the expression of several DC activation markers. Anisomycin synergised with LPS in driving release of IL-12 and TNF-alpha. Anisomycin also enhanced the formation of clusters between DC and T cells. Enhanced cytokine release and clustering were both inhibited by the selective p38 alpha and p38 beta inhibitor SB203580. This study demonstrates that the cellular stress response, mediated via p38 kinases, plays an important role in the regulation of several aspects of DC function.

Suppression of the clinical and cytokine response to endotoxin by RWJ-67657, a p38 mitogen-activated protein-kinase inhibitor, in healthy human volunteers

Sepsis resulting in multiorgan failure and death is still a major problem in intensive care medicine, despite extensive attempts to interfere in the supposed underlying mechanism of a deranged immune system. This is not only due to the persistent lacunae in knowledge about the immune system in sepsis but also due to the lack of sufficient instruments for intervention. Inhibitors of the p38 mitogen-activated protein kinase (p38MAPK) have been used to study the signalling pathway of the immune response. In vitro and animal studies have demonstrated that blocking p38MAPK could mitigate the pro-inflammatory response and improve survival after endotoxaemia. Using an endotoxaemia model in healthy human volunteers we evaluated the attenuation of clinical and cytokine response to endotoxin after inhibition of p38MAPK by an oral dose of RWJ-67657, a pyrindinyl imidazole. We measured the clinical parameters temperature, blood pressure and heart rate. The proinflammatory cytokines tumour necrosis factor-alpha, interleukin-6 and interleukin-8 were measured by ELISA at various points during a 24-h period. Drug toxicity was evaluated by routine clinical and laboratory examinations. After a single dose dose of RWJ-67657 the temperature and blood pressure response remained at the basal level. The inhibition of TNF-alpha, IL-6 and IL-8 response was a dose dependent. With the maximum dosage, reduction in peak serum levels of the proinflammatory cytokines was greater than 90%. There was no drug-related toxicity.

INTERPRETATION

We conclude that inhibition of p38MAPK by RWJ-67657 might be a tool to intervene in the deranged immune response in sepsis and other inflammatory diseases.