MAPKs ERK and p38, but not JNK phosphorylation, modulate IL-6 and TNF-α secretion following OK-432 in vitro stimulation of purified human monocytes

Interaction between the immune system and cancer allows for the use of biological response modifiers, e.g. OK-432, in cancer therapy. OK-432, penicillin-killed Streptococcus pyogenes, is used in treating carcinomas, but also lymphangiomas. We have studied the role of monocytes (MOs) in the immune response to OK-432 by examining IL-6 and tumour necrosis factor (TNF)-α secretion after in vitro MO stimulation with OK-432, to some extent in comparison with lipoteichoic acid (LTA) and lipopolysaccharide (LPS). LTA stimulation of whole blood gave IL-6 but not TNF-α secretion, as previously shown with OK-432 stimulation, whereas both cytokines were secreted following LPS stimulation. Addition of the MAPK kinase (MAPKK) MEK inhibitor U0126 inhibited IL-6/TNF-α secretion in a dose-dependent manner. Flow cytometry and to some extent Western blot (Wb) analyses showed that MAPK ERK, located downstream of MEK1/2, is predominantly phosphorylated at isolation from peripheral blood. Addition of the p38 MAP kinase inhibitor SB202190 decreased MO IL-6/TNF-α production upon OK-432 stimulation in a dose-dependent manner. Addition of the MAPK JNK inhibitor SP600125 did not systematically change the MO IL-6/TNF-α OK-432 response. Flow cytometry showed that when stimulating the MOs before isolation from blood, LPS yielded ERK phosphorylation and LPS/LTA p38 phosphorylation, whereas OK-432 had no effects on phosphorylation levels. In conclusion, we have shown that OK-432 resembles TLR2 more than TLR4 stimulation of MOs and depends on MAPKK MEK and MAPK p38, but not on JNK phosphorylation. The MEK and p38 MO OK-432 stimulation dependence is possibly related to the differentiation of cells of the MO lineage.     

Induction of inducible nitric oxide synthase-NO* by lipoarabinomannan of Mycobacterium tuberculosis is mediated by MEK1-ERK, MKK7-JNK, and NF-kappaB signaling pathways

Nitric oxide (NO*) expression by inducible nitric oxide synthase (iNOS) is an important host defense mechanism against Mycobacterium tuberculosis in mononuclear phagocytes. The objective of this investigation was to examine the role of mitogen-activated protein (MAP) kinase (MAPK) and nuclear factor kappaB (NF-kappaB) signaling pathways in the regulation of iNOS and NO* by a mycobacterial cell wall lipoglycan known as mannose-capped lipoarabinomannan (ManLAM). Specific pharmacologic inhibition of the extracellular-signal-regulated kinase (ERK) or NF-kappaB pathway revealed that both these signaling cascades were required in gamma interferon (IFN-gamma)-ManLAM-induced iNOS protein and NO2- expression in mouse macrophages. Transient cotransfection of dominant-negative protein mutants of the c-Jun NH2-terminal kinase (JNK) pathway revealed that the MAP kinase kinase 7 (MKK7)-JNK cascade also mediated IFN-gamma-ManLAM induction of iNOS promoter activity whereas MKK4 did not. Overexpression of null mutant IkappaBalpha, a potent inhibitor of NF-kappaB activation, confirmed that the IkappaBalpha kinase (IKK)-NF-kappaB signaling pathway enhanced IFN-gamma-ManLAM-induced iNOS promoter activity. By contrast, activated p38mapk inhibited iNOS induction. These results indicate that combined IFN-gamma and ManLAM stimulation induced iNOS and NO. expression and that MEK1-ERK, MKK7-JNK, IKK-NF-kappaB, and p38mapk signaling pathways play important regulatory roles.     

Paclitaxel causes mouse splenic lymphocytes to a state hyporesponsive to lipopolysaccharide stimulation

Multiple immune system actions have been ascribed to paclitaxel (taxol), a novel anticancer drug, including the capacity to induce macrophage antitumor cytotoxic molecule production. In the present studies, we demonstrated that paclitaxel produced a selective inhibition of lipopolysaccharide (LPS)-induced B cell proliferation. Similarly, in vitro polyclonal antibody-forming cell responses also were found to be inhibited by paclitaxel. Conversely, paclitaxel exhibited no inhibitory effects on concanavalin A (Con A)-induced T cell proliferation. To study the pathway leading to paclitaxel-induced immunosuppression, we analyzed Raf-1/ERK and JNK/p38 MAPK pathways, both of which have been reported to be involved in LPS signaling. Our results indicate that taxol treatment inhibits Raf-1 kinase activation while having no effect on ERK activation suggesting that ERK activation is distinct from upstream Raf-1 kinase in taxol-induced immunomodulation. Furthermore, paclitaxel pretreatment caused down-regulation of stress-activated MAPKs, JNK and p38 MAPK in lipopolysaccharide (LPS)-stimulated mouse splenic lymphocytes, demonstrating that spleen cells are induced to a state hyporesponsive to LPS stimulation by pre-exposing them to paclitaxel. Taken together, these results suggest that down-regulation of JNK/p38 MAP kinase may contribute to paclitaxel-induced immunosuppression in mouse splenic lymphocytes.     

Mechanisms of H4/ICOS costimulation: effects on proximal TCR signals and MAP kinase pathways

H4/ICOS is a costimulatory molecule related to CD28. Its effects on early TCR signals have been analyzed in mouse CD4(+) Th2 cells, expressing H4/ICOS at higher levels than Th1 clones. Anti-H4/ICOS antibodies strongly enhanced CD3-mediated tyrosine phosphorylation of ZAP-70, zeta, or Vav, as well as extracellular signal-regulated kinase (ERK), Jun N-terminal kinase (JNK) and p38 MAP kinase activation in these cells. The association of phosphoinositide 3-kinase (PI-3K) to H4/ICOS was enhanced by H4/ICOS cross-linking, and PI-3K inhibitors inhibited ERK and JNK activation and IL-4/IL-10 secretion, but not p38 MAP kinase or ZAP-70 activation. H4/ICOS-mediated activation of JNK, but not ERK or p38, is partially dependent on the expression of CD4 by the cells, whereas H4/ICOS costimulation is partially independent on CD28 expression. Cytochalasin D, an inhibitor of actin polymerization, inhibited ZAP-70, MAP kinase activation, or IL-4/IL-10 secretion. Neither cyclosporin A nor inhibitors of PKC produced detectable inhibition of ZAP-70 phosphorylation or MAP kinase activation in these Th2 cells. Cyclosporin A strongly inhibited IL-4, but not IL-10 secretion. ERK or JNKinhibitors partially inhibited IL-4 and IL-10 secretion, while PKC or p38 inhibitors had no significant effects on IL-4 or IL-10 secretion. Taken together, our data show clear similarities of costimulation mechanisms between H4/ICOS and CD28 during the early steps of TCR activation.     

Leishmania donovani promastigotes evade the activation of mitogen-activated protein kinases p38, c-Jun N-terminal kinase, and extracellular signal-regulated kinase-1/2 during infection of naive macrophages

The protozoan parasite Leishmania fails to activate naive macrophages for proinflammatory cytokines production, and selectively impairs signal transduction pathways in infected macrophages. Because mitogen-activated protein kinases (MAPK)- and NF-kappaB-dependent signaling pathways regulate proinflammatory cytokines release, we investigated their activation in mouse bone marrow-derived macrophages (BMM) exposed to Leishmania donovani promastigotes. In naive BMM, the parasite failed to induce the phosphorylation of p38 MAPK, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK)1/2, as well as the degradation of IkappaB-alpha. The use of L. donovani mutants defective in the biosynthesis of lipophosphoglycan revealed that evasion of ERK1/2 activation requires surface expression of the repeating unit moiety of this virulence determinant. In IFN-gamma-primed BMM, L. donovani promastigotes strongly induced the phosphorylation of p38 MAPK and ERK1/2, and the use of selective inhibitors for ERK (PD98059) and p38 MAPK (SB203580) revealed that both kinases are required for L. donovani-induced TNF-alpha but not NO(2)(-) release. Collectively, these data suggest that both p38 MAPK and ERK1/2 pathways participate in some Leishmania-induced responses in IFN-gamma-primed BMM. The ability of L. donovani promastigotes to avoid MAPK and NF-kappaB activation in naive macrophages may be part of the strategy evolved by this parasite to evade innate immune responses.     

p38 MAPK is a critical regulator of the constitutive and the beta4 integrin-regulated expression of IL-6 in human normal thymic epithelial cells

Cytokines and adhesion receptors are key mediators in the dialog occurring between thymic epithelial cells (TEC) and thymocytes and regulating T cell maturation and epithelial embryonic differentiation. Among cytokines, IL-6 can be critical in the thymus, fostering proliferation, differentiation and/or survival of both TEC and thymocytes. We have previously reported in human normal TEC that clustering of the laminin receptor alpha6beta4 integrin induced by thymocyte contact or monoclonal antibody-mediated cross-linking regulates IL-6 gene expression via activation of NF-kappaB and NF-IL6 transactivators. Here we show that alpha6beta4 integrin activates p38 mitogen-activated protein kinase (MAPK) and that p38 is essential for IL-6 gene expression. In fact, beta4 cross-linking activated p38 and extracellular signal-regulated kinase (ERK) MAPK, Rac1, p21-activated protein kinase 1 (PAK1) and MAPK kinases (MKK) 3/MKK6. However, pharmacological blockade of p38 or ERK demonstrated that p38 inhibition abrogated both basal and beta4 integrin-induced production of IL-6 preventing NF-kappaB and NF-IL6 activation, whereas ERK inhibition reduced IL-6 production, hampering only NF-kappaB activation. Overall, our results indicate that p38 MAPK and alpha6beta4 integrin, expressed by TEC throughout their life, are critical regulators of the intrathymic availability of a cytokine controlling fate and functions of cells governing development and maintenance of thymic architecture and immune responses.     

Low concentrations of nitric oxide (NO) induced cell death in PC12 cells through activation of p38 mitogen-activated protein kinase (p38 MAPK) but not via extracellular signal-regulated kinases (ERK1/2) or c-Jun N-terminal protein kinase (JNK)

Nitric oxide (NO), a highly reactive gaseous molecule, has been previously reported to induce apoptosis-like cell death even at a low concentration in PC12 cells. In this study, we examined NO-induced activation of members of the mitogen-activated protein kinase (MAPK) family, i.e., p38 MAPK, extracellular signal-regulated kinases (ERK1/2), and c-Jun N-terminal protein kinase (JNK). Following the exposure of PC12 cells to an NO donor, (+)-(E)-4-ethyl-2-[hydroxyimino]-5-nitro-3-hexenamide (NOR3; 100 muM), the phosphorylation level of p38 MAPK increased time dependently from 2 to 6 h, but that of both ERK1/2 and JNK did not. Treatment with a p38 MAPK inhibitor SB203580 partially blocked the NOR3-induced cell death. Neither PD98059, U0126 (inhibitors of ERK1/2) nor SP600125 (a specific inhibitor of JNK) treatments had any significant effect on the NOR3-induced cell death. These findings suggest that the activation of a p38 MAPK pathway, but not that of ERK1/2 or JNK, plays an essential role in the apoptosis-like cell death induced by low concentrations of NO.     

Hypoxia activates jun-N-terminal kinase, extracellular signal-regulated protein kinase, and p38 kinase in pulmonary arteries

Chronic alveolar hypoxia is the major cause of pulmonary hypertension. The cellular mechanisms involved in hypoxia- induced pulmonary arterial remodeling are still poorly understood. Mitogen-activated protein kinase (MAPK) is a key enzyme in the signaling pathway leading to cellular growth and proliferation. The purpose of this investigation was to determine the roles that MAPKs, specifically Jun-N-terminal kinase (JNK), extracellular signal-regulated protein kinase (ERK), and p38 kinase, play in the hypoxia-induced pulmonary arterial remodeling. Rats were exposed to normobaric hypoxia (10% O(2)) for 1, 3, 7, or 14 d. Hypoxia caused significant remodeling in the pulmonary artery characterized by thickening of pulmonary arterial wall and increases in tissue mass and total RNA. JNK, ERK, and p38 kinase tyrosine phosphorylations and their activities were significantly increased by hypoxia. JNK activation peaked at Day 1 and ERK/p38 kinase activation peaked after 7 d of hypoxia. The results from immunohistochemistry show that hypoxia increased phospho-MAPK staining in both large and small intrapulmonary arteries. Hypoxia also upregulated vascular endothelial growth factor messenger RNA (mRNA) and platelet-derived growth factor receptor mRNA levels in pulmonary artery with a time course correlated to the activation of ERK and p38 kinase. The gene expressions of c-jun, c-fos, and egr-1, known as downstream effectors of MAPK, were also investigated. Hypoxia upregulated egr-1 mRNA but downregulated c-jun and c-fos mRNAs. These data suggest that hypoxia-induced activation of JNK is an early response to hypoxic stress and that activation of ERK and p38 kinase appears to be associated with hypoxia-induced pulmonary arterial remodeling.