Role Of Stress-activated Protein Kinases Research Articles

Pathophysiological Roles of Stress-Activated Protein Kinases in Pulmonary Fibrosis.

Idiopathic pulmonary fibrosis (IPF) is one of the most symptomatic progressive fibrotic lung diseases, in which patients have an extremely poor prognosis. Therefore, understanding the precise molecular mechanisms underlying pulmonary fibrosis is necessary for the development of new therapeutic options. Stress-activated protein kinases (SAPKs), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (p38) are ubiquitously expressed in various types of cells and activated in response to cellular environmental stresses, including inflammatory and apoptotic stimuli. Type II alveolar epithelial cells, fibroblasts, and macrophages are known to participate in the progression of pulmonary fibrosis. SAPKs can control fibrogenesis by regulating the cellular processes and molecular functions in various types of lung cells (including cells of the epithelium, interstitial connective tissue, blood vessels, and hematopoietic and lymphoid tissue), all aspects of which remain to be elucidated. We recently reported that the stepwise elevation of intrinsic p38 signaling in the lungs is correlated with a worsening severity of bleomycin-induced fibrosis, indicating an importance of this pathway in the progression of pulmonary fibrosis. In addition, a transcriptome analysis of RNA-sequencing data from this unique model demonstrated that several lines of mechanisms are involved in the pathogenesis of pulmonary fibrosis, which provides a basis for further studies. Here, we review the accumulating evidence for the spatial and temporal roles of SAPKs in pulmonary fibrosis.

Stress-activated protein kinases are involved in the replication of porcine deltacoronavirus

This study was conducted to examine the role of stress-activated protein kinases (SAPKs), including c-Jun NH2-terminal kinases (JNK1/2) and p38 mitogen-activated protein kinase (MAPK), in porcine deltacoronavirus (PDCoV) infection. Results demonstrated the activation of JNK1/2 and p38 MAPK in PDCoV-infected cells, which occurred concomitant with viral biosynthesis and irrespective of cell type. Pharmacological inhibition or knockdown of either SAPK significantly attenuated PDCoV replication, whereas addition of a signaling activator augmented virus infectivity. Moreover, pharmacological inhibition of JNK1/2 or p38 MAPK activation was innocuous to viral entry but significantly detrimental to post uncoating stages of the replication cycle. Remarkably, cytokine gene expression in PDCoV-infected IPEC-J2 cells was modified by inhibiting the activation of either SAPK. Collectively, these data indicate that JNK1/2 and p38 MAPK signaling pathways contribute to viral biosynthesis and regulate immune responses, thereby favoring the replication of PDCoV.

Stress-Activated Protein Kinases in Spinal Cord Injury: Focus on Roles of p38.

Spinal cord injury (SCI) consists of three phases—acute, secondary, and chronic damages—and limiting the development of secondary damage possibly improves functional recovery after SCI. A major component of the secondary phase of SCI is regarded as inflammation-triggered events: induction of cytokines, edema, microglial activation, apoptosis of cells including oligodendrocytes and neurons, demyelination, formation of the astrocytic scar, and so on. Two major stress-activated protein kinases (SAPKs)—c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK)—are activated in various types of cells in response to cellular stresses such as apoptotic stimuli and inflammatory waves. In animal models of SCI, inhibition of either JNK or p38 has been shown to promote neuroprotection-associated functional recovery. Here, we provide an overview on the roles of SAPKs in SCI and, in particular, the pathological role of p38 will be discussed as a promising target for therapeutic intervention in SCI.

Sir2 plays a key role in cell fate determination upon SAPK activation

Although the benefit of sirtuin activation in age-related diseases is well-characterized, the benefit of sirtuin activation in acute diseases has been elusive. Here we discuss that, at least in yeast, Sir2 activation prevents programmed cell death induced by the sustained activation of the stress activated protein kinase (SAPK) Hog1, the yeast homologue of the p38 SAPK. Sir2 prevents ROS formation and maximize cell survival upon SAPK activation. The conserved function of Sir2 in age-related diseases and the conserved role of SAPKs open the possibility of a novel role for sirtuins in cell fate determination in eukaryotic cells.

Roles of stress-activated protein kinases in the replication of Singapore grouper iridovirus and regulation of the inflammatory responses in grouper cells

Stress-activated protein kinases (SAPKs), including p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal kinase (JNK), are usually activated in response to different environmental stimuli, including virus infection. In the present study, the roles of SAPKs during Singapore grouper iridovirus (SGIV) infection were investigated in fish cells. The results showed that increased phosphorylation of JNK1/2 and p38 MAPK occurred during active replication of SGIV in grouper cell cultures. Moreover, downstream effectors (c-Jun, MAPK-activated protein kinase 2, p53, activator protein 1, Myc and nuclear factor of activated T cells) were activated after SGIV infection, suggesting that SGIV replication activated the JNK and p38 MAPK signalling pathways. Notably, using specific inhibitors, it was found that viral gene transcripts, protein expression and viral titres were not affected by inhibition of p38 MAPK but were suppressed significantly by inhibiting JNK1/2 activation. In addition, transcription of grouper immune genes including interferon regulatory factor 1, interleukin-8 and tumour necrosis factor alpha (TNF-α) were regulated by JNK, whilst only TNF-α was regulated by p38 MAPK. It is proposed that the JNK pathway is important for SGIV replication and modulates the inflammatory responses during virus infection.

Distinct roles of stress-activated protein kinases in Fanconi anemia type C–deficient hematopoiesis

AbstractThe underlying molecular mechanisms that promote bone marrow failure in Fanconi anemia are incompletely understood. Evidence suggests that enhanced apoptosis of hematopoietic precursors is a major contributing factor. Previously, enhanced apoptosis of Fanconi anemia type C–deficient (Fancc−/−) progenitors was shown to involve aberrant p38 MAPK activation. Given the importance of c-Jun N-terminal kinase (JNK) in the stress response, we tested whether enhanced apoptosis of Fancc−/− cells also involved altered JNK activation. In Fancc−/− murine embryonic fibroblasts, tumor necrosis factor α (TNF-α) induced elevated JNK activity. In addition, JNK inhibition protected Fancc−/− murine embryonic fibroblasts and c-kit+ bone marrow cells from TNF-α-induced apoptosis. Importantly, hematopoietic progenitor assays demonstrated that JNK inhibition enhanced Fancc−/− colony formation in the presence of TNF-α. Competitive repopulation assays showed that Fancc−/− donor cells cultured with the JNK inhibitor had equivalent levels of donor chimerism compared with Fancc−/− donor cells cultured with vehicle control. In contrast, culturing Fancc−/− cells with a p38 MAPK inhibitor significantly increased repopulating ability, supporting an integral role of p38 MAPK in maintaining Fancc−/− hematopoietic stem cell function. Taken together, these data suggest that p38 MAPK, but not JNK, has a critical role in maintaining the engraftment of Fancc−/−-reconstituting cells under conditions of stress.

Purinergic inhibition of Na+,K+,Cl− cotransport in C11-MDCK cells: Role of stress-activated protein kinases

Previously, we observed that sustained activation of P2Y1 leads to inhibition of Na+,K+,Cl− cotransport (NKCC) in C11 cells resembling intercalated cells from collecting ducts of the Madin-Darby canine kidney. This study examined the role of stress-activated protein kinases (SAPK) in NKCC inhibition triggered by purinergic receptors. Treatment of C11 cells with ATP led to sustained phosphorylation of SAPK such as JNK and p38. Activation of these kinases also occurred in anisomycin-treated cells. Surprisingly, we observed that compounds SP600125 and SB202190, known as potent inhibitors of JNK and p38 in cell-free systems, activated rather than inhibited phosphorylation of the kinases in C11 cells. Importantly, similarly to ATP, all the above-listed activators of JNK and p38 phosphorylation inhibited NKCC. Thus, our results suggest that activation of JNK and/or p38 contributes to NKCC suppression detected in intercalated-like cells from distal tubules after their exposure to P2Y1 agonists.

P38MAPK activation is involved in androgen-independent proliferation of human prostate cancer cells by regulating IL-6 secretion

Increased levels of serum interleukin-6 (IL-6) are frequently observed in patients with advanced, hormone-refractory prostate cancer. However, the precise mechanism of IL-6 regulation is still largely unknown. Since prostate cancer gradually progresses to an androgen-independent state despite the stress caused by various therapeutic agents, we hypothesized the stress-activated protein kinases (SAPKs) involvement in androgen-independent growth or IL-6 secretion of prostate cancer cells. Using PC-3 and DU145 human prostate cancer cells, we analyzed the role of SAPKs in IL-6 mediated cell growth and found that the p38MAPK and JNK are involved in androgen-independent cancer cell growth. Furthermore, IL-6 secretion by PC-3 and DU145 cells was significantly suppressed by SAPKs inhibitor, especially by p38MAPK inhibitor SB203580, but not by JNK inhibitor SP600125 nor by MEK inhibitor, PD98059. These results raised the possibility that the IL-6 mediated androgen-independent proliferation of PC-3 and DU145 cells is regulated at least partly via SAPKs signaling pathway especially through p38MAPK activation.

Physiological roles of stress-activated protein kinases in skin

Stress-activated protein kinase (SAPK) cascades control a variety of cellular activities such as survival, differentiation and apoptosis. Recent studies have revealed that SAPKs play important roles in the regulation of homeostasis of skin. This report focuses on SAPK-mediated signal transduction and provides advanced findings on the physiological roles of SAPKs in skin.

Regulation of tyrosine hydroxylase by stress-activated protein kinases.

Recombinant human tyrosine hydroxylase (hTH1) was found to be phosphorylated by mitogen and stress-activated protein kinase 1 (MSK1) at Ser40 and by p38 regulated/activated kinase (PRAK) on Ser19. Phosphorylation by MSK1 induced an increase in Vmax and a decrease in Km for 6-(R)-5,6,7,8-tetrahydrobiopterin (BH4), while these kinetic parameters were unaffected as a result of phosphorylation by PRAK. Phosphorylation of both Ser40 and Ser19 induced a high-affinity binding of 14-3-3 proteins, but only the interaction of 14-3-3 with Ser19 increased the hTH1 activity. The 14-3-3 proteins also inhibited the rate of dephosphorylation of Ser19 and Ser40 by 82 and 36%, respectively. The phosphorylation of hTH1 on Ser19 caused a threefold increase in the rate of phosphorylation of Ser40. These studies provide new insights into the possible roles of stress-activated protein kinases in the regulation of catecholamine biosynthesis.

Phosphorylation of tyrosine hydroxylase in isolated mice adrenal glands.

The site-specific phosphorylation of tyrosine hydroxylase (TH) was studied in mouse adrenal tissue. On addition of arsenite, a rapid increase in Ser19 phosphorylation occurred, concomitant with phosphorylation of p38 protein kinase. This is consistent with studies in other mammals, indicating a role of stress-activated protein kinases in TH regulation.

SAPKs regulation of ischemic preconditioning.

The role of stress-activated protein kinases (SAPKs), c-Jun NH(2)-terminal kinase (JNK) and p38 mitogen-activated protein (MAP) kinase, in preconditioning (PC) was examined with the use of isolated rat hearts subjected to four cyclic episodes of 5-min ischemia and 10-min reperfusion followed by 30-min ischemia and 2-h reperfusion (I/R). A group of hearts was preperfused with 100 microM curcumin, a c-Jun and JNK1 inhibitor, or 5 microM SB 203580, a p38 MAP kinase inhibitor. Another group of hearts was preperfused with 20 microM anisomycin, a stimulator for both JNK and p38 MAP kinases. I/R increased the protein levels of JNK1, c-Jun, and p38 MAP kinase. PC also enhanced the induction of these kinases, but subsequent I/R-mediated increase was blocked by PC. Curcumin blocked I/R- and PC-mediated increase in JNK1 and c-Jun protein levels, whereas it had no effects on p38 MAP kinase. SB 203580, on the other hand, was equally effective in reducing the p38 MAP kinase activation but exerted no effects on JNK1 and c-Jun induction. I/R-mediated increased myocardial infarction was reduced by any of the following compounds: anisomycin, curcumin, and SB 203580. The cardioprotective effects of PC were abolished by either curcumin or SB 203580. The results demonstrate that PC is mediated by a signal-transduction pathway involving both JNK1 and p38 MAP kinase. Activation of SAPKs, although transient, is obligatory for PC.

Stress-activated Protein Kinases (JNK and p38/HOG) Are Essential for Vascular Endothelial Growth Factor mRNA Stability

Stability of the vascular endothelial growth factor (VEGF) mRNA is tightly regulated through its 3'-untranslated region (3'-UTR). Here, we demonstrate that VEGF mRNA levels are increased by anisomycin, a strong activator of stress-activated protein kinases. Hence, VEGF mRNA induction is inhibited by SB202190, an inhibitor of JNK and p38/HOG kinase. Furthermore, VEGF mRNA expression is increased in cells that overexpress JNK and p38/HOG by an increase in its stability. We show by two different approaches that anisomycin exerts its effect on the VEGF mRNA 3'-UTR. First, by using an in vitro mRNA degradation assay, the half-life of the VEGF mRNA 3'-UTR region transcript was found to be increased when incubated with extracts from anisomycin-treated cells; and second, the 3'-UTR was also sufficient to confer mRNA instability to the Nhe3 (Na(+)/H(+) exchanger 3) heterologous reporter gene, and anisomycin treatment stabilized the chimeric mRNA (Nhe3 fused to the VEGF mRNA 3'-UTR). This chimeric mRNA is also more stable in cells overexpressing p38/HOG and JNK that have been stimulated by anisomycin. We show that such regulation is mediated through an AU-rich region of the 3'-UTR contained within a stable hairpin structure. By RNA electrophoretic mobility shift assays, we show that this region binds proteins specifically induced by anisomycin treatment. These findings clearly demonstrate a major role of stress-activated protein kinases in the post-transcriptional regulation of VEGF.

Macrophage TNF Secretion in Endotoxin Tolerance: Role of SAPK, p38, and MAPK

Purpose.Endotoxin (LPS) activation of macrophages results in phosphorylation of mitogen-activated protein kinases (MAPK), stress-activated protein kinases (SAPK), and p38 kinase. LPS pretreatment inhibits subsequent LPS-stimulated MAPK activation and TNF release and both were reversed if macrophages were treated with phorbol myristate acetate (PMA) before LPS stimulation. In this study we sought to determine if SAPK and p38 tyrosine kinases are required for TNF production and if LPS pretreatment alters their activation.Methods.TNF production by murine peritoneal exudate macrophages was determined 6 h after stimulation with 100 ng/mL of LPS ± 24 h pretreatment with 10 ng/mL of LPS. The active, diphosphorylated forms of MAPK (p42, p44), SAPK (p46, p54), and p38 were assayed 30 min after LPS stimulation by Western immunoblot using specific antibodies. In some experiments a p38 kinase inhibitor (SB202190) or the protein kinase C activator (PMA) was added 1 h before LPS stimulation.Results.LPS activated MAPK, SAPK, and p38. LPS pretreatment significantly inhibited MAPK, SAPK, and p38 activation by LPS stimulation. TNF protein secretion and MAPK activation in tolerant macrophages were restored by PMA treatment, but this did not restore SAPK activation. The p38 inhibitor SB202190 blocked LPS-stimulated TNF production.Conclusion.LPS pretreatment-induced tolerance decreased LPS-stimulated MAP, SAP, and p38 kinase activation. LPS tolerance in murine macrophages appears to be associated with specific, PMA-reversible defects in MAPK and p38 kinase activation.