Molecular basis of MAP kinase regulation

Structure and dynamics of the MKK7-JNK signaling complex

Signaling specificity in the mitogen-activated protein kinase (MAPK) pathways is controlled by disordered domains of the MAPK kinases (MKKs) that specifically bind to their cognate MAPKs via linear docking motifs. MKK7 activates the c-Jun N-terminal kinase (JNK) pathway and is the only MKK containing three motifs within its regulatory domain. Here, we characterize the conformational behavior and interaction mechanism of the MKK7 regulatory domain. Using NMR spectroscopy, we develop an atomic resolution ensemble description of MKK7, revealing highly diverse intrinsic conformational propensities of the three docking sites, suggesting that prerecognition sampling of the bound-state conformation is not prerequisite for binding. Although the different sites exhibit similar affinities for JNK1, interaction kinetics differ considerably. Importantly, we determine the crystal structure of JNK1 in complex with the second docking site of MKK7, revealing two different binding modes of the docking motif correlating with observations from NMR exchange spectroscopy. Our results provide unique insight into how signaling specificity is regulated by linear motifs and, in general, into the role of conformational disorder in MAPK signaling.

PKM2 gene regulates the behavior of pancreatic cancer cells via mitogen-activated protein kinase pathways

The aim of the current study was to investigate the effect of the PKM2 gene on the proliferation, invasion, migration and apoptosis of Panc‑1 and Sw1990 pancreatic cancer cells via its interaction with the mitogen‑activated protein kinases (MAPKs) signaling pathways. The expression levels of PKM2 protein in pancreatic cancer cells and the corresponding normal tissues was determined with western blot analysis. Immunohistochemical analysis of PKM2 expression was carried out in paraffin‑embedded sections of pancreatic cancer tissue. Two human pancreatic cancer cell lines were cultured in vitro, and a small interfering RNA (siRNA) was designed for the PKM2 gene and transfected into the cells. Cell proliferation was measured via an MTT assay, cell migration and invasion was measured via Transwell® chambers, and the effect of PKM2 on apoptosis was detected from B‑cell lymphoma 2 (Bcl‑2) and Bcl‑2‑associated X protein expression levels. Protein expression levels of the MAPK pathway proteins extracellular signal‑regulated kinase 1/2 (ERK1/2), p38 and c‑Jun N‑terminal kinase (JNK) and their phosphorylated forms were measured via western blot analysis. The expression level of PKM2 was significantly upregulated in the pancreatic cancer tissue compared with that of the corresponding normal tissue. Downregulation of PKM2 expression reduced the proliferation, migration and invasion of pancreatic cancer cell lines, while increasing the levels of apoptosis. Additionally, the expression levels of the phosphorylated‑(p‑)ERK1/2 and p‑p38 of the MAPK pathway in the PKM2 siRNA groups were markedly downregulated compared with those of the controls; however, the expression levels of ERK1/2, p38, JNK, p‑p38 and p‑JNK had no significantly changes compared with those of the control groups. In summary, the PKM2 gene has an important role in the proliferation, invasion, migration and apoptosis of Panc‑1 and Sw1990 pancreatic cancer cells, which may be associated with the expression of ERK1/2 and p38 of the MAPK signaling cascade.

Compromised MAPK signaling in human diseases: an update

The mitogen-activated protein kinases (MAPKs) in mammals include c-Jun NH2-terminal kinase (JNK), p38 MAPK, and extracellular signal-regulated kinase (ERK). These enzymes are serine-threonine protein kinases that regulate various cellular activities including proliferation, differentiation, apoptosis or survival, inflammation, and innate immunity. The compromised MAPK signaling pathways contribute to the pathology of diverse human diseases including cancer and neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. The JNK and p38 MAPK signaling pathways are activated by various types of cellular stress such as oxidative, genotoxic, and osmotic stress as well as by proinflammatory cytokines such as tumor necrosis factor-α and interleukin 1β. The Ras-Raf-MEK-ERK signaling pathway plays a key role in cancer development through the stimulation of cell proliferation and metastasis. The p38 MAPK pathway contributes to neuroinflammation mediated by glial cells including microglia and astrocytes, and it has also been associated with anticancer drug resistance in colon and liver cancer. We here summarize recent research on the roles of MAPK signaling pathways in human diseases, with a focus on cancer and neurodegenerative conditions.

Bardoxolone methyl induces apoptosis and autophagy and inhibits epithelial-to-mesenchymal transition and stemness in esophageal squamous cancer cells

Natural and synthetic triterpenoids have been shown to kill cancer cells via multiple mechanisms. The therapeutic effect and underlying mechanism of the synthetic triterpenoid bardoxolone methyl (C-28 methyl ester of 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid; CDDO-Me) on esophageal cancer are unclear. Herein, we aimed to investigate the anticancer effects and underlying mechanisms of CDDO-Me in human esophageal squamous cell carcinoma (ESCC) cells. Our study showed that CDDO-Me suppressed the proliferation and arrested cells in G₂/M phase, and induced apoptosis in human ESCC Ec109 and KYSE70 cells. The G₂/M arrest was accompanied with upregulated p21Waf1/Cip1 and p53 expression. CDDO-Me significantly decreased B-cell lymphoma-extra large (Bcl-xl), B-cell lymphoma 2 (Bcl-2), cleaved caspase-9, and cleaved poly ADP ribose polymerase (PARP) levels but increased the expression level of Bcl-2-associated X (Bax). Furthermore, CDDO-Me induced autophagy in both Ec109 and KYSE70 cells via suppression of the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathway. There were interactions between the autophagic and apoptotic pathways in Ec109 and KYSE70 cells subject to CDDO-Me treatment. CDDO-Me also scavenged reactive oxygen species through activation of the nuclear factor (erythroid-derived 2)-related factor 2 (Nrf2) pathway in Ec109 and KYSE70 cells. CDDO-Me inhibited cell invasion, epithelial–mesenchymal transition, and stemness in Ec109 and KYSE70 cells. CDDO-Me significantly downregulated E-cadherin but upregulated Snail, Slug, and zinc finger E-box-binding homeobox 1 (TCF-8/ZEB1) in Ec109 and KYSE70 cells. CDDO-Me significantly decreased the expression of octamer-4, sex determining region Y-box 2 (Sox-2), Nanog, and B lymphoma Mo-MLV insertion region 1 homolog (Bmi-1), all markers of cancer cell stemness, in Ec109 and KYSE70 cells. Taken together, these results indicate that CDDO-Me is a promising anticancer agent against ESCC. Further studies are warranted to explore the molecular targets, efficacy and safety of CDDO-Me in the treatment of ESCC.

Aspafilioside B induces G2/M cell cycle arrest and apoptosis by up-regulating H-Ras and N-Ras via ERK and p38 MAPK signaling pathways in human hepatoma HepG2 cells

We recently establish that aspafilioside B, a steroidal saponin extracted from Asparagus filicinus, is an active cytotoxic component. However, its antitumor activity is till unknown. In this study, the anticancer effect of aspafilioside B against HCC cells and the underlying mechanisms were investigated. Our results showed that aspafilioside B inhibited the growth and proliferation of HCC cell lines. Further study revealed that aspafilioside B could significantly induce G2 phase cell cycle arrest and apoptosis, accompanying the accumulation of reactive oxygen species (ROS), but blocking ROS generation with N-acetyl-l-cysteine (NAC) could not prevent G2/M arrest and apoptosis. Additionally, treatment with aspafilioside B induced phosphorylation of extracellular signal-regulated kinase (ERK) and p38 MAP kinase. Moreover, both ERK inhibitor PD98059 and p38 inhibitor SB203580 almost abolished the G2/M phase arrest and apoptosis induced by aspafilioside B, and reversed the expression of cell cycle- and apoptosis-related proteins. We also found that aspafilioside B treatment increased both Ras and Raf activation, and transfection of cells with H-Ras and N-Ras shRNA almost attenuated aspafilioside B-induced G2 phase arrest and apoptosis as well as the ERK and p38 activation. Finally, in vivo, aspafilioside B suppressed tumor growth in mouse xenograft models, and the mechanism was the same as in vitro study. Collectively, these findings indicated that aspafilioside B may up-regulate H-Ras and N-Ras, causing c-Raf phosphorylation, and lead to ERK and p38 activation, which consequently induced the G2 phase arrest and apoptosis. This study provides the evidence that aspafilioside B is a promising therapeutic agent against HCC.

Effects of the JWA gene in the regulation of human breast cancer cells

The present study aimed to investigate whether the JWA gene can regulate the proliferation, migration and invasion of human breast cancer cells through the MAPK signaling pathway. The role of JWA in proliferation, migration, invasion and apoptosis was investigated in the MDA‑MB‑231 human breast cancer cell line. Following transfection with JWA‑small interfering (si)RNA, the effect of JWA on apoptosis was assessed by Western blot analysis, proliferation was determined using Transwell chambers and cell migration and invasion were analyzed by transwell assay. The expression levels of extracellular signal‑regulated kinase (ERK) 1/2, CSBP/RK/Mpk2 kinase (p38) and c‑Jun N‑terminal kinase (JNK) were detected using Western blot analysis in the siRNA and control groups. The expression of JWA in the breast cancer cells was significantly lower compared with the normal breast cells. Downregulation of JWA protein levels reduced the apoptosis and enhanced proliferation, migration and invasion of the MDA‑MB‑231 cells in vitro. The results of the Western blot analysis demonstrated that, compared with the control groups, the expression levels of phosphorylated (p‑)p38 decreased significantly in the JWA siRNA group. No significant changes were observed in the expression levels of p‑ERK1/2 or p‑JNK. Therefore, the JWA gene may regulate human breast cancer cells through the MAPK signaling pathway using different types of regulation.

Studies on mitogen-activated protein kinase signaling pathway in the alveolar macrophages of chronic bronchitis rats

Lipopolysaccharide (LPS), a potent stimulator of inflammatory responses in alveolar macrophages (AMs), activates several intracellular signaling pathways, including mitogen-activated protein kinases (MAPK). In the present study, we investigated the MAPK pathway in AMs of chronic bronchitis (CB) rats. CB was induced by endotracheal instillation of LPS followed by Bacillus Calmette Guerin injection through the caudal vein 1 week later. Specific inhibitors were used and protein phosphorylations were detected by Western blot. We found that Genistein (PTK inhibitor) could inhibit protein kinase C (PKC), phosphatidylinositol-3 kinase (PI3K)/protein kinase B (Akt or PKB) MAPK signaling pathway with different degrees, LY294002 (PI3K inhibitor) could not only inhibit phospho-PI3K/Akt expression, but also inhibit p38 and c-Jun NH2-terminal kinases (JNK) phosphorylation. Calphostin C (PKC inhibitor) could inhibit phospho-PKC expression and exerted significant effects on extracellular signal-regulated kinases (ERK) phosphorylation, however, it had no impact on p38 and JNK phosphorylation. These results demonstrated that the LPS mediated signaling pathway of MAPK in AMs of CB rats could be described as follows: PTK-PI3K-Akt-JNK/p38 or PTK-PI3K-PKC-ERK, and PI3K may have a negative regulation on the activation of downstream proteins.

Regulation of Macrophage Polarization by RON Receptor Tyrosine Kinase Signaling

The M1 and M2 states of macrophage polarization are the two extremes of a physiologic/phenotypic continuum that is dynamically influenced by environmental signals. The M1/M2 paradigm is an excellent framework to understand and appreciate some of the diverse functions that macrophages perform. Molecular analysis of mouse and human macrophages indicated that they gain M1 and M2-related functions after encountering specific ligands in the tissue environment. In this perspective, I discuss the function of recepteur d’origine nantais (RON) receptor tyrosine kinase in regulating the M2-like state of macrophage activation Besides decreasing pro-inflammatory cytokine production in response to toll-like receptor-4 activation, macrophage-stimulating protein strongly suppresses nitric oxide synthase and at the same time upregulates arginase, which is the rate limiting enzyme in the ornithine biosynthesis pathway. Interestingly, RON signaling preserved some of the characteristics of the M1 state, while still promoting the hallmarks of M2 polarization. Therefore, therapeutic modulation of RON activity can shift the activation state of macrophages between acute and chronic inflammatory states.

Neuroprotective effects of ginsenoside Rb1 on hippocampal neuronal injury and neurite outgrowth

Ginsenoside Rb1 has been reported to exert anti-aging and anti-neurodegenerative effects. In the present study, we investigate whether ginsenoside Rb1 is involved in neurite outgrowth and neuroprotection against damage induced by amyloid beta (25-35) in cultured hippocampal neurons, and explore the underlying mechanisms. Ginsenoside Rb1 significantly increased neurite outgrowth in hippocampal neurons, and increased the expression of phosphorylated-Akt and phosphorylated extracellular signal-regulated kinase 1/2. These effects were abrogated by API-2 and PD98059, inhibitors of the signaling proteins Akt and MEK. Additionally, cultured hippocampal neurons were exposed to amyloid beta (25-35) for 30 minutes; ginsenoside Rb1 prevented apoptosis induced by amyloid beta (25-35), and this effect was blocked by API-2 and PD98059. Furthermore, ginsenoside Rb1 significantly reversed the reduction in phosphorylated-Akt and phosphorylated extracellular signal-regulated kinase 1/2 levels induced by amyloid beta (25-35), and API-2 neutralized the effect of ginsenoside Rb1. The present results indicate that ginsenoside Rb1 enhances neurite outgrowth and protects against neurotoxicity induced by amyloid beta (25-35) via a mechanism involving Akt and extracellular signal-regulated kinase 1/2 signaling.

Cellular mechanosensing: getting to the nucleus of it all

Cells respond to mechanical forces by activating specific genes and signaling pathways that allow the cells to adapt to their physical environment. Examples include muscle growth in response to exercise, bone remodeling based on their mechanical load, or endothelial cells aligning under fluid shear stress. While the involved downstream signaling pathways and mechanoresponsive genes are generally well characterized, many of the molecular mechanisms of the initiating 'mechanosensing' remain still elusive. In this review, we discuss recent findings and accumulating evidence suggesting that the cell nucleus plays a crucial role in cellular mechanotransduction, including processing incoming mechanoresponsive signals and even directly responding to mechanical forces. Consequently, mutations in the involved proteins or changes in nuclear envelope composition can directly impact mechanotransduction signaling and contribute to the development and progression of a variety of human diseases, including muscular dystrophy, cancer, and the focus of this review, dilated cardiomyopathy. Improved insights into the molecular mechanisms underlying nuclear mechanotransduction, brought in part by the emergence of new technologies to study intracellular mechanics at high spatial and temporal resolution, will not only result in a better understanding of cellular mechanosensing in normal cells but may also lead to the development of novel therapies in the many diseases linked to defects in nuclear envelope proteins.

Activation of JNK1/2 and p38 MAPK signaling pathways promotes enterovirus 71 infection in immature dendritic cells

Background

c-Jun NH₂-terminal kinase/stress-activated kinase (JNK/SAPK) and the p38 mitogen-activated protein kinase (p38 MAPK) are important components of cellular signal transduction pathways, which have been reported to be involved in viral replication. However, little is known about JNK1/2 and p38 MAPK signaling pathways in enterovirus 71 (EV71)-infected immature dendritic cells (iDCs). Thus, iDCs were induced from peripheral blood mononuclear cells (PBMC) and performed to explore the expressions and phosphorylation of molecules in the two signaling pathways as well as secretions of inflammatory cytokines and interferons during EV71 replication.

Results

We showed that EV71 infection could activate both JNK1/2 and p38 MAPK in iDCs and phosphorylate their downstream transcription factors c-Fos and c-Jun, which further promoted the production of IL-2, IL-6, IL-10, and TNF-α. Moreover, EV71 infection also increased the release of IFN-β and IL-12 p40. Pretreatment of iDCs with SP600125 and SB203580 (20 μM) could severely impair viral replication and its induced phosphorylation of JNK1/2,p38 MAPK, c-Fos and c-Jun. In addition, treatment of EV71-infected iDCs with SP600125 and SB203580 could inhibit secretions of IL-6, IL-10 and TNF-α.

Conclusion

JNK1/2 and p38 MAPK signaling pathways are beneficial to EV71 infection and positively regulate secretions of inflammatory cytokines in iDCs.

Role of c-Jun N-terminal kinase (JNK) activation in micturition reflexes in cyclophosphamide (CYP)-induced cystitis in female rats

c-Jun N-terminal kinase (JNK) is member of the mitogen-activated protein kinase (MAPK) family, activated through phosphorylation following cytokine exposure and stress. In this study, phosphorylation of JNK was examined in the urinary bladder with cyclophosphamide (CYP)-induced cystitis and the effects of SP600125, a selective inhibitor of phosphorylation of JNK, on urinary bladder function were assessed using conscious, open outlet, cystometry with continuous instillation of intravesical saline. We induced bladder inflammation in adult female Wistar rats by injecting CYP intraperitoneally to produce acute (150 mg/kg; 4 h), intermediate (150 mg/kg; 48 h), and chronic (75 mg/kg; every third day for 10 days) treatments. Western blotting of urinary bladder demonstrated a significant (p ≤ 0.01) increase (i.e., phosphorylation) in JNK activation with 4- and 48-h CYP-induced cystitis. Immunohistochemistry and image analyses demonstrated a significant (p ≤ 0.01) increase in JNK activation in the urothelium with 4- and 48-h CYP-induced cystitis. Blockade of JNK phosphorylation significantly (p ≤ 0.01) increased bladder capacity and intercontraction void intervals in CYP-treated rats (4 and 48 h). Furthermore, blockade of JNK phosphorylation reduced (p ≤ 0.01) neuropeptide (substance P, calcitonin gene-related peptide) expression in the urinary bladder with CYP-induced cystitis (4 and 48 h). In contrast, blockade of JNK phosphorylation was without effect on bladder function or neuropeptide expression in urinary bladder in control (no inflammation) rats. Blockade of JNK phosphorylation may represent a novel target for improving urinary bladder function with CYP-induced cystitis.

The morphologic and molecular characteristics of pilocytic astrocytomas and the role of MAPK pathway: what does not kill you makes you stronger

In recent years, substantial progress has been made in the pathologic and molecular aspects of pilocytic astrocytomas. The advances in the pathologic characterization identified a variant that is currently considered WHO grade II, whereas the classic pilocytic astrocytoma is a WHO grade I neoplasm. Recognition of additional and rare histologic patterns also allowed us to better recognize some tumors that will do "well" in the long run. From a molecular pathologic perspective, recognition of the importance of MAPK pathways in these tumors allowed us to better understand tumors with spontaneous regression or dormant behavior, and tumors that become aggressive, especially those after radiation treatment. As the nature of this highly complex pathway is uncovered, we hope that the findings will allow us to better help the patients with this "chronic" disease.

The cellular mastermind(?)-mechanotransduction and the nucleus

Cells respond to mechanical stimulation by activation of specific signaling pathways and genes that allow the cell to adapt to its dynamic physical environment. How cells sense the various mechanical inputs and translate them into biochemical signals remains an area of active investigation. Recent reports suggest that the cell nucleus may be directly implicated in this cellular mechanotransduction process. Taken together, these findings paint a picture of the nucleus as a central hub in cellular mechanotransduction-both structurally and biochemically-with important implications in physiology and disease.