p38 MAPK: A dual role in hepatocyte proliferation through reactive oxygen species

Abstract

p38 MAPKs are important mediators of signal transduction that respond to a wide range of extracellular stressors such as UV radiation, osmotic shock, hypoxia, pro-inflammatory cytokines, and oxidative stress. The most abundant family member is p38α, which helps to couple cell proliferation and growth in response to certain damaging stimuli. In fact, increased proliferation and impaired differentiation are hallmarks of p38α-deficient cells. It has been reported that reactive oxygen species (ROS) play a critical role in cytokine-induced p38α activation. Under physiological conditions, p38α can function as a mediator of ROS signaling and either activate or suppress cell cycle progression depending on the activation stimulus. The interplay between cell proliferation, p38 MAPK activation, and ROS production plays an important role in hepatocytes. In fact, low levels of ROS seem to be needed to activate several signaling pathways in response to hepatectomy and to orchestrate liver regeneration. p38 MAPK works as a sensor of oxidative stress and cells that have developed mechanisms to uncouple p38 MAPK activation from oxidative stress are more likely to become tumorigenic. So far, p38α influences the redox balance, determining cell survival, terminal differentiation, proliferation, and senescence. Further studies would be necessary in order to clarify the precise role of p38 MAPK signaling as a redox therapeutical target.     

Acetaminophen attenuates glomerulosclerosis in obese Zucker rats via reactive oxygen species/p38MAPK signaling pathways

Focal segmental glomerulosclerosis is a critical pathological lesion in metabolic syndrome-associated kidney disease that, if allowed to proceed unchecked, can lead to renal failure. However, the exact mechanisms underlying glomerulosclerosis remain unclear, and effective prevention strategies against glomerulosclerosis are currently limited. Herein, we demonstrate that chronic low-dose ingestion of acetaminophen (30 mg/kg/day for 6 months) attenuates proteinuria, glomerulosclerosis, podocyte injury, and inflammation in the obese Zucker rat model of metabolic syndrome. Moreover, acetaminophen treatment attenuated renal fibrosis and the expression of profibrotic factors (fibronectin, connective tissue growth factor, transforming growth factor β), reduced inflammatory cell infiltration into the glomeruli, and decreased the expression of monocyte chemoattractant protein, glutathione (GSH) reductase, and nuclear factor erythroid 2-related factor 2, but increased the level of GSH synthetase in obese animals. Further in vivo and in vitro studies using human renal mesangial cells exposed to high glucose or hydrogen peroxide suggested that the renoprotective effects of acetaminophen are characterized by diminished renal oxidative stress and p38MAPK hyperphosphorylation.     

Nox4 overexpression activates reactive oxygen species and p38 MAPK in human endothelial cells

Nicotine adenine dinucleotide phosphate (NADPH) oxidase (Nox) complexes are the main sources of reactive oxygen species (ROS) formation in the vessel wall. We have used DNA microarray, real-time PCR and Western blot to demonstrate that the subunit Nox4 is the major Nox isoform in primary human endothelial cells; we also found high levels of NADPH oxidase subunit p22^phox expression. Nox4 was localized by laser scanning confocal microscopy within the cytoplasm of endothelial cells. Endothelial Nox4 overexpression enhanced superoxide anion formation and phosphorylation of p38 MAPK. Nox4 down-regulation by shRNA has in contrast to TGF-β no effect on p38 MAPK phosphorylation. We conclude that Nox4 is the major Nox isoform in human endothelial cells, and forms an active complex with p22^phox. The Nox4-containing complex mediates formation of reactive oxygen species and p38 MAPK activation. This is a novel mechanism of redox-sensitive signaling in human endothelial cells.     

AD-1, a novel ginsenoside derivative,shows anti-lung cancer activity via activation of p38 MAPK pathway and generation of reactive oxygen species

Background

Ginseng is a traditional Chinese herb that has been used for thousands of years. In the present study, effects and mechanisms of AD-1 were evaluated for its development as a novel anti-lung cancer drug.

Methods

The cytotoxic activity was evaluated by MTT assay. Flow cytometry was employed to detect cell cycle, apoptosis and ROS. Western blot and immunohistochemistry were used to analyze signaling pathways. Lung cancer xenograft models were established by subcutaneous implantation of A549 or H292 cells into nude mice.

Results

AD-1 concentration-dependently reduces lung cancer cell viability without affecting normal human lung epithelial cell viability. In A549 and H292 lung cancer cells, AD-1 induces G₀/G₁ cell cycle arrest, apoptosis and ROS production. The apoptosis can be attenuated by a ROS scavenger — N-acetylcysteine (NAC). In addition, AD-1 up-regulates the expression of p38 and ERK phosphorylation. Addition of a p38 inhibitor SB203580, suppresses the AD-1-induced decrease in cell viability. Furthermore, genetic silencing of p38 attenuates the expression of p38 and decreases the AD-1-induced apoptosis. Treatment with NAC reduces AD-1-induced p38 phosphorylation, which indicates that ROS generation is involved in the AD-1-induced p38 activation. In mice, oral administration of AD-1 (10–40 mg/kg) dose-dependently inhibited the growth of xenograft tumors without affecting body weight and decreases the expression of VEGF, MMP-9 and CD34 in tumor tissue. TUNEL staining confirms that the tumors from AD-1 treated mice exhibit a markedly higher apoptotic index.

Conclusions and general significance

These data support development of AD-1 as a potential agent for lung cancer therapy.     

Leptin regulates MMP-2, TIMP-1 and collagen synthesis via p38 MAPK in HL-1 murine cardiomyocytes

A clear association between obesity and heart failure exists and a significant role for leptin, the product of the obese gene, has been suggested. One aspect of myocardial remodeling which characterizes heart failure is a disruption in the balance of extracellular matrix synthesis and degradation. Here we investigated the effects of leptin on matrix metalloproteinase (MMP) activity, tissue inhibitor of metalloproteinase (TIMP) expression, as well as collagen synthesis in HL-1 cardiac muscle cells. Gelatin zymographic analysis of MMP activity in conditioned media showed that leptin enhanced MMP-2 activity in a dose- and time-dependent manner. Leptin is known to stimulate phosphorylation of p38 MAPK in cardiac cells and utilization of the p38 MAPK inhibitor, SB203580, demonstrated that this kinase also plays a role in regulating several extracellular matrix components, such that inhibition of p38 MAPK signaling prevented the leptin-induced increase in MMP-2 activation. We also observed that leptin enhanced collagen synthesis determined by both proline incorporation and picrosirius red staining of conditioned media. Pro-collagen type-I and pro-collagen type-III expression, measured by real-time PCR and Western blotting were also increased by leptin, effects which were again attenuated by SB203580. In summary, these results demonstrate the potential for leptin to play a role in mediating myocardial ECM remodeling and that the p38 MAPK pathway plays an important role in mediating these effects.     

Angiotensin II-induced negative inotropy in rat ventricular myocytes: role of reactive oxygen species and p38 MAPK

The octapeptide angiotensin II (ANG II) can modulate cardiac contractility and is increased in heart failure, where contractile function is impaired. In rat cardiac myocytes, 1 microM of ANG II produces a negative inotropic effect (NIE) (24.6 +/- 5% reduction). However, the subcellular signaling involved in this effect remains elusive. We examined the mechanisms and signaling events involved in the reduction in contractile function induced by the peptide in indo-1-loaded rat cardiomyocytes. The results showed that the NIE of ANG II was not associated with a parallel decrease in the intracellular Ca2+ transient, indicating that a decrease in myofilament responsiveness to Ca2+ underlies the reduction in contractility. We assessed the role of PKC, tyrosine kinases, reactive oxygen species (ROS), and mitogen-activated protein kinases (MAPKs) in the NIE of the peptide. Pretreatment of cells with the NAD(P)H oxidase inhibitor diphenyleneiodonium chloride or with the superoxide scavenger 4,5-dihydroxy-1,3-benzene-disulfonic acid did not affect the ANG II-induced NIE. Moreover, ANG II-induced ROS production, after 20 min of incubation with the peptide, could not be detected with the use of either the fluorophore 5-(6)-chloromethyl-2',7'-dichlorodihydrofluorecein diacetate or lucigenin-enhanced chemiluminescence. In contrast, the ANG II-induced NIE was abrogated by the inhibitors of PKC (calphostin C), tyrosine kinase (genistein), and p38 MAPK (SB-202190). Furthermore, the NIE was significantly exacerbated (60 +/- 10% reduction) by p38 MAPK overexpression. These results exclude the participation of ROS in the NIE of the peptide and point to PKC and tyrosine kinase as upstream mediators. Furthermore, they reveal p38 MAPK as the putative effector of the reduction in myofilament responsiveness to Ca2+ and the decrease in contractility induced by the peptide.     

Role of reactive oxygen species in LPS-induced production of prostaglandin E2 in microglia

We determined the roles of reactive oxygen species (ROS) in the expression of cyclooxygenase-2 (COX-2) and the production of prostaglandin E2 (PGE2) in lipopolysaccharide (LPS)-activated microglia. LPS treatment increased intracellular ROS in rat microglia dose-dependently. Pre-treatment with superoxide dismutase (SOD)/catalase, or SOD/catalase mimetics that can scavenge intracellular ROS, significantly attenuated LPS-induced release in PGE2. Diphenylene iodonium (DPI), a non-specific NADPH oxidase inhibitor, decreased LPS-induced PGE2 production. In addition, microglia from NADPH oxidase-deficient mice produced less PGE2 than those from wild-type mice following LPS treatment. Furthermore, LPS-stimulated expression of COX-2 (determined by RT-PCR analysis of COX-2 mRNA and western blot for its protein) was significantly reduced by pre-treatment with SOD/catalase or SOD/catalase mimetics. SOD/catalase mimetics were more potent than SOD/catalase in reducing COX-2 expression and PGE2 production. As a comparison, scavenging ROS had no effect on LPS-induced nitric oxide production in microglia. These results suggest that ROS play a regulatory role in the expression of COX-2 and the subsequent production of PGE2 during the activation process of microglia. Thus, inhibiting NADPH oxidase activity and subsequent ROS generation in microglia can reduce COX-2 expression and PGE2 production. These findings suggest a potential therapeutic intervention strategy for the treatment of inflammation-mediated neurodegenerative diseases.     

Capsaicin stimulates glucose uptake in C2C12 muscle cells via the reactive oxygen species (ROS)/AMPK/p38 MAPK pathway

Capsaicin has been reported to regulate blood glucose levels and to ameliorate insulin resistance in obese mice. This study demonstrates that capsaicin increases glucose uptake directly by activating AMP-activated protein kinase (AMPK) in C2C12 muscle cells, which manifested as an attenuation of glucose uptake when compound C, an AMPK inhibitor, was co-administered with capsaicin. However, the insulin signaling molecules insulin receptor substrate-1 (IRS-1) and Akt were not affected by capsaicin. Additional results showed that p38 mitogen-activated protein kinase (MAPK) is also involved in capsaicin-induced glucose transport downstream of AMPK because capsaicin increased p38 MAPK phosphorylation significantly and its specific inhibitor SB203580 inhibited capsaicin-mediated glucose uptake. Treatment with an AMPK inhibitor reduced p38 MAPK phosphorylation, but the p38 MAPK inhibitor had no effect on AMPK. Capsaicin stimulated ROS generation in C2C12 muscle cells, and when ROS were captured using the nonspecific antioxidant NAC, the increase in both capsaicin-induced AMPK phosphorylation and capsaicin-induced glucose uptake was attenuated, suggesting that ROS function as an upstream activator of AMPK. Taken together, these results suggest that capsaicin, independent of insulin, increases glucose uptake via ROS generation and consequent AMPK and p38 MAPK activations.     

Protein kinase C signaling regulates ZO-1 translocation and increased paracellular flux of T84 colonocytes exposed to Clostridium difficile toxin A.

Clostridium difficile toxin A increases paracellular permeability in colonic epithelial T84 cells by mechanisms involving RhoA glucosylation and actin depolymerization. However, we previously observed that toxin A-mediated decline in transepithelial electrical resistance preceded changes in cell morphology and tight junction ultrastructure (Hecht, G., Pothoulakis, C., LaMont, J. T., and Madara, J. L. (1988) J. Clin. Invest. 82, 1516-1524). Recent studies also showed that C. difficile toxins induce early cellular responses, including activation of mitogen-activated protein kinases, generation of reactive oxygen metabolites, and calcium influx. The aim of this study was to investigate whether toxin A-induced early cellular responses contribute to the permeability changes. We found that toxin A stimulated the activities of membrane and cytosolic protein kinase Calpha (PKCalpha) and cytosolic PKCbeta. A specific PKCalpha/beta antagonist (myristoylated PKCalpha/beta peptide) blocked toxin A-mediated RhoA glucosylation. Furthermore, decreased transepithelial electrical resistance and increased translocation of ZO-1 from tight junction occurred within 2-3 h of toxin A exposure and were also inhibited by PKCalpha/beta antagonist. During this time period, toxin exposure did not induce translocation of ZO-2, dephosphorylation or translocation of occludin, or cell rounding. Our data indicate that PKC signaling regulates toxin A-mediated paracellular permeability changes and ZO-1 translocation.     

Regulation of prostaglandin E2 biosynthesis by inducible membrane-associated prostaglandin E2 synthase that acts in concert with cyclooxygenase-2

Here we report the molecular identification of membrane-bound glutathione (GSH)-dependent prostaglandin (PG) E(2) synthase (mPGES), a terminal enzyme of the cyclooxygenase (COX)-2-mediated PGE(2) biosynthetic pathway. The activity of mPGES was increased markedly in macrophages and osteoblasts following proinflammatory stimuli. cDNA for mouse and rat mPGESs encoded functional proteins that showed high homology with the human ortholog (microsomal glutathione S-transferase-like 1). mPGES expression was markedly induced by proinflammatory stimuli in various tissues and cells and was down-regulated by dexamethasone, accompanied by changes in COX-2 expression and delayed PGE(2) generation. Arg(110), a residue well conserved in the microsomal GSH S-transferase family, was essential for catalytic function. mPGES was functionally coupled with COX-2 in marked preference to COX-1, particularly when the supply of arachidonic acid was limited. Increased supply of arachidonic acid by explosive activation of cytosolic phospholipase A(2) allowed mPGES to be coupled with COX-1. mPGES colocalized with both COX isozymes in the perinuclear envelope. Moreover, cells stably cotransfected with COX-2 and mPGES grew faster, were highly aggregated, and exhibited aberrant morphology. Thus, COX-2 and mPGES are essential components for delayed PGE(2) biosynthesis, which may be linked to inflammation, fever, osteogenesis, and even cancer.     

Spatially distinct production of reactive oxygen species regulates platelet activation

Platelets play a key role in hemostasis and changes in redox balance are known to alter platelet activation and aggregation. Interestingly, activation of platelets leads to production of reactive oxygen species (ROS), but the role(s) of these ROS remain unclear. Using flow cytometry and chemiluminescence, agonist-induced ROS generation was found to be spatially distinct with stimulation through the major collagen receptor GPVI inducing only intraplatelet ROS while thrombin induced production of extracellular ROS. Platelet activation by either the GPVI-selective agonist convulxin or thrombin was differentially regulated by ROS generation. Thus, surface expression of CD62P, CD40L, or activated integrin alphaIIbbeta3 was abrogated by pharmacologic antioxidants but externalization of phosphatidylserine was not inhibited. Furthermore, extracellular antioxidants SOD/catalase markedly inhibited thrombin-, but not convulxin-, induced CD62P expression and alphaIIbbeta3 activation. The data suggest that ROS selectively regulate biochemical steps in platelet activation and that distinct source(s) of ROS and discrete redox-sensitive pathway(s) may control platelet activation in response to GPVI or thrombin stimulation. Thus, targeting ROS with site-specific antioxidants may differentially regulate platelet activation via thrombin or collagen.     

Panaxydol induces apoptosis through an increased intracellular calcium level,activation of JNK and p38 MAPK and NADPH oxidase-dependent generation of reactive oxygen species

Panaxydol, a polyacetylenic compound derived from Panax ginseng roots, has been shown to inhibit the growth of cancer cells. In this study, we demonstrated that panaxydol induced apoptosis preferentially in transformed cells with a minimal effect on non-transformed cells. Furthermore, panaxydol was shown to induce apoptosis through an increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i), activation of JNK and p38 MAPK, and generation of reactive oxygen species (ROS) initially by NADPH oxidase and then by mitochondria. Panaxydol-induced apoptosis was caspase-dependent and occurred through a mitochondrial pathway. ROS generation by NADPH oxidase was critical for panaxydol-induced apoptosis. Mitochondrial ROS production was also required, however, it appeared to be secondary to the ROS generation by NADPH oxidase. Activation of NADPH oxidase was demonstrated by the membrane translocation of regulatory p47^phox and p67^phox subunits and shown to be necessary for ROS generation by panaxydol treatment. Panaxydol triggered a rapid and sustained increase of [Ca²⁺]_i, which resulted in activation of JNK and p38 MAPK. JNK and p38 MAPK play a key role in activation of NADPH oxidase, since inhibition of their expression or activity abrogated membrane translocation of p47^phox and p67^phox subunits and ROS generation. In summary, these data indicate that panaxydol induces apoptosis preferentially in cancer cells, and the signaling mechanisms involve a [Ca²⁺]_i increase, JNK and p38 MAPK activation, and ROS generation through NADPH oxidase and mitochondria.     

Src and Cas mediate JNK activation but not ERK1/2 and p38 kinases by reactive oxygen species

c-Jun NH(2)-terminal kinase (JNK) is activated by a number of cellular stimuli such as inflammatory cytokines and environmental stresses. Reactive oxygen species also cause activation of JNK; however, the signaling cascade that leads to JNK activation remains to be elucidated. Because recent reports showed that expression of Cas, a putative Src substrate, stimulates JNK activation, we hypothesized that the Src kinase family and Cas would be involved in JNK activation by reactive oxygen species. An essential role for both Src and Cas was demonstrated. First, the specific Src family tyrosine kinase inhibitor, PP2, inhibited JNK activation by H(2)O(2) in a concentration-dependent manner but had no effect on extracellular signal-regulated kinases 1 and 2 and p38 activation. Second, JNK activation in response to H(2)O(2) was completely inhibited in cells derived from transgenic mice deficient in Src but not Fyn. Third, expression of a dominant negative mutant of Cas prevented H(2)O(2)-mediated JNK activation but had no effect on extracellular signal-regulated kinases 1 and 2 and p38 activation. Finally, the importance of Src was further supported by the inhibition of both H(2)O(2)-mediated Cas tyrosine phosphorylation and Cas.Crk complex formation in Src-/- but not Fyn-/- cells. These results demonstrate an essential role for Src and Cas in H(2)O(2)-mediated activation of JNK and suggest a new redox-sensitive pathway for JNK activation mediated by Src.     

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.     

Cadmium induces vascular permeability via activation of the p38 MAPK pathway

The vasculature of various organs is a targeted by the environmental toxin, cadmium (Cd). However, mechanisms leading to pathological conditions are poorly understood. In the present study, we examined the effect of cadmium chloride (CdCl₂) on human umbilical vein endothelial cells (HUVECs). At 4 μM, CdCl₂ induced a hyper-permeability defect in HUVECs, but not the inhibition of cell growth up to 24 h. This effect of CdCl₂ was dependent on the activation of the p38 mitogen-activated protein kinase (MAPK) pathway. The p38 MAPK inhibitor SB203850 suppressed the CdCl₂-induced alteration in trans-endothelial electrical resistance in HUVEC monolayers, a model measurement of vascular endothelial barrier integrity. SB203850 also inhibited the Cd-induced membrane dissociation of vascular endothelial (VE) cadherin and β-catenin, the important components of the adherens junctional complex. In addition, SB203850 reduces the Cd-induced expression and secretion of tumor necrosis factor α (TNF-α). Taken together, our findings suggest that Cd induces vascular hyper-permeability and disruption of endothelial barrier integrity through stimulation of p38 MAPK signaling.     

Characterization of immunogenic p230 as the toxin A of Clostridium difficile

Abstract For the identification of toxin A of Clostridium difficile , a 2-dimensional gel system was used. In its first dimension, samples were separated in the absence of reducing and dissociating agents, conditions which maintained the activity of the enterotoxin. This was followed by reduction and dissociation in the second dimension where a 230 kDa polypeptide was electroeluted. Rabbits were immunized with polyacrylamide gel slices containing entrapped native toxin A and the denatured 230 kDa protein. As revealed by immunoblotting, neutralizing antisera derived from native protein samples recognized the native toxin, the denatured 230 kDa protein and another polypeptide of about M _r 35 000. Using both types of antisera as probes the pI of the enterotoxin was about 5.9. Preliminary evidence suggests that the enterotoxin is a multimeric protein of 230 kDa and 35 kDa subunits.