Differential regulation of extracellular signal-regulated kinase and nuclear factor-kappa B signal transduction pathways by hydrogen peroxide and tumor necrosis factor

Neuronal Agrin Promotes Proliferation of Primary Human Myoblasts in an Age-Dependent Manner

Neuronal agrin, a heparan sulphate proteoglycan secreted by the α-motor neurons, promotes the formation and maintenance of the neuromuscular junction by binding to Lrp4 and activating muscle-specific kinase (MuSK). Neuronal agrin also promotes myogenesis by enhancing differentiation and maturation of myotubes, but its effect on proliferating human myoblasts, which are often considered to be unresponsive to agrin, remains unclear. Using primary human myoblasts, we determined that neuronal agrin induced transient dephosphorylation of ERK1/2, while c-Abl, STAT3, and focal adhesion kinase were unresponsive. Gene silencing of Lrp4 and MuSK markedly reduced the BrdU incorporation, suggesting the functional importance of the Lrp4/MuSK complex for myoblast proliferation. Acute and chronic treatments with neuronal agrin increased the proliferation of human myoblasts in old donors, but they did not affect the proliferation of myoblasts in young donors. The C-terminal fragment of agrin which lacks the Lrp4-binding site and cannot activate MuSK had a similar age-dependent effect, indicating that the age-dependent signalling pathways activated by neuronal agrin involve the Lrp4/MuSK receptor complex as well as an Lrp4/MuSK-independent pathway which remained unknown. Collectively, our results highlight an age-dependent role for neuronal agrin in promoting the proliferation of human myoblasts.

The Quest to Quantify Selective and Synergistic Effects of Plasma for Cancer Treatment: Insights from Mathematical Modeling

Cold atmospheric plasma (CAP) and plasma-treated liquids (PTLs) have recently become a promising option for cancer treatment, but the underlying mechanisms of the anti-cancer effect are still to a large extent unknown. Although hydrogen peroxide (H2O2) has been recognized as the major anti-cancer agent of PTL and may enable selectivity in a certain concentration regime, the co-existence of nitrite can create a synergistic effect. We develop a mathematical model to describe the key species and features of the cellular response toward PTL. From the numerical solutions, we define a number of dependent variables, which represent feasible measures to quantify cell susceptibility in terms of the H2O2 membrane diffusion rate constant and the intracellular catalase concentration. For each of these dependent variables, we investigate the regimes of selective versus non-selective, and of synergistic versus non-synergistic effect to evaluate their potential role as a measure of cell susceptibility. Our results suggest that the maximal intracellular H2O2 concentration, which in the selective regime is almost four times greater for the most susceptible cells compared to the most resistant cells, could be used to quantify the cell susceptibility toward exogenous H2O2. We believe our theoretical approach brings novelty to the field of plasma oncology, and more broadly, to the field of redox biology, by proposing new ways to quantify the selective and synergistic anti-cancer effect of PTL in terms of inherent cell features.

The Vector - Host - Pathogen Interface: The Next Frontier in the Battle Against Mosquito-Borne Viral Diseases?

An unprecedented spread of mosquito-borne viruses and increasing populations of mosquito vectors has led to an increase in the frequency of mosquito-borne virus disease outbreaks. Recent outbreaks of Zika virus (ZIKV) and yellow fever virus (YFV), among others have led to a concerted effort to understand the biology of mosquito-borne viruses and their interaction with their vector mosquito and vertebrate hosts. Recent studies have aimed to understand the vector-host-pathogen interface and how it influences infection, tropism and disease severity in the vertebrate host. The initial replication of the pathogen at the skin bite site is crucial in determining the progression of the infection in the vertebrate host. Delineating the role of the commensal microbes in the mosquito saliva as well as how they interact with the vertebrate host keratinocytes will improve our understanding of disease immunopathology and may lead to new therapeutics.

Conflict in the Intracellular Lives of Endosymbionts and Viruses: A Mechanistic Look at Wolbachia-Mediated Pathogen-blocking

At the forefront of vector control efforts are strategies that leverage host-microbe associations to reduce vectorial capacity. The most promising of these efforts employs Wolbachia, a maternally transmitted endosymbiotic bacterium naturally found in 40% of insects. Wolbachia can spread through a population of insects while simultaneously inhibiting the replication of viruses within its host. Despite successes in using Wolbachia-transfected mosquitoes to limit dengue, Zika, and chikungunya transmission, the mechanisms behind pathogen-blocking have not been fully characterized. Firstly, we discuss how Wolbachia and viruses both require specific host-derived structures, compounds, and processes to initiate and maintain infection. There is significant overlap in these requirements, and infection with either microbe often manifests as cellular stress, which may be a key component of Wolbachia’s anti-viral effect. Secondly, we discuss the current understanding of pathogen-blocking through this lens of cellular stress and develop a comprehensive view of how the lives of Wolbachia and viruses are fundamentally in conflict with each other. A thorough understanding of the genetic and cellular determinants of pathogen-blocking will significantly enhance the ability of vector control programs to deploy and maintain effective Wolbachia-mediated control measures.

Recuperating lung decoction attenuates inflammation and oxidation in cigarette smoke-induced COPD in rats via activation of ERK and Nrf2 pathways

Oxidative/antioxidative imbalance and chronic inflammation are the main contributors to the pathogenesis of chronic obstructive pulmonary disease (COPD). This study evaluated the effect of recuperating lung decoction (RLD) on inflammation and oxidative stress in rats with COPD induced by cigarette smoke and lipopolysaccharides (LPS). We used intravenous infusion of LPS combined with cigarette smoke exposure as a COPD rat model. We observed that RLD treatment increased the protein level of GSH and the ratio of GSH/GSSG but decreased 8-OHdG and 4-HNE in the serum. Furthermore, RLD significantly inhibited the expressions of IL-1β, IL-6, TNF-α, and TGF-β induced by cigarette smoke exposure, reduced the number of inflammatory cells in the bronchoalveolar lavage fluid, and alleviated the severity of cigarette smoke-induced emphysema. Mechanistically, RLD treatment prevented disease through downregulation of phosphorylated-ERK and Nrf2 expression, which regulates the production of proinflammatory cytokines. RLD treatment exerted a dramatic therapeutic effect on COPD. This study revealed a mechanism that RLD functions on the regulation of ERK signalling to inhibit inflammation.

Postprandial control of fatty acid transport proteins' subcellular location is not dependent on insulin

Fatty acid transport proteins rapidly translocate to the plasma membrane in response to various stimuli, including insulin, influencing lipid uptake into muscle. However, our understanding of the mechanisms regulating postprandial fatty acid transporter subcellular location remains limited. We demonstrate that the response of fatty acid transporters to insulin stimulation is extremely brief and not temporally matched in the postprandial state. We further show that high-fat diet-induced accumulation of fatty acid transporters on the plasma membrane can occur in the absence of insulin. Altogether, these data suggest that insulin is not the primary signal regulating fatty acid transporter relocation in vivo.

Impact of ERK activation on fly survival and Wolbachia-mediated protection during virus infection

Elevated levels of reactive oxygen species (ROS) provide protection against virus-induced mortality in Drosophila. In addition to contributing to oxidative stress, ROS are known to activate a number of signalling pathways including the extracellular signal-regulated kinases (ERK) signalling cascade. It was recently shown that ERK signalling is important for resistance against viral replication and invasion in cultured Drosophila cells and the gut epithelium of adult flies. Here, using a Drosophila loss-of-function ERK (rolled) mutant we demonstrated that ERK is important for fly survival during virus infection. ERK mutant flies subjected to Drosophila C virus (DCV) oral and systemic infection were more susceptible to virus-induced mortality as compared with wild-type flies. We have demonstrated experimentally that ERK activation is important for fly survival during oral and systemic virus infection. Given that elevated ROS correlates with Wolbachia-mediated antiviral protection, we also investigated the involvement of ERK in antiviral protection in flies infected by Wolbachia. The results indicate that ERK activation is increased in the presence of Wolbachia but this does not appear to influence Wolbachia-mediated antiviral protection, at least during systemic infection.

Mechanism of action of (-)-epigallocatechin-3-gallate: auto-oxidation-dependent activation of extracellular signal-regulated kinase 1/2 in Jurkat cells

AIM

(-)-Epigallocatechin-3-gallate (EGCG), a major compound of tea polyphenols, exhibited antitumor activity in previous studies. In these studies, EGCG usually inhibits EGFR, and impairs the ERK1/2 phosphorylation in tumor cells. The aim was to clarify the mechanism of ERK1/2 activation induced by EGCG.

METHOD

Jurkat and 293T cells were treated with EGCG in different culture conditions. Western Blotting (WB) was employed to analyze ERK1/2 and MEK phosphorylation. Cetuximab and FR180204 were used to inhibit cell signaling. The stability of EGCG was assessed by HPLC. The concentration of hydrogen peroxide generated by the auto-oxidation of EGCG was determined by photocolorimetric analysis.

RESULTS

Activation of ERK1/2 was observed to be both time-and dose-dependent. Stimulation of cell signaling was dependent on MEK activity, but independent of EGFR activity. Unexpectedly, EGCG was depleted within one hour of incubation under traditional culture conditions. Auto-oxidation of EGCG generated a high level of hydrogen peroxide in the medium. Addition of catalase and SOD to the acidic medium inhibited the oxidation of EGCG. However, this particular condition also prevented the phosphorylation of ERK1/2. The generation of ROS by hydrogen peroxide may also induce ERK1/2 activation in Jurkat cells.

CONCLUSION

ERK1/2 phosphorylation was caused by auto-oxidation of EGCG. Traditional culture conditions were determined to be inappropriate for EGCG research.

Neuroprotective activity of peripherally administered liver growth factor in a rat model of Parkinson's disease

Liver growth factor (LGF) is a hepatic mitogen purified some years ago that promotes proliferation of different cell types and the regeneration of damaged tissues, including brain tissue. Considering the possibility that LGF could be used as a therapeutic agent in Parkinson’s disease, we analyzed its potential neuroregenerative and/or neuroprotective activity when peripherally administered to unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats. For these studies, rats subjected to nigrostriatal lesions were treated intraperitoneally twice a week with LGF (5 microg/rat) for 3 weeks. Animals were sacrificed 4 weeks after the last LGF treatment. The results show that LGF stimulates sprouting of tyrosine hydroxylase-positive terminals and increases tyrosine hydroxylase and dopamine transporter expression, as well as dopamine levels in the denervated striatum of 6-OHDA-lesioned rats. In this structure, LGF activates microglia and raises tumor necrosis factor-alpha protein levels, which have been reported to have a role in neuroregeneration and neuroprotection. Besides, LGF stimulates the phosphorylation of MAPK/ERK1/2 and CREB, and regulates the expression of proteins which are critical for cell survival such as Bcl2 and Akt. Because LGF partially protects dopamine neurons from 6-OHDA neurotoxicity in the substantia nigra, and reduces motor deficits in these animals, we propose LGF as a novel factor that may be useful in the treatment of Parkinson’s disease.

Anti-carcinogenic action of ellagic acid mediated via modulation of oxidative stress regulated genes in Dalton lymphoma bearing mice

An elevated level of reactive oxygen species (ROS) in a cancerous condition causes oxidative stress which in turn activates a number of genes, and therefore an interruption in the oxidative microenvironment should be able to inactivate these genes, contributing to cancer prevention. The present work was designed to evaluate the role of ellagic acid in the modulation of protein kinase Cα (PKCα) activity and expression and its correlation with the oncogene, c-Myc, and tumor suppressor gene, transforming growth factor-β (TGF-β1), in lymphoma bearing mice. We also evaluated its implication for cell viability. Our results show that ellagic acid leads to down-regulation of the expression and activity of PKCα via decreasing the oxidative stress, measured in terms of lipid peroxidation and protein carbonylation. It also reduces c-Myc expression and improves TGF-β1 expression besides decreasing cell viability in Dalton lymphoma bearing mice, which supports its anti-carcinogenic action.

Aristolochic acid I induced oxidative DNA damage associated with glutathione depletion and ERK1/2 activation in human cells

Aristolochic acid I (AAI) has been widely found in herbal remedies and linked to the development of nephropathy and urothelial carcinoma in humans. This study elucidated the mechanism of oxidative stress and DNA damage mediated by AAI in human cells. Treatment of human promyelocytic leukemia cells (HL-60) and human renal proximal tubular cells (HK-2) with AAI led to a dose-dependent increase of reactive oxygen species (ROS). AAI also elevated the levels of DNA strand breaks and 8-hydroxy guanosine in HL-60 and HK-2 cells. Antioxidants, including Tiron, N-acetyl-l-cysteine (NAC) and glutathione (GSH), effectively suppressed the AAI-induced ROS and AAI-elicited genotoxicity, indicating that AAI induced the DNA damage through oxidative stress. GSH depletion was also found in AAI-treated cultures and proceeded prior to ROS formation. Exposure of HL-60 cells with AAI activated both ERK1/2 and p38 kinase phosphorylation, while only MEK1/2 inhibitor, U0126, significantly decreased AAI-mediated ROS. Preincubation of cells with thiol-containing compounds (NAC and GSH) inhibited the caspase 3 activity triggered by AAI, but non-thiol Tiron did not show a similar effect. This study demonstrated that AAI treatment results in oxidative stress-related DNA damage through GSH depletion and ERK1/2 activation; AAI-induced apoptosis is associated with GSH loss, but is independent of ROS generation.

Plumbagin activates ERK1/2 and Akt via superoxide, Src and PI3-kinase in 3T3-L1 cells

Plumbagin, derived from the plant Plumbago zeylanica, has been shown to chronically activate ERK1/2 and inhibit Akt activity in cancer cells. However, the acute effects of plumbagin on ERK1/2 and Akt activities remain unknown. In this study, we examined the effects of plumbagin on ERK1/2 and Akt activities in 3T3-L1 cells. Exposure of 3T3-L1 cells to plumbagin generated superoxide and activated both ERK1/2 and Akt. The plumbagin-stimulated ERK1/2 and Akt activities were sensitive to an antioxidant NAC, superoxide dismutase mimetic MnTBAP, superoxide scavenger Tiron and NAD(P)H oxidase inhibitor DPI. Plumbagin-stimulated ERK1/2 activity was attenuated by the MEK1/2 inhibitor PD98059 and Ras inhibitor manumycin A, whereas plumbagin-stimulated Akt activity was blocked by the PI3K inhibitor LY294002. Both plumbagin-stimulated ERK1/2 and Akt activities were attenuated by PP2, a Src inhibitor. Interestingly, inhibition of phosphatidylinositol 3-kinase (PI3-kinase), but not Akt, activity leaded to attenuation of plumbagin-stimulated ERK1/2 activity. These results suggest that plumbagin activates NAD(P)H oxidase, Src, and PI3K, and that the activated PI3K or PDK1 subsequently stimulate Akt and Ras-Raf-MEK1/2-ERK1/2 in 3T3-L1 cells.

The omega-3 fatty acid docosahexaenoate attenuates endothelial cyclooxygenase-2 induction through both NADP(H) oxidase and PKC epsilon inhibition

A high intake of the omega-3 fatty acid docosahexaenoate [docosahexaenoic acid (DHA)] has been associated with systemic antiinflammatory effects and cardiovascular protection. Cyclooxygenase (COX)-2 is responsible for the overproduction of prostaglandins (PG) at inflammatory sites, and its expression is increased in atheroma. We studied the effects of DHA on COX-2 expression and activity in human saphenous vein endothelial cells challenged with proinflammatory stimuli. A>or=24-h exposure to DHA reduced COX-2 expression and activity induced by IL-1, without affecting COX-1 expression. DHA effect depended on the NF-kappaB-binding site in the COX-2 promoter. EMSAs confirmed that DHA attenuated NF-kappaB activation. Because MAPK, PKC, and NAD(P)H oxidase all participate in IL-1-mediated COX-2 expression, we also tested whether these enzymes were involved in DHA effects. Western blots showed that DHA blocked nuclear p65 NF-kappaB subunit translocation by decreasing cytokine-stimulated reactive oxygen species and ERK1/2 activation by effects on both NAD(P)H oxidase and PKCepsilon activities. Finally, to address the question whether DHA itself or DHA-derived products were responsible for these effects, we inhibited the most important enzymes involved in polyunsaturated fatty acid metabolism, showing that 15-lipoxygenase-1 products mediate part of DHA effects. These studies provide a mechanistic basis for antiinflammatory and possibly plaque-stabilizing effects of DHA.

TNF-alpha inhibits asbestos-induced cytotoxicity via a NF-kappaB-dependent pathway, a possible mechanism for asbestos-induced oncogenesis

Asbestos is the main cause of human malignant mesothelioma (MM). In vivo, macrophages phagocytize asbestos and, in response, release TNF-alpha and other cytokines that contribute to carcinogenesis through unknown mechanisms. In vitro, asbestos does not induce transformation of primary human mesothelial cells (HM); instead, asbestos is very cytotoxic to HM, causing extensive cell death. This finding raised an apparent paradox: How can asbestos cause MM if HM exposed to asbestos die? We found that asbestos induced the secretion of TNF-alpha and the expression of TNF-alpha receptor I in HM. Treatment of HM with TNF-alpha significantly reduced asbestos cytotoxicity. Through numerous technical approaches, including chemical inhibitors and small interfering RNA strategies, we demonstrate that, in HM, TNF-alpha activates NF-kappaB and that NF-kappaB activation leads to HM survival and resistance to the cytotoxic effects of asbestos. Our data show a critical role for TNF-alpha and NF-kappaB signaling in mediating HM responses to asbestos. TNF-alpha signaling through NF-kappaB-dependent mechanisms increases the percent of HM that survives asbestos exposure, thus increasing the pool of asbestos-damaged HM that are susceptible to malignant transformation. Cytogenetics supported this hypothesis, showing only rare, aberrant metaphases in HM exposed to asbestos and an increased mitotic rate with fewer irregular metaphases in HM exposed to both TNF-alpha and asbestos. Our findings provide a mechanistic rationale for the paradoxical inability of asbestos to transform HM in vitro, elucidate and underscore the role of TNF-alpha in asbestos pathogenesis in humans, and identify potential molecular targets for anti-MM prevention and therapy.

The Effect of Cigarette Smoke-derived Oxidants on the Inflammatory Response of the Lung

The inhalation of cigarette smoke triggers a marked cellular influx in the lung and this inflammation is believed to play a central role in the development of smoke-related lung diseases such as asthma and COPD. Studies demonstrate that smoke-derived oxidants are a major factor in this inflammatory reaction to cigarette smoke. These oxidants can overwhelm the lung's antioxidant defenses and they can up regulate inflammation by a number of mechanisms. Free radicals directly stimulate the production of chemotactic compounds such as 8-isoprostane. In addition, smoke-derived oxidants can activate several intracellular signaling cascades including NF-κB, MAPK and AP-1. This transcriptional activation induces the expression of cytokines and intracellular adhesion molecules that facilitates the trafficking of neutrophils, macrophages and lymphocytes into the lung. Moreover, oxidants can promote chromatin remodeling that facilitates the expression of proinflammatory genes by stimulating the acetylation of histone residues in the nucleosome. This leads to conformational changes that enhance expression by rendering the gene more accessible to binding to transcriptional factors. Thus, the oxidant-antioxidant imbalance generated by cigarette smoke can promote inflammation which is critical to the functional decline that occurs in both asthma and COPD patients. Future research is needed to better define the effects of smoke-derived oxidants on lung inflammation and to determine the most efficacious strategies for generating significant antioxidant protection in the lung.

Role of reactive oxygen species and protein kinase C in ischemic tolerance in the brain

It is now understood that the mechanisms leading to neuronal cell death after cerebral ischemia are highly complex. A well established fact in this field is that neurons continue to die over days and months after ischemia, and that reperfusion following cerebral ischemia contributes substantially to ischemic injury. It is now well accepted that central to ischemic/reperfusion-induced injury is what occurs to mitochondria hours to days following the ischemic insult. For many years, it has been established that reactive oxygen species (ROS) and reactive nitrogen species (RNS) promote lipid, protein, and DNA oxidation that affects normal cell physiology and eventually leads to neuronal demise. In addition to oxidation of neuronal molecules by ROS and RNS, a novel pathway for molecular modifications has risen from the concept that ROS can activate specific signal transduction pathways that, depending on the insult degree, can lead to either normal plasticity or pathology. Two examples of these pathways could explain why lethal ischemic insults lead to the translocation of protein kinase Cdelta (deltaPKC), which plays a role in apoptosis after cerebral ischemia, or why sublethal ischemic insults, such as in ischemic preconditioning, lead to the translocation of epsilonPKC, which plays a pivotal role in neuroprotection. A better understanding of the mechanisms by which ROS and/or RNS modulate key protein kinases that are involved in signaling pathways that lead to cell death and survival after cerebral ischemia will help devise novel therapeutic strategies.

The effects of antioxidants on radiation-induced apoptosis pathways in TK6 cells

This study was designed to determine if radiation-mediated activation of the apoptotic pathways would be influenced by antioxidants and if a correlation would be found between radioprotection and changes in transduction pathways. Human lymphoblastoid TK6 cells, known to undergo apoptosis as a result of radiation, were irradiated (6 Gy) with and without antioxidants, and then whole-cell lysates were collected. Parallel studies were conducted to assess the survival (clonogenic assay) and apoptotic index. The impacts of two nitroxide antioxidants, tempol and CAT-1, differing in cell permeability, as well as the sulfhydryl antioxidant N-acetyl-L-cysteine (L-NAC), were estimated. Changes in apoptotic pathway proteins and p53 were assessed by Western blotting. Fraction of apoptotic cells was determined by flow cytometry. Tempol (10 mM), which readily enters cells, partially radioprotected TK6 cells against clonogenic killing, but had no effect on radiation-induced apoptotic parameters such as cleaved caspase 3 or cleaved PARP. Tempol alone did not induce cytotoxicity, yet did increase cleaved PARP levels. The radiation-induced increase in p53 protein was partly inhibited by tempol, but was unaffected by CAT-1 and L-NAC. Both CAT-1 (10 mM), which does not enter cells, and L-NAC (10 mM) had no radioprotective effect on cell survival. Although L-NAC did not protect against radiation-induced cytotoxicity, it completely inhibited radiation-induced increase in cleaved caspase 3 and cleaved PARP. Collectively, the results question the validity of using selected apoptosis pathway members as sole indicators of cytotoxicity.

Nuclear factor kappa B activation by NADPH oxidases

Reactive oxygen species (ROS) initiate activation of the transcription factor NF-kappaB in a variety of cell systems. Perhaps the most potent biological source of ROS is the NADPH oxidase of phagocytic cells, a multi-component system that catalyzes the formation of superoxide anion. Although phagocytes use this oxidase to kill ingested microorganisms, the products also mediate a broad range of biological oxidation reactions and some evidence exists for activation of NF-kappaB through this mechanism. Moreover, the components of the phagocyte NADPH oxidase are present in certain non-phagocytic cells and recently discovered homologues of the catalytic component gp91(phox) are expressed in a number of tissues. We explored the hypothesis that the products of NADPH oxidases cause the activation of NF-kappaB. K562 human erythrokeukemia cells transfected with constructs for expression of gp91(phox), plus other essential NADPH oxidase components generated substantial amounts of superoxide when activated with phorbol ester, lesser amounts with arachidonic acid exposure, and none with TNFalpha. Gel shift assays demonstrated induction of NF-kappaB in K562 cells exposed to TNFalpha and specificity was shown by oligonucleotide competition. Supershift assays demonstrated the presence in nuclear complexes of the NF-kappaB components p65/RelA and p50. Nuclear complexes of identical electrophoretic mobility were induced in phorbol ester-stimulated K562 cells that expressed the complete NADPH oxidase system, but not in cells lacking one of the essential oxidase components. K562 cells were relatively resistant to NF-kappaB induction by exogenous peroxide, but certain other cell types (HEK293 and HeLaS3) demonstrated such induction upon exposure to reagent hydrogen peroxide or glucose oxidase plus glucose and this was blocked by catalase. Finally, we found a biphasic pattern of gp91(phox) expression in rat liver during aging. High levels observed in young animals decreased in middle age, but increased again in old age. Collectively, these studies demonstrate the potential for NADPH-dependent induction of NF-kappaB and raise the possibility of a role for this pathway in the biology of aging.

Extracellular Oxidation by Taurine Chloramine Activates ERK via the Epidermal Growth Factor Receptor

Taurine is present in high concentrations in neutrophils, and when the cells are stimulated taurine can react with hypochlorous acid (HOCl) to form taurine-chloramine (Tau-Cl). This compound retains oxidant activity and can affect the neutrophil itself or surrounding tissue cells. We have investigated the effects of Tau-Cl on MAPK signaling in human umbilical vein endothelial cells (HUVEC). Tau-Cl caused no loss in intracellular glutathione or inactivation of the thiol-sensitive enzyme glyceraldehyde-3-phosphate dehydrogenase, indicating that it had not entered the cells. However, stimulation of HUVEC with Tau-Cl (20-100 microM) induced the rapid activation of ERK within 10 min. This activation was abolished by inhibition of MEK by U0126, indicating that it was not because of direct oxidation of ERK. No activation of p38 was detected. These results suggest that Tau-Cl reacts with a cell membrane target that results in intracellular ERK activation. Tau-Cl over the same concentration range and time scale stimulated epidermal growth factor (EGF) receptor tyrosine phosphorylation in A431 cells and HUVEC. The EGF receptor inhibitor PD158780 significantly attenuated Tau-Cl-induced phosphorylation of both the EGF receptor and ERK. This implicates the EGF receptor in the upstream activation of ERK. The Src tyrosine kinase inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolol[3,4-d]pyrimidine had no effect on Tau-Cl-induced EGF receptor or ERK activation. We propose that Tau-Cl acts on an oxidant-sensitive target on the cell surface, this being either the EGF receptor itself or another target that can interact with the EGF receptor, with consequential activation of ERK.

Signalling pathways influencing basal and H2O2-induced P-glycoprotein expression in endothelial cells derived from the blood-brain barrier

The drug transporter, P-glycoprotein (P-gp) on brain microvessel endothelium, influences movement of lipophilic substances in and out of the brain. Pathways regulating P-gp expression, both basal and hydrogen peroxide (H2O2)-induced, are here examined in primary cultured rat brain endothelial cells. Activation of extracellular-signal regulated kinases (ERK1/2), protein kinase C (PKC), the p46 isoform of stress-activated protein kinase (SAPK) and its downstream transcription factor, c-Jun, occurred in a time- and concentration-dependent manner following exposure of cells to H2O2 with concomitant increases in P-gp expression. Blockade of ERK activation with U0126, of PKC with Gö6976 and of SAPK with SP600125 decreased basal P-gp but did not abolish the H2O2-induced increase. Blockade of Akt with PI3-kinase inhibitor, LY294002, lowered basal P-gp and prevented the H2O2-induced increase. Inhibition of nuclear factor-kappaB (NF-kappaB), either by blocking dissociation from its inhibitory factor, IkappaB, with MG132 or its nuclear translocation with SN50 enhanced basal P-gp, obscuring the H2O2-induced increase. H2O2 itself produced no detectable activation of IkappaB, but inhibited that induced by 5 ng/mL tumour necrosis factor-alpha (TNF-alpha). P-gp expression may involve positive inputs from ERK1/2, SAPK, Akt and PKC and inhibitory influences of NF-kappaB. By depressing NF-kappaB signalling, H2O2 may still augment P-gp expression when ERK1/2, PKC or SAPK are inhibited.

Redox regulation of reactive oxygen species-induced p38 MAP kinase activation and barrier dysfunction in lung microvascular endothelial cells

Reactive oxygen species (ROS)-mediated compromise of endothelial barrier integrity has been implicated in a number of pulmonary disorders, including adult respiratory distress syndrome, pulmonary edema, and vasculitis. The mechanisms by which ROS increase endothelial permeability are unclear. We hypothesized that ROS-induced changes in cellular redox status (thiols) may contribute to endothelial barrier dysfunction. To test this hypothesis, we used N-acetylcysteine (NAC) and diamide to modulate intracellular levels of cellular glutathione (GSH) and investigated hydrogen peroxide (H(2)O(2))-mediated mitogen-activated protein kinase (MAPK) activation and transendothelial electrical resistance (TER). Exposure of bovine lung microvascular endothelial cells (BLMVECs) to H(2)O(2), in a dose- and time-dependent fashion, increased endothelial permeability. Pretreatment of BLMVECs with NAC (5 mM) for 1 h resulted in partial attenuation of H(2)O(2)-induced TER (a measure of increase in permeability) and GSH. Furthermore, treatment of BLMVECs with diamide, which is known to reduce the intracellular GSH, resulted in significant reduction in TER, which was prevented by NAC. To understand further the role of MAPKs in ROS-induced barrier dysfunction, we examined the role of extracellular signal-regulated kinase (ERK) and p38 MAPK on H(2)O(2)- and diamide-mediated permeability changes. Both H(2)O(2) and diamide, in a dose-dependent manner, activated ERK and p38 MAPK in BLMVECs. However, SB203580, an inhibitor of p38 MAPK, but not PD98059, blocked H(2)O(2)- and diamide-induced TER. Also, NAC prevented H(2)O(2)- and diamide-induced p38 MAPK, but not ERK activation. These results suggest a role for redox regulation of p38 MAPK in ROS-dependent endothelial barrier dysfunction.

Effects of TNFalpha on expression of ICAM-1 in human airway epithelial cells in vitro: oxidant-mediated pathways and transcription factors

We demonstrate that two different cell-permeable antioxidants, pyrrolidine dithiocarbamate (PDTC) and dimethylthiourea (DMTU), inhibit TNFalpha-induced ICAM-1 surface and gene expression in primary cultures of differentiated normal human bronchial epithelial (NHBE) cells. In addition, TNFalpha stimulates binding of nuclear proteins to the nuclear factor kappa beta (NFkappaB) and the CAAT/enhancer binding protein (C/EBP) consensus sites in the ICAM-1 promoter in these cells. Because these transcription factors have been suggested to be oxidant-sensitive and important in ICAM-1 expression, the potential involvement of reactive oxygen species (ROS) in the response to TNFalpha was investigated. Interestingly, neither PDTC nor DMTU altered binding of NFkappaB complexes. In contrast, either the proteasome inhibitor carbobenzoxy-L-leucy-L-leucy-L-leucinal (MG 132) or the IkappaBalpha inhibitor BAY 11-7082 ablated TNFalpha-induced ICAM-1 gene expression and MG132 inhibited TNFalpha-induced NFkappaB complexes. Surprisingly, either PDTC or DMTU inhibited the binding of TNFalpha-enhanced C/EBP complexes to the consensus site directly adjacent to the NFkappaB site. These results suggest that although TNFalpha enhances binding of C/EBP and NFkappaB complexes in NHBE cells, C/EBP binding seems to involve an oxidant-dependent mechanism, whereas activation of NFkappaB complexes utilizes the ubiquitin-proteasome pathway, a mechanism that seems to be unaltered by the presence of antioxidants. Because interference with either signaling pathway abrogates TNFalpha-induced ICAM-1 expression, activation of both complexes seems to be involved in this response to TNFalpha, but this activation occurs via different intracellular pathways.

Hydrogen peroxide activates NF-kappa B through tyrosine phosphorylation of I kappa B alpha and serine phosphorylation of p65: evidence for the involvement of I kappa B alpha kinase and Syk protein-tyrosine kinase

Although it is well established that reactive oxygen intermediates mediate the NF-kappaB activation induced by most agents, how H2O2 activates this transcription factor is not well understood. We found that treatment of human myeloid KBM-5 cells with H2O2 activated NF-kappaB in a dose- and time-dependent manner much as tumor necrosis factor (TNF) did but unlike TNF, H2O2 had no effect on IkappaBalpha degradation. Unexpectedly, however, like TNF-induced activation, H2O2-induced NF-kappaB activation was blocked by the calpain inhibitor N-Ac-Leu-Leu-norleucinal, suggesting that a proteosomal pathway was involved. Although H2O2 activated IkappaBalpha kinase, it did not induce the serine phosphorylation of IkappaBalpha. Like TNF, H2O2 induced the serine phosphorylation of the p65 subunit of NF-kappaB, leading to its nuclear translocation. We found that H2O2 induced the tyrosine phosphorylation of IkappaBalpha, which is needed for NF-kappaB activation. We present several lines of evidence to suggest that the Syk protein-tyrosine kinase is involved in H2O2-induced NF-kappaB activation. First, H2O2 activated Syk in KBM-5 cells; second, H2O2 failed to activate NF-kappaB in cells that do not express Syk protein; third, overexpression of Syk increased H2O2-induced NF-kappaB activation; and fourth, reduction of Syk transcription using small interfering RNA inhibited H2O2-induced NF-kappaB activation. We also showed that Syk induced the tyrosine phosphorylation of IkappaBalpha, which caused the dissociation, phosphorylation, and nuclear translocation of p65. Thus, overall, our results demonstrate that H2O2 induces NF-kappaB activation, not through serine phosphorylation or degradation of IkappaBalpha, but through Syk-mediated tyrosine phosphorylation of IkappaBalpha

Geldanamycin induction of grp78 requires activation of reactive oxygen species via ER stress responsive elements in 9L rat brain tumour cells

The molecular mechanism whereby anticancer agent geldanamycin (GA) impacts endoplasmic reticulum (ER) stress pathway is largely unknown. Here, we investigate the effect of GA on the expression of grp78 coding for ER stress protein and the mechanistic relationship of GA signalling to ER stress. GA induces the expression of mRNA and protein of grp78 by Northern blot analysis and metabolic labelling experiment in cultured rat brain tumour 9L cells. The induced grp78 expression is sensitive to antioxidant N-acetylcysteine (NAC) addition, indicating the involvement of reactive oxygen species (ROS) in GA-induced ER stress. Results from direct determination of oxidation status using dichlorodihydrofluorescein diacetate (H(2)DCFDA) showed that accumulation of ROS elicited GA was quenched by addition of NAC. Reporter genes harbouring deletions of transcription elements from grp78 promoter demonstrated that controlling elements of ERSE1, ERSE2 and CRE are required in GA treatment. The critical ROS-dependent elements in grp78 promoter can be confined within ER stress responsive element (ERSE) region, since reporter constructs loss of ERSE elements that lost the susceptibility to be modulated by NAC after GA treatment. Hence, ER stress elements correlate well with ROS-mediated elements in grp78 promoter. Reporter construct loss of ERSE element retains the susceptibility by NAC after GA treatment, indicating that CRE element might represent a ROS-independent, GA-inductive element. Conclusively, we show that ROS is required for GA to launch the transactivation of grp78, and a firm link was established between the ROS signalling pathway to specific promoter elements-ERSE1 and ERSE2 elements in ER stress marker gene grp78 promoter.

The reactive adventitia: fibroblast oxidase in vascular function

The vascular adventitia is activated in a variety of cardiovascular disease states and has recently been shown to be a barrier to nitric oxide bioactivity. Vascular fibroblasts produce substantial amounts of NAD(P)H oxidase-derived reactive oxygen species (ROS) that appear to be involved in fibroblast proliferation, connective tissue deposition, and perhaps vascular tone. However, the physiological and pathophysiological roles of the adventitia have not been extensively studied, possibly because of its location in large blood vessels remote from the vascular endothelium. In recent years, substantial information has been gathered on pathways leading to oxidase activation in smooth muscle cells and fibroblasts and the downstream signaling pathways leading to hypertrophy and proliferation. A clearer understanding of the molecular mechanisms involved will likely lead to therapeutic strategies aimed at preventing vascular dysfunction in diseases such as atherosclerosis, in which these pathways are activated.

Hydrogen peroxide and tumour necrosis factor-alpha induce NF-kappaB-DNA binding in primary human T lymphocytes in addition to T cell lines

Reactive oxygen intermediates (ROIs), such as hydrogen peroxide (H2O2), have been implicated as second messengers in the activation of NF-kappaB by a variety of stimuli, including tumour necrosis factor-alpha (TNF-alpha). The aim of the present study was to examine the effects of ROIs on NF-kappaB activation in primary human CD3+ T lymphocytes and human peripheral blood mononuclear cells (PBMCs). For comparison purposes, Jurkat T cells (subclones JR and JE6.1) were also investigated. Cells were incubated in the presence of either H2O2 or TNF-alpha and nuclear proteins were extracted. NF-kappaB binding was assessed by electrophoretic mobility shift assays (EMSAs). The concentration of H2O2 required to activate NF-kappaB in human primary CD3+ T lymphocytes was as low as 1 microM. In contrast, much higher concentrations of H2O2 were required to activate NF-kappaB in PBMCs and in the JR subclone of Jurkat T cells. H2O2-induced NF-kappaB activation was not observed in the JE6.1 subclone of Jurkat T cells. NF-kappaB was activated by TNF-alpha in all four cell types tested. In PBMCs and Jurkat T cells (subclones JR and JE6.1), this activation could be inhibited by pre-treatment with the antioxidants, pyrrolidine dithiocarbamate (PDTC) and N-acetyl-L-cysteine (NAC). Our results support a role for ROIs in NF-kappaB-DNA binding in human primary T lymphocytes.

Hypochlorous acid stimulation of the mitogen-activated protein kinase pathway enhances cell survival

We investigated the activation of three subfamilies of mitogen-activated protein kinases (MAP kinase), the extracellular regulated kinase (ERK1/2), p38, and c-Jun N-terminal kinase (JNK), by the myeloperoxidase-derived oxidant HOCl, in human umbilical vein endothelial cells (HUVEC) and human skin fibroblasts. Treatment of fibroblasts with 10-30 microM HOCl induced a dose-dependent increase in the tyrosine phosphorylation of several proteins. ERK1/2 was activated by exposure to sublethal concentrations of reagent HOCl or by HOCl generated by myeloperoxidase as shown by immune complex kinase assays. Maximum activation was seen at 20 microM and peak activation occurred within 10 min. Western blot analysis demonstrated activation of p38 with 30 microM HOCl, occurring at 15-30 min. No activation of JNK was detected in the concentration range investigated. These results show that HOCl is able to activate MAP kinases. Effective doses were considerably lower than with H2O2 and the lack of JNK activation contrasts with the activation frequently seen with H2O2. Exposure to HOCl caused a loss of viability in HUVEC that was markedly enhanced when ERK1/2 activation was inhibited by U0126. This suggests that the activation of ERK promotes cell survival in response to the oxidative challenge.

Reactive oxygen species in cell signaling

Reactive oxygen species (ROS) are generated as by-products of cellular metabolism, primarily in the mitochondria. When cellular production of ROS overwhelms its antioxidant capacity, damage to cellular macromolecules such as lipids, protein, and DNA may ensue. Such a state of "oxidative stress" is thought to contribute to the pathogenesis of a number of human diseases including those of the lung. Recent studies have also implicated ROS that are generated by specialized plasma membrane oxidases in normal physiological signaling by growth factors and cytokines. In this review, we examine the evidence for ligand-induced generation of ROS, its cellular sources, and the signaling pathways that are activated. Emerging concepts on the mechanisms of signal transduction by ROS that involve alterations in cellular redox state and oxidative modifications of proteins are also discussed.

Specific pancreatic enzymes activate macrophages to produce tumor necrosis factor-alpha: role of nuclear factor kappa B and inhibitory kappa B proteins

The triggering events by which mononuclear cells throughout the body are induced to produce large amounts of cytokines during acute pancreatitis are unclear. However, recent work in our laboratory demonstrated that three specific pancreatic enzymes (elastase, carboxypeptidase A, and lipase) induced dramatic tumor necrosis factor-alpha (TNF-alpha) protein production from macrophages, whereas all others could not. This series of experiments was designed to examine the second messenger system by which this occurs. The rat macrophage cell line NR8383 was incubated for 3 hours with elastase, carboxypeptidase A, lipase, trypsin, or lipopolysaccharide (positive control). Activation of nuclear factor kappa B (NF-kappa B) was demonstrated by electrophoretic mobility shift assay, presence of inhibitory kappa B alpha and beta (I kappa B-alpha and I kappa B-beta) by Western blot analysis, and TNF-alpha protein production by enzyme-linked immunosorbent assay. Elastase, carboxypeptidase A, and lipase induced degradation of I kappa B-beta (but not I kappa B-alpha), activation of NF-kappa B, and production of TNF-alpha protein, whereas inhibition of I kappa B with pyrrolidine dithiocarbamate attenuated this response. Trypsin was unable to elicit any of these responses. Macrophages can be induced by specific activated pancreatic enzymes-elastase, carboxypeptidase A, and lipase-to produce TNF-alpha. This process is dependent on I kappa B-beta degradation and NF- kappa B activation, suggesting that these enzymes trigger this second messenger system through specific membrane-bound receptors.

Genetic, biochemical, and clinical features of chronic granulomatous disease

The reduced nicotinamide dinucleotide phosphate (NADPH) oxidase complex allows phagocytes to rapidly convert O2 to superoxide anion which then generates other antimicrobial reactive oxygen intermediates, such as H2O2, hydroxyl anion, and peroxynitrite anion. Chronic granulomatous disease (CGD) results from a defect in any of the 4 subunits of the NADPH oxidase and is characterized by recurrent life-threatening bacterial and fungal infections and abnormal tissue granuloma formation. Activation of the NADPH oxidase requires translocation of the cytosolic subunits p47phox (phagocyte oxidase), p67phox, and the low molecular weight GT-Pase Rac, to the membrane-bound flavocytochrome, a heterodimer composed of the heavy chain gp91phox and the light chain p22phox. This complex transfers electrons from NADPH on the cytoplasmic side to O2 on the vacuolar or extracellular side, thereby generating superoxide anion. Activation of the NADPH oxidase requires complex rearrangements between the protein subunits, which are in part mediated by noncovalent binding between src-homology 3 domains (SH3 domains) and proline-rich motifs. Outpatient management of CGD patients relies on the use of prophylactic antibiotics and interferon-gamma. When infection is suspected, aggressive effort to obtain culture material is required. Treatment of infections involves prolonged use of systemic antibiotics, surgical debridement when feasible, and, in severe infections, use of granulocyte transfusions. Mouse knockout models of CGD have been created in which to examine aspects of pathophysiology and therapy. Gene therapy and bone marrow transplantation trials in CGD patients are ongoing and show great promise.

Activator protein 1 (AP-1)- and nuclear factor kappaB (NF-kappaB)-dependent transcriptional events in carcinogenesis

Generation of reactive oxygen species (ROS) during metabolic conversion of molecular oxygen imposes a constant threat to aerobic organisms. Other than the cytotoxic effects, many ROS and oxidants are also potent tumor promoters linking oxidative stress to carcinogenesis. Clonal variants of mouse epidermal JB6 cells originally identified for their differential susceptibility to tumor promoters also show differential reduction-oxidation (redox) responses providing a unique model to study oxidative events in tumor promotion. AP-1 and NF-kappaB, inducible by tumor promoters or oxidative stimuli, show differential protein levels or activation in response to tumor promoters in JB6 cells. We further demonstrated that AP-1 and NF-kappaB are both required for maintaining the transformed phenotypes where inhibition of either activity suppresses transformation response in JB6 cells as well as human keratinocytes and transgenic mouse. NF-kappaB proteins or extracellular signal-regulated kinase (ERK) but not AP-1 proteins are shown to be sufficient for conversion from transformation-resistant to transformation-susceptible phenotype. Insofar as oxidative events regulate AP-1 and NF-kappaB transactivation, these oxidative events can be important molecular targets for cancer prevention.

Protein kinase C signaling and oxidative stress

Oxidative stress is involved in the pathogenesis of various degenerative diseases including cancer. It is now recognized that low levels of oxidants can modify cell-signaling proteins and that these modifications have functional consequences. Identifying the target proteins for redox modification is key to understanding how oxidants mediate pathological processes such as tumor promotion. These proteins are also likely to be important targets for chemopreventive antioxidants, which are known to block signaling induced by oxidants and to induce their own actions. Various antioxidant preventive agents also inhibit PKC-dependent cellular responses. Therefore, PKC is a logical candidate for redox modification by oxidants and antioxidants that may in part determine their cancer-promoting and anticancer activities, respectively. PKCs contain unique structural features that are susceptible to oxidative modification. The N-terminal regulatory domain contains zinc-binding, cysteine-rich motifs that are readily oxidized by peroxide. When oxidized, the autoinhibitory function of the regulatory domain is compromised and, consequently, cellular PKC activity is stimulated. The C-terminal catalytic domain contains several reactive cysteines that are targets for various chemopreventive antioxidants such as selenocompounds, polyphenolic agents such as curcumin, and vitamin E analogues. Modification of these cysteines decreases cellular PKC activity. Thus the two domains of PKC respond differently to two different type of agents: oxidants selectively react with the regulatory domain, stimulate cellular PKC, and signal for tumor promotion and cell growth. In contrast, antioxidant chemopreventive agents react with the catalytic domain, inhibit cellular PKC activity, and thus interfere with the action of tumor promoters.

Oxidative stress and gene regulation

Reactive oxygen species are produced by all aerobic cells and are widely believed to play a pivotal role in aging as well as a number of degenerative diseases. The consequences of the generation of oxidants in cells does not appear to be limited to promotion of deleterious effects. Alterations in oxidative metabolism have long been known to occur during differentiation and development. Experimental perturbations in cellular redox state have been shown to exert a strong impact on these processes. The discovery of specific genes and pathways affected by oxidants led to the hypothesis that reactive oxygen species serve as subcellular messengers in gene regulatory and signal transduction pathways. Additionally, antioxidants can activate numerous genes and pathways. The burgeoning growth in the number of pathways shown to be dependent on oxidation or antioxidation has accelerated during the last decade. In the discussion presented here, we provide a tabular summary of many of the redox effects on gene expression and signaling pathways that are currently known to exist.

Free radical mediated photoreceptor damage in uveitis

Uveitis is a major cause of blindness, with the visual loss that occurs being due primarily to retinal tissue damage. The tissue damage is mediated mainly by phagocytic inflammatory cells, such as macrophages, by the release of various proteolytic enzymes, arachidonic acid metabolites, cytokines and free radicals. The latter are found to be potent cytotoxic agents that readily cause tissue damage by peroxidation of lipid cell membranes. Recent studies of experimental uveitis indicate that other potent oxidants are generated in uveitis by macrophages. One of these is ONOO-, which is formed from *NO and O(-)2. The macrophages generate *NO preferentially in the outer retina following iNOS expression. In these phagocytes, outer retinal proteins, especially arrestin, are found to be potent iNOS inducers. Current studies of RPE show that these cells protect the retina from ONOO- mediated damage in uveitis by releasing a novel protein called retinal pigment epithelial protective protein. This protein is found to suppress O(-)2 and *NO generation by the phagocytes, in both in vitro and in vivo uveitis models. The protective protein expression is restricted to RPE, its suppressive effect is a result of the inhibition of the phosphorylation of cytosolic proteins, p47-phox, required for the assembly of NADPH and activation of NFkappaB, which are required for generation of 0(-)2 and expression of iNOS respectively. Either pharmacologically or chemically, up-regulation of RPP generation could help in preventing retinal degeneration in uveitis or other degenerative dis

Mitogen-activated protein kinase Mkp1 of Pneumocystis carinii complements the slt2Delta defect in the cell integrity pathway of Saccharomyces cerevisiae

Signal transduction pathways are important in the adaptive response of microbes to their environment. A Pneumocystis carinii extracellular signal-regulated protein kinase (MAPK) homologue, Mkp1, has been isolated by sequence similarity screening of P. carinii genomic DNA. The Mkp1 of P. carinii shows closest homology to other fungal MAP kinases involved in cell integrity signal transduction cascades, including Slt2p/Mpk1p of Saccharomyces cerevisiae, Mkc1 of Candida albicans and Mps1 of Magnaporthe grisea. Defects of Slt2p in S. cerevisiae result in phenotypes of slow growth, and temperature sensitivity in the absence of an osmostabilizer. Overexpression of mkp1 in a strain with the slt2Delta defect fully restored the normal growth rate, and partially reduced lysis at elevated temperatures. Complementation of the slt2Delta defect by Mkp1 demonstrates that Mkp1 is a functional MAP kinase, and that it may be the MAP kinase component of a similar signal transduction cascade within P. carinii. Furthermore, Mkp1 is activated in vitro upon the exposure of P. carinii to conditions of oxidative stress. The investigation of a MAP kinase signal transduction pathway of P. carinii will result in both a better understanding of the mechanism the organism utilizes to respond to environmental changes, and a system to assay responses to these changes.

Cell stress and MKK6b-mediated p38 MAP kinase activation inhibit tumor necrosis factor-induced IkappaB phosphorylation and NF-kappaB activation

Tumor necrosis factor (TNF) exerts many actions through activation of the transcription factor NF-kappaB. NF-kappaB is sequestered in the cytosol by an inhibitory subunit IkappaB, which is inducibly phosphorylated by an IkappaB kinase complex and subsequently degraded. Sodium salicylate (NaSal) can block NF-kappaB activation by inhibiting IkappaBalpha phosphorylation. Recently, we used the specific p38 mitogen-activated protein (MAP) kinase inhibitor SB203580 to demonstrate that inhibition of TNF-induced IkappaBalpha phosphorylation requires NaSal-induced p38 activation. We demonstrate that NaSal similarly inhibits TNF-induced IkappaBbeta degradation in a p38-dependent manner. To further examine the role of p38, we determined whether other agents that activate p38 can block TNF-induced IkappaB phosphorylation and degradation. Sorbitol, H(2)O(2), and arsenite each blocked IkappaBalpha phosphorylation induced by TNF, and SB203580 reversed the inhibitory effects of sorbitol and H(2)O(2), but not arsenite. In addition, sorbitol and H(2)O(2) blocked TNF-induced but not interleukin-1-induced IkappaBalpha phosphorylation, whereas arsenite inhibited IkappaBalpha phosphorylation induced by TNF and interleukin-1. Transient expression of MAP kinase kinase (MKK) 6b(E), a constitutive activator of p38, reduced both TNF-induced phosphorylation of IkappaBalpha and NF-kappaB-dependent reporter activity. However, MKK7(D), a constitutive activator of c-Jun N-terminal kinases, failed to inhibit these TNF actions. Thus, sustained p38 activation by various stimuli inhibits TNF-induced IkappaB phosphorylation and NF-kappaB activation.

Oxidative stress affects cytoskeletal structure and cell-matrix interactions in cells from an ocular tissue: the trabecular meshwork

The trabecular meshwork (TM) is a specialized eye tissue that regulates the aqueous humor outflow and controls intraocular pressure. Cells in this tissue are essential for maintenance of the outflow system. Disturbance of the TM cell status by insults such as oxidative stress may lead to elevation of the intraocular pressure and development of glaucoma. In the present study, we investigated the effect of oxidative stress on the adhesion of human TM cells to extracellular matrix (ECM) proteins. Treatment with 1 mM of H2O2 for 10 or 30 min did not affect cell viability, whereas the adhesion of TM cells to fibronectin, laminin, and collagen types I and IV was significantly reduced. Phalloidin and immunostaining also revealed reorganization of actin and vimentin structures. The level of integrins alpha5beta1, alphavbeta3, and beta1 was not altered, although the distribution of paxillin and focal adhesion kinase in focal contacts was reduced. Concomitantly, the level of transcription factor NF-kappaB was enhanced by the H2O2 treatment. Nuclear extracts of the treated cells also contained a heightened NF-kappaB binding activity. These changes persisted for up to 6 h after the H2O2 treatment but were partially recovered by 24 h. We concluded that under sublethal oxidative stress conditions, the TM cell adhesion to the ECM was impaired. The short-term loss of cell-matrix adhesiveness may be related to the rearrangement of cytoskeletal structures. Extensive and repeated oxidative stress in vivo may result in reduced TM cell adhesion, leading to cell loss, compromised TM integrity, and pathologic consequences.

NF kappa B activity and target gene expression in the rat brain after one and two exposures to ionizing radiation

The central nervous system injury that can result after radiotherapy has been suggested to involve induced gene expression and cytokine production. We have previously shown that irradiation of primary cultures of rat astrocytes results in the activation of NF kappa B. To determine whether such an effect also occurs in vivo, NF kappa B activity was analyzed in the cerebral cortex of the rat brain after whole body irradiation. After a single dose of 15 Gy, NF kappa B activity was increased by 2 h postirradiation, returning to unirradiated levels by 8 hours. The increase was dose-dependent beginning at 2 Gy and continuing to at least 22.5 Gy. NF kappa B activity in the irradiated cortex was not accompanied by I kappa B alpha degradation. When 7.5 Gy was delivered 24 h before the 15 Gy, the increase in NF kappa B activity after 15 Gy was significantly reduced. These results suggest that an initial exposure to radiation induced a refractory period in the brain during which the susceptibility of NF kappa B to activation by subsequent irradiation was significantly reduced. This period of reduced sensitivity to radiation was also apparent for the induction of the NF kappa B-regulated cytokines IL-1 beta, IL-6, and TNF alpha.