Hydrogen peroxide activates p70(S6k) signaling pathway

Hydrogen peroxide modulates the expression of the target of rapamycin (TOR) and cell division in Arabidopsis thaliana

Hydrogen peroxide (H2O2) is naturally produced by plant cells during normal development and serves as a messenger that regulates cell metabolism. Despite its importance, the relationship between hydrogen peroxide and the target of rapamycin (TOR) pathway, as well as its impact on cell division, has been poorly analyzed. In this study, we explore the interaction of H2O2 with TOR, a serine/threonine protein kinase that plays a central role in controlling cell growth, size, and metabolism in Arabidopsis thaliana. By applying two concentrations of H2O2 exogenously (0.5 and 1 mM), we could correlate developmental traits, such as primary root growth, lateral root formation, and fresh weight, with the expression of the cell cycle gene CYCB1;1, as well as TOR expression. When assessing the expression of the ribosome biogenesis-related gene RPS27B, an increase of 94.34% was noted following exposure to 1 mM H2O2 treatment. This increase was suppressed by the TOR inhibitor torin 2. The elimination of H2O2 accumulation with ascorbic acid (AA) resulted in decreased cell division as well as TOR expression. The potential molecular mechanisms associated with the effects of H2O2 on the cell cycle and TOR expression in roots are discussed in the context of the results.

Redox-Mediated Rewiring of Signalling Pathways: The Role of a Cellular Clock in Brain Health and Disease

Metazoan signalling pathways can be rewired to dampen or amplify the rate of events, such as those that occur in development and aging. Given that a linear network topology restricts the capacity to rewire signalling pathways, such scalability of the pace of biological events suggests the existence of programmable non-linear elements in the underlying signalling pathways. Here, we review the network topology of key signalling pathways with a focus on redox-sensitive proteins, including PTEN and Ras GTPase, that reshape the connectivity profile of signalling pathways in response to an altered redox state. While this network-level impact of redox is achieved by the modulation of individual redox-sensitive proteins, it is the population by these proteins of critical nodes in a network topology of signal transduction pathways that amplifies the impact of redox-mediated reprogramming. We propose that redox-mediated rewiring is essential to regulate the rate of transmission of biological signals, giving rise to a programmable cellular clock that orchestrates the pace of biological phenomena such as development and aging. We further review the evidence that an aberrant redox-mediated modulation of output of the cellular clock contributes to the emergence of pathological conditions affecting the human brain.

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.

NOX4/H2O2/mTORC1 Pathway in Salt-Induced Hypertension and Kidney Injury

We have reported that a high-salt (4.0% NaCl) dietary intake activates mTORC1 and inhibition of this pathway with rapamycin blunts the chronic phase of salt-induced hypertension and renal injury in Dahl salt-sensitive (SS) rats. In SS rats, high-salt intake is known to increase the renal production of H2O2 by NOX4, the most abundant NOX isoform in the kidney, and the global knockout of NOX4 blunts salt-sensitivity in these rats. Here, we explored the hypothesis that elevations of H2O2 by NOX4 in high-salt fed SS rat stimulate mTORC1 for the full development of salt-induced hypertension and renal injury. Our in vitro studies found that H2O2 activates mTORC1 independent of PI3K/AKT and AMPK pathways. To determine the in vivo relevance of NOX4/H2O2/mTORC1 in the salt-induced hypertension, SS-Nox4 knockout (SSNox4-/-) rats were daily administrated with vehicle/rapamycin fed a high-salt diet for 21 days. Rapamycin treatment of SSNox4-/- rats had shown no augmented effect on the salt-induced hypertension nor upon indices of renal injury. Significant reductions of renal T lymphocyte and macrophage together with inhibition of cell proliferation were observed in rapamycin treated rats suggesting a role of mTORC1 independent of NOX4 in the proliferation of immune cell. Given the direct activation of mTORC1 by H2O2 and absence of any further protection from salt-induced hypertension in rapamycin-treated SSNox4-/- rats, we conclude that NOX4-H2O2 is a major upstream activator of mTORC1 that contributes importantly to salt-induced hypertension and renal injury in the SS rat model.

PKG1α Cysteine-42 Redox State Controls mTORC1 Activation in Pathological Cardiac Hypertrophy

RATIONALE

Stimulated PKG1α (protein kinase G-1α) phosphorylates TSC2 (tuberous sclerosis complex 2) at serine 1365, potently suppressing mTORC1 (mechanistic [mammalian] target of rapamycin complex 1) activation by neurohormonal and hemodynamic stress. This reduces pathological hypertrophy and dysfunction and increases autophagy. PKG1α oxidation at cysteine-42 is also induced by these stressors, which blunts its cardioprotective effects.

OBJECTIVE

We tested the dependence of mTORC1 activation on PKG1α C42 oxidation and its capacity to suppress such activation by soluble GC-1 (guanylyl cyclase 1) activation.

METHODS AND RESULTS

Cardiomyocytes expressing wild-type (WT) PKG1α (PKG1α^WT) or cysteine-42 to serine mutation redox-dead (PKG1α^CS/CS) were exposed to ET-1 (endothelin 1). Cells expressing PKG1α^WT exhibited substantial mTORC1 activation (p70 S6K [p70 S6 kinase], 4EBP1 [elF4E binding protein-1], and Ulk1 [Unc-51-like kinase 1] phosphorylation), reduced autophagy/autophagic flux, and abnormal protein aggregation; all were markedly reversed by PKG1α^CS/CS expression. Mice with global knock-in of PKG1α^CS/CS subjected to pressure overload (PO) also displayed markedly reduced mTORC1 activation, protein aggregation, hypertrophy, and ventricular dysfunction versus PO in PKG1α^WT mice. Cardioprotection against PO was equalized between groups by co-treatment with the mTORC1 inhibitor everolimus. TSC2-S1365 phosphorylation increased in PKG1α^CS/CS more than PKG1α^WT myocardium following PO. TSC2^{S1365A/S1365A} (TSC2 S1365 phospho-null, created by a serine to alanine mutation) knock-in mice lack TSC2 phosphorylation by PKG1α, and when genetically crossed with PKG1α^CS/CS mice, protection against PO-induced mTORC1 activation, cardiodepression, and mortality in PKG1α^CS/CS mice was lost. Direct stimulation of GC-1 (BAY-602770) offset disparate mTORC1 activation between PKG1α^WT and PKG1α^CS/CS after PO and blocked ET-1 stimulated mTORC1 in TSC2^S1365A-expressing myocytes.

CONCLUSIONS

Oxidation of PKG1α at C42 reduces its phosphorylation of TSC2, resulting in amplified PO-stimulated mTORC1 activity and associated hypertrophy, dysfunction, and depressed autophagy. This is ameliorated by direct GC-1 stimulation.

Reactive oxygen species participate in liver function recovery during compensatory growth in zebrafish (Danio rerio)

Compensatory growth (CG) is defined as a phase of accelerated growth when the disadvantageous environment is improved, accompanied by metabolic adjustment. Here, we report that hepatic oxidative phosphorylation (OXPHOS) activity was enhanced during compensatory growth in zebrafish. Mitochondrial metabolism enabled the generation of reactive oxygen species (ROS), which activated the nrf2 (nuclear factor-erythroid 2-related factor 2) signaling pathway, as well as the mTOR signaling pathway. Tempol (a superoxide dismutase mimetic) treatment blocked ROS signaling in the liver as well as CG in zebrafish. These results demonstrated that mitochondrial ROS signaling are essential for the occurrence of compensatory growth in zebrafish.

Oxidative stress at low levels can induce clustered DNA lesions leading to NHEJ mediated mutations

DNA damage and mutations induced by oxidative stress are associated with various different human pathologies including cancer. The facts that most human tumors are characterized by large genome rearrangements and glutathione depletion in mice results in deletions in DNA suggest that reactive oxygen species (ROS) may cause gene and chromosome mutations through DNA double strand breaks (DSBs). However, the generation of DSBs at low levels of ROS is still controversial. In the present study, we show that H₂O₂ at biologically-relevant levels causes a marked increase in oxidative clustered DNA lesions (OCDLs) with a significant elevation of replication-independent DSBs. Although it is frequently reported that OCDLs are fingerprint of high-energy IR, our results indicate for the first time that H₂O₂, even at low levels, can also cause OCDLs leading to DSBs specifically in G1 cells. Furthermore, a reverse genetic approach revealed a significant contribution of the non-homologous end joining (NHEJ) pathway in H₂O₂-induced DNA repair & mutagenesis. This genomic instability induced by low levels of ROS may be involved in spontaneous mutagenesis and the etiology of a wide variety of human diseases like chronic inflammation-related disorders, carcinogenesis, neuro-degeneration and aging.

Vacuole-mediated selective regulation of TORC1-Sch9 signaling following oxidative stress

TORC1 modulates proteosynthesis, nitrogen metabolism, stress responses, and autophagy. Here it is shown that the Sch9 branch of TORC1 signaling depends specifically on vacuolar membranes and that this specificity allows the cells to regulate selectively the outputs of divergent downstream pathways in response to oxidative stress.

Target of rapamycin complex 1 (TORC1) is a central cellular signaling coordinator that allows eukaryotic cells to adapt to the environment. In the budding yeast, Saccharomyces cerevisiae, TORC1 senses nitrogen and various stressors and modulates proteosynthesis, nitrogen uptake and metabolism, stress responses, and autophagy. There is some indication that TORC1 may regulate these downstream pathways individually. However, the potential mechanisms for such differential regulation are unknown. Here we show that the serine/threonine protein kinase Sch9 branch of TORC1 signaling depends specifically on the integrity of the vacuolar membrane, and this dependency originates in changes in Sch9 localization reflected by phosphatidylinositol 3,5-bisphosphate. Moreover, oxidative stress induces the delocalization of Sch9 from vacuoles, contributing to the persistent inhibition of the Sch9 branch after stress. Thus, our results establish that regulation of the vacuolar localization of Sch9 serves as a selective switch for the Sch9 branch in divergent TORC1 signaling. We propose that the Sch9 branch integrates the intrinsic activity of TORC1 kinase and vacuolar status, which is monitored by the phospholipids of the vacuolar membrane, into the regulation of macromolecular synthesis.

Inhibition of Mammalian Target of Rapamycin Complex 1 Attenuates Salt-Induced Hypertension and Kidney Injury in Dahl Salt-Sensitive Rats

The goal of the present study was to explore the protective effects of mTORC1 (mammalian target of rapamycin complex 1) inhibition by rapamycin on salt-induced hypertension and kidney injury in Dahl salt-sensitive (SS) rats. We have previously demonstrated that H₂O₂ is elevated in the kidneys of SS rats. The present study showed a significant upregulation of renal mTORC1 activity in the SS rats fed a 4.0% NaCl for 3 days. In addition, renal interstitial infusion of H₂O₂ into salt-resistant Sprague Dawley rats for 3 days was also found to stimulate mTORC1 activity independent of a rise of arterial blood pressure. Together, these data indicate that the salt-induced increases of renal H₂O₂ in SS rats activated the mTORC1 pathway. Daily administration of rapamycin (IP, 1.5 mg/kg per day) for 21 days reduced salt-induced hypertension from 176.0±9.0 to 153.0±12.0 mm Hg in SS rats but had no effect on blood pressure salt sensitivity in Sprague Dawley treated rats. Compared with vehicle, rapamycin reduced albumin excretion rate in SS rats from 190.0±35.0 to 37.0±5.0 mg/d and reduced the renal infiltration of T lymphocytes (CD3⁺) and macrophages (ED1⁺) in the cortex and medulla. Renal hypertrophy and cell proliferation were also reduced in rapamycin-treated SS rats. We conclude that enhancement of intrarenal H₂O₂ with a 4.0% NaCl diet stimulates the mTORC1 pathway that is necessary for the full development of the salt-induced hypertension and kidney injury in the SS rat.

Gingival crevicular fluid and plasma oxidative stress markers and TGM-2 levels in chronic periodontitis

OBJECTIVE

This study was aimed to evaluate the gingival crevicular fluid (GCF) and plasma transglutaminase-2 (TGM-2), total antioxidant capacity (TAC), total oxidant status (TOS), ferric reducing antioxidant power (FRAP) and thiobarbituric acid reactive substances (TBARS) in patients with chronic periodontal disease.

MATERIALS AND METHODS

Twenty patients with chronic periodontitis (CP), 20 patients with gingivitis and 20 healthy subjects were enrolled in the study. Clinical periodontal parameters including probing depth, clinical attachment level, plaque index and papillary bleeding index were recorded. GCF and plasma levels of TGM-2, TAC, TOS, TBARS and FRAP were analyzed.

RESULTS

GCF TGM-2 was significantly lower in CP group than in gingivitis patients (P=0.006). GCF FRAP in CP and gingivitis groups was significantly lower than in healthy subjects (P<0.001). Plasma FRAP level was lower in gingivitis group when compared to healthy subjects (P=0.003). There was no significant difference in GCF and plasma TAC, TOS, TBARS and plasma TGM-2 levels among the study groups (P>0.05). GCF TGM-2 level was positively correlated with GCF TAC and negatively correlated with CAL.

CONCLUSIONS

Decreased FRAP in GCF and plasma indicating lower antioxidant status of CP patients might suggest the role of oxidative stress in periodontitis. GCF TGM-2 data might suggest that TGM2 is associated with stabilization of the extracellular matrix and wound healing in periodontium rather than gingival inflammation.

The role of oxidative stress on breast cancer development and therapy

Reactive oxygen species (ROS) are produced by both enzymatic and non-enzymatic systems within eukaryotic cells and play important roles in cellular physiology and pathophysiology. Although physiological concentrations are crucial for ensuring cell survival, ROS overproduction is detrimental to cells, and considered key-factors for the development of several diseases, such as neurodegenerative diseases, cardiovascular disorders, and cancer. Cancer cells are usually submitted to higher ROS levels that further stimulate malignant phenotype through stimulus to sustained proliferation, death evasion, angiogenesis, invasiveness, and metastasis. The role of ROS on breast cancer etiology and progression is being progressively elucidated. However, less attention has been given to the development of redox system-targeted strategies for breast cancer therapy. In this review, we address the basic mechanisms of ROS production and scavenging in breast tumor cells, and the emerging possibilities of breast cancer therapies targeting ROS homeostasis.

Primary chicken embryo fibroblasts seeded acellular dermal matrix (3-D ADM) improve regeneration of full thickness skin wounds in rats

Rat skins were deepithelialized and decellularized by hypertonic saline and sodium deoxycholate (SDC), respectively. Primary chicken embryo fibroblasts (P-CEF) were cultured and seeded on prepared acellular dermal matrix (ADM). A full thickness skin defect (20×20 mm(2)) was created in thirty-six rats and randomly divided into three equal groups. Defect was left open, repaired with ADM and ADM seeded with P-CEF (3-D ADM) in groups 1, 2 and 3, respectively. By day 28, the treated wounds healed completely without scar. By day 7 hydroxyproline contents was higher in group 3 as compared to groups 1 and 2. There was slightly more B cell response in animals implanted with ADM and 3-D ADM. At day 21, stimulation index was lower with acellular dermis antigen as compared to 3-D ADM antigen. In group 1 on day 3, the granulation tissue showed more inflammatory reaction, fibroplasia and neovascularization as compared to group 2 and 3. By day 28, there was complete epithelization was observed in all groups over. However, a large scar was observed in group 1. The graft was completely absorbed and replaced with densely thick and best arranged collagen fibers. On day 7, malonyldialdehyde and superoxide dismutase levels were significantly (P<0.05) increased in group 1. Reduced glutathione values increased and reached to near normal in groups 2 and 3. Catalase values were significantly (P<0.05) higher in group 1 at different time intervals. SEM samples of group 2 showed ingrowth of fibroblasts into acellular matrix at host graft junction. However, in group 3 fibroblasts were infiltrated within the pores of graft. It was concluded that P-CEF cells seeded ADM facilitated early and better healing.

Molecular mechanisms of mTOR regulation by stress

Tumors are prime examples of cell growth in unfavorable environments that elicit cellular stress. The high metabolic demand and insufficient vascularization of tumors cause a deficiency of oxygen and nutrients. Oncogenic mutations map to signaling events via mammalian target of rapamycin (mTOR), metabolic pathways, and mitochondrial function. These alterations have been linked with cellular stresses, in particular endoplasmic reticulum (ER) stress, hypoxia, and oxidative stress. Yet tumors survive these challenges and acquire highly energy-demanding traits, such as overgrowth and invasiveness. In this review we focus on stresses that occur in cancer cells and discuss them in the context of mTOR signaling. Of note, many tumor traits require mTOR complex 1 (mTORC1) activity, but mTORC1 hyperactivation eventually sensitizes cells to apoptosis. Thus, mTORC1 activity needs to be balanced in cancer cells. We provide an overview of the mechanisms contributing to mTOR regulation by stress and suggest a model wherein stress granules function as guardians of mTORC1 signaling, allowing cancer cells to escape stress-induced cell death.

Reversing translational suppression and induction of toxicity in pancreatic cancer cells using a chemoprevention gene therapy approach

Pancreatic cancer is an aggressive disease with limited therapeutic options. Melanoma differentiation-associated gene-7/interleukin-24 (mda-7/IL-24), a potent antitumor cytokine, shows cancer-specific toxicity in a vast array of human cancers, inducing endoplasmic reticulum stress and apoptosis, toxic autophagy, an antitumor immune response, an antiangiogenic effect, and a significant "bystander" anticancer effect that leads to enhanced production of this cytokine through autocrine and paracrine loops. Unfortunately, mda-7/IL-24 application in pancreatic cancer has been restricted because of a "translational block" occurring after Ad.5-mda-7 gene delivery. Our previous research focused on developing approaches to overcome this block and increase the translation of the MDA-7/IL-24 protein, thereby promoting its subsequent toxic effects in pancreatic cancer cells. We demonstrated that inducing reactive oxygen species (ROS) after adenoviral infection of mda-7/IL-24 leads to greater translation into MDA-7/IL-24 protein and results in toxicity in pancreatic cancer cells. In this study we demonstrate that a novel chimeric serotype adenovirus, Ad.5/3-mda-7, displays greater efficacy in delivering mda-7/IL-24 compared with Ad.5-mda-7, although overall translation of the protein still remains low. We additionally show that d-limonene, a dietary monoterpene known to induce ROS, is capable of overcoming the translational block when used in combination with adenoviral gene delivery. This novel combination results in increased polysome association of mda-7/IL-24 mRNA, activation of the preinitiation complex of the translational machinery in pancreatic cancer cells, and culminates in mda-7/IL-24-mediated toxicity.

Inhibition of mTORC1 by astrin and stress granules prevents apoptosis in cancer cells

Mammalian target of rapamycin complex 1 (mTORC1) controls growth and survival in response to metabolic cues. Oxidative stress affects mTORC1 via inhibitory and stimulatory inputs. Whereas downregulation of TSC1-TSC2 activates mTORC1 upon oxidative stress, the molecular mechanism of mTORC1 inhibition remains unknown. Here, we identify astrin as an essential negative mTORC1 regulator in the cellular stress response. Upon stress, astrin inhibits mTORC1 association and recruits the mTORC1 component raptor to stress granules (SGs), thereby preventing mTORC1-hyperactivation-induced apoptosis. In turn, balanced mTORC1 activity enables expression of stress factors. By identifying astrin as a direct molecular link between mTORC1, SG assembly, and the stress response, we establish a unifying model of mTORC1 inhibition and activation upon stress. Importantly, we show that in cancer cells, apoptosis suppression during stress depends on astrin. Being frequently upregulated in tumors, astrin is a potential clinically relevant target to sensitize tumors to apoptosis.

Destabilization of TNF-α mRNA by Rapamycin

Stimulation of mast cells through the high affinity IgE receptor (FcεRI) induces degranulation, lipid mediator release, and cytokine secretion leading to allergic reactions. Although various signaling pathways have been characterized to be involved in the FcεRI-mediated responses, little is known about the precious mechanism for the expression of tumor necrosis factor-α (TNF-α) in mast cells. Here, we report that rapamycin, a specific inhibitor of mammalian target of rapamycin (mTOR), reduces the expression of TNF-α in rat basophilic leukemia (RBL-2H3) cells. IgE or specific antigen stimulation of RBL-2H3 cells increases the expression of TNF-α and activates various signaling molecules including S6K1, Akt and p38 MAPK. Rapamycin specifically inhibits antigen-induced TNF-α mRNA level, while other kinase inhibitors have no effect on TNF-α mRNA level. These data indicate that mTOR signaling pathway is the main regulation mechanism for antigen-induced TNF-α expression. TNF-α mRNA stability analysis using reporter construct containing TNF-α adenylate/uridylate-rich elements (AREs) shows that rapamycin destabilizes TNF-α mRNA via regulating the AU-rich element of TNF-α mRNA. The antigen-induced activation of S6K1 is inhibited by specific kinase inhibitors including mTOR, PI3K, PKC and Ca²⁺chelator inhibitor, while TNF-α mRNA level is reduced only by rapamycin treatment. These data suggest that the effects of rapamycin on the expression of TNF-α mRNA are not mediated by S6K1 but regulated by mTOR. Taken together, our results reveal that mTOR signaling pathway is a novel regulation mechanism for antigen-induced TNF-α expression in RBL-2H3 cells.

A biodegradable hydrogel system containing curcumin encapsulated in micelles for cutaneous wound healing

A biodegradable in situ gel-forming controlled drug delivery system composed of curcumin loaded micelles and thermosensitive hydrogel was prepared and applied for cutaneous wound repair. Curcumin is believed to be a potent antioxidant and anti-inflammatory agent. Due to its high hydrophobicity, curcumin was encapsulated in polymeric micelles (Cur-M) with high drug loading and encapsulation efficiency. Cur-M loaded thermosensitive hydrogel (Cur-M-H) was prepared and applied as wound dressing to enhance the cutaneous wound healing. Cur-M-H was a free-flowing sol at ambient temperature and instantly converted into a non-flowing gel at body temperature. In vitro studies suggested that Cur-M-H exhibited well tissue adhesiveness and could release curcumin in an extended period. Furthermore, linear incision and full-thickness excision wound models were employed to evaluate the in vivo wound healing activity of Cur-M-H. In incision model, Cur-M-H-treated group showed higher tensile strength and thicker epidermis. In excision model, Cur-M-H group exhibited enhancement of wound closure. Besides, in both models, Cur-M-H-treated groups showed higher collagen content, better granulation, higher wound maturity, dramatic decrease in superoxide dismutase, and slight increase in catalase. Histopathologic examination also implied that Cur-M-H could enhance cutaneous wound repair. In conclusion, biodegradable Cur-M-H composite might have great application for wound healing.

MAP17 and SGLT1 protein expression levels as prognostic markers for cervical tumor patient survival

MAP17 is a membrane-associated protein that is overexpressed in human tumors. Because the expression of MAP17 increases reactive oxygen species (ROS) generation through SGLT1 in cancer cells, in the present work, we investigated whether MAP17 and/or SGLT1 might be markers for the activity of treatments involving oxidative stress, such as cisplatin or radiotherapy. First, we confirmed transcriptional alterations in genes involved in the oxidative stress induced by MAP17 expression in HeLa cervical tumor cells and found that Hela cells expressing MAP17 were more sensitive to therapies that induce ROS than were parental cells. Furthermore, MAP17 increased glucose uptake through SGLT receptors. We then analyzed MAP17 and SGLT1 expression levels in cervical tumors treated with cisplatin plus radiotherapy and correlated the expression levels with patient survival. MAP17 and SGLT1 were expressed in approximately 70% and 50% of cervical tumors of different types, respectively, but they were not expressed in adenoma tumors. Furthermore, there was a significant correlation between MAP17 and SGLT1 expression levels. High levels of either MAP17 or SGLT1 correlated with improved patient survival after treatment. However, the patients with high levels of both MAP17 and SGLT1 survived through the end of this study. Therefore, the combination of high MAP17 and SGLT1 levels is a marker for good prognosis in patients with cervical tumors after cisplatin plus radiotherapy treatment. These results also suggest that the use of MAP17 and SGLT1 markers may identify patients who are likely to exhibit a better response to treatments that boost oxidative stress in other cancer types.

MAP17, a ROS-dependent oncogene

MAP17 is a small 17 kDa non-glycosylated membrane protein previously identified as being overexpressed in carcinomas. Breast tumor cells that overexpress MAP17 show an increased tumoral phenotype with enhanced proliferative capabilities both in the presence or the absence of contact inhibition, decreased apoptotic sensitivity, and increased migration. MAP17-expressing clones also grow better in nude mice. The increased malignant cell behavior induced by MAP17 is associated with an increase in reactive oxygen species (ROS) production, and the treatment of MAP17-expressing cells with antioxidants results in a reduction in the tumorigenic properties of these cells. The MAP17-dependent increase in ROS and tumorigenesis relies on its PDZ-binding domain because disruption of this sequence by point mutations abolishes the ability of MAP17 to enhance ROS production and tumorigenesis. MAP17 is overexpressed in a great variety of human carcinomas, including breast tumors. Immunohistochemical analysis of MAP17 during cancer progression demonstrates that overexpression of the protein strongly correlates with tumoral progression. Generalized MAP17 overexpression in human carcinomas indicates that MAP17 can be a good marker for tumorigenesis and, especially, for malignant progression.

ROS in aging Caenorhabditis elegans: damage or signaling?

Many insights into the mechanisms and signaling pathways underlying aging have resulted from research on the nematode Caenorhabditis elegans. In this paper, we discuss the recent findings that emerged using this model organism concerning the role of reactive oxygen species (ROS) in the aging process. The accrual of oxidative stress and damage has been the predominant mechanistic explanation for the process of aging for many years, but reviewing the recent studies in C. elegans calls this theory into question. Thus, it becomes more and more evident that ROS are not merely toxic byproducts of the oxidative metabolism. Rather it seems more likely that tightly controlled concentrations of ROS and fluctuations in redox potential are important mediators of signaling processes. We therefore discuss some theories that explain how redox signaling may be involved in aging and provide some examples of ROS functions and signaling in C. elegans metabolism. To understand the role of ROS and the redox status in physiology, stress response, development, and aging, there is a rising need for accurate and reversible in vivo detection. Therefore, we comment on some methods of ROS and redox detection with emphasis on the implementation of genetically encoded biosensors in C. elegans.

Drosophila larvae lacking the bcl-2 gene, buffy, are sensitive to nutrient stress, maintain increased basal target of rapamycin (Tor) signaling and exhibit characteristics of altered basal energy metabolism

Background

B cell lymphoma 2 (Bcl-2) proteins are the central regulators of apoptosis. The two bcl-2 genes in Drosophila modulate the response to stress-induced cell death, but not developmental cell death. Because null mutants are viable, Drosophila provides an optimum model system to investigate alternate functions of Bcl-2 proteins. In this report, we explore the role of one bcl-2 gene in nutrient stress responses.

Results

We report that starvation of Drosophila larvae lacking the bcl-2 gene, buffy, decreases survival rate by more than twofold relative to wild-type larvae. The buffy null mutant reacted to starvation with the expected responses such as inhibition of target of rapamycin (Tor) signaling, autophagy initiation and mobilization of stored lipids. However, the autophagic response to starvation initiated faster in larvae lacking buffy and was inhibited by ectopic buffy. We demonstrate that unusually high basal Tor signaling, indicated by more phosphorylated S6K, was detected in the buffy mutant and that removal of a genomic copy of S6K, but not inactivation of Tor by rapamycin, reverted the precocious autophagy phenotype. Instead, Tor inactivation also required loss of a positive nutrient signal to trigger autophagy and loss of both was sufficient to activate autophagy in the buffy mutant even in the presence of enforced phosphoinositide 3-kinase (PI3K) signaling. Prior to starvation, the fed buffy mutant stored less lipid and glycogen, had high lactate levels and maintained a reduced pool of cellular ATP. These observations, together with the inability of buffy mutant larvae to adapt to nutrient restriction, indicate altered energy metabolism in the absence of buffy.

Conclusions

All animals in their natural habitats are faced with periods of reduced nutrient availability. This study demonstrates that buffy is required for adaptation to both starvation and nutrient restriction. Thus, Buffy is a Bcl-2 protein that plays an important non-apoptotic role to promote survival of the whole organism in a stressful situation.

MAP17 and the double-edged sword of ROS

Reactive oxygen species, ROS, are beneficially involved in many signaling pathways that control development and maintain cellular homeostasis. In physiological conditions, a tightly regulated redox balance protects cells from injurious ROS activity, but if the balance is altered, it promotes various pathological conditions including cancer. Understanding the duality of ROS as cytotoxic molecules and key mediators in signaling cascades may provide novel opportunities for improved cancer therapy. MAP17 is a small 17-kDa non-glycosylated membrane protein that is overexpressed in many tumors of different origins, including carcinomas. Immunohistochemical analysis of MAP17 during cancer progression demonstrates that overexpression of the protein strongly correlates with the progression of most types of tumor. Tumor cells that overexpress MAP17 show an increased tumoral phenotype associated with an increase in ROS. However, in non-tumor cells MAP17 increases ROS, resulting in senescence or apoptosis. Therefore, in tumor cells, MAP17 could be a marker for increased oxidative stress and could define new therapeutic approaches. Here, we review the role of MAP17 as a putative oncogene, as well as its role in cancer and anticancer therapies.

Arsenite induces cell transformation by reactive oxygen species, AKT, ERK1/2, and p70S6K1

Arsenic is naturally occurring element that exists in both organic and inorganic formulations. The inorganic form arsenite has a positive association with development of multiple cancer types. There are significant populations throughout the world with high exposure to arsenite via drinking water. Thus, human exposure to arsenic has become a significant public health problem. Recent evidence suggests that reactive oxygen species (ROS) mediate multiple changes to cell behavior after acute arsenic exposure, including activation of proliferative signaling and angiogenesis. However, the role of ROS in mediating cell transformation by chronic arsenic exposure is unknown. We found that cells chronically exposed to sodium arsenite increased proliferation and gained anchorage-independent growth. This cell transformation phenotype required constitutive activation of AKT, ERK1/2, mTOR, and p70S6K1. We also observed these cells constitutively produce ROS, which was required for the constitutive activation of AKT, ERK1/2, mTOR, and p70S6K1. Suppression of ROS levels by forced expression of catalase also reduced cell proliferation and anchorage-independent growth. These results indicate cell transformation induced by chronic arsenic exposure is mediated by increased cellular levels of ROS, which mediates activation of AKT, ERK1/2, and p70S6K1.

Extracellular ultrathin fibers sensitive to intracellular reactive oxygen species: formation of intercellular membrane bridges

Membrane bridges are key cellular structures involved in intercellular communication; however, dynamics for their formation are not well understood. We demonstrated the formation and regulation of novel extracellular ultrathin fibers in NIH3T3 cells using confocal and atomic force microscopy. At adjacent regions of neighboring cells, phorbol 12-myristate 13-acetate (PMA) and glucose oxidase induced ultrathin fiber formation, which was prevented by Trolox, a reactive oxygen species (ROS) scavenger. The height of ROS-sensitive ultrathin fibers ranged from 2 to 4 nm. PMA-induced formation of ultrathin fibers was inhibited by cytochalasin D, but not by Taxol or colchicine, indicating that ultrathin fibers mainly comprise microfilaments. PMA-induced ultrathin fibers underwent dynamic structural changes, resulting in formation of intercellular membrane bridges. Thus, these fibers are formed by a mechanism(s) involving ROS and involved in formation of intercellular membrane bridges. Furthermore, ultrastructural imaging of ultrathin fibers may contribute to understanding the diverse mechanisms of cell-to-cell communication and the intercellular transfer of biomolecules, including proteins and cell organelles.

Rapamycin inhibits hydrogen peroxide-induced loss of vascular contractility

Rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR) pathway, has been shown to extend the life span of mice, and oxidative stress plays critical roles in vascular aging involving loss of compliance of arteries. We examined, therefore, whether rapamycin has protective effects on the inhibition of vascular contractility by hydrogen peroxide (H₂O₂). Prolonged (3 h) exposure to H₂O₂ induced complete loss of contraction of mouse aortic rings and mesenteric (resistance) arteries to either KCl or phenylephrine, which was attenuated by pretreatment with rapamycin. H₂O₂-induced loss of contractility was unaffected by treatment with actinomycin D or cycloheximide, inhibitors of gene transcription and protein synthesis, respectively. Western blot analysis showed that there was no increase in phosphorylation of S6 kinase 1 (S6K) or factor 4E binding protein 1 (4EBP1) in response to H₂O₂ treatment, suggesting involvement of the mTOR complex-2 (mTORC2) rather than mTORC1. H₂O₂ treatment inhibited phosphorylation of the 20-kDa regulatory light chains of myosin (LC₂₀), which was partially blocked by rapamycin treatment. Interestingly, the calcineurin inhibitors cyclosporine A and FK506 were found to mimic the rapamycin effect, and rapamycin inhibited calcineurin activation induced by H₂O₂. We conclude that rapamycin inhibits H₂O₂-induced loss of vascular contractility, likely through an mTORC2-calcineurin pathway.

mTORC1 links protein quality and quantity control by sensing chaperone availability

Balanced protein synthesis and degradation are crucial for proper cellular function. Protein synthesis is tightly coupled to energy status and nutrient levels by the mammalian target of rapamycin complex 1 (mTORC1). Quality of newly synthesized polypeptides is maintained by the molecular chaperone and ubiquitin-proteasome systems. Little is known about how cells integrate information about the quantity and quality of translational products simultaneously. We demonstrate that cells distinguish moderate reductions in protein quality from severe protein misfolding using molecular chaperones to differentially regulate mTORC1 signaling. Moderate reduction of chaperone availability enhances mTORC1 signaling, whereas stress-induced complete depletion of chaperoning capacity suppresses mTORC1 signaling. Molecular chaperones regulate mTORC1 assembly in coordination with nutrient availability. This mechanism enables mTORC1 to rapidly detect and respond to environmental cues while also sensing intracellular protein misfolding. The tight linkage between protein quality and quantity control provides a plausible mechanism coupling protein misfolding with metabolic dyshomeostasis.

Hydrogen peroxide inhibits mTOR signaling by activation of AMPKalpha leading to apoptosis of neuronal cells

Oxidative stress results in apoptosis of neuronal cells, leading to neurodegenerative disorders. However, the underlying molecular mechanism remains to be elucidated. Here, we show that hydrogen peroxide (H(2)O(2)), a major oxidant generated when oxidative stress occurs, induced apoptosis of neuronal cells (PC12 cells and primary murine neurons), by inhibiting the mammalian target of rapamycin (mTOR)-mediated phosphorylation of ribosomal p70 S6 kinase (S6K1) and eukaryotic initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1). N-acetyl-L-cysteine (NAC), a scavenger of reactive oxygen species (ROS), blocked H(2)O(2) inhibition of mTOR signaling. Ectopic expression of wild-type (wt) mTOR, constitutively active S6K1 or downregulation of 4E-BP1 partially prevented H(2)O(2) induction of apoptosis. Furthermore, we identified that H(2)O(2) induction of ROS inhibited the upstream kinases, Akt and phosphoinositide-dependent kinase 1 (PDK1), but not the type I insulin-like growth factor receptor (IGFR), and activated the negative regulator, AMP-activated protein kinase alpha (AMPKalpha), but not the phosphatase and tensin homolog (PTEN) in the cells. Expression of a dominant negative AMPKalpha or downregulation of AMPKalpha1 conferred partial resistance to H(2)O(2) inhibition of phosphorylation of S6K1 and 4E-BP1, as well as cell viability, indicating that H(2)O(2) inhibition of mTOR signaling is at least in part through activation of AMPK. Our findings suggest that AMPK inhibitors may be exploited for prevention of H(2)O(2)-induced neurodegenerative diseases.

Reactive oxygen species-dependent signaling regulates cancer

Historically, it has been assumed that oxidative stress contributes to tumor initiation and progression solely by inducing genomic instability. Recent studies indicate that reactive oxygen species are upregulated in tumors and can lead to aberrant induction of signaling networks that cause tumorigenesis and metastasis. Here we review the role of redox-dependent signaling pathways and transcription factors that regulate tumorigenesis.

CaMKII knockdown attenuates H2O2-induced phosphorylation of ERK1/2, PKB/Akt, and IGF-1R in vascular smooth muscle cells

We have shown earlier a requirement for Ca(2+) and calmodulin (CaM) in the H(2)O(2)-induced activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and protein kinase B (PKB), key mediators of growth-promoting, proliferative, and hypertrophic responses in vascular smooth muscle cells (VSMC). Because the effect of CaM is mediated through CaM-dependent protein kinase II (CaMKII), we have investigated here the potential role of CaMKII in H(2)O(2)-induced ERK1/2 and PKB phosphorylation by using pharmacological inhibitors of CaM and CaMKII, a CaMKII inhibitor peptide, and siRNA knockdown strategies for CaMKII alpha. Calmidazolium and W-7, antagonists of CaM, as well as KN-93, a specific inhibitor of CaMKII, attenuated H(2)O(2)-induced responses of ERK1/2 and PKB phosphorylation in a dose-dependent fashion. Similar to H(2)O(2), calmidazolium and KN-93 also exhibited an inhibitory effect on glucose/glucose oxidase-induced phosphorylation of ERK1/2 and PKB in these cells. Transfection of VSMC with CaMKII autoinhibitory peptide corresponding to the autoinhibitory domain (aa 281-309) of CaMKII and with siRNA of CaMKII alpha attenuated the H(2)O(2)-induced phosphorylation of ERK1/2 and PKB. In addition, calmidazolium and KN-93 blocked H(2)O(2)-induced Pyk2 and insulin-like growth factor-1 receptor (IGF-1R) phosphorylation. Moreover, treatment of VSMC with CaMKII alpha siRNA abolished the H(2)O(2)-induced IGF-1R phosphorylation. H(2)O(2) treatment also induced Thr(286) phosphorylation of CaMKII, which was inhibited by both calmidazolium and KN-93. These results demonstrate that CaMKII plays a critical upstream role in mediating the effects of H(2)O(2) on ERK1/2, PKB, and IGF-1R phosphorylation.

mTOR's role in ageing: protein synthesis or autophagy?

The molecular and cellular mechanisms that regulate ageing are currently under scrutiny because ageing is linked to many human diseases. The nutrient sensing TOR pathway is emerging as a key regulator of ageing. TOR signaling is complex affecting several crucial cellular functions and two such functions, which show clear effects on ageing, are protein synthesis and autophagy. In this article we discuss the relative importance of both these processes in ageing, identify how TOR regulates translation and autophagy and speculate on links between the TOR signaling network and ageing pathways.

Wound healing, anti-microbial and antioxidant potential of Dendrophthoe falcata (L.f) Ettingsh

Dendrophthoe falcata (L.f) Ettingsh (Loranthaceae) of the order Santalales, is used ethnomedicinally for treating ulcers, asthma, impotence, paralysis, skin diseases, and wounds. In this context, validations of the ethnotherapeutic claims of the plant in wound healing activity was studied, besides anti-microbial activity and antioxidant activity were performed to understand the mechanism of wound healing potency. The ethanolic extract of aerial parts of Dendrophthoe falcata ethanolic extract (DFEE) was investigated for the evaluation of its healing efficiency on excision and incision wound models in rats. The results showed that Dendrophthoe falcata extract has potent wound healing capacity as evident from the wound contraction and increased tensile strength. Hydroxyproline and hexosamine expressions were also well correlative with the healing pattern observed. Three of the fractions A-C (petroleum ether, chloroform and ethanol, respectively) obtained from the extract exhibited significant antimicrobial activity against the organisms: Staphylococcus aureus, Staphylococcus pyogenes, Staphylococcus epidermidis, Micrococcus luteus, Bacillus subtilis, Bacillus cereus, Klebsiella pneumoniae, Enterobacter aerogenes, Pseudomonas aeroginosa, Serratia marcescens, and five fungi Candida albicans, Candida tropicalis: dimorphic fungi, Aspergillus fumigatus, Aspergillus niger: systemic fungi, and some infectious bacteria Escherichia coli, and Salmonella typhi. The results also indicated that DFEE possesses potent antioxidant activity by inhibiting lipid peroxidation, reduced glutathione, superoxide dismutase levels and increased the catalase activity.

The nitration of platelet vasodilator stimulated phosphoprotein following exposure to low concentrations of hydrogen peroxide

Hydrogen peroxide (H2O2) at biologically relevant concentrations acts as a signaling molecule. We have shown previously that H2O2 acts synergistically with nitric oxide (NO) to inhibit platelet aggregation. We found that this synergism may be associated with the increased serine phosphorylation of vasodilator-sensitive phosphoprotein (VASP) by H2O2. In this study we demonstrate that H2O2 in the absence of NO or exogenous haem- containing proteins induces nitration of plateletVASP and other unidentified proteins by a mechanism that may involve the formation of peroxynitrite. The nitration was NO-dependent, but independent of oxidative stress and guanylyl cyclcase. The flavanoid epigallocatechin gallate (ECGC) completely suppressed nitration and was also shown to inhibit partially platelet activation by other agonists. Importantly, protein nitration was reversible, or at least the nitrated tyrosine residues are converted to a form not recognized by anti-nitrotyrosine antibodies. The loss of nitrated VASP was still evident in the presence of membrane permeable protease inhibitors. In conclusion, as H2O2 can inhibit platelet function, the nitration of VASP, a protein critical for actin cytoskeletal rearrangement, may represent a novel mechanism important in the regulation of platelets shape change leading to inhibition of platelets aggregation and the formation of blood clot.

Program-like aging and mitochondria: instead of random damage by free radicals

As recently suggested, the target of rapamycin (TOR) pathway, rather than molecular damage by free radicals, drives aging and diseases of aging. But may mitochondria nevertheless contribute to aging? Here, I discuss aimless program-like aging (versus altruistic program), conflict between the cell and mitochondria, cell murder (versus cell suicide) and the role of mitochondria in aging. In particular, life-long selection among mitochondria may yield "selfish" (malignant) mitochondria resistant to autophagy. And TOR may create an intra-cellular environment that is permissive for such selfish mitochondria. In theory, pharmacologic inhibitors of the TOR pathway may reverse accumulation of defective mitochondria, while also inhibiting the aging process.

Oxidative stress and anti-oxidative mobilization in burn injury

A severe burn is associated with release of inflammatory mediators which ultimately cause local and distant pathophysiological effects. Mediators including Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS) are increased in affected tissue, which are implicated in pathophysiological events observed in burn patients. The purpose of this article is to understand the role of oxidative stress in burns, in order to develop therapeutic strategies. All peer-reviewed, original and review articles published in the English language literature relevant to the topic of oxidative stress in burns in animals and human subjects were selected for this review and the possible roles of ROS and RNS in the pathophysiology of burns are discussed. Both increased xanthine oxidase and neutrophil activation appear to be the oxidant sources in burns. Free radicals have been found to have beneficial effects on antimicrobial action and wound healing. However following a burn, there is an enormous production of ROS which is harmful and implicated in inflammation, systemic inflammatory response syndrome, immunosuppression, infection and sepsis, tissue damage and multiple organ failure. Thus clinical response to burn is dependent on the balance between production of free radicals and its detoxification. Supplementation of antioxidants in human and animal models has proven benefit in decreasing distant organ failure suggesting a cause and effect relationship. We conclude that oxidative damage is one of the mechanisms responsible for the local and distant pathophysiological events observed after burn, and therefore anti-oxidant therapy might be beneficial in minimizing injury in burned patients.

MAPK and mTOR pathways are involved in cadmium-induced neuronal apoptosis

Cadmium (Cd) may be accumulated in human body through long-term exposure to Cd-polluted environment, resulting in neurodegeneration and other diseases. To study the mechanism of Cd-induced neurodegeneration, PC12 and SH-SY5Y cells were exposed to Cd. We observed that Cd-induced apoptosis in the cells in a time- and concentration-dependent manner. Cd rapidly activated the mitogen-activated protein kinases (MAPK) including extracellular signal-regulated kinase 1/2 (Erk1/2), c-Jun N-terminal kinase (JNK) and p38. Inhibition of Erk1/2 and JNK, but not p38, partially protected the cells from Cd-induced apoptosis. Consistently, over-expression of dominant negative c-Jun or down-regulation of Erk1/2, but not p38 MAPK, partially prevented Cd-induced apoptosis. To our surprise, Cd also activated mammalian target of rapamycin (mTOR)-mediated signaling pathways. Treatment with rapamycin, an mTOR inhibitor, blocked Cd-induced phosphorylation of S6K1 and eukaryotic initiation factor 4E binding protein 1, and markedly inhibited Cd-induced apoptosis. Down-regulation of mTOR by RNA interference also in part, rescued cells from Cd-induced death. These findings indicate that activation of the signaling network of MAPK and mTOR is associated with Cd-induced neuronal apoptosis. Our results strongly suggest that inhibitors of MAPK and mTOR may have a potential for prevention of Cd-induced neurodegeneration.

Mitochondrial nitric oxide in the signaling of cell integrated responses

Mitochondria are the specialized organelles for energy metabolism, but, as a typical example of system biology, they also activate a multiplicity of pathways that modulate cell proliferation and mitochondrial biogenesis or oppositely promote cell arrest and programmed cell death by a limited number of oxidative or nitrosative reactions. These reactions are influenced by matrix nitric oxide (NO) steady-state concentration, either from local production or by gas diffusion to mitochondria from the canonical sources. Likewise, in a range of ∼30–200 nM, NO turns mitochondrial O2utilization down by binding to cytochrome oxidase and elicits a burst of superoxide anion and hydrogen peroxide that diffuses outside mitochondria. Depending on NO levels and antioxidant defenses, more or less H2O2accumulates in cytosol and nucleus, and the resulting redox grading contributes to dual activation of proliferating and proapoptotic cascades, like ERK1/2 or p38 MAPK. Moreover, these sequential activating pathways participate in rat liver and brain development and in thyroid modulation of mitochondrial metabolism and contribute to hypothyroid phenotype through complex I nitration. On the contrary, lack of NO disrupts pathways like S-nitrosylation or H2O2production and likewise is a gateway to disease in amyotrophic lateral sclerosis with superoxide dismutase 1 mutations or to cancer proliferation.