Activation of the calcium/calmodulin-dependent protein kinases as a consequence of oxidative stress

Therapeutic resistance in breast cancer cells can result from deregulated EGFR signaling

The epidermal growth factor receptor (EGFR) interacts with various downstream molecules including phospholipase C (PLC)/protein kinase C (PKC), Ras/Raf/MEK/ERK, PI3K/PTEN/Akt/GSK-3, Jak/STAT and others. Often these pathways are deregulated in human malignancies such as breast cancer. Various therapeutic approaches to inhibit the activity of EGFR family members including small molecule inhibitors and monoclonal antibodies (MoAb) have been developed. A common problem with cancer treatments is the development of drug-resistance. We examined the effects of a conditionally-activated EGFR (v-Erb-B:ER) on the resistance of breast cancer cells to commonly used chemotherapeutic drugs such as doxorubicin, daunorubicin, paclitaxel, cisplatin and 5-flurouracil as well as ionizing radiation (IR). v-Erb-B is similar to the EGFR-variant EGFRvIII, which is expressed in various cancers including breast, brain, prostate. Both v-Erb-B and EGFRvIII encode the EGFR kinase domain but lack key components present in the extracellular domain of EGFR which normally regulate its activity and ligand-dependence. The v-Erb-B oncogene was ligated to the hormone binding domain of the estrogen receptor (ER) which results in regulation of the activity of the v-Erb-ER construct by addition of either estrogen (E2) or 4-hydroxytamoxifen (4HT) to the culture media. Introduction of the v-Erb-B:ER construct into the MCF-7 breast cancer cell line increased the resistance to the cells to various chemotherapeutic drugs, hormonal-based therapeutics and IR. These results point to the important effects that aberrant expression of EGFR kinase domain can have on therapeutic resistance.

Oxidative Stress Orchestrates MAPK and Nitric-Oxide Synthase Signal

Reactive oxygen species (ROS) are not only harmful to cell survival but also essential to cell signaling through cysteine-based redox switches. In fact, ROS triggers the potential activation of mitogen-activated protein kinases (MAPKs). The 90 kDa ribosomal S6 kinase 1 (RSK1), one of the downstream mediators of the MAPK pathway, is implicated in various cellular processes through phosphorylating different substrates. As such, RSK1 associates with and phosphorylates neuronal nitric oxide (NO) synthase (nNOS) at Ser847, leading to a decrease in NO generation. In addition, the RSK1 activity is sensitive to inhibition by reversible cysteine-based redox modification of its Cys223 during oxidative stress. Aside from oxidative stress, nitrosative stress also contributes to cysteine-based redox modification. Thus, the protein kinases such as Ca²⁺/calmodulin (CaM)-dependent protein kinase I (CaMKI) and II (CaMKII) that phosphorylate nNOS could be potentially regulated by cysteine-based redox modification. In this review, we focus on the role of post-translational modifications in regulating nNOS and nNOS-phosphorylating protein kinases and communication among themselves.

Influences of TP53 and the anti-aging DDR1 receptor in controlling Raf/MEK/ERK and PI3K/Akt expression and chemotherapeutic drug sensitivity in prostate cancer cell lines

Background: TP53 plays critical roles in sensitivity to chemotherapy, and aging. Collagen is very important in aging. The molecular structure and biochemical properties of collagen changes during aging. The discoidin domain receptor (DDR1) is regulated in part by collagen. Elucidating the links between TP53 and DDR1 in chemosensitivity and aging could improve therapies against cancer and aging.

Results: Restoration of WT-TP53 activity resulted in increased sensitivity to chemotherapeutic drugs and elevated expression of key components of the Raf/MEK/ERK, PI3K/Akt and DDR1 pathways. DDR1 could modulate the levels of Raf/MEK/ERK and PI3K/Akt pathways as well as sensitize the cells to chemotherapeutic drugs. In contrast, suppression of WT TP53 with a dominant negative (DN) TP53 gene, suppressed DDR1 protein levels and increased their chemoresistance.

Conclusion: Restoration of WT TP53 activity or increased expression of the anti-aging DDR1 collagen receptor can result in enhanced sensitivity to chemotherapeutic drugs. Our innovative studies indicate the important links between WT TP53 and DDR1 which can modulate Raf/MEK/ERK and PI3K/Akt signaling as well as chemosensitivity and aging.

Methods: We investigated the roles of wild type (WT) and mutant TP53 on drug sensitivity of prostate cancer cells and the induction of Raf/MEK/ERK, PI3K/Akt and DDR1 expression and chemosensitivity.

Reactive sulfur species inactivate Ca2+/calmodulin-dependent protein kinase IV via S-polysulfidation of its active-site cysteine residue

Reactive sulfur species (RSS) modulate protein functions via S-polysulfidation of reactive Cys residues. Here, we report that Ca²⁺/calmodulin (CaM)-dependent protein kinase IV (CaMKIV) was reversibly inactivated by RSS via polysulfidation of the active-site Cys residue. CaMKIV is phosphorylated at Thr¹⁹⁶ by its upstream CaMK kinase (CaMKK), resulting in the induction of its full activity. In vitro incubation of CaMKIV with the exogenous RSS donors Na₂S _n (n = 2-4) resulted in dose-dependent inhibition of the CaMKK-induced phospho-Thr¹⁹⁶ and consequent inactivation of the enzyme activity. Conversely, mutated CaMKIV (C198V) was refractory to the Na₂S _n -induced enzyme inhibition. A biotin-polyethylene glycol-conjugated maleimide capture assay revealed that Cys¹⁹⁸ in CaMKIV represents a target for S-polysulfidation. Furthermore, phosho-Thr¹⁹⁶ and CaMKIV activity were inhibited by incubation with cysteine hydropersulfide, a newly identified RSS that is generated from cystine by cystathionine-γ-lyase. In transfected cells expressing CaMKIV, ionomycin-induced CaMKIV phosphorylation at Thr¹⁹⁶ was decreased upon treatment with either Na₂S₄ or the endoplasmic reticulum (ER) stress inducer thapsigargin, whereas cells expressing mutant CaMKIV (C198V) were resistant to this treatment. In addition, the ionomycin-induced phospho-Thr¹⁹⁶ of endogenous CaMKIV was also inhibited by treatment either with Na₂S₄ or thapsigargin in Jurkat T lymphocytes. Taken together, these data define a novel signaling function for intracellular RSS in inhibiting CaMKIV activity via S-polysulfidation of its Cys¹⁹⁸ during the response to ER stress.

Participation of protein kinases in cytotoxic and proapoptotic effects of ethylene glycol ethers and their metabolites in SH-SY5Y cells

Ethylene glycol ethers (EGEs) are compounds widely used in many branches of industry. Their toxicological profile in the peripheral tissues is relatively well described, but little is known about their action on the central nervous system (CNS). In this study, we evaluated the effect of 2-ethoxyethanol (EE), 2-butoxyethanol (BE), 2-phenoxyethanol (PHE) and their metabolites on necrotic (estimated by cell viability and lactate dehydrogenase release) and apoptotic (caspase-3 activity and mitochondrial membrane potential) processes and reactive oxygen species' (ROS) production in human neuroblastoma (SH-SY5Y) cells. We have shown that, similar to the peripheral tissues, EGE metabolites in most of the performed assays revealed greater potential to damage than the parent compounds in the CNS cells. Subsequently, we investigated the participation of some selected protein kinases in the degenerative activity of PHE and its main metabolite, phenoxyacetic acid (PHA). It has been found that a GSK3β inhibitor weakened the damaging effects of PHE and PHA in each of the performed assays. Furthermore, the kinases, p38-MAPK, JNK-MAPK and PKC, had a significant role in the cytotoxic and proapoptotic effects of PHA. These results indicate that the neurotoxic effect of EGEs may stem from their impact on many intracellular signal transduction pathways.

Roles of NGAL and MMP-9 in the tumor microenvironment and sensitivity to targeted therapy

Various, diverse molecules contribute to the tumor microenvironment and influence invasion and metastasis. In this review, the roles of neutrophil gelatinase-associated lipocalin (NGAL) and matrix metalloproteinase-9 (MMP-9) in the tumor microenvironment and sensitivity to therapy will be discussed. The lipocalin family of proteins has many important functions. For example when NGAL forms a complex with MMP-9 it increases its stability which is important in cancer metastasis. Small hydrophobic molecules are bound by NGAL which can alter their entry into and efflux from cells. Iron transport and storage are also influenced by NGAL activity. Regulation of iron levels is important for survival in the tumor microenvironment as well as metastasis. Innate immunity is also regulated by NGAL as it can have bacteriostatic properties. NGAL and MMP-9 expression may also affect the sensitivity of cancer cells to chemotherapy as well as targeted therapy. Thus NGAL and MMP-9 play important roles in key processes involved in metastasis as well as response to therapy. This article is part of a Special Issue entitled: Tumor Microenvironment Regulation of Cancer Cell Survival, Metastasis, Inflammation, and Immune Surveillance edited by Peter Ruvolo and Gregg L. Semenza.

ROS and RNS signaling in skeletal muscle: critical signals and therapeutic targets

The health of skeletal muscle is promoted by optimal nutrition and activity/exercise through the activation of molecular signaling pathways. Reactive oxygen species (ROS) or reactive nitrogen species (RNS) have been shown to modulate numerous biochemical processes including glucose uptake, gene expression, calcium signaling, and contractility. In pathological conditions, ROS/RNS signaling excess or dysfunction contributes to contractile dysfunction and myopathy in skeletal muscle. Here we provide a brief review of ROS/RNS chemistry and discuss concepts of ROS/RNS signaling and its role in physiological and pathophysiological processes within striated muscle.

Targeting breast cancer initiating cells: advances in breast cancer research and therapy

Over the past 10 years there have been significant advances in our understanding of breast cancer and the important roles that breast cancer initiating cells (CICs) play in the development and resistance of breast cancer. Breast CICs endowed with self-renewing and tumor-initiating capacities are believed to be responsible for the relapses which often occur after various breast cancer therapies. In this review, we will summarize some of the key developments in breast CICs which will include discussion of some of the key genes implicated: estrogen receptor (ER), HER2, BRCA1, TP53, PIK3CA, RB, P16INK1 and various miRs as well some drugs which are showing promise in targeting CICs. In addition, the concept of combined therapies will be discussed. Basic and clinical research is resulting in novel approaches to improve breast cancer therapy by targeting the breast CICs.

Vitamin D receptor-modulated Hsp70/AT1 expression may protect the kidneys of SHRs at the structural and functional levels

Previous hypertension studies have shown that low levels of vitamin D are linked to elevated renin-angiotensin system. The heat shock protein 70 regulates signaling pathways for cellular oxidative stress responses. Hsp70 has been shown to protect against angiotensin II-induced hypertension and exert a cytoprotective effect. Here, we wanted to evaluate whether the vitamin D receptor (VDR) associated with Hsp70/AT1 expression may be involved in the mechanism by which paricalcitol provides renal protection in spontaneously hypertensive rats (SHRs). One-month-old female SHRs were treated for 4 months with vehicle, paricalcitol, enalapril, or a combination of both paricalcitol and enalapril. The following were determined: blood pressure; biochemical parameters; fibrosis; apoptosis; mitochondrial morphology; and VDR, AT1 receptor, and Hsp70 expression in the renal cortex. Blood pressure was markedly reduced by enalapril or the combination but not by paricalcitol alone. However, VDR activation, enalapril or combination, prevented fibrosis, the number of TUNEL-positive apoptotic cells, mitochondrial damage, and NADPH oxidase activity in SHRs. Additionally, high AT1 receptor expression, like low Hsp70 expression (immunohistochemical/immunofluorescence studies), was reversed in the renal cortices of paricalcitol- and/or enalapril-treated animals (SHRs), and these changes were most marked in the combination therapy group. Finally, all of the recovery parameters were consistent with an improvement in VDR expression. Data suggest that Hsp70/AT1 modulated by VDR is involved in the mechanism by which paricalcitol provides renal protection in SHRs. We propose that low AT1 expression through VDR induction could be a consequence of the heat shock response Hsp70-mediated cell protection.

Cadmium and cellular signaling cascades: interactions between cell death and survival pathways

Cellular stress elicited by the toxic metal Cd(2+) does not coerce the cell into committing to die from the onset. Rather, detoxification and adaptive processes are triggered concurrently, allowing survival until normal function is restored. With high Cd(2+), death pathways predominate. However, if sublethal stress levels affect cells for prolonged periods, as in chronic low Cd(2+) exposure, adaptive and survival mechanisms may deregulate, such that tumorigenesis ensues. Hence, death and malignancy are the two ends of a continuum of cellular responses to Cd(2+), determined by magnitude and duration of Cd(2+) stress. Signaling cascades are the key factors affecting cellular reactions to Cd(2+). This review critically surveys recent literature to outline major features of death and survival signaling pathways as well as their activation, interactions and cross talk in cells exposed to Cd(2+). Under physiological conditions, receptor activation generates 2nd messengers, which are short-lived and act specifically on effectors through their spatial and temporal dynamics to transiently alter effector activity. Cd(2+) recruits physiological 2nd messenger systems, in particular Ca(2+) and reactive oxygen species (ROS), which control key Ca(2+)- and redox-sensitive molecular switches dictating cell function and fate. Severe ROS/Ca(2+) signals activate cell death effectors (ceramides, ASK1-JNK/p38, calpains, caspases) and/or cause irreversible damage to vital organelles, such as mitochondria and endoplasmic reticulum (ER), whereas low localized ROS/Ca(2+) levels act as 2nd messengers promoting cellular adaptation and survival through signal transduction (ERK1/2, PI3K/Akt-PKB) and transcriptional regulators (Ref1-Nrf2, NF-κB, Wnt, AP-1, bestrophin-3). Other cellular proteins and processes targeted by ROS/Ca(2+) (metallothioneins, Bcl-2 proteins, ubiquitin-proteasome system, ER stress-associated unfolded protein response, autophagy, cell cycle) can evoke death or survival. Hence, temporary or permanent disruptions of ROS/Ca(2+) induced by Cd(2+) play a crucial role in eliciting, modulating and linking downstream cell death and adaptive and survival signaling cascades.

Ectopic NGAL expression can alter sensitivity of breast cancer cells to EGFR, Bcl-2, CaM-K inhibitors and the plant natural product berberine

Neutrophil gelatinase-associated lipocalin (NGAL, a.k.a Lnc2) is a member of the lipocalin family and has diverse roles. NGAL can stabilize matrix metalloproteinase-9 from autodegradation. NGAL is considered as a siderocalin that is important in the transport of iron. NGAL expression has also been associated with certain neoplasias and is implicated in the metastasis of breast cancer. In a previous study, we examined whether ectopic NGAL expression would alter the sensitivity of breast epithelial, breast and colorectal cancer cells to the effects of the chemotherapeutic drug doxorubicin. While abundant NGAL expression was detected in all the cells infected with a retrovirus encoding NGAL, this expression did not alter the sensitivity of these cells to doxorubicin as compared with empty vector-transduced cells. We were also interested in determining the effects of ectopic NGAL expression on the sensitivity to small-molecule inhibitors targeting key signaling molecules. Ectopic NGAL expression increased the sensitivity of MCF-7 breast cancer cells to EGFR, Bcl-2 and calmodulin kinase inhibitors as well as the natural plant product berberine. Furthermore, when suboptimal concentrations of certain inhibitors were combined with doxorubicin, a reduction in the doxorubicin IC 50 was frequently observed. An exception was observed when doxorubicin was combined with rapamycin, as doxorubicin suppressed the sensitivity of the NGAL-transduced MCF-7 cells to rapamycin when compared with the empty vector controls. In contrast, changes in the sensitivities of the NGAL-transduced HT-29 colorectal cancer cell line and the breast epithelial MCF-10A cell line were not detected compared with empty vector-transduced cells. Doxorubicin-resistant MCF-7/Dox (R) cells were examined in these experiments as a control drug-resistant line; it displayed increased sensitivity to EGFR and Bcl-2 inhibitors compared with empty vector transduced MCF-7 cells. These results indicate that NGAL expression can alter the sensitivity of certain cancer cells to small-molecule inhibitors, suggesting that patients whose tumors exhibit elevated NGAL expression or have become drug-resistant may display altered responses to certain small-molecule inhibitors.

Role of mitochondria in paricalcitol-mediated cytoprotection during obstructive nephropathy

Vitamin D slows the progression of chronic kidney disease. Furthermore, activators of vitamin D receptors (VDR) have suppressant effects on the renin-angiotensin system, as well as anti-inflammatory and antifibrotic actions. This study aimed to evaluate the cytoprotective effects of paricalcitol, a VDR activator, at the mitochondrial level using an obstructive nephropathy model [unilateral ureteral obstruction (UUO)]. Rats subjected to UUO and controls were treated daily with vehicle or paricalcitol. The control group underwent a sham surgery. The treatment was done for 15 days (30 ng/kg). The following were determined: biochemical parameters; fibrosis; apoptosis; mitochondrial morphology; VDR, AT(1) receptor, and NADPH oxidase 4 expression; and NADPH oxidase activity (in total and in mitochondrial fractions from the renal cortex). VDR activation prevented fibrosis (20 ± 5 vs. 60 ± 10%) and the number of TUNEL-positive apoptotic cells (10 ± 3 vs. 25 ± 4) in UUO. Biochemical, histological, and molecular studies suggest mitochondrial injury. Electron microscopy revealed in UUO electronically luminous material in the nucleus. Some mitochondria were increased in size and contained dilated crests and larger than normal spaces in their interiors. These changes were not present with paricalcitol treatment. Additionally, high AT(1)-receptor mRNA and NADPH activity was reverted in mitochondrial fractions from obstructed paricalcitol-treated animals (0.58 ± 0.06 vs. 0.95 ± 0.05 relative densitometry units and 9,000 ± 800 vs. 15,000 ± 1,000 relative fluorescence units·μg protein(-1)·min(-1), respectively). These changes were consistent with an improvement in VDR expression (0.75 ± 0.05 vs. 0.35 ± 0.04 relative densitometry units). These results suggest that paricalcitol confers a protective effect and reveal, as well, a possible AT(1) receptor-dependent protective effect that occurs at the mitochondrial level.

Heme-induced ROS in Trypanosoma cruzi activates CaMKII-like that triggers epimastigote proliferation. One helpful effect of ROS

Heme is a ubiquitous molecule that has a number of physiological roles. The toxic effects of this molecule have been demonstrated in various models, based on both its pro-oxidant nature and through a detergent mechanism. It is estimated that about 10 mM of heme is released during blood digestion in the blood-sucking bug's midgut. The parasite Trypanosoma cruzi, the agent of Chagas' disease, proliferates in the midgut of the insect vector; however, heme metabolism in trypanosomatids remains to be elucidated. Here we provide a mechanistic explanation for the proliferative effects of heme on trypanosomatids. Heme, but not other porphyrins, induced T. cruzi proliferation, and this phenomenon was accompanied by a marked increase in reactive oxygen species (ROS) formation in epimastigotes when monitored by ROS-sensitive fluorescent probes. Heme-induced ROS production was time-and concentration-dependent. In addition, lipid peroxidation and the formation of 4-hydroxy-2-nonenal (4-HNE) adducts with parasite proteins were increased in epimastigotes in the presence of heme. Conversely, the antioxidants urate and GSH reversed the heme-induced ROS. Urate also decreased parasite proliferation. Among several protein kinase inhibitors tested only specific inhibitors of CaMKII, KN93 and Myr-AIP, were able to abolish heme-induced ROS formation in epimastigotes leading to parasite growth impairment. Taken together, these data provide new insight into T. cruzi- insect vector interactions: heme, a molecule from the blood digestion, triggers epimastigote proliferation through a redox-sensitive signalling mechanism.

Roles of the Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR pathways in controlling growth and sensitivity to therapy-implications for cancer and aging

Dysregulated signaling through the Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR pathways is often the result of genetic alterations in critical components in these pathways or upstream activators. Unrestricted cellular proliferation and decreased sensitivity to apoptotic-inducing agents are typically associated with activation of these pro-survival pathways. This review discusses the functions these pathways have in normal and neoplastic tissue growth and how they contribute to resistance to apoptotic stimuli. Crosstalk and commonly identified mutations that occur within these pathways that contribute to abnormal activation and cancer growth will also be addressed. Finally the recently described roles of these pathways in cancer stem cells, cellular senescence and aging will be evaluated. Controlling the expression of these pathways could ameliorate human health.

Roles of the Ras/Raf/MEK/ERK pathway in leukemia therapy

The Ras/Raf/mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway is often implicated in sensitivity and resistance to leukemia therapy. Dysregulated signaling through the Ras/Raf/MEK/ERK pathway is often the result of genetic alterations in critical components in this pathway as well as mutations at upstream growth factor receptors. Unrestricted leukemia proliferation and decreased sensitivity to apoptotic-inducing agents and chemoresistance are typically associated with activation of pro-survival pathways. Mutations in this pathway and upstream signaling molecules can alter sensitivity to small molecule inhibitors targeting components of this cascade as well as to inhibitors targeting other key pathways (for example, phosphatidylinositol 3 kinase (PI3K)/phosphatase and tensin homologue deleted on chromosome 10 (PTEN)/Akt/mammalian target of rapamycin (mTOR)) activated in leukemia. Similarly, PI3K mutations can result in resistance to inhibitors targeting the Ras/Raf/MEK/ERK pathway, indicating important interaction points between the pathways (cross-talk). Furthermore, the Ras/Raf/MEK/ERK pathway can be activated by chemotherapeutic drugs commonly used in leukemia therapy. This review discusses the mechanisms by which abnormal expression of the Ras/Raf/MEK/ERK pathway can contribute to drug resistance as well as resistance to targeted leukemia therapy. Controlling the expression of this pathway could improve leukemia therapy and ameliorate human health.

Calcium/calmodulin-dependent protein kinases as potential targets of nitric oxide

Nitric oxide (NO) synthesis is controlled by Ca(2+)/calmodulin (CaM) binding with and kinase-dependent phosphorylation of constitutive NO synthases, which catalyze the formation of NO and L-citrulline from L-arginine. NO operates as a mediator of important cell signaling pathways, such as cGMP signaling cascade. Another mechanism by which NO exerts biological effects is mediated via post-translational modification of redox-sensitive cysteine thiols of proteins. The Ca(2+)/CaM-dependent protein kinases (CaM kinases) such as CaM kinase I, CaM kinase II, and CaM kinase IV, are a family of protein kinases which requires binding of Ca(2+)/CaM to and subsequent phosphorylation of the enzymes to initiate its activation process. We report other regulation mechanisms of CaM kinases, such as S-glutathionylation of CaM kinase I at Cys(179) and S-nitrosylation of CaM kinase II at Cys(6/30). Such unique post-translational modification of CaMKs by NO shed light on a new area of mutual regulation of NO- and CaM kinases-signals. Based on the novel direct regulation of these kinases, we propose that CaM kinases/NO signaling would be good targets for understanding how they can participate in neuronal physiology and disease.

eNOS/Hsp70 interaction on rosuvastatin cytoprotective effect in neonatal obstructive nephropathy

There is growing evidence that statins may exert renoprotective effects beyond cholesterol reduction. The cholesterol-independent or "pleiotropic" effects of statins include the upregulation of endothelial nitric oxide synthase (eNOS). Here we determined whether eNOS associated with Hsp70 expression is involved in rosuvastatin resistance to obstruction-induced oxidative stress and cell death. Neonatal rats subjected to unilateral ureteral obstruction (UUO) within two days of birth and controls were treated daily with vehicle or rosuvastatin (10 mg/kg/day) for 14 days. Decreased endogenous nitric oxide (NO) and lower mRNA and protein eNOS expression associated with downregulation of heat shock factor 1 (Hsf1) mRNA and Hsp70 protein levels were observed in the obstructed kidney cortex. Increased nicotinamide adenine dinucleotide phosphate (NADHP) oxidase activity and apoptosis induction, regulated by mitochondrial signal pathway through an increased pro-apoptotic Bax/BcL(2) ratio and caspase 3 activity, were demonstrated. Conversely, in cortex membrane fractions from rosuvastatin-treated UUO rats, marked upregulation of eNOS expression at transcriptional and posttranscriptional levels linked to increased Hsf1 mRNA expression and enhanced mRNA and protein Hsp70 expression, were observed. Consequently, there was an absence of apoptotic response and transiently decreased NADPH oxidase activity. In addition, interaction between eNOS and Hsp70 was determined by communoprecipitation in cortex membrane fractions, showing an increased ratio of both proteins, after rosuvastatin treatment in obstructed kidney. In summary, our data demonstrate that the effect of rosuvastatin on eNOS interacting with Hsp70, results in the capacity of both to prevent mitochondrial apoptotic pathway and oxidative stress in neonatal early kidney obstruction.

Interactions between calcium and reactive oxygen species in pulmonary arterial smooth muscle responses to hypoxia

In contrast to the systemic vasculature, where hypoxia causes vasodilation, pulmonary arteries constrict in response to hypoxia. The mechanisms underlying this unique response have been the subject of investigation for over 50 years, and still remain a topic of great debate. Over the last 20 years, there has emerged a general consensus that both increases in intracellular calcium concentration and changes in reactive oxygen species (ROS) generation play key roles in the pulmonary vascular response to hypoxia. Controversy exists, however, regarding whether ROS increase or decrease during hypoxia, the source of ROS, and the mechanisms by which changes in ROS might impact intracellular calcium, and vice versa. This review will discuss the mechanisms regulating [Ca2+]i and ROS in PASMCs, and the interaction between ROS and Ca2+ signaling during exposure to acute hypoxia.

[Plant calcium sensors in osmotic signaling]

Calcium is an essential second messenger that mediates plant responses to developmental and environmental clues. Specific calcium signatures are sensed and decoded by diverse Ca(2+) sensors to induce appropriate downstream responses. Calmodulin is the most important and conserved Ca(2+) transducer in all eukaryotes. Additional plant-specific sensors are encoded by multigene families, i.e. calcineurin B-like and Ca(2+)-dependent protein kinases. Calcium binding induces structural conformational changes in Ca(2+) sensors, resulting in the modification of protein interaction or enzymatic activity. Activated Ca(2+) sensors subsequently regulate downstream targets which can be involved in signal transduction, like protein kinases and transcription factors, or in direct cell protection from stress damages, like ion transporters or detoxification enzymes. Ca(2+) plays an important role in osmotic signaling triggered by cold, drought and salinity. The multiplicity of plant calcium sensors associated with diverse cellular targets constitute a tightly regulated signaling network that induces specific stress responses to improve plant survival under unfavourable conditions.

Interplay between calcium and reactive oxygen/nitrogen species: an essential paradigm for vascular smooth muscle signaling

Signaling cascades initiated or regulated by calcium (Ca(2+)), reactive oxygen (ROS), and nitrogen (RNS) species are essential to diverse physiological and pathological processes in vascular smooth muscle. Stimuli-induced changes in intracellular Ca(2+) regulate the activity of primary ROS and RNS, producing enzymes including NADPH oxidases (Nox) and nitric oxide synthases (NOS). At the same time, alteration in intracellular ROS and RNS production reciprocates through redox-based post-translational modifications altering Ca(2+) signaling networks. These may include Ca(2+) pumps such as sarcoplasmic endoplasmic reticulum Ca(2+)-ATPase (SERCA), voltage-gated channels, transient receptor potential canonical (TRPC), melastatin2 (TRPM2), and ankyrin1 (TRPA1) channels, store operated Ca(2+) channels such as Orai1/stromal interaction molecule 1 (STIM1), and Ca(2+) effectors such as Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). In this review, we summarize and highlight current experimental evidence supporting the idea that cross-talk between Ca(2+) and ROS/RNS may represent a well-integrated signaling network in vascular smooth muscle.

SR/ER-mitochondrial local communication: calcium and ROS

Mitochondria form junctions with the sarco/endoplasmic reticulum (SR/ER), which support signal transduction and biosynthetic pathways and affect organellar distribution. Recently, these junctions have received attention because of their pivotal role in mediating calcium signal propagation to the mitochondria, which is important for both ATP production and mitochondrial cell death. Many of the SR/ER-mitochondrial calcium transporters and signaling proteins are sensitive to redox regulation and are directly exposed to the reactive oxygen species (ROS) produced in the mitochondria and SR/ER. Although ROS has been emerging as a novel signaling entity, the redox signaling of the SR/ER-mitochondrial interface is yet to be elucidated. We describe here possible mechanisms of the mutual interaction between local Ca(2+) and ROS signaling in the control of SR/ER-mitochondrial function.

Synthetic lethal RNAi screening identifies sensitizing targets for gemcitabine therapy in pancreatic cancer

Background

Pancreatic cancer retains a poor prognosis among the gastrointestinal cancers. It affects 230,000 individuals worldwide, has a very high mortality rate, and remains one of the most challenging malignancies to treat successfully. Treatment with gemcitabine, the most widely used chemotherapeutic against pancreatic cancer, is not curative and resistance may occur. Combinations of gemcitabine with other chemotherapeutic drugs or biological agents have resulted in limited improvement.

Methods

In order to improve gemcitabine response in pancreatic cancer cells, we utilized a synthetic lethal RNAi screen targeting 572 known kinases to identify genes that when silenced would sensitize pancreatic cancer cells to gemcitabine.

Results

Results from the RNAi screens identified several genes that, when silenced, potentiated the growth inhibitory effects of gemcitabine in pancreatic cancer cells. The greatest potentiation was shown by siRNA targeting checkpoint kinase 1 (CHK1). Validation of the screening results was performed in MIA PaCa-2 and BxPC3 pancreatic cancer cells by examining the dose response of gemcitabine treatment in the presence of either CHK1 or CHK2 siRNA. These results showed a three to ten-fold decrease in the EC₅₀ for CHK1 siRNA-treated cells versus control siRNA-treated cells while treatment with CHK2 siRNA resulted in no change compared to controls. CHK1 was further targeted with specific small molecule inhibitors SB 218078 and PD 407824 in combination with gemcitabine. Results showed that treatment of MIA PaCa-2 cells with either of the CHK1 inhibitors SB 218078 or PD 407824 led to sensitization of the pancreatic cancer cells to gemcitabine.

Conclusion

These findings demonstrate the effectiveness of synthetic lethal RNAi screening as a tool for identifying sensitizing targets to chemotherapeutic agents. These results also indicate that CHK1 could serve as a putative therapeutic target for sensitizing pancreatic cancer cells to gemcitabine.

Anion channels in Plasmodium-falciparum-infected erythrocytes and protein kinase A

By replicating within red blood cells, malaria parasites are largely hidden from immune recognition; however, in the cells, nutrients are limiting and hazardous metabolic end products can rapidly accumulate. Therefore, to survive within erythrocytes, parasites alter the permeability of the host plasma membrane, either by upregulating existing transporters or by creating new permeation pathways. Recent electrophysiological studies of Plasmodium-infected erythrocytes have demonstrated that membrane permeability is mediated by transmembrane transport through ion channels in the infected erythrocyte. This article discusses the evidence and controversies concerning the nature of these channels and surveys the potential role of phosphorylation in activating anion channels that could be important in developing novel strategies for future malarial chemotherapies.

The antioxidant mimetic, MnTE-2-PyP, reduces intracellular growth of Mycobacterium abscessus

Mycobacterium abscessus is a rapidly growing environmental mycobacterium that can cause severe skin, soft tissue, and lung infections. M. abscessus grows inside macrophages, and these cells release a vast number of proinflammatory cytokines in response to infections. The metalloporphyrin, MnTE-2-PyP, is a broad antioxidant that reduces inflammatory cell signaling. Macrophage-like THP-1 cells were infected with M. abscessus in the presence or absence of MnTE-2-PyP. MnTE-2-PyP significantly decreased, in a dose-dependent manner, the number of M. abscessus organisms recovered from infected THP-1 cells 4 and 8 days after infection. Furthermore, when combined with clarithromycin, MnTE-2-PyP additively reduced the number of cells associated with M. abscessus. A mechanism of bacterial growth inhibition by MnTE-2-PyP was then elucidated. It was found that MnTE-2-PyP promoted the survival of infected THP-1 cells and increased fusion of M. abscessus-containing phagosomes with lysosomes.

The chemistry of cell signaling by reactive oxygen and nitrogen species and 4-hydroxynonenal

During the past several years, major advances have been made in understanding how reactive oxygen species (ROS) and nitrogen species (RNS) participate in signal transduction. Identification of the specific targets and the chemical reactions involved still remains to be resolved with many of the signaling pathways in which the involvement of reactive species has been determined. Our understanding is that ROS and RNS have second messenger roles. While cysteine residues in the thiolate (ionized) form found in several classes of signaling proteins can be specific targets for reaction with H(2)O(2) and RNS, better understanding of the chemistry, particularly kinetics, suggests that for many signaling events in which ROS and RNS participate, enzymatic catalysis is more likely to be involved than non-enzymatic reaction. Due to increased interest in how oxidation products, particularly lipid peroxidation products, also are involved with signaling, a review of signaling by 4-hydroxy-2-nonenal (HNE) is included. This article focuses on the chemistry of signaling by ROS, RNS, and HNE and will describe reactions with selected target proteins as representatives of the mechanisms rather attempt to comprehensively review the many signaling pathways in which the reactive species are involved.

Oxidative stress as a therapeutic target during muscle wasting: considering the complex interactions

PURPOSE OF REVIEW

The aim of this overview is to highlight the multiple ways in which oxidative stress could be exacerbating muscle wasting. Understanding these interactions in vivo will assist in identifying opportunities for more targeted therapies to reduce skeletal muscle wasting.

RECENT FINDINGS

There are many excellent reviews describing how oxidative stress can damage cellular macromolecules, as well as cause deleterious effects through the modulation of signalling pathways. In this overview, we highlight the potential for complex and possibly paradoxical interactions in vivo. Signalling pathways are discussed, using examples involving nuclear factor-kappa B, apoptosis signal-regulating kinase 1 and Akt. Oxidative stress may also be involved in complex interactions with other factors capable of stimulating the loss of muscle mass, possibly through amplifying feedback cycles. This is discussed using examples related to calcium and tumour necrosis factor.

SUMMARY

There is convincing evidence that oxidative stress can increase protein catabolism. The challenge is to demonstrate that oxidative stress is a significant player in the complex interplay that leads to the in-vivo muscle wasting that is caused by a range of conditions and diseases.

Crosstalk between calcium and redox signaling: from molecular mechanisms to health implications

Studies done many years ago established unequivocally the key role of calcium as a universal second messenger. In contrast, the second messenger roles of reactive oxygen and nitrogen species have emerged only recently. Therefore, their contributions to physiological cell signaling pathways have not yet become universally accepted, and many biological researchers still regard them only as cellular noxious agents. Furthermore, it is becoming increasingly apparent that there are significant interactions between calcium and redox species, and that these interactions modify a variety of proteins that participate in signaling transduction pathways and in other fundamental cellular functions that determine cell life or death. This review article addresses first the central aspects of calcium and redox signaling pathways in animal cells, and continues with the molecular mechanisms that underlie crosstalk between calcium and redox signals under a number of physiological or pathological conditions. To conclude, the review focuses on conditions that, by promoting cellular oxidative stress, lead to the generation of abnormal calcium signals, and how this calcium imbalance may cause a variety of human diseases including, in particular, degenerative diseases of the central nervous system and cardiac pathologies.

HMGB1 release induced by liver ischemia involves Toll-like receptor 4 dependent reactive oxygen species production and calcium-mediated signaling

Ischemic tissues require mechanisms to alert the immune system of impending cell damage. The nuclear protein high-mobility group box 1 (HMGB1) can activate inflammatory pathways when released from ischemic cells. We elucidate the mechanism by which HMGB1, one of the key alarm molecules released during liver ischemia/reperfusion (I/R), is mobilized in response to hypoxia. HMGB1 release from cultured hepatocytes was found to be an active process regulated by reactive oxygen species (ROS). Optimal production of ROS and subsequent HMGB1 release by hypoxic hepatocytes required intact Toll-like receptor (TLR) 4 signaling. To elucidate the downstream signaling pathways involved in hypoxia-induced HMGB1 release from hepatocytes, we examined the role of calcium signaling in this process. HMGB1 release induced by oxidative stress was markedly reduced by inhibition of calcium/calmodulin-dependent kinases (CaMKs), a family of proteins involved in a wide range of calcium-linked signaling events. In addition, CaMK inhibition substantially decreased liver damage after I/R and resulted in accumulation of HMGB1 in the cytoplasm of hepatocytes. Collectively, these results demonstrate that hypoxia-induced HMGB1 release by hepatocytes is an active, regulated process that occurs through a mechanism promoted by TLR4-dependent ROS production and downstream CaMK-mediated signaling.