Reactive oxygen species signaling through regulation of protein tyrosine phosphorylation in endothelial cells

Isoflurane Rapidly Modifies Synaptic and Cytoskeletal Phosphoproteomes of the Supraoptic Nucleus of the Hypothalamus and the Cortex

INTRODUCTION

Despite the widespread use of general anaesthetics, the mechanisms mediating their effects are still not understood. Although suppressed in most parts of the brain, neuronal activity, as measured by FOS activation, is increased in the hypothalamic supraoptic nucleus (SON) by numerous general anaesthetics, and evidence points to this brain region being involved in the induction of general anaesthesia (GA) and natural sleep. Posttranslational modifications of proteins, including changes in phosphorylation, enable fast modulation of protein function which could be underlying the rapid effects of GA. In order to identify potential phosphorylation events in the brain-mediating GA effects, we have explored the phosphoproteome responses in the rat SON and compared these to cingulate cortex (CC) which displays no FOS activation in response to general anaesthetics.

METHODS

Adult Sprague-Dawley rats were treated with isoflurane for 15 min. Proteins from the CC and SON were extracted and processed for nano-LC mass spectrometry (LC-MS/MS). Phosphoproteomic determinations were performed by LC-MS/MS.

RESULTS

We found many changes in the phosphoproteomes of both the CC and SON in response to 15 min of isoflurane exposure. Pathway analysis indicated that proteins undergoing phosphorylation adaptations are involved in cytoskeleton remodelling and synaptic signalling events. Importantly, changes in protein phosphorylation appeared to be brain region specific suggesting that differential phosphorylation adaptations might underlie the different neuronal activity responses to GA between the CC and SON.

CONCLUSION

In summary, these data suggest that rapid posttranslational modifications in proteins involved in cytoskeleton remodelling and synaptic signalling events might mediate the central mechanisms mediating GA.

Classic Phytochemical Antioxidant and Lipoxygenase Inhibitor, Nordihydroguaiaretic Acid, Activates Phospholipase D through Oxidant Signaling and Tyrosine Phosphorylation Leading to Cytotoxicity in Lung Vascular Endothelial Cells

Nordihydroguaiaretic acid (NDGA), a dicatechol and phytochemical polyphenolic antioxidant and an established inhibitor of human arachidonic acid (AA) 5-lipoxygenase (LOX) and 15-LOX, is widely used to ascertain the role of LOXs in vascular endothelial cell (EC) function. As the modulatory effect of NDGA on phospholipase D (PLD), an important lipid signaling enzyme in ECs, thus far has not been reported, here we have investigated the modulation of PLD activity and its regulation by NDGA in the bovine pulmonary artery ECs (BPAECs). NDGA induced the activation of PLD (phosphatidic acid formation) in cells in a dose- and time-dependent fashion that was significantly attenuated by iron chelator and antioxidants. NDGA induced the formation of reactive oxygen species (ROS) in cells in a dose- and time-dependent manner as evidenced from fluorescence microscopy and fluorimetry of ROS and electron paramagnetic resonance spectroscopy of oxygen radicals. Also, NDGA caused a dose-dependent loss of intracellular glutathione (GSH) in BPAECs. Protein tyrosine kinase (PTyK)-specific inhibitors significantly attenuated NDGA-induced PLD activation in BPAECs. NDGA also induced a dose- and time-dependent phosphorylation of tyrosine in proteins in cells. NDGA caused in situ translocation and relocalization of both PLD₁ and PLD₂ isoforms, in a time-dependent fashion. Cyclooxygenase (COX) inhibitors were ineffective in attenuating NDGA-induced PLD activation in BPAECs, thus ruling out the activation of COXs by NDGA. NDGA inhibited the AA-LOX activity and leukotriene C₄ (LTC₄) formation in cells. On the other hand, the 5-LOX-specific inhibitors, 5, 8, 11, 14-eicosatetraynoic acid and kaempferol, were ineffective in activating PLD in BPAECs. Antioxidants and PTyK-specific inhibitors effectively attenuated NDGA cytotoxicity in BPAECs. The PLD-specific inhibitor, 5-fluoro-2-indolyl deschlorohalopemide (FIPI), significantly attenuated and protected against the NDGA-induced PLD activation and cytotoxicity in BPAECs. For the first time, these results demonstrated that NDGA, the classic phytochemical polyphenolic antioxidant and LOX inhibitor, activated PLD causing cytotoxicity in ECs through upstream oxidant signaling and protein tyrosine phosphorylation.

Effects of Peroxiredoxin 6 and Its Mutants on the Isoproterenol Induced Myocardial Injury in H9C2 Cells and Rats

Background

Peroxiredoxin 6 (PRDX6) is an important antioxidant enzyme, with a potential application value in the treatment of diseases caused by oxidative damage.

Methods

PRDX6 and a mutant (mPRDX6) were heterologously expressed by using an E.coli expression system and purified by Ni-affinity chromatography. Isoproterenol (ISO) was used to induce a myocardial cell injury model and an animal myocardial injury model. After the treatment with PRDX6 and mPRDX6, the proliferation activity of H9C2 cells was detected by Cell Counting Kit-8 (CCK8) method; the apoptosis was evaluated by flow cytometry, and the histological changes of myocardial cells were observed by hematoxylin and eosin (H&E) staining, the levels of catalase (CAT), glutathione peroxidase (GPX), malondialdehyde (MDA), and superoxide dismutase (SOD) in ISO-treated H9C2 cells as well as in the heart tissue and serum of rats treated with ISO were detected, and the expression levels of Bax, Bcl-2 and peroxisome proliferators-activated receptors-γ (PPAR-γ) proteins were detected by Western blot.

Results

PRDX6 and mPRDX6 were successfully expressed and purified. The results of efficacy study showed that the mutant mPRDX6, in which the phospholipaseA2 (PLA2) activity of PRDX6 was deleted by site directed mutation, had a better protective effect against the myocardial injury than PRDX6. CCK8 results showed that compared with that in ISO group, the proliferation activity of H9C2 cells was significantly enhanced (P < 0.01), the apoptosis rate was significantly decreased (P < 0.01), and the fluorescence intensity of reactive oxygen species (ROS) was significantly decreased (P < 0.01) in mPRDX6 group. The results of H&E staining showed that the myocardial injury was alleviated to a certain extent in mPRDX6 group. Compared with those in ISO group, the activities of CAT, GPX, and SOD in H9C2 cells and the heart tissue and serum of rats were significantly increased (P < 0.05), while the contents of MDA were significantly decreased (P < 0.05). Western blot analysis showed that the expression level of Bcl-2 in H9C2 cells was significantly decreased (P < 0.01), and that of Bax and PPAR-γ was significantly increased (P < 0.05).

Conclusion

mPRDX6 has a protective effect against the myocardial injury induced by ISO, and the mechanism may be related to its antioxidation. This study may provide a theoretical basis for the research and development of drugs used for the treatment of myocardial injury.

Molecular Mechanisms of Arsenic-Induced Disruption of DNA Repair

Exposure to arsenic in contaminated drinking water is an emerging public health problem that impacts more than 200 million people worldwide. Accumulating lines of evidence from epidemiological studies revealed that chronic exposure to arsenic can result in various human diseases including cancer, type 2 diabetes, and neurodegenerative disorders. Arsenic is also classified as a Group I human carcinogen. In this review, we survey extensively different modes of action for arsenic-induced carcinogenesis, with focus being placed on arsenic-mediated impairment of DNA repair pathways. Inorganic arsenic can be bioactivated by methylation, and the ensuing products are highly genotoxic. Bioactivation of arsenicals also elicits the production of reactive oxygen and nitrogen species (ROS and RNS), which can directly damage DNA and modify cysteine residues in proteins. Results from recent studies suggest zinc finger proteins as crucial molecular targets for direct binding to As3+ or for modifications by arsenic-induced ROS/RNS, which may constitute a common mechanism underlying arsenic-induced perturbations of DNA repair.

Skullcapflavone II Inhibits Degradation of Type I Collagen by Suppressing MMP-1 Transcription in Human Skin Fibroblasts

Skullcapflavone II is a flavonoid derived from the root of Scutellaria baicalensis, a herbal medicine used for anti-inflammatory and anti-cancer therapies. We analyzed the effect of skullcapflavone II on the expression of matrix metalloproteinase-1 (MMP-1) and integrity of type I collagen in foreskin fibroblasts. Skullcapflavone II did not affect the secretion of type I collagen but reduced the secretion of MMP-1 in a dose- and time-dependent manner. Real-time reverse transcription-PCR and reporter gene assays showed that skullcapflavone II reduced MMP-1 expression at the transcriptional level. Skullcapflavone II inhibited the serum-induced activation of the extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways required for MMP-1 transactivation. Skullcapflavone II also reduced tumor necrosis factor (TNF)-α-induced nuclear factor kappa light chain enhancer of activated B cells (NF-κB) activation and subsequent MMP-1 expression. In three-dimensional culture of fibroblasts, skullcapflavone II down-regulated TNF-α-induced MMP-1 secretion and reduced breakdown of type I collagen. These results indicate that skullcapflavone II is a novel biomolecule that down-regulates MMP-1 expression in foreskin fibroblasts and therefore could be useful in therapies for maintaining the integrity of extracellular matrix.

Toxicant-mediated redox control of proteostasis in neurodegeneration

Disruption in redox signaling and control of cellular processes has emerged as a key player in many pathologies including neurodegeneration. As protein aggregations are a common hallmark of several neuronal pathologies, a firm understanding of the interplay between redox signaling, oxidative and free radical stress, and proteinopathies is required to sort out the complex mechanisms in these diseases. Fortunately, models of toxicant-induced neurodegeneration can be utilized to evaluate and report mechanistic alterations in the proteostasis network (PN). The epidemiological links between environmental toxicants and neurological disease gives further credence into characterizing the toxicant-mediated PN disruptions observed in these conditions. Reviewed here are examples of mechanistic interaction between oxidative or free radical stress and PN alterations. Additionally, investigations into toxicant-mediated PN disruptions, specifically focusing on environmental metals and pesticides, are discussed. Finally, we emphasize the need to distinguish whether the presence of protein aggregations are contributory to phenotypes related to neurodegeneration, or if they are a byproduct of PN deficiencies.

Reduced FAK-STAT3 signaling contributes to ER stress-induced mitochondrial dysfunction and death in endothelial cells

Excessive endoplasmic reticulum (ER) stress leads to cell loss in many diseases, e.g., contributing to endothelial cell loss after spinal cord injury. Here, we determined whether ER stress-induced mitochondrial dysfunction could be explained by interruption of the focal adhesion kinase (FAK)-mitochondrial STAT3 pathway we recently discovered. ER stress was induced in brain-derived mouse bEnd5 endothelial cells by thapsigargin or tunicamycin and caused apoptotic cell death over a 72h period. In concert, ER stress caused mitochondrial dysfunction as shown by reduced bioenergetic function, loss of mitochondrial membrane potential and increased mitophagy. ER stress caused a reduction in mitochondrial phosphorylated S727-STAT3, known to be important for maintaining mitochondrial function. Normal activation or phosphorylation of the upstream cytoplasmic FAK was also reduced, through mechanisms that involve tyrosine phosphatases and calcium signaling, as shown by pharmacological inhibitors, bisperoxovanadium (bpV) and 2-aminoethoxydiphenylborane (APB), respectively. APB mitigated the reduction in FAK and STAT3 phosphorylation, and improved endothelial cell survival caused by ER stress. Transfection of cells rendered null for STAT3 using CRISPR technology with STAT3 mutants confirmed the specific involvement of S727-STAT3 inhibition in ER stress-mediated cell loss. These data suggest that loss of FAK signaling during ER stress causes mitochondrial dysfunction by reducing the protective effects of mitochondrial STAT3, leading to endothelial cell death. We propose that stimulation of the FAK-STAT3 pathway is a novel therapeutic approach against pathological ER stress.

Acquisition of the metastatic phenotype is accompanied by H2O2-dependent activation of the p130Cas signaling complex

Reactive oxygen species (ROS) have emerged as cellular signaling molecules and are implicated in metastatic disease by their ability to drive invasion and migration. Here, we define the signaling adaptor protein p130Cas (Crk-associated substrate) as a key redox-responsive molecular trigger that is engaged in highly invasive metastatic bladder tumor cell lines. Endogenous shifts in steady-state hydrogen peroxide (H2O2) that accompany the metastatic phenotype increase p130Cas phosphorylation, membrane recruitment and association with the scaffolding protein Crk, and subsequent Rac1 activation and actin reorganization. Both enzymatic and nonenzymatic scavenging of H2O2 abrogates p130Cas-dependent signaling and the migratory and invasive activity of the metastatic bladder tumor cells. Disruption of p130Cas attenuates both invasion and migration of the metastatic variant (253J-BV). 253J-BV cells displayed an increase in global thiol oxidation and a concomitant decrease in total phosphatase activity, common target proteins of active-site cysteine oxidation. The dependence of phosphatases on regulation of p130Cas was highlighted when depletion of PTPN12 enhanced p130cas phosphorylation and the migratory behavior of a noninvasive parental bladder tumor control (253J). These data show that the metastatic phenotype is accompanied by increases in steady-state H2O2 production that drive promigratory signaling and suggest that antioxidant-based therapeutics may prove useful in limiting bladder tumor invasiveness.

Human breast cancer cell metastasis is attenuated by lysyl oxidase inhibitors through down-regulation of focal adhesion kinase and the paxillin-signaling pathway

The extracellular matrix (ECM) plays a critical role in the development and invasion of primary breast tumors. Lysyl oxidase (LOX), which is an ECM remodeling enzyme, appears to play roles in promoting cancer cell motility and invasion. To ascertain whether LOX overexpression in breast tumor tissues from Asian patients is associated with decreases in metastasis-free and overall survival in breast cancer patients, the mRNA levels of LOX were examined in paired tumor/normal tissue samples using real-time RT-PCR analysis (n = 246 pair-matched samples). To test whether specifically targeting LOX by inhibiting its activity (using beta-aminopropionitrile (β-APN), a LOX inhibitor), mRNA expression (using siRNA), or protein expression (using 25 μM magnolol) attenuates the invasion of MDA-MB-231 breast cancer cells, a cancer cell migration assay was performed. Interestingly, only 78.5% (n = 193) of the breast cancer tumors displayed detectable LOX expression. Nearly 60% (n = 120) of the cases fell into Group 1 (tumor > normal, T > N); in this group, the mean LOX expression in the tumor cells was 20.2-fold greater than in normal cells. However, in Group 2 (normal > tumor, N > T), the LOX expression level in most of the normal tissues examined (80%, 59/73) was less than fivefold greater than in the tumor tissues. The increased level of active LOX in the invasive breast cancer cell line MDA-MB-231 was accompanied by the increased phosphorylation of focal adhesion kinase at Tyr-576 and of paxillin at Tyr-118. We also found that the addition of β-APN (300 μM) and magnolol (25 μM), synergistically inhibited the migration and invasion of MDA-MB-231 cells. In this article, we describe, for the first time, higher expression of a LOX protein in breast tumors compared with normal tissues from Asian patients. Moreover, the results indicate that the inhibition of LOX using magnolol may represent a more desirable strategy for breast cancer therapy than the use of β-APN.

Neutrophil transmigration, focal adhesion kinase and endothelial barrier function

Neutrophil activation is an essential component of innate immune defense against infection and injury. In response to inflammatory stimulation, circulating neutrophils undergo a series of dynamic and metabolic changes characterized by β2-intergrin mediated adhesion to microvascular endothelium and subsequent transendothelial migration. During this process, neutrophils release granular contents containing digestive enzymes and produce cytotoxic agents such as reactive oxygen species and cytokines. These products target endothelial barriers inducing phosphorylation-triggered junction dissociation, actin stress fiber formation, and actomyosin contraction, manifest as paracellular hyperpermeability. Endothelial cell-matrix focal adhesions play an integral role in this process by providing structural support for endothelial conformational changes that facilitate neutrophil transmigration, as well as by recruiting intracellular molecules that constitute the hyperpermeability signaling cascades. As a central connector of the complex signaling network, focal adhesion kinase (FAK) is activated following neutrophil adhesion, and further mediates the reorganization of endothelial integrin-matrix attachments in a pattern coordinating with cytoskeleton contraction and junction opening. In this review, we present recent experimental evidence supporting the importance of FAK in neutrophil-dependent regulation of endothelial permeability. The discussion focuses on the mechanisms by which neutrophils activate FAK and its downstream effects on endothelial barriers.

Pulmonary fibrosis inducer, bleomycin, causes redox-sensitive activation of phospholipase D and cytotoxicity through formation of bioactive lipid signal mediator, phosphatidic acid, in lung microvascular endothelial cells

The mechanisms of lung microvascular complications and pulmonary hypertension known to be associated with idiopathic pulmonary fibrosis (IPF), a debilitating lung disease, are not known. Therefore, we investigated whether bleomycin, the widely used experimental IPF inducer, would be capable of activating phospholipase D (PLD) and generating the bioactive lipid signal-mediator phosphatidic acid (PA) in our established bovine lung microvascular endothelial cell (BLMVEC) model. Our results revealed that bleomycin induced the activation of PLD and generation of PA in a dose-dependent (5, 10, and 100 µg) and time-dependent (2-12 hours) fashion that were significantly attenuated by the PLD-specific inhibitor, 5-fluoro-2-indolyl des-chlorohalopemide (FIPI). PLD activation and PA generation induced by bleomycin (5 µg) were significantly attenuated by the thiol protectant (N-acetyl-L-cysteine), antioxidants, and iron chelators suggesting the role of reactive oxygen species (ROS), lipid peroxidation, and iron therein. Furthermore, our study demonstrated the formation of ROS and loss of glutathione (GSH) in cells following bleomycin treatment, confirming oxidative stress as a key player in the bleomycin-induced PLD activation and PA generation in ECs. More noticeably, PLD activation and PA generation were observed to happen upstream of bleomycin-induced cytotoxicity in BLMVECs, which was protected by FIPI. This was also supported by our current findings that exposure of cells to exogenous PA led to internalization of PA and cytotoxicity in BLMVECs. For the first time, this study revealed novel mechanism of the bleomycin-induced redox-sensitive activation of PLD that led to the generation of PA, which was capable of inducing lung EC cytotoxicity, thus suggesting possible bioactive lipid-signaling mechanism/mechanisms of microvascular disorders encountered in IPF.

Microtubule stabilization opposes the (TNF-alpha)-induced loss in the barrier integrity of corneal endothelium

Microtubule disassembly breaks down the barrier integrity in a number of epithelial and endothelial monolayers. This study has investigated effects of TNF-alpha, which is implicated in corneal allograft rejection, on microtubules and barrier integrity in cultured bovine corneal endothelial cells. Exposure to TNF-alpha led to disassembly of the microtubules, and also caused disruption of the perijunctional actomyosin ring (PAMR). As a measure of barrier integrity, trans-endothelial electrical resistance (TER) was determined based on electrical cell-substrate impedance sensing in realtime. Exposure to TNF-alpha caused a slow decline in TER for > 20 h, and a similar exposure to cells grown on porous culture inserts led to a significant increase in permeability to FITC dextran. These changes, indicating a loss of barrier integrity, were also reflected by dislocation of ZO-1 at the cell border and disassembly of cadherins. These effects of TNF-alpha were inhibited upon stabilization of microtubules by pre-treatment with paclitaxel or epothilone B. Microtubule stabilization may be a useful strategy to overcome (TNF-alpha)-induced loss of the barrier integrity of corneal endothelium during inflammation associated with transplant rejection and uveitis.

Reactive oxygen species and boar sperm function

Boar spermatozoa are very susceptible to reactive oxygen species (ROS), but ROS involvement in damage and/or capacitation is unclear. The impact of exposing fresh boar spermatozoa to an ROS-generating system (xanthine/xanthine oxidase; XA/XO) on sperm ROS content, membrane lipid peroxidation, phospholipase (PL) A activity, and motility, viability, and capacitation was contrasted to ROS content and sperm function after cryopreservation. Exposing boar sperm (n = 4-5 ejaculates) to the ROS-generating system for 30 min rapidly increased hydrogen peroxide (H2O2) and lipid peroxidation in all sperm, increased PLA in dead sperm, and did not affect intracellular O2- (flow cytometry of sperm labeled with 2',7'-dichlorodihydrofluorscein diacetate, BODIPY 581/591 C11, bis-BODIPY-FL C11, hydroethidine, respectively; counterstained for viability). Sperm viability remained high, but sperm became immotile. Cryopreservation decreased sperm motility, viability, and intracellular O2- significantly, but did not affect H2O2. As expected, more sperm incubated in capacitating media than Beltsville thawing solution buffer underwent acrosome reactions and protein tyrosine phosphorylation (four proteins, 58-174 kDa); which proteins were tyrosine phosphorylated was pH dependent. Pre-exposing sperm to the ROS-generating system increased the percentage of sperm that underwent acrosome reactions after incubation in capacitating conditions (P < 0.025), and decreased capacitation-dependent increases in two tyrosine-phosphorylated proteins (P < or = 0.035). In summary, H2O2 is the major free radical mediating direct ROS effects, but not cryopreservation changes, on boar sperm. Boar sperm motility, acrosome integrity, and lipid peroxidation are more sensitive indicators of oxidative stress than viability and PLA activity. ROS may stimulate the acrosome reaction in boar sperm through membrane lipid peroxidation and PLA activation.

The PIM1 kinase is a critical component of a survival pathway activated by docetaxel and promotes survival of docetaxel-treated prostate cancer cells

A defining characteristic of solid tumors is the capacity to divide aggressively and disseminate under conditions of nutrient deprivation, limited oxygen availability, and exposure to cytotoxic drugs or radiation. Survival pathways are activated within tumor cells to cope with these ambient stresses. We here describe a survival pathway activated by the anti-cancer drug docetaxel in prostate cancer cells. Docetaxel activates STAT3 phosphorylation and transcriptional activity, which in turns induces expression of the PIM1 gene, encoding a serine-threonine kinase activated by many cellular stresses. Expression of PIM1 improves survival of docetaxel-treated prostate cancer cells, and PIM1 knockdown or expression of a dominant-negative PIM1 protein sensitize cells to the cytotoxic effects of docetaxel. PIM1 in turn mediates docetaxel-induced activation of NFkappaB transcriptional activity, and PIM1 depends in part on RELA/p65 proteins for its prosurvival effects. The PIM1 kinase plays a critical role in this STAT3 --> PIM1 --> NFkappaB stress response pathway and serves as a target for intervention to enhance the therapeutic effects of cytotoxic drugs such as docetaxel.

Disruption of FAK signaling: a side mechanism in cytotoxicity

Focal adhesion kinase (FAK) is a non-receptor protein tyrosine kinase (PTK) which acts as an early modulator in the integrin signaling cascade. FAK phosphorylation and its consequent activation regulate several basic biological cellular functions. On the contrary, dysregulation of FAK signaling is implicated in the malignant transformation of cells, as well as in nonmalignant pathological conditions. With respect to cytotoxicity, accumulating data indicate that FAK participates in the mechanism of action of the known cytotoxic reactive oxygen species (ROS). Additionally, evidence was presented that different cytotoxic substances, such as arsenic (As), lead (Pb), acrylamide, methylisothiazolinone (MIT), dichlorovinylcysteine (DCVC) and halothane, acted, at least in part, by downregulating FAK tyrosine phosphorylation, while the bacterial toxins Pasteurella multocida toxin and Escherichia coli cytotoxic necrotizing factor, have been shown to exert cytotoxic effects by inducing FAK tyrosine phosphorylation. The observation that upregulation as well as downregulation of FAK activity both result in cytotoxic effects seems contradictory. Even though a common mode of action, with respect to the dysregulation of FAK signaling, for these cytotoxic substances has not yet been discovered, a cumulative approach could be established by focusing on FAK activation and signaling cascade. According to these data, interfering with FAK signaling might be of a potential use in blocking these cytotoxic effects. Further studies are needed on the possible implication of FAK in substance-induced cytotoxicity, as well as the possibility that such effects might be hindered or even blocked by restoring FAK signaling.

Enhanced permeability and retention of macromolecular drugs in solid tumors: a royal gate for targeted anticancer nanomedicines

Over the past two decades cancer has ascended the causes of human death to be number one or two in many nations world wide. A major limitation inherent to most conventional anticancer chemotherapeutic agents is their lack of tumor selectivity. One way to achieve selective drug targeting to solid tumors is to exploit abnormalities of tumor vasculature, namely, hypervascularisation; aberrant vascular architecture; extensive production of vascular permeability factors stimulating extravasation within tumor tissues; and lack of lymphatic drainage. Maeda and his colleagues have extensively studied tumor vascular abnormalities in terms of active and selective delivery of anticancer drugs to tumor tissues, notably defining the enhanced permeability and retention effect (EPR effect) of macromolecular drugs in solid tumors. Due to their large molecular size, nanosized macromolecular anticancer drugs administered intravenously (i.v.) escape renal clearance. Often they can not penetrate the tight endothelial junctions of normal blood vessels, but they can extravasate in tumour vasculature and become trapped in the tumor vicinity. With time the tumor concentration will build up reaching several folds higher than that of the plasma due to lack of efficient lymphatic drainage in solid tumor; an ideal application for EPR-based selective anticancer drug delivery. Establishing this principle hastened development of various polymer conjugates and polymeric micelles as well as multifunctional nanoparticles for targeted cancer chemotherapy. Indeed this selective high local concentration of nanosized anticancer drugs in tumor tissues has proven superior in therapeutic effect with minimal side effects in both preclinical and clinical settings. In this review the mechanisms and factors involved in the EPR effect, as well as the uniqueness of nanoscale drugs for tumor targeting through EPR effect, will be discussed in detail.

Nitric oxide attenuates hydrogen peroxide-induced barrier disruption and protein tyrosine phosphorylation in monolayers of intestinal epithelial cell

The intestinal epithelium provides a barrier to the transport of harmful luminal molecules into the systemic circulation. A dysfunctional epithelial barrier is closely associated with the pathogenesis of a variety of intestinal and systemic disorders. We investigated here the effects of nitric oxide (NO) and hydrogen peroxide (H(2)O(2)) on the barrier function of a human intestinal epithelial cell line, Caco-2. When treated with H(2)O(2), Caco-2 cell monolayers grown on permeable supports exhibited several remarkable features of barrier dysfunction as follows: a decrease in transepithelial electrical resistance, an increase in paracellular permeability to dextran, and a disruption of the intercellular junctional localization of the scaffolding protein ZO-1. In addition, an induction of tyrosine phosphorylation of numerous cellular proteins including ZO-1, E-cadherin, and beta-catenin, components of tight and adherens junctions, was observed. On the other hand, combined treatment of Caco-2 monolayers with H(2)O(2) and an NO donor (NOC5 or NOC12) relieved the damage to the barrier function and suppressed the protein tyrosine phosphorylation induced by H(2)O(2) alone. These results suggest that NO protects the barrier function of intestinal epithelia from oxidative stress by modulating some intracellular signaling pathways of protein tyrosine phosphorylation in epithelial cells.

NADPH oxidase mediates vascular endothelial cadherin phosphorylation and endothelial dysfunction

Vascular endothelial activation is an early step during leukocyte/endothelial adhesion and transendothelial leukocyte migration in inflammatory states. Leukocyte transmigration occurs through intercellular gaps between endothelial cells. Vascular endothelial cadherin (VE-cadherin) is a predominant component of endothelial adherens junctions that regulates intercellular gap formation. We found that tumor necrosis factor (TNF) caused tyrosine phosphorylation of VE-cadherin, separation of lateral cell-cell junctions, and intercellular gap formation in human umbilical vein endothelial cell (HUVEC) monolayers. These events appear to be regulated by intracellular oxidant production through endothelial NAD(P)H (nicotinamide adenine dinucleotide phosphate) oxidase because antioxidants and expression of a transdominant inhibitor of the NADPH oxidase, p67(V204A), effectively blocked the effects of TNF on all 3 parameters of junctional integrity. Antioxidants and p67(V204A) also decreased TNF-induced JNK activation. Dominant-negative JNK abrogated VE-cadherin phosphorylation and junctional separation, suggesting a downstream role for JNK. Finally, adenoviral delivery of the kinase dead PAK1(K298A) decreased TNF-induced JNK activation, VE-cadherin phosphorylation, and lateral junctional separation, consistent with the proposed involvement of PAK1 upstream of the NADPH oxidase. Thus, PAK-1 acts in concert with oxidase during TNF-induced oxidant production and loss of endothelial cell junctional integrity.

Hydrogen peroxide-induced phospholipase D activation and its PKC dependence are modulated by pH changes in PC12 cells

Several factors for the hydrogen peroxide (H(2)O(2))-induced PLD stimulation have been proposed, including protein kinase C (PKC), tyrosine kinase, mitogen-activated protein kinase and Ca(2+), but their precise roles remain to be defined. As for involvement of PKC, there has been some discrepancy. Our previous study has demonstrated that phospholipase D (PLD) activity was increased by exposure of PC12 cells to 0.5mM H(2)O(2) in modified Krebs-Ringer buffer (KRB) and suggested that the PLD activation was independent of PKC activity. However, we have shown here that the H(2)O(2)-induced PLD stimulation was much greatly enhanced by incubation in Dulbecco's modified Eagle's medium (DMEM) and further that it was PKC-dependent. These results indicated that the markedly enhanced PLD activation and its PKC dependence were modulated by pH changes during incubation in DMEM. Furthermore, evidence has been presented for possible involvement of alkaline phosphatase in this pH-dependent profile of PLD activation by H(2)O(2).

Alpha2beta1-integrin signaling by itself controls G1/S transition in a human adenocarcinoma cell line (Caco-2): implication of NADPH oxidase-dependent production of ROS

In this work, we report that type IV collagen, mainly via alpha2beta1-integrin ligation, was able to induce cyclin expression and G1/S transition in a colic adenocarcinoma cell line (Caco-2) cultured without soluble growth factors or fetal bovine serum. This process involved Erk 1/2 activation and the production of reactive oxygen species (ROS) by a membrane-bound NADPH oxidase. Data presented here show that NADPH oxidase-dependent production of ROS increased following alpha2beta1-integrin ligation with type IV collagen or with a specific monoclonal antibody (Gi9 mAb). NADPH oxidase activation and, therefore, the production of ROS were shown to be involved in the increase of alpha2beta1-integrin plasma membrane expression, p38 MAPK phosphorylation, cyclin expression, and G1/S transition. We thus identified in this work a new integrin-signaling pathway in colon tumor cells involved in cell cycle regulation by the extracellular matrix.

Phospholipase D/phosphatidic acid signal transduction: role and physiological significance in lung

Phospholipase D (PLD), a phospholipid phosphohydrolase, catalyzes the hydrolysis of phosphatidylcholine and other membrane phospholipids to phosphatidic acid (PA) and choline. PLD, ubiquitous in mammals, is a critical enzyme in intracellular signal transduction. PA generated by agonist- or reactive oxygen species (ROS)-mediated activation of the PLDI and PLD2 isoforms can be subsequently converted to lysoPA (LPA) or diacylglycerol (DAG) by phospholipase A1/A2 or lipid phosphate phosphatases. In pulmonary epithelial and vascular endothelial cells, a wide variety of agonists stimulate PLD and involve Src kinases, p-38 mitogen activated protein kinase, calcium and small G proteins. PA derived from the PLD pathway has second-messenger functions. In endothelial cells, PA regulates NAD[P]H oxidase activity and barrier function. In airway epithelial cells, sphingosine-1-phosphate and PA-induced IL-8 secretion and ERKI/2 phosphorylation is regulated by PA. PA can be metabolized to LPA and DAG, which function as first- and second-messengers, respectively. Signaling enzymes such as Raf 1, protein kinase Czeta and type I phosphatidylinositol-4-phosphate 5-kinase are also regulated by PA in mammalian cells. Thus, PA and its metabolic products play a central role in modulating endothelial and epithelial cell functions.

Role of MAP kinase activation in Nramp1 mRNA stability in RAW264.7 macrophages expressing Nramp1(Gly169)

Nramp1 (natural resistance-associated macrophage protein 1) is a phagosomal iron transport molecule. In addition to its anti-microbial activity, Nramp1 exerts a wide range of pleiotropic effects, including increased stability of Nramp1 mRNA and a variety of other mRNA species. Previously, we showed that the increased stability of Nramp1 mRNA is regulated by an oxidant-generated signaling pathway that requires PKC. In the current study, we show that inhibition of ERK1,2 and p38 MAP kinase activities decreases Nramp1 mRNA stability in Mycobacterium avium infected RAW264.7 cells expressing Nramp1(Gly169) but not in RAW264.7-Nramp1(Asp169) cells. Phosphorylation of ERK1,2 and p38 MAP kinases, which could be inhibited by the anti-oxidant BHA and a protein kinase C inhibitor, was higher in M. avium infected RAW264.7-Nramp1(Gly169) cells than in RAW26.47-Nramp1(Asp169) cells. These results suggest that generation of oxidants by Nramp1 iron transport activates MAP kinase signaling cascades that result in stabilization of Nramp1 mRNA.

Role of Src kinase in diperoxovanadate-mediated activation of phospholipase D in endothelial cells

We have shown earlier that oxidant-induced activation of phospholipase D (PLD) in vascular endothelial cells (ECs) is regulated by protein tyrosine kinases. To further understand the regulation of oxidant-induced PLD activation, we investigated the role of Src kinase. Treatment of bovine pulmonary artery ECs (BPAECs) with a model oxidant, diperoxovanadate (DPV), at 5 microM concentration, for 30 min, stimulated PLD activity (four- to eightfold), which was attenuated by tyrosine kinase inhibitors and by Src kinase-specific inhibitors PP-1 and PP-2, in a dose- and time-dependent fashion. Furthermore, BPAECs exposed to DPV (5 microM) for 2 min showed activation of Src kinase as observed by increased tyrosine phosphorylation and autophosphorylation in Src immunoprecipitates, which was attenuated by PP-2. Src immunoprecipitates of cell lysates from control BPAECs exhibited PLD activity in cell-free preparations, which was Arf- and Rho-sensitive and was enhanced at 2 min of DPV (5 microM) treatment. Also, Western blots of Src immunoprecipitates of control cells revealed the presence of PLD(1) and PLD(2), suggesting the association of PLD with Src kinase under basal conditions. However, exposure of cells to DPV (5 microM) for 2 min enhanced the association of PLD(2) but not PLD(1) with Src. Western blotting of immunoprecipitates of PLD(1) and PLD(2) isoforms of control BPAECs revealed the presence of Src under basal conditions and exposure of cells to DPV (5 microM) for 2 min enhanced the association of PLD(2) with Src in PLD(2) immunoprecipitates. Transient expression of a dominant negative mutant of Src in BPAECs attenuated DPV- but not TPA-induced PLD activation. In cell-free preparations, Src did not phosphorylate either PLD(1) or PLD(2) compared to protein kinase Calpha or p38 mitogen-activated protein kinase. These data show for the first time a direct association of Src with PLD in ECs and regulation of PLD in intact cells.

Role of p38 MAP kinase in diperoxovanadate-induced phospholipase D activation in endothelial cells

We previously demonstrated that diperoxovanadate (DPV), a synthetic peroxovanadium compound and cell-permeable oxidant that acts as a protein tyrosine phosphatase inhibitor and insulinomimetic, increased phospholipase D (PLD) activation in endothelial cells (ECs). In this report, the regulation of DPV-induced PLD activation by mitogen-activated protein kinases (MAPKs) was investigated. DPV activated extracellular signal-regulated kinase, c-Jun NH2-terminal kinase (JNK), and p38 MAPK in a dose- and time-dependent fashion. Treatment of ECs with p38 MAPK inhibitors SB-203580 and SB-202190 or transient transfection with a p38 dominant negative mutant mitigated the PLD activation by DPV but not by phorbol ester. SB-202190 blocked DPV-mediated p38 MAPK activity as determined by activated transcription factor-2 phosphorylation. Immunoprecipitation of PLD from EC lysates with PLD1 and PLD2 antibodies revealed both PLD isoforms associated with p38 MAPK. Similarly, PLD1 and PLD2 were detected in p38 immunoprecipitates from control and DPV-challenged ECs. Binding assays demonstrated interaction of glutathione S-transferase-p38 fusion protein with PLD1 and PLD2. Both PLD1 and PLD2 were phosphorylated by p38 MAPK in vitro, and DPV increased phosphorylation of PLD1 and PLD2 in vivo. However, phosphorylation of PLD by p38 failed to affect PLD activity in vitro. These results provide evidence for p38 MAPK-mediated regulation of PLD in ECs.

Diperoxovanadate alters endothelial cell focal contacts and barrier function: role of tyrosine phosphorylation

Diperoxovanadate (DPV), a potent tyrosine kinase activator and protein tyrosine phosphatase inhibitor, was utilized to explore bovine pulmonary artery endothelial cell barrier regulation. DPV produced dose-dependent decreases in transendothelial electrical resistance (TER) and increases in permeability to albumin, which were preceded by brief increases in TER (peak TER effect at 10-15 min). The significant and sustained DPV-mediated TER reductions were primarily the result of decreased intercellular resistance, rather than decreased resistance between the cell and the extracellular matrix, and were reduced by pretreatment with the tyrosine kinase inhibitor genistein but not by inhibition of p42/p44 mitogen-activating protein kinases. Immunofluorescent analysis after DPV challenge revealed dramatic F-actin polymerization and stress-fiber assembly and increased colocalization of tyrosine phosphoproteins with F-actin in a circumferential pattern at the cell periphery, changes that were abolished by genistein. The phosphorylation of focal adhesion and adherens junction proteins on tyrosine residues was confirmed in immunoprecipitates of focal adhesion kinase and cadherin-associated proteins in which dramatic dose-dependent tyrosine phosphorylation was observed after DPV stimulation. We speculate that DPV enhances endothelial cell monolayer integrity via focal adhesion plaque phosphorylation and produces subsequent monolayer destabilization of adherens junctions initiated by adherens junction protein tyrosine phosphorylation catalyzed by p60(src) or Src-related tyrosine kinases.

Reactive oxygen species in cell signaling

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

Thiol oxidation activates a novel redox-regulated coronary vasodilator mechanism involving inhibition of Ca2+ influx

This study examines the mechanism of relaxation of isolated endothelium-removed bovine coronary arteries (BCAs) to the thiol oxidant diamide. BCAs precontracted with KCl or the thromboxane A(2) receptor agonist U46619 showed a concentration-dependent reversible relaxation on exposure to 10 micromol/L to 1 mmol/L diamide. This relaxation was enhanced by an inhibitor of glutathione reductase, and it was not altered by severe hypoxia, the presence of inhibitors of soluble guanylate cyclase, K(+) channels, tyrosine kinases, or probes that modulate levels of superoxide. The relaxation was almost eliminated when BCAs were precontracted with a phorbol ester that causes a contraction that is largely independent of extracellular Ca(2+). The initial transient contraction elicited by 5-hydroxytryptamine in Ca(2+)-free solution was not altered by the presence of 1 mmol/L diamide; however, a subsequent tonic contraction on addition of CaCl(2) was inhibited by diamide. Diamide also inhibited contractions caused by the addition of CaCl(2) to Ca(2+)-free Krebs' buffer containing Bay K8644 (an L-type Ca(2+) channel opener) or KCl. Relaxation to diamide was attenuated by L-type Ca(2+) channel blockers (nifedipine and diltiazem). Thus, thiol oxidation elicited by diamide appears to activate a novel redox-regulated vasodilator mechanism that seems to inhibit extracellular Ca(2+) influx.

Involvement of c-Src in diperoxovanadate-induced endothelial cell barrier dysfunction

Reactive oxygen species (ROS) generated by activated leukocytes play an important role in the disruption of endothelial cell (EC) integrity, leading to barrier dysfunction and pulmonary edema. Although ROS modulate cell signaling, information remains limited regarding the mechanism(s) of ROS-induced EC barrier dysfunction. We utilized diperoxovanadate (DPV) as a model agent to explore the role of tyrosine phosphorylation in the regulation of EC barrier function. DPV disrupted EC barrier function in a dose-dependent manner. Tyrosine kinase inhibitors, genistein, and PP-2, a specific inhibitor of Src, reduced the DPV-mediated barrier dysfunction. Consistent with these results, DPV-induced Src activation was attenuated by PP-2. Furthermore, DPV increased the association of Src with cortactin and myosin light chain kinase, indicating their potential role as cytoskeletal targets for Src. Transient overexpression of either wild-type Src or a constitutively active Src mutant potentiated the DPV-mediated decline in barrier dysfunction, whereas a dominant negative Src mutant attenuated the response. These studies provide the first direct evidence for Src involvement in DPV-induced EC barrier dysfunction.

Interactions of oxidants with vascular signaling systems

Individual reactive oxygen species (ROS) and oxidation products of NO interact with vascular signaling mechanisms in ways that appear to have fundamental roles in the control of vascular physiological and pathophysiological function. The activities of ROS-producing systems (including various NADPH and NADH oxidases, xanthine oxidase, and NO synthase) in endothelium and/or vascular smooth muscle are controlled by receptor activation, oxygen tension, metabolic processes, and physiological forces associated with blood pressure and flow. This review focuses on how the chemical properties and metabolic sensing interactions of individual ROS (including superoxide anion, hydrogen peroxide, and peroxynitrite) interact with cellular regulatory systems to produce vascular responses. These species appear to often function through producing selective alterations in individual heme or thiol redox-regulated systems (including guanylate cyclase, cyclooxygenase, mitochondrial electron transport, and tyrosine phosphatases) to initiate physiological responses through signaling pathways that control phospholipases, protein kinases, ion channels, contractile proteins, and gene expression.

Rapid and irreversible inactivation of protein tyrosine phosphatases PTP1B, CD45, and LAR by peroxynitrite

Protein tyrosine phosphatases (PTPs) contain an essential thiol in the active site which may be susceptible to attack by nitric oxide-derived biological oxidants. We assessed the effects of peroxynitrite, nitric oxide, and S-nitrosoglutathione on the activity of three human tyrosine phosphatases in vitro. The receptor-like T-cell tyrosine phosphatase (CD45), the non-receptor-like tyrosine phosphatase PTP1B, and leukocyte-antigen-related (LAR) phosphatase were all irreversibly inactivated by peroxynitrite in less than 1 s with IC(50) values of </=0.9 microM. PTP inactivation was also seen with equivalent concentrations of peroxynitrite generated by SIN-1, indicating that bolus peroxynitrite and cogeneration of superoxide and nitric oxide were equipotent. Rate constants for peroxynitrite-mediated PTP inactivation were determined by competition with cysteine and were among the fastest rates yet seen for reaction of peroxynitrite with any biological molecules. The bimolecular reaction rates for CD45, LAR, and PTP1B were 2.0 x 10(8), 2.3 x 10(7), and 2.2 x 10(7) M(-1) s(-1), respectively. Inactivation by peroxynitrite was essentially irreversible as incubation with dithiothreitol (DTT) restored less than 10% of the original phosphatase activity. Prolonged treatment with 0.4 mM DETA NONOate, which generated a steady-state concentration of 2 microM nitric oxide, was only slightly inhibitory. S-Nitrosoglutathione (1.0 mM) inhibited PTPs by approximately 50% after 30 min and the inhibition was completely reversed by DTT. Nitrotyrosine immunoblots of peroxynitrite-treated PTP1B revealed that peroxynitrite completely inactivated PTP1B prior to the appearance of protein tyrosine nitration. Peroxynitrite anion is structurally similar to phosphate anion both in terms of molecular diameter and charge. Thus, the extreme vulnerability of these PTPs to peroxynitrite-mediated inactivation is consistent with attraction of peroxynitrite anion to the active site and subsequent oxidation of the essential thiolate. These findings suggest that any PTP possessing the CXXXXXR active-site sequence could potentially be inactivated by peroxynitrite in vivo resulting in a net increase in tyrosine phosphorylation and profound effects on phosphotyrosine-dependent signaling cascades.

Activation of several MAP kinases upon stimulation of rat alveolar macrophages: role of the NADPH oxidase

Zymosan-activated serum (ZAS), a source of C5a, stimulates the rat alveolar macrophages (AM) to release superoxide anion. Here we show that treatment of rat AM with ZAS induced a time-dependent increase in the tyrosine phosphorylation of several proteins (116, 105-110, 82-78, 66-72, 62, 45, 42, and 38 kDa). This increase was sensitive to genistein, a tyrosine kinase inhibitor. ZAS stimulated the tyrosine phosphorylation and activation of three members of a family of serine/threonine kinases known as the mitogen-activated protein kinases (MAPK), i.e., ERK1 and ERK2, as assessed by immunoblotting, immunoprecipitation, and phosphotransferase activity, and p38 MAPK, as determined by immunoblotting with phospho-specific antibodies. In addition, ZAS induced the tyrosine phosphorylation of the SHC proteins and their association with GRB2, suggesting a role for this complex in the activation of the ERK pathway. Addition of extracellular catalase during ZAS stimulation significantly reduced the tyrosine phosphorylation response and the activation of ERK1 and ERK2 and their activator MEK1/2 while it did not affect that of p38 MAPK and MKK3/MKK6. Superoxide dismutase marginally increased the response to ZAS, supporting a role for hydrogen peroxide. In contrast to the results with AM, stimulation of human neutrophils with ZAS in the presence of catalase minimally altered the activation of ERK1 and ERK2. These data show that, in ZAS-stimulated rat AM, activation of the respiratory burst and production of hydrogen peroxide via superoxide dismutation are largely responsible for the activation of the ERK pathway through an upstream target.

Phospholipase D activation in endothelial cells is redox sensitive

Reactive oxygen species (ROS) are implicated in the pathophysiology of a number of vascular disorders, including atherosclerosis. Recent studies indicate that ROS modulate signal transduction in mammalian cells. Previously, we have shown that ROS (hydrogen peroxide, fatty acid hydroperoxide, diperoxovanadate, and 4-hydroxynonenal) enhance protein tyrosine phosphorylation and activate phospholipase D (PLD) in bovine pulmonary artery endothelial cells (BPAECs). In the present study, our aim was to investigate the role of exogenous thiol agents on ROS-induced PLD activation in conjunction with the role of cellular thiols--glutathione (GSH) and protein thiols--on PLD activation and protein tyrosine phosphorylation. Pretreatment of BPAECs with N-acetyl-L-cysteine (NAC) or 2-mercaptopropionylglycine (MPG) blocked ROS-induced changes in intracellular GSH and PLD activation. Also, pretreatment with NAC attenuated diperoxovanadate-induced protein tyrosine phosphorylation. Pretreatment of BPAECs with diamide or L-buthionine-(S,R)-sulfoximine (BSO), agents that lower intracellular GSH and thiols, enhanced PLD activity. Furthermore, NAC blocked diamide- or BSO-mediated changes in GSH levels, PLD activity, and protein tyrosine phosphorylation. NAC also attenuated diamide-induced tyrosine phosphorylation of proteins between 69 and 118 KDa. These results support the hypothesis that modulation of thiol-redox status (cellular nonprotein and protein thiols) may contribute to the regulation of ROS-induced protein tyrosine phosphorylation and PLD activation in vascular endothelium.