Protection from reoxygenation injury by inhibition of rac1

NADPH oxidase and endothelial cell function

Intracellular ROS (reactive oxygen species) such as superoxide and H2O2 have been increasingly appreciated to have a role in endothelial pathophysiology. Of the several sources within the vasculature, a family of multi-subunit NADPH oxidases appears to be a predominant contributor of endothelial superoxide. More importantly, this enzyme system is activated by numerous stimuli and is involved in triggering diverse intracellular signalling pathways (‘redox-sensitive’ signalling pathways) that have a central role in conditions such as endothelial activation and inflammation, cell growth, apoptosis and hypertrophy. Furthermore, NADPH oxidase-derived superoxide contributes to the impairment of endothelium-dependent vasodilatation by inactivating nitric oxide; the resultant endothelial dysfunction is implicated in the pathophysiology of diseases such as atherosclerosis, hypertension, diabetic vasculopathy and heart failure. A detailed understanding of the regulation of NADPH oxidases and their modulation and downstream effects may define novel therapeutic targets for cardiovascular disease prevention and treatment in the clinical setting, in contrast with global antioxidant therapy which has to date been disappointing.

Isoform-specific membrane targeting mechanism of Rac during Fc gamma R-mediated phagocytosis: positive charge-dependent and independent targeting mechanism of Rac to the phagosome

Rac1 and Rac2 are capable of stimulating superoxide production in vitro, but their targeting and functional mechanisms are still unknown. In the present study, we found that Rac1, 2, and 3 all accumulate at the phagosome during Fc gammaR-mediated phagocytosis, and that the order of accumulation (Rac1 > Rac3 > Rac2) depends on the net positive charge in their polybasic (PB) regions (183-188 aa). Although all GFP-tagged prenylated PB regions of Rac isoforms (GFP-Rac(PB)) and GFP-tagged prenylated 6 Ala (GFP-6A) accumulated during phagocytosis, GFP-Rac2(PB) and GFP-6A showed weak accumulation at the phagosome through a linear structure connecting the phagosome and endomembranes. The PB region of Rac1 showed strong phospholipid interaction with PI(3)P, PI(4)P, PI(5)P, PI(3,4,5)P3, and phosphatidic acid, however, that of Rac2 did not. Constitutively active Rac2, GFP-Rac2(Q61L), was predominantly localized at the endomembranes; these endomembranes fused to the phagosome through the linear structure during phagocytosis, and this accumulation mechanism did not depend on positive charge in the PB region. Our conclusion is that Rac1 directly targets to the phagosome using the positively charged PB region and this accumulation mechanism is likely enhanced by the phospholipids. In addition to this mechanism, Rac2 has a positive charge-independent mechanism in which Rac2 initially targets to endomembranes and then these endomembranes fuse to the phagosome.

Signal transducer and activator of transcription 3alpha and specificity protein 1 interact to upregulate intercellular adhesion molecule-1 in ischemic-reperfused myocardium and vascular endothelium

OBJECTIVE

Intercellular adhesion molecule-1 (ICAM-1) is upregulated rapidly on endothelial cells during ischemia-reperfusion (I-R) and mediates tissue leukocyte accumulation. The ICAM-1 proximal promoter contains a signal transducer and activator of transcription (Stat) binding motif (gamma-interferon activation site [GAS] sequence), which flanks a specificity protein 1 (Sp1) binding site. We examined the roles of Stat and Sp1 in the regulation of ICAM-1 after myocardial I-R.

METHODS AND RESULTS

Open-chest anesthetized rats underwent coronary artery occlusion for 35 minutes and reperfusion for 0 to 240 minutes. Stat became activated within 15 minutes after reperfusion, primarily in vascular endothelial cells; the activated Stat protein was identified as Stat3 (alpha-isoform). After phosphorylation on serine 727 (p-S727), Stat3alpha was found in association with the transcriptional regulator Sp1, and the complex bound to an ICAM-1-GAS probe. ICAM-1 expression increased after I-R and lagged shortly behind Stat3alpha activation. In cultured human umbilical vein endothelial (HUVE) cells, activation of Stat3alpha after hypoxia-reoxygenation (H-R) was dependent on the small GTPase Rac1. Transfection of a dominant-negative Stat3 (Y705F) adenovirus or a GAS decoy oligonucleotide reduced ICAM-1 mRNA expression after H-R. Using a reporter gene transfected into HUVE cells, mutation of the GAS element in the ICAM-1 promoter resulted in reduced transcriptional activity after H-R. Sp1 coimmunoprecipitated with p-S727 Stat3 during H-R, and Sp1 or Stat3alpha interfering RNA markedly reduced ICAM-1 mRNA expression.

CONCLUSIONS

The Sp1-Stat3 complex appears to play an important role in the upregulation of ICAM-1 transcription after reoxygenation or reperfusion.

Downregulation of Rac1 activation by caffeic acid in aortic smooth muscle cells

Caffeic acid, a dietary phenol from coffee, fruits and vegetables, is an efficient antioxidant. However, little is known about its anti-oxidative mechanism in the modulation of fundamental cellular processes. In this study, we investigated whether caffeic acid regulates Rac1 GTPase activity, a partner of NADPH oxidase. Our results showed that caffeic acid decrease Rac1 protein level under basal conditions and incubation with angiotensin II (ANG II) in vascular smooth muscle cells. In a Rac-bound-to-PAK pull down assay, caffeic acid clearly inhibited Rac1 activity. We also observed that caffeic acid suppressed the generation of superoxide anion stimulated by ANG II that activates NADPH oxidase. On the other hand, co-incubation with caffei caid and cycloheximide significantly accelerated the Rac1 degradation. In addition, pretreatment with caffeic acid for 24 hours was able to prevent phosphorylation of MLC and HSP27, when cells were challenged with ANG II through the redox sensitive pathway. These results support the hypothesis that caffeic acid reduces Rac1 GTPase protein and activity level, followed by a down-regulation of NADPH oxidase activity.

Endothelial cell superoxide generation: regulation and relevance for cardiovascular pathophysiology

The endothelial generation of reactive oxygen species (ROS) is important both physiologically and in the pathogenesis of many cardiovascular disorders. ROS generated by endothelial cells include superoxide (O2-*), hydrogen peroxide (H2O2), peroxynitrite (ONOO-*), nitric oxide (NO), and hydroxyl (*OH) radicals. The O2-* radical, the focus of the current review, may have several effects either directly or through the generation of other radicals, e.g., H2O2 and ONOO-*. These effects include 1) rapid inactivation of the potent signaling molecule and endothelium-derived relaxing factor NO, leading to endothelial dysfunction; 2) the mediation of signal transduction leading to altered gene transcription and protein and enzyme activities ("redox signaling"); and 3) oxidative damage. Multiple enzymes can generate O2-*, notably xanthine oxidase, uncoupled NO synthase, and mitochondria. Recent studies indicate that a major source of endothelial O2-* involved in redox signaling is a multicomponent phagocyte-type NADPH oxidase that is subject to specific regulation by stimuli such as oscillatory shear stress, hypoxia, angiotensin II, growth factors, cytokines, and hyperlipidemia. Depending on the level of oxidants generated and the relative balance between pro- and antioxidant pathways, ROS may be involved in cell growth, hypertrophy, apoptosis, endothelial activation, and adhesivity, for example, in diabetes, hypertension, atherosclerosis, heart failure, and ischemia-reperfusion. This article reviews our current knowledge regarding the sources of endothelial ROS generation, their regulation, their involvement in redox signaling, and the relevance of enhanced ROS generation and redox signaling to the pathophysiology of cardiovascular disorders where endothelial activation and dysfunction are implicated.

Kidney ischemia–reperfusion regulates expression and distribution of tubulin subunits, β-actin and rho GTPases in proximal tubules

Ischemic injury is characterized by a loss of cell polarity and a release of proximal tubule epithelial cells resulting from cytoskeletal reorganization. This study used a reversible unilateral renal ischemia-reperfusion model to investigate the expression and distribution of cytoskeletal components and Rho GTPases at protein and mRNA levels in proximal tubule fractions. Ischemia strongly increased beta-actin and alpha-tubulin expressions that were predominantly found in nuclear fractions. Rho GTPases and caveolin-1 expression were upregulated by ischemia and were enriched mainly in Triton-soluble membranes. Rac1 expression was stimulated in the soluble fractions during reperfusion. Rho GTPases mRNA levels were similarly regulated by ischemia-reperfusion suggesting that changes in their expressions could occur at gene or mRNA levels. ERM protein expression and distribution were unaffected by ischemia-reperfusion. Together, these data show that renal ischemia-reperfusion induced expression and redistribution of actin and microtubule cytoskeleton components in addition to Rho GTPases in proximal tubules, suggesting that they participate in an adaptive response to cellular lesions.

Novel approaches to augment adeno-associated virus type-2 endocytosis and transduction

Recombinant adeno-associated virus (rAAV) receptor binding, endocytosis, nuclear trafficking and second strand gene conversion have been described as potential rate-limiting steps in rAAV type-2 (rAAV-2) transduction. Several strategies have been developed to enhance rAAV-2 intracellular trafficking and gene conversion in an attempt to increase the efficiency of this virus as a gene therapy vector. To this end, the current study has investigated novel methods for augmenting rAAV transduction by enhancing endocytosis of rAAV-2. A selective trypsinization assay demonstrated that the abundance of internalized rAAV ssDNA was increased only in cells treated with both pyrrolidinedithiocarbonate (PDTC) and a genotoxic agent. Treating cells with each of these agents alone had no effect on rAAV endocytosis in comparison to controls. To investigate the mechanisms of this synergistic effect on rAAV transduction, the involvement of Rac1 protein was evaluated. Inhibition of the Rac1 pathway by expression of a dominant negative mutant of Rac1 (N17Rac1) decreased rAAV transduction. In contrast, expression of a dominant active form of Rac1 (V12Rac1) alone mimicked the up-regulated response seen in the presence of PDTC and genotoxic agents. These studies provide potential insights into the importance of the Rac1 pathway to enhance uptake of rAAV-2.

Requirement for Rac1-dependent NADPH oxidase in the cardiovascular and dipsogenic actions of angiotensin II in the brain

We have shown that intracellular superoxide (O(2)(*-)) production in CNS neurons plays a key role in the pressor, bradycardic, and dipsogenic actions of Ang II in the brain. In this study, we tested the hypothesis that a Rac1-dependent NADPH oxidase is a key source of O(2)(*-) in Ang II-sensitive neurons and is involved in these central Ang II-dependent effects. We performed both in vitro and in vivo studies using adenoviral (Ad)-mediated expression of dominant-negative Rac1 (AdN17Rac1) to inhibit Ang II-stimulated Rac1 activation, an obligatory step in NADPH oxidase activation. Ang II induced a time-dependent increase in Rac1 activation and O(2)(*-) production in Neuro-2A cells, and this was abolished by pretreatment with AdN17Rac1 or the NADPH oxidase inhibitors apocynin or diphenylene iodonium. AdN17Rac1 also inhibited Ang II-induced increases in NADPH oxidase activity in primary neurons cultured from central cardiovascular control regions. In contrast, overexpression of wild-type Rac1 (AdwtRac1) caused more robust NADPH oxidase-dependent O(2)(*-) production to Ang II. To extend the in vitro studies, the pressor, bradycardic, and drinking responses to intracerebroventricularly (ICV) injected Ang II were measured in mice that had undergone gene transfer of AdN17Rac1 or AdwtRac1 to the brain. AdN17Rac1 abolished the increase in blood pressure, decrease in heart rate, and drinking response induced by ICV injection of Ang II, whereas AdwtRac1 enhanced these physiological effects. The exaggerated physiological responses in AdwtRac1-treated mice were abolished by O(2)(*-) scavenging. These results, for the first time, identify a Rac1-dependent NADPH oxidase as the source of central Ang II-induced O(2)(*-) production, and implicate this oxidase in cardiovascular diseases associated with dysregulation of brain Ang II signaling, including hypertension.

Improved hepatic regeneration with reduced injury by redox factor-1 in a rat small-sized liver transplant model

Redox factor-1 (Ref-1) has been shown to function in a redox-dependent manner in the cell. This study was designed to examine the effects of Ref-1 on liver regeneration as well as protection against postischemic injury in a rat model of 20% partial liver transplantation. Adenovirus carrying the full length of Ref-1 gene was introduced into liver grafts by ex vivo perfusion via the portal vein during preservation. Liver graft weights were assessed, as well as graft histology, serum levels of alanine aminotransferase (ALT)/bilirubin, DNA binding activities of AP-1 and Stat3. Redox factor-1 successfully expressed in the liver graft, improved regeneration by promoting cell proliferation. Overexpression of Ref-1 protein also reduced post-transplant injury and inflammatory reactions in the grafts. The increased serum levels of ALT and bilirubin observed after transplantation were significantly reduced by Ref-1 overexpression. Furthermore, adenovirally overexpressed Ref-1 in mouse liver successfully promoted liver regeneration after simple partial hepatectomy. Interestingly, Ref-1 significantly increased DNA binding of Stat3, but not AP-1. Overexpressed Ref-1 effectively promoted graft regeneration and reduced postischemic injury in a small-sized liver transplantation model. The results of the present study may open a new avenue to clinical transplantation of disproportionately sized grafts in living-related liver transplantation.

Cerebral ischemia and reperfusion: the pathophysiologic concept as a basis for clinical therapy

The ischemic penumbra has been documented in the laboratory animal as severely hypoperfused, nonfunctional, but still viable brain tissue surrounding the irreversibly damaged ischemic core. Saving the penumbra is the main target of acute stroke therapy, and is the theoretical basis behind the reperfusion concept. In experimental focal ischemia, early reperfusion has been reported to both prevent infarct growth and aggravate edema formation and hemorrhage, depending on the severity and duration of prior ischemia and the efficiency of reperfusion, whereas neuronal damage with or without enlarged infarction also may result from reperfusion (so-called reperfusion injury). Activated neutrophils contribute to vascular reperfusion damage, yet posthypoxic cellular injury occurs in the absence of inflammatory species. Protein synthesis inhibition occurs in neurons during reperfusion after ischemia, underlying the role that these pathways play in prosurvival and proapoptotic processes that may be differentially expressed in vulnerable and resistant regions of the reperfused brain tissue. Ischemia-induced decreases in the mitochondrial capacity for respiratory activity probably contribute to the ongoing impairment of energy metabolism during reperfusion and possibly also the magnitude of changes seen during ischemia. From these experimental data, the concept of single-drug intervention cannot be effective. Further experimental research is needed, especially of the study of biochemical markers of the injury process to establish the role of several drugs.

NADPH oxidases: not just for leukocytes anymore!

In addition to their role in bacterial killing by leukocytes, reactive oxygen species (ROS) have been increasingly recognized as important components of signaling and host defense in other cell types. The formation of ROS in both phagocytic- and non-phagocytic cells involves membrane-localized NADPH oxidases (Noxs). Nox proteins show structural homology to the cytochrome b(558) of leukocytes but, until recently, their regulation has been poorly understood. Here, we describe our current understanding of Nox function, and discuss emerging paradigms for regulation of Nox activity by Rac GTPase and/or other cytosolic components.

Oxidative stress-induced signal transduction pathways in cardiac myocytes: involvement of ROS in heart diseases

Reactive oxygen species (ROS) are proposed to contribute to the deterioration of cardiac function in patients with heart diseases. It has been reported that ROS are increased in the failing heart and involved in atherosclerosis, myocardial ischemia/reperfusion injury, and heart failure. Antioxidant enzymes are decreased in the decompensated heart, depressing defense mechanisms against oxidative stress. A variety of proteins, including receptors, ionic channels, transporters, and components of signal transduction pathways, are substrates of oxidation by ROS. ROS also function as signal transduction intermediates to induce transcription factor activation, gene expression, cell growth, and apoptosis. Recently, the upstream and downstream molecules of ROS in signal transduction pathways have been the subjects of intense investigation. These molecules include the mitogen-activated protein kinase family, the Rho family of small GTP binding proteins, the Src family of tyrosine kinases, Ras, and cytokines. The modulation of oxidative stress-induced signaling pathways is effective for preventing the progression of heart diseases.

The general case for redox control of wound repair

The orthodox view has been that reactive oxygen species are primarily damaging to cells. There is general agreement that while high (3%) doses of H(2)O(2) may serve as a clinical disinfectant, its overall effect on healing is not positive. Current work shows that at very low concentrations, reactive oxygen species may regulate cellular signaling pathways by redox-dependent mechanisms. Recent discoveries show that almost all cells of the wound microenvironment contain specialized enzymes that utilize O(2) to generate reactive oxygen species. Numerous aspects of wound healing are subject to redox control. An understanding of how endogenous reactive oxygen species are generated in wound-related cells may influence the healing process and could result in new redox-based therapeutic strategies. Current results with growth factor therapy of wounds have not met clinical expectations. Many of these growth factors, such as platelet-derived growth factor, rely on reactive oxygen species for functioning. Redox-based strategies may serve as effective adjuncts to jump-start healing of chronic wounds. The understanding of wound-site redox biology is also likely to provide novel insights into the fundamental mechanisms that would help to optimize conditions for oxygen therapy. While a window of therapeutic opportunity seems to exist under conditions of low concentrations of reactive oxygen species, high levels may complicate regeneration and remodeling of nascent tissue.

Superoxide, H2O2, and iron are required for TNF-alpha-induced MCP-1 gene expression in endothelial cells: role of Rac1 and NADPH oxidase

Reactive oxygen species (ROS) play an important but not yet fully defined role in the expression of inflammatory genes such as monocyte chemoattractant protein (MCP)-1. We used complementary molecular and biochemical approaches to explore the roles of specific ROS and their molecular linkage to inflammatory signaling in endothelial cells. Adenovirus-mediated expression of superoxide dismutase and catalase inhibited TNF-alpha-induced MCP-1 gene expression, suggesting important roles of superoxide (O(2)(-).) and H(2)O(2) in MCP-1 gene activation. In addition, the iron chelator 1,2-dimethyl-3-hydroxypyridin-4-one and the hydroxyl radical scavengers dimethylthiourea and dimethyl sulfoxide inhibited TNF-alpha-induced MCP-1 expression, suggesting important roles of iron and hydroxyl radicals in inflammatory signal activation. In contrast, scavenging of peroxynitrite with 5,10,15,20-tetrakis-(4-sulfonatophenyl)prophyrinato iron (III) chloride had no effect on TNF-alpha-induced MCP-1 expression. Inhibition of NADPH oxidase, the major oxidase responsible for O(2)(-). generation, with diphenylene iodonium suppressed TNF-alpha-induced MCP-1 mRNA accumulation. Rac1 is an upstream signaling molecule for the activation of NADPH oxidase and O(2)(-). generation. Expression of dominant negative N17Rac1 by adenovirus suppressed TNF-alpha-induced MCP-1 mRNA levels and MCP-1 protein secretion. Expression of N17Rac1 inhibited TNF-alpha-induced MCP-1 and NF-kappaB transcriptional activity. These data suggest that ROS such as superoxide and H(2)O(2) derived from Rac1-activated NADPH oxidase mediate TNF-alpha-induced MCP-1 expression in endothelial cells.

Inactivation of the small GTPase Rac1 protects the liver from ischemia/reperfusion injury in the rat

BACKGROUND

In ischemia/reperfusion (I/R) injury, a massive generation of reactive oxygen species (ROS) after reperfusion is a critical factor. Rac, a member of the Rho GTPase superfamily, plays important roles in the production of ROS and activation of nuclear factor-kappaB (NF-kappaB) in vitro. However, the exact role of Rac in the ROS production and NF-kappaB activation in vivo after I/R is still obscure.

METHODS

We blocked Rac1 activity in the rat liver using adenovirus encoding a dominant negative rac1 mutant (Ad5N17Rac1) and examined whether inactivation of Rac1 could prevent ROS generation in the hepatic I/R injury. Seventy-two hours after the adenoviral infection, hepatic I/R was induced by Pringle's maneuver for 20 minutes, followed by reperfusion in the rats.

RESULTS

Ad5N17Rac1 infection significantly attenuated ROS production after reperfusion and suppressed the hepatic injury. Furthermore, N17Rac1 suppressed NF-kappaB activation and messenger RNA expression of tumor necrosis factor-alpha (TNF-alpha) and inducible nitric oxide synthetase (iNOS). Ad5LacZ, a control adenovirus, had no effect on the induced hepatic I/R injury, nor did it affect NF-kappaB activation. Immunohistochemical analysis of NF-kappaB (p65) revealed that translocation of p65 to the nucleus after reperfusion was blocked in many of non-parenchymal cells (NPCs) and in hepatocytes in the Ad5N17Rac1-infected liver.

CONCLUSION

We conclude that Rac1 is required in ROS generation and NF-kappaB activation after hepatic I/R in vivo, and that inactivation of NF-kappaB in NPCs and suppression of ROS generation in NPCs and hepatocytes possibly account for the protective effect of N17Rac1 in this study.

Thrombospondin 2 regulates cell proliferation induced by Rac1 redox-dependent signaling

Thrombospondin 2 (TSP2) is a matricellular protein controlling the apoptosis-proliferation balance in endothelial cells. Little is known about its transcriptional regulation compared with that of TSP1. We found that overexpression of a constitutively active mutant of Rac (Rac(V12)) specifically increases TSP2 mRNA levels without affecting TSP1 in human aortic endothelial cells (HAEC). Moreover, TSP2 induction by Rac(V12) is dependent upon reactive oxygen species (ROS) production, as gp91ds-tat peptide, an inhibitor of NADPH oxidase, and the flavoprotein inhibitor diphenylene iodinium (DPI) block TSP2 synthesis. Furthermore, we found that increasing Rac(V12) expression results in a biphasic proliferative curve, with proliferation initially increasing as Rac(V12) expression increases and then returning to levels less than that of control cells at higher expression. This growth inhibition is mediated by TSP2, as either DPI treatment, which blocks TSP2 synthesis, or pan-TSP blocking antibodies restore the proliferative ability of HAEC with high expression. Mechanistically, we show that the effect of TSP2 on cell proliferation is independent of the antiangiogenic TSP2 Hep1 sequence, which is capable of altering actin cytoskeletal reorganization but not proliferation in our experimental conditions. Finally, we show in vivo that Rac-induced TSP2 expression is observed in the aorta of transgenic mice selectively expressing Rac(V12) in smooth muscle cells. These results identify Rac-induced ROS as a new pathway involved in the regulation of TSP2 expression.

NAD(P)H oxidase participates in the signaling events in high glucose-induced proliferation of vascular smooth muscle cells

Reactive oxygen species (ROS) have been implicated in the pathogenesis of vascular dysfunction in diabetes mellitus, and NAD(P)H oxidase is known as the most important source of ROS in the vasculatures. To determine whether NAD(P)H oxidase is a major participant in the critical intermediary signaling events in high glucose (HG, 25 mM)-induced proliferation of vascular smooth muscle cells (VSMC), we investigated in explanted aortic VSMC from rats the role of NAD(P)H oxidase on the HG-related cellular proliferation and superoxide production. VSMC under HG condition had increased proliferative capacity that was inhibited by tiron (1 mM), a cell membrane permeable superoxide scavenger, but not by SOD, which is not permeable to cell membrane. The nitroblue tetrazolium staining in the HG-exposed VSMC was more prominent than that of VSMC under normal glucose (5.5 mM) condition, which was significantly inhibited by DPI (10 microM), an NAD(P)H oxidase inhibitor, but not by inhibitors for other oxidases such as NADH dehydrogenase, xanthine oxidase, and nitric oxide synthase. In the VSMC under HG condition, the enhanced NAD(P)H oxidase activity with increased membrane translocation of Rac1 was observed, but the protein expression of p22phox and gp91phox was not increased. These data suggest that HG-induced changes in VSMC proliferation are related to the intracellular production of superoxide through enhanced activity of NAD(P)H oxidase.

Inhibition of hypoxia/reoxygenation-induced oxidative stress in HGF-stimulated antiapoptotic signaling: role of PI3-K and Akt kinase upon rac1

Rac1-regulated reactive oxygen species (ROS) production has been implicated in apoptosis. In contrast, pleiotropic protein kinase Akt protects against apoptosis. However, the pro- and antiapoptotic mechanisms of rac1 and Akt, respectively, and the intersection between these mechanisms are incompletely understood. In a model of oxidative stress and apoptosis induced by hypoxia/reoxygenation (H/R) in primary hepatocytes, activation of the PI3-K Akt axis by the prosurvival hepatocyte growth factor (HGF) inhibited H/R-stimulated rac1 activation and intracellular ROS production, and suppressed apoptosis. Suppression of PI3-K or Akt activity abrogated the inhibitory effect of HGF on rac1 activity and rac1-regulated oxidative stress. Furthermore, constitutive activation of Akt or PI3-K in the absence of HGF was sufficient to phosphorylate rac1, inhibit rac1 activation, and suppress rac1-regulated ROS production. These findings demonstrate that growth factor-stimulated activation of PI3-K-Akt is necessary and sufficient to suppress intracellular oxidative stress and apoptosis by inhibiting activation of pro-apoptotic, prooxidative rac1 GTPase.

Dependence of liver injury after hemorrhage/resuscitation in mice on NADPH oxidase-derived superoxide

Hemorrhagic shock and resuscitation cause hepatocellular damage by mechanisms involving oxidative stress. However, the sources of free radicals mediating hepatocellular injury remain controversial. Thus, this study tested the hypothesis that NADPH oxidase plays a role in producing hepatocellular injury after hemorrhagic shock and resuscitation. Both wild-type and NADPH oxidase-deficient mice (p47(phox) knockout mice) were subjected to hemorrhagic shock (3 h at 30 mmHg). The mice were resuscitated over 30 min with the shed blood and additional lactated Ringer's solution (50% of the shed blood volume). Serum alanine aminotransferase (ALT) levels increased at 1 and 6 h postresuscitation in wild-type animals to 4735 +/- 1017 IU/L and 1450 +/- 275 IU/L (mean +/- SE), respectively, whereas in knockout mice, this ALT increase was blunted at both time points (732 +/- 241 IU/L and 328 +/- 69 IU/L, P < 0.05). Liver necrosis assessed histologically 6 h after the end of reperfusion was also attenuated in the knockout mice (3.5% +/- 0.95% of area vs. 0.9% +/- 0.26%, P < 0.05). In hemorrhaged wild-type mice, infiltrating neutrophils were twice as numerous compared with hemorrhaged NADPH oxidase-deficient animals 6 h after reperfusion. In knockout animals, hepatic 4-hydroxynonenal content, indicative of lipid peroxidation from reactive oxygen species, was blunted (6.7% +/- 0.6% vs. 26.4% +/- 2.3% of stained area, P < 0.05), as shown by immunohistochemistry. Immunohistochemical staining for 3-nitrotyrosine, indicative of reactive nitrogen species formation, was also blunted in the livers of knockout mice (11.6% +/- 2.8% vs. 37.4% +/- 3.4, P < 0.05). In conclusion, hemorrhagic shock and resuscitation cause hepatocellular damage via NADPH oxidase-mediated oxidative stress. The absence of NADPH oxidase substantially attenuates hepatocellular injury after hemorrhagic shock and resuscitation, blunts neutrophil infiltration, and decreases formation of reactive oxygen and reactive nitrogen species.

Down-regulation of Rac-1 GTPase by Estrogen

Rac1 GTPase is essential for the activation of the NAD(P)H oxidase complex and, thereby, regulates the release of reactive oxygen species (ROS) in the vessel wall. 17 beta-estradiol (E2) inhibits vascular ROS production. To elucidate the underlying molecular mechanisms we investigated the potential regulation of Rac1 by E2 in vascular smooth muscle cells. Treatment of vascular smooth muscle cells with angiotensin II as well as overexpression of the constitutively active mutant RacL61 increased ROS release as assessed by dichlorofluorescein fluorescence, whereas inhibition of Rac1 by Clostridium sordellii lethal toxin or overexpression of dominant-negative RacN17 inhibited ROS production. Treatment with E2 (100 nm) completely prevented angiotensin II-induced NAD(P)H oxidase activity and ROS production. E2 time and concentration dependently decreased angiotensin II-induced and basal Rac1 mRNA and protein expression as well as Rac1 activity. Down-regulation of Rac1 expression by E2 was mediated by inhibition of gene transcription (nuclear run-on assays), but E2 had no effect on Rac1 mRNA stability. Regulation of Rac1 was mediated by estrogen receptors since co-incubation with ICI 182.780 prevented down-regulation of Rac1. To test these observations in vivo, ovariectomized spontaneously hypertensive rats were treated with E2 or vehicle. Real-time PCR and Western blotting showed reduction of aortic Rac1 mRNA and protein by 32 and 58%, respectively. Furthermore, down-regulation of Rac1 by E2 was observed in human mononuclear cells of women with elevated E2 levels after controlled ovarian hyperstimulation. Rac1 GTPase gene-transcription and activity is regulated by 17 beta-estradiol, which may be an important molecular mechanism contributing to the cardiovascular effects of estrogens.

Necrosis: a specific form of programmed cell death?

For a long time necrosis was considered as an alternative to programmed cell death, apoptosis. Indeed, necrosis has distinct morphological features and it is accompanied by rapid permeabilization of plasma membrane. However, recent data indicate that, in contrast to necrosis caused by very extreme conditions, there are many examples when this form of cell death may be a normal physiological and regulated (programmed) event. Various stimuli (e.g., cytokines, ischemia, heat, irradiation, pathogens) can cause both apoptosis and necrosis in the same cell population. Furthermore, signaling pathways, such as death receptors, kinase cascades, and mitochondria, participate in both processes, and by modulating these pathways, it is possible to switch between apoptosis and necrosis. Moreover, antiapoptotic mechanisms (e.g., Bcl-2/Bcl-x proteins, heat shock proteins) are equally effective in protection against apoptosis and necrosis. Therefore, necrosis, along with apoptosis, appears to be a specific form of execution phase of programmed cell death, and there are several examples of necrosis during embryogenesis, a normal tissue renewal, and immune response. However, the consequences of necrotic and apoptotic cell death for a whole organism are quite different. In the case of necrosis, cytosolic constituents that spill into extracellular space through damaged plasma membrane may provoke inflammatory response; during apoptosis these products are safely isolated by membranes and then are consumed by macrophages. The inflammatory response caused by necrosis, however, may have obvious adaptive significance (i.e., emergence of a strong immune response) under some pathological conditions (such as cancer and infection). On the other hand, disturbance of a fine balance between necrosis and apoptosis may be a key element in development of some diseases.

Novel role of gp91(phox)-containing NAD(P)H oxidase in vascular endothelial growth factor-induced signaling and angiogenesis

Vascular endothelial growth factor (VEGF) induces angiogenesis by stimulating endothelial cell proliferation and migration, primarily through the receptor tyrosine kinase VEGF receptor2 (Flk1/KDR). Reactive oxygen species (ROS) derived from NAD(P)H oxidase are critically important in many aspects of vascular cell regulation, and both the small GTPase Rac1 and gp91(phox) are critical components of the endothelial NAD(P)H oxidase complex. A role of NAD(P)H oxidase in VEGF-induced angiogenesis, however, has not been defined. In the present study, electron spin resonance spectroscopy is utilized to demonstrate that VEGF stimulates O2*- production, which is inhibited by the NAD(P)H oxidase inhibitor, diphenylene iodonium, as well as by overexpression of dominant-negative Rac1 (N17Rac1) and transfection of gp91(phox) antisense oligonucleotides in human umbilical vein endothelial cells (ECs). Antioxidants, including N-acetylcysteine (NAC), various NAD(P)H oxidase inhibitors, and N17Rac1 significantly attenuate not only VEGF-induced KDR tyrosine phosphorylation but also proliferation and migration of ECs. Importantly, these effects of VEGF are dramatically inhibited in cells transfected with gp91(phox) antisense oligonucleotides. By contrast, ROS are not involved in mediating these effects of sphingosine 1-phosphate (S1P) on ECs. Sponge implant assays demonstrate that VEGF-, but not S1P-, induced angiogenesis is significantly reduced in wild-type mice treated with NAC and in gp91(phox-/-) mice, suggesting that ROS derived from gp91(phox)-containing NAD(P)H oxidase play an important role in angiogenesis in vivo. These studies indicate that VEGF-induced endothelial cell signaling and angiogenesis is tightly controlled by the reduction/oxidation environment at the level of VEGF receptor and provide novel insights into the NAD(P)H oxidase as a potential therapeutic target for angiogenesis-dependent diseases.

Rac-dependent monocyte chemoattractant protein-1 production is induced by nutrient deprivation

Under ischemic conditions, the vessel wall recruits inflammatory cells. Human aortic endothelial cells (HAECs) exposed to hypoxia followed by reoxygenation produce monocyte chemoattractant protein-1 (MCP-1); however, most experiments have been performed in the presence of nutrient deprivation (ND). We hypothesized that ND rather than hypoxia mediates endothelial MCP-1 production during ischemia, and that the small GTP-binding protein Rac1 and reactive oxygen species (ROS) are involved in this process. ND was generated by shifting HAECs from 10% to 1% FBS. Superoxide production by HAECs was increased 6 to 24 hours after ND, peaking at 18 hours. MCP-1 production was increased over a similar time frame, but peaked later at 24 hours. These effects were blocked by treatment with antioxidants such as superoxide dismutase mimetic and N-acetylcysteine (NAC), or NADPH oxidase inhibitors, DPI and gp91ds-tat. Superoxide and MCP-1 production were enhanced by RacV12 (constitutively active) in the absence of ND, and were inhibited by RacN17 (dominant-negative) adenoviral transduction under ND, suggesting that the small G-protein Rac1 is required. In conclusion, ND, an important component of ischemia, is sufficient to induce MCP-1 production by HAECs, and such production requires a functional Rac1, redox-dependent pathway.

Current molecular models for NADPH oxidase regulation by Rac GTPase

Reactive oxygen species (ROS) have been increasingly recognized as important components of cell signaling in addition to their well-established roles in host defense. The formation of ROS in phagocytic and nonphagocytic cells involves membrane-localized and Rac guanosine triphosphatase (GTPase)-regulated reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase(s). We discuss here the current molecular models for Rac GTPase action in the control of the phagocytic leukocyte NADPH oxidase. As a mechanistically detailed example of Rac GTPase signaling, the NADPH oxidase provides a potential paradigm for signaling by Rho family GTPases in general.

Mitogen-activated protein kinases regulate HO-1 gene transcription after ischemia-reperfusion lung injury

Lung ischemia-reperfusion (I-R) is an important model of oxidant-mediated acute lung and vascular injury. Heme oxygenase-1 (HO-1) is a cytoprotective gene that is markedly induced by lung I-R injury. HO-1 mRNA is increased in mouse lung after 30 min of lung hilar clamping (ischemia) followed by 2-6 h of unclamping (reperfusion) compared with control mice. In a variety of vascular cell types, HO-1 mRNA is induced after 24 h of anoxia followed by 30 min-1 h of reoxygenation (A-R). Transfection studies reveal that the promoter and 5'-distal enhancer E1 are necessary and sufficient for increased HO-1 gene transcription after A-R. Immunoblotting studies show all three subfamilies of MAPKs (ERK, JNK, and p38) are activated by 15 min of reperfusion. We also demonstrate that HO-1 gene transcription after A-R involves ERK, JNK, and p38 MAPK pathways. Together, our data show that I-R not only induces HO-1 gene expression in mouse lungs and vascular cells but that gene transcription occurs via the promoter and E1 enhancer and involves upstream MAPK pathways.

Oxidant-induced vascular endothelial growth factor expression in human keratinocytes and cutaneous wound healing

Neutrophils and macrophages, recruited to the wound site, release reactive oxygen species by respiratory burst. It is commonly understood that oxidants serve mainly to kill bacteria and prevent wound infection. We tested the hypothesis that oxidants generated at the wound site promote dermal wound repair. We observed that H(2)O(2) potently induces vascular endothelial growth factor (VEGF) expression in human keratinocytes. Deletion mutant studies with a VEGF promoter construct revealed that a GC-rich sequence from bp -194 to -50 of the VEGF promoter is responsible for the H(2)O(2) response. It was established that at microm concentrations oxidant induces VEGF expression and that oxidant-induced VEGF expression is independent of hypoxia-inducible factor (HIF)-1 and dependent on Sp1 activation. To test the effect of NADPH oxidase-generated reactive oxygen species on wound healing in vivo, Rac1 gene transfer was performed to dermal excisional wounds left to heal by secondary intention. Rac1 gene transfer accelerated wound contraction and closure. Rac1 overexpression was associated with higher VEGF expression both in vivo as well in human keratinocytes. Interestingly, Rac1 gene therapy was associated with a more well defined hyperproliferative epithelial region, higher cell density, enhanced deposition of connective tissue, and improved histological architecture. Overall, the histological data indicated that Rac1 might be an important stimulator of various aspects of the repair process, eventually enhancing the wound-healing process as a whole. Taken together, the results of this study indicate that wound healing is subject to redox control.

Redox factor-1: an extra-nuclear role in the regulation of endothelial oxidative stress and apoptosis

The rac1 GTPase promotes oxidative stress through reactive oxygen species (ROS) production, whereas the DNA repair enzyme and transcriptional regulator redox factor-1 (ref-1) protects against cell death due to oxidative stimuli. However, the function of ref-1 in regulating intracellular oxidative stress, particularly that induced by rac1, has not been defined. We examined the role of ref-1 in vascular endothelial cell oxidative stress and apoptosis. Ref-1 was expressed in both the cytoplasm and nuclei of resting endothelial cells. Cytoplasmic ref-1 translocated to the nucleus with the oxidative trigger hypoxia/reoxygenation (H/R). Forced cytoplasmic overexpression of ref-1 suppressed H/R-induced oxidative stress (H(2)O(2) production), NF-kappaB activation, and apoptosis, and also mitigated rac1-regulated H(2)O(2) production and NF-kappaB transcriptional activity. We conclude that inhibition of oxidative stress is another mechanism by which ref-1 protects against apoptosis, and that this is achieved through modulation of cytoplasmic rac1-regulated ROS generation. This suggests a novel extra-nuclear function of ref-1.

Adhesion of flowing monocytes to hypoxia-reoxygenation-exposed endothelial cells: role of Rac1, ROS, and VCAM-1

Production of reactive oxygen species (ROS) by ischemic tissue after ischemia-reperfusion (I/RP) is an important factor that contributes to tissue injury. The small GTPase Rac1 mediates the oxidative burst, and ROS act on signaling pathways involved in expression of inflammatory genes. Because there is evidence implicating monocytes in the pathogenesis of I/RP injury, our objective was to determine the molecular mechanisms that regulate adhesive interactions between monocytes and hypoxia-reoxygenation (H/RO)-exposed cultured endothelial cells (ECs). When U937 cells were perfused over human umbilical vein ECs at 1 dyn/cm2, H (1 h at 1% O2)/RO (13 h) significantly increased the fluxes of rolling and stably adherent U937 cells. Either EC treatment with the antioxidant pyrrolidine dithiocarbamate (PDTC) or infection with AdRac1N17, which results in expression of the dominant-negative form of Rac1, abolished H/RO-induced ROS production, attenuated rolling, and abolished stable adhesion of U937 cells to H/RO-exposed ECs. Infection with AdRac1N17 also abolished H/RO-induced upregulation of vascular cell adhesion molecule (VCAM)-1. In turn, blocking VCAM-1 abolished U937 cell stable adhesion and slightly increased rolling. We concluded that the Rac1-dependent ROS partially regulate rolling and exclusively regulate stable adhesion of monocytic cells to ECs after H/RO and that stable adhesion, but not rolling, is mediated by ROS-induced expression of VCAM-1.

Reactive oxygen species, mitochondria, and NAD(P)H oxidases in the development and progression of heart failure

Reactive oxygen species (ROS) released acutely in large amounts have been traditionally implicated in the cell death associated with myocardial infarction or reperfusion injury. These ROS can be released from the cardiac myocyte mitochondria, xanthine oxidase, and the phagocytic nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase. Interestingly, the chronic release of ROS has been recently linked to the development of left ventricular hypertrophy and heart failure progression. The chronic release of ROS appears to derive from the nonphagocytic NAD(P)H oxidase and mitochondria. Experimental data are accumulating suggesting that the release of ROS is required for the normal, physiologic activity of cardiac cells, but abnormal activation of the nonphagocytic NAD(P)H oxidase in response to neurohormones (angiotensin II, norepinephrine, tumor necrosis factor-a) has been shown to contribute to cardiac myocyte hypertrophy. Furthermore, the fibrosis, collagen deposition, and metalloproteinase activation involved in the remodeling of the failing myocardium are dependent on ROS released during the phenotypic transformation of fibroblasts to myofibroblasts associated with progression of end-stage heart failure. Future studies are necessary to identify the sources, mechanisms of activation of NAD(P)H oxidases, and downstream signaling targets implicated in the progression of chronic heart failure.

Preconditioning and postresuscitation injury

A major challenge in improving cardiac arrest survival is organ injury that occurs after the return of spontaneous circulation. This postresuscitation injury may result in as many as 90% of such patients not surviving to hospital discharge. Preconditioning, an adaptive physiologic response found in multiple organs and species, may help protect against such injury of ischemic tissue when reperfused at the return of spontaneous circulation. A better understanding of how preconditioning may alter postresuscitation injury is important for two major reasons. First, it is one of the most protective adaptations currently known in nature that attenuates ischemia-reperfusion injury. Pharmacologic and nonpharmacologic means to quickly trigger and perhaps augment this response have the potential to greatly improve survival from the global ischemia of cardiac arrest. Second, potential targets of preconditioning-such as the adenosine triphosphate-sensitive potassium channel and NAD(P)H oxidases-likely play important roles in the postresuscitation phase of cardiac arrest, and their modification may be important components of future treatment for patients with return of spontaneous circulation. The evidence for postresuscitation injury at the cellular level and its modification by preconditioning are discussed.

H(2)O(2) opens mitochondrial K(ATP) channels and inhibits GABA receptors via protein kinase C-epsilon in cardiomyocytes

Oxygen radicals and protein kinase C (PKC) mediate ischemic preconditioning. Using a cultured chick embryonic cardiomyocyte model of hypoxia and reoxygenation, we found that the oxygen radicals generated by ischemic preconditioning were H(2)O(2). Like preconditioning, H(2)O(2) selectively activated the epsilon-isoform of PKC in the particulate compartment and increased cell viability after 1 h of hypoxia and 3 h of reoxygenation. The glutathione peroxidase ebselen (converting H(2)O(2) to H(2)O) and the superoxide dismutase inhibitor diethyldithiocarbamic acid abolished the increased H(2)O(2) and the protection of preconditioning. PKC activation with phorbol 12-myristate 13-acetate increased cell survival; the protection of preconditioning was blocked by epsilonV(1-2), a selective PKC-epsilon antagonist. Similar to preconditioning, the protection of PKC activation was abolished by mitochondrial K(ATP) channel blockade with 5-hydroxydecanoate or by GABA receptor stimulation with midazolam or diazepam. In addition, PKC, mitochondrial ATP-sensitive K(+) (K(ATP)) channels, and GABA receptors had no effects on H(2)O(2) generated by ischemic preconditioning before prolonged hypoxia and reoxygenation. We conclude that H(2)O(2) opens mitochondrial K(ATP) channels and inhibits GABA receptors via activating PKC-epsilon. Through this signal transduction, preconditioning protects ischemic cardiomyocytes.

Essential role of the NADPH oxidase subunit p47(phox) in endothelial cell superoxide production in response to phorbol ester and tumor necrosis factor-alpha

A phagocyte-type NADPH oxidase complex is a major source of endothelial reactive oxygen species (ROS) production, but its biochemical function and regulation remain unclear. In neutrophils, the p47(phox) subunit is centrally involved in oxidase activation in response to agonists such as phorbol-12-myristate-13-acetate (PMA). We investigated the role of p47(phox) in endothelial cell ROS production in response to PMA or tumor necrosis factor-alpha (TNFalpha) stimulation. To specifically address the role of p47(phox), we studied coronary microvascular endothelial cells (CMECs) isolated from p47(phox-/-) mice and wild-type controls. p47(phox) was absent in hearts of knockout mice whereas the essential oxidase subunit, p22(phox), was expressed in both groups. In the absence of agonist stimulation, the lack of p47(phox) did not result in a reduction in NADPH-dependent ROS production in p47(phox-/-) CMECs compared with wild-type CMECs. Prestimulation with PMA (100 ng/mL) or TNFalpha (100 U/mL) for 10 minutes significantly increased NADPH-dependent O(2)(-) production in wild-type CMECs, assessed either by lucigenin (5 micromol/L) chemiluminescence or dichlorohydrofluorescein (DCF) fluorescence. This response was completely lost in p47(phox-/-) cells. Transfection of the full-length p47(phox) cDNA into p47(phox-/-) CMECs caused expression of p47(phox) protein and restoration of the O(2)(-) response to PMA and TNFalpha. In wild-type CMECs, transfection of antisense p47(phox) cDNA substantially reduced p47(phox) expression and caused loss of the O(2)(-) response to PMA and TNFalpha. These data show that endothelial cell p47(phox) is critical in the upregulation of NADPH oxidase activity by PMA and TNFalpha.

Reactive species mechanisms of cellular hypoxia-reoxygenation injury

Exacerbation of hypoxic injury after restoration of oxygenation (reoxygenation) is an important mechanism of cellular injury in transplantation and in myocardial, hepatic, intestinal, cerebral, renal, and other ischemic syndromes. Cellular hypoxia and reoxygenation are two essential elements of ischemia-reperfusion injury. Activated neutrophils contribute to vascular reperfusion injury, yet posthypoxic cellular injury occurs in the absence of inflammatory cells through mechanisms involving reactive oxygen (ROS) or nitrogen species (RNS). Xanthine oxidase (XO) produces ROS in some reoxygenated cells, but other intracellular sources of ROS are abundant, and XO is not required for reoxygenation injury. Hypoxic or reoxygenated mitochondria may produce excess superoxide (O) and release H(2)O(2), a diffusible long-lived oxidant that can activate signaling pathways or react vicinally with proteins and lipid membranes. This review focuses on the specific roles of ROS and RNS in the cellular response to hypoxia and subsequent cytolytic injury during reoxygenation.

Reactive oxygen species in mechanical stress-induced cardiac hypertrophy

Mechanical stress induces various hypertrophic responses including activation of mitogen-activated protein kinases (MAPKs) in cardiac myocytes. Here we examined the role of the small GTP-binding proteins of Rho family and reactive oxygen species (ROS) in stretch-induced activation of p38MAPK in cardiomyocytes. Overexpression of dominant-negative mutants of Rac1 (D.N. Rac1), D.N.RhoA and D.N.Cdc42 suppressed stretch-induced activation of p38MAPK. Overexpression of constitutively active mutants of Rac1 (C.A.Rac1) and C.A.Cdc42 increased the p38MAPK activity in the absence of mechanical stress. Pretreatment with N-acetyl-L-cysteine and N-(2-mercaptopropionyl)-glycine (NAC) suppressed stretch-induced activation of p38MAPK. Mechanical stretch increased intracellular ROS generation, which was abrogated by overexpression of D.N.Rac1 and attenuated by overexpression of D.N.RhoA and D.N.Cdc42. An increase in protein synthesis evoked by mechanical stretch was suppressed by overexpression of D.N.Rac1 and pretreatment with NAC. These results suggest that mechanical stress induces cardiac hypertrophy through the Rac1-ROS-p38MAPK pathway in cardiac myocytes.

NO modulates monocyte chemotactic protein-1 expression in endothelial cells under cyclic strain

Endothelial cells (ECs) under hemodynamic forces increase intracellular reactive oxygen species (ROS) that modulate gene expression. We previously showed that NO attenuated the shear flow-induced gene level. The present study explored the role of endothelial NO in cyclic strain-treated ECs. Treatment of ECs with S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, reduced cyclic strain-induced monocyte chemotactic protein (MCP)-1 expression. Conversely, exposure of ECs to an NO synthase inhibitor augmented MCP-1 mRNA levels. NO attenuated the binding of activator protein-1 to the 12-O-tetradecanoylphobol-13-acetate-responsive element (TRE) in the MCP-1 promoter region. ECs overexpressed with endothelial NO synthase (eNOS) inhibited cyclic strain-induced MCP-1 expression and MCP-1 promoter (-540 bp) activity. Consistently, ECs treated with SNAP or infected with adenovirus carrying eNOS reduced strain-induced superoxide levels. These strain-induced superoxide and MCP-1 expressions were greatly blunted by treating ECs with an NADPH oxidase inhibitor, diphenyleneiodonium chloride or apocynine, but not with a xanthine oxidase inhibitor. ECs infected with adenovirus carrying the dominant-negative mutant of Rac (RacN17), a component of NADPH oxidase, reduced the strain-induced superoxide and MCP-1 expression. In contrast, ECs transfected with a constitutively active Rac (RacV12) increased MCP-1 and 4x TRE promoter activities. However, ECs cotransfected with eNOS and RacV12 reduced those promoter activities. Consistently, the increases of superoxide levels and MCP-1 expression by overexpression of RacV12 were abolished after infecting ECs with eNOS. Our results show that NO from eNOS-inhibiting redox-sensitive MCP-1 expression is mediated via Rac-dependent NADPH oxidase by reducing ROS. This study provides a molecular basis to support the notion that endothelial NO acts as an antioxidant by negatively regulating redox-sensitive gene expression in ECs constantly under hemodynamic influence.

Simultaneous inhibition of Rac1 and IKK pathways sensitizes lung cancer cells to TNFalpha-mediated apoptosis

Lung cancer is the most frequently occurring cancer in the world and causes more deaths in the United States than does colon, breast, and prostate cancer combined. Despite advances in treatment modalities including radiation, surgery, and chemotherapy, the overall survival in lung cancer remains low. The cytokine tumor necrosis factor alpha (TNFalpha) has been shown to regulate both apoptotic and antiapoptotic pathways. Activation of the transcription factor NF-kappaB appears to be the critical determinant of the antiapoptotic response to TNFalpha exposure in epithelial cells. A549 human lung carcinoma cells were infected with adenoviral constructs carrying dominant negative mutants of Rac1 and IKK or constitutively active mutant of Rac1, upstream effectors in TNF-mediated NF-kappaB activation. Cell death, apoptosis, and NF-kappaB activation were subsequently measured in response to TNFalpha exposure. Although TNFalpha alone had no cytotoxic effect, the expression of the dominant negative mutant of IKKbeta (Ad.IKKbetaKA) resulted in apoptotic cell death following TNFalpha exposure. Similarly, dominant negative mutant to Rac1 (Ad.N17Rac1) further sensitized A549 cells to IKKbetaKA-mediated TNFalpha-induced cell death. Conversely, a dominant active form of Rac1 (Ad.V12Rac1) ameliorated the cell death response to concurrent IKKbeta dominant negative mutant infection and TNFalpha exposure. These results suggest that concurrent inhibition of Rac1 and IKK pathways sensitizes lung cancer cells to TNFalpha-induced apoptosis.

Lipopolysaccharide induces Rac1-dependent reactive oxygen species formation and coordinates tumor necrosis factor-alpha secretion through IKK regulation of NF-kappa B

Reactive oxygen species (ROS) are important second messengers generated in response to many types of environmental stress. In this setting, changes in intracellular ROS can activate signal transduction pathways that influence how cells react to their environment. In sepsis, a dynamic proinflammatory cellular response to bacterial toxins (e.g. lipopolysaccharide or LPS) leads to widespread organ damage and death. The present study demonstrates for the first time that the activation of Rac1 (a GTP-binding protein), and the subsequent production of ROS, constitutes a major pathway involved in NFkappaB-mediated tumor necrosis factor-alpha (TNFalpha) secretion following LPS challenge in macrophages. Expression of a dominant negative mutant of Rac1 (N17Rac1) reduced Rac1 activation, ROS formation, NFkappaB activation, and TNFalpha secretion following LPS stimulation. In contrast, expression of a dominant active form of Rac1 (V12Rac1) mimicked these effects in the absence of LPS stimulation. IKKalpha and IKKbeta were both required downstream modulators of LPS-activated Rac1, since the expression of either of the IKK dominant mutants (IKKalphaKM or IKKbetaKA) drastically reduced NFkappaB-dependent TNFalpha secretion. Moreover, studies using CD14 blocking antibodies suggest that Rac1 induces TNFalpha secretion through a pathway independent of CD14. However, a maximum therapeutic inhibition of LPS-induced TNFalpha secretion occurred when both CD14 and Rac1 pathways were inhibited. Our results suggest that targeting both Rac1- and CD14-dependent pathways could be a useful therapeutic strategy for attenuating the proinflammatory cytokine response during the course of sepsis.

Genetic demonstration of p47phox-dependent superoxide anion production in murine vascular smooth muscle cells

BACKGROUND

Previous investigations provide evidence that an enzyme related to the phagocyte NADPH oxidase produces superoxide in the blood vessel wall. These data, however, are confounded by observations that both NADPH and NADH serve as substrates for superoxide production in vascular cells. To clarify this issue, we compared the superoxide-generating capabilities of vascular smooth muscle cells (VSMCs) derived from wild-type (p47phox(+/+); phagocyte oxidase) mice with those from mice that lack p47phox (p47phox(-/-); "knockout"), an essential component of the phagocyte NADPH oxidase.

METHODS AND RESULTS

VSMCs were derived from aortic explants harvested from p47phox(+/+) or p47phox(-/-) mice. VSMCs from p47phox(+/+) but not those from p47phox(-/-) mice produced superoxide after stimulation by phorbol myristate acetate. Consistent with this, p47phox was detected only in p47phox(+/+) VSMCs. p47phox-transduced p47phox(-/-) but not enhanced green fluorescent protein-transduced p47phox(-/-) VSMCs generated significant levels of superoxide after stimulation by angiotensin II or platelet-derived growth factor-BB (PDGF-BB). Enhanced expression of recombinant p47phox in p47phox-transduced p47phox(-/-) cells correlated with superoxide production in these cells.

CONCLUSIONS

These data provide direct functional proof that an oxidase requiring the p47phox component mediates superoxide release from VSMCs in the blood vessel wall in response to angiotensin II or PDGF-BB.

Rac1 activity is required for the activation of hypoxia-inducible factor 1

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that mediates cellular and systemic homeostatic responses (including erythropoiesis, angiogenesis, and glycolysis) to reduced O(2) availability in mammals. Hypoxia induces both the protein expression and transcriptional activity of the HIF-1alpha subunit. However, the molecular mechanisms of sensing and signal transduction by which changes in O(2) concentration result in changes in HIF-1 activity are poorly understood. We report here that the small GTPase Rac1 is activated in response to hypoxia and is required for the induction of HIF-1alpha protein expression and transcriptional activity in hypoxic cells.

Gene therapeutic approaches to oxidative stress-induced cardiac disease: principles, progress, and prospects

Heart and vascular diseases continue to rank among the most frequent and devastating disorders to affect adults in many parts of the world. Increasing evidence from a variety of experimental models indicates that reactive oxygen species can play a key role in the development of myocardial damage from ischemia/reperfusion, the development of cardiac hypertrophy, and the transition of hypertrophy to cardiac failure. The recent dramatic increase in availability of genomic data has included information on the genetic modulation of reactive oxygen species and the antioxidant systems that normally prevent damage from these radicals. Nearly simultaneously, progressively more sophisticated and powerful methods for altering the genetic complement of selected tissues and cells have permitted application of gene therapeutic methods to understand better the pathophysiology of reactive oxygen species-mediated myocardial damage and to attenuate or treat that damage. Although exciting and promising, gene therapy approaches to these common disorders are still in the experimental and developmental stages. Improved understanding of pathophysiology, better gene delivery systems, and specific gene therapeutic strategies will be needed before gene therapy of oxyradical-mediated myocardial damage becomes a clinical reality.

H(2)O(2)-induced O(2) production by a non-phagocytic NAD(P)H oxidase causes oxidant injury

Non-phagocytic NAD(P)H oxidases have been implicated as major sources of reactive oxygen species in blood vessels. These oxidases can be activated by cytokines, thereby generating O(2), which is subsequently converted to H(2)O(2) and other oxidant species. The oxidants, in turn, act as important second messengers in cell signaling cascades. We hypothesized that reactive oxygen species, themselves, can activate the non-phagocytic NAD(P)H oxidases in vascular cells to induce oxidant production and, consequently, cellular injury. The current report demonstrates that exogenous exposure of non-phagocytic cell types of vascular origin (smooth muscle cells and fibroblasts) to H(2)O(2) activates these cell types to produce O(2) via an NAD(P)H oxidase. The ensuing endogenous production of O(2) contributes significantly to vascular cell injury following exposure to H(2)O(2). These results suggest the existence of a feed-forward mechanism, whereby reactive oxygen species such as H(2)O(2) can activate NAD(P)H oxidases in non-phagocytic cells to produce additional oxidant species, thereby amplifying the vascular injury process. Moreover, these findings implicate the non-phagocytic NAD(P)H oxidase as a novel therapeutic target for the amelioration of the biological effects of chronic oxidant stress.

Ras regulates NFAT3 activity in cardiac myocytes

Multiple distinct signal transduction pathways have been implicated in the development of cardiac myocyte hypertrophy. These hypertrophic pathways include those regulated by the Ras superfamily of small GTPases and a separate calcineurin-regulated pathway that culminates in the activation of the transcription factor NFAT3. In this report, we demonstrate a functional interaction between Ras-regulated and calcineurin-regulated pathways. In particular, expression in neonatal myocytes of a constitutively active form of Ras (V12ras), but not activating mutants of Rac1, RhoA, or Cdc42, results in an increase in NFAT activity. Similarly, expression of an activated Ras, but not other small GTPases, results in the nuclear translocation of an NFAT3 fusion protein. Expression of a dominant negative ras gene product blocks phenylephrine-stimulated NFAT transcriptional activity and the ligand-stimulated NFAT3 nuclear localization. Ras proteins appear to function upstream of calcineurin, because cyclosporin A blocks the ability of V12ras to stimulate NFAT-dependent transcription and nuclear localization. Similarly, expression of a dominant negative ras gene inhibits phenylephrine-stimulated calcineurin activity. Pharmacological inhibition of MEK1 or expression of a dominant negative form of c-Raf or ERK2 inhibits phenylephrine-stimulated NFAT3 activation. Conversely, NFAT activity was stimulated by expression of constitutively active forms of c-Raf or MEK1. Taken together, these results imply that, in cardiac myocytes, a Ras-regulated pathway involving stimulation of mitogen-activated protein kinase regulates NFAT3 activity.

G alpha(i) and G alpha(o) are target proteins of reactive oxygen species

Reactive oxygen species (ROS) have been identified as central mediators in certain signalling events. In the heart, ROS have important functions in ischaemia/reperfusion-induced cardiac injury and in cytokine-stimulated hypertrophy. Extracellular signal-regulated kinase (ERK) is one of the ROS-responsive serine/threonine kinases. Previous studies showed that tyrosine kinases and small G proteins are involved in the activation of ERK by ROS; however, the initial target protein of ROS that leads to ERK activation remains unknown. Here we show that inhibition of the betagamma-subunit of G protein (G betagamma) attenuates hydrogen peroxide (H2O2)-induced ERK activation in rat neonatal cardiomyocytes. The G betagamma-responsive ERK activation induced by H2O2 is independent of ligands binding to Gi-coupled receptors, but requires phosphatidylinositol-3-kinase and Src activation. In in vitro studies, however, treatment with H2O2 increases [35S]GTP-gammaS binding to cardiac membranes and directly activates purified heterotrimeric Gi and Go but not Gs. Analysis using heterotrimeric Go and its individual subunits indicates that H2O2 modifies G alpha(o) but not G betagamma, which leads to subunit dissociation. We conclude that G alpha(i) and G alpha(o) are critical targets of oxidative stress for activation of ERK.