Role of reactive oxygen species and p53 in chromium(VI)-induced apoptosis

Apoptosis is a programmed cell death mechanism to control cell number in tissues and to eliminate individual cells that may lead to disease states. The present study investigates chromium(VI) (Cr(VI))-induced apoptosis and the role of reactive oxygen species (ROS) and p53 in this response. Treatment of human lung epithelial cells (A549) with Cr(VI) caused apoptosis as measured by DNA fragmentation, mitochondria damage, and cell morphology. Cr(VI)-induced apoptosis is contributed to ROS generation, resulting from cellular reduction of Cr(VI) as measured by flow cytometric analysis of the stained cells, oxygen consumption, and electron spin resonance spin trapping. Scavengers of ROS, such as catalase, aspirin, and N-acetyl-L-cysteine, decreased Cr(VI)-induced apoptosis, whereas NADPH and glutathione reductase, enhancers of Cr(VI)-induced ROS generation, increased it. p53 is activated by Cr(VI), mostly by ROS-mediated free radical reactions. Cr(VI)-induced ROS generation occurred within a few minutes after Cr(VI) treatment of the cells, whereas p53 induction took at least 5 h. The level of Cr(VI)-induced apoptosis was similar in both p53-positive cells and p53-negative cells independent of p53 status in the early stage (0-3 h) of Cr(VI) treatment. However, at the later stage (3-24 h), the level of the apoptosis is higher in p53-positive cells than in p53-negative cells. These results suggest that ROS generated through Cr(VI) reduction is responsible to the early stage of apoptosis, whereas p53 contributes to the late stage of apoptosis and is responsible for the enhancement of Cr(VI)-induced apoptosis at this stage.     

Mitochondria: regulators of signal transduction by reactive oxygen and nitrogen species

The functional role of mitochondria in cell physiology has previously centered around metabolism, with oxidative phosphorylation playing a pivotal role. Recently, however, this perspective has changed significantly with the realization that mitochondria are active participants in signal transduction pathways, not simply the passive recipients of injunctions from the rest of the cell. In this review the emerging role of the mitochondrion in cell signaling is discussed in the context of cytochrome c release, hydrogen peroxide formation from the respiratory chain, and the nitric oxide-cytochrome c oxidase signaling pathway.     

Cr(VI) increases tyrosine phosphorylation through reactive oxygen species-mediated reactions

While Cr (VI)containing compounds are well established carcinogens, the mechanisms of their action remain to be investigated. In this study we show that Cr (VI) causes increased tyrosine phosphorylation in human lung epithelial A549 cells in a timedependent manner. Nacetylcysteine (NAC), a general antioxidant, inhibited Cr (VI)induced tyrosine phosphorylation. Catalase, a scavenger of H₂O₂, sodium formate and aspirin, scavengers of hydroxyl radical (OH), also inhibited the increased tyrosine phosphorylation induced by Cr (VI). SOD, an inhibitor of superoxide radical (O₂ ^–), caused less inhibition. ESR study shows that incubation of Cr (VI) with the A549 cells generates OH radical. The generation of radical was decreased by addition of catalase and sodium formate, while SOD did not have any inhibitory effect. Oxygen consumption measurements show that addition of f Cr (VI) to A549 cells resulted in enhanced molecular oxygen consumption. These results indicate that Cr (VI) can induce an increase in tyrosine phosphorylation. H₂O₂ and OH radicals generated during the process are responsible for the increased tyrosine phosphorylation induced by Cr (VI).     

Signal transduction by reactive oxygen species

Although historically viewed as purely harmful, recent evidence suggests that reactive oxygen species (ROS) function as important physiological regulators of intracellular signaling pathways. The specific effects of ROS are modulated in large part through the covalent modification of specific cysteine residues found within redox-sensitive target proteins. Oxidation of these specific and reactive cysteine residues in turn can lead to the reversible modification of enzymatic activity. Emerging evidence suggests that ROS regulate diverse physiological parameters ranging from the response to growth factor stimulation to the generation of the inflammatory response, and that dysregulated ROS signaling may contribute to a host of human diseases.     

Role of reactive oxygen species (ROS) in apoptosis induction

Reactive oxygen species (ROS) and mitochondria play an important role in apoptosis induction under both physiologic and pathologic conditions. Interestingly, mitochondria are both source and target of ROS. Cytochrome c release from mitochondria, that triggers caspase activation, appears to be largely mediated by direct or indirect ROS action. On the other hand, ROS have also anti-apoptotic effects. This review focuses on the role of ROS in the regulation of apoptosis, especially in inflammatory cells.     

Lipopolysaccharide-mediated reactive oxygen species and signal transduction in the regulation of interleukin-1 gene expression

Lipopolysaccharide (LPS) stimulates macrophages to release inflammatory cytokines, interleukin-1 beta (IL-1), and tumor necrosis factor (TNF). LPS-induced TNF suppresses scavenger receptor functions in macrophages (van Lenten, B. J., and Fogelman, A. M. (1992) J. Immunol. 148, 112-116), which is regulated by TNF-mediated protein kinases (Hsu, H. Y., and Twu, Y. C. (2000) J. Biol. Chem. 275, 41035-41048). To examine the molecular mechanism for LPS induction of IL-1 in macrophages, we demonstrated that LPS quickly stimulated reactive oxygen species (ROS), and 3 h later induced prointerleukin-1 beta (pro-IL-1, precursor of IL-1) production and IL-1 secretion. LPS stimulated pro-IL-1 message/protein between 3 and 10 h; however, there was a 40% reduction of pro-IL-1 in preincubation of the antioxidant, N-acetylcysteine (NAC). Moreover, NAC moderated LPS-induced IL-1 secretion partially via interleukin 1-converting enzyme. The maximal activity of LPS-induced ERK, JNK, and p38 was 12- (30 min), 5- (30 min), and 16-fold (15 min), respectively. In contrast, NAC reduced ERK activity to 60% and decreased p38 activity to the basal level, but JNK activity was induced 2-fold. Furthermore, the pharmacological antagonists LY294002, SB203580, curcumin, calphostin C, and PD98059 revealed the diverse roles of LPS-mediated protein kinases in pro-IL-1. On the other hand, NAC and diphenyleneiodonium chloride partially inhibited LPS-induced Rac activity and protein-tyrosine kinase (PTK), indicating that LPS-mediated ROS and NADPH oxidase correspond to Rac activation and IL-1 expression. Our findings establish for the first time that LPS-mediated PTK/phosphatidylinositol 3-kinase/Rac/p38 pathways play a more important role than pathways of PTK/PKC/MEK/ERK and of PTK/phosphatidylinositol 3-kinase/Rac/JNK in the regulation of pro-IL-1/IL-1. The findings also further elucidate the critical role of LPS-mediated ROS in signal transduction pathways. Our results suggest that understanding LPS-transduced signals in IL-1 induction upon the antibacterial action of macrophages should provide a therapeutic strategy for aberrant inflammatory responses leading to severe cellular injury or concurrent multiorgan septic damage.     

植物线粒体、活性氧与信号转导

活性氧(ROS)的产生是需氧代谢不可避免的结果。在植物细胞中,线粒体电子传递链(ETC)的复合物Ⅰ和Ⅱ是ROS产生的主要的部位。交替氧化酶和可能的内源鱼藤酮不敏感的NADH脱氢酶通过保持ETc的相对氧化状态限制线粒体产生ROS。线粒体基质中的抗氧化酶系统与小分子量的抗氧化剂一道起ROS的解毒作用。ROS除了引起细胞的伤害外,在植物中还能够作为一种普遍存在的信号分子起作用。在低浓度时,ROS能诱导防御基因的表达和引起适应反应;在高浓度时,引起细胞死亡。一氧化氮是植物合成和释放的一种气体,也可作为信号分子调节植物的生长和发育。     

Role of reactive oxygen species in cardiovascular aging

Biochemical and structural changes occurring in the myocardium with aging are mainly resulting from the association of a general tissue atrophy with the hypertrophy of the remaining myocytes. Whilst hypertrophy seems to be a compensatory process to the loss of cardiomyocytes and to a mild systolic hypertensive condition that accompanies elderly people, atrophy should be the modification more closely related to aging per se. In support to the free radical theory of aging, several signs of oxidative damage have been shown in the aged heart, such as lipofuscin accumulation, decreased phospholipid unsaturation index, greater formation of both hydrogen peroxide and 8-hydroxy-2deoxyguanosine. As a compensatory reaction, the activities of the main oxygen-radical scavenger enzymes are stimulated in the mitochondria of aged rat heart. Endothelium-mediated vasoregulation is more susceptible to oxidative stress in aged with respect to young rats, suggesting that also the vasculature can be negatively influenced by the oxygen free radicals generated during aging. The possible primary role of oxygen free radicals in the development of myocardial atrophy is also discussed.     

Role of reactive oxygen species in injury-induced insulin resistance

Acute insulin resistance is common after injury, infection, and critical illness. To investigate the role of reactive oxygen species (ROS) in critical illness diabetes, we measured hepatic ROS, which rapidly increased in mouse liver. Overexpression of superoxide dismutase 2, which decreased mitochondrial ROS levels, protected mice from the development of acute hepatic insulin resistance. Insulin-induced intracellular signaling was dramatically decreased, and cellular stress signaling was rapidly increased after injury, resulting in the hyperglycemia of critical illness diabetes. Insulin-induced intracellular signaling, activation of stress (c-Jun N-terminal kinase) signaling, and glucose metabolism were all normalized by superoxide dismutase 2 overexpression or by pretreatment with antioxidants. Thus, ROS play an important role in the development of acute hepatic insulin resistance and activation of stress signaling after injury.     

Role of reactive oxygen species in fungal cellular differentiations

Regulated synthesis of reactive oxygen species (ROS) by specific fungal NADPH oxidases (Noxs) plays a key role in fungal cellular differentiation and development. Fungi have up to three different Nox isoforms, NoxA, B and C. The NoxA isoform has a key role in triggering the development of fruiting bodies in several sexual species whereas NoxB plays a key role in ascospore germination. The function of NoxC remains unknown. Both NoxA and NoxB are required for the development of fungal infection structures by some plant pathogens. ROS production by NoxA is critical for maintaining a fungal-plant symbiosis. Localised synthesis of ROS is also important in establishing and maintaining polarised hyphal growth. Activation of NoxA/NoxB requires the regulatory subunit, NoxR, and the small GTPase RacA. The BemA scaffold protein may also be involved in the assembly of the Nox complex. By analogy with mammalian systems MAP and PAK kinases may regulate fungal Nox activation. How fungal cells sense and respond to ROS associated with cellular differentiations remains to be discovered.     

Role of reactive oxygen species in mast cell degranulation

Mast cells are a heterogeneous multifunctional cellular population that promotes connective tissue homeostasis by slow release of biologically active substances, affecting primarily the permeability of vessels and vascular tone, maintenance of electrolyte and water balance, and composition of the extracellular matrix. Along with this, they can rapidly release inflammatory mediators and chemotactic factors that ensure the mobilization of effector innate immune cells to fight against a variety of pathogens. Furthermore, they play a key role in initiation of allergic reactions. Aggregation of high affinity receptors to IgE (FcεRI) results in rapid degranulation and release of inflammatory mediators. It is known that reactive oxygen species (ROS) participate in intracellular signaling and, in particular, stimulate production of several proinflammatory cytokines that regulate the innate immune response. In this review, we focus on known molecular mechanisms of FcεRI-dependent activation of mast cells and discuss the role of ROS in the regulation of this pathway.     

Role of reactive oxygen species in intestinal diseases.

It is well known that reactive oxygen metabolites are generated during several pathologies, and that they are able to disturb many cellular processes and eventually lead to cellular injury. After intestinal ischemia, reactive oxygen species are produced when the ischemic tissue is reperfused. The enzyme xanthine oxidase is thought to play a key role in this process. As a result of this oxygen radical production, the permeability of the endothelium and the mucosa increases, allowing infiltration of inflammatory leukocytes into the ischemic area. Moreover, reactive oxygen species are also indirectly involved in leukocyte activation. In turn, these inflammatory cells respond with the production of oxygen radicals, which play an important role in the development of tissue injury. Thus, intestinal ischemia and reperfusion evokes an inflammatory response. Also during chronic intestinal inflammatory diseases, reactive oxygen metabolites are proposed to play an important role in the pathology. Scavenging of reactive oxygen species will thus be beneficial in these disorders.     

The oxygen sensing signal cascade under the influence of reactive oxygen species

Structural and functional integrity of organ function profoundly depends on a regular oxygen and glucose supply. Any disturbance of this supply becomes life threatening and may result in severe loss of organ function. Particular reductions in oxygen availability (hypoxia) caused by respiratory or blood circulation irregularities cannot be tolerated for longer periods due to an insufficient energy supply by anaerobic glycolysis. Complex cellular oxygen sensing systems have evolved to tightly regulate oxygen homeostasis. In response to variations in oxygen partial pressure (PO2), these systems induce adaptive and protective mechanisms to avoid or at least minimize tissue damage. These various responses might be based on a range of oxygen sensing signal cascades including an isoform of the neutrophil NADPH oxidase, different electron carrier units of the mitochondrial chain such as a specialized mitochondrial, low PO2 affinity cytochrome c oxidase (aa3) and a subfamily of 2-oxoglutarate dependent dioxygenases termed HIF (hypoxia inducible factor) prolyl-hydroxylase and HIF asparaginyl hydroxylase called factor-inhibiting HIF (FIH-1). Thus, specific oxygen sensing cascades involving reactive oxygen species as second messengers may by means of their different oxygen sensitivities, cell-specific and subcellular localization help to tailor various adaptive responses according to differences in tissue oxygen availability.     

Contrasting selection pressures on components of the Ras-mediated signal transduction pathway in Drosophila

The molecular genetics of several signal transduction pathways is well characterized, providing an opportunity to address the nature of the population genetic forces acting on functionally related suites of pleiotropic regulatory genes. Signal transduction is the process by which signals are transmitted from the cell surface to the nucleus or other cellular structures. It plays a fundamental role in regulating a wide range of developmental and physiological processes, many of which are likely to be subject to buffering mechanisms. Here we infer that contrasting selection pressures act on six components of the Ras signal transduction pathway by comparing sequences obtained from 25 alleles of Drosophila melanogaster with one allele of the sibling species D. simulans. The three most upstream components of the cascade, Ras, Drk and polehole, experience strong purifying selection, as they show no fixed amino acid differences between the species and just a handful of rare replacement polymorphisms within D. melanogaster. This portion of the pathway is likely to act as a control point in signal transduction, because the more downstream components Dsor1, corkscrew and Ksr, each show several amino acid replacements between the species. Furthermore, Ksr is nearly monomorphic within D. melanogaster, and application of the HKA and McDonald and Kreitman tests indicate that this gene may have experienced a recent selective sweep, suggesting that modifiers of Ras kinase signalling are the most likely source of quantitative variation associated with this core regulatory pathway.     

Role of reactive oxygen species in functional activity of neurons

The review covers participation of reactive oxygen species (ROS) in the metabolism of neuronal cells, their detrimental action on proteins, lipids and nucleic acids. Oxidative stress is associated with imbalance of ROS generation and dissipation that results in increase in ROS stationary level in the cells. Under normal conditions, ROS become involved in implementation of signal transduction, mechanisms ensuring metabolic response of cells to the external factors.     

Active oxygen species in blue light mediated signal transduction in coleoptile tips

Coleoptile tip is a blue-light sensitive tissue possessing a "blue light receptor" which, upon activation, elicits a signal cascade resulting in phototropic curvature of the coleoptile. In this context, the nature of the photoreceptors and the exact mechanism through which the photoreceptors transduces the signal across the membrane are not clear. In this study, we attempted to examine whether the blue light receptor perturbs redox status of the coleoptile tip and sensitizes molecular oxygen as part of the signal reactions. Coleoptile tips of Sorghum bicolor and wheat (Triticum vulgare) grown in the dark showed pronounced ascorbate free radical signal, which diminished upon illumination with weak blue light for one minute. Concomitantly, the generation of superoxide radical by the coleoptile tip was augmented upon illumination with blue light. Various thiol blockers tested in this study caused powerful inhibition of blue light induced superoxide anion radical generation. Treatment with these thiol blockers, with the exception of NEM, resulted in marked increase in the levels of ascorbic acid free radical in the blue light irradiated coleoptiles. The blue light stimulated O*-2-generation by the coleoptile tip homogenate is also inhibited by the inhibitors of blue light responses viz phenylacetic acid, potassium iodide, and sodium azide. Based on our observations, we postulate that the activated blue light receptor present in the coleoptile tip sensitizes molecular oxygen to superoxide anion radical in the tip initializing the blue light signal cascade reactions.