Redox regulation of transcriptional activators

Hydrogen peroxide is critical for UV-induced apoptosis inhibition

Apoptosis is an important cell death system that deletes damaged and mutated cells, preventing the induction of cancer. We previously have reported that UV irradiation inhibited the apoptosis induced by serum starvation and cell detachment. This phenomenon is suitable for clarifying the relationship between cancer and the dysregulation of apoptosis by UV irradiation. Here, we have studied the factors responsible for this inhibition of apoptosis, focusing on reactive oxygen species (ROS) and DNA damage. Treatment with xanthine oxidase in the presence of hypoxanthine, which is known to produce superoxide anion (O2*-) and hydrogen peroxide (H2O2), inhibited the induction of apoptosis. The xanthine oxidase-induced anti-apoptotic effect was suppressed in the presence of an H2O2-eliminating enzyme, catalase, but not in the presence of an O2*--eliminating enzyme, superoxide dismutase. Treatment with H2O2 itself significantly inhibited the induction of apoptosis. Furthermore, the effect of the inhibition of cell death by UVB irradiation and by H2O2 treatment decreased in H2O2-resistant cells. Although both UVB and H2O2 are known to induce DNA damage, other DNA damaging agents, like gamma-irradiation and treatment with cisplatin and bleomycin, showed no inhibition of apoptosis. These findings suggested that H2O2 was essential to the inhibition of apoptosis, in which DNA damage had no role.

Thioredoxin and protein kinases in redox signaling

Reactive oxygen species (ROS) play critical roles for the determination of cell fate by eliciting a wide variety of cellular responses, such as proliferation, differentiation and apoptosis. Many intracellular signaling pathways involved in such ROS-induced cellular responses are regulated by the intracellular redox state, which depends on the balance between the levels of oxidizing and reducing equivalents. Recently, increasing attention has been paid to the roles of thioredoxin (Trx) as a signaling intermediate beyond its intrinsic antioxidant activity. Especially, Trx participates in the control of the mitogen-activated protein kinase (MAPK) cascades through the redox state-dependent association and dissociation with apoptosis signal-regulating kinase 1 (ASK1), an upstream regulator of the cascades. This review highlights the current understanding of prototypical molecular mechanisms by which the redox signal is converted into the signaling through ROS-responsive protein kinases, with a special focus on the ASK1-Trx system. Understanding of such mechanisms may provide the basis for therapeutic interventions in redox-related diseases including various types of cancer.

Zinc coordination environments in proteins as redox sensors and signal transducers

Zinc/cysteine coordination environments in proteins are redox-active. Oxidation of the sulfur ligands mobilizes zinc, while reduction of the oxidized ligands enhances zinc binding, providing redox control over the availability of zinc ions. Some zinc proteins are redox sensors, in which zinc release is coupled to conformational changes that control varied functions such as enzymatic activity, binding interactions, and molecular chaperone activity. Whereas the released zinc ion in redox sensors has no known function, the redox signal is transduced to specific and sensitive zinc signals in redox transducers. Released zinc can bind to sites on other proteins and modulate signal transduction, generation of metabolic energy, mitochondrial function, and gene expression. The paradigm of such redox transducers is the zinc protein metallothionein, which, together with its apoprotein, thionein, functions at a central node in cellular signaling by redistributing cellular zinc, presiding over the availability of zinc, and interconverting redox and zinc signals. In this regard, the transduction of nitric oxide (NO) signals into zinc signals by metallothionein has received particular attention. It appears that redox-inert zinc has been chosen to control some aspects of cellular thiol/disulfide redox metabolism. Tight control of zinc is essential for redox homeostasis because both increases and decreases of cellular zinc elicit oxidative stress. Depending on its availability, zinc can be cytoprotective as a pro-antioxidant or cytotoxic as a pro-oxidant. Any condition with acute or chronic oxidative stress is expected to perturb zinc homeostasis.

An integrated view of oxidative stress in aging: basic mechanisms, functional effects, and pathological considerations

Aging is an inherently complex process that is manifested within an organism at genetic, molecular, cellular, organ, and system levels. Although the fundamental mechanisms are still poorly understood, a growing body of evidence points toward reactive oxygen species (ROS) as one of the primary determinants of aging. The "oxidative stress theory" holds that a progressive and irreversible accumulation of oxidative damage caused by ROS impacts on critical aspects of the aging process and contributes to impaired physiological function, increased incidence of disease, and a reduction in life span. While compelling correlative data have been generated to support the oxidative stress theory, a direct cause-and-effect relationship between the accumulation of oxidatively mediated damage and aging has not been strongly established. The goal of this minireview is to broadly describe mechanisms of in vivo ROS generation, examine the potential impact of ROS and oxidative damage on cellular function, and evaluate how these responses change with aging in physiologically relevant situations. In addition, the mounting genetic evidence that links oxidative stress to aging is discussed, as well as the potential challenges and benefits associated with the development of anti-aging interventions and therapies.

Free radicals and antioxidants in normal physiological functions and human disease

Reactive oxygen species (ROS) and reactive nitrogen species (RNS, e.g. nitric oxide, NO(*)) are well recognised for playing a dual role as both deleterious and beneficial species. ROS and RNS are normally generated by tightly regulated enzymes, such as NO synthase (NOS) and NAD(P)H oxidase isoforms, respectively. Overproduction of ROS (arising either from mitochondrial electron-transport chain or excessive stimulation of NAD(P)H) results in oxidative stress, a deleterious process that can be an important mediator of damage to cell structures, including lipids and membranes, proteins, and DNA. In contrast, beneficial effects of ROS/RNS (e.g. superoxide radical and nitric oxide) occur at low/moderate concentrations and involve physiological roles in cellular responses to noxia, as for example in defence against infectious agents, in the function of a number of cellular signalling pathways, and the induction of a mitogenic response. Ironically, various ROS-mediated actions in fact protect cells against ROS-induced oxidative stress and re-establish or maintain "redox balance" termed also "redox homeostasis". The "two-faced" character of ROS is clearly substantiated. For example, a growing body of evidence shows that ROS within cells act as secondary messengers in intracellular signalling cascades which induce and maintain the oncogenic phenotype of cancer cells, however, ROS can also induce cellular senescence and apoptosis and can therefore function as anti-tumourigenic species. This review will describe the: (i) chemistry and biochemistry of ROS/RNS and sources of free radical generation; (ii) damage to DNA, to proteins, and to lipids by free radicals; (iii) role of antioxidants (e.g. glutathione) in the maintenance of cellular "redox homeostasis"; (iv) overview of ROS-induced signaling pathways; (v) role of ROS in redox regulation of normal physiological functions, as well as (vi) role of ROS in pathophysiological implications of altered redox regulation (human diseases and ageing). Attention is focussed on the ROS/RNS-linked pathogenesis of cancer, cardiovascular disease, atherosclerosis, hypertension, ischemia/reperfusion injury, diabetes mellitus, neurodegenerative diseases (Alzheimer's disease and Parkinson's disease), rheumatoid arthritis, and ageing. Topics of current debate are also reviewed such as the question whether excessive formation of free radicals is a primary cause or a downstream consequence of tissue injury.

Antioxidant enzyme activities and lipid peroxidation levels in erythrocytes of patients with oesophageal and gastric cancer

In this study, levels of lipid peroxidation and antioxidant enzyme activities were investigated in the erythrocytes of patients with oesophageal and gastric cancers. Erythrocytes were obtained from 17 patients with oesophageal cancer, 37 patients with gastric cancer and 20 healthy controls. Levels of malondialdehyde (MDA), a lipid peroxidation marker, and activities of copper- and zinc-containing superoxide dismutase (CuZn-SOD), catalase (CAT) and glutathione peroxidase (GPx) were determined using spectrophotometric methods. MDA levels and CuZn-SOD activity were significantly higher and GPx and CAT activities significantly lower in patients with oesophageal and gastric cancer than in controls. There were no statistically significant differences in the parameters measured in relation to disease stage in either patient group. These results indicate significant changes in the antioxidant defence system in patients with oesophageal and gastric cancer. It is postulated that this may lead to enhanced action of oxygen radicals, resulting in lipid peroxidation.

Hyperosmotic stress-dependent NFkappaB activation is regulated by reactive oxygen species and IGF-1 in cultured cardiomyocytes

We have recently shown that hyperosmotic stress activates p65/RelB NFkappaB in cultured cardiomyocytes with dichotomic actions on caspase activation and cell death. It remains unexplored how NFkappaB is regulated in cultured rat cardiomyocytes exposed to hyperosmotic stress. We study here: (a) if hyperosmotic stress triggers reactive oxygen species (ROS) generation and in turn whether they regulate NFkappaB and (b) if insulin-like growth factor-1 (IGF-1) modulates ROS production and NFkappaB activation in hyperosmotically-stressed cardiomyocytes. The results showed that hyperosmotic stress generated ROS in cultured cardiac myocytes, in particular the hydroxyl and superoxide species, which were inhibited by N-acetylcysteine (NAC). Hyperosmotic stress-induced NFkappaB activation as determined by IkappaBalpha degradation and NFkappaB DNA binding. NFkappaB activation and procaspase-3 and -9 fragmentation were prevented by NAC and IGF-1. However, this growth factor did not decrease ROS generation induced by hyperosmotic stress, suggesting that its actions over NFkappaB and caspase activation may be due to modulation of events downstream of ROS generation. We conclude that hyperosmotic stress induces ROS, which in turn activates NFkappaB and caspases. IGF-1 prevents NFkappaB activation by a ROS-independent mechanism.

Inhibition of tumour metastasis by targeted delivery of antioxidant enzymes

Metastasis is one of the most harmful aspects of malignant neoplasm. Interaction of tumour cells with normal cells such as tissue macrophages may generate reactive oxygen species, which would affect various aspects of tumour metastasis. Reactive oxygen species cause damage to both tumour and normal cells and some of them, especially hydrogen peroxide, can also act as intracellular second messengers at sublethal concentrations to increase the transcription of various genes, which can then accelerate the proliferation of tumour cells in metastatic colonies. Therefore, eliminating hydrogen peroxide is one approach to inhibiting tumour metastasis. In this article, the roles of reactive oxygen species in tumour metastasis are reviewed, and the strategies to inhibit tumour metastasis by the targeted delivery of catalase, an enzyme that detoxifies hydrogen peroxide, are discussed.

Polyenylphosphatidylcholine pretreatment ameliorates ischemic acute renal injury in rats

AIM

Polyenylphosphatidycholine has been demonstrated to have antioxidant, cytoprotective and anti-inflammatory effects. Whether polyenylphosphatidycholine pretreatment affects ischemia/reperfusion-induced renal damage in vivo is not known and was investigated here in rats.

METHODS

Forty female Sprague-Dawley rats were divided into three groups. Group 1 (n = 10) was given saline (control, sham operated). Group 2 (n = 15) were given saline, and Group 3 (n = 15) were given polyenylphosphatidycholine (100 mg/day for 10 days prior to experiment). Groups 2 and 3 were subjected to bilateral renal ischemia (60 min) followed by reperfusion (6 h). After the reperfusion period, the rats were sacrificed and kidney tissue superoxide dismutase, glutathione, total nitrite and nitrate, malondialdehyde and myeloperoxidase levels, plasma aspartate aminotransferase, blood urea nitrogen and creatinine concentrations, and nuclear factor kappa beta expression were determined.

RESULTS

Serum levels of aspartate aminotransferase, blood urea nitrogen and creatinine were significantly decreased (P < 0.05) in the treatment group compared to those in the ischemic group. There were significant differences between treatment and ischemic groups regarding the tissue superoxide dismutase, glutathione, total nitrite and nitrate, malondialdehyde, and myeloperoxidase levels (P < 0.05). In addition, polyenylphosphatidycholine pretreatment reduced nuclear factor kappa beta expression in ischemic kidney tissue. Kidneys obtained from rats pretreated with polyenylphosphatidycholine demonstrated marked reduction of the histological features of renal injury compared to kidneys obtained from Group 2 rats, including a little vacuolization, pyknosis and necrosis.

CONCLUSIONS

Polyenylphosphatidycholine pretreatment provided significant protection against ischemia/reperfusion injury to the kidney. This treatment could be therapeutic in kidney transplantation and other conditions associated with ischemia/reperfusion injury to the kidney.

Redox signaling in cancer biology

Over the last three decades, it is has become increasing clear that intracellular signaling pathways are activated via changes in intracellular metabolic oxidation/reduction (redox) reactions involving reactive oxygen species (ROS; i.e., superoxide and hydrogen peroxide). The initial proposals hypothesized that signaling through metabolic oxidation/reduction (redox) reactions involving ROS could contribute to carcinogenesis and progression to malignancy. Strong evidence for this hypothesis was obtained from studies showing that environmental insults (i.e., ionizing radiation) as well as xenobiotics (i.e., polycyclic aromatic hydrocarbons and phorbol esters) capable of inducing steady-state increases in free radical production and ROS could act as both initiators and promoters of carcinogenesis. This Forum is directed at understanding possible redox signaling mechanisms governing cellular radiation response, tumor growth, and response to therapy, as well as the role of nitric oxide in cancer biology.

Combination of thiol antioxidant Silibinin with Brostallicin is associated with increase in the anti-apoptotic protein Bcl-2 and decrease in caspase 3 activity

The cytotoxic activity of Brostallicin was previously shown to be enhanced in the presence of high glutathione and glutathione transferase levels. We hypothesized that thiol antioxidants, N-acetylcysteine and Silibinin, could potentiate Brostallicin's cytotoxicity in a similar way. HepG2 and CNE-2 cells were treated with N-acetylcysteine, Silibinin and Brostallicin, either alone or in combination. Surprisingly, we found that NAC and Silibinin had adverse effects on Brostallicin's cytotoxicity. The mechanism underlying the interaction involved the apoptotic pathway as we demonstrated an increase in Bcl-2 protein levels and decrease in caspase 3 activity with the Silibinin-Brostallicin combination.

ERK1/2 and p38-MAPK signalling pathways, through MSK1, are involved in NF-kappaB transactivation during oxidative stress in skeletal myoblasts

Skeletal muscle is highly adapted to respond to oxidative imbalances, since it is continuously subjected to an increased production of reactive oxygen species (ROS) during exercise. Oxidative stress, however, has been associated with skeletal muscle atrophy and damage in many diseases. In this study, we examined whether MAPK and NF-kappaB pathways participate in the response of skeletal myoblasts to oxidative stress, and whether there is a cross talk between these pathways. H(2)O(2) induced a strong activation of ERKs, JNKs and p38-MAPK in a time- and dose-dependent profile. ERK and JNK activation by H(2)O(2), but not that of p38-MAPK, was mediated by Src kinase and, at least in part, by EGFR. H(2)O(2) also stimulated a mild translocation of NF-kappaB to the nucleus, as well as a moderate phosphorylation of its endogenous cytoplasmic inhibitor IkappaB (at Ser32/36), without any significant decrease in IkappaB total levels. Moreover, oxidative stress induced a strong phosphorylation of NF-kappaB p65 subunit at Ser536 and Ser276. Inhibition of MAPK pathways by selective inhibitors did not appear to affect H(2)O(2)-induced nuclear translocation of NF-kappaB or the phosphorylation of IkappaB. In contrast, phosphorylation of p65 at Ser276 was found to be mediated by MSK1, a substrate of both ERKs and p38-MAPK. In conclusion, it seems that, during oxidative stress, NF-kappaB translocation to the nucleus is most likely not related with the MAPK activation, while p65 phosphorylations are in part mediated by MAPKs pathways, probably modifying signal specificity.

Free radical theory of autoimmunity

Background

Despite great advances in clinical oncology, the molecular mechanisms underlying the failure of chemotherapeutic intervention in treating lymphoproliferative and related disorders are not well understood.

Hypothesis

A hypothetical scheme to explain the damage induced by chemotherapy and associated chronic oxidative stress is proposed on the basis of published literature, experimental data and anecdotal observations. Brief accounts of multidrug resistance, lymphoid malignancy, the cellular and molecular basis of autoimmunity and chronic oxidative stress are assembled to form a basis for the hypothesis and to indicate the likelihood that it is valid in vivo.

Conclusion

The argument set forward in this article suggests a possible mechanism for the development of autoimmunity. According to this view, the various sorts of damage induced by chemotherapy have a role in the pattern of drug resistance, which is associated with the initiation of autoimmunity.

Copper-1,10-Phenanthroline-Induced Apoptosis in Liver Carcinoma Bel-7402 Cells Associates with Copper Overload, Reactive Oxygen Species Production, Glutathione Depletion and Oxidative DNA Damage

The mechanism of cytotoxicity on liver carcinoma Bel-7402 cells induced by copper-1,10-phenanthroline, Cu(OP)2, has been studied. Cell viability and apoptotic rate were examined in cells treated with Cu(OP)2 or Cu2+ alone. It was found that the apoptosis induced by Cu(OP)2 could not be induced by Cu2+ or OP alone in our experimental conditions. Total copper content in cells was measured by atomic absorption spectrophotometry, and the abnormal elevation of intracellular copper transported by lipophilic OP ligand may play the role of initial factor in the apoptosis, which caused subsequent redox state changes in cells. Intracellular levels of reactive oxygen species (ROS) were detected by fluorescent probe 2',7'-dichlorofluorescein diacetate (DCFH-DA). Reduced (GSH) and total glutathione (GSSG + GSH) were determined by High-performance liquid chromatography (HPLC) after derivatization, and the ratios of GSH/GSSG were subsequently calculated. The overproduction of ROS and the decreased GSH/GSSG ratio were observed in cells which represented the occurrence of oxidative stress in the apoptosis. Oxidative DNA damage was also found in cells treated with Cu(OP)2 in the early stage of the apoptosis, and it suggests that the activation of DNA repair system may be involved in the pathway of the apoptosis induced by Cu(OP)2.

Regulation of the mitogen-activated protein kinase p44 ERK activity during anoxia/recovery in rainbow trout hypodermal fibroblasts

It is well known from various mammalian cells that anoxia has a major impact on the mitogen-activated protein kinase ERK, but a possible similar effect in fish cells has not been investigated. Here we characterise a p44ERK-like protein in the rainbow trout cell line RTHDF and study the effect of (i) serum stimulation, (ii) sodium azide (chemical anoxia) and removal of azide (recovery) and (iii) anoxia (PO2&lt;0.1%) and recovery. During both chemical and true anoxia p44ERK was inhibited and recovery resulted in robust reactivation of p44ERK activity, far above the initial level. The inhibition was secondary to activation of p38MAPK and the increase was MEK dependent, as SB203580 inhibited the dephosphorylation during anoxia and the presence of PD98059 inhibited phosphorylation of p44ERK during recovery. In addition, we demonstrated that the reactivation of p44ERK during recovery also was dependent on reactive oxygen species and a PP1/PP2A-like phosphatase.

Cellular metabolism as a basis for immune privilege

We hypothesize that the energy strategy of a cell is a key factor for determining how, or if, the immune system interacts with that cell. Cells have a limited number of metabolic states, in part, depending on the type of fuels the cell consumes. Cellular fuels include glucose (carbohydrates), lipids (fats), and proteins. We propose that the cell's ability to switch to, and efficiently use, fat for fuel confers immune privilege. Additionally, because uncoupling proteins are involved in the fat burning process and reportedly in protection from free radicals, we hypothesize that uncoupling proteins play an important role in immune privilege. Thus, changes in metabolism (caused by oxidative stresses, fuel availability, age, hormones, radiation, or drugs) will dictate and initiate changes in immune recognition and in the nature of the immune response. This has profound implications for controlling the symptoms of autoimmune diseases, for preventing graft rejection, and for targeting tumor cells for destruction.

Oxidative stress in asthma and COPD: antioxidants as a therapeutic strategy

Asthma and chronic obstructive pulmonary disease (COPD) are inflammatory lung diseases that are characterized by systemic and chronic localized inflammation and oxidative stress. Sources of oxidative stress arise from the increased burden of inhaled oxidants, as well as elevated amounts of reactive oxygen species (ROS) released from inflammatory cells. Increased levels of ROS, either directly or via the formation of lipid peroxidation products, may play a role in enhancing the inflammatory response in both asthma and COPD. Moreover, in COPD it is now recognized as the main pathogenic factor for driving disease progression and increasing severity. ROS and lipid peroxidation products can influence the inflammatory response at many levels through its impact on signal transduction mechanisms, activation of redox-sensitive transcriptions factors, and chromatin regulation resulting in pro-inflammatory gene expression. It is this impact of ROS on chromatin regulation by reducing the activity of the transcriptional co-repressor, histone deacetylase-2 (HDAC-2), that leads to the poor efficacy of corticosteroids in COPD, severe asthma, and smoking asthmatics. Thus, the presence of oxidative stress has important consequences for the pathogenesis, severity, and treatment of asthma and COPD. However, for ROS to have such an impact, it must first overcome a variety of antioxidant defenses. It is likely, therefore, that a combination of antioxidants may be effective in the treatment of asthma and COPD. Various approaches to enhance the lung antioxidant screen and clinical trials of antioxidant compounds are discussed.

Free radicals, metals and antioxidants in oxidative stress-induced cancer

Oxygen-free radicals, more generally known as reactive oxygen species (ROS) along with reactive nitrogen species (RNS) are well recognised for playing a dual role as both deleterious and beneficial species. The "two-faced" character of ROS is substantiated by growing body of evidence that ROS within cells act as secondary messengers in intracellular signalling cascades, which induce and maintain the oncogenic phenotype of cancer cells, however, ROS can also induce cellular senescence and apoptosis and can therefore function as anti-tumourigenic species. The cumulative production of ROS/RNS through either endogenous or exogenous insults is termed oxidative stress and is common for many types of cancer cell that are linked with altered redox regulation of cellular signalling pathways. Oxidative stress induces a cellular redox imbalance which has been found to be present in various cancer cells compared with normal cells; the redox imbalance thus may be related to oncogenic stimulation. DNA mutation is a critical step in carcinogenesis and elevated levels of oxidative DNA lesions (8-OH-G) have been noted in various tumours, strongly implicating such damage in the etiology of cancer. It appears that the DNA damage is predominantly linked with the initiation process. This review examines the evidence for involvement of the oxidative stress in the carcinogenesis process. Attention is focused on structural, chemical and biochemical aspects of free radicals, the endogenous and exogenous sources of their generation, the metal (iron, copper, chromium, cobalt, vanadium, cadmium, arsenic, nickel)-mediated formation of free radicals (e.g. Fenton chemistry), the DNA damage (both mitochondrial and nuclear), the damage to lipids and proteins by free radicals, the phenomenon of oxidative stress, cancer and the redox environment of a cell, the mechanisms of carcinogenesis and the role of signalling cascades by ROS; in particular, ROS activation of AP-1 (activator protein) and NF-kappaB (nuclear factor kappa B) signal transduction pathways, which in turn lead to the transcription of genes involved in cell growth regulatory pathways. The role of enzymatic (superoxide dismutase (Cu, Zn-SOD, Mn-SOD), catalase, glutathione peroxidase) and non-enzymatic antioxidants (Vitamin C, Vitamin E, carotenoids, thiol antioxidants (glutathione, thioredoxin and lipoic acid), flavonoids, selenium and others) in the process of carcinogenesis as well as the antioxidant interactions with various regulatory factors, including Ref-1, NF-kappaB, AP-1 are also reviewed.

The role of oxidative stress in the dysregulation of gene expression and protein metabolism in neurodegenerative disease

There are few examples for which the genetic basis for neurodegenerative disease has been identified. For the majority of these disorders, the key to their understanding lies in knowledge of the molecular changes that contribute to altered gene expression and the translational modification of the protein products. Environmental factors play a role in the development and chronicity of neurodegenerative disorders. Environmental stimuli such as hypoxia, toxins, or heavy metals, increase production of reactive oxygen species and lower energy reserves. Chronic exposure to oxidative radicals can adversely affect gene expression and proteolysis. This review summarizes what is currently known about some of the changes in gene expression and protein metabolism that occur after oxidative stress which contribute to neurodegeneration, and reveals areas where more research is clearly needed.

Redox-sensitive signaling factors as a novel molecular targets for cancer therapy

Tumor cells undergoing proliferation, de-differentiation and progression depend on a complex set of respiratory pathways to generate the necessary energy. The metabolites from these pathways produce significant oxidative stress and must be buffered to prevent permanent cell damage and cell death. It is now clear that, in order to cope with and defend against the detrimental effects of oxidative stress, a series of redox-sensitive, pro-survival signaling pathways and factors regulate a complex intracellular redox buffering network. This review develops the hypothesis that tumor cells use these redox-sensitive, pro-survival signaling pathways and factors - up-regulated due to increased tumor cell respiration - to evade the damaging and cytotoxic effects of specific anticancer agents. It further suggests that redox-sensitive, signaling factors may be potential novel targets for drug discovery.

Regulation of osteoclast differentiation by the redox-dependent modulation of nuclear import of transcription factors

This study sought to characterize the reduced glutathione (GSH)/oxidized GSSG ratio during osteoclast differentiation and determine whether changes in the intracellular redox status regulate its differentiation through a RANKL-dependent signaling pathway. A progressive decrease of the GSH/GSSG ratio was observed during osteoclast differentiation, and the phenomenon was dependent on a decrease in total glutathione via downregulation of expression of the gamma-glutamylcysteinyl synthetase modifier gene. Glutathione depletion by L-buthionine-(S,R)-sulfoximine (BSO) was found to inhibit osteoclastogenesis by blocking nuclear import of NF-kappaB and AP-1 in RANKL-propagated signaling and bone pit formation by increasing BSO concentrations in mature osteoclasts. Furthermore, intraperitoneal injection of BSO in mice resulted in an increase in bone density and a decrease of the number of osteoclasts in bone. Conversely, glutathione repletion with either N-acetylcysteine or GSH enhanced osteoclastogenesis. These findings indicate that redox status decreases during osteoclast differentiation and that this modification directly regulates RANKL-induced osteoclastogenesis.

HIV-1 Tat protein-induced alterations of ZO-1 expression are mediated by redox-regulated ERK 1/2 activation

HIV-1 Tat protein plays an important role in inducing monocyte infiltration into the brain and may alter the structure and functions of the blood-brain barrier (BBB). The BBB serves as a frontline defense system, protecting the central nervous system from infected monocytes entering the brain. Therefore, the aim of the present study was to examine the mechanisms of Tat effect on the integrity of the BBB in the mouse brain. Tat was injected into the right hippocampi of C57BL/6 mice and expression of tight junction protein zonula occludens-1 (ZO-1) was determined in control and treated mice. Tat administration resulted in decreased mRNA levels of ZO-1 and marked disruption of ZO-1 continuity. These changes were associated with accumulation of inflammatory cells in brain tissue of Tat-treated mice. Further experiments indicated that Tat-mediated alterations of redox-related signaling may be responsible for decreased ZO-1 expression. Specifically, injections with Tat resulted in activation of extracellular signal-regulated kinase 1/2 (ERK 1/2) and pretreatment with U 0126, a specific inhibitor of ERK kinase, effectively ameliorated the Tat-induced diminished ZO-1 levels. In addition, administration of N-acetylcysteine (NAC), a precursor of glutathione and a potent antioxidant, attenuated both Tat-induced ERK 1/2 activation and alterations in ZO-1 expression. These results indicate that Tat-induced oxidative stress can play an important role in affecting the integrity of the BBB through the ERK 1/2 pathway.

Molecular mechanisms of survival and apoptosis in RAW 264.7 macrophages under oxidative stress

Organisms living in an aerobic environment are continuously exposed to reactive oxygen species (ROS). Apoptosis of cells can be induced by ROS and cells also develop negative feedback mechanisms to limit ROS induced cell death. In this study, RAW264.7 murine macrophage cells were treated with H(2)O(2) and cDNA microarray technique was used to produce gene expression profiles. We found that H(2)O(2) treatment caused up-regulation of stress, survival and apoptosis related genes, and down-regulation of growth and cell cycle promoting genes. Numerous genes of metabolism pathways showed special expression patterns under oxidative stress: glycolysis and lipid synthesis related genes were down-regulated whereas the genes of lipid catabolism and protein synthesis were up-regulated. We also identified several signaling molecules as ROS-responsive, including p53, Akt, NF-kappa B, ERK, JNK, p38, PKC and INF-gamma . They played important roles in the process of apoptosis or cell survival. Finally, an interactive pathway involved in cellular response to oxidative stress was proposed to provide some insight into the molecular events of apoptosis induced by ROS and the feedback mechanisms involved in cell survival.

Identification of a mutant-like conformation of p53 in fibroblasts from sporadic Alzheimer's disease patients

Here we show that fibroblasts from sporadic Alzheimer's disease (AD) patients specifically express an anomalous and detectable conformational state of p53 that makes these cells distinct from fibroblasts of age-matched non-AD subjects. In particular, we found that, in contrast to non-AD fibroblasts, p53 in AD fibroblasts is expressed at higher levels in resting condition, and presents a significant impairment of its DNA binding and transcriptional activity. All together, these findings figured out the presence of a mutant-like p53 phenotype. However, gene sequencing of the entire p53 gene from either AD or non-AD did not unravel point mutations. Based on immunoprecipitation studies with conformation-specific p53 antibodies (PAb1620 and PAb240), which discriminated folded versus unfolded p53 tertiary structure, we found that a significant amount of p53 assumed an unfolded tertiary structure in fibroblasts from AD patients. This conformational mutant-like p53 form was virtually undetectable in fibroblasts from non-AD patients. These data, independently from their relevance in understanding the etiopathogenesis of AD, might be useful for supporting AD diagnosis.

A proposed mechanism to explain the stimulatory effect of melatonin on antioxidative enzymes

Melatonin, the main secretory product of the pineal gland, is known to collaborate against oxidative stress within cells, but its mechanism of action in terms of stimulating antioxidant enzymes remains unclear. Herein, we propose that melatonin modulates antioxidant enzyme activities via its interaction with calmodulin, which in turn inhibits downstream processes that lead to the inactivation of nuclear RORalpha melatonin receptor. Eventually, this nuclear transcription factor downregulates NF-kappaB-induced antioxidant enzyme expression. Therefore, the increment in antioxidant enzyme activities induced by melatonin involves the inhibition of the RORalpha pathway. Thus, in addition to its direct free radical scavenging activities, melatonin has important actions in oxidative defense by stimulating enzymes which metabolize free radicals and radical products to innocuous metabolites.

Mitochondria: A novel target for the chemoprevention of cancer

The mitochondria have emerged as a novel target for anticancer chemotherapy. This tenet is based on the observations that several conventional and experimental chemotherapeutic agents promote the permeabilization of mitochondrial membranes in cancerous cells to initiate the release of apoptogenic mitochondrial proteins. This ability to engage mitochondrial-mediated apoptosis directly using chemotherapy may be responsible for overcoming aberrant apoptosis regulatory mechanisms commonly encountered in cancerous cells. Interestingly, several putative cancer chemopreventive agents also possess the ability to trigger apoptosis in transformed, premalignant, or malignant cells in vitro via mitochondrial membrane permeabilization. This process may occur through the regulation of Bcl-2 family members, or by the induction of the mitochondrial permeability transition. Thus, by exploiting endogenous mitochondrial-mediated apoptosis-inducing mechanisms, certain chemopreventive agents may be able to block the progression of premalignant cells to malignant cells or the dissemination of malignant cells to distant organ sites as means of modulating carcinogenesis in vivo. This review will examine cancer chemoprevention with respect to apoptosis, carcinogenesis, and the proapoptotic activity of various chemopreventive agents observed in vitro. In doing so, I will construct a paradigm supporting the notion that the mitochondria are a novel target for the chemoprevention of cancer.

MAPK/AP-1 signal pathway in tobacco smoke-induced cell proliferation and squamous metaplasia in the lungs of rats

Overwhelming evidence has demonstrated tobacco smoke (TS) is causally associated with various types of cancers, especially lung cancer. Sustained epithelial cell hyperplasia and squamous metaplasia are considered as preneoplastic lesions during the formation of lung cancer. The cellular and molecular mechanisms leading to lung cancer due to TS are not clear. Mitogen-activated protein kinases (MAPK)/activator protein-1 (AP-1) can be activated by various stimuli and play a critical role in the control of cell proliferation and differentiation. To date, information on the response of the MAPK/AP-1 pathway during hyperplasia and squamous metaplasia induced by TS is lacking. We therefore investigated the effects of TS on the development of epithelial hyperplasia and squamous metaplasia, regulation of MAPK/AP-1 activation, and expression of AP-1-regulated cell cycle proteins and differentiation markers in the lungs of rats. Exposure of rats to TS (30 mg/m(3) or 80 mg/m(3), 6 h/day, 3 days/week for 14 weeks) dramatically induced cell proliferation and squamous metaplasia in a dose-dependent manner, effects that paralleled the activation of AP-1-DNA binding activity. Phosphorylated ERK1/2, JNK, p38 and ERK5 were significantly increased by exposure to TS, indicating the activation of these MAPK pathways. Expression of Jun and Fos proteins were differentially regulated by TS. TS upregulated the expression of AP-1-dependent cell cycle proteins including cyclin D1 and proliferating cell nuclear antigen (PCNA). Among the AP-1-dependent cell differentiation markers, keratin 5 and 14 were upregulated, while loricrin, filaggrin and involucrin were downregulated following TS exposure. These findings suggest the important role of MAPK/AP-1 pathway in TS-induced pathogenesis, thus providing new insights into the molecular mechanisms of TS-associated lung diseases including lung cancers.

Thioredoxin reductase as a novel molecular target for cancer therapy

Tumor cell proliferation, de-differentiation, and progression depend on a complex combination of altered cell cycle regulation, excessive growth factor pathway activation, and decreased apoptosis. The understanding of these complex mechanisms should lead to the identification of potential targets for therapeutic intervention. Redox-sensitive signaling factors also regulate multiple cellular processes including proliferation, cell cycle, and pro-survival signaling cascades, suggesting their potential as molecular targets for anticancer agents. These observations suggest that redox-sensitive signaling factors may be potential novel molecular markers. We hypothesized that thioredoxin reductase-1 (TR), a component of several redox-regulated pathways, may represent a potential molecular target candidate in response to agents that induce oxidative stress. There have been numerous biological studies over the last decade investigating the cell biological, biochemical, and genetic properties of TR both in culture and in in vivo models. In addition, using a series of permanent cell lines that express either a wild-type TR or a dominant mutant TR gene or a chemical agent that inhibits TR we demonstrated that TR meets most criteria that would identify a molecular target. Based on these results we believe TR is a potential molecular target and discuss potential clinical possibilities.

Chloroplasts as source and target of cellular redox regulation: a discussion on chloroplast redox signals in the context of plant physiology

During the evolution of plants, chloroplasts have lost the exclusive genetic control over redox regulation and antioxidant gene expression. Together with many other genes, all genes encoding antioxidant enzymes and enzymes involved in the biosynthesis of low molecular weight antioxidants were transferred to the nucleus. On the other hand, photosynthesis bears a high risk for photo-oxidative damage. Concomitantly, an intricate network for mutual regulation by anthero- and retrograde signals has emerged to co-ordinate the activities of the different genetic and metabolic compartments. A major focus of recent research in chloroplast regulation addressed the mechanisms of redox sensing and signal transmission, the identification of regulatory targets, and the understanding of adaptation mechanisms. In addition to redox signals communicated through signalling cascades also used in pathogen and wounding responses, specific chloroplast signals control nuclear gene expression. Signalling pathways are triggered by the redox state of the plastoquinone pool, the thioredoxin system, and the acceptor availability at photosystem I, in addition to control by oxolipins, tetrapyrroles, carbohydrates, and abscisic acid. The signalling function is discussed in the context of regulatory circuitries that control the expression of antioxidant enzymes and redox modulators, demonstrating the principal role of chloroplasts as the source and target of redox regulation.

Differentiation of normal and cancer cells induced by sulfhydryl reduction: biochemical and molecular mechanisms

We examined the morphological, biochemical and molecular outcome of a nonspecific sulfhydryl reduction in cells, obtained by supplementation of N-acetyl-L-cysteine (NAC) in a 0.1-10 mM concentration range. In human normal primary keratinocytes and in colon and ovary carcinoma cells we obtained evidences for: (i) a dose-dependent inhibition of proliferation without toxicity or apoptosis; (ii) a transition from a proliferative mesenchymal morphology to cell-specific differentiated structures; (iii) a noticeable increase in cell-cell and cell-substratum junctions; (iv) a relocation of the oncogenic beta-catenin at the cell-cell junctions; (v) inhibition of microtubules aggregation; (vi) upregulation of differentiation-related genes including p53, heat shock protein 27 gene, N-myc downstream-regulated gene 1, E-cadherin, and downregulation of cyclooxygenase-2; (vii) inhibition of c-Src tyrosine kinase. In conclusion, a thiol reduction devoid of toxicity as that operated by NAC apparently leads to terminal differentiation of normal and cancer cells through a pleiade of converging mechanisms, many of which are targets of the recently developed differentiation therapy.

Differential susceptibility of nonmalignant human breast epithelial cells and breast cancer cells to thiol antioxidant-induced G(1)-delay

Reactive oxygen species (ROS) and ROS signaling have been implicated in a variety of human pathophysiological conditions that involve aberrant cellular proliferation, particularly cancer. We hypothesize that intracellular redox state differentially affects cell-cycle progression in nonmalignant versus malignant cells. The thiol antioxidant, N-acetyl-L-cysteine (NAC), was used to alter intracellular redox state in nonmalignant human breast epithelial (MCF-10A) and breast cancer cells (MCF-7 and MDA-MB-231). Treatment of cells with NAC resulted in significant augmentation of intracellular small-molecular-weight thiols, glutathione and cysteine. In addition, NAC treatment decreased oxidation of a prooxidant-sensitive dye in MCF-10A cells, but not in MDA-MB-231 and MCF-7 cells. NAC-induced shifts in intracellular redox state toward a more reducing environment caused G(1) delays in MCF-10A cells without causing any significant changes in MCF-7 and MDA-MB-231 cell-cycle progression. NAC treatment of MCF-10A (but not MCF-7 and MDA-MB-231) was accompanied by a decrease in cyclin D1 and an increase in p27 protein levels, which correlated with increased retinoblastoma protein hypophosphorylation. These results show differential redox control of progression from G(1) to S in nonmalignant versus malignant cells and support the hypothesis that loss of a redox control of the cell cycle could contribute to aberrant proliferation seen in cancer cells.

36kDa Glycoprotein isolated from Rhus verniciflua Stokes fruit has a protective activity to glucose/glucose oxidase-induced apoptosis in NIH/3T3 cells

The present study was carried out to investigate the antioxidative and antiapoptotic activities of 36 kDa RVS glycoprotein isolated from Rhus verniciflua Stokes fruits (RVS) in NIH/3T3 cells in vitro. The results showed that the RVS glycoprotein has scavenging activities of free radicals and hydroxyl radicals, and protects from glucose/glucose oxidase (G/GO)-induced cellular damage in NIH/3T3 cells dose-dependently. For example, cell viability was 43.5% in the G/GO treatment alone, whereas it was 93.8% in the co-treatment with RVS glycoprotein (200 microg/ml). We also demonstrated that RVS glycoprotein inhibits activities of the nuclear factor-kappa B (NF-kappaB) and activator protein-1 (AP-1) induced by G/GO, and prevents from G/GO-induced apoptosis in the NIH/3T3 cells. In this regard, the results in this study indicated that RVS glycoprotein has a strong antioxidative activity and an antiapoptotic effect through the modulation activities of NF-kappaB and AP-1in NIH/3T3 cells.

Mechanism of the tumor suppressive effect of MnSOD overexpression

The mitochondrial antioxidant protein manganese-containing superoxide dismutase (MnSOD) has been shown to be a new type of tumor suppressor protein. Overexpression of MnSOD protein inhibits growth in a wide variety of cancer types. This review examines the molecular mechanism of the tumor suppressive effect of MnSOD. Three species have been proposed to cause the tumor suppressive effect: superoxide radical, hydrogen peroxide and nitric oxide. At the present time, the evidence appears strongest that hydrogen peroxide is the effector molecule since both catalase and glutathione peroxidase has been shown to modulate the effect. Surprisingly, in different cancer cell lines, overexpression of GPx has been found to both decrease and increase the growth inhibitory effect of MnSOD overexpression. Knowledge of which molecule causes the tumor suppressive effect of MnSOD and the mechanism of action will likely lead to new therapies for the treatment of cancer.

Proteomic analysis of human thyroid cell lines reveals reduced nuclear localization of Mn-SOD in poorly differentiated thyroid cancer cells

Differential protein arrays between nuclear extracts of human thyroid cell lines obtained from tumors with different degree of differentiation were exploited to define molecular alterations occurring during thyroid tumor progression. Nuclear extracts from the well differentiated TPC-1 (from papillary carcinoma) and the poorly differentiated ARO (from anaplastic carcinoma) cells showed an overall similar pattern of protein expression as revealed by two-dimensional gel electrophoresis analysis. However, manganese-superoxide dismutase (Mn-SOD) was clearly identified by mass spectrometry procedures as significantly less expressed in ARO compared to TPC-1 cells. A reduced expression of Mn-SOD in the nuclear compartment was confirmed by Western blot and immunofluorescence analysis. A similar expression pattern of nuclear Mn-SOD was detected by immunohistochemistry in human thyroid tumors, with the lowest or absent detection in anaplastic carcinomas. Moreover, the levels of nuclear Mn-SOD in tumor cells were lower than in the normal thyrocytes. These data indicate that an altered nuclear expression of Mn-SOD parallels, together with changes in other elements of the antioxidant protective system, the loss of differentiation occurring during the progression of thyroid tumors.

Glutathione peroxidase, glutathione-S-transferase, catalase, xanthine oxidase, Cu-Zn superoxide dismutase activities, total glutathione, nitric oxide, and malondialdehyde levels in erythrocytes of patients with small cell and non-small cell lung cancer

Lung cancer is a common pathology with high mortality due to late diagnosis. Glutathione peroxidase (GSH-Px), glutathione-S-transferase (GST), catalase (CAT), xanthine oxidase (XO), Cu-Zn superoxide dismutase (Cu-Zn SOD) activities, total glutathione (TGSH), nitric oxide (NO*), and malondialdehyde (MDA) levels were investigated in erythrocytes of patients with non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC), and healthy control group. We aimed to investigate serum GSH, GSH-dependent enzymes activities (GSH-Px and GST), XO, CAT, Cu-Zn SOD activity, and NO*, and MDA levels in patients with NSCLC and with SCLC and correlate with the cancer stage. Erythrocyte MDA, NO*, TGSH levels and erythrocyte SOD, CAT and XO activities were significantly higher in patients with NSCLC and SCLC than in controls. Slightly increased erythrocyte GSH-Px and GST activities were not significantly different from the controls. Erythrocyte MDA level positively correlated with erythrocyte NO* levels in patients with early stage (I+II) in NSCLC groups. Erythrocyte MDA level positively correlated with erythrocyte XO activity in patients with advanced stage (III+IV) in NSCLC groups. However, no other correlation could be found among the parameters in healthy controls and patients with NSCLC and with SCLC. Results obtained in this study indicate significant changes in antioxidant defence system in NSCLC and SCLC patients, which may lead to enhanced action of oxygen radical, resulting in lipid peroxidation.

A novel theory: biological processes mostly involve two types of mediators, namely general and specific mediators

A great number of papers have shown that free radicals as well as bioactive molecules can play a role of mediator in a wide spectrum of biological processes, but the biological actions and chemical reactivity of the free radicals are quite different from that of the bioactive molecules, and that a wide variety of bioactive molecules can be easily modified by free radicals due to having functional groups sensitive to redox, and the significance of the interaction between the free radicals and the bioactive molecules in biological processes has been confirmed by the results of some in vitro and in vivo studies. Based on these evidence, this article presented a novel theory about the mediators of biological processes. The essentials of the theory are: (a) mediators of biological processes can be classified into general and specific mediators; the general mediators include two types of free radicals, namely superoxide and nitric oxide; the specific mediators include a wide variety of bioactive molecules, such as specific enzymes, transcription factors, cytokines and eicosanoids; (b) a general mediator can modify almost any class of the biomolecules, and thus play a role of mediator in nearly every biological process via diverse mechanisms; a specific mediator always acts selectively on certain classes of the biomolecules, and may play a role of mediator in different biological processes via a same mechanism; (c) biological processes are mostly controlled by networks of their mediators, so the free radicals can regulate the last consequence of a biological process by modifying some types of the bioactive molecules, or in cooperation with these bioactive molecules; the biological actions of superoxide and nitric oxide may be synergistic or antagonistic. According to this theory, keeping the integrity of these networks and the balance between the free radicals and the bioactive molecules as well as the balance between the free radicals and the free radical scavengers would be of vital importance for physiological processes, and disturbance of these networks and balances would be a critical factor of pathological processes. Therefore, the investigators who want to get a deep and full understanding of the mechanism of a biological process should pay attention to the roles of both free radical and bioactive molecule species, and the free radical scavengers, which are used for health protection, such a vitamin E and carotenoid, should be taken in a suitable dosage.

Anti-fibrosclerotic effects of shock wave therapy in lipedema and cellulite

In vivo measurements in 26 female patients with lipedema and cellulite parameters were carried out before and after therapy by means of complex physical decongestive therapy (CPDT) including manual lymph drainage and compression as main components and/or shock wave therapy (SWT). Oxidative stress parameters of blood serum and biomechanic skin properties/smoothening of dermis and hypodermis surface were evaluated. Oxidative stress in lipedema and cellulite was demonstrated by increased serum concentrations of malondialdehyde (MDA) and plasma protein carbonyls compared with healthy control persons. Both MDA and protein carbonyls in blood plasma decreased after serial shock wave application and CPDT. The SWT itself and CPDT itself lead to MDA release from edematous tissue into the plasma. Obviously both therapy types, SWT and CPDT, mitigate oxidative stress in lipedema and cellulite. In parallel SWT improved significantly the biomechanic skin properties leading to smoothening of dermis and hypodermis surface. Significant correlation between MDA depletion of edematous and lipid enriched dermis and improvement of mechanic skin properties was demonstrated. From these findings it is concluded, that a release of lipid peroxidation (LPO) products from edematous dermis is an important sclerosis-preventing effect of SWT and/or CPDT in lipedema and cellulite. Expression of factors stimulating angiogenesis and lymphangiogenesis such as VEGF was not induced by SWT and/or CPDT and, therefore, not involved in beneficial effects by SWT and/or CPDT.

Role of 4-hydroxy-2,3-nonenal in the pathogenesis of fibrosis

Transient activation of fibroblasts or fibroblast-like cells to proliferate and to produce elevated quantities of extracellular matrix is essential to fibrosis. This activation is regulated by several cytokines produced by various inflammation-associated cells. Among these, transforming growth factor beta1 (TGFbeta1) is considered of major importance. Many studies have shown that lipid peroxidation play a key role in the initiation and progression of fibrosis in different organs. In fact, 4-hydroxy-2,3-nonenal (HNE), the major aldehydic product of lipid peroxidation, is able to induce TGFbeta1 expression and synthesis, and activation of activator protein-1 (AP-1) transcription factor. In this study, using the murine macrophage line J774-A1, we show that these effects are strictly related to the chemical structure of HNE, since neither 2-nonenal nor nonanal are biologically active to the same extent. Moreover, we demonstrate that HNE can indeed contribute to the onset of fibrosis by stimulating AP-1 binding to DNA and consequently inducing TGFbeta1 expression, since thiol-group reagents, such as N-ethylmaleimide and 4-(chloro-mercuri)-benzenesulfonic acid, that down-modulate HNE entrance and localisation inside the cell, prevent both phenomena. The possibility to control fibrogenic cytokine levels by means of antioxidant or dietetic treatments opens new potential pharmacological and nutritional horizons in the treatment of many chronic diseases characterised by excessive fibrosis.

Oxidative stress attenuates Fas-mediated apoptosis in Jurkat T cell line through Bfl-1 induction

Many types of mammalian cells produce ROS in response to many different stimuli to modulate a number of cellular functions, including apoptosis. However, the correlation between ROS and apoptosis remains controversial, and the mechanisms whereby ROS-induced signals are propagated to critical downstream targets remain largely undefined. Here, we demonstrate that hydrogen peroxide (H2O2) upregulates the expression of Bfl-1, an antiapoptotic member of the Bcl-2 family, and that this is responsible for the antiapoptotic activity of ROS. When Jurkat, human leukemic T cells, were pretreated with 100 microM H2O2 and then treated with anti-Fas antibody, apoptosis was impaired without change of cell surface Fas expression. An investigation of the expression patterns of Bcl-2 family genes revealed that H2O2 treatment induced Bfl-1 gene expression, but left other genes unchanged, and this Bfl-1 expression and H2O2 -induced antiapoptotic effect was inhibited by antioxidants or NF-kappaB inhibitor. In addition, an electromobility shift assay revealed that the p65/p50 subunits of NF-kappaB activated by H2O2 bound to a bfl-1 promoter. Neither the induction of Bfl-1 nor the antiapoptotic effect of H2O2 was detected in Bfl-1-knockdown Jurkat cell line containing Bfl-1 antisense (Bfl-1AS). These data indicate that oxidative stress induces the expression of Bfl-1 via NF-kappaB activation, and this early-response gene protects cells from Fas-mediated apoptosis. This may be a cellular survival mechanism of cells exposed to phagocytes-derived ROS.

Redox potential regulates binding of universal minicircle sequence binding protein at the kinetoplast DNA replication origin

Kinetoplast DNA, the mitochondrial DNA of the trypanosomatid Crithidia fasciculata, is a remarkable structure containing 5,000 topologically linked DNA minicircles. Their replication is initiated at two conserved sequences, a dodecamer, known as the universal minicircle sequence (UMS), and a hexamer, which are located at the replication origins of the minicircle L- and H-strands, respectively. A UMS-binding protein (UMSBP), binds specifically the conserved origin sequences in their single stranded conformation. The five CCHC-type zinc knuckle motifs, predicted in UMSBP, fold into zinc-dependent structures capable of binding a single-stranded nucleic acid ligand. Zinc knuckles that are involved in the binding of DNA differ from those mediating protein-protein interactions that lead to the dimerization of UMSBP. Both UMSBP DNA binding and its dimerization are sensitive to redox potential. Oxidation of UMSBP results in the protein dimerization, mediated through its N-terminal domain, with a concomitant inhibition of its DNA-binding activity. UMSBP reduction yields monomers that are active in the binding of DNA through the protein C-terminal region. C. fasciculata trypanothione-dependent tryparedoxin activates the binding of UMSBP to UMS DNA in vitro. The possibility that UMSBP binding at the minicircle replication origin is regulated in vivo by a redox potential-based mechanism is discussed.

Thioredoxin reductase as a potential molecular target for anticancer agents that induce oxidative stress

Redox-sensitive signaling factors regulate multiple cellular processes, including proliferation, cell cycle, and prosurvival signaling cascades, suggesting their potential as molecular targets for anticancer agents. It is logical to set constraints that a molecular target should meet at least one of the following criteria: (1) inhibition of prosurvival signaling pathways; (2) inhibition of cell cycle progression; or (3) enhancement of the cytotoxic effects of anticancer agents. Therefore, we hypothesized that thioredoxin reductase 1 (TR), a component of several redox-regulated pathways, might represent a potential molecular target candidate in response to agents that induce oxidative stress. To address this issue, permanent cell lines overexpressing either the wild-type (pCXN2-myc-TR-wt) or a Cys-Ser mutant (pCXN2-myc-mTR) TR gene were used, as were parental HeLa cells treated with 1-methyl-1-propyl-2-imidazolyl disulfide (IV-2), a pharmacologic inhibitor of TR. Cells were exposed to the oxidative stressors, H2O2 and ionizing radiation (IR), and analyzed for changes in signal transduction, cell cycle, and cytotoxicity. Analysis of HeLa cells overexpressing the pCXN2-myc-TR-wt gene showed increased basal activity of nuclear factor kappaB (NFkappaB) and activator protein (AP-1), whereas HeLa cells expressing a pCXN2-myc-mTR gene and HeLa cells treated with IV-2 were unable to induce NFkappaB or AP-1 activity following H2O2 or IR exposure. Fluorescence-activated cell sorting analysis showed a marked accumulation of pCXN2-myc-mTR cells in the late G1 phase, whereas pCXN2-myc-TR-wt cells showed a decreased G1 subpopulation. Chemical inhibition of TR with IV-2 also completely inhibited cellular proliferation at concentrations between 10 and 25 micromol/L, resulting in a G1 phase cell cycle arrest consistent with the results from cells expressing the pCXN2-myc-mTR gene. Following exposure to H2O2 and IR, pCXN2-myc-mTR- and IV-2-treated cells were significantly more sensitive to oxidative stress-induced cytotoxicity as measured by clonogenic survival assays. Finally, IV-2-treated cells showed increased tumor cell death when treated with H2O2 and IR. These results identify TR as a potential target to enhance the cytotoxic effects of agents that induce oxidative stress, including IR.

Dietary lipid hydroperoxides induce expression of vascular endothelial growth factor (VEGF) in human colorectal tumor cells

Fatty acid hydroperoxides arise from unsaturated fatty acids in the presence of oxygen and elevated temperature during processing of food. Here we have studied their effects on gene expression in colorectal tumor cells using linoleic acid hydroperoxide (LOOH) as a model compound. Its addition to the medium of LT97 human adenoma cells and SW480 human carcinoma cells enhanced the production of intracellular hydrogen peroxide. Furthermore, in both cell lines, increases in VEGF mRNA and protein were observed. Unoxidized linoleic acid had little or no activity. Concomitantly, COX-2 expression was up-regulated. In the LT97 cells, the COX inhibitors SC58560 and SC58236 completely prevented the VEGF induction, suggesting that the effect was dependent on prostaglandin synthesis. In vivo prostaglandin-mediated induction of VEGF secretion is known to be essential for the growth of adenomatous polyps and their progression to carcinomas. Therefore, our results for the first time implicate dietary lipid hydroperoxide as a key risk factor in colon carcinogenesis.

Plastid regulation of Lhcb1 transcription in the chlorophyte alga Dunaliella tertiolecta

We identify four novel DNA-binding complexes in the nuclear-encoded Lhcb1 promoter of the chlorophyte alga Dunaliella tertiolecta that are regulated by photosynthetic pathways in the plastid. The binding activities of three of the complexes were positively correlated with time-dependent changes in Lhcb1 transcript abundance, implicating their roles as transcriptional enhancers in a retrograde signal transduction pathway. Using a combination of inhibitors, uncouplers, and antimycin A, and by following the kinetic pattern of gene regulation, we infer two different sensors in the signal transduction pathway. On short time scales of 0.5 to about 4 h, the transthylakoid membrane potential appears to be a critical determinant of gene expression, whereas on time scales of 8 h or longer, the redox state of the plastoquinone pool becomes increasingly more important. The differentiation of these two types of signals was observed in parallel effects on gene transcription and on the patterns of DNA-binding activities in the Lhcb1 promoter. These signals appear to be transduced at the nuclear level via a coordinated ensemble of DNA-binding complexes located between -367 and -188 bp from the start codon of the gene. The regulation of these elements allows the cell to up- or down-regulate the expression on Lhcb1 in response to changes in irradiance.

Oral-aboral axis specification in the sea urchin embryo II. Mitochondrial distribution and redox state contribute to establishing polarity in Strongylocentrotus purpuratus

The initial asymmetry that specifies the oral-aboral (OA) axis of the sea urchin embryo has long been a mystery. It was shown previously that OA polarity can be entrained in embryos by imposing a respiratory asymmetry, with the most oxidizing side of the embryo tending to develop as the oral pole. This suggests that one of the earliest observable asymmetries along the incipient OA axis, a redox gradient established by a higher density and/or activity of mitochondria on the prospective oral side of the embryo, might play a causal role in establishing the axis. Here, we examine the origin and functional significance of this early redox gradient. Using MitoTracker Green, we show that mitochondria are asymmetrically distributed in the unfertilized egg of Strongylocentrotus purpuratus, and that the polarity of the maternal asymmetry is maintained in the zygote. Vital staining indicates that the side of the embryo that inherits the highest density of mitochondria tends to develop into the oral pole. This correlation holds when mitochondria are redistributed by centrifugation of eggs or by transfer of purified mitochondria into zygotes, indicating that an asymmetric mitochondrial distribution can entrain OA polarity, possibly through effects on intracellular redox state. In support of this possibility, we find that specification of oral ectoderm is suppressed when embryos are cultured under hypoxic conditions that enforce a relatively reducing redox state. This effect is reversed by overexpression of nodal, an early zygotic marker of oral specification whose localized expression suffices to organize the entire OA axis, indicating that redox state is upstream of nodal expression. We therefore propose that a threshold level of intracellular oxidation is required to effectively activate nodal, and that precocious attainment of this threshold within the blastomeres containing the highest density of mitochondria results in asymmetric nodal activity and consequent specification of the OA axis.

Enhancement by other compounds of the anti-cancer activity of vitamin D(3) and its analogs

Differentiation therapy holds promise as an alternative to cytotoxic drug therapy of cancer. Among compounds under scrutiny for this purpose is the physiologically active form of vitamin D(3), 1,25-dihydroxyvitamin D(3), and its chemically modified derivatives. However, the propensity of vitamin D(3) and its analogs to increase the levels of serum calcium has so far precluded their use in cancer patients except for limited clinical trials. This article summarizes the range of compounds that have been shown to increase the differentiation-inducing and antiproliferative activities of vitamin D(3) and its analogs, and discusses the possible mechanistic basis for this synergy in several selected combinations. The agents discussed include those that have differentiation-inducing activity of their own that is increased by combination with vitamin D(3) or analogs, such as retinoids or transforming growth factor-beta and plant-derived compounds and antioxidants, such as curcumin and carnosic acid. Among other compounds discussed here are dexamethasone, nonsteroidal anti-inflammatory drugs, and inhibitors of cytochrome P450 enzymes, for example, ketoconazole. Thus, recent data illustrate that there are extensive, but largely unexplored, opportunities to develop combinatorial, differentiation-based approaches to chemoprevention and chemotherapy of human cancer.

Replicative senescence: a critical review

Human cells in culture have a limited proliferative capacity. After a period of vigorous proliferation, the rate of cell division declines and a number of changes occur in the cells including increases in size, in secondary lysosomes and residual bodies, nuclear changes and a number of changes in gene expression which provide biomarkers for senescence. Although human cells in culture have been used for over 40 years as models for understanding the cellular basis of aging, the relationship of replicative senescence to aging of the organism is still not clear. In this review, we discuss replicative senescence in the light of current information on signal transduction and mitogenesis, cell stress, apoptosis, telomere changes and finally we discuss replicative senescence as a model of aging in vivo.

Antioxidant enzymes and redox regulating thiol proteins in malignancies of human lung

Oxidants are known to modulate cell proliferation and apoptosis, and induce synthesis of growth factors that play an important role in tumor growth and invasion. Antioxidant enzymes and thiol proteins regulating cellular redox state constitute the major cellular protection against oxidants. Consequently, they are also associated both with carcinogenesis and tumor progression. Superoxide dismutases, glutamate cysteine ligase, catalase, thioredoxins and peroxiredoxins, which are the most important of these enzymes, are expressed in lung malignancies, and especially in pleural mesothelioma. This has consequences not only for tumor behavior but also for resistance of tumor cells to cytotoxic drugs and radiation.

Decreased copper-zinc superoxide dismutase activity and increased resistance to oxidative stress in glia maturation factor-null astrocytes

Glia maturation factor (GMF) is a highly conserved protein found mainly in the nervous system. The current work was undertaken to investigate the effect of GMF expression in astrocytes on CuZn superoxide dismutase (CuZnSOD or SOD I) and on the vulnerability of the cells to H2O2 toxicity. Primary astrocyte cultures were derived from mice in which the GMF gene was completely deleted by homologous recombination (knockout). Astocytes derived from knockout animals displayed a lower level of CuZnSOD activity and protein. The reduction in CuZnSOD was restored by transfection with a GMF/adenovirus construct, and the resulting increase was blocked by the p38 MAP kinase inhibitor SB203580. There was no change in the other isoform of SOD (MnSOD or SOD II). Endogenous H2O2 was lower in the knockout cells, and the cells became more resistant to H2O2 toxicity compared to the wild type. In the GMF-null cells, concurrent with a decrease in CuZnSOD, the function of which is to convert superoxide to H2O2, there was an increase in the activity of the two enzymes that degrade H2O2: catalase and glutathione peroxidase. By regulating the redox state of the cell, GMF may be involved in a wide spectrum of cellular events ranging from survival, proliferation, differentiation, to death.

Free aminothiols, glutathione redox state and protein mixed disulphides in aging Drosophila melanogaster

The main purpose of the present study was to test the hypothesis that the aging process is associated with a pro-oxidizing shift in the cellular redox state. The amounts of the redox-sensitive free aminothiols (glutathione, cysteine, Cys-Gly and methionine) and protein mixed disulphides were measured at different ages and ambient temperatures in Drosophila melanogaster. GSH/GSSG ratios decreased significantly with increasing age of the flies, due to an increase in GSSG content. Concentrations of Cys-Gly increased and methionine decreased with age. The amounts of protein mixed disulphides, measured as protein-cysteinyl, protein-Cys-Gly and protein-glutathionyl mixed disulphides, increased as a function of age. The pattern of changes in free aminothiol content, glutathione-redox state and protein mixed disulphides varied in proportion to the ambient temperature, which is inversely related to the life expectancy of the flies. Collectively, these results support the idea that the pro-oxidizing shift in the glutathione-redox state, the decrease in methionine content and increase in abundance of protein mixed disulphides are associated with the life expectancy of flies, and are indicative of enhanced oxidative stress during aging.