Manganese superoxide dismutase overexpression inhibits the growth of androgen-independent prostate cancer cells

Mitochondria as oxidative signaling organelles in T-cell activation: physiological role and pathological implications

Early scientific reports limited the cell biological role of reactive oxygen species (ROS) to the cause of pathological damage. However, extensive research performed over the last decade led to a wide recognition of intracellular oxidative/redox signaling as a crucial mechanism of homeostatic regulation. Amongst different cellular processes known to be influenced by redox signaling, T-cell activation is one of the most established. Numerous studies reported an indispensible role for ROS as modulators of T-cell receptor-induced transcription. Nevertheless, mechanistic details regarding signaling pathways triggered by ROS are far from being delineated. The nature and interplay between enzymatic sources involved in the generation of "oxidative signals" are also a matter of ongoing research. In particular, active participation of the mitochondrial respiratory chain as ROS producer constitutes an intriguing issue with various implications for bioenergetics of activated T cells as well as for T-cell-mediated pathologies. The aim of the current review is to address these interesting concepts.

Curbing cancer's sweet tooth: is there a role for MnSOD in regulation of the Warburg effect?

Reactive oxygen species (ROS), while vital for normal cellular function, can have harmful effects on cells, leading to the development of diseases such as cancer. The Warburg effect, the shift from oxidative phosphorylation to glycolysis, even in the presence of adequate oxygen, is an important metabolic change that confers many growth and survival advantages to cancer cells. Reactive oxygen species are important regulators of the Warburg effect. The mitochondria-localized antioxidant enzyme manganese superoxide dismutase (MnSOD) is vital to survival in our oxygen-rich atmosphere because it scavenges mitochondrial ROS. MnSOD is important in cancer development and progression. However, the significance of MnSOD in the regulation of the Warburg effect is just now being revealed, and it may significantly impact the treatment of cancer in the future.

Comparative proteomic analysis suggests that mitochondria are involved in autosomal recessive polycystic kidney disease

Autosomal recessive polycystic kidney disease (ARPKD), characterized by ectatic collecting duct, is an infantile form of PKD occurring in 1 in 20 000 births. Despite having been studied for many years, little is known about the underlying mechanisms. In the current study, we employed, for the first time, a MS-based comparative proteomics approach to investigate the differently expressed proteins between kidney tissue samples of four ARPKD and five control individuals. Thirty two differently expressed proteins were identified and six of the identified protein encoding genes performed on an independent group (three ARPKD subjects, four control subjects) were verified by semi-quantitative RT-PCR, and part of them were further validated by Western blot and immunohistochemistry. Moreover, similar alteration tendency was detected after downregulation of PKHD1 by small interfering RNA in HEK293T cell. Interestingly, most of the identified proteins are associated with mitochondria. This implies that mitochondria may be implicated in ARPKD. Furthermore, the String software was utilized to investigate the biological association network, which is based on known and predicted protein interactions. In conclusion, our findings depicted a global understanding of ARPKD progression and provided a promising resource of targeting protein, and shed some light further investigation of ARPKD.

Exploring the electrostatic repulsion model in the role of Sirt3 in directing MnSOD acetylation status and enzymatic activity

Mitochondrial oxidative metabolism is the major site of ATP production as well as a significant source of reactive oxygen species (ROS) that can cause damage to critical biomolecules. It is well known that mitochondrial enzymes that scavenge ROS are targeted by stress responsive proteins to maintain the fidelity of mitochondrial function. Manganese superoxide dismutase (MnSOD) is a primary mitochondrial ROS scavenging enzyme, and in 1983 Irwin Fridovich proposed an elegant chemical mechanism/model whereby acetylation directs MnSOD enzymatic activity. He christened it the "electrostatic repulsion model." However, the biochemical and genetic mechanism(s) determining how acetylation directs activity and the reasons behind the evolutionarily conserved need for several layers of transcriptional and posttranslational MnSOD regulation remain unknown. In this regard, we and others have shown that MnSOD is regulated, at least in part, by the deacetylation of specific conserved lysines in a reaction catalyzed by the mitochondrial sirtuin, Sirt3. We speculate that the regulation of MnSOD activity by lysine acetylation via an electrostatic repulsion mechanism is a conserved and critical aspect of MnSOD regulation necessary to maintain mitochondrial homeostasis.

Manganese superoxide dismutase regulates a metabolic switch during the mammalian cell cycle

Proliferating cells consume more glucose to cope with the bioenergetics and biosynthetic demands of rapidly dividing cells as well as to counter a shift in cellular redox environment. This study investigates the hypothesis that manganese superoxide dismutase (MnSOD) regulates cellular redox flux and glucose consumption during the cell cycle. A direct correlation was observed between glucose consumption and percentage of S-phase cells in MnSOD wild-type fibroblasts, which was absent in MnSOD homozygous knockout fibroblasts. Results from electron paramagnetic resonance spectroscopy and flow cytometric assays showed a significant increase in cellular superoxide levels in S-phase cells, which was associated with an increase in glucose and oxygen consumption, and a decrease in MnSOD activity. Mass spectrometry results showed a complex pattern of MnSOD-methylation at both lysine (68, 89, 122, and 202) and arginine (197 and 216) residues. MnSOD protein carrying a K89A mutation had significantly lower activity compared with wild-type MnSOD. Computational-based simulations indicate that lysine and arginine methylation of MnSOD during quiescence would allow greater accessibility to the enzyme active site as well as increase the positive electrostatic potential around and within the active site. Methylation-dependent changes in the MnSOD conformation and subsequent changes in the electrostatic potential around the active site during quiescence versus proliferation could increase the accessibility of superoxide, a negatively charged substrate. These results support the hypothesis that MnSOD regulates a "metabolic switch" during progression from quiescent through the proliferative cycle. We propose MnSOD as a new molecular player contributing to the Warburg effect.

Redox modulation of the DNA damage response

Lesions to DNA trigger the DNA-damage response (DDR), a complex, multi-branched cell-intrinsic process targeted to DNA repair, or elimination of the damaged cells by apoptosis. DDR aims at reducing permanence of mutated cells, decreasing the risk of tumor development: the more stringent the response, the lower the likelihood that sub-lethally damaged, unrepaired cells survive and proliferate. Accordingly, leakage often occurs in tumor cells with compromised DDR, accumulating mutations and accelerating tumor progression. Oxidations mediate DNA damage upon different insults such as UV, X and γ radiation, pollutants, poisons, or endogenous disequilibria, producing different types of lesions that trigger DDR, which can be alleviated by antioxidants. But reactive oxygen species (ROS), and the enzymes involved in their production or scavenging, also participate in DDR signaling, modulating the activity of key enzymes, and regulating the stringency of DDR. Accordingly, antioxidant enzymes such as superoxide dismutase play intimate and complex roles in tumor development, exceeding the basal roles of preventing the initial DNA damage. Likewise, it is emerging that dietary antioxidants help controlling tumor onset and progression by preventing DNA damage and by acting on cell cycle checkpoints, opening a novel and promising frontier to anticancer therapy.

Upsides and downsides of reactive oxygen species for cancer: the roles of reactive oxygen species in tumorigenesis, prevention, and therapy

SIGNIFICANCE

Extensive research during the last quarter century has revealed that reactive oxygen species (ROS) produced in the body, primarily by the mitochondria, play a major role in various cell-signaling pathways. Most risk factors associated with chronic diseases (e.g., cancer), such as stress, tobacco, environmental pollutants, radiation, viral infection, diet, and bacterial infection, interact with cells through the generation of ROS.

RECENT ADVANCES

ROS, in turn, activate various transcription factors (e.g., nuclear factor kappa-light-chain-enhancer of activated B cells [NF-κB], activator protein-1, hypoxia-inducible factor-1α, and signal transducer and activator of transcription 3), resulting in the expression of proteins that control inflammation, cellular transformation, tumor cell survival, tumor cell proliferation and invasion, angiogenesis, and metastasis. Paradoxically, ROS also control the expression of various tumor suppressor genes (p53, Rb, and PTEN). Similarly, γ-radiation and various chemotherapeutic agents used to treat cancer mediate their effects through the production of ROS. Interestingly, ROS have also been implicated in the chemopreventive and anti-tumor action of nutraceuticals derived from fruits, vegetables, spices, and other natural products used in traditional medicine.

CRITICAL ISSUES

These statements suggest both "upside" (cancer-suppressing) and "downside" (cancer-promoting) actions of the ROS. Thus, similar to tumor necrosis factor-α, inflammation, and NF-κB, ROS act as a double-edged sword. This paradox provides a great challenge for researchers whose aim is to exploit ROS stress for the development of cancer therapies.

FUTURE DIRECTIONS

the various mechanisms by which ROS mediate paradoxical effects are discussed in this article. The outstanding questions and future directions raised by our current understanding are discussed.

Oxidative stress adaptation in aggressive prostate cancer may be counteracted by the reduction of glutathione reductase

Oxidative stress has been associated with prostate cancer development and progression due to an increase of reactive oxygen species (ROS). However, the mechanisms whereby ROS and the antioxidant system participate in cancer progression remain unclear.

In order to clarify the influence of oxidative stress in prostate cancer progression, we performed this study in two human prostate cancer cell lines, PC3 and HPV10 (from metastasis and from localized cancer, respectively) and RWPE1 cells derived from normal prostate epithelium. Cells were treated with hydrogen peroxide (H₂O₂) and PC3 cells were also treated with diethyl maleate (DEM). The effect on cell growth, viability, mitochondria membrane potential and oxidative stress was analysed. Oxidative stress was evaluated based on ROS production, oxidative lesion of lipids (MDA) and on determination of antioxidants, including enzyme activity of glutathione peroxidase (Gl-Px), glutathione reductase (Gl-Red) and on the quantification of glutathione (GSH), glutathione-s-transferase (GST) and total antioxidant status (TAS).

PC3 shows higher ROS production but also the highest GSH levels and Gl-Red activity, possibly contributing to oxidative stress resistance. This is also associated with higher mitochondrial membrane potential, TAS and lower lipid peroxidation. On the other hand, we identified Gl-Red activity reduction as a new strategy in overcoming oxidative stress resistance, by inducing H₂O₂ cytotoxicity. Therefore these results suggest Gl-Red activity reduction as a new potential therapeutic approach, in prostate cancer.

Radical decisions in cancer: redox control of cell growth and death

Free radicals play a key role in many physiological decisions in cells. Since free radicals are toxic to cellular components, it is known that they cause DNA damage, contribute to DNA instability and mutation and thus favor carcinogenesis. However, nowadays it is assumed that free radicals play a further complex role in cancer. Low levels of free radicals and steady state levels of antioxidant enzymes are responsible for the fine tuning of redox status inside cells. A change in redox state is a way to modify the physiological status of the cell, in fact, a more reduced status is found in resting cells while a more oxidative status is associated with proliferative cells. The mechanisms by which redox status can change the proliferative activity of cancer cells are related to transcriptional and posttranscriptional modifications of proteins that play a critical role in cell cycle control. Since cancer cells show higher levels of free radicals compared with their normal counterparts, it is believed that the anti-oxidative stress mechanism is also increased in cancer cells. In fact, the levels of some of the most important antioxidant enzymes are elevated in advanced status of some types of tumors. Anti-cancer treatment is compromised by survival mechanisms in cancer cells and collateral damage in normal non-pathological tissues. Though some resistance mechanisms have been described, they do not yet explain why treatment of cancer fails in several tumors. Given that some antitumoral treatments are based on the generation of free radicals, we will discuss in this review the possible role of antioxidant enzymes in the survival mechanism in cancer cells and then, its participation in the failure of cancer treatments.

Mathematical and computational models of oxidative and nitrosative stress

The importance of nitric oxide (NO), superoxide (O2-), and peroxynitrite (ONOO-), interactions in physiologic functions and pathophysiological conditions such as cardiovascular disease, hypertension, and diabetes have been established extensively in in vivo and in vitro studies. Despite intense investigation of NO, O2-, and ONOO- biochemical interactions, fundamental questions regarding the role of these molecules remain unanswered. Mathematical models based on fundamental principles of mass balance and reaction kinetics have provided significant results in the case of NO. However, the models that include interaction of NO, O2-, and ONOO- have been few because of the complexity of these interactions. Not only do these mathematical and computational models provided quantitative knowledge of distributions and concentrations of NO, O2-, and ONOO- under normal physiologic and pathophysiologic conditions, they also can help to answer specific hypotheses. The focus of this review article is on the models that involve more than one of the 3 molecules (NO, O2-, and ONOO-). Specifically, kinetic models of O2- dismutase and tyrosine nitration and biotransport models in the microcirculation are reviewed. In addition, integrated experimental and computational models of dynamics of NO/O2-/ONOO- in diverse systems are reviewed.

Manganese superoxide dismutase: a regulator of T cell activation-induced oxidative signaling and cell death

Mitochondrial reactive oxygen species (ROS) are indispensible for T cell activation-induced expression of interleukin 2 (IL-2) and CD95 ligand (CD95L, FasL/Apo-1L) genes, and in turn, for CD95L-mediated activation-induced cell death (AICD). Here, we show that manganese superoxide dismutase (MnSOD/SOD2), a major mitochondrial antioxidative enzyme, constitutes an important control switch in the process of activation-induced oxidative signal generation in T cells. Analysis of the kinetics of T cell receptor (TCR)-triggered ROS production revealed a temporal association between higher MnSOD abundance/activity and a shut-down phase of oxidative signal generation. Transient or inducible MnSOD overexpression abrogated T cell activation-triggered mitochondrial ROS production as well as NF-κB- and AP-1-mediated transcription. Consequently, lowered expression of IL-2 and CD95L genes resulted in decreased IL-2 secretion and CD95L-dependent AICD. Moreover, upregulation of the mitochondrial MnSOD level is dependent on oxidation-sensitive transcription and not on the increase of mitochondrial mass. Thus, MnSOD-mediated negative feedback regulation of activation-induced mitochondrial ROS generation exemplifies a process of retrograde mitochondria-to-nucleus communication. Our finding underlines the critical role for MnSOD and mitochondria in the regulation of human T cell activation.

Antioxidants for prostate cancer chemoprevention: challenges and opportunities

Extensive research has led to the firm conclusion that antioxidants protect cells from damage caused by oxidative stress and its associated pathological conditions including inflammation. It has also been established that inflammation is a precursor in neoplastic transformation of the prostate. Although, a vast body of experimental and clinical evidence shows efficacy of antioxidants as preventive strategies for prostate cancer, there is a lack of consistent agreement in outcomes especially from recent large-scale randomized clinical trials. Despite these concerns, our understanding of the preventive mechanisms as well as clinical efficacy and safety data indicate that novel antioxidant therapeutics still hold great promise for prostate cancer chemoprevention. We propose that for effective use of antioxidants for prostate cancer prevention, further high impact translational research is needed with special attention on selecting those patients who will benefit from such intervention. Therefore, it is important to validate predictive biomarkers from successful trials and combine this with knowledge of preclinical characterization of antioxidants (and combinations) that will eventually facilitate the development of 'personalized prostate cancer chemoprevention'. In this review, we briefly describe some common and emerging antioxidants that have shown benefits in preclinical and clinical settings. Above all, we focus on summarizing the progress we made thus far in prostate cancer chemoprevention using antioxidants, the heightened interest and challenges in the future.

Clair DK. Manganese superoxide dismutase: beyond life and death

Manganese superoxide dismutase (MnSOD) is a nuclear-encoded antioxidant enzyme that localizes to the mitochondria. Expression of MnSOD is essential for the survival of aerobic life. Transgenic mice expressing a luciferase reporter gene under the control of the human MnSOD promoter demonstrate that the level of MnSOD is reduced prior to the formation of cancer. Overexpression of MnSOD in transgenic mice reduces the incidences and multiplicity of papillomas in a DMBA/TPA skin carcinogenesis model. However, MnSOD deficiency does not lead to enhanced tumorigenicity of skin tissue similarly treated because MnSOD can modulate both the p53-mediated apoptosis and AP-1-mediated cell proliferation pathways. Apoptosis is associated with an increase in mitochondrial levels of p53 suggesting a link between MnSOD deficiency and mitochondrial-mediated apoptosis. Activation of p53 is preventable by application of a SOD mimetic (MnTE-2-PyP(5+)). Thus, p53 translocation to mitochondria and subsequent inactivation of MnSOD explain the observed mitochondrial dysfunction that leads to transcription-dependent mechanisms of p53-induced apoptosis. Administration of MnTE-2-PyP(5+) following apoptosis but prior to proliferation leads to suppression of protein carbonyls and reduces the activity of AP-1 and the level of the proliferating cellular nuclear antigen, without reducing the activity of p53 or DNA fragmentation following TPA treatment. Remarkably, the incidence and multiplicity of skin tumors are drastically reduced in mice that receive MnTE-2-PyP(5+) prior to cell proliferation. The results demonstrate the role of MnSOD beyond its essential role for survival and suggest a novel strategy for an antioxidant approach to cancer intervention.

SOD mimetics: a novel class of androgen receptor inhibitors that suppresses castration-resistant growth of prostate cancer

Advanced prostate cancer is the second leading cause of cancer-related deaths among American men. The androgen receptor (AR) is vital for prostate cancer progression, even in the face of castrate levels of serum testosterone following androgen ablation therapy, a mainstay therapy for advanced prostate cancer. Downregulation of superoxide dismutase 2 (SOD2), a major intracellular antioxidant enzyme, occurs progressively during prostate cancer progression to advanced states and is known to promote AR activity in prostate cancer. Therefore, this study investigated the effects of SOD mimetics on AR expression and function in AR-dependent LNCaP, CWR22Rv1, and LAPC-4AD prostate cancer cells. Treatment with Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), a SOD mimetic, not only lowered cellular superoxide levels but also concomitantly attenuated AR transcriptional activity and AR target gene expression in a dose- and time-dependent manner, in the presence and absence of dihydrotestosterone, the major endogenous AR agonist. Inhibition of AR by Tempol was mediated, in large part, by its ability to decrease AR protein via increased degradation, in the absence of any inhibitory effects on other nuclear receptors. Inhibitory effects of Tempol on AR were also reproducible with other SOD mimetics, MnTBAP and MnTMPyP. Importantly, effects of Tempol on AR function were accompanied by significant in vitro and in vivo reduction in castration-resistant prostate cancer (CRPC) survival and growth. Collectively, this study has shown for the first time that SOD mimetics, by virtue of their ability to suppress AR function, may be beneficial in treating the currently incurable CRPC, in which SOD2 expression is highly suppressed.

Hydrogen peroxide signaling mediates DHEA-induced vascular endothelial cell proliferation

Dehydroepiandrosterone (DHEA) activates a putative plasma membrane G(i)-protein coupled receptor to induce vascular endothelial proliferation. We now test the hypothesis that hydrogen peroxide (H(2)O(2)) signaling mediates this effect. Incubation of EA.hy926 cells, a human vascular endothelial cell line, with DHEA for 5 min produced a significant increase in H(2)O(2) production, measured by oxidation of either p-hydroxyphenylacetate or dichlorodihydrofluorescein. The DHEA effect on H(2)O(2) production was maximal at 1 nM DHEA, was evident within the first minute of incubation, and remained for 10 min. Similar results were present in primary bovine aortic endothelial cells. The induction of H(2)O(2) in EA.hy926 cells was mimicked by a membrane-impermeable albumin-conjugated DHEA and was inhibited by either catalase or pertussis toxin. Incubation of endothelial cells with DHEA for 5 min resulted in a 2-fold increase of cyclin D1 mRNA and protein expression at 4h. These effects were abolished by co-incubation with catalase. DHEA induced a 50 ± 7% increase in cell proliferation over 24h, measured as cellular Ki-67 immunoreactivity. This proliferative effect was abolished by either catalase or pertussis toxin co-incubation, indicating an H(2)O(2) and G(i)-protein-dependent effect. We conclude that H(2)O(2) is a key signaling molecule mediating the proliferative effects of DHEA in vascular endothelial cells, possibly by up-regulating cell-cycle associated genes, such as cyclin D1.

Clair DK. Manganese superoxide dismutase: guardian of the powerhouse

The mitochondrion is vital for many metabolic pathways in the cell, contributing all or important constituent enzymes for diverse functions such as β-oxidation of fatty acids, the urea cycle, the citric acid cycle, and ATP synthesis. The mitochondrion is also a major site of reactive oxygen species (ROS) production in the cell. Aberrant production of mitochondrial ROS can have dramatic effects on cellular function, in part, due to oxidative modification of key metabolic proteins localized in the mitochondrion. The cell is equipped with myriad antioxidant enzyme systems to combat deleterious ROS production in mitochondria, with the mitochondrial antioxidant enzyme manganese superoxide dismutase (MnSOD) acting as the chief ROS scavenging enzyme in the cell. Factors that affect the expression and/or the activity of MnSOD, resulting in diminished antioxidant capacity of the cell, can have extraordinary consequences on the overall health of the cell by altering mitochondrial metabolic function, leading to the development and progression of numerous diseases. A better understanding of the mechanisms by which MnSOD protects cells from the harmful effects of overproduction of ROS, in particular, the effects of ROS on mitochondrial metabolic enzymes, may contribute to the development of novel treatments for various diseases in which ROS are an important component.

Novel cancer suppressor gene for esophageal cancer: manganese superoxide dismutase

OBJECTIVES

To explore the expression of manganese superoxide dismutase (MnSOD) in esophageal squamous cell carcinoma (ESCC) and its relationship with clinicopathological characteristics and biological behavior.

METHODS

On 45 patients with ESCC, immunohistochemistry (SP method), reverse transcription-polymerase chain reaction (RT-PCR), and Western blot were used to detect MnSOD protein and mRNA expression in ESCC and in its adjacent normal tissue 5 cm apart from the edge of cancer lesion and without documented microscopic invasive cancer. Meanwhile, the relationship between the pathological features of esophageal cancer and its biological behavior was analyzed.

RESULTS

In ESCC and normal esophageal tissue, MnSOD protein expression was identified 31.1% (14/45) and 86.7% (31/45) (P= 0.000), respectively, with the relative expression levels of MnSOD mRNA 0.310 ± 0.036 and 0.482 ± 0.053 (P= 0.000), relatively. Western blot study showed that the relative expressions of MnSOD protein in cancer lesion and in adjacent normal tissue were 0.384 ± 0.038 and 0.766 ± 0.041, respectively (P= 0.000). With longer lesion, deeper invasion, and poorer differentiation, the expression of MnSOD would get lower, indicating that the levels of MnSOD protein and mRNA expression were closely related to the length of lesion, depth of invasion, and degree of differentiation in ESCC (P < 0.05). Nevertheless, the result showed no association with the presence of lymph node metastasis, cancer location, and macroscopic classification (P > 0.05).

CONCLUSIONS

MnSOD protein and mRNA expression both decreased in ESCC, which may be related to carcinogenesis and the development of esophageal cancer. Therefore, detecting the expression of MnSOD in esophageal carcinoma would be of clinical significance in understanding its biological behavior and in guiding therapeutic strategy of esophageal cancer.

Antiproliferative effect of estrogen in vascular smooth muscle cells is mediated by Kruppel-like factor-4 and manganese superoxide dismutase

The mitochondrial antioxidant enzyme manganese superoxide dismutase (MnSOD) and the zinc finger transcription factor Kruppel-like factor-4 (KLF4) are involved in the regulation of redox homeostasis, apoptosis and cell proliferation. We have shown that estrogen exerts antioxidative actions via induction of MnSOD in cultured rat aortic vascular smooth muscle cells (VSMC). The purpose of the present study was to investigate whether estrogen inhibits VSMC proliferation via alteration of KLF4 and MnSOD expression. In cultured rat aortic VSMC, estrogen binding to estrogen receptor-alpha led to rapid increase in KLF4 expression and reduction of cell proliferation by 50%. Protein separation revealed that KLF4 was shifted to the nucleus when VSMC were treated with estrogen. Estrogen-mediated induction of KLF4 and the antiproliferative effect involved activation of PI-3 kinase, Akt phosphorylation and induction of NO synthase activity. Experiments in freshly isolated denuded aortic segments revealed an increase in KLF4 abundance after estrogen treatment and demonstrated that eNOS is expressed in the media at low levels. Transfection experiments showed that estrogen-induced overexpression of MnSOD required KLF4 and that both KLF4 and MnSOD were indispensable for the observed antiproliferative effect of estrogen in VSMC. To confirm these data in vivo, we investigated neointima formation after carotid artery injury in wild-type (WT) and MnSOD+/- mice. Estrogen deficiency led to enhanced neointima formation and higher numbers of Ki67-positive proliferating cells in the neointima of ovariectomized WT and MnSOD+/- mice. Moreover, MnSOD+/- mice showed more extensive neointima formation and Ki67 immunostaining. Interestingly, estrogen replacement prevented neointima formation in WT mice but failed to completely inhibit neointima formation in MnSOD+/- mice. Cultured VSMC derived from MnSOD+/- mice showed enhanced proliferation as compared to WT VSMC, and estrogen treatment failed to inhibit proliferation in MnSOD+/- VSMC. In conclusion, these data demonstrate the importance of MnSOD and KLF4 for proliferation control in VSMC. Our results provide novel insights into how proliferation of VSMC is regulated by estrogen and may help to identify novel targets for the treatment of vascular diseases such as restenosis.

Caveolin-1 and mitochondrial SOD2 (MnSOD) function as tumor suppressors in the stromal microenvironment: a new genetically tractable model for human cancer associated fibroblasts

We have recently proposed a new model for understanding tumor metabolism, termed: "The Autophagic Tumor Stroma Model of Cancer Metabolism". In this new paradigm, catabolism (autophagy) in the tumor stroma fuels the anabolic growth of aggressive cancer cells. Mechanistically, tumor cells induce autophagy in adjacent cancer-associated fibroblasts via the loss of caveolin-1 (Cav-1), which is sufficient to promote oxidative stress in stromal fibroblasts. To further test this hypothesis, here we created human Cav-1 deficient immortalized fibroblasts using a targeted sh-RNA knock-down approach. Relative to control fibroblasts, Cav-1 deficient fibroblasts dramatically promoted tumor growth in xenograft assays employing an aggressive human breast cancer cell line, namely MDA-MB-231 cells. Co-injection of Cav-1 deficient fibroblasts, with MDA-MB-231 cells, increased both tumor mass and tumor volume by ~4-fold. Immuno-staining with CD31 indicated that this paracrine tumor promoting effect was clearly independent of angiogenesis. Mechanistically, proteomic analysis of these human Cav-1 deficient fibroblasts identified > 40 protein biomarkers that were upregulated, most of which were associated with i) myofibroblast differentiation, or ii) oxidative stress/hypoxia. In direct support of these findings, the tumor promoting effects of Cav-1 deficient fibroblasts could be functionally suppressed (nearly 2-fold) by the recombinant over-expression of SOD2 (superoxide dismutase 2), a known mitochondrial enzyme that de-activates superoxide, thereby reducing mitochondrial oxidative stress. In contrast, cytoplasmic soluble SOD1 had no effect, further highlighting a specific role for mitochondrial oxidative stress in this process. In summary, here we provide new evidence directly supporting a key role for a loss of stromal Cav-1 expression and oxidative stress in cancer-associated fibroblasts, in promoting tumor growth, which is consistent with "The Autophagic Tumor Stroma Model of Cancer". The human Cav-1 deficient fibroblasts that we have generated are a new genetically tractable model system for identifying other suppressors of the cancer-associated fibroblast phenotype, via a genetic "complementation" approach. This has important implications for understanding the pathogenesis of triple negative and basal breasts cancers, as well as tamoxifen-resistance in ER+ breast cancers, which are all associated with a Cav-1 deficient "lethal" tumor micro-environment, driving poor clinical outcome.

Teriflunomide (leflunomide) promotes cytostatic, antioxidant, and apoptotic effects in transformed prostate epithelial cells: evidence supporting a role for teriflunomide in prostate cancer chemoprevention

Teriflunomide (TFN) is an inhibitor of de novo pyrimidine synthesis and the active metabolite of leflunomide. Leflunomide is prescribed to patients worldwide as an immunomodulatory and anti-inflammatory disease-modifying prodrug. Leflunomide inhibited the growth of human prostate cancer xenographs in mice, and leflunomide or TFN promoted cytostasis and/or apoptosis in cultured cells. These findings suggest that TFN could be useful in prostate cancer chemoprevention. We investigated the possible mechanistic aspects of this tenet by characterizing the effects of TFN using premalignant PWR-1E and malignant DU-145 human prostate epithelial cells. TFN promoted a dose- and time-dependent cytostasis or apoptosis induction in these cells. The cytostatic effects of TFN, which were reversible but not by the presence of excess uridine in the culture medium, included diminished cellular uridine levels, an inhibition in oxygen consumption, a suppression of reactive oxygen species (ROS) generation, S-phase cell cycle arrest, and a conspicuous reduction in the size and number of the nucleoli in the nuclei of these cells. Conversely, TFN's apoptogenic effects were characteristic of catastrophic mitochondrial disruption (i.e., a dissipation of mitochondrial inner transmembrane potential, enhanced ROS production, mitochondrial cytochrome c release, and cytoplasmic vacuolization) and followed by DNA fragmentation. The respiration-deficient derivatives of the DU-145 cells, which are also uridine auxotrophs, were markedly resistant to the cytostatic and apoptotic effects of TFN, implicating de novo pyrimidine synthesis and mitochondrial bioenergetics as the primary targets for TFN in the respiration competent cells. These mechanistic findings advocate a role for TFN and mitochondrial bioenergetics in prostate cancer chemoprevention.

Manganese superoxide dismutase vs. p53: regulation of mitochondrial ROS

Coordination of mitochondrial and nuclear activities is vital for cellular homeostasis, and many signaling molecules and transcription factors are regulated by mitochondria-derived reactive oxygen species (ROS) to carry out this interorganellar communication. The tumor suppressor p53 regulates myriad cellular functions through transcription-dependent and -independent mechanisms at both the nucleus and mitochondria. p53 affect mitochondrial ROS production, in part, by regulating the expression of the mitochondrial antioxidant enzyme manganese superoxide dismutase (MnSOD). Recent evidence suggests mitochondrial regulation of p53 activity through mechanisms that affect ROS production, and a breakdown of communication amongst mitochondria, p53, and the nucleus can have broad implications in disease development.

Enhanced expression of mitochondrial superoxide dismutase leads to prolonged in vivo cell cycle progression and up-regulation of mitochondrial thioredoxin

Mn superoxide dismutase (MnSOD) is an important mitochondrial antioxidant enzyme, and elevated MnSOD levels have been shown to reduce tumor growth in part by suppressing cell proliferation. Studies with fibroblasts have shown that increased MnSOD expression prolongs cell cycle transition time in G1/S and favors entrance into the quiescent state. To determine if the same effect occurs during tissue regeneration in vivo, we used a transgenic mouse system with liver-specific MnSOD expression and a partial hepatectomy paradigm to induce synchronized in vivo cell proliferation during liver regeneration. We show in this experimental system that a 2.6-fold increase in MnSOD activity leads to delayed entry into S phase, as measured by reduction in bromodeoxyuridine (BrdU) incorporation and decreased expression of proliferative cell nuclear antigen (PCNA). Thus, compared to control mice with baseline MnSOD levels, transgenic mice with increased MnSOD expression in the liver have 23% fewer BrdU-positive cells and a marked attenuation of PCNA expression. The increase in MnSOD activity also leads to an increase in the mitochondrial form of thioredoxin (thioredoxin 2), but not in several other peroxidases examined, suggesting the importance of thioredoxin 2 in maintaining redox balance in mitochondria with elevated levels of MnSOD.

Protective signalling effect of manganese superoxide dismutase in hypoxia-reoxygenation of hepatocytes

This study investigates the mechanism by which MnSOD exerts its protective effect in hypoxia-reoxygenation (H/R) injury in hepatocytes. Following induction of H/R, MnSOD expression and activity levels increased and remained high for over 24 h. Hepatocytes silenced for MnSOD (siMnSOD) demonstrated increased susceptibility to H/R-induced apoptotic cell death and a lower capacity to generate mitochondrial reactive oxygen species. Microarray and real time PCR analysis of gene expression from siMnSOD cells revealed a number of down-regulated protective genes, including hemeoxygenase-1, glutamate-cysteine ligase and Nrf2, a master regulator of cellular adaptation to stress. Decreased Nrf2 protein expression and nuclear translocation were also confirmed in siMnSOD cells. siMnSOD cells showed low glutathione (GSH) content with no oxidation to GSSG, lower lipid peroxidation levels than their controls and lower mitochondrial membrane potential, which all were even more salient after H/R. Therefore, MnSOD appears to act as a signalling mediator for the activation of survival genes following H/R injury in hepatocytes.

Tumor-stroma co-evolution in prostate cancer progression and metastasis

Cancer development is complex and involves several layers of interactions and pleotropic signaling mechanisms leading to progression. Cancer cells associate with resident stromal fibroblasts, smooth muscle cells, macrophages, endothelium, neurons and migrating cells at metastatic sites and phenotypically and genotypically activate them. These become an integral part of the cancer cell community through activated cell signaling mechanisms. During this process, the cancer cells and cells in the cancer microenvironment "co-evolve" in part due to oxidative stress, and acquire the ability to mimic other cell types (which can be termed osteomimicry, vasculomimicry, neuromimicry and stem cell mimicry), and undergo transition from epithelium to mesenchyme with definitive morphologic and behavioral modifications. In our laboratory, we demonstrated that prostate cancer cells co-evolve in their genotypic and phenotypic characters with stroma and acquire osteomimetic properties allowing them to proliferate and survive in the skeleton as bone metastasis. Several signaling interactions in the bone microenvironment, mediated by reactive oxygen species, soluble and membrane bound factors, such as superoxide, beta2-microglobulin and RANKL have been described. Targeting the signaling pathways in the cancer-associated stromal microenvironment in combination with known conventional therapeutic modalities could have a synergistic effect on cancer treatment. Since cancer cells are constantly interacting and acquiring adaptive and survival changes primarily directed by their microenvironment, it is imperative to delineate these interactions and co-target both cancer and stroma to improve the treatment and overall survival of cancer patients.

Clinical utility of antioxidant gene expression levels in circulating cancer cell clusters for the detection of prostate cancer in patients with prostate-specific antigen levels of 4-10 ng/mL and disease prognostication after radical prostatectomy

OBJECTIVES

To test antioxidant genes (AOX) expression in circulating cancer cell clusters (CCC). A novel method using molecular, polymerase chain reaction (PCR)-based detection of CCC was applied for predicting prostate cancer and to assess the effect of radical prostatectomy (RP) on reducing CCC and for prognostication of relapse-free survival (RFS), as serum total prostate-specific antigen (tPSA) has limited specificity at 4-10 ng/mL.

PATIENTS AND METHODS

In all, 240 patients were enrolled in the study, 129 for tumour diagnosis and 111 after RP for disease prognostication. Filtration assay in previously fractionated mononuclear cells (MNC) was used to enrich the CCC and large cells, which were retained in a mesh of 20 microm width. To establish the malignant nature of these cells they were analysed for genomic imbalances detected via PCR-assays of loss of heterozygosity in tumour suppressor loci and of DNA amplification in protooncogen loci. As a screening test in daily practice, real-time reverse transcription (RT)-PCR of AOX was introduced to overcome the laborious and expensive DNA tests. The AOX chosen were glutathione peroxidase (GPX1), Mn-dependent superoxide dismutase 2 (SOD2) and thioredoxine reductase (TXNRD1); selected from 67 marker candidate genes according to sensitivity and specificity data. AOX overexpression in CCC serves as a general marker for solid tumours needing, however, organ markers to relate to the organ of origin. Androgen receptor (AR), PSA and prostate-specific membrane antigen mRNAs served as organ markers for the prostate. Signals were detected in patients' MNC and to a minor level in CCC, rendering to CCC a substantial loss in epithelial features equivalent to a lower grade of epithelial differentiation. Organ markers in the MNC fraction were positive in <85% of AOX testing.

RESULTS

The AOX test was tumour predicting (P < 0.001) with a sensitivity of 86%, specificity 82%, positive predictive value 69%, negative predictive value 92%, accuracy 83% and odds ratio (OR) of 28. SOD2 and TXNRD1 expression correlated to tumour size and Gleason score. Objective assessment for the evaluation of the molecular cell markers was achieved by receiver operating characteristic (ROC) curves. The areas under the ROC curve values of the AOXs were 0.7-0.9. RP was followed by a complete clearance of AOX-expressing cells. After RP, a subgroup of patients had residual CCC over-expressing only SOD2 and GPX1 indicating incomplete clearance by RP. Sustained overexpression of SOD2 and GPX1 accounted as risk factors for distant tumour recurrence (P = 0.003) mainly for bone metastases (97% M1b) as evaluated by Kaplan-Meier curves. In univariate analysis the tumour size had a limited effect on the probability of RFS (P = 0.05). In multivariate analysis tumour size, nodal status and Gleason score had no effect. This can partially be attributed to the higher risk level of pathological variables in the AOX over-expressing group but also to ineffective endocrine therapy resulting in marked overexpression of ARs and GPX1, the lead prognosticator gene. The AOX expression level allowed the identification of patients with high progression risk, who have more favourable pathological variables.

CONCLUSION

The AOX testing of CCC is a novel method with excellent prognostic and predictive properties enabling the monitoring of therapies, e.g. effects of RP and endocrine therapy. We speculate that the continuing elevated expression of AOX with special emphasis on GPX1 acts as survival and defence mechanism in CCC required in an atypical environment prone to escape from immune surveillance.

Antiangiogenic action of redox-modulating Mn(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin, MnTE-2-PyP(5+), via suppression of oxidative stress in a mouse model of breast tumor

MnTE-2-PyP(5+) is a potent catalytic scavenger of reactive oxygen and nitrogen species, primarily superoxide and peroxynitrite. It therefore not only attenuates primary oxidative damage, but was found to modulate redox-based signaling pathways (HIF-1alpha, NF-kappaB, SP-1, and AP-1) and thus, in turn, secondary oxidative injury also. Cancer has been widely considered an oxidative stress condition. The goal of this study was to prove if and why a catalytic SOD mimic/peroxynitrite scavenger would exert anti-cancer effects, i.e., to evaluate whether the attenuation of the oxidative stress by MnTE-2-PyP(5+) could suppress tumor growth in a 4T1 mouse breast tumor model. Tumor cells were implanted into Balb/C mouse flanks. Three groups of mice (n=25) were studied: control (PBS) and 2 and 15 mg/kg/day of MnTE-2-PyP(5+) given subcutaneously twice daily starting when the tumors averaged 200 mm(3) (until they reached approximately 5-fold the initial volume). Intratumoral hypoxia (pimonidazole, carbonic anhydrase), HIF-1alpha, VEGF, proliferating capillary index (CD105), microvessel density (CD31), protein nitration, DNA oxidation (8-OHdG), NADPH oxidase (Nox-4), apoptosis (CD31), macrophage infiltration (CD68), and tumor drug levels were assessed. With 2 mg/kg/day a trend toward tumor growth delay was observed, and a significant trend was observed with 15 mg/kg/day. The 7.5-fold increase in drug dose was accompanied by a similar (6-fold) increase in tumor drug levels. Oxidative stress was largely attenuated as observed through the decreased levels of DNA damage, protein 3-nitrotyrosine, macrophage infiltration, and NADPH oxidase. Further, hypoxia was significantly decreased as were the levels of HIF-1alpha and VEGF. Consequently, suppression of angiogenesis was observed; both the microvessel density and the endothelial cell proliferation were markedly decreased. Our study indicates for the first time that MnTE-2-PyP(5+) has anti-cancer activity in its own right. The anti-cancer activity via HIF/VEGF pathways probably arises from the impact of the drug on the oxidative stress. Therefore, the catalytic scavenging of ROS/RNS by antioxidants, which in turn suppresses cellular transcriptional activity, could be an appropriate strategy for anti-cancer therapy. Enhancement of the anti-cancer effects may be achieved by optimizing the dosing regime, utilizing more bioavailable Mn porphyrins (MnP), and combining MnP treatment with irradiation, hyperthermia, and chemotherapy. Mn porphyrins may be advantageous compared to other anti-cancer drugs, owing to their radioprotection of normal tissue and the ability to afford pain management in cancer patients via prevention of chronic morphine tolerance.

Selective apoptosis induction by the cancer chemopreventive agent N-(4-hydroxyphenyl)retinamide is achieved by modulating mitochondrial bioenergetics in premalignant and malignant human prostate epithelial cells

Prostate tumorigenesis is coupled with an early metabolic switch in transformed prostate epithelial cells that effectively increases their mitochondrial bioenergetic capacity. The synthetic retinoid N-(4-hydroxyphenyl)retinamide (4HPR) inhibits prostate cancer development in vivo, and triggers reactive oxygen species (ROS)-dependent prostate cancer cell apoptosis in vitro. The possibility that 4HPR-induced ROS production is associated with mitochondrial bioenergetics and required for apoptosis induction in transformed prostate epithelial cells in vitro would advocate a prospective mechanistic basis for 4HPR-mediated prostate cancer chemoprevention in vivo. We investigated this tenet by comparing and contrasting 4HPR's effects on premalignant PWR-1E and malignant DU-145 human prostate epithelial cells. 4HPR promoted a dose- and/or time-dependent apoptosis induction in PWR-1E and DU-145 cells, which was preceded by and dependent on an increase in mitochondrial ROS production. In this regard, the PWR-1E cells were more sensitive than the DU-145 cells, and they consumed roughly twice as much oxygen as the DU-145 cells suggesting oxidative phosphorylation was higher in the premalignant cells. Interestingly, increasing the [Ca(2+)] in the culture medium of the PWR-1E cells attenuated their proliferation as well as their mitochondrial bioenergetic capacity and 4HPR's cytotoxic effects. Correspondingly, the respiration-deficient derivatives (i.e., rho(0) cells lacking mitochondrial DNA) of DU-145 cells were markedly resistant to 4HPR-induced ROS production and apoptosis. Together, these observations implied that the reduction of mitochondrial bioenergetics protected PWR-1E and DU-145 cells against the cytotoxic effects of 4HPR, and support the concept that oxidative phosphorylation is an essential determinant in 4HPR's apoptogenic signaling in transformed human prostate epithelial cells.

Altered redox status accompanies progression to metastatic human bladder cancer

The role of reactive oxygen species (ROS) in bladder cancer progression remains an unexplored field. Expression levels of enzymes regulating ROS levels are often altered in cancer. A search of publicly available microarray data reveals that expression of mitochondrial manganese superoxide dismutase (Sod2), responsible for the conversion of superoxide (O(2)(-)) to hydrogen peroxide (H(2)O(2)), is consistently increased in high-grade and advanced-stage bladder tumors. We aimed to identify the role of Sod2 expression and ROS in bladder cancer. Using an in vitro human bladder tumor model we monitored the redox state of both nonmetastatic (253J) and highly metastatic (253J B-V) bladder tumor cell lines. 253J B-V cells displayed significantly higher Sod2 protein and activity levels compared to their parental 253J cell line. The increase in Sod2 expression was accompanied by a significant decrease in catalase activity, resulting in a net increase in H(2)O(2) production in the 253J B-V cell line. Expression of the prometastatic and proangiogenic factors matrix metalloproteinase 9 (MMP-9) and vascular endothelial-derived growth factor (VEGF), respectively, was upregulated in the metastatic line. Expression of both MMP-9 and VEGF was shown to be H(2)O(2)-dependent, as removal of H(2)O(2) by overexpression of catalase attenuated their expression. Similarly, expression of catalase effectively reduced the clonogenic activity of 253J B-V cells. These findings indicate that metastatic bladder cancer cells display an altered antioxidant expression profile, resulting in a net increase in ROS production, which leads to the induction of redox-sensitive protumorigenic and prometastatic genes such as VEGF and MMP-9.

Identification of RKIP as a differentially tyrosine-phosphorylated protein in nasopharyngeal carcinoma and normal nasopharyngeal epithelial tissues by phosphoproteomic approach

AIMS

To screen for differentially tyrosine-phosphorylated proteins between nasopharyngeal carcinoma (NPC) and normal nasopharyngeal epithelial tissues (NNET) to provide a basis for elucidate the molecular mechanisms of NPC carcinogenesis.

METHODS

Two-dimensional (2-D) electrophoresis was applied to separate proteins from NPC and NNET, respectively, and 2-D Western blotting was performed to detect tyrosine-phosphorylated proteins using antiphosphotyrosine antibody. Differentially tyrosine-phosphorylated proteins were identified by electrospray ionization-quadrupole time-of-flight MS (ESI-Q-TOF MS). NetPhos software was used to predict the tyrosine-phosphorylation sites of the identified proteins, and Western blotting was used to detect the tyrosine-phosphorylated levels of RKIP in NPC and NNET.

RESULTS

Twenty-five differentially tyrosine-phosphorylated proteins in the two types of tissues were found, 13 of which were identified by ESI-Q-TOF MS. Among the 13 identified proteins, tyrosine-phosphorylated levels of 7 proteins were increased, and those of 6 proteins were decreased in NPC compared with NNET. NetPhos software prediction showed that all the 13 identified proteins contained tyrosine phosphorylation sites, and the differentially tyrosine-phosphorylated level of RKIP in NPC and NNET was confirmed.

CONCLUSION

The 13 differentially tyrosine-phosphorylated proteins may be involved in the development and progression of NPC.

Effects of manganese superoxide dismutase silencing on androgen receptor function and gene regulation: implications for castration-resistant prostate cancer

PURPOSE

Advanced prostate cancer is first treated with androgen deprivation therapy. However, tumors become resistant to and grow despite castrate levels of testosterone. Growth and proliferation of CRPC is mediated by gain-of-function changes in the AR and AR reactivation. Expression of manganese superoxide dismutase (SOD2), which regulates cellular ROS, is markedly down-regulated in CRPC when compared with hormone-responsive tumors.

EXPERIMENTAL DESIGN

Here, we knocked down SOD2 expression in AR-expressing LNCaP prostate cancer cells and determined gene expression changes, transcription factor binding, and AR transcription activity in SOD2 knockdown cells.

RESULTS

SOD2 knockdown results in an increase in ROS. Gene expression changes induced by SOD2 knockdown results in the up-regulation of genes that are also androgen responsive and 46% of genes up-regulated 2-fold by the androgen ligand R1881 are also up-regulated to the same extent with SOD2 knockdown. The induction of many of these genes with SOD2 knockdown, such as VEGFA and FKBP5, is reversible with the antioxidant N-acetylcysteine, suggesting that this mechanism is directly linked to ROS. Furthermore, an array for transcription factor DNA-binding activity shows that SOD2 knockdown induces DNA binding by several transcription factors, including AR. SOD2 knockdown-induced AR activation was confirmed by electrophoretic mobility shift assay and luciferase activity, and both were readily reversible with N-acetylcysteine.

CONCLUSIONS

These findings show that down-regulation of SOD2 induces AR activity in a ROS-dependent manner, and suggest that there may be a role for antioxidant therapy in CRPC.

Manganese superoxide dismutase (MnSOD) gene polymorphism, interactions with carotenoid levels and prostate cancer risk

BACKGROUND

The manganese superoxide dismutase (MnSOD) gene encodes an antioxidant enzyme (SOD2) that may protect cells from oxidative damage. The MnSOD allele with Val as amino acid 16 encodes a protein that has 30-40% lower activity compared with the MnSOD Ala variant, hence possibly increasing susceptibility to oxidative stress. On the other hand, some epidemiologic studies suggest that the Ala allele is associated with a higher risk of cancer, including prostate cancer.

METHODS

We conducted a nested case-control study in the Health Professionals Follow-up Study with 612 incident prostate cancer cases and 612 matched controls to investigate the role of the MnSOD gene Ala16Val polymorphism and its joint association with plasma carotenoid concentrations in relation to risk of total prostate cancer and aggressive prostate cancer (advanced stage or Gleason sum > or =7).

RESULTS

The allele frequencies in the controls were 49.8% for Ala and 50.2% for Val. No association was found between the MnSOD genotype and risk of total and aggressive prostate cancer. Furthermore, no statistically significant interaction was observed between the MnSOD genotype and any of the plasma carotenoids in relation to risk of total and aggressive prostate cancer. In analyses in which we combined data from plasma and dietary carotenoids and created a quintile score to reflect long-term carotenoid status, a 3-fold [95% confidence interval: 1.37-7.02] increased risk of aggressive prostate cancer was observed among men with the Ala/Ala genotype in the presence of low long-term lycopene status (P-value, test for interaction = 0.02) as compared with men with the Ala/Val+Val/Val genotypes with low long-term lycopene status.

CONCLUSION

In this cohort of mainly white men, the MnSOD gene Ala16Val polymorphism was not associated with total or aggressive prostate cancer risk. However, men with the MnSOD Ala/Ala genotype who had low long-term lycopene status had a higher risk of aggressive prostate cancer compared with individuals with the other genotypes. These results are consistent with findings from earlier studies that reported when antioxidant status is low, the MnSOD Ala/Ala genotype may be associated with an increased risk of aggressive prostate cancer.

Maintenance of manganese superoxide dismutase (SOD2)-mediated delayed radioprotection induced by repeated administration of the free thiol form of amifostine

Thiol-containing drugs such as WR1065, the free thiol form of amifostine, have been shown to induce a delayed radioprotective effect in both malignant and non-malignant cells. In mammalian cells exposed to a dose as low as 40 microM WR1065, the redox-sensitive nuclear transcription factor kappaB (NFkappaB) is activated, leading to an elevation in the expression of the antioxidant gene manganese superoxide dismutase (SOD2) and a concomitant increase in active SOD2 enzyme levels that peaks 24 to 32 h later. Exposure of cells to ionizing radiation during the period of elevated SOD2 enzymatic activity results in an enhanced radiation resistance. This is seen as an increase in surviving fraction as determined by standard colony formation assays. To determine whether this delayed radioprotection can be maintained over a prolonged period in cells of either malignant or non-malignant origin, both human microvascular endothelial cells (HMEC) and SA-NH mouse sarcoma cells were grown to confluence and exposed to 40 muM WR1065 using three administration protocols: (1) daily drug exposure for 10 days followed each day by irradiation with 2 Gy; (2) drug exposure once every 48 h followed by irradiation with 2 Gy 48 h later for 14 days; and (3) drug exposure every 72 h followed by irradiation with 2 Gy 72 h later for 12 days. As a function of each experimental condition, cell numbers and associated SOD2 enzymatic activities were measured at the time of each irradiation. None of the treatment conditions were toxic to either HMEC or SA-NH cells. SOD2 activity was elevated 5.3- and 1.8-fold over background on average for HMEC exposed to 40 microM WR1065 every 24 or 48 h, respectively. Likewise, SOD2 activity was elevated in SA-NH mouse sarcoma cells 7.8- and 4.9-fold after daily exposure to WR1065 or exposure to WR1065 once every 48 h, respectively. Both HMEC and SA-NH cells exhibited enhanced radiation resistance that correlated with the increase in SOD2 activity. The average respective increases in cell survival were 1.33 +/- 0.01 (SEM), 1.23 +/- 0.01 and 1.04 +/- 0.01 for HMEC exposed to WR1065 every 24, 48 and 72 h, respectively, and 1.27 +/- 0.01, 1.18 +/- 0.02 and 1.02 +/- 0.02 for SA-NH cells exposed to WR1065 every 24, 48 and 72 h, respectively. Both the elevation in WR1065-induced SOD2 enzymatic activity and the corresponding increase in radiation resistance were completely inhibited in HMEC and SA-NH cells transfected with human or mouse SOD2 siRNA oligomers and irradiated 24 h later. These data demonstrate that a delayed radioprotective effect can be induced and maintained over a prolonged period in both non-malignant and malignant cells exposed to thiol-containing drugs such as WR1065. For non-malignant cells this represents a novel paradigm for radiation protection. The ability of WR1065 to induce a persistent elevated radiation resistance in malignant cells, however, suggests a new potential concern regarding the issue of tumor protection in patients exposed to thiol-containing drugs.

Cycling hypoxia and free radicals regulate angiogenesis and radiotherapy response

Hypoxia and free radicals, such as reactive oxygen and nitrogen species, can alter the function and/or activity of the transcription factor hypoxia-inducible factor 1 (HIF1). Interplay between free radicals, hypoxia and HIF1 activity is complex and can influence the earliest stages of tumour development. The hypoxic environment of tumours is heterogeneous, both spatially and temporally, and can change in response to cytotoxic therapy. Free radicals created by hypoxia, hypoxia-reoxygenation cycling and immune cell infiltration after cytotoxic therapy strongly influence HIF1 activity. HIF1 can then promote endothelial and tumour cell survival. As discussed here, a constant theme emerges: inhibition of HIF1 activity will have therapeutic benefit.

Manganese superoxide dismutase gene dosage affects chromosomal instability and tumor onset in a mouse model of T cell lymphoma

Increased reactive oxygen species (ROS) such as superoxide have been implicated as causal elements of oncogenesis. A variety of cancers have displayed changes in steady-state levels of key antioxidant enzymes, with the mitochondrial form of superoxide dismutase (MnSOD) being commonly implicated. Increasing MnSOD expression suppresses the malignant phenotype in various cancer cell lines and suppresses tumor formation in xenograft and transgenic mouse models. We examined the impact of MnSOD expression in the development of T cell lymphoma in mice expressing proapoptotic Bax. Lck-Bax38/1 transgenic mice were crossed to mice overexpressing MnSOD (Lck-MnSOD) as well as MnSOD+/- mice. The effects of MnSOD on apoptosis, cell cycle, chromosomal instability (CIN), and lymphoma development were determined. The apoptotic and cell cycle phenotypes observed in thymocytes from control and Bax transgenic mice were unaffected by variations in MnSOD levels. Remarkably, increased gene dosage of MnSOD significantly decreased aneuploidy in premalignant thymocytes as well as the onset of tumor formation in Lck-Bax38/1 mice. The observed effects of MnSOD support a role for ROS in CIN and tumor formation in this mouse model of T cell lymphoma.

The rate of cellular hydrogen peroxide removal shows dependency on GSH: mathematical insight into in vivo H2O2 and GPx concentrations

Although its concentration is generally not known, glutathione peroxidase-1 (GPx-1) is a key enzyme in the removal of hydrogen peroxide (H₂O₂) in biological systems. Extrapolating from kinetic results obtained in vitro using dilute, homogenous buffered solutions, it is generally accepted that the rate of elimination of H₂O₂in vivo by GPx is independent of glutathione concentration (GSH). To examine this doctrine, a mathematical analysis of a kinetic model for the removal of H₂O₂ by GPx was undertaken to determine how the reaction species (H₂O₂, GSH, and GPx-1) influence the rate of removal of H₂O₂. Using both the traditional kinetic rate law approximation (classical model) and the generalized kinetic expression, the results show that the rate of removal of H₂O₂ increases with initial GPx_r, as expected, but is a function of both GPx_r and GSH when the initial GPx_r is less than H₂O₂. This simulation is supported by the biological observations of Li et al.. Using genetically altered human glioma cells in in vitro cell culture and in an in vivo tumour model, they inferred that the rate of removal of H₂O₂ was a direct function of GPx activity × GSH (effective GPx activity). The predicted cellular average GPx_r and H₂O₂ for their study are approximately GPx_r ≤ 1 μm and H₂O₂ ≈ 5 μm based on available rate constants and an estimation of GSH. It was also found that results from the accepted kinetic rate law approximation significantly deviated from those obtained from the more generalized model in many cases that may be of physiological importance.

Molecular consequences of SOD2 expression in epigenetically silenced pancreatic carcinoma cell lines

Manganese superoxide dismutase (SOD2) is an enzyme that catalyses the dismutation of superoxide in the mitochondria, leading to reduced levels of reactive oxygen species. Reduced expression levels of SOD2 have been shown to result in increased DNA damage and sod2 heterozygous mice have increased incidences of cancer. It has also been shown that SOD2 expression is lost in pancreatic cell lines, with reintroduction of SOD2 resulting in decreased rate of proliferation. The mechanism of decreased SOD2 expression in pancreatic carcinoma has not been previously determined. We demonstrate, through sodium bisulphite sequencing, that the sod2 locus is methylated in some pancreatic cell lines leading to a corresponding decrease in SOD2 expression. Methylation can be reversed by treatment with zebularine, a methyltransferase inhibitor, resulting in restored SOD2 expression. Furthermore, we demonstrate that sensitivity of pancreatic carcinoma cell lines to 2-methoxyestradiol correlates with SOD2 expression and SOD2 modulation can alter the sensitivity of these cells. Using both genomics and proteomics, we also identify molecular consequences of SOD2 expression in MIA-PaCa2 cells, including dephosphorylation of VEGFR2 and the identification of both SOD2-regulated genes and transcription factors with altered binding activity in response to SOD2 expression.

Human manganese superoxide dismutase suppresses HER2/neu-mediated breast cancer malignancy

The up-regulation of HER2/neu is associated with human malignancies and is a useful target for developing anticancer drugs. Overexpression of human manganese superoxide dismutase (MnSOD) has been demonstrated to effectively suppress various carcinoma cells, including breast carcinomas, in vitro and in vivo. This study demonstrates that MnSOD effectively suppresses HER2/neu oncogene expression at the transcriptional level. Additionally, stable transfection was used and the MnSOD-transfected human breast cancer clones were found to be able to down-regulate the endogenous production of p185(HER2/neu). Furthermore, the MnSOD-overexpressing stable transfectants exhibited reduced soft-agarose colony-forming ability and metastatic properties, unlike control cell lines. These data suggest that MnSOD may be useful in treating HER2/neu-mediated human breast tumor malignancy.

Superoxide signaling mediates N-acetyl-L-cysteine-induced G1 arrest: regulatory role of cyclin D1 and manganese superoxide dismutase

Thiol antioxidants, including N-acetyl-L-cysteine (NAC), are widely used as modulators of the intracellular redox state. We investigated the hypothesis that NAC-induced reactive oxygen species (ROS) signaling perturbs cellular proliferation by regulating the cell cycle regulatory protein cyclin D1 and the ROS scavenging enzyme Mn-superoxide dismutase (MnSOD). When cultured in media containing NAC, mouse fibroblasts showed G(1) arrest with decreased cyclin D1 protein levels. The absence of a NAC-induced G(1) arrest in fibroblasts overexpressing cyclin D1 (or a nondegradable mutant of cyclin D1-T286A) indicates that cyclin D1 regulates this G(1) arrest. A delayed response to NAC exposure was an increase in both MnSOD protein and activity. NAC-induced G(1) arrest is exacerbated in MnSOD heterozygous fibroblasts. Results from electron spin resonance spectroscopy and flow cytometry measurements of dihydroethidine fluorescence showed an approximately 2-fold to 3-fold increase in the steady-state levels of superoxide (O(2)(*-)) in NAC-treated cells compared with control. Scavenging of O(2)(*-) with Tiron reversed the NAC-induced G(1) arrest. These results show that an O(2)(*-) signaling pathway regulates NAC-induced G(1) arrest by decreasing cyclin D1 protein levels and increasing MnSOD activity.

Functional variant of manganese superoxide dismutase (SOD2 V16A) polymorphism is associated with prostate cancer risk in the prostate, lung, colorectal, and ovarian cancer study

Superoxide dismutase (SOD) plays a key role in the detoxification of superoxide free radicals. We evaluated the association of prostate cancer with genetic polymorphisms in SOD1 (CuZn-SOD; IVS3-251A>G), SOD2 [MnSOD; Ex2+24T>C (V16A)], and SOD3 (EC-SOD; IVS1+186C>T, Ex3-631C>G, Ex3-516C>T, and Ex3-489C>T), the three main isoforms of SOD. Prostate cancer cases (n = 1,320) from the screening arm of the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial were frequency matched to nondiseased controls (n = 1,842) by age, race, time since initial screening, and year of blood draw. Conditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (95% CI); stratified analysis by the level of antioxidative vitamins was also conducted. The higher activity Ala variant at SOD2 Ex2+24T>C (V16A), which has been hypothesized to suppress prostate carcinogenesis, was associated with elevation of prostate cancer risk in Caucasians (Val/Ala versus Val/Val: OR, 1.17; 95% CI, 0.97-1.42; Ala/Ala versus Val/Val: OR, 1.28; 95% CI, 1.03-1.60; P(trend) = 0.03). Stratification by quartiles of dietary and supplemental vitamin E intake (IU/d) showed risks of prostate cancer tended to be increased among SOD2 Ala allele carriers, except at the highest quartile of vitamin E intake (>222; P(interaction) = 0.06, Q1-Q3 versus Q4). The association between Ala allele and prostate cancer risk among those with lower intake of vitamin E (</=222) was stronger for smokers (OR, 1.44; 95% CI, 1.10-1.90). No significant association with prostate cancer was observed for polymorphic variants in SOD3 or SOD1. These results suggest that the Ala variant of SOD2 is associated with moderately increased risk of prostate cancer, particularly among men with lower intakes of dietary and supplemental vitamin E.

Characterization of redox state of two human prostate carcinoma cell lines with different degrees of aggressiveness

We characterized the redox profiles in two different human prostate carcinoma cell lines (LNCaP vs PC3) that are known to exhibit varying degrees of invasiveness/metastatic ability. We confirmed that PC3 cells were more invasive than LNCaP cells through an in vitro analysis. The present study documented higher 8-hydroxy-2'-deoxyguanosine levels in PC3 cells than in LNCaP cells. The levels of lipid peroxidation were higher in LNCaP cells than in PC3 cells. The reduced glutathione (GSH)/glutathione disulfide (GSSG) ratio increased to a greater extent during cell growth in PC3 cells than in LNCaP cells, whereas both reduced GSH and GSSG levels were higher in the medium of PC3 cells than in that of LNCaP cells. The levels of reactive oxygen (ROS) and reactive nitrogen species (RNS), both intracellularly and in the medium, were higher for LNCaP cells than for PC3 cells during cell growth. In addition, our results demonstrated higher ROS/RNS levels in LNCaP cells than in PC3 cells in S and G(2)/M phases of the cell cycle during logarithmic growth. Each cell type showed distinct cytotoxic responses to low-molecular-weight redox-modulating compounds. Our results document that human prostate cancer cell lines of varying degrees of aggressive behavior have distinct redox properties, findings that could lead to novel therapeutic interventions.

Proteomic analysis of liver cancer cells treated with suberonylanilide hydroxamic acid

PURPOSE

Suberonylanilide hydroxamic acid (SAHA) is an orally administered histone deacetylase inhibitor (HDACI) that has shown significant antitumor activity in a variety of tumor cells. To evaluate if SAHA has an activity against liver cancer, and with an aim to identify the altered cellular factors upon SAHA treatment, human HepG2 cancer cell line was used as a model, and proteomic approach was utilized to elucidate the molecular mechanisms underlying SAHA's antitumor activity.

METHODS

Cell growth inhibition was measured by MTT method, and apoptosis was detected by means of flow cytometry analysis and TUNEL assay. Protein expression profiles were analyzed by 2-DE coupled with MALDI-Q-TOF MS/MS analysis.

RESULTS

A total of 55 differentially expressed proteins were visualized by 2-DE and Coomassie Brilliant Blue (CBB) staining. Of these, 34 proteins were identified via MS/MS analysis. Among the identified proteins, six proteins also displayed significant expression changes at earlier time points upon SAHA treatment, and such alterations were further confirmed by semi-quantitative RT-PCR. Together, at both the mRNA and protein levels, SAHA suppressed the expression of reticulocalbin 1 precursor (RCN1), annexin A3 (ANXA3) and heat shock 27 kDa protein 1 (HSP27), while increasing the expression of aldose reductase (AR), triosephosphate isomerase 1 (TPI) and manganese superoxide dismutase (SOD2).

CONCLUSION

SAHA remarkably inhibited proliferation of HepG2 cancer cells, and induced apoptosis in vitro. Using proteomics approaches, a variety of differentially expressed proteins were identified in HepG2 cancer cells before and after treatment with SAHA. This study will enable a better understanding of the molecular mechanisms underlying SAHA-mediated antitumor effects at the protein level.

The effects of superoxide dismutase on H2O2 formation

Numerous reports of the effects of overproduction of SODs have been explained on the basis of increased H2O2 production by the catalyzed dismutation of O2-. In this review we consider the effects of increasing [SOD] on H2O2 formation and question this explanation.