Reactive Oxygen Species: A Breath of Life or Death?: Fig. 1

Protein modifications as potential biomarkers in breast cancer

A variety of post-translational protein modifications (PTMs) are known to be altered as a result of cancer development. Thus, these PTMs are potentially useful biomarkers for breast cancer. Mass spectrometry, antibody microarrays and immunohistochemistry techniques have shown promise for identifying changes in PTMs. In this review, we summarize the current literature on PTMs identified in the plasma and tumor tissue of breast-cancer patients or in breast cell lines. We also discuss some of the analytical techniques currently being used to evaluate PTMs.

Reactive oxygen species: an Achilles' heel of melanoma?

The successful treatment of melanoma has been hampered by the unique biology of this cancer. Fortunately, research to further our understanding of how melanoma cells differ from normal tissues has led to the discovery of potential new avenues of attack. One promising strategy relates to targeting the excess free radicals produced by melanomas. Melanocyte transformation into cancer is associated with significant structural alterations in the melanosome. In addition to pigment production, melanosomes also protect the cell by scavenging free radicals generated by sunlight and cellular metabolism. In melanoma, the disrupted and disorganized melanosome structure reverses this process. Melanosomes found in melanoma produce free radicals, such as hydrogen peroxide, furthering DNA damage. Melanosome generation of reactive oxygen species (ROS), in tandem with those generated by cancer metabolism, activate cellular signal transduction pathways that prevent cell death. ROS activation of proto-oncogene pathways in melanoma contributes to their resistance to chemotherapy. Fortunately, it may be possible to target these free radicals, just as Paris was able to successfully target Achilles' heel. The use of agents that block ROS scavenging, such as ATN-224 and disulfiram, have been explored clinically. A recent randomized Phase II trial with elesclomol, an agent that generates ROS, in combination with paclitaxel led to improved patient survival, suggesting that this may be a viable approach to advance the treatment of melanoma.

Erythropoiesis: model systems, molecular regulators, and developmental programs

Human erythropoiesis is a complex multistep developmental process that begins at the level of pluripotent hematopoietic stem cells (HSCs) at bone marrow microenvironment (HSCs niche) and terminates with the production of erythrocytes (RBCs). This review covers the basic and contemporary aspects of erythropoiesis. These include the: (a) cell-lineage restricted pathways of differentiation originated from HSCs and going downward toward the blood cell development; (b) model systems employed to study erythropoiesis in culture (erythroleukemia cell lines and embryonic stem cells) and in vivo (knockout animals: avian, mice, zebrafish, and xenopus); (c) key regulators of erythropoiesis (iron, hypoxia, stress, and growth factors); (d) signaling pathways operating at hematopoietic stem cell niche for homeostatic regulation of self renewal (SCF/c-kit receptor, Wnt, Notch, and Hox) and for erythroid differentiation (HIF and EpoR). Furthermore, this review presents the mechanisms through which transcriptional factors (GATA-1, FOG-1, TAL-1/SCL/MO2/Ldb1/E2A, EKLF, Gfi-1b, and BCL11A) and miRNAs regulate gene pattern expression during erythroid differentiation. New insights regarding the transcriptional regulation of alpha- and beta-globin gene clusters were also presented. Emphasis was also given on (i) the developmental program of erythropoiesis, which consists of commitment to terminal erythroid maturation and hemoglobin production, (two closely coordinated events of erythropoieis) and (ii) the capacity of human embryonic and umbilical cord blood (UCB) stem cells to differentiate and produce RBCs in culture with highly selective media. These most recent developments will eventually permit customized red blood cell production needed for transfusion.

Rituximab sensitizes a Burkitt lymphoma cell line to cell killing by X-irradiation

Clinical trials with rituximab in combination with chemotherapeutic regimens have shown promising results. Data on the effects of rituximab treatment in combination with irradiation are, however, limited and inconsistent. This study aims to investigate the effects of rituximab (R) on cell death induced by X-irradiation in Raji lymphoma cells and to evaluate its mechanisms. We found the cell growth inhibition by irradiation was enhanced by additional rituximab exposure both in cells precultured with rituximab followed by irradiation (R + irradiation) or in cells treated in the reverse sequence (irradiation + R). R + irradiation combination treatment induced more apoptotic cells than irradiation and irradiation + R treatment as early as 12 h after treatment. At 24 h, both combination treatments, R + irradiation and irradiation + R, showed apoptotic cells, which were significantly different from irradiation alone. G2/M cell cycle arrest was observed after irradiation alone and the combination treatment. The combination treatment revealed an elevation in reactive oxygen species (ROS) generation in a radiation dose-dependent manner. In addition, rituximab enhanced the cell growth inhibition and apoptotic cell death induced by the oxidative agent, H(2)O(2). We propose that rituximab mediates a significant in vitro radiosensitizing effect and induces cell cycle changes and apoptosis in Raji cells. ROS probably play an important role in these events.

NOX enzymes and pulmonary disease

The primary function of the lung is to facilitate the transfer of molecular oxygen (O(2); dioxygen) from the atmosphere to the systemic circulation. In addition to its essential role in aerobic metabolism, O(2) serves as the physiologic terminal acceptor of electron transfer catalyzed by the NADPH oxidase (NOX) family of oxidoreductases. The evolution of the lungs and circulatory systems in vertebrates was accompanied by increasing diversification of NOX family enzymes, suggesting adaptive roles for NOX-derived reactive oxygen species in normal physiology. However, this adaptation may paradoxically carry detrimental consequences in the setting of overwhelming/persistent environmental stressors, both infectious and noninfectious, and during the process of aging. Here, we review current understanding of NOX enzymes in normal lung physiology and their pathophysiologic roles in a number of pulmonary diseases, including lung infections, acute lung injury, pulmonary arterial hypertension, obstructive lung disorders, fibrotic lung disease, and lung cancer.

Effects of cotreatment of 12-O-tetradecanoylphorbol-13-acetate and H2O2 on apoptotic regulation via AMP-activated protein kinase-cyclooxygenase-2 signals

Colorectal cancer displays elevated cyclooxygenase-2 (COX-2) expression, and several studies have suggested that COX-2 expression is associated with parameters of aggressive colon cancer. AMP-activated protein kinase (AMPK) is a sensor of cellular energy status, and recent studies indicate that AMPK activation strongly suppresses cell proliferation in nonmalignant cells as well as in tumor cells. As a metabolic sensing signal, AMPK is involved in cancer cell apoptosis. In HT-29 colon cancer cells, the regulation of COX-2 expression by treating with TPA (12-O-tetradecanoylphorbol-13-acetate), low-level H(2)O(2), high-level H(2)O(2), and finally the combinations of TPA and low H(2)O(2) or high H(2)O(2) was investigated. We found that COX-2 expression levels with treatment reacted as follows: with TPA alone > TPA and low H(2)O(2) > low H(2)O(2) > high H(2)O(2) > TPA and high H(2)O(2). COX-2 regulation by these agents was accompanied by the alteration of AMPK control. The apoptotic bodies were detected as follows: high level of H(2)O(2) > TPA > low level of H(2)O(2). The present findings suggest that both COX-2 stimulators (TPA and H(2)O(2)) might have differential effects on COX-2 and AMPK regulation and further apoptotic regulation.

Oxygen consumption can regulate the growth of tumors, a new perspective on the Warburg effect

Background

The unique metabolism of tumors was described many years ago by Otto Warburg, who identified tumor cells with increased glycolysis and decreased mitochondrial activity. However, “aerobic glycolysis” generates fewer ATP per glucose molecule than mitochondrial oxidative phosphorylation, so in terms of energy production, it is unclear how increasing a less efficient process provides tumors with a growth advantage.

Methods/Findings

We carried out a screen for loss of genetic elements in pancreatic tumor cells that accelerated their growth as tumors, and identified mitochondrial ribosomal protein L28 (MRPL28). Knockdown of MRPL28 in these cells decreased mitochondrial activity, and increased glycolysis, but paradoxically, decreased cellular growth in vitro. Following Warburg's observations, this mutation causes decreased mitochondrial function, compensatory increase in glycolysis and accelerated growth in vivo. Likewise, knockdown of either mitochondrial ribosomal protein L12 (MRPL12) or cytochrome oxidase had a similar effect. Conversely, expression of the mitochondrial uncoupling protein 1 (UCP1) increased oxygen consumption and decreased tumor growth. Finally, treatment of tumor bearing animals with dichloroacetate (DCA) increased pyruvate consumption in the mitochondria, increased total oxygen consumption, increased tumor hypoxia and slowed tumor growth.

Conclusions

We interpret these findings to show that non-oncogenic genetic changes that alter mitochondrial metabolism can regulate tumor growth through modulation of the consumption of oxygen, which appears to be a rate limiting substrate for tumor proliferation.

Profiling protein thiol oxidation in tumor cells using sulfenic acid-specific antibodies

Hydrogen peroxide (H2O2) functions as a second messenger that can activate cell proliferation through chemoselective oxidation of cysteine residues in signaling proteins. The connection between H2O2 signaling, thiol oxidation, and activation of growth pathways has emerged as fertile ground for the development of strategies for cancer treatment. Central to achieving this goal is the development of tools and assays that facilitate characterization of the molecular events associated with tumorigenesis and evaluation of patient response to therapy. Here we report on the development of an immunochemical method for detecting sulfenic acid, the initial oxidation product that results when a thiolate reacts with H2O2. For this approach, the sulfenic acid is derivatized with a chemical tag to generate a unique epitope for recognition. The elicited antibody is exquisitely specific, context-independent, and capable of visualizing sulfenic acid formation in cells. Applying this approach to several systems, including cancer cell lines, shows it can be used to monitor differences in thiol redox status and reveals a diverse pattern of sulfenic acid modifications across different subtypes of breast tumors. These studies demonstrate a general strategy for producing antibodies against a specific oxidation state of cysteine and show the utility of these reagents for profiling thiol oxidation associated with pathological conditions such as breast cancer.

Cell death and stress signaling in glycogen storage disease type I

Cell death has been traditionally classified in apoptosis and necrosis. Apoptosis, known as programmed cell death, is an active form of cell death mechanism that is tightly regulated by multiple cellular signaling pathways and requires ATP for its appropriate process. Apoptotic death plays essential roles for successful development and maintenance of normal cellular homeostasis in mammalian. In contrast to apoptosis, necrosis is classically considered as a passive cell death process that occurs rather by accident in disastrous conditions, is not required for energy and eventually induces inflammation. Regardless of different characteristics between apoptosis and necrosis, it has been well defined that both are responsible for a wide range of human diseases. Glycogen storage disease type I (GSD-I) is a kind of human genetic disorders and is caused by the deficiency of a microsomal protein, glucose-6-phosphatase-α (G6Pase-α) or glucose-6-phosphate transporter (G6PT) responsible for glucose homeostasis, leading to GSD-Ia or GSD-Ib, respectively. This review summarizes cell deaths in GSD-I and mostly focuses on current knowledge of the neutrophil apoptosis in GSD-Ib based upon ER stress and redox signaling.

What are melanocytes really doing all day long...?

Everyone knows and seems to agree that melanocytes are there to generate melanin - an intriguing, but underestimated multipurpose molecule that is capable of doing far more than providing pigment and UV protection to skin (1). What about the cell that generates melanin, then? Is this dendritic, neural crest-derived cell still serving useful (or even important) functions when no-one looks at the pigmentation of our skin and its appendages and when there is essentially no UV exposure? In other words, what do epidermal and hair follicle melanocytes do in their spare time - at night, under your bedcover? How much of the full portfolio of physiological melanocyte functions in mammalian skin has really been elucidated already? Does the presence or absence of melanocytes matter for normal epidermal and/or hair follicle functions (beyond pigmentation and UV protection), and for skin immune responses? Do melanocytes even deserve as much credit for UV protection as conventional wisdom attributes to them? In which interactions do these promiscuous cells engage with their immediate epithelial environment and who is controlling whom? What lessons might be distilled from looking at lower vertebrate melanophores and at extracutaneous melanocytes in the endeavour to reveal the 'secret identity' of melanocytes? The current Controversies feature explores these far too infrequently posed, biologically and clinically important questions. Complementing a companion viewpoint essay on malignant melanocytes (2), this critical re-examination of melanocyte biology provides a cornucopia of old, but under-appreciated concepts and novel ideas on the slowly emerging complexity of physiological melanocyte functions, and delineates important, thought-provoking questions that remain to be definitively answered by future research.

Apoptotic body engulfment by hepatic stellate cells promotes their survival by the JAK/STAT and Akt/NF-kappaB-dependent pathways

BACKGROUND/AIMS

We have previously shown that phagocytosis of apoptotic bodies (AB) by hepatic stellate cells (HSC) is profibrogenic. As HSC survival is central to the progression of liver fibrosis, our goal was to investigate if phagocytosis induces HSC survival.

METHODS

Apoptosis of phagocytosing HSC was studied in the presence of known apoptotic agents. The JAK/STAT- and PI3K/Akt-dependent pathways, NF-kappaB activation and expression of the anti-apoptotic proteins Mcl-1 and A1 were evaluated. Apoptosis was assessed after blocking A1 by an siRNA approach.

RESULTS

Phagocytosing HSC were resistant to FasL/cycloheximide or TRAIL-induced apoptosis. Inhibition of the JAK/STAT or PI3K-mediated pathways induced apoptosis of HSC. Phagocytosis induced JAK1/STAT3 phosphorylation, and this was prevented by inhibiting JAK. Translocation of STAT3 to the nucleus was also blocked by JAK inhibition. Mcl-1 expression was upregulated in a JAK-dependent manner. PI3K-dependent phosphorylation of Akt depended on NADPH oxidase activity and superoxide production. NF-kappaB activation and subsequent upregulation of A1 was observed, and A1 inhibition induced apoptosis of HSC.

CONCLUSION

Phagocytosis of AB promotes HSC survival by two pathways, of which the A1 dependent is more significant. This represents a new mechanism by which engulfment of AB contributes to the propagation of liver fibrosis.

Selective induction of apoptosis of human oral cancer cell lines by avocado extracts via a ROS-mediated mechanism

Avocados have a high content of phytochemicals with potential chemopreventive activity. Previously we reported that phytochemicals extracted from avocado meat into a chloroform partition (D003) selectively induced apoptosis in cancer but not normal, human oral epithelial cell lines. In the present study, we observed that treatment of human oral cancer cell lines containing high levels of reactive oxygen (ROS) with D003 increased ROS levels twofold to threefold and induced apoptosis. In contrast, ROS levels increased only 1.3-fold, and apoptosis was not induced in the normal cell lines containing much lower levels of basal ROS. When cellular ROS levels in the malignant cell lines were reduced by N-acetyl-l-cysteine (NAC), cells were resistant to D003 induced apoptosis. NAC also delayed the induction of apoptosis in dominant negative FADD-expressing malignant cell lines. D003 increased ROS levels via mitochondrial complex I in the electron transport chain to induce apoptosis. Normal human oral epithelial cell lines transformed with HPV16 E6 or E7 expressed higher basal levels of ROS and became sensitive to D003. These data suggest that perturbing the ROS levels in human oral cancer cell lines may be a key factor in selective apoptosis and molecular targeting for chemoprevention by phytochemicals.

Frequencies of NRAS and BRAF mutations increase from the radial to the vertical growth phase in cutaneous melanoma

A lack of consensus exists with regards to the relative rates of NRAS and BRAF mutations in the radial (RGP) and vertical (VGP) growth phases of individual melanoma tumors. This study was conducted to test the hypothesis that mutations are acquired with progression from RGP to VGP. Using laser capture microdissection, pure tumor DNA was obtained from 15 in situ melanomas, and from the RGP and VGP of 29 invasive tumors. NRAS exon 2 and BRAF exon 15 DNA were amplified by PCR and sequenced. Mutations were present in 6 of 15 in situ melanomas (40%). Of 29 invasive tumors, 16 exhibited RGP mutations (55.2%); 22 showed VGP mutations (75.9%). Paired RGP/VGP mutation analysis revealed a trend toward discordance in the distribution of mutations, favoring VGP localization (P=0.07). Of 15 samples, 12 with mutations in both phases had an increased proportion of mutated DNA in the VGP, measured on DNA chromatograms (P=0.08). Limitations of this study include a relatively small sample cohort selected for technical reasons from a larger population, presenting the risk of selection bias. These concerns notwithstanding our findings support the hypothesis that NRAS and BRAF mutations increase with tumor progression from superficial to invasive disease. JID JOURNAL CLUB ARTICLE: For questions, answers, and open discussion about this article, please go to http://network.nature.com/group/jidclub.

The role of cellular oxidative stress in regulating glycolysis energy metabolism in hepatoma cells

Background

The Warburg effect has been found in a wide spectrum of human cancers, however the underlying mechanisms are still unclear. This study aims to explore the role of cellular oxidative stress in relation to glycolysis and the Warburg effect in hepatoma cells.

Methods

Various cell lines combining environmental hypoxia was used as an in vitro model to mimic tumor microenvironment in vivo. Superoxide dismutases (SOD) and xanthine oxidase (XO) gene transfection were used to produce various cellular redox levels. 2',7'-dichlorofluorescin (DCF) fluorescence and ESR spectrum were used to detect cellular reactive oxygen species (ROS).

Results

We found that endogenous or exogenous interference with the cellular oxidative stress can sensitively regulate glycolysis and the Warburg effect in hepatoma cells. Hepatoma cells displayed a high level of free radicals compared to immortalized normal hepatocyte cells. Increasing the level of ROS stress in hepatoma cells can directly upregulate HIF-1 and activate glycolysis without requirement of a hypoxic condition. This explains the mechanism whereby aerobic glycolysis, i.e. the Warburg effect arises. Either endogenously upregulating SOD or exogenously administration with antioxidant can, through downregulating ROS level, effectively regulate energy pathways in hepatoma cells and can inhibit the growth of tumor cells and xenograft tumors.

Conclusion

This study suggests that the Warburg effect was related to an inherently high level of cellular ROS and HIF-1. Hepatoma cells adaptation to hypoxia for survival and rapid growth exploits oxidative stress ectopically activated glycolysis to compensate the energy supply. This specific mechanism in which tumor cells through cellular oxidative stress activate glycolysis to meet their energy metabolism requirement could be exploited to selectively kill tumor cells.

Proton-Resistant Quantum Dots: Stability in Gastrointestinal Fluids and Implications for Oral Delivery of Nanoparticle Agents

Semiconductor quantum dots (QDs) have shown great promise as fluorescent probes for molecular, cellular and in-vivo imaging. However, the fluorescence of traditional polymer-encapsulated QDs is often quenched by proton-induced etching in acidic environments. This is a major problem for QD applications in the gastrointestinal tract because the gastric (stomach) environment is strongly acidic (pH 1-2). Here we report the use of proton-resistant surface coatings to stabilize QD fluorescence under acidic conditions. Using both hyperbranched polyethylenimine (PEI) and its polyethylene glycol derivative (PEG grafted PEI), we show that the fluorescence of core-shell CdSe/CdS/ZnS QDs is effectively protected from quenching in simulated gastric fluids. In comparison, amphiphilic lipid or polymer coatings provide no protection under similarly acidic conditions. The proton-resistant QDs are found to cause moderate membrane damage to cultured epithelial cells, but PEGylation (PEG grafting) can be used to reduce cellular toxicity and to improved nanoparticle stability.

Mitochondrial reactive oxygen species production in excitable cells: modulators of mitochondrial and cell function

The mitochondrion is a major source of reactive oxygen species (ROS). Superoxide (O(2)(*-)) is generated under specific bioenergetic conditions at several sites within the electron-transport system; most is converted to H(2)O(2) inside and outside the mitochondrial matrix by superoxide dismutases. H(2)O(2) is a major chemical messenger that, in low amounts and with its products, physiologically modulates cell function. The redox state and ROS scavengers largely control the emission (generation scavenging) of O(2)(*-). Cell ischemia, hypoxia, or toxins can result in excess O(2)(*-) production when the redox state is altered and the ROS scavenger systems are overwhelmed. Too much H(2)O(2) can combine with Fe(2+) complexes to form reactive ferryl species (e.g., Fe(IV) = O(*)). In the presence of nitric oxide (NO(*)), O(2)(*-) forms the reactant peroxynitrite (ONOO(-)), and ONOOH-induced nitrosylation of proteins, DNA, and lipids can modify their structure and function. An initial increase in ROS can cause an even greater increase in ROS and allow excess mitochondrial Ca(2+) entry, both of which are factors that induce cell apoptosis and necrosis. Approaches to reduce excess O(2)(*-) emission include selectively boosting the antioxidant capacity, uncoupling of oxidative phosphorylation to reduce generation of O(2)(*-) by inducing proton leak, and reversibly inhibiting electron transport. Mitochondrial cation channels and exchangers function to maintain matrix homeostasis and likely play a role in modulating mitochondrial function, in part by regulating O(2)(*-) generation. Cell-signaling pathways induced physiologically by ROS include effects on thiol groups and disulfide linkages to modify posttranslationally protein structure to activate/inactivate specific kinase/phosphatase pathways. Hypoxia-inducible factors that stimulate a cascade of gene transcription may be mediated physiologically by ROS. Our knowledge of the role played by ROS and their scavenging systems in modulation of cell function and cell death has grown exponentially over the past few years, but we are still limited in how to apply this knowledge to develop its full therapeutic potential.

Targeting cancer cells by ROS-mediated mechanisms: a radical therapeutic approach?

Increased generation of reactive oxygen species (ROS) and an altered redox status have long been observed in cancer cells, and recent studies suggest that this biochemical property of cancer cells can be exploited for therapeutic benefits. Cancer cells in advanced stage tumours frequently exhibit multiple genetic alterations and high oxidative stress, suggesting that it might be possible to preferentially eliminate these cells by pharmacological ROS insults. However, the upregulation of antioxidant capacity in adaptation to intrinsic oxidative stress in cancer cells can confer drug resistance. Abrogation of such drug-resistant mechanisms by redox modulation could have significant therapeutic implications. We argue that modulating the unique redox regulatory mechanisms of cancer cells might be an effective strategy to eliminate these cells.

Aneuploidy involving chromosome 1 may be an early predictive marker of intestinal type gastric cancer

Intestinal type gastric cancer is a significant cause of mortality, therefore a better understanding of its molecular basis is required. We assessed if either aneuploidy or activity of the oncogenic transcription factor nuclear factor kappa B (NF-kappaB), increased incrementally during pre-malignant gastric histological progression and also if they correlated with each other in patient samples, as they are both induced by oxygen free radicals. In a prospective study of 54 (aneuploidy) and 59 (NF-kappaB) consecutive patients, aneuploidy was assessed by interphase fluorescent in situ hybridisation (FISH) for chromosome 1. NF-kappaB was assessed by expression of interleukin-8 (IL-8), and in a subset, by immunohistochemistry (IHC) for active p65. Aneuploidy levels increased incrementally across the histological series. 2.76% of cells with normal histology (95% CI, 2.14-3.38%) showed background levels of aneuploidy, this increased to averages of 3.78% (95% CI, 3.21-4.35%), 5.89% (95% CI, 3.72-8.06%) and 7.29% (95% CI, 4.73-9.85%) of cells from patients with gastritis, Helicobacter pylori positive gastritis and atrophy/intestinal metaplasia (IM) respectively. IL-8 expression was only increased in patients with current H. pylori infection. NF-kappaB analysis showed some increased p65 activity in inflamed tissues. IL-8 expression and aneuploidy level were not linked in individual patients. Aneuploidy levels increased incrementally during histological progression; were significantly elevated at very early stages of neoplastic progression and could well be linked to cancer development and used to assess cancer risk. Reactive oxygen species (ROS) induced in early gastric cancer are presumably responsible for the stepwise accumulation of this particular mutation, i.e. aneuploidy. Hence, aneuploidy measured by fluorescent in situ hybridisation (FISH) coupled to brush cytology, would be worthy of consideration as a predictive marker in gastric cancer and could be clinically useful in pre-malignant disease to stratify patients by their cancer risk.

Cyclophosphamide enhances human tumor growth in nude rat xenografted tumor models

The effect of the immunomodulatory chemotherapeutic agent cyclophosphamide (CTX) on tumor growth was investigated in primary and metastatic intracerebral and subcutaneous rat xenograft models. Nude rats were treated with CTX (100 mg/kg, intraperitoneally) 24 hours before human ovarian carcinoma (SKOV3), small cell lung carcinoma (LX-1 SCLC), and glioma (UW28, U87MG, and U251) tumor cells were inoculated subcutaneously, intraperitoneally, or in the right cerebral hemisphere or were infused into the right internal carotid artery. Tumor development was monitored and recorded. Potential mechanisms were further investigated. Only animals that received both CTX and Matrigel showed consistent growth of subcutaneous tumors. Cyclophosphamide pretreatment increased the percentage (83.3% vs 0%) of animals showing intraperitoneal tumors. In intracerebral implantation tumor models, CTX pretreatment increased the tumor volume and the percentage of animals showing tumors. Cyclophosphamide increased lung carcinoma bone and facial metastases after intra-arterial injection, and 20% of animals showed brain metastases. Cyclophosphamide transiently decreased nude rat white blood cell counts and glutathione concentration, whereas serum vascular endothelial growth factor was significantly elevated. Cyclophosphamide also increased CD31 reactivity, a marker of vascular endothelium, and macrophage (CD68-positive) infiltration into glioma cell-inoculated rat brains. Cyclophosphamide may enhance primary and metastatic tumor growth through multiple mechanisms, including immune modulation, decreased response to oxidative stress, increased tumor vascularization, and increased macrophage infiltration. These findings may be clinically relevant because chemotherapy may predispose human cancer subjects to tumor growth in the brain or other tissues.

Antimelanoma activity of the redox dye DCPIP (2,6-dichlorophenolindophenol) is antagonized by NQO1

Altered redox homeostasis involved in the control of cancer cell survival and proliferative signaling represents a chemical vulnerability that can be targeted by prooxidant redox intervention. Here, we demonstrate that the redox dye 2,6-dichlorophenolindophenol (DCPIP) may serve as a prooxidant chemotherapeutic targeting human melanoma cells in vitro and in vivo. DCPIP-apoptogenicity observed in the human melanoma cell lines A375 and G361 was inversely correlated with NAD(P)H:quinone oxidoreductase (NQO1) expression levels. In A375 cells displaying low NQO1 activity, DCPIP induced apoptosis with procaspase-3 and PARP cleavage, whereas G361 cells expressing high levels of enzymatically active NQO1 were resistant to DCPIP-cytotoxicity. Genetic (siRNA) or pharmacological (dicoumarol) antagonism of NQO1 strongly sensitized G361 cells to DCPIP apoptogenic activity. DCPIP-cytotoxicity was associated with the induction of oxidative stress and rapid depletion of glutathione in A375 and NQO1-modulated G361 cells. Expression array analysis revealed a DCPIP-induced stress response in A375 cells with massive upregulation of genes encoding Hsp70B' (HSPA6), Hsp70 (HSPA1A), heme oxygenase-1 (HMOX1), and early growth response protein 1 (EGR1) further confirmed by immunodetection. Systemic administration of DCPIP displayed significant antimelanoma activity in the A375 murine xenograft model. These findings suggest feasibility of targeting tumors that display low NQO1 enzymatic activity using DCPIP.

Glucose as a prognostic factor in ovarian carcinoma

BACKGROUND

Research suggests that glucose levels in cancer patients may be an important prognostic indicator. In ovarian tumors, increased expression of glucose transporter 1 (GLUT1), a transmembrane protein responsible for glucose uptake, is related to shorter survival time in ovarian cancer patients. This study tested the hypothesis that higher presurgical glucose levels predict shorter disease-specific survival time and time to recurrence in ovarian cancer patients.

METHODS

Nonfasting plasma glucose levels were determined for 74 patients with ovarian cancer at the time of their presurgical consultation and for 125 ovarian cancer patients in an independent validation set. Survival time and time to recurrence (disease-free interval [DFI]) were ascertained from medical records. Cox proportional hazards regression models were used to estimate the hazard ratio (HR) for survival time and DFI in relation to glucose level, adjusting for body mass index (BMI), stage, grade, and cytoreduction as appropriate.

RESULTS

Higher glucose levels were associated with shorter survival times in univariate analyses (HR, 1.88; P = .05). Multivariate analysis adjusting for stage showed that higher glucose levels were associated with shorter survival times (HR, 2.01; P = .04) and DFI (HR, 2.32; P = .05). In the validation set, higher glucose levels were associated with shorter survival times (HR, 2.01; P = .02) and DFI (HR, 2.48; P = .001) in univariate analysis, although glucose was not independent of the effect of cytoreduction when predicting survival time in this latter set.

CONCLUSIONS

These findings contribute to mounting evidence that glucose levels have prognostic value in ovarian carcinoma.

Regulation of autophagy by reactive oxygen species (ROS): implications for cancer progression and treatment

Reactive oxygen species (ROS) have been identified as signaling molecules in various pathways regulating both cell survival and cell death. Autophagy, a self-digestion process that degrades intracellular structures in response to stress, such as nutrient starvation, is also involved in both cell survival and cell death. Alterations in both ROS and autophagy regulation contribute to cancer initiation and progression, and both are targets for developing therapies to induce cell death selectively in cancer cells. Many stimuli that induce ROS generation also induce autophagy, including nutrient starvation, mitochondrial toxins, hypoxia, and oxidative stress. Some of these stimuli are under clinical investigation as cancer treatments, such as 2-methoxyestrodial and arsenic trioxide. Recently, it was demonstrated that ROS can induce autophagy through several distinct mechanisms involving Atg4, catalase, and the mitochondrial electron transport chain (mETC). This leads to both cell-survival and cell-death responses and could be selective toward cancer cells. In this review, we give an overview of the roles ROS and autophagy play in cell survival and cell death, and their importance to cancer. Furthermore, we describe how autophagy is mediated by ROS and the implications of this regulation to cancer treatments.

Degenerative diseases, oxidative stress and cytochrome c oxidase function

Aging and degenerative diseases are associated with increased levels of reactive oxygen species (ROS). ROS are mostly produced in mitochondria, and their levels increase with higher mitochondrial membrane potential. Cellular respiratory control is based on inhibition of respiration by high membrane potentials. However, we have described a second mechanism of respiratory control based on allosteric inhibition of cytochrome c oxidase (CcO), the terminal enzyme of the respiratory chain, at high ATP:ADP ratios. The mechanism is independent of membrane potential. We have proposed that feedback inhibition of CcO by ATP keeps the membrane potential and ROS production at low levels. Various forms of stress switch off allosteric ATP-inhibition via reversible dephosphorylation of CcO, resulting in increased membrane potential and cellular ROS levels. This mechanism is proposed to represent a missing molecular link between stress and degenerative diseases.

Retained features of embryonic metabolism in the adult MRL mouse

The MRL mouse is an inbred laboratory strain that was derived by selective breeding in 1960 from the rapidly growing LG/J (Large) strain. MRL mice grow to nearly twice the size of other commonly used mouse strains, display uncommonly robust healing and regeneration properties, and express later onset autoimmune traits similar to Systemic Lupus Erythematosis. The regeneration trait (heal) in the MRL mouse maps to 14-20 quantitative trait loci and the autoimmune traits map to 5-8 loci. In this paper we report the metabolic and biochemical features that characterize the adult MRL mouse and distinguish it from C57BL/6 control animals. We found that adult MRL mice have retained a number of features of embryonic metabolism that are normally lost during development in other strains. These include an emphasis on aerobic glycolytic energy metabolism, increased glutamate oxidation, and a reduced capacity for fatty acid oxidation. MRL tissues, including the heart, liver, and regenerating ear hole margins, showed considerable mitochondrial genetic and physiologic reserve, decreased mitochondrial transmembrane potential (DeltaPsi(m)), decreased reactive oxygen species (ROS), and decreased oxidative phosphorylation, yet increased mitochondrial DNA and protein content. The discovery of embryonic metabolic features led us to look for cells that express markers of embryonic stem cells. We found that the adult MRL mouse has retained populations of cells that express the stem cell markers Nanog, Islet-1, and Sox2. These are present in the heart at baseline and highly induced after myocardial injury. The retention of embryonic features of metabolism in adulthood is rare in mammals. The MRL mouse provides a unique experimental window into the relationship between metabolism, stem cell biology, and regeneration.

Identification of potential pathway mediation targets in Toll-like receptor signaling

Recent advances in reconstruction and analytical methods for signaling networks have spurred the development of large-scale models that incorporate fully functional and biologically relevant features. An extended reconstruction of the human Toll-like receptor signaling network is presented herein. This reconstruction contains an extensive complement of kinases, phosphatases, and other associated proteins that mediate the signaling cascade along with a delineation of their associated chemical reactions. A computational framework based on the methods of large-scale convex analysis was developed and applied to this network to characterize input–output relationships. The input–output relationships enabled significant modularization of the network into ten pathways. The analysis identified potential candidates for inhibitory mediation of TLR signaling with respect to their specificity and potency. Subsequently, we were able to identify eight novel inhibition targets through constraint-based modeling methods. The results of this study are expected to yield meaningful avenues for further research in the task of mediating the Toll-like receptor signaling network and its effects.

The human innate immune system, as the first line of defense against pathogens, is a vital component of our survival. One component of the innate immune system is the Toll-like receptor signaling network, which is responsible for transmitting activation signals from the outside of the cell to molecular machinery inside the cell. The innate immune system must be properly balanced, as excessive activation can lead to potentially lethal septic shock. Therefore, there is much interest in developing drugs that can mediate Toll-like receptor signaling so as to alleviate effects of excess activation. We present an in silico reconstruction of the Toll-like receptor signaling network and convert it into a mathematical framework that is suitable for constraint-based modeling and analysis. This approach leads to the identification of potential candidates for drug-based mediation. In addition to identifying targets for drug mediation of the Toll-like receptor network, we also supply a network model that may be continually updated and maintained.

Hydrogen peroxide-induced Akt phosphorylation regulates Bax activation

Reactive oxygen species such as hydrogen peroxide (H(2)O(2)) are involved in many cellular processes that positively and negatively regulate cell fate. H(2)O(2), acting as an intracellular messenger, activates phosphatidylinositol-3 kinase (PI3K) and its downstream target Akt, and promotes cell survival. The aim of the current study was to understand the mechanism by which PI3K/Akt signaling promotes survival in SH-SY5Y neuroblastoma cells. We demonstrate that PI3K/Akt mediates phosphorylation of the pro-apoptotic Bcl-2 family member Bax. This phosphorylation suppresses apoptosis and promotes cell survival. Increased survival in the presence of H(2)O(2) was blocked by LY294002, an inhibitor of PI3K activation. LY294002 prevented Bax phosphorylation and resulted in Bax translocation to the mitochondria, cytochrome c release, caspase-3 activation, and cell death. Collectively, these findings reveal a mechanism by which H(2)O(2)-induced activation of PI3K/Akt influences post-translational modification of Bax and inactivates a key component of the cell death machinery.

Modulation of reactive oxygen species by antioxidants in chronic myeloid leukemia cells enhances imatinib sensitivity through survivin downregulation

Survivin, a member of the inhibitor of apoptosis protein family and a target for new drugs, is modulated by reactive oxygen species in several types of neoplasms including leukemias. The aim of this study is to find mechanisms to enhance sensitivity to imatinib in imatinib-responsive cells. In this study, we demonstrated through fluorescein isothiocyanate-labeled annexin V for apoptotic cells detection and western blotting that by inhibiting catalase activity, imatinib apoptosis induction was significantly enhanced (P<0.05) through diminishing survivin expression in K562 cells. These findings might be of clinical relevance and might help improve the chemotherapeutic use of imatinib mesylate.

Antiinflammatory effects of hydrogen peroxide in neutrophil activation and acute lung injury

RATIONALE

Although reactive oxygen species (ROS) are generally considered to be proinflammatory and to contribute to cellular and organ dysfunction when present in excessive amounts, there is evidence that specific ROS, particularly hydrogen peroxide (H(2)O(2)), may have antiinflammatory properties.

OBJECTIVES

To address the role that increases in intracellular H(2)O(2) may play in acute inflammatory processes, we examined the effects of catalase inhibition or the absence of catalase on LPS-induced inflammatory responses.

METHODS

Neutrophils from control or acatalasemic mice, or control neutrophils incubated with the catalase inhibitor aminotriazole, were treated with LPS, and levels of reactive oxygen species, proteasomal activity, NF-kappaB activation, and proinflammatory cytokine expression were measured. Acute lung injury (ALI) was produced by intratracheal injection of LPS into control, acatalasemic-, or aminotriazole-treated mice.

MEASUREMENTS AND MAIN RESULTS

Intracellular levels of H(2)O(2) were increased in acatalasemic neutrophils and in neutrophils exposed to aminotriazole. Compared with LPS-stimulated neutrophils from control mice, neutrophils from acatalasemic mice or neutrophils treated with aminotriazole demonstrated reduced 20S and 26S proteasomal activity, IkappaB-alpha degradation, NF-kappaB nuclear accumulation, and production of the proinflammatory cytokines TNF-alpha and macrophage inhibitory protein (MIP)-2. The severity of LPS-induced ALI was less in acatalasemic mice and in mice treated with aminotriazole as compared with that found in control mice.

CONCLUSIONS

These results indicate that H(2)O(2) has antiinflammatory effects on neutrophil activation and inflammatory processes, such as ALI, in which activated neutrophils play a major role.

The cinnamon-derived Michael acceptor cinnamic aldehyde impairs melanoma cell proliferation, invasiveness, and tumor growth

Redox dysregulation in cancer cells represents a chemical vulnerability that can be targeted by pro-oxidant redox intervention. Dietary constituents that contain an electrophilic Michael acceptor pharmacophore may therefore display promising chemopreventive and chemotherapeutic anti-cancer activity. Here, we demonstrate that the cinnamon-derived dietary Michael acceptor trans-cinnamic aldehyde (CA) impairs melanoma cell proliferation and tumor growth. Feasibility of therapeutic intervention using high doses of CA (120 mg/kg, po, daily, 10 days) was demonstrated in a human A375 melanoma SCID mouse xenograft model. Low-micromolar concentrations (IC(50)< 10 microM) of CA, but not closely related CA derivatives devoid of Michael acceptor activity, suppressed proliferation of human metastatic melanoma cell lines (A375, G361, LOX) with G1 cell-cycle arrest, elevated intracellular ROS, and impaired invasiveness. Expression array analysis revealed that CA induced an oxidative stress response in A375 cells, up-regulating heme oxygenase 1, sulfiredoxin 1 homolog, thioredoxin reductase 1, and other genes, including the cell-cycle regulator and stress-responsive tumor suppressor gene cyclin-dependent kinase inhibitor 1A, a key mediator of G1-phase arrest. CA, but not Michael-inactive derivatives, inhibited NF-kappaB transcriptional activity and TNFalpha-induced IL-8 production in A375 cells. These findings support a previously unrecognized role of CA as a dietary Michael acceptor with potential anti-cancer activity.

Hypoxia-inducible factor 1alpha mediates anoikis resistance via suppression of alpha5 integrin

The transcription factor hypoxia-inducible factor 1 (HIF-1) alpha is abundantly expressed in the majority of human carcinomas and their metastases. HIF-1alpha controls central metastasis-associated pathways such as glycolysis, angiogenesis, and invasion. Functional inhibition of HIF-1alpha leads to impaired metastasis formation in murine tumor models. However, the precise molecular mechanisms underlying the metastasis-promoting role of HIF-1alpha have not been fully characterized. The ability of transformed epithelial cells to initiate the metastatic cascade relies on their ability to escape anoikis, a default program of apoptosis induction following loss of integrin anchoring to the extracellular matrix. Therefore, we addressed the function of HIF-1alpha in anoikis resistance and anchorage-independent growth. Inhibition of HIF-1alpha via RNA interference resulted in up-regulation of alpha5 integrin on the cell surface of human gastric cancer cells, whereas other integrins remained unaffected. Integrin alpha5 induction occurred at the level of transcription and was dependent on elevated intracellular superoxide in HIF-1alpha-knockdown cells. HIF-1alpha-deficient cells displayed significantly increased anoikis susceptibility due to up-regulated alpha5 integrin. Finally, colony formation in soft agar was shown to be dependent on HIF-1alpha as HIF-1alpha-deficient cells displayed a 70% reduction in anchorage-independent proliferation. Results obtained by RNA interference could be entirely confirmed by application of the pharmacologic HIF-1alpha-inhibitor 2-methoxyestradiol. Hence, our data argue for a pivotal role for HIF-1alpha in anoikis control via suppression of alpha5 integrin. HIF-1alpha-inhibiting drugs might therefore offer an innovative strategy for antimetastatic cancer therapy.

Effect of taurine on antioxidant enzyme system in B16F10 melanoma cells

There is now increasing evidence that free radicals and reactive oxygen species (ROS) are involved in a variety of pathological events. Reactive oxygen species are produced during normal cellular function and lead to lipid peroxidation, massive protein oxidation and degradation. Taurine is an abundant free amino acid in inflammatory cells, where it is thought to be cytoprotective. The aim of the present study was to examine whether taurine enhances endogenous antioxidant enzyme activity and/or regulates ROS generation in B16F10 mouse melanoma cells. B16F10 cells were exposed to medium containing taurine for a period of 24 h. Cell viability, measured by the MTT assay, exhibited a dose-dose dependent inhibition. Taurine increased the activities of superoxide dismutase, glutathione peroxidase and CAT compared to those of the control, an effect paralleling an increase in gene expression. Taurine also reduced ROS content in a dose-dependent manner. Taken together, our results suggest that taurine decreases ROS levels by increasing the levels of the antioxidant enzymes.

Survival of monocytes and macrophages and their role in health and disease

Macrophages are versatile cells involved in health and disease. These cells act as scavengers to rid the body of apoptotic and senescent cells and debris through their phagocytic function. Although this is a primary function of these cells, macrophages play vital roles in inflammation and repair of damaged tissue. Macrophages secrete a large number of cytokines, chemokines and growth factors that recruit and activate a variety of cell types to inflamed tissue compartments. These cells are also critical in cell-mediated immunity and in the resolution of inflammation. Since macrophages, and their precursors, blood monocytes, are important in regulating and resolving inflammation, prolonged cellular survival in tissue compartments could be detrimental. Thus, factors that regulate the fate of monocyte and macrophage survival are important in cellular homeostasis. In this article, we will explore stimuli and the intracellular pathways important in regulating macrophage survival and implication in human disease.

Salvia fruticosa, Salvia officinalis, and rosmarinic acid induce apoptosis and inhibit proliferation of human colorectal cell lines: the role in MAPK/ERK pathway

Epidemiological studies have shown that nutrition is a key factor in modulating sporadic colorectal carcinoma (CRC) risk. Aromatic plants of the genus Salvia (sage) have been attributed many medicinal properties, which include anticancer activity. In the present study, the antiproliferative and proapoptotic effects of water extracts of Salvia fruticosa (SF) and Salvia officinalis (SO) and of their main phenolic compound rosmarinic acid (RA) were evaluated in two human colon carcinoma-derived cell lines, HCT15 and CO115, which have different mutations in the MAPK/ERK and PI3K/Akt signalling pathways. These pathways are commonly altered in CRC, leading to increased proliferation and inhibition of apoptosis. Our results show that SF, SO, and RA induce apoptosis in both cell lines, whereas cell proliferation was inhibited by the two sage extracts only in HCT15. SO, SF, and RA inhibited ERK phosphorylation in HCT15 and had no effects on Akt phosphorylation in CO115 cells. The activity of sage extracts seems to be due, at least in part, to the inhibition of MAPK/ERK pathway.

Peroxiredoxin I, platelet-derived growth factor A, and platelet-derived growth factor receptor alpha are overexpressed in carcinoma ex pleomorphic adenoma: association with malignant transformation

Carcinoma ex pleomorphic adenoma is a rare salivary gland malignancy. It constitutes an important model for the study of carcinogenesis, as it can display the tumor in different stages of progression, from benign pleomorphic adenoma to frankly invasive carcinoma. Growth signaling pathways undergo continuous activation in human tumors, commonly as a consequence of the overexpression of ligands and receptors such as platelet-derived growth factor and platelet-derived growth factor receptor. Hydrogen peroxide is produced after platelet-derived growth factor receptor activation, and it is essential for the sequential phosphorylation cascade that drives cell proliferation and migration. By their ability to degrade hydrogen peroxide, peroxiredoxins are involved in growth factor signaling regulation and in the oxidative stress response. To verify the potential association of peroxiredoxin I, platelet-derived growth factor-A, and platelet-derived growth factor receptor-alpha with carcinoma ex pleomorphic adenoma progression, we investigated the expression of these molecules in carcinoma ex pleomorphic adenoma showing different degrees of invasion. The peroxiredoxin I, platelet-derived growth factor-A, and platelet-derived growth factor receptor-alpha proteins were present in remnant pleomorphic adenoma to only a small extent, but, collectively, they were highly expressed as soon as the malignant phenotype was achieved and remained at elevated concentrations during progression to the advanced stages of carcinoma ex pleomorphic adenoma. In addition, their locations overlapped significantly, strengthening their connection to this growth-signaling pathway. Our results indicate that carcinoma ex pleomorphic adenoma cells acquire at least 2 significant advantages relative to their normal counterparts: resistance to oxidative stress-induced apoptosis, conferred by high peroxiredoxin I concentrations, and sustained growth, reflecting platelet-derived growth factor-A and platelet-derived growth factor receptor-alpha overexpression.

The thioredoxin system mediates redox-induced cell death in human colon cancer cells: implications for the mechanism of action of anticancer agents

Anticancer agents act, at least in part, by inducing reactive oxygen and nitrogen species (RONS). We examined the redox effect on SW480 and HT-29 colon cancer cells of four anticancer compounds, arsenic trioxide, phosphoaspirin, phosphosulindac, and nitric oxide-donating aspirin (NO-ASA). All compounds inhibited the growth of both cell lines (IC(50), 10-90 micromol/L) and induced RONS detected by a general RONS molecular probe. NO-ASA, which induced at least four individual RONS (NO, H(2)O(2), superoxide anion, and peroxynitirte), induced apoptotic and necrotic cell death that was RONS-mediated (cell death paralleled RONS levels and was abrogated by N-acetyl cysteine but not by diphenylene iodonium, which displayed prooxidant activity and enhanced cell death). Nuclear factor-kappaB and mitogen-activated protein kinases were modulated by RONS. Thioredoxin-1 (Trx-1), an oxidoreductase involved in redox regulation, was heavily oxidized in response to RONS and mediated the growth inhibitory effect of the anticancer agents; knocking-down trx-1 expression by small interfering RNA abrogated cell death induced by them. These compounds also inhibited the activity of Trx reductase that reduces oxidized Trx-1, whereas the Trx reductase inhibitor aurothiomalate synergized with NO-ASA in the induction of cell death. Our findings indicate that the Trx system mediates to a large extent redox-induced cell death in response to anticancer agents. This mechanism of action may be shared by more anticancer agents and deserves further assessment as a candidate mechanism for the pharmacologic control of cancer.

Decreasing peroxiredoxin II expression decreases glutathione, alters cell cycle distribution, and sensitizes glioma cells to ionizing radiation and H(2)O(2)

Glioblastomas are notorious for their resistance to ionizing radiation and chemotherapy. We hypothesize that this resistance to ionizing radiation is due, in part, to alterations in antioxidant enzymes. Here, we show that rat and human glioma cells overexpress the antioxidant enzyme peroxiredoxin II (Prx II). Glioma cells in which Prx II is decreased using shRNA exhibit increased hyperoxidation of the remaining cellular Prxs, suggesting that the redox environment is more oxidizing. Of interest, decreasing Prx II does not alter other antioxidant enzymes (i.e., catalase, GPx, Prx I, Prx III, CuZnSOD, and MnSOD). Analysis of the redox environment revealed that decreasing Prx II increased intracellular reactive oxygen species in 36B10 cells; extracellular levels of H(2)O(2) were also increased in both C6 and 36B10 cells. Treatment with H(2)O(2) led to a further elevation in intracellular reactive oxygen species in cells where Prx II was decreased. Decreasing Prx II expression in glioma cells also reduced clonogenic cell survival following exposure to ionizing radiation and H(2)O(2). Furthermore, lowering Prx II expression decreased intracellular glutathione and resulted in a significant decline in glutathione reductase activity, suggesting a possible mechanism for the observed increased sensitivity to oxidative insults. Additionally, decreasing Prx II expression increased cell cycle doubling times, with fewer cells distributed to S phase in C6 glioma cells and more cells redistributed to the most radiosensitive phase of the cell cycle, G2/M, in 36B10 glioma cells. These findings support the hypothesis that inhibiting Prx II sensitizes glioma cells to oxidative stress, presenting Prxs as potential therapeutic targets.

Cytokinesis-blocked micronucleus cytome assay biomarkers identify lung cancer cases amongst smokers

The multi-endpoint cytokinesis-blocked micronucleus assay is used for assessing chromosome aberrations. We have recently reported that this assay is extremely sensitive to genetic damage caused by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and that the binucleated cells with micronuclei, nucleoplasmic bridges, and nuclear buds in lymphocytes (chromosome damage endpoints measured by the assay) are strong predictors of lung cancer risk. In the current study, we refined our analysis to include toxicity endpoints (micronuclei in mononucleated cells, apoptosis, necrosis, and nuclear division index) to investigate the benefit of including these variables on improving the predictive value of the assay. Baseline and NNK-induced micronuclei in mononucleated cells were significantly higher in patients (n = 139) than controls (n = 130; P < 0.001). Baseline apoptosis was higher among cases; however, the controls showed a significant higher fold increase in NNK-induced apoptosis compared with baseline (P < 0.001). Principal components analysis was used to derive a summary measure for all endpoints and calculate the positive predictive value (PPV) and negative predictive value (NPV) for disease status. First principal component for NNK-induced chromosome damage endpoints (binucleated cells with micronuclei, nucleoplasmic bridges, and nuclear buds) had an area under the curve = 97.9 (95% confidence interval, 95.9-99.0), PPV = 94.8, and NPV = 92.6. The discriminatory power improved when micronuclei in mononucleated cells were included: area under the curve = 99.1 (95% confidence interval, 97.9-100.0), PPV = 98.7 and NPV = 95.6. The simplicity, rapidity, and sensitivity of the assay together with potential for automation make it a valuable tool for screening and prioritizing potential cases for intensive screening.

Transformation by retroviral vectors of bone marrow-derived mesenchymal cells induces mitochondria-dependent cAMP-sensitive reactive oxygen species production

Retroviral vectors are used in human gene therapy trials to stably introduce therapeutic genes in the genome of patients' cells. Their applicability, however, is frustrated by the limited viability of transformed cells and/or by risks linked to selection of oncogene-mutated clones. The reasons for these drawbacks are not yet completely understood. In this study, we show that LXSN-NeoR gene/interleukin-7-engineered mesenchymal stromal cells exhibited a marked enhancement of reactive oxygen species production compared with untransfected cells. This effect resulted to be independent on the product of the gene carried by the retroviral vehicle as it was reproducible in cells transfected with the empty vector alone. Stable transfection of mesenchymal stromal cells with the different retroviral vectors pBabe-puro and PINCO-puro and the lentiviral vector pSico PGK-puro caused similar redox imbalance, unveiling a phenomenon of more general impact. The enhanced production of reactive oxygen species over the basal level was attributable to mitochondrial dysfunction and brought back to altered activity of the NADH-CoQ oxidoreductase (complex I) of the respiratory chain. The oxidative stress in transfected mesenchymal stem cells was completely reversed by treatment with a cAMP analog, thus pointing to alteration in the protein kinase A-dependent signaling pathway of the host cell. Transfection of mesenchymal stromal cells with a PINCO-parental vector harboring the green fluorescent protein gene as selection marker in place of the puromycin-resistance gene resulted in no alteration of the redox phenotype. These novel findings provide insights and caveats to the applicability of cell- or gene-based therapies and indicate possible intervention to improve them. Disclosure of potential conflicts of interest is found at the end of this article.

Reactive oxygen species-mediated cyclin D1 degradation mediates tumor growth retardation in hypoxia, independently of p21cip1 and hypoxia-inducible factor

Cell growth arrest is an adaptation process for tumor survival in hypoxic environments. As proliferation is a very complicated and dynamic process, hypoxic growth arrest is not considered to be simply determined by a few molecules. Recently, several research groups have demonstrated that hypoxia-inducible factor (HIF)-1alpha plays a crucial role in hypoxia-induced cell-cycle arrest by inhibiting c-Myc and subsequently inducing p21(cip1) expression. However, we found that hypoxic growth arrest could occur even in p21-null cancer cells, and addressed the p21-independent process of cell-cycle arrest. We show that cyclin D1 was downregulated in various cancer cell lines under hypoxic conditions, which was independent of p21 and HIF-1 and -2alpha expression. It was also found that cyclin D1 was destabilized by the ubiquitin-proteasome system and this degradation process was highly activated by hypoxia. Moreover, antioxidants prevented the hypoxic degradation of cyclin D1 and hydrogen peroxide destabilized cyclin D1 in normoxia. Finally, we demonstrated that ectopic expression of cyclin D1 rescued hypoxic growth arrest in both p21+/+ and p21-/- HCT116 cells. Given the results, we here propose that reactive oxygen species-mediated cyclin D1 degradation contributes to tumor growth retardation in hypoxic environments.

Redox regulation of cell survival

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play important roles in regulation of cell survival. In general, moderate levels of ROS/RNS may function as signals to promote cell proliferation and survival, whereas severe increase of ROS/RNS can induce cell death. Under physiologic conditions, the balance between generation and elimination of ROS/RNS maintains the proper function of redox-sensitive signaling proteins. Normally, the redox homeostasis ensures that the cells respond properly to endogenous and exogenous stimuli. However, when the redox homeostasis is disturbed, oxidative stress may lead to aberrant cell death and contribute to disease development. This review focuses on the roles of key transcription factors, signal-transduction pathways, and cell-death regulators in affecting cell survival, and how the redox systems regulate the functions of these molecules. The current understanding of how disturbance in redox homeostasis may affect cell death and contribute to the development of diseases such as cancer and degenerative disorders is reviewed. We also discuss how the basic knowledge on redox regulation of cell survival can be used to develop strategies for the treatment or prevention of those diseases.