A redox cycle within the cell cycle: ring in the old with the new

Functional interaction of Ugene and EBV infection mediates tumorigenic effects

Epstein-Barr virus (EBV) infection is associated with many human neoplasms, in which EBV-derived latent membrane protein-1 (LMP1) appears to be critical, but its exact oncogenic mechanism remains to be defined. To this end, our initial microarray analyses identified a LMP1-inducible gene, Ugene, originally characterized as a binding partner for uracil DNA glycosylase 2, which is highly expressed in malignant colon cancer. In this report, it was found that Ugene, designated herein as LMP1-induced protein (LMPIP), was induced, in a time-dependent manner, in EBV-infected peripheral blood mononuclear cells and LMP1-transfected 293 cells. Functionally, when compared with mock-transfected cells, overexpression of LMPIP in nasopharyngeal carcinoma (NPC) cell lines resulted in a decrease in reactive oxygen species production and maintained mitochondria membrane potential (Δψ) loss induced by H(2)O(2). The NPC cells transfected with LMPIP also showed a decrease in G1 population and an increase in the cell population in sub-G1 and multiploid phase, concomitant with increased levels of cell cycle activators, including cyclin D1 and CDK4. In contrast, silencing of LMPIP expression in the NPC tumor cell lines with short hairpin RNA interference revealed significantly decreased cell population at G1/S phase, while the number of cells in multiploid phase increased. Significantly, NPC cells with LMPIP knock-down also showed a decrease in tumorigenic and transforming activity induced by ectopic LMP1 expression, as determined by analyses of soft agar foci and tumor size in nude mice. Further, elevated LMPIP expression was also noted in cytoplasm and nuclei in EBV-infected NPC tumor cell mass and non-EBV-infected tumor cell lines. These results suggested that LMPIP may have an important mediator role in EBV-mediated neoplasm and may serve as a new target for therapy of tumors induced by EBV infection.

Recruitment of glutathione into the nucleus during cell proliferation adjusts whole-cell redox homeostasis in Arabidopsis thaliana and lowers the oxidative defence shield

Cellular redox homeostasis and signalling are important in progression of the eukaryotic cell cycle. In animals, the low-molecular-weight thiol tripeptide glutathione (GSH) is recruited into the nucleus early in the cell proliferation cycle. To determine whether a similar process occurs in plants, we studied cell proliferation in Arabidopsis thaliana. We show that GSH co-localizes with nuclear DNA during the proliferation of A. thaliana cells in culture. Moreover, GSH localization in the nucleus was observed in dividing pericycle cells of the lateral root meristem. There was pronounced accumulation of GSH in the nucleus at points in the growth cycle at which a high percentage of the cells were in G(1) phase, as identified by flow cytometry and marker transcripts. Recruitment of GSH into the nucleus led to a high abundance of GSH in the nucleus (GSHn) and severe depletion of the cytoplasmic GSH pool (GSHc). Sequestration of GSH in the nucleus was accompanied by significant decreases in transcripts associated with oxidative signalling and stress tolerance, and an increase in the abundance of hydrogen peroxide, an effect that was enhanced when the dividing cells were treated with salicylic acid. Total cellular GSH and the abundance of GSH1 and GSH2 transcripts increased after the initial recruitment of GSH into the nucleus. We conclude that GSH recruitment into the nucleus during cell proliferation has a profound effect on the whole-cell redox state. High GSHn levels trigger redox adjustments in the cytoplasm, favouring decreased oxidative signalling and enhanced GSH synthesis.

Enhanced expression of cyclins and cyclin-dependent kinases in aniline-induced cell proliferation in rat spleen

Aniline exposure is associated with toxicity to the spleen leading to splenomegaly, hyperplasia, fibrosis and a variety of sarcomas of the spleen on chronic exposure. In earlier studies, we have shown that aniline exposure leads to iron overload, oxidative stress and activation of redox-sensitive transcription factors, which could regulate various genes leading to a tumorigenic response in the spleen. However, molecular mechanisms leading to aniline-induced cellular proliferation in the spleen remain largely unknown. This study was, therefore, undertaken on the regulation of G1 phase cell cycle proteins (cyclins), expression of cyclin-dependent kinases (CDKs), phosphorylation of retinoblastoma protein (pRB) and cell proliferation in the spleen, in an experimental condition preceding a tumorigenic response. Male SD rats were treated with aniline (0.5 mmol/kg/day via drinking water) for 30 days (controls received drinking water only), and splenocyte proliferation, protein expression of G1 phase cyclins, CDKs and pRB were measured. Aniline treatment resulted in significant increases in splenocyte proliferation, based on cell counts, cell proliferation markers including proliferating cell nuclear antigen (PCNA), nuclear Ki67 protein (Ki67) and minichromosome maintenance (MCM), MTT assay and flow cytometric analysis. Western blot analysis of splenocyte proteins from aniline-treated rats showed significantly increased expression of cyclins D1, D2, D3 and E, as compared to the controls. Similarly, real-time PCR analysis showed significantly increased mRNA expression for cyclins D1, D2, D3 and E in the spleens of aniline-treated rats. The overexpression of these cyclins was associated with increases in the expression of CDK4, CDK6, CDK2 as well as phosphorylation of pRB protein. Our data suggest that increased expression of cyclins, CDKs and phosphorylation of pRB protein could be critical in cell proliferation, and may contribute to aniline-induced tumorigenic response in the spleen.

Redox control of protein-DNA interactions: from molecular mechanisms to significance in signal transduction, gene expression, and DNA replication

Protein-DNA interactions play a key role in the regulation of major cellular metabolic pathways, including gene expression, genome replication, and genomic stability. They are mediated through the interactions of regulatory proteins with their specific DNA-binding sites at promoters, enhancers, and replication origins in the genome. Redox signaling regulates these protein-DNA interactions using reactive oxygen species and reactive nitrogen species that interact with cysteine residues at target proteins and their regulators. This review describes the redox-mediated regulation of several master regulators of gene expression that control the induction and suppression of hundreds of genes in the genome, regulating multiple metabolic pathways, which are involved in cell growth, development, differentiation, and survival, as well as in the function of the immune system and cellular response to intracellular and extracellular stimuli. It also discusses the role of redox signaling in protein-DNA interactions that regulate DNA replication. Specificity of redox regulation is discussed, as well as the mechanisms providing several levels of redox-mediated regulation, from direct control of DNA-binding domains through the indirect control, mediated by release of negative regulators, regulation of redox-sensitive protein kinases, intracellular trafficking, and chromatin remodeling.

Regulatory T cells interfere with glutathione metabolism in dendritic cells and T cells

Naturally occurring CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) suppress proliferation of CD4(+)CD25(-) effector T cells (Teffs) by mechanisms that are not well understood. We have previously demonstrated a novel mechanism of Treg suppression, i.e. interference with extracellular redox remodeling that occurs during activation of T cells by dendritic cells. In this study, we demonstrate that Treg-mediated redox perturbation is antigen-dependent but not antigen-specific, is CTLA-4-dependent, and requires cell-cell contact. Furthermore, we show that Tregs use multiple strategies for extracellular redox remodeling, including diminished GSH synthesis in dendritic cells via decreased expression of γ-glutamylcysteine synthetase, the limiting enzyme for GSH synthesis. Tregs also consume extracellular cysteine and partition it more proficiently to the oxidation product (sulfate), whereas Teffs divert more of the cysteine pool toward protein and GSH synthesis. Tregs appear to block GSH redistribution from the nucleus to the cytoplasm in Teffs, which is abrogated by the addition of exogenous cysteine. Together, these data provide novel insights into modulation of sulfur-based redox metabolism by Tregs, leading to suppression of T cell activation and proliferation.

A nuclear glutathione cycle within the cell cycle

The complex antioxidant network of plant and animal cells has the thiol tripeptide GSH at its centre to buffer ROS (reactive oxygen species) and facilitate cellular redox signalling which controls growth, development and defence. GSH is found in nearly every compartment of the cell, including the nucleus. Transport between the different intracellular compartments is pivotal to the regulation of cell proliferation. GSH co-localizes with nuclear DNA at the early stages of proliferation in plant and animal cells. Moreover, GSH recruitment and sequestration in the nucleus during the G1- and S-phases of the cell cycle has a profound impact on cellular redox homoeostasis and on gene expression. For example, the abundance of transcripts encoding stress and defence proteins is decreased when GSH is sequestered in the nucleus. The functions of GSHn (nuclear GSH) are considered in the present review in the context of whole-cell redox homoeostasis and signalling, as well as potential mechanisms for GSH transport into the nucleus. We also discuss the possible role of GSHn as a regulator of nuclear proteins such as histones and PARP [poly(ADP-ribose) polymerase] that control genetic and epigenetic events. In this way, a high level of GSH in the nucleus may not only have an immediate effect on gene expression patterns, but also contribute to how cells retain a memory of the cellular redox environment that is transferred through generations.

Cactus pear extracts induce reactive oxygen species production and apoptosis in ovarian cancer cells

The protective effect of natural products such as fruits and vegetables against cancer has attracted great attention because of their fewer side effects and therefore, potentially greater safety. We have previously reported that cactus pear mixture aqueous extract (CME) reduces gynecologic cancer cells growth by inducting apoptosis. This study aimed to elucidate the cellular pathway(s) triggered by CME in cancer cells. Normal, immortalized ovarian and ovarian cancer cells (OVCA420, SKOV3) were treated with 5 and 10% CME. After 2 days of treatment, immortalized cells treated with 10% CME accumulated more ROS than untreated cells, whereas cancer cells cultured with 5% and 10% CME exhibited a dramatic increase of reactive oxygen species (ROS). Greater levels of DNA fragmentation, together with a perturbed expression of apoptotic-related (Bax, Bad, caspase 3, Bcl2, p53, and p21) and ROS-sensitive (NF-kappaB, c-jun/c-fos) genes were observed in the treated cancer cells. After three days of treatment, the NF-kappaB and p-/SAPK/JNK expressions were decreased, whereas p-AKT was upregulated. The CME significantly induced apoptosis in cancer cells. The results suggest an inhibitory effect of Arizona CME on cancer cell growth through the accumulation of intracellular ROS, which may activate a cascade of reactions leading to the apoptosis.

Garlic components inhibit angiotensin II-induced cell-cycle progression and migration: Involvement of cell-cycle inhibitor p27(Kip1) and mitogen-activated protein kinase

Garlic has been used for prevention and treatment of hypertension; however, the molecular mechanisms of garlic's effects remain to be elucidated. In this study, the mechanisms of the in vitro effect of organosulphur compounds derived from garlic on growth and migration of cultured aortic smooth muscle cells isolated from spontaneously hypertensive rats were investigated. We demonstrated that allyl methyl sulphide (AMS) and diallyl sulphide (DAS) inhibited aortic smooth muscle cell angiotensin II-stimulated cell-cycle progression and migration. Neither cell viability nor annexin-V-binding analysis revealed cytotoxic effects of both organosulphur compounds at the used concentrations. Instead, their inhibitory effects were associated to the prevention of the cell-cycle inhibitor p27(Kip1) (p27) downregulation and the reduction of extracellular signal-regulated kinase 1/2 phosphorylation. When we assessed the antioxidant activity of AMS and DAS, we found that both organosulphur compounds inhibited angiotensin II-reactive oxygen species generation. Our findings show that AMS and DAS, compounds derivate from garlic, could be effective antioxidants targeted at the arterial remodelling seen in hypertension.

Polychlorinated biphenyl induced ROS signaling delays the entry of quiescent human breast epithelial cells into the proliferative cycle

Polychlorinated biphenyls (PCBs) are environmental chemical contaminants that can produce reactive oxygen species (ROS) by autoxidation of dihydroxy-PCBs and redox-cycling. We investigate the hypothesis that PCB induced perturbations in ROS signaling regulate the entry of quiescent cells into the proliferative cycle. Quiescent MCF-10A human breast epithelial cells were incubated with 0-3 micromolar of 2-(4-chlorophenyl)benzo-1,4-quinone (4-Cl-BQ), 2, 2', 4, 4', 5, 5'-hexachlorobiphenyl (PCB 153), and Aroclor 1254 for 4 days. Cells were replated at a lower density and analyzed for cell cycle phase distributions, ROS levels, MnSOD expression, and cyclin D1 protein levels. Quiescent cells incubated with 4-Cl-BQ showed the maximal delay in entering S phase. This delay was associated with a decrease in MnSOD activity, protein and mRNA levels, and an increase in cellular ROS levels. Results from the mRNA turnover assay showed that the 4-Cl-BQ treatment selectively enhanced the degradation of the 4.2kb MnSOD transcript, while the half-life of the 1.5 kb transcript did not change. Accumulation of cyclin D1 protein levels in replated cells was suppressed in cells treated with 4-Cl-BQ. Pretreatment of quiescent cells with polyethylene glycol-conjugated superoxide dismutase and catalase suppressed 4-Cl-BQ induced increase in ROS levels, which was consistent with an increase in cyclin D1 accumulation, and entry into S phase. These results showed 4-Cl-BQ induced perturbations in ROS signaling inhibit the entry of quiescent cells into S phase.

Characterization of nuclear factors modulating the apolipoprotein D promoter during growth arrest: implication of PARP-1, APEX-1 and ERK1/2 catalytic activities

Human Apolipoprotein D (apoD) is upregulated under several stress conditions and pathological situations such as neurodegenerative diseases and cancers. We previously showed that apoD mRNA expression is induced in growth-arrested cells and demonstrated the specific binding of nuclear proteins to the region −514 to −475 of the promoter. Such region contains a pair of Serum Responsive Elements (SRE), an Ets-Binding Site (EBS) and a Glucocorticoid Responsive Element (GRE). In this study, we show that Parp-1, HnRNP-U, CBF-A, BUB-3, Kif4, APEX-1 and Ifi204 bind these regulatory elements of the apoD promoter. Specific binding of HnRNP-U and Parp-1 was confirmed by Electrophoretic Mobility Shift Assay (EMSA). In a biotin pull-down assay, Kif4 and BUB-3 bind preferentially the SRE1 and the EBS-GRE sites, respectively, while APEX-1 seems recruited indirectly to these elements. We found that the mRNA expression of some of these binding factors is upregulated in growth-arrested cells and that these proteins also transactivate the apoD promoter. In agreement with these results, mutants of APEX-1 and of Parp-1 defective for their DNA-binding and catalytic activities could not transactivate the promoter. The knockdown of Parp-1 and HnRNP-U and the use of specific inhibitors of MEK1/2 and of Parp-1 also inhibited the induction of apoD gene expression. Moreover, ERK1/2 was found activated in a biphasic manner post serum-starvation and the inhibition of Parp-1 causes a sustained activation of ERK2 but not ERK1 for up to 2 h. Altogether, these findings demonstrate the importance of Parp-1, APEX-1 and ERK1/2 catalytic activities in the growth arrest-induced apoD gene expression.

Redox remodeling as an immunoregulatory strategy

Activation and proliferation of T cells require a reducing extracellular microenvironment in the immune synapse that is provided by antigen presenting cells, especially dendritic cells. Stimulation of dendritic cells by T cells activates the NF-kappaB pathway in dendritic cells and induces an antioxidant response. It also enhances system x(c)(-)-dependent cystine uptake, leading to enhanced glutathione synthesis, export, and, finally, degradation to cysteine outside the cell. Accumulation of extracellular cysteine supports glutathione synthesis in T cells while also leading to a more reducing redox potential that is needed for T cell proliferation. Naturally occurring regulatory T cells, a suppressor subpopulation of T cells, prevent autoimmune diseases and maintain peripheral tolerance by suppressing self-reactive effector T cells. They also suppress beneficial immune responses to parasites, viruses, and tumors. However, their mechanism of suppression is still not fully understood. Recently, we have found that inhibition by regulatory T cells of dendritic cell-induced extracellular redox remodeling is a component of the regulatory T cell suppression mechanism. In this review, we describe recent advances in our understanding of redox regulation and signaling in the adaptive immune system with a focus on T cell activation by dendritic cells. The role of regulatory T cells in perturbing redox remodeling by dendritic cells and its implications as a general regulatory T cell suppression mechanism are discussed.

Chloride intracellular channel 1 (CLIC1): Sensor and effector during oxidative stress

Oxidative stress, characterized by overproduction of reactive oxygen species (ROS), is a major feature of several pathological states. Indeed, many cancers and neurodegenerative diseases are accompanied by altered redox balance, which results from dysregulation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. In this review, we consider the role of the intracellular chloride channel 1 (CLIC1) in microglial cells during oxidative stress. Following microglial activation, CLIC1 translocates from the cytosol to the plasma membrane where it promotes a chloride conductance. The resultant anionic current balances the excess charge extruded by the active NADPH oxidase, supporting the generation of superoxide by the enzyme. In this scenario, CLIC1 could be considered to act as both a second messenger and an executor.

Dihydroceramide desaturase activity is modulated by oxidative stress

Oxidative stress has been implicated previously in the regulation of ceramide metabolism. In the present study, its effects on dihydroceramide desaturase were investigated. To stimulate oxidative stress, HEK (human embyronic kidney)-293, MCF7, A549 and SMS-KCNR cells were treated with H2O2, menadione or tert-butylhydroperoxide. In all cell lines, an increase in dihydroceramide was observed upon oxidative stress as measured by LC (liquid chromatography)/MS. In contrast, total ceramide levels were relatively unchanged. Mechanistically, dihydroceramide desaturase activity was measured by an in situ assay and decreased in a time- and dose-dependent fashion. Interestingly, no detectable changes in the protein levels were observed, suggesting that oxidative stress does not induce degradation of dihydroceramide desaturase. In summary, oxidative stress leads to potent inhibition of dihydroceramide desaturase resulting in significant elevation in dihydroceramide levels in vivo.

Redox control of the cell cycle in health and disease

The cellular oxidation and reduction (redox) environment is influenced by the production and removal of reactive oxygen species (ROS). In recent years, several reports support the hypothesis that cellular ROS levels could function as ''second messengers'' regulating numerous cellular processes, including proliferation. Periodic oscillations in the cellular redox environment, a redox cycle, regulate cell-cycle progression from quiescence (G(0)) to proliferation (G(1), S, G(2), and M) and back to quiescence. A loss in the redox control of the cell cycle could lead to aberrant proliferation, a hallmark of various human pathologies. This review discusses the literature that supports the concept of a redox cycle controlling the mammalian cell cycle, with an emphasis on how this control relates to proliferative disorders including cancer, wound healing, fibrosis, cardiovascular diseases, diabetes, and neurodegenerative diseases. We hypothesize that reestablishing the redox control of the cell cycle by manipulating the cellular redox environment could improve many aspects of the proliferative disorders.

The cell cycle is a redox cycle: linking phase-specific targets to cell fate

Reactive oxygen species (ROS) regulate the strength and duration of signaling through redox-dependent signal transduction pathways via the cyclic oxidation/reduction of cysteine residues in kinases, phosphatases, and other regulatory factors. Signaling circuits may be segregated in organelles or other subcellular domains with distinct redox states, permitting them to respond independently to changes in the oxidation state of two major thiol reductants, glutathione and thioredoxin. Studies in yeast, and in complex eukaryotes, show that oscillations in oxygen consumption, energy metabolism, and redox state are intimately integrated with cell cycle progression. Because signaling pathways play specific roles in different phases of the cell cycle and the hierarchy of redox-dependent regulatory checkpoints changes during cell cycle progression, the effects of ROS on cell fate vary during the cell cycle. In G1, ROS stimulate mitogenic pathways that control the activity of cyclin-dependent kinases (CDKs) and phosphorylation of the retinoblastoma protein (pRB), thereby regulating S-phase entry. In response to oxidative stress, Nrf2 and Foxo3a promote cell survival by inducing the expression of antioxidant enzymes and factors involved in cell cycle withdrawal, such as the cyclin-dependent kinase inhibitor (CKI) p27. In S phase, ROS induce S-phase arrest via PP2A-dependent dephosphorylation of pRB. In precancerous cells, unconstrained mitogenic signaling by activated oncogenes induces replication stress in S phase, which activates the DNA-damage response and induces cell senescence. A number of studies suggest that interactions of ROS with the G1 CDK/CKI network play a fundamental role in senescence, which is considered a barrier to tumorigenesis. Adaptive responses and loss of checkpoint proteins such as p53 and p16(INK4a) allow tumor cells to tolerate constitutive mitogenic signaling and enhanced production of ROS, leading to altered redox status in many fully transformed cells. Alterations in oxidant and energy metabolism of cancer cells have emerged as fertile ground for new therapeutic targets. The present challenge is to identify redox-dependent targets relevant to each cell cycle phase, to understand how these targets control fate decisions, and to describe the mechanisms that link metabolism to cell cycle progression.

Reversible and irreversible modifications of skeletal muscle proteins in a rat model of acute oxidative stress

Oxidative stress caused by an imbalance of the production of "reactive oxygen species" (ROS) and cellular scavenging systems is known to a play a key role in the development of various diseases and aging processes. Such elevated ROS levels can damage all components of cells, including proteins, lipids and DNA. Here, we study the influence of highly reactive ROS species on skeletal muscle proteins in a rat model of acute oxidative stress caused by X-ray irradiation at different time points. Protein preparations depleted for functional actin by polymerization were separated by gel electrophoresis in two dimensions by applying first non-reductive and then reductive conditions in SDS-PAGE. This diagonal redox SDS-PAGE revealed significant alterations to intra- and inter-molecular disulfide bridges for several proteins, but especially actin, creatine kinase and different isoforms of the myosin light chain. Though the levels of these reversible modifications were increased by oxidative stress, all proteins followed different kinetics. Moreover, a significant degree of protein was irreversibly oxidized (carbonylated), as revealed by western blot analyses performed at different time points.

Pterostilbene inhibits breast cancer in vitro through mitochondrial depolarization and induction of caspase-dependent apoptosis

BACKGROUND

Epidemiologic studies suggest that diets high in fruits and vegetables reduce cancer risk. Resveratrol, a compound present in grapes, has been shown to inhibit a variety of primary tumors. Pterostilbene, an analogue of resveratrol found in blueberries, has both antioxidant and antiproliferative properties. We hypothesized that pterostilbene would induce apoptosis and inhibit breast cancer cell growth in vitro.

METHODS

Breast cancer cells were treated with graduated doses of pterostilbene. Cell viability was measured by MTT assay. Apoptosis was evaluated via DNA fragmentation assay and TUNEL assay. Apo-ONE caspase-3/7 assay was used to evaluate caspase activity. Flow cytometry was used to evaluate mitochondrial depolarization, superoxide formation, and cell cycle. Student's t-test and two-way ANOVA with Bonferroni posttests were utilized for statistical analysis.

RESULTS

Pterostilbene decreased breast cancer cell viability in a concentration- and time-dependent manner. Pterostilbene treatment increased caspase-3/7 activity and apoptosis in both cell lines. Caspase-3/7 inhibitors completely reversed pterostilbene's effects on cell viability. Pterostilbene treatment triggered mitochondrial depolarization, increased superoxide anion, and caused alteration in cell cycle.

CONCLUSIONS

Pterostilbene treatment inhibits the growth of breast cancer in vitro through caspase-dependent apoptosis. Mitochondrial membrane depolarization and increased superoxide anion may contribute to the activation downstream effector caspases. Caspase inhibition leads to complete reversal of pterostilbene's effect on cell viability. Further in vitro mechanistic studies and in vivo experiments are warranted to determine its potential for the treatment of breast cancer.

The depletion of nuclear glutathione impairs cell proliferation in 3t3 fibroblasts

Background

Glutathione is considered essential for survival in mammalian cells and yeast but not in prokaryotic cells. The presence of a nuclear pool of glutathione has been demonstrated but its role in cellular proliferation and differentiation is still a matter of debate.

Principal Findings

We have studied proliferation of 3T3 fibroblasts for a period of 5 days. Cells were treated with two well known depleting agents, diethyl maleate (DEM) and buthionine sulfoximine (BSO), and the cellular and nuclear glutathione levels were assessed by analytical and confocal microscopic techniques, respectively. Both agents decreased total cellular glutathione although depletion by BSO was more sustained. However, the nuclear glutathione pool resisted depletion by BSO but not with DEM. Interestingly, cell proliferation was impaired by DEM, but not by BSO. Treating the cells simultaneously with DEM and with glutathione ethyl ester to restore intracellular GSH levels completely prevented the effects of DEM on cell proliferation.

Conclusions

Our results demonstrate the importance of nuclear glutathione in the control of cell proliferation in 3T3 fibroblasts and suggest that a reduced nuclear environment is necessary for cells to progress in the cell cycle.

Implications of endoplasmic reticulum stress, the unfolded protein response and apoptosis for molecular cancer therapy. Part II: targeting cell cycle events, caspases, NF-κB and the proteasome

BACKGROUND

Endoplasmic reticulum stress (ERS), the unfolded protein response (UPR) and apoptosis signal transduction pathways are fundamental to normal cellular homeostasis and survival, but are exploited by cancer cells to promote the cancer phenotype.

OBJECTIVE

Collateral activation of ERS and UPR role players impact on cell growth, cell cycle arrest or apoptosis, genomic stability, tumour initiation and progression, tumour aggressiveness and drug resistance. An understanding of these processes affords promising prospects for specific cancer drug targeting of the ERS, UPR and apoptotic pathways.

METHOD

This review (Part II of II) brings forward the latest developments relevant to the molecular connections among cell cycle regulators, caspases, NF-κB, and the proteasome with ERS and UPR signalling cascades, their functions in apoptosis induction, apoptosis resistance and oncogenesis, and how these relationships can be exploited for targeted cancer therapy.

CONCLUSION

Overall, ERS, the UPR and apoptosis signalling cascades (the molecular therapeutic targets) and the development of drugs that attack these targets signify a success story in cancer drug discovery, but a more reductionist approach is necessary to determine the precise molecular switches that turn on antiapoptotic and pro-apoptotic programmes.

Differential expression of NADPH oxidases in megakaryocytes and their role in polyploidy

Megakaryocytes (MKs) undergo an endomitotic cell cycle, leading to polyploidy. We examined the expression of the flavoproteins and oxidative stress-promoting enzymes, NADPH oxidases (Nox's), in MKs because of their known role in promoting the cell cycle. Although the expression of Nox isoforms varies between cell types, they are induced at the mRNA level by mitogenic stimuli. Western blotting or reverse transcription-polymerase chain reaction of purified mouse MKs isolated from thrombopoietin (TPO)-treated bone marrow (BM) cultures indicated high expression of Nox1, a weak expression of Nox4, and no significant expression of Nox2. Immunofluorescence of freshly isolated MKs confirmed strong expression of Nox1 in one-third of MKs, whereas Nox1 staining was detected in nearly all MKs in TPO-stimulated BM cultures. Treatment of mouse BM cultures with Nox inhibitors resulted in accumulation of MKs with low DNA content levels and significant reduction of higher ploidy MKs. Purified, Nox-inhibited MKs showed a notable decrease in the level of the G(1) phase cyclin E, a cyclin associated with MK polyploidy, and its up-regulation restored most of the effect of Nox inhibitors. Hence, this study shows the expression of Nox isoforms in MKs and highlights a potential role of flavoproteins in promoting polyploidization in this lineage.

Lifestyle-induced metabolic inflexibility and accelerated ageing syndrome: insulin resistance, friend or foe?

The metabolic syndrome may have its origins in thriftiness, insulin resistance and one of the most ancient of all signalling systems, redox. Thriftiness results from an evolutionarily-driven propensity to minimise energy expenditure. This has to be balanced with the need to resist the oxidative stress from cellular signalling and pathogen resistance, giving rise to something we call 'redox-thriftiness'. This is based on the notion that mitochondria may be able to both amplify membrane-derived redox growth signals as well as negatively regulate them, resulting in an increased ATP/ROS ratio. We suggest that 'redox-thriftiness' leads to insulin resistance, which has the effect of both protecting the individual cell from excessive growth/inflammatory stress, while ensuring energy is channelled to the brain, the immune system, and for storage. We also suggest that fine tuning of redox-thriftiness is achieved by hormetic (mild stress) signals that stimulate mitochondrial biogenesis and resistance to oxidative stress, which improves metabolic flexibility. However, in a non-hormetic environment with excessive calories, the protective nature of this system may lead to escalating insulin resistance and rising oxidative stress due to metabolic inflexibility and mitochondrial overload. Thus, the mitochondrially-associated resistance to oxidative stress (and metabolic flexibility) may determine insulin resistance. Genetically and environmentally determined mitochondrial function may define a 'tipping point' where protective insulin resistance tips over to inflammatory insulin resistance. Many hormetic factors may induce mild mitochondrial stress and biogenesis, including exercise, fasting, temperature extremes, unsaturated fats, polyphenols, alcohol, and even metformin and statins. Without hormesis, a proposed redox-thriftiness tipping point might lead to a feed forward insulin resistance cycle in the presence of excess calories. We therefore suggest that as oxidative stress determines functional longevity, a rather more descriptive term for the metabolic syndrome is the 'lifestyle-induced metabolic inflexibility and accelerated ageing syndrome'. Ultimately, thriftiness is good for us as long as we have hormetic stimuli; unfortunately, mankind is attempting to remove all hormetic (stressful) stimuli from his environment.

Upregulation of Nox4 in the aging vasculature and its association with smooth muscle cell polyploidy

Our recent reports indicated that polyploidization of aortic vascular smooth muscle cells (VSMC) serves as a biomarker for aging, and that the polyploid state is linked to a higher incidence of senescence in vivo. Here, we found that NADPH oxidase 4 (Nox4) expression is augmented in VSMC from aortas of old rats and that Nox4 levels are increased in polyploid VSMC in comparison to diploid cells in vivo. Seeking to determine if Nox4 upregulation plays a causal role in the accumulation of polyploid cells, we performed ploidy analysis on primary VSMC transduced with Nox4 adenovirus. We observed a consistent accumulation of polyploid cells and a concomitant decrease in the percentage of diploid cells in Nox4 overexpressing cells in comparison to controls or to cells overexpressing dominant negative Nox4. Further exploration of this phenomenon in VSMC cultures identified a Nox4-induced decrease in the chromosome passenger protein, survivin, whose absence and mislocalization during polyploidization was previously shown to induce VSMC polyploidy. Taken together, our study is the first to show increased Nox4 levels in VSMC during aging, and to demonstrate its role in induction of polyploidy in this lineage.

Aminoguanidine impedes human pancreatic tumor growth and metastasis development in nude mice

AIM: To study the action of aminoguanidine on pancreatic cancer xenografts in relation to cell proliferation, apoptosis, redox status and vascularization.

METHODS: Xenografts of PANC-1 cells were developed in nude mice. The animals were separated into two groups: control and aminoguanidine treated. Tumor growth, survival and appearance of metastases were determined in vivo in both groups. Tumors were excised and ex vivo histochemical studies were performed. Cell growth was assessed by Ki-67 expression. Apoptosis was studied by intratumoral expression of B cell lymphoma-2 protein (Bcl-2) family proteins and Terminal deoxynucleotidyl transferase biotin-dUTP Nick End Labeling (Tunel). Redox status was evaluated by the expression of endothelial nitric oxide synthase (eNOS), catalase, copper-zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD) and glutathione peroxidase (GPx). Finally, vascularization was determined by Massons trichromic staining, and by VEGF and CD34 expression.

RESULTS: Tumor volumes after 32 d of treatment by aminoguanidine (AG) were significantly lower than in control mice (P < 0.01). Median survival of AG mice was significantly greater than control animals (P < 0.01). The appearance of both homolateral and contralateral palpable metastases was significantly delayed in AG group. Apoptotic cells, intratumoral vascularization (trichromic stain) and the expression of Ki-67, Bax, eNOS, CD34, VEGF, catalase, CuZnSOD and MnSOD were diminished in AG treated mice (P < 0.01), while the expression of Bcl-2 and GPx did not change.

CONCLUSION: The antitumoral action of aminoguanidine is associated with decreased cell proliferation, reduced angiogenesis, and reduced expression of antioxidant enzymes.

Low-intensity light therapy: exploring the role of redox mechanisms

Low-intensity light therapy (LILT) appears to be working through newly recognized photoacceptor systems. The mitochondrial electron transport chain has been shown to be photosensitive to red and near-infrared (NIR) light. Although the underlying mechanisms have not yet been clearly elucidated, mitochondrial photostimulation has been shown to increase ATP production and cause transient increases in reactive oxygen species (ROS). In some cells, this process appears to participate in reduction/oxidation (redox) signaling. Redox mechanisms are known to be involved in cellular homeostasis and proliferative control. In plants, photostimulation of the analogous photosynthetic electron transport chain leads to redox signaling known to be integral to cellular function. In gene therapy research, ultraviolet lasers are being used to photostimulate cells through a process that also appears to involve redox signaling. It seems that visible and near visible low-intensity light can be used to modulate cellular physiology in some nonphotosynthetic cells, acting through existing redox mechanisms of cellular physiology. In this manner, LILT may act to promote proliferation and/or cellular homeostasis. Understanding the role of redox state and signaling in LILT may be useful in guiding future therapies, particularly in conditions associated with pro-oxidant conditions.

Late ROS accumulation and radiosensitivity in SOD1-overexpressing human glioma cells

This study investigates the hypothesis that CuZn superoxide dismutase (SOD1) overexpression confers radioresistance to human glioma cells by regulating the late accumulation of reactive oxygen species (ROS) and the G(2)/M-checkpoint pathway. U118-9 human glioma cells (wild type, neo vector control, and stably overexpressing SOD1) were irradiated (0-10 Gy) and assayed for cell survival, cellular ROS levels, cell-cycle-phase distributions, and cyclin B1 expression. SOD1-overexpressing cells were radioresistant compared to wild-type (wt) and neo vector control (neo) cells. Irradiated wt and neo cells showed a significant increase (approximately twofold) in DHE fluorescence beginning at 2 days postirradiation, which remained elevated at 8 days postirradiation. Interestingly, the late accumulation of ROS was suppressed in irradiated SOD1-overexpressing cells. The increase in ROS levels was followed by a decrease in cell growth and viability and an increase in the percentage of cells with sub-G(1) DNA content. SOD1 overexpression enhanced radiation-induced G(2) accumulation within 24 h postirradiation, which was accompanied by a decrease in cyclin B1 mRNA and protein levels. These results support the hypothesis that long after radiation exposure a "metabolic redox response" regulates radiosensitivity of human glioma cells.

Catalase ameliorates polychlorinated biphenyl-induced cytotoxicity in nonmalignant human breast epithelial cells

Polychlorinated biphenyls (PCBs) are environmental chemical contaminants believed to adversely affect cellular processes. We investigated the hypothesis that PCB-induced changes in the levels of cellular reactive oxygen species (ROS) induce DNA damage resulting in cytotoxicity. Exponentially growing cultures of human nonmalignant breast epithelial cells (MCF10A) were incubated with PCBs for 3 days and assayed for cell number, ROS levels, DNA damage, and cytotoxicity. Exposure to 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153) or 2-(4-chlorophenyl)benzo-1,4-quinone (4-Cl-BQ), a metabolite of 4-chlorobiphenyl (PCB3), significantly decreased cell number and MTS reduction and increased the percentage of cells with sub-G1 DNA content. Results from electron paramagnetic resonance (EPR) spectroscopy showed a 4-fold increase in the steady-state levels of ROS, which was suppressed in cells pretreated with catalase. EPR measurements in cells treated with 4-Cl-BQ detected the presence of a semiquinone radical, suggesting that the increased levels of ROS could be due to the redox cycling of 4-Cl-BQ. A dose-dependent increase in micronuclei frequency was observed in PCB-treated cells, consistent with an increase in histone 2AX phosphorylation. Treatment of cells with catalase blunted the PCB-induced increase in micronuclei frequency and H2AX phosphorylation that was consistent with an increase in cell survival. Our results demonstrate a PCB-induced increase in cellular levels of ROS causing DNA damage, resulting in cell killing.

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.

The role of the RB tumour suppressor pathway in oxidative stress responses in the haematopoietic system

Exposure to pro-oxidants and defects in the repair of oxidative base damage are associated with disease and ageing and also contribute to the development of anaemia, bone marrow failure and haematopoietic malignancies. This Review assesses emerging data indicative of a specific role for the RB tumour suppressor pathway in the response of the haematopoietic system to oxidative stress. This is mediated through signalling pathways that involve DNA damage sensors, forkhead box O (Foxo) transcription factors and p38 mitogen-activated protein kinases and has downstream consequences for cell cycle progression, antioxidant capacity, mitochondrial mass and cellular metabolism.

The involvement of reactive oxygen species (ROS) in the cell cycle activation (G(0)-to-G(1) transition) of plant cells

Reactive oxygen species (ROS) are involved in various cellular processes in plants. Among those, resistance to abiotic stress, defence mechanisms and cell expansion have been intensively studied during the last years. We recently demonstrated that ROS, in concert with auxin, have a role in cell cycle activation of differentiated leaf cells.1 In this addendum we provide further evidence to show that oxidative stress/ROS accelerate auxin-mediated cell cycle entry (G(0)-to-G(1)) and may have a positive effect on the plant cell cycle machinery. A generalized model for concentration-dependent synergistic effect of auxin and ROS on differentiated plant cells is also shown.

Melatonin uptake in prostate cancer cells: intracellular transport versus simple passive diffusion

Melatonin, an indole mainly synthesized in the pineal gland during the dark phase, plays a role as an endogenous antioxidant and an anticancer agent in many tumors. Melatonin, at pharmacological concentrations, inhibits cell growth and induces neuroendocrine differentiation in prostate cancer cells. Classically it has been considered that melatonin enters freely into most of cells by passive diffusion through the cell membrane; however, there are few studies examining how melatonin is taken up by cancer cells. The aim of the present paper was to study the uptake of melatonin into human androgen-dependent LNCaP and androgen-independent PC-3 prostate cancer cells. Increased concentrations of melatonin induced a rapid and transitory rise in intracellular melatonin content in both cell types, with a peak of maximal content at 6 hr after melatonin addition, following a rhythmic uptake; melatonin was found in both cytoplasm and nuclear fractions. Inhibition of protein or RNA synthesis partially blocked melatonin uptake in both cell lines. Interestingly, melatonin pulse incubation led to a higher uptake after four cycles of pulse incubation. Neither extracellular Ca(2+)/K(+) alterations nor the presence of bovine serum albumin or charcoal-stripped serum modified the profile of melatonin uptake. On the contrary, chemical binding of melatonin to BSA totally prevented melatonin from entering into cells. The present data support the hypothesis that a facilitated diffusion or an active process rather than simple passive diffusion through the cell membrane is the major mechanism in melatonin uptake by prostate cancer cells and it accounts for its intracellular concentration (350 nM-3.3 microM), which is related to its anti-tumor actions.

Cell cycle regulation by oncogenic tyrosine kinases in myeloid neoplasias: from molecular redox mechanisms to health implications

Neoplastic expansion of myeloid cells is associated with specific genetic changes that lead to chronic activation of signaling pathways, as well as altered metabolism. It has become increasingly evident that transformation relies on the interdependency of both events. Among the various genetic changes, the oncogenic BCR-ABL tyrosine kinase in patients with Philadelphia chromosome positive chronic myeloid leukemia (CML) has been a focus of extensive research. Transformation by this oncogene is associated with elevated levels of intracellular reactive oxygen species (ROS). ROS have been implicated in processes that promote viability, cell growth, and regulation of other biological functions such as migration of cells or gene expression. Currently, the BCR-ABL inhibitor imatinib mesylate (Gleevec) is being used as a first-line therapy for the treatment of CML. However, BCR-ABL transformation is associated with genomic instability, and disease progression or resistance to imatinib can occur. Imatinib resistance is not known to cause or significantly alter signaling requirements in transformed cells. Elevated ROS are crucial for transformation, making them an ideal additional target for therapeutic intervention. The underlying mechanisms leading to elevated oxidative stress are reviewed, and signaling mechanisms that may serve as novel targeted approaches to overcome ROS-dependent cell growth are discussed.

Mitochondria-targeted antioxidant enzyme activity regulates radioresistance in human pancreatic cancer cells

In recent years, cellular redox environment gained significant attention as a critical regulator of cellular responses to oxidative stress. Cellular redox environment is a balance between production of reactive oxygen species and their removal by antioxidant enzymes. We investigated the hypothesis that mitochondrial antioxidant enzyme activity regulates radioresistance in human pancreatic cancer cells. Vector-control and manganese superoxide dismutase (MnSOD) overexpressing human pancreatic cancer cells were irradiated and assayed for cell survival and activation of the G(2)-checkpoint pathway. Increased MnSOD activity significantly increased cell survival following irradiation with 6 Gy of gamma-radiation (p < 0.05). The MnSOD overexpressing irradiated cells also revealed 3-4 folds increase in the percentage of G(2) cells compared to irradiated vector-control. Furthermore, MnSOD overexpressing irradiated cells exhibited increased loss of phosphorylated histone H2AX protein levels. The radiation-induced increase in cyclin B1 protein levels in irradiated vector-control cells was suppressed in irradiated MnSOD overexpressing cells. Mitochondria-targeted catalase overexpression increased the survival of irradiated cells. These results support the hypothesis that mitochondrial antioxidant enzyme activity and mitochondria-generated reactive oxygen species-signaling (superoxide and hydrogen peroxide) could regulate radiation-induced G(2) checkpoint activation and radioresistance in human pancreatic cancer cells.

Ramifications of a redox switch within a normal cell: its absence in a cancer cell

A previously described model for cellular proliferation, based on the relationship of the cell cycle to redox parameters, is explored here to account for the origin of the cancerous cell and some of its key abnormal characteristics, such as the Warburg effect, apoptosis, aneuploidy, and uncontrolled proliferation. We describe how the redox switch that characterizes normal cells and its absence in cancer cells is responsible for the origin and characteristics of cancer cells. Metabolic and chromosomal changes resulting from the lack of such a redox switch in cancer cells are described. The effects of a well-known carcinogen, cigarette smoking, are also applied to the model. This report emphasizes the role of the threshold intracellular redox potential in regulating cells.

Effects of ginsenosides Re and Rg3 on intracellular redox state and cell proliferation in C6 glioma cells

Background

Cellular redox state is important to cell growth and death. The growth of tumor cells may be modulated by intracellular reduced glutathione/oxidized glutathione (GSH/GSSG). The present study aims to investigate the effects of ginsenosides Re and Rg3 on cellular redox state and cell proliferation in C6 glioma cells.

Methods

Cultured C6 glioma cells were exposed to various concentrations of either Rg3 or Re for 24 hours. Cell growth and death were measured by the BrdU incorporation assay and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay respectively. Cellular redox state was determined by free radical production using flow cytometry and GSH/GSSG using spectrofluorometry.

Results

At a sub-lethal concentration, Re suppressed cell proliferation with a significant decrease in BrdU incorporation. Re did not increase reactive oxygen species (ROS) production but increased GSH/GSSG via increased activity of gamma glutamylcystenyl synthase (γ-GCS). In contrast, Rg3 increased free radical production and reduced GSH/GSSG. The effects of Rg3 were probably due to increased activity of glutathione peroxidase (GPx).

Conclusion

Re and Rg3 alter cellular redox state of C6 glioma cells in opposite directions. Changes in cellular redox state induced by Re and Rg3 are correlated with the proliferation rates of C6 glioma cells.

Nox enzymes and oxidative stress in the immunopathology of the gastrointestinal tract

Chronic inflammation caused by Helicobacter pylori infection or inflammatory bowel disease (IBD) is closely linked to cancer development. Innate immune abnormalities and enhanced production of reactive oxygen species through a phagocyte NADPH oxidase (Nox2) are key issues in understanding the pathogenesis of inflammation-dependent carcinogenesis. Besides Nox2, functionally distinct homologues (Nox1, Nox3, Nox4, Nox5, Duox1, and Duox2) have been identified. Nox1 and Duox2 are highly expressed in the gastrointestinal tract. Although the functional roles of Nox/Duox in the gastrointestinal tract are still unclear, we will review their potential roles in the gastrointestinal immunopathology, particularly in H. pylori-induced inflammation, IBD, and malignancy.

Manganese superoxide dismutase activity regulates transitions between quiescent and proliferative growth

In recent years, the intracellular reactive oxygen species (ROS) levels have gained increasing attention as a critical regulator of cellular proliferation. We investigated the hypothesis that manganese superoxide dismutase (MnSOD) activity regulates proliferative and quiescent growth by modulating cellular ROS levels. Decreasing MnSOD activity favored proliferation in mouse embryonic fibroblasts (MEF), while increasing MnSOD activity facilitated proliferating cells' transitions into quiescence. MnSOD +/- and -/- MEFs demonstrated increased superoxide steady-state levels; these fibroblasts failed to exit from the proliferative cycle, and showed increasing cyclin D1 and cyclin B1 protein levels. MnSOD +/- MEFs exhibited an increase in the percentage of G(2) cells compared to MnSOD +/+ MEFs. Overexpression of MnSOD in MnSOD +/- MEFs suppressed superoxide levels and G(2) accumulation, decreased cyclin B1 protein levels, and facilitated cells' transit into quiescence. While ROS are known to regulate differentiation and cell death pathways, both of which are irreversible processes, our results show MnSOD activity and, therefore, mitochondria-derived ROS levels regulate cellular proliferation and quiescence, which are reversible processes essential to prevent aberrant proliferation and subsequent exhaustion of normal cell proliferative capacity. These results support the hypothesis that MnSOD activity regulates a mitochondrial 'ROS-switch' favoring a superoxide-signaling regulating proliferation and a hydrogen peroxide-signaling supporting quiescence.

Real-time imaging of the intracellular glutathione redox potential

Dynamic analysis of redox-based processes in living cells is now restricted by the lack of appropriate redox biosensors. Conventional redox-sensitive GFPs (roGFPs) are limited by undefined specificity and slow response to changes in redox potential. In this study we demonstrate that the fusion of human glutaredoxin-1 (Grx1) to roGFP2 facilitates specific real-time equilibration between the sensor protein and the glutathione redox couple. The Grx1-roGFP2 fusion protein allowed dynamic live imaging of the glutathione redox potential (E(GSH)) in different cellular compartments with high sensitivity and temporal resolution. The biosensor detected nanomolar changes in oxidized glutathione (GSSG) against a backdrop of millimolar reduced glutathione (GSH) on a scale of seconds to minutes. It facilitated the observation of redox changes associated with growth factor availability, cell density, mitochondrial depolarization, respiratory burst activity and immune receptor stimulation.

ROS and p53: a versatile partnership

The tumor suppressor protein p53 is a redox-active transcription factor that organizes and directs cellular responses in the face of a variety of stresses that lead to genomic instability. One of the most important questions in the study of p53 is how selective transactivation of certain p53 target genes is achieved. Reactive oxygen species (ROS), generated by cells as products or by-products, can function either as signaling molecules or as cellular toxicants. Cellular generation of ROS is central to redox signaling. Recent studies have revealed that each cellular concentration and distribution of p53 has a distinct cellular function and that ROS act as both an upstream signal that triggers p53 activation and a downstream factor that mediates apoptosis. Here, we examine the newly discovered role of p53 in regulating cellular ROS generation and how ROS modulate selective transactivation of p53 target genes. The focus is on interlinks between ROS and p53.

Intraesophageal MnSOD-plasmid liposome enhances engraftment and self-renewal of bone marrow derived progenitors of esophageal squamous epithelium

We evaluated whether the improved esophageal radiation tolerance following Manganese Superoxide Dismutase (MnSOD)-Plasmid Liposomes was explained by improved engraftment of bone marrow-derived progenitors. C57BL/6NHsd female mice pretreated with intraesophageal MnSOD-PL were irradiated to 29 Gy to the esophagus and intravenously transplanted with marrow from male B6. 129S7-Gt (ROSA) 26S OR/J ROSA (Lac-Z+, G418-resistant) mice. After 14 days, esophagi were removed and side population and non-side population cells evaluated for donor multilineage (endothelin/vimentin/F480) positive esophageal cells. Serial intravenous transplantability was tested in second generation 29 Gy esophagus-irradiated mice. Esophagi from recipients receiving swallowed MnSOD-PL 24 h prior to irradiation demonstrated significantly increased esophageal repopulation with donor bone marrow-derived Lac-Z+, G418+, Y-probe+ multilineage cells (37.8+/-1.8>50 cell Lac-Z+ foci per esophagus) compared to irradiated controls (19.8+/-1.8) P<0.0001. Serial transfer to second-generation irradiated C57BL/6NHsd mice of intravenously injected SP or NSP first generation recipient esophagus cells was also significantly enhanced by MnSOD-PL intraesophageal pretreatment (74.4+/-3.6 SP-derived Lac-Z+ foci per esophagus, 48.6+/-5.4 NSP-derived) compared to irradiation controls (23.4+/-1.8 SP, 6.0+/-3.0 NSP), P<0.0001. Thus, intraesophageal MnSOD-PL administration enhances engraftment of marrow-derived progenitors.

DNA replication stress, genome instability and aging

Genome instability is a fundamentally important component of aging in all eukaryotes. How age-related genome instability occurs remains unclear. The free radical theory of aging posits oxidative damage to DNA and other cellular constituents as a primary determinant of aging. More recent versions of this theory predict that mitochondria are a major source of reactive oxygen species (ROS) that cause oxidative damage. Although substantial support for the free radical theory exists, the results of some tests of this theory have been contradictory or inconclusive. Enhanced growth signaling also has been implicated in aging. Many efforts to understand the effects of growth signaling on aging have focused on inhibition of oxidative stress responses that impact oxidative damage. However, recent experiments in the model organism Saccharomyces cerevisiae (budding yeast) and in higher eukaryotes suggest that growth signaling also impacts aging and/or age-related diseases—including cancer and neurodegeneration—by inducing DNA replication stress, which causes DNA damage. Replication stress, which has not been broadly considered as a factor in aging, may be enhanced by ROS that signal growth. In this article, we review evidence that points to DNA replication stress and replication stress-induced genome instability as important factors in aging.