Extra-nuclear histones: origin, significance and perspectives.

Histones are classically known to organize the eukaryotic DNA into chromatin. They are one of the key players in regulating transcriptionally permissive and non-permissive states of the chromatin. Nevertheless, their context-dependent appearance within the cytoplasm and systemic circulation has also been observed. The past decade has also witnessed few scientific communications on the existence of vesicle-associated histones. Diverse groups have attempted to determine the significance of these extra-nuclear histones so far, with many of those studies still underway. Of note amongst these are interactions of extra-nuclear or free histones with cellular membranes, mediated by mutual cationic and anionic natures, respectively. It is here aimed to consolidate the mechanism of formation of extra-nuclear histones; implications of histone-induced membrane destabilization and explore the mechanisms of their association/release with extracellular vesicles, along with the functional aspects of these extra-nuclear histones in cell and systemic physiology.

Evaluation of the Moonlighting Histone H3 Specific Protease (H3ase) Activity and the Dehydrogenase Activity of Glutamate Dehydrogenase (GDH).

The N-terminus of Histone H3 is proteolytically processed in aged chicken liver. A histone H3 N-terminus specific endopeptidase (named H3ase) has been purified from the nuclear extract of aged chicken liver. By sequencing and a series of biochemical methods including the demonstration of H3ase activity in bacterially expressed GDH, it was established that the H3ase activity was a moonlighting protease activity of glutamate dehydrogenase (GDH). However, the active site for the H3ase in the GDH remains elusive. Here, using cross-linking studies of the homogenously purified H3ase, we show that the GDH and the H3ase remain in the same native state. Further, the H3ase and GDH activities could be uncoupled by partial denaturation of GDH, suggesting strong evidence for the involvement of different active sites for GDH and H3ase activities. Through densitometry of the H3ase clipped H3 products, the H3ase activity was quantified and it was compared with the GDH activity of the chicken liver nuclear GDH. Furthermore, the H3ase mostly remained distributed in the perinuclear area as demonstrated by MNase digestion and immuno-localization of H3ase in chicken liver nuclei, as well as cultured mouse hepatocyte cells, suggesting that H3ase demonstrated regulated access to the chromatin. The present study thus broadly compares the H3ase and GDH activities of the chicken liver GDH.

SWI/SNF Chromatin Remodelers: Structural, Functional and Mechanistic Implications.

The nuclear events of a eukaryotic cell, such as replication, transcription, recombination and repair etc. require the transition of the compactly arranged chromatin into an uncompacted state and vice-versa. This is mediated by post-translational modification of the histones, exchange of histone variants and ATP-dependent chromatin remodeling. The SWI/SNF chromatin remodeling complexes are one of the most well characterized families of chromatin remodelers. In addition to their role in modulating chromatin, they have also been assigned roles in cancer and health-related anomalies such as developmental, neurocognitive, and intellectual disabilities. Owing to their vital cellular and medical connotations, developing an understanding of the structural and functional aspects of the complex becomes imperative. However, due to the intricate nature of higher-order chromatin as well as compositional heterogeneity of the SWI/SNF complex, intra-species isoforms and inter-species homologs, this often becomes challenging. To this end, the present review attempts to present an amalgamated perspective on the discovery, structure, function, and regulation of the SWI/SNF complex.

Crotepoxide chemosensitizes tumor cells through inhibition of expression of proliferation, invasion, and angiogenic proteins linked to proinflammatory pathway.

Crotepoxide (a substituted cyclohexane diepoxide), isolated from Kaempferia pulchra (peacock ginger), although linked to antitumor and anti-inflammatory activities, the mechanism by which it exhibits these activities, is not yet understood. Because nuclear factor kappaB (NF-kappaB) plays a critical role in these signaling pathways, we investigated the effects of crotepoxide on NF-kappaB-mediated cellular responses in human cancer cells. We found that crotepoxide potentiated tumor necrosis factor (TNF), and chemotherapeutic agents induced apoptosis and inhibited the expression of NF-kappaB-regulated gene products involved in anti-apoptosis (Bcl-2, Bcl-xL, IAP1,(2) MCl-1, survivin, and TRAF1), apoptosis (Bax, Bid), inflammation (COX-2), proliferation (cyclin D1 and c-myc), invasion (ICAM-1 and MMP-9), and angiogenesis (VEGF). We also found that crotepoxide inhibited both inducible and constitutive NF-kappaB activation. Crotepoxide inhibition of NF-kappaB was not inducer-specific; it inhibited NF-kappaB activation induced by TNF, phorbol 12-myristate 13-acetate, lipopolysaccharide, and cigarette smoke. Crotepoxide suppression of NF-kappaB was not cell type-specific because NF-kappaB activation was inhibited in myeloid, leukemia, and epithelial cells. Furthermore, we found that crotepoxide inhibited TAK1 activation, which led to suppression of IkappaBalpha kinase, abrogation of IkappaBalpha phosphorylation and degradation, nuclear translocation of p65, and suppression of NF-kappaB-dependent reporter gene expression. Overall, our results indicate that crotepoxide sensitizes tumor cells to cytokines and chemotherapeutic agents through inhibition of NF-kappaB and NF-kappaB-regulated gene products, and this may provide the molecular basis for crotepoxide ability to suppress inflammation and carcinogenesis.

Modification of cysteine 179 of IkappaBalpha kinase by nimbolide leads to down-regulation of NF-kappaB-regulated cell survival and proliferative proteins and sensitization of tumor cells to chemotherapeutic agents.

Reverse pharmacology, also called the "bedside to bench" approach, that deals with new uses for a well known molecular entity has been used extensively in cancer drug development to identify novel compounds and delineate their mechanisms of action. Here, we show that nimbolide, a triterpenoid isolated from Azadirachta indica, enhanced the apoptosis induced by inflammatory cytokines and chemotherapeutic agents in tumor cells. This limonoid abrogated the expression of proteins associated with cell survival (Bcl-2, Bcl-xL, IAP-1, and IAP-2), proliferation (cyclin D1), invasion (MMP-9), and angiogenesis (VEGF), all regulated by nuclear factor (NF)-κB. Nimbolide inhibited the activation of NF-κB induced by carcinogens and inflammatory stimuli. Constitutively active NF-κB found in most tumor cells was also inhibited. We found that suppression of NF-κB activation by nimbolide was caused by inhibition of IκB kinase (IKK), which led to suppression of IκBα phosphorylation and degradation, nuclear translocation, DNA binding, and gene transcription. Reducing agent reversed the action of the limonoid, suggesting the involvement of a cysteine residue. Replacement of Cys(179) of IKK-ß with alanine abolished the effect of nimbolide, suggesting that Cys(179) plays a critical role in inhibiting the NF-κB activation. Overall, our results indicate that nimbolide can sensitize tumor cells to chemotherapeutic agents through interaction with IKK, leading to inhibition of NF-κB-regulated proteins.

Anacardic acid (6-nonadecyl salicylic acid), an inhibitor of histone acetyltransferase, suppresses expression of nuclear factor-kappaB-regulated gene products involved in cell survival, proliferation, invasion, and inflammation through inhibition of the inhibitory subunit of nuclear factor-kappaBalpha kinase, leading to potentiation of apoptosis.

Anacardic acid (6-pentadecylsalicylic acid) is derived from traditional medicinal plants, such as cashew nuts, and has been linked to anticancer, anti-inflammatory, and radiosensitization activities through a mechanism that is not yet fully understood. Because of the role of nuclear factor-kappaB (NF-kappaB) activation in these cellular responses, we postulated that anacardic acid might interfere with this pathway. We found that this salicylic acid potentiated the apoptosis induced by cytokine and chemotherapeutic agents, which correlated with the down-regulation of various gene products that mediate proliferation (cyclin D1 and cyclooxygenase-2), survival (Bcl-2, Bcl-xL, cFLIP, cIAP-1, and survivin), invasion (matrix metalloproteinase-9 and intercellular adhesion molecule-1), and angiogenesis (vascular endothelial growth factor), all known to be regulated by the NF-kappaB. We found that anacardic acid inhibited both inducible and constitutive NF-kappaB activation; suppressed the activation of IkappaBalpha kinase that led to abrogation of phosphorylation and degradation of IkappaBalpha; inhibited acetylation and nuclear translocation of p65; and suppressed NF-kappaB-dependent reporter gene expression. Down-regulation of the p300 histone acetyltransferase gene by RNA interference abrogated the effect of anacardic acid on NF-kappaB suppression, suggesting the critical role of this enzyme. Overall, our results demonstrate a novel role for anacardic acid in potentially preventing or treating cancer through modulation of NF-kappaB signaling pathway.

Targeting inflammatory pathways by flavonoids for prevention and treatment of cancer.

Observational studies have suggested that lifestyle risk factors such as tobacco, alcohol, high-fat diet, radiation, and infections can cause cancer and that a diet consisting of fruits and vegetables can prevent cancer. Evidence from our laboratory and others suggests that agents either causing or preventing cancer are linked through the regulation of inflammatory pathways. Genes regulated by the transcription factor NF- kappaB have been shown to mediate inflammation, cellular transformation, tumor cell survival, proliferation, invasion, angiogenesis, and metastasis. Whereas various lifestyle risk factors have been found to activate NF- kappaB and NF- kappaB-regulated gene products, flavonoids derived from fruits and vegetables have been found to suppress this pathway. The present review describes various flavones, flavanones, flavonols, isoflavones, anthocyanins, and chalcones derived from fruits, vegetables, legumes, spices, and nuts that can suppress the proinflammatory cell signaling pathways and thus can prevent and even treat the cancer.

Deficiency of NRH:quinone oxidoreductase 2 differentially regulates TNF signaling in keratinocytes: up-regulation of apoptosis correlates with down-regulation of cell survival kinases.

NRH:quinone oxidoreductase 2 (NQO2) is a cytosolic flavoprotein that catalyzes the two-electron reduction of quinones and quinoid compounds to hydroquinones. Although the role of a homologue, NAD(P)H:quinone oxidoreductase 1 (NQO1), is well defined in oxidative stress, neoplasia, and carcinogenesis, little is known about the mechanism of actions of NQO2 in these cellular responses. Whether NQO2 has any role in tumor necrosis factor (TNF) signaling was investigated using keratinocytes derived from wild-type and NQO2 knockout (NQO2-/-) mice. Although exposure of wild-type cells to TNF led to activation of nuclear factor-kappaB (NF-kappaB) and IkappaBalpha kinase, IkappaBalpha degradation, p65 phosphorylation, and p65 nuclear translocation, this cytokine had no effect on NQO2-/- cells. Deletion of NQO2 also abolished TNF-induced c-Jun NH2-terminal kinase, Akt, p38, and p44/p42 mitogen-activated protein kinase activation. The induction of various antiapoptotic gene products (MMP-9, cyclin D1, COX-2, IAP1, IAP2, Bcl-2, cFLIP, and XIAP) by TNF was also abolished in NQO2-/- cells. This correlated with potentiation of TNF-induced apoptosis as indicated by cell viability, Annexin V staining, and caspase activation. In agreement with this, we also found that TNF activated NQO2, and NQO2-specific small interfering RNA abrogated the TNF-induced NQO2 activity and NF-kappaB activation. Overall, our results indicate that deletion of NQO2 plays a differential role in TNF signaling pathway: by suppressing cell survival signals and potentiating TNF-induced apoptosis.

Identification of a novel blocker of IkappaBalpha kinase activation that enhances apoptosis and inhibits proliferation and invasion by suppressing nuclear factor-kappaB.

3,4-dihydroxybenzalacetone (DBL) is a polyphenol derived from the medicinal plant Chaga [Inonotus obliquus (persoon) Pilat]. Although Chaga is used in Russia folk medicine to treat tumors, very little is known about its mechanism of action. Because most genes involved in inflammation, antiapoptosis, and cell proliferation are regulated by the transcription factor nuclear factor-kappaB (NF-kappaB), we postulated that DBL activity is mediated via modulation of the NF-kappaB activation pathway. We investigated the effects of DBL on NF-kappaB activation by electrophoretic mobility shift assay and on NF-kappaB-regulated gene expression by Western blot analysis. We found that DBL suppressed NF-kappaB activation by a wide variety of inflammatory agents, including tumor necrosis factor (TNF), interleukin-1beta, epidermal growth factor, okadaic acid, phorbol 12-myristate 13-acetate, and lipopolysaccharide. The suppression was not cell type specific and inhibited both inducible and constitutive NF-kappaB activation. DBL did not interfere with the binding of NF-kappaB to DNA but rather inhibited IkappaBalpha kinase activity, IkappaBalpha phosphorylation and degradation, p65 phosphorylation, and translocation. DBL also suppressed the expression of TNF-induced and NF-kappaB-regulated proliferative, antiapoptotic, and metastatic gene products. These effects correlated with enhancement of TNF-induced apoptosis and suppression of TNF-induced invasion. Together, our results indicate that DBL inhibits NF-kappaB activation and NF-kappaB-regulated gene expression, which may explain the ability of DBL to enhance apoptosis and inhibit invasion.

Simvastatin, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, suppresses osteoclastogenesis induced by receptor activator of nuclear factor-kappaB ligand through modulation of NF-kappaB pathway.

Simvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, is a cholesterol-lowering drug that may play a role in bone metabolism through a mechanism that is not fully understood. Recently, receptor activator of NF-kappaB ligand (RANKL), a member of the TNF superfamily, has emerged as a major mediator of bone loss via activation of osteoclastogenesis. The latter is also associated with certain cancers such as multiple myeloma and breast cancer. Whether simvastatin can modulate RANKL-induced or cancer induced osteoclastogenesis was investigated. The effect of simvastatin on RANKL signaling and consequent osteoclastogenesis was investigated. RANKL induced NF-kappaB activation, whereas pretreatment with simvastatin completely suppressed such activation and correlated with suppression of RANKL-induced activation of IkappaBalpha kinase, IkappaBalpha phosphorylation and IkappaBalpha degradation. Similarly, RANKL induced the differentiation of monocytic cells to osteoclasts, whereas simvastatin suppressed it. The inhibition was maximal when cells were exposed to both simvastatin and RANKL simultaneously and minimal when simvastatin was added 1 day after RANKL treatment. Simvastatin also inhibited the osteoclastogenesis induced by human breast cancer and by multiple myeloma cells. Together, our results indicate that simvastatin inhibits the RANKL-induced NF-kappaB activation pathway that leads to suppression of osteoclastogenesis induced by RANKL and by tumor cells, thereby suggesting its therapeutic potential in osteoporosis and in cancer-related bone loss.

Evidence that genetic deletion of the TNF receptor p60 or p80 inhibits Fas mediated apoptosis in macrophages.

Almost 19 members of the tumor necrosis factor (TNF) superfamily have been identified that interact with 29 different receptors. Whether these receptors communicate with each other is not understood. Recently, we have shown that receptor activator of NF-kappaB ligand signaling is modulated by genetic deletion of the TNF receptor. In the current report, we investigated the possibility of a cross-talk between Fas and TNF-alpha signaling pathway in macrophage cell lines derived from wild-type (WT) mice and from mice with genetic deletion of the type 1 TNF receptor (p60(-/-)), the type 2 TNF receptor (p80(-/-)), or both receptors (p60(-/-)p80(-/-)). We found that the macrophages expressing TNF receptors were highly sensitive to apoptosis induced by anti-Fas. The genetic deletion of TNF receptors, however, made the cells resistance to anti-Fas-induced apoptosis. Anti-Fas induced activation of caspase-3 and PARP cleavage in WT cells but not in TNF receptor-deleted cells. This difference was found to be independent of the expression of Fas, Fas-associated protein with death domain (FADD) or TNF receptor-associated death domain (TRADD). We found that anti-Fas induced recruitment of TNFR1 into Fas-complex. We also found that TRADD, which mediates TNF signaling, was constitutively bound to Fas receptor in TNF receptor-deleted cells but not in wild-type cells. Transient transfection of TNFR1 in TNFR1-deleted cells sensitized them to anti-Fas-induced apoptosis. Overall our results demonstrate that Fas signaling is modulated by the TNF receptors and thus provide the evidence of cross-talk between the receptors of two cytokines.

Modulation of transcription factors by curcumin.

Curcumin is the active ingredient of turmeric that has been consumed as a dietary spice for ages. Turmeric is widely used in traditional Indian medicine to cure biliary disorders, anorexia, cough, diabetic wounds, hepatic disorders, rheumatism, and sinusitis. Extensive investigation over the last five decades has indicated that curcumin reduces blood cholesterol, prevents low-density lipoprotein oxidation, inhibits platelet aggregation, suppresses thrombosis and myocardial infarction, suppresses symptoms associated with type II diabetes, rheumatoid arthritis, multiple sclerosis, and Alzheimer's disease, inhibits HIV replication, enhances wound healing, protects from liver injury, increases bile secretion, protects from cataract formation, and protects from pulmonary toxicity and fibrosis. Evidence indicates that the divergent effects of curcumin are dependent on its pleiotropic molecular effects. These include the regulation of signal transduction pathways and direct modulation of several enzymatic activities. Most of these signaling cascades lead to the activation of transcription factors. Curcumin has been found to modulate the activity of several key transcription factors and, in turn, the cellular expression profiles. Curcumin has been shown to elicit vital cellular responses such as cell cycle arrest, apoptosis, and differentiation by activating a cascade of molecular events. In this chapter, we briefly review the effects of curcumin on transcription factors NF-KB, AP-1, Egr-1, STATs, PPAR-gamma, beta-catenin, nrf2, EpRE, p53, CBP, and androgen receptor (AR) and AR-related cofactors giving major emphasis to the molecular mechanisms of its action.

Differential Expression of SWI/SNF Chromatin Remodeler Subunits Brahma and Brahma-Related Gene During Drug-Induced Liver Injury and Regeneration in Mouse Model.

The chromatin remodeling activity of mammalian SWI/SNF complex is carried out by either Brahma (BRM) or Brahma-related gene (BRG-1). The BRG-1 regulates genes involved in cell proliferation, whereas BRM is associated with cell differentiation, and arrest of cell growth. Global modifications of histones and expression of genes of chromatin-remodeling subunits have not been studied in in vivo model systems. In the present study, we investigate epigenetic modifications of histones and the expression of genes in thioacetamide (TAA)-induced liver injury and regeneration in a mouse model. In the present study, we report that hepatocyte proliferation and H3S10 phosphorylation occur during 60 to 72 h post TAA treatment in mice. Furthermore, there was change in the H3K9 acetylation and H3K9 trimethylation pattern with respect to liver injury and regeneration phase. Looking into the expression pattern of Brg-1 and Brm, it is evident that they contribute substantially to the process of liver regeneration. The SWI/SNF remodeler might contain BRG-1 as its ATPase subunit during injury phase. Whereas, BRM-associated SWI/SNF remodeler might probably be predominant during decline of injury phase and initiation of regeneration phase. Furthermore, during the regeneration phase, BRG-1-containing remodeler again predominates. Considering all these observations, the present study depicts an interplay between chromatin interacting machineries in different phases of thioacetamide-induced liver injury and regeneration.

Purification and characterization of a novel histone H2A specific protease (H2Asp) from chicken liver nuclear extract.

The proteolysis of the N- or the C-terminal tails of histones have recently emerged as a novel form of irreversible posttranslational modifications of histones. However, there are very few reports describing purification of a histone specific protease. Here, we report a histone H2A specific protease (H2Asp) activity in the chicken liver nuclear extract. The H2Asp was purified to homogeneity and was found to be a ~10.5kDa protein. It demonstrated high specificity to histone H2A and was an aspartic acid like protease as shown by protease inhibition assay. The H2Asp, in the in vitro cleavage assay generated a single clipped H2A product which comigrated along with histone H4 in the SDS-PAGE and migrated as a single band when single H2A was used as substrates. The expression of H2Asp was independent of age and was tissue specific, which was demonstrated only in the nuclear extracts of chicken liver and not from the same of other tissues like brain, muscles and erythrocytes. It was also seen that H2Asp activity also exists in other classes of vertebrates from Pisces to Mammals. This report forms the first such report describing purification of a histone H2A specific protease.

Chicken liver glutamate dehydrogenase (GDH) demonstrates a histone H3 specific protease (H3ase) activity in vitro.

Site-specific proteolysis of the N or C-terminus of histone tails has emerged as a novel form of irreversible post-translational modifications assigned to histones. Though there are many reports describing histone specific proteolysis, there are very few studies on purification of a histone specific protease. Here, we demonstrate a histone H3 specific protease (H3ase) activity in chicken liver nuclear extract. H3ase was purified to homogeneity and identified as glutamate dehydrogenase (GDH) by sequencing. A series of biochemical experiments further confirmed that the H3ase activity was due to GDH. The H3ase clipped histone H3 products were sequenced by N-terminal sequencing and the precise clipping sites of H3ase were mapped. H3ase activity was only specific to chicken liver as it was not demonstrated in other tissues like heart, muscle and brain of chicken. We assign a novel serine like protease activity to GDH which is specific to histone H3.

Triptolide, histone acetyltransferase inhibitor, suppresses growth and chemosensitizes leukemic cells through inhibition of gene expression regulated by TNF-TNFR1-TRADD-TRAF2-NIK-TAK1-IKK pathway.

Triptolide, a diterpene triepoxide, from the Chinese herb Tripterygium wilfordii Hook.f, exerts its anti-inflammatory and immunosuppressive activities by inhibiting the transcription factor nuclear factor-κB (NF-κB) pathway, through a mechanism not yet fully understood. We found that triptolide, in nanomolar concentrations, suppressed both constitutive and inducible NF-κB activation, but did not directly inhibit binding of p65 to the DNA. The diterpene did block TNF-induced ubiquitination, phosphorylation, and degradation of IκBα, the inhibitor of NF-κB and inhibited acetylation of p65 through suppression of binding of p65 to CBP/p300. Triptolide also inhibited the IκBα kinase (IKK) that activates NF-κB and phosphorylation of p65 at serine 276, 536. Furthermore, the NF-κB reporter activity induced by TNF-TNFR1-TRADD-TRAF2-NIK-TAK1-IKKß was abolished by the triepoxide. Triptolide also abrogated TNF-induced expression of cell survival proteins (XIAP, Bcl-x(L), Bcl-2, survivin, cIAP-1 and cIAP-2), cell proliferative proteins (cyclin D1, c-myc and cyclooxygenase-2), and metastasis proteins (ICAM-1 and MMP-9). This led to enhancement of apoptosis induced by TNF, taxol, and thalidomide by the diterpene and to suppression of tumor invasion. Overall, our results demonstrate that triptolide can block the inflammatory pathway activated by TNF-TNFR1-TRADD-TRAF2-NIK-TAK1-IKK, sensitizes cells to apoptosis, and inhibits invasion of tumor cells.

Identification of novel anti-inflammatory agents from Ayurvedic medicine for prevention of chronic diseases: "reverse pharmacology" and "bedside to bench" approach.

Inflammation, although first characterized by Cornelius Celsus, a physician in first Century Rome, it was Rudolf Virchow, a German physician in nineteenth century who suggested a link between inflammation and cancer, cardiovascular diseases, diabetes, pulmonary diseases, neurological diseases and other chronic diseases. Extensive research within last three decades has confirmed these observations and identified the molecular basis for most chronic diseases and for the associated inflammation. The transcription factor, Nuclear Factor-kappaB (NF-kappaB) that controls over 500 different gene products, has emerged as major mediator of inflammation. Thus agents that can inhibit NF-kappaB and diminish chronic inflammation have potential to prevent or delay the onset of the chronic diseases and further even treat them. In an attempt to identify novel anti-inflammatory agents which are safe and effective, in contrast to high throughput screen, we have turned to "reverse pharmacology" or "bed to benchside" approach. We found that Ayurveda, a science of long life, almost 6,000 years old, can serve as a "goldmine" for novel anti-inflammatory agents used for centuries to treat chronic diseases. The current review is an attempt to provide description of various Ayurvedic plants currently used for treatment, their active chemical components, and the inflammatory pathways that they inhibit.

Oxidative stress, inflammation, and cancer: how are they linked?

Extensive research during the past 2 decades has revealed the mechanism by which continued oxidative stress can lead to chronic inflammation, which in turn could mediate most chronic diseases including cancer, diabetes, and cardiovascular, neurological, and pulmonary diseases. Oxidative stress can activate a variety of transcription factors including NF-κB, AP-1, p53, HIF-1α, PPAR-γ, ß-catenin/Wnt, and Nrf2. Activation of these transcription factors can lead to the expression of over 500 different genes, including those for growth factors, inflammatory cytokines, chemokines, cell cycle regulatory molecules, and anti-inflammatory molecules. How oxidative stress activates inflammatory pathways leading to transformation of a normal cell to tumor cell, tumor cell survival, proliferation, chemoresistance, radioresistance, invasion, angiogenesis, and stem cell survival is the focus of this review. Overall, observations to date suggest that oxidative stress, chronic inflammation, and cancer are closely linked.