Reactive oxygen species (ROS) are a normal byproduct of cellular metabolism and are required components in cell signaling and immune responses. However, an imbalance of ROS can lead to oxidative ...stress in various pathological states. Increases in oxidative stress are one of the hallmarks in cancer cells, which display an altered metabolism when compared to corresponding normal cells. Extracellular superoxide dismutase (EcSOD) is an antioxidant enzyme that catalyzes the dismutation of superoxide anion (O2−) in the extracellular environment. By doing so, this enzyme provides the cell with a defense against oxidative damage by contributing to redox balance. Interestingly, EcSOD expression has been found to be decreased in a variety of cancers, and this loss of expression may contribute to the development and progression of malignancies. In addition, recent compounds can increase EcSOD activity and expression, which has the potential for altering this redox signaling and cellular proliferation. This review will explore the role that EcSOD expression plays in cancer in order to better understand its potential as a tool for the detection, predicted outcomes and potential treatment of malignancies.
Recent studies have demonstrated an important role for vitamin C in the epigenetic regulation of cancer-related genes via DNA demethylation by the ten-eleven translocation (TET) methylcytosine ...dioxygenase enzymes. DNA methyltransferase (DNMT) reverses this, increasing DNA methylation and decreasing gene expression. Dual oxidase (DUOX) enzymes produce hydrogen peroxide (H2O2) in normal pancreatic tissue but are silenced in pancreatic cancer (PDAC). Treatment of PDAC with pharmacologic ascorbate (P-AscH−, intravenous, high dose vitamin C) increases DUOX expression. We hypothesized that inhibiting DNMT may act synergistically with P-AscH− to further increase DUOX expression and cytotoxicity of PDAC. PDAC cells demonstrated dose-dependent increases in DUOX mRNA and protein expression when treated with DNMT inhibitors. PDAC cells treated with P-AscH− + DNMT inhibitors demonstrated increased DUOX expression, increased intracellular oxidation, and increased cytotoxicity in vitro and in vivo compared to either treatment alone. These findings suggest a potential therapeutic, epigenetic mechanism to treat PDAC.
Polychlorinated biphenyls (PCBs) and their metabolites are environmental pollutants that are known to have adverse health effects. 1-(4-Chlorophenyl)-benzo-2,5-quinone (4-ClBQ), a quinone metabolite ...of 4-monochlorobiphenyl (PCB3, present in the environment and human blood) is toxic to human skin keratinocytes, and breast and prostate epithelial cells. This study investigates the hypothesis that 4-ClBQ-induced metabolic oxidative stress regulates toxicity in human keratinocytes. Results from Seahorse XF96 Analyzer showed that the 4-ClBQ treatment increased extracellular acidification rate, proton production rate, oxygen consumption rate and ATP content, indicative of metabolic oxidative stress. Results from a q-RT-PCR assay showed significant increases in the mRNA levels of hexokinase 2 (
hk2
), pyruvate kinase M2 (
pkm2
) and glucose-6-phosphate dehydrogenase (
g6pd
), and decreases in the mRNA levels of succinate dehydrogenase (complex II) subunit C and D (
sdhc
and
sdhd
). Pharmacological inhibition of G6PD-activity enhanced the toxicity of 4-ClBQ, suggesting that the protective function of the pentose phosphate pathway is functional in 4-ClBQ-treated cells. The decrease in
sdhc
and
sdhd
expression was associated with a significant decrease in complex II activity and increase in mitochondrial levels of ROS. Overexpression of
sdhc
and
sdhd
suppressed 4-ClBQ-induced inhibition of complex II activity, increase in mitochondrial levels of ROS, and toxicity. These results suggest that the 4-ClBQ treatment induces metabolic oxidative stress in HaCaT cells, and while the protective function of the pentose phosphate pathway is active, inhibition of complex II activity sensitizes HaCaT cells to 4-ClBQ-induced toxicity.
Reactive oxygen species (ROS) are critical in a broad spectrum of cellular processes including signaling, tumor progression, and innate immunity. The essential nature of ROS signaling in the immune ...systems of Drosophila and zebrafish has been demonstrated; however, the role of ROS, if any, in mammalian adaptive immune system development and function remains unknown. This work provides the first clear demonstration that thymus-specific elevation of mitochondrial superoxide (O2•−) disrupts normal T cell development and impairs the function of the mammalian adaptive immune system. To assess the effect of elevated mitochondrial superoxide in the developing thymus, we used a T-cell-specific knockout of manganese superoxide dismutase (i.e., SOD2) and have thus established a murine model to examine the role of mitochondrial superoxide in T cell development. Conditional loss of SOD2 led to increased superoxide, apoptosis, and developmental defects in the T cell population, resulting in immunodeficiency and susceptibility to the influenza A virus H1N1. This phenotype was rescued with mitochondrially targeted superoxide-scavenging drugs. These findings demonstrate that loss of regulated levels of mitochondrial superoxide lead to aberrant T cell development and function, and further suggest that manipulations of mitochondrial superoxide levels may significantly alter clinical outcomes resulting from viral infection.
Many breast cancer cells typically exhibit lower expression of manganese superoxide dismutase (MnSOD) compared to the normal cells from which they arise. This decrease can often be attributed to a ...defect in the transcription of
SOD2, the gene encoding MnSOD; however, the mechanism responsible for this change remains unclear. Here, we describe how altered histone modifications and a repressive chromatin structure constitute an epigenetic process to down regulate
SOD2 in human breast carcinoma cell lines. Utilizing chromatin immunoprecipitation (ChIP) we observed decreased levels of dimethyl H3K4 and acetylated H3K9 at key regulatory elements of the
SOD2 gene. Consistent with these results, we show that loss of these histone modifications creates a repressive chromatin structure at
SOD2. Transcription factor ChIP experiments revealed that this repressive chromatin structure influences the binding of SP-1, AP-1, and NFκB to
SOD2 regulatory
cis-elements
in vivo. Lastly, we show that treatment with the histone deacetylase inhibitors trichostatin A and sodium butyrate can reactivate
SOD2 expression in breast cancer cell lines. Taken together, these results indicate that epigenetic silencing of
SOD2 could be facilitated by changes in histone modifications and represent one mechanism leading to the altered expression of MnSOD observed in many breast cancers.
Alpha-tocopheryl succinate (alpha-TOS) is a selective inducer of apoptosis in cancer cells, which involves the accumulation of reactive oxygen species (ROS). The molecular target of alpha-TOS has not ...been identified. Here, we show that alpha-TOS inhibits succinate dehydrogenase (SDH) activity of complex II (CII) by interacting with the proximal and distal ubiquinone (UbQ)-binding site (Q(P) and Q(D), respectively). This is based on biochemical analyses and molecular modelling, revealing similar or stronger interaction energy of alpha-TOS compared to that of UbQ for the Q(P) and Q(D) sites, respectively. CybL-mutant cells with dysfunctional CII failed to accumulate ROS and underwent apoptosis in the presence of alpha-TOS. Similar resistance was observed when CybL was knocked down with siRNA. Reconstitution of functional CII rendered CybL-mutant cells susceptible to alpha-TOS. We propose that alpha-TOS displaces UbQ in CII causing electrons generated by SDH to recombine with molecular oxygen to yield ROS. Our data highlight CII, a known tumour suppressor, as a novel target for cancer therapy.
Progesterone, acting through its receptor, PR (progesterone receptor), is the natural inhibitor of uterine endometrial carcinogenesis by inducing differentiation. PR is downregulated in more advanced ...cases of endometrial cancer, thereby limiting the effectiveness of hormonal therapy. Our objective was to understand and reverse the mechanisms underlying loss of PR expression in order to improve therapeutic outcomes. Using endometrial cancer cell lines and data from The Cancer Genome Atlas, our findings demonstrate that PR expression is downregulated at four distinct levels. In well-differentiated cancers, ligand-induced receptor activation and downregulation are intact. miRNAs mediate fine tuning of PR levels. As differentiation is lost, PR silencing is primarily at the epigenetic level. Initially, recruitment of the polycomb repressor complex 2 to the PR promoter suppresses transcription. Subsequently, DNA methylation prevents PR expression. Appropriate epigenetic modulators reverse these mechanisms. These data provide a rationale for combining epigenetic modulators with progestins as a therapeutic strategy for endometrial cancer.
Traditional hormonal therapy for women with endometrial cancer can be molecularly enhanced by combining progestins with epigenetic modulators, thereby increasing progesterone receptor expression and significantly improving treatment efficacy.
Expression of the imprinted genes H19 and insulin-like growthfactor 2 (Igf2), which lie in close proximity on mouse chromosome 7,is regulated by methylation of a differentially methylated domain ...(DMD)located 5' to H19. Biallelic expression of H19 has been observed in renal disease patients with hyperhomocysteinemia, a cardiovascular disease risk factor. The present study determined whether hyperhomocysteinemia produces decreased tissue methylation capacity,hypomethylation of the H19 DMD, and altered expression ofH19 and Igf2 in adult mice. Mice heterozygous for disruptionof the gene for cystathionine-beta-synthase (Cbs+/-) andC57BL/6 (Cbs+/+) mice were fed a hyperhomocysteinemic or controldiet, respectively, from weaning until 9-12 months of age. Higher plasmatotal homocysteine (p < 0.001) was found in hyperhomocysteinemicmice than in control mice (95 ± 12 versus 5.0 ± 0.3micromol/liter). Hyperhomocysteinemia was accompanied by higher levels ofS-adenosylhomocysteine (p < 0.05) and lowerS-adenosylmethionine/S-adenosylhomocysteine ratios(p < 0.001) in liver and brain. The effect of hyperhomocysteinemiaon H19 DMD methylation was tissue-specific. In liver,hyperhomocysteinemic mice had decreased H19 DMD methylation(p < 0.001). In brain, hyperhomocysteinemia was accompanied byincreased H19 DMD methylation (p < 0.001) and a decreasein the ratio of H19/Igf2 transcripts (p < 0.05).In aorta, hyperhomocysteinemia produced an increase in H19 DMDmethylation (p < 0.001) and a 2.5-fold increase in expression ofH19 transcripts (p < 0.05). Levels of H19transcripts in aorta correlated positively with plasma total homocysteineconcentration (p < 0.05, r = 0.620). We conclude thathyperhomocysteinemia produces tissue-specific changes in H19 DMDmethylation and increased vascular expression of H19 in adultmice.
Desmocollin 3 (DSC3) is a member of the cadherin superfamily of calcium-dependent cell adhesion molecules and a principle component of desmosomes. Desmosomal proteins such as DSC3 are integral to the ...maintenance of tissue architecture and the loss of these components leads to a lack of adhesion and a gain of cellular mobility. DSC3 expression is down-regulated in breast cancer cell lines and primary breast tumors; however, the loss of DSC3 is not due to gene deletion or gross rearrangement of the gene. In this study, we examined the prevalence of epigenetic silencing of DSC3 gene expression in primary breast tumor specimens.
We used bisulfite genomic sequencing to analyze the methylation state of the DSC3 promoter region from 32 primary breast tumor specimens. We also used a quantitative real-time RT-PCR approach, and analyzed all breast tumor specimens for DSC3 expression. Finally, in addition to bisulfite sequencing and RT-PCR, we used an in vivo nuclease accessibility assay to determine the chromatin architecture of the CpG island region from DSC3-negative breast cancer cells lines.
DSC3 expression was downregulated in 23 of 32 (72%) breast cancer specimens comprising: 22 invasive ductal carcinomas, 7 invasive lobular breast carcinomas, 2 invasive ductal carcinomas that metastasized to the lymph node, and a mucoid ductal carcinoma. Of the 23 specimens showing a loss of DSC3 expression, 13 (56%) were associated with cytosine hypermethylation of the promoter region. Furthermore, DSC3 expression is limited to cells of epithelial origin and its expression of mRNA and protein is lost in a high proportion of breast tumor cell lines (79%). Lastly, DNA hypermethylation of the DSC3 promoter is highly correlated with a closed chromatin structure.
These results indicate that the loss of DSC3 expression is a common event in primary breast tumor specimens, and that DSC3 gene silencing in breast tumors is frequently linked to aberrant cytosine methylation and concomitant changes in chromatin structure.
Most head and neck squamous cell carcinomas (HNSCCs) overexpress epidermal growth factor receptor (EGFR) and EGFR inhibitors are routinely used in the treatment of HNSCC. However, many HNSCC tumors ...do not respond or become refractory to EGFR inhibitors. Autophagy, which is a stress-induced cellular self-degradation process, has been reported to reduce the efficacy of chemotherapy in various disease models. The purpose of this study is to determine if the efficacy of the EGFR inhibitor erlotinib is reduced by activation of autophagy via NOX4-mediated oxidative stress in HNSCC cells. Erlotinib induced the expression of the autophagy marker LC3B-II and autophagosome formation in FaDu and Cal-27 cells. Inhibition of autophagy by chloroquine and knockdown of autophagy pathway genes Beclin-1 and Atg5 sensitized both cell lines to erlotinib-induced cytotoxicity, suggesting that autophagy may serve as a protective mechanism. Treatment with catalase (CAT) and diphenylene iodonium (DPI) in the presence of erlotinib suppressed the increase in LC3B-II expression in FaDu and Cal-27 cells. Erlotinib increased NOX4 mRNA and protein expression by increasing its promoter activity and mRNA stability in FaDu cells. Knockdown of NOX4 using adenoviral siNOX4 partially suppressed erlotinib-induced LC3B-II expression, while overexpression of NOX4 increased expression of LC3B-II. These studies suggest that erlotinib may activate autophagy in HNSCC cells as a pro-survival mechanism, and NOX4 may play a role in mediating this effect.
•Erlotinib increased LC3B-II and autophagosome formation in HNSCC cells.•Inhibition of autophagy sensitized HNSCC cells to erlotinib.•Erlotinib increased NOX4 promoter and 3′UTR luciferase activity.•Manipulating NOX4 decreases or increases autophagy.
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