Requirement of Arsenic Biomethylation for Oxidative DNA Damage

Inorganic Carcinogenesis Section, Laboratory of Comparative Carcinogenesis, Center for Cancer Research, National Cancer Institute at National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
Journal of the National Cancer Institute (Impact Factor: 12.58). 11/2009; 101(24):1670-81. DOI: 10.1093/jnci/djp414
Source: PubMed


Inorganic arsenic is an environmental carcinogen that may act through multiple mechanisms including formation of methylated derivatives in vivo. Sodium arsenite (up to 5.0 microM) renders arsenic methylation-competent TRL1215 rat liver epithelial cells tumorigenic in nude mice at 18 weeks of exposure and arsenic methylation-deficient RWPE-1 human prostate epithelial cells tumorigenic at 30 weeks of exposure. We assessed the role of arsenic biomethylation in oxidative DNA damage (ODD) using a recently developed immuno-spin trapping method.
Immuno-spin trapping was used to measure ODD after chronic exposure of cultured TRL1215 vs RWPE-1 cells, or of methylation-competent UROtsa/F35 vs methylation-deficient UROtsa human urothelial cells, to sodium arsenite. Secreted matrix metalloproteinase (MMP)-2 and -9 activity, as analyzed by zymography, cellular invasiveness by using a transwell assay, and colony formation by using soft agar assay were compared in cells exposed to arsenite with and without selenite, an arsenic biomethylation inhibitor, to assess the role of ODD in the transition to an in vitro cancer phenotype.
Exposure of methylation-competent TRL1215 cells to up to 1.0 microM sodium arsenite was followed by a substantial increase in ODD at 5-18 weeks (eg, at 16 weeks with 1.0 microM arsenite, 1138% of control, 95% confidence interval [CI] = 797% to 1481%), whereas exposure of methylation-deficient RWPE-1 cells to up to 5.0 microM arsenite did not increase ODD for a 30-week period. Inhibition of arsenic biomethylation with sodium selenite abolished arsenic-induced ODD and invasiveness, colony formation, and MMP-2 and -9 hypersecretion in TRL1215 cells. Arsenic induced ODD in methylation-competent UROtsa/F35 cells (eg, at 16 weeks, with 1.0 microM arsenite 225% of control, 95% CI = 188% to 262%) but not in arsenic methylation-deficient UROtsa cells, and ODD levels corresponded to the levels of increased invasiveness, colony formation, and hypersecretion of active MMP-2 and -9 seen after transformation to an in vitro cancer phenotype.
Arsenic biomethylation appears to be obligatory for arsenic-induced ODD and appears linked in some cells with the accelerated transition to an in vitro cancer phenotype.

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Available from: Ronald P Mason, Oct 01, 2015
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    • "After entering the cells, arsenic undergoes methylation reaction by the arsenite methyltransferase (AS3MT) enzyme producing several methylated arsenic compounds (Kojima et al., 2009). Arsenic methylation was initially believed to be a detoxification reaction (Gebel, 2002), but more recent evidence invalidated such a hypothesis showing an increased toxicity of specific methylated intermediate metabolites (Kojima et al., 2009; Sun et al., 2014). "
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    ABSTRACT: A complex interplay between multiple biological effects shapes the aging process. The advent of genome-wide quantitative approaches in the epigenetic field has highlighted the effective impact of epigenetic deregulation, particularly of DNA methylation, on aging. Age-associated alterations in DNA methylation are commonly grouped in the phenomenon known as "epigenetic drift" which is characterized by gradual extensive demethylation of genome and hypermethylation of a number of promoter-associated CpG islands. Surprisingly, specific DNA regions show directional epigenetic changes in aged individuals suggesting the importance of these events for the aging process. However, the epigenetic information obtained until now in aging needs a re-consideration due to the recent discovery of 5-hydroxymethylcytosine, a new DNA epigenetic mark present on genome. A recapitulation of the factors involved in the regulation of DNA methylation and the changes occurring in aging will be described in this review also considering the data available on 5hmC in aging. Copyright © 2015. Published by Elsevier Ireland Ltd.
    Mechanisms of Ageing and Development 02/2015; 58. DOI:10.1016/j.mad.2015.02.002 · 3.40 Impact Factor
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    • "Numerous studies have indicated that arsenic induces DNA damage (Kessel et al., 2002; Bhadauria and Flora, 2007; Lee and Ho, 1995; Dong and Luo, 1993; Kojima et al., 2009) and chromosome aberration such as chromosomal aneuploidy (Ochi et al., 1984; Sciandrello et al., 2002, 2004). MMA and DMA are directly genotoxic (Mass et al., 2001). "
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    ABSTRACT: Chronic exposure to arsenic may cause cancer. Many mechanisms have been suggested for arsenic carcinogenesis. Autophagy, an evolutionarily conserved cellular catabolic mechanism, has been implicated in cancer biology. Although being claimed as a type of cell death, autophagy may actually serve as a cell self-defense mechanism. In this review article, current understandings of the mechanisms of arsenic carcinogenesis, functions of autophagy and the role of autophagy in arsenic carcinogenesis are discussed.
    Experimental and toxicologic pathology: official journal of the Gesellschaft fur Toxikologische Pathologie 07/2014; 66(4). DOI:10.1016/j.etp.2014.01.004 · 1.86 Impact Factor
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    • "Interestingly, recent studies from the Waalkes groups showed that only methylationproficient cells exhibit oxidative DNA damage during inorganic arsenic exposure, and that MMA (III) causes oxidative DNA damage in cells that is independent from its ability to biomethylate inorganic arsenic (Kojima et al., 2009; Tokar et al., 2014). No evidence of ROS production was found at environmentally relevant concentrations (less than 100ppb) of arsenic exposure in BEAS-2B and lymphoblastoid cells (Bolt et al., 2010a; Bolt et al., 2010b; Bolt and Zhao et al., 2012; Zhao et al., 2013). "
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    ABSTRACT: Epidemiology studies have established a strong link between chronic arsenic exposure and lung cancer. Currently, contribution of perturbed energy metabolism to carcinogenesis is an intensive area of research. In several human cell culture models (primary, immortal, malignant), we observed that non-cytotoxic exposure to arsenite increased extracellular acidification rate. Lactate accumulation caused by extracellular acidification, could be inhibited by 2-deoxy-D-glucose, a non-metabolized glucose analog. This established that arsenite induces aerobic glycolysis (the Warburg effect), a metabolic shift frequently observed in the acquisition of malignancy. Our studies in BEAS-2B, a non-malignant pulmonary epithelial cell line, found that the metabolic perturbation began early in the course of malignant transformation by arsenite (6 weeks). Correlated with the surge of glycolysis, we found elevated levels of HIF-1A and loss of E-Cadherin during chronic arsenite exposure. Our evidence suggests that this metabolic shift is sustained by HIF-1A (hypoxia-inducible factor 1A). We found that arsenite-exposed BEAS-2B accumulated HIF-1A protein, and underwent transcriptional up-regulation of HIF-1A-target genes. Overexpression of HIF-1A increases glycolysis 15% (vs. control), confirming that HIF-1A can modulate glycolysis in BEAS-2B. Coincident with induction of glycolysis, we observed a decrease in E-cadherin expression, indicating loss of epithelial identity. HIF-1A stable knockdown in BEAS-2B abrogated the arsenite induction of glycolysis, and indicated suppression in colony formation. These findings suggest that the hypoxia-mimetic effect of arsenite plays an important role in arsenite-induced malignant transformation. The significance of this study is that arsenite-induced alteration of energy metabolism represents the type of fundamental perturbation that could extend to many diverse effects caused by arsenic.
    04/2014, Degree: Doctor of Philosophy
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