Interdependent genotoxic mechanisms of monomethylarsonous acid: Role of ROS-induced DNA damage and poly(ADP-ribose) polymerase-1 inhibition in the malignant transformation of urothelial cells

Abstract

Exposure of human bladder urothelial cells (UROtsa) to 50 nM of the arsenic metabolite, monomethylarsonous acid (MMAIII), for 12 weeks results in irreversible malignant transformation. The ability of continuous, low-level MMAIII exposure to cause an increase in genotoxic potential by inhibiting repair processes necessary to maintain genomic stability is unknown. Following genomic insult within cellular systems poly(ADP-ribose) polymerase-1 (PARP-1), a zinc finger protein, is rapidly activated and recruited to sites of DNA strand breaks. When UROtsa cells are continuously exposed to 50 nM MMAIII, PARP-1 activity does not increase despite the increase in MMAIII-induced DNA single-strand breaks through 12 weeks of exposure. When UROtsa cells are removed from continuous MMAIII exposure (2 weeks), PARP-1 activity increases coinciding with a subsequent decrease in DNA damage levels. Paradoxically, PARP-1 mRNA expression and protein levels are elevated in the presence of continuous MMAIII indicating a possible mechanism to compensate for the inhibition of PARP-1 activity in the presence of MMAIII. The zinc finger domains of PARP-1 contain vicinal sulfhydryl groups which may act as a potential site for MMAIII to bind, displace zinc ion, and render PARP-1 inactive. Mass spectrometry analysis demonstrates the ability of MMAIII to bind a synthetic peptide representing the zinc-finger domain of PARP-1, and displace zinc from the peptide in a dose-dependent manner. In the presence of continuous MMAIII exposure, continuous 4-week zinc supplementation restored PARP-1 activity levels and reduced the genotoxicity associated with MMAIII. Zinc supplementation did not produce an overall increase in PARP-1 protein levels, decrease the levels of MMAIII-induced reactive oxygen species, or alter Cu-Zn superoxide dismutase levels. Overall, these results present two potential interdependent mechanisms in which MMAIII may increase the susceptibility of UROtsa cells to genotoxic insult and/or malignant transformation: elevated levels of MMAIII-induced DNA damage through the production of reactive oxygen species, and the direct MMAIII-induced inhibition of PARP-1.

Global gene expression changes in human urothelial cells exposed to low-level monomethylarsonous acid

“…Although an elevation in DNA damage has been detected in UROtsa between one and three months of exposure to MMA(III) and attributed to elevation in ROS (Wnek et al, 2009, 2010, 2011), oxidative stress did not appear as a significant category in the Gene Ontology analysis of the first two months of exposure. It is certain that an increasing trend was observed with endogenous ROS, but only a significant change was measured at three months of exposure.…”

Methylarsonous acid causes oxidative DNA damage in cells independent of the ability to biomethylate inorganic arsenic

“…In addition, generation of ODD is often times reliable evidence of oxidative stress in malignantly transformed cells (Kryston et al 2011). In this regard, ROS-generated oxidative stress and mutation is believed to be to be an important mechanism in arsenic-induced cancers (Valko et al, 2006; Kitchin and Conolly, 2010) as exposure to arsenicals induces ODD in various cells (Nesnow et al, 2002; Gomez et al, 2006; Kojima et al 2009; Wnek et al, 2011). In the current study, MMA III caused a remarkably similar temporal pattern of ODD generation in both the methylation-deficient cells and methylation-proficient cells.…”

“…ROS generated during arsenic exposure or arsenic metabolism is suspected to play a role in arsenic-induced carcinogenesis (Valko et al, 2006; Kitchin and Conolly, 2010), although this has not been directly shown in tumor end-point studies. However, studies have shown exposure to iAs or MMA III will induce ODD as a result of ROS generation (Nesnow et al, 2002; Gomez et al, 2006; Kojima et al, 2009; Wnek et al, 2011). At least in some cells, this has been shown to be related to oncogenic transformation, as a blockade of arsenical-induced ODD effectively blocks acquisition of cancer phenotype (Kojima et al, 2009).…”

“…Chronic exposure to arsenic depletes the expression of PTEN during cancer formation in vivo and during malignant transformation in vitro (Cui et al 2004; Tokar et al, 2010a; Sun et al 2012). Thus, not only can exposure to arsenicals induce ROS-mediated ODD (Nesnow et al, 2002; Gomez et al, 2006; Kojima et al, 2009; Wnek et al, 2011), it can also inactivate various factors involved in DNA repair, thereby perturbing the repair process (Cui et al 2004; Tokar et al, 2010a; Wnek et al, 2011; Sun et al 2012). These different roles in DNA damage and DNA repair may actually work in combination to facilitate the arsenic-induced oncogenic process.…”

Knockout of arsenic (+3 oxidation state) methyltransferase is associated with adverse metabolic phenotype in mice: the role of sex and arsenic exposure

“…Based on the IARC review, chronic exposures to iAs in drinking water have been linked to an increased risk of skin, bladder, lung and possibly liver cancer. DNA damage by reactive oxygen species generated in response to iAs exposure and inhibition of DNA repair mechanisms by iAs or its metabolites have been suggested as potential mechanisms underlying the carcinogenic effects of iAs (Kligerman et al 2010; Wnek et al 2011). iAs and its trivalent methylated metabolites, MAs III and DMAs III , are also potent endocrine disruptors that affect several pathways and mechanisms regulating hormone production or function, including glucose stimulated insulin secretion by pancreas (Díaz-Villaseñor et al 2006; Douillet et al, 2013; Fu et al 2010) or insulin signaling and insulin-dependent glucose uptake in adipocytes (Walton et al 2004; Paul et al 2007a).…”