Chronic oral exposure to inorganic arsenate interferes with methylation status of p16INK4a and RASSF1A and induces lung cancer in A/J mice

Environmental Health Sciences Division, National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506, Japan.
Toxicological Sciences (Impact Factor: 3.85). 07/2006; 91(2):372-81. DOI: 10.1093/toxsci/kfj159
Source: PubMed


Although inorganic arsenate (iAsV) or arsenite (iAsIII) is clearly a human carcinogen, it has been difficult to produce tumors in rodents. In the present study, we orally administered
iAsV to A/J mice to examine arsenic carcinogenicity in rodent. A/J mice (male, n = 120) assigned to four groups were given drinking water containing 0, 1, 10, and 100 ppm iAsV for 18 months. At the end of experiment, the complete lungs were removed and used for examining histopathology and extracting
RNA and DNA. Epigenetic effects of iAsV on DNA methylation patterns of p16INK4a and RASSF1A genes were determined by methylation-specific polymerase chain reaction. Changes of p16INK4a and RASSF1A at mRNA and protein levels were examined by reverse transcriptase–polymerase chain reaction and immunohistochemistry.
Arsenic was accumulated dose dependently in the lung tissues of iAsV-exposed mice. Increase in lung tumor number and lung tumor size was observed in iAsV-exposed mice compared to the control. Histopathological examination showed that the rate of poorly differentiated lung adenocarcinoma
was much higher in iAsV-exposed mice than in the control. Methylation rates appeared to be higher in a dose-related tendency in lung tumors from
iAsV-exposed mice compared to the control. Lower or loss of p16INK4a and RASSF1A expression was found in lung tumors from iAsV-exposed mice, compared to that in nontumor lung tissues from both control and iAsV-exposed mice, and this reduced or lost expression was in accordance with hypermethylation of the genes. In conclusion, iAsV exposure increased lung tumor incidence and multiplicity in A/J mice. Epigenetic changes of tumor suppressor genes such as
p16INK4a and RASSF1A are involved in the iAsV-induced lung carcinogenesis.

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Available from: Toshifumi Wakai, Feb 06, 2014
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    • "Arsenic exposure alters DNA methylation of genes involved in tumorigenesis (reviewed in Bailey and Fry, 2014a). Tumor suppressor genes that are methylated in response to arsenic exposure include CDKN2A (Davis et al., 2000), tumor protein 53 (TP53) (Mass and Wang, 1997; Davis et al., 2000), von Hippel–Lindau tumor suppressor (VHL) (Zhong and Mass, 2001), RASSF1A (Cui et al., 2006a), DAPK (Chai et al., 2007), and reversion-inducingcysteine-rich protein with kazal motifs (RECK) (Huang et al., 2011). DNA methylation of oncogenes in response to arsenic include cyclin D1 (CCND1) (Chen et al., 2004), estrogen receptor alpha (ER-α) (Chen et al., 2004; Waalkes et al., 2004) and members of the RAS family of small G-proteins such as HRAS and KRAS (Benbrahim-Tallaa et al., 2005). "
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    ABSTRACT: Exposure to toxic metals poses a serious human health hazard based on ubiquitous environmental presence, the extent of exposure, and the toxicity and disease states associated with exposure. This global health issue warrants accurate and reliable models derived from the risk assessment process to predict disease risk in populations. There has been considerable interest recently in the impact of environmental toxicants such as toxic metals on the epigenome. Epigenetic modifications are alterations to an individual's genome without a change in the DNA sequence, and include, but are not limited to, three commonly studied alterations: DNA methylation, histone modification, and non-coding RNA expression. Given the role of epigenetic alterations in regulating gene and thus protein expression, there is the potential for the integration of toxic metal-induced epigenetic alterations as informative factors in the risk assessment process. In the present review, epigenetic alterations induced by five high priority toxic metals/metalloids are prioritized for analysis and their possible inclusion into the risk assessment process is discussed.
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    • "In accordance with the major studies published to date [26, 27], our results showed that the incidence of positive RASSF1A expression decreased progressively in the normal mucosa, adenoma, and tumor tissues. The loss of RASSF1A protein expression was found to be more obvious in tumor tissues than in the nontumor tissues. "
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    • "Lung cancer cell models have also shown that arsenic exposure resulted in P53 promoter hypermethylation and subsequent transcriptional silencing of this gene [78]. Promoter hypermethylation of tumor suppressors CDKN2A and RASSF1A was also observed in lung tumors of mice exposed to inorganic arsenate [75]. "
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