CpG island hypermethylation of multiple tumor suppressor genes associated with loss of their protein expression during rat lung carcinogenesis induced by 3-methylcholanthrene and diethylnitrosamine |
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Authors: | Liu Wen-bin Ao Lin Zhou Zi-yuan Cui Zhi-hong Zhou Yan-hong Yuan Xiao-yan Xiang Yun-long Cao Jia Liu Jin-yi |
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Institution: | Department of Hygiene Toxicology, Preventive Medical College, Third Military Medical University, Key Laboratory of Medical Protection for Electromagnetic Radiation, Ministry of Education of China, Chongqing 400038, PR China |
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Abstract: | The epigenetic mechanisms underlying the tumorigenesis caused by polycyclic aromatic hydrocarbons and nitrosamine compounds such as 3-methylcholanthrene (MCA) and diethylnitrosamine (DEN) are currently unknown. We reported previously that dynamic changes in DNA methylation occurred during MCA/DEN-induced rat lung carcinogenesis. Here, we used the same animal model to further study the evolution of methylation alterations in tumor suppressor genes (TSGs) DAPK1, FHIT, RASSF1A, and SOCS-3. We found that none of these genes were methylated in either normal or hyperplasia tissue. However, as the severity of the cancer progressed through squamous metaplasia and dysplasia to carcinoma in situ (CIS) and infiltrating carcinoma, so methylation became more prevalent. Particularly dramatic increases in the level of methylation, the average number of methylated genes, and the incidence of concurrent methylation in three genes were observed in CIS and infiltrating carcinoma. Similar but less profound changes were seen in squamous metaplasia and dysplasia. Furthermore, methylation status was closely correlated to loss of protein expression for these genes, with protein levels markedly declining along the continuum of carcinogenesis. These results suggest that progressive CpG island hypermethylation leading to inactivation of TSGs might be a vital molecular mechanism in the pathogenesis of MCA/DEN-induced multistep rat lung carcinogenesis. |
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Keywords: | CIS carcinoma in situ DEN diethylnitrosamine MCA 3-methylcholanthrene MSP methylation-specific polymerase chain reaction TSGs tumor suppressor genes |
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