title: Molecular analysis of DNA repair gene methylation and protein expression during chemical-induced rat lung carcinogenesis.
abstract: A defective ratio between DNA damage and repair may result in the occurrence of a malignant phenotype. Previous studies have found that many genetic alterations in DNA repair genes occur frequently in lung cancer. However, the epigenetic mechanisms underlying this tumorigenesis are not clear. Herein, we have used a chemical-induced rat lung carcinogenesis model to study the evolution of methylation alterations of DNA repair genes BRCA1, ERCC1, XRCC1, and MLH1. Methylation-specific PCR and immunohistochemistry were used to analyze gene methylation status and protein expression during the progression of lung carcinogenesis. Promoter hypermethylation of BRCA1 was only detected in three samples of infiltrating carcinoma. CpG island hypermethylation of ERCC1, XRCC1, and MLH1 was found to increase gradually throughout lung carcinogenesis progression. Both the prevalence of at least one methylated gene and the average number of methylated genes were heightened in squamous metaplasia and dysplasia compared with normal tissue and hyperplasia, and was further increased in carcinoma in situ (CIS) and infiltrating carcinoma. Immunohistochemical analysis showed that BRCA1 and MLH1 protein expression decreased progressively during the stages of lung carcinogenesis, whereas ERCC1 and XRCC1 expression were only found in later stages. Although methylation levels were elevated for ERCC1 and XRCC1 during carcinogenesis, an inverse correlation with protein expression was found only for BRCA1 and MLH1. These results suggest that a continuous accumulation of DNA repair gene hypermethylation and the consequent protein alterations might be a vital molecular mechanism during the process of multistep chemical-induced rat lung carcinogenesis.
authors.affiliation: 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, PR China.
authors.forename: Wen-bin
authors.initials: WB
authors.lastname: Liu
authors.forename: Lin
authors.initials: L
authors.lastname: Ao
authors.forename: Zhi-hong
authors.initials: ZH
authors.lastname: Cui
authors.forename: Zi-yuan
authors.initials: ZY
authors.lastname: Zhou
authors.forename: Yan-hong
authors.initials: YH
authors.lastname: Zhou
authors.forename: Xiao-yan
authors.initials: XY
authors.lastname: Yuan
authors.forename: Yun-long
authors.initials: YL
authors.lastname: Xiang
authors.forename: Jia
authors.initials: J
authors.lastname: Cao
authors.forename: Jin-yi
authors.initials: JY
authors.lastname: Liu
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics; D000818:Animals; D019313:BRCA1 Protein / Q000235:genetics; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced / Q000235:genetics*; D019175:DNA Methylation / Q000235:genetics*; D004260:DNA Repair / Q000235:genetics*; D045643:DNA Repair Enzymes / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D008175:Lung Neoplasms / Q000139:chemically induced / Q000235:genetics*; D008297:Male; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000235:genetics; D014176:Protein Biosynthesis / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D000076105:X-ray Repair Cross Complementing Protein 1
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D019313:BRCA1 Protein; D004268:DNA-Binding Proteins; C501484:Mlh1 protein, rat; D009687:Nuclear Proteins; D000076105:X-ray Repair Cross Complementing Protein 1; C000619372:Xrcc1 protein, rat; D000070957:MutL Protein Homolog 1; D045643:DNA Repair Enzymes; C559906:ERCC1 protein, rat