Aberrant Promoter Hypermethylation Of CYP2J2 Gene In Lung Cancers

Lung carcinoma is one of the most common causes of cancer deaths in the world. Despite much progress in the treatment and detection methods of lung cancer, the prognosis remains poor. This situation results largely from micrometastasis, which is present in greater than two-thirds of patients at the time of diagnosis. Therefore, it clearly is imperative that efficient diagnostic methods be developed to detect lung carcinoma at the earliest stages, during which curative surgical resection remains feasible. One promising approach to early detection involves the identification of lung carcinoma-specific molecular biomarkers, especially those associated with the initiation and progression of lung carcinoma in its earliest stage. Screening tests on long-term smokers used to date (radiography and sputum cytology) have failed to reduce lung carcinoma mortality.Epigenetic events are a critical force driving initiation and progression of cancer. Methylation is the most common epigenetic change. Recent studies show that silencing of tumor-related genes, resulting from epigenetic alterations, are an early event in many human malignancies, including non-small cell lung cancer (NSCLC). In lung cancer, several sets of genes including the tumor suppressor gene p16, the DNA repair gene O6-methylguanine-DNAmethyltransferase (MGMT), E-cadherin and retinoic acid receptor beta have been shown to be frequentlymethylated and inactivated. Epigenetic alterations in cancer, as opposed to genetic lesions, are potentially reversible. The DNA methylation inhibitor 5-aza-2-deoxycytidine (5-Aza-dC) can reactivate the expression of genes by demethylating.CYP2J2 gene plays an important role in tumor development including lung cancer. Currently, many studies focused on the metabolism of CYP2J2 on the drugs foreign. However, regulation of expression has not been reported. This study investigated methylation of CYP2J2 gene in lung cancer. We found that aberrant promoter hypermethylation of CYP2J2 gene in lung cancer, and promoter methylation of CYP2J2 gene partially regulated mRNA and protein expression. We confirm the relationship of sex and the methylation level of CYP2J2 gene promoter.We went first to evaluate CYP2J2 promoter methylation status by methylation-specific PCR in 3 lung cancer cell lines (A549, NCI-H446 and NCI-H460). They all displayed a clear methylated band. Then we treated lung cancer cell lines with the demethylating agent 5-aza-dC. Treatment with 5-Aza-dC increased the expression of CYP2J2 mRNA in both A549 and NCI-H460 cell lines. There is no significant change before and after treatment in NCI-H446. MSP revealed a reduction of the intensity of the band corresponding to methylated DNA in comparison to untreated cell lines, which was paralleled by an increase of amplification products when primers for unmethylated DNA were used. These results support the conclusion that CpG methylation of the CYP2J2 gene regulated expression in part.To elucidate methylation of CYP2J2 gene in vivo, CYP2J2 methylation was analyzed in normal and matching tumor tissue from 56 patients with lung cancer, and a control group of 10 patients without cancer using a methylation-specific PCR. CYP2J2 promoter hypermethylation was detectable by MSP in 44 of 56 (78.6%) tumor samples,28 of 56 (50%) matching normal lung of lung cancer patients, and none of 10 (0%) normal lung specimens of the control group without lung cancer. Indeed, the observation that methylated CYP2J2 was only present in noncancerous tissues when there was detectable methylation of CYP2J2 in tumor tissue and the lack of any CYP2J2 methylation in normal lung tissue from patients without lung cancer suggest that this methylation event is part of the process of malignant transformation, and, thus, a tumor-specific phenomenon in lung cancer. It is possible that this noncancerous tissue, although it appeared to be histologically normal, is abnormal because of environmental factors such as exposure to cigarette smoke.To further understand the correlation between CYP2J2 methylation and clinicopathological factors, we initially analyzed associations between the methylation of CYP2J2 gene and available clinical information including smoking status sex, age, tumor stage, and histologic subtype of the tumor. No association was found between methylation levels of CYP2J2 gene and most of the risk factors, except for sex. Lung cancers from men exhibited higher methylation levels of CYP2J2 than those from women.As noted above, we identified novel gene frequently methylated in lung cancer. Promoter hypermethylation of CYP2J2 gene was detected in three kinds of lung cancer cell lines, primary lung tumors, and the surrounding normal tissues, whereas hypermethylation of CYP2J2 gene was rarely found in normal sample without cancer patients. Promoter methylation of CYP2J2 gene partially regulated mRNA and protein expression. And, lung cancers from men exhibited higher methylation levels of CYP2J2 than those from women.In summary, we have systemically investigated the methylation of CYP2J2 gene in lung cancer. We propose that CYP2J2 hypermethylation is present in the lung of most patients with lung carcinoma, suggesting that this molecular alteration may be involved in the process of lung carcinogenesis, and that it is a potential target for diagnosis and treatment of lung carcinoma. Moreover, this study provides evidence of sex-specific differences in methylation patterns in lung cancers. And thus, exemplifies the mechanism by which environmental factors may interact with key genes involved in tumorigeness.