Aberrant promoter methylation of multiple genes in non-small cell lung cancers

Aberrant methylation of CpG islands acquired in tumor cells in promoter reg ions is one method for loss of gene function. We determined the frequency o f aberrant promoter methylation (referred to as methylation) of the genes r etinoic acid receptor beta -2 (RAR beta), tissue inhibitor of metalloprotei nase 3 (TIMP-3), p16(INK4a), O-6-methylguanine-DNA-methyltransferase (MGMT) , death-associated protein kinase (DAPK), E-cadherin (ECAD), p14(ARF), and glutathione S-transferase P1 (GSTP1) in 107 resected primary non-small cell lung cancers (NSCLCs) and in 104 corresponding nonmalignant lung tissues b y methylation-specific PCR. Methylation in the tumor samples was detected i n 40% for RAR beta, 26% for TIMP-3, 25% for p16(INK4a), 21% for MGMT, 19% f or DAPK, 18% for ECAD, 8% for p14(ARF), and 7% for GSTP1, whereas it was no t seen in the vast majority of the corresponding nonmalignant tissues. More over, p16(INK4a) methylation was correlated with loss of p16(INK4a) express ion by immunohistochemistry. A total of 82% of the NSCLCs had methylation o f at least one of these genes; 37% of the NSCLCs had one gene methylated, 2 2% of the NSCLCs had two genes methylated, 13% of the NSCLCs had three gene s methylated, 8% of the NSCLCs had four genes methylated, and 2% of the NSC LCs had five genes methylated. Methylation of these genes was correlated wi th some clinicopathological characteristics of the patients. In comparing t he methylation patterns of tumors and nonmalignant lung tissues from the sa me patients, there were many discordancies where the genes methylated in no nmalignant tissues were not methylated in the corresponding tumors. This su ggests that the methylation was occurring as a preneoplastic change. We con clude that these findings confirm in a large sample that methylation is a f requent event in NSCLC, can also occur in smoking-damaged nonmalignant lung tissues, and may be the most common mechanism to inactivate cancer-related genes in NSCLC.