부산대학교 도서관

Background: Retinoic acid plays an important role in lung development and differentiation, acting primarily via nuclear receptors encoded by the retinoic acid receptor-[Beta] (RAR[Beta]) gene. Because receptor isoforms RAR[Beta]2 and RAR[Beta]4 are repressed in human lung cancers, we investigated whether methylation of their promoter, P2, might lead to silencing of the RAR[Beta] gene in human lung tumors and cell lines. Methods: Methylation of the P2 promoter from small-cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC) cell lines and tumor samples was analyzed by the methylation-specific polymerase chain reaction (PCR). Expression of RAR[Beta]2 and RAR[Beta]4 was analyzed by reverse transcription--PCR. Loss of heterozygosity (LOH) was analyzed by PCR amplification followed by electrophoretic separation of PCR products. Statistical differences were analyzed by Fisher's exact test with continuity correction. Results: The P2 promoter was methylated in 72% (63 of 87) of SCLC and in 41% (52 of 1271) of NSCLC tumors and cell lines, and the difference was statistically significant (two-sided P [is less than] .001). By contrast, in 57 of 58 control samples, we observed only the unmethylated form of the gene. Four tumor cell lines with unmethylated promoter regions expressed both RAR[Beta]2 and RAR[Beta]4. Four tumor lines with methylated promoter regions lacked expression of these isoforms, but demethylation by exposure to 5-aza-2'-deoxycytidine restored their expression. LOH at chromosome 3p24 was observed in 100% (13 of 13) of SCLC lines and 67% (12 of 18) of NSCLC cell lines, and the difference was statistically significant (two-sided P = .028). Conclusions: Methylation of the RAR[Beta] P2 promoter is one mechanism that silences RAR[Beta]2 and RAR[Beta]4 expression in many lung cancers, particularly SCLC. Chemical demethylation is a potential approach to lung cancer therapy. [J Natl Cancer Inst 2000;92:1303-7]