[Novel miRNA genes methylated in lung tumors].

MicroRNAs play an important role in the regulation of expression of many genes and are involved in carcinogenesis. The regulation of miRNA gene expression can involve the methylation of promoter CpG islands. In this work, the methylation of six miRNA genes (mir-107, mir-125b-1, mir-130b, mir-137, mir-375, and mir-1258) in non-small-cell lung cancer (NSCLC) was studied for the first time by methylation-specific PCR using a representative set of specimens (39 cases). Four new genes (mir-125b-1, mir-137, mir-375, and mir-1258) methylated in primary NSCLC tumors were identified with frequencies of 56, 31, 56, and 36%, respectively. The frequencies of miRNA promoter methylation in DNA of tumors and histologically normal tissues differed significantly (P < or = 0.05 by Fisher's test). In lung tissues of 20 donors without a history of cancer, these genes were only methylated in a few cases. It was also shown that the previously unstudied promoter CpG islands of mir-107 and mir-130b were not methylated in NSCLC. The frequencies of mir-125b-1 and mir-137 methylation were shown for the first time to correlate with NSCLC progression (clinical stage and metastasis).