The expression of mir-29s is inversely correlated with that of DNMT3A and DNMT3B in lung cancer tissue, and the enforced expression of mir-29s in lung cancer cell lines restores the normal pattern of DNA methylation, induces the re-expression of methylation-silenced tumor suppressor genes (such as FHIT and WWOX), and inhibits tumorigenicity both in vitro and in vivo. The gene discussed is DNMT3A; the disease is lung cancer.