Ski is silenced by methylation and acts as tumor suppressor in non-small cell lung cancer.

Epigenetic silencing of tumor suppressors contributes to the development and progression of lung cancer. We recently found that Ski was hypermethylated in lung cancer. This study aimed to clarify its epigenetic alteration, molecular mechanisms and clinical significance in lung cancer. Ski methylation was evaluated by methylation-specific PCR (MS-PCR) and bisulfite sequencing. mRNA level of Ski was measured by RT-PCR and compared with the methylation status. Ski methylation correlated with decreased mRNA expression in human lung cancer cell lines. Ski hypermethylation was detected in 56.0% of primary lung tumors and associated with poor differentiation and late tumor stage. Demethylation agent 5-aza-2'-deoxycytidine (5-aza-2'dC) restored Ski expression. Re-expression of Ski in lung cancer cells inhibited cell proliferation, clonogenicity, migration, invasion and tumor formation. Ski decreased transcriptional activities of Smads and TAZ. Multivariate analysis showed that patients with Ski positive expression had a better overall survival in resected non-small cell lung cancer (NSCLC) patients. Our results revealed that Ski acts as a tumor suppressor inactivated by DNA methylation and is an independent prognostic factor of lung cancer.