Promoter hypermethylation of miR-34a contributes to the risk, progression, metastasis and poor survival of laryngeal squamous cell carcinoma.

MiR-34a is a direct transcriptional target of p53, which induces cell cycle arrest, senescence, and apoptosis. Recently, we and others identified abnormal expression of miR-34a in laryngeal squamous cell carcinoma (LSCC). The aim of our present study was to investigate the contribution of miR-34a promoter methylation to LSCC. Bisulfite pyrosequencing technology was applied to measure DNA methylation levels of six CpG sites in the miR-34a promoter from 104 LSCC tumor tissues and their corresponding adjacent tissues. Our results showed that the methylation levels of the miR-34a promoter were significantly higher in cancer tissues compared with the adjacent tissues (adjusted P=5.05E-10). A breakdown analysis for cigarette smoking behavior indicated a significantly elevated tendency of miR-34a methylation level in LSCC patients with smoking behavior but not in LSCC patients without smoking behavior (Smoking: Tumor vs Normal, adjusted P=3.12E-9; Non-smoking: Tumor vs Normal, adjusted P=0.073). In addition, miR-34a promoter methylation frequency remarkably increased in the advanced stage patients (adjusted P=0.003) and advanced T classified tumors (adjusted P=0.015). Moreover, significant association of miR-34a promoter hypermethylation with LSCC lymph metastasis was observed (adjusted P=0.002). Meanwhile, Kaplan-Meier survival curves results showed that high methylation of miR-34a promoter were associated with poor overall survival (log-rank test, P=0.023). Our study revealed that miR-34a promoter hypermethylation was a risk factor for LSCC, played a critical role in the disease progression and metastasis, and could serve as a poor prognostic factor for LSCC.