[Promoter hypermethylation of DNA repair gene O6-methylguanine DNA methyltransferase in laryngeal squamous cell carcinoma].

OBJECTIVE: O6-methylguanine DNA methyltransferase (MGMT) is a DNA repair protein. It plays a important role in the repair of DNA damage caused by the exposure to methylating agents. Hypermethylation of CpG islands in the promoter regions result in MGMT genes loss of transcription. This study explored the hypermethylation of CpG islands in the promoter regions of MGMT genes in laryngeal squamous cell carcinoma. METHODS: Methylation-specific PCR and semiquantify RT-PCR were used to study the promoter methylation of the MGMT gene and loss of transcription in laryngeal carcinoma tissues, tissues adjacent to the tumor and normal laryngeal tissues. RESULTS: Among the 46 laryngeal carcinoma, MGMT gene hypermethylation was present in 16 cases (34.8%). MGMT hypermethylation was not detected in all tissues adjacent to the tumors and 5 normal tissues. There is no statistical significant difference of promoter hypermethylation among the samples of different histological grade (chi2 = 3.130, P = 0.077) or samples from patients with different TNM stages (chi2 = 3.957, P = 0.138). No expression of MGMT mRNA was found in all hypermethylated laryngeal carcinoma tissues. Expression of MGMT mRNA was detected in all unmethylated laryngeal carcinoma tissues, tissues adjacent to the tumors and 5 normal tissues. Expression of MGMT mRNA in unmethylated laryngeal carcinoma tissues is higher than tissues adjacent to the tumors (t = 30.540, P < 0.01) and normal tissues (t = 31.882, P < 0.01). There is no statistical significant difference of MGMT mRNA expression between tissues adjacent to the tumors and normal tissues (t = 0.419, P = 0.677). CONCLUSION: MGMT gene promoter hypermethylation is associated with loss of its transcription.