Promoter hypermethylation contributes to the frequent suppression of the CDK10 gene in human nasopharyngeal carcinomas

BACKGROUND: Previous studies have shown a down-regulation of the gene encoding cyclin-dependent kinase 10 (CDK10) in hepatocellular carcinomas. Here we provide evidence that down-regulation of the CDK10 gene is mediated by promoter hypermethylation in primary human nasopharyngeal carcinomas (NPC) and NPC-derived cell lines. METHODS: RT-PCR, Western blotting, methylation-specific PCR and bisulfite sequencing were performed to assess the expression and methylation status of the CDK10 gene in primary NPC samples, NPC-derived cell lines and patient-derived peripheral blood samples. The NPC-derived cell line CNE-2 was selected for treatment with a methylation inhibitor to restore CDK10 expression. In addition, cell proliferation, invasion and colony formation assays were performed to assess the inhibitory effects of ectopic CDK10 expression in CNE-2 cells. RESULTS: Down-regulation of CDK10 expression in primary NPC samples (23/40, 57.5%) was found to be significantly correlated with the methylation status of its promoter CpG island (21/40, 52.5%). Demethylation by 5-aza-dC treatment led to reactivation of the CDK10 gene in the CNE-2 cell line. Additionally, exogenous expression of CDK10 in CNE-2 cells strongly suppressed its growth, invasion and colony formation capacities. The high sensitivity (15/40, 37.5%) and specificity (0% false positives) of detecting CDK10 promoter hypermethylation in NPC patient-derived peripheral blood samples suggest that it could be employed as an epigenetic marker for noninvasive cancer diagnosis and recurrence screening. CONCLUSION: Our findings implicate that aberrant methylation of the CDK10 gene promoter occurs frequently in NPC, and that reactivation of CDK10 might be utilized as a novel epigenetic strategy for the treatment of NPC patients.