Background: Epstein-Barr virus (EBV) is documented as the important etiologic agent of nasopharyngeal carcinoma (NPC) but the mechanism of development and pathogenesis induced by EBV is presently unclear. Hypermethylation of epithelial-cadherin (E-cadherin) promoter has been shown to be induced in NPC cell line by EBV LMP1 via DNA methyltransferase activation. EBV genomes and hypermethylation of E-cadherin promoter were investigated in NPC tissues to evaluate the role of EBV in the hypermethylation and pathogenesis of NPC.
Methods: Methylation-specific polymerase chain reaction (MSP) was performed to detect E-cadherin promoter hypermethylation in paraffin embedded tissues from patients with NPC and normal nasopharyngeal tissues. EBV genomes were detected by PCR in the tissue samples.
Results: Hypermethylation of E-cadherin promoter and EBV were predominantly detected in undifferentiated and non-keratinizing NPC compared to those in squamous cell NPC. Hypermethylation of E-cadherin was found in 28 of 38 (73.7%) patient samples. EBV was detected in 22 of the 28 (78.6%) NPC samples demonstrating E-cadherin hypermethylation. EBV genomes and hypermethylation were not detected in normal nasopharyngeal tissues. Significant association was found between E-cadherin hypermethylation and EBV genomes (p<0.001; Fisher's exact test). Hypermethylation of E-cadherin was more frequently detected in advanced stages compared to those in early stages of NPC (p=0.036; Fisher's exact test).
Conclusions: The high incidence of EBV with the consistency of E-cadherin hypermethylation, particularly in undifferentiated and non-keratinizing NPC suggests the role of EBV in the hypermethylation. EBV exists at early stage of NPC that induces the hypermethylation and contributes to progression of the disease to the advanced stage of NPC.