Epstein-Barr virus infection in precursor lesions of nasopharyngeal carcinoma

Abstract

Background & objective: The infiltrating neoplastic cells within early-stage nasopharyngeal carcinoma (NPC) are consistently infected with Epstein-Barr virus (EBV). The precursor lesions could often be found in paracancerous epithelium of early-stage NPC. This study was to investigate the role of EBV infection and the intrahost evolution of EBV genotype developed in nasopharyngeal carcinogenesis through detection of EBV harboring in precursor lesions.

Methods: EBV-encoded RNA (EBER) in 15 cases of early-stage NPC biopsy tissue was detected by nucleic acid in situ hybridization. EBV type and latent membrane protein 1 (LMP1) EBV strain in precursor lesions and carcinoma nests were detected by nested polymerase chain reaction (PCR). DNA sequencing of the representative PCR products of carboxyl-terminus of LMP1 gene was analyzed by using four-colored fluorescence terminator sequencing technique.

Results: Most infiltrating carcinoma cells of all 15 cases of NPC showed EBER-positive. EBER-positive abnormal epithelial cells and/or infiltrating lymphocytes were found in 14 of 15 cases of precursor lesion. Single A-type EBV was detected in 9 of 11 available DNA samples of carcinoma nest and 9 of 10 available DNA samples of precursor lesion. The carboxyl-terminus of EBV LMP1 gene was detected in all 15 DNA samples of carcinoma nest, among which 14 were single 30-bp deleted LMP1 (del-LMP1) EBV infection and 1 was coinfection of wild-type LMP1 (wt-LMP1) EBV strain and del-LMP1 EBV strain. Among the 11 available DNA samples of precursor lesion suitable for carboxyl-terminus amplification, 5 were coinfection of wt-LMP1 and del-LMP1 EBV, 4 were single del-LMP1 EBV infection, 1 was single wt-LMP1 EBV infection, and 1 showed negative reaction. The DNA sequence of the carboxyl-terminus of wt-LMP1 gene was identical with that of B95-8 cells, while that of del-LMP1 gene had a 30-bp deletion (codon: 346-355) and 4 missense point mutations (codon: 334, 335, 338, and 366).

Conclusion: EBV infection in nasopharyngeal epithelial cells is a preinvasive event of carcinogenesis of NPC, and the intrahost evolution of EBV genotype would take place during nasopharyngeal carcinogenesis.