Chromosomal integration of Epstein - Barr virus genomes in nasopharyngeal carcinoma cells

Little has been known about whether Epstein-Barr virus (EBV) could persist in nasopharyngeal carcinoma (NPC) cells by chromosomal integration, and no NPC cell line harboring integrated EBV has been reported. In this study, we explored this issue through isolating EBV-infected NPC cell clones generated from an in vitro infection system and examining the configuration of EBV DNA in these cells.EBV genomes were demonstrated in NPC cell clones using polymerase chain reaction and Southern hybridization. Viral nuclear antigens were also detected by use of an anticomplement immunofluorescence assay and an immunoblotting assay. Gardella gel analysis showed that two of the EBV-positive cell clones, H2B4 and H2B17-7, harbored no extrachromosomal form of the viral genome. Restriction analysis of EBV genomic termini indicated that EBV DNA in these two cell clones was not circularized, and the viral genomes were integrated into chromosomes as demonstrated by fluorescence in situ hybridization.This is the first in vitro model of EBV persistence in NPC cells by genomic integration, which represents a unique state of virus-cell interaction. Using this model, investigation into the association between EBV integration and chromosomal abnormality in tumor cells will help to reveal the underlying biologic significance.