Selective loss of integrated Epstein-Barr virus genomes after long-term cultivation of Burkitt's lymphoma x B-lymphoblastoid cell hybrids due to chromatin instability at the integration site

Abstract

Independently established somatic cell hybrid clones between the Burkitt's lymphoma (BL) cell line BL 60 and the autologous Epstein-Barr virus (EBV)-immortalized lymphoblastoid cell line (LCL) IARC 277 were analyzed with regard to physical state of EBV and karyotype changes in long-term culture. Early after fusion these hybrids carry EBV genomes of the parental BL cell line integrated near the breakpoint of a translocation chromosome der(19) t(11;19) as well as episomal viral DNA molecules of the parental LCL. During long-term culture, however, all hybrid cell lines lost the integrated EBV sequences and retained exclusively episomal EBV, whereas in parental BL cells the EBV genomes remained stably integrated. Loss of integrated EBV in all cases resulted from a break proximal to the EBV integration site. Fluorescence in situ hybridization revealed that this integration site had become a gap-like chromatin area. We thus conclude that the integration of the EBV genomes constitutes a chromosomal region prone to break events akin to the phenomenon of fragile sites. This instability might have led directly to the loss of the EBV DNA itself and of the chromosome 11 region distal to it.