SELECTIVE LOSS OF INTEGRATED EPSTEIN-BARR-VIRUS GENOMES AFTER LONG-TERM CULTIVATION OF BURKITTS-LYMPHOMA X B-LYMPHOBLASTOID CELL HYBRIDS DUE TO CHROMATIN INSTABILITY AT THE INTEGRATION SITE

Independently established somatic cell hybrid clones between the Burki tt's lymphoma (BL) cell line BL 60 and the autologous Epstein-Barr vir us (EBV)-immortalized lymphoblastoid cell line (LCL) IARC 277 were ana lyzed with regard to physical state of EBV and karyotype changes in lo ng-term culture. Early after fusion these hybrids carry EBV genomes of the parental BL cell line integrated near the breakpoint of a translo cation chromosome der(19) t(11;19) as well as episomal viral DNA molec ules of the parental LCL. During long-term culture, however, all hybri d cell lines lost the integrated EBV sequences and retained exclusivel y 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 hybr idization revealed that this integration site had become a gap-like ch romatin area. We thus conclude that the integration of the EBV genomes constitutes a chromosomal region prone to break events akin to the ph enomenon 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. (C) 1995 Academic Press, Inc.