Down‐regulation of integrated Epstein‐Barr virus nuclear antigen 1 and 2 genes in a burkitt lymphoma cell line after lymphoblastoid cells somatic cell fusion with autologous EBV‐immortalized

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Abstract
Epstein Barr virus (EBV) latent gene expression was analyzed in somatic cell hybrids between an EBV‐positive Burkitt lymphoma (BL) cell line (BL 60) and an autologous EBV‐immortalized lymphoblastoid cell line (LCL, IARC 277). The EBV genomes carried by the parental cell lines differ in sequence and in their physical state. The BL 60 EBV genome is integrated into the host cell genome whereas the LCL IARC 277 carries exclusively episomal EBV molecules. The hybrid cells contain both EBV genomes and display the differentiation phenotype of the parental LCL with regard to growth characteristics and cell‐surface antigen expression in vitro and in vivo. While the EBNA 1 and EBNA 2 gene expression of the LCL‐derived EBV is maintained in these hybrid cells, the BL‐60‐derived EBNA 1 and EBNA 2 genes are transcriptionally down‐regulated. Mapping of the genomic region surrounding the latent Cp promoter of the BL‐60‐derived EBV revealed an extensive deletion upstream of the Cp promoter including the enhancer element in the ori P region, the origin of latent viral replication (ori P), the coding sequences for the EBV latent membrane protein (LMP) and the EBV terminal protein (TP), and suggested that one viral‐cellular junction sequence is located near the Cp promoter. Integration of EBV into the host cell genome together with the extensive deletion might be causally related with the altered latent gene expression pattern after introduction of a lympho‐blastoid host‐cell background by somatic cell fusion. Down‐regulation of the BL‐60‐derived EBNA genes could be due to loss of regulatory sequences in the BL‐derived EBV necessary for EBNA 1 and EBNA 2 transcription in the lymphoblastoid hybrid cells, but not in the parental BL cells.