Epstein-Barr Virus (EBV) in Endemic Burkitt's Lymphoma: Molecular Analysis of Primary Tumor Tissue

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Abstract
Many aspects of Epstein-Barr virus (EBV) and tumor biology have been studied in Burkitt's lymphoma (BL)-derived cell lines. However, in tissue culture, patterns of gene expression and C promoter-G (CpG) methylation often change and viral strain selection may occur. In this report, 10 cases of snap-frozen endemic BL tumors are characterized in terms of viral gene expression, promoter usage, methylation, and viral strain. EBNA1 and BamHI-A rightward transcripts (BART) were detected in 7 of 7 and LMP2A transcripts in 5 of 7 tumors with well-preserved RNA. Transcripts for the other EBNAs and for LMP1 were not detected in any tumor. These tumors differ from BL cell lines in that they lack a variety of lytic cycle transcripts. This pattern of viral gene expression in endemic BL is similar to that reported in peripheral blood mononuclear cells (PBMCs) from healthy EBV–seropositive individuals. EBNA1 transcripts originated from the Q promoter (Qp) but not C, W, or F promoters that drive transcription of EBNA1 in other circumstances. Whereas Cp has been previously shown to be entirely CpG methylated in BL, bisulfite genomic sequencing showed virtually no methylation in Qp. Type-A EBV was detected in 6 of 10 and type B in 4 of 10 cases. A previously reported 30bp deletion variant in the carboxyl terminal of LMP1 gene was detected in 5 of 10 cases. The association with both A and B strains contrasts with EBV–associated Hodgkin's disease, nasopharyngeal carcinoma, and post-transplant lymphoproliferative disease, which are much more consistently associated with A strain virus.