BHRF1, the Epstein-Barr virus (EBV) homologue of the BCL-2 protooncogene, is transcribed in EBV-associated B-cell lymphomas and in reactive lymphocytes

BHRF1, one of many Epstein-Barr virus (EBV)-encoded proteins, shows strong functional homology to the human bcl-2 proto-oncogene product, a protein involved in the pathogenesis of a subset of B-cell lymphomas, ie, follicle center cell lymphomas (FCCL). We have investigated the presence of possible latent and lytic transcripts of BHRF1 using a reverse transcriptase-polymerase chain reaction (RT-PCR)-based assay in a group of EBV-associated B-cell lymphomas in patients with (N = 5) or without overt immunodeficiency (N = 4), in T-cell lymphomas (N = 9), and in cases of Hodgkin's disease (N = 6). BHRF1 transcription was found consistently in EBV-associated (ie, diffuse EBER 1/2-positive) B- cell lymphomas in patients with or without immune deficiency, whereas in EBV-associated T-cell lymphomas or in EBV-associated Hodgkin's disease, BHRF1 transcription was only detected in two T-cell lymphomas and one case of Hodgkin's disease, which also harbored EBER 1/2- positive reactive cells. Moreover, weak BHRF1 signals were found in two T-cell lymphomas where EBER 1/2 expression was detected mainly in sporadic reactive lymphocytes and in one reactive tonsil with sporadic EBER 1/2-positive lymphocytes. BHRF1 transcripts were found to be generated by the C or W promoter (associated with viral latency) and/or by the H promoter (associated with the virus lytic cycle). In all cases with H promoter-derived BHRF1 transcripts, transcripts encoding ZEBRA were also detected, suggesting a reactivation of the virus lytic cycle. Analysis of other EBV genes revealed transcription of BARFO in all tested EBV-harboring tissues. Transcription of EBNA1 and LMP1 was usually detected, whereas EBNA2 transcription was found exclusively in B-cell lymphomas in immunocompromised patients. These data demonstrate that BHRF1 transcripts are exclusively found in EBV-associated B-cell lymphomas. When BHRF1 transcripts are detected in T-cell lymphomas or in Hodgkin's disease, it is probably due to the presence of reactive EBER 1/2-positive lymphocytes. The consistent transcription of BHRF1 in EBV-associated B-cell lymphomas suggests a possible pathogenic role for this gene product in EBV-positive B-cell lymphomas analogous to bcl-2.