DUAL EBNA1 PROMOTER USAGE BY EPSTEIN-BARR-VIRUS IN HUMAN B-CELL LINESEXPRESSING UNIQUE INTERMEDIATE CELLULAR PHENOTYPES

The use of different viral promoters for the expression of the EBNA1 g ene product appears to be a critical step in the regulation of Epstein -Barr virus latent gene expression and may reflect the extent of diffe rentiation of B-cell hosts. Low-passage Burkitt lymphoma cell lines re semble immature B cells in that they express CD10 (CALLA) and do not e xpress B cell activation antigens. In these cells, transcription from a promoter located in the BamHI F fragment of the viral genome results in the exclusive expression of EBNAI, referred to as the latency I pa ttern of viral gene expression. In contrast, high-passage Burkitt lymp homa cells and lymphoblastoid cell lines resemble activated B cells in that they do not express CD10 but do express activation antigens such as CD23. In these cells, the use of two promoters located in the BamH I W and C fragments of the viral genome leads to the expression of all six EBNA gene products (latency III). We have found that four human B -cell lines, DB, LBW2, LBW14, and Josh 7, stably express a pattern of B-cell differentiation antigens intermediate between those found in la tency I and latency III cell lines and characterized by the coexpressi on of CD10 and CD23. The pattern of EBNA1 promoter usage in these cell lines was examined to determine whether their intermediate cellular p henotype was reflected in their patterns of viral gene expression. DB, LBW2, and LBW14 utilize both the BamHI F promoter region and BamHI W promoter region to transcribe the EBNAI gene. This stable pattern of m ixed promoter usage for the expression of the EBNA gene products in B cells has not previously been described. In addition, these three B-ce ll lines expressed lower levels of the viral latent gene product EBNA2 than those typically observed in latency III cells. The lower levels of activation of viral and cellular promoters known to be regulated by EBNA2 also correlated with the reduced levels of EBNA2 expression in these cells. These included the viral LMP1 and LMP2A promoters and the cellular CD23B promoter. The fourth B cell line, Josh 7, expressed EB NA1 mRNAs derived from both the BamHI W promoter and BamHI C promoter, similar to latency III cells. The intermediate cellular phenotype in Josh 7 cells appeared to be due, in part, to a deficiency in the expre ssion of viral LMP1. These results show that the B-cell lines express unique intermediate patterns of expression of viral and cellular gene products and suggest that a continuum of latency states may exist for Epstein Barr virus infected B lymphocytes.