Influence of Epstein-Barr virus latent gene expression on the apoptosis-inducing effects of cortisone and 2-chlorodeoxyadenosine (2-CDA) in B-cell lines.

Burkitt's lymphoma (BL) cell lines are heterogenous with regard to phenotype, growth characteristics, Epstein-Barr virus (EBV) latent gene and BCL-2 expression. Previously we have demonstrated that transfection with the EBV genes LMP or EBNA-2 upregulates BCL-2 in B-cell lines. In order to test the functional relevance of these findings, cell lines were examined with regard to their sensitivity towards different apoptosis-inducing agents. BL cell lines transfected with LMP expressed high levels of BCL-2, and were compared with the parental cell line expressing little or no BCL-2. We also studied EBV immortalized lymphoblastoid cell lines (LCL) with high BCL-2 expression and strong resistance towards low serum concentrations. Hydrocortisone (HC) and 2-chlorodeoxyadenosine (2-CDA) were used alone or in different combinations. Cell growth and apoptosis were studied morphologically and by determination of viability and DNA fragmentation. BL cell lines showed different sensitivity towards HC-induced apoptosis, and sensitive cell lines became more resistant towards HC after infection with EBV or transfection with LMP and subsequent upregulation of BCL-2 expression. BL cell lines and LCL were relatively insensitive towards 2-CDA-induced apoptosis, and high concentrations of 2-CDA were necessary, independently of the levels of BCL-2 expression. In contrast to low-grade non-Hodgkin's lymphomas, 2-CDA does not appear to be a valuable drug for the treatment of Burkitt's lymphoma. LMP expression provides resistance towards hydrocortisone-induced apoptosis in vitro, possible through upregulation of BCL-2.