Activators of the Epstein-Barr virus lytic program concomitantly induce apoptosis, but lytic gene expression protects from cell death

Expression of the lytic cycle genes of Epstain-Barr virus (EBV) is induced in type I Burkitt's lymphoma-derived cells by treatment with phorbol esters (e.g., phorbol myristate acetate [PMA]), anti-immunoglobulin, or the cytok ine transforming growth factor beta (TGF-beta), Concomitantly, all these ag ents induce apoptosis as judged by a sub-G(1) fluorescence-activated cell s orter (FACS) profile, proteolytic cleavage of poly(ADP-ribose) polymerase ( PARP) and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick en d labeling (TUNEL) staining. However, caspase activation is not required fo r induction of the lytic cycle since the latter is not blocked by the caspa se inhibitor ZVAD. Furthermore, not all agents that induce apoptosis in the se cultures (for example, cisplatin and ceramide) induce the EBV lytic prog ramme. Although it is closely associated with the lytic cycle, apoptosis is neither necessary nor sufficient for its activation. Multiparameter FAGS a nalysis of cultures treated with PMA, anti-Ig, or TGF-beta revealed BZLF1-e xpressing cells distributed in different phases of the cell cycle according to which inducer was used, However, BZLF1-positive cells did not appear to undergo apoptosis and accumulate with a sub-G(1) DNA content, irrespective of the inducer used. This result, which suggests that lytic gene expressio n is protective, was confirmed and extended by immunofluorescence staining doubled with TUNEL analysis. BZLF1- and also gp350-expressing cells were al most always shown to be negative for TUNEL staining. Similar experiments us ing EBV-positive and -negative subclones of Akata BL cells carrying an epis omal BZLF1 reporter plasmid confirmed that protection from apoptosis was as sociated with the presence of the EBV genome. Finally, treatment with phosp honoacetic acid or acyclovir prior to induction with PMA, anti-Ig, or TGF-b eta blocked the protective effect in Mutu-I cells. These data suggest that a late gene product(s) may be particularly important for protection against caspase activity and cell death.