Expression of the Epstein Barr virus transforming protein LMP1 causes a rapid and transient stimulation of the Bcl-2 homologue Mcl-1 levels in B-cell lines.

The EBV-encoded latent membrane protein 1 (LMP1) suppresses apoptosis in B lymphocytes through up-regulation of Bcl-2. However, the maximum induction of Bcl-2 by LMP1 takes about 48-72 h. We show in this report that up-regulation of the Bcl-2 homologue Mcl-1 by LMP1 preceded the induction of Bcl-2 and that the up-regulation was transient; therefore, Mcl-1 levels decreased when Bcl-2 levels started to increase. This finding supports the hypothesis that Mcl-1 functions as a rapidly inducible, short-term effector of cell viability. LMP1 also blocked the decline in the Mcl-1 levels in response to apoptotic stimulation triggered by elevated cyclic AMP. This effect of LMP1 was associated with a delayed cell death in the EBV-negative Burkitt lymphoma cell line BL41. The maintenance of Mcl-1 expression by LMP1 is likely to be a crucial immediate-early response that enables cells to survive until Bcl-2 can be up-regulated.