MOLECULAR MIMICRY OF THE ANTIGEN RECEPTOR SIGNALING MOTIF BY TRANSMEMBRANE PROTEINS OF THE EPSTEIN-BARR-VIRUS AND THE BOVINE LEUKEMIA-VIRUS

Background: Many transmembrane proteins of eukaryotic cells have only a short cytoplasmic tail of 10 - 100 amino acids, which has no obvious catalytic function. These tails are thought to be involved either in signal transduction or in the association of transmembrane proteins wi th the cytoskeleton. We have previously identified, in die cytoplasmic tails of components of B and T lymphocyte antigen receptors, an amino -acid motif that is required for signalling. The same motif is also fo und in the cytoplasmic tails of two viral proteins: the latent membran e protein, LMP2A, of Epstein-Barr virus and the envelope protein, gp30 , of bovine leukaemia virus. Interestingly, both viruses can activate infected B lymphocytes to proliferate, as does signalling by B-cell re ceptor. Results: In this study, we show that the cytoplasmic tails of the two viral proteins, and the cytoplasmic tail of the B-cell recepto r immunoglobulin-alpha chain, when linked to CD8 in chimeric transmemb rane proteins, can transduce signals in B cells. Cross-linking of thes e chimeric receptors activates B-cell protein tyrosine kinases and res ults in calcium mobilization. Furthermore, these cytoplasmic sequences are also protein tyrosine kinase substrates and may interact with cyt osolic proteins carrying SH2 protein-protein interaction domains. Conc lusion: Our findings suggest that viral transmembrane proteins can mim ic the antigen-induced stimulation of the B-cell antigen receptor and thus can influence the activation and/or survival of infected B lympho cytes.