Epstein-Barr virus leader protein enhances EBNA-2-mediated transactivation of latent membrane protein 1 expression: a role for the W1W2 repeat domain.
The Epstein-Barr virus (EBV)-encoded leader protein EBNA-LP is made up of several 66-amino-acid repeats (the W1W2 domains) linked to a unique 45-amino-acid C-terminal sequence (the Y1Y2 domain). This protein is highly expressed along with a second nuclear antigen, EBNA-2, during the initial stages of virus-induced B-cell transformation. While EBNA-2's essential role in transformation as a transcriptional activatory is well documented, very little is known about EBNA-LP function except that recombinant viruses lacking the EBNA-LP Y1Y2 exons show reduced, but still detectable, transforming ability. This was taken as evidence that EBNA-LP plays an auxiliary role but is not essential for transformation. A recent study showed that EBNA-LP could cooperate with EBNA-2 in activating cyclin D2 transcription in resting B cells (A.J. Sinclair, L Palmero, G. Peters, and P.J. Farrell, EMBO J. 13:3321-3328, 1994). Here we report that EBNA-LP can also cooperate with EBNA-2 in up-regulating expression of the major EBV effector protein of B-cell transformation, latent membrane protein 1 (LMP1). In transient-transfection assays, EBNA-LP enhanced the level of EBNA-2-induced LMP1 expression by 5- to 10-fold in one Latency I Burkitt's lymphoma cell line, Eli-BL, and was absolutely required, along with EBNA-2, to induce LMP1 in a second line, Akata-BL. These changes in LMP1 protein expression appeared to be reflected at the transcriptional level. A study of EBNA-LP mutants showed that this cooperative function mapped to the W1W2 repeat domain rather than to Y1Y2. Because a Y1Y2-deleted form of EBNA-LP may therefore retain some aspects of wild-type function, the original data from virus recombinants leave open the possibility that EBNA-LP is actually an essential transforming gene.
Nitsche
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CRC Institute for Cancer Studies, University of Birmingham, United Kingdom.
Bell
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Rickinson
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D000595:Amino Acid Sequence; D019309:Epstein-Barr Virus Nuclear Antigens / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D004854:Herpesvirus 4, Human / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D016254:Mutagenesis, Insertional; D012333:RNA, Messenger; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured; D014763:Viral Matrix Proteins / Q000096:biosynthesis* / Q000235:genetics
C037662:EBV-associated membrane antigen, Epstein-Barr virus; D019309:Epstein-Barr Virus Nuclear Antigens; D012333:RNA, Messenger; D014763:Viral Matrix Proteins