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J. Virol., Sep 1997, 6619-6628, Vol 71, No. 9
F Nitsche, A Bell and A Rickinson
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.
Copyright © 1997, American Society for Microbiology
Epstein-Barr virus leader protein enhances EBNA-2-mediated transactivation of latent membrane protein 1 expression: a role for the W1W2 repeat domain
CRC Institute for Cancer Studies, University of Birmingham, United Kingdom.
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