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Journal of Virology, March 2000, p. 2721-2730, Vol. 74, No. 6
New England Regional Primate Research Center,
Harvard Medical School, Southborough, Massachusetts 01772-9102
Received 11 November 1999/Accepted 17 December 1999
Rhesus monkey rhadinovirus (RRV) is a gamma-2
herpesvirus that exhibits a considerable degree of similarity to the
human Kaposi's sarcoma-associated herpesvirus (KSHV). The
R1 protein of RRV is distantly related to the K1 protein of KSHV, and
R1, like K1, can contribute to cell growth transformation. In this
study we analyzed the ability of the cytoplasmic tail of R1 to function as a signal transducer. The cytoplasmic domain of the R1 protein contains several tyrosine residues whose phosphorylation is induced in
cells expressing Syk kinase. Expression of a CD8 chimera protein containing the extracellular and transmembrane domains of CD8 fused to
the cytoplasmic domain of R1 mobilized intracellular calcium and
induced cellular tyrosine phosphorylation in B cells upon stimulation
with anti-CD8 antibody. None of the CD8-R1 cytoplasmic deletion mutants
tested were able to mobilize intracellular calcium or to induce
tyrosine phosphorylation to a significant extent upon addition of
anti-CD8 antibody. Expression of wild-type R1 protein activated nuclear
factor of activated T lymphocytes (NFAT) eightfold in B cells in the
absence of antibody stimulation; expression of the CD8-R1C chimera
strongly induced NFAT activity (60-fold) but only upon the addition of
anti-CD8 antibody. We conclude that the cytoplasmic domain of R1 is
capable of transducing signals that elicit B-lymphocyte activation
events. The signal-inducing properties of R1 appear to be similar to
those of K1 but differ in that the required sequences are distributed
over a much longer stretch of the cytoplasmic domain (>150 amino
acids). In addition, the induction of calcium mobilization was
considerably longer in duration and stronger with R1 than with K1.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Activation of Lymphocyte Signaling by the R1
Protein of Rhesus Monkey Rhadinovirus
*
Corresponding author. Mailing address: New England
Regional Primate Research Center, Harvard Medical School, One Pine Hill Dr., Box 9102, Southborough, MA 01772-9102. Phone: (508) 624-8041. Fax:
(508) 624-8190. E-mail:
ronald_desrosiers{at}hms.harvard.edu.
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