Activation of lymphocyte signaling by the R1 protein of rhesus monkey rhadinovirus.
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.
Damania
B
B
New England Regional Primate Research Center, Harvard Medical School, Southborough, Massachusetts 01772-9102, USA.
DeMaria
M
M
Jung
J U
JU
Desrosiers
R C
RC
D000595:Amino Acid Sequence; D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D001665:Binding Sites; D016827:CD8 Antigens / Q000235:genetics / Q000378:metabolism; D019556:COS Cells; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004792:Enzyme Precursors / Q000378:metabolism; D005818:Genetic Engineering; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008213:Lymphocyte Activation; D008253:Macaca mulatta / Q000821:virology; D008969:Molecular Sequence Data; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D018144:Rhadinovirus / Q000276:immunology* / Q000378:metabolism; D015398:Signal Transduction; D000072377:Syk Kinase; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*
D016827:CD8 Antigens; D004268:DNA-Binding Proteins; D004792:Enzyme Precursors; D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D009856:Oncogene Proteins, Viral; D014157:Transcription Factors; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D002118:Calcium