Damania B, DeMaria M, Jung J U, Desrosiers R C
New England Regional Primate Research Center, Harvard Medical School, Southborough, Massachusetts 01772-9102, USA.
J Virol. 2000 Mar;74(6):2721-30. doi: 10.1128/jvi.74.6.2721-2730.2000.
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.
恒河猴疱疹病毒（RRV）是一种γ-2疱疹病毒，与人类卡波西肉瘤相关疱疹病毒（KSHV）有相当程度的相似性。RRV的R1蛋白与KSHV的K1蛋白有远缘关系，并且R1与K1一样，可促进细胞生长转化。在本研究中，我们分析了R1蛋白的胞质尾作为信号转导分子的功能。R1蛋白的胞质结构域含有几个酪氨酸残基，在表达Syk激酶的细胞中其磷酸化被诱导。表达一种包含CD8胞外和跨膜结构域与R1胞质结构域融合的CD8嵌合蛋白，在用抗CD8抗体刺激时可动员B细胞内的钙离子并诱导细胞酪氨酸磷酸化。所测试的CD8-R1胞质缺失突变体在加入抗CD8抗体后均不能显著动员细胞内钙离子或诱导酪氨酸磷酸化。在无抗体刺激的情况下，野生型R1蛋白的表达可使B细胞中的活化T淋巴细胞核因子（NFAT）激活8倍；CD8-R1C嵌合蛋白的表达强烈诱导NFAT活性（60倍），但仅在加入抗CD8抗体后。我们得出结论，R1的胞质结构域能够转导引发B淋巴细胞激活事件的信号。R1的信号诱导特性似乎与K1相似，但不同之处在于所需序列分布在胞质结构域更长的一段上（>150个氨基酸）。此外，R1诱导的钙离子动员持续时间更长且比K1更强。
