Identification of an Immunoreceptor Tyrosine-Based Activation Motif of K1 Transforming Protein of Kaposi’s Sarcoma-Associated Herpesvirus

ABSTRACT

Kaposi’s sarcoma-associated herpesvirus (KSHV) is consistently identified in Kaposi’s sarcoma and body cavity-based lymphoma. KSHV encodes a transforming protein called K1 which is structurally similar to lymphocyte receptors. We have found that a highly conserved region of the cytoplasmic domain of K1 resembles the sequence of immunoreceptor tyrosine-based activation motifs (ITAMs). To demonstrate the signal-transducing activity of K1, we constructed a chimeric protein in which the cytoplasmic tail of the human CD8α polypeptide was replaced with that of KSHV K1. Expression of the CD8-K1 chimera in B cells induced cellular tyrosine phosphorylation and intracellular calcium mobilization upon stimulation with an anti-CD8 antibody. Mutational analyses showed that the putative ITAM of K1 was required for its signal-transducing activity. Furthermore, tyrosine residues of the putative ITAM of K1 were phosphorylated upon stimulation, and this allowed subsequent binding of SH2-containing proteins. These results demonstrate that the KSHV transforming protein K1 contains a functional ITAM in its cytoplasmic domain and that it can transduce signals to induce cellular activation.

ACKNOWLEDGEMENTS

We thank A. Dunn, T. Roberts, A. Veillette, and A. Weiss for providing plasmids. We especially thank R. Desrosiers and L. Alexander for discussion and critical reading of manuscript. We also thank J. Newton for manuscript preparation and K. Toohey for photography support.

This work was supported by Public Health Service grants CA31363 and RR00168.