Sulfotyrosines of the Kaposi's sarcoma-associated herpesvirus G protein-coupled receptor promote tumorigenesis through autocrine activation.

The Kaposi's sarcoma-associated herpesvirus (KSHV) G protein-coupled receptor (vGPCR) is a bona fide signaling molecule that is implicated in KSHV-associated malignancies. Whereas vGPCR activates specific cellular signaling pathways in a chemokine-independent fashion, vGPCR binds a broad spectrum of CC and CXC chemokines, and the roles of chemokines in vGPCR tumorigenesis remain poorly understood. We report here that vGPCR is posttranslationally modified by sulfate groups at tyrosine residues within its N-terminal extracellular domain. A chemokine-binding assay demonstrated that the tyrosine sulfate moieties were critical for vGPCR association with GRO-alpha (an agonist) but not with IP-10 (an inverse agonist). A sulfated peptide corresponding to residues 12 through 33 of vGPCR, but not the unsulfated equivalent, partially inhibited vGPCR association with GRO-alpha. Although the vGPCR variant lacking sulfotyrosines activated downstream signaling pathways, the ability of the unsulfated vGPCR variant to induce tumor growth in nude mice was significantly diminished. Furthermore, the unsulfated vGPCR variant was unable to induce the secretion of proliferative cytokines, some of which serve as vGPCR agonists. This implies that autocrine activation by agonist chemokines is critical for vGPCR tumorigenesis. Indeed, GRO-alpha increased vGPCR-mediated AKT phosphorylation and vGPCR tumorigenesis in a sulfotyrosine-dependent manner. Our findings support the conclusion that autocrine activation triggered by chemokine agonists via sulfotyrosines is necessary for vGPCR tumorigenesis, thereby providing a rationale for future therapeutic design targeting the tumorigenic vGPCR.