Inhibition of Constitutive Signaling of Kaposi's Sarcoma–associated Herpesvirus G Protein–Coupled Receptor by Protein Kinases in Mammalian Cells in Culture

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Abstract
Kaposi's sarcoma–associated herpesvirus (KSHV)/human herpesvirus 8, which is consistently present in tissues of patients with Kaposi's sarcoma and primary effusion lymphomas, contains a gene that encodes a G protein–coupled receptor (KSHV-GPCR). We recently showed that KSHV-GPCR exhibits constitutive signaling via activation of phosphoinositide-specific phospholipase C and stimulates cell proliferation and transformation. In this study, we determined whether normal cellular mechanisms could inhibit constitutive signaling by KSHV-GPCR and thereby KSHV-GPCR–stimulated proliferation. We show that coexpression of GPCR-specific kinases (GRKs) and activation of protein kinase C inhibit constitutive signaling by KSHV-GPCR in COS-1 monkey kidney cells and in mouse NIH 3T3 cells. Moreover, GRK-5 but not GRK-2 inhibits KSHV-GPCR–stimulated proliferation of rodent fibroblasts. These data provide evidence that cell regulatory pathways of receptor desensitization may be therapeutic targets in human diseases involving constitutively active receptors.