Characterization of the murine gammaherpesvirus 68 ORF74 product: a novel oncogenic G protein-coupled receptor

Murine gammaherpesvirus (MHV-68) is well established as a small animal mode l for the study of gammaherpesviruses. The MHV-68 genome contains an open r eading frame (ORF74) that has significant sequence homology with mammalian G-protein coupled receptors (GPCRs) and the GPCR from the related Kaposi's sarcoma-associated herpesvirus (KSHV). Here we show that the MHV-68 ORF74 i s predicted to encode a GPCR since it has seven potential transmembrane hel ices and that it has other sequence motifs in common with GPCRs. Of interes t is the observation that the sequence around a conserved arginine at the s tart of the second intracellular loop suggests that the ORF74 product may s ignal constitutively (agonist independent). Given that the ORF74 product is predicted to encode a GPCR we named it MHV-GPCR. In studies on the transcr iption of the MHV-GPCR, we determined that it was encoded on multiple early transcripts of 3.4, 4.4, 6.6 and 8.7 kb in size. At least one of these tra nscripts was bicistronic, containing the ORF encoding the Bcl-2 homologue a lso. In vivo, we found that MHV GPCR was expressed during acute infection b ut also during persistence, particularly in the lungs of infected mice. Imm unofluorescence studies indicated that the MHV GPCR protein was expressed o n the surface of cells in patches. Finally, like the KSHV GPCR, expression of the MHV GPCR resulted in transformation of NIH 3T3 cells. We surmise, th erefore, that the MHV GPCR may act in concert with genes with which it is e xpressed such as vBcl-2 to enhance the growth and survival of MHV-68-infect ed cells.