Expression of the open reading frame 74 (G-protein-coupled receptor) gene of Kaposi's sarcoma (KS)-associated herpesvirus: implications for KS pathogenesis.

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) encodes a G-protein-coupled receptor (GCR) homolog. This protein is a potent, constitutively active signalling molecule that can influence both proliferation and angiogenesis when ectopically expressed in fibroblasts in vitro. Here we have examined the expression of the KSHV GCR gene in virus-infected lymphoid cells and in KS tumors. Our results show that in both situations the gene is expressed primarily during lytic replication; its transcription is unaffected by inhibition of viral DNA synthesis, indicating that it is expressed in the early phases of the lytic program. The major transcript bearing GCR sequences is bicistronic, harboring coding sequences for another viral gene, K14, at its 5' end. Extensive searches for monocistronic GCR mRNAs using nuclease mapping and reverse transcription-PCR failed to detect such species. The 5' end of K14/GCR mRNA maps to nucleotide (nt) 127848, and its poly(A) addition site maps to nt 130546; a 149-nt intron is present in the K14/GCR intergenic region. These results suggest that the KSHV GCR is translated by unconventional mechanisms involving either translational reinitiation, internal ribosomal entry, or leaky ribosomal scanning. The restriction of GCR expression to the lytic cycle has important implications for the potential role(s) of the GCR in KS pathogenesis.