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-cou pled receptor (GCR) homolog. This protein is a potent, constitutively activ e signalling molecule that can influence both proliferation and angiogenesi s when ectopically expressed in fibroblasts in vitro. Here we have examined the expression of the KSHV GCR gene in virus-infected lymphoid cells and i n KS tumors. Our results show that in both situations the gene is expressed primarily during lytic replication; its transcription is unaffected by inh ibition of viral DNA synthesis, indicating that it is expressed in the earl y phases of the lytic program. The major transcript bearing GCR sequences i s bicistronic, harboring coding sequences for another viral gene, K14, at i ts 5' end. Extensive searches for monocistronic GCR mRNAs using nuclease ma pping and reverse transcription-PCR failed to detect such species. The 5' e nd 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 intergen ic region. These results suggest that the KSHV GCR is translated by unconve ntional mechanisms involving either translational reinitiation, internal ri bosomal entry, or leaky ribosomal scanning. The restriction of GCR expressi on to the lytic cycle has important implications for the potential role(s) of the GCR in KS pathogenesis.