EXPRESSION OF LATENT HHV-8 GENES

Abstract

39 Most spindle cells in a KS lesion display evidence of latent HHV-8 infection. To identify the viral genes expressed in latency we have employed several expression-based stragegies. Our earliest cDNA expression strategy yielded T0.7, a highly abundant small RNA widely expressed in KS lesions. Recently we have found that HHV8-infected B lymphoma cells contain variants of this transcript that are substantially longer than that initially described, and variable from tumor to tumor. Some of this variation is due to variations from isolate to isolate in the structure of genomic DNA in this region, and some to novel promoter usage. The new promoters described here are active in B, endothelial and epithelial cells, and their RNA products encode novel proteins whose structures differ greatly from that predicted to be generated from T0.7. Adjacent to this region is a cluster of latent genes identified by screening the HHV8 genome for sequences that are strongly expressed in BCBL-1 cells prior to induction with TPA. These include orfs 71,72 and 73. The fine structures of the transcripts spanning this region have been determined by Northern blotting, RNase mapping, primer extension and RACE procedures. Orf 73/LANA transcripts are polycistronic and exist in both spliced and unspliced forms. Orf 72/v-cyc transcripts are bicistronic and some may initiate just 5′ to the orf. Interestingly, no monocistronic orf 71 mRNAs have yet been identified. Sequences 5′ to orfs 73 and 72 are active in promoting expression of promoterless luciferase genes, suggesting that they contain functional latency promoters. The structure and regulation of these promoters is under study.