Differential regulation of the overlapping Kaposi's sarcoma-associated herpesvirus vGCR (orf74) and LANA (orf73) promoters

Similar to that of other herpesviruses, Kaposi's sarcoma-associated herpesv irus (KSHV/HHV-8) lytic replication destroys the host cell, while the virus can persist in a latent state in synchrony with the host. During latency o nly a few genes are transcribed, and the question becomes one of what deter mines latent versus lytic gene expression. Here we undertake a detailed ana lysis of the latency-associated nuclear antigen (LANA [orf73]) promoter (LA NAp). We characterized a minimal region that is necessary and sufficient to maintain high-level transcription in all tissues tested, including primary endothelial cells and B cells, which are the suspected natural host for KS HV. We show that in transient transfection assays LANAp mimics the expressi on pattern observed for the authentic promoter in the context of the KSHV e pisome. Unlike other KSHV promoters tested thus far, LANAp is not affected by tetradecanoyl phorbol acetate or viral lytic cycle functions. It is, how ever, subject to control by LANA itself and cellular regulatory factors, su ch as p53. This is in contrast to the K14/vGCR (orf74) promoter, which over laps LANAp and directs transcription on the opposite strand. We isolated a minimal cis-regulatory region sufficient for K14/vGCR promoter activity and show that it, too, mimics the regulation observed for the authentic viral promoter, In particular, we demonstrate that its activity is absolutely dep endent on the immediate-early transactivator orf50, the KSHV homolog of the Epstein-Barr virus Rta transactivator.