Identification of the Determinants of Latency and Replication for Rhesus Rhadinovirus (RRV)

Abstract

Kaposi's sarcoma herpesvirus (KSHV), the causative agent of Kaposi's sarcoma (KS), establishes a characteristic latent infection both in tumor cells in vivo and in cultured cells in vitro. The switch from latency to replication is a critical event in the KSHV life cycle, and the viral replication and transactivator (Rta) protein is sufficient to initiate the replicative program of gene expression leading to virus production. In contrast, rhesus rhadinovirus (RRV), a related virus of macaques, establishes a characteristic replicative program of infection in tumor cells and cultured cells. To understand the basis for the different outcomes of KSHV and RRV infection we have characterized the promoter of the RRV Rta homolog and compared it to the KSHV Rta promoter in the context of viral latency and replication. Using cell lines permissive for RRV replication and novel systems of latency in human salivary gland (HSG) and adenocarcinoma gastric (AGS) epithelial cells, we found that the RRV Rta promoter was strongly active in permissive cells and minimally active in non-permissive cells. An Sp1 element located at nucleotide -113 was required for Rta promoter activity in permissive cells and butyrate responsiveness in non-permissive cells. Ectopic expression of the latency-associated nuclear antigen (LANA) inhibited Rta promoter activity and RRV replication in permissive cells, suggesting that LANA inhibition of Rta expression could play a role in RRV latency. However, our results suggest that LANA inhibitory activity is restricted in RRV-infected cells. RRV lacks the Rta-inducible LANA promoter that is critical for the establishment of KSHV latency. We also identified an arginine-glycine rich motif that targets RRV LANA to the nucleolus, which may limit the inhibitory potential of LANA in infected cells. Based on these findings, we propose a model in which host factors, such as Sp1, determine high-level RRV Rta promoter activity that correlates with cellular permissivity for RRV replication.