Study on latent DNA replication of kaposi’s sarcoma-associated herpesvirus

Abstract

Kaposi``s sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi``s sarcoma and several lymphoproliferative diseases including primary effusion lymphoma, also called body-cavity based lymphoma, and some cases of multicentric Castleman``s disease. The latency-associated nuclear antigen (LANA) of KSHV has been implicated in the maintenance of the viral genome during latent infection. The C-terminal DNA-binding domain of LANA interacts with sequences located in terminal repeats (TRs) of viral genome, and the N-terminal chromosome-binding sequence (CBS) of LANA associates with host chromosomes. LANA co-localizes with KSHV genome on the host chromosome, suggesting that LANA tethers viral genome to host chromosome for its persistence in infected cells. This chromosome-tethering model seems to be conserved among DNA viruses such as papillomavirus and Epstein-Barr virus (EBV), which possess extra-chromosomal genome during their latent infection. Using a long-term replication assay, it has been previously shown that KSHV TR and LANA act as cis- and trans-elements for the persistence of viral genome, respectively. In this study, we established a transient replication assay with a methylation-sensitive restriction enzyme, Dpnl, and confirmed that LANA also actively participates in the replication of TR-containing plasmid. Using this assay system, we found that 293, 293T, BJAB, C33A, HCT116, and COS-1, but not NIH/3T3 cell lines are permissive for the replication of KSHV TR-containing plasmid by LANA, and further characterized viral cis- and trans-acting elements of KSHV latent replication. Transient reporter assay and transient replication assay disclosed that the orientation and basal transcriptional activity of TR constructs did not significantly affect the efficiency of replication. However, at least two TR units were necessary for efficient replication. The N-terminal 22 amino acids comprising the CBS of LANA were necessary and sufficient for the med...