Kaposi's sarcoma-associated herpesvirus open reading frame 50/Rta protein activates the entire viral lytic cycle in the HH-B2 primary effusion lymphoma cell line.

Rta, the gene product of Kaposi's sarcoma-associated herpesvirus (KSHV) encoded mainly in open reading frame 50 (ORF50), is capable of activating expression of viral lytic cycle genes. What was not demonstrated in previous studies was whether KSHV Rta was competent to initiate the entire viral lytic life cycle including lytic viral DNA replication, late-gene expression with appropriate kinetics, and virus release. In HH-B2, a newly established primary effusion lymphoma (PEL) cell line, KSHV ORF50 behaved as an immediate-early gene and autostimulated its own expression. Expression of late genes, ORF65, and K8.1 induced by KSHV Rta was eliminated by phosphonoacetic acid, an inhibitor of viral DNA polymerase. Transfection of KSHV Rta increased the production of encapsidated DNase-resistant viral DNA from HH-B2 cells. Thus, introduction of an ORF50 expression plasmid is sufficient to drive the lytic cycle to completion in cultured PEL cells.