Dissection of the Kaposi's sarcoma-associated herpesvirus gene expression program by using the viral DNA replication inhibitor cidofovir.

Treatment of primary effusion lymphoma cells latently infected by Kaposi's sarcoma-associated herpesvirus (KSHV; human herpesvirus-8 [HHV-8]) with agents such as 12-O-tetradecanoylphorbol-13-acetate (TPA) induces a lytic viral replication cycle, with an ordered gene expression program. Initial studies of the KSHV expression program following TPA induction using viral microarrays yielded useful information concerning the viral expression program, but precise kinetic assignments for some genes remained unclear. Classically, late herpesvirus genes require viral DNA replication for maximal expression. We used cidofovir (CDV), a nucleotide-analogue KSHV DNA polymerase inhibitor, to dissect KSHV expression into two components: genes expressed without viral DNA replication and those requiring it. The expression of known immediate-early or early genes (e.g., open reading frames [ORFs] 50, K8 bZIP, and 57) serving lytic regulatory roles was relatively unaffected by the presence of CDV, while known late capsid and tegument structural genes (e.g., ORFs 25, 26, 64, and 67) were CDV sensitive. Latency-associated transcript ORF 73 was unaffected by the presence of TPA or CDV, suggesting that it was constitutively expressed. Expression of several viral cellular gene homologs, including K2 (vIL-6), ORF 72 (vCyclin), ORF 74 (vGPCR), and K9 (vIRF-1), was unaffected by the presence of CDV, while that of others, such as K4.1 (vMIP-III), K11.1 (vIRF-2), and K10.5 (LANA2, vIRF-3), was inhibited. The results distinguish KSHV genes whose full expression required viral DNA replication from those that did not require it, providing additional insights into KSHV replication and pathogenesis strategies and helping to show which viral cell homologs are expressed at particular times during the lytic process.