FoxK1 and FoxK2 cooperate with ORF45 to promote late lytic replication of Kaposi’s sarcoma-associated herpesvirus

Lytic replication is essential for persistent infection of Kaposi’s sarcoma-associated herpesvirus (KSHV) and the pathogenesis of related diseases, and many cellular pathways are hijacked by KSHV proteins to initiate and control the lytic replication of this virus. However, the machinery involved in KSHV lytic replication from the early to the late phases remains largely undetermined. We previously revealed that KSHV ORF45 plays important roles in late transcription and translation. In the present study, we reveal that the Forkhead box proteins FoxK1 and FoxK2 are ORF45-binding proteins and are essential for KSHV lytic gene expression and virion production and that depletion of FoxK1 or FoxK2 significantly suppresses the expression of many late viral genes. FoxK1 and FoxK2 directly bind to the promoters of several late viral genes, ORF45 augments the promoter binding and transcriptional activity of FoxK1 and FoxK2, and then FoxK1 or FoxK2 cooperates with ORF45 to promote late viral gene expression. Our findings suggest that ORF45 interacts with FoxK1 and FoxK2 and promotes their occupancy on a cluster of late viral promoters and their subsequent transcriptional activity; consequently FoxK1 and FoxK2 promote late gene expression to facilitate KSHV lytic replication. To further investigate the roles of FoxK1 and FoxK2 in KSHV gene expression during lytic replication, FoxK1 and FoxK2 were separately depleted in iSLK.Bac16 cells by shRNA transduction, and genome-wide gene expression in iSLK.Bac16 cells with induction of lytic replication was analyzed by RNA sequencing.