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 mechanism involved in KSHV lytic replication from the early to the late phases remains largely undetermined. We previously revealed that KSHV open reading frame 45 (ORF45) plays important roles in late transcription and translation. In the present study, we revealed 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 viral gene expression to facilitate KSHV lytic replication.IMPORTANCEThe forkhead box proteins FoxK1 and FoxK2 can act as transcriptional inhibitors or activators to regulate several important processes, including aerobic glycolysis, metabolism, autophagy, and antiviral responses. However, the subversion and functions of FoxK1 and FoxK2 during KSHV infection and the pathogenesis of related diseases remain unknown. Here, we revealed that ORF45 binds to FoxK1 and FoxK2 and increases their transcriptional activity during KSHV lytic replication; consequently, FoxK1 and FoxK2 bind to late viral promoters and cooperate with ORF45 to promote late lytic gene expression. Our findings reveal two new ORF45 partners and a new function of ORF45 in which it utilizes FoxK1 and FoxK2 to promote transcription during late KSHV lytic replication.