Inhibition of KAP1 Enhances Hypoxia-Induced Kaposi's Sarcoma-Associated Herpesvirus Reactivation through RBP-Jκ

Hypoxia-inducible factor 1 alpha (HIF-1 alpha) has been frequently implicated in many cancers as well as viral pathogenesis. Kaposi's sarcoma-associated herpesvirus (KSHV) is linked to several human malignancies. It can stabilize HIF-1 alpha during latent infection and undergoes lytic replication in response to hypoxic stress. However, the mechanism by which KSHV controls its latent and lytic life cycle through the deregulation of HIF-1 alpha is not fully understood. Our previous studies showed that the hypoxia-sensitive chromatin remodeler KAP1 was targeted by the KSHV-encoded latency-associated nuclear antigen (LANA) to repress expression of the major lytic replication and transcriptional activator (RTA). Here we further report that an RNA interference-based knockdown of KAP1 in KSHV-infected primary effusion lymphoma (PEL) cells disrupted viral episome stability and abrogated sub-G(1)/G(1) arrest of the cell cycle while increasing the efficiency of KSHV lytic reactivation by hypoxia or using the chemical 12-O-tetradecanoylphorbol-13-acetate (TPA) or sodium butyrate (NaB). Moreover, KSHV genome-wide screening revealed that four hypoxia-responsive clusters have a high concurrence of both RBP-J kappa and HIF-1 alpha binding sites (RBS+HRE) within the same gene promoter and are tightly associated with KAP1. Inhibition of KAP1 greatly enhanced the association of RBP-J kappa with the HIF-1 alpha complex for driving RTA expression not only in normoxia but also in hypoxia. These results suggest that both KAP1 and the concurrence of RBS+HRE within the RTA promoter are essential for KSHV latency and hypoxia-induced lytic reactivation.