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Kaposi's sarcoma-associated herpesvirus (KSHV) has a significant contributory role in the development of three major human neoplastic or lymphoproliferative diseases: Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman's disease (MCD). These diseases are associated with chromosomal instability, a hallmark of human cancer. The latencyassociated nuclear antigen (LANA) encoded by KSHV plays a key role in regulating a number of cellular pathways critical for oncogenesis. KSHV LANA alone can induce the development of B-cell hyperplasia and lymphoma in mice expressing LANA. LANA also induces chromosomal instability, thus promoting oncogenesis. However, the precise mechanism underlying LANAmediated chromosomal instability remains uncharted. Here we report that LANA promoted the induction of chromosomal instability and the formation of micronuclei and multinucleation through its interaction with one of the critical spindle checkpoint proteins, Bub1, and the resulting degradation of Bub1. This interaction occurs through the Knl and kinase domains of Bub1, identified as important for stability and degradation. These results suggest that LANA can dysregulate Bub1 activity, which leads to aberrant chromosome replication and aneuploidy, thus contributing to KSHV-mediated oncogenesis. [ABSTRACT FROM AUTHOR]

Hypoxia-inducible factor 1α (HIF-1α) 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-1α 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-1α 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 interferencebased knockdown of KAP1 in KSHV-infected primary effusion lymphoma (PEL) cells disrupted viral episome stability and abrogated sub-G1/G1 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-Jκ and HIF-1α binding sites (RBSHRE) within the same gene promoter and are tightly associated with KAP1. Inhibition of KAP1 greatly enhanced the association of RBP-Jκ with the HIF-1α 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. [ABSTRACT FROM AUTHOR]