Yes / KSHV is the causative agent of commonly fatal malignancies of immuno-compromised individuals, including primary effusion lymphoma (PEL) and Kaposi's sarcoma (KS). A hallmark of all herpesviruses is their biphasic lifecycle – viral latency and the productive lytic cycle, and it is well established that reactivation of the KSHV lytic cycle is associated with KS pathogenesis. Therefore, a thorough appreciation of the mechanisms that govern reactivation is required to better understand disease progression. The viral protein, replication and transcription activator (RTA), is the KSHV lytic switch protein due to its ability to drive the expression of various lytic genes, leading to reactivation of the entire lytic cycle. While the mechanisms for activating lytic gene expression have received much attention, how RTA impacts on cellular function is less well understood. To address this, we developed a cell line with doxycycline-inducible RTA expression and applied SILAC-based quantitative proteomics. Using this methodology, we have identified a novel cellular protein (AT-rich interacting domain containing 3B, ARID3B) whose expression was enhanced by RTA and that relocalised to replication compartments upon lytic reactivation. We also show that siRNA knockdown or overexpression of ARID3B led to an enhancement or inhibition of lytic reactivation, respectively. Furthermore, DNA affinity and chromatin immunoprecipitation assays demonstrated that ARID3B specifically interacts with A/T-rich elements in the KSHV origin of lytic replication (oriLyt), and this was dependent on lytic cycle reactivation. Therefore, we have identified a novel cellular protein whose expression is enhanced by KSHV RTA with the ability to inhibit KSHV reactivation.

Kaposi's sarcoma-associated herpesvirus (KSHV) is a DNA tumor virus that has been associated with all epidemiological forms of Kaposi's sarcoma, primary effusion lymphoma (PEL) and multicentric Castleman disease (MCD). Like other herpesviruses, KSHV undergoes two phases of life cycle (latent and lytic replication). During latency, the viral genome persists as a circular episome in the nucleus of the host cell and only a few viral genes are expressed, namely LANA (latency- associated nuclear antigen), Kaposin, vFLIP (viral FLICE inhibitory protein), vCyclin, and vIRF3/LANA2 (viral interferon regulatory factor 3). These viral genes are responsible for regulation of host cell proliferation, prevention of apoptosis, facilitation of immune evasion, and maintenance of the extrachromosomal viral genome during cell divisions. vIRF3 is a multifunctional nuclear protein that is constitutively expressed in KSHV positive PEL cells and Castleman's disease tumors, which expression causes dramatic changes of critical host pathways that are involved in the regulation of apoptosis, cell cycle, antiviral immunity, and tumorigenesis. In our study, we have demonstrated and elucidated predicted mechanism, by which vIRF3 enhances transcription activity of c-Myc. Moreover, we have clarified the previously unappreciated...