Histone variant H3.3 and KSHV LANA in the pathogenesis of oral Kaposi's sarcoma

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DESCRIPTION (provided by applicant): Kaposi's sarcoma (KS) is the most common oral cancer in human immunodeficiency virus (HIV)-infected patients. Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of KS, and two lymphoproliferative diseases: primary effusion lymphoma (PEL) and multicentric Castleman's disease (MCD). AIDS-associated KS is highly frequent in the oral cavity which is also the major site for KSHV shedding via saliva. KSHV infected tumor cells are predominately latently infected. The viral encoded latency-associated nuclear antigen (LANA) is a multifunctional protein required for latency. Our preliminary data demonstrate that histone variant H3.3, which is frequently mutated in human malignancies and plays important roles in transcriptional regulation, occupies viral episomes at specific regions that correlate with LANA binding. We also demonstrate that LANA associates with Daxx and SSRP1, chaperone proteins responsible for the deposition of H3.3. We hypothesize that H3.3 deposition onto viral episomes is crucial for viral gene expression during latency, and furthermore that this process is mediated by LANA's interactions with H3.3 chaperones. Locus specific H3.3 incorporation may account for the tightly controlled gene expression pattern during latency and hence also affect the balance between latent and lytic replication, which may be crucial with respect to tumorigenesis and shedding in the oral cavity. Importantly, this study will not only utilize in vitro tissue cultre systems but for the first time propose a highly innovative approach to analyze complex chromatin architecture analysis in vivo using primary oral KS biopsies. To this end we provide preliminary data on our ability to detect endogenous histone H3.3 by both ChIP and IFA. The long-term goal of this interdisciplinary pilot project is to create proof of concept data that modulating histone variant deposition can be harnessed as a novel KSHV-specific therapeutic strategy.