KSHV Latent Infection Replication

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Abstract Kaposi's sarcoma (KS) herpesvirus (KSHV) is the etiologic agent of KS, primary effusion lymphoma (PEL), and multicentric Castleman's disease (MCD). These tumors occur most commonly in individuals with AIDS or other immunocompromising conditions. Currently, there are no specific therapies for these diseases. KS is the leading AIDS malignancy, and is epidemic throughout sub Saharan Africa. KS commonly involves the oral cavity and can widely disseminate to visceral organs. Saliva is the vehicle of transmission for KSHV. Following infection, epigenetic modifications associated with transcriptional activation are deposited on the KSHV genome, leading to widespread, but brief, viral gene expression. Failure to inhibit this expression leads to lytic replication. Repressive H2AK119ub and H3K27me3 modifications subsequently accumulate to silence lytic gene promoters. H2AK119ub accrues initially, followed by H3K27me3, in contrast to the classical model in which H3K27me3 marks precede H2AK119ub. Latency is the hallmark of KSHV and gammaherpesvirus infection. KSHV latently infects cells, including tumor cells, and viral genomes persist as circular, extrachromosomal, multi-copy, episomes. To persist in proliferating cells, viral episomes must replicate, and subsequently, segregate to daughter nuclei. Tumor cell viability is dependent on latent KSHV infection. The latency-associated nuclear antigen (LANA) is one of a limited number of virus genes expressed in latency. LANA is responsible for KSHV episome maintenance and is necessary and sufficient for virus episome persistence in the absence of other viral genes. In addition to episome persistence, LANA exerts important roles in transcriptional regulation and growth control. LANA is involved in silencing the viral genome. We have discovered LANA interacts with a component of the DNA damage response (DDR), and that the DDR silences the viral genome following infection, thereby inhibiting lytic replication and allowing latency establishment. This work will use rigorous, detailed, in depth approaches to investigate the mechanistic basis of these findings. Experiments will investigate the LANA-DDR interaction and its role in viral genome silencing, and suppression of lytic replication. We will investigate the dynamics and sites of deposition of key DDR factors on the KSHV genome and LANA’s role in these events. Experiments will also investigate the role of the DDR in establishing the KSHV repressive epigenome. The silencing of the KSHV genome following infection is central to the establishment of viral latency, and this work therefore provides novel and important insight into a fundamental component of KSHV biology.