Remodelling of the nuclear envelope during KSHV lytic infection

Kaposi’s sarcoma associated herpesvirus (KSHV) is a human tumour virus and key aetiological agent for several malignancies including Kaposi’s sarcoma. KSHV exhibits a biphasic life cycle split between a persistent latent period with minimal gene expression and a lytic period with an expression cascade that culminates in the release of nascent virions. Crucially, the lytic phase has been shown to be important for tumorigenesis and the spread of Kaposi’s sarcoma. The Nuclear Pore Complex (NPC) is a protein mega-complex that regulates nucleocytoplasmic transport. It is formed by multiple copies of individual nucleoporins that combine into a sophisticated protein gateway. The regulation of nuclear access makes it a target for viruses that subvert the NPC in order to hijack the cell for viral replication. Whilst herpesvirus can induce changes at the NPC, little is known about KSHV NPC remodelling. This study presents an investigation of how KSHV targets the NPC during its lytic infection highlighting the targeting a specific nucleoporin, Nup98, and an attempt at broader interactomic analysis using proximity dependent biotin identification. Nup98 is specifically downregulated early during lytic infection by the E3 ubiquitin ligase activity of viral protein RTA. This appears to be related to the repression of expression at viral ORF50 promoters when Nup98 is overexpressed in the nucleoplasm. This study also highlights how depletion of Nup98 is detrimental to the virus, leading to failed virion egress. In summary, this project highlights how KSHV specifically targets one population of Nup98 but requires NPC-bound Nup98 to sequester a cellular mRNA for CHMP7 protein to ensure virion egress. It also provides the first attempt at using interactomic techniques to create a comprehensive, semi-quantitative profile of changes to the NPC during KSHV lytic infection that can pave the way for further interaction studies and the development of targeted antivirals for KSHV