The role of cellular signalling pathways and translation initiation factors in Herpesvirus infection
McMahon, Robert (2011) The role of cellular signalling pathways and translation initiation factors in Herpesvirus infection. PhD thesis, Dublin City University.
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As obligate intracellular parasites, viruses rely on host cells to replicate. Hsv-1 is a large double stranded DNA virus which is the cause of common cold sores and corneal blindness in humans. The defining feature of HSV-1 is its ability to exist in two discrete states. During lytic infection, productive virus replication results in cell death. After primary infection HSV-1 enters a second state in non-permissive cells, termed latency in vivo or quiescence in vitro, in which minimal activity of the viral genome allows it to colonize its host. While the lytic state of viral replication is relatively well characterised, understanding of latency has lagged due to a lack of invitro models that can facilitate detailed mechanistic study. This thesis investigates aspects of HSV-1 quiescence, specifically the role of host cell signalling and translation initiation during reactivation from a non productive state. To achieve these
objectives, a new system was established to study HSV-1 quiescence. The system employs the use of serum starved and temperature elevated primary human cells which allow for efficient suppression of wild type HSV-1 replication, which that results in the formation of HSV-1 quiescent infection. Upon investigation of the kinase pathways required during reactivation from quiescence it was discovered that inhibition of the ERK signalling pathway resulted in a suppression of viral reactivation. Additionally, the activities of the down stream substrate of ERK, Mnk1, along with the mTORC1 substrate 4E-BP, both of which regulate the mRNA translation initiation factor eIF4E were shown to be required for efficient reactivation. To further investigate the role of translation initiation during reactivation, we employed the use 4EGi-1, a recently discovered small molecule inhibitor of eIF4F formation. During our investigations it was discovered that protein synthesis in primary cells was minimally dependent upon eIF4F yet highly sensitive to 4EGi-1 at concentrations that did not alter eIF4F levels but instead, increased the association of inactive eIF2a with initiation complexes. At these relatively low concentrations a potent suppression of mRNA translation was achieved yet tolerable to cells over prolonged periods. Critically, inhibition of translation resulted in suppression of both lytic replication and reactivation from quiescence suggesting that targeting mRNA translation may be a viable therapeutic avenue for treatment of HSV-1 infection.
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