StressEBOV · Ebola virus manipulation of the cellular stress responses

Ebola virus manipulation of the cellular stress responses

Ebola virus (EBOV) is a highly pathogenic filovirus causing severe haemorrhagic fever. It causes recurrent epidemics, like in 2014 in Western Africa where about 28,000 people were infected of which over 11,000 died or the current ongoing epidemic in Democratic Republic of Congo where so far 1926 people were infected of which 1287 died. Although potential vaccines and drugs are being used, no treatment has been approved. Therefore, understanding the molecular and cellular regulation of EBOV replication is fundamental to the development of novel treatments. EBOV is a nonsegmented negative-strand (NNS) RNA virus encoding nine proteins. After entry, EBOV replicates in the cytoplasm of infected cells in inclusion bodies, non-membranous organelles that separate by density from the rest of the cytoplasm. However, the exact mechanism of EBOV transcription and replication is mostly assumed based on other NNS viruses. Viruses replicate in host cells, hijacking the cell machinery as well as evading the antiviral response. Likewise, host cells have evolved mechanisms to sense the presence of foreign nucleic acids (e.g. vRNA). The synthesis of vRNAs triggers a cellular antiviral response via three distinct but linked mechanisms: (1) RNA-sensing by RIG-I and MDA5 leading to interferon (IFN) production, the host antiviral protein to activate innate cells, (2) RNA-sensing by the RNA-dependent protein kinase (PKR), inhibiting translation, leading to a host cell shut-off, and (3) formation of stress granules (SGs) to inhibit viral replication and store cellular mRNAs during stress to prevent them from degradation. However, the impact of SGs on EBOV still remains poorly understood. SGs are non-membrane-bound cytosolic mRNA-protein granules that form in response to stress, such as viral infection. Stress can lead to the activation of PKR which phosphorylates eIF2, inhibiting translation and leading to sequestration of mRNAs. The assembly and disassembly of SGs is dynamic and modulates the cellular stress response as well as viral replication. Moreover, antiviral SGs have been reported to form in response to viral infection serving as amplification sites for antiviral IFN induction. Therefore, RNA viruses have evolved mechanisms to dysregulate SGs in three ways: (1) inhibition of SG formation by PKR, (2) cleavage of SG proteins or (3) sequestration of SG components. Recently, EBOV has been reported to partially inhibit the formation of SGs by expression of the viral VP35. In addition, EBOV recruits some SG-inducing proteins to its inclusion bodies, whereas redistributing others. However, the impact of the cellular stress response on EBOV replication and how EBOV and VP35 regulate this response is poorly defined. Therefore, this proposal aims to investigate the anti-immunity and pro-replication functions of VP35 in the context of the polymerase complex and viral replication using a transcription- and replication-competent virus-like particle system (EBOV trVLP) by addressing the following aim: To investigate the impact of SG proteins on EBOV transcription/replication and manipulation by VP35

Data: CORDIS, © European Union