Development of a Plasmid-Based Reverse Genetics System for the Bluetongue and Epizootic Hemorrhagic Disease Viruses to Allow a Comparative Characterization of the Function of the NS3 Viroporin in Viral Egress

Project Title: "Development of a plasmid-based reverse genetics system for the Bluetongue and Epizootic Hemorrhagic Disease viruses to allow comparative characterization of the function of the NS3 viroporin in viral egress". Project details: No - IS-4192-09; Participants – Ehrlich M. (Tel Aviv University), Parker J.S. (Cornell University), DermodyT.S. (Vanderbilt University); Period - 2009-2013. Orbiviruses are insect-borne infectious agents of ruminants that cause diseases with considerable economical impact in Israel and the United States. The recent outbreaks of BTV in Europe and of Epizootic Hemorrhagic Disease Virus (EHDV) in Israel, underscore the need for: (i) a better comprehension of the infection process of orbiviruses, (ii) the identification of unique vs. common traits among different orbiviruses, (iii) the development of novel diagnosis and treatment techniques and approaches; all aimed at the achievement of more effective control and treatment measures. It is the context of these broad goals that the present project was carried out. To fulfill our long-term goal of identifying specific viral determinants of virulence, growth, and transmission of the orbiviruses, we proposed to: (i) develop reverse genetics systems for BTV and EHDV2-Ibaraki; and (ii) identify the molecular determinants of the NS3 nonstructural protein related to viroporin/viral egress activities. The first objective was pursued with a two-pronged approach: (i) development of a plasmid-based reverse genetics system for BTV-17, and (ii) development of an "in-vitro" transcription-based reverse genetics system for EHDV2-Ibaraki. Both approaches encountered technical problems that hampered their achievement. However, dissection of the possible causes of the failure to achieve viral spread of EHDV2-Ibaraki, following the transfection of in-vitro transcribed genomic segments of the virus, revealed a novel characteristic of EHDV2-Ibaraki infection: an uncharacteristically low fold increase in titer upon infection of different cell models. To address the function and regulation of NS3 we employed the following approaches: (i) development (together with Anima Cell Metrology) of a novel technique (based on the transfection of fluorescently-labeledtRNAs) that allows for the detection of the levels of synthesis of individual viral proteins (i.e. NS3) in single cells; (ii) development of a siRNA-mediated knockdown approach for the reduction in levels of expression of NS3 in EHDV2-Ibaraki infected cells; (iii) biochemical and microscopy-based analysis of the localization, levels and post-translational modifications of NS3 in infected cells. In addition, we identified the altered regulation and spatial compartmentalization of protein synthesis in cells infected with EHDV2-Ibaraki or the mammalian reovirus. In EHDV2-Ibaraki-infected cells such altered regulation in protein synthesis occurs in the context of a cell stress reponse that includes the induction of apoptosis, autophagy and activation of the stressrelated kinase c-Jun N-terminal Kinase (JNK). Interestingly, inhibition of such stress-related cellular processes diminishes the production of infectious virions, suggesting that EHDV usurps these responses for the benefit of efficient infection. Taken together, while the present project fell short of the generation of novel reverse genetics systems for orbiviruses, the development of novel experimental approaches and techniques, and their employment in the analysis of EHDV-infected cells, yielded novel insights in the interactions of orbiviruses with mammalian cells.