The role of FMDV proteins in immune evasion

Lead Research Organisation: The Pirbright Institute
Department Name: UNLISTED


The mechanisms by which FMDV counteracts the host’s innate and adaptive immune responses and the role of viral proteins in this process are not well understood. It is known that the viral leader proteinase, Lpro, inhibits the induction of IFNa/ß and blocks host cell mRNA translation. In addition, 2B in conjunction with 2C or their precursor protein 2BC inhibits protein trafficking through the ER and Golgi. Disruption of the secretory pathway could result in a decrease in MHC class I molecules on the cell surface, which may delay virus clearance in vivo. This project will determine the effect of 2BC on cell surface expression of MHC class I and NK cell receptor ligands and will determine if 2BC adversely affects the secretion of immunomodulatory molecules. Apoptosis is an innate cellular response that can limit viral propagation and many viruses express proteins that block apoptosis. However, apoptosis might also facilitate virus dissemination and viral pro-apoptotic mechanisms have been described. In this project, the interaction of FMDV with cellular proteins involved in the control of apoptosis will also be undertaken.


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Description The secretory pathway of cells is important for the trafficking of proteins to the cell surface. Virus-mediated perturbations in the secretory pathway can result in inhibition of expression of MHC I molecules on the cell surface and/or inhibition of the secretion of cytokines, which may contribute to virus evasion of the immune response. Previous studies have shown that the 3A protein of polio- and coxsackieviruses, and the 2BC protein of foot-and-mouth disease virus (FMDV) block protein trafficking. Using cells transfected with a plasmid expressing 2BC and fluorescent microscopy, western blotting and a range of protein expression systems the effects of the FMDV 2BC protein on the secretory pathway were investigated further. These studies confirmed that FMDV 2BC inhibits protein trafficking and demonstrated that 2BC co-localises with the ER protein calnexin and appeared to deplete the expression of the COP II marker Sec31A, the ERGIC marker ERGIC-53 and the COP I marker ß-Cop. Furthermore, FMDV 2BC and 2C expression inhibited the expression of secreted alkaline phosphatase (SEAP), used to monitor the secretory pathway. The effect of 2BC on SEAP expression was not mediated at the transcriptional level. FMDV 2BC also suppressed the expression of a non-secretory reporter protein, ß-galactosidase. In order to determine if these effects were mediated by ER stress and the unfolded protein response, the effect of FMDV infection on expression of ER stress proteins in cells was investigated. These preliminary studies suggested that FMDV infection stimulates or alters the expression of ER stress markers.
Further studies demonstrated that Foot-and-mouth disease virus also induces autophagosomes during cell entry via a class III phosphatidylinositol 3-kinase-independent pathway.
Exploitation Route The assays developed in this project were used to demonstrate that the p32, p39 and p30 proteins of feline calicivirus locate to the ER and lead to reorganization of ER membranes. This suggests that they may play a role in the generation of FCV replication complexes and that the endoplasmic reticulum may represent the potential source of the membrane vesicles induced during FCV infection.
Sectors Agriculture, Food and Drink