A role for endoplasmic reticulum exit sites (ERES) in foot-and-mouth disease virus infection

Picornaviruses replicate their genomes in association with cellular membranes. While enteroviruses are believed to utilise membranes of the early secretory pathway the origin of the membranes used by FMDV for replication are unknown. Secretory vesicle traffic through the early secretory pathway is mediated by the sequential acquisition of two distinct membrane coat-complexes, COPII and COPI and requires the coordinated actions of Sar1, Arf1 and Rab proteins. Sar1 is essential for generating COPII vesicles at ER exit sites while Arf1 and Rab1 are required for subsequent vesicle transport by COPI vesicles. In this present study, we provided evidence that FMDV requires pre-Golgi membranes of the early secretory pathway for infection. siRNA depletion of Sar1 or expression of a dominant-negative (DN) mutant of Sar1a inhibited FMDV infection. In contrast, a dominant-active mutant of Sar1a, which allows COPII vesicle formation but inhibits the secretory pathway by stabilizing COPII coats, caused major disruption to the ERGIC but did not inhibit infection. Treatment of cells with brefeldin-A, or expression of DN mutants of Arf1 and Rab1a disrupted the Golgi and enhanced FMDV infection. These results show that reagents that block the early secretory pathway at ER exit sites have an inhibitory effect on FMDV infection while reagents that block the early secretory pathway immediately after ER exit but before the ERGIC and Golgi make infection more favourable. Together these observations argue for a role for Sar1 in FMDV infection and that initial virus replication takes place on membranes that are formed at ER exit sites.