Restriction of picornavirus infection by a host cell mRNA decay protein

The cellular mRNA decay protein AUF1 acts as a restriction factor during infection by picornaviruses including poliovirus, coxsackievirus, and human rhinovirus. AUF1 relocalizes from the nucleus to the cytoplasm during infection by these viruses due to the disruption of nucleocytoplasmic trafficking by viral proteinases. Previous studies have demonstrated that AUF1 binds to poliovirus and coxsackievirus B3 (CVB3) RNA during infection, with binding shown to occur within the internal ribosome entry site (IRES) of the 5’ non-coding region (NCR) or the 3’ NCR, respectively. Binding to different sites within the viral RNA suggests that AUF1 may negatively regulate infection by these viruses using different mechanisms. The work presented in this dissertation addresses the mechanism of AUF1 inhibition of the replication of poliovirus and CVB3. It is demonstrated that AUF1 knockdown in human cells results in increased viral translation, RNA synthesis, and virus production and that negative regulation of some picornaviruses may occur in a cell type- or species-specific manner. AUF1 is shown to negatively regulate translation of poliovirus and CVB3 IRES reporter RNAs during infection, but not in uninfected cells. This inhibitory activity is not mediated through destabilization of viral genomic RNA; however, it does require virus-induced relocalization of AUF1 from the nucleus to the cytoplasm during the early phases of infection. All four isoforms of AUF1 are shown to inhibit poliovirus replication when expressed individually; however, endogenous AUF1 may associate with the poliovirus 5’ NCR in an isoform-specific manner during infection. These findings suggest that AUF1 restriction of poliovirus and CVB3 replication uses a common mechanism through the viral IRES, which is distinct from the canonical role that AUF1 plays in regulated mRNA decay in uninfected host cells