Cellular Protein HuR Regulates the Switching of Genomic RNA Templates for Differential Functions during the Coxsackievirus B3 Life Cycle

Abstract

The Coxsackievirus B3 (CVB3) is an enterovirus belonging to the family Picornaviridae. Its 5’ UTR contains a cloverleaf structure followed by an Internal Ribosome Entry Site (IRES). The cloverleaf forms an RNA-protein complex known to regulate virus replication, translation, and stability of the genome and the IRES regulates virus RNA translation. For positive-strand RNA containing viruses, such as members of Flaviviruses or enteroviruses, the genomic RNA is used for translation, replication, and encapsidation. Only a few regulatory mechanisms which govern the accessibility of genomic RNA templates for translation or replication, have been reported. Here, we report the role of Human antigen R (HuR) in regulating the fate of CVB3 positive-strand RNA into replication cycle or translation cycle. We have observed that synthesis of HuR is induced during CVB3 infection and it suppresses viral replication by displacing PCBP-2 (a positive regulator of virus replication) at the cloverleaf RNA. Silencing of HuR increases viral RNA replication and consequently reduces viral RNA translation in a replication-dependent manner. Further, we have shown that HuR level is upregulated upon CVB3 infection, Moreover, HuR limits virus replication and can coordinate the availability of genomic RNA templates for translation, replication or encapsidation. Our study highlights the fact that the relative abundance of translation factors and replication factors in the cell decides the outcome of viral infection. IMPORTANCE A positive-strand RNA virus must balance the availability of its genomic template for different viral processes at different stages of its life cycle. Few host proteins are shown to be important to help the virus in switching the usage of a template between these processes. These proteins inhibit translation either by displacing a stimulator of translation or by binding to an alternative site. Both mechanisms lead to ribosome clearance and availability of the genomic strand for replication. We have shown that HuR also helps in maintaining this balance but by inhibiting replication and subsequently promoting translation and packaging.