ITAF45 is a Pervasive Trans Acting Factor for Picornavirus Type II IRES Elements

Abstract

Viruses have evolved elaborate mechanisms to hijack the host mRNA translation machinery to direct viral protein synthesis. Picornaviruses, whose RNA genomes lack a cap structure, inhibit cap-dependent mRNA translation, and utilize an internal ribosome entry site (IRES) in the RNA 5'-UTR to recruit the 40S ribosomal subunit. IRES activity is stimulated by a set of host proteins termed IRES trans-acting factors (ITAFs). The cellular protein ITAF45 (also known as PA2G4 and EBP1) was identified as an essential ITAF for foot-and-mouth disease virus (FMDV), with no apparent role in cell-free systems for the closely related viruses harboring similar IRES elements such as encephalomyocarditis virus (EMCV) and Theilers murine encephalomyelitis virus (TMEV). Here, we demonstrate that ITAF45 is a pervasive host factor within cells for picornaviruses containing a Type II IRES. CRISPR/Cas9 knockout of ITAF45 in several human cell lines conferred resistance to infection with FMDV, EMCV, TMEV, and equine rhinitis A virus (ERAV). We show that ITAF45 enhances initiation of translation on type II IRESs in cell line models. This is mediated by the C-terminal lysine-rich region of ITAF45 known to enable binding to viral RNA. These findings challenge previous reports of a unique role for ITAF45 in FMDV infection, positioning ITAF45 as a promising antiviral target for various animal viruses and emerging human cardioviruses.