ITAF ₄₅ is a pervasive <i>trans</i> -acting factor for picornavirus Type II IRES elements

Viruses have evolved elaborate mechanisms to hijack the host mRNA translation machinery to direct viral protein synthesis. Picornaviruses, whose RNA genome lacks a cap structure, inhibit cap-dependent mRNA translation, and utilize an internal ribosome entry site (IRES) in the RNA 5' untranslated region to recruit the 40S ribosomal subunit. IRES activity is stimulated by a set of host proteins termed IRES <i>trans</i>-acting factors (ITAFs). The cellular protein ITAF₄₅ (also known as PA2G4 or EBP1) was documented as an essential ITAF for foot-and-mouth disease virus (FMDV), with no apparent role in cell-free systems for encephalomyocarditis virus (EMCV) and Theiler's murine encephalomyelitis virus (TMEV), which are closely related viruses harboring similar IRES elements. Here, we demonstrate that ITAF₄₅ is a pervasive host factor 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 restricted role for ITAF₄₅ in FMDV infection, thus positioning ITAF₄₅ as a potential antiviral target for various animal viruses and emerging human cardioviruses.