Interaction of Translation Initiation Factor eIF4B with the Poliovirus Internal Ribosome Entry Site

Abstract

Poliovirus translation is initiated at the internal ribosome entry site (IRES). Most likely involving the action of standard initiation factors, this highly structured cis element in the 5 noncoding region of the viral RNA guides the ribosome to an internal silent AUG. The actual start codon for viral protein synthesis further downstream is then reached by ribosomal scanning. In this study we show that two of the secondary structure elements of the poliovirus IRES, domain V and, to a minor extent, domain VI, are the determinants for binding of the eukaryotic initiation factor eIF4B. Several mutations in domain V which are known to greatly affect poliovirus growth also seriously impair the binding of eIF4B. The interaction of eIF4B with the IRES is not dependent on the presence of the polypyrimidine tract-binding protein, which also binds to the poliovirus IRES. In contrast to its weak interaction with cellular mRNAs, eIF4B remains tightly associated with the poliovirus IRES during the formation of complete 80S ribosomes. Binding of eIF4B to the IRES is energy dependent, and binding of the small ribosomal subunit to the IRES requires the previous energy-dependent association of initiation factors with the IRES. These results indicate that the interaction of eIF4B with the 3 region of the poliovirus IRES may be directly involved in translation initiation.When poliovirus, the paradigm of the family of picornaviruses, infects a susceptible cell, the positive-strand viral RNA can be used directly for translation of the viral polyprotein. In contrast to normal cellular mRNAs, translation of the picornaviral RNA is facilitated by an internal region of the viral RNA, the internal ribosome entry site (IRES). This strategy of internal initiation allows some picornaviruses to take advantage of the obvious opportunity and shut down the cap-dependent cellular translation, while synthesis of the picornaviral polyprotein is initiated cap independently from the IRES element (for an overview, see reference 3).Picornavirus IRES elements are large cis-acting RNA regions that guide ribosomes to an internal site of the viral RNA (17, 37, 51). They are classified into three groups according to their primary and secondary structures: the type I elements of the enterovirus-rhinovirus group (including poliovirus), the type II elements of the cardiovirus-aphthovirus group, and the type III element of hepatitis A virus (HAV). The IRES elements consist of highly conserved RNA secondary structure domains and have a characteristic oligopyrimidine tract followed by a conserved AUG triplet at their 3Ј borders (8,42,44). In poliovirus, this AUG is important but silent for translation, while the actual initiation codon further downstream is reached by ribosomal scanning (20,22,25,39). The small ribosomal subunit is guided to a starting window (43) containing the conserved AUG triplet, most likely by the action of initiation factors. In addition to the standard initiation factors, picornavirus IRES elements recruit other cellular RNA-binding prot...

Phosphorylation of Eukaryotic Translation Initiation Factor 4B (EIF4B) by Open Reading Frame 45/p90 Ribosomal S6 Kinase (ORF45/RSK) Signaling Axis Facilitates Protein Translation during Kaposi Sarcoma-associated Herpesvirus (KSHV) Lytic Replication

“…Some herpesviral genes are encoded on polycistronic mRNA whose translation relies on the IRES. eIF4B is known to interact with the IRESs of several RNA viruses (71)(72)(73)(74)(75) and the virion host shutoff protein of herpesvirus simplex 1 (76). How eIF4B is involved in the translation regulation of herpesviral mRNAs remains to be explored.…”

Picornavirus Internal Ribosome Entry Site Elements Can Stimulate Translation of Upstream Genes

“…pFM is renamed from pM12 (13) for clarity; it contains the FMDV IRES and the firefly luciferase gene. pMPolio (17) contains downstream of an SP6 polymerase promoter the complete poliovirus type 1 (Mahoney) 5Ј-UTR sequence with the authentic initiator AUG fused to the Fluc coding sequence. For construction of pRL-FM-wt, pRL-FM-up-CG, and pRL-FM-up-4, the CAT reporter gene was removed from the respective pCAT-FM-plasmid, and the T7 polymerase promoter sequence together with the Renilla luciferase (Rluc) gene from phRL-null (Promega) were inserted.…”

“…6A). In contrast to the picornavirus IRES elements, the HCV IRES can bind to the small ribosomal subunit in the absence of virtually any translation initiation factors (19,20), whereas binding of ribosomes to picornavirus IRES elements requires initiation factors (9,10,13,17,18). The results of translation at different K ϩ concentrations (Fig.…”

“…1A and 5A) (10 -16) or to a bulged domain in the poliovirus IRES (arrows in Fig. 5A) (17,18) and facilitate ribosome entry downstream of the IRES. On the other hand, picornavirus IRES RNAs recruit a variety of cellular RNA-binding proteins that are usually not involved in translation, like the La protein, poly(rC)-binding protein 2, and the polypyrimidine tract-binding protein PTB (8), to stimulate their IRES-mediated translation.…”

Translation of cellular inhibitor of apoptosis protein 1 (c-IAP1) mRNA is IRES mediated and regulated during cell stress

“…For example, poliovirus infection of permissive cells results in the cleavage of eIF4G by viral 2A proteinase that removes the eIF4E-binding domain and abrogates cap-dependent translation. Yet, IRES-mediated translation of picornavirus mRNA still occurs through the binding of truncated eIF4G, eIF4B, and the recruitment of 40S ribosomal subunits (Hambidge and Sarnow 1992;Ochs et al 2002). Also, it has been demonstrated that activation of both Apaf-1 and DAP5 IRES elements during apoptosis is caspase-3 dependent and mediated by the proteolytically cleaved forms of eIF4G and DAP5 (i.e., eIF4G(p76) and DAP5(p86), respectively; Henis- Korenblit et al 2002).…”