Functional involvement of polypyrimidine tract-binding protein in translation initiation complexes with the internal ribosome entry site of foot-and-mouth disease virus

Abstract

The synthesis of picornavirus polyproteins is initiated cap independently far downstream from the 5 end of the viral RNA at the internal ribosome entry site (IRES). The cellular polypyrimidine tract-binding protein (PTB) binds to the IRES of foot-and-mouth disease virus (FMDV). In this study, we demonstrate that PTB is a component of 48S and 80S ribosomal initiation complexes formed with FMDV IRES RNA. The incorporation of PTB into these initiation complexes is dependent on the entry of the IRES RNA, since PTB and IRES RNA can be enriched in parallel either in 48S or 80S ribosomal complexes by stage-specific inhibitors of translation initiation. The formation of the ribosomal initiation complexes with the IRES occurs slowly, is temperature dependent, and correlates with the incorporation of PTB into these complexes. In a first step, PTB binds to the IRES, and then the small ribosomal subunit encounters this PTB-IRES complex. Mutations in the major PTB-binding site interfere simultaneously with the formation of initiation complexes, translation efficiency, and PTB cross-linking. PTB stimulates translation directed by the FMDV IRES in a rabbit reticulocyte lysate depleted of internal PTB, and the efficiency of translation can be restored to the original level by the addition of PTB. These results indicate that PTB plays an important role in the formation of initiation complexes with FMDV IRES RNA and in stimulation of internal translation initiation with this picornavirus.

Synthesis of the translational apparatus is regulated at the translational level

“…Several mammalian pyrimidine‐binding proteins have been implicated so far in translational control: (a) polypyrimidine tract binding protein (PTB), which has been implicated in the regulation of translation initiation of picornavirus mRNAs [108,109]; (b) heterogeneous nuclear ribonucleoprotein K (hnRNP K), which selectively and strongly binds poly(C) homopolymer [110] (this protein has recently been shown to operate during erythroid differentiation, together with hnRNP E1, as a translational silencer of 15‐lipoxygenase mRNA [111]); (c) hnRNP E1 (also known as PCBP 1 or αCP1); and (d) hnRNP E2 (PCBP‐2, αCP2). The latter two proteins are closely related exhibiting an overall structural identity of about 85%, and displaying a high affinity for poly(rC) relative to other homoribopolymers [112].…”

Viral and Cellular Proteins Involved in Coronavirus Replication

“…Studies of picornaviruses revealed that PTB plays a role in internal ribosome entry site (IRES)-mediated translation by mechanisms distinct from those governing the cap-dependent translation of most eukaryotic mRNAs . PTB was found to be associated with the IRES elements of encephalomyocarditis virus and foot-and-mouth-disease virus and to stimulate translation ini-tiated from these IRES elements Niepmann 1996;Niepmann et al 1997).…”

Interaction of Eukaryotic Initiation Factor eIF4B with the Internal Ribosome Entry Site of Foot-and-Mouth Disease Virus Is Independent of the Polypyrimidine Tract-Binding Protein

“…In addition, picornaviruses recruit unconventional cellular proteins, e.g., the 57-kDa polypyrimidine tract-binding protein (PTB). PTB binds to several IRES elements and enhances translation of foot-andmouth disease virus (FMDV) (13,14), and EMCV (2,5).…”