Recognition of picornavirus internal ribosome entry sites within cells; influence of cellular and viral proteins (original) (raw)
Related papers
Proceedings of The National Academy of Sciences, 2003
We have proposed a cancer treatment modality based on poliovirus chimeras replicating under the translational control of an internal ribosomal entry site (IRES) derived from human rhinovirus type 2. Insertion of the heterologous IRES causes a neuron-specific propagation deficit and eliminates neurovirulence inherent in poliovirus without affecting viral growth in cells derived from malignant gliomas. We now report the elucidation of a molecular mechanism responsible for the cell type-specific defect mediated by the rhinovirus IRES. Rhinovirus IRES function in neuronal cell types depends on specific structural elements within the 3 nontranslated region of the viral genome. Our observations suggest long-range interactions between the IRES and the 3 terminus that control IRES-mediated gene expression and virus propagation. I nitiation of eukaryotic mRNA translation occurs on assembly of the 43S preinitiation complex at the 5Ј cap structure and 5Ј-3Ј ribosomal scanning until the initiation codon is encountered. Efficient translation depends on the interaction between the poly(A)-binding protein (PABP) and the eukaryotic initiation factor [(eIF)4G] (1, 2). The interaction of eIF4G with eIF4E (binding to the cap structure) and PABP results in circularization of mRNAs (3). Bridging of poly(A) and the initiation complex stimulates translation, possibly by favoring 3Ј-5Ј shunting of ribosomes or promoting initiation factor activity (reviewed in refs. 4, 5).
Nucleic Acids Research, 1995
On the basis of primary sequence comparisons and secondary structure predictions, picornavirus internal ribosome entry segments (IRESes) have been divided into three groups (enteroand rhinoviruses; cardioand aphthoviruses; and hepatitis A virus). Here, we describe a detailed comparison of the ability of IRESes from each group to direct internal initiation of translation in vitro using a single dicistronic mRNA (the only variable being the IRES inserted into the dicistronic region). We studied the influence of various parameters on the capacity of six different picornaviral IRESes, and the non-picornaviral hepatitis C virus IRES, to direct internal initiation of translation: salt concentration, the addition of HeLa cell proteins to rabbit reticulocyte lysate translation reactions, the presence of foot-and-mouth disease virus Lb or human rhinovirus 2A proteinase. On the basis of the characteristics of IRES-driven translation in vitro, the picornaviral IRESes can be classified in a similar manner to when sequence homologies are considered. IRESes from each of the three groups responded differently to all of the parameters tested, indicating that while all of these elements can direct internal ribosome entry, the functional requirements for efficient IRES activity vary dramatically. In the individual optimal conditions for translation initiation, the best IRESes were those from the cardioand aphthoviruses, followed by those from the enteroviruses, which exhibited up to 70% of the efficiency of the EMCV element in directing internal initiation of translation.
RNA-protein interactions in regulation of picornavirus RNA translation
Microbiological reviews, 1996
The translation of picornavirus RNA occurs by a cap-independent mechanism directed by a region of about 450 nucleotides from the 5' untranslated region, termed an internal ribosome entry site (IRES). Internal initiation of protein synthesis occurs without any requirement for viral proteins. Furthermore, it is maintained when host cell protein synthesis is almost abolished. By using in vitro translation systems, two distinct families of IRES elements which have very different predicted RNA secondary structures have been defined. The cardiovirus and aphthovirus elements function very efficiently in rabbit reticulocyte lysate, whereas the enterovirus and rhinovirus elements function poorly in this system. However, supplementation of this translation system with additional cellular proteins can stimulate translation directed by the enterovirus and rhinovirus RNAs and reduce production of aberrant initiation products. The characterization of cellular proteins interacting with the pic...
Picornavirus IRES elements: RNA structure and host protein interactions
Virus Research, 2015
Internal ribosome entry site (IRES) elements were discovered in picornaviruses. These elements are cis-acting RNA sequences that adopt diverse three-dimensional structures and recruit the translation machinery using a 5 end-independent mechanism assisted by a subset of translation initiation factors and various RNA binding proteins termed IRES transacting factors (ITAFs). Many of these factors suffer important modifications during infection including cleavage by picornavirus proteases, changes in the phosphorylation level and/or redistribution of the protein from the nuclear to the cytoplasm compartment. Picornavirus IRES are amongst the most potent elements described so far. However, given their large diversity and complexity, the mechanistic basis of its mode of action is not yet fully understood. This review is focused to describe recent advances on the studies of RNA structure and RNA-protein interactions modulating picornavirus IRES activity.
Virology, 1995
Poliovirus and human rhinovirus 2A proteinases are known to stimulate translation initiation on the cognate viral Internal Ribosome Entry Segments (IRESes). The molecular mechanism of this translational transactivation was investigated in vitro using dicistronic mRNAs containing picornaviral IRESes as the intercistronic spacer and purified human rhinovirus type 2 and coxsackievirus B4 2A proteinases. The stimulation achieved on the HRV2 IRES in the presence of the cognate 2A proteinase at 1 /~g/ml was twofold; the maximum stimulation at 100/~g/ml was fivefold. The IRESes and proteinases from rhino-and enteroviruses were interchangeable; however, stimulation of translation initiation on a cardiovirus IRES by these proteinases was minimal. Studies using an inhibitor or a mutant 2A proteinase demonstrated that translation stimulation requires 2A-mediated enzymatic conversion of some cellular component(s). The HRV2 2A proteinase also stimulated translation initiation on full-length viral RNA, suggesting that 2A proteinase-mediated stimulation of IRES-driven translation has a physiological role.
Proceedings of the National Academy of Sciences, 1993
Initiation of translation of the RNA genomes of picornaviruses such as poliovirus and encephalomyocarditis virus is cap-independent and results from interaction of ribosomes with a segment of the 5' noncoding region of these mRNAs termed the internal ribosomal entry site. Genetic and biochemical studies have previously shown that a 57-kDa cytoplasmic RNA-binding protein (p57) plays an essential role in this translation mechanism. We have now found that p57 shares physical, biochemical, and antigenic properties with the pyrimidine tract-binding protein (PTB), a nuclear protein that has been implicated in various processes involving pre-mRNA. These data indicate that p57 and PTB are the same protein. Purified recombinant PTB bound specifically to a bulged hairpin within the internal ribosomal entry site of encephalomyocarditis virus and had a much lower affinity for a mutated derivative of this hairpin and for unrelated RNAs. Immunodepletion of p57/PTB from a HeLa cell-free lysate...
Journal of Virology, 2002
The teschoviruses constitute a recently defined picornavirus genus. Most of the genome sequence of the porcine teschovirus-1 (PTV) Talfan and several other strains is known. We now demonstrate that initiation of protein synthesis occurs at nucleotide (nt) 412 on the PTV Talfan RNA and that nt 1 to 405 contains an internal ribosome entry site (IRES) that functions efficiently in vitro and within mammalian cells. In comparison with other picornavirus IRES elements, the PTV IRES is relatively short and lacks a significant polypyrimidine tract near the 3 end. Expression of an enterovirus 2A protease, which induces cleavage of eIF4G within the translation initiation complex eIF4F, has little effect on the PTV IRES activity within BHK cells. The PTV IRES has a unique set of properties and represents a new class of picornavirus IRES element.