Cell-Type-Specific Repression of Internal Ribosome Entry Site Activity by Double-Stranded RNA-Binding Protein 76

Abstract

Translation of picornavirus plus-strand RNA genomes occurs via internal ribosomal entry at highly structured 5 untranslated regions. In addition to canonical translation factors, translation rate is likely influenced by supplementary host and viral trans-acting factors. We previously reported that insertion of a heterologous human rhinovirus type 2 internal ribosomal entry site (IRES) into the poliovirus (PV) genome, generating the chimeric virus PV-RIPO, selectively abrogates viral translation and propagation in neurons, which eliminate poliovirus's signature neuropathogenicity. While severely deficient in cells of neuronal lineage, the rhinovirus IRES promotes efficient propagation of PV-RIPO in cancer cells. Tumor-specific IRES function can be therapeutically exploited to direct viral cytotoxicity to cancer cells. Neuron-glioma heterokaryon analysis implicates neuronal trans-dominant inhibition in this effect, suggesting that host trans-acting factors repress IRES function in a cell-type-specific manner. We identified a set of proteins from neuronal cells with affinity for the rhinovirus IRES, including double-stranded RNA-binding protein 76 (DRBP76). DRBP76 associates with the IRES in neuronal but not in malignant glioma cells. Moreover, DRBP76 depletion in neuronal cells enhances rhinovirus IRES-driven translation and virus propagation. Our observations suggest that cell-typespecific association of DRBP76 with the rhinovirus IRES represses PV-RIPO translation and propagation in neuronal cells. Posttranscriptional regulation constitutes an important level of control of gene expression. The global rate of protein synthesis is influenced by modification of translation initiation factors. In addition, the translation of many mRNAs is independently regulated by processes targeting their untranslated regions (UTRs). In many instances, specific UTRs bind ribonucleoprotein complexes that alter conditions for translation of individual messages.The plus-strand RNA genomes of Picornaviridae feature complex UTRs involved in the regulation of viral translation and genome replication. Translation of viral RNA occurs in competition with cellular mRNA in infected host cells (3). Accordingly, picornavirus genomes have adopted unconventional features enabling efficient viral translation while limiting host cell protein synthesis. In contrast to cellular mRNAs, picornaviral genomic RNAs are uncapped (34), and their uncommonly large and highly structured 5ЈUTRs contain internal ribosomal entry sites (IRESs) that mediate translation initiation in a 5Ј-end, cap-independent manner (26, 39). IRESmediated translation is unimpeded by virus-induced cleavage of canonical initiation factors eukaryotic initiation factor 4G and poly(A)-binding protein (13,27), indicating that their involvement in initiation at the IRES deviates from capped mRNAs. Moreover, divergent means of translation initiation imply the involvement of noncanonical translation factors or IRES trans-acting factors (ITAFs) (4). Such factors, by virtue of their cell and ...

Searching for IRES

“…This correlates well with the developmental problems found in the brains of Apaf-1 knockout mice (Cecconi et al 1998). In contrast, the IRES of HRV is repressed in neuronal cells because of the presence of the mRNA binding protein DRBP76/NF90 (Merrill et al 2006). A list of IRESes that are regulated can be found in the review by Komar and Hatzoglou (2005).…”

Ras Transformation of RIE-1 Cells Activates Cap-Independent Translation of Ornithine Decarboxylase: Regulation by the Raf/MEK/ERK and Phosphatidylinositol 3-Kinase Pathways

“…A possible explanation is that the HeLa cells are of human origin and these splice variants have been derived from the rat. Earlier studies have specified cell type differences in IRES-regulating factors (40). As this study was carried out in RIE-1 cells using splice variants derived from the same cell type, the ODC IRES may be in a more physiologically relevant context.…”

NF90 Exerts Antiviral Activity through Regulation of PKR Phosphorylation and Stress Granules in Infected Cells

“…NF90 was shown to inhibit replication of a broad range of viruses and to form complexes with NF45 and shuttle between the nucleus and cytoplasm (13)(14)(15)(16)(17)(18)(19). However, a detailed mechanism describing how NF90 negatively regulates virus replication remains unclear.…”

“…It suppresses the function of Ebola virus polymerases through interaction with VP35 (14), inhibits HIV replication through interaction with HIV-1 TAR RNA (15,16), represses internal ribosome entry sites in rhinoviruses (17,18) and negatively regulates influenza virus replication through interaction with viral nucleoprotein (NP) (19). However, other studies (20)(21)(22)(23) found that NF90 is required for the replication of some positivestranded RNA viruses and is important for expression of E6 protein in human papillomavirus-infected cells.…”