RT Journal Article SR Electronic T1 Recruitment of human eIF4G1 or DAP5 to the 5’ untranslated regions of a subset of cellular mRNAs drives cap-independent translation JF bioRxiv FD Cold Spring Harbor Laboratory SP 472498 DO 10.1101/472498 A1 Solomon A. Haizel A1 Usha Bhardwaj A1 Ruben L. Gonzalez, Jr. A1 Somdeb Mitra A1 Dixie J. Goss YR 2018 UL http://biorxiv.org/content/early/2018/11/16/472498.abstract AB During unfavorable cellular conditions (e.g., tumor hypoxia, viral infection, nutrient deprivation, etc.), the canonical, cap-dependent translation initiation pathway in human cells is suppressed by sequestration of the cap-binding protein, eukaryotic initiation factor (eIF) 4E, by 4E-binding proteins. Additionally, the expression levels of eIF4G and its cellular homolog, death associated protein 5 (DAP5), are elevated. Under these conditions, a subset of cellular mRNAs, including many encoding proteins with important roles in human health and disease, (e.g. HIF-1α, FGF-9, and p53) is translated in a cap-independent manner. Despite their physiological importance, however, the molecular mechanisms underlying cap-independent initiation of this subset of cellular mRNAs remain unknown. Here, we have used fluorescence anisotropy-based equilibrium binding assays developed in our laboratories to demonstrate that an N-terminal truncated form of human eIF4G1 that cannot interact with eIF4E (ΔN-4G1) or DAP5 directly bind to the 5’ untranslated regions (UTRs) of these mRNAs. Specifically, we have measured the differential affinities with which ΔN-4G1 and DAP5 interact with the 5’ UTRs of four distinct members of this subset of cellular mRNAs. Using a luciferase-based gene expression reporter assay, we further demonstrate that these same 5’ UTRs can promote cap-independent initiation in an ΔN-4G1 or DAP5-dependent manner in a rabbit reticulocyte lysate-based in vitro translation system. Integrating the results of our quantitative binding- and in vitro translation studies, we propose a model specifying how a subset of cellular mRNAs switch from cap-dependent to cap-independent modes of translation initiationSignificance Under cellular stress conditions (e.g., tumor hypoxia, viral infection, etc.), the canonical, cap-dependent initiation of eukaryotic protein synthesis, or translation, of a subset of cellular mRNAs switches to a cap-independent mechanism. Despite the important role they play in human health and disease, the mechanisms regulating this switch remain unknown. We have found that a variant of eukaryotic initiation factor (eIF) 4G1 and its homolog, DAP5, factors that are upregulated under stress conditions, bind with high affinity and specificity to the 5’ untranslated regions of these mRNAs and upregulate their translation. These results suggest that binding of eIF4G1 or DAP5 to these mRNAs plays an important role in regulating the switch between the cap-dependent and cap-independent initiation of these mRNAs.