Evidence That Ternary Complex (eIF2-GTP-tRNA_i^Met)–Deficient Preinitiation Complexes Are Core Constituents of Mammalian Stress Granules

Abstract

Environmental stress-induced phosphorylation of eIF2␣ inhibits protein translation by reducing the availability of eIF2-GTP-tRNA i Met, the ternary complex that joins initiator tRNA Met to the 43S preinitiation complex. The resulting untranslated mRNA is dynamically routed to discrete cytoplasmic foci known as stress granules (SGs), a process requiring the related RNA-binding proteins TIA-1 and TIAR. SGs appear to be in equilibrium with polysomes, but the nature of this relationship is obscure. We now show that most components of the 48S preinitiation complex (i.e., small, but not large, ribosomal subunits, eIF3, eIF4E, eIF4G) are coordinately recruited to SGs in arsenite-stressed cells. In contrast, eIF2 is not a component of newly assembled SGs. Cells expressing a phosphomimetic mutant (S51D) of eIF2␣ assemble SGs of similar composition, confirming that the recruitment of these factors is a direct consequence of blocked translational initiation and not due to other effects of arsenite. Surprisingly, phospho-eIF2␣ is recruited to SGs that are disassembling in cells recovering from arsenite-induced stress. We discuss these results in the context of a translational checkpoint model wherein TIA and eIF2 are functional antagonists of translational initiation, and in which lack of ternary complex drives SG assembly.

Arabidopsis CML38, a Calcium Sensor That Localizes to Ribonucleoprotein Complexes under Hypoxia Stress

“…In further support of this, treatment of complementation plants expressing CML38-YFP with cycloheximide, which prevents the assembly of SGs (Kedersha et al, 2002;Sorenson and Bailey-Serres, 2014), results in the loss of YFP signal in particulate structures and accumulation in the cell nucleus (Fig. 6).…”

“…SG particles consist of mRNA bound in an arrested state as a preinitiation (48S) complex composed of small 40S ribosomal subunits, eIFs, and mRNA-associated proteins like the poly(A)-binding protein (Kedersha et al, 2002;Kimball et al, 2003). Besides these core components, proteomic analyses of SGs reveal that these structures are complex, with a large array of protein components, including RNAprocessing proteins, metabolic enzymes, chaperone proteins, and cell signaling components, associated with the granule complex (Samaha et al, 2010;Isabelle et al, 2012;Sorenson and Bailey-Serres, 2014).…”

“…Similar to previous studies of time-resolved SG disassembly in plant tissues recovering from hypoxia (Sorenson and BaileySerres, 2014) and related heat stress (Gutierrez-Beltran et al, 2015), the CML38 foci disassemble upon reoxygenation. Second, MS analysis of immunoprecipitates of CML38 from hypoxic root samples reveals the presence of established SG-associated proteins, including poly(A)-binding protein (Kedersha et al, 2002;Kimball et al, 2003;Sorenson and Bailey-Serres, 2014), eukaryotic initiation factors (Li et al, 2010), eukaryotic elongation factors (Hafrén et al, 2013), RNA helicase (Koroleva et al, 2009), small ribosomal subunit proteins (Kedersha et al, 2002;Sorenson and Bailey-Serres, 2014), and others (Mazroui et al, 2007;Buchan et al, 2013;Yan et al, 2014, GutierrezBeltran et al, 2015. Third, coexpression of the core SG-nucleating RNA-binding protein RBP47 (Weber et al, 2008) with CML38 shows that, under hypoxia conditions, the two proteins colocalize to cytosolic granules.…”

Tudor domain containing 7 ( Tdrd7 ) is essential for dynamic ribonucleoprotein (RNP) remodeling of chromatoid bodies during spermatogenesis

“…S5 I and L), which, together with RNA-binding HuR (23), are all characteristics of stress granules. Stress granules are RNP aggregates induced by stress conditions, including DNA damage and viral infection, and are supposed to sequester translation initiation complexes (24). In somatic cells, stress granules intimately associate with processing bodies, and such a close association was also observed between chromatoid bodies and processing bodies in spermatogenesis (Fig.…”

Rôle de l’heme regulated inhibitor(HRI) dans la résistance à l’apoptose

“…Cette inhibition fait intervenir la phosphorylation du facteur d'initiation de la traduction eIF2 (eukaryotic translation initiation factor 2) [14]. Cette modification prévient la formation du complexe ternaire eIF2-GTP-ARNt fonctionnel, et résulte en la formation de complexes d'initiation incompétents pour la traduction, dont l'accumulation aboutit à la formation de granules de stress ( Figure 1) [15]. eIF2 est phosphorylée sur la sérine 51 par une kinase, qui diffère selon le type de stress.…”