Evidence that ternary complex (eIF2-GTP-tRNA(i)(Met))-deficient preinitiation complexes are core constituents of mammalian stress granules.
Environmental stress-induced phosphorylation of eIF2alpha 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 eIF2alpha 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-eIF2alpha 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.
Kedersha
Nancy
N
Division of Rheumatology and Immunology, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
Chen
Samantha
S
Gilks
Natalie
N
Li
Wei
W
Miller
Ira J
IJ
Stahl
Joachim
J
Anderson
Paul
P
D000818:Animals; D018053:Arsenites / Q000494:pharmacology; D019556:COS Cells; D002499:Centrifugation, Density Gradient; D002522:Chlorocebus aethiops; D003594:Cytoplasmic Granules / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D015852:Eukaryotic Initiation Factor-2 / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000032:analysis*; D006801:Humans; D046911:Macromolecular Substances; D008297:Male; D008856:Microscopy, Fluorescence; D010442:Peptide Chain Initiation, Translational; D010448:Peptide Initiation Factors / Q000032:analysis / Q000378:metabolism; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D012335:RNA, Ribosomal / Q000378:metabolism; D012358:RNA, Transfer, Met / Q000032:analysis* / Q000235:genetics; D016601:RNA-Binding Proteins / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured
D018053:Arsenites; D015852:Eukaryotic Initiation Factor-2; D046911:Macromolecular Substances; D010448:Peptide Initiation Factors; D012333:RNA, Messenger; D012335:RNA, Ribosomal; D012358:RNA, Transfer, Met; D016601:RNA-Binding Proteins; C076751:TIAL1 protein, human; D006160:Guanosine Triphosphate; C015001:arsenite