Translationally Repressed mRNA Transiently Cycles through Stress Granules during Stress

Abstract

In mammals, repression of translation during stress is associated with the assembly of stress granules in the cytoplasm, which contain a fraction of arrested mRNA and have been proposed to play a role in their storage. Because physical contacts are seen with GW bodies, which contain the mRNA degradation machinery, stress granules could also target arrested mRNA to degradation. Here we show that contacts between stress granules and GW bodies appear during stress-granule assembly and not after a movement of the two preassembled structures. Despite this close proximity, the GW body proteins, which in some conditions relocalize in stress granules, come from cytosol rather than from adjacent GW bodies. It was previously reported that several proteins actively traffic in and out of stress granules. Here we investigated the behavior of mRNAs. Their residence time in stress granules is brief, on the order of a minute, although stress granules persist over a few hours after stress relief. This short transit reflects rapid return to cytosol, rather than transfer to GW bodies for degradation. Accordingly, most arrested mRNAs are located outside stress granules. Overall, these kinetic data do not support a direct role of stress granules neither as storage site nor as intermediate location before degradation.

Nucleocytoplasmic Traffic of CPEB1 and Accumulation in Crm1 Nucleolar Bodies

“…Only 30% of the fluorescence was recovered in the foci 15 min after bleach, and no further recovery was observed in the subsequent 15 min. By comparison, photobleaching of the same CPEB1-GFP protein in cytoplasmic stress granules, which are induced in some cells of the same culture, led to full fluorescence recovery with a half-life of ϳ30 s (Mollet et al, 2008). Altogether, these data show that CPEB1 in nuclear foci is tightly, and stably, associated with the nuclear matrix.…”

PARP12, an Interferon-stimulated Gene Involved in the Control of Protein Translation and Inflammation

“…Murine Flag-tagged TRIF and RIPK1 were amplified by PCR and respectively cloned into the pCMV-SPORT6 vector between the EcoRI/XhoI and AgeI/XhoI sites. CFP-TIAR, RFP-Dcp1a, YFP-CIRP, the bidirectional Renilla/ Firefly luciferase constructs containing 0 or 8 MS2-loops and the NFKB-Luciferase reporter construct have been described elsewhere (22)(23)(24)(25). The pGL4.74 plasmid was from Clontech.…”

mRNP granules

“…[6][7][8][9] Second, they share many RNA binding proteins and mRNA species in common, 10 and indeed factors concentrated in one granule often re-localize to another granule type with time or changes in cellular conditions. [11][12][13] Third, mRNP granules exhibit dynamic interactions with one another such as docking, fusion, or apparent maturation from one granule type to the next. Examples include P-body-stress granule docking, fusion 11,14 and apparent maturation, 11,12 P-body-neuronal transport granule docking, 15 P-granule-P-body docking 16 and nuage-P-body fusion, and apparent maturation into sponge bodies.…”

“…Examples include P-body-stress granule docking, fusion 11,14 and apparent maturation, 11,12 P-body-neuronal transport granule docking, 15 P-granule-P-body docking 16 and nuage-P-body fusion, and apparent maturation into sponge bodies. 16,17 The simplest interpretation of such observations is that mRNPs are exchanged between different granules, though this has not been directly demonstrated, 13 and remains an important unresolved issue.…”