Stress granule condensation (SGC) of translationally arrested mRNAs requires G3BP, and G3BP-mediated SGC is inhibited by serine 149 phosphorylation, regulated by mutually exclusive binding of Caprin1 and USP10, and requires its RGG region for SGC and for interactions with 40S ribosomal subunits.

Angiogenin (ANG) is a secreted ribonuclease that cleaves tRNA to initiate a stress-response program in mammalian cells. Here we show that ANG inhibits protein synthesis and promotes arsenite-and pateamine A-induced assembly of stress granules (SGs). These effects are abrogated in cells transfected with the ANG inhibitor RNH1. Transfection of natural or synthetic 5-but not 3-tRNA fragments (tRNA-derived stress-induced RNAs; tiRNAs) induces the phospho-eukaryotic translation initiation factor 2␣-independent assembly of SGs. Natural 5-tiRNAs but not 3-tiRNAs are capped with a 5-monophosphate that is required for optimal SG assembly. These findings reveal that SG assembly is a component of the ANG-and tiRNA-induced stress response program.In response to environmental stress, eukaryotic cells activate stress response programs that down-regulate energy-expensive processes, such as transcription and translation. These regulatory programs reduce the expression of common housekeeping genes while increasing the expression of genes that repair stress-induced damage and promote cell survival. At the level of translation, this is achieved by exploiting the differential sensitivity of mRNAs to changes in the availability or activity of general initiation factors, such as eukaryotic translation initiation factor 2␣ (eIF2␣) 3 (1). Phosphorylation of eIF2␣ by one of several stress-activated kinases reduces the availability of the eIF2-GTP-tRNA i Met ternary complex to inhibit translation initiation. This reduces the translation of most transcripts but enhances the translation of transcripts possessing regulatory upstream open reading frames, such as transcription factor ATF4, a component of the integrated stress response program.Thus, phospho-eIF2␣ triggers a profound reprogramming of cellular protein synthesis that helps cells adapt to adverse environmental conditions.Stress-induced cleavage of tRNA initiates a complementary stress response program found in both prokaryotes and eukaryotes (2). In mammals, stress-induced tRNA cleavage is mediated by angiogenin (ANG) (3, 4), a 14-kDa member of the pancreatic RNase superfamily. ANG is a secreted endoribonuclease that possesses both angiogenic (5) and cytoprotective activities (6, 7). Secreted ANG enters cells via receptor-mediated endocytosis (8, 9), translocates to the nucleus (10), and promotes ribosomal RNA transcription and cellular proliferation (11-13). ANG secretion is stimulated by hypoxia, suggesting that it may serve as a stress-induced paracrine factor that protects neighboring cells from deleterious effects of stress.In a previous study, we showed that stress promotes ANGmediated tRNA cleavage to produce tRNA-derived stress-induced RNAs (tiRNAs) (4). Cleavage occurs preferentially in the anticodon loop of mature tRNA to produce 5Ј-and 3Ј-fragments (5Ј-and 3Ј-tiRNAs, respectively). The addition of recombinant wild type but not RNase-inactive mutant ANG to cultured cells promotes tiRNA production and inhibition of protein synthesis. Thus, the ribonuclease activity of ANG...

Stress granules (SGs) and processing bodies (PBs) are microscopically visible ribonucleoprotein granules that cooperatively regulate the translation and decay of messenger RNA1–3. Using an RNA-mediated interference-based screen, we identify 101 human genes required for SG assembly, 39 genes required for PB assembly, and 31 genes required for coordinate SG and PB assembly. Although 51 genes encode proteins involved in mRNA translation, splicing and transcription, most are not obviously associated with RNA metabolism. We find that several components of the hexosamine biosynthetic pathway, which reversibly modifies proteins with O-linked N-acetylglucosamine (O-GlcNAc) in response to stress, are required for SG and PB assembly. O-GlcNAc-modified proteins are prominent components of SGs but not PBs, and include RACK1 (receptor for activated C kinase 1), prohibitin-2, glyceraldehyde-3-phosphate dehydrogenase and numerous ribosomal proteins. Our results suggest that O-GlcNAc modification of the translational machinery is required for aggregation of untranslated messenger ribonucleoproteins into SGs. The lack of enzymes of the hexosamine biosynthetic pathway in budding yeast may contribute to differences between mammalian SGs and related yeast EGP (eIF4E, 4G and Pab1 containing) bodies.