G3BP–Caprin1–USP10 complexes mediate stress granule condensation and associate with 40S subunits

TLDR

Stress granules are assemblies of stalled translation preinitiation complexes that rely on RNA‑binding proteins such as G3BP, which also associates with 40S ribosomal subunits through an RGG motif essential for granule formation. We propose that G3BP drives SG condensation by switching between Caprin1‑bound and USP10‑bound states. By employing G3BP1 mutants that cannot bind Caprin1 or USP10 and performing rescue experiments, the authors showed that Caprin1 binding promotes SG assembly while USP10 binding suppresses it, revealing a mutually exclusive regulatory mechanism. Loss of both G3BP1 and G3BP2 abolishes SG formation in response to eIF2α phosphorylation or eIF4A inhibition, yet SGs still form under severe heat or osmotic stress, and the G3BP1‑F33W mutant restores SG assembly, demonstrating that Caprin1 binding promotes while USP10 binding inhibits SG condensation.

Abstract

Mammalian stress granules (SGs) contain stalled translation preinitiation complexes that are assembled into discrete granules by specific RNA-binding proteins such as G3BP. We now show that cells lacking both G3BP1 and G3BP2 cannot form SGs in response to eukaryotic initiation factor 2α phosphorylation or eIF4A inhibition, but are still SG-competent when challenged with severe heat or osmotic stress. Rescue experiments using G3BP1 mutants show that G3BP1-F33W, a mutant unable to bind G3BP partner proteins Caprin1 or USP10, rescues SG formation. Caprin1/USP10 binding to G3BP is mutually exclusive: Caprin binding promotes, but USP10 binding inhibits, SG formation. G3BP interacts with 40S ribosomal subunits through its RGG motif, which is also required for G3BP-mediated SG formation. We propose that G3BP mediates the condensation of SGs by shifting between two different states that are controlled by binding to Caprin1 or USP10.