Deubiquitylases USP5 and USP13 are recruited to and regulate heat-induced stress granules through their deubiquitylating activities

Stress granules are transient cytoplasmic foci induced by various stresses, which contain translation-stalled mRNAs and RNA-binding proteins and are proposed to modulate mRNA translation and stress responses. Here we show that deubiquitinases USP5 and USP13 are recruited to heat-induced stress granules. Heat-induced stress granules also contained Lys48- and Lys63-linked ubiquitin chains. Depletion of USP5 or USP13 resulted in elevated ubiquitin chain levels and accelerated assembly of heat-induced stress granules, suggesting that these enzymes regulate the stability of the stress granules through ubiquitin isopeptidase activity. Moreover, disassembly of heat-induced stress granules after returning the cells to normal temperatures was markedly repressed by individual depletion of USP5 or USP13. Finally, overexpression of a ubiquitin mutant lacking the C-terminal diglycine motif caused the accumulation of unanchored ubiquitin chains and the repression of the disassembly of heat-induced stress granules. As unanchored ubiquitin chains are preferred substrates for USP5, we suggest that USP5 regulates the assembly and disassembly of heat-induced stress granules by the hydrolysis of unanchored ubiquitin chains while USP13 regulates stress granules through deubiquitinating protein-conjugated ubiquitin chains.