Deubiquitination and the regulation of stress granule assembly.

Stress granules (SGs) are evolutionarily conserved ribonucleoprotein (RNP) structures that form in response to a variety of environmental and cellular cues. The presence of these RNP granules has been linked to a number of human diseases, including neurodegenerative disorders like amyotrophic lateral sclerosis (ALS) and spinocerebellar ataxia type 2 (Li et al., J Cell Biol 201:361-372, 2013; Nonhoff et al., Mol Biol Cell 18:1385-1396, 2007). Understanding how the assembly of these granules is controlled could, therefore, suggest possible routes of therapy for patients afflicted with these conditions. Interestingly, several reports have identified a potential role for protein deubiquitination in the assembly of these RNP granules. In particular, recent work has found that a specific deubiquitinase enzyme, Ubp3, is required for efficient SG formation in S. cerevisiae (Nostramo et al., Mol Cell Biol 36:173-183, 2016). This same enzyme has been linked to SGs in other organisms, including humans and the fission yeast, Schizosaccharomyces pombe (Takahashi et al., Mol Cell Biol 33:815-829, 2013; Wang et al., RNA 18:694-703, 2012). At first glance, these observations suggest that a striking degree of conservation exists for a ubiquitin-based mechanism controlling SG assembly. However, the devil is truly in the details here, as the precise nature of the involvement of this deubiquitinating enzyme seems to vary in each organism. Here, we briefly review these differences and attempt to provide an overarching model for the role of ubiquitin in SG formation.