PPP1R15A-mediated dephosphorylation of eIF2α is unaffected by Sephin1 or Guanabenz

Abstract

Dephosphorylation of translation initiation factor 2 (eIF2α) terminates signalling in the mammalian integrated stress response (ISR) and has emerged as a promising target for modifying the course of protein misfolding diseases. The [(o-chlorobenzylidene)amino]guanidines (Guanabenz and Sephin1) have been proposed to exert protective effects against misfolding by interfering with eIF2α-P dephosphorylation through selective disruption of a PP1-PPP1R15A holophosphatase complex. Surprisingly, they proved inert in vitro affecting neither stability of the PP1-PPP1R15A complex nor substrate-specific dephosphorylation. Furthermore, eIF2α-P dephosphorylation, assessed by a kinase shut-off experiment, progressed normally in Sephin1-treated cells. Consistent with its role in defending proteostasis, Sephin1 attenuated the IRE1 branch of the endoplasmic reticulum unfolded protein response. However, repression was noted in both wildtype and Ppp1r15a deleted cells and in cells rendered ISR-deficient by CRISPR editing of the Eif2s1 locus to encode a non-phosphorylatable eIF2α (eIF2αS51A). These findings challenge the view that [(o-chlorobenzylidene)amino]guanidines restore proteostasis by interfering with eIF2α-P dephosphorylation.DOI: http://dx.doi.org/10.7554/eLife.26109.001

Guanabenz treatment improves Oculopharyngeal muscular dystrophy phenotype

“…Several reports, in the context of other diseases, have shown that GA promotes the UPR to counteract ER stress (35,36,39). It has been proposed that GA binds the regulatory subunit of protein phosphatase 1 (PPP1R15A), thereby preventing the dephosphorylation of eiF2α and then protein translation recovery following stress (37, 39), although its exact mechanism of action remains controversial (41,53). Delaying protein translation recovery may thus allow the UPR downstream chaperones (e.g.…”

“…The third pathway is operated by the activating transcription factor 6 (ATF6), a receptor that under ER stress and its dissociation to Grp78 is translocated to the Golgi where it is cleaved to produce a fragment which then acts as a transcription factor to promote expression of XBP1 mRNA and other proteins involved in protein folding. It has been proposed that GA binds to PPP1R15A, thus preventing its binding to PP1c (37,38) and prolonging eIF2α phosphorylation with the effect of reducing the accumulation of misfolded proteins in the ER (37,39), but these data are controversial (40,41).…”

Developmentally regulated PERK activity renders dendritic cells insensitive to subtilase cytotoxin-induced integrated stress response

“…Recently, the importance of globular actin in the formation of a tripartite holophosphatase complex assembled with GADD34 and PP1c to dephosphorylate eIF2a was revealed (Crespillo-Casado et al, 2017, Chambers et al, 2015, Crespillo-Casado et al, 2018. Given the unusual regulation of eIF2α phosphorylation in DCs, we wondered whether actin organization could also impact this pathway in a different setting than artificial ER-stress induction.…”

Adapting Secretory Proteostasis and Function Through the Unfolded Protein Response

“…On the other hand, salubrinal (Boyce et al 2005), guanabenz (Tsaytler et al 2011), ISRIB (Sidrauski et al 2015), and Sephin1 (Das et al 2015) can modulate the PERK-induced translational block either up or down by altering eIF2α phosphorylation status (Figure 1). Other explanations for the biological phenotypes induced by guanabenz and Sephin1 may also prove relevant (Crespillo-Casado et al 2017). Notably, these compounds also modulate overlapping aspects of the integrated stress response, rendering such small molecules neither UPR- nor PERK-specific.…”