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Montréal, Canada

Hosokawa N.,Kyoto University | Tremblay L.O.,ll Cancer Center | Sleno B.,ll Cancer Center | Kamiya Y.,Okazaki Institute for Integrative Bioscience | And 7 more authors.
Glycobiology | Year: 2010

Glycoprotein folding and degradation in the endoplasmic reticulum (ER) is mediated by the ER quality control system. Mannose trimming plays an important role by forming specific N-glycans that permit the recognition and sorting of terminally misfolded conformers for ERAD (ER-associated degradation). The EDEM (ER degradation enhancing α-mannosidase-like protein) subgroup of proteins belonging to the Class I α1,2-mannosidase family (glycosylhydrolase family 47) has been shown to enhance ERAD.We recently reported that overexpression ofEDEM3 enhances glycoprotein ERAD with a concomitant increase in mannose-trimming activity in vivo. Herein, we report that overexpression of EDEM1 produces Glc1Man8GlcNAc2 isomer C on terminally misfolded null Hong Kong α1-antitrypsin (NHK) in vivo. Levels of this isomer increased throughout the chase period and comprised approximately 10% of the [3H]mannose-labeled N-glycans on NHK after a 3-h chase. Furthermore, overexpression of EDEM1 E220Q containing a mutation in a conserved catalytic residue essential for α1,2-mannosidase activity did not yield detectable levels of Glc1Man8GlcNAc2 isomer C. Yet, the same extent of NHK ERAD-enhancement was observed in both EDEM1 and EDEM1 E220Q overexpressing cells. This can be attributed to both wild-type and mutant EDEM1 inhibiting aberrant NHK dimer formation. We further analyzed the N-glycan profile of total cellular glycoproteins from HepG2 cells stably overexpressing EDEM1 and found that the relative amount of Man7GlcNAc2 isomer A, which lacks the terminal B and C branch mannoses, was increased compared to parental HepG2 cells. Based on this observation, we conclude that EDEM1 activity trims mannose from the C branch of N-glycans in vivo. © The Author 2010. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org. Source


Sidrauski C.,University of California at San Francisco | Sidrauski C.,Howard Hughes Medical Institute | Acosta-Alvear D.,University of California at San Francisco | Acosta-Alvear D.,Howard Hughes Medical Institute | And 19 more authors.
eLife | Year: 2013

Phosphorylation of the α-subunit of initiation factor 2 (eIF2) controls protein synthesis by a conserved mechanism. In metazoa, distinct stress conditions activate different eIF2α kinases (PERK, PKR, GCN2, and HRI) that converge on phosphorylating a unique serine in eIF2α. This collection of signaling pathways is termed the 'integrated stress response' (ISR). eIF2α phosphorylation diminishes protein synthesis, while allowing preferential translation of some mRNAs. Starting with a cell-based screen for inhibitors of PERK signaling, we identified a small molecule, named ISRIB, that potently (IC50 = 5 nM) reverses the effects of eIF2α phosphorylation. ISRIB reduces the viability of cells subjected to PERK-activation by chronic endoplasmic reticulum stress. eIF2α phosphorylation is implicated in memory consolidation. Remarkably, ISRIB-treated mice display significant enhancement in spatial and fear-associated learning. Thus, memory consolidation is inherently limited by the ISR, and ISRIB releases this brake. As such, ISRIB promises to contribute to our understanding and treatment of cognitive disorders. © Sidrauski et al. Source

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