scholarly journals Chaperone-Mediated Reflux of Secretory Proteins to the Cytosol During Endoplasmic Reticulum Stress

2019 ◽  
Author(s):  
Aeid Igbaria ◽  
Philip I. Merksamer ◽  
Ala Trusina ◽  
Firehiwot Tilahun ◽  
Jefferey R. Johnson ◽  
...  
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Secretory Pathway ◽  
Protein Quality ◽  
Fluorescent Protein ◽  
Control Process ◽  
Secretory Proteins ◽  
Er Quality Control ◽  
Quality Control Process

ABSTRACTDiverse perturbations to endoplasmic reticulum (ER) functions compromise the proper folding and structural maturation of secretory proteins. To study secretory pathway physiology during such “ER stress”, we employed an ER-targeted, redox-responsive, green fluorescent protein—eroGFP—that reports on ambient changes in oxidizing potential. Here we find that diverse ER stress agents cause properly folded, ER-resident eroGFP (and other ER luminal proteins) to “reflux” back to the reducing environment of the cytosol as intact, folded proteins. By utilizing eroGFP in a comprehensive genetic screen in S. cerevisiae, we show that ER protein reflux during ER stress requires specific chaperones and co-chaperones residing in both the ER and the cytosol. Chaperone-mediated ER protein reflux does not require E3 ligase activity, and proceeds even more vigorously when these ER-associated degradation (ERAD) factors are crippled, suggesting that reflux may work in parallel with ERAD. In summary, chaperone-mediated ER-protein reflux may be a conserved protein quality control process that evolved to maintain secretory pathway homeostasis during ER protein-folding stress.SIGNIFICANCEApproximately one third of eukaryotic proteins are synthesized on ribosomes attached to the endoplasmic reticulum (ER) membrane. Many of these polypeptides co- or post-translationally translocate into the ER, wherein they fold and mature. An ER quality-control system proofreads these proteins by facilitating their folding and modification, while eliminating misfolded proteins through ER-associated degradation (ERAD). Yet, the fate of many secretory proteins during ER stress is not completely understood. Here, we uncovered an ER-stress induced “protein reflux” system that delivers intact, folded ER luminal proteins back to the cytosol without degrading them. We found that ER protein reflux works in parallel to ERAD and requires distinct ER-resident and cytosolic chaperones and co-chaperones.

scholarly journals Chaperone-mediated reflux of secretory proteins to the cytosol during endoplasmic reticulum stress

2019 ◽  
Vol 116 (23) ◽  
pp. 11291-11298 ◽  
Author(s):  
Aeid Igbaria ◽  
Philip I. Merksamer ◽  
Ala Trusina ◽  
Firehiwot Tilahun ◽  
Jeffrey R. Johnson ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Secretory Pathway ◽  
Protein Quality ◽  
Fluorescent Protein ◽  
Control Process ◽  
Secretory Proteins ◽  
Quality Control Process ◽  
Folded Proteins ◽  
Green Fluorescent

Diverse perturbations to endoplasmic reticulum (ER) functions compromise the proper folding and structural maturation of secretory proteins. To study secretory pathway physiology during such “ER stress,” we employed an ER-targeted, redox-responsive, green fluorescent protein—eroGFP—that reports on ambient changes in oxidizing potential. Here we find that diverse ER stress regimes cause properly folded, ER-resident eroGFP (and other ER luminal proteins) to “reflux” back to the reducing environment of the cytosol as intact, folded proteins. By utilizing eroGFP in a comprehensive genetic screen in Saccharomyces cerevisiae, we show that ER protein reflux during ER stress requires specific chaperones and cochaperones residing in both the ER and the cytosol. Chaperone-mediated ER protein reflux does not require E3 ligase activity, and proceeds even more vigorously when these ER-associated degradation (ERAD) factors are crippled, suggesting that reflux may work in parallel with ERAD. In summary, chaperone-mediated ER protein reflux may be a conserved protein quality control process that evolved to maintain secretory pathway homeostasis during ER protein-folding stress.

Protein quality control at the endoplasmic reticulum

2016 ◽  
Vol 60 (2) ◽  
pp. 227-235 ◽  
Author(s):  
Kathleen McCaffrey ◽  
Ineke Braakman
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Secretory Pathway ◽  
Protein Quality ◽  
Bond Formation ◽  
Protein Quality Control ◽  
Secretory Proteins ◽  
Protein Quality Control System ◽  
And Function ◽  
Extracellular Environment

The ER (endoplasmic reticulum) is the protein folding ‘factory’ of the secretory pathway. Virtually all proteins destined for the plasma membrane, the extracellular space or other secretory compartments undergo folding and maturation within the ER. The ER hosts a unique PQC (protein quality control) system that allows specialized modifications such as glycosylation and disulfide bond formation essential for the correct folding and function of many secretory proteins. It is also the major checkpoint for misfolded or aggregation-prone proteins that may be toxic to the cell or extracellular environment. A failure of this system, due to aging or other factors, has therefore been implicated in a number of serious human diseases. In this article, we discuss several key features of ER PQC that maintain the health of the cellular secretome.

Positive contribution of ERdj5/JPDI to endoplasmic reticulum protein quality control in the salivary gland

2009 ◽  
Vol 425 (1) ◽  
pp. 117-128 ◽  
Author(s):  
Akira Hosoda ◽  
Mio Tokuda ◽  
Ryoko Akai ◽  
Kenji Kohno ◽  
Takao Iwawaki
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Salivary Gland ◽  
Er Stress ◽  
Knockout Mice ◽  
Protein Quality ◽  
Protein Quality Control ◽  
Whole Body ◽  
Secretory Proteins ◽  
Positive Contribution

In eukaryotic cells, most membrane and secretory proteins are modified post-translationally in the ER (endoplasmic reticulum) for correct folding and assembly. Disulfide-bond formation is one of the important modifications affecting folding and is catalysed by the PDI (protein disulfide isomerase) family proteins. ERdj5 [also known as JPDI (J-domain-containing PDI-like protein)] is a member of the PDI family proteins and has been reported to act as a reductase in ERAD (ER-associated degradation). However, the role of ERdj5 at the whole-body level remains unclear. Therefore in the present study we generated ERdj5-knockout mice {the mouse gene of ERdj5 is known as Dnajc10 [DnaJ (Hsp40) homologue, subfamily C, member 10]} and analysed them. Although ERdj5-knockout mice were viable and healthy, the ER stress response was activated in the salivary gland of the knockout mice more than that of control mice. Furthermore, in ERdj5-knockout cells, the expression of exogenous ERdj5 mitigated the ER stress caused by overproduction of α-amylase, which is one of the most abundant proteins in saliva and has five intramolecular disulfide bonds. This effect was dependent on the thioredoxin-like motifs of ERdj5. Thus we suggest that ERdj5 contributes to ER protein quality control in the salivary gland.

scholarly journals Size-Dependent Secretory Protein Reflux into the Cytosol in Association with Acute Endoplasmic Reticulum Stress

2019 ◽  
Author(s):  
Patrick Lajoie ◽  
Erik L. Snapp
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Fluorescent Protein ◽  
Secretory Protein ◽  
Secretory Proteins ◽  
Dependent Manner ◽  
Size Dependent ◽  
Heat Shock Stress ◽  
Shock Stress

ABSTRACTOnce secretory proteins have been targeted to the endoplasmic reticulum (ER), the proteins typically remain partitioned from the cytosol. If the secretory proteins misfold, they can be unfolded and retrotranslocated into the cytosol for destruction by the proteasome by ER-associated protein Degradation (ERAD). Here, we report that correctly folded and targeted luminal ER fluorescent protein reporters accumulate in the cytosol during acute misfolded secretory protein stress in yeast. Photoactivation fluorescence microscopy experiments reveal that luminal reporters already localized to the ER relocalize to the cytosol, even in the absence of essential ERAD machinery. We named this process “ER reflux.” Reflux appears to be regulated in a size-dependent manner for reporters. Interestingly, prior heat shock stress also prevents ER stress-induced reflux. Together, our findings establish a new ER stress-regulated pathway for relocalization of small luminal secretory proteins into the cytosol, distinct from the ERAD and pre-emptive quality control pathways.

scholarly journals Proteostasis In The Endoplasmic Reticulum: Road to Cure

Cancers ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1793 ◽  
Author(s):  
Nam ◽  
Jeon
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Protein Quality ◽  
Tumor Development ◽  
Therapeutic Interventions ◽  
Secretory Proteins ◽  
Unfolded Protein ◽  
Stress Signals ◽  
Protein Response

The endoplasmic reticulum (ER) is an interconnected organelle that is responsible for the biosynthesis, folding, maturation, stabilization, and trafficking of transmembrane and secretory proteins. Therefore, cells evolve protein quality-control equipment of the ER to ensure protein homeostasis, also termed proteostasis. However, disruption in the folding capacity of the ER caused by a large variety of pathophysiological insults leads to the accumulation of unfolded or misfolded proteins in this organelle, known as ER stress. Upon ER stress, unfolded protein response (UPR) of the ER is activated, integrates ER stress signals, and transduces the integrated signals to relive ER stress, thereby leading to the re-establishment of proteostasis. Intriguingly, severe and persistent ER stress and the subsequently sustained unfolded protein response (UPR) are closely associated with tumor development, angiogenesis, aggressiveness, immunosuppression, and therapeutic response of cancer. Additionally, the UPR interconnects various processes in and around the tumor microenvironment. Therefore, it has begun to be delineated that pharmacologically and genetically manipulating strategies directed to target the UPR of the ER might exhibit positive clinical outcome in cancer. In the present review, we summarize recent advances in our understanding of the UPR of the ER and the UPR of the ER–mitochondria interconnection. We also highlight new insights into how the UPR of the ER in response to pathophysiological perturbations is implicated in the pathogenesis of cancer. We provide the concept to target the UPR of the ER, eventually discussing the potential of therapeutic interventions for targeting the UPR of the ER for cancer treatment.

scholarly journals Reglucosylation by UDP-glucose:glycoprotein glucosyltransferase 1 delays glycoprotein secretion but not degradation

2015 ◽  
Vol 26 (3) ◽  
pp. 390-405 ◽  
Author(s):  
Abla Tannous ◽  
Nishant Patel ◽  
Taku Tamura ◽  
Daniel N. Hebert
Keyword(s):  
Quality Control ◽  
Secretory Pathway ◽  
Selection Process ◽  
Control Process ◽  
Degradation Pathway ◽  
Carbohydrate Binding ◽  
Wild Type ◽  
Mutant Proteins ◽  
Quality Control Process ◽  
Glycoprotein Secretion

UDP-glucose:glycoprotein glucosyltransferase 1 (UGT1) is a central quality control gatekeeper in the mammalian endoplasmic reticulum (ER). The reglucosylation of glycoproteins supports their rebinding to the carbohydrate-binding ER molecular chaperones calnexin and calreticulin. A cell-based reglucosylation assay was used to investigate the role of UGT1 in ER protein surveillance or the quality control process. UGT1 was found to modify wild-type proteins or proteins that are expected to eventually traffic out of the ER through the secretory pathway. Trapping of reglucosylated wild-type substrates in their monoglucosylated state delayed their secretion. Whereas terminally misfolded substrates or off-pathway proteins were most efficiently reglucosylated by UGT1, the trapping of these mutant substrates in their reglucosylated or monoglucosylated state did not delay their degradation by the ER-associated degradation pathway. This indicated that monoglucosylated mutant proteins were actively extracted from the calnexin/calreticulin binding-reglucosylation cycle for degradation. Therefore trapping proteins in their monoglucosylated state was sufficient to delay their exit to the Golgi but had no effect on their rate of degradation, suggesting that the degradation selection process progressed in a dominant manner that was independent of reglucosylation and the glucose-containing A-branch on the substrate glycans.

scholarly journals Activation of Mammalian Unfolded Protein Response Is Compatible with the Quality Control System Operating in the Endoplasmic Reticulum

2004 ◽  
Vol 15 (6) ◽  
pp. 2537-2548 ◽  
Author(s):  
Satomi Nadanaka ◽  
Hiderou Yoshida ◽  
Fumi Kano ◽  
Masayuki Murata ◽  
Kazutoshi Mori
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Control System ◽  
Golgi Apparatus ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Secretory Pathway ◽  
Unfolded Proteins ◽  
Unfolded Protein ◽  
Protein Response

Newly synthesized secretory and transmembrane proteins are folded and assembled in the endoplasmic reticulum (ER) where an efficient quality control system operates so that only correctly folded molecules are allowed to move along the secretory pathway. The productive folding process in the ER has been thought to be supported by the unfolded protein response (UPR), which is activated by the accumulation of unfolded proteins in the ER. However, a dilemma has emerged; activation of ATF6, a key regulator of mammalian UPR, requires intracellular transport from the ER to the Golgi apparatus. This suggests that unfolded proteins might be leaked from the ER together with ATF6 in response to ER stress, exhibiting proteotoxicity in the secretory pathway. We show here that ATF6 and correctly folded proteins are transported to the Golgi apparatus via the same route and by the same mechanism under conditions of ER stress, whereas unfolded proteins are retained in the ER. Thus, activation of the UPR is compatible with the quality control in the ER and the ER possesses a remarkable ability to select proteins to be transported in mammalian cells in marked contrast to yeast cells, which actively utilize intracellular traffic to deal with unfolded proteins accumulated in the ER.

scholarly journals Translational Regulation of Pmt1 and Pmt2 by Bfr1 Affects Unfolded Protein O-Mannosylation

2019 ◽  
Vol 20 (24) ◽  
pp. 6220 ◽  
Author(s):  
Joan Castells-Ballester ◽  
Natalie Rinis ◽  
Ilgin Kotan ◽  
Lihi Gal ◽  
Daniela Bausewein ◽  
...  
Keyword(s):  
Quality Control ◽  
Translational Regulation ◽  
Secretory Pathway ◽  
Rna Binding ◽  
Protein Quality ◽  
Fluorescent Protein ◽  
Brefeldin A ◽  
Protein Quality Control ◽  
Ribosome Profiling ◽  
Unfolded Protein

O-mannosylation is implicated in protein quality control in Saccharomyces cerevisiae due to the attachment of mannose to serine and threonine residues of un- or misfolded proteins in the endoplasmic reticulum (ER). This process also designated as unfolded protein O-mannosylation (UPOM) that ends futile folding cycles and saves cellular resources is mainly mediated by protein O-mannosyltransferases Pmt1 and Pmt2. Here we describe a genetic screen for factors that influence O-mannosylation in yeast, using slow-folding green fluorescent protein (GFP) as a reporter. Our screening identifies the RNA binding protein brefeldin A resistance factor 1 (Bfr1) that has not been linked to O-mannosylation and ER protein quality control before. We find that Bfr1 affects O-mannosylation through changes in Pmt1 and Pmt2 protein abundance but has no effect on PMT1 and PMT2 transcript levels, mRNA localization to the ER membrane or protein stability. Ribosome profiling reveals that Bfr1 is a crucial factor for Pmt1 and Pmt2 translation thereby affecting unfolded protein O-mannosylation. Our results uncover a new level of regulation of protein quality control in the secretory pathway.

scholarly journals ER-associated degradation: Protein quality control and beyond

2014 ◽  
Vol 204 (6) ◽  
pp. 869-879 ◽  
Author(s):  
Annamaria Ruggiano ◽  
Ombretta Foresti ◽  
Pedro Carvalho
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Protein Degradation ◽  
Control Systems ◽  
Protein Quality ◽  
Protein Quality Control ◽  
Secretory Proteins ◽  
Toxic Species ◽  
Cellular Factors

Even with the assistance of many cellular factors, a significant fraction of newly synthesized proteins ends up misfolded. Cells evolved protein quality control systems to ensure that these potentially toxic species are detected and eliminated. The best characterized of these pathways, the ER-associated protein degradation (ERAD), monitors the folding of membrane and secretory proteins whose biogenesis takes place in the endoplasmic reticulum (ER). There is also increasing evidence that ERAD controls other ER-related functions through regulated degradation of certain folded ER proteins, further highlighting the role of ERAD in cellular homeostasis.

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