scholarly journals Localization of GRP78 to mitochondria under the unfolded protein response

2006 ◽  
Vol 396 (1) ◽  
pp. 31-39 ◽  
Author(s):  
Fang-Chun Sun ◽  
Shou Wei ◽  
Chia-Wei Li ◽  
Yuo-Sheng Chang ◽  
Chih-Chung Chao ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Unfolded Protein Response ◽  
Calcium Ionophore ◽  
Ionophore A23187 ◽  
Intermembrane Space ◽  
Atpase Inhibitor ◽  
Unfolded Protein ◽  
Stressed Cells ◽  
Protein Response ◽  
In Cells

The ubiquitously expressed molecular chaperone GRP78 (78 kDa glucose-regulated protein) generally localizes to the ER (endoplasmic reticulum). GRP78 is specifically induced in cells under the UPR (unfolded protein response), which can be elicited by treatments with calcium ionophore A23187 and sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibitor TG (thapsigargin). By using confocal microscopy, we have demonstrated that GRP78 was concentrated in the perinuclear region and co-localized with the ER marker proteins, calnexin and PDI (protein disulphide-isomerase), in cells under normal growth conditions. However, treatments with A23187 and TG led to diminish its ER targeting, resulting in redirection into a cytoplasmic vesicular pattern, and overlapping with the mitochondrial marker MitoTracker. Cellular fractionation and protease digestion of isolated mitochondria from ER-stressed cells suggested that a significant portion of GRP78 is localized to the mitochondria and is protease-resistant. Localizations of GRP78 in ER and mitochondria were confirmed by using immunoelectron microscopy. In ER-stressed cells, GRP78 mainly localized within the mitochondria and decorated the mitochondrial membrane compartment. Submitochondrial fractionation studies indicated further that the mitochondria-resided GRP78 is mainly located in the intermembrane space, inner membrane and matrix, but is not associated with the outer membrane. Furthermore, radioactive labelling followed by subcellular fractionation showed that a significant portion of the newly synthesized GRP78 is localized to the mitochondria in cells under UPR. Taken together, our results indicate that, at least under certain circumstances, the ER-resided chaperone GRP78 can be retargeted to mitochondria and thereby may be involved in correlating UPR signalling between these two organelles.

Proliferation of the endoplasmic reticulum occurs normally in cells that lack a functional unfolded protein response

Yeast ◽  
2002 ◽  
Vol 19 (4) ◽  
pp. 373-393 ◽  
Author(s):  
Lynnelle L. Larson ◽  
Mark L. Parrish ◽  
Ann J. Koning ◽  
Robin L. Wright
Keyword(s):  
Endoplasmic Reticulum ◽  
Unfolded Protein Response ◽  
Unfolded Protein ◽  
Protein Response ◽  
In Cells

scholarly journals A CHCHD10 variant causing ALS elicits an unfolded protein response through the IRE1/XBP1 pathway

2020 ◽  
Author(s):  
Isabella R. Straub ◽  
Woranontee Weraarpachai ◽  
Eric A. Shoubridge
Keyword(s):  
Endoplasmic Reticulum ◽  
Unfolded Protein Response ◽  
Motor Neurons ◽  
Tca Cycle ◽  
Selective Vulnerability ◽  
Energy Deficit ◽  
Intermembrane Space ◽  
Metabolic Dysfunction ◽  
Unfolded Protein ◽  
Protein Response

AbstractMutations in CHCHD10, coding for a mitochondrial intermembrane space protein, are a rare cause of autosomal dominant amyotrophic lateral sclerosis (ALS). Mutation-specific toxic gain of function or haploinsuffuciency models have been proposed to explain pathogenicity. To decipher the metabolic dysfunction associated with the haploinsufficient p.R15L variant we integrated transcriptomic, metabolomic and proteomic data sets in patient cells subjected to nutrient stress. Patient cells had a complex I deficiency resulting in an increased NADH/NAD+ ratio, downregulation of the TCA cycle, and a reorganization of one carbon metabolism. This led to phosphorylation of AMPK, activation of an endoplasmic reticulum and mitochondrial unfolded protein response (UPR), and the production of GDF15 and FGF21, which are markers of mitochondrial disease. The endoplasmic reticulum UPR was mediated through the IRE1/XBP1 pathway, and was accompanied by reduced eIF2alpha phosphorylation, dephosphorylation of both JNK isoforms, and up regulation of several dual specific phosphatases. This study demonstrates that loss of CHCHD10 function elicits a striking energy deficit that activates cellular stress pathways, which may underlie the selective vulnerability of motor neurons.

Misfolded growth hormone causes fragmentation of the Golgi apparatus and disrupts endoplasmic reticulum-to-Golgi traffic

2001 ◽  
Vol 114 (20) ◽  
pp. 3685-3694
Author(s):  
Thomas K. Graves ◽  
Shilpa Patel ◽  
Priscilla S. Dannies ◽  
Patricia M. Hinkle
Keyword(s):  
Growth Hormone ◽  
Endoplasmic Reticulum ◽  
Golgi Apparatus ◽  
Unfolded Protein Response ◽  
Wild Type ◽  
Unfolded Protein ◽  
The Unfolded Protein Response ◽  
Protein Response ◽  
Trh Receptor ◽  
In Cells

In some individuals with autosomal dominant isolated growth hormone deficiency, one copy of growth hormone lacks amino acids 32-71 and is severely misfolded. We transfected COS7 cells with either wild-type human growth hormone or Δ32-71 growth hormone and investigated subcellular localization of growth hormone and other proteins. Δ32-71 growth hormone was retained in the endoplasmic reticulum, whereas wild-type hormone accumulated in the Golgi apparatus. When cells transfected with wild-type or Δ32-71 growth hormone were dually stained for growth hormone and the Golgi markers β-COP, membrin or 58K, wild-type growth hormone was colocalized with the Golgi markers, but β-COP, membrin and 58K immunoreactivity was highly dispersed or undetectable in cells expressing Δ32-71 growth hormone. Examination of α-tubulin immunostaining showed that the cytoplasmic microtubular arrangement was normal in cells expressing wild-type growth hormone, but microtubule-organizing centers were absent in nearly all cells expressing Δ32-71 growth hormone. To determine whether Δ32-71 growth hormone would alter trafficking of a plasma membrane protein, we cotransfected the cells with the thyrotropin-releasing hormone (TRH) receptor and either wild-type or Δ32-71 growth hormone. Cells expressing Δ32-71 growth hormone, unlike those expressing wild-type growth hormone, failed to show normal TRH receptor localization or binding. Expression of Δ32-71 growth hormone also disrupted the trafficking of two secretory proteins, prolactin and secreted alkaline phosphatase. Δ32-71 growth hormone only weakly elicited the unfolded protein response as indicated by induction of BiP mRNA. Pharmacological induction of the unfolded protein response partially prevented deletion mutant-induced Golgi fragmentation and partially restored normal TRH receptor trafficking. The ability of some misfolded proteins to block endoplasmic reticulum-to-Golgi traffic may explain their toxic effects on host cells and suggests possible strategies for therapeutic interventions.

scholarly journals Intrinsic Capacities of Molecular Sensors of the Unfolded Protein Response to Sense Alternate Forms of Endoplasmic Reticulum Stress

2006 ◽  
Vol 17 (7) ◽  
pp. 3095-3107 ◽  
Author(s):  
Jenny B. DuRose ◽  
Arvin B. Tam ◽  
Maho Niwa
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Mammalian Cells ◽  
Atpase Inhibitor ◽  
Molecular Sensors ◽  
Unfolded Protein ◽  
Alternate Forms ◽  
The Unfolded Protein Response ◽  
Protein Response

The unfolded protein response (UPR) regulates the protein-folding capacity of the endoplasmic reticulum (ER) according to cellular demand. In mammalian cells, three ER transmembrane components, IRE1, PERK, and ATF6, initiate distinct UPR signaling branches. We show that these UPR components display distinct sensitivities toward different forms of ER stress. ER stress induced by ER Ca2+ release in particular revealed fundamental differences in the properties of UPR signaling branches. Compared with the rapid response of both IRE1 and PERK to ER stress induced by thapsigargin, an ER Ca2+ ATPase inhibitor, the response of ATF6 was markedly delayed. These studies are the first side-by-side comparisons of UPR signaling branch activation and reveal intrinsic features of UPR stress sensor activation in response to alternate forms of ER stress. As such, they provide initial groundwork toward understanding how ER stress sensors can confer different responses and how optimal UPR responses are achieved in physiological settings.

scholarly journals Dynamic changes in oligomeric complexes of UPR sensors induced by misfolded proteins in the ER

2017 ◽  
Author(s):  
Arunkumar Sundaram ◽  
Suhila Appathurai ◽  
Malaiyalam Mariappan
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Mammalian Cells ◽  
Negative Regulator ◽  
Misfolded Proteins ◽  
Dynamic Changes ◽  
Unfolded Protein ◽  
Stressed Cells ◽  
Protein Response

AbstractThe endoplasmic reticulum (ER) localized unfolded protein response (UPR) sensors, IRE1α, PERK, and ATF6α, are activated upon accumulation of misfolded proteins caused by ER stress. It is debated whether these UPR sensors are activated either by the release of their negative regulator BiP chaperone or directly binding to misfolded proteins during ER stress. Here we simultaneously examined oligomerization and activation of all three endogenous UPR sensors. We found that UPR sensors existed as preformed oligomers even in unstressed cells, which shifted to large oligomers for PERK and small oligomers for ATF6α, but little changed for IRE1α upon ER stress. Neither depletion nor overexpression of BiP had significant effects on oligomeric complexes of UPR sensors both in unstressed and stressed cells. Thus, our results find less evidence for the BiP-mediated activation of UPR sensors in mammalian cells and support that misfolded proteins bind and activate the preformed oligomers of UPR sensors.

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