A Possible Role of ER-60 Protease in the Degradation of Misfolded Proteins in the Endoplasmic Reticulum

ABSTRACTER-phagy, the selective autophagy of endoplasmic reticulum (ER), safeguards organelle homeostasis by eliminating misfolded proteins and regulating ER size. ER-phagy can occur by macroautophagic and microautophagic mechanisms. While dedicated machinery for macro-ER-phagy has been discovered, the molecules and mechanisms mediating micro-ER-phagy remain unknown. Here, we first show that micro-ER-phagy in yeast involves the conversion of stacked cisternal ER into multilamellar ER whorls during microautophagic uptake into lysosomes. Second, we identify the conserved Nem1-Spo7 phosphatase complex and ESCRT proteins as key components for micro-ER-phagy. Third, we demonstrate that macro- and micro-ER-phagy are parallel pathways with distinct molecular requirements. Finally, we provide evidence that ESCRT proteins directly function in scission of the lysosomal membrane to complete the microautophagic uptake of ER. These findings establish a framework for a mechanistic understanding of micro-ER-phagy and, thus, a comprehensive appreciation of the role of autophagy in ER homeostasis.

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Potential Physiological Relevance of ERAD to the Biosynthesis of GPI-Anchored Proteins in Yeast

International Journal of Molecular Sciences ◽

10.3390/ijms22031061 ◽

2021 ◽

Vol 22 (3) ◽

pp. 1061

Author(s):

Kunio Nakatsukasa

Keyword(s):

Quality Control ◽

Endoplasmic Reticulum ◽

Membrane Proteins ◽

Physiological Role ◽

Misfolded Proteins ◽

Physiological Relevance ◽

Safe Mechanism ◽

Fail Safe

Misfolded and/or unassembled secretory and membrane proteins in the endoplasmic reticulum (ER) may be retro-translocated into the cytoplasm, where they undergo ER-associated degradation, or ERAD. The mechanisms by which misfolded proteins are recognized and degraded through this pathway have been studied extensively; however, our understanding of the physiological role of ERAD remains limited. This review describes the biosynthesis and quality control of glycosylphosphatidylinositol (GPI)-anchored proteins and briefly summarizes the relevance of ERAD to these processes. While recent studies suggest that ERAD functions as a fail-safe mechanism for the degradation of misfolded GPI-anchored proteins, several pieces of evidence suggest an intimate interaction between ERAD and the biosynthesis of GPI-anchored proteins.

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Endoplasmic reticulum turnover: ER-phagy and other flavors in selective and non-selective ER clearance

F1000Research ◽

10.12688/f1000research.13968.1 ◽

2018 ◽

Vol 7 ◽

pp. 454 ◽

Cited By ~ 33

Author(s):

Ilaria Fregno ◽

Maurizio Molinari

Keyword(s):

Endoplasmic Reticulum ◽

Protein Biosynthesis ◽

Misfolded Proteins ◽

Eukaryotic Cells ◽

Unfolded Protein ◽

Calcium Storage ◽

Live Bacteria ◽

And Function ◽

Developmental Conditions

The endoplasmic reticulum (ER) is a highly dynamic organelle in eukaryotic cells. It is deputed to lipid and protein biosynthesis, calcium storage, and the detoxification of various exogenous and endogenous harmful compounds. ER activity and size must be adapted rapidly to environmental and developmental conditions or biosynthetic demand. This is achieved on induction of thoroughly studied transcriptional/translational programs defined as “unfolded protein responses” that increase the ER volume and the expression of ER-resident proteins regulating the numerous ER functions. Less understood are the lysosomal catabolic processes that maintain ER size at steady state, that prevent excessive ER expansion during ER stresses, or that ensure return to physiologic ER size during recovery from ER stresses. These catabolic processes may also be activated to remove ER subdomains where proteasome-resistant misfolded proteins or damaged lipids have been segregated. Insights into these catabolic mechanisms have only recently emerged with the identification of so-called ER-phagy receptors, which label specific ER subdomains for selective lysosomal delivery for clearance. Here, in eight chapters and one addendum, we comment on recent advances in ER turnover pathways induced by ER stress, nutrient deprivation, misfolded proteins, and live bacteria. We highlight the role of yeast (Atg39 and Atg40) and mammalian (FAM134B, SEC62, RTN3, and CCPG1) ER-phagy receptors and of autophagy genes in selective and non-selective catabolic processes that regulate cellular proteostasis by controlling ER size, turnover, and function.

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Endoplasmic Reticulum Stress Caused by Lipoprotein Accumulation Suppresses Immunity against Bacterial Pathogens and Contributes to Immunosenescence

mBio ◽

10.1128/mbio.00778-17 ◽

2017 ◽

Vol 8 (3) ◽

Cited By ~ 12

Author(s):

Jogender Singh ◽

Alejandro Aballay

Keyword(s):

Endoplasmic Reticulum ◽

Stress Response ◽

Er Stress ◽

Life Span ◽

Mechanistic Explanation ◽

Misfolded Proteins ◽

Independent Manner ◽

Expression Of Genes ◽

Genes Encoding

ABSTRACT The unfolded protein response (UPR) is a stress response pathway that is activated upon increased unfolded and/or misfolded proteins in the endoplasmic reticulum (ER), and enhanced ER stress response prolongs life span and improves immunity. However, the mechanism by which ER stress affects immunity remains poorly understood. Using the nematode Caenorhabditis elegans , we show that mutations in the lipoproteins vitellogenins, which are homologs of human apolipoprotein B-100, resulted in upregulation of the UPR. Lipoprotein accumulation in the intestine adversely affects the immune response and the life span of the organism, suggesting that it could be a contributing factor to immunosenescence. We show that lipoprotein accumulation inhibited the expression of several immune genes encoding proteins secreted by the intestinal cells in an IRE-1-independent manner. Our studies provide a mechanistic explanation for adverse effects caused by protein aggregation and ER stress on immunity and highlight the role of an IRE-1-independent pathway in the suppression of the expression of genes encoding secreted proteins. IMPORTANCE Increased accumulation of unfolded and/or misfolded proteins in the endoplasmic reticulum (ER) leads to enhanced ER stress. However, the mechanism(s) by which ER stress affects immunity remain understudied. Using the nematode C. elegans , we showed that mutations in lipoproteins lead to their accumulation in the intestine, causing ER stress and adversely affecting the life span of the organisms and their resistance to pathogen infection. Our results indicate that the ER stress caused by lipoprotein accumulation significantly reduced the levels of expression of genes encoding secreted immune effectors, contributing to immunosenescence. It is known that ER stress may suppress gene expression via IRE-1, which is a sensor of ER stress. The novel mechanism uncovered in our study is IRE-1 independent, which highlights the role of a novel process by which ER stress suppresses innate immunity.

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The Role of the Effects of Endoplasmic Reticulum Stress on NLRP3 Inflammasome in Diabetes

Frontiers in Cell and Developmental Biology ◽

10.3389/fcell.2021.663528 ◽

2021 ◽

Vol 9 ◽

Author(s):

Shuangyu Lv ◽

Xiaotian Li ◽

Honggang Wang

Keyword(s):

Endoplasmic Reticulum ◽

Protein Synthesis ◽

Endoplasmic Reticulum Stress ◽

Nlrp3 Inflammasome ◽

Basic Research ◽

Misfolded Proteins ◽

Pyrin Domain ◽

Receptor Family ◽

Oligomerization Domain

Endoplasmic reticulum (ER) is an important organelle for the protein synthesis, modification, folding, assembly, and the transport of new peptide chains. When the folding ability of ER proteins is impaired, the accumulation of unfolded or misfolded proteins in ER leads to endoplasmic reticulum stress (ERS). The nucleotide-binding oligomerization domain-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome, can induce the maturation and secretion of interleukin-1beta (IL-1β) and IL-18 through activating caspase-1. It is associated with many diseases. Studies have shown that ERS can regulate NLRP3 inflammasome in many diseases including diabetes. However, the mechanism of the effects of ERS on NLRP3 inflammasome in diabetes has not been fully understood. This review summarizes the recent researches about the effects of ERS on NLRP3 inflammasome and the related mechanism in diabetes to provide ideas for the relevant basic research in the future.

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The Crucial Role of Demannosylating Asparagine-Linked Glycans in ERADicating Misfolded Glycoproteins in the Endoplasmic Reticulum

Frontiers in Plant Science ◽

10.3389/fpls.2020.625033 ◽

2021 ◽

Vol 11 ◽

Author(s):

Jianjun Zhang ◽

Jiarui Wu ◽

Linchuan Liu ◽

Jianming Li

Keyword(s):

Endoplasmic Reticulum ◽

Protein Folding ◽

Protein Quality ◽

Misfolded Proteins ◽

Cellular Events ◽

Eukaryotic Organisms ◽

And Function ◽

Distinct Features ◽

Functional Deficiency

Most membrane and secreted proteins are glycosylated on certain asparagine (N) residues in the endoplasmic reticulum (ER), which is crucial for their correct folding and function. Protein folding is a fundamentally inefficient and error-prone process that can be easily interfered by genetic mutations, stochastic cellular events, and environmental stresses. Because misfolded proteins not only lead to functional deficiency but also produce gain-of-function cellular toxicity, eukaryotic organisms have evolved highly conserved ER-mediated protein quality control (ERQC) mechanisms to monitor protein folding, retain and repair incompletely folded or misfolded proteins, or remove terminally misfolded proteins via a unique ER-associated degradation (ERAD) mechanism. A crucial event that terminates futile refolding attempts of a misfolded glycoprotein and diverts it into the ERAD pathway is executed by removal of certain terminal α1,2-mannose (Man) residues of their N-glycans. Earlier studies were centered around an ER-type α1,2-mannosidase that specifically cleaves the terminal α1,2Man residue from the B-branch of the three-branched N-linked Man9GlcNAc2 (GlcNAc for N-acetylglucosamine) glycan, but recent investigations revealed that the signal that marks a terminally misfolded glycoprotein for ERAD is an N-glycan with an exposed α1,6Man residue generated by members of a unique folding-sensitive α1,2-mannosidase family known as ER-degradation enhancing α-mannosidase-like proteins (EDEMs). This review provides a historical recount of major discoveries that led to our current understanding on the role of demannosylating N-glycans in sentencing irreparable misfolded glycoproteins into ERAD. It also discusses conserved and distinct features of the demannosylation processes of the ERAD systems of yeast, mammals, and plants.

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Localization of Intracisternal a Particle Antigens in Neoplastic Cells and Preimplantation Mouse Embryos

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600003044 ◽

1980 ◽

Vol 38 ◽

pp. 696-697

Author(s):

Thomas T.F. Huang ◽

Patricia G. Calarco

Keyword(s):

Endoplasmic Reticulum ◽

Normal Development ◽

Mouse Embryos ◽

Neoplastic Cells ◽

Large Numbers ◽

Preimplantation Mouse Embryos ◽

Preimplantation Mouse ◽

Intracisternal A Particle ◽

Normal Feature

The stage specific appearance of a retravirus, termed the Intracisternal A particle (IAP) is a normal feature of early preimplantation development. To date, all feral and laboratory strains of Mus musculus and even Asian species such as Mus cervicolor and Mus pahari express the particles during the 2-8 cell stages. IAP form by budding into the endoplasmic reticulum and appear singly or as groups of donut-shaped particles within the cisternae (fig. 1). IAP are also produced in large numbers in several neoplastic cells such as certain plasmacytomas and rhabdomyosarcomas. The role of IAP, either in normal development or in neoplastic behavior, is unknown.

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