scholarly journals The p97-UBXN1 complex regulates aggresome formation

2020 ◽  
Author(s):  
Sirisha Mukkavalli ◽  
Jacob Aaron Klickstein ◽  
Betty Ortiz ◽  
Peter Juo ◽  
Malavika Raman
Keyword(s):  
Protein Aggregation ◽  
Mammalian Cells ◽  
Proteasome Inhibition ◽  
Adaptor Proteins ◽  
Ubiquitin Proteasome System ◽  
Aaa Atpase ◽  
Evolutionarily Conserved ◽  
Ubiquitin Proteasome ◽  
Aggresome Formation

AbstractThe recognition and disposal of misfolded proteins are essential for the maintenance of cellular homeostasis. Perturbations in the pathways that promote degradation of aberrant proteins contribute to a variety of protein aggregation disorders broadly termed proteinopathies. It is presently unclear how diverse disease-relevant aggregates are recognized and processed for degradation. The p97 AAA-ATPase in combination with a host of adaptor proteins functions to identify ubiquitylated proteins and target them for degradation by the ubiquitin-proteasome system or through autophagy. Mutations in p97 cause multi-system proteinopathies; however, the precise defects underlying these disorders are unclear given the large number of pathways that rely on p97 function. Here, we systematically investigate the role of p97 and its adaptors in the process of formation of aggresomes which are membrane-less structures containing ubiquitylated proteins that arise upon proteasome inhibition. We demonstrate that p97 mediates both aggresome formation and clearance in proteasome-inhibited cells. We identify a novel and specific role for the p97 adaptor UBXN1 in the process of aggresome formation. UBXN1 is recruited to ubiquitin-positive aggresomes and UBXN1 knockout cells are unable to form a single aggresome, and instead display dispersed ubiquitin aggregates. Furthermore, loss of p97-UBXN1 results in the increase in Huntingtin polyQ aggregates both in mammalian cells as well as in a C.elegans model of Huntington’s Disease. Together our work identifies evolutionarily conserved roles for p97 and its adaptor UBXN1 in the disposal of protein aggregates.

scholarly journals The p97-UBXN1 complex regulates aggresome formation

2021 ◽  
pp. jcs.254201
Author(s):  
Sirisha Mukkavalli ◽  
Jacob Aaron Klickstein ◽  
Betty Ortiz ◽  
Peter Juo ◽  
Malavika Raman
Keyword(s):  
Protein Aggregation ◽  
Mammalian Cells ◽  
Inclusion Bodies ◽  
Proteasome Inhibition ◽  
Adaptor Proteins ◽  
Cellular Homeostasis ◽  
Aaa Atpase ◽  
Evolutionarily Conserved ◽  
Aggresome Formation

The recognition and disposal of misfolded proteins is essential for the maintenance of cellular homeostasis. Perturbations in the pathways that promote degradation of aberrant proteins contribute to a variety of protein aggregation disorders broadly termed proteinopathies. The p97 AAA-ATPase in combination with adaptor proteins functions to identify ubiquitylated proteins and target them for degradation by the proteasome or autophagy. Mutations in p97 cause multi-system proteinopathies; however, the precise defects underlying these disorders are unclear. Here, we systematically investigate the role of p97 and its adaptors in the process of formation of aggresomes, membrane-less structures containing ubiquitylated proteins that arise upon proteasome inhibition. We demonstrate that p97 mediates aggresome formation and clearance and identify a novel role for the adaptor UBXN1 in the process of aggresome formation. UBXN1 is recruited to aggresomes and UBXN1 knockout cells are unable to form aggresomes. Loss of p97-UBXN1 results in increased Huntingtin polyQ inclusion bodies both in mammalian cells as well as in a C.elegans model of Huntington's Disease. Together our work identifies evolutionarily conserved roles for p97-UBXN1 in the disposal of protein aggregates.

scholarly journals The Role of Autophagy in Chemical Proteasome Inhibition Model of Retinal Degeneration

2021 ◽  
Vol 22 (14) ◽  
pp. 7271
Author(s):  
Merry Gunawan ◽  
Choonbing Low ◽  
Kurt Neo ◽  
Siawey Yeo ◽  
Candice Ho ◽  
...  
Keyword(s):  
Retinal Degeneration ◽  
Structural Integrity ◽  
Mammalian Target Of Rapamycin ◽  
Neuroblastoma Cells ◽  
Proteasome Inhibition ◽  
Ubiquitin Proteasome System ◽  
Ocular Tissue ◽  
Protective Mechanism ◽  
Ubiquitin Proteasome

We recently demonstrated that chemical proteasome inhibition induced inner retinal degeneration, supporting the pivotal roles of the ubiquitin–proteasome system in retinal structural integrity maintenance. In this study, using beclin1-heterozygous (Becn1-Het) mice with autophagic dysfunction, we tested our hypothesis that autophagy could be a compensatory retinal protective mechanism for proteasomal impairment. Despite the reduced number of autophagosome, the ocular tissue morphology and intraocular pressure were normal. Surprisingly, Becn1-Het mice experienced the same extent of retinal degeneration as was observed in wild-type mice, following an intravitreal injection of a chemical proteasome inhibitor. Similarly, these mice equally responded to other chemical insults, including endoplasmic reticulum stress inducer, N-methyl-D-aspartate, and lipopolysaccharide. Interestingly, in cultured neuroblastoma cells, we found that the mammalian target of rapamycin-independent autophagy activators, lithium chloride and rilmenidine, rescued these cells against proteasome inhibition-induced death. These results suggest that Becn1-mediated autophagy is not an effective intrinsic protective mechanism for retinal damage induced by insults, including impaired proteasomal activity; furthermore, autophagic activation beyond normal levels is required to alleviate the cytotoxic effect of proteasomal inhibition. Further studies are underway to delineate the precise roles of different forms of autophagy, and investigate the effects of their activation in rescuing retinal neurons under various pathological conditions.

scholarly journals Proteaphagy in Mammalian Cells Can Function Independent of ATG5/ATG7

2020 ◽  
Vol 19 (7) ◽  
pp. 1120-1131 ◽  
Author(s):  
Tatjana Goebel ◽  
Simone Mausbach ◽  
Andreas Tuermer ◽  
Heba Eltahir ◽  
Dominic Winter ◽  
...  
Keyword(s):  
Gel Electrophoresis ◽  
Mammalian Cells ◽  
Adaptor Proteins ◽  
Cell Types ◽  
Ubiquitin Proteasome System ◽  
Extracellular Proteins ◽  
Ubiquitin Proteasome ◽  
Native Gel ◽  
Chaperone Mediated Autophagy ◽  
Coenzym A

The degradation of intra- and extracellular proteins is essential in all cell types and mediated by two systems, the ubiquitin-proteasome system (UPS) and the autophagy-lysosome pathway. This study investigates the changes in autophagosomal and lysosomal proteomes upon inhibition of proteasomes by bortezomib (BTZ) or MG132. We find an increased abundance of more than 50 proteins in lysosomes of cells in which the proteasome is inhibited. Among those are dihydrofolate reductase (DHFR), β-Catenin and 3-hydroxy-3-methylglutaryl-coenzym-A (HMGCoA)-reductase. Because these proteins are known to be degraded by the proteasome they seem to be compensatorily delivered to the autophagosomal pathway when the proteasome is inactivated. Surprisingly, most of the proteins which show increased amounts in the lysosomes of BTZ or MG132 treated cells are proteasomal subunits. Thus an inactivated, non-functional proteasome is delivered to the autophagic pathway. Native gel electrophoresis shows that the proteasome reaches the lysosome intact and not disassembled. Adaptor proteins, which target proteasomes to autophagy, have been described in Arabidopsis, Saccharomyces and upon starvation in mammalians. However, in cell lines deficient of these proteins or their mammalian orthologues, respectively, the transfer of proteasomes to the lysosome is not impaired. Obviously, these proteins do not play a role as autophagy adaptor proteins in mammalian cells. We can also show that chaperone-mediated autophagy (CMA) does not participate in the proteasome delivery to the lysosomes. In autophagy-related (ATG)-5 and ATG7 deficient cells the delivery of inactivated proteasomes to the autophagic pathway was only partially blocked, indicating the existence of at least two different pathways by which inactivated proteasomes can be delivered to the lysosome in mammalian cells.

scholarly journals Interaction of Gcn4 with target gene chromatin is modulated by proteasome function

2016 ◽  
Vol 27 (17) ◽  
pp. 2735-2741 ◽  
Author(s):  
Gregory C. Howard ◽  
William P. Tansey
Keyword(s):  
Ubiquitin Ligase ◽  
Target Gene ◽  
Target Genes ◽  
Proteasome Inhibition ◽  
Ubiquitin Proteasome System ◽  
Activation Of Transcription ◽  
Ubiquitin Proteasome ◽  
Promoter Occupancy ◽  
Per Se

The ubiquitin–proteasome system (UPS) influences gene transcription in multiple ways. One way in which the UPS affects transcription centers on transcriptional activators, the function of which can be stimulated by components of the UPS that also trigger their destruction. Activation of transcription by the yeast activator Gcn4, for example, is attenuated by mutations in the ubiquitin ligase that mediates Gcn4 ubiquitylation or by inhibition of the proteasome, leading to the idea that ubiquitin-mediated proteolysis of Gcn4 is required for its activity. Here we probe the steps in Gcn4 activity that are perturbed by disruption of the UPS. We show that the ubiquitylation machinery and the proteasome control different steps in Gcn4 function and that proteasome activity is required for the ability of Gcn4 to bind to its target genes in the context of chromatin. Curiously, the effect of proteasome inhibition on Gcn4 activity is suppressed by mutations in the ubiquitin-selective chaperone Cdc48, revealing that proteolysis per se is not required for Gcn4 activity. Our data highlight the role of Cdc48 in controlling promoter occupancy by Gcn4 and support a model in which ubiquitylation of activators—not their destruction—is important for function.

scholarly journals Immunoproteasome Function in Normal and Malignant Hematopoiesis

Cells ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1577
Author(s):  
Nuria Tubío-Santamaría ◽  
Frédéric Ebstein ◽  
Florian H. Heidel ◽  
Elke Krüger
Keyword(s):  
Proteasome Inhibition ◽  
Ubiquitin Proteasome System ◽  
Hematologic Malignancies ◽  
Protein Homeostasis ◽  
Efficacy And Safety ◽  
Hematopoietic System ◽  
Oxidized Proteins ◽  
Attractive Therapeutic Target ◽  
Ubiquitin Proteasome ◽  
Early Phases

The ubiquitin–proteasome system (UPS) is a central part of protein homeostasis, degrading not only misfolded or oxidized proteins but also proteins with essential functions. The fact that a healthy hematopoietic system relies on the regulation of protein homeostasis and that alterations in the UPS can lead to malignant transformation makes the UPS an attractive therapeutic target for the treatment of hematologic malignancies. Herein, inhibitors of the proteasome, the last and most important component of the UPS enzymatic cascade, have been approved for the treatment of these malignancies. However, their use has been associated with side effects, drug resistance, and relapse. Inhibitors of the immunoproteasome, a proteasomal variant constitutively expressed in the cells of hematopoietic origin, could potentially overcome the encountered problems of non-selective proteasome inhibition. Immunoproteasome inhibitors have demonstrated their efficacy and safety against inflammatory and autoimmune diseases, even though their development for the treatment of hematologic malignancies is still in the early phases. Various immunoproteasome inhibitors have shown promising preliminary results in pre-clinical studies, and one inhibitor is currently being investigated in clinical trials for the treatment of multiple myeloma. Here, we will review data on immunoproteasome function and inhibition in hematopoietic cells and hematologic cancers.

scholarly journals TTC3-Mediated Protein Quality Control, A Potential Mechanism for Cognitive Impairment

2021 ◽  
Author(s):  
Xu Zhou ◽  
Xiongjin Chen ◽  
Tingting Hong ◽  
Miaoping Zhang ◽  
Yujie Cai ◽  
...  
Keyword(s):  
Quality Control ◽  
Cognitive Impairment ◽  
Protein Quality ◽  
Protein Quality Control ◽  
Ubiquitin Proteasome System ◽  
Research Progress ◽  
Repeat Domain ◽  
Ubiquitin Proteasome ◽  
Domain 3

AbstractThe tetrapeptide repeat domain 3 (TTC3) gene falls within Down's syndrome (DS) critical region. Cognitive impairment is a common phenotype of DS and Alzheimer’s disease (AD), and overexpression of TTC3 can accelerate cognitive decline, but the specific mechanism is unknown. The TTC3-mediated protein quality control (PQC) mechanism, similar to the PQC system, is divided into three parts: it acts as a cochaperone to assist proteins in folding correctly; it acts as an E3 ubiquitin ligase (E3s) involved in protein degradation processes through the ubiquitin–proteasome system (UPS); and it may also eventually cause autophagy by affecting mitochondrial function. Thus, this article reviews the research progress on the structure, function, and metabolism of TTC3, including the recent research progress on TTC3 in DS and AD; the role of TTC3 in cognitive impairment through PQC in combination with the abovementioned attributes of TTC3; and the potential targets of TTC3 in the treatment of such diseases.

scholarly journals Noncoding RNA MaIL1 is an integral component of the TLR4–TRIF pathway

2020 ◽  
Vol 117 (16) ◽  
pp. 9042-9053 ◽  
Author(s):  
Marina Aznaourova ◽  
Harshavardhan Janga ◽  
Stephanie Sefried ◽  
Andreas Kaufmann ◽  
Jens Dorna ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Noncoding Rna ◽  
Signal Transduction Pathway ◽  
Ubiquitin Proteasome System ◽  
Lavage Fluid ◽  
Cellular Protein ◽  
Type I ◽  
Toll Like Receptor 4 ◽  
Ubiquitin Proteasome ◽  
Highly Correlated

RNA has been proposed as an important scaffolding factor in the nucleus, aiding protein complex assembly in the dense intracellular milieu. Architectural contributions of RNA to cytosolic signaling pathways, however, remain largely unknown. Here, we devised a multidimensional gradient approach, which systematically locates RNA components within cellular protein networks. Among a subset of noncoding RNAs (ncRNAs) cosedimenting with the ubiquitin–proteasome system, our approach unveiled ncRNA MaIL1 as a critical structural component of the Toll-like receptor 4 (TLR4) immune signal transduction pathway. RNA affinity antisense purification–mass spectrometry (RAP-MS) revealed MaIL1 binding to optineurin (OPTN), a ubiquitin-adapter platforming TBK1 kinase. MaIL1 binding stabilized OPTN, and consequently, loss of MaIL1 blunted OPTN aggregation, TBK1-dependent IRF3 phosphorylation, and type I interferon (IFN) gene transcription downstream of TLR4. MaIL1 expression was elevated in patients with active pulmonary infection and was highly correlated with IFN levels in bronchoalveolar lavage fluid. Our study uncovers MaIL1 as an integral RNA component of the TLR4–TRIF pathway and predicts further RNAs to be required for assembly and progression of cytosolic signaling networks in mammalian cells.

Protein Quality Control in Neurodegeneration and Neuroprotection

2020 ◽  
pp. 1-24
Author(s):  
Yasmeena Akhter ◽  
Jahangir Nabi ◽  
Hinna Hamid ◽  
Nahida Tabassum ◽  
Faheem Hyder Pottoo ◽  
...  
Keyword(s):  
Quality Control ◽  
Neurodegenerative Disorders ◽  
Protein Quality ◽  
Protein Quality Control ◽  
Ubiquitin Proteasome System ◽  
Security System ◽  
Conformational Disorders ◽  
Ubiquitin Proteasome ◽  
Multi Level

Proteostasis is essential for regulating the integrity of the proteome. Disruption of proteostasis under some rigorous conditions leads to the aggregation and accumulation of misfolded toxic proteins, which plays a central role in the pathogenesis of protein conformational disorders. The protein quality control (PQC) system serves as a multi-level security system to shield cells from abnormal proteins. The intrinsic PQC systems maintaining proteostasis include the ubiquitin-proteasome system (UPS), chaperon-mediated autophagy (CMA), and autophagy-lysosome pathway (ALP) that serve to target misfolded proteins for unfolding, refolding, or degradation. Alterations of PQC systems in neurons have been implicated in the pathogenesis of various neurodegenerative disorders. This chapter provides an overview of PQC pathways to set a framework for discussion of the role of PQC in neurodegenerative disorders. Additionally, various pharmacological approaches targeting PQC are summarized.

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