The F-box protein Ppa is a common regulator of core EMT factors Twist, Snail, Slug, and Sip1

A small group of core transcription factors, including Twist, Snail, Slug, and Sip1, control epithelial–mesenchymal transitions (EMTs) during both embryonic development and tumor metastasis. However, little is known about how these factors are coordinately regulated to mediate the requisite behavioral and fate changes. It was recently shown that a key mechanism for regulating Snail proteins is by modulating their stability. In this paper, we report that the stability of Twist is also regulated by the ubiquitin–proteasome system. We found that the same E3 ubiquitin ligase known to regulate Snail family proteins, Partner of paired (Ppa), also controlled Twist stability and did so in a manner dependent on the Twist WR-rich domain. Surprisingly, Ppa could also target the third core EMT regulatory factor Sip1 for proteasomal degradation. Together, these results indicate that despite the structural diversity of the core transcriptional regulatory factors implicated in EMT, a common mechanism has evolved for controlling their stability and therefore their function.

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The ubiquitin–proteasome system and skeletal muscle wasting

Essays in Biochemistry ◽

10.1042/bse0410173 ◽

2005 ◽

Vol 41 ◽

pp. 173-186 ◽

Cited By ~ 110

Author(s):

Didier Attaix ◽

Sophie Ventadour ◽

Audrey Codran ◽

Daniel Béchet ◽

Daniel Taillandier ◽

...

Keyword(s):

Skeletal Muscle ◽

Muscle Wasting ◽

Proteolytic Enzymes ◽

Cathepsin L ◽

Ubiquitin Proteasome System ◽

Complete Breakdown ◽

Skeletal Muscle Proteins ◽

Ubiquitin Proteasome ◽

Tripeptidyl Peptidase Ii ◽

F Box Protein

The ubiquitin–proteasome system (UPS) is believed to degrade the major contractile skeletal muscle proteins and plays a major role in muscle wasting. Different and multiple events in the ubiquitination, deubiquitination and proteolytic machineries are responsible for the activation of the system and subsequent muscle wasting. However, other proteolytic enzymes act upstream (possibly m-calpain, cathepsin L, and/or caspase 3) and downstream (tripeptidyl-peptidase II and aminopeptidases) of the UPS, for the complete breakdown of the myofibrillar proteins into free amino acids. Recent studies have identified a few critical proteins that seem necessary for muscle wasting {i.e. the MAFbx (muscle atrophy F-box protein, also called atrogin-1) and MuRF-1 [muscle-specific RING (really interesting new gene) finger 1] ubiquitin–protein ligases}. The characterization of their signalling pathways is leading to new pharmacological approaches that can be useful to block or partially prevent muscle wasting in human patients.

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An UBR-box from a non-N-recognin: Crystal Structure of the UBR domain of UBR6

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s2053273314096934 ◽

2014 ◽

Vol 70 (a1) ◽

pp. C306-C306

Author(s):

Juliana Muñoz-Escobar ◽

Guennadi Kozlov ◽

Jean-François Trempe ◽

Kalle Gehring

Keyword(s):

Crystal Structure ◽

Ubiquitin Proteasome System ◽

Zinc Binding ◽

Binding Motifs ◽

Clear Explanation ◽

Ubiquitin Ligase Complex ◽

Ubiquitin Proteasome ◽

Binding Pockets ◽

F Box Protein

The degradation of many short-lived proteins in eukaryotic cells is carried out by the Ubiquitin Proteasome System. The N-end rule pathway links the half-life of proteins to the identity of its N-terminal residue, also called N-degron. Destabilizing N-degrons, are recognized by E3 ubiquitin ligases termed N-recognins. N-degrons are grouped into type 1, composed of basic residues, and type 2, composed of bulky hydrophobic residues. In mammals, four N-recognins mediate the N-end rule pathway: UBR1, UBR2, UBR4 and UBR5. These proteins share a ~70-residue zinc finger-like motif termed the Ubiquitin Recognin (UBR) box, responsible for their specificity. The mammalian genome encodes at least three more UBR-box proteins: UBR3, UBR6/FBXO11 and UBR7. However, these UBRs cannot recognize any type of N-degrons. Our lab reported the crystal structures of the UBR boxes from the human UBR1 and UBR2, rationalizing the empirical rules for the classification of type 1 N-degrons. Despite the valuable information obtained from those structures there is not a clear explanation for the no recognition of N-degrons by other UBR-box proteins. Here we report the crystal structure of the UBR-box domain from UBR6 also known as FBXO11. UBR6 is a F-box protein of the SKP1-Cullin1-F-box (SCF) ubiquitin ligase complex and does not recognize any type of N-degrons. We crystallized a 77-residue fragment of the UBR-box of UBR6 and determined its structure at 1.7 Å resolution. Unexpectedly, this domain adopts an open conformation compared to UBR1-box, without any N-degron binding pockets. Its zinc-binding residues are conserved as in the N-recognins, but they are arranged in different zinc-binding motifs. Molecules form dimmers stabilized by zinc ions. The crystal had 4 molecules per asymmetric unit and space group P212121. For phasing we used Zn-SAD. With this structure we hope to obtain clues that explain the absence of N-degron recognition in some members of the UBR family.

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A Yeast-Based Functional Assay to Study Plant N-Degron – N-Recognin Interactions

Frontiers in Plant Science ◽

10.3389/fpls.2021.806129 ◽

2022 ◽

Vol 12 ◽

Author(s):

Aida Kozlic ◽

Nikola Winter ◽

Theresia Telser ◽

Jakob Reimann ◽

Katrin Rose ◽

...

Keyword(s):

Ubiquitin Proteasome System ◽

Functional Assay ◽

The Novel ◽

In Planta ◽

Amino Terminal ◽

Weak Binding ◽

Ubiquitin Conjugating Enzyme ◽

Ubiquitin Proteasome ◽

The Stability

The N-degron pathway is a branch of the ubiquitin-proteasome system where amino-terminal residues serve as degradation signals. In a synthetic biology approach, we expressed ubiquitin ligase PRT6 and ubiquitin conjugating enzyme 2 (AtUBC2) from Arabidopsis thaliana in a Saccharomyces cerevisiae strain with mutation in its endogenous N-degron pathway. The two enzymes re-constitute part of the plant N-degron pathway and were probed by monitoring the stability of co-expressed GFP-linked plant proteins starting with Arginine N-degrons. The novel assay allows for straightforward analysis, whereas in vitro interaction assays often do not allow detection of the weak binding of N-degron recognizing ubiquitin ligases to their substrates, and in planta testing is usually complex and time-consuming.

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Fbp1-Mediated Ubiquitin-Proteasome Pathway Controls Cryptococcus neoformans Virulence by Regulating Fungal Intracellular Growth in Macrophages

Infection and Immunity ◽

10.1128/iai.00994-13 ◽

2013 ◽

Vol 82 (2) ◽

pp. 557-568 ◽

Cited By ~ 21

Author(s):

Tong-Bao Liu ◽

Chaoyang Xue

Keyword(s):

Cryptococcus Neoformans ◽

Time Course ◽

Ubiquitin Proteasome System ◽

Phenotypic Analysis ◽

Fungal Virulence ◽

Content Type ◽

Brain Infection ◽

Virulence Attenuation ◽

Ubiquitin Proteasome ◽

F Box Protein

ABSTRACTCryptococcus neoformansis a human fungal pathogen that often causes lung and brain infections in immunocompromised patients, with a high fatality rate. Our previous results showed that an F-box protein, Fbp1, is essential forCryptococcusvirulence independent of the classical virulence factors, suggesting a novel virulence control mechanism. In this study, we show that Fbp1 is part of the ubiquitin-proteasome system, and we further investigated the mechanism of Fbp1 function during infection. Time course studies revealed that thefbp1Δ mutant causes little damage in the infected lung and that the fungal burden in the lung remains at a low but persistent level throughout infection. Thefbp1Δ mutant cannot disseminate to other organs following pulmonary infection in the murine inhalation model of cryptococcosis but still causes brain infection in a murine intravenous injection model, suggesting that the block of dissemination of thefbp1Δ mutant is due to its inability to leave the lung. Thefbp1Δ mutant showed a defect in intracellular proliferation after phagocytosis in aCryptococcus-macrophage interaction assay, which likely contributes to its virulence attenuation. To elucidate the molecular basis of the SCF(Fbp1) E3 ligase function, we analyzed potential Fbp1 substrates based on proteomic approaches combined with phenotypic analysis. One substrate, the inositol phosphosphingolipid-phospholipase C1 (Isc1), is required for fungal survival inside macrophage cells, which is consistent with the role of Fbp1 in regulatingCryptococcus-macrophage interaction and fungal virulence. Our results thus reveal a new determinant of fungal virulence that involves the posttranslational regulation of inositol sphingolipid biosynthesis.

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Killing by Degradation: Regulation of Apoptosis by the Ubiquitin-Proteasome-System

Cells ◽

10.3390/cells10123465 ◽

2021 ◽

Vol 10 (12) ◽

pp. 3465

Author(s):

Ruqaia Abbas ◽

Sarit Larisch

Keyword(s):

Apoptotic Cell ◽

Ubiquitin Proteasome System ◽

Cancer Therapies ◽

E3 Ligases ◽

Ubiquitin Proteasome ◽

A Cell ◽

Positive And Negative Feedback ◽

Apoptotic Proteins ◽

The Stability ◽

Cell Suicide

Apoptosis is a cell suicide process that is essential for development, tissue homeostasis and human health. Impaired apoptosis is associated with a variety of human diseases, including neurodegenerative disorders, autoimmunity and cancer. As the levels of pro- and anti-apoptotic proteins can determine the life or death of cells, tight regulation of these proteins is critical. The ubiquitin proteasome system (UPS) is essential for maintaining protein turnover, which can either trigger or inhibit apoptosis. In this review, we will describe the E3 ligases that regulate the levels of pro- and anti-apoptotic proteins and assisting proteins that regulate the levels of these E3 ligases. We will provide examples of apoptotic cell death modulations using the UPS, determined by positive and negative feedback loop reactions. Specifically, we will review how the stability of p53, Bcl-2 family members and IAPs (Inhibitor of Apoptosis proteins) are regulated upon initiation of apoptosis. As increased levels of oncogenes and decreased levels of tumor suppressor proteins can promote tumorigenesis, targeting these pathways offers opportunities to develop novel anti-cancer therapies, which act by recruiting the UPS for the effective and selective killing of cancer cells.

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Phosphorylation and activation of ubiquitin-specific protease-14 by Akt regulates the ubiquitin-proteasome system

eLife ◽

10.7554/elife.10510 ◽

2015 ◽

Vol 4 ◽

Cited By ~ 55

Author(s):

Daichao Xu ◽

Bing Shan ◽

Byung-Hoon Lee ◽

Kezhou Zhu ◽

Tao Zhang ◽

...

Keyword(s):

Growth Factors ◽

Intracellular Signaling ◽

Ubiquitin Proteasome System ◽

Specific Protein ◽

Negative Control ◽

Common Mechanism ◽

Wide Range ◽

Specific Protease ◽

Ubiquitin Proteasome

Regulation of ubiquitin-proteasome system (UPS), which controls the turnover of short-lived proteins in eukaryotic cells, is critical in maintaining cellular proteostasis. Here we show that USP14, a major deubiquitinating enzyme that regulates the UPS, is a substrate of Akt, a serine/threonine-specific protein kinase critical in mediating intracellular signaling transducer for growth factors. We report that Akt-mediated phosphorylation of USP14 at Ser432, which normally blocks its catalytic site in the inactive conformation, activates its deubiquitinating activity in vitro and in cells. We also demonstrate that phosphorylation of USP14 is critical for Akt to regulate proteasome activity and consequently global protein degradation. Since Akt can be activated by a wide range of growth factors and is under negative control by phosphoinosotide phosphatase PTEN, we suggest that regulation of UPS by Akt-mediated phosphorylation of USP14 may provide a common mechanism for growth factors to control global proteostasis and for promoting tumorigenesis in PTEN-negative cancer cells.

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The ubiquitin–proteasome system regulates the stability and activity of the glucose sensor glucokinase in pancreatic β-cells

Biochemical Journal ◽

10.1042/bj20130262 ◽

2013 ◽

Vol 456 (2) ◽

pp. 173-184 ◽

Cited By ~ 18

Author(s):

Anke Hofmeister-Brix ◽

Sigurd Lenzen ◽

Simone Baltrusch

Keyword(s):

Protein Misfolding ◽

Glucose Sensor ◽

Ubiquitin Proteasome System ◽

Β Cells ◽

Pancreatic Β Cells ◽

Insulin Secreting Cells ◽

Ubiquitin Proteasome ◽

The Stability

The glucose phosphorylating enzyme glucokinase is regulated by the ubiquitin–proteasome system. Inhibition of the proteasome leads to reduced glucokinase activity, glucokinase protein misfolding and localization of glucokinase in aggresomes in insulin-secreting cells, pancreatic β-cells and hepatocytes.

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The Control Operated by the Cell Cycle Machinery on MEF2 Stability Contributes to the Downregulation of CDKN1A and Entry into S Phase

Molecular and Cellular Biology ◽

10.1128/mcb.01461-14 ◽

2015 ◽

Vol 35 (9) ◽

pp. 1633-1647 ◽

Cited By ~ 30

Author(s):

Eros Di Giorgio ◽

Enrico Gagliostro ◽

Andrea Clocchiatti ◽

Claudio Brancolini

Keyword(s):

Cell Cycle ◽

Ubiquitin Proteasome System ◽

S Phase ◽

Open Chromatin ◽

Cyclin Dependent Kinase ◽

Murine Fibroblasts ◽

Subsequent Degradation ◽

Ubiquitin Proteasome ◽

F Box Protein ◽

Cdkn1a Gene

MEF2s are pleiotropic transcription factors (TFs) which supervise multiple cellular activities. During the cell cycle, MEF2s are activated at the G0/G1transition to orchestrate the expression of the immediate early genes in response to growth factor stimulation. Here we show that, in human and murine fibroblasts, MEF2 activities are downregulated during late G1. MEF2C and MEF2D interact with the E3 ligase F-box protein SKP2, which mediates their subsequent degradation through the ubiquitin-proteasome system. The cyclin-dependent kinase 4 (CDK4)/cyclin D1 complex phosphorylates MEF2D on serine residues 98 and 110, and phosphorylation of these residues is an important determinant for SKP2 binding. Unscheduled MEF2 transcription during the cell cycle reduces cell proliferation, whereas its containment sustains DNA replication. The CDK inhibitor p21/CDKN1A gene is a MEF2 target gene required to exert this antiproliferative influence. MEF2C and MEF2D bind a region within the first intron ofCDKN1A, presenting epigenetic markers of open chromatin. Importantly, H3K27 acetylation within this regulative region depends on the presence of MEF2D. We propose that following the initial engagement in the G0/G1transition, MEF2C and MEF2D must be polyubiquitylated and degraded during G1progression to diminish the transcription of theCDKN1Agene, thus favoring entry into S phase.

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The Emerging Role of CSN6 in Biological Behavior and Cancer Progress

Anti-Cancer Agents in Medicinal Chemistry ◽

10.2174/1871520619666190408142131 ◽

2019 ◽

Vol 19 (10) ◽

pp. 1198-1204

Author(s):

Zun Mao ◽

Cheng Chen ◽

Dong-Sheng Pei

Keyword(s):

Clinical Care ◽

Protein Molecule ◽

Ubiquitin Proteasome System ◽

Biological Behavior ◽

Developmental Defects ◽

Normal Tissues ◽

Wide Range ◽

Ubiquitin Proteasome ◽

Regulatory Capacity ◽

The Stability

Background:The Constitutive Photomorphogenesis 9 (COP9) signalosome (CSN) subunit 6 (CSN6) noticeably acts as a regulator of the degradation of cancer-related proteins, which contributes to cancerogenesis. The aims of this paper are to expound the research advances of CSN6, particularly focusing on roles of CSN6 in the regulation of biological behavior and cancer progress.Methods:Literature from PubMed and Web of Science databases about biological characteristics and application of CSN6 published in recent years was collected to conduct a review.Results:CSN6, not only the non-catalytic Mpr1p and Pad1p N-terminal (MPN) subunit of CSN, but also a relatively independent protein molecule, has received great attention as a regulator of a wide range of developmental processes by taking part in the ubiquitin-proteasome system and signal transduction, as well as regulating genome integrity and DNA damage response. In addition, phosphorylation of CSN6 increases the stability of CSN6, thereby promoting its regulatory capacity. Moreover, CSN6 is overexpressed in many types of cancer compared with normal tissues and is involved in the regulation of several important intracellular pathways, consisting of cell proliferation, migration, invasion, transformation, and tumorigenesis.Conclusion:We mainly present insights into the function and research development of CSN6, hoping that it can help guide the treatment of developmental defects and improve clinical care, especially in the regulation of cancer signaling pathways.

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Mutant Ubiquitin-Mediated β-Secretase Stability via Activation of Caspase-3 is Related to β-Amyloid Accumulation in Ischemic Striatum in Rats

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/jcbfm.2009.228 ◽

2009 ◽

Vol 30 (3) ◽

pp. 566-575 ◽

Cited By ~ 16

Author(s):

Yong Zhang ◽

Man Xiong ◽

Ri-Qiang Yan ◽

Feng-Yan Sun

Keyword(s):

Caspase 3 ◽

Ubiquitin Proteasome System ◽

Artery Occlusion ◽

Amyloid Accumulation ◽

Ipsilateral Striatum ◽

Ubiquitin Proteasome ◽

Amyloid Aβ ◽

Β Amyloid ◽

The Stability ◽

Cerebral Artery Occlusion

Previous studies have demonstrated that ischemic stroke increases β-amyloid (Aβ) production by increasing β-secretase (BACE1) through activation of caspase-3, and stimulates generation of mutant ubiquitin (UBB+1) in rat brains. In this study, we examined whether caspase-3 activation participates in the regulation of UBB+1 generation and UBB+1-mediated BACE1 stability in ischemic injured brains. The results showed that UBB+1 and activated caspase-3-immunopositive-stained cells were time dependently increased in the ipsilateral striatum of rat brains after middle cerebral artery occlusion. UBB+1-immunopositive cells could be co-stained with caspase-3, Aβ (UBB+1–Aβ), and BACE1 (UBB+1–BACE1). BACE1 protein could also be pulled down by immunoprecipitation with UBB+1 antibody. Z-DEVD-FMK (DEVD), a caspase-3 inhibitor, significantly decreased the level of UBB+1 protein and the number of UBB+1–Aβ and UBB+1–BACE1 double-stained cells in the ischemic striatum, as well as the level of UBB+1/BACE1 protein complex. We conclude that activation of caspase-3 might be upstream of UBB+1 formation and that excessive UBB+1 could bind to BACE1 and increase the stability of BACE1, thereby increasing Aβ in ischemic injured brains. These results suggest new biological and pathological effects of caspases and regulation of the ubiquitin–proteasome system in the brain. Our results provide new therapeutic targets to prevent further neurodegeneration in patients after stroke.

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