Dual roles of mTORC1-dependent activation of the ubiquitin-proteasome system in muscle proteostasis

Muscle size is controlled by the PI3K-PKB/Akt-mTORC1-FoxO pathway, which integrates signals from growth factors, energy and amino acids to activate protein synthesis and inhibit protein breakdown. While mTORC1 activity is necessary for PKB/Akt-induced muscle hypertrophy, its constant activation alone induces muscle atrophy. Here we show that this paradox is based on mTORC1 activity promoting protein breakdown through the ubiquitin-proteasome system (UPS) by simultaneously inducing ubiquitin E3 ligase expression via feedback inhibition of PKB/Akt and proteasome biogenesis via Nuclear Factor Erythroid 2-Like 1 (Nrf1). Muscle growth was restored by reactivation of PKB/Akt, but not by Nrf1 knockdown, implicating ubiquitination as the limiting step. However, both PKB/Akt activation and proteasome depletion by Nrf1 knockdown led to an immediate disruption of proteome integrity with rapid accumulation of damaged material. These data highlight the physiological importance of mTORC1-mediated PKB/Akt inhibition and point to juxtaposed roles of the UPS in atrophy and proteome integrity.

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The HECT ubiquitin E3 ligase Smurf2 degrades μ-opioid receptor 1 in the ubiquitin-proteasome system in lung epithelial cells

AJP Cell Physiology ◽

10.1152/ajpcell.00443.2018 ◽

2019 ◽

Vol 316 (5) ◽

pp. C632-C640

Author(s):

Su Dong ◽

Jia Liu ◽

Lian Li ◽

Heather Wang ◽

Haichun Ma ◽

...

Keyword(s):

Cell Migration ◽

Epithelial Cells ◽

Opioid Receptor ◽

Ubiquitin Proteasome System ◽

Lung Epithelial Cells ◽

Ubiquitin E3 Ligase ◽

Lung Epithelial ◽

Ubiquitin Proteasome ◽

Μ Opioid Receptor ◽

Cell Migration And Proliferation

Opioids are widely used for relieving clinical acute or chronic pain. The biological effects of opioids are through activating μ-opioid receptor 1 (MOR1). Most studies have focused on the consequences of agonist-induced MOR1 phosphorylation, ubiquitination, and internalization. Agonist-mediated MOR1 degradation, which is crucial for receptor stability and responsiveness, has not been well studied. E3 ubiquitin-protein ligase SMURF2 (Smurf2), a homolog to E6AP carboxy terminus (HECT) ubiquitin E3 ligase, has been shown to regulate MOR1 ubiquitination and internalization; however, its role in MOR1 degradation has not been studied. Here, we demonstrate that Smurf2 mediates [d-Ala2, N-MePhe4,Gly5-ol]-enkephalin (DAMGO, an agonist of MOR1)-induced MOR1 ubiquitination and degradation. DAMGO decreased MOR1 levels in the ubiquitin-proteasome system. MOR1 was modified by a Lys48-linked polyubiquitin chain. Overexpression of Smurf2 induced MOR1 ubiquitination and accelerated DAMGO-induced MOR1 degradation, whereas downregulation of Smurf2 attenuated MOR1 degradation. Furthermore, DAMGO increased lung epithelial cell migration and proliferation, and the effect was attenuated by overexpressing Smurf2. Collectively, these data unveil that Smurf2 negatively regulates MOR1 activity by reducing its stability. We also demonstrate an unrevealed biological function of MOR1 in lung epithelial cells. DAMGO-MOR1 promote cell migration and proliferation in lung epithelial cells, suggesting a potential effect of DAMGO in lung repair and remodeling after lung injury.

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Skeletal-muscle growth and protein turnover

Biochemical Journal ◽

10.1042/bj1500235 ◽

1975 ◽

Vol 150 (2) ◽

pp. 235-243 ◽

Cited By ~ 222

Author(s):

D J Millward ◽

P J Garlick ◽

R J C Stewart ◽

D O Nnanyelugo ◽

J C Waterlow

Keyword(s):

Skeletal Muscle ◽

Growth Rate ◽

Protein Synthesis ◽

Muscle Protein ◽

Muscle Growth ◽

Muscle Size ◽

Synthesis Rate ◽

Protein Breakdown ◽

Breakdown Rate ◽

Breakdown Rates

Because of turnover, protein synthesis and breakdown can each be involved in the regulation of the growth of tissue protein. To investigate the regulation of skeletal-muscle-protein growth we measured rates of protein synthesis and breakdown in growing rats during development on a good diet, during development on a marginally low-protein diet and during rehabilitation on a good diet after a period of severe protein deficiency. Rates of protein synthesis were measured in vivo with a constant intravenous infusion of [14C]tyrosine. The growth rate of muscle protein was measured and the rate of breakdown calculated as breakdown rate=synthesis rate-growth rate. These measurements showed that during development on a good diet there was a fall with age in the rate of protein synthesis resulting from a fall in capacity (RNA concentration) and activity (synthesis rate per unit of RNA). There was a fall with age in the breakdown rate so that the rate was highest in the weaning rats, with a half-life of 3 days. There was a direct correlation between the fractional growth and breakdown rates. During rehabilitation on the good diet, rapid growth was also accompanied by high rates of protein breakdown. During growth on the inadequate diet protein synthesis rates were lesss than in controls, but growth occurred because of decreased rates of protein breakdown. This compression was not complete, however, since ultimate muscle size was only one-half that of controls. It is suggested that increased rates of protein breakdown are a necessary accompaniment to muscle growth and may result from the way in which myofibrils proliferate.

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Proteasome activity is altered in skeletal muscle tissue of tumour-bearing rats a leucine-rich diet

Endocrine Related Cancer ◽

10.1677/erc.1.00828 ◽

2004 ◽

Vol 11 (4) ◽

pp. 887-895 ◽

Cited By ~ 37

Author(s):

G Ventrucci ◽

M A R Mello ◽

M C C Gomes-Marcondes

Keyword(s):

Skeletal Muscle ◽

Protein Synthesis ◽

Tumour Growth ◽

Ubiquitin Proteasome System ◽

Protein Breakdown ◽

Pregnant Rats ◽

Α Subunit ◽

Proteasome Subunit ◽

Tumour Bearing ◽

Ubiquitin Proteasome

Leucine can modulate skeletal muscle metabolism by enhancing protein synthesis and decreasing proteolysis. In this study, we investigated the effects of leucine on the ubiquitin–proteasome system in skeletal muscle of pregnant tumour-bearing rats fed a leucine-rich diet. Pregnant Wistar rats were distributed into three groups that were fed a semi-purified control diet (C, control; W, Walker tumour-bearing; P, pair-fed) and three other groups of pregnant rats fed a semi-purified leucine-rich diet (L, leucine; WL, Walker tumour-bearing; PL, pair-fed). The tumour-bearing rats were injected subcutaneously with a suspension of Walker 256 tumour cells. Protein synthesis and degradation were measured in gastrocnemius muscle; the total protein content and tissue chymotrypsin-like and alkaline phosphatase enzyme activities were also determined. Muscle protein extracts were run on SDS-PAGE to assess the expression of the myosin heavy chain (MHC), 20S α proteasome subunit, 19S MSSI ATPase regulator subunit and 11S α subunit. Although tumour growth decreased the incorporation of [3H]-Phe, the concomitant feeding of a leucine-rich diet increased the rate of protein synthesis. Muscle proteolysis in both tumour-bearing groups was increased more than in the respective control groups. Conversely, the leucine-rich diet caused less protein breakdown in the WL group than in the W group. Only the W group showed a significant reduction (71%) in the myosin content. In WL rats, the 20S proteasome content (32 kDa band) was reduced, while the expression of the 19S subunit was 3-fold less than in the W group and the 11S proteasome subunit reduced, to around 32% less than in the W group. These findings clearly indicate that leucine can stimulate protein synthesis and inhibit protein breakdown in pregnant rats, probably by modulating the activation of the ubiquitin–proteasome system during tumour growth.

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FAT10 protects against ischemia-induced ventricular arrhythmia by decreasing Nedd4-2/Nav1.5 complex formation

Cell Death and Disease ◽

10.1038/s41419-020-03290-3 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Xiao Liu ◽

Jin Ge ◽

Chen Chen ◽

Yang Shen ◽

Jinyan Xie ◽

...

Keyword(s):

Ventricular Arrhythmia ◽

Cardiac Myocytes ◽

Cardiac Arrhythmias ◽

Protein A ◽

Human Leukocyte ◽

Ubiquitin Proteasome System ◽

Leukocyte Antigen ◽

Ubiquitin E3 Ligase ◽

Lysine Residues ◽

Ubiquitin Proteasome

AbstractThe human leukocyte antigen F-associated transcript 10 (FAT10) is a member of the small ubiquitin-like protein family that binds to its target proteins and subjects them to degradation by the ubiquitin–proteasome system (UPS). In the heart, FAT10 plays a cardioprotective role and affects predisposition to cardiac arrhythmias after myocardial ischemia (MI). However, whether and how FAT10 influences cardiac arrhythmias is unknown. We investigated the role of FAT10 in regulating the sodium channel Nav1.5, a major regulator of cardiac arrhythmias. Fat10 was conditionally deleted in cardiac myocytes using Myh6-Cre and Fat10F/F mice (cFat10−/−). Compared with their wild-type littermates, cFat10−/− mice showed prolonged RR, PR, and corrected QT (QTc) intervals, were more likely to develop ventricular arrhythmia, and had increased mortality after MI. Patch-clamp studies showed that the peak Na+ current was reduced, and the late Na+ current was significantly augmented, resulting in a decreased action potential amplitude and delayed depolarization. Immunoblot and immunofluorescence analyses showed that the expression of the membrane protein Nav1.5 was decreased. Coimmunoprecipitation experiments demonstrated that FAT10 stabilized Nav1.5 expression by antagonizing Nav1.5 ubiquitination and degradation. Specifically, FAT10 bound to the lysine residues in the C-terminal fragments of Nav1.5 and decreased the binding of Nav1.5 to the Nedd4-2 protein, a ubiquitin E3 ligase, preventing degradation of the Nav1.5 protein. Collectively, our findings showed that deletion of the Fat10 in cardiac myocytes led to increased cardiac arrhythmias and increased mortality after MI. Thus, FAT10 protects against ischemia-induced ventricular arrhythmia by binding to Nav1.5 and preventing its Neddylation and degradation by the UPS after MI.

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Inhibitor of apoptosis proteins as E3 ligases for ubiquitin and NEDD8

BioMolecular Concepts ◽

10.1515/bmc-2012-0036 ◽

2013 ◽

Vol 4 (2) ◽

pp. 161-171 ◽

Cited By ~ 3

Author(s):

Shinji Kamada

Keyword(s):

E3 Ligase ◽

Ubiquitin Proteasome System ◽

E3 Ligases ◽

Ubiquitin E3 Ligase ◽

The Family ◽

Ubiquitin Proteasome ◽

Inhibitors Of Apoptosis Proteins ◽

New Gene ◽

Neuronal Precursor Cell ◽

Apoptosis Proteins

AbstractThe inhibitors of apoptosis proteins (IAPs) are endogenous inhibitors for apoptosis. Apoptosis is carried out by caspases, which are the family of cystein proteases. IAPs regulate caspases through two conserved regions, the baculovirus IAP repeats (BIRs) and the really interesting new gene (RING) domains. Although the BIRs are responsible for binding to caspases, the RING domain can act as a ubiquitin-E3 ligase, leading to ubiquitylation of IAPs themselves and their pro-apoptotic IAP counterparts such as caspases. Recently, it is reported that another ubiquitin-like protein, neuronal precursor cell-expressed developmentally downregulated protein 8 (NEDD8), is also involved in the regulation of apoptosis through neddylation of caspases mediated by IAPs. On the contrary, the results against the function of IAPs as a NEDD8-E3 ligase are also suggested. This review presents the summary of IAPs, caspases, and the ubiquitin-proteasome system and how their interactions influence the regulation of apoptosis.

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Irf2bp2a regulates terminal granulopoiesis through proteasomal degradation of Gfi1aa in zebrafish

PLoS Genetics ◽

10.1371/journal.pgen.1009693 ◽

2021 ◽

Vol 17 (8) ◽

pp. e1009693

Author(s):

Shuo Gao ◽

Zixuan Wang ◽

Luxiang Wang ◽

Haihong Wang ◽

Hao Yuan ◽

...

Keyword(s):

Drug Targets ◽

Ring Finger ◽

E3 Ligase ◽

Ubiquitin Proteasome System ◽

Proteasomal Degradation ◽

Link Type ◽

Ubiquitin E3 Ligase ◽

Anti Cancer ◽

Ubiquitin Proteasome ◽

Transcription Regulators

The ubiquitin-proteasome system plays important roles in various biological processes as it degrades the majority of cellular proteins. Adequate proteasomal degradation of crucial transcription regulators ensures the proper development of neutrophils. The ubiquitin E3 ligase of Growth factor independent 1 (GFI1), a key transcription repressor governing terminal granulopoiesis, remains obscure. Here we report that the deficiency of the ring finger protein Interferon regulatory factor 2 binding protein 2a (Irf2bp2a) leads to an impairment of neutrophils differentiation in zebrafish. Mechanistically, Irf2bp2a functions as a ubiquitin E3 ligase targeting Gfi1aa for proteasomal degradation. Moreover, irf2bp2a gene is repressed by Gfi1aa, thus forming a negative feedback loop between Irf2bp2a and Gfi1aa during neutrophils maturation. Different levels of GFI1 may turn it into a tumor suppressor or an oncogene in malignant myelopoiesis. Therefore, discovery of certain drug targets GFI1 for proteasomal degradation by IRF2BP2 might be an effective anti-cancer strategy.

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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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