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Cells Jul 2023The proteasome is a multi-catalytic protease complex that is involved in protein quality control via three proteolytic activities (i.e., caspase-, trypsin-, and... (Review)
Review
The proteasome is a multi-catalytic protease complex that is involved in protein quality control via three proteolytic activities (i.e., caspase-, trypsin-, and chymotrypsin-like activities). Most cellular proteins are selectively degraded by the proteasome via ubiquitination. Moreover, the ubiquitin-proteasome system is a critical process for maintaining protein homeostasis. Here, we briefly summarize the structure of the proteasome, its regulatory mechanisms, proteins that regulate proteasome activity, and alterations to proteasome activity found in diverse diseases, chemoresistant cells, and cancer stem cells. Finally, we describe potential therapeutic modalities that use the ubiquitin-proteasome system.
Topics: Proteasome Endopeptidase Complex; Proteolysis; Ubiquitination; Ubiquitin; Proteins
PubMed: 37508510
DOI: 10.3390/cells12141846 -
Nature Communications Jul 2023Perturbed cellular protein homeostasis (proteostasis) and mitochondrial dysfunction play an important role in neurodegenerative diseases, however, the interplay between...
Perturbed cellular protein homeostasis (proteostasis) and mitochondrial dysfunction play an important role in neurodegenerative diseases, however, the interplay between these two phenomena remains unclear. Mitochondrial dysfunction leads to a delay in mitochondrial protein import, causing accumulation of non-imported mitochondrial proteins in the cytosol and challenging proteostasis. Cells respond by increasing proteasome activity and molecular chaperones in yeast and C. elegans. Here, we demonstrate that in human cells mitochondrial dysfunction leads to the upregulation of a chaperone HSPB1 and, interestingly, an immunoproteasome-specific subunit PSMB9. Moreover, PSMB9 expression is dependent on the translation elongation factor EEF1A2. These mechanisms constitute a defense response to preserve cellular proteostasis under mitochondrial stress. Our findings define a mode of proteasomal activation through the change in proteasome composition driven by EEF1A2 and its spatial regulation, and are useful to formulate therapies to prevent neurodegenerative diseases.
Topics: Humans; Cytoplasm; Mitochondria; Peptide Elongation Factor 1; Proteasome Endopeptidase Complex; Proteostasis; Cysteine Endopeptidases
PubMed: 37433777
DOI: 10.1038/s41467-023-39642-8 -
Cells Aug 2023Cellular senescence contributes importantly to aging and aging-related diseases, including idiopathic pulmonary fibrosis (IPF). Alveolar epithelial type II (ATII) cells...
Cellular senescence contributes importantly to aging and aging-related diseases, including idiopathic pulmonary fibrosis (IPF). Alveolar epithelial type II (ATII) cells are progenitors of alveolar epithelium, and ATII cell senescence is evident in IPF. Previous studies from this lab have shown that increased expression of plasminogen activator inhibitor 1 (PAI-1), a serine protease inhibitor, promotes ATII cell senescence through inducing p53, a master cell cycle repressor, and activating p53-p21-pRb cell cycle repression pathway. In this study, we further show that PAI-1 binds to proteasome components and inhibits proteasome activity and p53 degradation in human lung epithelial A549 cells and primary mouse ATII cells. This is associated with a senescence phenotype of these cells, manifested as increased p53 and p21 expression, decreased phosphorylated retinoblastoma protein (pRb), and increased senescence-associated beta-galactose (SA-β-gal) activity. Moreover, we find that, although overexpression of wild-type PAI-1 (wtPAI-1) or a secretion-deficient, mature form of PAI-1 (sdPAI-1) alone induces ATII cell senescence (increases SA-β-gal activity), only wtPAI-1 induces p53, suggesting that the premature form of PAI-1 is required for the interaction with the proteasome. In summary, our data indicate that PAI-1 can bind to proteasome components and thus inhibit proteasome activity and p53 degradation in ATII cells. As p53 is a master cell cycle repressor and PAI-1 expression is increased in many senescent cells, the results from this study will have a significant impact not only on ATII cell senescence/lung fibrosis but also on the senescence of other types of cells in different diseases.
Topics: Animals; Humans; Mice; Alveolar Epithelial Cells; Idiopathic Pulmonary Fibrosis; Plasminogen Activator Inhibitor 1; Proteasome Endopeptidase Complex; Tumor Suppressor Protein p53
PubMed: 37566086
DOI: 10.3390/cells12152008 -
EMBO Reports Sep 2023Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two aging-related neurodegenerative diseases that share common key features, including...
Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two aging-related neurodegenerative diseases that share common key features, including aggregation of pathogenic proteins, dysfunction of mitochondria, and impairment of autophagy. Mutations in ubiquilin 2 (UBQLN2), a shuttle protein in the ubiquitin-proteasome system (UPS), can cause ALS/FTD, but the mechanism underlying UBQLN2-mediated pathogenesis is still uncertain. Recent studies indicate that mitophagy, a selective form of autophagy which is crucial for mitochondrial quality control, is tightly associated with neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and ALS. In this study, we show that after Parkin-dependent ubiquitination of damaged mitochondria, UBQLN2 is recruited to poly-ubiquitinated mitochondria through the UBA domain. UBQLN2 cooperates with the chaperone HSP70 to promote UPS-driven degradation of outer mitochondrial membrane (OMM) proteins. The resulting rupture of the OMM triggers the autophagosomal recognition of the inner mitochondrial membrane receptor PHB2. UBQLN2 is required for Parkin-mediated mitophagy and neuronal survival upon mitochondrial damage, and the ALS/FTD pathogenic mutations in UBQLN2 impair mitophagy in primary cultured neurons. Taken together, our findings link dysfunctional mitophagy to UBQLN2-mediated neurodegeneration.
Topics: Humans; Mitochondrial Membranes; Amyotrophic Lateral Sclerosis; Mitophagy; Frontotemporal Dementia; Adaptor Proteins, Signal Transducing; Autophagy-Related Proteins; Proteasome Endopeptidase Complex; Ubiquitin; Neurodegenerative Diseases; Transcription Factors; Ubiquitin-Protein Ligases
PubMed: 37501540
DOI: 10.15252/embr.202255859 -
International Journal of Molecular... Oct 2023This study investigated modifications to the ubiquitin proteasome system (UPS) in a mouse model of type 2 diabetes mellitus (T2DM) and their relationship to heart...
This study investigated modifications to the ubiquitin proteasome system (UPS) in a mouse model of type 2 diabetes mellitus (T2DM) and their relationship to heart complications. mice heart tissues were compared with mice tissues using RNA sequencing, qRT-PCR, and protein analysis to identify cardiac UPS modifications associated with diabetes. The findings unveiled a distinctive gene profile in the hearts of mice with decreased levels of mRNA and increased levels of , indicating potential cardiac dysfunction. The mRNA levels of (deubiquitinating enzyme), , and (proteasome β-subunits) were down-regulated in mice, while the mRNA levels of RNF167 (E3 ligase) were increased. Corresponding LMP2 and LMP7 proteins were down-regulated in mice, and RNF167 was elevated in diabetic mice. The reduced expression of LMP2 and LMP7, along with increased RNF167 expression, may contribute to the future cardiac deterioration commonly observed in diabetes. This study enhances our understanding of UPS imbalances in the hearts of diabetic mice and raises questions about the interplay between the UPS and other cellular processes, such as autophagy. Further exploration in this area could provide valuable insights into the mechanisms underlying diabetic heart complications and potential therapeutic targets.
Topics: Mice; Animals; Proteasome Endopeptidase Complex; Ubiquitin; Diabetes Mellitus, Type 2; Diabetes Mellitus, Experimental; Diabetic Cardiomyopathies; Diabetes Complications; RNA, Messenger
PubMed: 37895057
DOI: 10.3390/ijms242015376 -
Cell Reports Aug 2023The proteasome plays a central role in intracellular protein degradation. Age-dependent decline in proteasome activity is associated with cellular senescence and...
The proteasome plays a central role in intracellular protein degradation. Age-dependent decline in proteasome activity is associated with cellular senescence and organismal aging; however, the mechanism by which the proteasome plays a role in senescent cells remains elusive. Here, we show that nuclear foci that contain the proteasome and exhibit liquid-like properties are formed in senescent cells. The formation of senescence-associated nuclear proteasome foci (SANPs) is dependent on ubiquitination and RAD23B, similar to previously known nuclear proteasome foci, but also requires proteasome activity. RAD23B knockdown suppresses SANP formation and increases mitochondrial activity, leading to reactive oxygen species production without affecting other senescence traits such as cell-cycle arrest and cell morphology. These findings suggest that SANPs are an important feature of senescent cells and uncover a mechanism by which the proteasome plays a role in senescent cells.
Topics: Proteasome Endopeptidase Complex; Cell Nucleus; Ubiquitination; Cellular Senescence
PubMed: 37541257
DOI: 10.1016/j.celrep.2023.112880 -
Circulation Research Sep 2023A better understanding of the regulation of proteasome activities can facilitate the search for new therapeutic strategies. A cell culture study shows that PKA...
BACKGROUND
A better understanding of the regulation of proteasome activities can facilitate the search for new therapeutic strategies. A cell culture study shows that PKA (cAMP-dependent protein kinase or protein kinase A) activates the 26S proteasome by pS14-Rpn6 (serine14-phosphorylated Rpn6), but this discovery and its physiological significance remain to be established in vivo.
METHODS
Male and female mice with Ser14 of Rpn6 (regulatory particle non-ATPase 6) mutated to Ala (S14A [Rpn6/Psmd11]) or Asp (S14D) to respectively block or mimic pS14-Rpn6 were created and used along with cells derived from them. cAMP/PKA were manipulated pharmacologically. Ubiquitin-proteasome system functioning was evaluated with the GFPdgn (green fluorescence protein with carboxyl fusion of the CL1 degron) reporter mouse and proteasomal activity assays. Impact of S14A and S14D on proteotoxicity was tested in mice and cardiomyocytes overexpressing the misfolded protein R120G-CryAB (R120G [arginine120 to glycine missense mutant alpha B-crystallin]).
RESULTS
PKA activation increased pS14-Rpn6 and 26S proteasome activities in wild-type but not S14A embryonic fibroblasts (mouse embryonic fibroblasts), adult cardiomyocytes, and mouse hearts. Basal 26S proteasome activities were significantly greater in S14D myocardium and adult mouse cardiomyocytes than in wild-type counterparts. S14D::GFPdgn mice displayed significantly lower myocardial GFPdgn protein but not mRNA levels than GFPdgn mice. In R120G mice, a classic model of cardiac proteotoxicity, basal myocardial pS14-Rpn6 was significantly lower compared with nontransgenic littermates, which was not always associated with reduction of other phosphorylated PKA substrates. Cultured S14D neonatal cardiomyocytes displayed significantly faster proteasomal degradation of R120G than wild-type neonatal cardiomyocytes. Compared with R120G mice, S14D/S14D::R120G mice showed significantly greater myocardial proteasome activities, lower levels of total and K48-linked ubiquitin conjugates, and of aberrant CryAB (alpha B-crystallin) protein aggregates, less fetal gene reactivation, and cardiac hypertrophy, and delays in cardiac malfunction.
CONCLUSIONS
This study establishes in animals that pS14-Rpn6 mediates the activation of 26S proteasomes by PKA and that the reduced pS14-Rpn6 is a key pathogenic factor in cardiac proteinopathy, thereby identifying a new therapeutic target to reduce cardiac proteotoxicity.
Topics: Female; Male; Animals; Mice; Proteasome Endopeptidase Complex; alpha-Crystallin B Chain; Fibroblasts; Myocytes, Cardiac; Cyclic AMP-Dependent Protein Kinases; Ubiquitins
PubMed: 37641975
DOI: 10.1161/CIRCRESAHA.123.322887 -
MedComm Dec 2023Overexpression of immediate-early genes (IEGs) has been linked to was associated with cancer progression and prognosis. In a recent study, Gu et al. reported the...
Overexpression of immediate-early genes (IEGs) has been linked to was associated with cancer progression and prognosis. In a recent study, Gu et al. reported the midnolin-proteasome pathway, a novel ubiquitin-independent proteasomal degradation. 1 The study provided the mechanism of rapid degradation for nuclear proteins with high unsteadiness. Targeting the midnolin-proteasome pathway might be beneficial for cancer therapy.
PubMed: 38084259
DOI: 10.1002/mco2.450 -
Life Science Alliance Dec 2023p300 is an important transcriptional co-factor. By stimulating the transfer of acetyl residues onto histones and several key transcription factors, p300 enhances...
p300 is an important transcriptional co-factor. By stimulating the transfer of acetyl residues onto histones and several key transcription factors, p300 enhances transcriptional initiation and impacts cellular processes including cell proliferation and cell division. Despite its importance for cellular homeostasis, its regulation is poorly understood. We show that TRIM25, a member of the TRIM protein family, targets p300 for proteasomal degradation. However, despite TRIM25's RING domain and E3 activity, degradation of p300 by TRIM25 is independent of TRIM25-mediated p300 ubiquitination. Instead, TRIM25 promotes the interaction of p300 with dynein, which ensures a microtubule-dependent transport of p300 to cellular proteasomes. Through mediating p300 degradation, TRIM25 affects p300-dependent gene expression.
PubMed: 37770115
DOI: 10.26508/lsa.202301980 -
Clinical and Translational Medicine Aug 2023CCN6 is a matricellular protein that critically regulates the tumourigenesis and progression of breast cancer. Although the tumour-suppressive function of CCN6 has been...
BACKGROUND
CCN6 is a matricellular protein that critically regulates the tumourigenesis and progression of breast cancer. Although the tumour-suppressive function of CCN6 has been extensively studied, molecular mechanisms regulating protein levels of CCN6 remain largely unclear. This study aims to investigate the regulation of CCN6 by ubiquitination and deubiquitinating enzymes (DUBs) in breast cancer.
METHODS
A screening assay was performed to identify OTUB1 as the DUB for CCN6. Various biochemical methods were applied to elucidate the molecular mechanism of OTUB1 in the regulation of CCN6. The role of OTUB1-CCN6 interaction in breast cancer was studied with cell experiments and the allograft model. The correlation of OTUB1 and CCN6 in human breast cancer was determined by immunohistochemistry and Western blot.
RESULTS
We found that CCN6 protein levels were controlled by the ubiquitin-proteasome system. The K48 ubiquitination and degradation of CCN6 was inhibited by OTUB1, which directly interacted with CCN6 through its linker domain. Furthermore, OTUB1 inhibited the ubiquitination of CCN6 in a non-canonical manner. Deletion of OTUB1, concomitant with reduced CCN6 abundance, increased the migration, proliferation and viability of breast cancer cells. Supplementation of CCN6 abolished the effect of OTUB1 deletion on breast cancer. Importantly, OTUB1 expression was downregulated in human breast cancer and positively correlated with CCN6 levels.
CONCLUSION
This study identified OTUB1 as a novel regulator of CCN6 in breast cancer.
Topics: Humans; Blotting, Western; Carcinogenesis; Cell Transformation, Neoplastic; Cytoplasm; Proteasome Endopeptidase Complex; Deubiquitinating Enzymes; CCN Intercellular Signaling Proteins
PubMed: 37608493
DOI: 10.1002/ctm2.1385