Exploring the proteasome system: A novel concept of proteasome inhibition and regulation

Ubiquitin-like modification dependent proteasomal degradation and disease therapy

Although it is believed that ubiquitin (Ub) modification is required for protein degradation in the proteasome system (UPS), several proteins are subject to Ub-independent proteasome degradation, and in many cases ubiquitin-like (UBL) modifications, including neddylation, FAT10ylation, SUMOylation, ISGylation, and urmylation, are essential instead. In this Review, we focus on UBL-dependent proteasome degradation (UBLPD), on proteasome regulators especially shuttle factors and receptors, as well as potential competition and coordination with UPS. We propose that there is a distinct UBL-proteasome system (UBLPS) that might be underestimated in protein degradation. Finally, we investigate the association of UBLPD with muscle wasting and neurodegenerative diseases in which the proteasome is abnormally activated and impaired, respectively, and suggest strategies to modulate UBLPD for disease therapy.

Oleuropein enhances proteasomal activity and reduces mutant huntingtin-induced cytotoxicity

Introduction

Huntington's disease (HD) is a hereditary neurodegenerative disorder that primarily affects the striatum, a brain region responsible for movement control. The disease is characterized by the mutant huntingtin (mHtt) proteins with an extended polyQ stretch, which are prone to aggregation. These mHtt aggregates accumulate in neurons and are the primary cause of the neuropathology associated with HD. To date, no effective cure for HD has been developed.

Methods

The immortalized STHdh Q111/Q111 striatal cell line, the mHtt-transfected wild-type STHdh Q7/Q7 striatal cell line, and N2a cells were used as Huntington's disease cell models. Flow cytometry was used to assess cellular reactive oxygen species and transfection efficiency. The CCK-8 assay was used to measure cell viability, while fluorescence microscopy was used to quantify aggregates. Immunoblotting analyses were used to evaluate the effects on protein expression.

Results

Polyphenols are natural antioxidants that offer neuroprotection in neurological disorders. In this study, we provide evidence that oleuropein, the primary polyphenol in olive leaves and olive oil, enhances cell viability in HD cell models, including. STHdh Q7/Q7 STHdh Q7/Q7 striatal cells, N2a cells ectopically expressing the truncated mHtt, and STHdh Q111/Q111 striatal cells expressing the full-length mHtt. Oleuropein effectively reduced both soluble and aggregated forms of mHtt protein in these HD model cells. Notably, the reduction of mHtt aggregates associated with oleuropein was linked to increased proteasome activity rather than changes in autophagic flux. Oleuropein seems to modulate proteasome activity through an unidentified pathway, as it did not affect the 20S proteasome catalytic β subunits, the proteasome regulator PA28γ, or multiple MAPK pathways.

Discussion

We demonstrated that oleuropein enhances the degradation of mHtt by increasing proteasomal protease activities and alleviates mHtt-induced cytotoxicity. Hence, we propose that oleuropein and potentially other polyphenols hold promise as a candidate for alleviating Huntington's disease.

Safety of proteasome inhibitor drugs for the treatment of multiple myeloma post-marketing: a pharmacovigilance investigation based on the FDA adverse event reporting system

BACKGROUND

The use of proteasome inhibitors (PIs), namely Bortezomib and Carfilzomib, revolutionized multiple myeloma (MM) treatment. Understanding their distinct adverse event (AE) profiles aids in tailored treatment plans.

RESEARCH DESIGN AND METHODS

We analyzed FDA Adverse Event Reporting System (FAERS) data (Q1 2012-Q4 2023) for Bortezomib and Carfilzomib, utilizing reporting odds ratio (ROR), proportional reporting ratio (PRR), and Bayesian confidence propagation neural network (BCPNN).

RESULTS

FAERS yielded 19,720 Bortezomib and 12,252 Carfilzomib AE reports. Males aged 45-65 exhibited higher AE susceptibility. Common AE systems included Infections, Nervous System Disorders, Blood Disorders, General Disorders, Cardiac Disorders, and Renal Disorders. New Bortezomib signals were sepsis and colitis. Carfilzomib exhibited elevated cardiac and renal toxicity but reduced peripheral neuropathy and thrombocytopenia.

CONCLUSIONS

FAERS analysis revealed new AE signals (sepsis, colitis) for Bortezomib and highlighted Carfilzomib's heightened cardiac and renal risks compared to Bortezomib. Balancing PIs' benefits and risks is crucial for clinical decision-making.

Knockout of PA200 improves proteasomal degradation and myelination in a proteotoxic neuropathy

The cellular response to a decrease in protein degradation by 26S proteasomes in chronic diseases is poorly understood. Pharmacological inhibition of proteasomes increases the expression of proteasome subunits and Proteasome Activator 200 (PA200), an alternative proteasome activator. In the S63del mouse model of the peripheral neuropathy Charcot Marie Tooth 1B (CMT1B), proteasomal protein degradation is decreased and proteasome gene expression is increased. Here, we show an increase in PA200 and PA200-bound proteasomes in the peripheral nerves of S63del mice. To test genetically whether the upregulation of PA200 was compensatory, we generated S63del//PA200-/- mice. Unexpectedly, in the sciatic nerves of these mice, there was greater proteasomal protein degradation than in S63del, less polyubiquitinated proteins and markers of the unfolded protein response, and a greater amount of assembled, active 26S proteasomes. These changes were not seen in PA200-/- controls and were therefore specific to the neuropathy. Furthermore, in S63del//PA200-/- mice, myelin thickness and nerve conduction were restored to WT levels. Thus, the upregulation of PA200 is maladaptive in S63del mice and its genetic ablation prevented neuropathy.

Studying Antifatigue Mechanism of Tyr-Pro-Leu-Pro in Exercise Mice Using Label-Free Proteomics

In our previous study, yeast-derived peptide Tyr-Pro-Leu-Pro (YPLP) was found to prolong treadmill time and relieve muscle fatigue in ICR mice. The present study aimed to further investigate the antifatigue mechanism of YPLP. Three doses of YPLP (10, 25, and 50 mg/kg·d) were given to exercise mice for 4 weeks. Results showed that YPLP reduced the oxidative response via the nuclear factor erythroid-2-related factor 2 (Nrf2) pathway and promoted energy metabolism through the AMP-activated protein kinase (AMPK) pathway. Label-free proteomics results showed that 81 differential abundance proteins (DAPs) were regulated by high-dose YPLP. These DAPs belonged to proteasome, mitochondrial, and muscle proteins. YPLP was mainly involved in proteasome, aminoacyl-tRNA biosynthesis, focal adhesion, and MAPK signal pathways to enhance muscle endurance. Furthermore, real-time quantitative PCR and Western blotting results proved that YPLP upregulated Psmd14 expression and downregulated p38 MAPK expression. Overall, this study revealed the mechanism behind YPLP to alleviate exercise fatigue.

The coherence between PSMC6 and α-ring in the 26S proteasome is associated with Alzheimer's disease

Alzheimer's disease (AD) is a heterogeneous age-dependent neurodegenerative disorder. Its hallmarks involve abnormal proteostasis, which triggers proteotoxicity and induces neuronal dysfunction. The 26S proteasome is an ATP-dependent proteolytic nanomachine of the ubiquitin-proteasome system (UPS) and contributes to eliminating these abnormal proteins. This study focused on the relationship between proteasome and AD, the hub genes of proteasome, PSMC6, and 7 genes of α-ring, are selected as targets to study. The following three characteristics were observed: 1. The total number of proteasomes decreased with AD progression because the proteotoxicity damaged the expression of proteasome proteins, as evidenced by the downregulation of hub genes. 2. The existing proteasomes exhibit increased activity and efficiency to counterbalance the decline in total proteasome numbers, as evidenced by enhanced global coordination and reduced systemic disorder of proteasomal subunits as AD advances. 3. The synergy of PSMC6 and α-ring subunits is associated with AD. Synergistic downregulation of PSMC6 and α-ring subunits reflects a high probability of AD risk. Regarding the above discovery, the following hypothesis is proposed: The aggregation of pathogenic proteins intensifies with AD progression, then proteasome becomes more active and facilitates the UPS selectively targets the degradation of abnormal proteins to maintain CNS proteostasis. In this paper, bioinformatics and support vector machine learning methods are applied and combined with multivariate statistical analysis of microarray data. Additionally, the concept of entropy was used to detect the disorder of proteasome system, it was discovered that entropy is down-regulated continually with AD progression against system chaos caused by AD. Another conception of the matrix determinant was used to detect the global coordination of proteasome, it was discovered that the coordination is enhanced to maintain the efficiency of degradation. The features of entropy and determinant suggest that active proteasomes resist the attack caused by AD like defenders, on the one hand, to protect themselves (entropy reduces), and on the other hand, to fight the enemy (determinant reduces). It is noted that these are results from biocomputing and need to be supported by further biological experiments.

Advances in research on potential inhibitors of multiple myeloma

Multiple myeloma (MM) is a common hematological malignancy. Although recent clinical applications of immunomodulatory drugs, proteasome inhibitors and CD38-targeting antibodies have significantly improved the outcome of MM patient with increased survival, the incidence of drug resistance and severe treatment-related complications is gradually on the rise. This review article summarizes the characteristics and clinical investigations of several MM drugs in clinical trials, including their structures, mechanisms of action, structure-activity relationships, and clinical study progress. Furthermore, the application potentials of the drugs that have not yet entered clinical trials are also reviewed. The review also outlines the future directions of MM drug development.

Proteasome inhibition potentiates Kv1.3 potassium channel expression as therapeutic target in drug-sensitive and -resistant human melanoma cells

Primary and acquired therapy resistance is a major problem in patients with BRAF-mutant melanomas being treated with BRAF and MEK inhibitors (BRAFI, MEKi). Therefore, development of alternative therapy regimes is still required. In this regard, new drug combinations targeting different pathways to induce apoptosis could offer promising alternative approaches. Here, we investigated the combination of proteasome and Kv1.3 potassium channel inhibition on chemo-resistant, BRAF inhibitor-resistant as well as sensitive human melanoma cells. Our experiments demonstrated that all analyzed melanoma cell lines were sensitive to proteasome inhibitor treatment at concentrations that are not toxic to primary human fibroblasts. To further reduce proteasome inhibitor-associated side effects, and to foster apoptosis, potassium channels, which are other targets to induce pro-apoptotic effects in cancer cells, were blocked. In support, combined exposure of melanoma cells to proteasome and Kv1.3 channel inhibitor resulted in synergistic effects and significantly reduced cell viability. On the molecular level, enhanced apoptosis correlated with an increase of intracellular Kv1.3 channels and pro-apoptotic proteins such as Noxa and Bak and a reduction of anti-apoptotic proteins. Thus, use of combined therapeutic strategies triggering different apoptotic pathways may efficiently prevent the outgrowth of drug-resistant and -sensitive BRAF-mutant melanoma cells. In addition, this could be the basis for an alternative approach to treat other tumors expressing mutated BRAF such as non-small-cell lung cancer.

ADRB2 inhibition combined with antioxidant treatment alleviates lung fibrosis by attenuating TGFβ/SMAD signaling in lung fibroblasts

Idiopathic pulmonary fibrosis is a progressive and fatal interstitial lung disease with a poor prognosis and limited therapeutic options, which is characterized by aberrant myofibroblast activation and pathological remodeling of the extracellular matrix, while the mechanism remains elusive. In the present investigation, we observed a reduction in ADRB2 expression within both IPF and bleomycin-induced fibrotic lung samples, as well as in fibroblasts treated with TGF-β1. ADRB2 inhibition blunted bleomycin-induced lung fibrosis. Blockage of the ADRB2 suppressed proliferation, migration, and invasion and attenuated TGF-β1-induced fibroblast activation. Conversely, the enhancement of ADRB2 expression or functionality proved capable of inducing fibroblast-to-myofibroblast differentiation. Subsequent mechanistic investigation revealed that inhibition of ADRB2 suppressed the activation of SMAD2/3 in lung fibroblasts and increased phos-SMAD2/3 proteasome degradation, and vice versa. Finally, ADRB2 inhibition combined with antioxidants showed increased efficacy in the therapy of bleomycin-induced lung fibrosis. In short, these data indicate that ADRB2 is involved in lung fibroblast differentiation, and targeting ADRB2 could emerge as a promising and innovative therapeutic approach for pulmonary fibrosis.

Development and validation of a ubiquitin-proteasome system gene signature for prognostic prediction and immune microenvironment evaluation in hepatocellular carcinoma

BACKGROUND

The ubiquitin proteasome has a major role in the development of many tumors. However, the prognostic importance of ubiquitin proteasome-system genes (UPSGs) in hepatocellular carcinoma (HCC) is not fully defined.

METHODS

The TCGA and ICGC datasets were utilized to obtain transcriptional profiling data as well as clinicopathological information about HCC. The 3-UPSGs signature for the TCGA cohort was developed via univariate and LASSO Cox regression analyses. Differential expression of genes was demonstrated by qRT-PCR and immunohistochemistry (IHC). Biological pathways were studied using GSVA and GSEA. Six algorithms were used to compare immune infiltration between the two risk groups. Furthermore, drug sensitivity was measured using the "pRRophetic" R package. The predictive capacity of the 3-UPSGs signature for sensitivity to immunotherapy was also explored. Moreover, we performed a pan-cancer analysis of the 3-UPSGs signature.

RESULTS

A risk model containing 3 UPSGs (DCAF13, CDC20 and PSMB5) was developed. IHC and qRT-PCR results showed that signature genes were significantly overexpressed in HCC tissues. The high-risk group had a worse prognosis, with a higher clinicopathological grade, higher levels of tumor mutation burden (TMB), elevated levels of immune checkpoint (IC) expression, as well as increased sensitivity to immunotherapy. The two risk groups also differ in their sensitivity to chemotherapeutic drugs. Furthermore, the three UPSGs may play crucial roles in the progression of multiple types of cancers.

CONCLUSION

We created a 3-UPSGs signature to estimate the prognosis of HCC and to assist in individualized treatment.

Exploration of anti-stress mechanisms in high temperature exposed juvenile golden cuttlefish (Sepia esculenta) based on transcriptome profiling

Sepia esculenta is a cephalopod widely distributed in the Western Pacific Ocean, and there has been growing research interest due to its high economic and nutritional value. The limited anti-stress capacity of larvae renders challenges for their adaptation to high ambient temperatures. Exposure to high temperatures produces intense stress responses, thereby affecting survival, metabolism, immunity, and other life activities. Notably, the molecular mechanisms by which larval cuttlefish cope with high temperatures are not well understood. As such, in the present study, transcriptome sequencing of S. esculenta larvae was performed and 1,927 differentially expressed genes (DEGs) were identified. DEGs were subjected to functional enrichment analyses using the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The top 20 terms of biological processes in GO and 20 high-temperature stress-related pathways in KEGG functional enrichment analysis were identified. A protein-protein interaction network was constructed to investigate the interaction between temperature stress-related genes. A total of 30 key genes with a high degree of participation in KEGG signaling pathways or protein-protein interactions were identified and subsequently validated using quantitative RT-PCR. Through a comprehensive analysis of the protein-protein interaction network and KEGG signaling pathway, the functions of three hub genes (HSP90AA1, PSMD6, and PSMA5), which belong to the heat shock protein family and proteasome, were explored. The present results can facilitate further understanding of the mechanism of high temperature resistance in invertebrates and provide a reference for the S. esculenta industry in the context of global warming.

New trends in synthetic drugs and natural products targeting 20S proteasomes in cancers

Cancer is a global health challenge that remains to be a field of extensive research aiming to find new anticancer therapeutics. The 20S proteasome complex is one of the targets of anticancerdrugs, as it is correlated with several cancer types. Herein, we aim to discuss the 20S proteasome subunits and investigatethe currently studied proteasome inhibitors targeting the catalytically active proteasome subunits. In this review, we summarize the proteindegradation mechanism of the 20S proteasome complex and compareit with the 26S proteasome complex. Afterwards, the localization of the 20S proteasome is summarized as well as its use as a diagnosticandprognostic marker. The FDA-approved proteasome inhibitors (PIs) under clinical trials are summarized and their current limited use in solid tumors is also reviewed in addition to the expression of theβ5 subunit in differentcell lines. The review discusses in-silico analysis of the active subunit of the 20S proteasome complex. For development of new proteasome inhibitor drugs, the natural products inhibiting the 20S proteasome are summarized, as well as novel methodologies and challenges for the natural product discovery and current information about the biosynthetic gene clusters encoding them. We herein briefly summarize some resistancemechanismsto the proteasomeinhibitors. Additionally, we focus on the three main classes of proteasome inhibitors: 1] boronic acid, 2] beta-lactone and 3] epoxide inhibitor classes, as well as other PI classes, and their IC₅₀ values and their structure-activity relationship (SAR). Lastly,we summarize several future prospects of developing new proteasome inhibitors towards the treatment of tumors, especially solid tumors.

Recent Advances and Future Perspectives of Noncompetitive Proteasome Inhibitors

The proteasome regulates intracellular processes, maintains biological homeostasis, and has shown great significance in the study of various diseases, such as neurodegenerative diseases, immune-related diseases, and cancer, especially in hematologic malignancies such as multiple myeloma (MM) and mantle cell lymphoma (MCL). All clinically used proteasome inhibitors bind to the active site of the proteasome and thus exhibit a competitive mechanism. The development of resistance and intolerance during treatment drives the search for inhibitors with different mechanisms of action. In this review, we provide an overview of noncompetitive proteasome inhibitors, including their mechanisms of action, function, possible applications, and their advantages and disadvantages compared with competitive inhibitors.

Degradome-focused RNA interference screens to identify proteases important for breast cancer cell growth

Proteases are known to promote or impair breast cancer progression and metastasis. However, while a small number of the 588 human and 672 murine protease genes have been extensively studied, others were neglected. For an unbiased functional analysis of all genome-encoded proteases, i.e., the degradome, in breast cancer cell growth, we applied an inducible RNA interference library for protease-focused genetic screens. Importantly, these functional screens were performed in two phenotypically different murine breast cancer cell lines, including one stem cell-like cell line that showed phenotypic plasticity under changed nutrient and oxygen availability. Our unbiased genetic screens identified 252 protease genes involved in breast cancer cell growth that were further restricted to 100 hits by a selection process. Many of those hits were supported by literature, but some proteases were novel in their functional link to breast cancer. Interestingly, we discovered that the environmental conditions influence the degree of breast cancer cell dependency on certain proteases. For example, breast cancer stem cell-like cells were less susceptible to depletion of several mitochondrial proteases in hypoxic conditions. From the 100 hits, nine proteases were functionally validated in murine breast cancer cell lines using individual knockdown constructs, highlighting the high reliability of our screens. Specifically, we focused on mitochondrial processing peptidase (MPP) subunits alpha (Pmpca) and beta (Pmpcb) and discovered that MPP depletion led to a disadvantage in cell growth, which was linked to mitochondrial dysfunction.

PKR Protects the Major Catalytic Subunit of PKA Cpk1 from FgBlm10-Mediated Proteasome Degradation in Fusarium graminearum

For optimal proteolytic function, the proteasome core (CP or 20S) must associate with activators. The cAMP-PKA pathway is reported to affect the activity of the proteasome in humans. However, the relationship between the proteasome and PKA is not well characterized. Our results showed that the major catalytic subunit Cpk1 was degraded without the protection of Pkr. Eleven (out of 67) pkr suppressors had FgBlm10 C-terminal truncation, one suppressor had an amino acid change mutation in the PRE6 ortholog (FGRRES_07282), and one in the PRE5 ortholog (FGRRES_05222). These mutations rescued the defects in growth and conidial morphology, Cpk1 stability, and PKA activities in the pkr mutant. The interaction of FgBlm10 with FgPre5 and FgPre6 were detected by co-immunoprecipitation, and the essential elements for their interaction were characterized, including the FgBlm10 C-terminus, amino acid D82 of FgPre6 and K62 of FgPre5. Additional FgBlm10-interacting proteins were identified in the wild type and pkr mutant, suggesting that PKA regulates the preference of FgBlm10-mediated proteasome assembly. In addition, PKA indirectly affected the phosphorylation of FgBlm10, and its localization in the nucleus. The truncation of the FgBlm10 C terminus also enhanced nuclear import and bleomycin resistance, suggesting its role in proteasome assembly at DNA damage sites. Collectively, our data demonstrated that regulation between PKA and proteasome degradation is critical for the vegetative growth of F. graminearum.

Metformin Induces Resistance of Cancer Cells to the Proteasome Inhibitor Bortezomib

The anti-diabetic drug metformin is currently tested for the treatment of hematological and solid cancers. Proteasome inhibitors, e.g., Bortezomib, are approved for the treatment of multiple myeloma and mantle cell lymphoma but are also studied for lung cancer therapy. We here analyzed the interaction of the two drugs in two cell lines, namely the mantle cell lymphoma Jeko-1 and the non-small-cell lung cancer (NSCLC) H1299 cells, using proliferation and survival assays, native-gel analysis for proteasome activity and assembly, and expression analysis of proteasome assembly factors. Our results demonstrate that metformin treatment induces resistance of cancer cells to the proteasome inhibitor Bortezomib by impairing the activity and assembly of the 26S proteasome complexes. These effects of metformin on proteasome inhibitor sensitivity in cancer cells are of potential relevance for patients that receive proteasome inhibitor therapy.

Indirubin-3'-monoxime acts as proteasome inhibitor: Therapeutic application in multiple myeloma

BACKGROUND

Multiple myeloma (MM) is still an incurable malignancy of plasma cells. Proteasome inhibitors (PIs) work as the backbone agent and have greatly improved the outcome in majority of newly diagnosed patients with myeloma. However, drug resistance remains the major obstacle causing treatment failure in clinical practice. Here, we investigated the effects of Indirubin-3'-monoxime (I3MO), one of the derivatives of Indirubin, in the treatment of MM.

METHODS

MM patient primary samples and human cell lines were examined. I3MO effects on myeloma treatment and the underling molecular mechanisms were investigated via in vivo and in vitro study.

FINDINGS

Our results demonstrated the anti-MM activity of I3MO in both drug- sensitive and -resistance MM cells. I3MO sensitizes MM cells to bortezomib-induced apoptosis. Mechanistically, I3MO acts as a multifaceted regulator of cell death, which induced DNA damage, cell cycle arrest, and abrogates NF-κB activation. I3MO efficiently down-regulated USP7 expression, promoted NEK2 degradation, and suppressed NF-κB signaling in MM. Our study reported that I3MO directly bound with and caused the down-regulation of PA28γ (PSME3), and PA200 (PSME4), the proteasome activators. Knockdown of PSME3 or PSME4 caused the inhibition of proteasome capacity and the overload of paraprotein, which sensitizes MM cells to bortezomib-mediated growth arrest. Clinical data demonstrated that PSME3 and PSME4 are over-expressed in relapsed/refractory MM (RRMM) and associated with inferior outcome.

INTERPRETATION

Altogether, our study indicates that I3MO is agent triggering proteasome inhibition and represents a promising therapeutic strategy to improve patient outcome in MM.

FUNDINGS

A full list of funding can be found in the acknowledgements.

A Redox-Silent Analogue of Tocotrienol May Break the Homeostasis of Proteasomes in Human Malignant Mesothelioma Cells by Inhibiting STAT3 and NRF1

6-O-Carboxypropyl-alpha-tocotrienol (α-T3E) is a multi-target redox-silent analogue of tocotrienol that exhibits cytotoxicity against many cancer cells, including malignant mesothelioma (MM) cells. α-T3E has several molecular targets to effectively induce cytotoxicity against MM cells; however, the mechanisms underlying this cytotoxicity remain unclear. In the present study, we demonstrated that the α-T3E-dependent disruption of the homeostasis of proteasomes strongly induced endoplasmic reticulum (ER) stress, which resulted in effective cytotoxicity against MM cells. The α-T3E-dependent disruption of the homeostasis of proteasomes depended on decreases in proteasome subunits via the inactivation of signal transducer and activator of transcription 3 (STAT3) and nuclear factor erythroid 2 related factor-1 (NRF1), which inhibited protease activity, such as chymotrypsin-like activity, in proteasomes. The α-T3E-dependent inhibition of this activity also induced severe ER stress and ultimately resulted in effective cytotoxicity against MM cells with chemoresistance. The present results indicate that α-T3E acts as an effective anti-mesothelioma agent by disrupting the homeostasis of proteasomes through the simultaneous inactivation of STAT3 and NRF1.

Immuno-oncological role of 20S proteasome alpha-subunit 3 in aggravating the progression of esophageal squamous cell carcinoma

PSMA3, a member of the proteasome subunit, has been shown to play a major player in protein degradation. Reportedly, PSMA3 functions as a negative regulator in various cancers including colon, pancreatic and gastric cancers. However, the contributions of PSMA3 to the progression of esophageal squamous cell carcinoma (ESCC) and the underlying mechanism remain unclear. Therefore, in this study, we investigated whether PSMA3 is involved in ESCC progression and the potential underlying mechanism. The results revealed that PSMA3 was highly expressed in the ESCC tumor tissues and functioned as a negative indicator according to the data from The Cancer Genome Atlas (TCGA)/Gene Expression Omnibus (GEO) datasets and clinical patients' samples. Pathway enrichment analysis showed that PSMA3 was closely correlated with ESCC cancer stemness and the inflammatory response; however, this correlation was absent after knockdown of PSMA3 in vitro. We further demonstrated that PSMA3 suppressed CD8⁺ T-cells infiltration depending on the C-C motif chemokine ligand 3 (CCL3)/C-C motif chemokine receptor 5 (CCR5) axis. Collectively, these results demonstrate the role of PSMA3 in ESCC cancer stemness and the negative regulation of CD8 T-cells infiltration mediated by PSMA3. The results of this study may provide a potential target for the immuno-oncology effect of PSMA3 in ESCC therapy.

At the Cutting Edge against Cancer: A Perspective on Immunoproteasome and Immune Checkpoints Modulation as a Potential Therapeutic Intervention

Immunoproteasome is a noncanonical form of proteasome with enzymological properties optimized for the generation of antigenic peptides presented in complex with class I MHC molecules. This enzymatic property makes the modulation of its activity a promising area of research. Nevertheless, immunotherapy has emerged as a front-line treatment of advanced/metastatic tumors providing outstanding improvement of life expectancy, even though not all patients achieve a long-lasting clinical benefit. To enhance the efficacy of the currently available immunotherapies and enable the development of new strategies, a broader knowledge of the dynamics of antigen repertoire processing by cancer cells is needed. Therefore, a better understanding of the role of immunoproteasome in antigen processing and of the therapeutic implication of its modulation is mandatory. Studies on the potential crosstalk between proteasome modulators and immune checkpoint inhibitors could provide novel perspectives and an unexplored treatment option for a variety of cancers.

Activation of immune cell proteasomes in peripheral blood of smokers and COPD patients - implications for therapy

Immune cells contain a specialised type of proteasome, i.e. the immunoproteasome, which is required for intracellular protein degradation. Immunoproteasomes are key regulators of immune cell differentiation, inflammatory activation and autoimmunity. Immunoproteasome function in peripheral immune cells might be altered by smoking and in COPD thereby affecting immune cell responses.We here analysed the expression and activity of proteasome complexes in peripheral blood mononuclear cells (PBMC) isolated from healthy male young smokers as well as from patients with severe COPD and compared them to matching controls. Proteasome expression was upregulated in COPD patients as assessed by RT-qPCR and mass spectrometry-based proteomics analysis. Proteasome activity was quantified using activity-based probes and native gel analysis. We observed distinct activation of immunoproteasomes in the peripheral blood cells of young male smokers and severely ill COPD patients. Native gel analysis and linear regression modeling confirmed robust activation and elevated assembly of 20S proteasomes, which correlated significantly with reduced lung function parameters in COPD patients. The immunoproteasome was distinctly activated in COPD patients upon inflammatory cytokine stimulation of PBMCs in vitro Inhibition of the immunoproteasome reduced proinflammatory cytokine expression in COPD-derived blood immune cells.Given the crucial role of chronic inflammatory signalling and the emerging involvement of autoimmune responses in COPD, therapeutic targeting of the immunoproteasome might represent a novel therapeutic concept for COPD.

Mitochondrial Regulation of the 26S Proteasome

The proteasome is the main proteolytic system for targeted protein degradation in the cell and is fine-tuned according to cellular needs. Here, we demonstrate that mitochondrial dysfunction and concomitant metabolic reprogramming of the tricarboxylic acid (TCA) cycle reduce the assembly and activity of the 26S proteasome. Both mitochondrial mutations in respiratory complex I and treatment with the anti-diabetic drug metformin impair 26S proteasome activity. Defective 26S assembly is reversible and can be overcome by supplementation of aspartate or pyruvate. This metabolic regulation of 26S activity involves specific regulation of proteasome assembly factors via the mTORC1 pathway. Of note, reducing 26S activity by metformin confers increased resistance toward the proteasome inhibitor bortezomib, which is reversible upon pyruvate supplementation. Our study uncovers unexpected consequences of defective mitochondrial metabolism for proteasomal protein degradation in the cell, which has important pathophysiological and therapeutic implications.

In-gel proteasome assay to determine the activity, amount, and composition of proteasome complexes from mammalian cells or tissues

This protocol describes an easy and reliable in-gel proteasome assay to quantify the activity and composition of different proteasome complexes in cells and tissues. The assay works well with limited amounts of total cell protein lysates. Although this assay is optimized specifically for the proteasome chymotrypsin-like activity, it can be expanded to other proteasome activities as well. Using antibodies that detect distinct proteasome subunits or regulators, we can determine the composition and relative quantity of active proteasome complexes.

For complete details on the use and execution of this protocol, please refer to Meul et al. (2020).

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Maintain the activity of proteasome complexes by nondenaturing conditions

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Quantify the specific activities of each proteasome complex

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Determine the subunits and the bound regulators of proteasome complexes

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Analyze the relative distribution of proteasome complexes upon treatments

Proteomic analysis of body wall and coelomic fluid in Sipunculus nudus

In order to make clear the protein compositions of Sipunculus nudus and investigate its immune-related proteins, proteomic analysis was performed on body wall and coelomic fluid of Sipunculus nudus. A total of 1659 proteins were identified, and 539 proteins were differentially expressed in the coelomic fluid compared to those in the body wall, of which 415 proteins were up-regulated while 124 proteins were down-regulated. Gene Ontology (GO) analysis showed that the GO terms involved in the two parts of Sipunculus nudus were similar, with metabolic processes, catalytic activity and cell occupying the top categories of biological process, molecular function and cellular component, respectively. KEGG pathway analysis showed that 49 pathways in body wall and 48 in coelomic fluid were mapped respectively, and these pathways were mainly related to cellular processes, environmental information processing, genetic information processing and metabolism. The COG analysis showed that 757 proteins from body wall and 889 from coelomic fluid were classified into 26 COG categories, respectively. Pfam annotation revealed the mainly immune-related proteins contained in Sipunculus nudus, such as insulin-like growth factor binding protein, catalase, basement membrane proteoglycan, titin. Our research provides the first proteomic information of Sipunculus nudus, which contributes to the study of functional proteins in Sipunculus nudus and is of great significance for the application of Sipunculus nudus in functional foods and medicines.

Antitumor Effect of Inula viscosa Extracts on DMBA-Induced Skin Carcinoma Are Mediated by Proteasome Inhibition

The aim of this work is to evaluate the antitumor effect mediated by the proteasome inhibitors of Inula viscosa extracts on skin carcinogenesis. Female Swiss albino mice were divided into five groups depending on the combination of skin cancer-inducing 7,12-dimethylbenz(a)anthracene (DMBA) and extract of Inula viscosa treatments. Histology of the affected skin and measurement of proteasome activity were performed to demonstrate the effect of Inula viscosa on mice. The identification of the molecules responsible for this inhibitory activity was carried out through the docking studies. The results showed that Inula viscosa extracts inhibit the development of papilloma in mice. Therefore, the best chemopreventive action of Inula viscosa was observed on mice in which extract treatment was performed before and after the induction of skin carcinogenesis. It was revealed that the ingestion of extracts Inula viscosa delays the formation of skin papillomas in animals and simultaneously decreases the size and number of papillomas, which is also reflected on the skin histology of the mice treated. Structure-activity relationship information obtained from component of Inula viscosa particularly tomentosin, inuviscolide, and isocosticacid demonstrated that distinct bonding modes in β ₁, β ₂, and β ₅ subunits determine its selectivity and potent inhibition for β ₅ subunit.