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Adams JThe proteasome: a suitable antineoplastic target. Nat Rev Cancer 4:349-360
Abstract
The proteasome is an abundant multi-enzyme complex that provides the main pathway for degradation of intracellular proteins in eukaryotic cells. As such, it controls the levels of proteins that are important for cell-cycle progression and apoptosis in normal and malignant cells; for example, cyclins, caspases, BCL2 and nuclear factor of κB. A proteasome inhibitor — bortezomib — has been developed that has shown efficacy as an anticancer agent in the clinic. How can targeting such a universal, broadly active cellular component provide the selectivity and specificity that are required for cancer therapeutics?
... [22] Some of these proteins are related to cell cycle progression, DNA repair, and transcription, such as cyclins, p53, caspases, BCL2, and NF-kB members, which are involved in apoptosis. [23] Leukemia cells are highly dependent on this proteolytic pathway, since uninterrupted proliferation results in increased protein synthesis, requiring protein degradation for homeostasis maintenance. This explains the higher sensitivity of cancer cells to proteasome inhibition, [24] and its validation as a target for leukemia and other hematological disorders. ...
... The proteasome is constituted by the 20S proteasome, which contains α and β subunits forming regulatory and enzymatic units. [23] Its function is to identify proteins previously tagged with ubiquitin and then perform its chymotrypsin-like activity to degrade these pro-growth proteins. [21] It is well established that the inhibition of the chymotrypsin-like activity of the 20S proteasome relates to the induction of cancer cell apoptosis, thus supporting its consolidation as an anti-cancer strategy. ...
... [10] The 20S proteasome is responsible for the degradation of the IkB protein (an inhibitor of NF-kB signaling), which activates this pathway. [23] Therefore, inhibition of the proteasome by 8HQ molecules may lead to disruption of NF-kB signalling due to increased IkB. This correlation implies that all proteasome inhibitors are also NF-kB inhibitors and ultimately induce apoptosis. ...
8‐Hydroxyquinoline and its derivatives consist of a group of metal‐binding ligands capable of reaching complexes that present several biological activities. In the present study, we collate and discuss data regarding the antileukemia activities of 8‐hydroxyquinoline (8HQ) compounds to provide an overview of their mechanisms of actions, and a compilation of cytotoxicity data against diverse leukemia cell lines. The pharmacological activities of this class of agents are associated primarily with their ability to coordinate metals and interact with multiple biological targets. We found consistent evidence that 8HQ exerts promising proapoptotic features through its direct interaction with deoxyribonucleic acid (DNA) and inhibition of multiple targets, such as the proteasome, nuclear factor kappa B (NF‐κB), histone deacetylase (HDAC), bromodomain and extra terminal (BET) proteins and janus kinases (JAKs), in addition to inducing autophagy associated cell death. Thus, we provide substantial evidence for the repositioning potential of the 8HQ class for the treatment of leukemia, a hematological malignancy for which urgent advances in therapeutic approaches are needed to overcome conventional therapy limitations.
... This system includes hundreds of components that target proteins for degradation [6]. The proteasome is localized in the nucleus and cytoplasm of eukaryotic cells, although its subcellular distribution varies from one organ to another [7]. Because the ubiquitin-proteasome system interferes with various cellular metabolic processes, deregulation of these components can cause many diseases, including neurodegenerative diseases, certain cancers, and autoimmune diseases [8,9]. ...
... The relationship between clinical condition and concentration of the proteasome has been reported in several diseases, particularly in patients with systemic lupus erythematosus, rheumatoid arthritis [15] and also in the case of solid tumors and blood cancers [16,17]. In 2004, Adams reported that the rapid and large storage misfolded proteins and/or mutant is certainly the origin of the dependence of malignant cells onan active intracellular proteasome [7]. Indeed, Matondo in 2010 showed that the most immature cells (KG1a) possess a greater amount of proteasome than the more mature cells (U937). ...
... This system includes hundreds of components that target proteins for degradation [6]. The proteasome is localized in the nucleus and cytoplasm of eukaryotic cells, although its subcellular distribution varies from one organ to another [7]. Because the ubiquitin-proteasome system interferes with various cellular metabolic processes, deregulation of these components can cause many diseases, including neurodegenerative diseases, certain cancers, and autoimmune diseases [8,9]. ...
... The relationship between clinical condition and concentration of the proteasome has been reported in several diseases, particularly in patients with systemic lupus erythematosus, rheumatoid arthritis [15] and also in the case of solid tumors and blood cancers [16,17]. In 2004, Adams reported that the rapid and large storage misfolded proteins and/or mutant is certainly the origin of the dependence of malignant cells onan active intracellular proteasome [7]. Indeed, Matondo in 2010 showed that the most immature cells (KG1a) possess a greater amount of proteasome than the more mature cells (U937). ...
Background:
Regulatory degradation of intracellular proteins plays an essential role in most biological processes, particularly in the control of cell proliferation and differentiation. In eukaryotes, intracellular proteolysis is largely provided by the Ubiquitin / Proteasome system. Alterations and dysfunction of protein degradation by the Ubiquitin / Proteasome system, such as transcription factors, cell cycle regulators or tumor suppressor proteins, have been linked to human. Pathologies, including blood cancers. Mainly localized in the nucleus and cytoplasm of cells, the proteasome can be detected in the cell culture supernatant or in the peripheral blood of patients. This study deals with the problems of the search for serum markers specific to certain pathologies and which would be useful in the prevention, diagnosis and monitoring of cancers and which could be used as a therapeutic tool.
Methods:
The functional and quantitative analysis of the proteasome is carried out at the serum and subcellular level during a pathological phenomenon in a population of 145 Moroccan patients (sex ratio: 1.10 / average age: 47.9 ± 15, 3 years) using an indirect ELISA test and a follow-up of the fluorescence emitted after enzymatic digestion of specific peptides by proteolytic activity (chymotrypsin-like).
Results:
The evolutionary trend proteasome subcellular is significantly linked to the rate of chymotrypsin-like activity. The entire population of 60 patients called back for a second blood test. After three months of treatment reported a significant drop in the rate and the activity of the proteasome in serum and intracellular level.
Conclusions:
Although the serum proteasome level is a potential new tool for the monitoring of. Patientswithliquid cancer.
Trial registration:
retrospectively registered.
... In the 2000s, proteasome inhibitors helped revolutionize MM treatment by targeting the proteostasis of the malignant plasma cells. Proteasome inhibitors (PIs) achieve this by blocking the disposal of protein byproducts produced during sustained antibody synthesis (1,2). Efforts to inhibit other facets of the degradation pathways of protein homeostasis have shown preclinical potential (3,4,5). ...
Protein homeostasis is critical to the survival of multiple myeloma (MM) cells. While this is targeted with proteasome inhibitors, mRNA translation inhibition has not entered trials. Recent work illustrates broad sensitivity MM cells to translation inhibitor omacetaxine. We hypothesized that understanding how MM cells become omacetaxine resistant will lead to the development of drug combinations to prevent or delay relapse. We generated omacetaxine resistance in H929 and MM1S MM cell lines and compared them to their parental lines. Resistant lines displayed decreased sensitivity to omacetaxine, with EC50 > 100 nM, compared to parental line sensitivity of 24-54 nM. To adapt to omacetaxine, H929 and MM1S exhibited an increased percentage of multi-nucleated polyaneuploid cells that led to distinct molecular mechanisms of resistance. Interestingly, both resistant lines showed a defect in oncologic potential via extended survival in a MM xenograft model. Since omacetaxine inhibits protein synthesis, we performed both RNA-sequencing and ribosome profiling (Ribo-seq) to identify shared and unique regulatory strategies of resistance. Transcripts encoding translation factors and containing Terminal OligoPyrimidine (TOP) motifs in their 5' UTR were translationally upregulated in both resistant cell lines. The mTOR pathway promotes the translation of TOP motif containing mRNAs. Indeed, mTOR inhibition restored partial sensitivity to omacetaxine in both resistant cell lines. Primary MM cells from patient samples were sensitive to combinations of omacetaxine and mTOR inhibitors rapamycin and Torin 1. These results provide a rational approach for omacetaxine-based combination in patients with multiple myeloma, which have historically shown better responses to
multi-agent regimens.
... (15,26,27,44,45) We had hoped to observe limited BRD4 degradation which could be attributed to lower Rpn-13 expression Excitingly, we were able to see dramatically reduced to no BRD4 degradation with our best degraders, Figure 4 and S5. We hypothesize that BRD4 is not degraded using our methodology as HEK-293T cells could have lower expression of Rpn-13 or 26S proteasomes in HEK-293T cells have less Rpn-13 associated with their 19S RP. (46) Additional studies are required to validate this hypothesis, but these results indicate we should able to obtain a significant therapeutic window between cells that are highly dependent on Rpn-13 complexed to the 26S proteasome and the healthy cell population. (24,45,47) Thus far, we have been able to demonstrate the ByeTAC degrader series can initiate the destruction of BRD4 in cells that rely on Rpn-13 highly for survival, the degradation is proteasome dependent, and both binding moieties are required to target the POI to the 26S proteasome for degradation. ...
Targeted protein degradation utilizing a bifunctional molecule to initiate ubiquitination and subsequent degradation by the 26S proteasome has been shown to be a powerful therapeutic intervention. Many bifunctional molecules, including covalent and non-covalent ligands to proteins of interest, have been developed. The traditional target protein degradation methodology targets the protein of interest in both healthy and diseased cell populations, and a therapeutic window is obtained based on the overexpression of the targeted protein. We report here a series of bifunctional degraders that do not rely on interacting with an E3 ligase, but rather a 26S proteasome subunit, which we have named ByeTACs: Bypassing E3 Targeting Chimeras. Rpn-13 is a non-essential ubiquitin receptor for the 26S proteasome. Cells under significant stress or require significant ubiquitin-dependent degradation of proteins for survival, incorporate Rpn-13 in the 26S to increase protein degradation rates. The targeted protein degraders reported here are bifunctional molecules that include a ligand to Rpn-13 and BRD4, the protein of interest we wish to degrade. We synthesized a suite of degraders with varying PEG chain lengths and showed that bifunctional molecules that incorporate a Rpn-13 binder (TCL1) and a BRD4 binder (JQ1) with a PEG linker of 3 or 4 units are the most effective to induce BRD4 degradation. We also demonstrate that our new targeted protein degraders are dependent upon proteasome activity and Rpn-13 expression levels. This establishes a new mechanism of action for our ByeTACs that can be employed for the targeted degradation of a wide variety of protein substrates.
... Clinical studies have shown that bortezomib, the 26S proteasome inhibitor, has emerged as a targeted drug in certain malignant proliferative diseases, such as multiple myeloma. This encouraging success suggests that drugs acting on UPS-related targets are also prospective in the treatment of BC and may even help to overcome BC resistance to chemotherapy and immunotherapy [8,36]. However, BC biomarkers associated with UPS-related genes remain blank in the existing literature. ...
The ubiquitin–proteasome system (UPS) is an essential regulatory system for maintaining homeostasis, and its dysfunction may cause various diseases. The activity of proteasome and ubiquitin-conjugating enzymes has been found to be greatly increased in breast cancer (BC), indicating that the heterogeneity of UPS may be related to the progression of BC. Gene data was obtained from The Cancer Genome Atlas and Gene Expression Omnibus databases and performed in multiple algorithms to construct a UPS-related signature for BC. Patients in the UPS low-risk group had greater overall and recurrence-free survival probability than those in the UPS high-risk group. This signature was closely associated with functional enrichment. Some high metabolism-related pathways were more active in the UPS high-risk group. The UPS low-risk group had more abundant anti-tumor immune cells, while in the UPS high-risk group, immunosuppressive cells were dominant. More importantly, we found that the UPS low-risk group was more sensitive to immunotherapy, while the UPS high-risk group responded better to radiotherapy. Drug sensitivity analysis identified more effective chemotherapy drugs in different UPS-related risk groups. This UPS-related signature may serve as a novel biomarker and independent prognostic factor for BC. It can effectively predict prognosis, immune infiltration, and therapy efficacy, providing new strategies for individualized treatment.
... The UPS, an extensively regulated complex of multiple enzymes, plays a crucial role in maintaining protein homeostasis. It has garnered significant attention as a promising therapeutic target against tumors [19]. It functions through the 19S regulatory complex and the 20S core complex. ...
This work intends to examine the diagnostic, prognostic, and biological roles of PSMD1 (proteasome 26S subunit, non-ATPase 1) in liver hepatocellular carcinoma (LIHC) and other malignancies, using bioinformatics techniques. PSMD1 is an innate immune gene that has been identified as a biomarker for several cancers. By analyzing TCGA data, we determined that PSMD1 has excellent diagnostic and prognostic value in LIHC. We also examined its correlation with stage-matching clinical features, particularly T staging and stage staging. Independent prognostic analysis, nomogram, and Decision Curve Analysis (DCA) analysis confirmed the predictive ability of PSMD1 on patient clinical outcomes. Our focus was on exploring the biological process, immune infiltration, and genetic variation in which PSMD1 is involved in LIHC. We found a close relationship between PSMD1 and the tumor microenvironment (TME), as well as various immune cell infiltration, immune function, and immune checkpoints. Furthermore, our results suggested that liver cancer patients with low PSMD1 expression were more actively responsive to immunotherapy according to TIDE predictions. Additionally, we observed significant differences in patient survival based on the different immune molecular types of tumors and their correlation with PSMD1 expression. The close relationship between PSMD1 and copy number variation (CNV), tumor mutational burden (TMB), and methylation was also confirmed, showing a significant impact on patient survival. Moreover, the pan-cancer analysis revealed that PSMD1 is closely related to the diagnosis and prognosis of various cancers, as well as immune infiltration across different cancer types. In summary, PSMD1 has the potential to be a useful diagnostic and prognostic biomarker for LIHC and other types of cancers. It is closely associated with indicators such as immune infiltration, CNV, TMB, and methylation. The identification of PSMD1 may offer a potential intervention target for LIHC and various cancers.
... To overcome this, plasma cells, a main site of autoantibody synthesis, can be affected from "inside" . This strategy is currently realized with the use of proteasome inhibitors, a class of drug which is able to stop the proteasome activity that results in accumulation of defective immunoglobulin chains, misfolded proteins, overflow of the endocytoplasmatic reticulum and directly leads to plasma cell apoptosis [114][115][116]. ...
Citation: Lastname, F.; Lastname, F.; Last-name, F. Title. Phar-maceuticals 2022, 15, x. https://doi.org/10.3390/xxxxx Academic Editor: Firstname Lastname Received: date Accepted: date Published: date Publisher’s Note: MDPI stays neutral with regard to jurisdic-tional claims in pub-lished maps and insti-tutional affiliations. Copyright: © 2023 by the authors. Submitted for possible open access publication under the terms and conditions of the Creative Commons 1Olga Gumkowska-Sroka, 2Kacper Kotyla, 3Ewa Mojs, 2Klaudia Palka, 1,2*Przemysław Kotyla 1. Department of Rheumatology and Clinical Immunology Voivodeship Hospital No5 in Sosnowiec Medical University of Silesia Katowice, Poland 2. Department of Internal Medicine Rheumatology and Clinical Immunology Medical University of Silesia Katowice , Poland 3. 3. Department of Clinical Psychology, Poznan University of Medical Sciences Poznan, Poland *Correspondence: Prof Przemysław Kotyla Department of Internal Medicine Rheumatology and Clinical Immunology Medical University of Silesia, Katowice, Poland- Summary Systemic sclerosis is a connective tissue disease of unknown origin and unpredictable course, with both cutaneous and internal organ manifestations. In spite of enormous progress in rheumatology and clinical immunology, the background of diseases is largely unknown and no specific therapy exists. The therapeutic approach to the disease is aimed to treat and preserve the function of internal organs, and this approach is commonly referred to as an organ-based treatment. However, in modern times data from the other branches of medicine may help to treat disease-related complications, making it possible to find a group of drugs to be utilized in the treatment of the disease. In this review, we present possible therapeutic options aiming to stop the progression of fibrotic processes, restore aberrant immune response, stop improper signalling from proinflammatory cytokines, and halt the production of disease-related autoantibodies.
... To overcome this, plasma cells, a main site of autoantibody synthesis, can be affected from "inside". This strategy is currently being realized with the use of proteasome inhibitors, a class of drug which is able to stop the proteasome activity that results in the accumulation of defective immunoglobulin chains, misfolded proteins, and the overflow of the endocytoplasmatic reticulum and directly leads to plasma-cell apoptosis [127][128][129]. ...
Systemic sclerosis is a connective tissue disease of unknown origin and with an unpredictable course, with both cutaneous and internal organ manifestations. Despite the enormous progress in rheumatology and clinical immunology, the background of this disease is largely unknown, and no specific therapy exists. The therapeutic approach aims to treat and preserve the function of internal organs, and this approach is commonly referred to as organ-based treatment. However, in modern times, data from other branches of medicine may offer insight into how to treat disease-related complications, making it possible to find new drugs to treat this disease. In this review, we present therapeutic options aiming to stop the progression of fibrotic processes, restore the aberrant immune response, stop improper signalling from proinflammatory cytokines, and halt the production of disease-related autoantibodies.
... 6 One type of proteosome, the 26S proteasome, consists of a cylindrical 20S complex and one or two regulatory 19S complexes. 7,8 The 20S core is constructed from inner α-rings and outer β-rings, which are both divided into 7 structurally similar subunits: proteasome 20S subunit α (PSMA1-7) and β (PSMB1-7). The 19S cap complex is composed of a base and a lid subcomplex, which are further categorized into ATPase subunits (PSMC1-6) and non-ATPase subunits (PSMD1-14). ...
Aims
PSMD family members, as important components of the 26S proteasome, are well known to be involved in protein degradation. However, their role in glioblastoma (GBM) has not been rigorously investigated. We aimed to perform systematic analysis of the expression signature, prognostic significance and functions of PSMD family genes in GBM to reveal potential prognostic markers and new therapeutic targets among PSMD family members.
Methods
In this study, we systemically analyzed PSMD family members in terms of their expression profiles, prognostic implications, DNA methylation levels, and genetic alterations; the relationships between their expression levels and immune infiltration and drug sensitivity; and their potential functional enrichment in GBM through bioinformatics assessment. Moreover, in vitro and in vivo experiments were used to validate the biological functions of PSMD9 and its targeted therapeutic effect in GBM.
Results
The mRNA levels of PSMD5/8/9/10/11/13/14 were higher in GBM than in normal brain tissues, and the mRNA levels of PSMD1/4/5/8/9/11/12 were higher in high‐grade glioma (WHO grade III & IV) than in low‐grade glioma (WHO grade II). High mRNA expression of PSMD2/6/8/9/12/13/14 and low mRNA expression of PSMD7 were associated with poor overall survival (OS). Multivariate Cox regression analysis identified PSMD2/5/6/8/9/10/11/12 as independent prognostic factors for OS prediction. In addition, the protein–protein interaction network and gene set enrichment analysis results suggested that PSMD family members and their interacting molecules were involved in the regulation of the cell cycle, cell invasion and migration, and other biological processes in GBM. In addition, knockdown of PSMD9 inhibited cell proliferation, invasion and migration and induced G2/M cell cycle arrest in LN229 and A172 GBM cells. Moreover, PSMD9 promoted the malignant progression of GBM in vivo. GBM cell lines with high PSMD9 expression were more resistant to panobinostat, a potent deacetylase inhibitor, than those with low PSMD9 expression. In vitro and in vivo experiments further validated that PSMD9 overexpression rescued the GBM inhibitory effect of panobinostat.
Conclusion
This study provides new insights into the value of the PSMD family in human GBM diagnosis and prognosis evaluation, and we further identified PSMD9 as a potential therapeutic target. These findings may lead to the development of effective therapeutic strategies for GBM.
... To decipher how PRMT1 regulates c-Fos stability, we used the protein degradation inhibitors MG132 (a proteasomal degradation inhibitor) and 3-MA (an autophagy inhibitor). Proteasomal degradation and autophagy are the two main mechanisms of protein degradation [63,64]. The addition of 3-MA enhanced PRMT1-mediated c-Fos/AP-1 activity, whereas MG132 inhibited AP1 activity (Fig. 4A). ...
Both AP-1 and PRMT1 are vital molecules in variety of cellular progresssion, but the interaction between these proteins in the context of cellular functions is less clear. Gastric cancer (GC) is one of the pernicious diseases worldwide. An in-depth understanding of the molecular mode of action underlying gastric tumorigenesis is still elusive. In this study, we found that PRMT1 directly interacts with c-Fos and enhances AP-1 activation. PRMT1-mediated arginine methylation (mono- and dimethylation) of c-Fos synergistically enhances c-Fos-mediated AP-1 liveliness and consequently increases c-Fos protein stabilization. Consistent with this finding, PRMT1 knockdown decreases the protein level of c-Fos. We discovered that the c-Fos protein undergoes autophagic degradation and found that PRMT1-mediated methylation at R287 protects c-Fos from autophagosomal degradation and is linked to clinicopathologic variables as well as prognosis in stomach tumor. Together, our data demonstrate that PRMT1-mediated c-Fos protein stabilization promotes gastric tumorigenesis. We contend that targeting this modification could constitute a new therapeutic strategy in gastric cancer.
... These small molecule inhibitors have shown potential in preclinical studies and earlyphase clinical trials, with some, like bortezomib, already approved for specific clinical indications [132,133]. However, their safety profiles and potential side effects, which may include gastrointestinal symptoms, fatigue, hematological toxicities, and hepatotoxicity, need to be carefully evaluated. ...
Oxidative stress (OS) arises as a consequence of an imbalance between the formation of reactive oxygen species (ROS) and the capacity of antioxidant defense mechanisms to neutralize them. Excessive ROS production can lead to the damage of critical biomolecules, such as lipids, proteins, and DNA, ultimately contributing to the onset and progression of a multitude of diseases, including atherosclerosis, chronic obstructive pulmonary disease, Alzheimer’s disease, and cancer. Cylindromatosis (CYLD), initially identified as a gene linked to familial cylindromatosis, has a well-established and increasingly well-characterized function in tumor inhibition and anti-inflammatory processes. Nevertheless, burgeoning evidence suggests that CYLD, as a conserved deubiquitination enzyme, also plays a pivotal role in various key signaling pathways and is implicated in the pathogenesis of numerous diseases driven by oxidative stress. In this review, we systematically examine the current research on the function and pathogenesis of CYLD in diseases instigated by oxidative stress. Therapeutic interventions targeting CYLD may hold significant promise for the treatment and management of oxidative stress-induced human diseases.
... with a length of 4,013 bp. 69 Studies have shown that USP7 mRNA and protein levels were significantly increased in HCC cells compared to adjacent nontumor tissues. Pathologically, USP7 expression was positively correlated with the number of tumor cells, tumor size, AFP level, and MVI (p=0.021). ...
Hepatocellular carcinoma (HCC) being a leading cause of cancer-related death, has high associated mortality and recurrence rates. It has been of great necessity and urgency to find effective HCC diagnosis and treatment measures. Studies have shown that microvascular invasion (MVI) is an independent risk factor for poor prognosis after hepatectomy. The abnormal expression of biomacromolecules such as circ-RNAs, lncRNAs, STIP1, and PD-L1 in HCC patients is strongly correlated with MVI. Deregulation of several markers mentioned in this review affects the proliferation, invasion, metastasis, EMT, and anti-apoptotic processes of HCC cells through multiple complex mechanisms. Therefore, these biomarkers may have an important clinical role and serve as promising interventional targets for HCC. In this review, we provide a comprehensive overview on the functions and regulatory mechanisms of MVI-related biomarkers in HCC.
... Proteasomes control the equilibrium between protein synthesis and degradation and maintain cellular function and survival. Proteasome inhibition results in the accumulation of misfolded and functional proteins in the lumen of the endoplasmic reticulum (ER) and the cytosol, thereby resulting in ER overload, reactive oxygen species (ROS) overproduction, functional intracellular protein disorders, and apoptosis in MM cells [11][12][13]. ...
Proteasome inhibitors (PIs) can preferentially restore bone in bone-defective lesions in patients with multiple myeloma (MM) who respond favorably to these drugs. Most prior in vitro studies on PIs were conducted using continuous exposures to low PI concentrations, although pharmacokinetics of PIs in patients shows a pulsatile change of their serum concentrations. In the present study, we therefore explored the effects on bone metabolisms of pulsatile treatment with PIs to simulate their in vivo pharmacokinetics. Pulsatile treatment with bortezomib, carfilzomib, or ixazomib induced MM cell death but only marginally affected the viability of osteoclasts (OCs) with F-actin ring formation. The pulsatile PI treatment suppressed osteoclastogenesis in OC precursors and bone resorption by mature OCs. OCs robustly enhanced osteoblastogenesis in cocultures with OCs and MC3T3-E1 pre-osteoblastic cells, indicating OC-mediated coupling to osteoblastogenesis. Importantly, the pulsatile PI treatment did not impair the robust OC-mediated osteoblastogenesis. The foregoing results suggest that PIs might sufficiently reduce MM cell-derived osteoblastogenesis inhibitors to permit OC-driven bone formation coupling while suppressing OC differentiation and activity in good responders to PIs. The OC-mediated coupling to osteoblastogenesis appears to be a predominant mechanism for preferential occurrence of bone regeneration in osteoclastic bone-destructive lesions in good responders.
... MM cells are particularly susceptible to proteasome inhibition due to their high immunoglobulins production rate. Since proteasome also degrades mediators of cell-cycle progression, apoptosis, angiogenesis, and inflammation, PIs potentially also affect these cellular functions [14]. ...
Background:
Multiple myeloma (MM) is associated with increased cardiovascular morbidity and mortality, while MM therapies also result in adverse cardiac effects. Endothelial dysfunction and impaired nitric oxide (NO) pathway is their possible mediator.
Objective:
Since MM is associated with increased arginase expression, resulting in the consumption of ʟ-arginine, precursor for NO synthesis, our aim was to test if cardiotoxicity mediated by MM and MM therapeutic, bortezomib (a proteasome inhibitor), can be ameliorated by an arginase inhibitor through improved endothelial function.
Methods:
We used a mouse Vĸ*MYC model of non-light chain MM. Cardiac function was assessed by echocardiography.
Results:
MM resulted in progressive left ventricular (LV) systolic dysfunction, and bortezomib exacerbated this effect, leading to significant impairment of LV performance. An arginase inhibitor, OAT-1746, protected the heart against bortezomib- or MM-induced toxicity but did not completely prevent the effects of the MM+bortezomib combination. MM was associated with improved endothelial function (assessed as NO production) vs. healthy controls, while bortezomib did not affect it. OAT-1746 improved endothelial function only in healthy mice. NO plasma concentration was increased by OAT-1746 but was not affected by MM or bortezomib.
Conclusions:
Bortezomib exacerbates MM-mediated LV systolic dysfunction in a mouse model of MM, while an arginase inhibitor partially prevents it. Endothelium does not mediate either these adverse or beneficial effects. This suggests that proteasome inhibitors should be used with caution in patients with advanced myeloma, where the summation of cardiotoxicity could be expected. Therapies aimed at the NO pathway, in particular arginase inhibitors, could offer promise in the prevention/treatment of cardiotoxicity in MM.
... The different sensitivity of proteasome inhibition between tumour and normal cells can be explained by different mechanisms. One is that tumour cells grow faster, leading to the accumulation of defective proteins, that need to be degraded depending on the proteasome [94]. Bortezomib (BOR) was the first clinically approved proteasome inhibitor for the treatment of multiple myeloma. ...
The conversion of many drugs into toxic or less toxic metabolites depends on the first-pass effect of the liver. Toxic metabolites are associated with drug-induced liver injury, often causing liver failure. Thus, therapies often have to be interrupted despite a promising drug effect. The development of an improved drug metabolism model consisting of liver-derived CYP3A4-overexpressing cells and tumour cells should be used to study drugs in vitro for their efficacy on tumour cells considering the first-pass effect. Two different co-culture system approaches were tested (transwell insert-based and liver cell supernatant transfer) with HepG2 CYP3A4 cells, originally derived from a tumor characterized by genetic instability, serving as an in vitro liver cell model for establishment. PANC-1 cells (pancreatic cancer) or MCF-7 cells (breast cancer) were used as prototypical tumour cell lines. For cell treatment, three PANC-1 or MCF-7 active drugs MG-132 (MG), Taxol (TX) and Tamoxifen (TAM), were used as these drugs are inactivated (MG and TX) or activated (TAM) by the liver first-pass effect. Three widely used cytotoxicity assays (XTT-, CellTiter-Glo™ 2.0-, and trypan blue exclusion assay) were used to determine acute cytotoxicity to both liver and tumour cells. For co-culture validation, HepG2 CYP3A4 cells were replaced by CYP3A4-overexpressing immortalized primary-like hepatocytes, the FH3 CYP3A4 cells, representing the human liver cell model more closely. Finally, in a pilot project, primary colon carcinoma cells (pCC-cells) were tested along with HepG2 CYP3A4 and MG. The use of co-cultures with HepG2 CYP3A4 showed, that first-pass metabolism of MG resulted in reduced cytostatic effects in PANC-1 cells. The TX-induced cytotoxic effect on PANC-1 and MCF-7 cell lines is only slightly attenuated by the first-pass effect. Activation of TAM with FH3 CYP3A4 liver cells in indirect co-culture with transwell inserts most efficiently enhanced the cytotoxic effect on MCF-7 cells. In contrast, the use of HepG2 CYP3A4 proved to be insufficient. PCC-cells were affected by MG in MC in a dose-dependent manner. Using co-culture systems with HepG2 CYP3A4 cells, colon cancer cells were clearly protected from MG up to a concentration of 2 μM. In conclusion, first-pass effect could be simulated in vitro in MG- and TX-treated PANC-1 cells and TX-treated MCF-7 cells as well as on MG-treated pCC-cells using HepG2 CYP3A4 cells. Obtained results with PANC-1 and MCF-7 could be validated with FH3 CYP3A4 cells. However, demonstration of the first-pass effect using different end-point measurement methods yielded different results and further studies are needed for definite conclusions.
... The growing body of research relating to aneuploidy, a faulty proteome, and cancer development is significant because it suggests that antineoplastic drugs targeting the proteostasis machinery might be used to treat aneuploid cancer cells. Defective protein structure is another proposed explanation for proteomics alterations in malignancies (Adams, 2004). Defective protein structure can result from mutations in cancer-related genes. ...
... Multiple myeloma (MM) is a kind of hematological malignancy characterized by clonal accumulation of plasma cells and monoclonal secretion of immunoglobulin or light chain proteins [7]. A large amount of protein secretion accelerates protein metabolism, driving proteasomes in malignant plasma cells in highly active states, and thus normal proteins controlling proliferation, cell cycle, apoptosis, and DNA repair were over ubiquitinated and degraded by proteasomes, which makes the proteasome a rational candidate target for MM therapy [8][9][10]. Bortezomib was the rst proteasome inhibitor on clinical practice [11]. ...
Background
Multiple myeloma (MM) is a ubiquitin proteasome system (UPS)-dysfunction disease. We previously reported that the PRAME transcript level at diagnosis was prognostic for MM, which was related to proteasome inhibitor bortezomib treatment. In the present study, we aimed to investigate molecular mechanisms underlying the above clinical performance in MM cells.
Methods
MM cell lines with PRAME knockdown and overexpression were established by lentivirus transduction. Cell viability, cell cycle analysis, immunohistochemistry staining, cell migration and invasion, colony-forming and xeno-transplant assays were performed to evaluate the biological effects of PRAME on MM cells in vivo and in vitro. Proteomics and IP combined with MS were further performed to explore the downstream signaling. Co-IP, western blot, cycloheximide (CHX)-chase assay, and endogenous ubiquitination assay were utilized to examine the interactions and ubiquitination relations between PRAME and CTMP as well as p21. Assessment of apoptosis and CHX-chase assay were applied to analyze the role of PRAME under the effect of bortezomib on MM cells.
Results
Proliferation-promoting role of PRAME was demonstrated in MM cell models. CTMP and p21 were found to be the novel targets of PRAME in the Cul2-dependent substrate recognition process. PRAME interacted with and mediated ubiquitination of CTMP and p21, and subsequently elevated p-Akt and CCND3 protein levels, and promoted apoptosis of MM cells under bortezomib treatment.
Conclusions
PRAME promoted proliferation and increased bortezomib sensibility by regulating ubiquitination and degradation of CTMP and p21, which provided new targets for more precise and effective treatment choices for MM.
... Regulated protein degradation has been established as a vital controlling factor during tumorigenesis, with related oncogenic proteins considered potential therapeutic targets in the treatment of many cancers [5,6]. Protein ubiquitination is the dominant post-translational modification that mediates protein degradation [7] and involves a wide range of cellular activities, such as apoptosis and cell survival. ...
Glioblastoma (GBM) is a malignant brain tumor. The purpose of this study is to estimate the potential effects and underlying mechanisms of a ubiquitin-specific protease 8 (USP8) small-molecule inhibitor on the phenotypic characteristics of GBM cells. The growth, migration, invasion, and stemness of GBM LN229 and T98G cells were evaluated by conducting cell proliferation, colony formation, wound healing, transwell, Ki-67 staining, spheroid formation, and ionizing radiation assays, and the results collectively showed the suppressive effects of USP8 inhibition on GBM cells. Furthermore, transcriptomic profiling of GBM cells treated with the USP8 inhibitor deubiquitinase (DUB)-IN-1 revealed significantly altered mRNA expression induced by pharmacological USP8 inhibition, from which we confirmed downregulated Aurora kinase A (AURKA) protein levels using immunoblotting assays. Our findings indicated that the proliferation, invasion, and stemness of LN229 and T98G cells were markedly suppressed by USP8 inhibition. Pharmacological USP8 suppression elicits multiple tumor-inhibitory effects, likely through dysregulating various mRNA expression events, including that of the key cell cycle regulator and oncogenic protein AURKA. Therefore, our observations corroborate the GBM-supportive roles of USP8 and suggest pharmacological USP8 inhibition is a viable therapeutic approach to target GBM. The purpose of this study was to investigate the effect and mechanism of action of the USP8 inhibitor DUB-IN-1 on GBM.
... Compound 6 was synthesized following the procedure used for 5. 1 H NMR (500 MHz, DMSO- 17 (s, 9H). 13 3-((4-(tert-Butylamino)-2-((4-methylphenyl)sulfonamido)-4oxobutanamido)methyl)benzoic Acid (7). Compound 7 was synthesized following the procedure used for 5. 1 16 (s, 9H). ...
We describe our discovery and development of potent and highly selective inhibitors of human constitutive proteasome chymotryptic activity (β5c). Structure-activity relationship studies of the novel class of inhibitors focused on optimization of N-cap, C-cap, and side chain of the chemophore asparagine. Compound 32 is the most potent and selective β5c inhibitor in this study. A docking study provides a structure rationale for potency and selectivity. Kinetic studies show a reversible and noncompetitive inhibition mechanism. It enters the cells to engage the proteasome target, potently and selectively kills multiple myeloma cells, and does so by synergizing with a β5i-selective inhibitor.
... Carfilzomib belongs to the group of epoxyketones which modify the hydroxyl group and the free N-terminus of Thr1 of the active sites, leading to irreversible inhibition of proteasome activity (176). The toxicity profile limited the chronic use of these inhibitors in non-life-threatening diseases and thus, researchers focused on neoplastic malignancies with high protein turnover such as B cell malignancies (175,177). Increasing insight into the role of the IP in immune cells prompted researchers to develop IP-specific inhibitors, resulting in the discovery of ONX 0914 (previously called PR-957) (178). ONX 0914 is a tripeptide analog of the tetrapeptide epoxyketone inhibitor carfilzomib with at least 10-fold selectivity for LMP7 over β5c which contains a tyrosine residue at position P1. ...
... The proteasome was originally thought to be a recycler of damaged or misfolded proteins, but in the last decade, the function of this enzyme has been discovered to be critical for the cell cycle, cell survival, and cellular homeostasis [9]. In addition to maintaining protein balance in the organism, the proteasome also plays a key role in regulating many physiological processes, including nuclear factor kb (NF-kB) activation, neuronal function, and endoplasmic reticulum (ER)-associated protein degradation [10]. Both type A and type B members of the grass carp proteasome subunit (PS) gene family have been found to be involved in some important physiological functions [11], but this gene family member has not been systematically studied at the genomic level. ...
The proteasome is a highly conserved polycatalytic enzyme that is required for cellular processes and is widely present in the nucleus and cytoplasm of archaea, as well as all eukaryotes. A total of 22 members of the proteasome subunit (CiPS) gene family were identified and characterized by scanning the grass carp (Ctenopharyngodon idella) genome. These genes were classified into two subfamilies, CiPSA and CiPSB, based on phylogenetic analysis, which was consistent with the results from other species. We examined the response of this gene family to high density and saline-alkali stresses in aquaculture using publicly available transcriptome data resources. In grass carp, CiPS member transcripts were detected in all tested tissues, with the highest expression level in the head kidney and the lowest in the liver. According to transcriptome-based expression analysis, CiPS genes play a role in response to environmental stresses in grass carp, mainly in the form of negative regulation. Interestingly, a cluster of members belonging to the CiPSB subfamily on a 15 kb region on chromosome segment CI01000319, including CiPSB8, 9, 9b, and 10, showed marked responses to high density and saline-alkali stress. It appears that CiPS genes confer stress tolerance through the regulation of common genes, as well as specific genes. In summary, our genome-wide characterization, evolutionary, and transcriptomic analysis of CiPS genes in grass carp provides valuable information for characterizing the molecular functions of these genes and utilizing them to improve stress tolerance in aquaculture.
... Ciglitazone is known to reduce expressions of both cyclins B and D1 in GBM [34]. In this study, we found that ciglitazone inhibited the expression of CDK2, CDK4, cyclin D1, and cyclin E. Regarding the degradation of the above-said proteins, three major pathways are known, including ER Stress, proteosome, and lysosome activity [35][36][37]. Results showed that ciglitazone activated the expression of Ubiquitin and LAMP1 expressions, and these activations were attenuated by inhibitors. Findings confirmed that the degradation of cell cycle proteins by ciglitazone was mediated through activated proteosomes and lysosomes. ...
Glioblastoma multiforme (GBM) is the most common and aggressive primary malignant tumor of the central nervous system. GBM has a very low 5-year survival rate and reaching merely a median of ~15 months even with aggressive treatments. PPARγ (Peroxisome proliferator- activated receptor gamma) agonists (ciglitazone), while being widely used on patients of type 2 diabetes mellitus, also have approved anticancer effects. Their action mechanisms on malignant glioma are not fully understood. The aim of this study is to investigate the potential therapeutic effect of PPARγ agonists on maligant glioma. Glioma cell line and in-vivo/ex-vivo animal model intervened by ciglitazone were used to assess the associated mechanism and therapeutic effect. Our results from in vivo and ex vivo experiments showed that ciglitazone not only inhibited tumor growth and its associated angiogenesis, but it also reduced colony formation and migration of tumors. Ciglitazone inhibited the phosphorylation of STAT3 (signal transducer and activator of transcription 3) (at the point of tyrosine 705 by increasing both the amount and activity of SHP-2 (Src homology region 2-containing protein tyrosine phosphatase 2) proteins, based on evidence obtained from immunoprecipitation and immunohistochemistry. Furthermore, ciglitazone activated proteasomes and lysosomes to degrade cell-cycle-related proteins like Cyclin D1, Cyclin E, CDK2 (Cyclin-dependent kinase 2), and CDK4 (Cyclin-dependent kinase 4). Ciglitazone triggered expressions of LC3 (Microtubule-associated protein 1A/1B-light chain 3) and formation of acidic vesicular organelles (AVOs), both of which were implicated in the autophagy pathway. In conclusion, ciglitazone showed the multiple actions to regulate the growth of glioma, which appeared to be a potential candidate for treating malignant glioma.
... The ubiquitin-proteasome system plays an essential role in the selective degradation of intracellular proteins and, therefore, influences many key cellular biological processes, including cell proliferation, cell cycle, apoptosis, and signal transduction. Several studies have revealed that excessive proteasome activation is correlated with many pathological states, such as cancer, neurodegenerative diseases, and inflammation (Adams, 2004a;Rubinsztein, 2006;Schmidt et al., 2010). In cancer, proteasome inhibition can induce tumor apoptosis and enhance sensitivity to chemotherapy and radiotherapy by altering the balance between proapoptotic and antiapoptotic signaling pathways (Adams, 2004b). ...
Background: Intrahepatic Cholangiocarcinoma (iCCA) is a highly malignant tumor with limited treatment options that contributes largely to cancer-related deaths worldwide. Compared with traditional transcriptomic analysis, single-cell RNA sequencing (scRNA-seq) is emerging as a more advanced and popular tool for the in-depth exploration of cellular diversity and molecular complexity. As a next-generation proteasome inhibitor, MLN2238 presents better pharmacodynamics, pharmacokinetics, and therapeutic responses in various cancers. However, its effects and mechanisms of action in iCCA remain unknown.
Methods: iCCA tumor heterogeneity was determined based on 4,239 qualified scRNA-seq data from 10 iCCA samples. The potential biological roles of proteasome-related genes in iCCA were investigated using a pseudo-trajectory reconstruction. The effect of MLN2238 on iCCA cell proliferation was estimated using the CCK-8, EdU, and clone formation assays. Flow cytometry was used to examine the effect of added MLN2238 on cell cycle and apoptosis levels. Autophagic flux was detected using AdPlus-mCherry-GFP-LC3B cells. ROS levels and mitochondrial membrane potential were determined using DCFH-DA probing and JC-1 staining. JNK activation and mitochondrial apoptosis were observed using western blotting and immunofluorescence microscopy, respectively. Finally, we used a tumor-bearing mouse model to validate its efficacy in vivo for iCCA treatment.
Results: Proteasome-related genes were dysregulated in iCCA progression and expressed at higher levels in tumor tissues. MLN2238 suppressed cell proliferation, blocked the cell cycle in the G2/M phase, promoted apoptosis, and induced cytoprotective autophagy in iCCA cells. Furthermore, MLN2238 increased ROS levels and activated the JNK signaling pathway. Inhibition of ROS and JNK activation by NAC and SP600125 significantly reversed MLN2238-induced apoptosis. MLN2238 also suppressed the growth of iCCA tumors in vivo .
Conclusion: Proteasome-related genes play pivotal roles in iCCA development. MLN2238, as a proteasome inhibitor, induces apoptosis in iCCA cells through ROS/JNK/mitochondrial signaling pathways, and hence, making MLN2238 a potential therapeutic choice for iCCA.
Monoclonal antibody (mAb)-based immunotherapy currently is considered to be an optimal therapeutic approach to cancer treatment, either in combination with surgery, radiation, and/or chemotherapy or alone. Various solid tumors and hematological malignancies have been characterized by distinct molecular targets, which could be utilized as innovative anticancer agents. Notably, receptor tyrosine kinases, including HER2, EGFR, VEGFR, and PDGFR, which act as receptors for growth factors, serve as crucial target proteins, expanding their role in the cancer therapeutic market. In contrast to conventional anticancer agents that directly target cancer cells, the advent of immunotherapy introduces novel approaches, such as immune checkpoint blockers (ICBs) and mAbs targeting surface antigens on immune cells in hematological malignancies and lymphomas. While these immunotherapies have mitigated the acquired resistance observed in traditional targeted therapies, they also exhibit diverse toxicities. Herein, this review focuses on describing the well-established toxicities and newly proposed mechanisms of monoclonal antibody toxicity in recent studies. Understanding these molecular mechanisms is indispensable to overcoming the limitations of mAbs-based therapies, facilitating the development of innovative anticancer agents, and uncovering novel indications for cancer treatment in the future.
The current scientific literature has extensively explored the potential role of proteasome inhibitors (PIs) in the NF-κB pathway of leukemia and lymphoma. The ubiquitin-proteasome system (UPS) is a critical component in regulating protein degradation in eukaryotic cells. PIs, such as BTZ, are used to target the 26S proteasome in hematologic malignancies, resulting in the prevention of the degradation of tumor suppressor proteins, the activation of intrinsic mitochondrial-dependent cell death, and the inhibition of the NF-κB signaling pathway. NF-κB is a transcription factor that plays a critical role in the regulation of apoptosis, cell proliferation, differentiation, inflammation, angiogenesis, and tumor migration. Despite the successful use of PIs in various hematologic malignancies, there are limitations such as resistant to these inhibitors. Some reports suggest that PIs can induce NF-κB activation, which increases the survival of malignant cells. This article discusses the various aspects of PIs’ effects on the NF-κB pathway and their limitations.
Video Abstract
Supplementary Information
The online version contains supplementary material available at 10.1186/s12964-023-01433-5.
Resistance to proteasome inhibitors (PIs) has emerged as an important clinical issue. We investigated the mechanisms underlying multiple myeloma (MM) cell resistance to PIs. To mimic their pharmacokinetic/pharmacodynamic (PK/PD) profiles, MM cells were treated with bortezomib and carfilzomib for 1 h at concentrations up to 400 and 1,000 nM, respectively. Susceptibility to these PIs markedly varied among MM cell lines. Pulsatile treatments with PIs suppressed translation, as demonstrated by incorporation of puromycin at 24 h in PI-susceptible MM.1S cells, but not PI-resistant KMS-11 cells. Inhibition of β5 subunit activity decreased at 24 h in KMS-11 cells, even with the irreversible PI carfilzomib, but not under suppression of protein synthesis with cycloheximide. Furthermore, the proteasome-degradable pro-survival factors PIM2 and NRF2 acutely accumulated in MM cells subjected to pulsatile PI treatments. Accumulated NRF2 was trans-localized into the nucleus to induce the expression of its target gene, HMOX1, in MM cells. PIM and Akt inhibition restored the anti-MM effects of PIs, even against PI-resistant KMS-11 cells. Collectively, these results suggest that increased synthesis of β5 proteasome subunit and acute accumulation of PIM2 and NRF2 reduce the anti-MM effects of PIs.
Zinc (Zn) is a crucial trace element involved in various cellular processes, including oxidative stress, apoptosis and immune response, contributing to cellular homeostasis. Dysregulation of Zn homeostasis occurs in certain cancers. This review discusses the role of Zn in cancer and its associated components, such as Zn‐related proteins, their potential as biomarkers and the use of Zn‐based strategies for tumor treatment. ZIP and ZnT proteins regulate Zn metabolism under normal conditions, but their expression is aberrant in cancer. These Zn proteins can serve as prognostic or diagnostic biomarkers, aiding in early cancer detection and disease monitoring. Moreover, targeting Zn and its pathways offers potential therapeutic approaches for cancer treatment. Modulating Zn biodistribution within cells using metal‐binding agents allows for the control of downstream signaling pathways. Direct utilization of zinc as a therapeutic agent, including Zn supplementation or Zn oxide nanoparticle administration, holds promise for improving the prognosis of cancer patients.
Multiple myeloma (MM) is the prototypic cancer model for proteotoxicity due to the extensive and sustained synthesis of immunoglobulin or free light chain in the face of insufficient proteasome activity. A large body of work has shown that the baseline ratio between load on the proteasome and proteasome activity can predict response to proteasome inhibitors (PIs), and that an increase in proteasome capacity or load can increase or reduce PI sensitivity, respectively. As the proteasome is part of an extensive network of proteins participating in maintaining protein homeostasis (or proteostasis), there has been an interest in identifying novel molecular targets for MM and other forms of lymphoma therapy within the proteostasis network. In this chapter, we will review FDA-approved and investigational agents targeting the proteostasis network, with an emphasis on the molecular mechanisms driving PI resistance and laboratory-based combination treatments to overcome it.
Background:
Cancer is an ailment with having a very low survival rate globally. Poor cancer prognosis is primarily caused by the fact that people are found to have the disease when it is already well advanced. The goal of this study is to compile information on new avenues of investigation into biomarkers that may facilitate the routine detection of cancer. Proteomic analysis has recently developed into a crucial technique for cancer biology research, working in tandem with genomic analysis. Mass spectrometry techniques are one of several proteome analysis techniques that allow for the highly precise quantitative and qualitative recognition of hundreds of proteins in small quantities from various biological materials. These findings might soon serve as the foundation for better cancer diagnostic techniques.
Methods:
An exhaustive literature survey has been conducted using electronic databases such as Google Scholar, Science Direct, and PubMed with keywords of proteomics, applications of proteomics, the technology of proteomics, biomarkers, and patents related to biomarkers.
Result:
Studies reported till 2021 focusing on cancer proteomics and the related patents have been included in the present review to obtain concrete findings, highlighting the applications of proteomics in cancer.
Conclusion:
The present review aims to present the overview and insights into cancer proteomics, recent breakthroughs in proteomics techniques, and applications of proteomics with technological advancements, ranging from searching biomarkers to the characterization of molecular pathways, though the entire process is still in its infancy.
Simple Summary
Autophagy and mitophagy are important processes in the regulation of cancer progression. Although autophagy and mitophagy have dual roles in cancer, targeting their regulation has potential for developing an effective cancer treatment strategy. Thus, it is important to understand how ubiquitination and deubiquitination of autophagy-related proteins are regulated to exploit autophagy and mitophagy during cancer development.
Abstract
Autophagy is essential for organismal development, maintenance of energy homeostasis, and quality control of organelles and proteins. As a selective form of autophagy, mitophagy is necessary for effectively eliminating dysfunctional mitochondria. Both autophagy and mitophagy are linked with tumor progression and inhibition. The regulation of mitophagy and autophagy depend upon tumor type and stage. In tumors, mitophagy has dual roles: it removes damaged mitochondria to maintain healthy mitochondria and energy production, which are necessary for tumor growth. In contrast, mitophagy has been shown to inhibit tumor growth by mitigating excessive ROS production, thus preventing mutation and chromosomal instability. Ubiquitination and deubiquitination are important modifications that regulate autophagy. Multiple E3 ubiquitin ligases and DUBs modulate the activity of the autophagy and mitophagy machinery, thereby influencing cancer progression. In this review, we summarize the mechanistic association between cancer development and autophagy/mitophagy activities regulated by the ubiquitin modification of autophagic proteins. In addition, we discuss the function of multiple proteins involved in autophagy/mitophagy in tumors that may represent potential therapeutic targets.
PSMD4/Rpn10 is a subunit of the 19S proteasome unit that is involved with feeding target proteins into the catalytic machinery of the 26S proteasome. Since proteasome inhibition is a common therapeutic strategy in multiple myeloma (MM), we investigated Rpn10 and found that it is highly expressed in MM cells versus normal plasma cells. Rpn10 levels inversely correlated with overall survival in MM patients. Inducible knockout or knockdown of Rpn10 decreased MM cell viability both in vitro and in vivo by triggering the accumulation of polyubiquitinated proteins, cell cycle arrest, and apoptosis associated with activation of caspases and unfolded protein response-related pathways. Proteomic analysis revealed that inhibiting Rpn10 increased autophagy, antigen presentation and the activation of CD4+ T and NK cells. We developed an in vitro AlphaScreen binding assay for high-throughput screening and identified a novel Rpn10 inhibitor, SB699551 (SB). Treating MM cell lines, leukemic cell lines, and primary MM patient cells with SB decreased cell viability without affecting the viability of normal PBMCs. SB inhibited the proliferation of MM cells even in the presence of the tumor-promoting bone marrow milieu and overcame proteasome inhibitor (PI)-resistance without blocking the 20S proteasome catalytic function or the 19S deubiquitinating activity. Rpn10 blockade by SB triggered MM cell death via similar pathways as the genetic strategy. In MM xenograft models, SB was well-tolerated, inhibited tumor growth, and prolonged survival. Our data suggests that inhibiting Rpn10 will enhance cytotoxicity and overcome PI-resistance in MM, providing the basis for further optimization studies of Rpn10 inhibitors for clinical application.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
Hematologic malignancies were the first human cancers to be studied in depth at the molecular level, and recent years have seen important advances in treatment. This comprehensive reference book covers the full range of hematologic malignancies, including all subtypes of leukemias, lymphomas, and plasma cell dyscrasias. Authored by internationally known experts, each chapter emphasizes diagnostic work-up, staging, and therapeutic approaches. Up-to-date hematopathology, treatment, and outcomes data are presented in a way which is directly applicable to patient care. Highly illustrated with color images, graphs, flowcharts and treatment algorithms, the book is perfect for quick clinical reference as well as providing detailed reference lists for further study. With its authoritative and practical focus and visually stimulating presentation, this is a key text for hematology and oncology fellows, physicians, oncology nurses, physician assistants and other healthcare workers in the field of oncology.
The antitumor drug aclacinomycin A was previously shown to inhibit the degradation of ubiquitinated proteins in rabbit reticulocyte lysates with an IC50 of 52 μM (Isoe, T., Naito, M., Shirai, A., Hirai, R., and Tsuruo, T. (1992) Biochim. Biophys. Acta 1117, 131-135). We report here that from all the catalytic activities of the 20 S proteasome tested, the chymotrypsin-like activity was the only one affected by the antitumor drug. An important requirement for inhibition of the chymotrypsin-like activity seemed to be the presence of hydrophobic nonpolar residues in positions P1 to P3. Degradation of Z-E(OtBu)AL-pNA and Z-LLL-AMC at pH 7.5 was dramatically (87-98%) inhibited by 50 μm of the drug, while that of Z-GGL-pNA (containing uncharged polar residues in positions P2 and P3) and succinyl-LLVY-AMC (containing an uncharged polar residue in the P1 position) was inhibited only 11 and 24%, respectively. Aclacinomycin A had no effect on cathepsin B, stimulated trypsin, and inhibited chymotrypsin and, to a lesser extent, calpain. The aglycone and sugar moieties of the cytotoxic drug are essential for inhibition. The results presented here support a major role for the chymotrypsin-like activity in the degradation of ubiquitinated proteins. Aclacinomycin A is the first described non-peptidic inhibitor showing discrete selectivity for the chymotrypsin-like activity of the 20 S proteasome.
Inhibitors of the protease of HIV-1 have been used successfully for the treatment of HIV-1-infected patients and AIDS disease.
We tested whether these protease inhibitory drugs exerted effects in addition to their antiviral activity. Here, we show in
mice infected with lymphocytic choriomeningitis virus and treated with the HIV-1 protease inhibitor ritonavir a marked inhibition
of antiviral cytotoxic T lymphocyte (CTL) activity and impaired major histocompatibility complex class I-restricted epitope
presentation in the absence of direct effects on lymphocytic choriomeningitis virus replication. A potential molecular target
was found: ritonavir selectively inhibited the chymotrypsin-like activity of the 20S proteasome. In view of the possible role
of T cell-mediated immunopathology in AIDS pathogenesis, the two mechanisms of action (i.e., reduction of HIV replication
and impairment of CTL responses) may complement each other beneficially. Thus, the surprising ability of ritonavir to block
the presentation of antigen to CTLs may possibly contribute to therapy of HIV infections but potentially also to the therapy
of virally induced immunopathology, autoimmune diseases, and transplantation reactions.
Two members of the proteasome activator, PA28 and PA28, form a heteropolymer that binds to both ends of the 20S proteasome. Evidence in vitro indicates that this interferon- (IFN-)-inducible heteropolymer is involved in the processing of intracellular antigens, but its functions in vivo remain elusive. To investigate the role of PA28/ in vivo, we generated mice deficient in both PA28 and PA28 genes. The ATP-dependent proteolytic activities were decreased in PA28-/-/-/- cells, suggesting that 'hybrid proteasomes' are involved in protein degradation. Treatment of PA28-/-/-/- cells with IFN- resulted in sufficient induction of the 'immunoproteasome'. Moreover, splenocytes from PA28-/-/-/- mice displayed no apparent defects in processing of ovalbumin. These results are in marked contrast to the previous finding that immunoproteasome assembly and immune responses were impaired in PA28-/- mice. PA28-/-/-/- mice also showed apparently normal immune responses against infection with influenza A virus. However, they almost completely lost the ability to process a melanoma antigen TRP2-derived peptide. Hence, PA28/ is not a prerequisite for antigen presentation in general, but plays an essential role for the processing of certain antigens.
Full-length cDNAs for three human proteasome activator subunits, called REGα, REGβ, and REGγ, have been expressed in Escherichia coli, and the purified recombinant proteins have been characterized. Recombinant α or γ subunits form heptameric species; recombinant
β subunits are found largely as monomers or small multimers. Each recombinant REG stimulates cleavage of fluorogenic peptides
by human red cell proteasomes. The pattern of activated peptide hydrolysis is virtually identical for REGα and REGβ. These
two subunits, alone or in combination, stimulate cleavage after basic, acidic, and most hydrophobic residues in many peptides.
Recombinant α and β subunits bind each other with high affinity, and the REGα/β heteromeric complex activates hydrolysis of
LLVY-methylcoumaryl-7-amide (LLVY-MCA) and LLE-β-nitroanilide (LLE-βNA) more than REGα or REGβ alone. Using filter binding
and gel filtration assays, recombinant REGγ subunits were shown to bind themselves but not α or β subunits. REGγ differs from
REGα and REGβ in that it markedly stimulates hydrolysis of peptides with basic residues in the P1 position but only modestly
activates cleavage of LLVY-MCA or LLE-βNA by the proteasome. REGγ binds the proteasome with higher affinity than REGα or REGβ
yet with lower affinity than complexes containing both REGα and REGβ. In summary, each of the three REG homologs is a proteasome
activator with unique biochemical properties.
While two structurally related epoxyketone-containing antitumor natural products, epoxomicin and eponemycin, share the proteasome as a common intracellular target, they differ in their antiproliferative activity, proteasome subunit binding specificity, and rates of proteasome inhibition. As a first step towards understanding such differences and developing novel proteasome subunit-specific inhibitors, we report here the synthesis and characterization of epoxomicin/dihydroeponemycin chimerae.
A protein that greatly stimulates the multiple peptidase activities of the 20 S proteasome (also known as macropain, the multicatalytic protease complex, and 20 S protease) has been purified from bovine red blood cells and from bovine heart. The activator protein was a single polypeptide with an apparent molecular weight of 28,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and had a native molecular weight of approximately 180,000. This protein, which we have termed PA28, regulated all three of the putatively distinct peptidase activities displayed by each of two functionally different forms of the proteasome. This regulation usually included both an increase in the maximal reaction velocity and a decrease in the concentration of substrate required for half-maximal velocity and indicated that PA28 acted as a positive allosteric effector of the proteasome. PA28 failed, however, to stimulate the hydrolysis of large protein substrates such as casein and lysozyme. These results suggested that the hydrolysis of protein substrates occurred at a site or sites distinct from those that hydrolyzed small peptides and that the regulation of the two processes could be uncoupled. Evidence for direct binding of PA28 to the proteasome was obtained by glycerol density gradient centrifugation. PA28 may play an important regulatory role in intracellular proteolytic pathways mediated by the proteasome.
Reticulocytes contain a nonlysosomal proteolytic pathway that requires ATP and ubiquitin. By DEAE chromatography and gel filtration, we were able to fractionate the ATP-dependent system into a 30-300-kDa fraction that catalyzes the ATP-dependent conjugation of ubiquitin to substrates ("Conjugation Fraction") and a high mass fraction (greater than 450 kDa) necessary for hydrolysis of the conjugated proteins. The latter contains two distinct proteases. One protease is unusually large, approximately 1500 kDa, and degrades proteins only when ATP and the conjugating fractions are added. This activity precipitates at 0-38% (NH4)2SO4 saturation and is essential for ATP-dependent proteolysis. Like crude extracts, it is labile in the absence of nucleotides and is inhibited by heparin, poly(Glu-Ala-Tyr), 3,4-dichloroisocoumarin, hemin, decavanadate, N-ethylmaleimide, and various peptide chloromethyl ketones. It lacks amino-peptidase and insulin-degrading activities and does not require tRNA for activity. The ubiquitin-conjugate degrading enzyme, which we suggest be named UCDEN, is inactive against substrates that cannot undergo ubiquitin conjugation. The smaller protease (670 kDa), which precipitates at 40-80% (NH4)2SO4 saturation, does not require ATP or ubiquitin and is therefore not required for ATP-dependent proteolysis. It is stimulated by N-ethylmaleimide and 3,4-dichloroisocoumarin and is stable at 37 degrees C. It hydrolyzes fluorometric tetrapeptides and proteins, including proteins which cannot be conjugated to ubiquitin. Thus, reticulocytes contain two large cytosolic proteases: one is essential for the degradation of ubiquitin conjugates, while the function of the other is uncertain.
We have purified two high molecular weight proteases approximately 400-fold from rabbit reticulocyte lysate. Both enzymes hydrolyze 125I-alpha-casein and 4-methylcoumaryl-7-amide peptides with tyrosine, phenylalanine, or arginine at the P1 position. Both are inhibited by hemin, thiol reagents, chymostatin, and leupeptin. They differ, however, by other criteria. Degradation of 125I-lysozyme-ubiquitin conjugates and succinyl-Leu-Leu-Val-Tyr-4-methylcoumaryl-7-amide by the larger 26 S protease is stimulated by ATP. Based on sedimentation, gel filtration, and nondenaturing polyacrylamide gel electrophoresis, the ATP-dependent protease has a molecular weight of 1,000,000 +/- 100,000 and is a multisubunit complex. The smaller 20 S protease has a molecular weight of 700,000 +/- 20,000 and is composed of 8-10 separate subunits with Mr values between 21,000 and 32,000. It does not require nucleotides for degradation of protein or peptide substrates. This smaller enzyme is similar, if not identical, to the "multicatalytic proteinase complex" first described by Wilk and Orlowski (Wilk, S., and Orlowski, M. (1983) J. Neurochem. 40, 842-849).
The p27 mammalian cell cycle protein is an inhibitor of cyclin-dependent kinases. Both in vivo and in vitro, p27 was found to be degraded by the ubiquitin-proteasome pathway. The human ubiquitin-conjugating enzymes Ubc2 and Ubc3 were specifically involved in the ubiquitination of p27. Compared with proliferating cells, quiescent cells exhibited a smaller amount of p27 ubiquitinating activity, which accounted for the marked increase of p27 half-life measured in these cells. Thus, the abundance of p27 in cells is regulated by degradation. The specific proteolysis of p27 may represent a mechanism for regulating the activity of cyclin-dependent kinases.
PA28, one of a series of a positive allosteric regulators of the 20 S proteasome, stimulates the enzyme's peptidase activities in an ATP-independent manner by binding to the terminal rings of the 20 S complex. PA28 has a native molecular mass of 180,000 Da and contains at least six subunits of approximately 28,000 Da. In this study we show that PA28 prepared from bovine heart contains two different subunits separable by reverse phase high performance liquid chromatography and that these subunits occur in approximately equal abundance. The subunits display mass values of 27,290 +/- 3.7 and 28,606 +/- 2.8 Da by electrospray mass spectrometry, showing that they differ in covalent structure. Partial amino acid sequence analysis of the subunits indicates that the subunits are the products of two different but homologous genes. A pair of subunits has also been isolated from rabbit heart, and partial amino acid sequence analysis shows each to be homologous to the corresponding subunit in bovine tissues. This indicates that the genes encoding two different polypeptide components of PA28 have been conserved during evolution and suggests the possibility that the two subunits play functionally distinct roles. Isolation of complexes formed between purified PA28 and the 20 S proteasome using density gradient centrifugation reveals that both PA28 subunits bind to the proteasome, indicating that both are components of functional PA28 molecules. These results are consistent with two alternative models for the subunit structure of PA28. There may exist two different PA28 molecules that are homooligomers of the 27,290- and 28,606-Da subunits, respectively. Alternatively, PA28 oligomers may contain mixtures of the 27,290- and 28,606-Da subunits either of fixed or variable stoichiometry.
The presentation of intracellular proteins to the immune system requires their degradation to small peptides that then become associated with major histocompatibility complex (MHC) class I molecules. The generation of these peptides may involve the 20S or 26S proteasome particles, which contain multiple proteolytic activities including distinct sites that preferentially cleave small peptides on the carboxyl side of hydrophobic, basic or acidic residues. Degradation of most cell proteins requires their conjugation to ubiquitin before hydrolysis by the 26S proteasome. This large complex contains the 20S proteasome as its proteolytic core. This ubiquitin-dependent proteolytic pathway is implicated in MHC class I presentation. gamma-Interferon (gamma-IFN), a stimulator of antigen presentation, induces a subclass of proteasomes that contain two MHC-encoded subunits, LMP2 and 7 (refs 5-10). Here we show that gamma-interferon alters the peptidase activities of the 20S and 26S proteasomes without affecting the rates of breakdown of proteins or of ubiquitinated proteins. By enhancing the expression of MHC genes, gamma-IFN increases the proteasomes' capacity to cleave small peptides after hydrophobic and basic residues but reduces cleavage after acidic residues. Moreover, proteasomes of mutants lacking LMP subunits show decreased rates of cleavage after hydrophobic and basic residues. Thus, gamma-IFN and expression of these MHC genes should favour the production by proteasomes of the types of peptides found on MHC class I molecules, which terminate almost exclusively with hydrophobic or basic residues.
Cytotoxic T cells recognize viral proteins as peptide fragments which are produced in the cytosol and transported on major histocompatibility complex (MHC) class I proteins to the cell surface. Viral peptides that meet the stringent binding characteristics of class I proteins are generated by the 20S proteasome. The interferon (IFN)-gamma-inducible activator of the 20S proteasome, PA28, strongly influences the proteasomal cleavage pattern in vitro. This led us to investigate whether changes in cellular levels of PA28 affect the efficiency of viral antigen processing. A mouse fibroblast line expressing the murine cytomegalovirus pp89 protein was transfected with either the human or murine gene encoding the PA28alpha subunit, which is sufficient to activate the peptide-hydrolysing activity of the 20S proteasome in vitro. Here we report that enhanced expression of PA28alpha at a level similar to that obtained after IFN-gamma induction resulted in a marked enhancement of recognition by pp89-specific cytotoxic T cells; the presentation of influenza nucleoprotein was also significantly improved. These results demonstrate a fundamental in vivo function for PA28alpha in antigen processing.
The antitumor drug aclacinomycin A was previously shown to inhibit the degradation of ubiquitinated proteins in rabbit reticulocyte lysates with an IC50 of 52 microM (Isoe, T., Naito, M., Shirai, A., Hirai, R., and Tsuruo, T.(1992) Biochim. Biophys. Acta 1117, 131-135). We report here that from all the catalytic activities of the 20 S proteasome tested, the chymotrypsin-like activity was the only one affected by the antitumor drug. An important requirement for inhibition of the chymotrypsin-like activity seemed to be the presence of hydrophobic nonpolar residues in positions P1 to P3. Degradation of Z-E(OtBu)AL-pNA and Z-LLL-AMC at pH 7.5 was dramatically (87-98%) inhibited by 50 microM of the drug, while that of Z-GGL-pNA (containing uncharged polar residues in positions P2 and P3) and succinyl-LLVY-AMC (containing an uncharged polar residue in the P1 position) was inhibited only 11 and 24%, respectively. Aclacinomycin A had no effect on cathepsin B, stimulated trypsin, and inhibited chymotrypsin and, to a lesser extent, calpain. The aglycone and sugar moieties of the cytotoxic drug are essential for inhibition. The results presented here support a major role for the chymotrypsin-like activity in the degradation of ubiquitinated proteins. Aclacinomycin A is the first described non-peptidic inhibitor showing discrete selectivity for the chymotrypsin-like activity of the 20 S proteasome.
A proteasome regulator, termed PA28, has been shown to modulate peptidase activities of the proteasomes in vitro. Two different but homologous PA28 molecules, designated as PA28α and PA28β, have been cloned. Both α and β polypeptides
of PA28 are found in PA28 complexes isolated from cells, indicating that both are constituents of functional PA28 complexes.
Using antisera specific to PA28α, PA28β, and epitope-tagged PA28 molecules, we show that expression of PA28α and PA28β is
coordinately induced by various cytokines in different cell lines and that PA28 subunits and proteasomes have almost identical
half-lives. In addition, we show that PA28 complexes are associated with 20 S but not 26 S proteasomes in vivo. Moreover, we demonstrate that PA28 complex is a heterohexamer composed of both α and β subunits with a stoichiometry of
α3β3 in an alternating order.
Mammalian proteasomes are composed of 14-17 different types of subunits, some of which, including major-histocompatibility-complex-encoded subunits LMP2 and LMP7, are non-essential and present in variable amounts. We have investigated the distribution of total proteasomes and some individual subunits in rat liver by quantitative immunoblot analysis of purified subcellular fractions (nuclei, mitochondria, microsomes and cytosol). Proteasomes were mainly found in the cytosol but were also present in the purified nuclear and microsomal fractions. In the nuclei, proteasomes were soluble or loosely attached to the chromatin, since they could be easily extracted by treatment with nucleases or high concentrations of salt. In the microsomes, proteasomes were on the outside of the membranes. Further subfractionation of the microsomes showed that the proteasomes in this fraction were associated with the smooth endoplasmic reticulum and with the cis-Golgi but were practically absent from the rough endoplasmic reticulum. Using monospecific antibodies for some proteasomal subunits (C8, C9, LMP2 and Z), the composition of proteasomes in nuclei, microsomes and cytosol was investigated. Although there appear not to be differences in proteasome composition in the alpha subunits (C8 and C9) in the different locations, the relative amounts of some beta subunits varied. Subunit Z was enriched in nuclear proteasomes but low in microsome-associated proteasomes, whereas LMP2, which was relatively low in nuclei, showed a small enrichment in the microsomes. These differences in subunit composition of proteasomes probably reflect differences in the function of proteasomes in distinct cell compartments.
Cyclin E is a mammalian G1 cyclin that is both required and rate limiting for entry into S phase. The expression of cyclin E is periodic, peaking at the G1-S transition and then decaying as S phase progresses. To understand the mechanisms underlying cyclin E periodicity, we have investigated the regulation of cyclin E degradation. We find that cyclin E is degraded by the ubiquitin-proteasome system, and that this degradation is regulated by both cdk2 binding and cdk2 catalytic activity. Free cyclin E is readily ubiquitinated and degraded by the proteasome. Binding to cdk2 protects cyclin E from ubiquitination, and this protection is reversed by cdk2 activity in a process that involves phosphorylation of cyclin E itself. The data are most consistent with a model in which cdk2 activity initiates cyclin E degradation by promoting the disassembly of cyclin E-cdk2 complexes, followed by the ubiquitination and degradation of free cyclin E.
Oscillations in the activity of cyclin-dependent kinases (CDKs) promote progression through the eukaryotic cell cycle. This
review examines how proteolysis regulates CDK activity—by degrading CDK activators or inhibitors—and also how proteolysis
may directly trigger the transition from metaphase to anaphase. Proteolysis during the cell cycle is mediated by two distinct
ubiquitin-conjugation pathways. One pathway, requiring CDC34, initiates DNA replication by degrading a CDK inhibitor. The
second pathway, involving a large protein complex called the anaphase-promoting complex or cyclosome, initiates chromosome
segregation and exit from mitosis by degrading anaphase inhibitors and mitotic cyclins. Proteolysis therefore drives cell
cycle progression not only by regulating CDK activity, but by directly influencing chromosome and spindle dynamics.
Activation of proteolytic enzymes, including cysteine proteases of the ced-3/ICE family, is a characteristic feature of the apoptotic program. In contrast, the role of the proteasome as the major nonlysosomal machinery to degrade or process proteins by ATP/ubiquitin-dependent proteolysis in this process is less clear. In human leukemic HL60 cells, inhibition of proteasome-mediated proteolysis by specific proteasomal inhibitors leads to the rapid induction of apoptosis as judged by morphological changes as well as by nuclear condensation and DNA fragmentation. HL60 apoptosis is due to activation of CPP32, a member of the ced-3/ICE family of cysteine proteases, and appears to occur independently from ICE activity. HL60 apoptosis is accompanied by an increase in the concentration of the cyclin-dependent kinase inhibitor p27Kip1. Labeling of the cells by the TUNEL technique demonstrates that HL60 cells undergoing apoptosis are primarily in the G1 phase of the cell cycle. Proteasomal activity therefore appears to be required in proliferating, but not in quiescent, HL60 cells for cell survival as well as normal progression through the cell cycle.
The expression of D-type G1 cyclins and their assembly with their catalytic partners, the cyclin-dependent kinases 4 and 6 (CDK4 and CDK6), into active holoenzyme complexes are regulated by growth factor-induced signals. In turn, the ability of cyclin D-dependent kinases to trigger phosphorylation of the retinoblastoma (Rb) protein in the mid- to late G1 phase of the cell cycle makes the inactivation of Rb's growth suppressive function a mitogen-dependent step. The ability of D-type cyclins to act as growth factor sensors depends not only on their rapid induction by mitogens but also on their inherent instability, which ensures their precipitous degradation in cells deprived of growth factors. However, the mechanisms governing the turnover of D-type cyclins have not yet been elucidated. We now show that cyclin D1 turnover is governed by ubiquitination and proteasomal degradation, which are positively regulated by cyclin D1 phosphorylation on threonine-286. Although "free" or CDK4-bound cyclin D1 molecules are intrinsically unstable (t1/2 < 30 min), a cyclin D1 mutant (T286A) containing an alanine for threonine-286 substitution fails to undergo efficient polyubiquitination in an in vitro system or in vivo, and it is markedly stabilized (t1/2 approximately 3.5 hr) when inducibly expressed in either quiescent or proliferating mouse fibroblasts. Phosphorylation of cyclin D1 on threonine-286 also occurs in insect Sf9 cells, and although the process is enhanced significantly by the binding of cyclin D1 to CDK4, it does not depend on CDK4 catalytic activity. This implies that another kinase can phosphorylate cyclin D1 to accelerate its destruction and points to yet another means by which cyclin D-dependent kinase activity may be exogenously regulated.
Proteolysis by the ubiquitin/proteasome pathway controls the intracellular levels of a number of proteins that regulate cell proliferation and cell cycle progression. To determine whether this pathway of protein turnover was also linked to apoptosis, we treated Rat-1 and PC12 cells with specific proteasome inhibitors. The peptide aldehydes PSI and MG115, which specifically inhibit the chymotrypsin-like activity of the proteasome, induced apoptosis of both cell types. In contrast, apoptosis was not induced by inhibitors of lysosomal proteases or by an alcohol analog of PSI. The tumor suppressor p53 rapidly accumulated in cells treated with proteasome inhibitors, as did the p53-inducible gene products p21 and Mdm-2. In addition, apoptosis induced by proteasome inhibitors was inhibited by expression of dominant-negative p53, whereas overexpression of wild-type p53 was sufficient to induce apoptosis of Rat-1 cells in transient transfection assays. Although other molecules may also be involved, these results suggest that stabilization and accumulation of p53 plays a key role in apoptosis induced by proteasome inhibitors.
The tumour-suppressor p53 is a short-lived protein that is maintained at low, often undetectable, levels in normal cells. Stabilization of the protein in response to an activating signal, such as DNA damage, results in a rapid rise in p53 levels and subsequent inhibition of cell growth. Tight regulation of p53 function is critical for normal cell growth and development, and one mechanism by which p53 function is controlled is through interaction with the Mdm2 protein. Mdm2 inhibits p53 cell-cycle arrest and apoptic functions and we show here that interaction with Mdm2 can also result in a large reduction in p53 protein levels through enhanced proteasome-dependent degradation. Endogenous levels of Mdm2 are sufficient to regulate p53 stability, and overexpression of Mdm2 can reduce the amount of endogenous p53. Because mdm2 is transcriptionally activated by p53, this degradative pathway may contribute to the maintenance of low p53 concentrations in normal cells. Furthermore, mechanisms regulating the Mdm2-induced degradation of p53 may play a role in controlling the extent and duration of the p53 response.
Interleukin-2 (IL-2) activates the receptor-associated Janus family tyrosine kinases, Jak1 and Jak3, which in turn phosphorylate
and activate specific STAT proteins (signal transducers and activators of transcription), such as STAT5. Activation of Jak
and STAT proteins by IL-2 is transient and the mechanism for the subsequent down-regulation of their activity is largely unknown.
We report here that IL-2-induced DNA-binding activity and tyrosine phosphorylation of STAT5 are stabilized by a proteasome
inhibitor MG132; however, no detectable ubiquitination of the STAT proteins is observed. This sustained STAT5 activation can
be blocked by protein kinase inhibitors, which is consistent with the ability of the proteasome inhibitor to stabilize IL-2-induced
tyrosine phosphorylation of Jak1 and Jak3. These results suggest that proteasome-mediated protein degradation modulates protein-tyrosine
phosphatase activity that negatively regulates the Jak-STAT signaling pathways.
The proteasome is a multicatalytic protease complex that plays a key role in diverse cellular functions. The peptide vinyl sulfone, carboxybenzyl-leucyl-leucyl-leucine vinyl sulfone (Z-L3VS) covalently inhibits the trypsin-like, chymotrypsin-like and, unlike lactacystin, also the peptidylglutamyl peptidase activity in isolated proteasomes, and blocks their function in living cells. Although described as a class of mechanism-based inhibitors for cysteine proteases, the peptide vinyl sulfone Z-L3VS and a 125I-labeled nitrophenol derivative (125I-NIP-L3VS) covalently modify the active site threonine of the catalytic beta subunits of the proteasome. Modification of Thermoplasma proteasomes demonstrates the requirement for a hydroxyl amino acid (threonine, serine) as nucleophile at the beta subunit's NH2 terminus. 125I-NIP-L3VS covalently modifies the HslV subunit of the Escherichia coli protease complex HslV/HslU, a reaction that requires ATP, and supports a catalytic mechanism shared with that of the eukaryotic proteasome.
Our previous work showed that the nuclear scaffold (NS) protease is required for apoptosis of both thymocytes and chronic lymphocytic leukemic (CLL) lymphocytes. Because partial sequencing of one of the subunits of the NS protease revealed homology to the proteasome, we tested the effects of classical proteasome inhibitors on apoptosis in CLL cells. Here we report that proteasome inhibition caused high levels of DNA fragmentation in all patients analyzed, including those resistant to glucocorticoids or nucleoside analogs, in vitro. Proteasome inhibitor-induced DNA fragmentation was associated with activation of caspase/ICE family cysteine protease(s) and was blocked by the caspase antagonist, zVADfmk. Analysis of the biochemical mechanisms involved showed that proteasome inhibition resulted in mitochondrial dysregulation leading to the release of cytochrome c and a drop in mitochondrial transmembrane potential (▵Ψ). These changes were associated with inhibition of NFκB, a proteasome-regulated transcription factor that has been implicated in the suppression of apoptosis in other systems. Together, our results suggest that drugs that target the proteasome might be capable of bypassing resistance to conventional chemotherapy in CLL.
Integrin-mediated adhesion influences cell survival and may prevent programmed cell death. Little is known about how drug-sensitive tumor cell lines survive initial exposures to cytotoxic drugs and eventually select for drug-resistant populations. Factors that allow for cell survival following acute cytotoxic drug exposure may differ from drug resistance mechanisms selected for by chronic drug exposure. We show here that drug-sensitive 8226 human myeloma cells, demonstrated to express both VLA-4 (4β1) and VLA-5 (5β1) integrin fibronectin (FN) receptors, are relatively resistant to the apoptotic effects of doxorubicin and melphalan when pre-adhered to FN and compared with cells grown in suspension. This cell adhesion mediated drug resistance, or CAM-DR, was not due to reduced drug accumulation or upregulation of anti-apoptotic Bcl-2 family members. As determined by flow cytometry, myeloma cell lines selected for drug resistance, with either doxorubicin or melphalan, overexpress VLA-4. Functional assays revealed a significant increase in 4-mediated cell adhesion in both drug-resistant variants compared with the drug-sensitive parent line. When removed from selection pressure, drug-resistant cell lines reverted to a drug sensitive and 4-low phenotype. Whether VLA-4–mediated FN adhesion offers a survival advantage over VLA-5–mediated adhesion remains to be determined. In conclusion, we have demonstrated that FN-mediated adhesion confers a survival advantage for myeloma cells acutely exposed to cytotoxic drugs by inhibiting drug-induced apoptosis. This finding may explain how some cells survive initial drug exposure and eventually express classical mechanisms of drug resistance such as MDR1 overexpression.
We recently reported increased sensitivity of B-cell chronic lymphocytic leukemia (B-CLL) lymphocytes to apoptotic death activation by the proteasome-specific inhibitor lactacystin. Here, we show that only specific—not nonspecific—proteasomal inhibitors can discriminate between malignant and normal lymphocytes in inducing the apoptotic death response. Indeed, lactacystin and its active metaboliteclasto-lactacystin β-lactone induced apoptotic death in CLL but not in normal lymphocytes. This difference was completely abolished when tripeptide aldehydes such as MG132 or LLnL (which can also inhibit calpains) were used as less specific proteasomal inhibitors. Moreover, B-CLL cells exhibited a constitutive altered ubiquitin-proteasome system, including a threefold higher chymotrypsin-like proteasomal activity and high levels of nuclear ubiquitin-conjugated proteins compared with normal lymphocytes. Interestingly, B-CLL cells also displayed altered proteolytic regulation of wild-type p53, an apoptotic factor reported to be a substrate for the ubiquitin-proteasome system. Nuclear wild-type p53 accumulated after lactacystin treatment used at the discriminating concentration in malignant, but not in normal, lymphocytes. In contrast, p53 was stabilized by MG132 or LLnL in malignant and normal cells undergoing apoptosis, indicating that in normal lymphocytes p53 is regulated mainly by calpains and not by the ubiquitin-proteasome system. This work raises the possibility that two different proteolytic pathways controlling p53 stability may be pathologically imbalanced. This could result in modification of apoptosis control, since in CLL-lymphocytes a highly upregulated ubiquitin-proteasome system, which controls p53 stability among other apoptotic factors, was correlated with an increased propensity of these cells to apoptosis triggered by lactacystin.
One facet of cytokine receptor signaling involves the activation of signal transducers and activators of transcription (STATs). STATs are rapidly activated via tyrosine phosphorylation by Janus kinase (JAK) family members and subsequently inactivated within a short period. We investigated the effect of proteasome inhibition on interleukin-3 (IL-3) activation of the JAK/STAT pathway following stimulation of Ba/F3 cells. Treatment of Ba/F3 cells with the proteasome inhibitor,N-acetyl-l-leucinyl-l-leucinyl-norleucinal (LLnL), led to stable tyrosine phosphorylation of the IL-3 receptor, beta common (βc), and STAT5 following stimulation. The effects of LLnL were not restricted to the JAK/STAT pathway, as Shc and mitogen-activated protein kinase (MAPK) phosphorylation were also prolonged in LLnL-treated cells. Further investigation showed these stable phosphorylation events were the result of prolonged activation of JAK2 and JAK1. These observations were confirmed using pharmacologic inhibitors. In the presence of LLnL, stable phosphorylation of STAT5 and βc was abrogated if the tyrosine kinase inhibitor, staurosporine, was added. The effect of staurosporine on STAT5 phosphorylation could be overcome if the phosphatase inhibitor, vanadate, was also added, suggesting phosphorylated STAT5 could be stabilized by phosphatase, but not by proteasome inhibition per se. These observations are consistent with the hypothesis that proteasome-mediated protein degradation can modulate the activity of the JAK/STAT pathway by regulating the deactivation of JAK.
Integrin-mediated adhesion influences cell survival and may prevent programmed cell death. Little is known about how drug-sensitive tumor cell lines survive initial exposures to cytotoxic drugs and eventually select for drug-resistant populations. Factors that allow for cell survival following acute cytotoxic drug exposure may differ from drug resistance mechanisms selected for by chronic drug exposure. We show here that drug-sensitive 8226 human myeloma cells, demonstrated to express both VLA-4 (4β1) and VLA-5 (5β1) integrin fibronectin (FN) receptors, are relatively resistant to the apoptotic effects of doxorubicin and melphalan when pre-adhered to FN and compared with cells grown in suspension. This cell adhesion mediated drug resistance, or CAM-DR, was not due to reduced drug accumulation or upregulation of anti-apoptotic Bcl-2 family members. As determined by flow cytometry, myeloma cell lines selected for drug resistance, with either doxorubicin or melphalan, overexpress VLA-4. Functional assays revealed a significant increase in 4-mediated cell adhesion in both drug-resistant variants compared with the drug-sensitive parent line. When removed from selection pressure, drug-resistant cell lines reverted to a drug sensitive and 4-low phenotype. Whether VLA-4–mediated FN adhesion offers a survival advantage over VLA-5–mediated adhesion remains to be determined. In conclusion, we have demonstrated that FN-mediated adhesion confers a survival advantage for myeloma cells acutely exposed to cytotoxic drugs by inhibiting drug-induced apoptosis. This finding may explain how some cells survive initial drug exposure and eventually express classical mechanisms of drug resistance such as MDR1 overexpression.
To assess whether the progression of plasma cell tumors is accompanied by angiogenesis and secretion of matrix-degrading enzymes, bone marrow biopsy specimens from 20 patients with monoclonal gammopathy of undetermined significance (MGUS), 18 patients with nonactive multiple myeloma (MM), and 26 patients with active MM were evaluated for their angiogenic potential and matrix-metalloproteinase (MMP) production. A fivefold increase of the factor VIII+microvessel area was measured by a planimetric method of point counting in the bone marrow of patients with active MM as compared with nonactive MM and MGUS patients (P < .01). When serum-free conditioned media (CM) of plasma cells isolated from the bone marrow of each patient were tested in vivo for their angiogenic activity in the chick embryo chorioallantoic membrane (CAM) assay, the incidence of angiogenic samples was significantly higher (P< .01) in the active MM group (76%) compared with nonactive MM (33%) and MGUS (20%) groups. Moreover, a linear correlation (P < .01) was found between the extent of vascularization of the bone marrow of a given patient and the angiogenic activity exerted in the CAM assay by the plasma cells isolated from the same bone marrow. In vitro, a significantly higher fraction of the plasma cell CM samples from the active MM group stimulated human umbilical vein endothelial cell (HUVEC) proliferation (53%, P < .01), migration (42%, P < .05), and/or monocyte chemotaxis (38%,P < .05) when compared with nonactive MM and MGUS groups (ranging between 5% and 15% of the samples). Also, immunoassay of plasma cell extracts showed significantly higher (P < .01) levels of the angiogenic basic fibroblast growth factor (FGF)-2 in the active MM patients than in nonactive MM and MGUS patients (153 ± 59, 23 ± 17, and 31 ± 18 pg FGF-2/100 μg of protein, respectively). Accordingly, neutralizing anti–FGF-2 antibody caused a significant inhibition (ranging from 54% to 68%) of the biological activity exerted on cultured endothelial cells and in the CAM assay by plasma cell CM samples from active MM patients. Finally, in situ hybridization of bone marrow plasma cells and gelatin-zymography of their CM showed that active MM patients express significantly higher (P < .01) levels of MMP-2 mRNA and protein when compared with nonactive MM and MGUS patients, whereas MMP-9 expression was similar in all groups. Taken together, these findings indicate that the progression of plasma cell tumors is accompanied by an increase of bone marrow neovascularization. This is paralleled by an increased angiogenic and invasive potential of bone marrow plasma cells, which is dependent, at least in part, by FGF-2 and MMP-2 production. Induction of angiogenesis and secretion of MMPs by plasma cells in active disease may play a role in their medullary and extramedullary dissemination, raising the hypothesis that angiostatic/anti-MMP agents may be used for therapy of MM.
PA28, one of a series of a positive allosteric regulators of the 20 S proteasome, stimulates the enzyme's peptidase activities in an ATP-independent manner by binding to the terminal rings of the 20 S complex, PA28 has a native molecular mass of 180,000 Pa and contains at least six subunits of approximately 28,000 Pa, In this study we show that PA28 prepared from bovine heart contains two different subunits separable by reverse phase high performance liquid chromatography and that these subunits occur in approximately equal abundance, The subunits display mass values of 27,290 +/- 3.7 and 28,606 +/- 2.8 Da by electrospray mass spectrometry, showing that they differ in covalent structure, Partial amino acid sequence analysis of the subunits indicates that the subunits are the products of two different but homologous genes. A pair of subunits has also been isolated from rabbit heart, and partial amino acid sequence analysis shows each to be homologous to the corresponding subunit in bovine tissues. This indicates that the genes encoding two different polypeptide components of PA28 have been conserved during evolution and suggests the possibility that the two subunits play functionally distinct roles, Isolation of complexes formed between purified PA28 and the 20 S proteasome using density gradient centrifugation reveals that both PA28 subunits bind to the proteasome, indicating that both are components of functional PA28 molecules, These results are consistent with two alternative models for the subunit structure of PA28, There may exist two different PA28 molecules that are homooligomers of the 27,290- and 28,606-Da subunits, respectively, Alternatively PA28 oligomers may contain mixtures of the 27,290- and 28,606-Da subunits either of fixed or variable stoichiometry.
In mammalian cells proteasomes can be activated by two different types of regulatory-complexes which bind to the ends of the proteasome cylinder. Addition of two 19 S (PA700; ATPase) complexes forms the 26 S proteasome, which is responsible for ATP-dependent non-lysosomal degradation of intracellular proteins, whereas 11 S complexes (PA28; REG) have been implicated in antigen processing. The PA28 complex is upregulated in response to γ-interferon (γ-IFN) as are three non-essential subunits of the 20 S proteasome. In the present study we have investigated the effects of γ-IFN on the level of different proteasome complexes and on the phosphorylation of proteasome subunits. After treatment of cells with γ-IFN, the level of 26 S proteasomes decreased and there was a concomitant increase in PA28 - proteasome complexes. However, no free 19 S regulatory complexes were detected. The majority of the γ-IFN-inducible proteasome subunits LMP2 and LMP7 were present in PA28 - proteasome complexes, but these subunits were also found in 26 S proteasomes. The level of phosphorylation of both 20 S and 26 S proteasome subunits was found to decrease after γ-IFN treatment of cells. The C8 alpha subunit showed more than a 50% decrease in phosphorylation, and the phosphorylation of C9 was only barely detectable after γ-IFN treatment. These results suggest that association of regulatory components to 20S proteasomes is regulated, and that phosphorylation of proteasome alpha subunits may be one mode of regulation.
Objective
Although peripheral blood B-CLL cells are arrested in G0 phase of the cell cycle, a proliferating pool of cells in proliferation centers might be involved in disease progression. We have previously described an in vitro model of this proliferating pool of cells using B-CLL cells stimulated with immunostimulatory oligonucleotides (CpG-ODN) and interleukin-2. Lactacystin is a specific inhibitor of the proteasome and is a potent apoptosis inductor in resting peripheral B-CLL cells. In the present study, we investigated the effect of proteasome inhibition in proliferating B-CLL cells.
The main objective of this study was to investigate the safety, tolerability and pharmacodynamics of the novel proteasome inhibitor PS-519 in young male volunteers. Many pro-inflammatory mediators such as cytokines and cell adhesion molecules that are responsible for the development of the cerebral infarct are under the control of the transcription factor Nuclear Factor kappa-B (NF-kappaB). The activity of NF-kappaB is itself tightly regulated through the multicatalytic enzyme known as the proteasome. PS-519 is a novel and highly selective small molecule that inhibits the proteasome. An ex vivo assay of 20S proteasome activity allows monitoring of the drug effect in blood. PS-519 is protective in multiple animal models of cerebral ischaemia over a range of doses that achieve 20S inhibition of 40%-80%.
PS-519 has been administered to healthy male volunteers as single and repeated doses up to 1.6 mg m(-2). It was given as an intravenous bolus over 20-30 s in a double blind, randomized, placebo-controlled phase I study, examining vital signs, safety, tolerability and blood 20S proteasome inhibition.
Thirty-nine subjects received single doses of 0.012 mg m-2-1.6 mg m(-2) and 28 subjects received doses of 0.5 mg m(-2)-1.6 mg m(-2) on three consecutive days. The drug was well tolerated. There was no clear treatment-emergent symptom or abnormality of laboratory tests. Proteasome inhibition in blood samples as measured by 20S assay achieved the intended maximum target level of 70-80% with 1.6 mg m(-2), and was reproducible with repeated dosing.
This study has demonstrated that proteasome inhibition is well tolerated by healthy subjects at levels that are maximally neuroprotective in experimental conditions. Further clinical evaluation appears justified.
The tumor suppressor p53 is a phosphoprotein barely detectable in the nucleus of normal cells. Upon cellular stress, particularly that induced by DNA damage, p53 can arrest cell cycle progression, thus allowing the DNA to be repaired; or it can lead to apoptosis. These functions are achieved, in part, by the transactivational properties of p53, which activate a series of genes involved in cell cycle regulation. In cancer cells bearing a mutant p53, this protein is no longer able to control cell proliferation, resulting in inefficient DNA repair and the emergence of genetically unstable cells. The most common changes of p53 in human cancers are point missense mutations within the coding sequences of the gene. Such mutations are found in all major histogenetic groups, including cancers of the colon (60%), stomach (60%), breast (20%), lung (70%), brain (40%), and esophagus (60%). It is estimated that p53 mutations are the most frequent genetic event in human cancers, accounting for more than 50% of cases. One of the most striking features of the inactive mutant p53 protein is its increased stability (half-life of several hours, compared to 20 min for wild-type p53) and its accumulation in the nucleus of neoplastic cells. Therefore, positive immunostaining is indicative of abnormalities of the p53 gene and its product. Several studies have shown that p53 mutations are associated with short survival in colorectal cancer, but the use of p53 as a tumoral marker is still a matter of debate.
Cyclin degradation is the key step governing exit from mitosis and progress into the next cell cycle. When a region in the N terminus of cyclin is fused to a foreign protein, it produces a hybrid protein susceptible to proteolysis at mitosis. During the course of degradation, both cyclin and the hybrid form conjugates with ubiquitin. The kinetic properties of the conjugates indicate that cyclin is degraded by ubiquitin-dependent proteolysis. Thus anaphase may be triggered by the recognition of cyclin by the ubiquitin-conjugating system.
Patients with systemic lupus erythematosus (SLE) produce autoantibodies against a variety of nuclear antigens including Ki antigen. Although anti-Ki autoantibodies were found in a significant number of SLE patients, the nature of Ki antigen is poorly characterized. By using anti-Ki serum as a probe we have cloned a bovine cDNA directing the synthesis in Escherichia coli of a polypeptide immunologically indistinguishable from the authentic Ki antigen. A homologous human cDNA was also cloned and its nucleotide sequence predicted the entire primary structure of a novel nuclear protein with a molecular weight of 29 508 and with highly hydrophilic and weakly acidic character. The gene is highly conserved not only in the coding region but also in the 3'-untranslated region. The bacterially produced Ki antigen would be valuable for diagnosis of SLE.
Multiple cell adhesion proteins are up-regulated in vascular endothelial cells in response to TNF alpha and other inflammatory cytokines. This increase in cell adhesion gene expression is thought to require the transcription factor NF-kappa B. Here, we show that peptide aldehyde inhibitors of the proteasome, a multicatalytic protease recently shown to be required for the activation of NF-kappa B, block TNF alpha induction of the leukocyte adhesion molecules E-selectin, VCAM-1, and ICAM-1. Striking functional consequences of this inhibition were observed in analyses of leukocyte-endothelial interactions under defined flow conditions. Lymphocyte attachment to TNF alpha-treated endothelial monolayers was totally blocked, while neutrophil attachment was partially reduced but transmigration was essentially prevented.
In most cells, the inactive dimeric NF-kappa B complexes are retained in the cytoplasm by binding to a group of inhibitory proteins. I kappa B. In response to extracellular stimuli, I kappa B is rapidly phosphorylated and degraded, thus, liberating the active NF-kappa B. To investigate the mechanisms involved, we have developed a cell-free system to study the degradation of the prototype I kappa B protein, I kappa B alpha. In this in vitro assay, ubiquitin, proteasome-containing S100 fraction and ATP are required for the proteolysis of I kappa B alpha. Both bound and free forms of I kappa B alpha isolated from intact cells can be degraded through this pathway. We also identified polyubiquitinated I kappa B alpha molecules and N-terminal truncated I kappa B alpha degradation product(s) both in vivo and in vitro. We conclude that the inactivation of I kappa B alpha occurs through a series of processes including phosphorylation, ATP-dependent ubiquitin conjugation and proteasome-mediated proteolysis.
Mammalian cells contain two distinct proteolytic pathways that are involved in different aspects of protein breakdown. Proteins that enter the cell from the extracellular milieu (such as receptor-mediated endocytosed proteins) are degraded in lysosomes. Lysosomal degradation of intracellular proteins occurs mostly under stressed conditions. Nonlysosomal mechanisms are responsible for the highly selective turnover of intracellular proteins that occurs under basal metabolic conditions, but also for some aspects of degradation of intracellular proteins under stress. An important nonlysosomal proteolytic pathway is the ubiquitin system in which proteins are degraded by a 26s protease complex following conjugation by multiple molecules of ubiquitin. The “catalytic core” of the complex is a 20s protease complex also known as the proteasome. Three recent papers, describing three apparently independent biological processes, highlight the role of the ubiquitin-proteasome system as a major, however selective, proteolytic and regulatory pathway. Using specific inhibitors to the proteasome, Rock et al. (1994) demonstrate a role for this protease in the degradation of the major bulk of cellular proteins, but also in specific processing and subsequent presentation of major histocompatibility complex (MHC) class l-restricted antigens. A previous study by the same researchers (Michalek et al., 1993) showed that antigen processing requires the ubiquitin-activating enzyme, El, the first enzyme in the ubiquitin pathway cascade. Thus, it appears that antigen processing is both ubiquitin dependent and proteasome dependent. Palombella et al. (1994) show that maturation of ~105 NF-~6 precursor into the active ~50 subunit of the transcriptional activator also proceeds in a ubiquitin- and proteasomedependent manner. Furthermore, inhibitors to the proteasome block degradation of h&a and thus prevent tumor necrosis factor a (TNFa)-induced activation of mature NFKB and its entry into the nucleus. The two studies clearly demonstrate that the ubiquitin-proteasome system is involved not only in complete destruction of its protein substrates, but also in limited proteolysis and posttranslational processing in which biologically active peptides or fragments are generated. Treier et al. (1994) show that the unstable c-Jut% but not the stable v-Jun, is multiubiquitinated and degraded. The escape of the oncogenic v-Jun from ubiquitin-dependent degradation suggests a novel route to malignant transformation. Presented here is a review of the components, mechanisms of action, and cellular physiology of the ubiquitin-proteasome pathway.
We have investigated proteasome localization in synchronized cells using polyclonal anti-proteasome antibodies. Proteasomes were localized in the nucleus and cytoplasm at all phases of the cycle, but changes in localization were observed which explain the different immunofluorescence patterns found in asynchronous cells. In the nucleus, the intensity of staining in early S phase was low and showed a punctate distribution which changed to a more diffuse and intense labeling during S to G1. In the cytoplasm, proteasomes were concentrated in the perinuclear region at G1 and at the start of S phase and gradually moved towards the periphery of the cell as the cell cycle progressed to G2. No cell cycle-dependent changes were detected in the rate of synthesis or level of proteasomes. An apparent colocalization of proteasomes with elements of the cytoskeleton mainly observed in G2 was investigated further in PtK2 cells. The overall distribution of proteasomes and cell cycle-dependent changes in PtK2 cells were similar to those in L-132 cells. Double-label immunofluorescence studies using anti-proteasome and anti-cytokeratin (TROMA-1) antibodies showed that proteasomes do colocalize with intermediate filaments of the cytokeratin type, mainly during G2. In mitosis, proteasomes were found by immunogold electron microscopy to be localized around the chromosomes in both PtK2 and L-132 cells. Cell cycle-dependent changes in the localization of proteasomes suggest that they may have a regulatory function related to the cell cycle, for example, in the degradation of proteins which control its progression.
A stretch of 28 'alternating' lysine (K) and glutamate (E) residues is found in an activator of the multicatalytic protease. Such 'KEKE sequences' are also present in subunits of the multicatalytic protease, in subunits of the 26S protease and in a variety of chaperonins. We propose that KEKE regions promote association between protein complexes. Furthermore, they may contribute to the selection of peptides presented on MHC Class I receptors.
We demonstrate an essential role for the proteasome complex in two proteolytic processes required for activation of the transcription factor NF-kappa B. The p105 precursor of the p50 subunit of NF-kappa B is processed in vitro by an ATP-dependent process that requires proteasomes and ubiquitin conjugation. The C-terminal region of p105 is rapidly degraded, leaving the N-terminal p50 domain. p105 processing can be blocked in intact cells with inhibitors of the proteasome or in yeast with proteasome mutants. These inhibitors also block the activation of NF-kappa B and the rapid degradation of I kappa B alpha induced by tumor necrosis factor alpha. Thus, the ubiquitin-proteasome pathway functions not only in the complete degradation of polypeptides, but also in the regulated processing of precursors into active proteins.
Proteasomes play a key role in the degradation of abnormal proteins, of short-lived regulatory proteins and in antigen processing. Evidence is accumulating that the 20 S proteasome represents the proteolytic core of the 26 S protease complex (26 S proteasome) which contains several additional subunits implicated in regulation and substrate recognition. Using electron microscopy and digital image analysis we obtained first insights into the structure of this complex which has an estimated molecular weight of approximately 2000 kDa. Two highly asymmetric masses which presumably contain the regulatory subunits of the 26 S complex are attached to both ends of the dimeric 20 S proteasome clearly reflecting its C2 symmetry. The structural uniformity of the complex, i.e. the absence of significant inter-image variations, has important implications for the structure of the latter: It indicates that, in spite of their sequence similarities, the various alpha-type and beta-type subunits of the 20 S proteasome are not promiscuous but occupy precisely defined positions.
We describe the isolation and characterization of proteasomes from recently established immortalized ovarian granulosa cell lines and their intracellular distribution during mitosis and during cAMP-induced differentiation, as revealed by immunofluorescence microscopy. In interphase, proteasomes were localized in small clusters throughout the cytoplasm and the nuclear matrix. In prophase, a substantial increase in proteasomal staining was observed in the perichromosomal area. A dramatic increase occurred in metaphase and in early anaphase; the chromosomes remained unstained. In late anaphase, intensive staining remained associated mainly with the spindle fibers. In telophase and early interphase of the daughter cells, intensive staining of proteasomes persisted in the nuclei. In contrast, in cells stimulated to differentiate by forskolin, which substantially elevates intracellular cAMP in these cell lines, only a weak staining of proteasomes was revealed in both the nucleus and the cytoplasm. Double staining of nondividing cells with antibodies to proteasomes and to tubulin did not show colocalization of proteasomes and microtubules. In contrast, dividing cells show a preferential concentration of proteasomes around spindle microtubules during metaphase and anaphase. The observed spatial and temporal distribution pattern of proteasomes during mitosis is highly reminiscent of the behavior of cyclins [Pines, J. & Hunter, T. (1991) J. Cell Biol. 115, 1-17]. Since proteasome accumulation appears to coincide with disappearance of cyclins A and B1 from the spindle apparatus, it is suggested that proteasomes may play a role in termination of mitosis by degrading the cyclins, which act as regulatory elements.
Initial studies on the specificity of the multicatalytic proteinase complex (MPC; EC 3.4.99.46) led to the identification of three distinct proteolytic components designated as trypsin-like, chymotrypsin-like, and peptidylglutamyl-peptide hydrolyzing, all sensitive to inactivation by 3,4-dichloroisocoumarin (DCI), a general serine proteinase inhibitor. The three components cleave the peptidyl-arylamide bonds in the model synthetic substrates, Z-(D)-Ala-Leu-Arg-2-naphthylamide, Z-Gly-Gly-Leu-p-nitroanilide, and Z-Leu-Leu-Glu-2-naphthylamide, respectively. We report here evidence for the presence in the MPC of two additional distinct components, neither of them capable of cleaving the three model substrates. One of these components cleaves the Leu-Gly and the Leu-Ala bonds in the substrates Cbz-Gly-Pro-Ala-Leu-Gly-p-aminobenzoate and Cbz-Gly-Pro-Ala-Leu-Ala-p-aminobenzoate, respectively, and is activated by treatment of the MPC with DCI, N-ethylmaleimide, Mg2+, Ca2+, and low concentrations of sodium dodecyl sulfate and fatty acids. This component is apparently identical with the previously identified DCI-resistant component of the MPC that cleaves preferentially bonds on the carboxyl side of branched chain amino acids in natural peptides including neurotensin and proinsulin [Cardozo, C., Vinitsky, A., Hidalgo, M. C., Michaud, C., & Orlowski, M. (1992) Biochemistry 31, 7373-7380]. It is probably also identical with the component proposed to be the main factor responsible for the caseinolytic activity [Pereira, M. E., Nguyen, T., Wagner, B. J., Margolis, J. W., Yu, B., & Wilk, S. (1992a) J. Biol. Chem. 267, 7949-7955]. The designation "branched chain amino acid preferring" (BrAAP) is proposed for this component. The second component cleaves peptide bonds between the small neutral amino acids Ala-Gly and Gly-Gly in the substrates Cbz-Gly-Pro-Ala-Ala-Gly-p-aminobenzoate and Cbz-Gly-Pro-Ala-Gly-Gly-p-aminobenzoate, respectively. This component is sensitive to inactivation by DCI, N-ethylmaleimide, and organic mercurials, but unlike the BrAAP it is significantly activated neither by Mg2+ or Ca2+ nor by fatty acids or sodium dodecyl sulfate. The designation "small neutral amino acid preferring" (SNAAP) is proposed for this component. Both components are sensitive to inhibition by the peptidyl-aldehydes N-acetyl-Leu-Leu-norleucinal (Ac-LLnL-CHO; calpain inhibitor I) and N-acetyl-Leu-Leu-methioninal (Ac-LLM-CHO; calpain inhibitor II) but are resistant to inhibition by Z-LLF-CHO, a potent inhibitor of the chymotrypsin-like activity.(ABSTRACT TRUNCATED AT 400 WORDS)
The levels of the tumor suppressor protein p53 are generally quite low in normal cells, due in part to its rapid turnover. Previous studies have implicated ubiquitin-dependent proteolysis in the turnover of wild-type p53 but have not established whether or not p53 is itself a substrate of the ubiquitin system. In this study, inhibitors of the 26S proteasome have been used to further explore the role of ubiquitin proteolysis in regulating p53 turnover. Increased levels of the tumor suppressor protein p53 were observed in normal cells, as well as in cells expressing the human papillomavirus 16 E6 oncoprotein, on exposure of the cells to proteasome inhibitors. Pulse-chase experiments indicated that the increased p53 levels resulted from stabilization of the protein. Furthermore, ubiquitin-p53 conjugates were detected in untreated as well as gamma-irradiated cells, indicating that ubiquitin-dependent proteolysis plays a role in the normal turnover of p53. Increased levels of the cyclin:cyclin-dependent kinase inhibitor p21, a downstream effector of p53 function, were also observed in proteasome inhibitor-treated cells, and this increase was due in part to an increase in p2l mRNA.
Proteases are known to play important roles in cell growth control, although the underlying mechanisms are still poorly understood. Here we show that the protease inhibitor N-acetyl-L-leucinyl-L-leucinyl-L-norleucinal induced cell cycle arrest in platelet-derived growth factor-stimulated human fibroblasts at the G1/S boundary of the cell cycle by inhibiting the proteasome. Inhibition of the proteasome resulted in accumulation of the tumor suppressor p53, which was followed by an increase in the amount of the cyclin-dependent kinase-inhibitor p21. As a consequence, both phosphorylation and activity of the cyclin-dependent kinase 2/cyclin E complex were inhibited. We further observed that the retinoblastoma gene product, pRb, remained in the hypophosphorylated state, thus preventing cells from progression into the S-phase. These studies strongly support the hypothesis that the proteasome is a key regulator in the G1-phase of cell cycle progression.
The p53 tumour-suppressor protein exerts antiproliferative effects, including growth arrest and apoptosis, in response to various types of stress. The activity of p53 is abrogated by mutations that occur frequently in tumours, as well as by several viral and cellular proteins. The Mdm2 oncoprotein is a potent inhibitor of p53. Mdm2 binds the transcriptional activation domain of p53 and blocks its ability to regulate target genes and to exert antiproliferative effects. On the other hand, p53 activates the expression of the mdm2 gene in an autoregulatory feedback loop. The interval between p53 activation and consequent Mdm2 accumulation defines a time window during which p53 exerts its effects. We now report that Mdm2 also promotes the rapid degradation of p53 under conditions in which p53 is otherwise stabilized. This effect of Mdm2 requires binding of p53; moreover, a small domain of p53, encompassing the Mdm2-binding site, confers Mdm2-dependent detstabilization upon heterologous proteins. Raised amounts of Mdm2 strongly repress mutant p53 accumulation in tumour-derived cells. During recovery from DNA damage, maximal Mdm2 induction coincides with rapid p53 loss. We propose that the Mdm2-promoted degradation of p53 provides a new mechanism to ensure effective termination of the p53 signal.
The cell cycle has been the object of extensive studies for the past years. A complex network of molecular interactions has been identified. In particular, a class of cell cycle inhibitory proteins has been identified but details of the molecular mechanism of their action have yet to be resolved. These inhibitors regulate the progression through G1 and the G1/S transition via the inhibition of the cyclin-dependent kinase (Cdk) activity. The potential function of these negative regulators as tumor suppressors provides new insights into the link between the cell cycle and oncogenesis. Kip1 is a potent inhibitor of Cdks. In quiescent cells Kip1 accumulates without an increase in mRNA or protein synthesis. We demonstrated that cell cycle regulation of Kip1 levels, both in normal and transformed human cells, occurs via the ubiquitin-proteasome pathway. In a crude in vitro system, Kip1 is ubiquitinated and degraded in an ATP dependent manner and inhibition or depletion of the proteasome blocks Kip1 degradation. Human Ubc2 and Ubc3, the homologs of yeast Rad6 and Cdc34 gene products respectively, are specifically involved in the ubiquitination of Kip1. Compared to proliferating cells, quiescent cells contain a far lower amount of Kip1 ubiquitinating activity. These results represent the first demonstration that the ubiquitin-proteasome pathway plays a role in the regulation of a cell cycle protein in human cells, namely the Cdk inhibitor Kip1. The specific proteolysis of Kip1 may be involved in the pathway of inactivation of Cdks.