The ubiquitin-proteasome pathway and proteasome inhibitors

Background: Proteasome inhibitors such as bortezomib, a chemotherapeutic used to treat multiple myeloma, induce thrombocytopenia within days of initiation. The mechanism for this thrombocytopenia has been tied to data revealing that proteasome activity is essential for platelet formation. The major pathway of selective protein degradation uses ubiquitin as a marker that targets proteins for proteolysis by the proteasome. This pathway is previously unexplored in megakaryocytes (MKs). Objectives: We aim to define the mechanism by which the ubiquitin-proteasome pathway affects MK maturation and platelet production. Results: Pharmacologic inhibition of proteasome activity blocks proplatelet formation in megakaryocytes. To further characterize how this degradation was occurring, we probed distinct ubiquitin pathways. Inhibition of the ubiquitin-activating enzyme E1 significantly inhibited proplatelet formation up to 73%. In addition, inhibition of the deubiquitinase proteins UCHL5 and USP14 significantly inhibited proplatelet formation up to 83%. These data suggest that an intact ubiquitin pathway is necessary for proplatelet formation. Proteomic and polysome analyses of MKs undergoing proplatelet formation revealed a subset of proteins decreased in proplatelet-producing megakaryocytes, consistent with data showing that protein degradation is necessary for proplatelet formation. Specifically, the centrosome stabilizing proteins Aurora kinase (Aurk) A/B, Tpx2, Cdk1, and Plk1 were decreased in proplatelet-producing MKs. Furthermore, inhibition of AurkA and Plk1, but not Cdk1, significantly inhibited proplatelet formation in vitro over 83%. Conclusions: We hypothesize that proplatelet formation is triggered by centrosome destabilization and disassembly, and that the ubiquitin-proteasome pathway plays a crucial role in this transformation. Specifically, regulation of the AurkA/Plk1/Tpx2 pathway may be key in centrosome integrity and initiation of proplatelet formation. Determination of the mechanism by which the ubiquitin-proteasome pathway regulates the centrosome and facilitates proplatelet formation will allow us to design better strategies to target and reverse thrombocytopenia.

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The Ubiquitin Proteasome Pathway from Bench to Bedside

Hematology ◽

10.1182/asheducation-2005.1.220 ◽

2005 ◽

Vol 2005 (1) ◽

pp. 220-225 ◽

Cited By ~ 18

Author(s):

Robert Z. Orlowski

Keyword(s):

Phase I ◽

Hematological Malignancies ◽

Expression Profiles ◽

Proteasome Inhibitors ◽

Rational Approach ◽

Significant Activity ◽

Ubiquitin Proteasome Pathway ◽

Gene And Protein Expression ◽

Ubiquitin Proteasome ◽

Proteasome Pathway

Abstract The validation of the ubiquitin-proteasome pathway as a target for therapy of hematological malignancies stands out as one salient example of the ability to translate laboratory-based findings from the bench to the bedside. Preclinical studies showed that proteasome inhibitors had significant activity against models of non-Hodgkin lymphoma and multiple myeloma, and identified some of the relevant mechanisms of action. These led to phase I through III trials of the first clinically available proteasome inhibitor, bortezomib, which confirmed its activity as a single agent in these diseases. Modulation of proteasome function was then found to be a rational approach to achieve both chemosensitization in vitro and in vivo, as well as to overcome chemotherapy resistance. Based on these findings, first-generation bortezomib-based regimens incorporating traditional chemotherapeutics such as alkylating agents, anthracyclines, immunomodulatory agents, or steroids have been evaluated, and many show promise of enhanced clinical anti-tumor efficacy. Further studies of the pro-and anti-apoptotic actions of proteasome inhibitors, and of their effects on gene and protein expression profiles, suggest that novel agents, such as those targeting the heat shock protein pathways, are exciting candidates for incorporation into these combinations. Phase I trials to test these concepts are just beginning, but have already shown some encouraging results. Finally, novel proteasome inhibitors are being developed with unique properties that may also have therapeutic applications. Taken together, these studies demonstrate the power of rational drug design and development to provide novel, effective therapies for patients with hematological malignancies.

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Proteasome Inhibitors Block a Late Step in Lysosomal Transport of Selected Membrane but not Soluble Proteins

Molecular Biology of the Cell ◽

10.1091/mbc.12.8.2556 ◽

2001 ◽

Vol 12 (8) ◽

pp. 2556-2566 ◽

Cited By ~ 84

Author(s):

Peter van Kerkhof ◽

Cristina M. Alves dos Santos ◽

Martin Sachse ◽

Judith Klumperman ◽

Guojun Bu ◽

...

Keyword(s):

Membrane Proteins ◽

Proteasome Inhibitors ◽

Endocytic Pathway ◽

Endosomal Sorting ◽

Ubiquitin Proteasome Pathway ◽

Late Step ◽

Ubiquitin Proteasome ◽

Proteasome Pathway ◽

Lysosomal Transport

The ubiquitin-proteasome pathway acts as a regulator of the endocytosis of selected membrane proteins. Recent evidence suggests that it may also function in the intracellular trafficking of membrane proteins. In this study, several models were used to address the role of the ubiquitin-proteasome pathway in sorting of internalized proteins to the lysosome. We found that lysosomal degradation of ligands, which remain bound to their receptors within the endocytic pathway, is blocked in the presence of specific proteasome inhibitors. In contrast, a ligand that dissociates from its receptor upon endosome acidification is degraded under the same conditions. Quantitative electron microscopy showed that neither the uptake nor the overall distribution of the endocytic marker bovine serum albumin-gold is substantially altered in the presence of a proteasome inhibitor. The data suggest that the ubiquitin-proteasome pathway is involved in an endosomal sorting step of selected membrane proteins to lysosomes, thereby providing a mechanism for regulated degradation.

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Regulation of elastin gene transcription by proteasome dysfunction

AJP Cell Physiology ◽

10.1152/ajpcell.00525.2004 ◽

2005 ◽

Vol 289 (3) ◽

pp. C766-C773 ◽

Cited By ~ 12

Author(s):

Ping-Ping Kuang ◽

Ronald H. Goldstein

Keyword(s):

Gene Expression ◽

Gene Transcription ◽

Proteasome Inhibitors ◽

Lung Fibroblasts ◽

Extracellular Matrix Protein ◽

Mrna Levels ◽

Ubiquitin Proteasome Pathway ◽

Ubiquitin Proteasome ◽

Proteasome Pathway ◽

Elastin Gene

Elastin, a major extracellular matrix protein and the core component of elastic fiber, is essential to maintain lung structural integrity and normal physiological function. We previously found that the downregulation of elastin gene transcription by IL-1β is mediated via activation of NF-κB and CCAAT/enhancer binding protein (C/EBP)β, both targets of the ubiquitin-proteasome pathway. To further investigate the molecular mechanisms that underlie the control of elastin gene expression, we disrupted the ubiquitin-proteasome pathway with specific proteasome inhibitors. We found that specific proteasome inhibitors decreased the steady-state level of elastin mRNA in a dose-responsive manner. Run-on assay and promoter reporter study indicated that the proteasome inhibitor MG-132 repressed the rate of elastin transcription. MG-132 did not affect mRNA levels of NF-κB and C/EBPβ, or the nuclear presence of NF-κB, but markedly increased C/EBPβ isoforms, including liver-enriched transcriptional activating protein and liver-enriched transcriptional inhibitory protein. Addition of cycloheximide blocked these increases and the downregulation of elastin mRNA by MG-132. The MG-132-induced downregulation of elastin transcription was dependent on C/EBPβ expression as assessed with small interfering RNA. These results indicate that the ubiquitin-proteasome pathway plays an essential role in maintaining elastin gene expression in lung fibroblasts. Disruption of this pathway results in the downregulation of tropoelastin transcription via posttranscriptionally induced C/EBPβ isoforms.

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The ubiquitin-proteasome pathway regulates survivin degradation in a cell cycle-dependent manner

Journal of Cell Science ◽

10.1242/jcs.113.23.4363 ◽

2000 ◽

Vol 113 (23) ◽

pp. 4363-4371 ◽

Cited By ~ 3

Author(s):

J. Zhao ◽

T. Tenev ◽

L.M. Martins ◽

J. Downward ◽

N.R. Lemoine

Keyword(s):

Cell Cycle ◽

Proteasome Inhibitors ◽

Dependent Manner ◽

Ubiquitin Proteasome Pathway ◽

Apoptosis Protein ◽

Ubiquitin Proteasome ◽

A Cell ◽

Proteasome Pathway ◽

Cycle Dependent

Survivin, a human inhibitor of apoptosis protein (IAP), plays an important role in both cell cycle regulation and inhibition of apoptosis. Survivin is expressed in cells during the G(2)/M phase of the cell cycle, followed by rapid decline of both mRNA and protein levels at the G(1) phase. It has been suggested that cell cycle-dependent expression of survivin is regulated at the transcriptional level. In this study we demonstrate involvement of the ubiquitin-proteasome pathway in post-translational regulation of survivin. Survivin is a short-lived protein with a half-life of about 30 minutes and proteasome inhibitors greatly stabilise survivin in vivo. Expression of the survivin gene under the control of the CMV promoter cannot block cell cycle-dependent degradation of the protein. Proteasome inhibitors can block survivin degradation during the G(1) phase and polyubiquitinated derivatives can be detected in vivo. Mutation of critical amino acid residues within the baculovirus IAP repeat (BIR) domain or truncation of the N terminus or the C terminus sensitises survivin to proteasome degradation. Together, these results indicate that the ubiquitin-proteasome pathway regulates survivin degradation in a cell cycle-dependent manner and structural changes greatly destabilise the survivin protein.

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The ubiquitin-proteasome pathway regulates lysosomal degradation of the growth hormone receptor and its ligand

Biochemical Society Transactions ◽

10.1042/bst0290488 ◽

2001 ◽

Vol 29 (4) ◽

pp. 488-493 ◽

Cited By ~ 34

Author(s):

P. van Kerkhof ◽

G. J. Strous

Keyword(s):

Growth Hormone ◽

Proteasome Inhibitor ◽

Growth Hormone Receptor ◽

Proteasome Inhibitors ◽

Plasma Membrane Protein ◽

Lysosomal Degradation ◽

Ubiquitin Proteasome Pathway ◽

Gh Receptor ◽

Ubiquitin Proteasome ◽

Proteasome Pathway

The growth hormone (GH) receptor (GHR) is a mammalian plasma membrane protein whose internalization is mediated by the ubiquitin-proteasome pathway. GH internalization and degradation are inhibited when cells are treated with proteasome inhibitors. Here we show that a GHR truncated at residue 369 can enter the cells in the presence of a proteasome inhibitor, but that the subsequent lysosomal degradation of GH is blocked. Lysosomal inhibitors prolong the half-life of both receptor and ligand. Experiments with antibodies against different receptor tail sections show that degradation of the GHR cytosolic domain precedes degradation of the extracellular GH-binding domain. A possible role for the ubiquitin-proteasome pathway in the degradation of the receptor and ligand is discussed.

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ChemInform Abstract: The Ubiquitin-Proteasome Pathway and Proteasome Inhibitors

ChemInform ◽

10.1002/chin.200136283 ◽

2010 ◽

Vol 32 (36) ◽

pp. no-no

Author(s):

Jayhyuk Myung ◽

Kyung Bo Kim ◽

Craig M. Crews

Keyword(s):

Proteasome Inhibitors ◽

Ubiquitin Proteasome Pathway ◽

Ubiquitin Proteasome ◽

Proteasome Pathway

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Use of proteasome inhibitors in anticancer therapy

Reviews in Health Care ◽

10.7175/rhc.v2i4.60 ◽

2011 ◽

Vol 2 (4) ◽

pp. 259-287 ◽

Cited By ~ 1

Author(s):

Sara M. Schmitt ◽

Lillian Lu ◽

Q. Ping Dou

Keyword(s):

Drug Targets ◽

Proteasome Inhibitors ◽

New Drugs ◽

Ubiquitin Proteasome Pathway ◽

Human Cancers ◽

Green Tea Polyphenol ◽

Ubiquitin Proteasome ◽

Proteasome Pathway ◽

Approved Drugs ◽

Toxic Drugs

The importance of the ubiquitin-proteasome pathway to cellular function has brought it to the forefront in the search for new anticancer therapies. The ubiquitin-proteasome pathway has proven promising in targeting various human cancers. The approval of the proteasome inhibitor bortezomib for clinical treatment of relapsed/refractory multiple myeloma and mantle cell lymphoma has validated the ubiquitin-proteasome as a rational target. Bortezomib has shown positive results in clinical use but some toxicity and side effects, as well as resistance, have been observed, indicating that further development of novel, less toxic drugs is necessary. Because less toxic drugs are necessary and drug development can be expensive and time-consuming, using existing drugs that can target the ubiquitin-proteasome pathway in new applications, such as cancer therapy, may be effective in expediting the regulatory process and bringing new drugs to the clinic. Toward this goal, previously approved drugs, such as disulfiram, as well as natural compounds found in common foods, such as green tea polyphenol (-)-EGCG and the flavonoid apigenin, have been investigated for their possible proteasome inhibitory and cell death inducing abilities. These compounds proved quite promising in preclinical studies and have now moved into clinical trials, with preliminary results that are encouraging. In addition to targeting the catalytic activity of the proteasome pathway, upstream regulators, such as the 19S regulatory cap, as well as E1, E2, and E3, are now being investigated as potential drug targets. This review outlines the development of novel proteasome inhibitors from preclinical to clinical studies, highlighting their abilities to inhibit the tumor proteasome and induce apoptosis in several human cancers.

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Heat Shock Response and Protein Degradation: Regulation of HSF2 by the Ubiquitin-Proteasome Pathway

Molecular and Cellular Biology ◽

10.1128/mcb.18.9.5091 ◽

1998 ◽

Vol 18 (9) ◽

pp. 5091-5098 ◽

Cited By ~ 142

Author(s):

Anu Mathew ◽

Sameer K. Mathur ◽

Richard I. Morimoto

Keyword(s):

Heat Shock ◽

Mammalian Cells ◽

Proteasome Inhibitors ◽

Heat Shock Gene ◽

Heat Shock Factors ◽

Heat Shock Genes ◽

Ubiquitin Proteasome Pathway ◽

Stress Signal ◽

Ubiquitin Proteasome ◽

Proteasome Pathway

ABSTRACT Mammalian cells coexpress a family of heat shock factors (HSFs) whose activities are regulated by diverse stress conditions to coordinate the inducible expression of heat shock genes. Distinct from HSF1, which is expressed ubiquitously and activated by heat shock and other stresses that result in the appearance of nonnative proteins, the stress signal for HSF2 has not been identified. HSF2 activity has been associated with development and differentiation, and the activation properties of HSF2 have been characterized in hemin-treated human K562 erythroleukemia cells. Here, we demonstrate that a stress signal for HSF2 activation occurs when the ubiquitin-proteasome pathway is inhibited. HSF2 DNA-binding activity is induced upon exposure of mammalian cells to the proteasome inhibitors hemin, MG132, and lactacystin, and in the mouse ts85 cell line, which carries a temperature sensitivity mutation in the ubiquitin-activating enzyme (E1) upon shift to the nonpermissive temperature. HSF2 is labile, and its activation requires both continued protein synthesis and reduced degradation. The downstream effect of HSF2 activation by proteasome inhibitors is the induction of the same set of heat shock genes that are induced during heat shock by HSF1, thus revealing that HSF2 affords the cell with a novel heat shock gene-regulatory mechanism to respond to changes in the protein-degradative machinery.

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The Ubiquitin-Proteasome Pathway and Resistance Mechanisms Developed Against the Proteasomal Inhibitors in Cancer Cells

Current Drug Targets ◽

10.2174/1389450121666200525004714 ◽

2020 ◽

Vol 21 (13) ◽

pp. 1313-1325

Author(s):

Azmi Yerlikaya ◽

Ertan Kanbur

Keyword(s):

Cancer Cells ◽

Proteasome Inhibitor ◽

Molecular Mechanisms ◽

Proteasome Inhibitors ◽

Resistance Mechanisms ◽

New Drugs ◽

Drug Pressure ◽

Ubiquitin Proteasome Pathway ◽

Ubiquitin Proteasome ◽

Proteasome Pathway

Background: The ubiquitin-proteasome pathway is crucial for all cellular processes and is, therefore, a critical target for the investigation and development of novel strategies for cancer treatment. In addition, approximately 30% of newly synthesized proteins never attain their final conformations due to translational errors or defects in post-translational modifications; therefore, they are also rapidly eliminated by the ubiquitin-proteasome pathway. Objective: Here, an effort was made to outline the recent findings deciphering the new molecular mechanisms involved in the regulation of ubiquitin-proteasome pathway as well as the resistance mechanisms developed against proteasome inhibitors in cell culture experiments and in the clinical trials. Results: Since cancer cells have higher proliferation rates and are more prone to translational errors, they require the ubiquitin-proteasome pathway for selective advantage and sustained proliferation. Therefore, drugs targeting the ubiquitin-proteasome pathway are promising agents for the treatment of both hematological and solid cancers. Conclusions: A number of proteasome inhibitors are approved and used for the treatment of advanced and relapsed multiple myeloma. Unfortunately, drug resistance mechanisms may develop very fast within days of the start of the proteasome inhibitor-treatment either due to the inherent or acquired resistance mechanisms under selective drug pressure. However, a comprehensive understanding of the mechanisms leading to the proteasome inhibitor-resistance will eventually help the design and development of novel strategies involving new drugs and/or drug combinations for the treatment of a number of cancers.

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