Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.25.1 (proteasome)
28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In proliferating cells the turnover rate of proteins responsible for regulation of the cell cycle progression, namely cyclins and inhibitors of the cyclin-dependent kinases (CDKs) and phosphatases, is rapid and their cellular level is modulated at the transcriptional, translational and/or degradation (via proteasome pathway) stages. Inhibition of proteasome function results in accumulation of rapidly turning over proteins and, thus, causes an imbalance of the cell cycle regulatory components, and loss of their regulatory function. Indeed, it has been shown that proteasome inhibitors perturb the cell cycle progression. Onconase, a novel RNase which has anti-tumor activity and is in clinical trials, has previously been shown to suppress protein synthesis, presumably by degradation of intracellular RNA, preferentially tRNA. By interfering with regulation of expression of cyclins and/or CDK-inhibitors, onconase also may induce the imbalance of these proteins and potentiate the effect of proteasome inhibitors. In the present study, we observed that the combinations of onconase with peptide-aldehyde inhibitors of calpain and proteasome such as the N-acetyl-leucinyl-leucinyl-norleucinal (LLnL) and the N-acetyl-leucinyl-valinyl-phenylalaninal (LVP), but not N-acetyl-leucinyl-leucinyl-methioninal (LLM), were synergistic in suppressing cell proliferation and inducing apoptosis in three human tumor cell lines: A-549 lung adenocarcinoma, DU-145 prostatic carcinoma, and MDA-MB-231 breast carcinoma. The observed cytotoxicity may also be a result of prevention of the induction of the 'survival' genes by the nuclear factor kappaB (NFkappaB) by onconase and proteasome inhibitors. The data indicate that such combinations should be further tested as potential anti-cancer regimens.
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PMID:Enhanced in vitro cytotoxicity and cytostasis of the combination of onconase with a proteasome inhibitor. 973 89

A high proportion of tumors arise due to mutation of the p53 tumor suppressor protein. A p53 hotspot mutation at amino acid position 273 from R to H, flanking a peptide epitope that spans residues 264-272, renders cells resistant to killing by human histocompatibility leukocyte antigen (HLA)-A*0201-restricted cytotoxic T lymphocytes (CTLs) specific for this epitope. Acquisition of the R to H mutation at residue 273 of the human p53 protein promotes tumor growth in vivo by selective escape from recognition by p53.264-272 peptide-specific CTLs. Synthetic 27-mer p53 polypeptides covering the antigenic nonamer region 264-272 of p53 were used as proteasome substrates to investigate whether the R to H mutation at the P1' position of the COOH terminus of the epitope affects proteasome-mediated processing of the protein. Analysis of the generated products by tandem mass spectrometry and the kinetics of polypeptide processing in conjunction with CTL assays demonstrate that the R to H mutation alters proteasomal processing of the p53 protein by inhibiting proteolytic cleavage between residues 272 and 273. This prevents the release of the natural CTL epitope that spans flanking residues 264-272 as well as a putative precursor peptide. These results demonstrate that mutation of p53 not only leads to malignant transformation but may also, in some instances, affect immune surveillance and should be considered in the design of cancer vaccines.
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PMID:The sequence alteration associated with a mutational hotspot in p53 protects cells from lysis by cytotoxic T lymphocytes specific for a flanking peptide epitope. 974 20

The implantation of the Lewis lung carcinoma (a fast-growing mouse tumour that induces cachexia) to both wild-type and transgenic mice for the soluble TNF receptor type I protein (sTNF-R1) resulted in a considerable loss of carcass weight in both groups. However, while in the wild-type mice there was a loss of both fat and muscle, in the transgenic mice muscle waste was not affected to the same extent as in the wild-type group. Muscle waste in wild-type mice was accompanied by an increase in the fractional rate of protein degradation, while no changes were observed in protein synthesis. The result was a decreased rate of protein accumulation which accounted for the muscle weight loss observed as a result of the tumour burden. In contrast, transgenic mice did not have such low rates of protein accumulation after tumour implantation. The increase in protein degradation in the tumour-bearing transgenic mice was accompanied by a similar increase in protein synthesis which compensated for the loss of muscle protein by degradation. Both tumour-bearing groups showed an enhanced expression of ubiquitin and proteasome C8 subunit genes, all of them related to the activation of the ATP-dependent proteolytic system in skeletal muscle. It is suggested that TNF may, in part, be responsible for the loss of protein in skeletal muscle of tumour-bearing mice.
Cancer Lett 1998 Aug 14
PMID:Protein turnover in skeletal muscle of tumour-bearing transgenic mice overexpressing the soluble TNF receptor-1. 975 Dec 52

A proteolysis-inducing factor (PIF) isolated from a cachexia-inducing murine tumour (MAC16) produced a decrease in body weight (1.6 g, P < or = 0.01 compared with control subjects) within 24 h after i.v. administration to non-tumour-bearing mice. Weight loss was associated with significant decreases in the weight of the spleen and soleus and gastrocnemius muscles, with no effect on the weight of the heart or kidney and with an increase in weight of the liver. Protein degradation in isolated soleus muscle was significantly increased in mice bearing the MAC16 tumour. To define which proteolytic pathways contribute to this increase, soleus muscles from mice bearing the MAC16 tumour and non-tumour-bearing animals administered PIF were incubated under conditions that modify different proteolytic systems. In mice bearing the MAC16 tumour, there were increases in both cathepsin B and L, and the Ca2+-dependent lysosomal and ATP-dependent pathways were found to contribute to the increased proteolysis; whereas, in PIF-injected animals, there was activation only of the ATP-dependent pathway. Further studies in mice bearing the MAC16 tumour have provided evidence for increased levels of ubiquitin-conjugated proteins and increased mRNA levels for the 14 kDa ubiquitin carrier protein E2 and the C9 proteasome subunit in gastrocnemius muscle, suggesting activation of the ATP-ubiquitin-dependent proteolytic pathway. A monoclonal antibody to PIF attenuated the enhanced protein degradation in soleus muscle from mice bearing the MAC16 tumour, confirming that PIF is responsible for the loss of skeletal muscle in cachectic mice.
Br J Cancer 1998 Oct
PMID:Mechanism of muscle protein degradation induced by a cancer cachectic factor. 976 74

Cell growth and viability are dependent on the function of the multicatalytic proteinase complex (proteasome), a multisubunit particle that affects progression through the mitotic cycle by degradation of cyclins. Exposure of rodent fibroblasts and human lymphoblasts in culture to benzyloxycarbonyl-leucyl-leucyl-phenylalaninal (Z-LLF-CHO), a cell-permeable peptidyl aldehyde inhibitor of the chymotrypsin-like activity of the proteasome, resulted in the induction of apoptosis in a rapid, dose-dependent fashion. Fibroblasts transformed with ras and myc, lymphoblasts transformed by c-myc alone, and a Burkitt's lymphoma (BL) cell line that overexpresses c-Myc were up to 40-fold more susceptible to apoptosis than were either primary rodent fibroblasts or immortalized nontransformed human lymphoblasts, respectively. To determine whether such preferential apoptosis could impact upon tumor growth in vivo, toxicological studies were performed in mice with severe combined immunodeficiency and showed that mice tolerated single interscapular doses of Z-LLF-CHO without unacceptable toxicity. Severe combined immunodeficient mice bearing s.c. BL tumors in the flank were treated interscapularly with Z-LLF-CHO or a comparable dose of the peptidyl alcohol (Z-LLF-OH), which does not induce proteasome inhibition or apoptosis. Single doses of Z-LLF-CHO induced statistically significant (P < 0.0001) early tumor regression and a significant (P < 0.0001) delay in tumor progression. Analysis of tumor specimens revealed increased apoptosis in BL tumors from mice treated with Z-LLF-CHO. These results, showing a 42% tumor growth delay, indicate that proteasome inhibitors have the potential of curbing the growth of a c-myc-related tumor.
Cancer Res 1998 Oct 01
PMID:Tumor growth inhibition induced in a murine model of human Burkitt's lymphoma by a proteasome inhibitor. 976 62

Mutations of the p53 gene are the most common abnormalities in human cancer. In contrast to mutant p53, wild-type (wt) p53 protein is present at low levels due to rapid degradation by proteasome. We demonstrated that wt p53 protein stabilization following DNA damage or proteasome inhibition did not abolish the wild-type conformation. DNA damage did not cause accumulation of ubiquitinated forms of wt p53, suggesting abrogation of ubiquitination. Consistent with this, the E6 oncoprotein which targets p53 for ubiquitination abolished stabilization of p53 protein by DNA-damaging drugs but not by proteasome inhibitors. In contrast to the effects on wt p53, inhibitors of proteolysis downregulated mutant p53. Regulation of p53 levels can be explained by a feedback mechanism where wt p53 transcriptionally induces "sensor" proteins (Mdm-2, as an example) and these, in turn, target p53 for degradation. Like p53, Mdm-2 is degraded by proteasome. Therefore, inhibition of proteasome caused accumulation of Mdm-2, leading to degradation of mutant p53 by the remaining proteolytic activity of the cell. We propose that inhibition of transcription should increase wt p53 protein due to inhibition of Mdm-2 synthesis. An inhibitor of transcription, alpha-amanitin, dramatically induced wt p53 protein, whereas Mdm-2 protein was downregulated. Moreover, alpha-amanitin increased p53 protein levels in E6-transfected cells. Although inhibitors of transcription, such as actinomycin D, also damage DNA, reduction of Mdm-2 or other putative "sensor" proteins may contribute to their p53-stabilizing activity. Similarly, antimetabolites augment accumulation of wt p53 due to interference with RNA synthesis.
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PMID:Inhibitors of transcription, proteasome inhibitors, and DNA-damaging drugs differentially affect feedback of p53 degradation. 977 Mar 48

The rapid loss of muscle mass that accompanies many disease states, such as cancer or sepsis, is primarily a result of increased protein breakdown in muscle, and several observations have suggested an activation of the ubiquitin-proteasome system. Accordingly, in extracts of atrophying muscles from tumor-bearing or septic rats, rates of 125I-ubiquitin conjugation to endogenous proteins were found to be higher than in control extracts. On the other hand, in extracts of muscles from hypothyroid rats, where overall proteolysis is reduced below normal, the conjugation of 125I-ubiquitin to soluble proteins decreased by 50%, and treatment with triiodothyronine (T3) restored ubiquitination to control levels. Surprisingly, the N-end rule pathway, which selectively degrades proteins with basic or large hydrophobic N-terminal residues, was found to be responsible for most of these changes in ubiquitin conjugation. Competitive inhibitors of this pathway that specifically block the ubiquitin ligase, E3alpha, suppressed most of the increased ubiquitin conjugation in the muscle extracts from tumor-bearing and septic rats. These inhibitors also suppressed ubiquitination in normal extracts toward levels in hypothyroid extracts, which showed little E3alpha-dependent ubiquitination. Thus, the inhibitors eliminated most of the differences in ubiquitination under these different pathological conditions. Moreover, 125I-lysozyme, a model N-end rule substrate, was ubiquitinated more rapidly in extracts from tumor-bearing and septic rats, and more slowly in those from hypothyroid rats, than in controls. Thus, the rate of ubiquitin conjugation increases in atrophying muscles, and these hormone- and cytokine-dependent responses are in large part due to activation of the N-end rule pathway.
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PMID:Rates of ubiquitin conjugation increase when muscles atrophy, largely through activation of the N-end rule pathway. 977 May 32

Some human tumor cells exhibit deficient expression of the peptide transporters TAP1 and TAP2 and of the proteasome subunits low molecular weight protein (LMP)-2 and LMP-7, which could be partially restored by cytokine treatment. Here, we show that IFN-gamma stimulation of human renal cell carcinoma lines increased the MHC class I, transporter associated with antigen processing (TAP), and LMP transcript and protein levels, but TAP and LMP expression are more rapidly induced by IFN-gamma than MHC class I molecules. No correlation between the level of induction of the MHC class I antigen presentation genes and IFN sensitivity/resistance was detected. The IFN-gamma-mediated increase of MHC class I, TAP-1, and LMP-2 expression was independent of de novo protein synthesis. Analysis of the dual TAP-1/LMP-2 promoter activity revealed that TAP-1 and LMP-2 expression are controlled by IFN-gamma at the transcriptional level. Site-specific mutations in the IFN-gamma-responsive element of the TAP-1/LMP-2 promoter blocked induction by IFN-gamma. Thus, the IFN-gamma-mediated coordinated transcriptional up-regulation of TAP-1 and LMP-2 expression occurs through the use of a common regulatory element, which might result in enhanced recognition of renal cell carcinoma cells by the immune system.
Clin Cancer Res 1997 Apr
PMID:IFN-gamma-mediated coordinated transcriptional regulation of the human TAP-1 and LMP-2 genes in human renal cell carcinoma. 981 22

Specific CD8(+) CTL recognition of melanoma requires expression of MHC class I molecules as well as melanoma-associated peptide epitopes. Human melanoma cells may escape immune recognition by a variety of means, including global or allelic down-regulation of MHC class I molecules. Stable MHC class I cell surface expression requires delivery of cytosolic peptides into the endoplasmic reticulum by the peptide transporter molecules TAP1 and TAP2, with peptides subsequently transported to the cell surface in complexes containing MHC class I heavy chain and beta2-microglobulin. We have evaluated a series of mechanisms resulting in MHC class I down-regulation in a human melanoma cell line, Mz18, typed as HLA-A2(+), A3(+), B7(+), B57(+), Cw1(+), and Cw6(+) by genomic PCR analysis. The melanoma cell line Mz18 exhibits a global down-regulation of MHC class I heavy chain transcripts; beta2-microglobulin; the proteasome subunits LMP2/7, involved in generating cytosolic peptide fragments; and the peptide transporter molecules TAP1 and TAP2, involved in peptide transport from the cytosol into the endoplasmic reticulum. IFN-gamma treatment of Mz18 melanoma cells leads to up-regulation of LMP2/7 and TAP1/2, as well as to up-regulation of HLA-B and HLA-C MHC loci alleles, but not HLA-A2 or HLA-A3. Karyotypic analysis and fluorescence in situ hybridization with chromosome 6 and MHC class I-specific probes showed complex rearrangement of one chromosome 6 involving the MHC class I locus on 6p and translocation of 6q to the long arm of chromosome 19. To evaluate the capability of melanoma Mz18 to present tumor-specific peptides to HLA-A2-restricted, melanoma-specific CTLs, we restored HLA-A2 surface expression by retroviral-mediated transfer of functional HLA-A2 cDNA. Melanoma peptides could only be presented and recognized by CTLs if the HLA-A2-transfected Mz18 cell line was first treated with IFN-gamma, thereby restoring LMP2/7 and TAP1/2 expression and function. Because several melanoma antigens recognized by T cells have been reported to be presented by HLA-A2 (MART-1/Melan-A, tyrosinase, gp100, and MAGE-3), the loss of HLA-A2 molecules may represent an important mechanism by which many melanomas evade immune recognition. These findings suggest that patients entering clinical trials for immunotherapy with melanoma vaccines should be carefully examined for tumor cell allelic MHC class I loss and whether such MHC class I antigen down-regulation can be restored by cytokines.
Clin Cancer Res 1996 Apr
PMID:Tumor escape from immune recognition: loss of HLA-A2 melanoma cell surface expression is associated with a complex rearrangement of the short arm of chromosome 6. 981 14

Suppression of MHC class I expression is thought to allow tumor cells to escape immune surveillance mediated by CD8(+) CTLs. For stable MHC class I surface expression, multiple protein interactions are required for efficient assembly of MHC class I heavy chain and beta 2-microglobulin with endogenous peptides. Peptide processing and transport into the endoplasmic reticulum involves the genes of the transporters associated with antigen processing, TAP-1 and TAP-2, and the two components of the proteasome complex, the low molecular weight proteins LMP-2 and LMP-7. We selected human renal cell carcinoma (RCC) cells derived from a tumor that is thought to be controlled by host immunity to study the MHC class I antigen presentation machinery. Eleven RCC lines established from primary tumors were investigated for the mRNA and protein expression of MHC class I, TAP, and LMP genes. In addition, membrane stability of MHC class I was determined by incubation of the RCC cell lines at low temperature and in the presence of exogenous HLA-binding peptides. Our results revealed the existence of two different phenotypes of RCC cell lines. Group I displayed temperature-stable MHC class I surface expression associated with high, and in most cases coordinated, expression of MHC class I heavy and light chain, TAP and LMP transcripts, and proteins. Group II demonstrated a marked MHC class I instability at 37 degreesC associated with low but coordinated expression of the respective transcripts and proteins. MHC class I membrane expression of group II, but not of group I RCC cells, could be stabilized by incubation with specific MHC class I binding peptides. These results suggest an important role of the genes of the antigen presentation machinery in stable and efficient MHC class I surface expression of RCC cells. However, it has still to be defined whether deficient antigen processing is one of the mechanisms of RCC cells to escape the surveillance of the immune system.
Clin Cancer Res 1996 Aug
PMID:Reduced membrane major histocompatibility complex class I density and stability in a subset of human renal cell carcinomas with low TAP and LMP expression. 981 17


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