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: UMLS:C0027651 (tumor)
685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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

The implantation of the Lewis lung carcinoma (a fast-growing mouse tumour that induces cachexia) to both wild-type and gene-deficient mice for the TNF-alpha receptor type I protein (Tnfr1 degree/Tnfr1 degree), 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 gene-knockout mice muscle wastage was not affected to the same extent. In both groups, tumour burden resulted in significant increases in circulating TNF-alpha, a cytokine which, as we have previously demonstrated, can induce protein breakdown in skeletal muscle. Muscle wastage 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 is a decreased rate of protein accumulation that accounts for the muscle weight loss observed as a result of tumour burden. In contrast, gene knockout mice did not have significantly lower rates of protein accumulation as a result of tumour implantation. The increase in protein degradation in the tumour-bearing wild mice was accompanied by an enhanced expression of both ubiquitin and proteasome subunit genes, all of them related to the activation of the ATP-dependent proteolytic system in skeletal muscle. Tumour-bearing gene-deficient mice did not show any increase in gene expression. It is concluded that TNF-alpha (alone or in combination with other cytokines) is responsible for the activation of protein breakdown in skeletal muscle of tumour-bearing mice.
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PMID:Role of TNF receptor 1 in protein turnover during cancer cachexia using gene knockout mice. 978 14

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.
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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.
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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.
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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

Progressive weight loss is a common feature of many types of cancer and is responsible not only for a poor quality of life and poor response to chemotherapy, but also a shorter survival time than is found in patients with comparable tumors without weight loss. Although anorexia is common, a decreased food intake alone is unable to account for the changes in body composition seen in cancer patients, and increasing nutrient intake is unable to reverse the wasting syndrome. Although energy expenditure is increased in some patients, cachexia can occur even with a normal energy expenditure. Various factors have been investigated as mediators of tissue wasting in cachexia. These include cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), interferon-gamma (IFN-gamma) and leukemia inhibitory factor (LIF), as well as tumor-derived factors such as lipid mobilizing factor (LMF) and protein mobilizing factor (PMF), which can directly mobilize fatty acids and amino acids from adipose tissue and skeletal muscle respectively. Induction of lipolysis by the cytokines is thought to result from an inhibition of lipoprotein lipase (LPL), although clinical studies provide no evidence for an inhibition of LPL in the adipose tissue of cancer patients. Instead there is an increased expression of hormone sensitive lipase, the enzyme activated by LMF. Protein degradation in cachexia is associated with an increased activity of the ATP-ubiquitin-proteasome pathway. The biological activity of both the LMF and PMF was shown to be attenuated by eicosapentaenoic acid (EPA). Clinical studies show that this polyunsaturated fatty acid is able to stabilize the rate of weight loss and adipose tissue and muscle mass in cachectic patients with unresectable pancreatic cancer. Knowledge of the mechanism of cancer cachexia should lead to the development of new therapeutic agents.
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PMID:Wasting in cancer. 991 7

p27kip1 (p27) is a member of the universal cyclin-dependent kinase inhibitor (CDKI) family. p27 expression is regulated by cell contact inhibition and by specific growth factors, such as transforming growth factor (TGF)-beta. Since the cloning of the p27 gene in 1994, a host of other functions have been associated with this cell cycle protein. In addition to its role as a CDKI, p27 is a putative tumor suppressor gene, regulator of drug resistance in solid tumors, and promoter of apoptosis; acts as a safeguard against inflammatory injury; and has a role in cell differentiation. The level of p27 protein expression decreases during tumor development and progression in some epithelial, lymphoid, and endocrine tissues. This decrease occurs mainly at the post-translational level with protein degradation by the ubiquitin-proteasome pathway. A large number of studies have characterized p27 as an independent prognostic factor in various human cancers, including breast, colon, and prostate adenocarcinomas. Here we review the role of p27 in the regulation of the cell cycle and other cell functions and as a diagnostic and prognostic marker in human neoplasms. We also review studies indicating the increasingly important roles of p27, other CDKIs, and cyclins in endocrine cell hyperplasia and tumor development.
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PMID:p27kip1: a multifunctional cyclin-dependent kinase inhibitor with prognostic significance in human cancers. 1002 89

We have analyzed the presentation of human histocompatability leukocyte antigen-A*0201-associated tumor peptide antigen MAGE-3271-279 by melanoma cells. We show that specific cytotoxic T lymphocyte (CTL)-recognizing cells transfected with a minigene encoding the preprocessed fragment MAGE-3271-279 failed to recognize cells expressing the full length MAGE-3 protein. Digestion of synthetic peptides extended at the NH2 or COOH terminus of MAGE-3271-279 with purified human proteasome revealed that the generation of the COOH terminus of the antigenic peptide was impaired. Surprisingly, addition of lactacystin to purified proteasome, though partially inhibitory, resulted in the generation of the antigenic peptide. Furthermore, treatment of melanoma cells expressing the MAGE-3 protein with lactacystin resulted in efficient lysis by MAGE-3271-279-specific CTL. We therefore postulate that the generation of antigenic peptides by the proteasome in cells can be modulated by the selective inhibition of certain of its enzymaticactivities.
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PMID:Modulation of proteasomal activity required for the generation of a cytotoxic T lymphocyte-defined peptide derived from the tumor antigen MAGE-3. 1007 73

The proliferation of mammalian cells is under strict control, and the cyclin-dependent-kinase inhibitory protein p27Kip1 is an essential participant in this regulation both in vitro and in vivo. Although mutations in p27Kip1 are rarely found in human tumours, reduced expression of the protein correlates well with poor survival among patients with breast or colorectal carcinomas, suggesting that disruption of the p27Kip1 regulatory mechanisms contributes to neoplasia. The abundance of p27Kip1 in the cell is determined either at or after translation, for example as a result of phosphorylation by cyclinE/Cdk2 complexes, degradation by the ubiquitin/proteasome pathway, sequestration by unknown Myc-inducible proteins, binding to cyclinD/Cdk4 complexes, or inactivation by the viral E1A oncoprotein. We have found that a mouse 38K protein (p38) encoded by the Jab1 gene interacts specifically with p27Kip1 and show here that overexpression of p38 in mammalian cells causes the translocation of p27Kip1 from the nucleus to the cytoplasm, decreasing the amount of p27Kip1 in the cell by accelerating its degradation. Ectopic expression of p38 in mouse fibroblasts partially overcomes p27Kip1-mediated arrest in the G1 phase of the cell cycle and markedly reduces their dependence on serum. Our findings indicate that p38 functions as a negative regulator of p27Kip1 by promoting its degradation.
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PMID:Degradation of the cyclin-dependent-kinase inhibitor p27Kip1 is instigated by Jab1. 1008 52

beta-catenin plays an essential role in the Wingless/Wnt signaling cascade and is a component of the cadherin cell adhesion complex. Deregulation of beta-catenin accumulation as a result of mutations in adenomatous polyposis coli (APC) tumor suppressor protein is believed to initiate colorectal neoplasia. beta-catenin levels are regulated by the ubiquitin-dependent proteolysis system and beta-catenin ubiquitination is preceded by phosphorylation of its N-terminal region by the glycogen synthase kinase-3beta (GSK-3beta)/Axin kinase complex. Here we show that FWD1 (the mouse homologue of Slimb/betaTrCP), an F-box/WD40-repeat protein, specifically formed a multi-molecular complex with beta-catenin, Axin, GSK-3beta and APC. Mutations at the signal-induced phosphorylation site of beta-catenin inhibited its association with FWD1. FWD1 facilitated ubiquitination and promoted degradation of beta-catenin, resulting in reduced cytoplasmic beta-catenin levels. In contrast, a dominant-negative mutant form of FWD1 inhibited the ubiquitination process and stabilized beta-catenin. These results suggest that the Skp1/Cullin/F-box protein FWD1 (SCFFWD1)-ubiquitin ligase complex is involved in beta-catenin ubiquitination and that FWD1 serves as an intracellular receptor for phosphorylated beta-catenin. FWD1 also links the phosphorylation machinery to the ubiquitin-proteasome pathway to ensure prompt and efficient proteolysis of beta-catenin in response to external signals. SCFFWD1 may be critical for tumor development and suppression through regulation of beta-catenin protein stability.
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PMID:An F-box protein, FWD1, mediates ubiquitin-dependent proteolysis of beta-catenin. 1022 55


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