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

---

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

We investigated the expression of interferon gamma (IFN-gamma)-regulated subunits and the enzymatic activity of proteasomes purified from tumor-derived and normal B lymphocytes representing different stages of B-cell activation/differentiation. The catalytic beta subunits (Lmp2 and Lmp7) and the regulatory subunits (PA28alpha and PA28beta) were expressed at equally high levels in Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCLs), freshly isolated B-chronic lymphocytic leukemia (B-CLL) cells and normal CD23(-) B lymphocytes. Lmp2 and Lmp7 were selectively down-regulated in germinal center cell-derived Burkitt's lymphoma (BL) and Hodgkin's lymphoma (HD) cell lines. There was a direct correlation between the expression of Lmp2/7 and the chymotrypsin and trypsin-like activities in proteasomes purified from LCLs, BLs and CLL cells, whereas 5 HD cell lines expressing B or T-cell markers exhibited a variable pattern of subunit expression and enzymatic activity. Poor hydrolysis of the fluorogenic substrates by proteasomes from BL cells correlated with a distinct pattern of cleavage of a reference 50mer peptide, production of different sets of degradation products and significantly reduced recovery of a known cytotoxic T-lymphocyte (CTL) target epitope. The enzymatic activity of proteasomes from normal CD23(-) "resting" B lymphocytes resembled that of BL cells in spite of high Lmp2/7 expression. This pattern was not reversed by treatment with the B-cell mitogen, lipopolysaccharide (LPS). The results suggest that different stages of B-cell activation/differentiation are associated with distinct profiles of IFN-gamma-regulated subunit composition and enzymatic activity of the proteasome. This may have important implications for the analysis and manipulation of tumor-specific immune responses.
...
PMID:Variations in proteasome subunit composition and enzymatic activity in B-lymphoma lines and normal B cells. 1109 9

In murine tumor cell lines, downregulation of MHC class I surface expression has been frequently detected, but the underlying molecular mechanisms of such deficiencies have not been defined. In this study, murine tumor cell lines of different histology derived from spontaneous or from chemical-induced tumors were analyzed for the expression of multiple components of the major histocompatibility complex (MHC) class I antigen-processing machinery (APM), including the peptide transporter TAP, the interferon (IFN)-gamma inducible proteasome subunits and several chaperones. The tumor cell lines analyzed demonstrated a heterogeneous expression pattern of various APM components. In comparison to control cells an impaired coordinated expression of at least three APM components was detected. In particular, extensive APM deficiencies were found in cell lines derived from chemical-induced tumors. A strong coordinated downregulation of expression and/or function of TAP, the low molecular weight proteins (LMP) subunits, the proteasome activator PA28 and/or tapasin was found in 5 of 10 tumor cells, which was associated with impaired MHC class I surface expression. In contrast, the expression of beta2-microglobulin (beta2-m), PA28beta, the constitutive proteasome subunits X, Y, Z and of the chaperones calnexin, calreticulin, ER60 and phospho disulfide isomerase (PDI) was unaltered or only weakly decreased. The deficient expression of APM components could be corrected by IFN-gamma treatment, which also reconstituted MHC class I surface expression. However, impaired expression of APM molecules appears not to be the only cause of abnormal MHC class I expression, since it could neither be corrected by the addition of exogeneous MHC class I binding peptides nor by incubation at low temperature. These results suggest that one major mechanism of murine tumor cells, in particular chemical-induced tumors, to evade the immune system is the combined dysregulation of various APM components and other factors, which still have to be identified.
...
PMID:Coordinate downregulation of multiple MHC class I antigen processing genes in chemical-induced murine tumor cell lines of distinct origin. 1109 32

The proteasome activator PA28 (11S REG) is composed of two homologous subunits termed alpha and beta. The properties of the recombinant beta-subunit were explored and compared to the properties of the recombinant alpha-subunit. PA28beta produced in an Escherichia coli expression system migrates on a calibrated gel filtration column as an apparent heptamer (Mr = 250,000). Low concentrations of SDS (0.005%), dissociate the protein to a monomer (Mr = 33,000). PA28beta, has a complex effect on proteasome activity. At concentrations which favor oligomerization (> 2 microM), PA28beta is a strong proteasome activator although its affinity for the proteasome is about 10-fold less than recombinant PA28alpha. The catalytic properties of the PA28alpha and PA28beta-activated proteasome are similar. At low concentrations, PA28beta is a monomer and a potent allosteric proteasome inhibitor. These studies show that oligomerization of PA28beta is required for proteasome activation and that PA28beta monomers are potent proteasome inhibitors.
...
PMID:Properties of the beta subunit of the proteasome activator PA28 (11S REG). 1114 28

PA28alpha/beta is a regulatory complex of the 20S proteasome which consists of two IFN-gamma inducible subunits. Both subunits, alpha and beta, contribute equally to the formation of hexa- or heptameric rings which can associate with the 20S proteasome. Previously, we have shown that overexpression of the PA28alpha subunit enhanced the MHC class I-restricted presentation of two viral epitopes and that purified PA28alpha/beta accelerated T cell epitope generation by the 20S proteasome in vitro, indicating a role for PA28alpha/beta in antigen presentation. This conclusion was recently confirmed in PA28beta gene targeted mice which were severely deficient in MHC class I-restricted antigen presentation. These mice displayed a defect in the assembly of immunoproteasomes, suggesting that a lack of the proteasome subunits LMP2, LMP7, and MECL-1 may account for the deficiency in antigen presentation. In this study we investigated whether the effect of PA28alpha/beta on antigen presentation is dependent on a change of proteasome subunit composition. We have analyzed the assembly and subunit composition of proteasomes in fibroblast transfectants overexpressing both, alpha and beta subunits of PA28. In these transfectants we found a marked enhancement in the presentation of the immunodominant H-2Ld-restricted pp89 epitope of murine cytomegalovirus, although the 20S proteasome composition was the same as in recipient cells. We, therefore, conclude that PA28alpha/beta can enhance antigen processing independently of changes in 20S proteasome subunit composition or assembly.
...
PMID:The proteasome regulator PA28alpha/beta can enhance antigen presentation without affecting 20S proteasome subunit composition. 1116 10

Two members of the proteasome activator, PA28alpha and PA28beta, form a heteropolymer that binds to both ends of the 20S proteasome. Evidence in vitro indicates that this interferon-gamma (IFN-gamma)-inducible heteropolymer is involved in the processing of intracellular antigens, but its functions in vivo remain elusive. To investigate the role of PA28alpha/beta in vivo, we generated mice deficient in both PA28alpha and PA28beta genes. The ATP-dependent proteolytic activities were decreased in PA28alpha(-/-)/beta(-/-) cells, suggesting that 'hybrid proteasomes' are involved in protein degradation. Treatment of PA28alpha(-/-)/beta(-/-) cells with IFN-gamma resulted in sufficient induction of the 'immunoproteasome'. Moreover, splenocytes from PA28alpha(-/-)/beta(-/-) 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 PA28beta(-/-) mice. PA28alpha(-/-)/beta(-/-) 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, PA28alpha/beta is not a prerequisite for antigen presentation in general, but plays an essential role for the processing of certain antigens.
...
PMID:Immunoproteasome assembly and antigen presentation in mice lacking both PA28alpha and PA28beta. 1168 30

The human immunodeficiency virus-1 Tat protein inhibits the peptidase activity of the 20S proteasome and competes with the 11S regulator/PA28 for binding to the 20S proteasome. Structural comparison revealed a common site in the Tat protein and the 11S regulator alpha-subunit (REGalpha) called the REG/Tat-proteasome-binding (RTP) site. Kinetic assays found amino acid residues Lys51, Arg52 and Asp67 forming the RTP site of Tat to be responsible for the effects on proteasomes in vitro. The RTP site identified in REGalpha consists of the residues Glu235, Lys236 and Lys239. Mutation of the REGalpha amino acid residues Glu235 and Lys236 to Ala resulted in an REGalpha mutant that lost the ability to activate the 20S proteasome even though it still forms complexes with REGbeta and binds to the 20S proteasome. The REGalpha RTP site is needed to enhance the presentation of a cytomegalovirus pp89 protein-derived epitope by MHC class I molecules in mouse fibroblasts. Cell experiments demonstrate that the Tat amino acid residues 37-72 are necessary for the interaction of the viral protein with proteasomes in vivo. Full-length Tat and the Tat peptide 37-72 suppressed 11S regulator-mediated presentation of the pp89 epitope. In contrast, the Tat peptide 37-72 with mutations of amino acid residues Lys51, Arg52 and Asp67 to Ala was not able to reduce antigen presentation.
...
PMID:The RTP site shared by the HIV-1 Tat protein and the 11S regulator subunit alpha is crucial for their effects on proteasome function including antigen processing. 1241 64

Because of its amplification and/or overexpression in many human tumors, the HER-2/neu proto-oncogene represents an attractive target for T-cell-mediated vaccination strategies. However, overexpression of oncogenes is often associated with defective expression of components of the MHC class I antigen-processing machinery (APM), thereby resulting in an immune escape phenotype of oncogene-transformed cells. To determine whether HER-2/neu influences the MHC class I antigen-processing pathway, the expression pattern of different APM components was examined in murine in vitro models of constitutive and tetracycline-controlled HER-2/neu expression. In comparison with HER-2/neu(-) control cells, HER-2/neu(+) fibroblasts exhibit reduced levels of MHC class I surface antigens that were associated with impaired expression and/or function of the peptide transporter associated with antigen processing, the proteasome subunits low molecular weight protein 2 and low molecular weight protein 10, the proteasome activators PA28alpha and PA28beta, and tapasin. These APM abnormalities resulted in reduced sensitivity to lysis by CTLs. The HER-2/neu-mediated immune escape phenotype could be corrected by IFN-gamma treatment. The clinical relevance of this finding was supported by an inverse correlation between HER-2/neu and the peptide transporter associated with antigen-processing protein expression as determined by immunhistochemical analysis of a series of HER-2/neu(-) and HER-2/neu(+) breast cancer specimens. Thus, a functional link between deficient APM component expression and HER-2/neu overexpression is proposed that might influence the design of HER-2/neu-targeted T-cell-based immunotherapeutic strategies.
...
PMID:HER-2/neu-mediated regulation of components of the MHC class I antigen-processing pathway. 1472 27

Activation of dendritic cells (DC) by Th-dependent (CD40) or -independent (LPS, CpG, or immune complexes) agonistic stimuli strongly enhances the expression of the proteasome activator PA28alphabeta complex. Upon activation of DC, increased MHC class I presentation occurred of the melanocyte-associated epitope tyrosinase-related protein 2(180-188) in a PA28alphabeta-dependent manner. In contrast to other cell types, regulation of PA28alphabeta expression in DC after maturation was found to be IFN-gamma independent. In the present study, we show that expression of PA28alpha and beta subunits was differentially regulated. Firstly, PA28alpha expression is high in both immature and mature DC. In contrast, PA28beta expression is low in immature DC and strongly increased in mature DC. Secondly, we show the presence of a functional NF-kappaB site in the PA28beta promoter, which is absent in the PA28alpha promoter, indicating regulation of PA28beta expression by transcription factors of the NF-kappaB family. In addition, glycerol gradient analysis of DC lysates revealed elevated PA28alphabeta complex formation upon maturation. Thus, induction of PA28beta expression allows proper PA28alphabeta complex formation, thereby enhancing proteasome activity in activated DC. Therefore, maturation of DC not only improves costimulation but also MHC class I processing. This mechanism enhances the CD8(+) CTL (cross)-priming capacity of mature DC.
...
PMID:Differential expression regulation of the alpha and beta subunits of the PA28 proteasome activator in mature dendritic cells. 1594 86

Most forms of neuronal plasticity are associated with induction of the transcription factor Zif268 (Egr1/Krox24/NGF-IA). In a genome-wide scan, we obtained evidence for potential modulation of proteasome subunit and regulatory genes by Zif268 in neurons, a finding of significance considering emerging evidence that the proteasome modulates synaptic function. Bioinformatic analysis indicated that the candidate proteasome Zif268 target genes had a rich concentration of putative Zif268 binding sites immediately upstream of the transcriptional start sites. Regulation of the mRNAs encoding the psmb9 (Lmp2) and psme2 (PA28beta) proteasome subunits, along with the proteasome-regulatory kinase serum/glucocorticoid-regulated kinase (SGK) and the proteasome-associated antigen peptide transporter subunit 1 (Tap1), was confirmed after transfection of a neuronal cell line with Zif268. Conversely, these mRNAs were upregulated in cerebral cortex tissue from Zif268 knock-out mice relative to controls, confirming that Zif268 suppresses their expression in the CNS. Transfected Zif268 reduced the activity of psmb9, SGK, and Tap1 promoter-reporter constructs. Altered psmb9, SGK, and Tap1 mRNA levels were also observed in an in vivo model of neuronal plasticity involving Zif268 induction: the effect of haloperidol administration on striatal gene expression. Consistent with these effects on proteasome gene expression, increased Zif268 expression suppressed proteasome activity, whereas Zif268 knock-out mice exhibited elevated cortical proteasome activity. Our findings reveal that Zif268 regulates the expression of proteasome and related genes in neuronal cells and provide new evidence that altered expression of proteasome activity after Zif268 induction may be a key component of long-lasting CNS plasticity.
...
PMID:Regulation of the neuronal proteasome by Zif268 (Egr1). 1645 86

Gastric cancers with and without high-frequency microsatellite instability (MSI-H) represent distinctive pathways of carcinogenesis. The aim of this study was to clarify if human leukocyte antigen (HLA) class I antigen subunits and antigen processing machinery (APM) components are differentially downregulated in these two groups of tumours. Using reverse transcription PCR (RT-PCR), loss of heterozygosity (LOH) analysis, methylation-specific PCR (MSP), DNA sequencing, immunohistochemistry, and flow cytometry, we analysed expression and/or alteration of HLA class I antigen subunits and APM components, including low molecular weight polypeptide proteasome subunit (LMP)2, LMP7, LMP10, transporter associated with antigen processing (TAP)1, TAP2, tapasin, proteasome activator (PA) 28alpha, and PA28beta in two stage-matched panels of 30 MSI-H and 30 microsatellite stable (MSS) gastric cancers. Mutations at coding microsatellites (cMS) located within beta2-microglobulin (beta2m) and genes encoding APM components, including endoplasmic reticulum (ER) chaperone protein genes, such as calnexin, SEC63, SEC31, and P4HB (p55), were also analysed. HLA class Ia transcripts were totally downregulated in 18.3% of cancer cases. Locus-specific downexpression of HLA-A, -B, and -C was detected in 41.7%, 45.0%, and 31.7% of cases. Loss of HLA-A was significantly more frequent in MSI-H cancers. The LOH ratios of the HLA-A, -B, and -C loci microsatellite markers were relatively low: 5/32 (15.6%) for D6S306, 4/32 (12.5%) for D6S258, 4/33 (12.1%) for D6S273, and 4/30 (13.3%) for D6S1666. Methylation of HLA-A, -B, and -C was detected in 38.3%, 40.0%, and 28.3% of cases. A significant association between methylation and reduction in expression was observed in gastric cancer tissues. Mutations at cMS of beta2m and APM components were detected in 3.3-46.7% of MSI-H cancers but in none of MSS cancers. These data show that gastric cancers have various defects in HLA class I antigen subunits and APM components and that the MSI phenotype is associated with frequent HLA-A inactivation and frameshift mutations of the beta2m and APM genes.
...
PMID:Characterization of the immune escape phenotype of human gastric cancers with and without high-frequency microsatellite instability. 1731 12


<< Previous 1 2 3 4 Next >>

---