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)

The human wild-type (wt) p53.264-272 peptide is a universal tumor antigen and recognized by HLA-A*0201 (A2.1)-restricted CTL. Generation of this epitope by constitutive 20S proteasomes is prevented by a p53 R to H hotspot mutation at the C-terminal flanking residue 273. We report on the impact of the interferon-gamma (IFN-gamma)-inducible proteasomal activator PA28 (11S regulator) and the immunoproteasome on the in vitro and cellular processing of wt and mutant (mut) p53 substrates. We found that production of the antigenic 264-272 peptide from wt p53 by constitutive as well as immunoproteasomes is accelerated and amplified by the PA28 activator. PA28 and (immuno)proteasomes were not capable to reconvert the resistance of epitope release from mut p53. Maximum and accelerated antigen production in vitro and on the cellular level required the IFN-gamma-inducible interaction of immunoproteasomes and PA28. We conclude that efficient processing of p53.264272 from wt p53 is governed by the proteasome/PA28 complex. These studies have important implications for p53-specific cancer immunotherapy and demonstrate that the effects of the immunoproteasome and PA28 are influenced by the individual epitope and its flanking sequence context.
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PMID:The effect of the interferon-gamma-inducible processing machinery on the generation of a naturally tumor-associated human cytotoxic T lymphocyte epitope within a wild-type and mutant p53 sequence context. 1198 24

The proteasome system represents a major source of HLA class I- presented peptides exposed to CTLs. Stimulation of cells with IFN-gamma instantly induces the expression of the proteasome immunosubunits as well as the proteasome activator PA28. These proteins have been shown to optimize class I antigen presentation of several viral CTL epitopes; however, their contribution to tumor antigen processing remains poorly understood. Here, we analyzed the generation of an HLA-A*0201-presented epitope derived from the melanoma antigen tyrosinase-related protein 2 (TRP2). Melanoma cells that lacked the IFN-gamma-inducible proteasome activator PA28 and immunoproteasomes did not display the TRP2(360-368) epitope to specific CTLs. Our experiments demonstrate that epitope presentation correlated with the presence of PA28 and could be completely rescued by restoration of PA28 expression. In vitro digestion of TRP2 polypeptides with 20S proteasomes confirmed that PA28 is essential for epitope liberation. Thus, our experiments indicate that PA28 provides the threshold for CTL recognition of this epitope. Importantly, processing of a second TRP2-derived epitope, TRP2(288-296), was diminished in IFN-gamma-treated cells, even in the absence of immunoproteasome up-regulation. Therefore, the reported IFN-gamma-induced self-regulation of epitopes may not necessarily be a consequence of immunoproteasomes as suggested previously.
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PMID:Expression of the proteasome activator PA28 rescues the presentation of a cytotoxic T lymphocyte epitope on melanoma cells. 1201 67

Professional antigen-presenting cells (APC), e.g. dendritic cells, express immuno-proteasome components and process proteins for MHC presentation differently from non-immune cells. Thus, they induce reactivities against sets of peptides that do not overlap with those generated by non-professional APC, i.e., tumor cells, and stimulate cytotoxic T lymphocytes (CTL) that may not recognize them. The goal of this work was to establish a system for antigen presentation and in vitro stimulation of human CTL using "tumor-cell-like" engineered APC. Murine fibroblasts were transfected with human HLA Class I alleles, together with the B7.1, ICAM-1 and germ-line TROP2 genes. The last encodes a cell surface glycoprotein widely expressed by human cancers. Unseparated peripheral blood mononuclear cells from HLA Class I-matched individuals were stimulated in vitro by the engineered APC. These efficiently induced the activation and proliferation of antigen-specific HLA-restricted CTL lines and clones. The Trop-2-specific CTL demonstrated high specific cytotoxicity against the appropriate transfected target cells. They also efficiently lysed MCF-7 human tumor cells expressing endogenous HLA-A2.1, Trop-2 together with ICAM-1. These results demonstrate that Trop-2 is a target molecule recognized by human CTL. Moreover, they demonstrate that non-immune engineered APC efficiently process and present native tumor-specific proteins in the context of human MHC Class I, and stimulate the growth and cytotoxicity of specific anti-tumor CTL.
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PMID:Presentation of native TROP-2 tumor antigens to human cytotoxic T lymphocytes by engineered antigen-presenting cells. 1220 60

Human minor histocompatibility antigens (mHag) are target antigens of the graft-versus-leukemia response observed after allogeneic HLA-identical stem cell transplantation. We previously defined the molecular nature of the B cell lineage-specific mHag HB-1. The CTL epitope was identified as the decamer peptide EEKRGSLHVW presented in the context of HLA-B44. The HB-1 antigen is encoded by a locus of yet unknown function on chromosome 5q32. A single nucleotide polymorphism within this locus results in an amino acid change from histidine (H) to tyrosine (Y) at position P8 within the CTL epitope. Based on genomic information, we have developed a PCR-RFLP assay to perform HB-1 typing at the DNA level. We determined that the allelic frequency for the H and Y variant is 0.79 and 0.21, respectively. From these data, we calculated that the expected recipient disparity between HLA-B44-matched sibling pairs for HB-1H is 2.8%, whereas recipient disparity for HB-1Y is expected to be 12.4%. Therefore, we addressed whether the HB-1Y peptide is reciprocally immunogenic. We revealed that both peptide variants bind equally efficient to HLA-B44 molecules and that the H/Y substitution has no influence on formation of epitope precursor peptides by 20 S proteasome-mediated degradation. More directly, CTL recognizing the naturally presented HB-1Y peptide could be generated from a HB-1H homozygous donor using peptide-pulsed dendritic cells. Using a set of synthetic structurally related peptide variants, we found that the H/Y substitution has a major impact on TCR recognition by CTL specific for either of the HB-1 allelic homologues. HB-1 is the first human mHag described that induces bi-directional allogeneic CTL responses that may contribute to a specific graft-versus-leukemia response following allogeneic stem cell transplantation.
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PMID:Bi-directional allelic recognition of the human minor histocompatibility antigen HB-1 by cytotoxic T lymphocytes. 1235 26

Cytolytic T lymphocytes (CTL) play a major role in the recognition and destruction of tumor cells by the immune system. In the last ten years, our team has identified at the molecular level a number of markers, called antigens, whose presence at the surface of tumor cells allow CTL to recognize such cells. Some of these antigens, including those encoded by the MAGE genes, are absent on all normal cells, and therefore constitute ideal targets for cancer vaccines aimed at increasing the activity of anti-tumor lymphocytes. Such vaccines are currently tested in clinical trials with melanoma patients. These antigens consist of small peptides that are presented by HLA molecules and that result from the degradation of intracellular proteins. This degradation is performed by an intracellular proteolytic complex called the proteasome. We recently observed that dendritic cells, which in the lymph node are responsible for antigen presentation to the lymphocytes in order to initiate the immune response, are inefficient to produce some peptides because they contain a different proteasome called "immunoproteasome". This unexpected observation may have important implications for the choice of vaccination strategies.
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PMID:[Identification of cancer antigens of relevance for specific cancer immunotherapy]. 1237 Dec 73

Bone marrow failure has been regarded as one of the triad of clinical manifestations of paroxysmal noctumal hemoglobinuria (PNH), and PNH in turn has been described as a late clonal disease evolving in patients recovering from aplastic anemia. Better understanding of the pathophysiology of both diseases and improved tests for cell surface glycosylphosphatidylinositol (GPI)-linked proteins has radically altered this view. Flow cytometry of granulocytes shows evidence of an expanded PNH clone in a large proportion of marrow failure patients at the time of presentation: in our large NIH series, about 1/3 of over 200 aplastic anemia cases and almost 20% of more than 100 myelodysplasia cases. Clonal PNH expansion (rather than bone marrow failure) is strongly linked to the histocompatability antigen HLA.-DR2 in all clinical varieties of the disease, suggesting an immune component to its pathophysiology. An extrinsic mechanism of clonal expansion is also more consistent with knock-out mouse models and culture experiments with primary cells and cell lines, which have failed to demonstrate an intrinsic proliferative advantage for PNH cells. DNA chip analysis of multiple paired normal and PIG-A mutant cell lines and lymphoblastoid cells do not show any consistent differences in levels of gene expression. In aplastic anemia/PNH there is surprisingly limited utilization of the V-beta chain of the T cell receptor, and patients' dominant T cell clones, which are functionally inhibitory of autologous hematopoiesis, use identical CDR3 regions for antigen binding. Phenotypically normal cells from PNH patients proliferate more poorly in culture than do the same patient's PNH cells, and the normal cells are damaged as a result of apoptosis and overexpress Fas. Differences in protein degradation might play a dual role in pathophysiology, as GPI-linked proteins lacking an anchor would be predicted to be processed by the proteasome machinery and displayed in a class I H.A. context, in contrast to the normal pathway of cell surface membrane recycling, lysosomal degradation, and presentation by class II HLA. The strong relationship between a chronic, organ-specific immune destructive process and the expansion of a single mutant stem cell clone remains frustratingly enigmatic but likely to be the result of interesting biologic processes, with mechanisms that potentially can be extended to the role of inflammation in producing premalignant syndromes.
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PMID:The relationship of aplastic anemia and PNH. 1243 Sep 20

An efficient vaccine against human immunodeficiency virus (HIV) must induce good cellular immune responses. To do this, it must be processed and presented by dendritic cells, which are required for primary T-lymphocyte stimulation. We have previously shown that a model lipopeptide containing a short epitopic peptide from HIV-1 was endocytosed and presented in association with major histocompatibility complex class I molecules by human dendritic cells to specific CD8(+) T lymphocytes, but the cross-presentation pathway needed to be precisely determined. We have studied a longer lipopeptide (Pol(461-484)) and another lipopeptide (Nef(66-97)) currently being used in vaccine trials. Like the shorter lipopeptide, the rhodamine-labeled Pol(461-484) lipopeptide was internalized by endocytosis, as assessed by confocal microscopy. The lipopeptides were processed by dendritic cells and presented to CD8(+) T cells specific for the HLA-A*0201-restricted Pol(476-484) and the HLA-A*0301-restricted Nef(73-82) epitope, respectively. Presentation of both lipopeptides was inhibited by brefeldin A. Presentation of the Pol lipopeptide was inhibited by epoxomycin, a proteasome-specific inhibitor, but not by monensin. This shows that it gained access to the cytosol to be digested by the proteasome. In contrast, presentation of the Nef lipopeptide was not inhibited by epoxomycin but was inhibited by monensin, a classical inhibitor of acid-dependent endosomal enzyme activity, indicating an endocytic processing pathway yielding to major histocompatibility complex class I-restricted presentation. Therefore, the two lipopeptides followed different cross-presentation pathways, both resulting in efficient presentation to CD8(+) T lymphocytes.
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PMID:Two human immunodeficiency virus vaccinal lipopeptides follow different cross-presentation pathways in human dendritic cells. 1250 69

HIV-1 is a fundamentally difficult target for vaccines because of its high mutation rate and its repertoire of immune evasion strategies. To address these difficulties, a multivalent genetic vaccine or "live genetic vaccine" was recently developed against HIV-1 using the expression library immunization (ELI) approach. In this HIV-1 vaccine, all open reading frames of HTLV-IIIb are expressed as protein fragments to retain all viral T cell epitopes, but destroy protein toxicity, inactivate immune escape functions, and reveal subdominant epitopes. In addition, each antigen fragment is fused to the ubiquitin protein to increase antigen expression and target these antigens to the proteasome to enhance cytotoxic T lymphocyte (CTL) responses. This multivalent vaccine also has the advantage of being incapable of generating infectious HIV-1 virus because of the segregation of the HIV genome into 32 separate plasmids. In this work, we demonstrate the ability of this genetic vaccine to provoke robust HLA-A*0201-restricted T cell responses in MHC class I humanized mice against gag, pol, env, and nef after a single round of immunization. In addition, this HTLV-IIIb-derived vaccine demonstrated cross-clade, envelope-specific, HLA-restricted CD8 responses against clades A, D, and E. HLA-restricted CD8 responses were generated against all 32 open reading frames encoded by the multi-plasmid genetic vaccine demonstrating that a broad repertoire of human relevant CD8 responses are provoked by this vaccine. This work supports this approach to generate multivalent T cell responses to control the highly mutable and immuno-evasive HIV-1 virus.
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PMID:Generation of multivalent genome-wide T cell responses in HLA-A*0201 transgenic mice by an HIV-1 expression library immunization (ELI) vaccine. 1284 72

HOM-MEL-40/SSX2 is a SEREX-defined cancer testis antigen with frequent expression in various human neoplasms. To search for HLA-A*0201 restricted peptides that induce HOM-MEL-40/SSX2-specific CD8+ responses in breast cancer patients, we used the SYFPEITHI algorithm to identify three HOM-MEL-40/SSX2-derived nonamers with high binding affinity for HLA-A*0201, which has a prevalence of 40% in the Caucasian population. Of the three peptides, p41-49 and p103-111 but not p167-175 had been shown to be processed by the proteasome. Only stimulation with p103-111 induced HOM-MEL-40-specific CTLs in 5/7 patients with HOM-MEL-40/SSX2 positive breast cancers and in 6/11 healthy controls. HLA-A*0201 restriction of p103-111 was demonstrated by blocking with specific antibodies. The natural processing and presentation of p103-111 was demonstrated by the recognition of the HOM-MEL-40/SSX2 positive cell line SK-MEL-37 and of COS7/A2 cells transfected with HOM-MEL-40/SSX2 by p103-111 specific CD8+ cells. No correlation was found between CD8+ T-cell responses against p103-111 and anti-HOM-MEL-40/SSX2 antibody titers in the serum of patients, suggesting that CD8+ and B-cell responses against HOM-MEL-40/SSX2 are regulated independently. p103-111 holds promise as a broadly applicable peptide vaccine for patients with HOM-MEL-40/SSX2 positive neoplasms.
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PMID:Identification of an HLA-A*02 restricted immunogenic peptide derived from the cancer testis antigen HOM-MEL-40/SSX2. 1467 25

Since the publication of the complete genome of a pathogenic bacterium in 1995, more than 50 bacterial pathogens have been sequenced and at least 120 additional projects are currently underway. Faced with the expanding volume of information now available from genome databases, vaccinologists are turning to epitope mapping tools to screen vaccine candidates. Bioinformatics tools such as EpiMatrix and Conservatrix, which search for unique or multi-HLA-restricted (promiscuous) T cell epitopes and can find epitopes that are conserved across variant strains of the same pathogen, have accelerated the process of epitope mapping. Additional tools for screening epitopes for similarity to 'self' (BlastiMer) and for assembling putative epitopes into strings if they overlap (EpiAssembler) have been developed at EpiVax. Tools that map proteasome cleavage sires are available on the Internet. When used together, these bioinformatics tools offer a significant advantage over traditional methods of vaccine design since high throughput screening and design is performed in silico, followed by confirmatory studies in vitro. These new tools are being used to develop novel vaccines and therapeutics for the prevention and treatment of infectious diseases such as HIV, hepatitis C, tuberculosis, and some cancers. More recent applications of the tools involve deriving novel vaccine candidates directly from whole genomes, an approach that has been named 'genome to vaccine'.
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PMID:From immunome to vaccine: epitope mapping and vaccine design tools. 1471 32


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