Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.69 (APC)
 16,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

There is a subtle duality in the role of proteolytic enzymes in Ag processing. They are required to fragment protein Ag ingested by APC. However, prolonged exposure to proteolytic enzymes may lead to a complete degradation of the Ag, leaving nothing for the T cell system to recognize. What ensures that some of the Ag is salvaged? Using a cell-free system we demonstrate that an Ag fragment, once bound to a MHC class II molecule, is effectively protected against proteolytic destruction by cathepsin B and pronase E. The bound fragment, however, can be modified by aminopeptidase N. We suggest that MHC class II molecules play an important regulatory role in the physiologic processing of Ag.
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PMID:MHC molecules protect T cell epitopes against proteolytic destruction. 138 92

By using the model Ag, chicken OVA, the proteolytic events required for effective presentation of the antigenic epitope, OVA323-339 to H-2d-restricted Th cells were investigated. First, the ability of aspartyl and thiol proteases to generate antigenic fragments of Ova in vitro was determined. It was found that cathepsin D, an aspartyl protease, digested OVA to fragments that could be recognized by Th cells without further processing by APC. Cathepsin B, a thiol protease, was unable to generate antigenic fragments of OVA in vitro. These results provide evidence that APC do not require thiol protease activity for processing OVA. In contrast, APC were unable to present OVA to Th cells when thiol protease inhibitors were added to the incubation. Taken together, these observations indicate that thiol proteases may be important, not for processing, OVA, but for presentation of processed fragments by APC. This conclusion is supported by evidence obtained from experiments in which APC were treated with thiol protease inhibitors before addition of the antigenic peptide, OVA323-339. Under these conditions, the capacity of I-Ad at the cell surface to present OVA323-339 to Th cells was reduced. The results of these experiments provide evidence that Ag presentation of OVA may be achieved through the action of two different classes of proteases: aspartyl proteases such as cathepsin D, which process OVA to antigenic fragments, and thiol proteases such as cathepsin B, which are important for expression of functional MHC II molecules by APC.
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PMID:Different roles for thiol and aspartyl proteases in antigen presentation of ovalbumin. 169 78

We report on a computer algorithm capable of predicting the location of T-helper-cell epitopes in protein antigen (Ag) by analysing the Ag amino acid sequence. The algorithm was constructed with the aim of identifying segments in Ag which are resistant to proteolytic degradation by the enzymes cathepsin B, L, and D. These are prominent enzymes in the endocytic pathway through which soluble protein Ag enter APC, and resistant segments in Ag may, therefore, be expected to contain more T-cell determinants than susceptible segments. From information available in the literature on the substrate specificity of the three enzymes, it is clear that a cysteine is not accepted in any of the S2, S1, S1', and S2' subsites of cathepsin B and L, and not in the S1 and S1' subsites of cathepsin D. Moreover, we have noticed that cysteine-containing T-cell determinants in a number of protein Ag are particularly rich in the amino acids alanine, glycine, lysine, leucine, serine, threonine, and valine. By searching protein Ag for clusters of amino acids containing cysteine and two of the other amino acids we were able to predict 17 out of 23 empirically known T-cell determinants in the Ag with a relatively low number of false (positive) predictions. Furthermore, we present a new principle for searching Ag for potential amphipatic alpha-helical protein segments. Such segments accord well with empirically known T-cell determinants and our algorithm produces a lower number of false positive predictions than the principle based on discrete Fourier transformations previously described.
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PMID:T-helper-cell determinants in protein antigens are preferentially located in cysteine-rich antigen segments resistant to proteolytic cleavage by cathepsin B, L, and D. 171 25

Orthotopic liver transplantation is frequently associated with a complex coagulation disorder, influencing the outcome of the procedure. In this respect, disseminated intravascular coagulation (DIC) had been suggested to be of causative importance for bleeding complications after reperfusion of the liver graft. In 10 consecutive patients undergoing orthotopic liver transplantations, we studied the occurrence of two phagocyte proteinases of different origin in the graft liver perfusate and in systemic blood during the operation, as well as their effects on hemostasis. As compared with plasma samples taken at the end of the anhepatic phase, highly significant increases of cathepsin B and thrombin-anti-thrombin III complexes (TAT), as well as highly significant decreases in antithrombin III, protein C, and C1-inhibitor were observed in graft liver perfusate. Von Willebrand factor and fibrinogen were slightly decreased, whereas the elastase-alpha 1 proteinase inhibitor complexes (EPI) were elevated. In plasma the activity of cathepsin B remained unchanged during the prereperfusion phases, but immediately after revascularization of the graft this cysteine proteinase increased. The EPI showed a gradual increase in plasma during the preanhepatic and anhepatic phases but a more pronounced increase in the reperfusion phase. In parallel with the rise in these two proteinases TAT increased and the activities of antithrombin III and C1-inhibitor in plasma decreased after reperfusion. At 12 hr after revascularization plasma levels of TAT, antithrombin III, and C1-inhibitor had returned to the prereperfusion ranges, whereas cathepsin B and EPI were significantly above the baseline levels. These observations are consistent with the hypothesis that extracellularly released lysosomal proteinases may play a role in the development of a DIC-like constellation, including thrombin formation after revascularization of the liver graft. For the first time we could prove the occurrence of phagocyte proteinases in graft liver perfusate and evaluate the importance of these proteinases for the understanding of the pathophysiology leading to bleeding complications in patients undergoing orthotopic liver transplantation.
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PMID:Possible role of extracellularly released phagocyte proteinases in coagulation disorder during liver transplantation. 189 20

We have previously prepared beta-lactoglobulin (beta-LG)-carboxymethyl dextran (CMD) conjugates with water-soluble carbodiimide and achieved reduced immunogenicity of beta-LG. In the present study, to elucidate the mechanism for the reduced immunogenicity of beta-LG, we investigated changes in the T cell response to beta-LG after conjugation with CMDs differing in molecular weight (about 40 and 162 kDa). Lymph node cells from BALB/c, C3H/He, and C57BL/6 mice that had been immunized with beta-LG or the conjugates were stimulated with beta-LG, and the in vivo T cell response was then evaluated by BrdU (5-bromo-2'-deoxyuridine) ELISA as the ex vivo proliferative response. T cells from the conjugate-immunized mice showed a lower proliferative response than those from the beta-LG-immunized mice. T cell epitope scanning, using synthesized peptides, showed that the T cell epitope profiles of the conjugates were similar to those of beta-LG, whereas the proliferative response to each epitope was reduced. These results indicate that the lower in vivo T cell response with the conjugates was not due to induction of conjugate-specific T cells, but due to a decrease in the number of beta-LG-specific T cells. After the lymph node cells from beta-LG-immunized mice had been stimulated with beta-LG or the conjugates, the efficiency of the antigen presentation of the conjugate to beta-LG-specific T cells was evaluated by BrdU ELISA as the in vitro proliferative response. The antigen presentation of beta-LG to the T cells was reduced by conjugation with CMD. In addition, conjugation with CMD enhanced the resistance of beta-LG to cathepsin B and cathepsin D, which suggest that conjugation with CMD inhibited the degradation of beta-LG by proteases in APC and led to suppression of the generation of antigenic peptides including T cell epitopes from beta-LG. It is therefore considered that the suppressive effect on the generation of T cell epitopes reduced the antigen presentation of the conjugates and that this reduction led to a decrease in the number of beta-LG-specific T cells in vivo. As a result, the decreased help to B cells by T cells would have reduced the antibody response to beta-LG. We conclude that suppression of the generation of T cell epitopes by conjugation with CMD is important to the mechanism for the reduced immunogenicity of beta-LG.
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PMID:Modulation of the T cell response to beta-lactoglobulin by conjugation with carboxymethyl dextran. 1252 6

Proteases regulate numerous biological processes with a degree of specificity often dictated by the amino acid sequence of the substrate cleavage site. To map protease/substrate interactions, a 722-member library of fluorogenic protease substrates of the general format Ac-Ala-X-X-(Arg/Lys)-coumarin was synthesized (X=all natural amino acids except cysteine) and microarrayed with fluorescent calibration standards in glycerol nanodroplets on glass slides. Specificities of 13 serine proteases (activated protein C, plasma kallikrein, factor VIIa, factor IXabeta, factor XIa and factor alpha XIIa, activated complement C1s, C1r, and D, tryptase, trypsin, subtilisin Carlsberg, and cathepsin G) and 11 papain-like cysteine proteases (cathepsin B, H, K, L, S, and V, rhodesain, papain, chymopapain, ficin, and stem bromelain) were obtained from 103,968 separate microarray fluorogenic reactions (722 substrates x 24 different proteases x 6 replicates). This is the first comprehensive study to report the substrate specificity of rhodesain, a papain-like cysteine protease expressed by Trypanasoma brucei rhodesiense, a parasitic protozoa responsible for causing sleeping sickness. Rhodesain displayed a strong P2 preference for Leu, Val, Phe, and Tyr in both the P1=Lys and Arg libraries. Solution-phase microarrays facilitate protease/substrate specificity profiling in a rapid manner with minimal peptide library or enzyme usage.
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PMID:High throughput substrate specificity profiling of serine and cysteine proteases using solution-phase fluorogenic peptide microarrays. 1570 70

Lysosomal cysteine cathepsins belong to a family of 11 human proteolytic enzymes. Some of them correlate with progression in a variety of cancers and therefore are considered as potential therapeutic targets. Until recently, the contribution of individual cathepsins to tumorigenesis and tumor progression remained unknown. By crossing various types of mouse cancer models with mice where specific cathepsins have been ablated, we contributed to this gap of knowledge and will summarize the results in this report. The employed models are the Rip1-Tag2 model for pancreatic neuroendocrine tumors, the K14-HPV16 model for squamous skin and cervical cancers, and the MMTV-PyMT model for metastasizing breast cancer, the KPC model for pancreatic ductal adenocarcinoma, and the APC(min) mice developing early stages of intestinal neoplasia. All models harbor mutations in relevant tumor suppressors and/or cell-type specific expression of potent oncogenes, which initiate de novo carcinogenesis in the targeted tissues. In all these models deletion of cathepsin B led to suppression of the aggressiveness of the respective cancer phenotype. Cathepsin B is networking with other proteases as it was shown for cathepsin X/Z. In contrast, deletion of cathepsin L was beneficial in the RiP1-Tag2 model, but enhanced tumorigenesis in the APC(min), and the K14-HPV16 mice. A logical consequence of these results would be to further pursue selective inhibition of cathepsin B. Moreover, it became clear that cathepsins B and S derived from cells of the tumor microenvironment support cancer growth. Strikingly, delivery of broad spectrum cysteine cathepsin inhibitors in the tumor microenvironment disrupts the permissive ecosystem of the cancer and results in impaired growth or even in regression of the tumor. In addition, combination of cysteine cathepsin inhibition and standard chemotherapy improves the therapeutic response of the latter. Taken together, the next preclinical challenges for developing cathepsin inhibition as cancer therapy might be the improvement of inhibitor selectivity and targeted delivery to the tumor microenvironment and investigation of the biological context of the individual factors within the complex proteolytic network.
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PMID:Differential Impact of Cysteine Cathepsins on Genetic Mouse Models of De novo Carcinogenesis: Cathepsin B as Emerging Therapeutic Target. 2279 52