Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0033036 (APC)
 10,214 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Modification of protein Ag by proteolysis is one of the principal steps in the presentation of Ag to Th cells. However, little is known about the enzymes participating in these events, their specificity or the characteristics of the natural fragments that they produce. Cathepsin D (CD) is an aspartyl protease identified in endosomes of APC. In this report, the role of CD in the processing of OVA has been investigated. OVA digested in vitro with purified CD was able to stimulate IL-2 secretion by three different OVA-specific I-Ad restricted Th cell hybridomas when it was presented by fixed APC. The digest of OVA was recognized in the context of I-Ad, but not by I-Ak-restricted OVA-specific Th cells. No difference was observed in the ability of OVA digested with CD to stimulate Th cells in the absence of FCS or in the presence of protease inhibitors indicating that extracellular proteases were not likely to contribute to processing of OVA. Taken together, these results suggest that CD is necessary and sufficient for the generation of an antigenic epitope from OVA. A fragment containing the epitope was isolated from the OVA digest by reverse phase HPLC. This fragment, which migrates in SDS-PAGE as a 10-kDa polypeptide, is a potent epitope. Its capacity to activate Th cells is compared to that of the tryptic peptide OVA323-339.
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PMID:Role of cathepsin D in antigen presentation of ovalbumin. 132 88

The glycosylation inhibiting factor (GIF) was detected in EGTA extracts of the OVA-specific Ts cell hybridoma, 231F1 cells and 71B4 cells, which constitutively secrete GIF. The lymphokine in both culture supernatants and EGTA extracts failed to bind to OVA-Sepharose. Association of GIF with the plasma membrane was confirmed by surface labeling of the 231F1 cells with 125I. The major species of GIF in the extract was 14.4-kDa peptide as determined by SDS-PAGE, and was identical to that detected in culture supernatants. Pretreatment of the cells with monoclonal anti-GIF switched the cells from the formation of unglycosylated IgE-BF to the formation of glycosylated IgE-BF, indicating that the membrane-associated GIF is involved in the determination of the nature of IgE-binding factor during their biosynthesis. When the hybridoma was stimulated with OVA-pulsed APC, EGTA extracts of the cells contained GIF having affinity for OVA. The binding of the OVA-binding GIF in the EGTA extracts to OVA-Sepharose was inhibited by a synthetic peptide, which corresponds to amino acid residues 307-317 in the OVA molecule and represents the epitope recognized by TCR on the cells. The OVA-binding GIF in the extracts bound to the monoclonal anti-TCR-alpha chain, H-28-710 and the mAb 14-12, which is specific for the Ag-binding chain of effector type suppressor factor, and suppressed the in vivo antibody response of BDF1 mice to DNP-OVA in a carrier-specific manner. Evidence was obtained that indicated that the Ag-binding chain was associated with nonspecific GIF chain on the cell surface of the Ag-stimulated cells.
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PMID:Association of glycosylation-inhibiting factor with plasma membranes of T suppressor cell hybridomas. 214 96

The cellular localization of glutathione-requiring PGD synthetase, which catalyzes the predominant formation of PGD2 in various peripheral tissues, was investigated in adult rats by immunoperoxidase-staining with a polyclonal antibody specific for this enzyme. Although the 25 N-terminal amino acid residues of synthetase are 56% identical and 76% similar to those of several rat glutathione S-transferase subunits, the antibody cross-reacted only with synthetase in dot blotting and was nearly completely inactive with all transferase isozymes thus far purified. In Western blotting after SDS-PAGE of crude extracts of rat spleen, the antibody showed a single positive band at the same position as that of the purified enzyme (Mr = 26,000). The positive immunocytochemical stain was found in a number of histiocytes and/or dendritic cells in spleen, thymus, and Peyer's patch of intestine. The immunostain was also observed in such cells in lamina propria of the villus in small intestine and colon, in submucosal layer of stomach, and in Kupffer cells in liver. Immunoelectron microscopy confirmed that immunoreactivity of this enzyme was distributed in cytoplasm of those cells. Such immunoreactive cells were not observed in brain, spinal cord, kidney, heart, testis, and skeletal muscle. These observations suggest that PGD2 is produced by glutathione-requiring PGD synthetase localized in these types of APC in various tissues and may play a critical role in dictating the progression of immune responses.
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PMID:The major source of endogenous prostaglandin D2 production is likely antigen-presenting cells. Localization of glutathione-requiring prostaglandin D synthetase in histiocytes, dendritic, and Kupffer cells in various rat tissues. 250 61

NADP-dependent glutamate dehydrogenase (NADP-GDH) was purified to homogeneity from Pseudomonas aeruginosa strain 8602 (PAC 1). The Mr determined by Sephadex gel filtration was 280,000; the subunit Mr determined by SDS-PAGE was 45,000. Mutant strains lacking NADP-GDH and glutamate synthase (Gdh-Glt-) required glutamate for growth. Transductants that lacked only NADP-GDH were indistinguishable from the wild-type strain in growth properties. It was concluded that NADP-GDH is not essential for growth of the wild-type organism and that glutamate formation via NAD-dependent glutamate dehydrogenase does not occur to a significant extent. A mutant strain, 39, producing high NADP-GDH activity, synthesized normal NADP-GDH and had the same intracellular glutamate concentrations as its parent. The mutation responsible for the synthesis of high levels of NADP-GDH was shown, by transduction, to be closely linked to the NADP-GDH structural gene (gdhA).
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PMID:Mutations affecting the synthesis of NADP-dependent glutamate dehydrogenase in Pseudomonas aeruginosa. 284 62

Two different monoclonal antibodies against the heparin-dependent inhibitor of human activated protein C were produced, using cleaved modified inhibitor for immunization and partially purified inhibitor for screening of the hybridomas. One of the antibodies recognized free and complexed forms of the inhibitor in immunoblotting experiments. The other antibody was used to develop an assay for APC-PCI inhibitor complexes. Using the assay the formation of complexes was studied in plasma, both in the presence and absence of heparin. The rate of complex formation was similar to that reported previously for the loss of activated protein C amidolytic activity in plasma. The same antibody was also immobilized on Sepharose and used to purify the inhibitor from fresh human plasma. The purified material appeared as two narrowly spaced bands with Mr about 57,000 in SDS-PAGE. The average yield from 1 liter of fresh plasma was 1 mg of inhibitor. The purified inhibitor formed SDS stable complexes with activated protein C and urokinase that could be identified in immunoblots using specific antibodies.
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PMID:Monoclonal antibodies against the heparin-dependent protein C inhibitor suitable for inhibitor purification and assay of inhibitor complexes. 321 24

The behavior of mouse I-Ak molecules was studied in the human Ag presentation mutants T2 and 9.5.3, which contain deleted or mutated HLA DM genes. HLA class II molecules expressed by these APC are defective in presentation of native Ag and are mostly complexed with class II-associated invariant chain peptides (CLIP). In contrast to human class II molecules, a significant proportion of mouse I-Ak molecules expressed in T2 and 9.5.3 were associated with antigenic peptides, indicating that I-Ak/peptide assembly is possible in the absence of the Dm proteins. Thus, the presentation of determinants derived from hen egg lysozyme (HEL), keyhole limpet hemocyanin, and conalbumin was normal in 9.5.3Ak and a conalbumin determinant was presented normally by T2.Ak. However, the keyhole limpet hemocyanin determinant was not presented by T2.Ak, and HEL46-61 was only presented at a low level by these APC. SDS-stable, dimeric I-Ak molecules were expressed by both T2.Ak and 9.5.3Ak and formed late in their intracellular transport. Presentation of HEL46-61 was partially inhibited by disrupting vacuolar acidification in 9.5.3Ak, consistent with I-Ak/peptide assembly in a post-Golgi endosomal compartment. Accordingly, Dm is not an obligatory requirement for MHC class II/peptide assembly. We propose that Dm influences the displacement of CLIP from recently synthesized class II molecules, a process that is likely to be less critical for I-Ak because of its low affinity for CLIP.
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PMID:Antigen presentation and assembly by mouse I-Ak class II molecules in human APC containing deleted or mutated HLA DM genes. 798 44

Ag presentation by APC to class II MHC-restricted T cells involves a sequence of events: 1) intracellular processing of protein Ag into immunogenic peptides, 2) specific binding of peptides to class II MHC molecules, and then 3) transport of the MHC-peptide complexes to the plasma membrane. The critical event in the activation of T cells by APC is the recognition of MHC-associated antigenic determinants by the TCR/CD3 complex. In this report we describe the isolation and characterization of a mutant APC with a defect in an intracellular process that results in its inability to form MHC-peptide complexes for recognition by T cells. The mutant APC cannot present many different protein Ag with both I-A and I-E molecules but is able to present processing-independent peptides. The functional defect in the mutant APC is not caused by either a decrease in expression or a structural mutation in class II MHC molecules. Further, there is no mutation in the invariant chain (li) and it displays a normal kinetics of association and dissociation from the class II MHC molecules during biosynthesis. Although the mutation is not in the genes encoding for the class II MHC molecules or li, the mutant APC expresses class II MHC molecules with distinct serological epitopes suggestive of an altered conformation. Pulse-chase experiments suggest that a conformational difference between I-Ad molecules of wild-type and mutant cells occurs after the class II molecules exit from the endoplasmic reticulum but while they are still associated with li. The mutant cell produces few compact (SDS-resistant) class II heterodimers. This mutant APC provides a tool for studying the cell biology of Ag processing and presentation.
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PMID:A mutant antigen-presenting cell defective in antigen presentation expresses class II MHC molecules with an altered conformation. 848 33

The class II molecules of the diabetes-prone NOD mice, I-Ag7, showed very limited amounts of stable form when analyzed by SDS-PAGE. We included the analysis of spleen B cells and B lymphoma cells transfected with I-Ag7 genes. Early during bio-synthesis there was invariant chain binding to the alpha beta-chains. Examination of APCs from F1 mice (NOD x C57BL/6) indicated that the same APC expressed high levels of unstable I-Ag7 and normal amounts of stable class II molecules compared with the other haplotype (I-Ab). The half-life of I-Ag7-peptide complexes on the cell surface of APC was significantly shorter than that of other class II haplotypes. Direct biochemical demonstration of peptide interactions with I-Ag7 was difficult to demonstrate. In T cell assays, the immunogenic peptides, including the diabetogenic Ag, were rapidly lost when peptide-pulsed APCs were washed free of peptide. We hypothesize that the weak and unstable peptide-binding property of I-Ag7 molecules does not favor the elimination or inactivation of autoreactive T cells.
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PMID:The class II MHC I-Ag7 molecules from non-obese diabetic mice are poor peptide binders. 854 93

The APC gene is mutated in familial adenomatous polyposis and sporadic colorectal tumors. The product of this gene is a 300 kDa cytoplasmic protein and its overexpression results in the block of cell cycle progression from the G0/G1 to the S phase. In the present study, we studied the expression and phosphorylation of the APC protein through the cell cycle. The APC protein was found to be constantly expressed and phosphorylated at serine and threonine residues. Moreover, the APC protein immunoprecipitated from cells arrested in the M phase by nocodazole treatment migrated in SDS-PAGE more slowly than those from the G1 and S phases. Phosphatase treatment abolished this M phase-specific retarded migration, suggesting that APC is transiently hyperphosphorylated in the M phase.
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PMID:The tumor suppressor gene product APC is hyperphosphorylated during the M phase. 860 42

The bactericidal activity of normal human serum (NHS) and treated NHS to avoid either the classical complement pathway (CPC) or the alternative complement pathway (APC) was studied with four strains identified as Acinetobacter baumanii. Three of them were sensitive to serum whereas only one was serum resistant. The serum sensitive strains showed different susceptibility mechanisms: one strain was sensitive to both the CPC and the APC and the others were sensitive only to APC. Serum sensitive and serum resistant strains showed on PAGE-SDS and silver strain incomplete profiles of lipopolysaccharides (LPS). In all cases the carbohydrate percentage of LPS was lower than the value corresponding to Salmonella enteritidis with complete profiles of LPS. The strain sensitive to CPC and APC had a lower carbohydrate content. The serum sensitivity of the three strains could be attributed to the presence of incomplete LPS, while the serum resistance could be assigned either to small variations in the LPS composition or to some particular membrane component.
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PMID:Behaviour of Acinetobacter strains with normal human serum. 888 57


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