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Biomedical subjects

J Magae

Publications and source records attributed to J Magae.

At least 37 records · Page 2Linked to original sources
PubMed1995

Thiol-protease inhibitors selectively inhibit presentation of antigen incorporated through B cell antigen receptors.

B cells efficiently uptake exogenous antigens through cell surface IgM molecules and present them to specific T cells. Although it is implicated that antigens taken up by surface IgM associate with newly synthesized class II molecules, the precise pathway of the presentation is still unclear. Here we report that thiol-protease inhibitors inhibit the presentation of trinitrophenol-conjugated ovalbumin by a leukemic B cell line, A20.HL, which constitutively expresses trinitrophenol-specific surface IgM although they had only a minimum effect on the presentation of unconjugated ovalbumin. In addition, thiol-protease inhibitors slightly reduced the surface expression of class II molecules. Our results suggest that exogenous antigen taken up through surface IgM is presented by a pathway which involves proteolysis by thiol-proteases and distinct from that for the antigens taken up through non-specific endocytosis.

Antigen Presentation↗
PubMed1995

Prodigiosin 25-C uncouples vacuolar type H(+)-ATPase, inhibits vacuolar acidification and affects glycoprotein processing.

Prodigiosin 25-C inhibited the accumulation of 3-(2,4-dinitroanilino)-3'-amino-N-methyldipropylamine and acridine orange in the acidic compartments of baby hamster kidney cells with little perturbation of cellular ATP levels. In rat liver lysosomes, prodigiosin 25-C inhibited the proton pump activity with an IC50 of approximately 30 nM, but did not affect ATPase activity up to 1 microM. It also delayed the transport of vesicular stomatitis virus G protein and induced a drastic swelling of Golgi apparatus and mitochondria. These results indicate that prodigiosin 25-C raises the pH of acidic compartments through inhibition of the proton pump activity of vacuolar type H(+)-ATPase, thereby causing the functional and morphological changes to the Golgi apparatus.

Adenosine Triphosphate↗
PubMed1995

Anucleate cell production by Escherichia coli delta hns mutant lacking a histone-like protein, H-NS.

Normal-sized anucleate cells were observed in the cultures of a delta hns mutant strain. Even in nucleate cells, some populations showed irregular intracellular localization of the nucleoids. The delta hns mutant showed reduced ploidy, although initiation of chromosome replication was essentially synchronous as defined by flow cytometric analysis. These results indicate that the delta hns mutant is defective in the mechanisms of chromosome partitioning and chromosome replication.

Bacterial Outer Membrane Proteins↗
PubMed1995

Prodigiosin 25-C suppression of cytotoxic T cells in vitro and in vivo similar to that of concanamycin B, a specific inhibitor of vacuolar type H(+)-ATPase.

The effects of prodigiosin 25-C (PrG) which preferentially suppresses cytotoxic T cells (CTL), was examined in comparison with concanamycin B (CMB), a specific inhibitor of vacuolar type H(+)-ATPase (V-ATPase). PrG and CMB directly inhibited the cytotoxic function of CTL and neutralized acidic organelles of CTL in vitro. In addition, PrG or CMB was injected in C57BL/6 mice after immunization with an allogeneic mastocytoma, P815. PrG and CMB inhibited the killing activity of CTL against the tumor and reduced the population of CD8+ cells without affecting CD4+ and B220+ populations in the spleen. PrG and CMB had only a negligible effect on antibody production induced by sheep red blood cells (SRBC) and mitogenic responses of lymphocytes. These results suggest that PrG and CMB have similar immunosuppressive properties at least through their inhibitory effects on acidification of intracellular organelles required for the effective function of CTL.

Adenosine Triphosphatases↗
PubMed1995

1'-Acetoxychavicol acetate as an inhibitor of phagocytosis of macrophages.

We screened extracts of edible plants for inhibitors of phagocytosis by peritoneal exudate macrophages. 1'-Acetoxychavicol acetate was isolated from the ethyl acetate extract of Languas galanga, and this compound strongly inhibited phagocytosis at an IC50 value of 1.2 microM with negligible effects on pinocytosis and cell viability. Target(s) of 1'-acetoxychavicol acetate was suggested to be downstream of the signal transduction pathway that is mediated by protein kinase C.

Animals↗
PubMed1995

Prodigiosin 25-C perturbs permeation of acetate in a cultured cell line.

Prodigiosin 25-C had little effect on DNA, RNA, and protein synthesis, and cellular ATP content, but the drug markedly inhibited the incorporation of acetate into lipid fractions. Under the same conditions, the incorporation of other lipid precursors including glycerol, mevalonate, palmitate, and oleate was not affected. A decrease in the incorporation of acetate was not due to the inhibition of fatty acid biosynthesis, because prodigiosin 25-C did not affect the activity of acetyl-CoA synthetase, acetyl-CoA carboxylase or fatty acid synthase in cell-free assay systems prepared from rat liver cytosol. In contrast, prodigiosin 25-C strongly inhibited the rapid uptake of acetate into acid-soluble fraction in intact cells. The results suggest that prodigiosin 25-C specifically perturbs the permeation of acetate through plasma membranes.

Acetate-CoA Ligase↗
PubMed1995

Costunolide and dehydrocostus lactone as inhibitors of killing function of cytotoxic T lymphocytes.

Costunolide and dehydrocostus lactone were isolated from an extract of mokko (Saussurea lappa Clarke) as inhibitors of killing activity of cytotoxic T lymphocytes (CTL). Mokko lactone was also isolated as an inactive compound from the extract. The structure-activity relationship indicated that alpha-methylene-gamma-butyrolactone is required for the inhibitory effect. Costunolide markedly inhibited the granule exocytosis and the production of inositol phosphates in response to anti-CD3 monoclonal antibody (mAb) stimulation at a concentration that did not affect the binding of anti-CD3 mAb. Tyrosine phosphorylation induced by crosslinking of CD3 molecules was significantly inhibited by costunolide in a dose-dependent manner. These results suggest that costunolide inhibits the killing activity of CTL through preventing the increase in tyrosine phosphorylation in response to the crosslinking of T-cell receptors.

4-Butyrolactone↗
PubMed1994

Acidification is essential for maintaining the structure and function of lytic granules of CTL. Effect of concanamycin A, an inhibitor of vacuolar type H(+)-ATPase, on CTL-mediated cytotoxicity.

An inhibitor of vacuolar type H(+)-ATPase, concanamycin A (CMA), inhibited the specific cytolytic activity of a CD8+ CTL clone, OE4. The inhibitory effect was observed when the effector cells, and not the target cells, were pretreated with CMA. CMA did not seem to inhibit early events, inasmuch as effector/target conjugate formation remained unaffected. Although CMA treatment of OE4 resulted in a slight decrease in the efficiency of granule exocytosis in response to anti-CD3 stimulation, the most prominent effect was a marked reduction of perforin activity and DNA degradation activity in lytic granules. Western blotting analysis indicated a drastic decrease in the amount of perforin in CMA-treated cells. Fluorescent microscopic observation of OE4 stained with acridine orange indicated that CMA raised the pH of the lytic granules. Under transmission electron microscopy, striking morphologic changes in cytoplasmic granular structures were observed after CMA treatment of OE4. The lytic granules of OE4 had homogeneously stained large cores and numerous small vesicles that filled peripheral areas. In contrast, the lytic granules of CMA-treated OE4 showed irregular shapes with no small vesicles, but with cores that became rough and loose. Vacuoles with no structure in them were seen occasionally. These results suggest that acidification through vacuolar type H(+)-ATPase is essential to maintain the structure and function of lytic granules.

Acid-Base Equilibrium↗
PubMed1994

Screening for specific inhibitors of phagocytosis of thioglycollate-elicited macrophages.

Phagocytosis is one of the basic and characteristic properties of macrophages. We screened metabolites of Actinomyces for low molecular weight substances that selectively inhibited phagocytosis of dried yeast but not pinocytosis of neutral red by thioglycollate-elicited peritoneal macrophages. Inhibitors of actin filament organization, protein kinases, respiration, and lipid synthesis selectively inhibited phagocytosis, and blockers of proton gradients selectively inhibited pinocytosis. This suggests that these functions are differently regulated. We applied this system to screening of metabolites of Actinomyces, and identified mycotrienin, piericidin, and genistein as selective inhibitors of phagocytosis.

Actinomyces↗
PubMed1994

Development and characterization of macrophage hybridomas derived from murine peritoneal exudate cells.

Mouse macrophage (Mphi) hybridoma clones were generated by somatic cell hybridization of myeloma X63 cells (H-2d) with C57BL/6 (H-2b) peritoneal exudate cells elicited with a streptococcal preparation, OK432, or thioglycollate medium. Although they hardly adhered to plastic dishes and could not be morphologically distinguished from parental X63 tumor cells, the clones retained Mphi characteristics. These included phagocytosis and production of lysozyme and nonspecific esterase, suggesting that they were hybridomas derived from Mphi. Some of them expressed various levels of Ia antigen and Fc receptor. Because they induced proliferation of T cells from Balb/c mice but not those from C57BL/6 mice, the Ia antigen of Mphi hybridoma was assumed to be derived from peritoneal Mphi. The level of proliferation induction was correlated to the level of Ia antigen expression. Several clones produced a factor that cytostatically inhibited growth of murine mammary carcinoma and was serologically identified with arginine deiminase.

Animals↗
PubMed1993

Morphological changes and reorganization of actinfilaments in human myeloid leukemia cells induced by a novel protein phosphatase inhibitor, tautomycin.

A protein phosphatase inhibitor, tautomycin induces blebs on the surface of human myeloid leukemia K562 cells within 10 min. In this paper we examined the cytoskeleton of tautomycin-treated cells. In the presence of tautomycin, cells with blebs turned into segmented forms with smooth surfaces after 15 min and into smooth round shapes without microprotuberance after 60 min. Observation with fluorescence microscopy showed that F-actin detached from the plasma membrane at the site of the blebs. Further treatment with tautomycin induced the accumulation of F-actin at the segmentation centers. Under electron microscopy, an electron dense ring-structure was detected at the segmentation center. Tautomycin did not induce major changes of the microtubule network although F-actin accumulated near the microtubule organizing center. The amount of F-actin increased in tautomycin-treated cells. These results indicate that the morphological changes are induced by reorganization of actinfilaments.

Actin Cytoskeleton↗
PubMed1993

Effects of microbial products on glucose consumption and morphology of macrophages.

We studied the effects of microbial products on glucose consumption and morphology of macrophages which were elicited with thioglycollate medium. Macromolecules such as lipopolysaccharide (LPS), tumor promoters, and respiratory inhibitors increased macrophage glucose consumption without inducing evident morphological changes. The assay system was used to screen for active substances in culture broth extracts from actinomycetes. Among them, aureothin increased glucose consumption of macrophages and inhibited respiration of a rat mitochondrial fraction. Concanamycin A induced morphological changes of macrophages into needle-like shapes but not of cloned cells including the macrophage-like cells J774.1. This compound changed fibrosarcoma L929 cells into round shapes without affecting the shape of a nontransformed fibroblast, BALB/3T3 cells. Antimycin and concanamycin A increased tumor-killing activity of macrophages when added during the effector phase. These results suggest that this assay system is simple and sufficiently reproducible and thus usable for screening for modulators of macrophage function among natural products.

3T3 Cells↗
PubMed1993

Melastin, a novel product of Streptomyces that selectively inhibits leukemia cell growth.

In the course of our screening for new immunomodulators, a novel compound, melastin, was purified from the culture broth of Streptomyces. Melastin was purified through absorption to Diaion HP-20, ethanol precipitation, and anion exchange column as a brown powder. The molecular weight was estimated as 5000 +/- 3000 by gel filtration HPLC. Melastin suppressed lipopolysaccharide (LPS)-induced blastogenesis of B cells more profoundly than concanavalin A (con A)- or phytohemagglutinin (PHA)-induced blastogenesis of T cells. Moreover, it selectively inhibited the growth of several leukemia cells as compared with interleukin-dependent nontransformed leukocytes. No selectivity was observed between nontransformed fibroblasts and their oncogene-transformed variants. Melastin did not selectively inhibit macromolecule synthesis of leukemia cells.

Amino Acids↗
PubMed1992

Preferential suppression of delayed-type hypersensitivity by L-156,602, a C5a receptor antagonist.

In the course of our screening for in vivo immunomodulating substances in which sheep red blood cells (SRBC) and heat-killed Brucella abortus cells (thymus dependent and independent antigens, respectively) for antibody production assays, and trinitrobenzene sulfonic acid (TNBS) for delayed-type hypersensitivity (DTH) assay were adopted as antigens, we detected a DTH-specific suppressive activity. The producing organism was isolated from a soil sample collected in Ushiku City, Ibaraki, Japan and identified with Streptomyces sp. A1502 (FERM P-12448). The active component was identified with L-156,602, a C5a receptor antagonist. L-156,602 suppressed both TNBS-induced and TNP-SRBC-induced DTH while it enhanced antibody production against SRBC, Brucella abortus, and TNP-SRBC. L-156,602 significantly suppressed DTH induced by direct injection of type 1 helper T cells and its relevant antigen into hind-footpads, indicating that the efferent phase of DTH was affected by L-156,602. The results demonstrated that L-156,602 preferentially suppressed the DTH response.

Adjuvants, Immunologic↗
PubMed1992

Effects of L-156,602, a C5a receptor antagonist, on mouse experimental models of inflammation.

L-156,602, a C5a receptor antagonist, was found as an immunosuppressant with preferential effects on delayed-type hypersensitivity (DTH) in our screening program and it was shown that L-156,602 suppressed the efferent phase of DTH. Here, we tested its effects on experimental models of inflammation induced in mice. L-156,602 did not suppress serotonin- and carrageenan- induced inflammation while it completely suppressed concanavalin A-induced inflammation 4 h after elicitation. The inflammation appeared 24 h after the elicitation with concanavalin A and it was significantly suppressed by L-156,602. Muramyl dipeptide (MDP)-induced acute joint inflammation was also significantly suppressed by L-156,602. These results demonstrated the unique immunomodulating properties of L-156,602 in mouse experimental models of inflammation.

Animals↗