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Biomedical subjects

R T Dean

Publications and source records attributed to R T Dean.

At least 163 records · Page 9Linked to original sources
PubMed1983

Inhibition of some spontaneous secretory processes in macrophages and fibroblasts by ammonium chloride.

Ammonium chloride inhibits the spontaneous secretion of lysozyme by mouse macrophages and the murine macrophage-like cell line P388D1 and the spontaneous secretion of lysosomal enzymes by P388D1 cells, normal human fibroblasts and the hypersecretory mucolipidosis II (I-cell) fibroblasts. NH4Cl can also inhibit protein synthesis, but this is shown to occur mainly at higher concentrations, or after longer periods of exposure, than are needed for the inhibition of the spontaneous secretory processes. It is confirmed that this amine can also interfere with the continuous endocytosis of fluid in the murine cell types. The nature of the inhibitions is discussed.

Ammonium Chloride↗
PubMed1983

Inhibition by trifluoperazine and digitonin of several forms of pinocytosis.

The effect of the calmodulin antagonist trifluoperazine on fluid phase, adsorptive and receptor-mediated pinocytosis in cultured human fibroblasts and mouse peritoneal macrophages was studied. Uptake in each case was reversibly inhibited by about 20% without toxic effects. Low concentrations of the detergent digitonin had a similar effect. Thus the three uptake mechanisms have common features, and we suggest that in both fibroblasts and macrophages they may reflect uptake within vesicles participating in receptor-mediated endocytosis. These effects of trifluoperazine may operate directly on membranes without the participation of calmodulin.

Animals↗
PubMed1983

Lysosomal hydrolases in macrophages exposed to swainsonine.

Swainsonine reversibly inhibits macrophage lysosomal acid alpha-mannosidase in vitro. When supplied to cultured cells for periods of up to 24 h, swainsonine penetrates the cells and produces a dose- and time-dependent inhibition of cellular alpha-mannosidase. Exposure of macrophages to swainsonine for 24 h, followed by continued incubation in the absence of this agent, produces elevated cellular activity of alpha-mannosidase, relative to unexposed controls; prolonged incubation of macrophage cultures with swainsonine for 1-2 weeks results also in significant increases in cell protein, lactate dehydrogenase activity and in that of another lysosomal enzyme, beta-hexosaminidase.

Alkaloids↗
PubMed1983

Mechanisms of lysosomal enzyme secretion by human monocytes.

Secretion of lysosomal enzymes by human monocytes in response to various stimuli and the effect of conditioned media from lymphocytes and neutrophils was studied. Monocytes were found to release beta-glucosaminidase in response to NH4Cl and to particles (zymosan, opsonised zymosan, asbestos and latex), but do not respond to some soluble stimuli like formyl-methionyl-leucyl-phenylalanine, phorbol myristate acetate, cytochalasin B, concanavalin A and N-acetylmuramyl-L-alanyl-D-isoglutamine. Neutrophil conditioned medium or neutrophil components did not have any effect on secretion. When treated with lymphokines the cells are more responsive, especially to zymosan. Even through there are similarities in the secretory activities of mouse macrophages and human monocytes, there are several differences both in the quantity of the response and in the mechanisms involved.

Acetylglucosaminidase↗
PubMed1983

Does the induction of macrophage lysosomal enzyme secretion by zymosan involve the mannose receptor?

Secretion of the lysosomal enzyme hexosaminidase induced by zymosan is inhibited by mannose and by high concentrations of mannose-6-phosphate and 2-deoxy-glucose but not by mannan. Secretion of hexosaminidase from cells storing previously endocytosed zymosan is unaffected by mannose. Exposure of the cells to mannose does not affect secretion caused by subsequent exposure to zymosan. These findings suggest a role for the mannose-glycoprotein receptor in initiation of lysosomal enzyme secretion by zymosan.

Animals↗
PubMed1983

Inflammatory particles stimulate thromboplastin production by human monocytes.

Several inflammatory particles (zymosan, two forms of asbestos, carrageenan) and the soluble inflammatory agent dextran sulphate induced a dose- and time-dependent increase in thromboplastin activity of cultured human monocytes. Two weakly inflammatory particles (latex and anatase) had little effect. The increase largely depended on protein synthesis; was slow, reaching a peak at about 18 h; and was not due to endotoxin. This procoagulant may contribute to the fibrin deposition frequently seen in inflammatory lesions.

Asbestos↗
PubMed1983

Endocytosis and intracellular protein degradation in cystic fibrosis fibroblasts.

Normal rates of pinocytosis of [3H]sucrose were measured in cystic fibrosis fibroblasts, and were not affected by the addition of cystic fibrosis serum. Bulk protein degradation (a significant proportion of which occurs intralysosomally following autophagy) and its regulation by growth state was apparently identical in normal and cystic fibrosis cultures.

Cell Line↗
PubMed1983

Amines induce increased thromboplastin activity in human monocytes.

A variety of amines induced a dose-dependent and time-dependent increase in thromboplastin activity of cultured human monocytes. The increase required protein synthesis, and reached a peak after about 18 h. Some inhibitory effects were noted at low concentrations of NH4Cl. It is suggested that the amines act by raising the pH of acidic intracellular compartments.

Amines↗
PubMed1983

Receptor-mediated phagocytosis of zymosan is unaffected by some conditions which reduce macrophage lysosomal enzyme secretion.

We have previously shown that several agents which interfere with binding of ligands to the mannose-glycoprotein receptor on macrophages can inhibit zymosan-induced lysosomal enzyme secretion. Here we show that mannose only reduces the association of zymosan with macrophages during the first hour of exposure; after longer periods of uptake no effect is detectable. We have previously shown that mannose reduces surface binding of zymosan, probably by interfering selectively with binding to the mannose receptor. The present inhibition of association of zymosan with macrophages during short exposures can be entirely explained by this reduction of binding. Macrophages must therefore internalize zymosan at sites in addition to the mannose receptor. In contrast to macrophages the murine macrophage-like cell line P388D1 is lacking the mannose-glycoprotein receptor. Accordingly we find that binding of zymosan to P388D1 is much slighter than to macrophages and is unaffected by mannose or mannose-6-phosphate. The spontaneous lysosomal enzyme secretion of P388D1 is also unaffected by mannose. The data on macrophages confirm our previous suggestion that agents interfering with the mannose receptor inhibit the induction of lysosomal enzyme secretion by acting directly on the receptor. The data on P388D1 cells support this assertion by excluding effects at later steps in the secretory pathway.

Animals↗
PubMed1983

Mechanisms of lysosomal enzyme secretion by human U-937 monocytes.

Lysosomal enzyme secretion was studied in U-937, a mononuclear phagocyte cell line. The secretion of the marker enzyme, beta-N-acetyl-D-glucosaminidase, was low when the cells were challenged with phagocytosable stimuli (asbestos, zymosan, opsonised zymosan). Ammonium chloride and cytochalasin B induced secretion over 24 h of incubation. Phorbol myristate acetate and F-methyl-leucyl-phenylalanine, did not have any effect on secretion. It is suggested that U-937 cells may provide a useful model for the study of mononuclear phagocyte secretory pathways.

Acetylglucosaminidase↗
PubMed1983

Interferon as a macrophage activating factor. I. Enhancement of cytotoxicity by fresh and matured human monocytes in the absence of other soluble signals.

The cytolytic activity of human peripheral blood monocytes in vitro against K-562 human leukaemic target cells was stimulated by human fibroblast (beta-) and leucocyte (alpha-) interferon (IFN). Stimulation was by up to several times the corresponding control activity, and was observed with freshly isolated monocytes, and with monocytes cultured for various periods up to 10 days. The cytolytic activity of untreated monocytes was detectable at very low effector: target ratios (less than 5:1), and fell between days 1 and 4 in culture, normally rising again towards the initial activity at day 8; this pattern was also observed when IFN was present continuously, although the activities were then always higher than in the corresponding control cells. Cytolysis showed a lag of about 6 hr, in contrast to that by natural killer (NK) cells, and was routinely measured over 24 hr. The course of stimulation by IFN and its dose-response were studied. Stimulation required the presence of IFN for at least 24 hr, and was maximal with between 1,000 and 10,000 units of IFN/ml. When IFN containing media were removed and replaced with control media, the monocyte activity remained stimulated for at least 4 days. Stimulation by beta-IFN was blocked by a specific antibody to beta-IFN, under conditions in which assayable IFN activity was also neutralized. Several control experiments indicated that the action of IFN was on the monocytes and not on the target cells. The morphological maturation of monocytes was retarded by IFN, even in cultures containing up to 50% serum. The effectiveness of fibroblast IFN indicated that stimulation could not be attributed to the lymphokines which might contaminate alpha-IFN. The action of IFN did not require simultaneous or antecedent in vitro stimulation by endotoxin. This was indicated both by serum free experiments, and also by others in which polymixin B was used to complex with and render unavailable any endotoxin present. Endotoxin showed an independent stimulatory effect, which could be prevented by polymixin.

Cells, Cultured↗
PubMed1982

Lysosomal enzyme secretion by cystic fibrosis fibroblasts is normal.

Lysosomal enzyme secretion by skin fibroblasts derived from cystic fibrosis homozygotes and normal donors of the same range of age, sex and culture passage number were compared. No differences were detected between these groups in their rates of spontaneous lysosomal enzyme release. Incubation of either normal or cystic fibrosis fibroblasts with cystic fibrosis serum did not alter these secretion rates. The lysosomal enzyme secretion of both normal and cystic fibrosis fibroblasts responded similarly to incubation with NH4Cl, monensin, A23187, trifluoperazine or Cytochalasin B. It was concluded that lysosomal enzyme hypersecretion, which has previously been suggested to occur in cystic fibrosis, is unlikely to provide a reliable diagnostic test for the disease.

Acetylglucosaminidase↗
PubMed1982

The regulation of proteolysis in normal fibroblasts as they approach confluence. Evidence for the participation of the lysosomal system.

The effect of the lysosomotropic agent NH4Cl and the proteinase inhibitors leupeptin, Z-Phe-Ala-CHN2 (benzyloxycarbonylphenylalanylalanyldiazomethane) and pepstatin on the degradation of intracellular proteins in Swiss 3T3 mouse and normal human fibroblasts in both the exponential and stationary (confluent) growth phases in nutritionally complete conditions was investigated. Inhibitory effects of all four agents on degradation in both growth states were detected. The increase in proteolysis normally occurring as cells approach confluence could be completely blocked by NH4Cl, by Z-Phe-Ala-CHN2, or by pepstatin in the presence of leupeptin. These results suggest that the lysosomal system is responsible for the regulation of proteolysis at confluence and further confirm its role in 'basal' proteolysis in growing cells.

Ammonium Chloride↗
PubMed1982

The effect of weak bases on lysosomal enzyme secretion by mononuclear phagocytes.

NH4Cl induces a dose-dependent secretion of lysosomal enzymes by mouse peritoneal macrophages and human peripheral blood monocytes. The mechanism of NH4Cl-stimulated hexosaminidase release is distinct from that initiated by the inflammatory stimulus, zymosan. The spontaneous lysosomal secretion of the continuous murine macrophage-like cell line, P388D1, is inhibited by up to 50% in the presence of NH4Cl and other weak bases.

Ammonium Chloride↗
PubMed1982

Derangement of regulation of protein degradation in transforming fibroblasts.

Changes in endogenous protein degradation of stable proteins with growth state have been observed in a number of normal cell lines: increases in degradation of between 15 and 40% occurred in 10 cell lines at confluence. No such regulation of proteolysis was observed in 4 cell lines which were clonogenic in soft agar. We have evidence that this derangement of regulation coincides with the transformation of cells, because such regulation disappears in spontaneously transforming fibroblasts and is decreased by the tumour promoter 12-0-tetradecanoyl-phorbol-13-acetate. In addition, regulation reappears in a growth control revertant of a transformed line.

Animals↗