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Biomedical subjects

G Poste

Publications and source records attributed to G Poste.

At least 127 records · Page 7Linked to original sources
PubMed1979

Cells transformed by temperature-sensitive mutants of avian sarcoma virus cause tumors in vivo at permissive and nonpermissive temperatures.

Chick embryo (CE) fibroblasts and normal rat kidney (NRK) cells transformed by temperature-sensitive (ts) mutants of avian sarcoma virus (NY68, LA23, LA24, LA25, LA29, LA31, GI201, GI202, GI251, GI253 induce tumors on the chorioallantoic membrane (CAM) of chick eggs at temperatures that correspond to the permissive and nonpermissive temperatures used to induce conditional expression of the "transformed" phenotype in these cells when cultured in vitro. Chick embryo cells infected with transformation-defective mutants of ASV (td101, td108) or RAV-50 were nontumorigenic under the same conditions, as were nontransformed CE and NRK cells. This indicates that the CAM is not an unusually susceptible substrate for cell growth and that the ability of tsASV-transformed cells to form tumors at nonpermissive temperatures reflects their true tumorigenicity. In contrast, a ts mutant chemically transformed rat liver cell line, ts-223, only formed tumors on the CAM under permissive conditions. The wild-type parent cells (W-8) of this mutant produced tumors at both permissive and nonpermissive temperatures. Direct implantation of microprobe thermometers into tumors caused by ts-ASV-transformed cells at nonpermissive temperatures confirmed that tumor formation occurred in a stable temperature environment and was not due to temperature fluctuations which might have created semi-permissive conditions for tumor growth. Cells isolated from tumors formed at nonpermissive temperatures and recultured in vitro displayed temperature-dependent hexose transport and colony formation in agar similar to the orginal parent cell inoculum. Similarly, virus recovered from tumors at nonpermissive temperatures retained the ts mutation.

Alpharetrovirus↗
PubMed1979

The tumoricidal properties of inflammatory tissue macrophages and multinucleate giant cells.

Peritoneal exudate cells from C3H/HeN mice infected with bacille Calmette Guérin (BCG) and subcutaneous inflammatory macrophages from uninfected mice exhibit spontaneous cytotoxicity for tumor cells in vitro, but their tumoricidal activity can be increased by incubation in vitro with lymphokines released by mitogen- or antigen-stimulated lymphocytes. Inflammatory macrophages from these sites are only susceptible to activation in vitro by lymphokines for a short period (less than 4 days) following their initial emigration from the circulation to the site of inflammation. The expression of tumoricidal activity by activated macrophages is similarly short-lived (less than 4 days). Once the tumoricidal state is lost it cannot be restored by further incubation with lymphokines in vitro. Fusion of macrophages to form multinucleate giant cells (MGCs) accompanies the loss of tumoricidal activity and the onset of resistance to activation by lymphokines, but the fusion process is not responsible for these changes, since unfused macrophages are similarly affected. Activation and acquisition of tumoricidal properties is confined to young macrophages recruited from the circulation during acute inflammation. Older macrophages and MGCs in chronic inflammatory lesions in which recruitment of new macrophages has ceased are nontumoricidal and are refractory to activation by lymphokines in vitro. These findings are discussed in relation to the efficiency of macrophage-mediated destruction of tumors in vivo and the amplification of macrophage antitumor activity by immunotherapeutic agents.

Animals↗
PubMed1979

Activation of tumoricidal properties in mouse macrophages by lymphokines encapsulated in liposomes.

Cell-free culture supernatants rich in macrophage-activating factor (MAF) activity obtained from mitogen-stimulated F344 rat lymphocytes have been encapsulated within liposomes of differing size and lipid composition and their ability to render normal mouse macrophages cytotoxic for tumor cells in vitro has been compared with that of unencapsulated (free) MAF added to the extracellular medium. Normal macrophages from C57BL/6, C3H/Hen, and C57BL/6 X C3H F1 mice treated with liposome-encapsulated MAF exhibited significant in vitro cytotoxicity against syngeneic and allogeneic tumor cells but did not kill nontumorigenic normal cells. Dose-response measurements revealed that liposome-encapsulated MAF was able to render macrophages tumoricidal at concentrations of at least 20,000 times lower than free MAF. Liposomes containing MAF were able to activate macrophages in the presence of p-nitrophenyl-2-O-alpha-L-fucopyranosyl-beta-D-galactopyranoside, a potent inhibitor of free MAF, indicating that encapsulated MAF was protected within liposomes and that liposome-mediated activation was not caused by small amounts of MAF released into the culture medium from "leaky" liposomes. Liposome-encapsulated MAF was also able to activate macrophages which were refractory to activation by free MAF following either removal of presumably surface receptors for MAF by pronase and/or alpha-L-fucosidase or occupation of the MAF receptor on macrophages by fucose-binding plant lectins (Ulex europaeus 1 and Lotus tetragonolobus agglutinins). Also, populations of nontumoricidal inflammatory tissue macrophages, which were inherently unresponsive to free MAF, would be rendered tumoricidal in vitro by incubation with liposome-encapsulated MAF. Collectively, the data suggest that MAF can render macrophages tumoricidal by acting on intracellular sites.

Animals↗
PubMed1979

Rapid decay of tumoricidal activity and loss of responsiveness to lymphokines in inflammatory macrophages.

The ability of inflammatory tissue macrophages harvested on glass coverslips implanted in the s.c. tissue of C57BL/6 mice to kill tumor cells in vitro has been examined. Macrophage present on coverslips implanted for less than 4 days are devoid of spontaneous tumoricidal activity but can be rendered cytotoxic for syngeneic and allogeneic tumor cells in vitro by incubation in vitro with lymphokines release by mitogen-stimulated lymphocytes. Inflammatory macrophages on coverslips implanted for 4 to 7 days show significant spontaneous cytotoxicity for tumor cells in vitro, and their tumoricidal activity is further increased by additional incubation in vitro with lymphokines. With progression, the inflammatory macrophages harvested on coverslips implanted for longer than 7 days lack spontaneous cytotoxic activity and are also resistant to activation by lymphokines in vitro. These alterations in tumoricidal activity and responsiveness to lymphokines are accompanied by a marked reduction in the number of peroxidase-positive macrophages within the population, suggesting that maintenance of tumoricidal activity requires continuous influx of new peroxidase-positive macrophages from the circulation. Previously activated macrophages which have lost their tumoricidal activity and become refractory to reactivation by lymphokines in the extracellular environment can be reactivated by treatment in vitro with liposomes containing encapsulated lymphokines.

Animals↗
PubMed1978

Identification of a potential artifact in the use of electron microscope autoradiography to localize saturated phospholipids in cells.

The suitability of electron microscope autoradiography for sutdying the uptake and intracellular localization of lipid vesicles (liposomes) containing radiolabeled saturated phospholipids has been examined. Data are presented showing that preparation of specimens for electron microscope autoradiography by conventional methods is accompanied by significant translocation and intercellular redistribution of radiolabeled saturated lipids, causing spurious labeling patterns. Intercellular redistribution of radiolabeled lipid was demonstrated by mixing glutaraldehyde-fixed mous L1210 cells that had been incubated with sonicated lipid vesicles containing [H] dipalmitoyl phosphatidylcholine with an indicator cell population (fixed avian erythrocytes) which had not been exposed to vesicles and showing that after electron microscope processing radiolabeled grains were present in both cell types. The same redistribution artifact also probably affects the intracellular localization of radiolabeled lipids. This artifact is discussed in relation to previous work in which autoradiographic methods have been used for ultrastructural localization saturated phospholipids in cells and tissues.

Animals↗
PubMed1977

Studies on membrane fusion. III. The role of calcium-induced phase changes.

The interaction of phosphatidylserine vesicles with Ca2+ and Mg2+ has been examined by several techniques to study the mechanism of membrane fusion. Data are presented on the effects of Ca2+ and Mg2+ on vesicle permeability, thermotropic phase transitions and morphology determined by differential scanning calorimetry, X-ray diffraction, and freeze-fracture electron microscopy. These data are discussed in relation to information concerning Ca2+ binding, charge neutralization, molecular packing, vesicle aggregation, phase transitions, phase separations and vesicle fusion. The results indicate that at Ca2+ concentrations of 1.0-2.0 mM, a highly cooperative phenomenon occurs which results in increased vesicle permeability, aggregation and fusion of the vesicles. Under these conditions the hydrocarbon chains of the lipid bilayers undergo a phase change from a fluid to a crystalline state. The aggregation of vesicles that is observed during fusion is not sufficient range of 2.0-5.0 mM induces aggregation of phosphatidylserine vesicles but no significant fusion nor a phase change. From the effect of variations in pH, temperature, Ca2+ and Mg2+ concentration on the fusion of vesicles, it is concluded that the key event leading to vesicle membrane fusion is the isothermic phase change induced by the bivalent metals. It is proposed that this phase change induces a transient destabilization of the bilayer membranes that become susceptible to fusion at domain boundaries.

Calcium↗
PubMed1976

Studies on membrane fusion. II. Induction of fusion in pure phospholipid membranes by calcium ions and other divalent metals.

The effect of divalent metals on the interaction and mixing of membrane components in vesicles prepared from acidic phospholipids has been examined using freeze-fracture electron microscopy and differential scanning calorimetry. Ca2+, and to a certain extent Mg2+, induce extensive mixing of vesicle membrane components and drastic structural rearrangements to form new membranous structures. In contrast to the mixing of vesicle membrane components in the absence of Ca2+ described in the accompanying paper which occurs via diffusion of lipid molecules between vesicles, mixing of membrane components induced by Ca2+ or Mg2+ results from true fusion of entire vesicles. There appears to be a "threshold" concentration at which Ca2+ and Mg2+ become effective in inducing vesicle fusion and the threshold concentration varies for different acidic phospholipid species. Different phospholipids also vary markedly in their relative responsiveness to Ca2+ and Mg2+, with certain phospholipids being much more susceptible to fusion by Ca2+ than Mg2+. Vesicle fusion induced by divalent cations also requires that the lipids of the interacting membranes be in a "fluid" state (T greater than Tc). Fusion of vesicle membranes by Ca2+ and Mg2+ does not appear to be due to simple electrostatic charge neutralization. Rather the action of these cations in inducing fusion is related to their ability to induce isothermal phase transitions and phase separations in phospholipid membranes. It is suggested that under these conditions membranes become transiently susceptible to fusion as a result of changes in molecular packing and creation of new phase boundaries induced by Ca2+ (or Mg2+).

Calcium↗
PubMed1976

Studies on membrane fusion. I. Interactions of pure phospholipid membranes and the effect of myristic acid, lysolecithin, proteins and dimethylsulfoxide.

The interaction and mixing of membrane components in sonicated unilamellar vesicles and also non-sonicated multilamellar vesicles prepared from highly purified phospholipids suspended in NaCl solutions has been examined. Electron microscopy and differential scanning calorimetry were used to characterize the extent and kinetics of mixing of membrane components between different vesicle populations. No appreciable fusion was detected between populations of non-sonicated phospholipid vesicles incubated in aqueous salt (NaCl) solutions. Mixing of vesicle membrane components via diffusion of phospholipid molecules between vesicles was observed in populations of negatively charged phosphatidylglycerol vesicles but similar exchange diffusion was not detected in populations of neutral phosphatidylcholine vesicles. Incubation of sonicated vesicle populations at temperatures close to or above the phospholipid transition temperature resulted in an increase in vesicle size and mixing of vesicle membrane components as determined by a gradual change in the thermotropic properties of the mixed vesicle population. The interaction of purified phospholipid vesicles was also examined in the presence of myristic acid and lysolecithin. Our results indicate that while these agents enhance mixing of vesicle membrane components, in most cases mixing probably proceeds via diffusion of phospholipid molecules rather than by fusion of entire vesicles. Increased mixing of vesicle membrane components was also produced when vesicles were prepared containing a purified hydrophobic protein (myelin proteolipid apoprotein) or were incubated in the presence of dimethylsulfoxide. In these two systems, however, the evidence suggests that mixing of membrane components results from the fusion of entire vesicles.

Calorimetry↗
PubMed1976

Measurement of the translational mobility of concanavalin A in glycerol-saline solutions and on the cell surface by fluorescence recovery after photobleaching.

The fluorescence recovery kinetics of succinyl-fluorescein Concanavalin A (S-F-ConA) in glycerol-physiological saline solutions of high viscosity and when bound to the surface of mouse fibroblasts were measured following brief photobleaching using a laser excited fluorescence microscope. In the high viscosity solutions, the recovery kinetics, interpreted on the basis of a simple diffusion model, yielded a diffusion coefficient in close agreement with the values predicted by the Stokes-Einstein equation. Recovery kinetics for S-F-ConA bound to the surface of mouse 3T3 and SV3T3 cells cultured in vitro yielded diffusion coefficients in the range of 5-10-10(-11) cm2/s, values considerably lower than those reported previously for membrane proteins. These measurements indicated that a considerable fraction of the S-F-ConA molecules bound to the cell surface are immobilized. These results are discussed in relation to current concepts of lateral motion of protein components within natural membranes.

Binding Sites↗
PubMed1976

Calcium ionophores A23187 and X537A affect cell agglutination by lectins and capping of lymphocyte surface immunoglobulins.

The microtubule-disruptive drugs colchicine and vinblastine alter ligand-induced redistribution of cell surface immunoglobulins and lectin receptors. These effects can be duplicated by treatment of cells with the divalent cation ionophores A23187 and X537A. Ionophore activity was dependent upon the presence of Ca2+ (1.8 - 10(-3)-4 - 10(-4) M) in the culture medium. The K+-selective ionophore valinomycin had no effect on ligand-induced redistribution of surface receptors. It is suggested that A23187 and X537A impair membrane-associated microtubules involved in transmembrane control of receptor mobility and topography. In contrast to the action of colchicine and vinblastine that bind directly to microtubules, it is proposed that ionophores indirectly affect microtubules by raising the concentration of Ca2+ in the cytoplasm to levels that favor microtubule depolymerization and inhibit microtubule assembly.

Animals↗