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P Seth

Publications and source records attributed to P Seth.

At least 181 records · Page 10Linked to original sources
PubMed1987

Adenovirus-dependent changes in cell membrane permeability: role of Na+, K+-ATPase.

Adenovirus-dependent release of choline phosphate from KB cells at pH 6.0 was partially blocked by ouabain. In K+-containing medium, maximum inhibition of release was obtained by 10(-5) M ouabain and half-maximal inhibition was achieved by about 0.5 X 10(-6)M ouabain. Ouabain did not block either the binding or the uptake of adenovirus by KB cells. Without K+, about 25% of cell-associated choline phosphate was released by adenovirus, whereas with 1 mM K+ about 50% was released. This activation by K+ was blocked by 0.1 mM ouabain. HeLa cells behaved like KB cells, but a mutant of HeLa cells resistant to ouabain (D98-OR) released much lower amounts of choline phosphate in response to human adenovirus type 2 (Ad2). Wild-type D98-OR cells bound nearly the same amount of adenovirus as did normal HeLa cells. Ad2 also increased the activity of Na+,K+-ATPase in KB cells, with maximum activation at 50 micrograms of Ad2 per ml. In D98-OR cells, Ad2 failed to activate Na+,K+-ATPase activity. Ad2-dependent lysis of endocytic vesicles (receptosomes) was assayed by measuring Ad2-dependent enhancement of epidermal growth factor-Pseudomonas exotoxin toxicity. This action of adenovirus was increased when K+ was present in the medium. Under the conditions used, K+ had no effect on the amount of Ad2 or epidermal growth factor taken up by the cells. On the basis of these results, it is suggested that Ad2-dependent cellular efflux of choline phosphate and adenovirus-dependent lysis of receptosomes may require Na+,K+-ATPase activity.

Adenoviruses, Human↗
PubMed1987

Proplatelets and stress platelets.

The process of platelet formation by the fragmentation of megakaryocyte pseudopodia, termed proplatelets, demonstrable in the marrow sinusoids is poorly understood. "Stress" platelets produced under conditions of stimulated platelet production differ from normal circulating platelets with respect to volume and a number of functional characteristics. To clarify the relationship of stress platelets to proplatelets, rats were injected with heterologous platelet antiserum. Nondiscoid platelet forms, some characteristically beaded in appearance, strongly resembling bone marrow proplatelets, can be recovered in the circulation of normal rats. During the early period of recovery from acute thrombocytopenia, there was a substantial increase in the proportion of these elongated platelets in the citrated platelet rich plasma. Exposure to EDTA rendered them spherical. Circulating proplatelets may contribute significantly to the prompt increase in platelet volume during recovery from acute thrombocytopenia at a time prior to significant increase in megakaryocyte size and ploidy.

Animals↗
PubMed1986

pH-dependent lysis of liposomes by adenovirus.

Purified adenovirus induced a dose-dependent release of the water-soluble markers calcein and carboxyfluorescein from liposomes. Marker release was strongly dependent on pH, and at temperatures below 5 degrees C, the rate of release showed an optimum at a pH of about 6. This pH dependence parallels disruption of endocytic vesicles by adenovirus and the permeabilization that adenovirus induces on the cell surface. There did not seem to be a striking dependence on the lipid composition of the liposomes. Electron microscopy using a negative stain shows liposomes bound to adenovirus. In some cases, the liposomes were still intact, but many liposomes, which were attached to the vertices of the virus, appeared lysed. These data support the notion that adenovirus, which enters the host cell by receptor-mediated endocytosis, gains access to the cytoplasm by a subsequent pH-dependent disruption of the membrane of the endocytic vesicle.

Adenoviruses, Human↗
PubMed1985

Binding of adenovirus and its external proteins to Triton X-114. Dependence on pH.

35S-Labeled adenovirus type 2 (Ad2) (10 ng/ml) was incubated with 1% Triton X-114 at various pH values varying from 3.0 to 8.0. The detergent phase was separated from the aqueous phase by centrifugation, and the amounts of Ad2 were determined in the two phases. At pH 7.0-8.0, less than 5% of Ad2 was associated with the detergent phase; at pH 5.0 or below, about 60% of Ad2 was associated with the detergent phase. When a mixture of 35S-labeled capsid proteins was used at pH 7.0, 60-70% of the total proteins were associated with the detergent at pH 5.0, but less than 5% of the proteins interacted with detergent at pH 7.0. Among the three major external proteins (hexon, penton base, and fiber), penton base had the highest association with Triton X-114 at pH 5.0. Both intact virus and the capsid proteins that were associated with Triton X-114 at pH 5.0 were released into the aqueous phase on subsequent incubation at pH 7.0. On the basis of these results, it is suggested that mildly acidic pH induces amphiphilic properties in adenovirus capsid proteins and may help Ad2 escape from acidic endocytic vesicles.

Adenoviruses, Human↗
PubMed1985

Adenovirus-dependent increase in cell membrane permeability.

When KB cells were labeled with either 51Cr (1 microCi/ml) or [35S]methionine (5 microCi/ml) and treated with 10 micrograms/ml of adenovirus type 2 (Ad2) at pH 6.0 for 60 min at 37 degrees C, about 25% of the cell-associated 51Cr and 5% of the [35S]methionine were released into the medium. The 51Cr was mainly associated with molecules of 1500 Da or less. When KB cells were labeled with either [3H] choline, alpha-[3H]aminobutyric acid, or [3H]deoxy-2-fluoro-D-glucose and exposed to Ad2, these molecules were released in amounts much higher than 51Cr. The Ad2-dependent release of choline was found to be dependent on Ad2 concentration, with maximum release (nearly 60%) at 10 micrograms/ml of Ad2, on the length of the incubation with Ad2, with maximum release at about 90 min, and on the medium pH with maximum activity at pH 6.0 to 6.5. Greater than 95% of the choline released was water-soluble and identified as choline phosphate. Less than 5% of the choline released was associated with lipids, and none was released as a phospholipid vesicle or micelle. The ability of Ad2 to release choline was abolished by incubating Ad2 for 10 min at 45 degrees C, whereas the binding of Ad2 to the cells was not affected. Fetal calf serum also blocked Ad2-dependent choline release.

Adenoviridae↗
PubMed1985

Potentiation of cytotoxic activity of immunotoxins on cultured human cells.

The cytotoxic activity against human tumor cells of toxic conjugates of Pseudomonas exotoxin with anti-transferrin receptor antibody or epidermal growth factor was potentiated up to 10 to 20-fold by the calcium antagonists verapamil, D-600, and diltiazem and by the lysosomotropic agent beta-glycylphenyl-naphthylamide. The potentiating activity of these agents could be predicted by measuring the inhibition of protein synthesis by the immunotoxins on various cell lines. The use of potentiating agents such as these in combination with immunotoxins may prove useful in the treatment of some human cancers.

Antibodies, Neoplasm↗
PubMed1984

Adenovirus-dependent release of 51Cr from KB cells at an acidic pH.

When KB cells labeled with 51Cr (1 muCi/ml) were treated with adenovirus type 2 (Ad2) at pH 6, 51Cr was released in a concentration-dependent manner with half-maximal release at 1 microgram/ml of virus. The 51Cr release was maximum at 10 micrograms/ml and represented nearly 20% of cell-associated 51Cr. 51Cr release depended on the length of incubation with Ad2 and the pH of the medium; maximum release was at pH 6 with very little release at pH 7.5. An antiserum against the penton base of Ad2 specifically neutralized the ability of Ad2 to release 51Cr. Chloroquine up to 200 microM did not block Ad2-dependent 51Cr release. DEAE-dextran stimulated Ad2-dependent 51Cr release; 4-5-fold stimulation was observed at 50 micrograms/ml of DEAE-dextran. We have compared the ability of Ad2 to release 51Cr with its ability to disrupt endocytic vesicles. Vesicle disruption was independent of pH of the medium in the range of pH 6 to 7.5 and was blocked by chloroquine, whereas, 51Cr release was much greater at pH 6 than at pH 7.5 and was not affected by chloroquine. These results suggest that Ad2 possess a lytic activity which ordinarily lyses acidic endocytic vesicles but, if the cells are maintained at acidic pH, can also directly disrupt the plasma membrane.

ADP Ribose Transferases↗
PubMed1984

Role of a low-pH environment in adenovirus enhancement of the toxicity of a Pseudomonas exotoxin-epidermal growth factor conjugate.

A conjugate of Pseudomonas exotoxin and epidermal growth factor (PE-EGF) inhibits proteins synthesis in KB cells, and this inhibition is increased by adenovirus. Protein synthesis inhibition is dependent on the amount of adenovirus and PE-EGF used and the time of incubation of cells with these agents. With 1 microgram of adenovirus and 0.5 micrograms of PE-EGF per ml, protein synthesis is inhibited about 80% in a 60-min experiment. Under these conditions neither adenovirus nor PE-EGF alone has any effect. In the presence of several weak bases or monensin, the enhancement of toxicity was substantially inhibited; half-maximal inhibition was achieved with 40 microM chloroquine, 10 mM ammonium chloride, 5 mM methylamine, 0.1 mM N-hexylamine and 1 microM monensin. At the concentrations employed, none of the inhibitors affected the amount of virus taken up or bound to the cell surface, and chloroquine had no effect on the amount of EGF taken up in 60 min. Chloroquine did not prevent the toxicity of the PE-EGF (5 micrograms/ml) alone. Because these compounds are known to elevate the pH in receptosomes, it seems likely that the acidification of the receptosome either enhances the lysis of the membrane by adenovirus or enhances some other step in the release of PE-EGF.

Adenoviruses, Human↗
PubMed1984

Evidence that the penton base of adenovirus is involved in potentiation of toxicity of Pseudomonas exotoxin conjugated to epidermal growth factor.

When KB cells are incubated for 1 h with human adenovirus type 2 or type 5 (1 microgram/ml) and a conjugate of epidermal growth factor and Pseudomonas exotoxin (EGF-PE), protein synthesis is inhibited by 80 to 90%. Under these conditions, neither adenovirus nor EGF-PE alone has any effect on host protein synthesis. Thus, adenovirus enhances the toxicity of EGF-PE. A number of antibodies to intact virus and capsid components were tested for their ability to block the enhancing activity and virus uptake. At appropriate dilutions, antibodies prepared against intact virus and penton base blocked the enhancing activity without affecting virus uptake. Antibodies against hexon and fiber blocked virus uptake and enhancing activity in parallel. These studies suggest that the penton base is important in lysis of the vesicles which contain adenovirus and EGF-PE, and this base allows virus and toxin to enter the cytoplasm.

Adenoviruses, Human↗