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Biomedical subjects

M Lubin

Publications and source records attributed to M Lubin.

At least 37 records · Page 2Linked to original sources
PubMed1979

Transfer of potassium. A new measure of cell-cell coupling.

Mammalian cells of different species differ in sensitivity to ouabain. This sensitivity is expressed as reduced intracellular K+ content, reduced rates of protein synthesis, and cessation of cell multiplication. Using 86Rb+ as a measure of intracellular K+, we found higher levels of radioactivity in mixtures of ouabain-sensitive and -resistant cells cultured in the presence of ouabain than predicted from pure cultures of the two component cell types. The simplest explanation is that K+ and 86Rb+ are being transferred from ouabain-resistant to ouabain-sensitive cells, enhancing the total intracellular 86Rb+ in the culture. A function, "index of cooperation," expresses this enhancement as a number ranging from 0 to 1, and permits comparisons to be made under various culture conditions and using various cell types. An index of cooperation greater than 0 requires cell contact, since no enhancement occurs when contact between two cell types in the same culture is prevented. The index of cooperation for a number of different cell combinations agrees with other measures of cell-cell interaction associated with gap junctions, such as electrical coupling and metabolic cooperation. Coculture of ouabain-sensitive and ouabain-resistant cells in the presence of ouabain also leads to restoration of the capacity for protein synthesis. Autoradiography shows that this restoration occurs in the sensitive cell type and is dependent upon contact with ouabain-resistant cells. Furthermore, sensitive cells are able to multiply in the presence of ouabain when cocultured with resistant cells. Thus K+, presumably transferred to sensitive cells through gap junctions, is able to counteract the toxic effects of ouabain on intracellular K+ levels and protein synthesis, and to restore growth.

Cell Communication↗
PubMed1978

Inhibition of elongation steps of protein synthesis at reduced potassium concentrations in reticulocytes and reticulocyte lysate.

We treated intact reticulocytes with nystatin to make them permeable to small cations and varied the concentration of K+ in the medium; the ionic strength was kept constant by adjusting Na+. As the intracellular K+ was lowered, the rate of protein synthesis decreased. In a reticulocyte lysate, the dependence of the rate of protein synthesis on K+ concentration (at constant ionic strength) was similar to that seen in nystatin-treated cells. We observed no loss of polysomes at low K+. Even when initiation was blocked with aurintricarboxylic acid, decreased K+ inhibited protein synthesis. Analysis of the kinetics of synthesis showed that lowering the K+ concentration inhibits the rate of elongation of nascent chains, but has little effect on the relative rate of initiation of chains.

Animals↗
PubMed1978

Increased tumor immunity in mice inoculated with muconomycin A-treated B16 melanoma cells.

B16 melanoma cells were treated in vitro with muconomycin A, a long-lasting inhibitor of protein and glycoprotein synthesis, to reduce cellular sialic acid. Two i.p. inoculations of 10(7) muconomycin-treated cells into female C57BL/6 mice, followed by challenge with homologous live cells, resulted in a significant decrease in tumor incidence when compared to the results of inoculation with untreated cells (p less than 0.01). Inoculation of mice with cells treated with neuraminidase resulted in little or no decrease in tumor incidence. Effective immunity was dependent on the number of cells injected and was found only with the i.p. route of inoculation into female mice.

Animals↗
PubMed1977

Prolonged inhibition of protein and glycoprotein synthesis in tumor cells treated with muconomycin A.

Several agents were compared for their ability to inhibit protein synthesis for long periods in tumor cells growing in culture. Mouse B16 melanoma cells, treated with high concentrations of cycloheximide or pactamycin for 1 hour and then washed repeatedly, recovered their ability to incorporate [3H]leucine into protein in about 4 hours, while cells treated with emetine recovered in 12 hours. After similar treatment with muconomycin A, however, incorporation of [3H]leucine remained inhibited for at least 30 hours. During this time the cells remained attached to the culture dishes, were able to exclude trypan blue dye, and retained nearly normal levels of rubidium-86 content. When another, untreated, population of cells was added to the muconomycin-treated cells, protein synthesis was not inhibited in the untreated population; action of the drug was thus shown to be confined to the treated cells. In melanoma cells treated with neuraminidase and muconomycin, measurement of glycoprotein synthesis (as determined by sialic acid analysis) showed that muconomycin also inhibited restoration of sialic acid content. Brief treatment with muconomycin, therefore, appeared to be sufficient for prolonged inhibition of protein and glycoprotein synthesis.

Anti-Bacterial Agents↗
PubMed1975

Interaction of the 5'-ends of 28S RNA in dimerization of hamster ribosomes.

Free ribosomes extracted from hamster cells and 28S RNA purified from these ribosomes are known to form dimers. We find that spleen phosphodiesterase inhibits ribosomal dimer formation, but only when a free 5'-hydroxyl end group, produced by the action of alkaline phosphatase, is present. Hence, formation of dimer ribosomes probably involves interaction at or near the phosphorylated 5'-ends of 28S RNA. Dimer RNA molecules show a modal length, when measured on electrom micrographs, of 2.1 mum, which is about double the length of 28S RNA. Electron micrographs of 115S dimer ribosomes often show profiles consistent with our interpretation that in dimers the 28S RNA chains are loosely linked by their 5'-ends.

Animals↗