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Biomedical subjects

I Tamm

Publications and source records attributed to I Tamm.

At least 73 records · Page 4Linked to original sources
PubMed1984

Interferon suppresses pinocytosis but stimulates phagocytosis in mouse peritoneal macrophages: related changes in cytoskeletal organization.

Treatment of thioglycolate-elicited macrophages with mouse beta-interferon markedly reduces pinocytosis of horseradish peroxidase and fluorescein isothiocyanate (FITC)-dextran but stimulates phagocytosis of IgG-coated sheep erythrocytes. Experiments with FITC-dextran have revealed that the overall decrease in pinocytosis is due to a nearly complete inhibition of pinocytosis in a large fraction of interferon-treated macrophages. In the remaining cells pinocytosis continues at a rate similar to that in untreated control cells. A considerable reduction in the number of cells pinocytosing FITC-dextran was observed within 12 h from the beginning of interferon treatment. Measurement of the overall level of pinocytic activity with horseradish peroxidase showed a progressive decline through 72 h of treatment. In the interferon-sensitive subpopulation, there were marked changes in cytoskeletal organization. Microtubules and 10-nm filaments were aggregated in the perinuclear region while most of the peripheral cytoplasm became devoid of these cytoskeletal structures as observed by fluorescence and electron microscopy. In addition, interferon treatment of macrophages appeared to disrupt the close topological association between bundles of 10-nm filaments and organelles such as mitochondria, lysosomes, and elements of the Golgi apparatus and endoplasmic reticulum. Such alterations in the distribution of microtubules and 10-nm filaments were not seen in the interferon-insensitive subpopulation. We have investigated the mechanism of the interferon-induced enhancement of phagocytic activity by binding IgG-coated sheep erythrocytes to mouse peritoneal macrophages at 4 degrees C and then initiating a synchronous round of ingestion by warming the cells to 37 degrees C. Thioglycolate-elicited macrophages that had been treated with mouse beta-interferon ingested IgG-coated erythrocytes faster and to a higher level than control cells in a single round of phagocytosis. In interferon-treated cultures, phagocytic cups became evident within 30 s of the shift of cultures from 4 degrees to 37 degrees C, whereas in control cultures, they appeared in 2 min. Cytochalasin D, an inhibitor of actin assembly and polymerization, abolished phagocytic activity in both control and beta-interferon-treated macrophages. However, to inhibit phagocytosis completely in thioglycolate-elicited interferon-treated macrophages, twice as much cytochalasin D was required in the treated as in control cultures.(ABSTRACT TRUNCATED AT 400 WORDS)

Actins↗
PubMed1984

Growth rate of control and beta-interferon-treated human fibroblast populations over the course of their in vitro life span.

The estimated growth rates for five lines of human fibroblasts (Human Genetic Mutant Cell Repository designations 0011, 2936B , 0038A , 2912A , and 3529), during the first few population doublings after establishment of the lines, were within the expected range, i.e., equivalent to doubling times from 16 to 28 hr, with a mean of 20 hr. The lines were derived from donors aged 8 fetal weeks, 20 days, 9 years, 26 years, and 66 years, respectively. The growth rates of the five lines declined as an exponential function of the population doubling level in all cases. The rate of decline of the growth rate varied for different lines and appeared to be related to the life span of the lines, which in turn was related to donor age. After 30 population doublings, the population doubling times had increased 1.3, 1.3, 1.7, 3.4, and 4.7 times for the five cell lines of the corresponding replicative life spans of 65, 57, 56, 31, and 28 population doublings. Sensitivity of the fibroblast lines to the cell growth-inhibitory effect of beta-interferon was independent of the population doubling level of the lines, i.e., interferon depressed the population growth rate of low population doubling level cells as much as that of middle or late population doubling level cells for any given line. However, the fibroblast lines showed differences in their sensitivity to the cell growth-inhibitory effect of interferon, probably as an expression of genotypic differences among the lines.

Adult↗
PubMed1983

Recovery of HeLa cell population growth after treatment with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB).

Dose-response curves for the inhibition of heterogeneous nuclear RNA (hnRNA) synthesis in HeLa cells by 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB; 5-100 microM; 30 min) are biphasic and indicate the existence of two subpopulations of hnRNA molecules, one highly sensitive and the other completely resistant, as previously reported for molecules greater than 1,000 nucleotides long (Tamm et al., 1976; Sehgal et al., 1976a). In the short-term experiments, the drug-sensitive synthesis of hnRNA was inhibited 50% at a DRB concentration of approximately 7 microM, and 70% at 20 microM, whereas drug-resistant synthesis, which comprises approximately 20% of total, continued at DRB concentrations as high as 100 microM. After 24 hr of DRB treatment in medium containing 5% fetal calf serum, the increase in cell number in the exponentially growing population was inhibited by only 42% at 20 microM DRB, and the formation of colonies of greater than or equal to ten cells was not decreased. DRB at 40 microM concentration decreased population growth by 76% and colony formation by 63%. Treatment with 60 microM DRB was sufficient to prevent a net increase in cell number and to reduce colony formation by 78%. After termination of treatment, the time required for the surviving population to begin rapid proliferation was directly related to the concentration of DRB used to treat cells and to the duration of treatment. After 24-hr treatment with 40 microM DRB, cultures recovered within 1 day, whereas after 60 microM DRB, 3-4 days were required. After 40-hr treatment with 60 microM DRB, 5-6 days were required for recovery, and after 80 microM DRB, 9-11 days. During the "dormant" period the cell number ranged from 15 to 60% of the initial number and was fairly stable for given conditions. After the "dormant" period, recovery was rapid. The population growth rate in cultures undergoing treatment with DRB is directly related to serum concentration; however, the recovery rate during the post-treatment period is unaffected by serum concentration.

Blood↗
PubMed1983

Comparison of the effects of alpha and beta interferons on the proliferation and volume of human tumor cells (HeLa-S3, Daudi, P3HR-1).

Treatment of three lines of tumor cells (epidermoid carcinoma: HeLa-S3, and Burkitt's lymphoma: Daudi and P3HR-1) with human alpha or beta interferon (HuIFN-alpha or HuIFN-beta) results in inhibition of cell proliferation as well as in increased modal cell volume and heterogeneity of the populations with respect to cell volume. In all three cell lines the IFN-alpha- or IFN-beta-induced changes in cell proliferation and in cell volume are inversely related to each other. However, these lines differ significantly in their sensitivity to the effects of IFN-alpha and IFN-beta.

Burkitt Lymphoma↗
PubMed1983

Reduced synthesis of pp60src and expression of the transformation-related phenotype in interferon-treated Rous sarcoma virus-transformed rat cells.

Treatment of Rous sarcoma virus-transformed rat cells with rat interferon-alpha (specific activity, 10(6) U/mg of protein) for 24 h caused a 50% reduction in intracellular pp60src-associated protein kinase activity. Staphylococcus aureus V8 protease digestion of pp60src, derived from 32P-labeled monolayer cultures incubated with or without interferon, revealed no differences either in the phosphopeptide pattern or in the phosphoserine-phosphotyrosine ratio. However, [3H]leucine pulse-labeling experiments showed that the synthesis of pp60src was reduced by 42 to 48%, relative to the level of bulk protein synthesis, in the interferon-treated cultures. Rat interferon-alpha also reduced the growth rate of Rous sarcoma virus-transformed rat cells in a dose-dependent manner over a 72-h period. The decrease in growth rate was accompanied by increases in the thickness and number of actin fibers per cell and by a decline in intracellular tyrosine phosphorylation by pp60src. The results suggest that interferon can inhibit the expression of the transformation-related phenotype by selectively reducing the synthesis of the Rous sarcoma virus transforming gene product. However, the interferon effects on the cytoskeletal organization and proliferation of Rous sarcoma virus-transformed cells may be due at least in part to the predominance of interferon-induced phenotypic changes over those caused by pp60src.

Actins↗
PubMed1983

Inhibition of HeLa-S3 cell proliferation and biosynthesis by 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB).

Treatment of HeLa-S3 cells in suspension cultures with 60 microM 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) for 18-30 hr stops the growth of the cell population when treatment is carried out at 37 degrees C in Eagle's spinner culture medium supplemented with 5% fetal bovine serum. The length of the period of no growth after termination of treatment is directly related to the duration of DRB treatment. Upon resumption of growth, the rate becomes exponential and is not distinguishably different from the control rate (doubling time: 19 hr). The growth of the progeny population of the previously DRB-treated cells is as sensitive to inhibition by DRB as the growth of control populations not treated with DRB. After treatment of cells with DRB for 30 hr at 39.5-40 degrees C, the population which grows out has a prolonged doubling time. DRB treatment at 37 degrees C for 5 hr markedly inhibits uridine uptake and cellular RNA synthesis in the presence either of 5 or 15% serum. After treatment for 48 hr in 15% serum, inhibition of RNA synthesis by DRB is significantly decreased. DRB treatment does not inhibit leucine uptake in HeLa cells growing in suspension cultures. Protein synthesis is moderately inhibited in 5% serum and only slightly inhibited in 15% serum after either 5- or 48-hr period of treatment.

Blood↗
PubMed1982

Serum enhances the cycling and survival of HeLa cells treated with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole.

We have defined the growth kinetics of HeLa cell populations by determining the frequencies of mitoses and deaths and the lengths of intermitotic intervals. This was done by time-lapse cinemicrography. Untreated control cells proliferated at closely similar rates in medium enriched with 5% or 15% fetal calf serum, with an average of 4% dividing and less than 0.1% dying per hr. The mean intermitotic interval was 16 hr during exponential growth of the control populations. In contrast, in cultures treated with 40 or 60 microM 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), a selective inhibitor of heterogeneous nuclear RNA synthesis, the frequency of mitoses was markedly and directly dependent on serum concentration, whereas the frequency of deaths was inversely dependent. DRB prolonged the intermitotic interval in cells cycling in the presence of the drug, but the effect was less in 15% than in 5% serum. After prolonged treatment of HeLa cells with DRB, the inhibition of heterogeneous nuclear RNA synthesis by DRB appeared to be reduced, which was not due to inactivation of DRB in the culture medium.

Cell Cycle↗
PubMed1982

Effects of beta interferon on concanavalin A binding and size of HeLa cells.

Treatment of HeLa-S3 cells with 640 u/ml of human beta interferon (HuIFN-beta) in suspension culture increases the cell volume and the heterogeneity of the population with respect to cell size, as measured by Coulter electronic volume analysis. Based on such analysis, the cell surface area is increased 11% by 24 h, and 42% by 48 h after beginning of interferon treatment. Binding of [125I] Concanavalin A (measured at 22 degrees C) is increased 75% by 24 h, and 120% by 48 h on a per-cell basis. It follows that interferon treatment for 24 h causes a 58% increase in the abundance of functional Con A receptor sites per unit area of cell surface. The further increase in Con A binding after treatment of cells with interferon for 48 h can be attributed to increased surface area of cells.

Cell Membrane↗
PubMed1982

Effect of simian virus 40 on the temporal and spatial organization of DNA replication in Muntjac cells.

We examined the effects of simian virus 40 infection on the temporal and spatial organization of initiation sites for DNA replication in Muntjac cells by means of light microscopic DNA fiber autoradiography. Initiation at multiple sites along the DNA fiber in virus-infected confluent Muntjac cells was more nearly synchronous than in serum-deprived controls, although temporal control in the infected cells did not reach the level observed in cells incubated in serum-enriched medium. Initiation sites in virus-infected cells appeared to be spatially closer together than in either uninfected serum-deprived or uninfected serum-enriched cells. This change did not appear to be the result of the induction or repression by simian virus 40 of clusters of replication units with new and different organizations.

Animals↗
PubMed1981

Interferon increases the abundance of submembranous microfilaments in HeLa-S3 cells in suspension culture.

Human beta (fibroblast) interferon inhibits the proliferation of human HeLa-S3 carcinoma cells in suspension culture. Accompanying this effect, the lateral mobility of cell surface receptors for concanavalin A is decreased and the rigidity of the plasma membrane lipid bilayer is increased. The present findings show a marked increase in the number of polymerized actin-containing microfilaments 3 days after treatment of HeLa-S3 cells with beta-interferon (640 units/ml). The cortical region of the treated enlarged cells contains a thick and dense meshwork of 40-70 A microfilaments. The actin nature of the filaments was verified by their ability to bind heavy meromyosin. These results support the concept that beta-interferon induces a coordinated response in the plasma membrane and the underlying microfilaments in both tumor and normal cells.

Cell Membrane↗
PubMed1981

Beta-interferon-induced time-dependent changes in the plasma membrane lipid bilayer of cultured cells.

The time-dependent interferon-induced structural changes in the plasma membrane lipid bilayer have been investigated in cultured cells using spin label electron spin resonance techniques. Treatment of human HeLa-S3 cells in suspension culture with human beta 1 interferon (640 u/ml) for as short a time as 30 min causes an increase in the rigidity of the plasma membrane lipid bilayer (Landsberger, Pfeffer and Tamm, in preparation). The plasma membrane rigidity of interferon-treated cells returns to the level of control cells within 3 to 5 hr, but by 24 hr after beginning of treatment, the rigidity of the plasma membrane is increased again and remains so for at least 2 days. Mouse beta interferon causes both an early (Landsberger, Pfeffer and Tamm, in preparation) and a late increase in membrane rigidity in homologous mouse L-929 cells, but not in heterologous HeLa-S3 cells. Thus, the interferon-induced perturbation of membrane structure is species specific. The late increase in membrane rigidity may have a different underlying mechanism from that of the early increase. While the early and transient change probably is related to signal generation and transmission, the later and persistent change may be an aspect of the phenotype and interferon-treated cells and may reflect changes in the plasma membrane-cytoskeletal complex.

Cell Membrane↗
PubMed1980

Interferon inhibits the redistribution of cell surface components.

Interferon treatment impairs the ability of cells to redistribute cell surface receptors for concanavalin A (Con A). The effect of interferon becomes evident within 3-6 h and is maximal within 36-48 h. Highly purified human fibroblast interferon (> 2 x 10(8) U/mg of protein sp act; concentration; 640 U/ml) caused approximately 85% inhibition of capping of fluorescein-conjugated Con A in interferon-sensitive HeLa-S3 cells at 36 h from the beginning of treatment.

Cell Membrane↗
PubMed1980

Short capped hnRNA precursor chains in HeLa cells: continued synthesis in the presence of 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole.

The labeling of m7GpppN1mpN2p caps with L-[methyl-3H]methionine on short (100-500 nucleotides) heterogeneous nuclear RNA (hnRNA) chains of HeLa cells is increased 2-3 times but the labeling of caps on longer (greater than 2000 nucleotides) hnRNA chains is decreased by approximately 80% by treatment of the HeLa cells with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB). The experimental conditions were as follows: HeLa cells were treated with 75 muM DRB for 40 min before labeling and also during the 30-min pulse of L-[methyl-3H]methionine; actinomycin D (0.05 microgram/mL) was used to suppress ribosomal RNA synthesis. Control cells received no DRB. The RNA was separated in Me2SO gradients to ensure no aggregation. Labeling of cells with [3H]uridine for 10 min and separation of RNA by these techniques reconfirmed the findings [Tamm, I., Hand, R., & Caliguiri, L. A. (1976) J. Cell Biol. 69, 229-240; Sehgal, P. B., Darnell, J. E., Jr., & Tamm, I. (1976) Cell 9, 473-480] that 70-80% of the synthesis of hnRNA (GREATER THAN 1000 NUCLEOTIDES) IS SENSITIVE TO INHIBITIOn by DRB but that 20-30% is resistant. This analysis of the methyl-labeled caps provides evidence that DRB causes early termination of a large fraction (approximately 70-80%) of hnRNA precursor chains. In contrast to the finding of continued synthesis and accumulation of short m7GpppN1mpN2p-capped chains in the presence of DRB, the synthesis of m2,2,7GpppN1mpN2mp-capped small nuclear RNAs was inhibited by approximately 70% by DRB.

Chromatography, High Pressure Liquid↗
PubMed1980

Effects of reovirus infection on the spatial and temporal organization of DNA replication in L cells.

DNA fiber autoradiography was used to analyze the spatial and temporal organization of activated initiation sites for DNA replication in mouse L929 cells infected with reovirus type 3 (Dearing strain) and in uninfected control cells. Cells were labeled for 10 min with 3H-thymidine at high specific activity followed by 3 h of low specific activity labeling. Reovirus infection causes no change in the rate of replication fork progression, but increases both the mean distance between activated initiation sites by approximately 30% and the nonrandomness in the spatial distribution of the sites along the DNA fibers. Significant synchronization of initiation in adjacent activated sites was detected on DNA fibers from uninfected cells and from reovirus-infected cells. The mean relative initiation time for pairs of initiation events which had occurred prior to high specific activity labeling did not differ significantly between the infected and uninfected cells. The data are consistent with the interpretation that reovirus infection shuts off initiation sites in a coordinated fashion, possibly by preventing activation of entire clusters of potential initiation sites.

Animals↗