Differences in Membrane Fluidity and Structure in Contact-Inhibited and Transformed Cells (original) (raw)
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Changes in Membrane Structure Associated with Cell Contact
Proceedings of the National Academy of Sciences, 1973
Ultrastructural analysis of 3T3 fibroblasts by freeze-cleavage has demonstrated significant changes in cell-membrane structure associated with cellto-cell contact and malignant transformation. These changes consist of a rearrangement and redistribution of intramembranous particles on the membrane fracture faces exposed by freeze-cleavage. The results show that noncontacted 3T3 cells in low density contain randomly distributed intramembranous particles. With the development of cell-to-cell contacts during the logarithmic phase of growth however, a pronounced aggregation of intramembranous particles is seen. A direct correlation
Experimental Cell Research, 1974
Freeze fracture ultrastructure studies have shown that contact inhibited 3T3 cells contain aggregated intramembranous particles (IMP) while transformed 3T3 cells have randomly distributed IMP. The results of this study show that the aggregation of IMP in 3T3 cells is primarily related to the degree of cell contact and not significantly affected by inhibition of cell movement. Cell cycle studies do, however, show a transient disaggregation of IMP during the mitotic phase of the cell cycle. These observations are interpreted to suggest that changes in membrane structure which occur during mitosis or following cell-to-cell contact may be associated with changes in membrane fluidity and the activity of membrane enzymes that appear to be critical for control of cell growth and cell division.
Plasma membrane alteration associated with malignant transformation in culture
Proceedings of the National Academy of Sciences, 1975
The intramembrane organization of the plasma membranes of nonmalignant cells in culture has been compared by freeze-fracturing with that of virally-transformed malignant cells. No dramatic differences are present in the distribution of intramembrane particles in the plasma membranes of these cells when the cells are examined without fixation or with mild fixation (glutaraldehyde treatment) prior to freezing. However, a redistribution of intramembrane particles into aggregates occurs in the membranes of nontransformed cells after treatment with glycerol. The
Biochemical Medicine and Metabolic Biology, 1987
The 3T3 cells in culture exhibit density-dependent inhibition of growth (1) in opposition to the simian virus-transformed 3T3 (SV3T3) cells which have the ability to grow to much higher densities (2). The density-dependent inhibition of growth is associated with decreases in the uptake of amino acid (3,4), phosphate (5-S), and glucose (9-12), while in the virus-transformed cells the uptake of these nutrients has been shown to be consistently high (3,5,13-l@. Since the transport of amino acid, glucose, and phosphate is a Na-dependent process (19-21), the maintenance of the sodium gradient across the cell membrane which is largely regulated by the Na-K pump is of importance in regulating cell growth. The activity of the Na-K pump in cultured cells has been shown by Aiton and Lamb (22) to be affected by serum concentration in the growth media. We have shown that sera types can also affect the activity of the Na-K pump in 3T3 cells (23) and also of several other membrane-bound enzymes (24). Since the 3T3 cells when first established were grown in medium supplemented with fetal bovine serum (l), while the SV3T3 cells were established in medium supplemented with newborn calf serum (2), we thought that the use of these two cell lines for comparing normal and malignant growth is only meaningful if the SV3T3 cells are grown in the same serum as that used in establishing the 3T3 cells. In this paper we report the effects of cell population density on the activity of Na-K pump and their roles in growth regulation in 3T3 and SV3T3 cells grown in medium supplemented with fetal bovine serum. Materials MATERIALS AND METHODS Swiss 3T3 and SV3T3 cells and materials needed for the growth of the cells which includes Dulbecco's modification of Eagle's minimal essential medium, fetal bovine serum, and trypsin were obtained from Flow Laboratories (Irvive,
Membrane lipid dynamics and density dependent growth control in normal and transformed avian cells
Experimental Cell Research, 1978
Membrane fluidity of normal chick embryo fibroblasts and normal Japanese quail fibroblasts and their Rous sarcoma virus and methylcholanthrene transformed counterparts was investigated using the technique of fluorescence depolarisation of 1,6-diphenylhexatriene incorporated in the whole cells and in their isolated plasma membrane vesicles. Normal cells and isolated plasma membranes of normal cells showed significant changes in fluidity as a function of population density while neither ROW sarcoma virus transformed nor methylcholanthrene tumor cells or their isolated plasma membrane showed this effect. Stimulation of growth by addition of calf serum to cultures of quiescent, density-inhibited normal cells was accompanied by rapid changes in the direction of increased membrane lipid fluidity. Neither sparse normal cells, nor sparse or dense transformed cells showed any significant fluidity change in their membrane lipids upon addition of serum. Enzyme and electron microscopic analysis of the ratios of different membrane types in each cell type showed that this ratio was invariant with respect to cell population density but different between transformed and normal cells. Hence, the fluidity changes observed,, measured as the mean rotational correlation time of the fluorescene probe in the membrane hpids, truly reflect organisational differences, occurring as a function of population density in cultures of cells which retain density-dependent growth control.
Different cyclic changes in the surface membrane of normal and malignant transformed cells
Experimental Cell Research, 1974
Transformed fibroblasts in interphase and normal fibroblasts in mitosis were agglutinated by Con A and the lectin from wheat germ, whereas normal fibrob!asts in interphase and transformed fibroblasts in mitosis were not agglutinated by these lectins. The percentage of fluorescent cells at non-saturation concentrations of fluorescent ConA was also higher with transformed interphase and normal mitotic cells, than with normal interphase and transformed mitotic cells. Under the same conditions, a similar number of radioactively labeled ConA molecules were bound to normal and transformed cells in interphase and mitosis. Our results indicate different cyclic changes in the surface membrane of normal and transformed fibroblasts, so that regarding interaction with these lectins, normal mitotic cells resemble transformed interphase cells and transformed mitotic resemble normal interphase cells. The data suggest that there is a reversed cyclic change in the mobility of specific surface membrane sites in normal and transformed cells.
Experimental Cell Research, 1975
Differences in the distribution of plasma membrane intramembranous particles (PMP) have been demonstrated in normal and transformed fibroblasts using freeze fracture and electron microscopy. Transformed 3T3 cells contain randomly distributed PMP and contact-inhibited 3T3 cells have aggregated PMP when frozen in medium, glycerol, sucrose, or following stabilization in I % formaldehyde. To define some of the mechanisms controlling the organization of PMP in this system we have examined the effects of microtubule disruptive drugs including vinblastine sulfate and colchicine on SV3T3 cells. These drugs were observed to induce a dose-and time-dependent aggregation of PMP at concentrations between 10m9 and 10W5 M. These results suggest that modulation of PMP distribution in these cells may be influenced by an interaction of microtubules with plasma membrane components. However, the observation that lumicolchicine, a derivative of colchicine which does not disrupt microtubules, also promotes PMP aggregation, suggests that these drugs may also have a primary effect on the plasma membrane in addition to the disruption of microtubules. This is supported by the observation that reduced temperature (4°C) which is known to disrupt microtubules fails to induce PMP aggregation in SV3T3 cells, suggesting the hypothesis that changes in the interaction of plasma membrane or plasma membrane associated constituents may control the distribution of PMP in this cell system.