Requirement of serum for DNA synthesis in BHK 21 cells: effects of density, suspension and virus transformation

Fibrinolysis associated with oncogenic transformation. Requirement of plasminogen for correlated changes in cellular morphology, colony formation in agar, and cell migration

Fetal bovine and dog serum were selectively freed of plasminogen by affinity chromatography. The resulting serum as well as native and reconstituted serum (obtained by the addition of purified plasminogen to the plasminogen-depleted serum) were used to examine the role of plasminogen in (a) growth of normal and SV-40-transformed hamster embryo fibroblasts in liquid medium, (b) growth of SV-40-transformed hamster embryo fibroblasts in soft agar, (c) aggregation - a characteristic morphological change of SV-40-transformed hamster cells, and (d) migration of SV-40-transformed and control 3T3 cells from a monolayer into a "wound." The results demonstrated that exponential growth of both normal and transformed cells in liquid medium proceeded at the same rate in the presence or absence of plasminogen. In contrast, removal of plasminogen markedly depressed the plating efficiency of transformed cells in soft agar, eliminated their characteristic aggregation, and substantially reduced the extent of migration. The role of plasminogen and its activation in oncogenic transformation is discussed.

Pituitary extracts and steroid hormones in the control of 3T3 cell growth

Results are reported showing that pituitary extracts stimulate growth of 3T3 cells, an established line of mouse fibroblast. Cells were cultured in medium containing an organic buffer (HEPES; N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid), which increases the serum requirement for cell growth. The pituitary growth-prompting activity is (a) not dialyzable; (b) thermolabile; (c) protease sensitive; and (d) enhanced by hydrocortisone (a steroid hormone). Activity was quantitatively assayed by measurement of stimulation of cell division or [(3)H]thymidine uptake into DNA. The active species is probably different from pituitary protein hormones and it seems to be effective at concentrations observed for protein hormones in vivo. 3T3 cells transformed by simian virus 40 are not responsive to this activity.

Cell contact-dependent increase in membrane D-galactopyranosyl-like residues on normal, but not virus- or spontaneously-transformed, murine fibroblasts

Ricinus communis agglutinin (a lectin specific for beta-D-galactopyranosyl-like oligosaccharide residues) was used to investigate differences in lectin-binding sites on normal 3T3 and transformed SV3T3 and 3T12 cells grown to various cell densities in culture. The agglutinability of SV3T3 cells by R. communis agglutinin decreased when cells were grown to confluency or to a point where the cells were in contact. The agglutinability of 3T3 cells also decreased at confluency, but this result was variable and not as dramatic as with SV3T3 cells. Saturation-binding experiments performed at 4 degrees with (125)I-labeled R. communis agglutinin were used to monitor the number of lectin-binding sites on cells grown to different densities. Transformed cells (SV3T3 and 3T12) did not show cell-culture density-dependent changes in R. communis sites; sparse, touching, and confluent transformed cells had equivalent numbers of sites. However, touching (or confluent) 3T3 cells possessed 2.5-times the number of R. communis sites per cell compared to growing, sparsely populated 3T3 cells. When growing sparse 3T3 cells are compared to growing SV3T3 or 3T12 cells, there are 5-times R. communis sites per unit surface area on the transformed cells. The change in R. communis sites during cell growth in culture is discussed in relation to membrane fluidity and topography of plasma membrane oligosaccharides and glycosyl transferases, which can modify cell surfaces at contact.

Environmental stimuli in the progression of BHK-21 cells through the cell cycle

An L-cell line adapted to grow in protein-free medium is a source of material that stimulates the proliferation of serum-dependent BHK cells under otherwise protein-free conditions. The material produced by the L-cells is resolvable into separate DNA-synthetic and mitotic stimulatory activities. The stimulation of mitosis is dependent upon the presence of one or more heat-labile macromolecules, which can be concentrated by ultrafiltration, and at least one dialyzable component is essential for the initiation of DNA synthesis.

Increased uptake of amino acids and 2-deoxy-D-glucose by virus-transformed cells in culture

Transformed and nontransformed cells in tissue culture differ in their rate of uptake of certain nutrients, as determined by a polyester-coverslip technique. A 2.5- to 3.5-fold increased rate of uptake of alpha-aminoisobutyric acid, cycloleucine, and 2-deoxy-D-glucose was observed with polyoma virus-transformed baby hamster kidney (BHK) 21 cells and simian virus 40 (SV40)-transformed BALB/3T3 (mouse fibroblast) cells, compared to their nontransformed counterparts. Kinetic analysis suggested that the increased uptake by cells transformed with virus was associated with a 3-fold greater V(max), with no detectable changes in apparent K(m). Limited studies also revealed increased initial rates of uptake by murine sarcoma virus-transformed rat liver cells, as compared to the parental line. Exposure of cells to concanavalin A and wheat-germ agglutinin led to significant reductions in amino-acid uptake by both transformed and nontransformed cells; however, transformed cells showed a greater decrease in uptake after exposure to wheat-germ agglutinin. Increased initial rates of uptake of certain amino acids and sugars may be a feature common to transformed cells, compared to their parental control.

Migration of mouse 3T3 fibroblasts in response to a serum factor

A serum factor that promotes migration of (mouse) 3T3 fibroblast cells is shown to be distinct from the growth-promoting and cell-survival factors of serum. The factor promotes migration of cells from the edge of a wound in confluent 3T3 cells, but cell migration under these conditions does not lead to the initiation of DNA synthesis. Subsequent addition of serum initiates DNA synthesis in the migrating cells. The results establish that breaking contacts between quiescent 3T3 cells is not sufficient to initiate DNA synthesis. The DNA synthesis observed in migrating 3T3 cells in the typical "woundhealing" experiment presumably results because the migrating cells have an increased ability to use serum factors. Serum-factor requirements for "wound healing" in cultured 3T3 cells are discussed.

Serum-stimulated release of cell contacts and the initiation of growth in contact-inhibited chick fibroblasts

Increased serum concentration in the medium of a confluent culture increases the overlapping of cells and the average rate of cell movement. The relationship between these two serum activities and serum release of growth inhibition was studied. The increase in overlaps does not appear to be directly related to release of growth since it occurs well after growth has been initiated. The increased rate of cell movement occurred immediately after the addition of serum and was quantitatively proportional to the stimulation of DNA synthesis over a range of serum concentrations, implying that both movement and growth are released by a common serum activity. Direct microscopic observation and time-lapse films reveal a reduction in cell contacts concurrent with the increase in cell movement. Experiments showed that cell movement at low cell densities, where cell contacts are minimal, was rapid in low serum concentration and was not stimulated by increasing the serum concentration. This suggests that the serum effect on cell movement involves cell contacts and is due to release of cell contacts in the confluent monolayer. The primary action of serum may be the disruption of adhesive cell contacts.

Initiation of DNA synthesis in cell cultures by colcemid

Mitotic inhibitors (colcemid, colchicine, and vinblastine) initiate DNA synthesis in dense stationary cultures of mouse embryo fibroblast-like cells. This initiation is not due to any changes in local cell population density. Relationships between the activation of proliferation and other changes of interphase fibroblast-like cells produced by the mitotic inhibitors (disappearance of cytoplasmic microtubules and activation of movements of cell surface) are discussed.

Serum factor requirements of normal and simian virus 40-transformed 3T3 mouse fibroplasts

Evidence is presented to show the presence in normal rat serum of four different serum factors essential for growth of 3T3 or SV40-transformed 3T3 mouse fibroblasts: a factor that specifically promotes growth of normal 3T3 cells; two factors that specifically promote growth of transformed 3T3 cells; and a factor that sustains viability of both normal and transformed 3T3 cells in serum-free medium, probably without inducing growth of the cells. These factors are separated and partially purified.