Uptake of low molecular weight substances by SV40-transformed 3T3 cells is invariant with growth rates in the presence and absence of serum

Stimulatory effect of serum albumin on the proliferation of serum-free SV40-transformed Balb/c 3T3 cells

Commercial serum albumins have been found to be able to stimulate the proliferation of Balb/c 3T3 cells transformed by SV40, but not that of the normal counterpart. The effect is most pronounced with crystalline samples of albumin depleted of both globulin and fatty acid components, and depends on conditions used for the attachment and on seeding density. Physical and chemical treatments aimed to remove tightly bound impurities do not abolish the activity of fatty acid free serum albumin, thus supporting the idea that albumin per se is mitogenic towards these cells.

Hexose sugar transport activity in a mouse fibroblast cell line temperature sensitive for expression of the transformed phenotype

A temperature-sensitive mouse fibroblast cell line was used to examine the relationship between hexose sugar uptake rates and the control of cell growth. The cell line (ts-H6-15) is a derivative of SV-3T3 cells, exhibiting a transformed phenotype at 32 degrees C and a normal phenotype at 39 degrees C. For cells actively growing at either temperature, a marked decrease in the rate of 3-O-methyl-D-glucose (3-O-MeG) transport is observed as cell population density increases. At cell population densities tested, 3-O-MeG transport rates (at a common assay temperature) were greater in H6-15 cells grown at 32 degrees C than at 39 degrees C, with the enhancement being maximal at the lowest cell densities. The effect of low serum-arrest on H6-15 cells revealed that cells growing at 39 degrees C arrest in G1, while cells at 32 degrees C stop more randomly throughout their cycle. Under conditions of low serum-arrest the rate of 3-O-MeG transport remained as high as in actively growing cells at both 32 degrees C and 39 degrees C. However, 2-deoxyglucose uptake rates were growth state-dependent at 39 degrees C, indicating perhaps metabolic as well as membrane-level control of sugar accumulation. These results further demonstrate that rates of hexose sugar transport by themselves are not always absolutely correlated with rates of cell proliferation and, thus, may be reliable predictors of cell growth potential.

Growth inhibitory protein(s) in the 3T3 cell plasma membrane. Partial purification and dissociation of growth inhibitory events from inhibition of amino acid transport

It has been reported previously that a plasma membrane-enriched fraction from 3T3 cells arrests the growth of sparse 3T3 cells early in the G1 phase of growth (Whittenberger et al., '78, '79). Addition of membranes to sparse 3T3 cells also results in a decrease of the rate of transport of alpha-aminoisobutyric acid (Lieberman et al., '79). We have partially purified the growth-inhibitory proteins from plasma membrane of 3T3 cells. These growth-inhibitory proteins behave as intrinsic membrane proteins and do not require membrane lipids for activity. The partially purified proteins arrest cell growth without affecting the rate of alpha-aminoisobutyric transport; thus, inhibition of both transport and cell growth are not obligatorily coupled events.

The growth requirements of SV40 virus transformed Balb/c-3T3 cells in serum-free monolayer culture

The growth requirements of SV40 transformed Balb/c-3T3 cells have been studied in the absence of serum. For growth in serum-free medium, the cells require (i) insulin, (ii) transferrin, and (iii) cis-unsaturated fatty acids added in combination with fatty acid free bovine serum albumin. The growth rate, saturation density, and morphology of cells grown in this serum-free medium are the same as those of cells grown in serum supplemented medium. This mixture also supports the growth of SV40 transformed Swiss-3T3 cells and SV40 transformed primary mouse embryo cells, but does not support the growth of untransformed Balb/c-3T3 cells. The addition of fibronectin to this mixture allows routine subculture, repeated passage, and indefinite propagation of SV40 transformed Balb/c-3T3 cells. Cells grown in this medium for a period of two months retain their ability to induce tumors when injected into athymic nude mice.