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The human breast cancer cell line, MCF-7, has been adapted to long-term growth in chemically defined medium without loss of estrogen and progesterone receptors or tumorigenicity in athymic mice. An estrogen reversible inhibition of cell proliferation is exerted by newborn calf serum (NCS) 10%, athymic mouse serum (AMS) 2% or tamoxifen 0.1 to 1.0 microM. The mamma-related hormones, hydrocortisone, progesterone, prolactin, and insulin could not mimic this growth inhibitory effect, and estradiol alone or combined with these hormones did not stimulate cell proliferation in chemically defined medium.

In two sublines of the estrogen receptor-positive human breast cancer cell line, MCF-7, propagated with 0.5% fetal calf serum (FCS) (subline 0.5) and without serum (subline 9), respectively, addition of 10% newborn calf serum (NCS) inhibits cell proliferation and stimulates the secretion of a 42 kDa protein. Both with and without NCS, estradiol (E2) stimulates the secretion of a 61 kDa and a 52 kDa protein in subline 9, and an additional third protein (66 kDa) is stimulated in subline 0.5. E2 inhibits the synthesis of the 42 kDa protein in both sublines. Different cell proliferation rates of MCF-7 cells can be established in cultures with 10% NCS and varying concentrations of E2. In such experiments final cell number after 6 days is positively correlated to the relative amount of the 66 kDa, the 61 kDa and the 52 kDa proteins, whereas the relative amount of the 42 kDa protein is negatively correlated to the final cell number. These results indicate that the 52 kDa, the 61 kDa and the 66 kDa proteins may act as positive growth factors, whereas the 42 kDa protein may act as a negative growth factor. The 42 kDa, the 52 kDa and the 61 kDa proteins are apparently glycoproteins, and the 66 kDa protein is not glycosylated. The 61 kDa protein is immunoreactive with antitrypsin antibodies.

The human breast cancer cell line MCF-7 can be growth stimulated by estradiol (10(-8) M) when grown in the presence of high concentration of newborn calf serum (NCS, 10%) or high concentration of estrogen depleted fetal calf serum (FCS, 10%). Estradiol stimulated cultures grow with an increased growth rate and also the final cell number in the culture flasks is increased. Analysis of the cell cycle parameters revealed that the proportion of cells in the G1 phase is decreased and the proportion of S phase cells is increased. In comparison, the increase in growth fraction is less significant. These results show that estradiol stimulated cultures grow with a shorter cell cycle time and a shortening of the G1 transit time may explain the observed changes in cell cycle parameters. We assume that the shorter cell cycle time as well as the ability to grow without density inhibition may be prerequisites for tumor formation. MCF-7 cells can be growth inhibited by the antiestrogen tamoxifen (10(-6) M). The growth inhibition is estrogen reversible, but estradiol has no growth stimulatory effect under the described growth conditions (0.5% FCS). Growth inhibited cultures accumulate cells with a G1 amount of DNA and the majority of this accumulation is due to non cycling cells. Tamoxifen is not a cell cycle phase specific growth inhibitory agent since cells with a G2 amount of DNA are non cycling. Long term treatment with tamoxifen results in cell death, but a few colonies of cells survive more than 10 days' treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The human breast cancer cell line MCF-7 has been adapted to long-term growth at 0.5 and 0.05% fetal bovine serum. Free cytoplasmic and filled nuclear estrogen receptors were found in cells grown at 5, 0.5, and 0.05% fetal bovine serum. Cells grown in medium with 0.05% dextran-charcoal-treated serum contained cytoplasmic receptors but no filled nuclear receptors, indicating that this medium did not contain biologically active concentrations of estrogen. Addition of estradiol to the medium translocated the cytoplasmic receptor to the nucleus and stimulated progesterone receptor synthesis but did not increase the growth rate. The antiestrogen tamoxifen (TAM) inhibited cell growth at all serum concentrations investigated, at least in part by a reduction of the growth fraction. The sensitivity to TAM was highest at low serum concentrations. The effect of TAM could be reversed by estradiol at TAM concentrations of 10(-6) M or lower. It is concluded that estradiol does not have a direct growth-stimulatory effect on our MCF-7 cells in monolayer cultures although the cells contain functional estrogen receptors and growth of the cells in athymic mice requires estrogens. TAM has an estrogen-competitive, inhibitory effect on the growth of MCF-7 cells at concentrations lower than 10(-6) M. At higher concentrations, the growth inhibition is unspecific and noncompetitive by estradiol.

Tetrahymena cells secrete a factor which inhibits RNA synthesis in vivo and in vitro. The factor is a relatively small peptide with a molecular weight between 300 and 1500 Daltons. Other, non-specific peptides in the broth medium or added to a chemically defined medium have a stimulatory effect on RNA synthesis in vivo and such peptides also stimulate the in vitro synthesis of RNA in a r-chromatin preparation. On the basis of these results we conclude that such extracellular small peptides compete with a specific factor which is part of the intracellular regulatory mechanism controlling the rate of RNA synthesis. The consequence of such competition is a high overproduction of ribosomal RNA in cells inoculated on peptide-rich broth media.

Medium which has been dialyzed against a dense population of Tetrahymena cells contains a factor which reduces the rate of RNA synthesis in other Tetrahymena cells inoculated on that medium. Furthermore, this extracellular factor inhibits the ribosomal RNA synthesis in vitro when added to an RNA synthesizing r-chromatin preparation.