epidermal-growth-factor and 16-alpha-ethyl-21-hydroxy-19-nor-4-pregnene-3-20-dione

This study documents a biphasic change in the rate of cell cycle progression and proliferation of T-47D human breast cancer cells treated with synthetic progestins, consisting of an initial transient acceleration in transit through G1, followed by cell cycle arrest and growth inhibition. Both components of the response were mediated via the progesterone receptor. The data are consistent with a model in which the action of progestins is to accelerate cells already progressing through G1, which are then arrested early in G1 after completing a round of replication, as are cells initially in other phases of the cell cycle. Such acceleration implies that progestins act on genes or gene products which are rate limiting for cell cycle progression. Increased production of epidermal growth factor and transforming growth factor alpha, putative autocrine growth factors in breast cancer cells, does not appear to account for the initial response to progestins, since although the mRNA abundance for these growth factors is rapidly induced by progestins, cells treated with epidermal growth factor or transforming growth factor alpha did not enter S phase until 5 to 6 h later than those stimulated by progestin. The proto-oncogenes c-fos and c-myc were rapidly but transiently induced by progestin treatment, paralleling the well-known response of these genes to mitogenic signals in other cell types. The progestin antagonist RU 486 inhibited progestin regulation of both cell cycle progression and c-myc expression, suggesting that this proto-oncogene may participate in growth modulation by progestins.

Topics: Blotting, Northern; Breast Neoplasms; Cell Cycle; Epidermal Growth Factor; ErbB Receptors; Gene Expression Regulation, Neoplastic; Genes, myc; Humans; Kinetics; Mifepristone; Pregnenediones; Progesterone Congeners; Proto-Oncogene Mas; Proto-Oncogene Proteins c-fos; Transforming Growth Factor alpha; Tumor Cells, Cultured

The molecular basis of the growth-inhibitory effects of progestins or antiestrogens in human breast cancer has not been fully elucidated. Both direct actions and indirect actions, where the growth inhibition results from modulation of the production of, and/or the response to, growth factors, have been proposed. In this study the ability of some growth factors to modulate progestin-induced inhibition of cell proliferation was investigated in vitro, using T-47D human breast cancer cells. When T-47D cells grown in insulin-containing medium were treated for 4 to 5 days with the synthetic progestin, ORG 2058, at a concentration of 10 nM, cell numbers were reduced to 10 to 20% of control. Simultaneous treatment with epidermal growth factor (EGF) and ORG 2058 led to a partial reversal of the growth-inhibitory effect of the progestin. The magnitude of the effect of EGF was concentration dependent, being half-maximal at 0.48 ng/ml (0.08 nM) and maximal at concentrations greater than 5 ng/ml (greater than 0.8 nM), where cell numbers were increased by 50% compared to those in the presence of ORG 2058 alone. ORG 2058 was no more potent in the absence of insulin, and, after several passages in insulin-free medium, addition of insulin failed to modulate the effect of ORG 2058. However, when maximal concentrations of insulin (5 micrograms/ml) and EGF (10 ng/ml) were administered together with ORG 2058, insulin and EGF appeared to act synergistically to reduce the ORG 2058-induced inhibition of proliferation. In similar experiments in which cells were treated with hydroxyclomiphene, a potent antiestrogen, insulin was shown to partially reverse the growth-inhibitory effects of hydroxyclomiphene. Significant increases in cell number above hydroxyclomiphene-treated controls were apparent at insulin concentrations greater than 50 ng/ml, and at 5 micrograms/ml the increase was approximately 2-fold. In contrast to the situation with progestins, simultaneous treatment with EGF and insulin had only an additive effect in reversing the growth-inhibitory effect of the antiestrogen. The results are compatible with the hypothesis that part of the growth-inhibitory effects of progestin and antiestrogen on human breast cancer cell proliferation is mediated by inhibition of autocrine growth factor production. However, they do not exclude more direct mechanisms involving modulation of progesterone and/or estrogen receptors by EGF and/or insulin.(ABSTRACT TRUNCATED AT 400 WORDS)

Topics: Breast Neoplasms; Cell Division; Clomiphene; Epidermal Growth Factor; Estrogen Antagonists; Female; Growth Inhibitors; Humans; Insulin; Pregnenediones; Progestins; Tumor Cells, Cultured

A 24 hr incubation of T-47D human breast cancer cells with R5020, a synthetic progestin, resulted in a 200-250% increase in the specific binding of human growth hormone (hGH) and epidermal growth factor (EGF) by these cells. This effect was specific for progestins in that similar responses were observed with progesterone, medroxyprogesterone acetate and ORG 2058 but no significant increases in hGH or EGF binding were observed in cells incubated with testosterone, estradiol or hydrocortisone. Increased binding was due to an increase in the concentration of receptors (hGH, control = 6,490 +/- 500, progestin treated = 13,180 +/- 3,270 sites/cell; EGF, control = 33,380 +/- 7,410, progestin treated = 67,460 +/- 20,330 sites/cell) while the affinity constants for the hormone-receptor interactions were unchanged by progestin treatment. The specific binding of insulin, calcitonin, transferrin and concanavalin A was unaffected by these treatments. It is concluded that expression of hGH and EGF receptors in this breast cancer cell line is regulated by progestins.

Topics: Breast Neoplasms; Cell Line; Epidermal Growth Factor; ErbB Receptors; Female; Growth Hormone; Humans; Medroxyprogesterone; Medroxyprogesterone Acetate; Pregnenediones; Progesterone; Progestins; Promegestone; Receptors, Cell Surface; Receptors, Somatotropin