Synthetic estrogen-mediated activation of ERK 2 intracellular signaling molecule

Ovarian steroids are important modulators of normal cell growth and differentiation as well as of carcinogenesis. External stimuli trigger cell surface receptors, resulting in activation of central signal transduction pathways, that are mediated by members of the mitogen-activated protein kinase (MAPK) family. These in turn, indirectly regulate cellular functions such as cell proliferation, cell cycle, and maintenance of malignant phenotype. In our in vitro study, we have investigated the effects of two synthetic estrogens on ERK 2 activation. Estrogen receptor positive cells were incubated with the synthetic estrogens, ethinylestradiol (10(-9) mol/l) and 17 beta-estradiol valerate (10(-9) mol/l), epidermal growth factor (EGF) (10 ng/ml) and the natural estrogen 17 beta-estradiol (10(-9) mol/l), for 5 min. The same experiments were repeated prior to preincubation with the antiestrogen ICI 182780. ERK 2 or the active form alone were detected by immunoblotting. A cell proliferation assay was used to study the response of cells to various treatments. Time kinetics were performed to study duration of kinase activated state. Cell incubation with EGF as well as with either natural or synthetic estrogen stimulated proliferation. ICI 182780 inhibited this effect, but only in the case of estrogen. Synthetic estrogens activated MAP kinase in a time-dependent fashion, similar to 17 beta-estradiol. The estrogen receptor antagonist ICI 182780 blocked this effect. EGF induced a more pronounced and prolonged activation, even in the presence of the antiestrogen. Ethinylestradiol as used in oral contraceptives, and 17 beta-estradiol and 17 beta-estradiol valerate as used in hormone replacement therapy, are able to activate MAP kinase. This activation was blocked by an antiestrogen.