Synthetic estrogens-mediated activation of JNK intracellular signaling molecule

Signal transduction pathways regulate the transmission of specific signals to the cells from the surface to the nucleus. Activation of protein kinases such as JNKs (c-jun amino-terminal kinase), a subgroup of the mitogen activated protein kinase (MAPK) family, results in regulation of important cellular functions like cell growth and differentiation. The involvement of estrogens in stimulation of growth of already transformed breast cancer cells in vivo and in vitro accompanied with activation of JNKs prompted us to investigate the role of synthetic estrogens in the regulation of JNK expression. T 47D breast cancer cells were incubated with the synthetic estrogens, ethinylestradiol (10(-9)M) and 17 beta-estradiol valerate (10(-9)M), epidermal growth factor (EGF) (10 ng/ml) and the natural estrogen, 17 beta-estradiol (10(-9)M), for 5 minutes. The same experiments were repeated after pretreatment of the cells with ICI 182780 for 24 hours. EGF as well as natural and synthetic estrogens stimulated proliferation. This effect was reversed by the estrogen receptor blocker ICI 182780, but only in the case of both natural and synthetic estrogen. Like 17 beta-estradiol, synthetic estrogens induced a rapid and transient activation of JNK kinase. ICI 182780 blocked this effect, but not that mediated by EGF. Ethinylestradiol used in oral contraceptives, and 17 beta-estradiol and 17 beta-estradiol valerate for hormone replacement therapy, are able to activate JNK. The estrogen receptor is necessary for JNK activation upon estrogen stimulation.