Estrogen-induced activation of mitogen-activated protein kinase requires mobilization of intracellular calcium

Abstract

Estrogens and growth factors such as epidermal growth factor (EGF) act as mitogens promoting cellular proliferation in the breast and in the reproductive tract. Although it was considered originally that these agents manifested their mitogenic actions through separate pathways, there is a growing body of evidence suggesting that the EGF and estrogen-mediated signaling pathways are intertwined. Indeed, it has been demonstrated recently that 17␤-estradiol (E2) can induce a rapid activation of mitogenactivated protein kinase (MAPK) in mammalian cells, an event that is independent of both transcription and protein synthesis. In this study, we have used a pharmacological approach to dissect this novel pathway in MCF-7 breast cancer cells and have determined that in the presence of endogenous estrogen receptor, activation of MAPK by E2 is preceded by a rapid increase in cytosolic calcium. The involvement of intracellular calcium in this process was supported by the finding that the presence of EGTA and Ca 2؉ -free medium did not affect the activation of MAPK by E2 and, additionally, that this response was blocked by the addition of the intracellular calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetate. Cumulatively, these data indicate that the estrogen receptor, in addition to functioning as a transcription factor, is also involved, through a nongenomic mechanism, in the regulation of both intracellular calcium homeostasis and MAPK-signaling pathways. Although nongenomic actions of estrogens have been suggested by numerous studies in the past, the ability to link estradiol and the estrogen receptor to a well defined signaling pathway strongly supports a physiological role for this activity.

Rapid signalling by androgen receptor in prostate cancer cells

“…These e ects are very rapid (5 and 60 s) compared to the 2 ± 60 min response we have described here for activation of MAP kinase. As estrogen-induced activation of MAP kinase is reported to involve mobilization of intracellular calcium (Improta-Brears et al, 1999), it is likely that these very rapid e ects in intracellular calcium concentrations seen with androgens may preceed the activation of MAP kinase reported here in our work. This idea is being investigated at the moment.…”

“…Other mechanisms have been proposed to explain the ER-mediated activation of MAP kinase. In one report it was shown that it occurs via the release of calcium from intracellular stores (Improta-Brears et al, 1999). Another study on the mechanism of ERmediated activation of MAP kinase showed the involvement of Gaq and Gas proteins (Razandi et al, 1999).…”

Functional significance of the rapid regulation of brain estrogen action: Where do the estrogens come from?

“…1), including the modulation of intracellular calcium [44,55,122,165,175,209] and protein kinase C (PKC; [266,276]). There is also evidence that membrane effects of estrogens can activate intracellular signaling pathways involving cyclic AMP (cAMP; [103,170,254]), protein kinase A (PKA; [104,141,266]), the "mitogen activated protein kinases" (or MAP kinases; [39,122,153,205,260,269,276]), and the tyrosine kinases [39]. The activation of these intracellular signaling pathways results primarily in phosphorylations/dephosphorylations producing different kinds of physiological responses such as the decoupling of a receptor from its effector system [141,[171][172][173] or the modulation of the catalytic activity of an enzyme [191].…”

“…The fastest of these effects appear to be associated with the allosteric modulations of ionotropic receptors [190,277,278], but most effects on electrical activity result from a modulation of ion channel activity through G protein linkage (for review see [132,176]). Estrogen-induced changes in intracellular calcium concentrations have also been identified with latencies of a few seconds [44,54,175,209] to several minutes [55,122]. Finally, the time-course of protein phosphorylations and of changes in kinase activity following estradiol treatment ranges between 5 and 30 min [39,122,153,168,260,269,276].…”

“…Estrogen-induced changes in intracellular calcium concentrations have also been identified with latencies of a few seconds [44,54,175,209] to several minutes [55,122]. Finally, the time-course of protein phosphorylations and of changes in kinase activity following estradiol treatment ranges between 5 and 30 min [39,122,153,168,260,269,276].…”