We showed previously in neocortical explants, derived from developing wild-type and estrogen receptor (ER)-α genedisrupted (ERKO) mice, that both 17α- and 17β-estradiol elicit the rapid and sustained phosphorylation and activation of the mitogen-activated protein kinase (MAPK) isoforms, the extracellular signal-regulated kinases ERK1 and ERK2. We proposed that the ER mediating activation of the MAPK cascade, a signaling pathway important for cell division, neuronal differentiation, and neuronal survival in the developing brain, is neither ER-α nor ER-β but a novel, plasma membrane-associated, putative ER with unique properties. The data presented here provide further evidence that points strongly to the existence of a high-affinity, saturable, 3H-estradiol binding site (Kd, -1.6 nM) in the plasma membrane. Unlike neocortical ER-α, which is intranuclear and developmentally regulated, and neocortical ER-β, which is intranuclear and expressed throughout life, this functional, plasma membrane-associated ER, which we have designated "ER-X," is enriched in caveolar-like microdomains (CLMs) of postnatal, but not adult, wild-type and ERKO neocortical and uterine plasma membranes. We show further that ER-X is functionally distinct from ER-α and ER-β, and that, like ER-α, it is re-expressed in the adult brain, after ischemic stroke injury. We also confirmed in a cell-free system that ER-α is an inhibitory regulator of ERK activation, as we showed previously in neocortical cultures. Association with CLM complexes positions ER-X uniquely to interact rapidly with kinases of the MAPK cascade and other signaling pathways, providing a novel mechanism for mediation of the influences of estrogen on neuronal differentiation, survival, and plasticity.
CITATION STYLE
Toran-Allerand, C. D., Guan, X., MacLusky, N. J., Horvath, T. L., Diano, S., Singh, M., … Tinnikov, A. A. (2002). ER-X: A novel, plasma membrane-associated, putative estrogen receptor that is regulated during development and after ischemic brain injury. Journal of Neuroscience, 22(19), 8391–8401. https://doi.org/10.1523/jneurosci.22-19-08391.2002
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