title: ER-X: a novel, plasma membrane-associated, putative estrogen receptor that is regulated during development and after ischemic brain injury.
abstract: We showed previously in neocortical explants, derived from developing wild-type and estrogen receptor (ER)-alpha gene-disrupted (ERKO) mice, that both 17alpha- and 17beta-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-alpha nor ER-beta 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 (K(d), approximately 1.6 nm) in the plasma membrane. Unlike neocortical ER-alpha, which is intranuclear and developmentally regulated, and neocortical ER-beta, 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-alpha and ER-beta, and that, like ER-alpha, it is re-expressed in the adult brain, after ischemic stroke injury. We also confirmed in a cell-free system that ER-alpha 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.
mesh_terms: D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D015153:Blotting, Western; D002545:Brain Ischemia / Q000503:physiopathology*; D021941:Caveolae / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D002474:Cell-Free System; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004958:Estradiol / Q000493:pharmacokinetics / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental; D007476:Ionophores / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019579:Neocortex / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D011960:Receptors, Estrogen / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013347:Subcellular Fractions / Q000737:chemistry; D013379:Substrate Specificity
chemical_list: C466423:ER-X protein, mouse; D007476:Ionophores; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D004958:Estradiol; D002784:Cholesterol; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases