Rapid actions of estrogens in GH3/B6 pituitary tumor cells via a plasma membrane version of estrogen receptor-α

The focus of our work on rapid actions of estrogens has been on the immuno-identification of a membrane version of the estrogen receptor-alpha (mER alpha) and the correlation of the presence of this receptor to the rapid secretion of prolactin in pituitary tumor cells. We demonstrated the mER alpha by both fluorescence and immuno-enzyme-cytochemistry and with bath conventional and confocal microscopy in the cell line GH(3)/B6 and its sublines. Its presence on cells (including recently subcloned ones) is very heterogenous, unlike the nuclear ER alpha, which is present in every cell. An impeded ligand (estradiol covalently linked to BSA) binds to mER alpha and elicits the same response. A total of eight antibodies to ER alpha recognize mER alpha, making it likely that the membrane and nuclear proteins are highly related. Immunoidentification techniques have also been used to identify mER alpha on the MCF-7 human breast cancer cell line. Estradiol at very low concentrations elicits prolactin release from GH(3)/B6 cells within a few minutes of application. This response is bimodal, with effective concentrations in both the picomolar and nanomolar ranges. Prolactin release is also elicited or inhibited by ER alpha-specific antibodies. The characteristics of mER alpha and the membrane receptor for glucocorticoids have many similarities, suggesting that this, mode of subcellular location/function alternative might be used by other members of the gene family. (C) 1999 Elsevier Science Inc. All rights reserved.