Estradiol signaling via sequestrable surface receptors

Estradiol (E-2)-signaling is widely considered to be exclusively mediated through the transcription-regulating intracellular estrogen receptor (ER) alpha and ER beta. The aim of this study was to investigate transcription-independent E-2-signaling in mouse IC-21 macrophages. E-2 and E-2-BSA induce a rapid rise in the intracellular free Ca2+ concentration ( [Ca2+](i)) of Fura-2 loaded IC-21 cells as examined by spectrofluorometry. These changes in [Ca2+](i) can be inhibited by pertussis toxin, but not by the ER-blockers tamoxifen and raloxifene. The E-2-signaling initiated at the plasma membrane is mediated through neither ER alpha nor ER beta, but rather through a novel G protein-coupled membrane E-2-receptor as revealed by RT-PCR, flow cytometry, and confocal laser scanning microscopy. A special feature of this E-2-receptor is its sequestration upon agonist stimulation. Sequestration depends on energy and temperature, and it proceeds through a clathrin- and caveolin-independent pathway.