Estradiol-mediated internalisation of the non-activated estrogen receptor from the goat uterine plasma membrane: Identification of the proteins involved

An indirect approach has been made to study the molecular details associated with the estradiol-induced internalisation of the non-activated estrogen receptor (naER) from the goat uterine plasma membrane. The internalisation of naER appears to be an energy dependent process. Exposure of the plasma membrane to estradiol results in the activation of a Mg2+ dependent ATPase associated with the membrane fraction. Presence of quercetin in the medium prevented the activation of the Mg2+ ATPase as well as the dissociation of naER from the plasma membrane. Using isolated plasma membrane preparations it has been possible to identify the proteins which interact with naER during various stages of its internalisation. The main proteins identified are: (1) a 58 kDa protein, p58, which apparently recognizes the nuclear localization signals on the naER and transports it to the nucleus: (2) hsp70: (3) hsp90, the functional roles of which remain unknown at this stage; (4) a 50 kDa protein associated with the clathrin coated vesicles, presumed to be involved in recognizing the tyrosine based internalisation signals on the naER; (5) actin which mediates the plasma membrane-to-nucleus movement of the naER-p58 complex.