Transformation and translocation of 17 beta-estradiol receptor in rat pituitary

The association of 17 beta-(3H)-estradiol with its pituitary cytosol receptor is described. The transformation products of this 8 S receptor complex at high salt concentration was analyzed by 5-20% linear sucrose gradients. KCl was found to reversibly convert the 8 S moiety into a 4-5 S species. The transformation by CaCl2 and trypsin was found to be irreversible. In addition, the nuclear translocation of the estrogen-receptor complex was investigated in vitro. Translocation was found to be temperature-dependent, since a 6 S nuclear receptor complex could be extracted from crude nuclei only after incubation of whole pituitaries at 37 degrees C and not at 4 degrees C incubation temperature. Similarly, a 6 S species was found upon sucrose gradient analysis of nuclear extract after a cell free incubation of isolated nuclei and cytosol with 17 beta-(3H)-estradiol. Maximal translocation was observed in this in vitro system within 60 to 90 min, resulting in a concomitant loss of cytosol receptor. The present data combine to suggest that nuclear translocation resembles one of the early events involved in the molecular action of estrogen at the pituitary level.