GELDANAMYCIN, A HEAT-SHOCK-PROTEIN 90-BINDING STEROID-DEPENDENT TRANSLOCATION OF THE GLUCOCORTICOID RECEPTOR FROM THE CYTOPLASM TO THE NUCLEUS

When they are translated, steroid receptors are assembled into a multi protein complex containing hsp90, p23, an immunophilin, and often some hsp70. Some of the receptors, such as that for progesterone, have nuc lear localization signals that are functional in the absence of hormon e, and they move into the nucleus where they exist in the same multipr otein heterocomplex with hsp901. Other receptors, such as the glucocor ticoid receptor, are localized predominantly in the cytoplasm in the a bsence of hormone and move into the nucleus in a hormone-dependent fas hion. We have previously proposed that hsp90 and the immunophilin play a role in receptor trafficking [Pratt, W. B. (1993) J. Biol. Chem. 26 8, 21455-21458]. In this work, we show that treatment of L cells with geldanamycin, a benzoquinone ansamycin that binds to hsp90 and disrupt s its function, impedes dexamethasone-dependent trafficking of the glu cocorticoid receptor from the cytoplasm to the nucleus. Because geldan amycin treatment of hormone-free cells causes a rapid loss of steroid binding activity, receptors were prebound with dexamethasone by incuba ting cells with hormone at 0 degrees C prior to shifting the temperatu re to 37 degrees C for 20 min to permit receptor transformation and tr anslocation in the presence or absence of geldanamycin. Geldanamycin d oes not cause steroid to dissociate from prebound receptors, and it do es not inhibit hormone-mediated receptor transformation assayed by con version to the DNA-binding state. However, as reported previously for the progesterone receptor, geldanamycin blocks assembly of the glucoco rticoid receptor hsp90 heterocomplex at an intermediate state of assem bly where the receptor is bound to hsp70 and p60, broth of which are r equired components in the assembly mechanism. Our observations support the proposal that dynamic association of receptors with hsp90 is requ ired for receptor translocation from the cytoplasm to the nucleus.