EVIDENCE THAT THE FK506-BINDING IMMUNOPHILIN HEAT-SHOCK-PROTEIN-56 ISREQUIRED FOR TRAFFICKING OF THE GLUCOCORTICOID RECEPTOR FROM THE CYTOPLASM TO THE NUCLEUS

The FK506-binding immunophilin hsp56 (FKBP52) is one of several chaper one proteins associated with untransformed steroid receptors in a mult iprotein heterocomplex. The function of heat shock protein 56 (hsp56) with respect to receptor action is unknown, hsp56 is not required for glucocorticoid receptor heterocomplex assembly or for proper folding o f the receptor hormone-binding domain into a high affinity steroid-bin ding conformation, In intact cells, the majority of the hsp56 is locat ed in the nucleus, with a minority colocalizing with microtubules in t he cytoplasm, hsp56 contains a conserved negatively charged domain tha t we speculate might serve as a nuclear localization signal recognitio n sequence. Here we show that injection of an antibody raised against this negative sequence into intact L cells impedes subsequent dexameth asone-mediated shift of the glucocorticoid receptor into the nucleus. Nonimmune rabbit serum and an antibody raised against another site on hsp56 do not affect receptor movement, Inhibition of receptor movement by the 419 antibody against the negative sequence is blocked by prein cubation with purified hsp56, but not by preincubation with purified h sp90, hsp70, or BSA. These observations are consistent with the possib ility that hsp56 is involved in receptor trafficking to the nucleus, p ossibly functioning as the nuclear localization signal recognition pro tein. Receptor trafficking to the nucleus is not affected by FK506, in dicating that the peptidylprolyl isomerase activity of hsp56 is not in volved.