Evidence that the peptidylprolyl isomerase domain of the hsp90-binding immunophilin FKBP52 is involved in both dynein interaction and glucocorticoid receptor movement to the nucleus

We have previously shown that immunoadsorption of the FKBP52 immunophilin c omponent of steroid receptor.hsp90 heterocomplexes is accompanied by coadso rption of cytoplasmic dynein, a motor protein involved in retrograde transp ort of vesicles toward the nucleus. Coimmunoadsorption of dynein is compete d by an expressed fragment of FKBP52 comprising its peptidylprolyl isomeras e (PPIase) domain (Silverstein, A. M,, Galigniana, M, D., Kanelakis, K. C,, Radanyi, C,, Renoir, J.-M,, and Pratt, W, B, (1999) J, Biol. Chem. 52, 369 80-36986), Here we show that cotransfection of 3T3 cells with the FKBP52 PP Iase domain and a green fluorescent protein (GFP) glucocorticoid receptor ( GR) chimera inhibits dexamethasone-dependent movement of the GFP-GR from th e cytoplasm to the nucleus. Cotransfection with FKBP12 does not affect GFP- GR movement. Inhibition of movement by the FKBP52 PPIase domain is abrogate d in cells treated with colcemid to eliminate microtubules prior to steroid addition, After withdrawal of colcemid, microtubules reform, and PPIase in hibition of GFP-GR movement is restored. These observations are consistent with the notion that FRBP52 targets retrograde movement of the GFP-GR along microtubules by linking the receptor to the dynein motor. Here, we also sh ow that native GR.hsp90 heterocomplexes immunoadsorbed from L cell cytosol contain dynein and that GR.hsp90 heterocomplexes assembled in reticulocyte lysate contain cytoplasmic dynein in a manner that is competed by the PPIas e domain of FKBP52.