In this study, we demonstrate that the subcellular localization of the mineralocorticoid receptor (MR) is regulated by tetratricopeptide domain (TPR) proteins. The high-molecular-weight immunophilin (IMM) FKBP52 links the MR-hsp90 complex to dynein/dynactin motors favoring the cytoplasmic transport of MR to the nucleus. Replacement of this hsp90-binding IMM by FKBP51 or the TPR peptide favored the cytoplasmic localization of MR. The complete movement machinery, including dynein and tubulin, could be recovered from paclitaxel/GTP-stabilized cytosol and was fully reassembled on stripped MR immune pellets. The whole MR-hsp90-based heterocomplex was transiently recovered in the soluble fraction of the nucleus after 10 min of incubation with aldosterone. Moreover, cross-linked MR-hsp90 heterocomplexes accumulated in the nucleus in a hormone-dependent manner, demonstrating that the heterocomplex can pass undissociated through the nuclear pore. On the other hand, a peptide that comprises the DNA-binding domain of MR impaired the nuclear export of MR, suggesting the involvement of this domain in the process. This study represents the first report describing the entire molecular system that commands MR nucleocytoplasmic trafficking and proposes that the MR-hsp90-TPR protein heterocomplex is dissociated in the nucleus rather than in the cytoplasm.The mineralocorticoid receptor (MR) is a member of the steroid/thyroid superfamily of nuclear receptors whose transcriptional activity is triggered by aldosterone binding under normal physiologic conditions. Polarized epithelial tissues such as the distal nephron and colon are considered the classical targets of mineralocorticoids to control salt-water balance by induction of sodium reabsorption and thereby regulation of extracellular fluid volume and blood pressure. MR expression and function also extend to nonepithelial cells, such as hippocampal and hypothalamic neurons, cardiomyocytes, vascular endothelium, and adipocytes (for recent reviews, see references 65 and 52 and references therein).MR shares considerable homology with the glucocorticoid receptor (GR), which is exemplified by the ability of some glucocorticoids to bind both receptors. It is now well established (45) that the GR (the best-studied member of the family) forms heterocomplexes with the 90-kDa and 70-kDa heat shock proteins (hsp90 and hsp70, respectively), the acidic protein p23, and proteins that possess sequences of 34 amino acids repeated in tandems, the tetratricopeptide repeat (TPR) proteins. Some of these hsp90-binding TPR proteins have peptidylprolyl-isomerase activity and are intracellular receptors for immunosuppressant drugs such as FK506, rapamycin, and cyclosporine. They belong to the relatively conserved large family of proteins known as immunophilins (IMMs) (48). Among the members of this family, some IMMs have been recovered in steroid receptor-hsp90 complexes, i.e., FKBP52, FKBP51, CyP40, and three IMM-like proteins, protein phosphatase 5 (PP5), XAP2/ARA9, and WISp39 (33, 44). Even though th...

Background: Hsp90 binding immunophilins may be regulators of the NF-B mechanism of action. Results: FKBP51 and FKBP52 show antagonistic properties on the nuclear accumulation and transcriptional activity of NF-B. Conclusion: Both immunophilins modulate NF-B trafficking and NF-B transcription when they are recruited to the promoter regions of target genes. Significance: The competitive effect between both immunophilins in different cell types may explain the pleiotropic actions of NF-B.