T47D human breast carcinoma cells and the chicken oviduct were used to study the structure of the nonactivated progesterone receptor (PR) complex. Immunoprecipitation of PR (B form) from cytosol extracts was performed using monoclonal antibody PR6, a cross-reactive antibody prepared to chicken PR. Analysis of the PR complex by sodium dodecyl sulfate gels and Western immuno-blotting revealed the presence of several specific copurifying proteins. Consistent with previous reports, the two heat shock proteins, hsp90 and hsp70, were shown to be present. A third 59-kilodalton (kDa) protein observed previously was confirmed to be p59 (also called hsp56 or FKBP52), which has been shown to bind the immunosuppressant drug FK506. Two additional PR-associated proteins were observed that had not been previously recognized with human PR. These have molecular masses of 54-kDa and 23-kDa and have been shown by Western blotting to be related to the proteins p54 and p23 that are associated with chicken PR. P23 is a novel protein of unknown function and p54 or FKBP54 has been recently shown to be another FK506-binding protein related to p59. Finally, the cyclosporin A-binding protein, CyP-40, could be detected in isolated chicken PR complexes and in PR complexes that were reconstituted in vitro, but this protein was not detected in human PR complexes, which are less stable than chicken PR complexes in cytosol extracts. The functional significance of FK506 and cyclosporin A-binding proteins to hormone action was tested using a T47D cell line that contained a progestin reporter gene, MMTV-CAT. Treatment with cyclosporin A had no effect on the basal level of CAT expression, but it caused a dramatic increase in the sensitivity and magnitude of the response to the synthetic progestin, R5020. The enhanced response elicited by drug treatment was blocked by the antiprogestin RU486 indicating that this effect was receptor-mediated. While cyclosporin A enhanced progestin action in T47D cells, it inhibited a PR/reporter gene system in L cells. The drugs FK506 and rapamycin had no effect on progestin action in T47D cells, but they stimulated glucocorticoid action in T47D cells. Thus, the effects of these immunosuppressant drugs vary with the cell type and hormonal system that is tested. Whether these drug effects relate directly to the immunophilins bound in receptor complexes remains unknown.
ASJC Scopus subject areas
- Molecular Biology