No abstract

No abstract

The membrane glucocorticoid receptor (mGR), previously correlated with glucocorticoid-induced lymphocytolytic competency, was purified under nondenaturing conditions from mGR-enriched mouse S-49 T lymphoma cells. Proteins were immunoaffinity batch adsorbed to BUGR-2 monoclonal antibody-coupled protein A Sepharose 4B beads, and elution by epitope competition was compared with standard denaturation procedures. Elution with BUGR-2 epitope peptides released multiple mGRs (42-150 kDa) and heat shock proteins 70 and 90, suggesting that mGR interacts with these protein chaperones under physiological conditions. The mGR-heat shock protein 90 interaction was inhibited by 1 microM geldanamycin. Several other mGR binding partners were captured and most were dissociated from mGR by 0.6 M salt. Peptide maps of purified mGR displayed immunoreactive bands unique to mGR. Scatchard analysis estimated a k(d) value of 239 nM and a Bmax of 384 fmol/mg protein for mGR, compared to a k(d) of 19.5 nM and a Bmax of 90.3 fmol/mg protein for the intracellular GR (iGR). The rank order of affinities for mGR were RU-486 > dexamethasone > triamcinolone acetonide = aldosterone. Other steroids had no significant binding affinity. These results show that epitope-purified mGR on the plasma membrane of mouse lymphoma cells is similar but not identical to iGR.

Androgens control the proliferation of their target cells first by increasing cell proliferation and later by inhibiting the proliferation of those same cells. Recently, we reported that the AS3 protein mediates the androgen-induced quiescence in androgen-target human cell lines. Our aims were to investigate the expression of the AS3 protein in the rat prostate in situ and in human cells in culture. Adult rats were separated into four groups (intact, castrated, castrated plus 3-d testosterone propionate replacement, and castrated plus 7-d testosterone propionate replacement). S9 cells expressing a tetracycline-regulated sense AS3 were also used. AS3 was expressed in the nuclei of over 90% of the epithelial cells and about 40% of the smooth muscle cells of the intact rat prostate. AS3 was not expressed in castrated rats or during the proliferative phase of androgen-induced regeneration. It was expressed in intact and castrated animals when the prostate has reached adult organ size. The AS3 protein was not expressed in cells that incorporate bromodeoxyuridine. These data suggest that AS3 is a mediator of the proliferative arrest in the normal rat prostate in situ and human prostate cell lines and that its expression is androgen-induced.

No abstract