Cloning and expression of the glucocorticoid receptor from the squirrel monkey (Saimiri boliviensis boliviensis), a glucocorticoid-resistant primate

Characterization of inhibitors of glucocorticoid receptor nuclear translocation: a model of cytoplasmic dynein-mediated cargo transport

Agonist-induced glucocorticoid receptor [GR] transport from the cytoplasm to the nucleus was used as a model to identify dynein-mediated cargo transport inhibitors. Cell-based screening of the library of pharmacologically active compound (LOPAC)-1280 collection identified several small molecules that stalled the agonist-induced transport of GR-green fluorescent protein (GFP) in a concentration-dependent manner. Fluorescent images of microtubule organization, nuclear DNA staining, expression of GR-GFP, and its subcellular distribution were inspected and quantified by image analysis to evaluate the impact of compounds on cell morphology, toxicity, and GR transport. Given the complexity of the multi-protein complex involved in dynein-mediated cargo transport and the variety of potential mechanisms for interruption of that process, we therefore developed and validated a panel of biochemical assays to investigate some of the more likely intracellular target(s) of the GR transport inhibitors. Although the apomorphine enantiomers exhibited the most potency toward the ATPase activities of cytoplasmic dynein, myosin, and the heat-shock proteins (HSPs), their apparent lack of specificity made them unattractive for further study in our quest. Other molecules appeared to be nonspecific inhibitors that targeted reactive cysteines of proteins. Ideally, specific retrograde transport inhibitors would either target dynein itself or one of the other important proteins associated with the transport process. Although the hits from the cell-based screen of the LOPAC-1280 collection did not exhibit this desired profile, this screening platform provided a promising phenotypic system for the discovery of dynein/HSP modulators.

Structure of the large FK506-binding protein FKBP51, an Hsp90-binding protein and a component of steroid receptor complexes

The ability to bind immunosuppressive drugs such as cyclosporin and FK506 defines the immunophilin family of proteins, and the FK506-binding proteins form the FKBP subfamily of immunophilins. Some FKBPs, notably FKBP12 (the 12-kDa FK506-binding protein), have defined roles in regulating ion channels or cell signaling, and well established structures. Other FKBPs, especially the larger ones, participate in important biological processes, but their exact roles and the structural bases for these roles are poorly defined. FKBP51 (the 51-kDa FKBP) associates with heat shock protein 90 (Hsp90) and appears in functionally mature steroid receptor complexes. In New World monkeys, FKBP51 has been implicated in cortisol resistance. We report here the x-ray structures of human FKBP51, to 2.7 A, and squirrel monkey FKBP51, to 2.8 A, by using multiwavelength anomalous dispersion phasing. FKBP51 is composed of three domains: two consecutive FKBP domains and a three-unit repeat of the TPR (tetratricopeptide repeat) domain. This structure of a multi-FKBP domain protein clarifies the arrangement of these domains and their possible interactions with other proteins. The two FKBP domains differ by an insertion in the second that affects the formation of the progesterone receptor complex.

Analysis of glucocorticoid and androgen receptor gene fusions delineates domains required for transcriptional specificity

Androgen receptor (AR) and glucocorticoid receptor (GR) influence distinct physiologic responses in steroid-responsive cells despite their shared ability to selectively bind in vitro to the same canonical DNA sequence (TGTTCT). While the DNA-binding domains (DBDs) of these receptors are highly conserved, the amino N-terminal domain (NTD) and hormone-binding domain (HBD) are evolutionarily divergent. To determine the relative contribution of these functional domains to steroid-specific effects in vivo, we constructed a panel of AR/GR gene fusions by interchanging the NTD, DBD, and HBD regions of each receptor and measured transcriptional regulatory activities in transfected kidney and prostate cell lines. We found that GR was approximately 10-fold more active than AR when tested with the mouse mammary tumor virus promoter, and that this difference in activity was primarily owing to sequence divergence in the NTDs. We also tested transcriptional activation of the androgen-dependent rat probasin promoter, and in this case, AR was at least twofold more active than GR. Analysis of the chimeric receptors revealed that this difference mapped to the DBD region of the two receptors. Transcriptional repression functions of the wild-type and chimeric receptors were measured using an activator protein 1 (AP-1) transrepression assay and identified the GR HBD as a more potent transrepressor of AP-1 transcriptional activation than the AR HBD. Taken together, our analyses reveal that evolutionary sequence divergence between AR and GR functional domains results in unique promoter-specific activities within biologic systems in which both AR and GR are normally expressed.