Functional analysis of R651 mutations in the putative helix 6 of rat glucocorticoid receptors

Drug-regulatable cancer cell death induced by BID under control of the tissue-specific, lung cancer-targeted TTS promoter system

Gene therapy and virotherapy are among the approaches currently being used to treat lung cancer. The success of cancer gene therapy depends on treatments where different types of tumors can be selectively targeted and destroyed without affecting normal cells and tissue. Previously, we described a promoter system (TTS) that we designed that is specifically targeted to lung cancer cells but which does not affect other types of cells including stem cells. In our study, we have enhanced the utility of the TTS system by inserting the pro-apoptotic gene BH3 domain interacting death agonist (Bid) into the TTS promoter system (TTS/Bid) to create a drug regulatable lung cancer-specific gene therapy. A recombinant adenoviral vector was used to introduce TTS/Bid (Ad-TTS/Bid) into lung cancer cells. BID expression and apoptosis occurred in A549 pulmonary adenocarcinoma cells but little Bid expression or apoptosis occurred in MCF7 breast cancer cells or in normal human lung fibroblasts. The use of cisplatin enhanced the processing of full length BID to t-BID which significantly increased lung cancer-specific cell death. In in vivo experiments, intraperitonal injection of cisplatin enhanced the antitumor effects of the vector in a lung cancer xeno-graft mouse model. Moreover, dexamethasone effectively suppressed exogenous BID expression and the antitumor effect of Ad-TTS/Bid both in vitro and in vivo. Here, we describe the efficacy of the use of cisplatin and dexamethasone with the anti lung cancer promoter system (Ad-TTS/Bid) for a safe and effective gene therapy against advanced lung cancer.

Mutations of glucocorticoid receptor differentially affect AF2 domain activity in a steroid-selective manner to alter the potency and efficacy of gene induction and repression

The transcriptional activity of steroid hormones is intimately associated with their structure. Deacylcortivazol (DAC) contains several features that were predicted to make it an inactive glucocorticoid. Nevertheless, gene induction and repression by complexes of glucocorticoid receptor (GR) with DAC occur with potency (lower EC 50) greater than and efficacy (maximal activity, or A max) equal to those of the very active and smaller synthetic glucocorticoid dexamethasone (Dex). Guided by a recent X-ray structure of DAC bound to the GR ligand binding domain (LBD), we now report that several point mutants in the LBD have little effect on the binding of either agonist steroid. However, these same mutations dramatically alter the A max and/or EC 50 of exogenous and endogenous genes in a manner that depends on steroid structure. In some cases, Dex is no longer a full agonist. These properties appear to result from a preferential inactivation of the AF2 activation domain in the GR LBD of Dex-bound, but not DAC-bound, receptors. The Dex-bound receptors display normal binding to, but a greatly reduced response to, the coactivator TIF2, thus indicating a defect in the transmission efficiency of GR-steroid complex information to the coactivator TIF2. In addition, all GR mutants that are active in gene induction with either Dex or DAC have greatly reduced activity in gene repression. This contrasts with the reports of GR mutations preferentially suppressing GR-mediated induction. The properties of these GR mutants in gene induction support the hypothesis that the A max and EC 50 of GR-controlled gene expression can be independently modified, indicate that the receptor can be modified to favor activity with a specific agonist steroid, and suggest that new ligands with suitable substituents may be able to affect the same LBD conformational changes and thereby broaden the therapeutic applications of glucocorticoid steroids.

Structure and function of the glucocorticoid receptor ligand binding domain

After binding to an activating ligand, such as corticosteroid, the glucocorticoid receptor (GR) performs an impressive array of functions ranging from nuclear translocation, oligomerization, cofactor/kinase/transcription factor association, and DNA binding. One of the central functions of the receptor is to regulate gene expression, an activity triggered by ligand binding. In this role, GR acts as an adapter molecule by encoding the ligand's message within the structural flexibility of the ligand binding domain (LBD). The purpose of this review is to discuss the many structural and functional features of the GR LBD in light of recent successful biochemical and crystallographic studies. Progress in this area of research promises to reveal new strategies and insights allowing for the design of novel drugs to treat inflammatory diseases, diabetic conditions, steroid resistance, and cancers.

New antiprogestins with partial agonist activity: potential selective progesterone receptor modulators (SPRMs) and probes for receptor- and coregulator-induced changes in progesterone receptor induction properties

A pharmacologically relevant property of steroid hormone-regulated gene induction is the partial agonist activity of antisteroid complexes. We now report that dexamethasone-mesylate (Dex-Mes) and dexamethasone-oxetanone (Dex-Ox), each a derivative of the glucocorticoid-selective steroid dexamethasone (Dex), are two new antiprogestins with significant amounts of agonist activity with both the A and B isoforms of progesterone receptor (PR), for different progesterone-responsive elements, and in several cell lines. These compounds continue to display activity under conditions where another partial antiprogestin (RTI-020) is inactive. These new antiprogestins were used to determine whether the partial agonist activity of PR complexes can be modified by changing concentrations of receptor or coregulator, as we have recently demonstrated for glucocorticoid receptors (GRs). Because GR and coregulator concentrations simultaneously altered the position of the physiologically relevant dose-response curve, and associated EC(50), of GR-agonist complexes, we also examined this phenomenon with PR. We find that elevated PR or transcriptional intermediary factor 2 (TIF2) concentrations increase the partial agonist activity of Dex-Mes and Dex-Ox, and the EC(50) of agonists, independently of changes in total gene transactivation. Furthermore, the corepressors SMRT (silencing mediator for retinoid and thyroid receptors) and NCoR (nuclear receptor corepressor) each suppresses gene induction but NCoR acts opposite to SMRT and, like the coactivator TIF2, reduces the EC(50) and increases the partial agonist activity of antiprogestins. These comparable responses of GR and PR suggest that variations in receptor and coregulator concentrations may be a general mechanism for altering the induction properties of other steroid receptors. Finally, the magnitude of coregulator effects on PR induction properties are often not identical for agonists and the new antagonists, suggesting subtle mechanistic differences. These properties of Dex-Mes and Dex-Ox, plus the sensitivity of their activity to cellular differences in PR and coregulator concentrations, make these steroids potential new SPRMs (selective progesterone receptor modulators) that should prove useful as probes of PR induction properties.