A glucocorticoid-resistant rat hepatoma cell variant contains functional glucocorticoid receptor

Glucocorticoid receptors in lung cancer: new perspectives

Proper expression of the glucocorticoid receptor (GR) plays an essential role in the development of the lung. GR expression and signalling in the lung is manipulated by administration of synthetic glucocorticoids (Gcs) for the treatment of neonatal, childhood and adult lung diseases. In lung cancers, Gcs are also commonly used as co-treatment during chemotherapy. This review summarises the effect of Gc monotherapy and co-therapy on lung cancers in vitro, in mouse models of lung cancer, in xenograft, ex vivo and in vivo The disparity between the effects of pre-clinical and in vivo Gc therapy is commented on in light of the recent discovery of GR as a novel tumour suppressor gene.

The effects of red ginseng saponin fraction-A (RGSF-A) on phagocytosis and intracellular signaling in Brucella abortus infected RAW 264.7 cells

This study indicated that RGSF-A caused a marked reduction in the adherence, internalization and intracellular growth of Brucella abortus in RGSF-A-treated cells. Furthermore, a decline in the intensity of F-actin fluorescence was observed in RGSF-A-treated cells compared with untreated B. abortus-infected cells. In addition, an evaluation of phagocytic signaling proteins by Western blot analysis revealed an apparent reduction of ERK and p38α phosphorylation levels in B. abortus-infected RGSF-A-treated cells compared with the control. Upon intracellular trafficking of the pathogen, a higher number of B. abortus-containing phagosomes colocalized with LAMP-1 in RGSF-A-treated cells compared with control cells. These results strongly suggest that inhibition of B. abortus uptake could be mediated by suppression in the activation of MAPKs signaling proteins phospho-ERK 1/2, and p38 levels. On the other hand, inhibition of intracellular replication results from the enhancement of phagolysosome fusion in host macrophages. This study highlights the phagocytic and intracellular modulating effect of RGSF-A and its potential as an alternative remedy to control B. abortus infection.

Ginsenoside-Rg1, one of the major active molecules from Panax ginseng, is a functional ligand of glucocorticoid receptor

We have examined the possibility that a component of Panax ginseng, ginsenoside-Rg1 (G-Rg1), acts by binding to the glucocorticoid receptor (GR). G-Rg1 competed for [3H]dexamethasone (Dex) binding to GR with a specific affinity of 1-10 microM and activated a glucocorticoid responsive element-containing luciferase reporter gene. The dose-dependence patterns of G-Rg1 and Dex for these two effects were nearly identical, although two to three orders of magnitude higher concentration of G-Rg1 than that of Dex was required for the same magnitude of response. At the cellular level, the growth of FT02B cells was suppressed by G-Rg1 as well as by Dex, each of whose effects were abolished by RU486. These results demonstrate that G-Rg1 is a functional ligand of GR.

Differential binding of mutant glucocorticoid receptors to the glucocorticoid response element of the tyrosine aminotransferase gene

Glucocorticoid receptors (GCRs) in sublines of the mouse P1798 lymphosarcoma that are sensitive (S) or resistant (R) to glucocorticoid-induced cell lysis were examined for their ability to bind to a single glucocorticoid responsive element (GRE). Mobility shift assays detected two specific complexes that were identical in both S and R cellular extracts. Antibodies against the GCR N-terminus supershifted complexes, suggesting that the 97 kDa wild-type GCR (WT-GCR) in S cells, and the variant, 97 kDa non-steroid-binding GCR (NSB-GCR) in R cells were components of both complexes. Sephacryl S300 gel filtration column fractions containing the WT-GCR and NSB-GCR formed complexes with the GRE, while fractions containing a second GCR variant in R cells, the 45 kDa steroid-binding truncated GCR (TR-GCR), did not. Southwestern blotting detected a GRE-binding, 97 kDa protein band in both S and R extracts. A 45 kDa band was not detected. UV crosslinking of protein to DNA revealed protein in the range of 92-120 kDa crosslinked to the GRE in both S and R extracts. No crosslinking was detected at 45 kDa. Strong interaction of the NSB-GCR with GREs and lack of binding of the TR-GCR to single GREs illustrate a complex receptor system in the P1798 lymphosarcoma.

Glucocorticoid receptor phosphorylation in v-mos-transformed cells

Nucleocytoplasmic shuttling of glucocorticoid receptors (GRs) is disrupted in v-mos-transformed cells leading to the redistribution of hormone-bound receptors from the nuclear to cytoplasmic compartments. We show here that GRs from v-mos-transformed cells are hyperphosphorylated on a specific peptide and maintain hormone-induced phosphorylations upon a prolonged hormone treatment that is associated with disruptions in its nucleocytoplasmic shuttling. Since similar effects on GR nucleocytoplasmic shuttling and phosphorylation were exerted upon treatment of nontransformed cells with the protein phosphatase inhibitor okadaic acid, we examined whether hyperphosphorylation of GRs in v-mos-transformed cells resulted from inhibition of receptor dephosphorylation. Protein phosphatase activity, measured using various substrates in vitro, was identical in cell-free extracts prepared from v-mos-transformed and nontransformed cells. Analysis of phosphate turnover in vivo from either the sum of all GR phosphorylation sites or from individual sites using pulse-chase analysis, did not reveal any significant difference between v-mos-transformed cells versus nontransformed cells. Thus, hyperphosphorylation of GR in v-mos-transformed cells does not appear to result from inhibition of GR dephosphorylation, but rather from stimulation of GR phosphorylation.

Identification and localization of steroid-binding and nonsteroid-binding forms of the glucocorticoid receptor in the mouse P1798 lymphosarcoma

Glucocorticoid receptors (GCRs) were characterized in sublines of the mouse P1798 lymphosarcoma that are sensitive (S) or resistant (R) to glucocorticoid-mediated apoptosis. Previous work had identified two steroid-binding GCRs in S and R cells: a 97 kDa wild-type GCR in S cells (WT-GCR), and a 45 kDa truncated GCR in R cells (TR-GCR). A third GCR, a 97 kDa nonsteroid-binding GCR (NSB-GCR), was also identified in R cells. Using subcellular fractionation and Western blotting, we now show that in contrast to the WT-GCR which is localized in both the cytoplasm and nucleus of S cells, the NSB-GCR is localized predominantly in R cell nuclei. Moreover, gel filtration chromatography revealed that treatment with 400 mM NaCl and heat did not significantly alter the Stokes radius of the NSB-GCR suggesting that this receptor is not present in a heterooligomeric complex with other proteins. The TR-GCR was localized predominantly in the soluble cytoplasmic fraction but also in the crude membrane fractions of R cell nuclei, suggesting that this receptor is tightly associated with nuclear structures. It was not detected in the soluble nuclear fraction. Unexpectedly, a 45 kDa nonsteroid-binding immunoreactive protein was detected in crude membrane fractions of S cells. These studies describe a complex GCR system in the P1798 lymphosarcoma that necessitates a further consideration of glucocorticoid signaling in S and R cells.

Regulation of glucocorticoid receptor (GR) mRNA and protein levels by phorbol ester in MCF-7 cells. Mechanism of GR mRNA induction and decay

Treatment of MCF-7 cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) (10(-7) M) was associated with a time-dependent increase in specific binding of [3H]dexamethasone (34.8 +/- 4.6 fmol/mg protein after 9 h of TPA treatment compared with 16.0 +/- 2.3 fmol/mg protein in control cells) as well as a transient induction in the level of glucocorticoid receptor (GR) mRNA (4- to 8-fold stimulation after 2-3 h, followed by a decline towards the control value after 6 h). In the presence of the transcription inhibitor actinomycin D (AMD) (5.0 micrograms/ml) the TPA-dependent induction of GR mRNA was completely abolished, and GR mRNA showed a gradual decline with a half-life of 2-3 h. In contrast, treatment with TPA and the protein synthesis inhibitor cycloheximide (50 microM) resulted in a superinduction of GR mRNA (> 50-fold after 6 h). Inhibition of a half-life of 2-3 h, which is identical to that observed in non-treated cells. We conclude that the increase in GR mRNA in the presence of TPA is dependent on ongoing transcription, whereas the rate by which GR transcripts are degraded, is not altered by TPA.

Glucocorticoid receptors in bovine adrenal medullary cells in culture: regulation by cyclic nucleotides

Glucocorticoid receptor levels within a given cell determine the glucocorticoid effect in the target tissue. Glucocorticoid receptors are present in adrenal medullary cells in culture where they are involved in the regulation of catecholamine biosynthesis. Modulation of glucocorticoid receptor protein and/or messenger RNA levels in response to cyclic nucleotides has been found in various cell types. In this study, we have investigated the effects of cyclic AMP and cyclic GMP on glucocorticoid receptor binding and glucocorticoid receptor-mediated function in Percoll-isolated bovine adrenal medullary cells in culture. Four-day treatment of cells with 8-bromo-cyclic AMP (10(-3) M) an analogue of cAMP, or forskolin (10(-5) M), an activator of adenylate cyclase, decreased soluble [3H]dexamethasone binding by 55 and 54%, respectively. 8-Bromo-cyclic GMP treatment decreased [3H]dexamethasone binding by 31 and 34% at 10(-5) and 10(-4) M, respectively. Treatment with 8-bromo-cyclic AMP or forskolin, but not 8-bromo-cyclic GMP, elevated cortisol levels in the medium of treated cells, presumably by elevating steroidogenesis in contaminating cortical cells. Cultures further purified to produce chromaffin-enriched cell cultures, also showed a loss (41%) in soluble [3H]dexamethasone binding when treated with 8-bromo-cyclic AMP (10(-3) M). Four-day treatment of standard Percoll-isolated cells with low concentrations of cortisol (10(-9) to 2 x 10(-7) M) similar to that found in the medium of 8-bromo-cyclic AMP-treated cells, did not decrease soluble [3H]dexamethasone binding, whereas higher cortisol concentrations (10(-6) M) produced a 62% loss in soluble binding. Adsorption of cortisol with bovine serum albumin (5 mg/ml) prevented a cortisol (10(-6) M)-induced loss in soluble [3H]dexamethasone binding with no effect on the 8-bromo-cyclic AMP-induced loss in binding, suggesting that the decrease in binding observed following 8-bromo-cyclic AMP treatment is not due to the release of cortisol from contaminating cortical cells. Finally, we report a loss in the ability of 8-bromo-cyclic AMP- or 8-bromo-cyclic GMP-treated cells to fully induce the activity of phenylethanolamine N-methyltransferase in response to cortisol, indicating that decreases in soluble [3H]dexamethasone binding translate into a decrease in the functional consequence of glucocorticoid receptor binding in adrenal medullary cells. In conclusion, these results indicate that long-term increases in cyclic nucleotide second messengers are able to decrease glucocorticoid receptor binding in bovine adrenal medullary cells, via a mechanism independent of released cortisol.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of glucocorticoid receptor expression

A limiting factor determining the sensitivity of a cell to glucocorticoid hormones is the intracellular concentration of the glucocorticoid receptor (GR) protein. By regulating the expression of GR the cell is able to adapt to both changes in its hormone environment and to the varying requirements for biological response. Studies on the regulation of GR expression have shown this to be a complex process which involves both transcriptional and posttranscriptional mechanisms. Although GR is more or less constitutively expressed in most tissues its concentration varies under different physiological conditions. GR expression is regulated by a number of different agents including factors which act through a second messenger pathway. This allows the cell to control glucocorticoid regulated gene expression through a complex but integrated hormonal network. Here we summarize our studies on GR regulation with emphasis on: i), GR autoregulation; ii), the effect of cAMP on GR expression, and iii), GR expression during fetal rat lung development.