Genes mediating glucocorticoid effects and mechanisms of their regulation

Glucocorticoid receptor activity contributes to resistance to androgen-targeted therapy in prostate cancer

Despite new treatments for castrate-resistant prostate cancer (CRPC), the prognosis of patients with CRPC remains bleak due to acquired resistance to androgen receptor (AR)-directed therapy. The glucocorticoid receptor (GR) and AR share several transcriptional targets, including the anti-apoptotic genes serum and glucocorticoid-regulated kinase 1 (SGK1) and Map kinase phosphatase 1 (MKP1)/dual specificity phosphatase 1 (DUSP1). Because GR expression increases in a subset of primary prostate cancer (PC) following androgen deprivation therapy, we sought to determine whether GR activation can contribute to resistance to AR-directed therapy. We studied CWR-22Rv1 and LAPC4 AR/GR-expressing PC cell lines following treatment with combinations of the androgen R1881, AR antagonist MDV3100, GR agonist dexamethasone, GR antagonists mifepristone and CORT 122928, or the SGK1 inhibitor GSK650394. Cell lines stably expressing GR (NR3C1)-targeted shRNA or ectopic SGK1-Flag were also studied in vivo. GR activation diminished the effects of the AR antagonist MDV3100 on tumor cell viability. In addition, GR activation increased prostate-specific antigen (PSA) secretion and induced SGKI and MKP1/DUSP gene expression. Glucocorticoid-mediated cell viability was diminished by a GR antagonist or by co-treatment with the SGK1 inhibitor GSK650394. In vivo, GR depletion delayed castrate-resistant tumor formation, while SGK1-Flag-overexpressing PC xenografts displayed accelerated castrate-resistant tumor initiation, supporting a role for SGK1 in GR-mediated CRPC progression. We studied several PC models before and following treatment with androgen blockade and found that increased GR expression and activity contributed to tumor-promoting PC cell viability. Increased GR-regulated SGK1 expression appears, at least in part, to mediate enhanced PC cell survival. Therefore, GR and/or SGK1 inhibition may be useful adjuncts to AR blockade for treating CRPC.

Bim polymorphisms: influence on function and response to treatment in children with acute lymphoblastic leukemia

PURPOSE

Corticosteroids induce apoptosis in the malignant lymphoid cells and are critical component of combination therapy for acute lymphoblastic leukemia (ALL). Several genome-wide microarray studies showed major implication of proapoptotic Bim in mediating corticosteroid-related resistance in leukemia cells.

EXPERIMENTAL DESIGN

We investigated Bim gene polymorphisms and their association with childhood ALL outcome, and the mechanism underlying the observed finding.

RESULTS

Lower overall survival (OS) was associated with Bim C29201T located in Bcl-2 homology 3 (BH3) domain (P = 0.01). An association remained significant in multivariate model (P = 0.007), was more apparent in high-risk patients (P = 0.004) and patients treated with dexamethasone (P = 0.009), and was subsequently confirmed in the replication patient cohort (P = 0.03). RNA analysis revealed that C29201T affects generation of γ isoforms (γ1) that lack proapoptotic BH3 domain. The phenotypic effect was minor suggesting the influence of additional factors that may act in conjunction with Bim genotype. Combined analysis with Mcl gene polymorphism (G-486T) revealed profound reduction in OS in individuals with both risk genotypes (P < 0.0005 in discovery and P = 0.002 in replication cohort) and particularly in high-risk patients (P ≤ 0.008).

CONCLUSIONS

Increased expression of prosurvival Mcl1 and presence of Bim isoforms lacking proapoptotic function might explain marked reduction of OS in a disease and dose-dependent manner in ALL patients carrying Bim- and Mcl1-risk genotypes.

Establishing a sensitive and specific assay for determination of glucocorticoid bioactivity

Glucocorticoids are hormones that play a major role in energy homeostasis and stress response of the body. As drugs they are most frequently used for immunosuppressive and anti-inflammatory purposes. Glucocorticoids are exploited successfully in the treatment of a wide variety of diseases; however, some patients develop side-effects, while others fail to respond to this form of therapy. Alterations in pharmacodynamic and pharmacokinetic actions might contribute to individual differences in glucocorticoid sensitivity. Antibody-based methods such as RIA (Radioimmunoassay) and ELISA (Enzyme-linked immunosorbent assay) are routinely used to determine glucocorticoid serum levels. However, as these techniques measure the total amount of a specific glucocorticoid and do not discriminate between protein-bound and freely available (i.e. biologically active) glucocorticoids, the results do not necessarily reflect the active levels of glucocorticoid, i.e. the "glucocorticoid milieu" in a patient. Being able to determine glucocorticoid bioactivity in serum or other body fluids could help identifying glucocorticoid-sensitive or -resistant patients and help finding explanations for different responses in individual patients. For this reason, we established a glucocorticoid bioactivity assay that is based on the measurement of glucocorticoid-dependent reporter gene activity. Making use of a human T-cell leukemia line, equipped with the glucocorticoid receptor and the fluorescence protein Venus as the assay's reporter (Jurkat(GR)-MMTV-VNP), glucocorticoid bioactivity can be determined from small amounts of serum or other biologic fluids. The developed glucocorticoid bioassay is both sensitive and reproducible, without any relevant cross-reactivity with steroid hormones other than glucocorticoids and can be practically applied in daily laboratory routine.

Cortisol-induced masculinization: does thermal stress affect gonadal fate in pejerrey, a teleost fish with temperature-dependent sex determination?

Background

Gonadal fate in many reptiles, fish, and amphibians is modulated by the temperature experienced during a critical period early in life (temperature-dependent sex determination; TSD). Several molecular processes involved in TSD have been described but how the animals “sense” environmental temperature remains unknown. We examined whether the stress-related hormone cortisol mediates between temperature and sex differentiation of pejerrey, a gonochoristic teleost fish with marked TSD, and the possibility that it involves glucocorticoid receptor- and/or steroid biosynthesis-modulation.

Methodology/Principal Findings

Larvae maintained during the period of gonadal sex differentiation at a masculinizing temperature (29°C; 100% males) consistently had higher cortisol, 11-ketotestoterone (11-KT), and testosterone (T) titres than those at a feminizing temperature (17°C; 100% females). Cortisol-treated animals had elevated 11-KT and T, and showed a typical molecular signature of masculinization including amh upregulation, cyp19a1a downregulation, and higher incidence of gonadal apoptosis during sex differentiation. Administration of cortisol and a non-metabolizable glucocorticoid receptor (GR) agonist (Dexamethasone) to larvae at a “sexually neutral” temperature (24°C) caused significant increases in the proportion of males.

Conclusions/Significance

Our results suggest a role of cortisol in the masculinization of pejerrey and provide a possible link between stress and testicular differentiation in this gonochoristic TSD species. Cortisol role or roles during TSD of pejerrey seem(s) to involve both androgen biosynthesis- and GR-mediated processes. These findings and recent reports of cortisol effects on sex determination of sequential hermaphroditic fishes, TSD reptiles, and birds provide support to the notion that stress responses might be involved in various forms of environmental sex determination.

Expression profiling of glucocorticoid-treated T-ALL cell lines: rapid repression of multiple genes involved in RNA-, protein- and nucleotide synthesis

To arrive at a better understanding of the effects of the glucocorticoid component of chemotherapy protocols on lymphocytic leukemia cells, we analysed early responses of T-lymphocytic leukemia cell lines Jurkat and CEM-C7, both of which undergo apoptosis in response to dexamethasone, via gene chips. Among genes identified as repressed, a notable cluster seemed to be of importance for the processes of transcription, mRNA splicing and protein synthesis. Consequently, we assessed time-resolved uptake of uridine and methionine to monitor RNA and protein synthesis, along with parameters quantifying apoptosis. Repression of uptake to about 65% of that in untreated cells preceded the first sign of apoptosis by several hours in both cell lines. In addition to this general repression of RNA and protein synthesis, several genes were found to be regulated that may contribute to synergistic action of glucocorticoids with other components of frequently used chemotherapy protocols such as antimetabolites, methotrexate and alkylating agents.

Mmip-2/Rnf-17 enhances c-Myc function and regulates some target genes in common with glucocorticoid hormones

Members of the Mad family of basic-helix-loop-helix-leucine zipper proteins inhibit the transcriptional activity of the c-Myc oncoprotein. Mmip-2/Rnf-17 is a RING-finger protein that interacts with all four known Mad proteins, redistributes them to the cytoplasm, and thus enhances c-Myc function. We generated cell lines in which Mmip-2/Rnf-17 was rendered glucocorticoid (GC)-inducible. Stable expression of Mmip-/Rnf-17 resulted in the expected transport of the most abundant endogenous mad protein, Mxi1, to the cytoplasm. Compensatory increases in Mxi1 and Mad3 transcripts, similar to those previously described in Mad1 null hematopoietic cells, were also seen. Mmip-2/Rnf-17 also sensitized cells to several different pro-apoptotic stimuli and regulated a subset of c-Myc target genes. Unexpectedly, some of these genes were also found to be modulated solely by GCs. Thus, the inhibition of Mad proteins by Mmip-2/Rnf-17 modulates c-Myc function by enhancing its ability to regulate a subset of its potential target genes. Our results also identify a previously unrecognized overlap between genes regulated by c-Myc- and GCs and provide a potential molecular basis for their regulation of common cellular functions.

c-Myc does not prevent glucocorticoid-induced apoptosis of human leukemic lymphoblasts

Due to their growth arrest- and apoptosis-inducing ability, glucocorticoids (GC) are widely used in the therapy of various lymphoid malignancies. The signal transduction pathways leading to this clinically-relevant form of apoptosis have, however, not been sufficiently elucidated. GC bind to their specific receptor, a ligand-activated transcription factor of the Zn-finger type, that activates or represses transcription of GC-responsive genes. Previous studies in leukemia cells suggested that transcriptional repression of c-myc expression might be the crucial event in GC-induced apoptosis, although in other systems, c-Myc apparently increased the sensitivity to cell-death inducers. To address this controversy, we stably transfected the GC-sensitive human T-ALL cell line CEM-C7H2 with constructs allowing tetracycline-regulated expression of c-Myc. Subsequent analyses of these cell lines showed that overexpression of c-Myc per se had little, if any, effect on cell viability, although it rendered the cells more sensitive to apoptosis induced by low serum, confirming the functionality of the expressed transgene. More importantly, however, when the cells were treated with GC in the presence of exogenous c-Myc, they underwent apoptosis exceeding that in cells treated in the absence of transgenic c-Myc. The data indicate that c-myc downregulation is not critical for induction of cell-death by GC in this system, and support the notion that c-Myc sensitizes cells to apoptosis-inducing agents.

Bcl-2 interferes with the execution phase, but not upstream events, in glucocorticoid-induced leukemia apoptosis

Due to their growth arrest- and apoptosis-inducing ability, glucocorticoids (GC) are widely used in the therapy of various lymphoid malignancies. Cell death is associated with activation of members of the interleukin-1beta-converting enzyme (ICE) protease/caspase family and, is presumably prevented by the anti-apoptotic protein Bcl-2. To further address the role of Bcl-2 in GC-mediated cytotoxicity, we generated subclones of the GC-sensitive human T-cell acute lymphoblastic leukemia line CCRF-CEM, in which transgenic Bcl-2 expression is regulated by tetracycline. Up to about 48 h, exogenous Bcl-2 almost completely protected these cells from apoptosis, digestion of poly-ADP ribose polymerase (PARP) and generation of Asp-Glu-Val-Asp cleaving (DEVDase) activity. However, when the cells were cultured for another 24 h in the continuous presence of GC, they underwent massive apoptosis that was associated with DEVDase activity and PARP cleavage. Bcl-2 did not markedly affect GC-mediated growth arrest, thereby separating the anti-proliferative from the apoptosis-inducing effect of GC. Moreover, Bcl-2 did not prevent the dramatic reduction in the levels of several mRNAs observed during GC treatment, including the transgenic Bcl-2 mRNA. Thus, Bcl-2 can be placed upstream of effector caspase activation, but downstream of other GC-regulated events, such as growth arrest and the potentially critical repression of steady state levels of multiple mRNA.