Coactivator Steroid Receptor Coactivator-1 Research Articles

Panaxytriol upregulates CYP3A4 expression through the interaction between nuclear regulators and DNA response elements.

Cytochrome P3A4 (CYP3A4) is a crucial drug-metabolizing enzyme, and its expression is regulated by the pregnane X receptor (PXR), constitutive androstane receptor (CAR), steroid receptor coactivator 1 (SRC-1), and acetyltransferase P300. Panaxytriol is a naturally derived active substance extracted from the roots of Panax ginseng C. A. Mey. which is widely used clinically. Our previous studies have shown that panaxytriol induces CYP3A4 expression through PXR activation, which is antagonized by high CAR expression. However, the underlying mechanism remains unclear. This study aimed to investigate the mechanism of panaxytriol in inducing CYP3A4 expression via interactions between nuclear regulators and DNA response elements. Immunoprecipitation technique was used to assess the binding levels of PXR and CAR with the coactivators SRC-1 and P300 in HepG2 and Huh-7cells. Furthermore, chromatin immunoprecipitation assay was used to investigate the PXR and CAR interaction with the CYP3A4 promoter response element ER-6/DR-3. The binding of PXR to SRC-1, P300, and the response elements ER-6 and DR-3 was improved with an increase in panaxytriol concentration (10-80μM), and the binding affinity was further enhanced upon CAR silencing. The binding of CAR to SRC-1 and the response elements ER-6 and DR-3 was significantly higher at 80μM panaxytriol, whereas no significant binding was observed between CAR and P300. Panaxytriol promoted the recruitment of PXR to SRC-1 and P300, binding to ER-6 and DR-3, and upregulating CYP3A4 expression. Furthermore, an interactive dialogue regulatory mechanism between PXR and CAR was observed.

Nuclear receptor coactivator SRC-1 promotes colorectal cancer progression through enhancing GLI2-mediated Hedgehog signaling.

Overexpression of nuclear coactivator steroid receptor coactivator 1 (SRC-1) and aberrant activation of the Hedgehog (Hh) signaling pathway are associated with various tumorigenesis; however, the significance of SRC-1 in colorectal cancer (CRC) and its contribution to the activation of Hh signaling are unclear. Here, we identified a conserved Hh signaling signature positively correlated with SRC-1 expression in CRC based on TCGA database; SRC-1 deficiency significantly inhibited the proliferation, survival, migration, invasion, and tumorigenesis of both human and mouse CRC cells, and SRC-1 knockout significantly suppressed azoxymethane/dextran sodium sulfate (AOM/DSS)-induced CRC in mice. Mechanistically, SRC-1 promoted the expression of GLI family zinc finger 2 (GLI2), a major downstream transcription factor of Hh pathway, and cooperated with GLI2 to enhance multiple Hh-regulated oncogene expression, including Cyclin D1, Bcl-2, and Slug. Pharmacological blockages of SRC-1 and Hh signaling retarded CRC progression in human CRC cell xenograft mouse model. Together, our studies uncover an SRC-1/GLI2-regulated Hh signaling looping axis that promotes CRC tumorigenesis, offering an attractive strategy for CRC treatment.

Phytosterols in hull-less pumpkin seed oil, rich in ∆7-phytosterols, ameliorate benign prostatic hyperplasia by lowing 5α-reductase and regulating balance between cell proliferation and apoptosis in rats.

BackgroundPumpkin seed oil is widely used to treat benign prostatic hyperplasia (BPH), a common disease in elder men. However, its active components and mechanism have remained to be elucidated.ObjectiveThe objective of the present study was to investigate the active components of pumpkin seed oil and its mechanism against BPH.DesignTotal phytosterol (TPS) was isolated from hull-less pumpkin (Cucurbita pepo L. var. Styriaca) seed oil and analyzed by gas chromatography/mass spectrometry (GC/MS). Three phytosterols were purified by preparative HPLC (high performance liquid chromatography) and confirmed by NMR (nuclear magnetic resonance). TPS (3.3 mg/kg body weight, 1 mL/day/rat) was administered intragastrically to the testosterone propionate-induced BPH rats for 4 weeks. The structure changes of prostate tissues were assessed by hematoxylin & eosin (H&E) staining. The expression of androgen receptor (AR) and steroid receptor coactivator 1 (SRC-1) was analyzed by immunohistochemistry, while that of 5α-reductase (5AR), apoptosis, or proliferation-related growth factors/proteins was detected by real-time quantitative polymerase chain reaction or western blotting.ResultsThe ∆7-phytosterols in TPS reached up to 87.64%. Among them, 24β-ethylcholesta-7,22,25-trienol, 24β-ethylcholesta-7,25(27)-dien-3-ol, and ∆7-avenasterol were confirmed by NMR. TPS treatment significantly ameliorated the pathological prostate enlargement and restored histopathological alterations of prostate in BPH rats. It effectively suppressed the expressions of 5AR, AR, and coactivator SRC-1. TPS inhibited the expression of proliferation-related growth factor epidermal growth factor, whereas it increased the expressions of apoptosis-related growth factor/gene transforming growth factor-β1. The proliferation-inhibiting effect was achieved by decreasing the ERK (extracellular signal-regulated kinase) phosphorylation, while apoptosis was induced by Caspase 3 activation through JNK (c-Jun N-terminal kinase) and p38 phosphorylation.ConclusionTPS from hull-less pumpkin seed oil, with ∆7-phytosterols as its main ingredients, is a potential nutraceutical for BPH prevention.

Hydrophobic Tagging-Mediated Degradation of Transcription Coactivator SRC-1.

Steroid receptor coactivator-1 (SRC-1) is a transcription coactivator playing a pivotal role in mediating a wide range of signaling pathways by interacting with related transcription factors and nuclear receptors. Aberrantly elevated SRC-1 activity is associated with cancer metastasis and progression, and therefore, suppression of SRC-1 is emerging as a promising therapeutic strategy. In this study, we developed a novel SRC-1 degrader for targeted degradation of cellular SRC-1. This molecule consists of a selective ligand for SRC-1 and a bulky hydrophobic group. Since the hydrophobic moiety on the protein surface could mimic a partially denatured hydrophobic region of a protein, SRC-1 could be recognized as an unfolded protein and experience the chaperone-mediated degradation in the cells through the ubiquitin–proteasome system (UPS). Our results demonstrate that a hydrophobic-tagged chimeric molecule is shown to significantly reduce cellular levels of SRC-1 and suppress cancer cell migration and invasion. Together, these results highlight that our SRC-1 degrader represents a novel class of therapeutic candidates for targeting cancer metastasis. Moreover, we believe that the hydrophobic tagging strategy would be widely applicable to develop peptide-based protein degraders with enhanced cellular activity.

Targeted Degradation of Transcription Coactivator SRC-1 through the N-Degron Pathway.

Aberrantly elevated steroid receptor coactivator-1 (SRC-1) expression and activity are strongly correlated with cancer progression and metastasis. Here we report, for the first time, the development of a proteolysis targeting chimera (PROTAC) that is composed of a selective SRC-1 binder linked to a specific ligand for UBR box, a unique class of E3 ligases recognizing N-degrons. We showed that the bifunctional molecule efficiently and selectively induced the degradation of SRC-1 in cells through the N-degron pathway. Importantly, given the ubiquitous expression of the UBR protein in most cells, PROTACs targeting the UBR box could degrade a protein of interest regardless of cell types. We also showed that the SRC-1 degrader significantly suppressed cancer cell invasion and migration in vitro and in vivo. Together, these results demonstrate that the SRC-1 degrader can be an invaluable chemical tool in the studies of SRC-1 functions. Moreover, our findings suggest PROTACs based on the N-degron pathway as a widely useful strategy to degrade disease-relevant proteins.

Progesterone Receptor Isoforms, Nuclear Corepressor-1 and Steroid Receptor Coactivator-1 and B-Cell Lymphoma 2 and Akt and Akt Phosphorylation Status in Uterine Myomas after Ulipristal Acetate Treatment: A Systematic Immunohistochemical Evaluation

Objective: To investigate whether ulipristal acetate (UPA) treatment modifies the expression of progesterone receptor (PR), its nuclear cofactors steroid receptor coactivator-1 (SRC1) and nuclear corepressor-1 (NCoR1), prosurvival factor B-cell lymphoma 2 (Bcl-2), and Akt in uterine myomas. Patients: Prospective study of 59 women with symptomatic myomas undergoing myomectomy. Forty-two patients were treated preoperatively with UPA; the remaining 17 were not and they served as controls. Method: Tissue microarrays were obtained from surgical specimens and immunohistochemistry was performed. Blinded quantification of expression of PR (PR-A vs. PR-B), coactivator SRC1 and corepressor NCoR1, and prosurvival factor Bcl-2, and Akt and evaluation of Akt phosphorylation levels. Results: Compared with the control group, UPA does not alter PR protein levels or expression patterns in myomas, and the PR-A/PR-B ratio was similar, as well as cytoplasmic or nuclear expression of cofactors SRC1 and NCoR1. Bcl-2 was heterogeneously expressed throughout the samples and no significant modification in expression was evidenced. No significant difference was found in Akt expression and phosphorylation between treated and untreated myomas. Conclusion: This study did not find any significant change in the expression of the studied factors in myomas after UPA exposure. In conclusion, various theories on myomas cells proposed on the basis of in vitro studies are not supported in vivo.

Abstract P3-04-17: Global transcriptional repression by the coactivator SRC-1 mediates disease progression in treatment-resistant breast cancer

Abstract Despite the effectiveness of endocrine therapy in treating estrogen receptor (ER) positive breast cancer, nearly 40% of breast cancer patients may develop resistance which can lead to metastatic disease progression. Steroid receptor co-activator-1 (SRC-1), a key regulator of ER signalling, is overexpressed in 35% of breast cancer patients and is strongly associated with the development of endocrine resistant metastasis(1). Recent studies highlighted the ability of SRC-1 to also act as transcriptional repressor. SRC-1 can therefore bi-directionally regulate gene expression to promote the resistant phenotype (2). This study employed a genome-wide multi-omics sequencing approach to determine the SRC-1 repression signature in endocrine resistance and elucidate the mechanism by which SRC-1 mediates this repression. RNA-sequencing identified 736 genes significantly downregulated by SRC-1, with common functional pathways such as differentiation, cell morphogenesis and extracellular matrix enriched in the gene set. Parallel global methylation sequencing analysis revealed distinct differentially methylated regions specific to SRC-1 repressed target genes. Mechanistic studies in endocrine resistant cells revealed a role for methylation proteins, DNMTs and MBD, in SRC-1 directed repression. Through combined analysis of our global sequencing data we identified a network hub of five differentiation genes directly repressed by SRC-1. High expression of this signature predicts enhanced recurrence free survival in tamoxifen treated patients (n=335, p=0.032). A reduction in expression of these genes was shown to have functional output on proliferation, migration and mammosphere formation. Finally, we use tumour explant models to show that targeting DNA methylation can be used to reverse the SRC-1 driven suppression of this differentiation hub. Here we report a novel mechanism by which SRC-1 may be driving endocrine resistant tumorigenesis. Our genome-wide discovery approach revealed a global epigenetic re-programming pathway whereby concerted differential DNA methylation is potentiated by the activation of SRC-1 in the presence of tamoxifen in the endocrine resistant setting. This study suggests that therapeutic strategies of combined targeted epigenetic therapy with estrogen deprivation could be a successful strategy to prevent acquired resistance to endocrine therapy. Citation Format: Ward E, Varešlija D, Fagan A, Hill A, Young L. Global transcriptional repression by the coactivator SRC-1 mediates disease progression in treatment-resistant breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-04-17.

The co-regulators SRC-1 and SMRT are involved in interleukin-6-induced androgen receptor activation.

The androgen receptor (AR) can be stimulated by interleukin-6 (IL-6) in the absence of androgens to induce prostate cancer progression. The purpose of this study was to investigate whether the co-activator steroid receptor coactivator-1 (SRC-1) and co-repressor silencing mediator for retinoid and thyroid hormone receptors (SMRT) are involved in IL-6-induced AR activation. The effects of IL-6 on LNCaP cell proliferation were monitored using real-time cell analysis (RTCA) iCELLigence system. The impacts of IL-6 on the association of the AR with SRC-1 and SMRT were investigated using the mammalian two-hybrid assay. IL-6 increased the proliferation of LNCaP cells with maximal induction at 50ng/mL. The AR-SRC-1interaction was enhanced by IL-6, with maximal induction at the concentration of 50ng/mL (P<0.05). IL-6 decreased the AR-SMRT interaction and a marked reduction was detected at 50ng/mL (P<0.05). IL-6 enhances LNCaP cells proliferation, which suggests that IL-6 might cause AR-positive prostate cancer growth through activation of the AR. The mechanism of IL-6-induced AR activation is mediated through enhancing AR-SRC-1 interaction and inhibiting AR-SMRT interaction. We have shown a significant role for SRC-1 and SMRT in modulating IL-6-induced AR transactivation.

Ubiquitination of RORγt at Lysine 446 Limits Th17 Differentiation by Controlling Coactivator Recruitment.

The transcription factor retinoid acid-related orphan receptor γ t (RORγt) directs the differentiation of Th17 cells. Th17 cells mediate pathological immune responses responsible for autoimmune diseases, including psoriasis and multiple sclerosis. Previous studies focused on RORγt target genes and their function in Th17 differentiation. In this study, we assessed posttranscriptional regulation of RORγt and identified a functional ubiquitination site, K446. Mutation of K446 to arginine to prevent ubiquitination greatly enhanced recruitment of steroid receptor coactivator 1 (SRC1), a coactivator critical for RORγt activity. Correspondingly, the K446 to arginine mutation potentiated Th17 differentiation. We also showed that ubiquitin-specific protease (USP)15 interacted with RORγt, removed ubiquitin from K446, and stimulated RORγt activity by enhancing coactivator SRC1 recruitment. Knockdown of USP15 or expression of inactive USP15 impaired Th17 differentiation, suggesting a positive role for USP15-mediated deubiquitination of RORγt in Th17 differentiation. Therefore, ubiquitination of K446 limits RORγt-mediated Th17 differentiation by inhibiting the recruitment of coactivator SRC1. Our study will inform the development of treatments that target RORγt ubiquitination pathways to limit Th17-mediated autoimmunity.

Abstract 861: Global transcription factor repression by the coactivator SRC-1 mediates disease progression in endocrine-resistant breast cancer

Abstract Despite the clinical utility of endocrine therapies to treat ER positive breast cancer, 40% of patients eventually develop resistance, leading to disease progression. Steroid receptor co-activators have been described as “the powerhouses of transcription” with a role in mediating hormone receptor responsiveness. There is now substantial evidence that steroid receptor coactivator-1 (SRC-1) is central to the ability of endocrine tumours to adapt and overcome targeted therapy thereby facilitating metastatic disease progression. Recent work highlighted the potential ability of SRC-1 to also act as transcriptional repressor that can bi-directionally regulate genes that help it promote the resistant phenotype. This study employed a genome-wide multi-omics sequencing approach to determine the SRC-1 repression signature in endocrine resistance and elucidate the mechanism by which SRC-1 mediates this repression. RNA-sequencing was used to investigate the transcriptional network affected by SRC-1 in an endocrine resistant cell line model. This approach identified 1,495 genes significantly downregulated by SRC-1, with common functional pathways such as differentiation, cell morphogenesis and extracellular matrix enriched in the gene set. Parallel global methylation sequencing analysis revealed methylation as a possible mechanism by which SRC-1 was repressing target genes, which was confirmed with mechanistic studies utilising 5-AZA-2’-deoxycitidine. Through combined analysis of our global sequencing data we identified a SRC-1 regulated transcriptional hub of differentiation genes, that have protective roles in normal and treatment- sensitive breast cancer cells and which associate with poor disease-free survival in breast cancer patients. Furthermore, our work demonstrated that SRC-1 can re-programme cells to become poorly differentiated by supressing this normally protective transcriptional hub, and thereby promote aggressive endocrine resistant phenotype. Here we report a novel mechanism by which SRC-1 can drive endocrine resistant tumorigenesis. Our genome-wide discovery approach revealed an epigenetic re-programming pathway, whereby concerted differential DNA methylation is potentiated by the activation of SRC-1 in the endocrine resistant setting. This study suggests that therapeutic strategies of combined targeted epigenetic therapy with estrogen deprivation could be successful strategy to prevent acquired resistance to endocrine therapy. Citation Format: Damir Vareslija, Elspeth Ward, Ailis Fagan, William Gallagher, Arnold DK Hill, Leonie S. Young. Global transcription factor repression by the coactivator SRC-1 mediates disease progression in endocrine-resistant breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 861.

Implications of a peroxisome proliferator-activated receptor alpha (PPARα) ligand clofibrate in breast cancer.

Inflammatory and invasive breast cancers are aggressive and require better understanding for the development of new treatments and more accurate prognosis. Here, we detected high expression of PPARα in human primary inflammatory (SUM149PT) and highly invasive (SUM1315MO2) breast cancer cells, and tissue sections of human breast cancer. PPARα ligands are clinically used to treat dyslipidemia. Among lipid lowering drugs clofibrate, fenofibrate and WY14643, clofibrate showed high chemo-sensitivity towards breast cancer cells. Clofibrate treatment significantly induced PPARα DNA binding activity, and remarkably reduced cyclooxygenase-2/PGE2 and 5-lipoxygenase/LTB4 inflammatory pathways. Clofibrate treatment reduced the proliferation of breast cancer cells probably by inhibiting NF-κB and ERK1/2 activation, reducing cyclinD1, cyclinA, cyclinE, and inducing pro-apoptotic P21 levels. Surprisingly, the expression of lipogenic pathway genes including SREBP-1c (sterol regulatory element-binding protein-1c), HMG-CoA synthase, SPTLC1 (serine palmitoyltransferase long-chain), and Acyl-CoA oxidase (ACO) decreased with a concurrent increase in fatty acid oxidation genes such as CPT-1a (carnitine palmitoyltransferase 1a) and SREBP-2 (Sterol regulatory element-binding protein-2). Clofibrate treatment induced secretion of free fatty acids and effectively decreased the level of phosphorylated active form of fatty acid synthase (FASN), an enzyme catalyzing de novo synthesis of fatty acids. High level of coactivators steroid receptor coactivator-1 (SRC-1) and histone acetylase CBP-300 (CREB binding protein-300) were observed in the nuclear complexes of clofibrate treated breast cancer cells. These findings implicate that stimulating PPARα by safe, well-tolerated, and clinically approved clofibrate may provide a safer and more effective strategy to target the signaling, lipogenic, and inflammatory pathways in aggressive forms of breast cancer.

Progesterone receptor and SRC-1 participate in the regulation of VEGF, EGFR and Cyclin D1 expression in human astrocytoma cell lines

Astrocytomas are the most common primary brain tumors in humans. It has been reported that vascular endothelial growth factor (VEGF), epidermal growth factor receptor (EGFR), cyclin D1 and progesterone receptor (PR) expression levels are elevated in patients with high-grade astrocytomas. Progesterone (P) regulates astrocytomas growth through its interaction with PR, which recruits coregulatory proteins such as steroid receptor coactivator-1 (SRC-1) that are required for efficient transcriptional activation. The regulation of VEGF, EGFR and cyclin D1 expression by P in human astrocytoma cells is not known. We studied the role of PR and SRC-1 in the expression of VEGF, EGFR and cyclin D1 mediated by P in human astrocytoma cell lines grade III (U373) and IV (D54). P significantly increased VEGF and EGFR mRNA expression after 12h of treatment in D54 cells that was reflected at protein level 24h after treatment. This effect was blocked by the PR antagonist, RU 486. In U373 cells cyclin D1 mRNA and protein expression was induced by P after 6 and 8h of treatment, respectively, and this effect was blocked with RU 486. Transfection with short hairpin RNA targeting coactivator SRC-1 significantly reduced VEGF expression after 24h of treatment. Collectively, our results indicate that P regulates VEGF and EGFR expression in D54 cells and cyclin D1 expression in U373 through PR, and that SRC-1 participates in the regulation of VEGF expression.

Organotin Compounds Act as Inhibitor of Transcriptional Activation with Human Estrogen Receptor

In aquatic invertebrates, particularly marine gastropods, organotin compounds induce irreversible sexual abnormality in females, which is termed imposex, at very low concentrations. Organotin compounds are agonists for nuclear receptors such as RXRs and PPARgamma. However, the imposex phenomenon has not been reported to act as an antagonist on estrogen receptors in other species, including vertebrates and invertebrates. In order to gain insights into the antagonistic activity of organotin compounds on estrogen receptors (ERs), we examined the inhibitive effect of these compounds on estradiol-dependent beta-galactosidase activity using the yeast two-hybrid detection system consisting of a combination of the human estrogen receptor (hERbeta) ligand-binding domain and the co-activator steroid receptor co-activator-1 (SRC1). Tributyltin-hydroxide (TBT-OH) and triphenyltin-chlorine (TPT-Cl) exhibited an inhibitive effect on E₂-dependent transcriptional activity, similar to antagonistic chemicals such as 4-hydroxytamoxifen (OHT) or ICI 182,780, at a very low concentration of 10⁻¹⁴ M TBT or 10⁻¹⁰ M TPT, respectively. The yeast growth and transcriptional activity with transcriptional factor GAL4 did not exhibit any effect at the tested concentration of TBT or TPT. Moreover, the yeast two-hybrid system using the interaction between p53 and the T antigen of SV40 large did not describe any effect at the tested concentration of OHT or ICI 182,780. However, the interaction between p53 and T antigen was inhibited at a TBT or TPT concentration of 10⁻⁹ M, respectively. These results indicate that TBT and TPT act as inhibitors of ER-dependent reporter gene transcriptional activation and of the interaction between hERbeta LBD and the co-activator SRC1 in the yeast two-hybrid system. Consequently, our data could partly explain the occurrence of organotin compound-induced imposex on the endocrine system of mammals, including humans.

Sesquiterpenoids from myrrh inhibit androgen receptor expression and function in human prostate cancer cells

To examine whether two naturally occurring sesquiterpenoids (ST1 and ST2) with anti-proliferative activity in prostate cancer cells inhibit androgen receptor (AR) signaling. Human prostate cancer cell lines LNCaP and PC3 were used. The expression of AR, AR translocation into the nucleus, and expression levels of AR coactivators ARA70 and steroid receptor coactivator-1 (SRC-1) in LNCaP cells were examined using real-time PCR and Western blot. Changes in prostate-specific antigen (PSA) protein levels, PSA promoter activity, and androgen response element (ARE)-mediated reporter gene activity were examined using enzyme-linked immunoabsorbent assay (ELISA) and transient transfection assays. Co-immunoprecipitation was performed to analyze the interaction between AR and the AR coactivators in ST1- and ST2-treated cells. In LNCaP cells, ST1 and ST2 (40 μmol/L) led to a significant decrease in the expression of AR as well as a reduction of AR translocation into the nucleus, but had no effect on AR protein translation. ST1 and ST2 treatment also resulted in a significant decrease in the level of PSA protein secreted into the medium and was able to suppress PSA promoter-dependent and ARE-dependent luciferase activity. Furthermore, decreased expression of ARA70 and SRC-1 was observed when LNCaP cells were exposed to ST1 and ST2, which interfered with their ability to interact with AR. The observations suggest that suppression of AR transactivation by ST1 and ST2 may be mediated, in part, by inhibiting AR nuclear translocation and/or interfering with the interaction between AR and its coactivators ARA70 and SRC-1. Therefore, sesquiterpenoids could be developed as novel therapeutic agents for treating prostate cancer.

Drug–drug interactions by azole antifungals: Beyond a dogma of CYP3A4 enzyme activity inhibition

Azoles antifungals are widespread used drugs for various medicinal indications. These drugs are well known for their numerous drug–drug interactions, which are believed to occur via inhibition of CYP3A4 enzymatic activity and consequently altering pharmacokinetic of co-administered drugs. In the current communication a complex view on the molecular interactions between azoles antimycotics and CYP3A4 is presented. Beside inhibition of CYP3A4 catalytic activity, azoles influence transcriptional activity of pregnane X receptor (PXR) and consequently expression of drug-metabolizing enzymes, including CYP3A4. Interactions between azoles and PXR occur by multiple mechanisms, including modulation of ligand-dependent activation of PXR (agonism, antagonism) or affecting recruitment of PXR co-activators SRC-1 (steroid receptor co-activator 1) and HNF4α (hepatocyte nuclear factor 4α). Miconazole and ketoconazole are antagonists of glucocorticoid receptor (GR), therefore these drugs inhibit GR-mediated expression of PXR and drug metabolizing cytochromes P450. In addition, PXR and GR are key regulators of intermediary metabolism (e.g. carbohydrate, lipids or bile acids homeostasis) and many other cellular functions (e.g. immune response), hence, the interactions between azoles and PXR/GR are of broader physiological importance. In conclusion, while inhibition of CYP3A4 enzymatic activity by azoles is considered as primary cause of azoles drug–drug interactions, the effects of azoles on PXR and GR should be taken in account. Apart from CYP3A4, azoles influence the expression and activity of others drug-metabolizing cytochromes P450.

Ligand-dependent degradation of SRC-1 is pivotal for progesterone receptor transcriptional activity.

The progesterone receptor (PR), a ligand-activated transcription factor, recruits the primary coactivator steroid receptor coactivator-1 (SRC-1) gene promoters. It is known that PR transcriptional activity is paradoxically coupled to its ligand-dependent down-regulation. However, despite its importance in PR function, the regulation of SRC-1 expression level during hormonal exposure is poorly understood. Here we report that SRC-1 expression level (but not other p160 family members) is down-regulated by the agonist ligand R5020 in a PR-dependent manner. In contrast, the antagonist RU486 fails to induce down-regulation of the coactivator and impairs PR agonist-dependent degradation of SRC-1. We show that SRC-1 proteolysis is a proteasome- and ubiquitin-mediated process that, predominantly but not exclusively, occurs in the cytoplasmic compartment in which SRC-1 colocalizes with proteasome antigens as demonstrated by confocal imaging. Moreover, SRC-1 was stabilized in the presence of leptomycin B or several proteasomal inhibitors. Two degradation motifs, amino-acids 2-16 corresponding to a PEST motif and amino acids 41-136 located in the basic helix loop helix domain of the coactivator, were identified and shown to control the stability as well as the hormone-dependent down-regulation of the coactivator. SRC-1 degradation is of physiological importance because the two nondegradable mutants that still interacted with PR as demonstrated by coimmunoprecipitation failed to stimulate transcription of exogenous and endogenous target genes, suggesting that concomitant PR/SRC-1 ligand-dependent degradation is a necessary step for PR transactivation activity. Collectively our findings are consistent with the emerging role of proteasome-mediated proteolysis in the gene-regulating process and indicate that the ligand-dependent down-regulation of SRC-1 is critical for PR transcriptional activity.

PIASy inhibits LRH-1-dependent CYP11A1 expression by competing for SRC-1 binding

The orphan nuclear receptor LRH-1 (liver receptor homologue-1; NR5A2) plays a critical role in development, bile acid synthesis and cholesterol metabolism. LRH-1 is also expressed in the ovary where it is implicated in the regulation of steroidogenic genes for steroid hormone synthesis. In the present study, we investigated the molecular mechanisms of the transcriptional regulation of CYP11A1 by LRH-1 and found that LRH-1-mediated transactivation was markedly repressed by PIASy [protein inhibitor of activated STAT (signal transducer and activator of transcription) y], the shortest member of the PIAS family. The suppression of LRH-1 activity requires the N-terminal repression domain. Although PIAS proteins also function as E3 SUMO (small ubiquitin-related modifier) ligases and enhance SUMO conjugation, PIASy-mediated repression was independent of LRH-1 SUMOylation status. In addition, histone deacetylase activity was not involved in the inhibition of LRH-1 by PIASy. Immunoprecipitation and mammalian two-hybrid analyses indicated that PIASy interacted with LRH-1 through the C-terminal region, including the AF-2 (activation function-2) motif, which was also involved in the interaction between LRH-1 and the co-activator SRC-1 (steroid receptor co-activator-1). PIASy inhibited the binding of SRC-1 to LRH-1, although overexpression of SRC-1 partially overcame the PIASy inhibition of LRH-1 induction of the CYP11A1 promoter. The results of the present study suggest that competition with co-activators may be an important mechanism underlying the PIASy repression of LRH-1-mediated transactivation.

AN S296R MUTATION IN THE HUMAN ANDROGEN RECEPTOR CAUSES ACTIVATION OF THE RECEPTOR BY NON-ANDROGENIC STEROIDS AND STRONGER INHIBITION BY THE NUCLEAR RECEPTOR COREPRESSOR N-coR

Mutation of the androgen receptor (AR) is believed to contribute to androgen-independent growth of prostate cancer. In the present study, we examined the functional changes associated with the novel somatic mutation S296R in the N-terminal domain of the AR identified from one recurrent prostate cancer sample. The results indicate that the S296R mutation does not differ obviously from the wild-type AR in its ability to bind the synthetic androgen methyltrienolone, or in its transcriptional activity induced by dihydrotestosterone (DHT) in the absence or presence of the overexpression of coactivators (steroid receptor coactivator-1, transcription intermediary factor-2, cAMP response element-binding protein-binding protein and p300). However, S296R was found to differ from wild-type AR in that its transcriptional activity could be activated by high concentrations (1 micromol/L) of 17beta-oestradiol and progesterone and its transactivity induced by DHT was more obviously inhibited by overexpression of the nuclear receptor corepressor N-coR in CV-1 cells. These findings indicate that a point mutation (S296R) in the N-terminal domain of the AR can decrease the ligand specificity of the AR and alter the interaction between S296R and the corepressor N-coR.

The Peripheral Benzodiazepine Receptor Ligand 1-(2-Chlorophenyl-methylpropyl)-3-isoquinoline-carboxamide Is a Novel Antagonist of Human Constitutive Androstane Receptor

As a promiscuous xenobiotic sensor, the constitutive androstane receptor (CAR; NR1I3) regulates the expression of multiple drug-metabolizing enzymes and transporters in liver. The constitutively activated nature of CAR in the cell-based transfection assays has hindered its use as a predictor of metabolism-based drug-drug interactions. Here, we have identified 1-(2-chlorophenylmethylpropyl)-3-isoquinoline-carboxamide (PK11195), a typical peripheral benzodiazepine receptor (PBR) ligand, as a selective and potent inhibitor of human (h) CAR. In cell-based transfection assays, PK11195 inhibited the constitutive activity of hCAR more than 80% at the concentration of 10 microM, and the PK11195-inhibited activity was efficiently reactivated by the direct CAR activator, 6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl) oxime, but not by the indirect hCAR activator, phenobarbital. Mammalian two-hybrid and GST pull-down assays showed that PK11195 repressed the interactions of hCAR with the coactivators steroid receptor coactivator-1 and glucocorticoid receptor-interacting protein 1 to inhibit hCAR activity. The inhibition by PK11195 specifically occurred to the hCAR: PK1195 strongly activated human pregnane X receptor (PXR), whereas it did not alter the activity of the mouse CAR and mouse PXR. In addition, PBR played no role in the PK11195 inhibition of hCAR because the inhibition fully occurred in the HeLa cells in which the PBR was knocked down by small interfering RNA. In the Car(-/-) mouse liver, PK11195 translocated enhanced yellow fluorescent protein-hCAR into the nucleus. These results are consistent with the conclusion that PK11195 is a novel hCAR-specific antagonist that represses the CAR-coactivator interactions to inhibit the receptor activity inside the nucleus. Thus, PK11195 can be used as a chemical tool for studying the molecular basis of CAR function.

Estradiol Regulates Corticotropin-Releasing Hormone Gene (crh) Expression in a Rapid and Phasic Manner that Parallels Estrogen Receptor-α and -β Recruitment to a 3′,5′-Cyclic Adenosine 5′-Monophosphate Regulatory Region of the Proximal crh Promoter

In the central nervous system, CRH regulates several affective states. Dysregulation of neuronal crh expression in the paraventricular nucleus of the hypothalamus correlates with some forms of depression, and amygdalar crh expression may modulate levels of anxiety. Because estrogens modulate these states, we sought to determine 17beta-estradiol (E2) effects on crh expression. CRH mRNA levels were measured in the AR-5 amygdaloid cell line by RT-PCR analysis. They increased by 1 min of E2 treatment, suggesting that crh behaves as an immediate-early gene. After peaking at 3 min, CRH mRNA returned to basal levels and then increased by 60 min. To dissect some of the molecular mechanisms underlying these events, we measured occupancy of the crh promoter by estrogen receptors (ERs) and coactivators, using chromatin immunoprecipitation. Because this promoter does not contain palindromic estrogen response elements, we targeted the region of a cAMP regulatory element (CRE), implicated in crh regulation. The temporal pattern of the mRNA response was mimicked by recruitment of ERalpha and -beta, phospho-CRE-binding protein, coactivators steroid receptor coactivator-1 and CRE-binding protein-binding protein (CBP), and an increase in histone 3 and 4 acetylation. Lastly, ERalpha and -beta loading were temporally dissociated, peaking at 1 and 3 min, respectively. The ER peaks were associated with coactivators and acetylation patterns. ERalpha associated with phospho-CRE-binding protein, CBP, steroid receptor coactivator-1, and increased acetylated histone 3. ERbeta associated with CBP and increased acetylated histone 4. The tight temporal correlation between E2-induced CRH mRNA levels and promoter occupancy by ERs strongly suggest that E2 regulates crh expression through an ERalpha- and/or ERbeta-CRE alternate pathway.