Differential targeting of androgen and glucocorticoid receptors induces ER stress and apoptosis in prostate cancer cells: a novel therapeutic modality

Glucocorticoid Receptor (GR) Activation Is Associated with Increased cAMP/PKA Signaling in Castration-Resistant Prostate Cancer

In castration-resistant prostate cancer (CRPC), increased glucocorticoid receptor (GR) expression and ensuing transcriptional activity have been proposed as an oncogenic "bypass" mechanism in response to androgen receptor (AR) signaling inhibition (ARSi). Here, we report that GR transcriptional activity acquired following ARSi is associated with the upregulation of cyclic adenosine monophosphate (cAMP)-associated gene expression pathways in both model systems and metastatic prostate cancer patient samples. In the context of ARSi, the expression of GR-mediated genes encoding cAMP signaling pathway-associated proteins can be inhibited by treatment with selective GR modulators (SGRMs). For example, in the context of ARSi, we found that GR activation resulted in upregulation of protein kinase inhibitor beta (PKIB) mRNA and protein levels, leading to nuclear accumulation of the cAMP-dependent protein kinase A catalytic subunit (PKA-c). Increased PKA-c, in turn, is associated with increased cAMP response element-binding protein phosphorylation and activity. Furthermore, enzalutamide and SGRM combination therapy in mice bearing CRPC xenografts delayed CRPC progression compared with enzalutamide therapy alone, and reduced tumor PKIB mRNA expression. Supporting the clinical importance of GR/PKA signaling activation in CRPC, we found a significant enrichment of both cAMP pathway signaling-associated gene expression and high NR3C1 (GR) activity in patient-derived xenograft models and metastatic human CRPC samples. These findings suggest a novel mechanism linking CRPC-induced GR transcriptional activity with increased cAMP signaling in AR-antagonized CRPC. Furthermore, our findings suggest that GR-specific modulation in addition to AR antagonism may delay GR+ CRPC time to recurrence, at least in part, by inhibiting tumor cAMP/PKA pathways.

Glucocorticoid Receptor and β-Catenin Interact in Prostate Cancer Cells and Their Co-Inhibition Attenuates Tumorsphere Formation, Stemness, and Docetaxel Resistance

Therapy resistance hinders the efficacy of anti-androgen therapies and taxane-based chemotherapy for advanced prostate cancer (PCa). Glucocorticoid receptor (GR) signaling mediates resistance to androgen receptor signaling inhibitors (ARSI) and has also been recently implicated in PCa resistance to docetaxel (DTX), suggesting a role in therapy cross-resistance. Like GR, β-catenin is upregulated in metastatic and therapy-resistant tumors and is a crucial regulator of cancer stemness and ARSI resistance. β-catenin interacts with AR to promote PCa progression. Given the structural and functional similarities between AR and GR, we hypothesized that β-catenin also interacts with GR to influence PCa stemness and chemoresistance. As expected, we observed that treatment with the glucocorticoid dexamethasone promotednuclear accumulation of GR and active β-catenin in PCa cells. Co-immunoprecipitation studies showed that GR and β-catenin interact in DTX-resistant and DTX-sensitive PCa cells. Pharmacological co-inhibition of GR and β-catenin, using the GR modulator CORT-108297 and the selective β-catenin inhibitor MSAB, enhanced cytotoxicity in DTX-resistant PCa cells grown in adherent and spheroid cultures and decreased CD44+/CD24- cell populations in tumorspheres. These results indicate that GR and β-catenin influence cell survival, stemness, and tumorsphere formation in DTX-resistant cells. Their co-inhibition could be a promising therapeutic strategy to overcome PCa therapy cross-resistance.

Antiproliferative Activity of Two Unusual Dimeric Flavonoids, Brachydin E and Brachydin F, Isolated from Fridericia platyphylla (Cham.) L.G.Lohmann: In Vitro and Molecular Docking Evaluation

Despite the breakthrough in the development of anticancer therapies, plant-derived chemotherapeutics continue to be the basis of treatment for most types of cancers. Fridericia platyphylla is a shrub found in Brazilian cerrado biome which has cytotoxic, anti-inflammatory, and analgesic properties. The aim of this study was to investigate the antiproliferative potential of the crude hydroethanolic extract, subfraction (containing 59.3% of unusual dimeric flavonoids Brachydin E and 40.7% Brachydin F), as well as Brachydin E and Brachydin F isolated from F. platyphylla roots. The cytotoxic activity was evaluated in glioblastoma, lung, prostate, and colorectal human tumor cell lines. The crude hydroethanolic extract did not present cytotoxic activity, but its subfraction presented lower IC50 values for glioblastoma (U-251) and prostate adenocarcinoma (PC-3) cell lines. Brachydins E and F significantly reduced cell viability, proliferation, and clonogenic potential of PC-3, inducing them to the process of regulated cell death. In silico studies have indicated nuclear receptors as targets for Brachydins E and F, and molecular docking has pointed out their binding into glucocorticoid receptor (GR) ligand pocket. Targeting GR pathway has been described as a therapeutic strategy, especially for prostate cancer. These results suggest that Brachydin E and Brachydin F are promising compounds to be further explored for their antitumor effects.

Phase I/II trial of enzalutamide and mifepristone, a glucocorticoid receptor antagonist, for metastatic castration-resistant prostate cancer

PURPOSE

Although androgen deprivation therapy (ADT) and androgen receptor signaling inhibitors (ARSI) are effective in metastatic prostate cancer (PC), resistance occurs in most patients. This phase I/II trial assessed the safety, pharmacokinetic impact, and efficacy of the glucocorticoid receptor (GR) antagonist mifepristone (Mif) in combination with enzalutamide (Enz) for castration-resistant PC (CRPC).

PATIENTS AND METHODS

106 patients with CRPC were accrued. Phase I subjects were treated with Enz monotherapy at 160 mg per day for 28 days to allow steady-state accumulation. Patients then entered the dose escalation combination portion of the study. In phase II, patients were randomized 1:1 to either receive Enz alone or Enz plus Mif. The primary endpoint was PSA progression free survival (PFS), with radiographic PFS, and PSA response rate (RR) as key secondary endpoints. Circulating tumor cells were collected before randomization for exploratory translational biomarker studies.

RESULTS

We determined a 25% dose reduction in Enz, when added to Mif resulted in equivalent drug levels compared to full dose Enz and was well tolerated. However, the addition of Mif to Enz following a 12-week Enz lead-in did not delay time to PSA, radiographic or clinical PFS. The trial was terminated early due to futility.

CONCLUSION

This is the first prospective trial of dual AR-GR antagonism in CRPC. Enz combined with Mif was safe and well tolerated but did not meet its primary endpoint. The development of more specific GR antagonists combined with AR antagonists, potentially studied in an earlier disease state, should be explored.

The efficacy and mechanism of proteasome inhibitors in solid tumor treatment

BACKGROUND

The ubiquitin-proteasome system (UPS) is critical in cellular protein degradation and widely involved in the regulations of cancer hallmarks. Targeting the UPS pathway has emerged as a promising novel treatment in hematological malignancies and solid tumors.

OBJECTIVE

This review mainly focuses on the preclinical results of proteasome inhibitors in solid tumors.

METHODS

We analyzed the published articles associated with the anticancer results of proteasome inhibitors alone or combination chemotherapy in solid tumors. Important data presented in abstract form were also discussed in this review.

RESULTS/CONCLUSION

Proteasome inhibitors, such as bortezomib and carfilzomib, are highly effective in treating solid tumors. The anticancer efficacy is not limited to affect the proteasomal inhibition-associated signaling pathways but also widely involves the signaling pathways related to cell cycle, apoptosis, and epithelial-mesenchymal transition (EMT). In addition, proteasome inhibitors overcome the conventional chemo-resistance of standard chemotherapeutics by inhibiting signaling pathways, such as NF-κB or PI3K/Akt. Combination chemotherapy of proteasome inhibitors and standard chemotherapeutics are widely investigated in multiple relapsed or chemo-resistant solid tumor types, such as breast cancer and pancreatic cancer. The proteasome inhibitors re-sensitize the standard chemotherapeutic regimens and induce synergistic anticancer effects. The development of novel proteasome inhibitors and delivery systems also improves the proteasome inhibitors' anticancer efficacy in solid tumors. This review summarizes the current preclinical results of proteasome inhibitors in solid tumors and reveals the potential anticancer mechanisms.

Preclinical Models in Prostate Cancer: Resistance to AR Targeting Therapies in Prostate Cancer

Prostate cancer is an androgen-driven tumor. Different prostate cancer therapies consequently focus on blocking the androgen receptor pathway. Clinical studies reported tumor resistance mechanisms by reactivating and bypassing the androgen pathway. Preclinical models allowed the identification, confirmation, and thorough study of these pathways. This review looks into the current and future role of preclinical models to understand resistance to androgen receptor-targeted therapies. Increasing knowledge on this resistance will greatly improve insights into tumor pathophysiology and future treatment strategies in prostate cancer.

SGK1 in Human Cancer: Emerging Roles and Mechanisms

Serum and glucocorticoid-induced protein kinase 1 (SGK1) is a member of the "AGC" subfamily of protein kinases, which shares structural and functional similarities with the AKT family of kinases and displays serine/threonine kinase activity. Aberrant expression of SGK1 has profound cellular consequences and is closely correlated with human cancer. SGK1 is considered a canonical factor affecting the expression and signal transduction of multiple genes involved in the genesis and development of many human cancers. Abnormal expression of SGK1 has been found in tissue and may hopefully become a useful indicator of cancer progression. In addition, SGK1 acts as a prognostic factor for cancer patient survival. This review systematically summarizes and discusses the role of SGK1 as a diagnostic and prognostic biomarker of diverse cancer types; focuses on its essential roles and functions in tumorigenesis, cancer cell proliferation, apoptosis, invasion, metastasis, autophagy, metabolism, and therapy resistance and in the tumor microenvironment; and finally summarizes the current understanding of the regulatory mechanisms of SGK1 at the molecular level. Taken together, this evidence highlights the crucial role of SGK1 in tumorigenesis and cancer progression, revealing why it has emerged as a potential target for cancer therapy.

Preclinical studies using cisplatin/carboplatin to restore the Enzalutamide sensitivity via degrading the androgen receptor splicing variant 7 (ARv7) to further suppress Enzalutamide resistant prostate cancer

The FDA-approved anti-androgen Enzalutamide (Enz) has been used successfully as the last line therapy to extend castration-resistant prostate cancer (CRPC) patients’ survival by an extra 4.8 months. However, CRPC patients eventually develop Enz-resistance that may involve the induction of the androgen receptor (AR) splicing variant ARv7. Here we found that Cisplatin (Cis) or Carboplatin, currently used in chemotherapy/radiation therapy to suppress tumor progression, could restore the Enz sensitivity in multiple Enz-resistant (EnzR) CRPC cells via directly degrading/suppressing the ARv7. Combining Cis or Carboplatin with Enz therapy can also delay the development of Enz-resistance in CRPC C4-2 cells. Mechanism dissection found that Cis or Carboplatin might decrease the ARv7 expression via multiple mechanisms including targeting the lncRNA-Malat1/SF2 RNA splicing complex and increasing ARv7 degradation via altering ubiquitination. Preclinical studies using in vivo mouse model with implanted EnzR1-C4-2 cells also demonstrated that Cis plus Enz therapy resulted in better suppression of EnzR CRPC progression than Enz treatment alone. These results not only unveil the previously unrecognized Cis mechanism to degrade ARv7 via targeting the Malat1/SF2 complex and ubiquitination signals, it may also provide a novel and ready therapy to further suppress the EnzR CRPC progression in the near future.

Anti-Proliferative Effects of Compound A and Its Effect in Combination with Cisplatin in Cholangiocarcinoma Cells

BACKGROUND

Cholangiocarcinoma (CCA) is a fatal cancer with high resistance to anticancer drugs.  The development of new drugs or compounds to be used alone or in combination with currently available chemotherapeutic agents to improve the treatment of CCA is needed. Compound A (CpdA), which is a small plant-derived glucocorticoid receptor modulator, strongly inhibited the growth and survival of several cancers.  However, the effect of CpdA on cholangiocarcinoma has not been elucidated. The aim of this study was to investigate the effect of CpdA on CCA.

METHODS

Cytotoxicity of CpdA was tested in primary cells including peripheral blood mononuclear cells (PBMCs), fibroblasts, and human umbilical vein endothelial cells (HUVECs), as well as on CCA cell lines (KKU-100, KKU-055, and KKU-213) was examined. Cell cycle distribution and IL-6 expression was assessed by flow cytometry and real-time polymerase chain reaction, respectively.  The effect of combination CpdA and cisplatin was evaluated by cell viability assay.

RESULTS

CpdA significantly inhibited cell cycle at G1 phase in CCA cell lines, and reduced IL-6 mRNA expression.  However, combination CpdA and cisplatin did not enhance the inhibitory effect. TGFβR-II expression was increased in CCA cells after the combination treatment.

CONCLUSIONS

These results indicate the potential of CpdA for CCA treatment. However, combination treatment with CpdA and cisplatin increased CCA cell survival. The molecular mechanism is likely attributable to promotes cell survival via the TGFβR-II signaling pathway. The combination of CpdA with other anticancer drugs for CCA treatment should be further examined.

The prospect of serum and glucocorticoid-inducible kinase 1 (SGK1) in cancer therapy: a rising star

Serum and glucocorticoid-inducible kinase 1 (SGK1) is an AGC kinase that has been reported to be involved in a variety of physiological and pathological processes. Recent evidence has accumulated that SGK1 acts as an essential Akt-independent mediator of phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) signaling pathway in cancer. SGK1 is overexpressed in several tumors, including prostate cancer, colorectal carcinoma, glioblastoma, breast cancer, and endometrial cancer. The functions of SGK1 include regulating tumor growth, survival, metastasis, autophagy, immunoregulation, calcium (Ca²⁺) signaling, cancer stem cells, cell cycle, and therapeutic resistance. In this review, we introduce the pleiotropic role of SGK1 in the development and progression of tumors, summarize its downstream targets, and integrate the knowledge provided by preclinical studies that the prospect of SGK1 inhibition as a potential therapeutic approach.

Cellular rewiring in lethal prostate cancer: the architect of drug resistance

Over the past 5 years, the advent of combination therapeutic strategies has substantially reshaped the clinical management of patients with advanced prostate cancer. However, most of these combination regimens were developed empirically and, despite offering survival benefits, are not enough to halt disease progression. Thus, the development of effective therapeutic strategies that target the mechanisms involved in the acquisition of drug resistance and improve clinical trial design are an unmet clinical need. In this context, we hypothesize that the tumour engineers a dynamic response through the process of cellular rewiring, in which it adapts to the therapy used and develops mechanisms of drug resistance via downstream signalling of key regulatory cascades such as the androgen receptor, PI3K-AKT or GATA2-dependent pathways, as well as initiation of biological processes to revert tumour cells to undifferentiated aggressive states via phenotype switching towards a neuroendocrine phenotype or acquisition of stem-like properties. These dynamic responses are specific for each patient and could be responsible for treatment failure despite multi-target approaches. Understanding the common stages of these cellular rewiring mechanisms to gain a new perspective on the molecular underpinnings of drug resistance might help formulate novel combination therapeutic regimens.

Lineage plasticity-mediated therapy resistance in prostate cancer

Therapy resistance is a significant challenge for prostate cancer treatment in clinic. Although targeted therapies such as androgen deprivation and androgen receptor (AR) inhibition are effective initially, tumor cells eventually evade these strategies through multiple mechanisms. Lineage reprogramming in response to hormone therapy represents a key mechanism that is increasingly observed. The studies in this area have revealed specific combinations of alterations present in adenocarcinomas that provide cells with the ability to transdifferentiate and perpetuate AR-independent tumor growth after androgen-based therapies. Interestingly, several master regulators have been identified that drive plasticity, some of which also play key roles during development and differentiation of the cell lineages in the normal prostate. Thus, further study of each AR-independent tumor type and understanding underlying mechanisms are warranted to develop combinational therapies that combat lineage plasticity in prostate cancer.

Disease- and treatment-associated acquired glucocorticoid resistance

The development of resistance to glucocorticoids (GCs) in therapeutic regimens poses a major threat. Generally, GC resistance is congenital or acquired over time as a result of disease progression, prolonged GC treatment or, in some cases, both. Essentially, disruptions in the function and/or pool of the glucocorticoid receptor α (GRα) underlie this resistance. Many studies have detailed how alterations in GRα function lead to diminished GC sensitivity; however, the current review highlights the wealth of data concerning reductions in the GRα pool, mediated by disease-associated and treatment-associated effects, which contribute to a significant decrease in GC sensitivity. Additionally, the current understanding of the molecular mechanisms involved in driving reductions in the GRα pool is discussed. After highlighting the importance of maintaining the level of the GRα pool to combat GC resistance, we present current strategies and argue that future strategies to prevent GC resistance should involve biased ligands with a predisposition for reduced GR dimerization, a strategy originally proposed as the SEMOGRAM-SEDIGRAM concept to reduce the side-effect profile of GCs.

Lessons from the SWITCH trial: changing glucocorticoids in the management of metastatic castration-resistant prostate cancer (mCRPC)

Abiraterone acetate plus prednisone is a standard treatment option for mCRPC. The phase II SWITCH trial showed that further prostate-specific antigen (PSA) responses can be obtained in a subset of patients when prednisone was switched to dexamethasone at progression. Here, we discuss the potential underlying mechanisms, including the activation of glucocorticoid receptors (GR) in progressive mCRPC and the implications for clinical practice.

ADT with antiandrogens in prostate cancer induces adverse effect of increasing resistance, neuroendocrine differentiation and tumor metastasis

Prostate cancer (PCa) is the most common cancer and the 2nd leading cause of cancer-related deaths among men in the United States. Androgen-deprivation-therapy (ADT) with antiandrogens to target the androgens/androgen receptor (AR) signals remains the standard therapy for advanced PCa. However, most of the PCa patients who received ADT with antiandrogens, including the recently developed Enzalutamide (Enz) that might extend PCa patients survival an extra 4.8 months, will still develop the castration (or antiandrogen) resistance. Mechanism dissection studies suggest these antiandrogen resistances may involve the induction of AR splicing variants and/or AR mutants. Further preclinical in vitro/in vivo studies suggest ADT-antiandrogens may also enhance the neuroendocrine differentiation (NED) and PCa cell invasion, and these unwanted side-effects may function through various mechanisms including altering the infiltrating inflammatory cells within the prostate tumor microenvironment. This review summarizes these unwanted ADT-induced side-effects and discusses multiple approaches to overcome these side-effects to better suppress the PCa at the castration resistant stage.

Glucocorticoid-activated IRE1α/XBP-1s signaling: an autophagy-associated protective pathway against endotheliocyte damage

Glucocorticoid-induced endothelial injury has been reported in several diseases. Although there are several theories, the exact mechanism underlying the role of glucocorticoids in this process remains unclear. Autophagy has been reported to occur as a response to different stimuli and can affect cell survival and function. In this study, we found that glucocorticoids induced apoptosis and endoplasmic reticulum (ER) stress in endotheliocytes. Furthermore, we discovered that glucocorticoids induced autophagy in these cells and the inositol requiring protein 1 (IRE1α)/X-box binding protein 1s (XBP-1s) axis, one of the downstream signaling pathways of ER stress, was associated with the glucocorticoid-induced autophagy. The autophagy partly protected endotheliocytes from glucocorticoid-induced apoptosis and inhibition of proliferation. In conclusion, glucocorticoid-induced endoplasmic reticulum stress activated the IRE1α/XBP-1s signaling and induced autophagy, which, in turn, played a protective role in endotheliocyte survival and proliferation, avoiding further cellular damage caused by glucocorticoids.

Targeting the Hsp40/Hsp70 Chaperone Axis as a Novel Strategy to Treat Castration-Resistant Prostate Cancer

Castration-resistant prostate cancer (CRPC) is characterized by reactivation of androgen receptor (AR) signaling, in part by elevated expression of AR splice variants (ARv) including ARv7, a constitutively active, ligand binding domain (LBD)-deficient variant whose expression has been correlated with therapeutic resistance and poor prognosis. In a screen to identify small-molecule dual inhibitors of both androgen-dependent and androgen-independent AR gene signatures, we identified the chalcone C86. Binding studies using purified proteins and CRPC cell lysates revealed C86 to interact with Hsp40. Pull-down studies using biotinylated-C86 found Hsp40 present in a multiprotein complex with full-length (FL-) AR, ARv7, and Hsp70 in CRPC cells. Treatment of CRPC cells with C86 or the allosteric Hsp70 inhibitor JG98 resulted in rapid protein destabilization of both FL-AR and ARv, including ARv7, concomitant with reduced FL-AR- and ARv7-mediated transcriptional activity. The glucocorticoid receptor, whose elevated expression in a subset of CRPC also leads to androgen-independent AR target gene transcription, was also destabilized by inhibition of Hsp40 or Hsp70. In vivo, Hsp40 or Hsp70 inhibition demonstrated single-agent and combinatorial activity in a 22Rv1 CRPC xenograft model. These data reveal that, in addition to recognized roles of Hsp40 and Hsp70 in FL-AR LBD remodeling, ARv lacking the LBD remain dependent on molecular chaperones for stability and function. Our findings highlight the feasibility and potential benefit of targeting the Hsp40/Hsp70 chaperone axis to treat prostate cancer that has become resistant to standard antiandrogen therapy.Significance: These findings highlight the feasibility of targeting the Hsp40/Hsp70 chaperone axis to treat CRPC that has become resistant to standard antiandrogen therapy. Cancer Res; 78(14); 4022-35. ©2018 AACR.

Effect of combining glucocorticoids with Compound A on glucocorticoid receptor responsiveness in lymphoid malignancies

Glucocorticoids (GCs) are a cornerstone in the treatment of lymphoid malignancies such as multiple myeloma (MM) and acute lymphoblastic leukemia (ALL). Yet, prolonged GC use is hampered by deleterious GC-related side effects and the emergence of GC resistance. To tackle and overcome these GC-related problems, the applicability of selective glucocorticoid receptor agonists and modulators was studied, in search of fewer side-effects and at least equal therapeutic efficacy as classic GCs. Compound A (CpdA) is a prototypical example of such a selective glucocorticoid receptor modulator and does not support GR-mediated transactivation. Here, we examined whether the combination of CpdA with the classic GC dexamethasone (Dex) may improve GC responsiveness of MM and ALL cell lines. We find that the combination of Dex and CpdA does not substantially enhance GC-mediated cell killing. In line, several apoptosis hallmarks, such as caspase 3/7 activity, PARP cleavage and the levels of cleaved-caspase 3 remain unchanged upon combining Dex with CpdA. Moreover, we monitor no additional inhibition of cell proliferation and the homologous downregulation of GR is not counteracted by the combination of Dex and CpdA. In addition, CpdA is unable to modulate Dex-liganded GR transactivation and transrepression, yet, Dex-mediated transrepression is also aberrant in these lymphoid cell lines. Together, transrepression-favoring compounds, alone or combined with GCs, do not seem a valid strategy in the treatment of lymphoid malignancies.

Compound A attenuates toll-like receptor 4-mediated paclitaxel resistance in breast cancer and melanoma through suppression of IL-8

Background

Paclitaxel (PTX) is a potent anti-cancer drug commonly used for the treatment of advanced breast cancer (BCA) and melanoma. Toll-like receptor 4 (TLR4) promotes the production of pro-inflammatory cytokines associated with cancer chemoresistance. This study aims to explore the effect of TLR4 in PTX resistance in triple-negative BCA and advanced melanoma and the effect of compound A (CpdA) to attenuate this resistance.

Methods

BCA and melanoma cell lines were checked for the response to PTX by cytotoxic assay. The response to PTX of TLR4-transient knockdown cells by siRNA transfection was evaluated compared to the control cells. Levels of pro-inflammatory cytokines, IL-6 and IL-8, and anti-apoptotic protein, XIAP were measured by real-time PCR whereas the secreted IL-8 was quantitated by ELISA in TLR4-transient knockdown cancer cells with or without CpdA treatment. The apoptotic cells after adding PTX alone or in combination with CpdA were detected by caspase-3/7 assay.

Results

PTX could markedly induce TLR4 expression in both MDA-MB-231 BCA and MDA-MB-435 melanoma cell lines having a basal level of TLR4 whereas no significant induction in TLR4-transient knockdown cells occurred. The siTLR4-treated BCA cells revealed more dead cells after PTX treatment than that of mock control cells. IL-6, IL-8 and XIAP showed increased expressions in PTX-treated cells and this over-production effect was inhibited in TLR4-transient knockdown cells. Apoptotic cells were detected higher when PTX and CpdA were combined than PTX treatment alone. Isobologram exhibited the synergistic effect of CpdA and PTX. CpdA could significantly decrease expressions of IL-6, XIAP and IL-8, as well as excreted IL-8 levels together with reduced cancer viability after PTX treatment.

Conclusions

The acquired TLR4-mediated PTX resistance in BCA and melanoma is explained partly by the paracrine effect of IL-6 and IL-8 released into the tumor microenvironment and over-production of anti-apoptotic protein, XIAP, in BCA cells and importantly CpdA could reduce this effect and sensitize PTX-induced apoptosis in a synergistic manner. In conclusion, the possible impact of TLR4-dependent signaling pathway in PTX resistance in BCA and melanoma is proposed and using PTX in combination with CpdA may attenuate TLR4-mediated PTX resistance in the treatment of the patients.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4155-6) contains supplementary material, which is available to authorized users.

Age-related cataracts: Role of unfolded protein response, Ca2+ mobilization, epigenetic DNA modifications, and loss of Nrf2/Keap1 dependent cytoprotection

Age-related cataracts are closely associated with lens chronological aging, oxidation, calcium imbalance, hydration and crystallin modifications. Accumulating evidence indicates that misfolded proteins are generated in the endoplasmic reticulum (ER) by most cataractogenic stresses. To eliminate misfolded proteins from cells before they can induce senescence, the cells activate a clean-up machinery called the ER stress/unfolded protein response (UPR). The UPR also activates the nuclear factor-erythroid-2-related factor 2 (Nrf2), a central transcriptional factor for cytoprotection against stress. Nrf2 activates nearly 600 cytoprotective target genes. However, if ER stress reaches critically high levels, the UPR activates destructive outputs to trigger programmed cell death. The UPR activates mobilization of ER-Ca2+ to the cytoplasm and results in activation of Ca2+-dependent proteases to cleave various enzymes and proteins which cause the loss of normal lens function. The UPR also enhances the overproduction of reactive oxygen species (ROS), which damage lens constituents and induce failure of the Nrf2 dependent cytoprotection. Kelch-like ECH-associated protein 1 (Keap1) is an oxygen sensor protein and regulates the levels of Nrf2 by the proteasomal degradation. A significant loss of DNA methylation in diabetic cataracts was found in the Keap1 promoter, which overexpresses the Keap1 protein. Overexpressed Keap1 significantly decreases the levels of Nrf2. Lower levels of Nrf2 induces loss of the redox balance toward to oxidative stress thereby leading to failure of lens cytoprotection. Here, this review summarizes the overall view of ER stress, increases in Ca2+ levels, protein cleavage, and loss of the well-established stress protection in somatic lens cells.

Strategies to avoid treatment-induced lineage crisis in advanced prostate cancer

The increasing potency of therapies that target the androgen receptor (AR) signalling axis has correlated with a rise in the proportion of patients with prostate cancer harbouring an adaptive phenotype, termed treatment-induced lineage crisis. This phenotype is characterized by features that include soft-tissue metastasis and/or resistance to standard anticancer therapies. Potent anticancer treatments might force cancer cells to evolve and develop alternative cell lineages that are resistant to primary therapies, a mechanism similar to the generation of multidrug- resistant microorganisms after continued antibiotic use. Herein, we assess the hypothesis that treatment-adapted phenotypes harbour reduced AR expression and/or activity, and acquire compensatory strategies for cell survival. We highlight the striking similarities between castration-resistant prostate cancer and triple-negative breast cancer, another poorly differentiated endocrine malignancy. Alternative treatment paradigms are needed to avoid therapy-induced resistance. Herein, we present a new clinical trial strategy designed to evaluate the potential of rapid drug cycling as an approach to delay the onset of resistance and treatment-induced lineage crisis in patients with metastatic castration-resistant prostate cancer.

Selective Glucocorticoid Receptor Modulators (SGRMs) Delay Castrate-Resistant Prostate Cancer Growth

Increased glucocorticoid receptor (GR) expression and activity following androgen blockade can contribute to castration-resistant prostate cancer (CRPC) progression. Therefore, we hypothesized that GR antagonism will have therapeutic benefit in CRPC. However, the FDA-approved nonselective, steroidal GR antagonist, mifepristone, lacks GR specificity, reducing its therapeutic potential. Here, we report that two novel nonsteroidal and highly selective GR modulators (SGRM), CORT118335 and CORT108297, have the ability to block GR activity in prostate cancer and slow CRPC progression. In contrast to mifepristone, these novel SGRMs did not affect androgen receptor (AR) signaling, but potently inhibited GR transcriptional activity. Importantly, SGRMs decreased GR-mediated tumor cell viability following AR blockade. In vivo, SGRMs significantly inhibited CRPC progression in high GR-expressing, but not in low GR-expressing xenograft models. Transcriptome analysis following AR blockade and GR activation revealed that these SGRMs block GR-mediated proliferative gene expression pathways. Furthermore, GR-regulated proliferation-associated genes AKAP12, FKBP5, SGK1, CEBPD, and ZBTB16 are inhibited by CORT108297 treatment in vivo Together, these data suggest that GR-selective nonsteroidal SGRMs potently inhibit GR activity and prostate cancer growth despite AR pathway inhibition, demonstrating the therapeutic potential of SGRMs in GR-expressing CRPC. Mol Cancer Ther; 16(8); 1680-92. ©2017 AACR.

Role of steroid receptor and coregulator mutations in hormone-dependent cancers

Steroid hormones mediate critical lineage-specific developmental and physiologic responses. They function by binding their cognate receptors, which are transcription factors that drive specific gene expression programs. The requirement of most prostate cancers for androgen and most breast cancers for estrogen has led to the development of endocrine therapies that block the action of these hormones in these tumors. While initial endocrine interventions are successful, resistance to therapy often arises. We will review how steroid receptor-dependent genomic signaling is affected by genetic alterations in endocrine therapy resistance. The detailed understanding of these interactions will not only provide improved treatment options to overcome resistance, but, in the future, will also be the basis for implementing precision cancer medicine approaches.

Discovery of Compound A--a selective activator of the glucocorticoid receptor with anti-inflammatory and anti-cancer activity

Glucocorticoids are among the most effective anti-inflammatory drugs, and are widely used for cancer therapy. Unfortunately, chronic treatment with glucocorticoids results in multiple side effects. Thus, there was an intensive search for selective glucocorticoid receptor (GR) activators (SEGRA), which retain therapeutic potential of glucocorticoids, but with fewer adverse effects. GR regulates gene expression by transactivation (TA), by binding as homodimer to gene promoters, or transrepression (TR), via diverse mechanisms including negative interaction between monomeric GR and other transcription factors. It is well accepted that metabolic and atrophogenic effects of glucocorticoids are mediated by GR TA. Here we summarized the results of extensive international collaboration that led to discovery and characterization of Compound A (CpdA), a unique SEGRA with a proven “dissociating” GR ligand profile, preventing GR dimerization and shifting GR activity towards TR both in vitro and in vivo. We outlined here the unusual story of compound's discovery, and presented a comprehensive overview of CpdA ligand properties, its anti-inflammatory effects in numerous animal models of inflammation and autoimmune diseases, as well as its anti-cancer effects. Finally, we presented mechanistic analysis of CpdA and glucocorticoid effects in skin, muscle, bone, and regulation of glucose and fat metabolism to explain decreased CpdA side effects compared to glucocorticoids. Overall, the results obtained by our and other laboratories underline translational potential of CpdA and its derivatives for treatment of inflammation, autoimmune diseases and cancer.

Glucocorticoid receptor antagonism reverts docetaxel resistance in human prostate cancer

Resistance to docetaxel is a major clinical problem in advanced prostate cancer (PCa). Although glucocorticoids (GCs) are frequently used in combination with docetaxel, it is unclear to what extent GCs and their receptor, the glucocorticoid receptor (GR), contribute to the chemotherapy resistance. In this study, we aim to elucidate the role of the GR in docetaxel-resistant PCa in order to improve the current PCa therapies. GR expression was analyzed in a tissue microarray of primary PCa specimens from chemonaive and docetaxel-treated patients, and in cultured PCa cell lines with an acquired docetaxel resistance (PC3-DR, DU145-DR, and 22Rv1-DR). We found a robust overexpression of the GR in primary PCa from docetaxel-treated patients and enhanced GR levels in cultured docetaxel-resistant human PCa cells, indicating a key role of the GR in docetaxel resistance. The capability of the GR antagonists (RU-486 and cyproterone acetate) to revert docetaxel resistance was investigated and revealed significant resensitization of docetaxel-resistant PCa cells for docetaxel treatment in a dose- and time-dependent manner, in which a complete restoration of docetaxel sensitivity was achieved in both androgen receptor (AR)-negative and AR-positive cell lines. Mechanistically, we demonstrated down-regulation of Bcl-xL and Bcl-2 upon GR antagonism, thereby defining potential treatment targets. In conclusion, we describe the involvement of the GR in the acquisition of docetaxel resistance in human PCa. Therapeutic targeting of the GR effectively resensitizes docetaxel-resistant PCa cells. These findings warrant further investigation of the clinical utility of the GR antagonists in the management of patients with advanced and docetaxel-resistant PCa.

Selective Activator of the Glucocorticoid Receptor Compound A Dissociates Therapeutic and Atrophogenic Effects of Glucocorticoid Receptor Signaling in Skin

Background:

Glucocorticoids are effective anti-inflammatory drugs widely used in dermatology and for the treatment of blood cancer patients. Unfortunately, chronic treatment with glucocorticoids results in serious metabolic and atrophogenic adverse effects including skin atrophy. Glucocorticoids act via the glucocorticoid receptor (GR), a transcription factor that causes either gene transactivation (TA) or transrepression (TR). Compound A (CpdA), a novel non-steroidal GR ligand, does not promote GR dimerization and TA, retains anti-inflammatory potential but induces fewer metabolic side effects compared to classical glucocorticoids when used systemically. As topical effects of CpdA have not been well studied, this work goal was to compare the anti-inflammatory and side effects of topical CpdA and glucocorticoids and to assess their effect on GR TA and TR in keratinocytes.

Methods:

We used murine immortalized keratinocytes and F1 C57BlxDBA mice. Effect of glucocorticoid fluocinolone acetonide (FA) and CpdA on gene expression in keratinocytes in vitro and in vivo was evaluated by reverse transcription-PCR. The anti-inflammatory effects were assessed in the model of tumor promoter 12-O-tertradecanoyl-acetate (TPA)-induced dermatitis and in croton oil-induced ear edema test. Skin atrophy was assessed by analysis of epidermal thickness, keratinocyte proliferation, subcutaneous adipose hypoplasia, and dermal changes after chronic treatment with FA and CpdA.

Results:

In mouse keratinocytes in vitro and in vivo, CpdA did not activate GR-dependent genes but mimicked closely the inhibitory effect of glucocorticoid FA on the expression of inflammatory cytokines and matrix metalloproteinases. When applied topically, CpdA inhibited TPA-induced skin inflammation and hyperplasia. Unlike glucocorticoids, CpdA itself did not induce skin atrophy which correlated with lack of induction of atrophogene regulated in development and DNA damage response 1 (REDD1) causatively involved in skin and muscle steroid-induced atrophy.

Conclusions:

Overall, our results suggest that CpdA and its derivatives represent novel promising class of anti-inflammatory compounds with reduced topical side effects.

The influence of prednisone on the efficacy of docetaxel in men with metastatic castration-resistant prostate cancer

BACKGROUND

Prednisone and other corticosteroids can provide palliation and tumor responses in patients with prostate cancer. The combination of docetaxel and prednisone was the first treatment shown to prolong survival in men with metastatic castration-resistant prostate cancer (mCRPC). Since the approval of docetaxel in 2004, additional treatments are available, including abiraterone, which is also administered with prednisone. Therefore, patients are increasingly likely to have prednisone therapy several times throughout their disease course, and the contribution of prednisone to the efficacy of docetaxel is unknown.

METHODS

We conducted a retrospective study of patients with mCPRC treated with docetaxel at our institution between 2004–2014. Patients were divided into 2 cohorts based upon whether prednisone was co-administered with docetaxel. Cohorts were further stratified based upon prior prednisone (with abiraterone) or hydrocortisone (with ketoconazole) use. The primary endpoint was clinical/radiographic progression-free survival (PFS). The secondary endpoints were >50% PSA response rate and PSA progression-free survival (PSA-PFS). A multivariable cox regression model was constructed to determine if prednisone use was independently predictive of PFS.

RESULTS

We identified 200 consecutive patients for inclusion in the study: 131 men received docetaxel with prednisone and 69 received docetaxel alone. The docetaxel-prednisone cohort had superior PFS compared to the docetaxel-alone cohort (median PFS: 7.8 vs 6.2 months, HR 0.68 [95% CI 0.48–0.97], p=0.03). Prednisone was associated with a reduced risk of progression on docetaxel in the propensity score-weighted multivariable Cox model (p=0.002). Among abiraterone- or ketoconazole-pretreated patients, no difference in PFS was observed between prednisone-containing and non-prednisone containing cohorts (median PFS: 7.1 vs 6.3 months, HR 0.96 [95% CI 0.59–1.57], p=0.87).

CONCLUSIONS

The incorporation of prednisone potentially augments the efficacy of docetaxel in patients with mCRPC. We hypothesize that this advantage is limited to patients who have not previously received corticosteroids. Prospective confirmation is needed.

EGCG antagonizes Bortezomib cytotoxicity in prostate cancer cells by an autophagic mechanism

The proteasome inhibitors Bortezomib (BZM) and MG132 trigger cancer cell death via induction of endoplasmic reticulum (ER) stress and unfolded protein response. Epigallocatechin gallate (EGCG), the most bioactive green tea polyphenol, is known to display strong anticancer properties as it inhibits proteasome activity and induces ER stress. We investigated whether combined delivery of a proteasome inhibitor with EGCG enhances prostate cancer cell death through increased induction of ER stress. Paradoxically, EGCG antagonized BZM cytotoxicity even when used at low concentrations. Conversely, the MG132 dose-response curve was unaffected by co-administration of EGCG. Moreover, apoptosis, proteasome inhibition and ER stress were inhibited in PC3 cells simultaneously treated with BZM and EGCG but not with a combination of MG132 and EGCG; EGCG enhanced autophagy induction in BZM-treated cells only. Autophagy inhibition restored cytotoxicity concomitantly with CHOP and p-eIF2α up-regulation in cells treated with BZM and EGCG. Overall, these findings demonstrate that EGCG antagonizes BZM toxicity by exacerbating the activation of autophagy, which in turn mitigates ER stress and reduces CHOP up-regulation, finally protecting PC3 cells from cell death.

Therapy escape mechanisms in the malignant prostate

Androgen receptor (AR) is the main target for prostate cancer therapy. Clinical approaches for AR inactivation include chemical castration, inhibition of androgen synthesis and AR antagonists (anti-androgens). However, treatment resistance occurs for which an important number of therapy escape mechanisms have been identified. Herein, we summarise the current knowledge of molecular mechanisms underlying therapy resistance in prostate cancer. Moreover, the tumour escape mechanisms are arranged into the concepts of target modification, bypass signalling, histologic transformation, cancer stem cells and miscellaneous mechanisms. This may help researchers to compare and understand same or similar concepts of therapy resistance in prostate cancer and other cancer types.

Maternal Obesity, Cage Density, and Age Contribute to Prostate Hyperplasia in Mice

Identification of modifiable risk factors is gravely needed to prevent adverse prostate health outcomes. We previously developed a murine precancer model in which exposure to maternal obesity stimulated prostate hyperplasia in offspring. Here, we used generalized linear modeling to evaluate the influence of additional environmental covariates on prostate hyperplasia. As expected from our previous work, the model revealed that aging and maternal diet-induced obesity (DIO) each correlated with prostate hyperplasia. However, prostate hyperplasia was not correlated with the length of maternal DIO. Cage density positively associated with both prostate hyperplasia and offspring body weight. Expression of the glucocorticoid receptor in prostates also positively correlated with cage density and negatively correlated with age of the animal. Together, these findings suggest that prostate tissue was adversely patterned during early life by maternal overnutrition and was susceptible to alteration by environmental factors such as cage density. Additionally, prostate hyperplasia may be acutely influenced by exposure to DIO, rather than occurring as a response to worsening obesity and comorbidities experienced by the mother. Finally, cage density correlated with both corticosteroid receptor abundance and prostate hyperplasia, suggesting that overcrowding influenced offspring prostate hyperplasia. These results emphasize the need for multivariate regression models to evaluate the influence of coordinated variables in complicated animal systems.

Determinants of Receptor- and Tissue-Specific Actions in Androgen Signaling

The physiological androgens testosterone and 5α-dihydrotestosterone regulate the development and maintenance of primary and secondary male sexual characteristics through binding to the androgen receptor (AR), a ligand-dependent transcription factor. In addition, a number of nonreproductive tissues of both genders are subject to androgen regulation. AR is also a central target in the treatment of prostate cancer. A large number of studies over the last decade have characterized many regulatory aspects of the AR pathway, such as androgen-dependent transcription programs, AR cistromes, and coregulatory proteins, mostly in cultured cells of prostate cancer origin. Moreover, recent work has revealed the presence of pioneer/licensing factors and chromatin modifications that are important to guide receptor recruitment onto appropriate chromatin loci in cell lines and in tissues under physiological conditions. Despite these advances, current knowledge related to the mechanisms responsible for receptor- and tissue-specific actions of androgens is still relatively limited. Here, we review topics that pertain to these specificity issues at different levels, both in cultured cells and tissues in vivo, with a particular emphasis on the nature of the steroid, the response element sequence, the AR cistromes, pioneer/licensing factors, and coregulatory proteins. We conclude that liganded AR and its DNA-response elements are required but are not sufficient for establishment of tissue-specific transcription programs in vivo, and that AR-selective actions over other steroid receptors rely on relaxed rather than increased stringency of cis-elements on chromatin.

Investigation the mechanism of the apoptosis induced by lactacystin in gastric cancer cells

The study aims to investigate the relationship between nuclear factor (nuclear factor kappa B (NF-κB)) viability and lactacystin-mediated cell apoptosis in gastric cancer cells. Two gastric cancer cell lines (MKN28 and SGC7901) were treated with lactacystin-a proteasome inhibitor for 24 h. The cell viability, toxicity, and death were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. DNA binding viability of NF-κB and caspase-3 viability were analyzed by ELISA; the expression of p65 NF-κB nuclear protein was detected by immunocytochemistry and Western blot. Lactacystin reduced DNA binding viability of NF-κB (t = 3.0,P = 0.013) and the NF-κB viability (compared to the 5, 10 μmol/L MKN28 cell (p53 mutant) line, P < 0.001) and the expression of p65 NF-κB nuclear protein decreased parallelled to concentrations of lactacystin in MKN28 cell line, while without obvious effects on NF-κB viability in SGC7901 cell line (P = 0.381), while the viability of caspase-3 increased also along with the raising of lactacystin concentrations (compared to control, 5 μmol/L: SGC7901 cell line P = 0.029, MKN28 cell line P < 0.001; 10 μmol/L: SGC7901 cell line, P < 0.001, MKN28 cell line, P < 0.001). It was concluded that lactacystin had diversified killing effects on gastric cancer cells. The mechanism may be related to induce the apoptosis by downregulation of nuclear factor kappa B viability. There may be additional cell survival/death pathway in SGC7901 gastric cancer cells.

Emerging mechanisms of enzalutamide resistance in prostate cancer

The majority of prostate cancers are hormone-dependent at diagnosis highlighting the central role of androgen signalling in this disease. Surprisingly, most forms of castration-resistant prostate cancer (CRPC) are still dependent on the androgen receptor (AR) for survival. Therefore, the advent of new AR-targeting drugs, such as enzalutamide, is certainly beneficial for the many patients with metastatic CRPC. Indeed, this compound provides a substantial survival benefit-but it is not curative. This Perspectives article describes the different ways through which cancer cells can become resistant to enzalutamide, such as AR truncation and other mutations, as well as by-pass of the AR dependence of prostate cancer cells through expression of the glucocorticoid receptor. The clinical relevance of these mechanisms and emerging questions concerning new therapeutic regimens in the treatment of metastatic CRPC are being discussed.

Reduced glucocorticoid receptor expression predicts bladder tumor recurrence and progression

OBJECTIVES

To assess the levels of glucocorticoid receptor (GR) expression in bladder tumors because the status and its prognostic value remain largely unknown.

METHODS

We immunohistochemically stained for GR in bladder tumor and matched non-neoplastic bladder tissue specimens.

RESULTS

Overall, GR was positive in 129 (87%) of 149 urothelial tumors, which was significantly (P=.026) lower than in non-neoplastic urothelium (90 [96%] of 94). Forty-two (79%) of 53 low-grade tumors vs 45 (47%) of 96 high-grade carcinomas (P<.001) and 61 (73%) of 84 non-muscle-invasive (NMI) tumors vs 26 (40%) of 65 muscle-invasive (MI) carcinomas (P<.001) were moderately to strongly immunoreactive for GR. Kaplan-Meier and log-rank tests revealed that loss or weak positivity of GR significantly or marginally correlated with recurrence of NMI tumors (P=.025), progression of MI tumors (P=.082), and cancer-specific survival of MI tumors (P=.067). Multivariate analysis identified low GR expression as a strong predictor for recurrence of NMI tumors (P=.034).

CONCLUSIONS

GR expression was downregulated in bladder tumors compared with nonneoplastic bladder tumors and in high-grade/MI tumors compared with low-grade/NMI tumors. Decreased expression of GR, as an independent prognosticator, predicted recurrence of NMI tumors. These results support experimental evidence suggesting an inhibitory role of GR signals in bladder cancer outgrowth.

Interaction of the glucocorticoid and androgen receptors in adipogenesis

Glucocorticoids and androgens are important regulators of adipose tissue function. A new study by Hartig et al. in this issue of Chemistry & Biology provides relevant information regarding androgen receptor activity and its link to glucocorticoid action in human adipocytes during the process of preadipocyte differentiation.

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.

Receptor-based targeting of therapeutics

Receptor-based targeting of therapeutics may be a fascinating proposition to improve the therapeutic efficacy of encapsulated drugs. The development of safe and effective nanomedicines is a prerequisite in the current nanotechnological scenario. Currently, the surface engineering of nanocarriers has attracted great attention for targeted therapeutic delivery by selective binding of targeting ligand to the specific receptors present on the surface of cells. In this review, we have discussed the current status of various receptors such as transferrin, lectoferrin, lectin, folate, human EGF receptor, scavenger, nuclear and integrin, which are over-expressed on the surface of cancer cells; along with the relevance of targeted delivery systems such as nanoparticles, polymersomes, dendrimers, liposomes and carbon nanotubes. The review also focuses on the effective utilization of receptor-based targeted delivery systems for the management of cancer in effective ways by minimizing the drug-associated side effects and improving the therapeutic efficacy of developed nano-architectures.

Transcriptional cross talk between orphan nuclear receptor ERRγ and transmembrane transcription factor ATF6α coordinates endoplasmic reticulum stress response

Orphan nuclear receptor ERRγ is a member of nuclear receptor superfamily that regulates several important cellular processes including hepatic glucose and alcohol metabolism. However, mechanistic understanding of transcriptional regulation of the ERRγ gene remains to be elucidated. Here, we report that activating transcription factor 6α (ATF6α), an endoplasmic reticulum (ER)-membrane–bound basic leucine zipper (bZip) transcription factor, directly regulates ERRγ gene expression in response to ER stress. ATF6α binds to ATF6α responsive element in the ERRγ promoter. The transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α) is required for this transactivation. Chromatin immunoprecipitation (ChIP) assay confirmed the binding of both ATF6α and PGC1α on the ERRγ promoter. ChIP assay demonstrated histone H3 and H4 acetylation occurs at the ATF6α and PGC1α binding site. Of interest, ERRγ along with PGC1α induce ATF6α gene transcription upon ER stress. ERRγ binds to an ERRγ responsive element in the ATF6α promoter. ChIP assay confirmed that both ERRγ and PGC1α bind to a site in the ATF6α promoter that exhibits histone H3 and H4 acetylation. Overall, for the first time our data show a novel pathway of cross talk between nuclear receptors and ER-membrane–bound transcription factors and suggest a positive feed-forward loop regulates ERRγ and ATF6α gene transcription.

FoxA1 specifies unique androgen and glucocorticoid receptor binding events in prostate cancer cells

The forkhead protein FoxA1 has functions other than a pioneer factor, in that its depletion brings about a significant redistribution in the androgen receptor (AR) and glucocorticoid receptor (GR) cistromes. In this study, we found a novel function for FoxA1 in defining the cell-type specificity of AR- and GR-binding events in a distinct fashion, namely, for AR in LNCaP-1F5 cells and for GR in VCaP cells. We also found different, cell-type and receptor-specific compilations of cis-elements enriched adjacent to the AR- and GR-binding sites. The AR pathway is central in prostate cancer biology, but the role of GR is poorly known. We find that AR and GR cistromes and transcription programs exhibit significant overlap, and GR regulates a large number of genes considered to be AR pathway-specific. This raises questions about the role of GR in maintaining the AR pathway under androgen-deprived conditions in castration-resistant prostate cancer patients. However, in the presence of androgen, ligand-occupied GR acts as a partial antiandrogen and attenuates the AR-dependent transcription program. .

Combination of a selective activator of the glucocorticoid receptor Compound A with a proteasome inhibitor as a novel strategy for chemotherapy of hematologic malignancies

Glucocorticoids are widely used for the treatment of hematological malignancies; however, their chronic use results in numerous metabolic side effects. Thus, the development of selective glucocorticoid receptor (GR) activators (SEGRA) with improved therapeutic index is important. GR regulates gene expression via (1) transactivation that requires GR homodimer binding to gene promoters and is linked to side effects and (2) transrepression-mediated via negative GR interaction with other transcription factors. Novel GR modulator Compound A (CpdA) prevents GR dimerization, retains glucocorticoid anti-inflammatory activity and has fewer side effects compared with glucocorticoids in vivo. Here we tested CpdA anticancer activity in human T- and B-lymphoma and multiple myeloma cells expressing GR and their counterparts with silenced GR. We found that CpdA in GR-dependent manner strongly inhibited growth and viability of human T-, B-lymphoma and multiple myeloma cells. Furthermore, primary leukemia cell cultures from T-ALL patients appeared to be equally sensitive to glucocorticoid dexamethasone and CpdA. It is known that GR expression is controlled by proteasome. We showed that pretreatment of lymphoma CEM and NCEB cells with proteasome-inhibitor Bortezomib resulted in GR accumulation and enhanced ligand properties of CpdA, shifting GR activity toward transrepression evaluated by inhibition of NFкB and AP-1 transcription factors. We also revealed remarkable GR-dependent cooperation between CpdA and Bortezomib in suppressing growth and survival of T- and B-lymphoma and multiple myeloma MM.1S cells. Overall, our data provide the rationale for novel GR-based therapy for hematological malignancies based on combination of SEGRA with proteasome inhibitors.