c-Myb interacts with the glucocorticoid receptor and regulates its level in pre-B-acute lymphoblastic leukemia cells

Glucocorticoid enhances presenilin1-dependent Aβ production at ER's mitochondrial-associated membrane by downregulating Rer1 in neuronal cells

Stress-induced release of glucocorticoid is an important amyloidogenic factor that upregulates amyloid precursor protein (APP) and β secretase 1 (BACE1) levels. Glucocorticoid also contributes to the pathogenesis of Alzheimer's disease (AD) by increasing ER-mitochondria connectivity, in which amyloid β (Aβ) processing occurs rigorously because of its lipid raft-rich characteristics. However, the mechanism by which glucocorticoid enhances γ-secretase activity in the mitochondrial-associated membrane of ER (MAM) and subsequent accumulation of mitochondrial Aβ is unclear. In this study, we determined how glucocorticoid enhances Aβ production in MAM using SH-SY5Y cells and ICR mice. First, we observed that cortisol-induced Aβ accumulation in mitochondria preceded its extracellular apposition by enhancing γ-secretase activity, which was the result of increased presenilin 1 (PSEN1) localization in MAM. Screening data revealed that cortisol selectively downregulated the ER retrieval protein Rer1, which triggered its maturation and subsequent entry into the endocytic secretory pathway of PSEN1. Accordingly, overexpression of RER1 reversed the deleterious effects of mitochondrial Aβ on mitochondrial respiratory function and neuronal cell viability. Notably, we found that cortisol guided the glucocorticoid receptor (GR) to bind directly to the RER1 promoter, thus trans-repressing its expression. Inhibiting GR function reduced Aβ accumulation at mitochondria and improved the outcome of a spatial memory task in mice exposed to corticosterone. Taken together, glucocorticoid enhances PSEN1-mediated Aβ generation at MAM by downregulating Rer1, which is a potential target at early stages of AD pathogenesis.

A phase I study of the combination of palbociclib and dexamethasone for the treatment of relapsed or refractory B-cell acute lymphoblastic leukemia

PURPOSE

Despite advances in the treatment of B-cell acute lymphoblastic leukemia (B-ALL), outcomes for relapsed/refractory (R/R) disease remain poor. Preclinical studies suggest that the combination of the CDK4/6 inhibitor palbociclib and dexamethasone may be effective in targeting leukemic cell growth. We conducted a phase I study of escalating doses of palbociclib in combination with dexamethasone in adults with R/R B-ALL.

METHODS

Cycle 1 consisted of single agent palbociclib given for 7 days and continued for 28 additional days in combination with dexamethasone 20 mg daily. Palbociclib dosing began at 100 mg daily. Patients with a response were eligible for maintenance consisting of 1 week of palbociclib plus dexamethasone (20 mg daily × 2 days, 16 mg daily × 2 days, 12 mg daily × 2 days, 6 mg daily × 1 day), followed by 3 weeks of palbociclib alone. Safety, efficacy, and the expression of phospho-RB and c-MYB/BCL-2 were measured.

CONCLUSIONS

Seven patients were treated on study before it was closed early due to slow accrual. No dose limiting toxicities were identified. One patient had a complete response with incomplete hematologic recovery, suggesting possible efficacy of the treatment. Reduction in CD34+ cells, p-RB, c-MYB, and BCL-2 expression also suggested on-target therapy effects.

MYB interacts with androgen receptor, sustains its ligand-independent activation and promotes castration resistance in prostate cancer

BACKGROUND

Aberrant activation of androgen receptor signalling following castration therapy is a common clinical observation in prostate cancer (PCa). Earlier, we demonstrated the role of MYB overexpression in androgen-depletion resistance and PCa aggressiveness. Here, we investigated MYB-androgen receptor (AR) crosstalk and its functional significance.

METHODS

Interaction and co-localization of MYB and AR were examined by co-immunoprecipitation and immunofluorescence analyses, respectively. Protein levels were measured by immunoblot analysis and enzyme-linked immunosorbent assay. The role of MYB in ligand-independent AR transcriptional activity and combinatorial gene regulation was studied by promoter-reporter and chromatin immunoprecipitation assays. The functional significance of MYB in castration resistance was determined using an orthotopic mouse model.

RESULTS

MYB and AR interact and co-localize in the PCa cells. MYB-overexpressing PCa cells retain AR in the nucleus even when cultured under androgen-deprived conditions. AR transcriptional activity is also sustained in MYB-overexpressing cells in the absence of androgens. MYB binds and promotes AR occupancy to the KLK3 promoter. MYB-overexpressing PCa cells exhibit greater tumorigenicity when implanted orthotopically and quickly regain growth following castration leading to shorter mice survival, compared to those carrying low-MYB-expressing prostate tumours.

CONCLUSIONS

Our findings reveal a novel MYB-AR crosstalk in PCa and establish its role in castration resistance.

Overcoming Glucocorticoid Resistance in Acute Lymphoblastic Leukemia: Repurposed Drugs Can Improve the Protocol

Glucocorticoids (GCs) are a central component of multi-drug treatment protocols against T and B acute lymphoblastic leukemia (ALL), which are used intensively during the remission induction to rapidly eliminate the leukemic blasts. The primary response to GCs predicts the overall response to treatment and clinical outcome. In this review, we have critically analyzed the available data on the effects of GCs on sensitive and resistant leukemic cells, in order to reveal the mechanisms of GC resistance and how these mechanisms may determine a poor outcome in ALL. Apart of the GC resistance, associated with a decreased expression of receptors to GCs, there are several additional mechanisms, triggered by alterations of different signaling pathways, which cause the metabolic reprogramming, with an enhanced level of glycolysis and oxidative phosphorylation, apoptosis resistance, and multidrug resistance. Due to all this, the GC-resistant ALL show a poor sensitivity to conventional chemotherapeutic protocols. We propose pharmacological strategies that can trigger alternative intracellular pathways to revert or overcome GC resistance. Specifically, we focused our search on drugs, which are already approved for treatment of other diseases and demonstrated anti-ALL effects in experimental pre-clinical models. Among them are some “truly” re-purposed drugs, which have different targets in ALL as compared to other diseases: cannabidiol, which targets mitochondria and causes the mitochondrial permeability transition-driven necrosis, tamoxifen, which induces autophagy and cell death, and reverts GC resistance through the mechanisms independent of nuclear estrogen receptors (“off-target effects”), antibiotic tigecycline, which inhibits mitochondrial respiration, causing energy crisis and cell death, and some anthelmintic drugs. Additionally, we have listed compounds that show a classical mechanism of action in ALL but are not used still in treatment protocols: the BH3 mimetic venetoclax, which inhibits the anti-apoptotic protein Bcl-2, the hypomethylating agent 5-azacytidine, which restores the expression of the pro-apoptotic BIM, and compounds targeting the PI3K-Akt-mTOR axis. Accordingly, these drugs may be considered for the inclusion into chemotherapeutic protocols for GC-resistant ALL treatments.

The role of glucocorticoid receptor (GR) polymorphisms in human erythropoiesis

Glucocorticoids are endogenous steroid hormones that regulate several biological functions including proliferation, differentiation and apoptosis in numerous cell types in response to stress. Synthetic glucocorticoids, such as dexamethasone (Dex) are used to treat a variety of diseases ranging from allergy to depression. Glucocorticoids exert their effects by passively entering into cells and binding to a specific Glucocorticoid Receptor (GR) present in the cytoplasm. Once activated by its ligand, GR may elicit cytoplasmic (mainly suppression of p53), and nuclear (regulation of transcription of GR responsive genes), responses. Human GR is highly polymorphic and may encode > 260 different isoforms. This polymorphism is emerging as the leading cause for the variability of phenotype and response to glucocorticoid therapy observed in human populations. Studies in mice and clinical observations indicate that GR controls also the response to erythroid stress. This knowledge has been exploited in-vivo by using synthetic GR agonists for treatment of the erythropoietin-refractory congenic Diamond Blackfan Anemia and in-vitro to develop culture conditions that may theoretically generate red cells in numbers sufficient for transfusion. However, the effect exerted by GR polymorphism on the variability of the phenotype of genetic and acquired erythroid disorders observed in the human population is still poorly appreciated. This review will summarize current knowledge on the biological activity of GR and of its polymorphism in non-hematopoietic diseases and discuss the implications of these observations for erythropoiesis.

Ectopic microRNA-150-5p transcription sensitizes glucocorticoid therapy response in MM1S multiple myeloma cells but fails to overcome hormone therapy resistance in MM1R cells

Glucocorticoids (GCs) selectively trigger cell death in the multiple myeloma cell line MM1S which express NR3C1/Glucocorticoid Receptor (GR) protein, but fail to kill MM1R cells which lack GR protein. Given recent demonstrations of altered microRNA profiles in a diverse range of haematological malignancies and drug resistance, we characterized GC inducible mRNA and microRNA transcription profiles in GC sensitive MM1S as compared to GC resistant MM1R cells. Transcriptome analysis revealed that GCs regulate expression of multiple genes involved in cell cycle control, cell organization, cell death and immunological disease in MM1S cells, which remain unaffected in MM1R cells. With respect to microRNAs, mir-150-5p was identified as the most time persistent GC regulated microRNA, out of 5 QPCR validated microRNAs (mir-26b, mir-125a-5p, mir-146-5p, mir-150-5p, and mir-184), which are GC inducible in MM1S but not in MM1R cells. Functional studies further revealed that ectopic transfection of a synthetic mir-150-5p mimics GR dependent gene expression changes involved in cell death and cell proliferation pathways. Remarkably, despite the gene expression changes observed, overexpression of mir-150-5p in absence of GCs did not trigger significant cytotoxicity in MM1S or MM1R cells. This suggests the requirement of additional steps in GC induced cell death, which can not be mimicked by mir-150-5p overexpression alone. Interestingly, a combination of mir-150-5p transfection with low doses GC in MM1S cells was found to sensitize therapy response, whereas opposite effects could be observed with a mir-150-5p specific antagomir. Although mir-150-5p overexpression did not substantially change GR expression levels, it was found that mir-150-5p evokes GR specific effects through indirect mRNA regulation of GR interacting transcription factors and hormone receptors, GR chaperones, as well as various effectors of unfolded protein stress and chemokine signalling. Altogether GC-inducible mir-150-5p adds another level of regulation to GC specific therapeutic responses in multiple myeloma.

Modulation of the long terminal repeat promoter activity of small ruminant lentiviruses by steroids

Production and excretion of small ruminant lentiviruses (SRLVs) varies with the stage of the host reproductive cycle, suggesting hormonal involvement in this variation. Stress may also affect viral expression. To determine if hormones affect SRLV transcriptional activity, the expression of green fluorescent protein (GFP) driven by the promoters in the U3-cap region of the long terminal repeats (LTRs) of different strains of SRLV was assessed in cell culture. High concentrations of steroids (progesterone, cortisol and dehydroepiandrosterone) inhibited expression of GFP driven by SRLV promoters. This effect decreased in a dose-dependent manner with decreasing concentrations of steroids. In some strains, physiological concentrations of cortisol or dehydroepiandrosterone (DHEA) induced the expression of GFP above the baseline. There was strain variation in sensitivity to hormones, but this differed for different hormones. The presence of deletions and a 43 base repeat in the U3 region upstream of the TATA box of the LTR made strain EV1 less sensitive to DHEA. However, no clear tendencies or patterns were observed when comparing strains of different genotypes and/or subtypes, or those triggering different forms of disease.

Epigenetic alteration by DNA-demethylating treatment restores apoptotic response to glucocorticoids in dexamethasone-resistant human malignant lymphoid cells

Background

Glucocorticoids (GCs) are often included in the therapy of lymphoid malignancies because they kill several types of malignant lymphoid cells. GCs activate the glucocorticoid receptor (GR), to regulate a complex genetic network, culminating in apoptosis. Normal lymphoblasts and many lymphoid malignancies are sensitive to GC-driven apoptosis. Resistance to GCs can be a significant clinical problem, however, and correlates with resistance to several other major chemotherapeutic agents.

Methods

We analyzed the effect of treatment with the cytosine analogue 5 aza-2’ deoxycytidine (AZA) on GC resistance in two acute lymphoblastic leukemia (T or pre-T ALL) cell lines- CEM and Molt-4- and a (B-cell) myeloma cell line, RPMI 8226. Methods employed included tissue culture, flow cytometry, and assays for clonogenicity, cytosine extension, immunochemical identification of proteins, and gene transactivation. High throughput DNA sequencing was used to confirm DNA methylation status.

Conclusions

Treatment of these cells with AZA resulted in altered DNA methylation and restored GC-evoked apoptosis in all 3 cell lines. In CEM cells the altered epigenetic state resulted in site-specific phosphorylation of the GR, increased GR potency, and GC-driven induction of the GR from promoters that lie in CpG islands. In RPMI 8226 cells, expression of relevant coregulators of GR function was altered. Activation of p38 mitogen-activated protein kinase (MAPK), which is central to a feed-forward mechanism of site-specific GR phosphorylation and ultimately, apoptosis, occurred in all 3 cell lines. These data show that in certain malignant hematologic B- and T-cell types, epigenetically controlled GC resistance can be reversed by cell exposure to a compound that causes DNA demethylation. The results encourage studies of application to in vivo systems, looking towards eventual clinical applications.