90 results found
Perone Y, Magnani L, 2016, Going off the grid: ERα breast cancer beyond estradiol, Journal of Molecular Endocrinology, Vol: 57, Pages: F1-F5, ISSN: 1479-6813
Novel studies have linked cholesterol biosynthesis to drug resistance in luminal breast cancer. Structural data suggest that cholesterol metabolites, including 27-hydroxycholesterol (27-HC), can act as ERα ligands in these cells. Additionally, hypercholesterolemia has now been linked to breast cancer progression. The focus of this review is to briefly summarize these recent finding and discuss how epigenetic reprogramming is definitively connected to endogenous cholesterol biosynthesis. We elaborate on how these data support a working model in which cholesterol biosynthesis promotes autocrine, pro- invasive signaling via activation of a series of closely related transcription factors. Importantly, we discuss how this mechanism of resistance is specifically associated with aromatase inhibitors. Finally, we examine how the field is now considering the development of anti-cholesterol therapeutics and companion biomarkers to stratify and treat ERα breast cancer patients. In particular, we review recent progress in pharmaceutical strategies targeting the cholesterol molecular machinery in primary and secondary breast cancers.
Patel H, Abduljabbar R, Lai CF, et al., 2016, CDK7, cyclin H and MAT1 is elevated in breast cancer and is prognostic in estrogen receptor- positive breast cancer, Clinical Cancer Research, Vol: 22, Pages: 5929-5938, ISSN: 1557-3265
PURPOSE: CDK-activation kinase (CAK) is required for the regulation of the cell-cycle and is a trimeric complex consisting of Cyclin Dependent Kinase 7 (CDK7), Cyclin H and the accessory protein, MAT1. CDK7 also plays a critical role in regulating transcription, primarily by phosphorylating RNA polymerase II, as well as transcription factors such as estrogen receptor-alpha(ERalpha).). Deregulation of cell cycle and transcriptional control is aare general featurefeatures of cancertumor cells, highlighting the potential for the use of CDK7 inhibitors as novel cancer therapeutics in cancer. EXPERIMENTAL DESIGN: mRNA and protein expression of CDK7 and its essential co-factors cyclinH and MAT1, were evaluated in breast cancer samples to determine if their levels are altered in cancer. Immunohistochemical staining of >900 breast cancers was used to determine the association with clinicopathological features and patient outcome. RESULTS: We show that expression of CDK7, cyclinH and MAT1 are all closely linked at the mRNA and protein level and their expression is elevated in breast cancer compared with the normal breast tissue. Intriguingly, CDK7 expression was inversely proportional to tumour grade and size and outcome analysis showed an association between CAK levels and better outcome. Moreover, CDK7 expression was positively associated with ERalpha expression and in particular with phosphorylation of ERalpha at serine 118, a site important for ERalpha transcriptional activity. CONCLUSIONS: Expression of components of the CAK complex, CDK7, MAT1 and Cyclin H are elevated in breast cancer and correlates with ERalpha.. Like ERalpha, CDK7 expression is inversely proportional to poor prognostic factors and survival.
Bhat-Nakshatri P, Goswami CP, Badve S, et al., 2016, Molecular insights of pathways resulting from two common PIK3CA mutations in breast cancer, Cancer Research, Vol: 76, Pages: 3989-4001, ISSN: 1538-7445
The phosphatidylinositol 3-kinase (PI3K) pathway is activated in ~70% of breast cancers. PIK3CA gene mutations or amplifications that affect the PI3K p110α subunit account for activation of this pathway in 20-40% of cases, particularly in estrogen-receptor alpha (ERα)-positive breast cancers. AKT family of kinases, AKT1-3, are the downstream targets of PI3K and these kinases activate ERα. Although several inhibitors of PI3K have been developed, none has proven effective in the clinic, partly due to an incomplete understanding of the selective routing of PI3K signaling to specific AKT isoforms. Accordingly, we investigated in this study the contribution of specific AKT isoforms in connecting PI3K activation to ERα signaling, and we also assessed the utility of using the components of PI3K-AKT isoform-ERα signaling axis as predictive biomarkers of response to PI3K inhibitors. Using a variety of physiologically relevant model systems with defined natural or knock-in PIK3CA mutations and/or PI3K hyperactivation, we show that PIK3CA-E545K mutations (found in ~20% of PIK3CA-mutant breast cancers), but not PIK3CA-H1047R mutations (found in 55% of PIK3CA-mutant breast cancers), preferentially activate AKT1. Our findings argue that AKT1 signaling is needed to respond to estrogen and PI3K inhibitors in breast cancer cells with PIK3CA-E545K mutation, but not in breast cancer cells with other PIK3CA mutations. This study offers evidence that personalizing treatment of ER-positive breast cancers to PI3K inhibitor therapy may benefit from an analysis of PIK3CA-E545K-AKT1-estrogen signaling pathways.
Zhang Y, Clausmeyer J, Babakinejad B, et al., 2016, Spearhead Nanometric Field-Effect Transistor Sensors for Single-Cell Analysis., ACS Nano, Vol: 10, Pages: 3214-3221, ISSN: 1936-086X
Nanometric field-effect-transistor (FET) sensors are made on the tip of spear-shaped dual carbon nanoelectrodes derived from carbon deposition inside double-barrel nanopipettes. The easy fabrication route allows deposition of semiconductors or conducting polymers to comprise the transistor channel. A channel from electrodeposited poly pyrrole (PPy) exhibits high sensitivity toward pH changes. This property is exploited by immobilizing hexokinase on PPy nano-FETs to give rise to a selective ATP biosensor. Extracellular pH and ATP gradients are key biochemical constituents in the microenvironment of living cells; we monitor their real-time changes in relation to cancer cells and cardiomyocytes. The highly localized detection is possible because of the high aspect ratio and the spear-like design of the nano-FET probes. The accurately positioned nano-FET sensors can detect concentration gradients in three-dimensional space, identify biochemical properties of a single living cell, and after cell membrane penetration perform intracellular measurements.
Magnani L, Louloupi A, Zwart W, 2016, Histone Posttranslational Modifications in Breast Cancer and Their Use in Clinical Diagnosis and Prognosis, Epigenetic Biomarkers and Diagnostics, Pages: 467-477, ISBN: 9780128018996
© 2016 Elsevier Inc. All rights reserved. Epigenetic regulation plays a key role in normal physiology and disease. In breast cancer, multiple epigenetic regulators have been found to be causally involved in tumorigenesis and treatment resistance. Since treatment resistance in breast cancer is commonly observed, epigenetic modifiers may represent promising targets for pharmaceutical intervention. Multiple epigenetic modifiers are currently being targeted in clinical trials with varying success rates. Yet, biological roles of epigenetic modifiers are complex and lack tissue specificity, which may diminish any therapeutic window. Is epigenetic profiling the "new black" of biomarker discovery in breast cancer? and would epigenetic drugs yield the new "silver bullet" in breast cancer treatment, or are we dealing with a "red herring"?
Chen X, Jung JG, Shajahan-Haq AN, et al., 2015, ChIP-BIT: Bayesian inference of target genes using a novel joint probabilistic model of ChIP-seq profiles., Nucleic Acids Research, Vol: 44, ISSN: 1362-4962
Chromatin immunoprecipitation with massively parallel DNA sequencing (ChIP-seq) has greatly improved the reliability with which transcription factor binding sites (TFBSs) can be identified from genome-wide profiling studies. Many computational tools are developed to detect binding events or peaks, however the robust detection of weak binding events remains a challenge for current peak calling tools. We have developed a novel Bayesian approach (ChIP-BIT) to reliably detect TFBSs and their target genes by jointly modeling binding signal intensities and binding locations of TFBSs. Specifically, a Gaussian mixture model is used to capture both binding and background signals in sample data. As a unique feature of ChIP-BIT, background signals are modeled by a local Gaussian distribution that is accurately estimated from the input data. Extensive simulation studies showed a significantly improved performance of ChIP-BIT in target gene prediction, particularly for detecting weak binding signals at gene promoter regions. We applied ChIP-BIT to find target genes from NOTCH3 and PBX1 ChIP-seq data acquired from MCF-7 breast cancer cells. TF knockdown experiments have initially validated about 30% of co-regulated target genes identified by ChIP-BIT as being differentially expressed in MCF-7 cells. Functional analysis on these genes further revealed the existence of crosstalk between Notch and Wnt signaling pathways.
Nguyen VTM, Barozzi I, Faronato M, et al., 2015, Differential epigenetic reprogramming in response to specific endocrine therapies promotes cholesterol biosynthesis and cellular invasion, Nature Communications, Vol: 6, ISSN: 2041-1723
Endocrine therapies target the activation of the oestrogen receptor alpha (ERa) via distinctmechanisms, but it is not clear whether breast cancer cells can adapt to treatment usingdrug-specific mechanisms. Here we demonstrate that resistance emerges via drug-specificepigenetic reprogramming. Resistant cells display a spectrum of phenotypical changes withinvasive phenotypes evolving in lines resistant to the aromatase inhibitor (AI). Orthogonalgenomics analysis of reprogrammed regulatory regions identifies individual drug-inducedepigenetic states involving large topologically associating domains (TADs) and the activationof super-enhancers. AI-resistant cells activate endogenous cholesterol biosynthesis (CB)through stable epigenetic activation in vitro and in vivo. Mechanistically, CB sparks theconstitutive activation of oestrogen receptors alpha (ERa) in AI-resistant cells, partly via thebiosynthesis of 27-hydroxycholesterol. By targeting CB using statins, ERa binding is reducedand cell invasion is prevented. Epigenomic-led stratification can predict resistance to AI in asubset of ERa-positive patients.
Ali S, Periyasamy M, Patel H, et al., 2015, APOBEC3B mediated cytidine deamination is required for estrogen receptor action in breast cancer, Cell Reports, Vol: 13, Pages: 108-121, ISSN: 2211-1247
Estrogen receptor α (ERα) is the key transcriptional driver in a large proportion of breast cancers. We report that APOBEC3B (A3B) is required for regulation of gene expression by ER and acts by causing C-to-U deamination at ER binding regions. We show that these C-to-U changes lead to the generation of DNA strand breaks through activation of base excision repair (BER) and to repair by non-homologous end-joining (NHEJ) pathways. We provide evidence that transient cytidine deamination by A3B aids chromatin modification and remodelling at the regulatory regions of ER target genes that promotes their expression. A3B expression is associated with poor patient survival in ER+ breast cancer, reinforcing the physiological significance of A3B for ER action.
Xu Y, Zhang H, Van TMN, et al., 2015, LMTK3 represses tumor suppressor-like genes through chromatin remodeling in breast cancer, Cell Reports, Vol: 12, Pages: 837-849, ISSN: 2211-1247
LMTK3 is an oncogenic receptor tyrosine kinase (RTK) implicated in various types of cancer, including breast, lung, gastric, and colorectal cancer. It is localized in different cellular compartments, but its nuclear function has not been investigated so far. We mapped LMTK3 binding across the genome using ChIP-seq and found that LMTK3 binding events are correlated with repressive chromatin markers. We further identified KRAB-associated protein 1 (KAP1) as a binding partner of LMTK3. The LMTK3/KAP1 interaction is stabilized by PP1α, which suppresses KAP1 phosphorylation specifically at LMTK3-associated chromatin regions, inducing chromatin condensation and resulting in transcriptional repression of LMTK3-bound tumor suppressor-like genes. Furthermore, LMTK3 functions at distal regions in tethering the chromatin to the nuclear periphery, resulting in H3K9me3 modification and gene silencing. In summary, we propose a model where a scaffolding function of nuclear LMTK3 promotes cancer progression through chromatin remodeling.
Magnani L, Patten DK, Nguyen VTM, et al., 2015, The pioneer factor PBX1 is a novel driver of metastatic progression in ERα-positive breast cancer., Oncotarget, Vol: 6, Pages: 21878-24891, ISSN: 1949-2553
Over 30% of ERα breast cancer patients develop relapses and progress to metastatic disease despite treatment with endocrine therapies. The pioneer factor PBX1 translates epigenetic cues and mediates estrogen induced ERα binding. Here we demonstrate that PBX1 plays a central role in regulating the ERα transcriptional response to epidermal growth factor (EGF) signaling. PBX1 regulates a subset of EGF-ERα genes highly expressed in aggressive breast tumours. Retrospective stratification of luminal patients using PBX1 protein levels in primary cancer further demonstrates that elevated PBX1 protein levels correlate with earlier metastatic progression. In agreement, PBX1 protein levels are significantly upregulated during metastatic progression in ERα-positive breast cancer patients. Finally we reveal that PBX1 upregulation in aggressive tumours is partly mediated by genomic amplification of the PBX1 locus. Correspondingly, ERα-positive breast cancer patients carrying PBX1 amplification are characterized by poor survival. Notably, we demonstrate that PBX1 amplification can be identified in tumor derived-circulating free DNA of ERα-positive metastatic patients. Metastatic patients with PBX1 amplification are also characterized by shorter relapse-free survival. Our data identifies PBX1 amplification as a functional hallmark of aggressive ERα-positive breast cancers. Mechanistically, PBX1 amplification impinges on several critical pathways associated with aggressive ERα-positive breast cancer.
Faronato M, Nguyen VTM, Patten DK, et al., 2015, DMXL2 drives epithelial to mesenchymal transition in hormonal therapy resistant breast cancer through Notch hyper-activation, Oncotarget, Vol: 6, Pages: 22467-22479, ISSN: 1949-2553
The acquisition of endocrine therapy resistance in estrogen receptor α (ERα) breast cancer patients represents a major clinical problem. Notch signalling has been extensively linked to breast cancer especially in patients who fail to respond to endocrine therapy. Following activation, Notch intracellular domain is released and enters the nucleus where activates transcription of target genes. The numerous steps that cascade after activation of the receptor complicate using Notch as biomarker. Hence, this warrants the development of reliable indicators of Notch activity. DMXL2 is a novel regulator of Notch signalling not yet investigated in breast cancer. Here, we demonstrate that DMXL2 is overexpressed in a subset of endocrine therapy resistant breast cancer cell lines where it promotes epithelial to mesenchymal transition through hyper-activation of Notch signalling via V-ATPase dependent acidification. Following DMXL2 depletion or treatment with Bafilomycin A1, both EMT targets and Notch signalling pathway significantly decrease. We show for the first time that DMXL2 protein levels are significantly increased in ERα positive breast cancer patients that progress after endocrine therapy. Finally, we demonstrate that DMXL2 is a transmembrane protein with a potential extra-cellular domain. These findings identify DMXL2 as a novel, functional biomarker for ERα positive breast cancer.
Okamoto OK, Matheu A, Magnani L, 2015, Stem cells in translational cancer research, Stem Cells International, Vol: 2015, ISSN: 1687-9678
Nakshatri H, Goswami C, Badve S, et al., 2015, Divergent activation of AKT1 and AKT2 isoforms downstream of PI3K mutation impacts response of breast cancer cells to estradiol and PI3K inhibitors, 37th Annual CTRC-AACR San Antonio Breast Cancer Symposium, Publisher: AMER ASSOC CANCER RESEARCH, ISSN: 0008-5472
Varghese V, Magnani L, Harada N, et al., 2015, Inhibition of FOXM1 by thiostrepton increases sensitivity to 5-fluorouracil (5-FU) by downregulating thymidylate synthase (TS) in colorectal cancer, AACR Precision Medicine Conference on Drug Sensitivity and Resistance - Improving Cancer Therapy, Publisher: AMER ASSOC CANCER RESEARCH, ISSN: 1078-0432
Brown R, Curry E, Magnani L, et al., 2014, Poised epigenetic states and acquired drug resistance in cancer, Nature Reviews Cancer, Vol: 14, Pages: 747-753, ISSN: 1474-1768
Varghese V, Magnani L, Harada N, et al., 2014, Forkhead box transciption factor M1 (FOXM1) plays a critical role in colorectal cancer resistance by regulating thymidylate synthase (TS), 105th Annual Meeting of the American-Association-for-Cancer-Research (AACR), Publisher: AMER ASSOC CANCER RESEARCH, ISSN: 0008-5472
Jangal M, Couture J-P, Bianco S, et al., 2014, The transcriptional co-repressor TLE3 suppresses basal signaling on a subset of estrogen receptor alpha target genes, Nucleic Acids Research, Vol: 42, Pages: 11339-11348, ISSN: 1362-4962
Chromatin constitutes a repressive barrier to the process of ligand-dependent transcriptional activity of nuclear receptors. Nucleosomes prevent the binding of estrogen receptor α (ERα) in absence of ligand and thus represent an important level of transcriptional regulation. Here, we show that in breast cancer MCF-7 cells, TLE3, a co-repressor of the Groucho/Grg/TLE family, interacts with FoxA1 and is detected at regulatory elements of ERα target genes in absence of estrogen. As a result, the chromatin is maintained in a basal state of acetylation, thus preventing ligand-independent activation of transcription. In absence of TLE3, the basal expression of ERα target genes induced by E2 is increased. At the TFF1 gene, the recruitment of TLE3 to the chromatin is FoxA1-dependent and prevents ERα and RNA polymerase II recruitment to TFF1 gene regulatory elements. Moreover, the interaction of TLE3 with HDAC2 results in the maintenance of acetylation at a basal level. We also provide evidence that TLE3 is recruited at several other regulatory elements of ERα target genes and is probably an important co-regulator of the E2 signaling pathway. In sum, our results describe a mechanism by which TLE3 affects ligand dependency in ERα-regulated gene expression via its binding restricting function and its role in gene regulation by histone acetylation.
Magnani L, 2014, Epigenetic engineering and the art of epigenetic manipulation, Genome Biology, Vol: 15, ISSN: 1474-760X
This short and focused meeting was set up to bring the audience up to date with a specific set of techniques broadly categorized as epigenetic engineering (or epigenetic editing). The speakers reminded us of very important questions that still linger, like Damocles’ sword, over the field of epigenetics: what is the real role of epigenetics during gene transcription and development? Are epigenetic modifications the cause or consequence of these processes? While the jury is still out, this meeting reminded us that the tools needed to answer these philosophical questions are finally available and improving by the hour. Moreover, there was also a general consensus that epigenetic editing might provide the next big advance in cancer treatment. Epigenetic-editing treatments might finally allow targeted modulation of gene expression and could bypass the side effects of current epigenetic drugs.
Lombardo Y, Faronato M, Filipovic A, et al., 2014, Nicastrin and Notch4 drive endocrine therapy resistance and epithelial to mesenchymal transition in MCF7 breast cancer cells, Breast Cancer Research, Vol: 16, ISSN: 1465-542X
IntroductionResistance to anti-estrogen therapies is a major cause of disease relapse and mortality in estrogen receptor alpha (ERα)-positive breast cancers. Tamoxifen or estrogen withdrawal increases the dependence of breast cancer cells on Notch signalling. Here, we investigated the contribution of Nicastrin and Notch signalling in endocrine-resistant breast cancer cells.MethodsWe used two models of endocrine therapies resistant (ETR) breast cancer: tamoxifen-resistant (TamR) and long-term estrogen-deprived (LTED) MCF7 cells. We evaluated the migratory and invasive capacity of these cells by Transwell assays. Expression of epithelial to mesenchymal transition (EMT) regulators as well as Notch receptors and targets were evaluated by real-time PCR and western blot analysis. Moreover, we tested in vitro anti-Nicastrin monoclonal antibodies (mAbs) and gamma secretase inhibitors (GSIs) as potential EMT reversal therapeutic agents. Finally, we generated stable Nicastrin overexpessing MCF7 cells and evaluated their EMT features and response to tamoxifen.ResultsWe found that ETR cells acquired an epithelial to mesenchymal transition (EMT) phenotype and displayed increased levels of Nicastrin and Notch targets. Interestingly, we detected higher level of Notch4 but lower levels of Notch1 and Notch2 suggesting a switch to signalling through different Notch receptors after acquisition of resistance. Anti-Nicastrin monoclonal antibodies and the GSI PF03084014 were effective in blocking the Nicastrin/Notch4 axis and partially inhibiting the EMT process. As a result of this, cell migration and invasion were attenuated and the stem cell-like population was significantly reduced. Genetic silencing of Nicastrin and Notch4 led to equivalent effects. Finally, stable overexpression of Nicastrin was sufficient to make MCF7 unresponsive to tamoxifen by Notch4 activation.ConclusionsETR cells express high levels of Nicastrin and Notch4, whose activation ultimately drives invasive be
Bianco S, Brunelle M, Jangal M, et al., 2014, LRH-1 Governs Vital Transcriptional Programs in Endocrine-Sensitive and -Resistant Breast Cancer Cells, CANCER RESEARCH, Vol: 74, Pages: 2015-2025, ISSN: 0008-5472
Gadaleta RM, Magnani L, 2014, Nuclear receptors and chromatin: an inducible couple, JOURNAL OF MOLECULAR ENDOCRINOLOGY, Vol: 52, Pages: R137-R149, ISSN: 0952-5041
Magnani L, Lupien M, 2014, Chromatin and epigenetic determinants of estrogen receptor alpha (ESR1) signaling, MOLECULAR AND CELLULAR ENDOCRINOLOGY, Vol: 382, Pages: 633-641, ISSN: 0303-7207
Magnani L, Stoeck A, Zhang X, et al., 2013, Genome-wide reprogramming of the chromatin landscape underlies endocrine therapy resistance in breast cancer, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, Vol: 110, Pages: E1490-E1499, ISSN: 0027-8424
Magnani L, Brunelle M, Gevry N, et al., 2012, Chromatin landscape and endocrine response in breast cancer, EPIGENOMICS, Vol: 4, Pages: 675-683, ISSN: 1750-1911
Thiaville MM, Stoeck A, Chen L, et al., 2012, Identification of PBX1 target genes in cancer cells by global mapping of PBX1 binding sites, PLOS One, Vol: 7, ISSN: 1932-6203
PBX1 is a TALE homeodomain transcription factor involved in organogenesis and tumorigenesis. Although it has been shown that ovarian, breast, and melanoma cancer cells depend on PBX1 for cell growth and survival, the molecular mechanism of how PBX1 promotes tumorigenesis remains unclear. Here, we applied an integrated approach by overlapping PBX1 ChIP-chip targets with the PBX1-regulated transcriptome in ovarian cancer cells to identify genes whose transcription was directly regulated by PBX1. We further determined if PBX1 target genes identified in ovarian cancer cells were co-overexpressed with PBX1 in carcinoma tissues. By analyzing TCGA gene expression microarray datasets from ovarian serous carcinomas, we found co-upregulation of PBX1 and a significant number of its direct target genes. Among the PBX1 target genes, a homeodomain protein MEOX1 whose DNA binding motif was enriched in PBX1-immunoprecipicated DNA sequences was selected for functional analysis. We demonstrated that MEOX1 protein interacts with PBX1 protein and inhibition of MEOX1 yields a similar growth inhibitory phenotype as PBX1 suppression. Furthermore, ectopically expressed MEOX1 functionally rescued the PBX1-withdrawn effect, suggesting MEOX1 mediates the cellular growth signal of PBX1. These results demonstrate that MEOX1 is a critical target gene and cofactor of PBX1 in ovarian cancers.
Wang X, Park K-E, Koser S, et al., 2012, KPNA7, an oocyte- and embryo-specific karyopherin alpha subtype, is required for porcine embryo development, REPRODUCTION FERTILITY AND DEVELOPMENT, Vol: 24, Pages: 382-391, ISSN: 1031-3613
Magnani L, Ballantyne EB, Zhang X, et al., 2011, PBX1 Genomic Pioneer Function Drives ER alpha Signaling Underlying Progression in Breast Cancer, PLOS GENETICS, Vol: 7, ISSN: 1553-7404
Magnani L, Eeckhoute J, Lupien M, 2011, Pioneer factors: directing transcriptional regulators within the chromatin environment, TRENDS IN GENETICS, Vol: 27, Pages: 465-474, ISSN: 0168-9525
Wang K, Sengupta S, Magnani L, et al., 2010, Brg1 is required for Cdx2-mediated repression of Oct4 expression in mouse blastocysts, PLOS One, Vol: 5, ISSN: 1932-6203
During blastocyst formation the segregation of the inner cell mass (ICM) and trophectoderm is governed by the mutually antagonistic effects of the transcription factors Oct4 and Cdx2. Evidence indicates that suppression of Oct4 expression in the trophectoderm is mediated by Cdx2. Nonetheless, the underlying epigenetic modifiers required for Cdx2-dependent repression of Oct4 are largely unknown. Here we show that the chromatin remodeling protein Brg1 is required for Cdx2-mediated repression of Oct4 expression in mouse blastocysts. By employing a combination of RNA interference (RNAi) and gene expression analysis we found that both Brg1 Knockdown (KD) and Cdx2 KD blastocysts exhibit widespread expression of Oct4 in the trophectoderm. Interestingly, in Brg1 KD blastocysts and Cdx2 KD blastocysts, the expression of Cdx2 and Brg1 is unchanged, respectively. To address whether Brg1 cooperates with Cdx2 to repress Oct4 transcription in the developing trophectoderm, we utilized preimplantation embryos, trophoblast stem (TS) cells and Cdx2-inducible embryonic stem (ES) cells as model systems. We found that: (1) combined knockdown (KD) of Brg1 and Cdx2 levels in blastocysts resulted in increased levels of Oct4 transcripts compared to KD of Brg1 or Cdx2 alone, (2) endogenous Brg1 co-immunoprecipitated with Cdx2 in TS cell extracts, (3) in blastocysts Brg1 and Cdx2 co-localize in trophectoderm nuclei and (4) in Cdx2-induced ES cells Brg1 and Cdx2 are recruited to the Oct4 promoter. Lastly, to determine how Brg1 may induce epigenetic silencing of the Oct4 gene, we evaluated CpG methylation at the Oct4 promoter in the trophectoderm of Brg1 KD blastocysts. This analysis revealed that Brg1-dependent repression of Oct4 expression is independent of DNA methylation at the blastocyst stage. In toto, these results demonstrate that Brg1 cooperates with Cdx2 to repress Oct4 expression in the developing trophectoderm to ensure normal development.
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