SIN3A

Gene Summary

Gene:SIN3A; SIN3 transcription regulator family member A
Aliases: WITKOS
Location:15q24.2
Summary:The protein encoded by this gene is a transcriptional regulatory protein. It contains paired amphipathic helix (PAH) domains, which are important for protein-protein interactions and may mediate repression by the Mad-Max complex. [provided by RefSeq, Jul 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:paired amphipathic helix protein Sin3a
Source:NCBIAccessed: 11 March, 2017

Ontology:

What does this gene/protein do?
Show (30)
Pathways:What pathways are this gene/protein implicaed in?
Show (1)

Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 11 March 2017 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Gene Silencing
  • Protein Binding
  • Nuclear Proteins
  • Two-Hybrid System Techniques
  • Histone Deacetylase 1
  • alpha-Fetoproteins
  • MicroRNAs
  • Core Binding Factor Alpha 2 Subunit
  • Tumor Suppressor Proteins
  • Protein Structure, Tertiary
  • Trans-Activators
  • DNA-Binding Proteins
  • Translocation
  • Western Blotting
  • HEK293 Cells
  • Transcription
  • Cell Differentiation
  • Chromosome 15
  • Base Sequence
  • Promoter Regions
  • Mutation
  • Breast Cancer
  • Apoptosis
  • p53 Protein
  • Proto-Oncogene Proteins
  • Repressor Proteins
  • Oncogene Fusion Proteins
  • Histone Deacetylases
  • Cell Movement
  • Cancer Gene Expression Regulation
  • Transcriptional Activation
  • Chromatin
  • Transfection
  • Cell Line
  • Gene Expression Regulation
  • Epigenetics
  • Transcription Factors
  • Signal Transduction
  • Down-Regulation
  • Zinc Fingers
Tag cloud generated 11 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (1)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: SIN3A (cancer-related)

Bansal N, David G, Farias E, Waxman S
Emerging Roles of Epigenetic Regulator Sin3 in Cancer.
Adv Cancer Res. 2016; 130:113-35 [PubMed] Related Publications
Revolutionizing treatment strategies is an urgent clinical need in the fight against cancer. Recently the scientific community has recognized chromatin-associated proteins as promising therapeutic candidates. However, there is a need to develop more targeted epigenetic inhibitors with less toxicity. Sin3 family is one such target which consists of evolutionary conserved proteins with two paralogues Sin3A and Sin3B. Sin3A/B are global transcription regulators that provide a versatile platform for diverse chromatin-modifying activities. Sin3 proteins regulate key cellular functions that include cell cycle, proliferation, and differentiation, and have recently been implicated in cancer pathogenesis. In this chapter, we summarize the key concepts of Sin3 biology and elaborate the recent advancements in the role of Sin3 proteins in cancer with specific examples in multiple endocrine neoplasia type 2, pancreatic ductal adenocarcinoma, and triple negative breast cancer. Finally, a program to create an integrative approach for screening antitumor agents that target chromatin-associated factors like Sin3 is presented.

Suryo Rahmanto Y, Jung JG, Wu RC, et al.
Inactivating ARID1A Tumor Suppressor Enhances TERT Transcription and Maintains Telomere Length in Cancer Cells.
J Biol Chem. 2016; 291(18):9690-9 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
ARID1A is a tumor suppressor gene that belongs to the switch/sucrose non-fermentable chromatin remodeling gene family. It is mutated in many types of human cancer with the highest frequency in endometrium-related ovarian and uterine neoplasms including ovarian clear cell, ovarian endometrioid, and uterine endometrioid carcinomas. We have previously reported that mutations in the promoter of human telomerase reverse transcriptase (TERT) rarely co-occur with the loss of ARID1A protein expression, suggesting a potential role of ARID1A in telomere biology. In this study, we demonstrate that ARID1A negatively regulates TERT transcriptional regulation and activity via binding to the regulatory element of TERT and promotes a repressive histone mode. Induction of ARID1A expression was associated with increased occupancy of SIN3A and H3K9me3, known transcription repressor and histone repressor marks, respectively. Thus, loss of ARID1A protein expression caused by inactivating mutations reactivates TERT transcriptional activity and confers a survival advantage of tumor cells by maintaining their telomeres.

L'Abbate A, Tolomeo D, De Astis F, et al.
t(15;21) translocations leading to the concurrent downregulation of RUNX1 and its transcription factor partner genes SIN3A and TCF12 in myeloid disorders.
Mol Cancer. 2015; 14:211 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Through a combined approach integrating RNA-Seq, SNP-array, FISH and PCR techniques, we identified two novel t(15;21) translocations leading to the inactivation of RUNX1 and its partners SIN3A and TCF12. One is a complex t(15;21)(q24;q22), with both breakpoints mapped at the nucleotide level, joining RUNX1 to SIN3A and UBL7-AS1 in a patient with myelodysplasia. The other is a recurrent t(15;21)(q21;q22), juxtaposing RUNX1 and TCF12, with an opposite transcriptional orientation, in three myeloid leukemia cases. Since our transcriptome analysis indicated a significant number of differentially expressed genes associated with both translocations, we speculate an important pathogenetic role for these alterations involving RUNX1.

Farhana L, Dawson MI, Fontana JA
Down regulation of miR-202 modulates Mxd1 and Sin3A repressor complexes to induce apoptosis of pancreatic cancer cells.
Cancer Biol Ther. 2015; 16(1):115-24 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Aberrant regulation of microRNA expression in pancreatic cancers has been shown to play an important role in its inherent poor prognosis and malignant potential. MicroRNAs have also been shown to inhibit translation of genes by targeting the 3'-untranslated region (3-UTR) of mRNAs resulting in the inhibition of translation and often destruction of the mRNA. In the present study we investigated the role of the microRNA miR-202 in the apoptotic pathways of pancreatic cancer cells. The adamantyl-related molecule, 3-Cl-AHPC down-regulated expression of miR-202 and miR-578 resulting in the increased expression of mRNA and protein expression of their target genes, Max dimerization protein 1 (Mxd1/Mad1) and the Sin3A associated protein 18 (SAP18). Overexpression of pre-miR-202 led to diminished levels of Mxd1 and blocked the 3-Cl-AHPC-mediated increase in Mxd1 mRNA expression. The addition of the microRNA inhibitor 2'-O-methylated miR-202 enhanced the 3-Cl-AHPC-mediated increase of Mxd1 mRNA levels as well as 3-CI-AHPC-mediated apoptosis. We found increased Mxd1 bound to the Sin3A repressor protein complex through its increased binding with HDAC-2 and subsequently enhanced transcriptional repression in cells as evidenced by increased HDAC activity. Mxd1 also repressed human telomerase reverse transcriptase (hTERT) mRNA expression through its increased binding to the hTERT promoter site and resulted in decreased telomerase activity in cells. Our results demonstrate that down regulation of miR-202 increased the expression of its target Mxd1, followed by Mxd1 recruitment to the Sin3A repressor complex and through its dimerization with Max, and increased repression of Myc-Max target proteins.

Shang C, Hong Y, Guo Y, et al.
MiR-210 up-regulation inhibits proliferation and induces apoptosis in glioma cells by targeting SIN3A.
Med Sci Monit. 2014; 20:2571-7 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
BACKGROUND: The aim of this study was to determine whether miR-210 can affect the apoptosis and proliferation of human U251 glioma cells from down-regulating SIN3A.
MATERIAL AND METHODS: The expression of miRNA-210 was detected by quantitative real-time PCR in normal brain tissue and glioma samples. The apoptosis and proliferation ability of U251 cells were analyzed by MTT and flow cytometry assay after anti-miR-210 transfection. For the regulation mechanism analysis of miR-210, TargetScan, PicTar, and microRNA were selected to predict some potential target genes of miR-210. The predicted gene was identified to be the direct and specific target gene of miR-210 by luciferase activities assay and Western blot. RNA interference technology was used to confirm that the apoptosis and proliferation effects of miR-210 were directly induced by SIN3A.
RESULTS: The expression of miR-210 increased significantly in glioma in comparison with normal brain tissue. The silence of miR-210 expression could inhibit the proliferation of U251 cells and induce the apoptosis. Mechanism analysis revealed that SIN3A was a specific and direct target gene of miR-210. The siRNA-SIN3A could down-regulate the expression of SIN3A protein, which was up-regulated in U251 cells by anti-miR-210 transfection, and our experiments found that silence of SIN3A could inhibit the apoptosis and sharply increase the proliferation of U251 cells. The regulation effects of anti-miR-210 on apoptosis and proliferation can be reversed respectively by the expression silence of SIN3A.
CONCLUSIONS: Aberrantly expressed miR-210 regulates human U251 glioma cells apoptosis and proliferation partly through directly down-regulating SIN3A protein expression. This might offer a new potential therapeutic stratagem for glioma.

Gong C, Qu S, Lv XB, et al.
BRMS1L suppresses breast cancer metastasis by inducing epigenetic silence of FZD10.
Nat Commun. 2014; 5:5406 [PubMed] Related Publications
BRMS1L (breast cancer metastasis suppressor 1 like, BRMS1-like) is a component of Sin3A-histone deacetylase (HDAC) co-repressor complex that suppresses target gene transcription. Here we show that reduced BRMS1L in breast cancer tissues is associated with metastasis and poor patient survival. Functionally, BRMS1L inhibits breast cancer cells migration and invasion by inhibiting epithelial-mesenchymal transition. These effects are mediated by epigenetic silencing of FZD10, a receptor for Wnt signalling, through HDAC1 recruitment and histone H3K9 deacetylation at the promoter. Consequently, BRMS1L-induced FZD10 silencing inhibits aberrant activation of WNT3-FZD10-β-catenin signalling. Furthermore, BRMS1L is a target of miR-106b and miR-106b upregulation leads to BRMS1L reduction in breast cancer cells. RNA interference-mediated silencing of BRMS1L expression promotes metastasis of breast cancer xenografts in immunocompromised mice, whereas ectopic BRMS1L expression inhibits metastasis. Therefore, BRMS1L provides an epigenetic regulation of Wnt signalling in breast cancer cells and acts as a breast cancer metastasis suppressor.

Garcia-Sanz P, Quintanilla A, Lafita MC, et al.
Sin3b interacts with Myc and decreases Myc levels.
J Biol Chem. 2014; 289(32):22221-36 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Myc expression is deregulated in many human cancers. A yeast two-hybrid screen has revealed that the transcriptional repressor Sin3b interacts with Myc protein. Endogenous Myc and Sin3b co-localize and interact in the nuclei of human and rat cells, as assessed by co-immunoprecipitation, immunofluorescence, and proximity ligation assay. The interaction is Max-independent. A conserved Myc region (amino acids 186-203) is required for the interaction with Sin3 proteins. Histone deacetylase 1 is recruited to Myc-Sin3b complexes, and its deacetylase activity is required for the effects of Sin3b on Myc. Myc and Sin3a/b co-occupied many sites on the chromatin of human leukemia cells, although the presence of Sin3 was not associated with gene down-regulation. In leukemia cells and fibroblasts, Sin3b silencing led to Myc up-regulation, whereas Sin3b overexpression induced Myc deacetylation and degradation. An analysis of Sin3b expression in breast tumors revealed an association between low Sin3b expression and disease progression. The data suggest that Sin3b decreases Myc protein levels upon Myc deacetylation. As Sin3b is also required for transcriptional repression by Mxd-Max complexes, our results suggest that, at least in some cell types, Sin3b limits Myc activity through two complementary activities: Mxd-dependent gene repression and reduction of Myc levels.

Gu X, Hu Z, Ebrahem Q, et al.
Runx1 regulation of Pu.1 corepressor/coactivator exchange identifies specific molecular targets for leukemia differentiation therapy.
J Biol Chem. 2014; 289(21):14881-95 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Gene activation requires cooperative assembly of multiprotein transcription factor-coregulator complexes. Disruption to cooperative assemblage could underlie repression of tumor suppressor genes in leukemia cells. Mechanisms of cooperation and its disruption were therefore examined for PU.1 and RUNX1, transcription factors that cooperate to activate hematopoietic differentiation genes. PU.1 is highly expressed in leukemia cells, whereas RUNX1 is frequently inactivated by mutation or translocation. Thus, coregulator interactions of Pu.1 were examined by immunoprecipitation coupled with tandem mass spectrometry/Western blot in wild-type and Runx1-deficient hematopoietic cells. In wild-type cells, the NuAT and Baf families of coactivators coimmunoprecipitated with Pu.1. Runx1 deficiency produced a striking switch to Pu.1 interaction with the Dnmt1, Sin3A, Nurd, CoRest, and B-Wich corepressor families. Corepressors of the Polycomb family, which are frequently inactivated by mutation or deletion in myeloid leukemia, did not interact with Pu.1. The most significant gene ontology association of Runx1-Pu.1 co-bound genes was with macrophages, therefore, functional consequences of altered corepressor/coactivator exchange were examined at Mcsfr, a key macrophage differentiation gene. In chromatin immunoprecipitation analyses, high level Pu.1 binding to the Mcsfr promoter was not decreased by Runx1 deficiency. However, the Pu.1-driven shift from histone repression to activation marks at this locus, and terminal macrophage differentiation, were substantially diminished. DNMT1 inhibition, but not Polycomb inhibition, in RUNX1-translocated leukemia cells induced terminal differentiation. Thus, RUNX1 and PU.1 cooperate to exchange corepressors for coactivators, and the specific corepressors recruited to PU.1 as a consequence of RUNX1 deficiency could be rational targets for leukemia differentiation therapy.

Jiang S, Willox B, Zhou H, et al.
Epstein-Barr virus nuclear antigen 3C binds to BATF/IRF4 or SPI1/IRF4 composite sites and recruits Sin3A to repress CDKN2A.
Proc Natl Acad Sci U S A. 2014; 111(1):421-6 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Epstein-Barr virus nuclear antigen 3C (EBNA3C) repression of CDKN2A p14(ARF) and p16(INK4A) is essential for immortal human B-lymphoblastoid cell line (LCL) growth. EBNA3C ChIP-sequencing identified >13,000 EBNA3C sites in LCL DNA. Most EBNA3C sites were associated with active transcription; 64% were strong H3K4me1- and H3K27ac-marked enhancers and 16% were active promoters marked by H3K4me3 and H3K9ac. Using ENCODE LCL transcription factor ChIP-sequencing data, EBNA3C sites coincided (±250 bp) with RUNX3 (64%), BATF (55%), ATF2 (51%), IRF4 (41%), MEF2A (35%), PAX5 (34%), SPI1 (29%), BCL11a (28%), SP1 (26%), TCF12 (23%), NF-κB (23%), POU2F2 (23%), and RBPJ (16%). EBNA3C sites separated into five distinct clusters: (i) Sin3A, (ii) EBNA2/RBPJ, (iii) SPI1, and (iv) strong or (v) weak BATF/IRF4. EBNA3C signals were positively affected by RUNX3, BATF/IRF4 (AICE) and SPI1/IRF4 (EICE) cooccupancy. Gene set enrichment analyses correlated EBNA3C/Sin3A promoter sites with transcription down-regulation (P < 1.6 × 10(-4)). EBNA3C signals were strongest at BATF/IRF4 and SPI1/IRF4 composite sites. EBNA3C bound strongly to the p14(ARF) promoter through SPI1/IRF4/BATF/RUNX3, establishing RBPJ-, Sin3A-, and REST-mediated repression. EBNA3C immune precipitated with Sin3A and conditional EBNA3C inactivation significantly decreased Sin3A binding at the p14(ARF) promoter (P < 0.05). These data support a model in which EBNA3C binds strongly to BATF/IRF4/SPI1/RUNX3 sites to enhance transcription and recruits RBPJ/Sin3A- and REST/NRSF-repressive complexes to repress p14(ARF) and p16(INK4A) expression.

Cai Q, Cai S, Zhu C, et al.
A unique SUMO-2-interacting motif within LANA is essential for KSHV latency.
PLoS Pathog. 2013; 9(11):e1003750 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Kaposi's sarcoma-associated herpesvirus (KSHV) stabilizes hypoxia-inducible factor α (HIF-1α) during latent infection, and HIF-1α reactivates lytic replication under hypoxic stress. However, the mechanism utilized by KSHV to block lytic reactivation with the accumulation of HIF-1α in latency remains unclear. Here, we report that LANA encoded by KSHV contains a unique SUMO-interacting motif (LANA(SIM)) which is specific for interaction with SUMO-2 and facilitates LANA SUMOylation at lysine 1140. Proteomic and co-immunoprecipitation analysis further reveal that the SUMO-2 modified transcription repressor KAP1 is a critical factor recruited by LANA(SIM). Deletion of LANA(SIM) led to functional loss of both LANA-mediated viral episome maintenance and lytic gene silencing. Moreover, hypoxia reduced KAP1 SUMOylation and resulted in dissociation of both KAP1 and Sin3A repressors from LANA(SIM)-associated complex. Therefore, the LANA(SIM) motif plays an essential role in KSHV latency and is a potential drug target against KSHV-associated cancers.

Kadamb R, Mittal S, Bansal N, et al.
Sin3: insight into its transcription regulatory functions.
Eur J Cell Biol. 2013 Aug-Sep; 92(8-9):237-46 [PubMed] Related Publications
Sin3, a large acidic protein, shares structural similarity with the helix-loop-helix dimerization domain of proteins of the Myc family of transcription factors. Sin3/HDAC corepressor complex functions in transcriptional regulation of several genes and is therefore implicated in the regulation of key biological processes. Knockdown studies have confirmed the role of Sin3 in cellular proliferation, differentiation, apoptosis and cell cycle regulation, emphasizing Sin3 as an essential regulator of critical cellular events in normal and pathological processes. The present review covers the diverse functions of this master transcriptional regulator as well as illustrates the redundant and distinct functions of its two mammalian isoforms.

Poos K, Smida J, Nathrath M, et al.
How microRNA and transcription factor co-regulatory networks affect osteosarcoma cell proliferation.
PLoS Comput Biol. 2013; 9(8):e1003210 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Osteosarcomas (OS) are complex bone tumors with various genomic alterations. These alterations affect the expression and function of several genes due to drastic changes in the underlying gene regulatory network. However, we know little about critical gene regulators and their functional consequences on the pathogenesis of OS. Therefore, we aimed to determine microRNA and transcription factor (TF) co-regulatory networks in OS cell proliferation. Cell proliferation is an essential part in the pathogenesis of OS and deeper understanding of its regulation might help to identify potential therapeutic targets. Based on expression data of OS cell lines divided according to their proliferative activity, we obtained 12 proliferation-related microRNAs and corresponding target genes. Therewith, microRNA and TF co-regulatory networks were generated and analyzed regarding their structure and functional influence. We identified key co-regulators comprising the microRNAs miR-9-5p, miR-138, and miR-214 and the TFs SP1 and MYC in the derived networks. These regulators are implicated in NFKB- and RB1-signaling and focal adhesion processes based on their common or interacting target genes (e.g., CDK6, CTNNB1, E2F4, HES1, ITGA6, NFKB1, NOTCH1, and SIN3A). Thus, we proposed a model of OS cell proliferation which is primarily co-regulated through the interactions of the mentioned microRNA and TF combinations. This study illustrates the benefit of systems biological approaches in the analysis of complex diseases. We integrated experimental data with publicly available information to unravel the coordinated (post)-transcriptional control of microRNAs and TFs to identify potential therapeutic targets in OS. The resulting microRNA and TF co-regulatory networks are publicly available for further exploration to generate or evaluate own hypotheses of the pathogenesis of OS (http://www.complex-systems.uni-muenster.de/co_networks.html).

Piazza R, Magistroni V, Mogavero A, et al.
Epigenetic silencing of the proapoptotic gene BIM in anaplastic large cell lymphoma through an MeCP2/SIN3a deacetylating complex.
Neoplasia. 2013; 15(5):511-22 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
BIM is a proapoptotic member of the Bcl-2 family. Here, we investigated the epigenetic status of the BIM locus in NPM/ALK+ anaplastic large cell lymphoma (ALCL) cell lines and in lymph node biopsies from NPM/ALK+ ALCL patients. We show that BIM is epigenetically silenced in cell lines and lymph node specimens and that treatment with the deacetylase inhibitor trichostatin A restores the histone acetylation, strongly upregulates BIM expression, and induces cell death. BIM silencing occurs through recruitment of MeCP2 and the SIN3a/histone deacetylase 1/2 (HDAC1/2) corepressor complex. This event requires BIM CpG methylation/demethylation with 5-azacytidine that leads to detachment of the MeCP2 corepressor complex and reacetylation of the histone tails. Treatment with the ALK inhibitor PF2341066 or with an inducible shRNA targeting NPM/ALK does not restore BIM locus reacetylation; however, enforced expression of NPM/ALK in an NPM/ALK-negative cell line significantly increases the methylation at the BIM locus. This study demonstrates that BIM is epigenetically silenced in NPM/ALK-positive cells through recruitment of the SIN3a/HDAC1/2 corepressor complex and that NPM/ALK is dispensable to maintain BIM epigenetic silencing but is able to act as an inducer of BIM methylation.

Hurst DR, Xie Y, Thomas JW, et al.
The C-terminal putative nuclear localization sequence of breast cancer metastasis suppressor 1, BRMS1, is necessary for metastasis suppression.
PLoS One. 2013; 8(2):e55966 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Breast cancer metastasis suppressor 1 (BRMS1) is a predominantly nuclear protein that suppresses metastasis in multiple human and murine carcinoma cell lines. BRMS1 interacts with several nuclear proteins including SIN3:HDAC chromatin remodeling complexes that are involved in repressing transcription. However, recent reports suggest BRMS1 may function in the cytoplasm. BRMS1 has two predicted nuclear localization sequences (NLS) that are located near the C-terminus (amino acids 198-205 and 238-244, NLS1 and NLS2 respectively). We hypothesized that nuclear localization sequences of BRMS1 were essential for BRMS1 mediated metastasis suppression. Replacement of NLS2 with NLS1 (BRMS1(NLS1,1)), truncation at 238 (BRMS1(ΔNLS2)), or switching the location of NLS1 and NLS2 (BRMS1(NLS2,1)) did not affect nuclear localization; but, replacement of NLS1 with NLS2 (BRMS1(NLS2,2)) or truncation at 197 (BRMS1(ΔNLS) which removes both NLS) promoted cytoplasmic localization. MDA-MB-231 human metastatic breast cancer cells transduced with BRMS1(NLS1,1), BRMS1(NLS2,2) or BRMS1(NLS2,1) were evaluated for metastasis suppression in an experimental xenograft mouse model. Interestingly, while NLS2 was not necessary for nuclear localization, it was found to be important for metastasis suppression since BRMS1(NLS2,2) suppressed metastasis by 85%. In contrast, BRMS1(NLS2,1) and BRMS1(NLS1,1) did not significantly suppress metastasis. Both BRMS1 and BRMS1(NLS2,2) co-immunoprecipitated with SIN3A in the nucleus and cytoplasm; however, BRMS1(NLS1,1) and BRMS1(NLS2,1) were associated with SIN3A in the nucleus only. Moreover, BRMS1 and BRMS1(NLS2,2), but not BRMS1(NLS1,1) and BRMS1(NLS2,1), down-regulated the pro-metastatic microRNA, miR-10b. Together, these data demonstrate an important role for NLS2 in the cytoplasm that is critical for metastasis suppression and is distinct from nuclear localization.

Cartron PF, Blanquart C, Hervouet E, et al.
HDAC1-mSin3a-NCOR1, Dnmt3b-HDAC1-Egr1 and Dnmt1-PCNA-UHRF1-G9a regulate the NY-ESO1 gene expression.
Mol Oncol. 2013; 7(3):452-63 [PubMed] Related Publications
The NY-ESO1 gene is a cancer/testis antigen considered to be suitable target for the immunotherapy of human malignancies. Despite the identification of the epigenetical silencing of the NY-ESO1 gene in a large variety of tumors, the molecular mechanism involved in this phenomenon is not fully elucidated. In two non epithelial cancers (glioma and mesothelioma), we found that the epigenetic regulation of the NY-ESO1 gene requires the sequential recruitment of the HDAC1-mSin3a-NCOR, Dnmt3b-HDAC1-Egr1 and Dnmt1-PCNA-UHRF1-G9a complexes. Thus, our data illustrate the orchestration of a sequential epigenetic mechanism including the histone deacetylation and methylation, and the DNA methylation processes.

Das TK, Sangodkar J, Negre N, et al.
Sin3a acts through a multi-gene module to regulate invasion in Drosophila and human tumors.
Oncogene. 2013; 32(26):3184-97 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Chromatin remodeling proteins regulate multiple aspects of cell homeostasis, making them ideal candidates for misregulation in transformed cells. Here, we explore Sin3A, a member of the Sin3 family of proteins linked to tumorigenesis that are thought to regulate gene expression through their role as histone deacetylases (HDACs). We identified Drosophila Sin3a as an important mediator of oncogenic Ret receptor in a fly model of Multiple Endocrine Neoplasia Type 2. Reducing Drosophila Sin3a activity led to metastasis-like behavior and, in the presence of Diap1, secondary tumors distant from the site of origin. Genetic and Chip-Seq analyses identified previously undescribed Sin3a targets including genes involved in cell motility and actin dynamics, as well as signaling pathways including Src, Jnk and Rho. A key Sin3a oncogenic target, PP1B, regulates stability of β-Catenin/Armadillo: the outcome is to oppose T-cell factor (TCF) function and Wg/Wnt pathway signaling in both fly and mammalian cancer cells. Reducing Sin3A strongly increased the invasive behavior of A549 human lung adenocarcinoma cells. We show that Sin3A is downregulated in a variety of human tumors and that Src, JNK, RhoA and PP1B/β-Catenin are regulated in a manner analogous to our Drosophila models. Our data suggest that Sin3A influences a specific step of tumorigenesis by regulating a module of genes involved in cell invasion. Tumor progression may commonly rely on such 'modules of invasion' under the control of broad transcriptional regulators.

Winter SF, Lukes L, Walker RC, et al.
Allelic variation and differential expression of the mSIN3A histone deacetylase complex gene Arid4b promote mammary tumor growth and metastasis.
PLoS Genet. 2012; 8(5):e1002735 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Accumulating evidence suggests that breast cancer metastatic progression is modified by germline polymorphism, although specific modifier genes have remained largely undefined. In the current study, we employ the MMTV-PyMT transgenic mouse model and the AKXD panel of recombinant inbred mice to identify AT-rich interactive domain 4B (Arid4b; NM_194262) as a breast cancer progression modifier gene. Ectopic expression of Arid4b promoted primary tumor growth in vivo as well as increased migration and invasion in vitro, and the phenotype was associated with polymorphisms identified between the AKR/J and DBA/2J alleles as predicted by our genetic analyses. Stable shRNA-mediated knockdown of Arid4b caused a significant reduction in pulmonary metastases, validating a role for Arid4b as a metastasis modifier gene. ARID4B physically interacts with the breast cancer metastasis suppressor BRMS1, and we detected differential binding of the Arid4b alleles to histone deacetylase complex members mSIN3A and mSDS3, suggesting that the mechanism of Arid4b action likely involves interactions with chromatin modifying complexes. Downregulation of the conserved Tpx2 gene network, which is comprised of many factors regulating cell cycle and mitotic spindle biology, was observed concomitant with loss of metastatic efficiency in Arid4b knockdown cells. Consistent with our genetic analysis and in vivo experiments in our mouse model system, ARID4B expression was also an independent predictor of distant metastasis-free survival in breast cancer patients with ER+ tumors. These studies support a causative role of ARID4B in metastatic progression of breast cancer.

De Amicis F, Giordano F, Vivacqua A, et al.
Resveratrol, through NF-Y/p53/Sin3/HDAC1 complex phosphorylation, inhibits estrogen receptor alpha gene expression via p38MAPK/CK2 signaling in human breast cancer cells.
FASEB J. 2011; 25(10):3695-707 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Agents to counteract acquired resistance to hormonal therapy for breast cancer would substantially enhance the long-term benefits of hormonal therapy. In the present study, we demonstrate how resveratrol (Res) inhibits human breast cancer cell proliferation, including MCF-7 tamoxifen-resistant cells (IC(50) values for viability were in the 30-45 μM range). We show that Res, through p38(MAPK) phosphorylation, causes induction of p53, which recruits at the estrogen receptor α (ERα) proximal promoter, leading to an inhibition of ERα expression in terms of mRNA and protein content. These events appear specifically p53 dependent, since they are drastically abrogated with p53-targeting siRNA. Coimmunoprecipitation assay showed specific interaction between p53, the Sin3A corepressor, and histone deacetylase 1 (HDAC1), which was phosphorylated. The enhancement of the tripartite complex p53/Sin3A/HDAC1, together with NF-Y on Res treatment, was confirmed by chromatin immunoprecipitation analyses, with a concomitant release of Sp1 and RNA polymerase II, thereby inhibiting the cell transcriptional machinery. The persistence of such effects in MCF-7 tamoxifen-resistant cells at a higher extent than parental MCF-7 cells addresses how Res may be considered a useful pharmacological tool to be exploited in the adjuvant settings for treatment of breast cancer developing hormonal resistance.

Arzumanyan A, Friedman T, Kotei E, et al.
Epigenetic repression of E-cadherin expression by hepatitis B virus x antigen in liver cancer.
Oncogene. 2012; 31(5):563-72 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Loss of E-cadherin is associated with acquisition of metastatic capacity. Numerous studies suggest that histone deacetylation and/or hypermethylation of CpG islands in E-cadherin gene (CDH1) are major mechanisms responsible for E-cadherin silencing in different tumors and cancer cell lines. The hepatitis B virus (HBV)-encoded X antigen, HBx, contributes importantly to the development of hepatocellular carcinoma using multiple mechanisms. Experiments were designed to test if in addition to CDH1 hypermethylation HBx promotes epigenetic modulation of E-cadherin transcriptional activity through histone deacetylation and miR-373. The relationships between HBx, E-cadherin, mSin3A, Snail-1 and miR-373 were evaluated in HBx expressing (HepG2X) and control (HepG2CAT) cells by western blotting, immunoprecipitation (IP), chromatin IP as well as by immunohistochemical staining of liver and tumor tissue sections from HBV-infected patients. In HepG2X cells, decreased levels of E-cadherin and elevated levels of mSin3A and Snail-1 were detected. Reciprocal IP with anti-HBx and anti-mSin3A demonstrated mutual binding. Furthermore, HBx-mSin3A colocalization was detected by immunofluorescent staining. HBx downregulated E-cadherin expression by the recruitment of the mSin3A/histone deacetylase complex to the Snail-binding sites in human CDH1. Histone deacetylation inhibition by Trichostatin-A treatment restored E-cadherin expression. Mir-373, a positive regulator of E-cadherin expression, was downregulated by HBx in HepG2X cells and tissue sections from HBV-infected patients. Thus, histone deacetylation of CDH1 and downregulation of miR-373, together with the previously demonstrated hypermethylation of CDH1 by HBx, may be important for the understanding of HBV-related carcinogenesis.

Angrisano T, Sacchetti S, Natale F, et al.
Chromatin and DNA methylation dynamics during retinoic acid-induced RET gene transcriptional activation in neuroblastoma cells.
Nucleic Acids Res. 2011; 39(6):1993-2006 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Although it is well known that RET gene is strongly activated by retinoic acid (RA) in neuroblastoma cells, the mechanisms underlying such activation are still poorly understood. Here we show that a complex series of molecular events, that include modifications of both chromatin and DNA methylation state, accompany RA-mediated RET activation. Our results indicate that the primary epigenetic determinants of RA-induced RET activation differ between enhancer and promoter regions. At promoter region, the main mark of RET activation was the increase of H3K4me3 levels while no significant changes of the methylation state of H3K27 and H3K9 were observed. At RET enhancer region a bipartite chromatin domain was detected in unstimulated cells and a prompt demethylation of H3K27me3 marked RET gene activation upon RA exposure. Moreover, ChIP experiments demonstrated that EZH2 and MeCP2 repressor complexes were associated to the heavily methylated enhancer region in the absence of RA while both complexes were displaced during RA stimulation. Finally, our data show that a demethylation of a specific CpG site at the enhancer region could favor the displacement of MeCP2 from the heavily methylated RET enhancer region providing a novel potential mechanism for transcriptional regulation of methylated RA-regulated loci.

Ellison-Zelski SJ, Alarid ET
Maximum growth and survival of estrogen receptor-alpha positive breast cancer cells requires the Sin3A transcriptional repressor.
Mol Cancer. 2010; 9:263 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
BACKGROUND: Sin3A is an evolutionarily conserved transcriptional repressor which regulates gene expression as part of the multi-protein Sin3 repressive complex. It functions as a scaffold upon which proteins with enzymatic activity dock, including chromatin modifying histone deacetylases. Although regulation of transcription by Sin3A has been studied in detail, little is understood about the function of Sin3A in cancer cells. We previously showed that Sin3A is expressed in breast cancer cells and is a repressor of estrogen receptor-alpha (ERα, ESR1) gene expression. Here, we expand our previous studies to elucidate the function of Sin3A in the control of gene expression and growth of breast cancer cells.
RESULTS: Analysis of gene expression following knockdown of Sin3A revealed changes in both basal and regulated gene transcription. Genes of known importance in breast cancer and estrogen signaling, including ERBB2, PGR, MYC, CLU, and NCOA2, were among those identified as Sin3A-responsive. The mechanism of Sin3A action varied among genes and was found to be mediated through both HDAC1/2 -dependent and -independent activities. Loss of Sin3A inhibited breast cancer cell growth by increasing apoptosis without affecting cell cycle progression. Analysis of both ERα-positive and ERα-negative cell lines revealed that the effects of Sin3A on growth were cell-type specific, as Sin3A expression promoted maximum growth of only the ERα-positive cells, and, notably, Sin3A protein itself was increased by estrogen. Further gene expression experiments revealed that Sin3A repressed expression of key apoptotic genes, including TRAIL, TRAILR1, CASP10, and APAF1, in ERα-positive, but not ERα-negative, cell lines, which could provide a mechanistic explanation for cell-type differences in growth.
CONCLUSIONS: This study identifies Sin3A as a regulator of gene expression, survival, and growth in ERα-positive breast cancer cells. Sin3A regulates the transcription of genes involved in breast cancer and apoptosis and acts through multiple mechanisms not limited to histone deacetylase function. These findings reveal previously undescribed functions of Sin3A in breast cancer and provide evidence for an important role of this transcriptional repressor in ERα-positive tumor cell growth.

Mathison A, Liebl A, Bharucha J, et al.
Pancreatic stellate cell models for transcriptional studies of desmoplasia-associated genes.
Pancreatology. 2010; 10(4):505-16 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
BACKGROUND: Pancreatic stellate cells are emerging as key players in pathophysiopathological processes underlying the development of pancreatic disease, including pancreatitis and cancer. The cells are scarce in the pancreas making their isolation time and resource use consuming.
METHODS: Therefore, with the ultimate goal of facilitating mechanistic studies, here we report the isolation, characterization, and immortalization of stellate cell lines from rat and mouse origin.
RESULTS: These cell lines display morphological and molecular markers as well as non-tumorigenic characteristics similar to the frequently used hepatic counterparts. In addition, we have tested their robustness as a model for transcriptional regulatory studies. We find that these cells respond well to TGFβ signaling by triggering a distinct cascade of gene expression, some genes overlap with the TGFβ response of LX2 cells. These cells express several key chromatin proteins and epigenetic regulators involved in the regulation of gene expression, including co-repressors such as Sin3A (short-term repression), HP1 (long-term repression), as well as CBP/p300 (activation). Furthermore, these cells are well suited for Gal4-based transcriptional activation and repression assays.
CONCLUSIONS: The cell model reported here may therefore help fuel investigations in the field of signaling, transcription, and perhaps other studies on similarly exciting cellular processes. and IAP.

Farias EF, Petrie K, Leibovitch B, et al.
Interference with Sin3 function induces epigenetic reprogramming and differentiation in breast cancer cells.
Proc Natl Acad Sci U S A. 2010; 107(26):11811-6 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Sin3A/B is a master transcriptional scaffold and corepressor that plays an essential role in the regulation of gene transcription and maintenance of chromatin structure, and its inappropriate recruitment has been associated with aberrant gene silencing in cancer. Sin3A/B are highly related, large, multidomian proteins that interact with a wide variety of transcription factors and corepressor components, and we examined whether disruption of the function of a specific domain could lead to epigenetic reprogramming and derepression of specific subsets of genes. To this end, we selected the Sin3A/B-paired amphipathic alpha-helices (PAH2) domain based on its established role in mediating the effects of a relatively small number of transcription factors containing a PAH2-binding motif known as the Sin3 interaction domain (SID). Here, we show that in both human and mouse breast cancer cells, the targeted disruption of Sin3 function by introduction of a SID decoy that interferes with PAH2 binding to SID-containing partner proteins reverted the silencing of genes involved in cell growth and differentiation. In particular, the SID decoy led to epigenetic reprogramming and reexpression of the important breast cancer-associated silenced genes encoding E-cadherin, estrogen receptor alpha, and retinoic acid receptor beta and impaired tumor growth in vivo. Interestingly, the SID decoy was effective in the triple-negative M.D. Anderson-Metastatic Breast-231 (MDA-MB-231) breast cancer cell line, restoring sensitivity to 17beta-estradiol, tamoxifen, and retinoids. Therefore, the development of small molecules that can block interactions between PAH2 and SID-containing proteins offers a targeted epigenetic approach for treating this type of breast cancer that may also have wider therapeutic implications.

Sugimoto T, Tomita A, Hiraga J, et al.
Escape mechanisms from antibody therapy to lymphoma cells: downregulation of CD20 mRNA by recruitment of the HDAC complex and not by DNA methylation.
Biochem Biophys Res Commun. 2009; 390(1):48-53 [PubMed] Related Publications
Although rituximab is a critical monoclonal antibody therapy for CD20-positive B-cell lymphomas, rituximab resistance showing a CD20-negative phenotypic change has been a considerable clinical problem. Here we demonstrate that CD20 mRNA and protein expression is repressed by recruitment of a histone deacetylase protein complex to the MS4A1 (CD20) gene promoter in CD20-negative transformed cells after treatment with rituximab. CD20 mRNA and protein expression were stimulated by decitabine (5-Aza-dC) in CD20-negative transformed cells, and was enhanced by trichostation A (TSA). Immunoblotting indicated that DNMT1 expression was first downregulated 1 day after treatment with 5-Aza-dC, but IRF4 and Pu.1, the transcriptional regulators of MS4A1, were still expressed with or without 5-Aza-dC. Interestingly, CpG methylation of the MS4A1 promoter was not observed in CD20-negative transformed cells without 5-Aza-dC. A chromatin immunoprecipitation (ChIP) assay indicated that the Sin3A-HDAC1 co-repressor complex was recruited to the promoter and dissociated from the promoter with 5-Aza-dC and TSA, resulting in histone acetylation. Under these conditions, IRF4 and Pu.1 were continually recruited to the promoter with or without 5-Aza-dC and TSA. These results suggest that recruitment of the Sin3A-HDAC1 complex is related to downregulation of CD20 expression in CD20-negative B-cells after treatment with rituximab.

Kumamoto K, Fujita K, Kurotani R, et al.
ING2 is upregulated in colon cancer and increases invasion by enhanced MMP13 expression.
Int J Cancer. 2009; 125(6):1306-15 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Inhibitor of growth 2 (ING2) is associated with chromatin remodeling and regulation of gene expression by binding to a methylated histone H3K4 residue and recruiting HDAC complexes to the region. The aim of our study is to investigate the regulation of ING2 expression and the clinical significance of upregulated ING2 in colon cancer. Here, we show that the ING2 mRNA level in colon cancer tissue increased to more than twice than that in normal mucosa in the 45% of colorectal cancer cases that we examined. A putative NF-kappaB binding site was found in the ING2 promoter region. We confirmed that NF-kappaB could bind to the ING2 promoter by EMSA and luciferase assays. Subsequent microarray analyses revealed that ING2 upregulates expression of matrix metalloproteinase 13 (MMP13), which enhances cancer invasion and metastasis. ING2 regulation of MMP13 expression was confirmed in both ING2 overexpression and knock down experiments. MMP13 expression was further induced by coexpression of ING2 with HDAC1 or with mSin3A, suggesting that the ING2-HDAC1-mSin3A complex members regulates expression of MMP13. In vitro invasion assay was performed to determine functional significance of ING2 upregulation. ING2 overexpressed cells exhibited greater invasive potential. Taken together, upregulation of ING2 was associated with colon cancer and MMP13-dependent cellular invasion, indicating that ING2 expression might be involved with cancer invasion and metastasis.

Daigeler A, Adrien D, Klein-Hitpass L, et al.
Malignant fibrous histiocytoma--pleomorphic sarcoma, NOS gene expression, histology, and clinical course. A pilot study.
Langenbecks Arch Surg. 2010; 395(3):261-75 [PubMed] Related Publications
PURPOSE: The new classification of malignant fibrous histiocytoma leaves only a small group of tumors without further line of differentiation, so-called pleomorphic sarcomas, not otherwise specified (NOS) as a pseudo-entity. This study focused on these tumors and analyzed the association of gene expression profiles to clinical outcome.
MATERIALS AND METHODS: Ten fresh samples of pleomorphic NOS sarcomas were evaluated histopathologically and by means of microarray analysis. Analysis of expression profiles was performed by clustering methods as well as by statistical analysis of primary vs recurrent tumors, irradiated vs nonirradiated tumors, tumors of patients above and below 60 years of age, male and female, and of tumors that developed metastatic or recurrent disease during the clinical course and those that did not.
RESULTS: Tumor clustering did not correlate to any histopathological or clinical finding. Detailed gene expression analysis showed a variety of genes whose upregulation (platelet-derived growth factor receptor alpha polypeptide, solute carrier family 39 member 14, solute carrier family 2 member 3, pleiotrophin, trophinin, pleckstrin and Sec7 domain containing 3, enolase 2, biglycan, SH3 and cysteine-rich domain, matrix metalloproteinases 16) and whose downregulation (tissue inhibitor of metalloproteinase 4, hairy/enhancer of split related with YRPW motif 2, protein tyrosine phosphatase receptor-type Z polypeptide 1, SH3 domain GRB2-like 2, microtubule-associated protein 7, potassium voltage-gated channel shaker-related subfamily member 1, RUN and FYVE domain containing 3, Sin3A-associated protein 18 kDa, proline-rich 4, calcium/calmodulin-dependent protein kinase ID, myeloid/lymphoid or mixed-lineage leukemia translocated to 3, insulin-like growth factor binding protein 5, nucleoside diphosphate-linked moiety X-type motif 9, NudC domain containing 3, imprinted in Prader-Willi syndrome, TAF6-like RNA polymerase II p300/CBP-associated factor 65 kDa, WD repeat and SOCS box-containing 2, adenosine diphosphate ribosylation factor 3, KRR1, proliferation-associated 2G4; CD36, complement component (3b/4b) receptor 1, solute carrier family 4 sodium bicarbonate cotransporter member 4, lipoprotein lipase (LPL), GATA binding protein 3, LPL, glutathione peroxidase 3, D: -aspartate oxidase, apolipoprotein E, sphingomyelin phosphodiesterase acid-like 3A) were associated with poor clinical outcome in terms of development of metastatic or recurrent disease.
CONCLUSIONS: The classification of these tumors may undergo further changes in the future. Gene expression profiling can provide additional information to categorize pleomorphic sarcoma (NOS) and reveal potential prognostic factors in this "entity."

Weber A, Marquardt J, Elzi D, et al.
Zbtb4 represses transcription of P21CIP1 and controls the cellular response to p53 activation.
EMBO J. 2008; 27(11):1563-74 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
In response to stimuli that activate p53, cells can undergo either apoptosis or cell cycle arrest, depending on the precise pattern of p53 target genes that is activated. We show here that Zbtb4, a transcriptional repressor protein, associates with the Sin3/histone deacetylase co-repressor and represses expression of P21CIP1 as part of a heterodimeric complex with Miz1. In vivo, expression of ZBTB4 is downregulated in advanced stages of multiple human tumours. In cell culture, depletion of ZBTB4 promotes cell cycle arrest in response to activation of p53 and suppresses apoptosis through regulation of P21CIP1, thereby promoting long-term cell survival. Our data suggest that Zbtb4 is a critical determinant of the cellular response to p53 activation and reinforce the notion that p21Cip1 can provide an essential survival signal in cells with activated p53.

Wilkinson DS, Tsai WW, Schumacher MA, Barton MC
Chromatin-bound p53 anchors activated Smads and the mSin3A corepressor to confer transforming-growth-factor-beta-mediated transcription repression.
Mol Cell Biol. 2008; 28(6):1988-98 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
In hepatic cells, Smad and SnoN proteins converge with p53 to repress transcription of AFP, an oncodevelopmental tumor marker aberrantly reactivated in hepatoma cells. Using p53- and SnoN-depleted hepatoma cell clones, we define a mechanism for repression mediated by this novel transcriptional partnership. We find that p53 anchors activated Smads and the corepressor mSin3A to the AFP distal promoter. Sequential chromatin immunoprecipitation analyses and molecular modeling indicate that p53 and Smad proteins simultaneously occupy overlapping p53 and Smad regulatory elements to establish repression of AFP transcription. In addition to its well-known function in antagonizing transforming growth factor beta (TGF-beta) responses, we find that SnoN actively participates in AFP repression by positively regulating mSin3A protein levels. We propose that activation of TGF-beta signaling restores a dynamic interplay between p53 and TGF-beta effectors that cooperate to effectively target mSin3A to tumor marker AFP and reestablish transcription repression.

Suzuki H, Ouchida M, Yamamoto H, et al.
Decreased expression of the SIN3A gene, a candidate tumor suppressor located at the prevalent allelic loss region 15q23 in non-small cell lung cancer.
Lung Cancer. 2008; 59(1):24-31 [PubMed] Related Publications
To identify the tumor suppressor genes (TSG) associated with non-small cell lung cancers (NSCLC), we performed the loss of heterozygosity (LOH) analysis in NSCLC samples from 66 patients. We focused on the novel hot spot region on 15q14-24 with eight polymorphic microsatellite markers. Frequent allelic loss was detected in 33 of 48 informative cases (69%) at D15S984 on 15q23. We defined the fine map on the region and identified the SIN3A gene as a candidate TSG. The SIN3A gene product is a component of the histone deacetylase (HDAC) complex and plays essential roles in early embryonic development and the proliferation and survival of a variety of cells through the repression of diverse signaling pathways. Our expression analysis revealed more frequent down-regulation of the SIN3A mRNA in 19 of 31 cases (61%) of NSCLCs in comparison to those of other flanking genes (16-42%), albeit the correlation of the decreased expression with the LOH did not attain statistic significance. These results suggest that the attenuated function of SIN3A due to a decreased level of expression may result in epigenetic de-regulation of growth-related genes through histone acetylation, which leads to the tumorigenesis of lung cancer cells. To our knowledge, this is the first evidence of the down-regulation of the SIN3A gene in human cancer.

Sharma D, Saxena NK, Davidson NE, Vertino PM
Restoration of tamoxifen sensitivity in estrogen receptor-negative breast cancer cells: tamoxifen-bound reactivated ER recruits distinctive corepressor complexes.
Cancer Res. 2006; 66(12):6370-8 [PubMed] Article available free on PMC after 29/04/2017 Related Publications
Breast tumors expressing estrogen receptor-alpha (ER) respond well to therapeutic strategies using selective ER modulators, such as tamoxifen. However, approximately 30% of invasive breast cancers are hormone independent because they lack ER expression due to hypermethylation of ER promoter. Treatment of ER-negative breast cancer cells with demethylating agents [5-aza-2'-deoxycytidine (5-aza-dC)] and histone deacetylase (HDAC) inhibitors (trichostatin A) leads to expression of ER mRNA and functional protein. Here, we examined whether epigenetically reactivated ER is a target for tamoxifen therapy. Following treatment with trichostatin A and 5-aza-dC, the formerly unresponsive ER-negative MDA-MB-231 breast cancer cells became responsive to tamoxifen. Tamoxifen-mediated inhibition of cell growth in these cells is mediated at least in part by the tamoxifen-bound ER. Tamoxifen-bound reactivated ER induces transcriptional repression at estrogen-responsive genes by ordered recruitment of multiple distinct chromatin-modifying complexes. Using chromatin immunoprecipitation, we show recruitment of two different corepressor complexes to ER-responsive promoters in a mutually exclusive and sequential manner: the nuclear receptor corepressor-HDAC3 complex followed by nucleosome remodeling and histone deacetylation complex. The mechanistic insight provided by this study might help in designing therapeutic strategies directed toward epigenetic mechanisms in the prevention or treatment of breast cancer.

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