Modulates Breast Cancer Progression Research Articles

Design and Structural Investigation of a Series of Prodigiosin and 1,10-Phenanthroline Derivatives as Novel and Highly Potent Anticancer Therapeutic Drugs or Active Pharmaceutical Ingredients

Breast cancer is considered as a leading cancer type with the secondary highest possibility of brain metastasis. Most research in breast cancer is currently directed into the mortality of brain metastatic breast cancer. However, there is no effective treatment or anticancer therapeutics specifically for this cancer type. Hence, development of effective and novel anticancer therapeutic drugs/APIs to inhibit HDAC and mTOR, playing very important role on modulating breast cancer progression is an increasing demand. In this study, the structure-activity relationship and in silico modeling of a series of prodigiosin and 1,10-phenanthroline derivatives as highly potent anticancer therapeutic drugs/APIs against mTOR and HDAC enzymes have been investigated. Compared to the natural product Ps, 20 of the highly potent ligands, especially 2a, 6b, 13 and 13a, have exhibited very promising binding energies ranging from –9.4 to –7.1 kcal/mol and inhibition constants ranging from 225 to 569 nM against HDAC1 and/or mTOR enzymes. Ligands 2a, 5, 6b, 7b and 13 in particular show effective dual action against both enzymes. The findings from the in silico modeling studies have also been supported with MD simulations and ADMET study with Lipinski’s rule of five, providing outstanding therapeutic potential for the breast cancer brain metastasis.

Modulatory effects of point-mutated IL-32θ (A94V) on tumor progression in triple-negative breast cancer cells.

Breast cancer is a frequently diagnosed cancer and the leading cause of death among women worldwide. Tumor-associated macrophages stimulate cytokines and chemokines, which induce angiogenesis, metastasis, proliferation, and tumor-infiltrating immune cells. Although interleukin-32 (IL-32) has been implicated in the development and modulation of several cancers, its function in breast cancer remains elusive. Mutation of interleukin-32θ (IL-32θ) in the tissues of patients with breast cancer was detected by Sanger sequencing. RT-qPCR was used to detect the mRNA levels of inflammatory cytokines, chemokines, and mediators. The secreted proteins were detected using respective enzyme-linked immunosorbent assays. Evaluation of the inhibitory effect of mutant IL-32θ on proliferation, migration, epithelial-mesenchymal transition (EMT), and cell cycle arrest in breast cancer cells was conducted using MTS assays, migration assays, and Western blotting. A point mutation (281C>T, Ala94Val) was detected in IL-32θ in both breast tumors and adjacent normal tissues, which suppressed the expression of pro-inflammatory factors, EMT factors, and cell cycle related factors. Mutated IL-32θ inhibited the expression of inflammatory factors by regulating the NF-κB pathway. Furthermore, mutated IL-32θ suppressed EMT markers and cell cycle related factors through the FAK/PI3K/AKT pathway. It was inferred that mutated IL-32θ modulates breast cancer progression. Mutated IL-32θ (A94V) inhibited inflammation, EMT, and proliferation in breast cancer by regulating the NF-κB (p65/p50) and FAK-PI3K-GSK3 pathways.

Targeted Inhibition of Fibroblast Growth Factor Receptor 1-GLI Through AZD4547 and GANT61 Modulates Breast Cancer Progression.

The underlying mechanism of fibroblast growth factor receptor 1 (FGFR1) mediated carcinogenesis is still not fully understood. For instance, FGFR1 upregulation leads to endocrine therapy resistance in breast cancer patients. The current study aimed to identify FGFR1-linked genes to devise improved therapeutic strategies. RNA-seq and microarray expression data of 1,425 breast cancer patients from two independent cohorts were downloaded for the analysis. Gene Set Enrichment Analysis (GSEA) was performed to identify differentially expressed pathways associated with FGFR1 expression. Validation was done using 150 fresh tumor biopsy samples of breast cancer patients. The clinical relevance of mRNA and protein expression of FGFR1 and its associated genes were also evaluated in mouse embryonic fibroblasts (MEFs) and breast cancer cell line (MDA-MB-231). Furthermore, MDA-MB-231 cell line was treated with AZD4547 and GANT61 to identify the probable role of FGFR1 and its associated genes on cells motility and invasion. According to GSEA results, SHH pathway genes were significantly upregulated in FGFR1 patients in both discovery cohorts of breast cancer. Statistical analyses using both discovery cohorts and 150 fresh biopsy samples revealed strong association of FGFR1 and GLI1, a member of SHH pathway. The increase in the expression of these molecules was associated with poor prognosis, lymph node involvement, late stage, and metastasis. Combined exposures to AZD4547 (FGFR1 inhibitor) and GANT61 (GLI1 inhibitor) significantly reduced cell proliferation, cell motility, and invasion, suggesting molecular crosstalk in breast cancer progression and metastasis. A strong positive feedback mechanism between FGFR1–GLI1 axis was observed, which significantly increased cell proliferation and metastasis. Targeting FGFR1–GLI1 simultaneously will significantly improve the prognosis of breast cancer in patients.

An exploration of the role of exercise in modulating breast cancer progression in vitro: a systematic review and meta-analysis.

Breast cancer is the most prevalent cancer in women worldwide. In the United Kingdom, approximately 5% of all breast cancers are already metastatic at the time of diagnosis. An abundance of literature shows that exercise can have beneficial effects on the outcome and prognosis of breast cancer patients, yet the molecular mechanisms remain poorly understood. There are several in vitro models that aim to recapitulate the response of breast cancer to exercise in vivo; this systematic review and meta-analysis summarizes the existing literature. The following search terms were used to conduct a systematic literature search using a collection of databases (last search performed May 2020): "in vitro," "exercise," and "breast cancer." Only studies that investigated the effects of exercise on breast cancer in vitro were included. Standardized mean differences (SMD) were calculated to determine pooled effect sizes. This meta-analysis has successfully demonstrated that various identified exercise interventions on breast cancer cells in vitro significantly reduced breast cancer cell viability, proliferation, and tumorigenic potential (SMD = -1.76, P = 0.004, SMD = -2.85, P = 0.003, and SMD = -3.15, P = 0.0008, respectively). A clear direction of effect was found with exercise on breast cancer cell migration in vitro, however this effect was not significant (SMD = -0.62, P = 0.317). To our knowledge, this is the first meta-analysis and systematic review investigating and summarizing literature on exercise and breast cancer in vitro, highlighting models used and priority areas for future research focus.

Abstract P3-01-11: Targeting RAGE inhibits breast cancer invasion and metastasis

Abstract Background: Breast cancer (BC) is treatable with early detection, but once metastasis occurs, there is no cure. Therefore, it is of upmost importance to find targetable biomarkers that are involved in modulating the multi-step metastatic process. The Receptor for Advanced Glycation Endproducts (RAGE) and its ligands are an inflammatory pathway that are involved in modulating breast cancer progression and metastasis. We recently demonstrated that genetic or pharmacological interruption of RAGE signaling affected tumor progression and metastasis. However, no studies have dissected the role of RAGE in tumor growth from the metastatic cascade. Here, we show for the first time in multiple metastatic breast cancer models that targeting RAGE impairs BC metastasis. Methods: We tested the anti-metastatic effect of RAGE in vitro using the RAGE inhibitor FPS-ZM1 or RAGE shRNA knockdown in cell invasion, proliferation, migration and sphere formation assays (with 4T1, Py8119 and E0771 mouse BC cells). For in vivo assays we used orthotopic BC models (4T1/BALB/c and E0771 & Py8119/C57BL6) and experimental metastasis assays (tail vein injection of 4T1/BALB/c and Py8119/C57BL6). To target RAGE, we used genetic (shRNA in 4T1 cells and RAGE knockout in C57BL6 mice) and pharmacological approaches (I.P. injection of FPS-ZM1). To investigate the synergistic effects of RAGE inhibition on progression and metastasis, we tested combination therapy of low-dose doxorubicin and FPS-ZM1. Results: Inhibition of RAGE with FPS-ZM1 (1-5uM) impaired tumor cell invasion of 4T1, E0771 and Py8119 cells. Similarly, in spheroid assays, treatment of cells with FPS-ZM1 resulted in fewer and smaller colonies. However, FPS-ZM1 treatment did not affect cell proliferation. In vivo studies revealed that FPS-ZM1 (1mg/kg) has a modest effect on tumor growth in 4T1/BALB/c injected mice but displayed a dramatic inhibitory effect on metastasis to the lungs. In experimental metastasis assays, tail-vein injection of 4T1 cells in BALB/c mice demonstrated that FPS-ZM1 treatment strongly impaired metastatic disease in mice compared to controls. To dissect the genetic role of RAGE in the tumor versus host, we test the effect of RAGE knockdown in 4T1 cells in experimental metastasis assays. RAGE shRNA impaired metastasis to the lungs, albeit to a lower degree seen with the RAGE inhibitor. To test the role of the host, we injected Py8119 cells into wild-type and RAGE knockout (RKO) mice. RKO mice displayed fewer metastatic burden compared to wild-type mice. Finally, in our combination treatment experiments, treatment of 4T1-injected BALB/c mice with Doxorubicin and FPS-ZM1 (alone and in combination), demonstrated that drug combination was more effective in inhibiting lung metastasis than either reagent alone. We are currently assessing how RAGE mechanistically drives these metastatic changes. Conclusion: Our data strongly suggests RAGE plays an important role in breast cancer metastasis, with less of an effect on tumor growth. Ongoing studies in our lab are testing which stage of the metastatic cascade RAGE is involved in, and the underlying mechanisms driving these processes. In conclusion, the use of RAGE inhibitors could represent a novel therapeutic approach for metastatic breast cancer. Citation Format: Gyong Ha Hwang, Melinda Magna, Barbara Mera, Toni Yeasky, Taekyoung Kwak, Lucas Outcault, Masaru Takabatake, Thuy-Mai Le, Marc E. Lippman, Barry I. Hudson. Targeting RAGE inhibits breast cancer invasion and metastasis [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-01-11.

The deubiquitinating enzyme USP1 modulates ERα and modulates breast cancer progression.

Breast cancer is one of the most common malignancies worldwide, while the luminal types (ERα positive) accounts for two third of all breast cancer cases. Although ERα positive breast cancer could be effective controlled by endocrine therapy, most of the patients will develop endocrine resistance, which becomes a headache clinical issue for breast cancer field. Endocrine resistance could be caused by multiple pathway disorders, the dys-regulation of ERα signaling might be a critical factor, which makes it urgent and important to reveal the potential molecular mechanism of ERα signaling. In our current study, we identified a new deubiquitination enzyme USP1 through screening the whole DUB (Deubiquitinases) siRNA library. The expression of USP1 is elevated in human breast cancer compared with normal mammary tissues. Importantly, USP1 expression levels are specially correlated with poor survival in ERα positive patients. USP1 depletion inhibited breast cancer cell progression and ERα signaling activity. Immuno-precipitation assays indicate that USP1 associates with ERα and promotes its stability possibly via inhibiting ERα K48-linked poly-ubiquitination. In conclusion, our data implicate a non-genomic mechanism by USP1 via stabilizing ERα protein controls ERα target gene expression linked to breast cancer progression.

NMT1 inhibition modulates breast cancer progression through stress-triggered JNK pathway

Myristoylation is one of key post-translational modifications that involved in signal transduction, cellular transformation and tumorigenesis. Increasing evidence demonstrates that targeting myristoylation might provide a new strategy for eliminating cancers. However, the underlying mechanisms are still yielded unclear. In this study, we demonstrated that genetic inhibition of N-myristoyltransferase NMT1 suppressed initiation, proliferation and invasion of breast cancer cells either in vitro or in vivo. We identified ROS could negatively regulate NMT1 expression and NMT1 knockdown conversely promoted oxidative stress, which formed a feedback loop. Furthermore, inhibition of NMT1 caused degraded proteins increase and ER stress, which cross-talked with mitochondria to produce more ROS. And both of oxidative stress and ER stress could activate JNK pathway, leading to autophagy which abrogated breast cancer progression especially triple-negative breast cancer (TNBC). These studies provide a preclinical proof of concept for targeting NMT1 as a strategy to treat breast cancer.

Expression and Functional Characterization of Breast Cancer-Associated Cytochrome P450 4Z1 in Saccharomyces cerevisiae.

CYP4Z1 is an "orphan" cytochrome P450 (P450) enzyme that has provoked interest because of its hypothesized role in breast cancer through formation of the signaling molecule 20-hydroxyeicosatetraenoic acid (20-HETE). We expressed human CYP4Z1 in Saccharomyces cerevisiae and evaluated its catalytic capabilities toward arachidonic and lauric acids (AA and LA). Specific and sensitive mass spectrometry assays enabled discrimination of the regioselectivity of hydroxylation of these two fatty acids. CYP4Z1 generated 7-, 8-, 9-, 10-, and 11-hydroxy LA, whereas the 12-hydroxy metabolite was not detected. HET0016, the prototypic CYP4 inhibitor, only weakly inhibited laurate metabolite formation (IC50 ∼15 μM). CYP4Z1 preferentially oxidized AA to the 14(S),15(R)-epoxide with high regioselectivity and stereoselectivity, a reaction that was also insensitive to HET0016, but neither 20-HETE nor 20-carboxy-AA were detectable metabolites. Docking of LA and AA into a CYP4Z1 homology model was consistent with this preference for internal fatty acid oxidation. Thus, human CYP4Z1 has an inhibitor profile and product regioselectivity distinct from most other CYP4 enzymes, consistent with CYP4Z1's lack of a covalently linked heme. These data suggest that, if CYP4Z1 modulates breast cancer progression, it does so by a mechanism other than direct production of 20-HETE.

Oral Administration of Tualang and Manuka Honeys Modulates Breast Cancer Progression in Sprague-Dawley Rats Model.

Breast cancer has been recognized as the leading cause of death in women worldwide. Research has shown the importance of complementary and alternative therapies in cancer. In this study, we investigated the antitumoural therapeutic effects of Malaysian Tualang honey (TH) and Australian/New Zealand Manuka honey (MH) against breast cancer in rats. Thirty syngeneic virgin female Sprague-Dawley (SD) rats were induced by the carcinogen 1-methyl-1-nitrosourea (MNU) 80 mg/kg. The treatment started when first palpable tumour reached 10–12 mm in size by dividing rats into following groups: Group 0 (negative control); Group 1 (positive control); and Groups 2 and 3 which received 1.0 g/kg body weight/day of TH and MH, respectively, for 120 days. The data demonstrate that cancer masses in TH and MH treated groups showed a lower median tumour size, weight, and multiplicity compared with the nontreated positive control (p < 0.05). Treatment also showed a dramatic slower growth rate (up to 70.82%) compared with the nontreated control (0%) (p < 0.05). The antitumoural effect was mediated through modulation of tumour growth, tumour grading, estrogenic activity, and haematological parameters. Our findings demonstrate that systemic administration of TH and MH increases the susceptibility of expression of proapoptotic proteins (Apaf-1, Caspase-9, IFN-γ, IFNGR1, and p53) and decreases the expression of antiapoptotic proteins (TNF-α, COX-2, and Bcl-xL 1) in its mechanism of action. This highlights a potential novel role for TH and MH in alleviating breast cancer.

Abstract P1-07-27: Neutrophil elastase modulates breast cancer progression by fostering collective cell detachment and tumor emboli dissemination

Abstract Proteases constitute a large family of enzymes involved in several processes, including degradation and remodeling of the extracellular matrix to drive dissemination of cancer cells into adjacent tissue. Within this large family, the serine protease neutrophil elastase (NE) has been proven clinically meaningful in breast cancer. Indeed, high levels of NE correlate with poor outcome and endocrine resistance in breast cancer patients. In an experimental model it has been demonstrated that estrogen receptor positive (ER+) MCF7 breast cancer cells grow in suspension as 3D-spheroids in NE-addicted medium, thus resembling the micropapillae of a human breast cancer characterized by high propensity to metastasize, i.e. the micropapillary carcinoma. We hypothesized that NE may produce disarrangement of tumor cell adhesion to the substrate fostering neoplastic lymphovascular invasion (LVI) and metastasis. ER+/E-Cadherin (E-CAD)+/HER2- (MCF7, T-47D, ZR-75-1), ER+/E-CAD+/HER2+ (BT-474), ER-/E-CAD-/HER2+ (SK-BR-3) and ER-/E-CAD-/HER2- (MDA-MB-231) cells were grown with serine proteases (NE, cathepsin-G), hyaluronidase and collagenase. NE and cathepsin-G led to 3D-spheroid formation of ER+/E-CAD+ cells only. In 3D-spheroids from MCF7 cells grown with NE the luminal Epithelial Membrane Antigen (EMA) lined the external border of cell clusters, which faced cancer associated fibroblasts in co-cultures experiments, thus recapitulating the inverted polarity of MPCs. MCF7 3D-spheroids were tamoxifen resistant. Injection of NE in tumors of MCF7 cells in SCID mice triggered neoplastic cluster detachment, micropapillae, vascular emboli similar to 3D-spheorids and metastases. In a cohort of human breast carcinomas with LVI the MCF7-3D-spheroid-alike pattern was the most prevalent in tumor emboli. Immunohistochemical NE expression was mainly detected in polymorphous neutrophilic granulocytes (PMNs) within vessels and in the stroma and PMNs were significantly higher in breast carcinomas with LVI. In fully developed metastases within lymph-nodes, which reverted the EMA expression as in the primary tumor, no NE+ PMNs were observed. Our results may explain why high levels of NE negatively act on patient prognosis by creating a favorable environment for breast cancer invasion and metastasis. Citation Format: Caterina Marchio, Laura Annaratone, Davide Balmativola, Maria Stella Scalzo, Stefania Bolla, Silvia Grasso, Isabella Russo, Federica Fusella, Luigia Macrì, Mara Brancaccio, Paola Defilippi, Anna Sapino. Neutrophil elastase modulates breast cancer progression by fostering collective cell detachment and tumor emboli dissemination [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-07-27.

The relationship between semaphorin 3C and microvessel density in the progression of breast and oral neoplasia

This study aimed to identify the expression of semaphorin 3C (SEMA3C) in the normal-metastatic spectrum of breast and oral cancers, and correlate expression with microvessel density (MVD, CD31), a surrogate marker of angiogenesis. Histological analysis revealed that SEMA3C expression was reduced in the development of oral cancer from normal oral tissue (P<0.0001) and expression was inversely correlated with MVD (r=−0.394, P=0.05). In contrast, SEMA3C expression increased in the transition from normal to invasive breast disease in epithelial/tumour cells (P=0.001) and endothelial cells (P=0.006), with both correlating weakly with MVD (r=0.35, p=0.03 and r=0.243, p=0.041 respectively). Furthermore, histological analysis of a breast cancer tissue microarray revealed a weak positive correlation with tumour grade (r=0.305, P=<0.001) and biological phenotype (r=0.237, p=0.004) with tumour cell expression of SEMA3C highest in triple negative and ER−, PR−, HER2+ subtypes. These data suggest that SEMA3C expression is differentially regulated in the development and progression of breast versus oral neoplasia, and that increased expression of SEMA3C may be modulating breast cancer progression and angiogenesis, and could represent a biomarker of metastatic disease.

Nogo-B Receptor (NgBR): A New Receptor that Modulates Blood Vessel Formation

Nogo-B is an isoform of reticulon-4 (RTN4) that distributes mainly in the endoplasmic reticulum. Nogo-B binds to its receptor, Nogo-B receptor (NgBR), to modulate blood vessel formation. Animal with Nogo-B knockout is phenotypically normal. NgBR is a type I receptor with a single transmembrane domain that binds Nogo-B and probably other angiogenic factors. NgBR knockout in zebra fish leads to abnormal formation of intersomite vessels suggesting NgBR plays a more important role in the Nogo-B/NgBR signaling pathway. It is reported that NgBR plays a role in dolichol biosynthesis, protein N-glycosylation, stabilizes Niemann-Pick type C2 protein, regulates intracellular cholesterol trafficking, controls blood vessel development, and modulates breast cancer progression. However, the research in NgBR remains in its early stage and needs further exploration.

DEC1 is positively associated with the malignant phenotype of invasive breast cancers and negatively correlated with the expression of claudin-1

Differentiated embryo-chondrocyte expressed gene 1 (DEC1) is a basic helix-loop-helix transcriptional regulator, reportedly involved in cell growth, differentiation, apoptosis and tumorigenesis. In breast cancer, DEC1 expression correlates with increased malignant potential and invasiveness. Nevertheless, the detailed mechanisms by which DEC1 modulates breast cancer progression are still unclear. Claudin-1, an important tight junction protein, functions as a tumor invasion suppressor. In the present study, the relationship between DEC1 and claudin-1 in 147 cases of invasive breast ductal carcinomas was examined by immunohistochemistry. Based on the data, DEC1 expression was elevated in invasive breast ductal carcinomas and DEC1 levels were positively correlated with tumor grade (P=0.023). Moreover, DEC1 expression was negatively correlated with the claudin-1 level (correlation coefficient=-0.245, P=0.003). We further identified that, in MCF-7 and MDA-MB-231 breast cancer cell lines, DEC1 knockdown led to the enhanced expression of claudin-1 at both the mRNA and protein levels, and reduced cell invasive capacity. Collectively, our data suggest that overexpression of DEC1 may promote the invasiveness of breast cancer through downregulation of claudin-1.

Abstract 91: The CUL4A ubiquitin ligase, a putative target gene at the 13q34 amplicon and its role in breast cancer pathogenesis &amp; progression

Abstract Breast cancer is a complex and heterogeneous disease and one of the most frequent causes of cancer deaths in developed countries. DNA copy number alterations occur frequently in breast tumours. Regions of DNA amplification are of major interest since often contain oncogenes whose increased expression confers tumour cells a selective advantage and contributes to the carcinogenesis process. In our laboratory prior analysis of familiar and sporadic breast tumours by using array-CGH identified an amplification event at the 13q34 region with an overall frequency of 4.5% that increased to 8.1% in BRCA1-associated tumours. Comprehensive characterization of the amplicon allowed us to define CUL4A as one of the most likely putative oncogenes. CUL4A is an E3 Ubiquitin Ligase which is amplified and/or overexpressed in primary breast tumours and involved in functions such as chromatin regulation, cell cycle regulation or DNA repair through ubiquitylation of NER pathway members. Its deregulation could have implications for oncogenic transformation and treatment response to DNA-damaging agents. One of such compounds is Trabectedin a marine-derived drug that presents antitumor activity in sarcomas and ovarian cancer. To elucidate the possible implication of CUL4A in the initial steps of the tumorigenic process we conducted the stable up-regulation of CUL4A in human mammary epithelial cells (184B5), and in NIH3T3 mouse-derived cell line by lentiviral infection. We also stably silenced CUL4A in the human breast cancer cell lines MDA-MB-157 and HCC1937 that present amplification and/or overexpression of CUL4A. With these modified cell lines we performed functional assays in different in vitro systems such as viability experiments, colony formation both in plastic and in soft agar and 3-D cultures in Matrigel. In order to measure sensitivity to Trabectedin we used silenced CUL4A breast cancer cell lines to perform clonogenic assays. Our preliminary results in CUL4A overexpression in 184B5 model system showed increase in proliferation and colony formation ability. On the other hand, CUL4A silencing in breast cancer cell lines resulted in diminished proliferation and decreased colony-forming abilities in both anchorage dependent and independent conditions. Concerning DNA-repair implication, it seems that high levels of CUL4A could be a good predictor of Trabectedin response. Our results indicate that CUL4A would play a role in promoting oncogenesis and/or in modulating breast cancer progression. Further evaluation of CUL4A amplification/overexpression impact on the maintenance of genome integrity will help elucidate its full potential for therapeutic intervention in breast and other cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 91. doi:1538-7445.AM2012-91

Overexpression of histone deacetylase HDAC1 modulates breast cancer progression by negative regulation of estrogen receptor alpha.

The interaction between 17beta-estradiol and estrogen receptor alpha (ER-alpha) plays an important role in breast carcinogenesis and breast cancer treatment. ER-alpha is a critical growth regulatory gene in breast cancer and its expression level is tightly linked to the prognosis and treatment outcomes of breast cancer patients. Loss of ER-alpha expression in breast epithelial cells is critical for breast cancer progression. The underlying molecular mechanisms for this loss, however, are poorly defined. Histone deacetylases (HDACs) are implicated in the alteration of chromatin assembly and tumorigenesis. We show that histone deacetylase 1 (HDAC1) interacts with ER-alpha in vitro and in vivo and suppresses ER-alpha transcription activity. The interaction of HDAC1 with ER-alpha was mediated by the AF-2 and DBD domains of ER-alpha. We observed an endogenous interaction of HDAC1 with ER-alpha in breast cancer cells, which was decreased in the presence of estrogen. Interestingly, overexpression of HDAC1 in stable transfected MCF-7 clones induced loss of ER-alpha and significantly increased cell proliferation and colony formation, as compared to the control MCF-7 cells, whereas treatment of stable MCF-7 clones with the HDAC specific inhibitor trichostatin A (TSA) induced re-expression of ER-alpha mRNA and protein. Our findings strongly suggest that HDAC1 affects breast cancer progression by promoting cellular proliferation in association with a reduction in both ER-alpha protein expression and transcriptional activity. Thus, HDAC1 may be a potential target for therapeutic intervention in the treatment of a subset of ER-negative breast cancers.