Publications by authors named "Suzanne A W Fuqua"

62 Publications

Hormonal modulation of ESR1 mutant metastasis.

Oncogene 2021 Feb 15;40(5):997-1011. Epub 2020 Dec 15.

Lester & Sue Smith Breast Center, Baylor College of Medicine, Houston, TX, USA.

Estrogen receptor alpha gene (ESR1) mutations occur frequently in ER-positive metastatic breast cancer, and confer clinical resistance to aromatase inhibitors. Expression of the ESR1 Y537S mutation induced an epithelial-mesenchymal transition (EMT) with cells exhibiting enhanced migration and invasion potential in vitro. When small subpopulations of Y537S ESR1 mutant cells were injected along with WT parental cells, tumor growth was enhanced with mutant cells becoming the predominant population in distant metastases. Y537S mutant primary xenograft tumors were resistant to the antiestrogen tamoxifen (Tam) as well as to estradiol (E) withdrawal. Y537S ESR1 mutant primary tumors metastasized efficiently in the absence of E; however, Tam treatment significantly inhibited metastasis to distant sites. We identified a nine-gene expression signature, which predicted clinical outcomes of ER-positive breast cancer patients, as well as breast cancer metastasis to the lung. Androgen receptor (AR) protein levels were increased in mutant models, and the AR agonist dihydrotestosterone significantly inhibited estrogen-regulated gene expression, EMT, and distant metastasis in vivo, suggesting that AR may play a role in distant metastatic progression of ESR1 mutant tumors.
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http://dx.doi.org/10.1038/s41388-020-01563-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8020875PMC
February 2021

RON signalling promotes therapeutic resistance in ESR1 mutant breast cancer.

Br J Cancer 2021 01 1;124(1):191-206. Epub 2020 Dec 1.

Lester & Sue Smith Breast Center, Baylor College of Medicine, Houston, TX, USA.

Background: Oestrogen Receptor 1 (ESR1) mutations are frequently acquired in oestrogen receptor (ER)-positive metastatic breast cancer (MBC) patients who were treated with aromatase inhibitors (AI) in the metastatic setting. Acquired ESR1 mutations are associated with poor prognosis and there is a lack of effective therapies that selectively target these cancers.

Methods: We performed a proteomic kinome analysis in ESR1 Y537S mutant cells to identify hyperactivated kinases in ESR1 mutant cells. We validated Recepteur d'Origine Nantais (RON) and PI3K hyperactivity through phospho-immunoblot analysis, organoid growth assays, and in an in vivo patient-derived xenograft (PDX) metastatic model.

Results: We demonstrated that RON was hyperactivated in ESR1 mutant models, and in acquired palbociclib-resistant (PalbR) models. RON and insulin-like growth factor 1 receptor (IGF-1R) interacted as shown through pharmacological and genetic inhibition and were regulated by the mutant ER as demonstrated by reduced phospho-protein expression with endocrine therapies (ET). We show that ET in combination with a RON inhibitor (RONi) decreased ex vivo organoid growth of ESR1 mutant models, and as a monotherapy in PalbR models, demonstrating its therapeutic efficacy. Significantly, ET in combination with the RONi reduced metastasis of an ESR1 Y537S mutant PDX model.

Conclusions: Our results demonstrate that RON/PI3K pathway inhibition may be an effective treatment strategy in ESR1 mutant and PalbR MBC patients. Clinically our data predict that ET resistance mechanisms can also contribute to CDK4/6 inhibitor resistance.
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http://dx.doi.org/10.1038/s41416-020-01174-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7782501PMC
January 2021

Estrogen-induced transcription at individual alleles is independent of receptor level and active conformation but can be modulated by coactivators activity.

Nucleic Acids Res 2020 02;48(4):1800-1810

Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA.

Steroid hormones are pivotal modulators of pathophysiological processes in many organs, where they interact with nuclear receptors to regulate gene transcription. However, our understanding of hormone action at the single cell level remains incomplete. Here, we focused on estrogen stimulation of the well-characterized GREB1 and MYC target genes that revealed large differences in cell-by-cell responses, and, more interestingly, between alleles within the same cell, both over time and hormone concentration. We specifically analyzed the role of receptor level and activity state during allele-by-allele regulation and found that neither receptor level nor activation status are the determinant of maximal hormonal response, indicating that additional pathways are potentially in place to modulate cell- and allele-specific responses. Interestingly, we found that a small molecule inhibitor of the arginine methyltransferases CARM1 and PRMT6 was able to increase, in a gene specific manner, the number of active alleles/cell before and after hormonal stimulation, suggesting that mechanisms do indeed exist to modulate hormone receptor responses at the single cell and allele level.
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http://dx.doi.org/10.1093/nar/gkz1172DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7039002PMC
February 2020

ESR1 mutations in breast cancer.

Cancer 2019 11 18;125(21):3714-3728. Epub 2019 Jul 18.

Lester and Sue Smith Breast Center, Baylor College of Medicine, Houston, Texas.

The acquisition of ligand-independent ESR1 mutations during aromatase inhibitor therapy in metastatic estrogen receptor (ER)-positive breast cancer is a common mechanism of hormonal therapy resistance. Preclinical and clinical studies have demonstrated that ESR1 mutations can preexist in primary tumors and can be enriched during metastasis. Furthermore, ESR1 mutations express a unique transcriptional profile that favors tumor progression, suggesting that selected ESR1 mutations may influence metastasis. Several groups have used sensitive detection methods using patient liquid biopsies to track ESR1 or truncal somatic mutations to predict treatment outcome and tumor progression, and some of these techniques may eventually be used to guide sequential treatment options in patients. Further development and standardization of mutation tracking in circulating tumor DNA is ongoing. Clinically, patients with ESR1 mutations derive clinical benefit when treated with fulvestrant and CDK4/6-targeted therapies, but the development of more potent selective ER degraders and/or new targeted biotherapies are needed to overcome the endocrine-resistant phenotype of ESR1 mutant-bearing tumors. In this review, we discuss the mechanisms of resistance and dissemination of ESR1 mutations as well as the detection methods for ESR1 mutation tracking, newly discovered potential therapeutic targets, and the clinical implications and treatment options for treating patients with ESR1 mutant-bearing tumors.
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http://dx.doi.org/10.1002/cncr.32345DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6788940PMC
November 2019

Proteomic profiling identifies key coactivators utilized by mutant ERα proteins as potential new therapeutic targets.

Oncogene 2018 08 11;37(33):4581-4598. Epub 2018 May 11.

Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, 77030, USA.

Approximately 75% of breast cancers are estrogen receptor alpha (ERα)-positive and are treatable with endocrine therapies, but often patients develop lethal resistant disease. Frequent mutations (10-40%) in the ligand-binding domain (LBD) codons in the gene encoding ERα (ESR1) have been identified, resulting in ligand-independent, constitutively active receptors. In addition, ESR1 chromosomal translocations can occur, resulting in fusion proteins that lack the LBD and are entirely unresponsive to all endocrine treatments. Thus, identifying coactivators that bind to these mutant ERα proteins may offer new therapeutic targets for endocrine-resistant cancer. To define coactivator candidate targets, a proteomics approach was performed profiling proteins recruited to the two most common ERα LBD mutants, Y537S and D538G, and an ESR1-YAP1 fusion protein. These mutants displayed enhanced coactivator interactions as compared to unliganded wild-type ERα. Inhibition of these coactivators decreased the ability of ESR1 mutants to activate transcription and promote breast cancer growth in vitro and in vivo. Thus, we have identified specific coactivators that may be useful as targets for endocrine-resistant breast cancers.
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http://dx.doi.org/10.1038/s41388-018-0284-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6095836PMC
August 2018

The Impact of ESR1 Mutations on the Treatment of Metastatic Breast Cancer.

Horm Cancer 2018 08 7;9(4):215-228. Epub 2018 May 7.

Lester and Sue Smith Breast Center, Baylor College of Medicine, One Baylor Plaza, MS: 600, Houston, TX, 77030, USA.

After nearly 20 years of research, it is now established that mutations within the estrogen receptor (ER) gene, ESR1, frequently occur in metastatic breast cancer and influence response to hormone therapy. Though early studies presented differing results, sensitive sequencing techniques now show that ESR1 mutations occur at a frequency between 20 and 40% depending on the assay method. Recent studies have focused on several "hot spot mutations," a cluster of mutations found in the hormone-binding domain of the ESR1 gene. Throughout the course of treatment, tumor evolution can occur, and ESR1 mutations emerge and become enriched in the metastatic setting. Sensitive techniques to continually monitor mutant burden in vivo are needed to effectively treat patients with mutant ESR1. The full impact of these mutations on tumor response to different therapies remains to be determined. However, recent studies indicate that mutant-bearing tumors may be less responsive to specific hormonal therapies, and suggest that aromatase inhibitor (AI) therapy may select for the emergence of ESR1 mutations. Additionally, different mutations may respond discretely to targeted therapies. The need for more preclinical mechanistic studies on ESR1 mutations and the development of better agents to target these mutations are urgently needed. In the future, sequential monitoring of ESR1 mutational status will likely direct personalized therapeutic regimens appropriate to each tumor's unique mutational landscape.
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http://dx.doi.org/10.1007/s12672-017-0306-5DOI Listing
August 2018

Low PTEN levels and PIK3CA mutations predict resistance to neoadjuvant lapatinib and trastuzumab without chemotherapy in patients with HER2 over-expressing breast cancer.

Breast Cancer Res Treat 2018 02 7;167(3):731-740. Epub 2017 Nov 7.

Dan L. Duncan Comprehensive Cancer Center at Baylor College of Medicine and Baylor St. Luke's Medical Center, BCM 600, One Baylor Plaza, Houston, TX, 77030, USA.

Purpose: Aberrant activation of the PI3K pathway has been implicated in resistance to HER2-targeted therapy, but results of clinical trials are confounded by the co-administration of chemotherapy. We investigated the effect of perturbations of this pathway in breast cancers from patients treated with neoadjuvant anti-HER2-targeted therapy without chemotherapy.

Patients And Methods: Baseline tumor samples from patients with HER2-positive breast cancer enrolled in TBCRC006 (NCT00548184), a 12-week neoadjuvant clinical trial with lapatinib plus trastuzumab [plus endocrine therapy for estrogen receptor (ER)-positive tumors], were assessed for PTEN status by immunohistochemistry and PIK3CA mutations by sequencing. Results were correlated with pathologic complete response (pCR).

Results: Of 64 evaluable patients, PTEN immunohistochemistry and PIK3CA mutation analysis were performed for 59 and 46 patients, respectively. PTEN status (dichotomized by H-score median) was correlated with pCR (32% in high PTEN vs. 9% in low PTEN, p = 0.04). PIK3CA mutations were identified in 14/46 tumors at baseline (30%) and did not correlate with ER or PTEN status. One patient whose tumor harbored a PIK3CA mutation achieved pCR (p = 0.14). When considered together (43 cases), 1/25 cases (4%) with a PIK3CA mutation and/or low PTEN expression levels had a pCR compared to 7/18 cases (39%) with wild-type PI3KCA and high PTEN expression levels (p = 0.006).

Conclusion: PI3K pathway activation is associated with resistance to lapatinib and trastuzumab in breast cancers, without chemotherapy. Further studies are warranted to investigate how to use these biomarkers to identify upfront patients who may respond to anti-HER2 alone, without chemotherapy.
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http://dx.doi.org/10.1007/s10549-017-4533-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5821069PMC
February 2018

Tumour and cellular distribution of activated forms of PR in breast cancers: a novel immunohistochemical analysis of a large clinical cohort.

ESMO Open 2016 22;1(4):e000072. Epub 2016 Aug 22.

Baylor-Sammons Cancer Center, Texas Oncology, US Oncology , Dallas, Texas , USA.

Background: The progesterone receptor (PR) is expressed by ∼70% of early breast tumours and is implicated in the progression of breast cancer. In cancerous tissues PR may be activated in the absence of a ligand, or when ligand concentrations are very low, resulting in aberrantly activated PR (APR). The presence of APR may indicate that patients with breast cancer are more likely to respond to antiprogestins. The aims of this study were to describe and classify the histological subnuclear morphology of active and inactive PR in archival breast cancer samples.

Methods: Archived tumour specimens from 801 women with invasive breast cancer were collected. Tissue samples (n=789) were analysed for PR isoforms A and B (PRA and PRB), Ki67 and estrogen receptors (ERα) status, using immunohistochemistry. Medical records were used to determine human epidermal growth factor 2 (HER2) status, tumour stage and grade.

Results: A total of 79% of tumours stained positive for either PRA or PRB, and of these 25% of PRA-positive and 23% of PRB-positive tumours had PR present in the activated form. APRA was associated with higher tumour grade (p=0.001). APRB was associated with a higher tumour grade (p=0.046) and a trend for a more advanced stage. Patients with PR-positive tumours treated with antiestrogens had better disease-free survival (DFS) than those with PR-negative tumours (p<0.0001). Cumulative progression rate and DFS were similar irrespective of APR status. Both APRA and APRB were independent of HER2, ERα and Ki67 expression.

Conclusions: APR had a binary mode of expression in the breast cancer specimens tested, allowing separation into two tumour subsets. APR is an independent target at the cellular and tumour level and may therefore be a suitable predictive marker for antiprogestins, such as onapristone. Using the described technique, a companion diagnostic is under development to identify APR in solid tumours.
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http://dx.doi.org/10.1136/esmoopen-2016-000072DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5070234PMC
August 2016

ESR1 Mutations in Cell-Free DNA of Breast Cancer: Predictive "Tip of the Iceberg".

JAMA Oncol 2016 10;2(10):1315-1316

Lester and Sue Smith Breast Center, Dan L. Duncan Cancer Center, Departments of Medicine and Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas.

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http://dx.doi.org/10.1001/jamaoncol.2016.1268DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5605796PMC
October 2016

ESR1 mutations affect anti-proliferative responses to tamoxifen through enhanced cross-talk with IGF signaling.

Breast Cancer Res Treat 2016 06 13;157(2):253-265. Epub 2016 May 13.

Lester & Sue Smith Breast Center, Baylor College of Medicine, One Baylor Plaza, Houston, TX, 77030, USA.

The purpose of this study was to address the role of ESR1 hormone-binding mutations in breast cancer. Soft agar anchorage-independent growth assay, Western blot, ERE reporter transactivation assay, proximity ligation assay (PLA), coimmunoprecipitation assay, silencing assay, digital droplet PCR (ddPCR), Kaplan-Meier analysis, and statistical analysis. It is now generally accepted that estrogen receptor (ESR1) mutations occur frequently in metastatic breast cancers; however, we do not yet know how to best treat these patients. We have modeled the three most frequent hormone-binding ESR1 (HBD-ESR1) mutations (Y537N, Y537S, and D538G) using stable lentiviral transduction in human breast cancer cell lines. Effects on growth were examined in response to hormonal and targeted agents, and mutation-specific changes were studied using microarray and Western blot analysis. We determined that the HBD-ESR1 mutations alter anti-proliferative effects to tamoxifen (Tam), due to cell-intrinsic changes in activation of the insulin-like growth factor receptor (IGF1R) signaling pathway and levels of PIK3R1/PIK3R3. The selective estrogen receptor degrader, fulvestrant, significantly reduced the anchorage-independent growth of ESR1 mutant-expressing cells, while combination treatments with the mTOR inhibitor everolimus, or an inhibitor blocking IGF1R, and the insulin receptor significantly enhanced anti-proliferative responses. Using digital drop (dd) PCR, we identified mutations at high frequencies ranging from 12 % for Y537N, 5 % for Y537S, and 2 % for D538G in archived primary breast tumors from women treated with adjuvant mono-tamoxifen therapy. The HBD-ESR1 mutations were not associated with recurrence-free or overall survival in response in this patient cohort and suggest that knowledge of other cell-intrinsic factors in combination with ESR1 mutation status will be needed determine anti-proliferative responses to Tam.
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http://dx.doi.org/10.1007/s10549-016-3829-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5510243PMC
June 2016

Phosphatase PTP4A3 Promotes Triple-Negative Breast Cancer Growth and Predicts Poor Patient Survival.

Cancer Res 2016 04 26;76(7):1942-53. Epub 2016 Feb 26.

Department of Clinical Cancer Prevention, The University of Texas MD Anderson Cancer Center, Houston, Texas. Department of Breast Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.

Triple-negative breast cancer (TNBC) has the worst prognosis of all breast cancers, and women diagnosed with TNBC currently lack targeted treatment options. To identify novel targets for TNBC, we evaluated phosphatase expression in breast tumors and characterized their contributions to in vitro and in vivo growth of TNBC. Using Affymetrix microarray analysis of 102 breast cancers, we identified 146 phosphatases that were significantly differentially expressed in TNBC compared with estrogen receptor (ER)-positive tumors. Of these, 19 phosphatases were upregulated (0.66-fold; FDR = 0.05) in TNBC compared with ER-positive breast cancers. We knocked down 17 overexpressed phosphatases in four triple-negative and four ER-positive breast cancer lines using specific siRNAs and found that depletion of six of these phosphatases significantly reduced growth and anchorage-independent growth of TNBC cells to a greater extent than ER-positive cell lines. Further analysis of the phosphatase PTP4A3 (also known as PRL-3) demonstrated its requirement for G1-S cell-cycle progression in all breast cancer cells, but PTP4A3 regulated apoptosis selectively in TNBC cells. In addition, PTP4A3 inhibition reduced the growth of TNBC tumors in vivo Moreover, in silico analysis revealed the PTP4A3 gene to be amplified in 29% of basal-like breast cancers, and high expression of PTP4A3 could serve as an independent prognostic indicator for worse overall survival. Collectively, these studies define the importance of phosphatase overexpression in TNBC and lay the foundation for the development of new targeted therapies directed against phosphatases or their respective signaling pathways for TNBC patients. Cancer Res; 76(7); 1942-53. ©2016 AACR.
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http://dx.doi.org/10.1158/0008-5472.CAN-14-0673DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4873402PMC
April 2016

ESR1 Mutations in Breast Cancer: Proof-of-Concept Challenges Clinical Action.

Clin Cancer Res 2016 Mar 23;22(5):1034-6. Epub 2015 Dec 23.

Lester and Sue Smith Breast Center, Baylor College of Medicine, Houston, Texas. Dan L Duncan Cancer Center, Baylor College of Medicine, Houston, Texas.

Wang and colleagues demonstrate that digital droplet PCR (ddPCR) identified ESR1 mutations in 7% of primary breast cancers. ESR1 mutations were also readily detected in metastatic tissues and circulating tumor DNA in the blood. These results suggest that ddPCR may be amendable for monitoring tumor burden, and to predict relapse. See related article by Wang et al., p. 1130.
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http://dx.doi.org/10.1158/1078-0432.CCR-15-2549DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4775407PMC
March 2016

Androgen receptor promotes tamoxifen agonist activity by activation of EGFR in ERα-positive breast cancer.

Breast Cancer Res Treat 2015 Nov 20;154(2):225-37. Epub 2015 Oct 20.

Lester and Sue Smith Breast Center, Baylor College of Medicine, One Baylor Plaza, Houston, TX, 77030, USA.

Tamoxifen (Tam) resistance represents a significant clinical problem in estrogen receptor (ER) α-positive breast cancer. We previously showed that decreased expression of Rho guanine nucleotide dissociation inhibitor (Rho GDI) α, a negative regulator of the Rho GTPase pathway, is associated with Tam resistance. We now discover that androgen receptor (AR) is overexpressed in cells with decreased Rho GDIα and seek to determine AR's contribution to resistance. We engineered ERα-positive cell lines with stable knockdown (KD) of Rho GDIα (KD cells). Resistance mechanisms were examined using microarray profiling, protein-interaction studies, growth and reporter gene assays, and Western blot analysis combined with a specific AR antagonist and other signaling inhibitors. Tam-resistant tumors and cell lines with low Rho GDIα levels exhibited upregulated AR expression. Microarray of Rho GDIα KD cells indicated that activation of EGFR and ERα was associated with Tam treatment. When AR levels were elevated, interaction between AR and EGFR was detected. Constitutive and Tam-induced phosphorylation of EGFR and ERK1/2 was blocked by the AR antagonist Enzalutamide, suggesting that AR-mediated EGFR activation was a mechanism of resistance in these cells. Constitutive ERα phosphorylation and transcriptional activity was inhibited by Enzalutamide and the EGFR inhibitor gefitinib, demonstrating that AR-mediated EGFR signaling activated ERα. Tam exhibited agonist activity in AR overexpressing cells, stimulating ERα transcriptional activity and proliferation, which was blocked by Enzalutamide and gefitinib. We describe a novel model of AR-mediated Tam resistance through activation of EGFR signaling leading to ER activation in ERα-positive cells with low expression of Rho GDIα.
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http://dx.doi.org/10.1007/s10549-015-3609-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4749407PMC
November 2015

Targeting thyroid hormone receptor beta in triple-negative breast cancer.

Breast Cancer Res Treat 2015 Apr 28;150(3):535-45. Epub 2015 Mar 28.

Lester and Sue Smith Breast Center, Dan L Duncan Cancer Center, Baylor College of Medicine, One Baylor Plaza, Houston, TX, 77030, USA.

The purpose of this study was to discover novel nuclear receptor targets in triple-negative breast cancer. Expression microarray, Western blot, qRT-PCR analyses, MTT growth assay, soft agar anchorage-independent growth assay, TRE reporter transactivation assay, and statistical analysis were performed in this study. We performed microarray analysis using 227 triple-negative breast tumors, and clustered the tumors into five groups according to their nuclear receptor expression. Thyroid hormone receptor beta (TRβ) was one of the most differentially expressed nuclear receptors in group 5 compared to other groups. TRβ low expressing patients were associated with poor outcome. We evaluated the role of TRβ in triple-negative breast cancer cell lines representing group 5 tumors. Knockdown of TRβ increased soft agar colony and reduced sensitivity to docetaxel and doxorubicin treatment. Docetaxel or doxorubicin long-term cultured cell lines also expressed decreased TRβ protein. Microarray analysis revealed cAMP/PKA signaling was the only KEGG pathways upregulated in TRβ knockdown cells. Inhibitors of cAMP or PKA, in combination with doxorubicin further enhanced cell apoptosis and restored sensitivity to chemotherapy. TRβ-specific agonists enhanced TRβ expression, and further sensitized cells to both docetaxel and doxorubicin. Sensitization was mediated by increased apoptosis with elevated cleaved PARP and caspase 3. TRβ represents a novel nuclear receptor target in triple-negative breast cancer; low TRβ levels were associated with enhanced resistance to both docetaxel and doxorubicin treatment. TRβ-specific agonists enhance chemosensitivity to these two agents. Mechanistically enhanced cAMP/PKA signaling was associated with TRβ's effects on response to chemotherapy.
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http://dx.doi.org/10.1007/s10549-015-3354-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4418174PMC
April 2015

Role of MTA2 in human cancer.

Cancer Metastasis Rev 2014 Dec;33(4):921-8

Lester and Sue Smith Breast Center, One Baylor Plaza, Baylor College of Medicine, 1220 N. Alkek, MS: 600, Houston, TX, 77030, USA,

Metastasis is the ultimate cause of death for most cancer patients. While many mechanisms have been delineated for regulation of growth and tumor initiation of the primary tumor, very little is known about the process of metastasis. Metastasis requires dynamic alteration of cellular processes in order for cells to disseminate from the primary tumor to distant sites. These alterations often involve dramatic changes in the regulation of cytoskeletal and cell-environment interactions. Furthermore, controlled refinement of these interactions requires feedback to regulatory networks in the nucleus. MTA2 is a member of the metastasis tumor-associated family of transcriptional regulators and is a central component of the nucleosome remodeling and histone deacetylation complex. MTA2 acts as a central hub for cytoskeletal organization and transcription and provides a link between nuclear and cytoskeletal organization. We will focus on MTA2 in this chapter, especially its role in breast cancer metastasis.
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http://dx.doi.org/10.1007/s10555-014-9518-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4425804PMC
December 2014

Comprehensive genomic analysis identifies novel subtypes and targets of triple-negative breast cancer.

Clin Cancer Res 2015 Apr 10;21(7):1688-98. Epub 2014 Sep 10.

Department of Clinical Cancer Prevention, MD Anderson Cancer Center, Houston, Texas.

Purpose: Genomic profiling studies suggest that triple-negative breast cancer (TNBC) is a heterogeneous disease. In this study, we sought to define TNBC subtypes and identify subtype-specific markers and targets.

Experimental Design: RNA and DNA profiling analyses were conducted on 198 TNBC tumors [estrogen receptor (ER) negativity defined as Allred scale value ≤ 2] with >50% cellularity (discovery set: n = 84; validation set: n = 114) collected at Baylor College of Medicine (Houston, TX). An external dataset of seven publically accessible TNBC studies was used to confirm results. DNA copy number, disease-free survival (DFS), and disease-specific survival (DSS) were analyzed independently using these datasets.

Results: We identified and confirmed four distinct TNBC subtypes: (i) luminal androgen receptor (AR; LAR), (ii) mesenchymal (MES), (iii) basal-like immunosuppressed (BLIS), and (iv) basal-like immune-activated (BLIA). Of these, prognosis is worst for BLIS tumors and best for BLIA tumors for both DFS (log-rank test: P = 0.042 and 0.041, respectively) and DSS (log-rank test: P = 0.039 and 0.029, respectively). DNA copy number analysis produced two major groups (LAR and MES/BLIS/BLIA) and suggested that gene amplification drives gene expression in some cases [FGFR2 (BLIS)]. Putative subtype-specific targets were identified: (i) LAR: androgen receptor and the cell surface mucin MUC1, (ii) MES: growth factor receptors [platelet-derived growth factor (PDGF) receptor A; c-Kit], (iii) BLIS: an immunosuppressing molecule (VTCN1), and (iv) BLIA: Stat signal transduction molecules and cytokines.

Conclusion: There are four stable TNBC subtypes characterized by the expression of distinct molecular profiles that have distinct prognoses. These studies identify novel subtype-specific targets that can be targeted in the future for the effective treatment of TNBCs.
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http://dx.doi.org/10.1158/1078-0432.CCR-14-0432DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4362882PMC
April 2015

AR collaborates with ERα in aromatase inhibitor-resistant breast cancer.

Breast Cancer Res Treat 2014 Oct 2;147(3):473-85. Epub 2014 Sep 2.

Lester and Sue Smith Breast Center, Baylor College of Medicine, One Baylor Plaza, Houston, TX, 77030, USA.

Androgen receptor (AR) is an attractive target in breast cancer because of its frequent expression in all the molecular subtypes, especially in estrogen receptor (ER)-positive luminal breast cancers. We have previously shown a role for AR overexpression in tamoxifen resistance. We engineered ER-positive MCF-7 cells to overexpress aromatase and AR (MCF-7 AR Arom cells) to explore the role of AR in aromatase inhibitor (AI) resistance. Androstendione (AD) was used as a substrate for aromatization to estrogen. The nonsteroidal AI anastrazole (Ana) inhibited AD-stimulated growth and ER transcriptional activity in MCF-7 Arom cells, but not in MCF-7 AR Arom cells. Enhanced activation of pIGF-1R and pAKT was found in AR-overexpressing cells, and their inhibitors restored sensitivity to Ana, suggesting that these pathways represent escape survival mechanisms. Sensitivity to Ana was restored with AR antagonists, or the antiestrogen fulvestrant. These results suggest that both AR and ERα must be blocked to restore sensitivity to hormonal therapies in AR-overexpressing ERα-positive breast cancers. AR contributed to ERα transcriptional activity in MCF-7 AR Arom cells, and AR and ERα co-localized in AD + Ana-treated cells, suggesting cooperation between the two receptors. AR-mediated resistance was associated with a failure to block ER transcriptional activity and enhanced up-regulation of AR and ER-responsive gene expression. Clinically, it may be necessary to block both AR and ERα in patients whose tumors express elevated levels of AR. In addition, inhibitors to the AKT/IGF-1R signaling pathways may provide alternative approaches to block escape pathways and restore hormone sensitivity in resistant breast tumors.
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http://dx.doi.org/10.1007/s10549-014-3082-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4337991PMC
October 2014

Tamoxifen through GPER upregulates aromatase expression: a novel mechanism sustaining tamoxifen-resistant breast cancer cell growth.

Breast Cancer Res Treat 2014 Jul 14;146(2):273-85. Epub 2014 Jun 14.

Department of Pharmacy, Health and Nutritional Sciences, University of Calabria, 87036, Arcavacata di Rende, CS, Italy.

Tamoxifen resistance is a major clinical challenge in breast cancer treatment. Aromatase inhibitors are effective in women who progressed or recurred on tamoxifen, suggesting a role of local estrogen production by aromatase in driving tamoxifen-resistant phenotype. However, the link between aromatase activity and tamoxifen resistance has not yet been reported. We investigated whether long-term tamoxifen exposure may affect aromatase activity and/or expression, which may then sustain tamoxifen-resistant breast cancer cell growth. We employed MCF-7 breast cancer cells, tamoxifen-resistant MCF-7 cells (MCF-7 TR1 and TR2), SKBR-3 breast cancer cells, cancer-associated fibroblasts (CAFs1 and CAFs2). We used tritiated-water release assay, realtime-RT-PCR, and immunoblotting analysis for evaluating aromatase activity and expression; anchorage-independent assays for growth; reporter-gene, electrophoretic-mobility-shift, and chromatin-immunoprecipitation assays for promoter activity studies. We demonstrated an increased aromatase activity and expression, which supports proliferation in tamoxifen-resistant breast cancer cells. This is mediated by the G-protein-coupled receptor GPR30/GPER, since knocking-down GPER expression or treatment with a GPER antagonist reversed the enhanced aromatase levels induced by long-term tamoxifen exposure. The molecular mechanism was investigated in ER-negative, GPER/aromatase-positive SKBR3 cells, in which tamoxifen acts as a GPER agonist. Tamoxifen treatment increased aromatase promoter activity through an enhanced recruitment of c-fos/c-jun complex to AP-1 responsive elements located within the promoter region. As tamoxifen via GPER induced aromatase expression also in CAFs, this pathway may be involved in promoting aggressive behavior of breast tumors in response to tamoxifen treatment. Blocking estrogen production and/or GPER signaling activation may represent a valid option to overcome tamoxifen-resistance in breast cancers.
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http://dx.doi.org/10.1007/s10549-014-3017-4DOI Listing
July 2014

Estrogen receptor (ER) α mutations in breast cancer: hidden in plain sight.

Breast Cancer Res Treat 2014 Feb 1;144(1):11-9. Epub 2014 Feb 1.

Lester and Sue Smith Breast Center, Dan L Duncan Cancer Center, Baylor College of Medicine, One Baylor Plaza, Houston, TX, 77030, USA,

The idea that somatic ERα mutations could play an important role in the evolution of hormone-dependent breast cancers was proposed some years ago (Fuqua J Mammary Gland Biol Neoplasia 6(4):407-417, 2001; Dasgupta et al. Annu Rev Med 65:279-292, 2013), but has remained controversial until recently. A significant amount of new data has confirmed these initial observations and shown their significance, along with much additional work relevant to the treatment of breast cancer. Thus, it is the purpose of this review to summarize the research to date on the existence and clinical consequences of ERα mutations in primary and metastatic breast cancer.
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http://dx.doi.org/10.1007/s10549-014-2847-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4123761PMC
February 2014

Metastasis tumor-associated protein 2 enhances metastatic behavior and is associated with poor outcomes in estrogen receptor-negative breast cancer.

Breast Cancer Res Treat 2013 Oct 28;141(3):375-384. Epub 2013 Sep 28.

Lester and Sue Smith Breast Center, Baylor College of Medicine, One Baylor Plaza, MS:600, Houston, TX, 77030, USA.

Metastasis remains a major clinical problem in breast cancer. One family of genes previously linked with metastasis is the metastasis tumor-associated (MTA) family, with members MTA1 enhancing and MTA3 inhibiting cancer metastasis. We have previously found that MTA2 enhances anchorage-independent growth in estrogen receptor α (ERα) breast cancers, and, in combination with other genes, performed as a predictive biomarker in ERα-positive breast cancer. We therefore hypothesized that MTA2 enhances breast cancer progression. To test this, cell growth, soft-agar colony formation, migration, and in vivo metastasis were examined in MTA2-overexpressing and Vector control transfected ERα-negative breast cancer cells. Pathways regulating cell-cell interaction, adhesion, and signaling through the Rho pathway were also investigated. Effects of the inhibition of the Rho pathway using a Rho Kinase inhibitor were assessed in soft-agar colony formation and motility assays in MTA2-overexpressing cells. MTA2 expression was associated with poor prognostic markers, and levels of MTA2 were associated with increased risk of early recurrence in retrospective analyses. MTA2 overexpression was associated with enhanced metastasis, and pathways regulating cell-cell interactions in vitro and in vivo. Most critically, MTA2-enhanced motility could be blocked by inhibiting Rho pathway signaling. We present the novel finding that MTA2 defined a subset of ERα-negative patients with a particularly poor outcome.
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http://dx.doi.org/10.1007/s10549-013-2709-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3969415PMC
October 2013

Novel insights into breast cancer genetic variance through RNA sequencing.

Sci Rep 2013 ;3:2256

McCormick Genomic and Proteomics Center, Washington, District of Columbia 20037, USA.

Using RNA sequencing of triple-negative breast cancer (TNBC), non-TBNC and HER2-positive breast cancer sub-types, here we report novel expressed variants, allelic prevalence and abundance, and coexpression with other variation, and splicing signatures. To reveal the most prevalent variant alleles, we overlaid our findings with cancer- and population-based datasets and validated a subset of novel variants of cancer-related genes: ESRP2, GBP1, TPP1, MAD2L1BP, GLUD2 and SLC30A8. As a proof-of-principle, we demonstrated that a rare substitution in the splicing coordinator ESRP2 (R353Q) impairs its ability to bind to its substrate FGFR2 pre-mRNA. In addition, we describe novel SNPs and INDELs in cancer relevant genes with no prior reported association of point mutations with cancer, such as MTAP and MAGED1. For the first time, this study illustrates the power of RNA-sequencing in revealing the variation landscape of breast transcriptome and exemplifies analytical strategies to search regulatory interactions among cancer relevant molecules.
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http://dx.doi.org/10.1038/srep02256DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3722564PMC
February 2014

RNA sequencing of cancer reveals novel splicing alterations.

Sci Rep 2013 ;3:1689

McCormick Genomic and Proteomics Center, The George Washington University, Washington, District of Columbia 20037, USA.

Breast cancer transcriptome acquires a myriad of regulation changes, and splicing is critical for the cell to "tailor-make" specific functional transcripts. We systematically revealed splicing signatures of the three most common types of breast tumors using RNA sequencing: TNBC, non-TNBC and HER2-positive breast cancer. We discovered subtype specific differentially spliced genes and splice isoforms not previously recognized in human transcriptome. Further, we showed that exon skip and intron retention are predominant splice events in breast cancer. In addition, we found that differential expression of primary transcripts and promoter switching are significantly deregulated in breast cancer compared to normal breast. We validated the presence of novel hybrid isoforms of critical molecules like CDK4, LARP1, ADD3, and PHLPP2. Our study provides the first comprehensive portrait of transcriptional and splicing signatures specific to breast cancer sub-types, as well as previously unknown transcripts that prompt the need for complete annotation of tissue and disease specific transcriptome.
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http://dx.doi.org/10.1038/srep01689DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3631769PMC
October 2013

In vitro mechanism for downregulation of ER-α expression by epigallocatechin gallate in ER+/PR+ human breast cancer cells.

Mol Nutr Food Res 2013 May 16;57(5):840-53. Epub 2013 Jan 16.

Centro Sanitario, University of Calabria, Arcavacata di Rende (CS), Italy.

Scope: Exposure of the breast to estrogens and other sex hormones is an important cancer risk factor and estrogen receptor downregulators are attracting significant clinical interest. Epigallocatechin gallate (EGCG), a polyphenolic compound found in green tea, has gained considerable attention for its antitumor properties. Here we aimed to investigate the molecular mechanisms through which EGCG regulates ER-α expression in ER+ PR+ breast cancer cells.

Material And Methods: Western blotting analysis, real-time PCR, and transient transfections of deletion fragments of the ER-α gene promoter show that EGCG downregulates ER-α protein, mRNA, and gene promoter activity with a concomitant reduction of ER-α genomic and nongenomic signal. These events occur through p38(MAPK) /CK2 activation, causing the release from Hsp90 of progesterone receptor B (PR-B) and its consequent nuclear translocation as evidenced by immunofluorescence studies. EMSA, and ChIP assay reveal that, upon EGCG treatment, PR-B is recruited at the half-PRE site on ER-α promoter. This is concomitant with the formation of a corepressor complex containing NCoR and HDAC1 while RNA polymerase II is displaced. The events are crucially mediated by PR-B isoform, since they are abrogated with PR-B siRNA.

Conclusion: Our data provide evidence for a mechanism by which EGCG downregulates ER-α and explains the inhibitory action of EGCG on the proliferation of ER+ PR+ cancer cells tested. We suggest that the EGCG/PR-B signaling should be further exploited for clinical approach.
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http://dx.doi.org/10.1002/mnfr.201200560DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4642730PMC
May 2013

Leptin increases HER2 protein levels through a STAT3-mediated up-regulation of Hsp90 in breast cancer cells.

Mol Oncol 2013 Jun 23;7(3):379-91. Epub 2012 Nov 23.

Centro Sanitario, University of Calabria, 87036 Arcavacata di Rende (CS), Italy.

Obesity condition confers risks to breast cancer development and progression, and several reports indicate that the adipokine leptin, whose synthesis and plasma levels increase with obesity, might play an important role in modulating breast cancer cell phenotype. Functional crosstalk occurring between leptin and different signaling molecules contribute to breast carcinogenesis. In this study, we show, in different human breast cancer cell lines, that leptin enhanced the expression of a chaperone protein Hsp90 resulting in increased HER2 protein levels. Silencing of Hsp90 gene expression by RNA interference abrogated leptin-mediated HER2 up-regulation. Leptin effects were dependent on JAK2/STAT3 activation, since inhibition of this signaling cascade by AG490 or ectopic expression of a STAT3 dominant negative abrogated leptin-induced HER2 and Hsp90 expressions. Functional experiments showed that leptin treatment significantly up-regulated human Hsp90 promoter activity. This occurred through an enhanced STAT3 transcription factor binding to its specific responsive element located in the Hsp90 promoter region as revealed by electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Analysis of HER2, Akt and MAPK phosphorylation levels revealed that leptin treatment amplified the responsiveness of breast cancer cells to growth factor stimulation. Furthermore, we found that long-term leptin exposure reduced sensitivity of breast cancer cells to the antiestrogen tamoxifen. In the same experimental conditions, the combined treatment of tamoxifen with the Hsp90 inhibitor 17-AAG completely abrogated leptin-induced anchorage-independent breast cancer cell growth. In conclusion, our results highlight, for the first time, the ability of the adipocyte-secreted factor leptin to modulate Hsp90/HER2 expressions in breast cancer cells providing novel insights into the molecular mechanism linking obesity to breast cancer growth and progression.
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http://dx.doi.org/10.1016/j.molonc.2012.11.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5528468PMC
June 2013

Transcriptomic landscape of breast cancers through mRNA sequencing.

Sci Rep 2012 14;2:264. Epub 2012 Feb 14.

McCormick Genomic and Proteomics Center, The George Washington University, Washington, DC 20037, USA.

Breast cancer is a heterogeneous disease with a poorly defined genetic landscape, which poses a major challenge in diagnosis and treatment. By massively parallel mRNA sequencing, we obtained 1.2 billion reads from 17 individual human tissues belonging to TNBC, Non-TNBC, and HER2-positive breast cancers and defined their comprehensive digital transcriptome for the first time. Surprisingly, we identified a high number of novel and unannotated transcripts, revealing the global breast cancer transcriptomic adaptations. Comparative transcriptomic analyses elucidated differentially expressed transcripts between the three breast cancer groups, identifying several new modulators of breast cancer. Our study also identified common transcriptional regulatory elements, such as highly abundant primary transcripts, including osteonectin, RACK1, calnexin, calreticulin, FTL, and B2M, and "genomic hotspots" enriched in primary transcripts between the three groups. Thus, our study opens previously unexplored niches that could enable a better understanding of the disease and the development of potential intervention strategies.
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http://dx.doi.org/10.1038/srep00264DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3278922PMC
April 2013

Leptin mediates tumor-stromal interactions that promote the invasive growth of breast cancer cells.

Cancer Res 2012 Mar 26;72(6):1416-27. Epub 2012 Jan 26.

Centro Sanitario, University of Calabria, Rende, Italy.

Obesity confers risks to cancer development and progression but the mechanisms underlying these risks remain unclear. In this study, we identify a role for the obesity cytokine leptin, which has been implicated previously in breast cancer development, as a determinant for the tumor-promoting activity of cancer-associated fibroblasts (CAF) in both wild-type (WT) and K303R mutant estrogen receptor-α (ERα)-expressing breast cancer cells. Human CAFs stimulated a greater increase in the proliferation and migration of breast cancer cells expressing the K303R-ERα hyperactive receptor than WT-ERα-expressing cells. A concomitant increase was seen in leptin receptor isoform expression and activation of the leptin signaling pathway in cells expressing K303R-ERα compared with WT-ERα, correlating with leptin effects on cell growth, motility, and invasiveness in mutant cells. Epidermal growth factor and other factors secreted by K303R-ERα cells stimulated CAF proliferation, migration, and subsequent leptin secretion. Moreover, K303R-ERα expression generated a leptin hypersensitive phenotype in vivo. Together, our results reveal a bidirectional cross-talk between breast cancer cells and "educated" CAFs that drives tumor progression via leptin signaling. In elucidating a mechanism that connects obesity and cancer, these findings reinforce the concept that blocking cancer-stromal cell communication may represent an effective strategy for targeted therapy of breast cancer.
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http://dx.doi.org/10.1158/0008-5472.CAN-11-2558DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4123759PMC
March 2012

Dicer-mediated upregulation of BCRP confers tamoxifen resistance in human breast cancer cells.

Clin Cancer Res 2011 Oct 30;17(20):6510-21. Epub 2011 Aug 30.

Lester and Sue Smith Breast Center, Baylor College of Medicine, Houston, Texas, USA.

Purpose: Tamoxifen (Tam) is the most prescribed hormonal agent for treatment of estrogen receptor α (ERα)-positive breast cancer patients. Using microarray analysis, we observed that metastatic breast tumors resistant to Tam therapy had elevated levels of Dicer.

Experimental Design: We overexpressed Dicer in ERα-positive MCF-7 human breast cancer cells and observed a concomitant increase in expression of the breast cancer resistance protein (BCRP). We thus hypothesized that Tam resistance associated with Dicer overexpression in ERα-positive breast cancer cells may involve BCRP. We analyzed BCRP function in Dicer-overexpressing cells using growth in soft agar and mammosphere formation and evaluated intracellular Tam efflux.

Results: In the presence of Tam, Dicer-overexpressing cells formed resistant colonies in soft agar, and treatment with BCRP inhibitors restored Tam sensitivity. Tumor xenograft studies confirmed that Dicer-overexpressing cells were resistant to Tam in vivo. Tumors and distant metastases could be initiated with as few as five mammosphere cells from both vector and Dicer-overexpressing cells, indicating that the mammosphere assay selected for cells with enhanced tumor-initiating and metastatic capacity. Dicer-overexpressing cells with elevated levels of BCRP effluxed Tam more efficiently than control cells, and BCRP inhibitors were able to inhibit efflux.

Conclusion: Dicer-overexpressing breast cancer cells enriched for cells with enhanced BCRP function. We hypothesize that it is this population which may be involved in the emergence of Tam-resistant growth. BCRP may be a novel clinical target to restore Tam sensitivity.
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http://dx.doi.org/10.1158/1078-0432.CCR-11-1403DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3281508PMC
October 2011

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 Oct 7;25(10):3695-707. Epub 2011 Jul 7.

Centro Sanitario, Department of Pharmaco-Biology, University of Calabria, Arcavacata di Rende (CS) 87030, Italy.

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.
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http://dx.doi.org/10.1096/fj.10-178871DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3177579PMC
October 2011

Loss of Rho GDIα and resistance to tamoxifen via effects on estrogen receptor α.

J Natl Cancer Inst 2011 Apr 29;103(7):538-52. Epub 2011 Mar 29.

Lester and Sue Smith Breast Center, Breast Center, Baylor College of Medicine, Houston, TX 77479, USA.

Background: Estrogen receptor (ER) α is a successful therapeutic target in breast cancer, but patients eventually develop resistance to antiestrogens such as tamoxifen.

Methods: To identify genes whose expression was associated with the development of tamoxifen resistance and metastasis, we used microarrays to compare gene expression in four primary tumors from tamoxifen-treated patients whose breast cancers did not recur vs five metastatic tumors from patients whose cancers progressed during adjuvant tamoxifen treatment. Because Rho guanine dissociation inhibitor (GDI) α was underexpressed in the tamoxifen-resistant group, we stably transfected ERα-positive MCF-7 breast cancer cells with a plasmid encoding a short hairpin (sh) RNA to silence Rho GDIα expression. We used immunoblots and transcription assays to examine the role of Rho GDIα in ER-related signaling and growth of cells in vitro and as xenografts in treated nude mice (n = 8-9 per group) to examine the effects of Rho GDIα blockade on hormone responsiveness and metastatic behavior. The time to tumor tripling as the time in weeks from randomization to a threefold increase in total tumor volume over baseline was examined in treated mice. The associations of Rho GDIα and MTA2 levels with tamoxifen resistance were examined in microarray data from patients. All statistical tests were two-sided.

Results: Rho GDIα was expressed at lower levels in ERα-positive tumors that recurred during tamoxifen treatment than in ERα-positive tamoxifen-sensitive primary tumors. MCF-7 breast cancer cells in which Rho GDIα expression had been silenced were tamoxifen-resistant, had increased Rho GTPase and p21-activated kinase 1 activity, increased phosphorylation of ERα at serine 305, and enhanced tamoxifen-induced ERα transcriptional activity compared with control cells. MCF-7 cells in which Rho GDIα expression was silenced metastasized with high frequency when grown as tumor xenografts. When mice were treated with estrogen or estrogen withdrawal, tripling times for xenografts from cells with Rho GDIα silencing were similar to those from vector-containing control cells; however, tripling times were statistically significantly faster than control when mice were treated with tamoxifen (median tripling time for tumors with Rho GDIα small interfering RNA = 2.34 weeks; for control tumors = not reached, hazard ratio = 4.13, 95% confidence interval = 1.07 to 15.96, P = .040 [adjusted for multiple comparisons, P = .119]). Levels of the metastasis-associated protein MTA2 were also increased upon Rho GDIα silencing, and combined Rho GDIα and MTA2 levels were associated with recurrence in 250 tamoxifen-treated patients.

Conclusion: Loss of Rho GDIα enhances metastasis and resistance to tamoxifen via effects on both ERα and MTA2 in models of ERα-positive breast cancer and in tumors of tamoxifen-treated patients.
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http://dx.doi.org/10.1093/jnci/djr058DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3071355PMC
April 2011