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Recurrent breast cancer presents significant challenges with aggressive phenotypes and treatment resistance. Therefore, novel therapeutics are urgently needed. Here, we report that murine recurrent breast tumor cells, when compared with primary tumor cells, are highly sensitive to ferroptosis. Discoidin Domain Receptor Tyrosine Kinase 2 (DDR2), the receptor for collagen I, is highly expressed in ferroptosis-sensitive recurrent tumor cells and human mesenchymal breast cancer cells. EMT regulators, TWIST and SNAIL, significantly induce DDR2 expression and sensitize ferroptosis in a DDR2-dependent manner. Erastin treatment induces DDR2 upregulation and phosphorylation, independent of collagen I. Furthermore, DDR2 knockdown in recurrent tumor cells reduces clonogenic proliferation. Importantly, both the ferroptosis protection and reduced clonogenic growth may be compatible with the compromised YAP/TAZ upon DDR2 inhibition. Collectively, these findings identify the important role of EMT-driven DDR2 upregulation in recurrent tumors in maintaining growth advantage but activating YAP/TAZ-mediated ferroptosis susceptibility, providing potential strategies to eradicate recurrent breast cancer cells with mesenchymal features.

High-grade serous ovarian carcinoma (HGSOC) and basal-like breast cancer (BLBC) share many features including TP53 mutations, genomic instability and poor prognosis. We recently reported that Elafin is overexpressed by HGSOC and is associated with poor overall survival. Here, we confirm that Elafin overexpression is associated with shorter survival in 1000 HGSOC patients. Elafin confers a proliferative advantage to tumor cells through the activation of the MAP kinase pathway. This mitogenic effect can be neutralized by RNA interference, specific antibodies and a MEK inhibitor. Elafin expression in patient-derived samples was also associated with chemoresistance and strongly correlates with bcl-xL expression. We extended these findings into the examination of 1100 primary breast tumors and six breast cancer cell lines. We observed that Elafin is overexpressed and secreted specifically by BLBC tumors and cell lines, leading to a similar mitogenic effect through activation of the MAP kinase pathway. Here too, Elafin overexpression is associated with poor overall survival, suggesting that it may serve as a biomarker and therapeutic target in this setting.

MAP17 is a small, 17-kDa, non-glycosylated membrane protein that is overexpressed in a percentage of carcinomas. In the present work, we have analyzed the role of MAP17 expression during mammary cancer progression. We have found that MAP17 is expressed in 60% human mammary tumors while it is not expressed in normal or benign neoplasias. MAP17 levels increased with breast tumor stage and were strongly correlated with mammary tumoral progression. A significant increase in the levels of reactive oxygen species (ROS) was observed in MAP17-expressing cells, as compared with parental cells. This increase was further paralleled by an increase in the tumorigenic capacity of carcinoma cells but not in immortal non-tumoral breast epithelial cells, which provides a selective advantage once tumorigenesis has begun. Expression of specific MAP17 shRNA in protein-expressing tumor cells reduced their tumorigenic capabilities, which suggests that this effect is dependent upon MAP17 protein expression. Our data show that ROS functions as a second messenger that enhances tumoral properties, which are inhibited in non-tumoral cells. We have found that p38α activation mediates this response. MAP17 triggers a ROS-dependent, senescence-like response that is abolished in the absence of p38a activation. Furthermore, in human breast tumors, MAP17 activation is correlated with a lack of phosphorylation of p38α. Therefore, MAP17 is overexpressed in late-stage breast tumors, in which oncogenic activity relies on p38 insensitivity to induce intracellular ROS.

Triple-negative breast cancer is a heterogeneous disease characterized by the expression of basal cell markers, no estrogen or progesterone receptor expression and a lack of HER2 overexpression. Triple-negative tumors often display activated Wnt/β-catenin signaling and most have impaired p53 function. We studied the interplay between p53 loss and Wnt/β-catenin signaling in stem cell function and tumorigenesis, by deleting p53 from the mammary epithelium of K5ΔNβcat mice displaying a constitutive activation of Wnt/β-catenin signaling in basal cells. K5ΔNβcat transgenic mice present amplification of the basal stem cell pool and develop triple-negative mammary carcinomas. The loss of p53 in K5ΔNβcat mice led to an early expansion of mammary stem/progenitor cells and accelerated the formation of triple-negative tumors. In particular, p53-deficient tumors expressed high levels of integrins and extracellular matrix components and were enriched in cancer stem cells. They also overexpressed the tyrosine kinase receptor Met, a feature characteristic of human triple-negative breast tumors. The inhibition of Met kinase activity impaired tumorsphere formation, demonstrating the requirement of Met signaling for cancer stem cell growth in this model. Human basal-like breast cancers with predicted mutated p53 status had higher levels of MET expression than tumors with wild-type p53. These results connect p53 loss and β-catenin activation to stem cell regulation and tumorigenesis in triple-negative cancer and highlight the role of Met signaling in maintaining cancer stem cell properties, revealing new cues for targeted therapies.

The spinophilin (Spn, PPP1R9B) gene is located at 17q21.33, a region frequently associated with microsatellite instability and loss of heterozygosity, especially in breast tumors. Spn is a regulatory subunit of phosphatase1a (PP1), which targets the catalytic subunit to distinct subcellular locations. Spn downregulation reduces PPP1CA activity against the retinoblastoma protein, pRb, thereby maintaining higher levels of phosphorylated pRb. This effect contributes to an increase in the tumorigenic properties of cells in certain contexts. Here, we explored the mechanism of how Spn downregulation contributes to the malignant phenotype and poor prognosis in breast tumors and found an increase in the stemness phenotype. Analysis of human breast tumors showed that Spn mRNA and protein are reduced or lost in 15% of carcinomas, correlating with a worse prognosis, a more aggressive tumor phenotype and triple-negative tumors, whereas luminal tumors showed high Spn levels. Downregulation of Spn by shRNA increased the stemness properties along with the expression of stem-related genes (Sox2, KLF4, Nanog and OCT4), whereas ectopic overexpression of Spn cDNA reduced these properties. Breast tumor stem cells appeared to have low levels of Spn mRNA, and Spn loss correlated with increased stem-like cell appearance in breast tumors as indicated by an increase in CD44+/CD24- cells. A reduction of the levels of PPP1CA mimicked the cancer stem-like cell phenotype of Spn downregulation, suggesting that the mechanism of Spn involves PP1a. These increased cancer stem cell-like properties with reduced Spn might account for the malignant phenotype observed in Spn-loss tumors and may contribute to a worse patient prognosis.

Junctional adhesion molecule-A (JAM-A) is a membranous cell-cell adhesion protein involved in tight-junction formation in epithelial and endothelial cells. Its overexpression in breast tumors has recently been linked with increased risk of metastasis. We sought to identify if JAM-A overexpression was associated with specific subtypes of breast cancer as defined by the expression of human epidermal growth factor receptor-2 (HER2), estrogen receptor (ER) and progesterone receptor. To this end, JAM-A immunohistochemistry was performed in two breast cancer tissue microarrays. In parallel, cross-talk between JAM-A, HER2 and ER was examined in several breast cell lines, using complementary genetic and pharmacological approaches. High JAM-A expression correlated significantly with HER2 protein expression, ER negativity, lower patient age, high-grade breast cancers, and aggressive luminal B, HER2 and basal subtypes of breast cancer. JAM-A and HER2 were co-expressed at high levels in vitro in SKBR3, UACC-812, UACC-893 and MCF7-HER2 cells. Knockdown or functional antagonism of HER2 did not alter JAM-A expression in any cell line tested. Interestingly, however, JAM-A knockdown decreased HER2 and ER-α expression, resulting in reduced levels of phospho-(active) AKT without an effect on the extracellular signal-related kinase phosphorylation. The downstream effects of JAM-A knockdown on HER2 and phospho-AKT were partially reversed upon treatment with the proteasomal inhibitor MG132. We conclude that JAM-A is co-expressed with HER2 and associates with aggressive breast cancer phenotypes. Furthermore, we speculate that JAM-A may regulate HER2 proteasomal degradation and activity, potentially offering a promise as a therapeutic target in HER2-positive breast cancers.

Suppression of tropomyosins (TMs), a family of actin-binding, microfilament-associated proteins, is a prominent feature of many transformed cells. Yet it is unclear whether downregulation of TMs occur in human tumors. We have investigated the expression of tropomyosin-1 (TM1) in human breast carcinoma tissues by in situ hybridization and immunofluorescence. TM1 mRNA and protein are readily detectable in normal mammary tissue. In contrast, TM1 expression is abolished in the primary human breast tumors. Expression of other TM isoforms, however, is variable among the tumors. The consistent and profound downregulation of TM1 suggests that TM1 may be a novel and useful biomarker of mammary neoplasms. These data also support the hypothesis that suppression of TM1 expression during the malignant conversion of mammary epithelium as a contributing factor of breast cancer. In support of this hypothesis, we show that the ability to suppress malignant growth properties of breast cancer cells is specific to TM1 isoform. Investigations into the mechanisms of TM1-induced tumor suppression reveal that TM1 induces anoikis (detachment induced apoptosis) in breast cancer cells. Downregulation of TM1 in breast tumors may destabilize microfilament architecture and confer resistance to anoikis, which facilitates survival of neoplastic cells outside the normal microenvironment and promote malignant growth.

The increased expression of G(1) cyclins has been associated with the many types of human tumors. In primary solid tumors however, the expression and activity of cyclin E2, the newest member of the G(1) cyclin family, is largely unknown. In this study we have analysed the expression of the E-type cyclins in primary solid tumors from breast, lung, uterus, ovary, colon, and rectal tissues. Relative gene expression was analysed by quantitative real-time reverse transcription polymerase chain reaction (Taqman). The levels of cyclin E1 and cyclin E2 were significantly elevated (23 vs 38%, respectively) in primary breast tumor samples relative to normal breast tissue controls. We also observed an inverse correlation between the expression of cyclin E1/E2 and estrogen receptor in breast tumors. Our results demonstrate that the expression and associated catalytic activity for both cyclin E1 and cyclin E2 is elevated in primary breast tumors when compared to normal breast tissue. The increased level of cyclin E2 in breast tumors suggests that, similar to cyclin E1, it may contribute to the pathogenesis of breast cancer.

The Akt pathway is commonly deregulated in many cancers. Clinical trials are currently underway to test the effectiveness of breast cancer treatment by inhibition of various Akt pathway intermediates. A set of genes induced by Akt in a transgenic mouse model, a subset of which were sensitive to mammalian target of rapamycin (mTOR) inhibitor RAD001, was examined in five public gene expression profile data sets of clinical breast tumor specimens (representing >1000 different samples in all). In each of the clinical data sets, the Akt mouse model genes as a group were significantly overexpressed in human tumors having high levels of AKT1 mRNA. The subset of genes both upregulated by Akt and dependent on mTOR activity were associated with estrogen receptor-negative status, higher grade, increasing tumor size and poor prognosis in multiple patient cohorts; these associations were either not present or not as strong for the Akt-induced, mTOR-independent genes or for AKT1 expression alone. The genes shown here to be relevant to Akt-mTOR both experimentally and pathologically have the potential for use in a molecular diagnostic to determine which patients should receive mTOR antagonist treatment.

Tumors arising in BRCA1 and BRCA2 mutation carriers appear to have specific pathological and gene expression profiles, which show a high level of concordance. BRCA1 tumors are high-grade, negative for hormone receptors, have a high proliferation rate, and are positive for some cell cycle promoter genes. BRCA2 tumors present a phenotype opposite to BRCA1 tumors but very similar to sporadic tumors, except that BRCA2 overexpress some DNA repair markers such as CHEK2, show high cytoplasmic expression of RAD51, and are negative for HER-2 amplification and expression. Some of these characteristics have also been found in cDNA expression studies, although more analysis are necessary in order to obtain new markers that can be associated with a germ line mutation in BRCA1 or BRCA2. In this way, some studies in normal tissues of BRCA1/2 carriers suggest that differences exist in the level of expression of some genes when compared with noncarriers. Finally, IHC studies in tumors carrying a mutation in CHEK2 are rare and show contradictory results, probably due to the low number of these cases. However, they represent an example showing how different mutations of the same gene may be associated with specific histological subtypes of cancer.

Up to date clinical tests for predicting cancer chemotherapy response are not available and individual markers have shown little predictive value. We hypothesized that gene expression patterns attributable to chemotherapy-resistant cells can predict response and cancer prognosis. We contrasted the expression profiles of 13 different human tumor cell lines of gastric (EPG85-257), pancreatic (EPP85-181), colon (HT29) and breast (MCF7 and MDA-MB-231) origin and their counterparts resistant to the topoisomerase inhibitors daunorubicin, doxorubicin or mitoxantrone. We interrogated cDNA arrays with 43 000 cDNA clones ( approximately 30 000 unique genes) to study the expression pattern of these cell lines. We divided gene expression profiles into two sets: we compared the expression patterns of the daunorubicin/doxorubicin-resistant cell lines and the mitoxantrone-resistant cell lines independently to the parental cell lines. For identifying predictive genes, the Prediction Analysis for Mircorarrays algorithm was used. The analysis revealed 79 genes best correlated with doxorubicin resistance and 70 genes with mitoxantrone resistance. In an independent classification experiment, we applied our model of resistance for predicting the sensitivity of 44 previously characterized breast cancer samples. The patient group characterized by the gene expression profile similar to those of doxorubicin-sensitive cell lines exhibited longer survival (49.7+/-26.1 months, n=21, P=0.034) than the resistant group (32.9+/-18.7 months, n=23). The application of gene expression signatures derived from doxorubicin-resistant and -sensitive cell lines allowed to predict effectively clinical survival after doxorubicin monotherapy. Our approach demonstrates the significance of in vitro experiments in the development of new strategies for cancer response prediction.

The presence of putative tumor-suppressor genes on chromosome 16q23.2-24.1 has been suggested by LOH analysis in several cancer types. This region overlaps with the fragile site FRA16D and the region of homozygous deletions found in several cancer types. The candidate gene WWOX/FOR has been mapped within this region. The mouse homologue of the WWOX protein has been defined as an apoptogenic protein and an essential partner of p53 in cell death, supporting WWOX as a tumor suppressor gene candidate. We performed an expression study of the WWOX/FOR gene in a series of human breast tumors and breast cancer cell lines, and detected reduced expression of the WWOX/FOR transcript in a series of breast cancer cells. Furthermore, identification of two distinct alternative WWOX transcripts expressed at high levels in human tumors suggests an involvement of the WWOX gene in breast cancer progression.

p62 is a multifunctional cytoplasmic protein able to noncovalently bind ubiquitin and several signaling proteins, suggesting a regulatory role connected to the ubiquitin-proteasome pathway. No studies to date have linked p62 protein expression with pathological states. Here we demonstrate the overabundance of p62 protein in malignant breast tissue relative to normal breast tissue. The proteasome inhibitor PSI increased p62 mRNA and protein; however, PSI treatment of breast epithelial cells transfected with the p62 promoter did not affect promoter activity. High levels of prostate-derived Ets factor (PDEF) mRNA have been identified in breast cancer compared to normal breast. Only the PSA and maspin promoters have been identified as targets of this transcription factor. Here we show that PDEF stimulates the p62 promoter through at least two sites, and likely acts as a coactivator. PSI treatment abrogates the PDEF-stimulated increase of p62 promoter activity by 50%. Thus, multiple mechanisms for the induction of p62 exist. We conclude that (1) p62 protein is overexpressed in breast cancer; (2) p62 mRNA and protein increase in response to PSI, with no change of basal promoter activity; (3) PDEF upregulates p62 promoter activity through at least two sites; and (4) PSI downregulates PDEF-induced p62 promoter activation through one of these sites.

International audience; Appropriate 'in vivo' models are crucial for studying breast cancer biology and evaluating the efficacy of therapeutic agents. Thus, we engineered a novel transgenic mouse line expressing the human Ki-Ras bearing an activating mutation (Ki-Ras (G12V)) selectively in the mammary epithelium after lactation. These mice develop invasive ductal adenocarcinomas with 100% incidence within 3 to 9 months after Ki-Ras (G12V) induction. Immunophenotyping revealed that the mammary tumors express luminal markers, are positive for estrogen and progesterone receptors, negative for HER2, and have a low proliferation index. Moreover, cell lines derived from such tumors are estrogenresponsive, and when transplanted into nude mice, form tumors that respond to the antiestrogen ICI 182780. In conclusion, the mammary tumors of these transgenic mice and the derived cell lines exhibit key features of the major form of human breast cancer, i.e. luminal A subtype, and thus have a high potential for breast cancer research and treatment.

Contains fulltext : 283431.pdf (Publisher’s version ) (Closed access) Aberrations in nuclear size and shape are commonly used to identify cancerous tissue. However, it remains unclear whether the disturbed nuclear structure directly contributes to the cancer pathology or is merely a consequence of other events occurring during tumorigenesis. Here, we show that highly invasive and proliferative breast cancer cells frequently exhibit Akt-driven lower expression of the nuclear envelope proteins lamin A/C, leading to increased nuclear deformability that permits enhanced cell migration through confined environments that mimic interstitial spaces encountered during metastasis. Importantly, increasing lamin A/C expression in highly invasive breast cancer cells reflected gene expression changes characteristic of human breast tumors with higher LMNA expression, and specifically affected pathways related to cell-ECM interactions, cell metabolism, and PI3K/Akt signaling. Further supporting an important role of lamins in breast cancer metastasis, analysis of lamin levels in human breast tumors revealed a significant association between lower lamin A levels, Akt signaling, and decreased disease-free survival. These findings suggest that downregulation of lamin A/C in breast cancer cells may influence both cellular physical properties and biochemical signaling to promote metastatic progression.

Expression of β-crystallin B2 (CRYβB2) is elevated in African American (AA) breast tumors. The underlying mechanisms of CRYβB2-induced malignancy and the association of CRYβB2 protein expression with survival have not yet been described. Here, we report that the expression of CRYβB2 in breast cancer cells increases stemness, growth, and metastasis. Transcriptomics data revealed that CRYβB2 upregulates genes that are functionally associated with unfolded protein response, oxidative phosphorylation, and DNA repair, while down-regulating genes related to apoptosis. CRYβB2 in tumors promotes de-differentiation, an increase in mesenchymal markers and cancer-associated fibroblasts, and enlargement of nucleoli. Proteome microarrays identified a direct interaction between CRYβB2 and the nucleolar protein, nucleolin. CRYβB2 induces nucleolin, leading to the activation of AKT and EGFR signaling. CRISPR studies revealed a dependency on nucleolin for the pro-tumorigenic effects of CRYβB2. Triple-negative breast cancer (TNBC) xenografts with upregulated CRYβB2 are distinctively sensitive to the nucleolin aptamer, AS-1411. Lastly, in AA patients, higher levels of nucleolar CRYβB2 in primary TNBC correlates with decreased survival. In summary, CRYβB2 is upregulated in breast tumors of AA patients and induces oncogenic alterations consistent with an aggressive cancer phenotype. CRYβB2 increases sensitivity to nucleolin inhibitors and may promote breast cancer disparity.

Membrane Type 1 Matrix Metalloprotease (MT1-MMP) contributes to the invasive progression of breast cancers by degrading extracellular matrix tissues. Nucleoside diphosphate kinase, NME1/NM23-H1, has been identified as a metastasis suppressor; however, its contribution to local invasion in breast cancer is not known. Here, we report that NME1 is up-regulated in ductal carcinoma in situ (DCIS) as compared to normal breast epithelial tissues. NME1 levels drop in microinvasive and invasive components of breast tumor cells relative to synchronous DCIS foci. We find a strong anti-correlation between NME1 and plasma membrane MT1-MMP levels in the invasive components of breast tumors, particularly in aggressive histological grade III and triple-negative breast cancers. Knockout of NME1 accelerates the invasive transition of breast tumors in the intraductal xenograft model. At the mechanistic level, we find that MT1-MMP, NME1 and dynamin-2, a GTPase known to require GTP production by NME1 for its membrane fission activity in the endocytic pathway, interact in clathrin-coated vesicles at the plasma membrane. Loss of NME1 function increases MT1-MMP surface levels by inhibiting endocytic clearance. As a consequence, the ECM degradation and invasive potentials of breast cancer cells are enhanced. This study identifies the down-modulation of NME1 as a potent driver of the in situ-to invasive transition during breast cancer progression.

Tamoxifen resistance is one of the major challenges for its medical uses in estrogen receptor (ER)-positive breast cancer. Aerobic glycolysis, an anomalous characteristic of glucose metabolism in cancer cells, has been shown to associate with the resistance to chemotherapeutic agents. It remains, however, largely unclear whether and how tamoxifen resistance contributes to aerobic glycolysis in breast cancer. Here, we report that tamoxifen resistance is associated with enhanced glycolysis in ER-positive breast cancer cells. We demonstrate that EREG, an agonist of EGFR, has an important role in enhancing glycolysis via activating EGFR signaling and its downstream glycolytic genes in tamoxifen-resistant breast cancer cells. We further show that EREG is a direct target of miR-186-3p and that downregulation of miR-186-3p by tamoxifen results in EREG upregulation in tamoxifen-resistant breast cancer cells. Importantly, systemic delivery of cholesterol-modified agomiR-186-3p to mice bearing tamoxifen-resistant breast tumors effectively attenuates both tumor growth and [18F]-fluoro-deoxyglucose ([18F]-FDG) uptake. Together, our results reveal a novel molecular mechanism of resistance to hormone therapies in which the miR-186-3p/EREG axis orchestrates tamoxifen resistance and aerobic glycolysis in ER-positive breast cancer, suggesting targeting miR-186-3p as a promising strategy for therapeutic intervention in endocrine-resistant breast tumors.

The receptor tyrosine kinase Ret, a key gain-of-function mutated oncoprotein in thyroid carcinomas, has recently been implicated in other cancer types. While Ret copy number gains and mutations have been reported at low frequencies in breast tumors, we and others have reported that Ret is overexpressed in about 40% of human tumors and this correlates with poor patient prognosis. Ret activation regulates numerous intracellular pathways related to proliferation and inflammation, but it is not known whether abnormal Ret expression is sufficient to induce mammary carcinomas. Using a novel doxycycline-inducible transgenic mouse model with the MMTV promoter controlling Ret expression, we show that overexpression of wild-type Ret in the mammary epithelium produces mammary tumors, displaying a morphology that recapitulates characteristics of human luminal breast tumors. Ret-evoked tumors are estrogen receptor positive and negative for progesterone receptor. Moreover, tumors rapidly regress after doxycycline withdrawal, indicating that Ret is the driving oncoprotein. Using next-generation sequencing, we examined the levels of transcripts in these tumors, confirming a luminal signature. Ret-evoked tumors have been passaged in mice and used to test novel therapeutic approaches. Importantly, we have determined that tumors are resistant to endocrine therapy, but respond successfully to treatment with a Ret kinase inhibitor. Our data provide the first compelling evidence for an oncogenic role of non-mutated Ret in the mammary gland and are an incentive for clinical development of Ret as a cancer biomarker and therapeutic target.

Hepcidin is a peptide hormone that negatively regulates iron efflux and plays an important role in controlling the growth of breast tumors. In patients with breast cancer, the combined expression of hepcidin and its membrane target, ferroportin, predict disease outcome. However, mechanisms that control hepcidin expression in breast cancer cells remain largely unknown. Here, we use three-dimensional breast cancer spheroids derived from cell lines and breast cancer patients to probe mechanisms of hepcidin regulation in breast cancer. We observe that the extent of hepcidin induction and pathways of its regulation are markedly changed in breast cancer cells grown in three dimensions. In monolayer culture, BMPs, particularly BMP6, regulate hepcidin transcription. When breast cancer cells are grown as spheroids, there is a >10-fold induction in hepcidin transcripts. Microarray analysis combined with knockdown experiments reveal that GDF-15 is the primary mediator of this change. The increase in hepcidin as breast cells develop a three-dimensional architecture increases intracellular iron, as indicated by an increase in the iron storage protein ferritin. Immunohistochemical staining of human breast tumors confirms that both GDF-15 and hepcidin are expressed in breast cancer specimens. Further, levels of GDF-15 are significantly correlated with levels of hepcidin at both the mRNA and protein level in patient samples, consistent with a role for GDF-15 in control of hepcidin in human breast tumors. Inclusion of tumor-associated fibroblasts in breast cancer spheroids further induces hepcidin. This induction is mediated by fibroblast-dependent secretion of IL-6. Breast cancer cells grown as spheroids are uniquely receptive to IL-6-dependent induction of hepcidin by tumor-associated fibroblasts, since IL-6 does not induce hepcidin in cells grown as monolayers. Collectively, our results suggest a new paradigm for tumor-mediated control of iron through the control of hepcidin by tumor architecture and the breast tumor microenvironment.

Signal transducer and activator of transcription 3 (STAT3), glioma oncogene homolog 1 (GLI1), and truncated GLI1 (tGLI1) are oncogenic transcription factors playing important roles in breast cancer. tGLI1 is a gain-of-function GLI1 isoform. Whether STAT3 physically and/or functionally interacts with GLI1/tGLI1 has not been explored. To address this knowledge gap, we analyzed 47 node-positive breast cancer specimens using immunohistochemical staining and found that phosphorylated-STAT3 (Y705), GLI1, and tGLI1 are co-overexpressed in the majority of triple-negative breast carcinomas (64%) and HER2-enriched (68%) breast carcinomas, and in lymph node metastases (65%). Using gene set enrichment analysis, we analyzed 710 breast tumors and found that STAT3 activation and GLI1/tGLI1 activation signatures are co-enriched in triple-negative subtypes of breast cancers and HER2-enriched subtypes of breast cancers, but not in luminal subtypes of breast cancers. Patients with high levels of STAT3 and GLI1/tGLI1 co-activation in their breast tumors had worse metastasis-free survival compared to those with low levels. Since these proteins co-overexpress in breast tumors, we examined whether they form complexes and observed that STAT3 interacted with both GLI1 and tGLI1. We further found that the STAT3-GLI1 and STAT3-tGLI1 complexes bind to both consensus GLI1-binding and STAT3-binding sites using chromatin immunoprecipitation (ChIP) assay, and that the co-overexpression markedly activated a promoter controlled by GLI1-binding sites. To identify genes that can be directly co-activated by STAT3 and GLI1/tGLI1, we analyzed three ChIP-seq datasets and identified 34 potential target genes. Following validations using reverse transcription polymerase chain reaction and survival analysis, we identified three genes as novel transcriptional targets of STAT3 and GLI1/tGLI1, R-Ras2, Cep70, and UPF3A. Finally, we observed that co-overexpression of STAT3 with GLI1/tGLI1 promoted the ability of breast cancer cells to form mammospheres and that STAT3 only cooperates with tGLI1 in immortalized mammary epithelial cells. In summary, our study identified novel physical and functional cooperation between two families of oncogenic transcription factors, and the interaction contributes to aggressiveness of breast cancer cells and poor prognosis of triple-negative breast cancers and HER2-enriched breast cancers.

Antiestrogen-resistant and triple-negative breast tumors pose a serious clinical challenge because of limited treatment options. We assessed global gene expression changes in antiestrogen-sensitive compared with antiestrogen-resistant (two tamoxifen resistant and two fulvestrant resistant) MCF-7 breast cancer cell lines. The branched-chain amino acid transaminase 1 (BCAT1), which catalyzes the first step in the breakdown of branched-chain amino acids, was among the most upregulated transcripts in antiestrogen-resistant cells. Elevated BCAT1 expression was confirmed in relapsed tamoxifen-resistant breast tumor specimens. High intratumoral BCAT1 levels were associated with a reduced relapse-free survival in adjuvant tamoxifen-treated patients and overall survival in unselected patients. On a tissue microarray (n=1421), BCAT1 expression was detectable in 58% of unselected primary breast carcinomas and linked to a higher Ki-67 proliferation index, as well as histological grade. Interestingly, BCAT1 was predominantly expressed in estrogen receptor-α-negative/human epidermal growth factor receptor-2-positive (ERα-negative/HER-2-positive) and triple-negative breast cancers in independent patient cohorts. The inverse relationship between BCAT1 and ERα was corroborated in various breast cancer cell lines and pharmacological long-term depletion of ERα induced BCAT1 expression in vitro. Mechanistically, BCAT1 indirectly controlled expression of the cell cycle inhibitor p27Kip1 thereby affecting pRB. Correspondingly, phenotypic analyses using a lentiviral-mediated BCAT1 short hairpin RNA knockdown revealed that BCAT1 sustains proliferation in addition to migration and invasion and that its overexpression enhanced the capacity of antiestrogen-sensitive cells to grow in the presence of antiestrogens. Importantly, silencing of BCAT1 in an orthotopic triple-negative xenograft model resulted in a massive reduction of tumor volume in vivo, supporting our findings that BCAT1 is necessary for the growth of hormone-independent breast tumors.

Cancer-associated fibroblasts (CAFs) are important components in breast tumors and essential for tumor progression and metastasis. However, the role of epigenetic modification in driving the function of CAFs within breast tumors is only marginally known. Herein, we reported that histone deacetylase 6 (HDAC6), one of class II histone deacetylases, was frequently upregulated in the CAFs of breast tumor and promotes an immunosuppressive microenvironment. The genetic or pharmacologic disruption of HDAC6 in CAFs delays tumor growth, inhibits the tumor recruitment of myeloid-derived suppressor cells and regulatory T cells, alters the macrophage phenotype switch, and increases the CD8+ and CD4+ T-cell activation in vivo. Mechanistically, we identified prostaglandin E2/cyclooxygenase-2 (COX2) as a major target of HDAC6 in CAFs by regulating STAT3 activation. Overexpressing COX2 in HDAC6-knockdown CAFs can completely restore the immunosuppressive properties of the fibroblasts. Clinically, a positive correlation among the stromal expression levels of HDAC6, p-STAT3, and COX2 in human breast cancer was observed. High-stromal expression of HDAC6 was markedly associated with poor survival outcome. Overall, our findings indicated that fibroblastic HDAC6 was a vital epigenetic mediator involved in programming an immunosuppressive tumor microenvironment that dampens antitumor immunity. Thus, HDAC6 may be a good potential target to improve breast cancer immunotherapy.

Breast cancer is the most common cancer among women and 30% of patients will be diagnosed with an ErbB2-positive tumor. Forty percent of ErbB2-positive breast tumors have an activating mutation in p110α, a catalytic subunit of phosphoinositide 3-kinase. Clinical and experimental data show that breast tumors treated with a p110α-specific inhibitor often circumvent inhibition and resume growth. To understand this mechanism of resistance, we crossed a p110α conditional (p110αflx/flx) mouse model with mice that overexpress the ErbB2/Neu-IRES-Cre transgene (NIC) specifically in the mammary epithelium. Although mammary-specific deletion of p110α dramatically delays tumor onset, tumors eventually arise and are dependent on p110β. Through biochemical analyses we find that a proportion of p110α-deficient tumors (23%) display downregulation of the Pten tumor suppressor. We further demonstrate that loss of one allele of PTEN is sufficient to shift isoform dependency from p110α to p110β in vivo. These results provide insight into the molecular mechanism by which ErbB2-positive breast cancer escapes p110α inhibition.

Somatic mutations or deletions of TP53 and PTEN in ductal carcinoma in situ lesions have been implicated in progression to invasive ductal carcinomas. A recent molecular and mutational analysis of breast cancers revealed that inactivation of tumor suppressors, p53 and PTEN, are strongly associated with triple negative breast cancer. In addition, these tumor suppressors have important roles in regulating self-renewal in normal and malignant stem cells. To investigate their role in breast carcinogenesis, we knocked down these genes in human mammary cells and in non-transformed MCF10A cells. p53 and PTEN knockdown synergized to activate pro-inflammatory interleukin-6 (IL6)/Stat3/nuclear factor κB signaling. This resulted in generation of highly metastatic epithelial-to-mesenchymal transition-like cancer stem cells resulting in tumors whose gene expression profile mimicked that found in basal/claudin-low molecular subtype within the triple negative breast tumors. Constitutive activation of this loop in transformed cells was dependent on proteolytic degradation of suppressor of cytokine signaling 3 (SOCS3) resulting in low levels of this protein in basal/claudin-low cell lines and primary tumors. In non-transformed cells, transient activation of the IL6 inflammatory loop induced SOCS3 expression leading to pathway inactivation. In transformed cells, enforced expression of SOCS3 or interfering with IL6 pathway via IL6R blockade inhibited tumor growth and metastasis in mouse xenograft models. Furthermore, circulating tumor cells were significantly reduced in tumor-bearing animals when treated with anti-IL6R antibodies. These studies uncover important connections between inflammation and carcinogenesis and suggest that blocking pro-inflammatory cytokines may be utilized as an attractive strategy to target triple negative breast tumors, which currently lacks molecularly targeted therapies.

Human breast tumors comprise a minor sub-population of tumor-initiating cells (TICs), commonly termed cancer stem cells. TICs are thought to sustain tumor growth and to confer resistance to current anticancer therapies. Hence, targeting TIC may be essential to achieving durable cancer cures. To identify molecular targets in breast TIC, we employed a transgenic mouse model of ERBB2 breast cancer; tumors arising in this model comprise a very high frequency of TIC, which is maintained in tumor cell populations propagated in vitro as non-adherent tumorspheres. The Notch pathway is dysregulated in human breast tumors and overexpression of constitutively active Notch proteins induces mammary tumors in mice. The Notch pathway has also been implicated in stem cell processes including those of mammary epithelial stem cells. Hence, we investigated the potential that the Notch pathway is required for TIC activity. We found that an antagonist of Notch signaling, a gamma (γ)-secretase inhibitor termed MRK-003, inhibited the survival of tumorsphere-derived cells in vitro and eliminated TIC as assessed by cell transplantation into syngeneic mice. Whereas MRK-003 also inhibited the self-renewal and/or proliferation of mammosphere-resident cells, this effect of the inhibitor was reversible thus suggesting that it did not compromise the survival of these cells. MRK-003 administration to tumor-bearing mice eliminated tumor-resident TIC and resulted in rapid and durable tumor regression. MRK-003 inhibited the proliferation of tumor cells, and induced their apoptosis and differentiation. These findings suggest that MRK-003 targets breast TIC and illustrate that eradicating these cells in breast tumors ensures long-term, recurrence-free survival.

Signal transducer and activator of transcription 1 (STAT1) is activated in the inflammatory response to interferons. The MUC1 oncoprotein is overexpressed in human breast cancers. Analysis of genes differentially expressed in MUC1-transformed cells has identified a network linking MUC1 and STAT1 that is associated with cellular growth and inflammation. The results further demonstrate that the MUC1-C subunit associates with STAT1 in cells and that the MUC1-C cytoplasmic domain binds directly to the STAT1 DNA binding domain. The interaction between MUC1-C and STAT1 is inducible by IFNγ in non-malignant epithelial cells and constitutive in breast cancer cells. Moreover, the MUC1-STAT1 interaction contributes to the activation of STAT1 target genes, including MUC1 itself. Analysis of two independent databases demonstrated that MUC1 and STAT1 are coexpressed in about 15% of primary human breast tumors. Coexpression of MUC1 and the STAT1 pathway was found to be significantly associated with decreased recurrence-free and overall survival. These findings indicate that (i) MUC1 and STAT1 function in an auto-inductive loop, and (ii) activation of both MUC1 and the STAT1 pathway in breast tumors confers a poor prognosis for patients.

The human DLC-1 (deleted in liver cancer 1) gene was cloned from a primary human hepatocellular carcinoma (HCC) and mapped to the chromosome 8p21-22 region frequently deleted in common human cancers and suspected to harbor tumor suppressor genes. DLC-1 was found to be deleted or downregulated in a significant number of HCCs. We expanded our investigations to other cancers with recurrent deletions of 8p22, and in this study examined alterations of DLC-1 in primary human breast tumors, human breast, colon, and prostate tumor cell lines. Genomic deletion of DLC-1 was observed in 40% of primary breast tumors, whereas reduced or undetectable levels of DLC-1 mRNA were seen in 70% of breast, 70% of colon, and 50% of prostate tumor cell lines To see whether DLC-1 expression affects cell growth and tumorigenicity, two breast carcinoma cell lines lacking the expression of endogenous gene were transfected with the DLC-1 cDNA. In both cell lines, DLC-1 transfection caused significant growth inhibition and reduction of colony formation. Furthermore, introduction of the DLC-1 cDNA abolished the in vivo tumorigenicity in nude mice, suggesting that the DLC-1 gene plays a role in breast cancer by acting as a bona fide tumor suppressor gene.

Identifying novel and known genes that are differentially expressed in breast cancer has important implications in understanding the biology of breast tumorigenesis and developing new diagnostic and therapeutic agents. In this study we have combined two powerful technologies, PCR-based cDNA subtraction and cDNA microarray, as a high throughput methodology designed to identify cDNA clones that are breast tumor- and tissue-specific and are overexpressed in breast tumors. Approximately 2000 cDNA clones generated from the subtracted breast tumor library were arrayed on the microarray chips. The arrayed target cDNAs were then hybridized with 30 pairs of fluorescent-labeled cDNA probes generated from breast tumors and normal tissues to determine the tissue distribution and tumor specificity. cDNA clones showing overexpression in breast tumors by microarray were further analysed by DNA sequencing, GenBank and EST database searches, and quantitative real time PCR. We identified several known genes, including mammaglobin, cytokeratin 19, fibronectin, and hair-specific type II keratin, which have previously been shown to be overexpressed in breast tumors and may play an important role in the malignance of breast. We also discovered B726P which appears to be an isoform of NY-BR-1, a breast tissue-specific gene. Two additional clones discovered, B709P and GABA(A) receptor pi subunit, were not previously described for their overexpression profile in breast tumors. Thus, combining PCR-based cDNA subtraction and cDNA microarray allowed for an efficient way to identify and validate genes with elevated mRNA expression levels in breast cancer that may potentially be involved in breast cancer progression. These differentially expressed genes may be of potential utility as therapeutic and diagnostic targets for breast cancer.

Protein kinase A (PKA) hyperactivation causes hereditary endocrine neoplasias; however, its role in sporadic epithelial cancers is unknown. Here, we show that heightened PKA activity in the mammary epithelium generates tumors. Mammary-restricted biallelic ablation of Prkar1a, which encodes for the critical type-I PKA regulatory subunit, induced spontaneous breast tumors characterized by enhanced type-II PKA activity. Downstream of this, Src phosphorylation occurs at residues serine-17 and tyrosine-416 and mammary cell transformation is driven through a mechanism involving Src signaling. The phenotypic consequences of these alterations consisted of increased cell proliferation and, accordingly, expansion of both luminal and basal epithelial cell populations. In human breast cancer, low PRKAR1A/high SRC expression defines basal-like and HER2 breast tumors associated with poor clinical outcome. Together, the results of this study define a novel molecular mechanism altered in breast carcinogenesis and highlight the potential strategy of inhibiting SRC signaling in treating this cancer subtype in humans.

Despite advances in breast cancer treatment, residual disease driven by dormant tumor cells continues to be a significant clinical problem. Leukemia inhibitory factor receptor (LIFR) promotes a dormancy phenotype in breast cancer cells and LIFR loss is correlated with poor patient survival. Herein, we demonstrate that histone deacetylase inhibitors (HDACi), which are in phase III clinical trials for breast cancer, epigenetically induced LIFR and activated a pro-dormancy program in breast cancer cells. HDACi slowed breast cancer cell proliferation and reduced primary tumor growth. Primary breast tumors from HDACi-treated patients had increased LIFR levels and reduced proliferation rates compared to pre-treatment levels. Recent Phase II clinical trial data studying entinostat and azacitidine in metastatic breast cancer revealed that induction of several pro-dormancy genes post-treatment was associated with prolonged patient survival. Together, these findings suggest HDACi as a potential therapeutic avenue to promote dormancy, prevent recurrence, and improve patient outcomes in breast cancer.

Somatostatin receptors (sst1-5) are present in different types of tumors, where they inhibit key cellular processes such as proliferation and invasion. Although ssts are densely expressed in breast cancer, especially sst2, their role and therapeutic potential remain uncertain. Recently, we identified a new truncated sst5 variant, sst5TMD4, which is related to the abnormal response of certain pituitary tumors to treatment with somatostatin analogs. Here, we investigated the possible role of sst5TMD4 in breast cancer. This study revealed that sst5TMD4 is absent in normal mammary gland, but is abundant in a subset of poorly differentiated human breast tumors, where its expression correlated to that of sst2. Moreover, in the MCF-7 breast cancer model cell, sst5TMD4 expression increased malignancy features such as invasion and proliferation abilities (both in cell cultures and nude mice). This was likely mediated by sst5TMD4-induced increase in phosphorylated extracellular signal-regulated kinases 1 and 2 and p-Akt levels, and cyclin D3 and Arp2/3 complex expression, which also led to mesenchymal-like phenotype. Interestingly, sst5TMD4 interacts physically with sst2 and thereby alters its signaling, enabling disruption of sst2 inhibitory feedback and providing a plausible basis for our findings. These results suggest that sst5TMD4 could be involved in the pathophysiology of certain types of breast tumors., This work was supported by BIO-0139, CTS-01705, CTS-5051, BFU2004-03883, BFU2007-60180/BFI, BFU2008-01136-BFI, BFU2010-19300, FPU-AP20052473, FI06-00804, SAF2007-63075, SAF2007-63075/FMM07, SAF2010-201075, CD07/00246, RYC-2007-00186 and IPSEN. Ciber is an initiative of the Instituto de Salud Carlos III.

Triple-negative breast cancer (TNBC) is the most aggressive molecular subtype among breast tumors and remains a challenge even for the most current therapeutic regimes. Here, we demonstrate that oncolytic alphavirus M1 effectively kills both TNBC and non-TNBC. ER-stress and apoptosis pathways are responsible for the cell death in non-TNBC as reported in other cancer types, yet the cell death in TNBC does not depend on these pathways. Transcriptomic analysis reveals that the M1 virus activates necroptosis in TNBC, which can be pharmacologically blocked by necroptosis inhibitors. By screening a library of clinically available compounds commonly used for breast cancer treatment, we find that Doxorubicin enhances the oncolytic effect of the M1 virus by up to 100-fold specifically in TNBC in vitro, and significantly stalls the tumor growth of TNBC in vivo, through promoting intratumoral virus replication and further triggering apoptosis in addition to necroptosis. These findings reveal a novel antitumor mechanism and a new combination regimen of the M1 oncolytic virus in TNBC, and highlight a need to bridge molecular diagnosis with virotherapy.

Metabolic reprogramming is considered hallmarks of cancer. Aerobic glycolysis in tumors cells has been well-known for almost a century, but specific factors that regulate lactate generation and the effects of lactate in both cancer cells and stroma are not yet well understood. In the present study using breast cancer cell lines, human primary cultures of breast tumors, and immune deficient murine models, we demonstrate that the POU1F1 transcription factor is functionally and clinically related to both metabolic reprogramming in breast cancer cells and fibroblasts activation. Mechanistically, we demonstrate that POU1F1 transcriptionally regulates the lactate dehydrogenase A (LDHA) gene. LDHA catalyzes pyruvate into lactate instead of leading into the tricarboxylic acid cycle. Lactate increases breast cancer cell proliferation, migration, and invasion. In addition, it activates normal-associated fibroblasts (NAFs) into cancer-associated fibroblasts (CAFs). Conversely, LDHA knockdown in breast cancer cells that overexpress POU1F1 decreases tumor volume and [18F]FDG uptake in tumor xenografts of mice. Clinically, POU1F1 and LDHA expression correlate with relapse- and metastasis-free survival. Our data indicate that POU1F1 induces a metabolic reprogramming through LDHA regulation in human breast tumor cells, modifying the phenotype of both cancer cells and fibroblasts to promote cancer progression This study was supported by FEDER/Ministerio de Ciencia, Innovación y Universidades- Agencia Estatal de Investigación-PGC2018-100776-B-I00 and from Conselleria de Cultura, Educación e Ordenacion Universitaria (GPC2014/001), AM-O was supported by an FPU grant (Ministerio de Educación—FPU14/00548) SI

Amplification of 8p11–12 is a well-known alteration in human breast cancers but the driving oncogene has not been identified. We have developed a high-resolution comparative genomic hybridization array covering 8p11–12 and analysed 33 primary breast tumors, 20 primary ovarian tumors and 27 breast cancer cell lines. Expression analysis of the genes in the region was carried out by using real-time quantitative PCR and/or oligo-microarray profiling. In all, 24% (8/33) of the breast tumors, 5% (1/20) of the ovary tumors and 15% (4/27) of the cell lines showed 8p11–12 amplification. We identified a 1 Mb segment of common amplification that excludes previously proposed candidate genes. Some of the amplified genes did not show overexpression, whereas for others, overexpression was not specifically attributable to amplification. The genes FLJ14299, C8orf2, BRF2 and RAB11FIP, map within the 8p11–12 minimal amplicon, two have a putative function consistent with an oncogenic role, these four genes showed a strong correlation between amplification and overexpression and are therefore the best candidate driver oncogenes at 8p12.

Several epidemiological studies on ataxia-telangiectasia families indicate that obligate ATM heterozygotes display an elevated risk for developing breast cancer. However, a molecular basis for a potential link between diminished ATM function and sporadic breast malignancy remains elusive. Here, we show that 78% (18 out of a panel of 23) of surgically removed breast tumors (stage II or greater) displayed aberrant methylation of the ATM proximal promoter region as judged by methylation-specific PCR. Aberrant methylation of the ATM promoter was independently confirmed in several tumors by bisulfite sequencing. Moreover, bisulfite sequencing indicated that this region of the genome is subject to dense methylation. Further, we found a highly significant correlation (P = 0.0006) between reduced ATM mRNA abundance, as measured by real-time RT-PCR, and aberrant methylation of the ATM gene promoter. These findings indicate that epigenetic silencing of ATM expression occurs in locally advanced breast tumors, and establish a link at the molecular level between reduced ATM function and sporadic breast malignancy.

Breast cancer is associated with the second highest cancer-associated deaths worldwide. Therefore, understanding the key events that determine breast cancer progression, modulation of the tumor-microenvironment and metastasis, which is the main cause of cancer-associated death, are of great importance. The mammary specific polyomavirus middle T antigen overexpression mouse model (MMTV-PyMT), first published in 1992, is the most commonly used genetically engineered mouse model (GEMM) for cancer research. Mammary lesions arising in MMTV-PyMT mice follow similar molecular and histological progression as human breast tumors, making it an invaluable tool for cancer researchers and instrumental in understanding tumor biology. In this review, we will highlight key studies that demonstrate the utility of PyMT derived GEMMs in understanding the molecular basis of breast cancer progression, metastasis and highlight its use as a pre-clinical tool for therapeutic discovery.

ERα positive breast cancer accounts for 70% of breast malignancies. Compared with ERα negative types, ERα positive breast cancer could be effective controlled by endocrine therapy. However, more than half of the patients will develop endocrine resistance, making it an important clinical issue for breast cancer therapy. Endocrine resistance might be caused by multiple alternations, including the components of ERα signaling, during tumor progression. Thus, it is urgent and necessary to uncover the molecular mechanisms that controls ERα expression and stability to improve breast cancer therapeutics. In our current study, we identifies that the ubiquitin ligase RNF181 stabilizes ERα and facilitates breast cancer progression. The expression of RNF181 is correlated with ERα level in human breast tumors and relates to poor survival in endocrine-treated patients. RNF181 depletion inhibits breast cancer progression in vivo and in vitro, reduces ERα protein level and its target gene expression, such as PS2 and GREB1. Unbiased RNA sequencing analysis indicates RNF181 is necessary for ERα signature gene expression in whole genomic level. Immuno-precipitation assays indicate that RNF181 associates with ERα and promotes its stability possibly via inducing ERα K63-linked poly-ubiquitination. In conclusion, our data implicate a non-genomic mechanism by RNF181 via stabilizing ERα protein controls ERα target gene expression linked to breast cancer progression.

Members of the NF-kappa B/Rel transcription factor family have been shown recently to be required for cellular transformation by oncogenic Ras and by other oncoproteins and to suppress transformation-associated apoptosis. Furthermore, NF-kappa B has been shown to be activated by several oncoproteins including HER2/Neu, a receptor tyrosine kinase often expressed in human breast cancer. Human breast cancer cell lines, human breast tumors and normal adjacent tissue were analysed by gel mobility shift assay, immunoblotting of nuclear extracts and immunohistochemistry for activation of NF-kappa B. Furthermore, RNA levels for NF-kappa B-activated genes were analysed in order to determine if NF-kappa B is functionally active in human breast cancer. Our data indicate that the p65/RelA subunit of NF-kappa B is activated (i.e., nuclear) in breast cancer cell lines. However, breast tumors exhibit an absence or low level of nuclear p65/RelA but show activated c-Rel, p50 and p52 as compared to nontumorigenic adjacent tissue. Additionally, the I kappa B homolog Bcl-3, which functions to stimulate transcription with p50 or p52, was also activated in breast tumors. There was no apparent correlation between estrogen receptor status and levels of nuclear NF-kappa B complexes. Transcripts of NF-kappa B-regulated genes were found elevated in breast tumors, as compared to adjacent normal tissue, indicating functional NF-kappa B activity. These data suggest a potential role for a subset of NF-kappa B and I kappa B family proteins, particularly NF-kappa B/p52 and Bcl-3, in human breast cancer. Additionally, the activation of functional NF-kappa B in these tumors likely involves a signal transduction pathway distinct from that utilized by cytokines.

Loss of chromosome 6q21-qter is the second most frequent loss of chromosomal material in sporadic breast neoplasms suggesting the presence of at least one tumor suppressor gene on 6q. We recently isolated a cDNA encoding a new zinc finger protein which we named ZAC according to its functional properties, namely induction of apoptosis and control of cell cycle progression. ZAC is expressed in normal mammary gland and maps to 6q24-q25, a recognized breast cancer hot spot on 6q. In the present report, we investigated the possible inactivation of ZAC in breast cancer cell lines and primary tumors. We detected no mutation in ZAC coding region in a panel of 45 breast tumors with allelic imbalance of 6q24-q25. However, a survey of eight breast cancer cell lines showed a deeply reduced (three cell lines) or complete loss of (five cell lines) ZAC expression. Treatment of three of these cell lines with the methylation-interfering agent 5-azacytidine induced ZAC re-expression. In addition, Northern blot and RNase protection assay analysis of ZAC expression in 23 unselected primary breast tumors showed a reduced expression in several samples. Together with its functional properties and chromosomal localization, these findings substantiate ZAC as a good candidate for the tumor suppressor gene on 6q24-q25.

FGF-1 is expressed in a high proportion of breast tumors. While overexpression of FGF-4 in the MCF-7 breast carcinoma cell line confers the ability to form spontaneously metastasizing tumors in ovariectomized nude mice without estrogen supplementation and in mice that receive tamoxifen pellets, the response of a cell to individual FGFs can be controlled at multiple levels, and the significance of FGF-1 expression in human breast tumors is uncertain. To study the role of FGF-1, MCF-7 human breast cancer carcinoma cells, previously transfected with bacterial beta-galactosidase, were retransfected with FGF-1 expression vectors. FGF-1 transfectants formed large, vascularized tumors in ovariectomized nude mice without estrogen supplementation as well as in mice that received tamoxifen pellets. Lymphatic and pulmonary micrometastases were detected as deposits of X-gal-stained cells as early as 17 days after cell inoculation whereas no metastases were detected in estrogen-supplemented mice bearing similar-sized control tumors. When compared with controls, both clonal and polyclonal populations of FGF-1 overexpressing cells exhibited increased anchorage-independent growth and decreased population doubling times in estrogen-depleted or 4-hydroxytamoxifen containing medium. These results suggest that FGF signaling may be important in the transition of breast cancer cells from hormone-dependent to hormone-independent and from nonmetastatic to metastatic.

Collective invasion into adjacent tissue is a hallmark of luminal breast cancer, and ~20% of these cases eventually undergo metastasis. How less aggressive luminal-like breast cancer transitions to invasive cancer remains unclear. Our study revealed that CD44hi cancer cells are the leading subpopulation in collectively invading luminal cancer cells and efficiently promote the collective invasion of CD44lo/follower cells. The CD44hi/leader subpopulation showed a specific gene signature of various hybrid epithelial/mesenchymal genes and key functional coregulators of collective invasion, which was distinct from that of CD44lo/follower cells. However, the CD44hi/leader cells, which showed a partial epithelial-mesenchymal transition (EMT) phenotype, readily switched to the CD44lo phenotype along with collective migration and vice versa; this phenomenon was spontaneous and sensitive to the tumor microenvironment. The CD44lo-to-CD44hi conversion was accompanied by a shift in CD44s to CD44v but not a conversion of non-cancer stem cells to cancer stem cells (CSCs). Therefore, the CD44hi leader cells, as currently identified, are not a stable subpopulation in breast tumors. This plasticity and ability to generate CD44hi carcinoma cells with enhanced migratory and invasive behavior might be responsible for the transition from in situ to invasive behavior of luminal-type breast cancer.

Metastasis is the main cause of death in breast cancer patients. The initial step of metastasis is invadopodia-mediated extracellular matrix (ECM) degradation, which enables local breast tumor cells to invade surrounding tissues. However, the molecular mechanism underlying invadopodia-mediated metastasis remains largely unknown. Here we found that the RNA-binding protein Musashi1 (Msi1) exhibited elevated expression in invasive breast tumors and promoted lung metastasis of mammary cancer cells. Suppression of Msi1 reduced invadopodia formation in mammary cancer cells. Furthermore, Msi1 deficiency decreased the expression and activity of Mmp9, an important enzyme in ECM degradation. Mechanistically, Msi1 directly suppressed Timp3, an endogenous inhibitor of Mmp9. In clinical breast cancer specimens, TIMP3 and MSI1 levels were significantly inversely correlated both in normal breast tissue and breast cancer tissues and associated with overall survival in breast cancer patients. Taken together, our findings demonstrate that the MSI1-TIMP3-MMP9 cascade is critical for invadopodia-mediated onset of metastasis in breast cancer, providing novel insights into a promising therapeutic strategy for breast cancer metastasis.

SummarySolid tumors are often characterized by a hypoxic microenvironment which contributes, through the hypoxia-inducible factor HIF-1, to the invasion-metastasis cascade. Endoplasmic reticulum (ER) stress also leads tumor cells to thrive and spread by inducing a transcriptional and translational program, the Unfolded Protein Response (UPR), aimed at restoring ER homeostasis. We studied ERO1 alpha (henceforth ERO1), a protein disulfide oxidase with the tumor-relevant characteristic of being positively regulated by both ER stress and hypoxia. Analysis of the redox secretome indicated that pro-angiogenic HIF-1 targets, were blunted in ERO1-devoid breast cancer cells under hypoxic conditions. ERO1 deficiency reduced tumor cell migration and lung metastases by impinging on tumor angiogenesis, negatively regulating the upstream ATF4/CHOP branch of the UPR and selectively impeding oxidative folding of angiogenic factors, among which VEGF-A. Thus, ERO1 deficiency acted synergistically with the otherwise feeble curative effects of anti-angiogenic therapy in aggressive breast cancer murine models and it might be exploited to treat cancers with pathological HIF-1-dependent angiogenesis. Furthermore, ERO1 levels are higher in the more aggressive basal breast tumors and correlate inversely with the disease- and metastasis-free interval of breast cancer patients. Thus, taking advantage of our in vitro data on ERO1-regulated gene products we identified a gene set associated with ERO1 expression in basal tumors and related to UPR, hypoxia, and angiogenesis, whose levels might be investigated in patients as a hallmark of tumor aggressiveness and orient those with lower levels toward an effective anti-angiogenic therapy.

Development of human tumors is driven by accumulation of alterations in tumor suppressor genes and oncogenes in cells. The POU1F1 transcription factor (also known Pit-1) is expressed in the mammary gland and its overexpression induces profound phenotypic changes in proteins involved in breast cancer progression. Patients with breast cancer and elevated expression of Pit-1 show a positive correlation with the occurrence of distant metastasis and poor overall survival. However, some mediators of Pit-1 actions are still unknown. Here, we show that CXCR4 chemokine receptor and its ligand CXCL12 play a critical role in the pro-tumoral process induced by Pit-1. We found that Pit-1 increases mRNA and protein in both CXCR4 and CXCL12. Knock-down of CXCR4 reduces tumor growth and spread of Pit-1 overexpressing cells in a zebrafish xenograft model. Furthermore, we described for the first time pro-angiogenic effects of Pit-1 through the CXCL12-CXCR4 axis, and that extravasation of Pit-1 overexpressing breast cancer cells is strongly reduced in CXCL12-deprived target tissues. Finally, in breast cancer patients, expression of Pit-1 in primary tumors was found to be positively correlated with CXCR4 and CXCL12, with specific metastasis in liver and lung, and with clinical outcome. Our results suggest that Pit-1-CXCL12-CXCR4 axis could be involved in chemotaxis guidance during the metastatic process, and may represent prognostic and/or therapeutic targets in breast tumors.

The protein p38 mitogen-activated protein kinase (MAPK) delta isoform (p38δ) is a poorly studied member of the MAPK family. Data analysis from The Cancer Genome Atlas database revealed that p38δ is highly expressed in all types of human breast cancers. Using a human breast cancer tissue array, we confirmed elevation in cancer tissue. The breast cancer mouse model, MMTV-PyMT (PyMT), developed breast tumors with lung metastasis; however, mice deleted in p38δ (PyMT/p38δ-/-) exhibited delayed primary tumor formation and highly reduced lung metastatic burden. At the cellular level, we demonstrate that targeting of p38δ in breast cancer cells, MCF-7 and MDA-MB-231 resulted in a reduced rate of cell proliferation. In addition, cells lacking p38δ also displayed an increased cell-matrix adhesion and reduced cell detachment. This effect on cell adhesion was molecularly supported by the regulation of the focal adhesion kinase by p38δ in the human breast cell lines. These studies define a previously unappreciated role for p38δ in breast cancer development and evolution by regulating tumor growth and altering metastatic properties. This study proposes MAPK p38δ protein as a key factor in breast cancer. Lack of p38δ resulted in reduced primary tumor size and blocked the metastatic potential to the lungs.

Adhesion turnover is critical for cell motility and invasion. We previously demonstrated that the adaptor molecule breast cancer antiestrogen resistance 3 (BCAR3) promotes adhesion disassembly and breast tumor cell invasion. One of two established binding partners of BCAR3 is the adaptor molecule, p130Cas. In this study, we sought to determine whether signaling through the BCAR3-Cas complex was responsible for the cellular functions of BCAR3. We show that the entire pool of BCAR3 is in complex with Cas in invasive breast tumor cells and that these proteins colocalize in dynamic cellular adhesions. Although accumulation of BCAR3 in adhesions did not require Cas binding, a direct interaction between BCAR3 and Cas was necessary for efficient dissociation of BCAR3 from adhesions. The dissociation rates of Cas and two other adhesion molecules, α-actinin and talin, were also significantly slower in the presence of a Cas-binding mutant of BCAR3, suggesting that turnover of the entire adhesion complex was delayed under these conditions. As was the case for adhesion turnover, BCAR3-Cas interactions were found to be important for BCAR3-mediated breast tumor cell chemotaxis toward serum and invasion in Matrigel. Previous work demonstrated that BCAR3 is a potent activator of Rac1, which in turn is an important regulator of adhesion dynamics and invasion. However, in contrast to wild-type BCAR3, ectopic expression of the Cas-binding mutant of BCAR3 failed to induce Rac1 activity in breast cancer cells. Together, these data show that the ability of BCAR3 to promote adhesion disassembly, tumor cell migration and invasion, and Rac1 activity is dependent on its ability to bind to Cas. The activity of BCAR3-Cas complexes as a functional unit in breast cancer is further supported by the co-expression of these molecules in multiple subtypes of human breast tumors.

The WASF3 gene is overexpressed in high-grade breast cancer and promotes invasion and metastasis, but does not affect proliferation. The HER2/ERBB2/NEU gene is also frequently overexpressed in breast cancer, and has been shown to promote invasion and metastasis in these tumors. Here, we show that WASF3 is present in the HER2 immunocomplex and suppression of WASF3 function leads to suppression of invasion even in the presence of HER2 expression. Overexpression of both HER2 and WASF3 in non-metastatic MCF7 breast cancer cells promotes invasion and metastasis more significantly than either gene alone. HER2 forms homodimers as well as heterodimers with other HER family members and we now show that the ability of WASF3 to promote invasion is highly dependent on the HER2/HER3 heterodimer. The engagement of WASF3 with the HER2/HER3 complex facilitates its phospho-activation and transcriptional upregulation, which is facilitated by HER2/HER3 activation of JAK/STAT signaling. In breast cancer cells overexpressing HER2, therefore, WASF3 is specifically required to facilitate the invasion/metastasis response. Targeting WASF3, therefore, could be a potential therapeutic approach to suppress metastasis of HER2-overexpressing breast tumors.

Mucin-like 1 (MUCL1) was first identified as a breast-specific gene over a decade ago. Based on its highly restricted mRNA expression in breast tissue and continued expression during breast tumorigenesis and progression, MUCL1 is an attractive tumor-associated antigen and a potential therapeutic target. However, very little is known about the cellular location, biological functions and regulation of the MUCL1 protein, which will have a major impact on its druggability. Here we describe our efforts to fully characterize the cellular localization of MUCL1, investigate its regulation by key breast cancer oncogenes such as human epidermal growth factor receptor 2 (HER2) and discover its functional roles in breast cancer. Although some mucins are membrane bound, our data indicate that MUCL1 is secreted by some breast cancer cells, whereas others only express high levels of intracellular MUCL1. MUCL1 expression is highest in HER2-amplified breast tumors and inhibiting HER2 activity in tumor cells resulted in a decreased MUCL1 expression. In-depth investigation demonstrated that phosphoinositide3-kinase/Akt pathway, but not Ras/MEK pathway, controls MUCL1 expression downstream of HER2. Phenotypic assays revealed a strong dependence of HER2-positive cells on MUCL1 for cell proliferation. We further identified the mechanism by which MUCL1 regulates cell growth. Knockdown of MUCL1 induced a G1/S phase arrest concomitant with decreased cyclin D and increased p21 and p27 levels. Finally, we investigated the impact of MUCL1 loss on kinase signaling pathways in breast cancer cells through phospho-kinase array profiling. MUCL1 silencing abrogated phospho-focal adhesion kinase (FAK), Jun NH2-terminal kinase (JNK) and c-Jun signals, but not extracellular signal-regulated kinase or Akt pathway activities, thereby pointing to FAK/JNK pathway as the downstream effector of MUCL1 signaling. We are the first to identify an important role for MUCL1 in the proliferation of breast cancer cells, probably mediated via the FAK/JNK signaling pathway. Taken together, these data suggest a potential utility for therapeutic targeting of this protein in breast cancer.

The median survival time of breast cancer patients with brain metastasis is less than 6 months, and even a small metastatic lesion often causes severe neurological disabilities. Because of the location of metastatic lesions, a surgical approach is limited and most chemotherapeutic drugs are ineffective owing to the blood brain barrier (BBB). Despite this clinical importance, the molecular basis of the brain metastasis is poorly understood. In this study, we have isolated RNA from samples obtained from primary breast tumors and also from brain metastatic lesions followed by microRNA profiling analysis. Our results revealed that the miR-509 is highly expressed in the primary tumors, whereas the expression of this microRNA is significantly decreased in the brain metastatic lesions. MicroRNA target prediction and the analysis of cytokine array for the cells ectopically expressed with miR-509 demonstrated that this microRNA was capable of modulating the two genes essential for brain invasion, RhoC and TNF-α that affect the invasion of cancer cells and permeability of BBB, respectively. Importantly, high levels of TNF-α and RhoC-induced MMP9 were significantly correlated with brain metastasis-free survival of breast cancer patients. Furthermore, the results of our in vivo experiments indicate that miR-509 significantly suppressed the ability of cancer cells to metastasize to the brain. These findings suggest that miR-509 has a critical role in brain metastasis of breast cancer by modulating the RhoC-TNF-α network and that this miR-509 axis may represent a potential therapeutic target or serve as a prognostic tool for brain metastasis.