Parental MCF10A Cells Research Articles

Abstract 2425: Mechano-response via ATP alters calcium signaling in breast epithelial cells with oncogenic KRas mutation

Abstract The majority of breast cancer patient deaths occur when tumor cells migrate away from the primary tumors and disseminate metastatically. Cancer cells at the invasive front mimic the behaviors of non-tumorigenic epithelial cells at wound edges but show less coordinated migration comparatively. While most wound healing studies use a timeframe of 24-48 hours, our previous studies have shown that ATP released from wounded cells initiates a calcium (Ca2+) signal within seconds that spreads to neighboring cells through activation of the P2Y2 surface receptor. RNAseq data of MCF10A mammary epithelial cells with stepwise mutations of PTEN knockout and KRas activation alone or in combination, demonstrate that P2Y2 is downregulated specifically by active KRas. Fluorescence microscopy was used to measure Ca2+ signaling and mitochondrial membrane potential in parental and mutant MCF10A cells. Change in total fluorescence was measured and compared to baseline using Fluo-4, a Ca2+ fluorescent indicator, and TMRM (tetramethylrhodamine, methyl ester), a fluorescent mitochondrial membrane potential dye on Nikon analysis software. We show that KRas activation disrupts ATP stimulation and Ca2+ signaling. This change was further quantified using a FlexStation III plate reader with Fluo-4 to read specific fluorescent changes in Ca2+ after ATP addition. ATP-stimulated Ca2+ was also disrupted in other breast tumor cell lines harboring Ras activating mutations, MDA-MB-231 and MDA-MB-436, both showing a similar decrease in P2Y2 expression. These data show that ATP stimulation can be used to further understand the differences in Ca2+ signaling and mechanical-response between normal breast epithelial cells and cancer cells. Clarifying these molecular mechanisms could reveal targets for new cancer treatments, especially since 90% of human tumors are epithelial carcinomas. Citation Format: Makenzy Mull, Stephen Pratt, Rachel Lee, Abanoub Gad, Katarina Chang, David Annis, Keyata Thompson, Michele Vitolo, Liron Boyman, Stuart Martin. Mechano-response via ATP alters calcium signaling in breast epithelial cells with oncogenic KRas mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2425.

PIK3CA C2 Domain Deletions Hyperactivate Phosphoinositide 3-kinase (PI3K), Generate Oncogene Dependence, and Are Exquisitely Sensitive to PI3Kα Inhibitors.

Purpose: We describe herein a novel P447_L455 deletion in the C2 domain of PIK3CA in a patient with an ER+ breast cancer with an excellent response to the PI3Kα inhibitor alpelisib. Although PIK3CA deletions are relatively rare, a significant portion of deletions cluster within amino acids 446-460 of the C2 domain, suggesting these residues are critical for p110α function.Experimental Design: A computational structural model of PIK3CAdelP447-L455 in complex with the p85 regulatory subunit and MCF10A cells expressing PIK3CAdelP447-L455 and PIK3CAH450_P458del were used to understand the phenotype of C2 domain deletions.Results: Computational modeling revealed specific favorable inter-residue contacts that would be lost as a result of the deletion, predicting a significant decrease in binding energy. Coimmunoprecipitation experiments showed reduced binding of the C2 deletion mutants with p85 compared with wild-type p110α. The MCF10A cells expressing PIK3CA C2 deletions exhibited growth factor-independent growth, an invasive phenotype, and higher phosphorylation of AKT, ERK, and S6 compared with parental MCF10A cells. All these changes were ablated by alpelisib treatment.Conclusions: C2 domain deletions in PIK3CA generate PI3K dependence and should be considered biomarkers of sensitivity to PI3K inhibitors. Clin Cancer Res; 24(6); 1426-35. ©2017 AACR.

Abstract 1772: PIK3CA C2 domain deletions hyperactivate PI3K, generate oncogene dependence and are exquisitely sensitive to PI3Kα inhibitors

Abstract Background: A 63 year old postmenopausal woman with advanced ER+ breast cancer resistant to endocrine therapy exhibited an exceptional response to the PI3Kα inhibitor alpelisib (BYL719) and the aromatase inhibitor letrozole (Mayer et al. Clin Cancer Res 2016). Targeted capture next generation sequence (NGS) of DNA from a liver metastasis identified a P447_L455 deletion in the C2 domain of PIK3CA. About 80% of PIK3CA activating mutations are in ‘hot spots’ within the helical and kinase domains. C2 domain mutations make up ~10% of all PIK3CA mutations in breast cancer (TCGA, Foundation Medicine) and are frequently not reported by tumor and plasma cell-free DNA NGS panels. Deletions and mutations in this domain cluster in a region encompassing amino acids 446-460 of PIK3CA. We investigated herein the functional role of PIK3CA C2 domain mutations and their response to PI3K inhibitors. Methods: V5-tagged lentiviral vectors encoding wild type, delP447-L455, and delH450-P458 were stably transduced into MCF10A non-tumorigenic human breast epithelial cells. Cell viability and acini formation in 3D Matrigel were examined in media ± EGF or insulin or alpelisib. Markers of PI3K activation were examined by immunoblot and phosphoflow analysis. The Rosetta software suite was used to construct a structural model that would predict the change in stability of the p85/p110α complex. Physical association of p85α and p110α was determined by precipitation with V5 antibodies and immunoblot analysis. Results: MCF10A cells stably expressing V5-tagged PIK3CAdelP447-L455 and PIK3CAdelH450-P458 exhibited EGF- and insulin-independent growth and higher phosphorylation of AKT, ERK and S6 when compared to parental MCF10A cells. In 3D Matrigel, MCF10A cells with PIK3CA C2 domain deletions formed invasive acini with increased protrusions, spindling, and bridging between acini. All these changes were ablated upon the addition of 1 µM of alpelisib whereas parental MCF10A cells were unaffected by alpelisib. We hypothesized that delP447-L455 would reduce the binding affinity of p110α with the p85 regulatory subunit of PI3K. A structural model of PIK3CAdelP447-L455 in the context of the regulatory complex revealed specific favorable inter-residue contacts that would be lost as a result of the deletion, predicting a significant decrease in binding energy. Consistent with this structural analysis, coimmunoprecipitation of p85 with V5 antibodies showed reduced binding of the C2 domain deletion mutants with p85 compared to wild type p110α. Conclusions: These data suggest that C2 domain deletions in PIK3CA are activating mutations and generate oncogene dependence. As a result, tumors expressing these mutations are exquisitely sensitive to PI3Kα inhibitors. Thus, in addition to PIK3CA ‘hot spot’ mutations, C2 domain mutations should also be considered biomarkers of sensitivity to PI3K inhibitors. Citation Format: Sarah Croessmann, Jonathan Sheehan, Gregory Sliwoski, Nalin Leelatian, Jie He, Rebecca Nagy, Justin M. Balko, Ingrid A. Mayer, Richard B. Lanman, Vincent Miller, Lewis C. Cantley, Jonathan M. Irish, Jens Meiler, Carlos L. Arteaga. PIK3CA C2 domain deletions hyperactivate PI3K, generate oncogene dependence and are exquisitely sensitive to PI3Kα inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1772. doi:10.1158/1538-7445.AM2017-1772

Abstract 3838: Functional crosstalk between histone deacetylase 5 (HDAC5) and lysine-specific demethylase 1 (LSD1) as a novel therapeutic target in triple-negative breast cancer cells

Abstract Our previous work has shown that HDAC5 knockdown led to significant increase of H3K4me2 in the TNBC cell line, MDA-MB-231, suggesting a potential role of HDAC5 in regulating LSD1 activity in breast cancer. In this study, we demonstrated that HDAC5 physically interacts with LSD1 in MDA-MB-231 cells. Overexpression of HDAC5 increased LSD1 protein level through a reduction of LSD1 polyubiquitination. siRNA-mediated knockdown of HDAC5 mRNA, but not other class II HDACs or LSD1-containing complex members (HDAC1, HDAC2 and CoREST), significantly decreased LSD1 protein expression and half-life. HDAC5 overexpression reduced levels of H3K4me1/2, suggesting that HDAC5 acts as a positive regulator of LSD1-mediated H3K4 demethylation activity. Enhanced proliferation mediated by HDAC5 overexpression in MDA-MB-231 cells was diminished by LSD1-KD, suggesting a critical role of LSD1 in regulating oncogenic activity of HDAC5. We also observed that high-grade tumorigenic MCF10A-CA1a cells (triple negative) expressed higher levels of LSD1 and HDAC5 compared with parental counterpart MCF10A cells. By gain- and loss-of-function studies using this TNBC progression model, we observed that HDAC5 possesses a critical oncogenic function in driving TNBC development by blocking LSD1 protein degradation and re-shaping epigenetic landscape. Several HDAC inhibitors were tested for their ability to inhibit LSD1 and HDAC5 interaction. Treatment with sulforaphane, a natural HDAC inhibitor found in cruciferous vegetables, blocked the association of HDAC5 and LSD1 through down-regulation of HDAC5 mRNA and protein expression that led to LSD1 protein destabilization. Sulforaphane treatment also re-expressed a unique subset of tumor suppressor genes (RGS16, BIK, PCDH1, CDKN1a, ING1, etc), which are abnormally silenced in TNBC cells, but are expressed in other breast cancer subtypes and normal breast cells. Addition of a novel LSD1 inhibitor, HCI-2509, significantly promoted antineoplastic efficacy of sulforaphane in breast cancer cells, and TNBC cells were more susceptible than other subtypes to the combination therapy. In an in vivo study, while treatment with either sulforaphane or HCI-2509 alone each displayed significant anti-tumor effects against MDA-MB-231 xenografts, combined treatment with both compounds exhibited synergistic inhibitory effect on tumor growth in the MDA-MB-231 xenografts. Taken together, these results suggest that HDAC5 promotes LSD1 protein stabilization, leading to a dysregulated chromatin landscape which functions as an antibraking system in TNBC development. Crosstalk between LSD1 and HDAC5 may represent a novel and effective therapeutic target for this devastating disease. (Supported by DOD W81XWH-14-1-0237/W81XWH-14-1-0238, Breast Cancer Research Foundation, and UPCI Core Grant NIH P30CA047904) Citation Format: Chunyu Cao, Shauna Vasilatos, Steffi Oesterreich, Nancy E. Davidson, Yi Huang. Functional crosstalk between histone deacetylase 5 (HDAC5) and lysine-specific demethylase 1 (LSD1) as a novel therapeutic target in triple-negative breast cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3838. doi:10.1158/1538-7445.AM2015-3838

Overexpression of MERTK Receptor Tyrosine Kinase in Epithelial Cancer Cells Drives Efferocytosis in a Gain-of-Function Capacity

MERTK, a member of the TAM (TYRO3, AXL, and MERTK) receptor tyrosine kinases, has complex and diverse roles in cell biology. On the one hand, knock-out of MERTK results in age-dependent autoimmunity characterized by failure of apoptotic cell clearance, while on the other, MERTK overexpression in cancer drives classical oncogene pathways leading to cell transformation. To better understand the interplay between cell transformation and efferocytosis, we stably expressed MERTK in human MCF10A cells, a non-tumorigenic breast epithelial cell line devoid of endogenous MERTK. While stable expression of MERTK in MCF10A resulted in enhanced motility and AKT-mediated chemoprotection, MERTK-10A cells did not form stable colonies in soft agar, or enhance proliferation compared with parental MCF10A cells. Concomitant to chemoresistance, MERTK also stimulated efferocytosis in a gain-of-function capacity. However, unlike AXL, MERTK activation was highly dependent on apoptotic cells, suggesting MERTK may preferentially interface with phosphatidylserine. Consistent with this idea, knockdown of MERTK in breast cancer cells MDA-MB 231 reduced efferocytosis, while transient or stable expression of MERTK stimulated apoptotic cell clearance in all cell lines tested. Moreover, human breast cancer cells with higher endogenous MERTK showed higher levels of efferocytosis that could be blocked by soluble TAM receptors. Finally, through MERTK, apoptotic cells induced PD-L1 expression, an immune checkpoint blockade, suggesting that cancer cells may adopt MERTK-driven efferocytosis as an immune suppression mechanism for their advantage. These data collectively identify MERTK as a significant link between cancer progression and efferocytosis, and a potentially unrealized tumor-promoting event when MERTK is overexpressed in epithelial cells.

The Function of Vacuolar ATPase (V-ATPase) a Subunit Isoforms in Invasiveness of MCF10a and MCF10CA1a Human Breast Cancer Cells

The vacuolar H(+) ATPases (V-ATPases) are ATP-driven proton pumps that transport protons across both intracellular and plasma membranes. Previous studies have implicated V-ATPases in the invasiveness of various cancer cell lines. In this study, we evaluated the role of V-ATPases in the invasiveness of two closely matched human breast cancer lines. MCF10a cells are a non-invasive, immortalized breast epithelial cell line, and MCF10CA1a cells are a highly invasive, H-Ras-transformed derivative of MCF10a cells selected for their metastatic potential. Using an in vitro Matrigel assay, MCF10CA1a cells showed a much higher invasion than the parental MCF10a cells. Moreover, this increased invasion was completely sensitive to the specific V-ATPase inhibitor concanamycin. MCF10CA1a cells expressed much higher levels of both a1 and a3 subunit isoforms relative to the parental line. Isoforms of subunit a are responsible for subcellular localization of V-ATPases, with a3 and a4 targeting V-ATPases to the plasma membrane of specialized cells. Knockdown of either a3 alone or a3 and a4 together using isoform-specific siRNAs inhibited invasion by MCF10CA1a cells. Importantly, overexpression of a3 but not the other a subunit isoforms greatly increased the invasiveness of the parental MCF10a cells. Similarly, overexpression of a3 significantly increased expression of V-ATPases at the plasma membrane. These studies suggest that breast tumor cells employ particular a subunit isoforms to target V-ATPases to the plasma membrane, where they function in tumor cell invasion.

Abstract 1678: Metastatic breast cancer cell phenotype is regulated by autophagy.

Abstract Autophagy is a catabolic process that is tightly regulated during normal cell growth, development, and homeostasis. Although it may be death inducing, it is also an important survival mechanism for cells in stressful environments, including hypoxia, nutrient deprivation, chemical or physical pressure, or detachment from colonies. Considering the stress associated with the process of metastasis, we hypothesized that autophagy may play a role in the ability of breast cancer cells to survive and metastasize. To test this, we first compared cell proliferation after autophagic induction between metastatic breast cancer cell lines (MDA-MB-231 and -435), a non-metastatic breast cancer cell line (MDA-MB-436), and a ‘normal’ breast epithelial cell line (MCF10A). Both metastatic cell lines continued to proliferate following induction of autophagy; however, the non-metastatic and normal cell lines were growth-inhibited. Autophagy was also more rapidly induced by rapamycin in the metastatic cell lines as demonstrated by an increase in LC3II expression. To test the different survival capabilities between metastatic and normal cells, we selected cells through five rounds of starvation with Earle's balanced salt solution (EBSS) and compared their ability to induce autophagy. Although both the normal and metastatic cells maintained their ability to proliferate under normal conditions, the MDA-MB-231 cells that survived starvation (231-EB5) proliferated more rapidly than the parental population following induction of autophagy. In contrast, both MCF10A and MCF10A-EB5 cells were growth-inhibited. The 231-EB5 cells induced autophagy more rapidly than the parental population as demonstrated by increased expression of LC3II (analyzed by immunoblot) and increased LC3 puncta (analyzed by immunofluorescence). Migration of parental 231 cells was inhibited by rapamycin; however, there was no change in the ability of 231-EB5 cells to migrate after treatment with rapamycin. Growth in three dimensions also was significantly altered. MCF10A-EB5 cells were more extended compared to the spherical growth of the parental MCF10A cells. Protrusions emitted from the 231-EB5 cells were more rounded compared to the extended spikes of the parental 231 cells. Altogether, these results demonstrate that select populations derived from metastatic breast cancer cells have different abilities to survive, proliferate, and migrate following induction of autophagy, suggesting that autophagy may be a key mechanism for tumor progression and metastasis. Citation Format: Yi Li, Monica J. Lewis, Jianzhong Liu, James J. Cody, Douglas R. Hurst. Metastatic breast cancer cell phenotype is regulated by autophagy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1678. doi:10.1158/1538-7445.AM2013-1678

Abstract PR14: ErbB2-induced epithelium to mesenchyme transition (EMT) is blocked by p38α/β signaling to restrict early dissemination in breast cancer

Abstract Our aim is to better understand the mechanisms dictating the early dissemination of cells from pre-malignant lesions, as well as those controlling cell fate decisions at secondary sites to develop more effective therapies for eradicating these populations. The majority of breast cancer patients die from metastatic disease, and not from their primary tumor. The current paradigm argues that dissemination of tumor cells can only occur from invasive lesions observed during late stages of the disease. However, clinical evidence suggests that “pre-malignant” mammary epithelial cells can disseminate and accumulate in target organs like the bone. This can occur from non-invasive lesions such as those found in Ductal Carcinoma in Situ (DCIS) patients. Thus, “early” disseminated tumor cells (DTCs) might be critical contributors to metastasis, but the mechanisms behind these events remain largely unknown. We had shown that p38-alpha/beta signaling maintains mammary gland ductal architecture by promoting anoikis and preventing disorganization of the luminal and basal epithelial compartments. We propose that, in addition to regulating mammary gland morphogenesis, p38-alpha/beta regulates a switch controlling early dissemination. In clinical samples we have found that ErbB2+ DCIS or invasive lesions show a down-regulation of the p38-signaling pathway, suggesting a role for the inhibition of p38-alpha/beta during cancer progression. In MMTV-Neu mammary glands ErbB2 is inversely correlated to membranous beta-catenin (inactive beta-catenin). Further, loss of P-ATF2 (p38 target) also coincides with reduced E-cadherin in this ErbB2+ epithelium. We also reveal that inhibition of p38-alpha/beta in MCF10A-ErbB2 or “pre-malignant” MMTV-ErbB2 acini results in increased invasion and disruption of normal acinar structure. In the MCF10A-ErbB2 model this correlated with E-cadherin down-regulation and induction of an 11-gene Wnt signaling EMT signature (e.g. up-regulation of Wnt5a/b, Wnt11, SNAIL, TWIST, N-cadherin, ZEB2, and SLUG). This EMT signature was also induced simply by p38-alpha/beta inhibition or ErbB2 overexpression in parental MCF10A cells. Further, treatment of MCF10A cells with Wnt3a inhibited p38-alpha and ATF2 phosphorylation. Inhibition of p38-alpha/beta signaling in MMTV-ErbB2 mice strongly increased the accumulation of pre-malignant MECs (detected by surface ErbB2) in the lungs and bone marrow. However, at least in lungs, >80% of these DTCs remained dormant as measure by P-Rb staining. We propose that in pre-malignant lesions p38-alpha/beta acts as an inhibitor to ErbB2-induced EMT, anoikis resistance and early dissemination. We further propose that Wnt signaling executes the EMT and also the silencing of p38-alpha/beta signaling to allow for early dissemination. This abstract is also presented as Poster B74. Citation Format: Kathryn Harper, Maria Soledad Sosa, Alvaro Avivar-Valderas, Huei-Chi Wen, Julio Aguirre-Ghiso. ErbB2-induced epithelium to mesenchyme transition (EMT) is blocked by p38α/β signaling to restrict early dissemination in breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr PR14.

Abstract LB-212: Ionizing radiation selectively promotes invasion of ErbB2-expressing breast cancer cells via regulation of FoxM1

Abstract ErbB2 is frequently amplified in premalignant breast cancers including ductal carcinoma in situ (DCIS); however, little is known about the signals or pathways it modulates in the progression into the invasive/malignant state. Radiotherapy is often used to treat early premalignant lesions regardless of ErbB2 status. Here we show that clinically relevant doses of ionizing radiation (IR) induce cellular invasion of ErbB2-expressing breast cancer cells, such as SKBR3 and BT-474, as well as MCF10A cells transduced to express ErbB2. This effect is specific to ErbB2 expression, as ErbB2-negative breast cancer cells, such as MCF7 and T47D, do not invade following treatment with IR, nor do parental MCF10A cells or MCF10A cells overexpressing EGF receptor alone. Exposure of cells to X-rays leads to ErbB2 phosphorylation at Y877 in a dose- and time-dependent manner, and activates signaling pathways, including Src and PI3K/Akt. Inhibition of these pathways, as well as inactivation of IR-induced reactive oxygen species with the antioxidant N-acetylcysteine, prevented invasion. Activation of ErbB2-dependent signaling resulted in the upregulation of the transcription factor, FoxM1, a member of the forkhead family which has previously been shown to have a role in invasion, in part through transcriptional regulation of MMP2. Indeed, we have seen upregulation of MMP2 in irradiated ErbB2-expressing breast cancer cells, which is abolished when Src or ErbB2 is inhibited. Inhibition of FoxM1 by shRNA abrogated the increase in MMP2 level and prevented induction of invasion by IR, and overexpression of FoxM1 alone in MCF10A cells was sufficient to promote IR-induced invasion. Our data show that low level IR stimulates invasion of ErbB2-expressing breast cancer cells in a FoxM1-dependent manner. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-212. doi:1538-7445.AM2012-LB-212

TRIM29 Functions as a Tumor Suppressor in Nontumorigenic Breast Cells and Invasive ER+ Breast Cancer

Tripartite motif-containing 29 (TRIM29) is a member of the TRIM protein family that has been implicated in hematologic and solid tumor cancers. We found that TRIM29 functions as a tumor suppressor in both the nontumorigenic MCF10A [estrogen receptor (ER)-/TRIM29+] breast cell line and the invasive MCF7 (ER+/TRIM29-) breast cell line. Silencing TRIM29 in MCF10A cells resulted in preneoplastic changes that included loss of polarity in three-dimensional culture, increased proliferation, anchorage-independent growth, and increased migration and invasion. Conversely, the introduction of TRIM29 into MCF7 cells caused reversion to a less aggressive phenotype by antagonizing the growth effect of 17β-estradiol. The interaction between TRIM29 and ER signaling in MCF7 cells was supported by a reduction in ERE binding in the presence of TRIM29 and suppression of ER-dependent gene expression of TFF1, FOS, and GREB1. By microarray analyses, we showed that younger women (<55 years of age) with early-stage, ER+ breast cancer who were given no adjuvant systemic therapy had a significantly lower risk of relapse when their tumor had high TRIM29 expression (P = 0.02). This effect was not observed in older women (>55 years of age) and thus may be due to menopause and loss of circulating estrogens. Our results suggest that loss of TRIM29 expression in normal breast luminal cells can contribute to malignant transformation and lead to progression of ER+ breast cancer in premenopausal women.

Antagonistic regulation of EMT by TIF1γ and Smad4 in mammary epithelial cells

TGF-β is a potent inducer of epithelial-to-mesenchymal transition (EMT), a process involved in tumour invasion. TIF1γ participates in TGF-β signalling. To understand the role of TIF1γ in TGF-β signalling and its requirement for EMT, we analysed the TGF-β1 response of human mammary epithelial cell lines. A strong EMT increase was observed in TIF1γ-silenced cells after TGF-β1 treatment, whereas Smad4 inactivation completely blocked this process. Accordingly, the functions of several TIF1γ target genes can be linked to EMT, as shown by microarray analysis. As a negative regulator of Smad4, TIF1γ could be crucial for the regulation of TGF-β signalling. Furthermore, TIF1γ binds to and represses the plasminogen activator inhibitor 1 promoter, demonstrating a direct role of TIF1γ in TGF-β-dependent gene expression. This study shows the molecular relationship between TIF1γ and Smad4 in TGF-β signalling and EMT.

Abstract 1274: Investigation into the influence of the H1047R PIK3CA mutation on the bioenergetic dependency of a cell

Abstract Background: During tumorigenesis, cells acquire mutations that confer selective advantages for growth. These mutations may reprogram cellular metabolism to meet the requirements of rapid proliferation and survival in an environment of fluctuating and scarce nutrients. Phosphoinositide-3-kinases (PI3Ks) play key roles in fundamental cellular processes and are frequently mutated in a broad range of cancers. The aim of this study was to investigate how a single endogenous activating mutation in PI3K, H1047R, affects the metabolic programming of human breast epithelial cells. Methods: We utilized X-MAN isogenic cells derived from MCF10a mammary epithelial cells, which harbour a single H1047R PIK3CA mutation introduced via AAV-mediated homologous recombination and compared them to matched parental cells with a wild type (WT) allele. This system allows use of endogenous promoters thereby more accurately recapitulating the genomic architecture in human tumours. Metabolic gene expression profiles were measured by RT-PCR. Results: We identified a multi-gene expression signature indicative of increased dependency on the glycolytic pathway. Hexokinase 2, which is involved at an early stage of the glycolytic pathway, was strongly up-regulated along with the lactate transporters MCT1 and 4. The fructose transporter GLUT5 was nearly undetectable in H1047R PIK3CA cells, suggesting a strong preference for glucose and elevated levels of aerobic glycolysis. PI3K mutant cells also down-regulated genes in the pentose phosphate pathway-shunt, tricarboxylic acid cycle and glutaminolysis pathways, indicating that aerobic glycolysis is heavily favoured. Treatment with the PI3K inhibitor GDC-0941 led to a general reversal of gene expression for these pathways, confirming the PI3K specificity of these metabolic alterations. We proceeded to investigate growth dependence of the H1047R PIK3CA and parental MCF10a cells on various nutrient sources (e.g. glucose, fructose, galactose and glutamine). While the growth rates of cells WT for PIK3CA were not significantly affected by glucose withdrawal and nutrient replacement, growth of mutant PIK3CA cells was dramatically compromised in the absence of glucose, revealing a specific dependency for this nutrient as an energy substrate. Consistent with PI3K activation mediating glucose dependency, treatment of H1047R PIK3CA cells with GDC-0941 promoted growth of the cells under low or no glucose conditions. Conclusion: Isogenic cells WT for PIK3CA are capable of utilizing a range of nutrient sources, while cells harboring H1047R PIK3CA appear hard-wired to exclusively utilize glucose. These data suggest that targeting glucose transporters or glycolytic enzymes may be a powerful therapeutic strategy for mutant PI3K-cancers. The overt glucose dependence of cells with this mutation may also offer routes to non-invasively image PI3K-pathway activated tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1274. doi:10.1158/1538-7445.AM2011-1274

Abstract 2062: HIF-1 is required for ErbB2-mediated anoikis resistance

Abstract We have previously established hypoxia as an inhibitor of anoikis in mammary epithelial cells as exposure to hypoxic conditions results in suppression of anoikis and delays lumen formation in 3D acinar structures. Inhibition of anoikis in this system is dependent upon both maintenance of EGFR-mediated MAPK signaling and the hypoxia-inducible transcription factor HIF-1. In an effort to determine the mechanism through which hypoxic exposure maintains MAPK signaling in MCF-10As, we compared the gene expression profiles of normoxic and hypoxic 3D acinar structures using microarray analysis. Interestingly, of the more than 70 genes found to be significantly upregulated under hypoxic conditions, a subset of genes emerged that have been implicated in oncogenesis as mediated by, a well-established regulator of anoikis resistance in breast cancer cells. Based on this intersection between HIF and ErbB2 in anoikis-associated signaling as well as the fact that oncogenes, including ErbB2, are known to stabilize HIF under normoxic conditions, we sought to determine what role, if any, HIF-1 plays in ErbB2-mediated oncogenesis. MCF-10A cells overexpressing ErbB2 indeed show increased levels of HIF-1α mRNA and protein under normoxic conditions. We show, for the first time, that depletion of HIF-1 from ErbB2-expressing cells using RNAi leads to restoration of anoikis sensitivity which is associated with both decreased Akt and Erk signaling and the induction of the pro-anoikis protein Bim. This effect was specific to anoikis as depletion of HIF-1 had no effect on survival of attached cells. Similar effects of HIF-1 depletion on anoikis resistance were seen in the human breast cancer cell line SK-BR-3 in which ErbB2 is amplified. Further, expression of at least four genes (integrin alpha 5, angiopoeitin-like 4, endothelin 2 and lysyl oxidase) identified in our microarray analysis as being upregulated by hypoxia also show enhanced expression in normoxic ErbB2-overexpressing cells as compared to parental MCF-10A cells. Here, we suggest that HIF-1 stabilization by ErbB2 under normoxic conditions is novel mechanism through which oncogenes protect cells from anoikis and plan to further explore the mechanism through which HIF-1 augments anoikis resistance in ErbB2-overexpressing cells, possibly by regulating metabolic activity. In addition, we predict that genes whose expression is upregulated by both ErbB2 and HIF-1 may serve as potential new therapeutic targets in the treatment of both hypoxic and ErbB2-positive cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2062. doi:10.1158/1538-7445.AM2011-2062

Abstract 5196: Granulocyte-colony stimulating factor (G-CSF) plays a causative role for H-Ras-mediated invasion and migration of human breast epithelial cells

Abstract The whole human genome microarray on normal MCF10A, N-Ras-transformed, non-invasive MCF10A and H-Ras-transformed invasive MCF10A human breast epithelial cells revealed that the granulocyte-colony stimulating factor (G-CSF) was most highly upregulated in an H-Ras-specific manner. The present study investigated whether G-CSF plays a causative role for H-Ras-mediated MCF10A cell invasion and migration. Importantly, siRNA-mediated knockdown of G-CSF expression significantly reduced H-Ras-induced matrix metalloproteinase(MMP)-2 expression as well as invasion/migration. Activations of Rac1, MKK3/6 and p38 MAPK were inhibited by siRNA-knockdown of G-CSF. The induction of G-CSF expression conferred the invasive/migratory phenotype to parental MCF10A cells. Expression of MMP-2 and activation of signaling molecules Rac1, MKK3/6 and p38 MAPK were increased by G-CSF induction. Taken together, this study revealed G-CSF gene as a candidate marker for metastatic potential of breast epithelial cells. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5196.

Ethidium bromide as a vital probe of mitochondrial DNA in carcinoma cells

The interaction of ethidium bromide (EB) with mitochondria in human breast and lung carcinoma cells was investigated under living conditions, employing a laser scanning confocal fluorescence microscopy (LSCFM) with a photon counting detection to reduce drastically the laser power excitation and the fluorescent probe concentration. In sensitive and multidrug-resistant MCF-7 cell lines, which are important model systems for the study of mitochondria in tumour cells, two distinct populations of mitochondria were observed, each characterised by a different EB fluorescence, membrane potential, cellular localisation and morphology. By image analysis, these peripheral mitochondria showed a peculiar morphology, consisting of punctuate organelles (0.8 μm in size) organised in rosette-like assemblies. Unexpectedly, an intense EB fluorescence was observed in these mitochondria, indicating a high accessibility to EB of their mtDNA, which is likely to be in an active replicative or transcriptional state. These results might, therefore, suggest an active biogenesis and metabolism of the peripheral mitochondria that could be a consequence of the increased energetic needs of the cells, after their tumour transformation. Indeed, the pool of peripheral mitochondria, as well as their peculiar morphology and spatial organisation, was found to be a characteristic feature of all the carcinoma cells examined here, but not of their non-transformed parental MCF10A cells.

Phosphorylation of α6-Tubulin by Protein Kinase Cα Activates Motility of Human Breast Cells

Engineered overexpression of protein kinase Calpha (PKCalpha) was previously shown to endow nonmotile MCF-10A human breast cells with aggressive motility. A traceable mutant of PKCalpha (Abeyweera, T. P., and Rotenberg, S. A. (2007) Biochemistry 46, 2364-2370) revealed that alpha6-tubulin is phosphorylated in cells expressing traceable PKCalpha and in vitro by wild type PKCalpha. Gain-of-function, single site mutations (Ser-->Asp) were constructed at each PKC consensus site in alpha6-tubulin (Ser158, Ser165, Ser241, and Thr337) to simulate phosphorylation. Following expression of each construct in MCF-10A cells, motility assays identified Ser165 as the only site in alpha6-tubulin whose pseudophosphorylation reproduced the motile behavior engendered by PKCalpha. Expression of a phosphorylation-resistant mutant (S165N-alpha6-tubulin) resulted in suppression of MCF-10A cell motility stimulated either by expression of PKCalpha or by treatment with PKCalpha-selective activator diacylglycerol-lactone. MCF-10A cells treated with diacylglycerol-lactone showed strong phosphorylation of endogenous alpha-tubulin that could be blocked when S165N-alpha6-tubulin was expressed. The S165N mutant also inhibited intrinsically motile human breast tumor cells that express high endogenous PKCalpha levels (MDA-MB-231 cells) or lack PKCalpha and other conventional isoforms (MDA-MB-468 cells). Comparison of Myc-tagged wild type alpha6-tubulin and S165N-alpha6-tubulin expressed in MDA-MB-468 cells demonstrated that Ser165 is also a major site of phosphorylation for endogenously active, nonconventional PKC isoforms. PKC-stimulated motility of MCF-10A cells was nocodazole-sensitive, thereby implicating microtubule elongation in the mechanism. These findings support a model in which PKC phosphorylates alpha-tubulin at Ser165, leading to microtubule elongation and motility.

Expression of estrogenicity genes in a lineage cell culture model of human breast cancer progression

TaqMan Gene Expression assays were used to profile the mRNA expression of estrogen receptor (ERalpha and ERbeta) and estrogen metabolism enzymes including cytosolic sulfotransferases (SULT1E1, SULT1A1, SULT2A1, and SULT2B1), steroid sulfatase (STS), aromatase (CYP19), 17beta-hydroxysteroid dehydrogenases (17betaHSD1 and 2), CYP1B1, and catechol-O-methyltransferase (COMT) in an MCF10A-derived lineage cell culture model for basal-like human breast cancer progression and in ERalpha-positive luminal MCF7 breast cancer cells. Low levels of ERalpha and ERbeta mRNA were present in MCF10A-derived cell lines. SULT1E1 mRNA was more abundant in confluent relative to subconfluent MCF10A cells, a non-tumorigenic proliferative breast disease cell line. SULT1E1 was also expressed in preneoplastic MCF10AT1 and MCF10AT1K.cl2 cells, but was markedly repressed in neoplastic MCF10A-derived cell lines as well as in MCF7 cells. Steroid-metabolizing enzymes SULT1A1 and SULT2B1 were only expressed in MCF7 cells. STS and COMT were widely detected across cell lines. Pro-estrogenic 17betaHSD1 mRNA was most abundant in neoplastic MCF10CA1a and MCF10DCIS.com cells, while 17betaHSD2 mRNA was more prominent in parental MCF10A cells. CYP1B1 mRNA was most abundant in MCF7 cells. Treatment with the histone deacetylase inhibitor trichostatin A (TSA) induced SULT1E1 and CYP19 mRNA but suppressed CYP1B1, STS, COMT, 17betaHSD1, and 17betaHSD2 mRNA in MCF10A lineage cell lines. In MCF7 cells, TSA treatment suppressed ERalpha, CYP1B1, STS, COMT, SULT1A1, and SULT2B1 but induced ERbeta, CYP19 and SULT2A1 mRNA expression. The results indicate that relative to the MCF7 breast cancer cell line, key determinants of breast estrogen metabolism are differentially regulated in the MCF10A-derived lineage model for breast cancer progression.

Global Gene Expression Profiling Unveils S100A8/A9 as Candidate Markers in H-Ras-Mediated Human Breast Epithelial Cell Invasion

The goal of the present study is to unveil the gene expression profile specific to the biological processes of human breast epithelial cell invasion and migration using an MCF10A model genetically engineered to constitutively activate the H-ras or N-ras signaling pathway. We previously showed that H-Ras, but not N-Ras, induces MCF10A cell invasion/migration, whereas both H-Ras and N-Ras induce cell proliferation and phenotypic transformation. Thus, these cell lines provide an experimental system to separate the gene expression profile associated with cell invasion apart from cell proliferation/transformation. Analysis of whole human genome microarray revealed that 412 genes were differentially expressed among MCF10A, N-Ras MCF10A, and H-Ras MCF10A cells and hierarchical clustering separated 412 genes into four clusters. We then tested whether S100A8 and S100A9, two of the genes which are most highly up-regulated in an H-Ras-specific manner, play a causative role for H-Ras-mediated MCF10A cell invasion and migration. Importantly, small interfering RNA-mediated knockdown of S100A8/A9 expression significantly reduced H-Ras-induced invasion/migration. Conversely, the induction of S100A8/A9 expression conferred the invasive/migratory phenotype to parental MCF10A cells. Furthermore, we provided evidence of signaling cross-talk between S100A8/A9 and the mitogen-activated protein kinase signaling pathways essential for H-Ras-mediated cell invasion and migration. Taken together, this study revealed S100A8/A9 genes as candidate markers for metastatic potential of breast epithelial cells. Our gene profile data provide useful information which may lead to the identification of additional potential targets for the prognosis and/or therapy of metastatic breast cancer.

Suppression of autophagy enhances the cytotoxicity of the DNA-damaging aromatic amine p-anilinoaniline

p-Anilinoaniline ( pAA) is an aromatic amine that is widely used in hair dying applications. It is also a metabolite of metanil yellow, an azo dye that is commonly used as a food coloring agent. Concentrations of pAA between 10 and 25 μM were cytostatic to cultures of the normal human mammary epithelia cell line MCF10A. Concentrations ≥ 50 μM were cytotoxic. Cytostatic concentrations induced transient G 1 and S cell cycle phase arrests; whereas cytotoxic concentrations induced protracted arrests. Cytotoxic concentrations of pAA caused DNA damage, as monitored by the alkaline single-cell gel electrophoresis (Comet) assay, and morphological changes consistent with cells undergoing apoptosis and/or autophagy. Enzymatic and western blot analyses, and binding analyses of fluorescent labeled VAD-FMK, suggested that caspase family members were activated by pAA. Western blot analyses documented the conversion of LC3-I to LC3-II, a post-translational modification involved in the development of the autophagosome. Suppression of autophagosome formation, via knockdown of ATG7 with shRNA, prevented pAA-induced vacuolization, enhanced the activation of pro-caspase-3, and increased susceptibility of ATG7-deficient cells to the cytostatic and cytotoxic activities of markedly lower concentrations of pAA. Cells stably transfected with a nonsense shRNA behaved like parental MCF10A cells. Collectively, these data suggest that MCF10A cultures undergo autophagy as a pro-survival response to concentrations of pAA sufficient to induce DNA damage.

Cyclin‐dependent kinase inhibitors and basement membrane interact to regulate breast epithelial cell differentiation and acinar morphogenesis

The cyclin-dependent kinase inhibitors (CDKIs), p21(CIP1) and p27(KIP1) regulate growth and differentiation in diverse tissue types. We aimed to determine whether p21(CIP1) or p27(KIP1) could induce a terminally differentiated phenotype in breast cells, and to examine if CDKI expression is regulated by basement membrane interactions. Effects of increased CDKI expression on the phenotype of MCF-10A breast epithelial cells were examined by retroviral transduction of p21(CIP1) or p27(KIP1) cDNA. Overexpression of p21(CIP1) or p27(KIP1) reduced MCF-10A growth rates in monolayer cultures, altered cellular morphology and stimulated accumulation of neutral lipid droplets, suggesting partial lactational differentiation. However, markers of luminal differentiation (oestrogen and progesterone receptors, alpha-lactalbumin, beta-casein and adipophilin) were absent when examined by reverse transcriptase-polymerase chain reaction and immunohistochemistry. Cell-basement membrane contacts are known to be essential for full mammary epithelial cell differentiation and therefore parental MCF-10A cells were cultured on a basement membrane preparation (Matrigel) in which they form acini. Immunocytochemistry showed that Ki67, the cell proliferation marker, was initially expressed at high levels and as growth decreased p27(KIP1) expression steadily increased. Surprisingly, p21(CIP1) was highest at the early stages of acinus growth and was detected in proliferating cells, as demonstrated by colocalization in dual Ki67/p21(CIP1) immunofluorescence. Overexpression of p21(CIP1) or p27(KIP1) impaired formation of acini, whereas their knockdown, using siRNA, increased acinus formation. We conclude that both p21(CIP1) and p27(KIP1) induce partial secretory differentiation of mammary cells in monolayer, but during acinus morphogenesis in 3D culture they have a highly regulated temporal expression pattern.