Phenotypic changes in MCF-7 cells during prolonged exposure to tamoxifen

Caspase-1-dependent spatiality in triple-negative breast cancer and response to immunotherapy

Tumor immune microenvironment (TIME) spatial organization predicts outcome and therapy response in triple-negative breast cancer (TNBC). An immunosuppressive TIME containing elevated tumor-associated macrophages (TAM) and scarce CD8+ T cells is associated with poor outcome, but the regulatory mechanisms are poorly understood. Here we show that ETS1-driven caspase-1 expression, required for IL1β processing and TAM recruitment, is negatively regulated by estrogen receptors alpha (ERα) and a defining feature of TNBC. Elevated tumoral caspase-1 is associated with a distinct TIME characterized by increased pro-tumoral TAMs and CD8+ T cell exclusion from tumor nests. Mouse models prove the functional importance of ERα, ETS1, caspase-1 and IL1β in TIME conformation. Caspase-1 inhibition induces an immunoreactive TIME and reverses resistance to immune checkpoint blockade, identifying a therapeutically targetable mechanism that governs TNBC spatial organization.

Regulation of early growth response 2 expression by secreted frizzled related protein 1

BACKGROUND

Secreted frizzled-related protein 1 (SFRP1) expression is down-regulated in a multitude of cancers, including breast cancer. Loss of Sfrp1 also exacerbates weight gain as well as inflammation. Additionally, loss of SFRP1 enhances TGF-β signaling and the downstream MAPK pathway. TGF-β has been shown to increase the expression of Early Growth Response 2 (EGR2), a transcription factor implicated in immune function in a wide variety of cell types. The work described here was initiated to determine whether SFRP1 modulation affects TGF-β mediated EGR2 expression in mammary tissues as well as macrophage polarization.

METHODS

Real-time PCR analysis was performed to examine EGR2 expression in human and murine mammary epithelial cells and tissues in response to SFRP1 modulation. Chemical inhibition was employed to investigate the roles TGF-β and MAPK signaling play in the control of EGR2 expression in response to SFRP1 loss. Primary murine macrophages were isolated from Sfrp1^-/- mice and stimulated to become either M1 or M2 macrophages, treated with recombinant SFRP1, and real-time PCR was used to measure the expression of murine specific M1/M2 markers [Egr2 (M2) and Gpr18 (M1)]. Immunohistochemical analysis was used to measure the expression of human specific M1/M2 markers [CD163 (M2) and HLA-DRA (M2)] in response to rSFRP1 treatment in human mammary explant tissue.

RESULTS

Knockdown of SFRP1 expression increases the expression of EGR2 mRNA in human mammary epithelial cells and addition of rSFRP1 decreases the expression of EGR2 when added to explant mammary gland tissues. Chemical inhibition of both TGF-β and MAPK signaling in Sfrp1^-/- or knockdown mammary epithelial cells results in decreased expression of EGR2. Stimulated murine macrophages obtained from Sfrp1^-/- mice and treated with rSFRP1 exhibit a reduction in Egr2 expression and an increase in Gpr18 mRNA expression. Human mammary explant tissue treated with rSFRP1 decreases CD163 protein expression whereas there was no effect on the expression of HLA-DRA.

CONCLUSIONS

Loss of SFRP1 likely contributes to tumor progression by altering the expression of a critical transcription factor in both the epithelium and the immune system.

Selective Adhesive Cell Capture without Molecular Specificity: New Surfaces Exploiting Nanoscopic Polycationic Features as Discrete Adhesive Units

This work explored how molecularly non-specific polycationic nanoscale features on a collecting surface control kinetic and selectivity aspects of mammalian cell capture. Key principles for selective collector design were demonstrated by comparing the capture of two closely related breast cancer cell lines: MCF-7 and TMX2-28. TMX2-28 is a tamoxifen-selected clone of MCF-7. The collector was a silica surface, negatively-charged at pH 7.4, containing isolated molecules (~ 8 nm diameter) of the cationic polymer, poly(dimethyl-aminoethylmethacrylate), pDMAEMA. Important in this work is the non-selective nature of the pDMAEMA interactions with cells: pDMAEMA generally adheres negatively charged particles and cells in solution. We show here that selectivity towards cells results from collector design: this includes competition between repulsive interactions involving the negative silica and attractions to the immobilized pDMAEMA molecules, the random pDMAEMA arrangement on the surface, and the concentration of positive charge in the vicinity of the adsorbed pDMAEMA chains. The latter act as nanoscopic cationic surface patches, each weakly attracted to negatively-charged cells. Collecting surfaces engineered with an appropriate amount pDMAEMA, exposed to mixtures of MCF-7 and TMX2-28 cells preferentially captured TMX2-28 with a selectivity of 2.5. (This means that the ratio of TMX2-28 to MCF cells on the surface was 2.5 times their compositional ratio in free solution.) The ionic strength-dependence of cell capture was shown to be similar to that of silica microparticles on the same surfaces. This suggests that the mechanism of selective cell capture involves nanoscopic differences in the contact areas of the cells with the collector, allowing discrimination of closely related cell line-based small scale features of the cell surface. This work demonstrated that even without molecular specificity, selectivity for physical cell attributes produces adhesive discrimination.

Guanylate-Binding Protein-1 protects ovarian cancer cell lines but not breast cancer cell lines from killing by paclitaxel

Forced expression of the cytokine-induced large GTPase, human Guanylate-Binding Protein-1 (hGBP-1), in ovarian cancer cell lines increases resistance to paclitaxel. Elevated hGBP-1 RNA in ovarian tumors correlates with shorter recurrence-free survival. In contract, hGBP-1 is part of a gene signature predicting improved prognosis in all subtypes of breast cancers. hGBP-1 does not confer paclitaxel resistance on MCF-7 and TMX2-28 breast cancer cells. Expression of the isotype of the hGBP-1-interacting protein, PIM1, which may contribute to paclitaxel resistance when associated with hGBP-1, is different in breast and ovarian cancer cell lines. Breast cancer cell lines express the 44 kDa isoform of PIM-1, and ovarian cancer cell lines express the 33 kDa isoform.

Prolactin-induced PAK1 tyrosyl phosphorylation promotes FAK dephosphorylation, breast cancer cell motility, invasion and metastasis

BACKGROUND

The serine/threonine kinase PAK1 is an important regulator of cell motility. Both PAK1 and the hormone/cytokine prolactin (PRL) have been implicated in breast cancer cell motility, however, the exact mechanisms guiding PRL/PAK1 signaling in breast cancer cells have not been fully elucidated. Our lab has previously demonstrated that PRL-activated tyrosine kinase JAK2 phosphorylates PAK1 on tyrosines 153, 201, and 285, and that tyrosyl phosphorylated PAK1 (pTyr-PAK1) augments migration and invasion of breast cancer cells.

RESULTS

Here we further investigate the mechanisms by which pTyr-PAK1 enhances breast cancer cell motility in response to PRL. We demonstrate a distinct reduction in PRL-induced FAK auto-phosphorylation in T47D and TMX2-28 breast cancer cells overexpressing wild-type PAK1 (PAK1 WT) when compared to cells overexpressing either GFP or phospho-tyrosine-deficient mutant PAK1 (PAK1 Y3F). Furthermore, pTyr-PAK1 phosphorylates MEK1 on Ser298 resulting in subsequent ERK1/2 activation. PRL-induced FAK auto-phosphorylation is rescued in PAK1 WT cells by inhibiting tyrosine phosphatases and tyrosine phosphatase inhibition abrogates cell motility and invasion in response to PRL. siRNA-mediated knockdown of the tyrosine phosphatase PTP-PEST rescues FAK auto-phosphorylation in PAK1 WT cells and reduces both cell motility and invasion. Finally, we provide evidence that PRL-induced pTyr-PAK1 stimulates tumor cell metastasis in vivo.

CONCLUSION

These data provide insight into the mechanisms guiding PRL-mediated breast cancer cell motility and invasion and highlight a significant role for pTyr-PAK1 in breast cancer metastasis.

Synergistic Activation of ERα by Estrogen and Prolactin in Breast Cancer Cells Requires Tyrosyl Phosphorylation of PAK1

Serine/threonine kinase PAK1 is activated by estrogen and plays an important role in breast cancer. However, the integration of PAK1 into the estrogen response is not fully understood. In this study, we investigated the mechanisms underlying the hormone-induced activation of estrogen receptor (ERα, ESR1). We show that estrogen activated PAK1 through both the ERα and GPER1 membrane receptors. Estrogen-dependent activation of PAK1 required the phosphorylation of tyrosine residues by Etk/Bmx and protein kinase A (PKA) within an assembled signaling complex comprising pTyr-PAK1, Etk/Bmx, the heterotrimer G-protein subunits Gβ1, Gγ2, and/or Gγ5, PAK-associated guanine nucleotide exchange factor (βPIX, ARHGEF7), and PKA. Moreover, the PKA RIIβ subunit is a direct target of PAK1, and thus in response to estrogen, the activated pTyr-PAK1 complex reciprocally potentiated PKA activity, suggesting a positive feedback mechanism. We also demonstrate that PKA phosphorylated Ser305-ERα in response to estrogen, but pTyr-PAK1 phosphorylated Ser305-ERα in response to prolactin (PRL), implying that maximal ERα phosphorylation is achieved when cells are exposed to both PRL and estrogen. Furthermore, S305-ERα activation led to enhanced phosphorylation of Ser118-ERα and promoted cell proliferation and tumor growth. Together, these data strongly support a critical interplay between PRL and estrogen via PAK1 and suggest that ligand-independent activation of ERα through PRL/PAK1 may impart resistance to anti-estrogen therapies. Cancer Res; 76(9); 2600-11. ©2016 AACR.

ELF5 and DOK7 regulation in anti-estrogen treated cells and tumors

BACKGROUND

Most women with primary breast cancers that express estrogen receptor alpha (ER or ESR1) are treated with endocrine therapies including the anti-estrogen tamoxifen, but resistance to these anti-endocrine therapies often develops. This study characterizes the expression of hormone receptors, and the mRNA and DNA methylation levels of docking protein 7 (DOK7), and E74-like factor 5 (ELF5), in 21 novel tamoxifen-resistant cell lines and extends the findings to primary and recurrent human breast tumors.

METHODS

Twenty-one tamoxifen-selected cell lines were developed through cloning by limiting dilution of an MCF-7 cell culture treated with 1 μM tamoxifen for 6 months. The parent (MCF-7) and tamoxifen-selected cell lines were characterized for protein expression of ER, progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) using immunohistochemistry (IHC). The mRNA levels of ER, DOK7, and ELF5 were assessed using quantitative RT-PCR. Promoter methylation levels of DOK7 and ELF5 were determined by pyrosequencing of bisulfite-modified DNA. The relationship between hormone receptor status and promoter methylation of DOK7 and ELF5 was further examined using available methylation array data (Illumina HM450) from a set of paired primary and second breast tumors from 24 women.

RESULTS

All 21 of the novel tamoxifen-selected cell lines are ER-positive, and HER2-negative, and 18 of the cell lines are PR-negative while the MCF-7 cells were scored as ER-positive, modestly PR-positive and HER2 negative. Expression of DOK7 and ELF5 is significantly up-regulated in half of the tamoxifen-selected cell lines as compared to the parental MCF-7. In contrast, the previously established ER-negative TMX2-28 cell line has decreased expression of both DOK7 and ELF5 and increased DNA methylation in the transcriptional start site region of these genes. ELF5 methylation was lower in second versus primary tumors in women who received anti-estrogen treatment, in PR-negative versus PR-positive tumors, and in the subset of PR-positive first tumors from the group of women who had second PR-negative tumors as compared to those who had second PR-positive tumors.

CONCLUSIONS

The distinct ELF5 methylation of PR-positive primary tumors from women who had a PR-negative recurrence indicates the possibility of stratification of women for tailored treatment in the early stages of disease.

Src tyrosyl phosphorylates cortactin in response to prolactin

The hormone/cytokine prolactin (PRL) is implicated in breast cancer cell invasion and metastasis. PRL-induced pathways are mediated by two non-receptor tyrosine kinases, JAK2 and Src. We previously demonstrated that prolactin stimulates invasion of breast cancer cells TMX2-28 through JAK2 and its target serine/threonine kinase PAK1. We hypothesize herein that the actin-binding protein cortactin, a protein involved in invadopodia formation and cell invasion, is activated by PRL. We demonstrate that TMX2-28 cells are more invasive than T47D breast cancer cells in response to PRL. We determine that cortactin is tyrosyl phosphorylated in response to PRL in a time and dose-dependent manner in TMX2-28 cells, but not in T47D cells. Furthermore, we show that PRL mediates cortactin tyrosyl phosphorylation via Src, but not JAK2. Finally, we demonstrate that maximal PRL-mediated TMX2-28 cell invasion requires both Src and JAK2 kinase activity, while T47D cell invasion is JAK2- but not Src-dependent. Thus PRL may induce cell invasion via two pathways: through a JAK2/PAK1 mediated pathway that we have previously demonstrated, and Src-dependent activation and tyrosyl phosphorylation of cortactin.

The RhoA pathway mediates MMP-2 and MMP-9-independent invasive behavior in a triple-negative breast cancer cell line

Breast cancer is a heterogeneous disease that varies in its biology and response to therapy. A foremost threat to patients is tumor invasion and metastasis, with the greatest risk among patients diagnosed with triple-negative and/or basal-like breast cancers. A greater understanding of the molecular mechanisms underlying cancer cell spreading is needed as 90% of cancer-associated deaths result from metastasis. We previously demonstrated that the Tamoxifen-selected, MCF-7 derivative, TMX2-28, lacks expression of estrogen receptor α (ERα) and is highly invasive, yet maintains an epithelial morphology. The present study was designed to further characterize TMX2-28 cells and elucidate their invasion mechanism. We found that TMX2-28 cells do not express human epidermal growth factor receptor 2 (HER2) and progesterone receptor (PR), in addition to lacking ERα, making the cells triple-negative. We then determined that TMX2-28 cells lack expression of active matrix metalloproteinases (MMPs)-1, MMP-2, MMP-9, and other genes involved in epithelial-mesenchymal transition (EMT) suggesting that TMX2-28 may not utilize mesenchymal invasion. In contrast, TMX2-28 cells have high expression of Ras Homolog Gene Family Member, A (RhoA), a protein known to play a critical role in amoeboid invasion. Blocking RhoA activity with the RhoA pathway specific inhibitor H-1152, or a RhoA specific siRNA, resulted in inhibition of invasive behavior. Collectively, these results suggest that TMX2-28 breast cancer cells exploit a RhoA-dependent, proteolytic-independent invasion mechanism. Targeting the RhoA pathway in triple-negative, basal-like breast cancers that have a proteolytic-independent invasion mechanism may provide therapeutic strategies for the treatment of patients with increased risk of metastasis.

High-density array analysis of DNA methylation in Tamoxifen-resistant breast cancer cell lines

Roughly two-thirds of all breast cancers are ERα-positive and can be treated with the antiestrogen, Tamoxifen, however resistance occurs in 33% of women who take the drug for more than 5 y. Aberrant DNA methylation, an epigenetic mechanism that alters gene expression in cancer, is thought to play a role in this resistance. To develop an understanding of Tamoxifen-resistance and identify novel pathways and targets of aberrant methylation, DNA from MCF-7 breast cancer cells and Tamoxifen-resistant derivatives, TMX2-11 and TMX2-28, were analyzed using the Illumina HumanMethylation450 BeadChip. Normalizing against MCF-7 values, ERα-positive TMX2-11 had 4000 hypermethylated sites and ERα-negative TMX2-28 had over 33 000. Analysis of CpG sites altered in both TMX2-11 and TMX2-28 revealed that the Tamoxifen-resistant cell lines share 3000 hypermethylated and 200 hypomethylated CpGs. ZNF350 and MAGED1, two genes hypermethylated in both cell lines, were examined in greater detail. Treatment with 5-aza-2ꞌdeoxycitidine caused a significant reduction in promoter methylation of both ZNF350 and MAGED1 and a corresponding increase in expression in TMX2-28. A similar relationship between methylation and expression was not detected in TMX2-11. Our findings are indicative of the variable responses to methylation-targeted breast cancer therapy and highlight the need for biomarkers that accurately predict treatment outcome.

PAK1 regulates breast cancer cell invasion through secretion of matrix metalloproteinases in response to prolactin and three-dimensional collagen IV

p21-Activated serine-threonine kinase (PAK1) is implicated in breast cancer. We have shown previously that PAK1 is tyrosyl phosphorylated by prolactin (PRL)-activated Janus tyrosine kinase (JAK2). Although a role for both PRL and PAK1 in breast cancer is widely acknowledged, the mechanism remains poorly understood. In the present study, PRL-activated PAK1 stimulates the invasion of TMX2-28 human breast cancer cells through Matrigel. Three-dimensional (3D) collagen IV stimulates the secretion of the matrix proteases, metalloproteinase (MMP)-1 and -3 that is further enhanced by the PRL-dependent tyrosyl phosphorylation of PAK1. 3D collagen IV also stimulates the expression and secretion of MMP-2, but in contrast to MMP-1 and -3, PRL/PAK1 signaling down-regulates MMP-2 expression and secretion. In contrast, MMP-9 expression and secretion are stimulated by 3D collagen I, not collagen IV, and are not affected by PRL but are down-regulated by PAK1. MMP-1 and -3 are required and MMP-2 contributes to PRL-dependent invasion. ERK1/2 signaling appears to be required for the enhanced expression and secretion of MMP-1 and -3 and enhanced PRL-dependent invasion. p38 MAPK and c-Jun N-terminal kinase 1/2 pathways participate in production of MMP-1 and -3 as well as in PRL/PAK1-dependent cell invasion. Together, these data illustrate the complex interaction between the substratum and PRL/PAK1 signaling in human breast cancer cells and suggest a pivotal role for PRL-dependent PAK1 tyrosyl phosphorylation in MMP secretion.

Genome-wide reprogramming of the chromatin landscape underlies endocrine therapy resistance in breast cancer

The estrogen receptor (ER)α drives growth in two-thirds of all breast cancers. Several targeted therapies, collectively termed endocrine therapy, impinge on estrogen-induced ERα activation to block tumor growth. However, half of ERα-positive breast cancers are tolerant or acquire resistance to endocrine therapy. We demonstrate that genome-wide reprogramming of the chromatin landscape, defined by epigenomic maps for regulatory elements or transcriptional activation and chromatin openness, underlies resistance to endocrine therapy. This annotation reveals endocrine therapy-response specific regulatory networks where NOTCH pathway is overactivated in resistant breast cancer cells, whereas classical ERα signaling is epigenetically disengaged. Blocking NOTCH signaling abrogates growth of resistant breast cancer cells. Its activation state in primary breast tumors is a prognostic factor of resistance in endocrine treated patients. Overall, our work demonstrates that chromatin landscape reprogramming underlies changes in regulatory networks driving endocrine therapy resistance in breast cancer.

Expression of a dominant negative estrogen receptor alpha variant in transgenic mice accelerates uterine cancer induced by the potent estrogen diethylstilbestrol

ERΔ3 transgenic mice expressing a dominant negative estrogen receptor α (ERα) variant lacking the second zinc finger in the DNA binding domain were developed to examine its potential to inhibit estrogen action in vivo. To investigate if ERΔ3 expression influences uterine carcinogenesis, ERΔ3 transgenic mice were exposed to diethylstilbestrol (DES) on post-natal days 1-5. Neonatal DES treatment induced uterine adenocarcinomas in 81% of 8-month-old ERΔ3 mice compared to 49% of wild-type females (p<0.016). ERΔ3 did not inhibit the expression of the estrogen-responsive progesterone receptor and lactoferrin genes in the presence of ERα or modify their expression in ERα knockout (αERKO) mice. Higher circulating 17β-estradiol levels and non-classical signaling by ERΔ3 may be related to the earlier incidence of uterine cancer. These findings indicate that expression of this ERα variant can influence determining events in uterine cancer development and its natural occurrence in the human uterus would unlikely be protective.

Inhibition of Neu-induced mammary carcinogenesis in transgenic mice expressing ERΔ3, a dominant negative estrogen receptor α variant

The estrogen receptor α (ERα) splicing variant with an in-frame deletion of exon 3 (ERΔ3) is frequently expressed in the normal breast, but its influence on tumorigenesis has not been explored. In vitro, ERΔ3 has dominant negative activity, suggesting it may suppress estrogen stimulation in the breast. ERΔ3 may inhibit classical signaling on estrogen response element (ERE)-regulated genes as well as activate non-classical pathways at Sp1 and AP-1 sites. Transgenic mice were developed that express mouse ERΔ3 in all tissues examined, including the mammary gland. To investigate if ERΔ3 expression affects tumorigenesis, ERΔ3 mice were crossbred with MMTV-Neu mice. Mammary tumor onset was significantly delayed in ERΔ3/Neu versus MMTV-Neu females and metastatic incidence and burden was significantly reduced. Consequently, ERΔ3 expression suppressed tumor development and metastasis in this aggressive model of HER2/Neu-positive breast cancer. To determine if ER ligands with anticancer activity may augment ERΔ3 protection, the bitransgenic mice were treated with tamoxifen and soy isoflavones starting at age 2 months. Soy protein with isoflavones (181 mg/1,800 kcal) did not affect tumor development in MMTV-Neu or ERΔ3/Neu mice; however, metastatic progression was not inhibited in soy-treated ERΔ3/Neu mice, as it was in untreated ERΔ3/Neu mice. In contrast, tamoxifen (20 mg/1,800 kcal) significantly enhanced tumor prevention in ERΔ3/Neu versus MMTV-Neu mice (98% vs. 81% tumor free). The results in ERΔ3/Neu mice demonstrate that ERΔ3 influences estrogen-dependent mammary carcinogenesis and, thus, may be protective in women expressing ERΔ3 in the breast. However, exposure to different estrogens may augment or block its beneficial effects.

Expression of the aryl hydrocarbon receptor is not required for the proliferation, migration, invasion, or estrogen-dependent tumorigenesis of MCF-7 breast cancer cells

The AhR was initially identified as a ligand-activated transcription factor mediating effects of chlorinated dioxins and polycyclic aromatic hydrocarbons on cytochrome P450 1 (CYP1) expression. Recently, evidence supporting involvement of the AhR in cell-cycle regulation and tumorigenesis has been presented. To further define the roles of the AhR in cancer, we investigated the effects of AhR expression on cell proliferation, migration, invasion, and tumorigenesis of MCF-7 human breast cancer cells. In these studies, the properties of MCF-7 cells were compared with those of two MCF-7-derived sublines: AH(R100) , which express minimal AhR, and AhR(exp) , which overexpress AhR. Quantitative PCR, Western immunoblots, 17β-estradiol (E2 ) metabolism assays, and ethoxyresorufin O-deethylase assays showed the lack of AhR expression and AhR-regulated CYP1 expression in AH(R100) cells, and enhanced AhR and CYP1 expression in AhR(exp) cells. In the presence of 1 nM E2 , rates of cell proliferation of the three cell lines showed an inverse correlation with the levels of AhR mRNA. In comparison with MCF-7 and AhR(exp) cells, AH(R100) cells produced more colonies in soft agar and showed enhanced migration and invasion in chamber assays with E2 as the chemoattractant. Despite the lack of significant AhR expression, AH(R100) cells retained the ability to form tumors in severe combined immunodeficient mice when supplemented with E2 , producing mean tumor volumes comparable to those observed with MCF-7 cells. These studies indicate that, while CYP1 expression and inducibility are highly dependent on AhR expression, the proliferation, invasion, migration, anchorage-independent growth, and estrogen-stimulated tumor formation of MCF-7 cells do not require the AhR.

Expression of aromatase and estrogen receptor alpha in chondrosarcoma, but no beneficial effect of inhibiting estrogen signaling both in vitro and in vivo

Background

Chondrosarcomas are malignant cartilage-forming tumors which are highly resistant to conventional chemotherapy and radiotherapy. Estrogen signaling is known to play an important role in proliferation and differentiation of chondrocytes and in growth plate regulation at puberty. Our experiments focus on unraveling the role of estrogen signaling in the regulation of neoplastic cartilage growth and on interference with estrogen signaling in chondrosarcomas in vitro and in vivo.

Methods

We investigated the protein expression of estrogen receptor alpha (ESR1), androgen receptor (AR), and aromatase in tumor specimens of various chondrosarcoma subtypes, and (primary) chondrosarcoma cultures. Dose-response curves were generated of conventional central chondrosarcoma cell lines cultured in the presence of 17β-estradiol, dihydrotestosterone, 4-androstene-3,17 dione, 4-hydroxytamoxifen, fulvestrant and aromatase inhibitors. In a pilot series, the effect of anastrozole (n = 4) or exemestane (n = 2) treatment in 6 chondrosarcoma patients with progressive disease was explored.

Results

We showed protein expression of ESR1 and aromatase in a large majority of all subtypes. Only a minority of the tumors showed few AR positive cells. The dose-response assays showed no effect of any of the compounds on proliferation of conventional chondrosarcoma in vitro. The median progression-free survival of the patients treated with aromatase inhibitors did not significantly deviate from untreated patients.

Conclusions

The presence of ESR1 and aromatase in chondrosarcoma tumors and primary cultures supports a possible role of estrogen signaling in chondrosarcoma proliferation. However, our in vitro and pilot in vivo studies have shown no effect of estrogen-signaling inhibition on tumor growth.

Role of the insulin-like growth factor system on an estrogen-dependent cancer phenotype in the MCF-7 human breast cancer cell line

We previously established that exposure of the estrogen receptor (ER) alpha positive MCF-7 human breast cancer cell line to 17-beta-estradiol (E2) results in the post-confluent development of multilayered cellular aggregates (foci) which is consistent with the in vivo cancer phenotype of uncontrolled cellular proliferation. In this investigation, the interaction between the insulin-like growth factor receptor (IGF-IR) and ER-signaling systems in regard to post-confluent focus development was studied. We demonstrated that focus development requires the presence of E2 and insulin-like growth factor I (IGF-I) or insulin-like growth factor II (IGF-II), as well as intact ER and IGF-IR. Focus development in MCF-7 cultures, which occurs only after formation of a confluent monolayer, coincides with E2 regulation of key members of the IGF-signaling system such as IGF-IR, IGF-II, insulin receptor substrate 1 (IRS-1), and insulin-like growth factor binding protein 3 (IGFBP-3), as demonstrated by real-time polymerase chain reaction (PCR). To establish the relevancy of an intact IGF-signaling system for foci formation, we generated stable clones from MCF-7 with IGF-IR suppressed by siRNA. Results from these studies implicate signaling through the IGF-IR to be an integral requirement for E2-dependent post-confluent proliferation and focus formation. In summary, these studies establish the interactive roles of IGFs and E2 in the post-confluent development of foci, and will allow subsequent identification of targets for therapeutic intervention in the control and treatment of estrogen-dependent breast cancer.

PLD1 is overexpressed in an ER-negative MCF-7 cell line variant and a subset of phospho-Akt-negative breast carcinomas

We have used a novel variant of the human oestrogen receptor (ER)-positive MCF-7 cell line, TMX2-28, as a model to study breast cancer. TMX2-28 cells show no detectable levels of mRNA or protein expression for the ER and express basal cytokeratins (CKs) 5, 14, and 17. cDNA microarray comparison between TMX2-28 and its parent cell line, MCF-7, identified 1402 differentially expressed transcripts, one of which was, phospholipase D1 (PLD1). Using real-time RT–PCR, we confirmed that PLD1 mRNA levels are 10-fold higher in TMX2-28 cells than in MCF-7 cells. We next examined PLD1 expression in human breast carcinomas. Phospholipase D1 mRNA levels were higher in breast tumours that expressed high-mRNA levels of basal CKs 5 and/or 17, but PLD1 mRNA levels were not significantly higher in ER-negative tumours. Phospholipase D1 protein was overexpressed in 10 of 42 (24%) breast tumours examined by IHC. Phospholipase D1 was overexpressed in 6 of 31 ER-positive tumours and 4 of 11 ER-negative tumours. Phospholipase D1 was overexpressed in three of the four tumours that showed high CK5/17 expression. Five PLD1-positive tumours were negative for phospho-Akt expression, but positive for phospho-mammalian target of rapamycin (mTOR) expression. The other five PLD1-positive breast tumours showed positive expression for phospho-Akt; however, only two of these cases were positive for phospho-mTOR. In this study, we report that PLD1 and phospho-mTOR are coexpressed in a subset of phospho-Akt-negative breast carcinomas.

Use of an aggressive MCF-7 cell line variant, TMX2-28, to study cell invasion in breast cancer

An estrogen receptor-negative variant of the MCF-7 breast cancer cell line, TMX2-28, was used as a model in which to study breast cancer cell invasion. Using a reconstituted basement membrane (Matrigel) assay to evaluate cell invasion, we determined that TMX2-28 cells are more invasive than MCF-7 cells and that the invasiveness of TMX2-28 is similar to that of the aggressive MDA-MB-231 breast cancer cell line. TMX2-28 cells displayed a rounded, epithelial cell-like morphology, suggesting an amoeboid mode of cell invasion, in contrast to the mesenchymal mode of invasion characteristic of spindle-shaped, fibroblast-like MDA-MB-231 cells. Using real-time reverse transcription-PCR, we found that mitogen-inducible gene 2 (MIG2) is expressed at a 17-fold higher level in TMX2-28 cells than in nonaggressive MCF-7 cells and that MIG2 mRNA levels are low in the nontumorigenic human mammary epithelial cell line, 184. We determined that MIG2 plays a role in cell invasion by using small interfering RNA (siRNA) to suppress the expression of MIG2 mRNA levels in TMX2-28 cells. TMX2-28 cell invasion was reduced by 48% when the cells were transfected with siRNAs targeting MIG2, relative to cells transfected with siRNAs against glyceraldehyde-3-phosphate dehydrogenase. Finally, MIG2 expression was evaluated in reductive mammoplasty and breast tumor tissue. Although all 21 normal tissues from reduction mammoplasty showed immunoreactivity for MIG2, ranging from weak (62%) to strong (24%), only half of the 34 formalin-fixed breast tumors showed immunoreactivity for MIG2. Of these 17 positive cases, 10 were considered to overexpress MIG2 (moderate to strong staining). Examination of 30 frozen breast tumors supported the finding that MIG2 is overexpressed in a subset of breast cancers. We suggest that MIG2's normal regulation and function are disrupted in breast cancer.

Decreased chicken ovalbumin upstream promoter transcription factor II expression in tamoxifen-resistant breast cancer cells

Tamoxifen (TAM) is successfully used for the treatment and prevention of breast cancer. However, many patients that are initially TAM responsive develop tumors that are antiestrogen/TAM resistant (TAM-R). The mechanism behind TAM resistance in estrogen receptor alpha (ERalpha)-positive tumors is not understood. The orphan nuclear receptor chicken ovalbumin upstream promoter transcription factor (COUP-TF)-I interacts directly with 4-hydroxytamoxifen (4-OHT)- and estradiol (E(2))-occupied ERalpha, corepressors NCoR and SMRT, and inhibit E(2)-induced gene transcription in breast cancer cells. Here we tested the hypothesis that reduced COUP-TFI and COUP-TFII correlate with TAM resistance. We report for the first time that COUP-TFII, but not COUP-TFI, is reduced in three antiestrogen/TAM-R cell lines derived from TAM-sensitive (TAM-S) MCF-7 human breast cancer cells and in MDA-MB-231 cells compared with MCF-7. ERalpha and ERbeta protein expression was not different between TAM-S and TAM-R cells, but progesterone receptor (PR) was decreased in TAM-R cells. Further, E(2) increased COUP-TFII transcription in MCF-7, but not TAM-R, cells. Importantly, reexpression of COUP-TFII in TAM-S cells to levels comparable to those in MCF-7 was shown to increase 4-OHT-mediated growth inhibition and increased apoptosis. Conversely, knockdown of COUP-TFII in TAM-S MCF-7 cells blocked growth inhibitory activity and increased 4-OHT agonist activity. 4-OHT increased COUP-TFII-ERalpha interaction approximately 2-fold in MCF-7 cells. COUP-TFII expression in TAM-R cells also inhibited 4-OHT-induced endogenous PR and pS2 mRNA expression. These data indicate that reduced COUP-TFII expression correlates with acquired TAM resistance in human breast cancer cell lines and that COUP-TFII plays a role in regulating the growth inhibitory activity of TAM in breast cancer cells.

Differential action of polycyclic aromatic hydrocarbons on endogenous estrogen-responsive genes and on a transfected estrogen-responsive reporter in MCF-7 cells

Polycyclic aromatic hydrocarbons (PAHs) are common environmental pollutants that have been extensively studied for multiple toxicological endpoints in both laboratory animals and humans. The purpose of this study was to investigate the estrogenicity of PAHs in the human breast cancer cell line MCF-7. We investigated 14 PAHs for their ability to bind either the estrogen receptor (ER) or the aryl hydrocarbon receptor (AhR) and to activate target gene expression. PAHs were tested in a human recombinant estrogen receptor (hrER) competitive binding assay, and in both an estrogen response element (ERE)- and xenobiotic response element (XRE)-mediated reporter gene assay. We used quantitative RT-PCR to examine selected PAHs that showed activity in the ERE reporter gene assay for their ability to upregulate estrogen-responsive genes HEM45, progesterone receptor, and pS2, and the aryl hydrocarbon-responsive CYP1A1 gene. None of the 14 PAHs bound the hrER, but five of the PAHs (anthracene, B[a]A, chrysene, B[b]F, and B[a]P) induced ER-reporter activity. This activity was dependent on the metabolism of PAHs in MCF-7 cells via the AhR pathway, which resulted in the formation of metabolites that bound the ER. None of the five PAHs that induced the ER-reporter were found to upregulate estrogen-responsive genes, yet four of the five PAHs induced AhR-dependent CYP1A1 gene expression. In contrast, a metabolite of B[a]P, 3'OH-B[a]P, and a PCB metabolite, 4'OH-2,4,6-BP, did weakly upregulate all three estrogen-responsive genes. Data from these studies indicate that induction of ER-reporter activity alone does not necessarily parallel endogenous gene transcription, and that the reporter gene assay may detect interactions that are not functional in vivo.