Role of PTEN promoter methylation in tamoxifen-resistant breast cancer cells

The preferential metastasis of breast cancer cells to bone is a complex set of events including homing and preferential growth which may include unique factors produced by bone cells in the immediate microenvironment. In this study, we evaluated the suitability of bone cells derived from orthoplastic surgeries for use in an in vitro co-culture system representing a model of the bone microenvironment. Using a limiting dilution assay we determined the relative survival and proliferation potentials of breast cancer cell lines co-cultured on bone-derived cells or on Hs68 fibroblasts. The comparison of bone and skin fibroblastic substrata indicates that MCF-7 cells preferentially survive and grow in a bone microenvironment (P < 0.001). Overall, we show that bone-derived cells enhance survival, proliferation, and migration of breast cancer cells, where migration is in part mediated by bone cell-produced osteopontin. Our in vitro co-culture model system provides a robust cost-effective method to study the various factors that mediate cancer/bone-derived cell interactions.     

Heregulin β1 drives gefitinib-resistant growth and invasion in tamoxifen-resistant MCF-7 breast cancer cells

Introduction  

Resistance to anti-epidermal growth factor receptor (anti-EGFR) therapies is an emerging clinical problem. The efficacy of anti-EGFR therapies can be influenced by the presence of heregulins (HRGs), which can bind erbB3/4 receptors and can activate alternative signalling pathways. In the present study we have examined whether HRG signalling can circumvent EGFR blockade in an EGFR-positive tamoxifen-resistant MCF-7 (Tam-R) breast cancer cell line.     

Macroautophagy inhibition sensitizes tamoxifen-resistant breast cancer cells and enhances mitochondrial depolarization

Macroautophagy (autophagy), a process for lysosomal degradation of organelles and long-lived proteins, has been linked to various pathologies including cancer and to the cellular response to anticancer therapies. In the human estrogen receptor positive MCF7 breast adenocarcinoma cell line, treatment with the endocrine therapeutic tamoxifen was shown previously to induce cell cycle arrest, cell death, and autophagy. To investigate specifically the role of autophagy in tamoxifen treated breast cancer cell lines, we used a siRNA approach, targeting three different autophagy genes, Atg5, Beclin-1, and Atg7. We found that knockdown of autophagy, in combination with tamoxifen in MCF7 cells, results in decreased cell viability concomitant with increased mitochondrial-mediated apoptosis. The combination of autophagy knockdown and tamoxifen treatment similarly resulted in reduced cell viability in the breast cancer cell lines, estrogen receptor positive T-47D and tamoxifen-resistant MCF7-HER2. Together, these results indicate that autophagy has a primary pro-survival role following tamoxifen treatment, and suggest that autophagy knockdown may be useful in a combination therapy setting to sensitize breast cancer cells, including tamoxifen-resistant breast cancer cells, to tamoxifen therapy. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

CAMK1D amplification implicated in epithelial–mesenchymal transition in basal-like breast cancer

Breast cancer exhibits clinical and molecular heterogeneity, where expression profiling studies have identified five major molecular subtypes. The basal-like subtype, expressing basal epithelial markers and negative for estrogen receptor (ER), progesterone receptor (PR) and HER2, is associated with higher overall levels of DNA copy number alteration (CNA), specific CNAs (like gain on chromosome 10p), and poor prognosis. Discovering the molecular genetic basis of tumor subtypes may provide new opportunities for therapy. To identify the driver oncogene on 10p associated with basal-like tumors, we analyzed genomic profiles of 172 breast carcinomas. The smallest shared region of gain spanned just seven genes at 10p13, including calcium/calmodulin-dependent protein kinase ID (CAMK1D), functioning in intracellular signaling but not previously linked to cancer. By microarray, CAMK1D was overexpressed when amplified, and by immunohistochemistry exhibited elevated expression in invasive carcinomas compared to carcinoma in situ. Engineered overexpression of CAMK1D in non-tumorigenic breast epithelial cells led to increased cell proliferation, and molecular and phenotypic alterations indicative of epithelial–mesenchymal transition (EMT), including loss of cell–cell adhesions and increased cell migration and invasion. Our findings identify CAMK1D as a novel amplified oncogene linked to EMT in breast cancer, and as a potential therapeutic target with particular relevance to clinically unfavorable basal-like tumors.     

Phloroglucinol suppresses metastatic ability of breast cancer cells by inhibition of epithelial‐mesenchymal cell transition

Metastasis is a challenging clinical problem and the primary cause of death in breast cancer patients. However, there is no therapeutic agent against metastasis of breast cancer cells. Here we report that phloroglucinol, a natural phlorotannin component of brown algae suppresses metastatic ability of breast cancer cells. Treatment with phloroglucinol effectively inhibited mesenchymal phenotypes of basal type breast cancer cells through downregulation of SLUG without causing a cytotoxic effect. Importantly, phloroglucinol decreased SLUG through inhibition of PI3K/AKT and RAS/RAF‐1/ERK signaling. In agreement with in vitro data, phloroglucinol was also effective against in vivo metastasis of breast cancer cells, drastically suppressing their metastatic ability to lungs, and extending the survival time of mice. Collectively, our findings demonstrate a novel anticancer activity of phloroglucinol against metastasis of breast cancer cells, implicating its clinical relevance.     

MicroRNA control of epithelial‐mesenchymal transition in cancer stem cells

Cancer stem cells (CSCs) represent a small subset of cancer cell populations that possess characteristics associated with normal stem cells. They have the ability to self‐renew, and are able to generate diverse tumor cells and account for metastases. Therefore, CSCs are widely accepted as potential mediators of therapeutic resistance and novel targets for anti‐cancer treatments. Recent progress has highlighted the significance of epithelial–mesenchymal transition (EMT) process in CSC formation, as well as the crucial role of microRNAs in controlling EMT and cancer metastasis. MicroRNAs are also reported to take part in the control of CSC functions and the regulation of cancer progression by affecting EMT process. Thus, it is highly crucial to develop deeper understanding of the mechanisms that how microRNAs control EMT processes and regulate CSC functions for better therapeutics of cancer disease. Herein we make this review to summarize the current understanding of the regulatory mechanisms of EMT in CSC initiation, with a special focus on the role of microRNAs in EMT control, and discuss the implications of targeting CSCs for cancer therapeutics.     

Involvement of activator protein-1 (AP-1) in induction of apoptosis by vitamin E succinate in human breast cancer cells

The purpose of this study was to document induction of apoptosis by vitamin E succinate (VES; RRR-α-tocopheryl succinate) in human breast cancer cells in culture and to characterize potential c-jun involvement. VES at 18.8 μM (10 μg/mL) induced DNA synthesis arrest, reduced total cell numbers, and induced apoptosis in estrogen receptor–positive and estrogen-responsive MCF-7 human breast cancer cells. VES at 10 μg/mL induced apoptosis in greater than 60% of cells within 3 d of treatment. Apoptosis was documented by detection of fragmented or condensed nuclei in 4′,6-diamindino-2-phenylindole–stained cells, detection of terminal deoxynucleotidyl transferase–mediated dUTP-biotin nick-end labeled DNA, and DNA laddering. Analyses of mRNA and protein levels of candidate molecules involved in apoptosis showed that MCF-7 cells treated with VES exhibited elevated and persistent expression of c-jun. MCF-7 cells stably transfected with a dominant-negative interfering mutant c-jun, TAM-67, and expressing high levels of mutant jun exhibited approximately 50% blockage of VES-mediated apoptosis. In addition to increased c-jun expression after VES treatment, VES-treated MCF-7 cells exhibited elevated activator protein-1 (AP-1) binding activity. Comparisons of AP-1 binding factors by super-shift analyses with jun-specific antibodies in cells sensitive to VES-induced apoptosis (empty-vector control 7-1 cells) and cells resistant to VES-induced apoptosis (TAM-67–containing TAM-9 cells) showed that the sensitive cells expressed c-jun and jun D and the resistant cells TAM-67 AP-1 binding proteins after VES treatment. These studies suggested that c-jun may be involved in the apoptotic process initiated by VES treatment of human MCF-7 breast cancer cells. Mol. Carcinog. 19:180–190, 1997. © 1997 Wiley-Liss, Inc.     

Host microenvironment in breast cancer development: Epithelial–mesenchymal transition in breast cancer development

The epithelial–mesenchymal transition (EMT) is a developmental mechanism of crucial importance in establishing the body plan in many multicellular organisms. Several transduction pathways controlling the various steps of the morphological transition have been identified by molecular analyses of this process in cell lines and in vivo. The newly formed mesenchymal cells can exhibit locomotory and invasive phenotypes, suggesting that EMTs contribute to the progression of carcinoma. Diverse evidence indicates that EMT subprograms are involved in the appearance of different breast carcinoma types. Several normal and malignant breast cell lines are currently being analyzed to define key steps in EMT and to identify candidate genes. DNA profiling technology is also being applied to uncover pathways that lead to a metastatic phenotype.     

Hepatic nonparenchymal cells drive metastatic breast cancer outgrowth and partial epithelial to mesenchymal transition

Nearly half of breast carcinoma metastases will become clinically evident five or more years after primary tumor ablation. This implies that metastatic cancer cells survived over an extended timeframe without emerging as detectable nodules. The liver is a common metastatic destination, whose parenchymal hepatocytes have been shown to impart a less invasive, dormant phenotype on metastatic cancer cells. We investigated whether hepatic nonparenchymal cells (NPCs) contributed to metastatic breast cancer cell outgrowth and a mesenchymal phenotypic shift indicative of emergence. Co-culture experiments of primary human hepatocytes, NPCs or endothelial cell lines (TMNK-1 or HMEC-1) and breast cancer cell lines (MCF-7 or MDA-MB-231) were conducted. Exposure of carcinoma cells to NPC-conditioned medium isolated soluble factors contributing to outgrowth. To elucidate outgrowth mechanism, epidermal growth factor receptor (EGFR) inhibition co-culture experiments were performed. Flow cytometry analyses and immunofluorescence staining were conducted to quantify breast cancer cell outgrowth and phenotype, respectively. Outgrowth of the MDA-MB-231 cells within primary NPC co-cultures was substantially greater than in hepatocyte-only or hepatocyte+NPC co-cultures. MCF-7 cells co-cultured with human NPCs as well as with the endothelial NPC subtypes grew out significantly more than controls. MCF-7 cells underwent a mesenchymal shift as indicated by spindle morphology, membrane clearance of E-cadherin, and p38 nuclear translocation when in HMEC-1 co-culture. HMEC-1-conditioned medium induced similar results suggesting that secretory factors are responsible for this transition while blocking EGFR blunted the MCF-7 outgrowth. We conclude that NPCs in the metastatic hepatic niche secrete factors that can induce a partial mesenchymal shift in epithelial breast cancer cells thus initiating outgrowth, and that this is in part mediated by EGFR activation. These data suggest that changes in the parenchymal cell and NPC ratios (or activation status) in the liver metastatic microenvironment may contribute to emergence from metastatic dormancy.     

The prolyl isomerase Pin1 in breast development and cancer

The prolyl isomerase Pin1 specifically isomerizes certain phosphorylated Ser/Thr-Pro bonds and thereby regulates various cellular processes. Pin1 is a target of several oncogenic pathways and is overexpressed in human breast cancer. Its overexpression can lead to upregulation of cyclin D1 and transformation of breast epithelial cells in collaboration with the oncogenic pathways. In contrast, inhibition of Pin1 can suppress the transformation of breast epithelial cells. In addition, Pin1 knockout in mice prevents massive proliferation of breast epithelial cells during pregnancy. Pin1 plays a pivotal role in breast development and may be a promising new anticancer target.     

The prolyl isomerase Pin1 in breast development and cancer

The prolyl isomerase Pin1 specifically isomerizes certain phosphorylated Ser/Thr-Pro bonds and thereby regulates various cellular processes. Pin1 is a target of several oncogenic pathways and is overexpressed in human breast cancer. Its overexpression can lead to upregulation of cyclin D1 and transformation of breast epithelial cells in collaboration with the oncogenic pathways. In contrast, inhibition of Pin1 can suppress the transformation of breast epithelial cells. In addition, Pin1 knockout in mice prevents massive proliferation of breast epithelial cells during pregnancy. Pin1 plays a pivotal role in breast development and may be a promising new anticancer target.