Distinct contributions of partial and full EMT to breast cancer malignancy.

Epithelial-mesenchymal transition (EMT) is a transient, reversible process of cell de-differentiation where cancer cells transit between various stages of an EMT continuum, including epithelial, partial EMT, and mesenchymal cell states. We have employed Tamoxifen-inducible dual recombinase lineage tracing systems combined with live imaging and 5-cell RNA sequencing to track cancer cells undergoing partial or full EMT in the MMTV-PyMT mouse model of metastatic breast cancer. In primary tumors, cancer cells infrequently undergo EMT and mostly transition between epithelial and partial EMT states but rarely reach full EMT. Cells undergoing partial EMT contribute to lung metastasis and chemoresistance, whereas full EMT cells mostly retain a mesenchymal phenotype and fail to colonize the lungs. However, full EMT cancer cells are enriched in recurrent tumors upon chemotherapy. Hence, cancer cells in various stages of the EMT continuum differentially contribute to hallmarks of breast cancer malignancy, such as tumor invasion, metastasis, and chemoresistance.

Breast cancer as an example of tumour heterogeneity and tumour cell plasticity during malignant progression.

Heterogeneity within a tumour increases its ability to adapt to constantly changing constraints, but adversely affects a patient's prognosis, therapy response and clinical outcome. Intratumoural heterogeneity results from a combination of extrinsic factors from the tumour microenvironment and intrinsic parameters from the cancer cells themselves, including their genetic, epigenetic and transcriptomic traits, their ability to proliferate, migrate and invade, and their stemness and plasticity attributes. Cell plasticity constitutes the ability of cancer cells to rapidly reprogramme their gene expression repertoire, to change their behaviour and identities, and to adapt to microenvironmental cues. These features also directly contribute to tumour heterogeneity and are critical for malignant tumour progression. In this article, we use breast cancer as an example of the origins of tumour heterogeneity (in particular, the mutational spectrum and clonal evolution of progressing tumours) and of tumour cell plasticity (in particular, that shown by tumour cells undergoing epithelial-to-mesenchymal transition), as well as considering interclonal cooperativity and cell plasticity as sources of cancer cell heterogeneity. We review current knowledge on the functional contribution of cell plasticity and tumour heterogeneity to malignant tumour progression, metastasis formation and therapy resistance.

Multi-color clonal tracking reveals intra-stage proliferative heterogeneity during mammary tumor progression.

Despite major progress in breast cancer research, the functional contribution of distinct cancer cell clones to malignant tumor progression and metastasis remains largely elusive. We have assessed clonal heterogeneity within individual primary tumors and metastases and also during the distinct stages of malignant tumor progression using clonal tracking of cancer cells in the MMTV-PyMT mouse model of metastatic breast cancer. Comparative gene expression analysis of clonal subpopulations reveals a substantial level of heterogeneity across and also within the various stages of breast carcinogenesis. The intra-stage heterogeneity is primarily manifested by differences in cell proliferation, also found within invasive carcinomas of luminal A-, luminal B-, and HER2-enriched human breast cancer. Surprisingly, in the mouse model of clonal tracing of cancer cells, chemotherapy mainly targets the slow-proliferative clonal populations and fails to efficiently repress the fast-proliferative populations. These insights may have considerable impact on therapy selection and response in breast cancer patients.

A dual role of Irf1 in maintaining epithelial identity but also enabling EMT and metastasis formation of breast cancer cells.

An epithelial to mesenchymal transition (EMT) is an embryonic dedifferentiation program which is aberrantly activated in cancer cells to acquire cellular plasticity. This plasticity increases the ability of breast cancer cells to invade into surrounding tissue, to seed metastasis at distant sites and to resist to chemotherapy. In this study, we have observed a higher expression of interferon-related factors in basal-like and claudin-low subtypes of breast cancer in patients, known to be associated with EMT. Notably, Irf1 exerts essential functions during the EMT process, yet it is also required for the maintenance of an epithelial differentiation status of mammary gland epithelial cells: RNAi-mediated ablation of Irf1 in mammary epithelial cells results in the expression of mesenchymal factors and Smad transcriptional activity. Conversely, ablation of Irf1 during TGFß-induced EMT prevents a mesenchymal transition and stabilizes the expression of E-cadherin. In the basal-like murine breast cancer cell line 4T1, RNAi-mediated ablation of Irf1 reduces colony formation and cell migration in vitro and shedding of circulating tumor cells and metastasis formation in vivo. This context-dependent dual role of Irf1 in the regulation of epithelial-mesenchymal plasticity provides important new insights into the functional contribution and therapeutic potential of interferon-regulated factors in breast cancer.

A Hierarchical Regulatory Landscape during the Multiple Stages of EMT.

Epithelial-mesenchymal transition (EMT) enables cells to gain migratory and invasive features underlined by major transcriptional and epigenetic reprogramming. However, most studies have focused on the endpoints of the EMT process, and the epistatic hierarchy of the transcriptional networks underlying EMT has remained elusive. We have used a siRNA-based, functional high-content microscopy screen to identify 46 (co)transcription factors ((co)TFs) and 13 miRNAs critically required for EMT in normal murine mammary gland (NMuMG) cells. We compared dynamic gene expression during EMT kinetics and used functional perturbation of critical (co)TFs and miRNAs to identify groups and networks of EMT genes. Computational analysis as well as functional validation experiments revealed interaction networks between TFs and miRNAs and delineated the hierarchical and functional interactions of multiple EMT regulatory networks in NMuMG cells.

Gain Fat-Lose Metastasis: Converting Invasive Breast Cancer Cells into Adipocytes Inhibits Cancer Metastasis.

Cancer cell plasticity facilitates the development of therapy resistance and malignant progression. De-differentiation processes, such as an epithelial-mesenchymal transition (EMT), are known to enhance cellular plasticity. Here, we demonstrate that cancer cell plasticity can be exploited therapeutically by forcing the trans-differentiation of EMT-derived breast cancer cells into post-mitotic and functional adipocytes. Delineation of the molecular pathways underlying such trans-differentiation has motivated a combination therapy with MEK inhibitors and the anti-diabetic drug Rosiglitazone in various mouse models of murine and human breast cancer in vivo. This combination therapy provokes the conversion of invasive and disseminating cancer cells into post-mitotic adipocytes leading to the repression of primary tumor invasion and metastasis formation.

Foxf2 plays a dual role during transforming growth factor beta-induced epithelial to mesenchymal transition by promoting apoptosis yet enabling cell junction dissolution and migration.

BACKGROUND: The most life-threatening step during malignant tumor progression is reached when cancer cells leave the primary tumor mass and seed metastasis in distant organs. To infiltrate the surrounding tissue and disseminate throughout the body, single motile tumor cells leave the tumor mass by breaking down cell-cell contacts in a process called epithelial to mesenchymal transition (EMT). An EMT is a complex molecular and cellular program enabling epithelial cells to abandon their differentiated phenotype, including cell-cell adhesion and cell polarity, and to acquire mesenchymal features and invasive properties. METHODS: We employed gene expression profiling and functional experiments to study transcriptional control of transforming growth factor (TGF)ß-induced EMT in normal murine mammary gland epithelial (NMuMG) cells. RESULTS: We identified that expression of the transcription factor forkhead box protein F2 (Foxf2) is upregulated during the EMT process. Although it is not required to gain mesenchymal markers, Foxf2 is essential for the disruption of cell junctions and the downregulation of epithelial markers in NMuMG cells treated with TGFß. Foxf2 is critical for the downregulation of E-cadherin by promoting the expression of the transcriptional repressors of E-cadherin, Zeb1 and Zeb2, while repressing expression of the epithelial maintenance factor Id2 and miRNA 200 family members. Moreover, Foxf2 is required for TGFß-mediated apoptosis during EMT by the transcriptional activation of the proapoptotic BH3-only protein Noxa and by the negative regulation of epidermal growth factor receptor (EGFR)-mediated survival signaling through direct repression of its ligands betacellulin and amphiregulin. The dual function of Foxf2 during EMT is underscored by the finding that high Foxf2 expression correlates with good prognosis in patients with early noninvasive stages of breast cancer, but with poor prognosis in advanced breast cancer. CONCLUSIONS: Our data identify the transcription factor Foxf2 as one of the important regulators of EMT, displaying a dual function in promoting tumor cell apoptosis as well as tumor cell migration.

The FAK inhibitor BI 853520 exerts anti-tumor effects in breast cancer.

Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that regulates a plethora of downstream signaling pathways essential for cell migration, proliferation and death, processes that are exploited by cancer cells during malignant progression. These well-established tumorigenic activities, together with its high expression and activity in different cancer types, highlight FAK as an attractive target for cancer therapy. We have assessed and characterized the therapeutic potential and the biological effects of BI 853520, a novel small chemical inhibitor of FAK, in several preclinical mouse models of breast cancer. Treatment with BI 853520 elicits a significant reduction in primary tumor growth caused by an anti-proliferative activity by BI 853520. In contrast, BI 853520 exerts effects with varying degrees of robustness on the different stages of the metastatic cascade. Together, the data demonstrate that the repression of FAK activity by the specific FAK inhibitor BI 853520 offers a promising anti-proliferative approach for cancer therapy.

miR-1199-5p and Zeb1 function in a double-negative feedback loop potentially coordinating EMT and tumour metastasis.

Epithelial tumour cells can gain invasive and metastatic capabilities by undergoing an epithelial-mesenchymal transition. Transcriptional regulators and post-transcriptional effectors like microRNAs orchestrate this process of high cellular plasticity and its malignant consequences. Here, using microRNA sequencing in a time-resolved manner and functional validation, we have identified microRNAs that are critical for the regulation of an epithelial-mesenchymal transition and of mesenchymal tumour cell migration. We report that miR-1199-5p is downregulated in its expression during an epithelial-mesenchymal transition, while its forced expression prevents an epithelial-mesenchymal transition, tumour cell migration and invasion in vitro, and lung metastasis in vivo. Mechanistically, miR-1199-5p acts in a reciprocal double-negative feedback loop with the epithelial-mesenchymal transition transcription factor Zeb1. This function resembles the activities of miR-200 family members, guardians of an epithelial cell phenotype. However, miR-1199-5p and miR-200 family members share only six target genes, indicating that, besides regulating Zeb1 expression, they exert distinct functions during an epithelial-mesenchymal transition.

ROMP-Derived cyclooctene-based monolithic polymeric materials reinforced with inorganic nanoparticles for applications in tissue engineering.

Porous monolithic inorganic/polymeric hybrid materials have been prepared via ring-opening metathesis copolymerization starting from a highly polar monomer, i.e., cis-5-cyclooctene-trans-1,2-diol and a 7-oxanorborn-2-ene-derived cross-linker in the presence of porogenic solvents and two types of inorganic nanoparticles (i.e., CaCO3 and calcium hydroxyapatite, respectively) using the third-generation Grubbs initiator RuCl2(Py)2(IMesH2)(CHPh). The physico-chemical properties of the monolithic materials, such as pore size distribution and microhardness were studied with regard to the nanoparticle type and content. Moreover, the reinforced monoliths were tested for the possible use as scaffold materials in tissue engineering, by carrying out cell cultivation experiments with human adipose tissue-derived stromal cells.

Ring-Opening Metathesis Polymerization-Based Synthesis of CaCO(3) Nanoparticle-Reinforced Polymeric Monoliths for Tissue Engineering.

Porous monolithic materials have been prepared via ring-opening metathesis polymerization from norborn-2-ene and a 7-oxanorborn-2-ene-based cross-linker in the presence of porogenic solvents (i.e., 2-propanol and toluene) and norborn-2-enephosphonate surface-modified CaCO(3) nanoparticles, using the 3(rd) -generation Grubbs-initiator RuCl(2) (Py)(2) (IMesH(2) )(CHPh). The experimental setup and the conditions chosen allowed for the manufacturing of polymeric monoliths characterized by a homogeneous distribution of the inorganic nanoparticles throughout the polymeric monolith. Depending on the nanoparticle content, the macropore diameters could be varied in the 30-120 µm regime. Noteworthy, the addition of nanoparticles did not affect the phase separation-triggered formation of the monolithic matrix nor the meso- and microporosity as evidenced by N(2) -adsorption experiments.