Immune-induced epithelial to mesenchymal transition in vivo generates breast cancer stem cells

Alteration of cancer stem cell-like phenotype by histone deacetylase inhibitors in squamous cell carcinoma of the head and neck

Recent progression in the understanding of stem cell biology has greatly facilitated the identification and characterization of cancer stem cells (CSCs). Moreover, evidence has accumulated indicating that conventional cancer treatments are potentially ineffective against CSCs. Histone deacetylase inhibitors (HDACi) have multiple biologic effects consequent to alterations in the patterns of acetylation of histones and are a promising new group of anticancer agents. In this study, we investigated the effects of two HDACi, suberoylanilide hydroxamic acid (SAHA) and trichostatin A (TSA), on two CD44+ cancer stem-like cell lines from squamous cell carcinoma of the head and neck (SCCHN) cultured in serum-free medium containing epidermal growth factor and basic fibroblast growth factor. Histone deacetylase inhibitors inhibited the growth of SCCHN cell lines in a dose-dependent manner as measured by MTS assays. Moreover, HDACi induced cell cycle arrest and apoptosis in these SCCHN cell lines. Interestingly, the expression of cancer stem cell markers, CD44 and ABCG2, on SCCHN cell lines was decreased by HDACi treatment. In addition, HDACi decreased mRNA expression levels of stemness-related genes and suppressed the epithelial-mesencymal transition phenotype of CSCs. As expected, the combination of HDACi and chemotherapeutic agents, including cisplatin and docetaxel, had a synergistic effect on SCCHN cell lines. Taken together, our data indicate that HDACi not only inhibit the growth of SCCHN cell lines by inducing apoptosis and cell cycle arrest, but also alter the cancer stem cell phenotype in SCCHN, raising the possibility that HDACi may have therapeutic potential for cancer stem cells of SCCHN.

A new perspective of vasculogenic mimicry: EMT and cancer stem cells (Review)

Vasculogenic mimicry (VM), a new pattern of tumor microcirculation, is important for the growth and progression of tumors. Epithelial-mesenchymal transition (EMT) is pivotal in malignant tumor progression and VM formation. With increasing knowledge of cancer stem cell (CSC) phenotypes and functions, increasing evidence suggests that CSCs are involved in VM formation. Recent studies have indicated that EMT is relevant to the acquisition and maintenance of stem cell-like characteristics. Thus, in this review we discuss the correlation between CSCs, EMT and VM formation.

Effect of AKT inhibition on epithelial-mesenchymal transition and ZEB1-potentiated radiotherapy in nasopharyngeal carcinoma

Radiotherapy is a major treatment regime for nasopharyngeal carcinoma (NPC), and although initial responses to a complete course of radiation are good, recurrence and metastasis are frequent events. A number of previous studies have observed that ionizing radiation (IR) may enhance the migratory and invasive properties of cancer cells through epithelial-mesenchymal transition (EMT). In the present study, a tumor cohort of 22 NPC and 7 normal cases (chronic inflammation only) were investigated and the expression of AKT was demonstrated to positively correlate with the expression of ZEB1. Following treatment with IR, 7/10 patients suffered recurrence and metastasis, in addition to high expression levels of phosphorylated AKT (S473) and ZEB1. The AKT inhibitor, GSK690693, inhibited AKT, blocked the expression of ZEB1 and vimentin and restored the expression of E-cadherin following IR, thus preventing the migration and EMT of the tumor cells. In addition, the inhibition of AKT via GSK690693 was shown to markedly increase the sensitivity of tumor cells to IR in vitro and in vivo. These observations indicate that GSK690693 may aid in the prevention of recurrence and metastasis following IR therapy in NPC patients.

Breast cancer stem cells

Cancer metastasis, resistance to therapies and disease recurrence are significant hurdles to successful treatment of breast cancer. Identifying mechanisms by which cancer spreads, survives treatment regimes and regenerates more aggressive tumors are critical to improving patient survival. Substantial evidence gathered over the last 10 years suggests that breast cancer progression and recurrence is supported by cancer stem cells (CSCs). Understanding how CSCs form and how they contribute to the pathology of breast cancer will greatly aid the pursuit of novel therapies targeted at eliminating these cells. This review will summarize what is currently known about the origins of breast CSCs, their role in disease progression and ways in which they may be targeted therapeutically.

Oncogenic transformation of mammary epithelial cells by transforming growth factor beta independent of mammary stem cell regulation

Background

Transforming growth factor beta (TGFβ) is transiently increased in the mammary gland during involution and by radiation. While TGFβ normally has a tumour suppressor role, prolonged exposure to TGFβ can induce an oncogenic epithelial to mesenchymal transition (EMT) program in permissive cells and initiate the generation of cancer stem cells. Our objective is to mimic the transient exposure to TGFβ during involution to determine the persistent effects on premalignant mammary epithelium.

Method

CDβGeo cells, a transplantable mouse mammary epithelial cell line, were treated in vitro for 14 days with TGFβ (5 ng/ml). The cells were passaged for an additional 14 days in media without TGFβ and then assessed for markers of EMT and transformation.

Results

The 14-day exposure to TGFβ induced EMT and transdifferentiation in vitro that persists after withdrawal of TGFβ. TGFβ-treated cells are highly tumorigenic in vivo, producing invasive solid de-differentiated tumours (100%; latency 6.7 weeks) compared to control (43%; latency 32.7 weeks). Although the TGFβ-treated cells have initiated a persistent EMT program, the stem cell population was unchanged relative to the controls. The gene expression profiles of TGFβ-treated cells demonstrate de-differentiation with decreases in the expression of genes that define luminal, basal and stem cells. Additionally, the gene expression profiles demonstrate increases in markers of EMT, growth factor signalling, TGFβ2 and changes in extra cellular matrix.

Conclusion

This model demonstrates full oncogenic EMT without an increase in stem cells, serving to separate EMT markers from stem cell markers.

ROCK1 inhibition promotes the self-renewal of a novel mouse mammary cancer stem cell

The differentiation of stem-like tumor cells may contribute to the cellular heterogeneity of breast cancers. We report the propagation of highly enriched mouse mammary cancer stem cells that retain the potential to differentiate both in vivo and in culture and their use to identify chemical compounds that influence both self-renewal and differentiation. We identify epithelial tumor-initiating cells (ETICs) that express lineage markers of both basal and luminal mammary cell lineages and retain the potential, from even single cells, to generate heterogeneous tumors similar to the tumor of origin. ETICs can progress through a Rho-associated coiled-coil containing protein kinase 1 dependent, epithelial to mesenchymal transition to generate mesenchymal tumor-initiating cells capable of initiating tumors of limited heterogeneity. The propagation of ETICs may allow for the identification of new therapeutic compounds that may inhibit or prevent progression of some types of breast cancer.

Functional cloning of recurrence-specific antigens identifies molecular targets to treat tumor relapse

Aggressive regrowth of recurrent tumors following treatment-induced dormancy represents a major clinical challenge for treatment of malignant disease. We reported previously that recurrent prostate tumors, which underwent complete macroscopic regression followed by aggressive regrowth, could be cured with a vesicular stomatitis virus (VSV)-expressed cDNA library derived from recurrent tumor cells. By screening the protective, recurrence-derived VSV-cDNA library, here we identify topoisomerase-IIα (TOPO-IIα) as a recurrence-specific tumor antigen against which tolerance can be broken. Tumor recurrences, in two different types of tumor (prostate and melanoma), which had evaded two different frontline treatments (immunotherapy or chemotherapy), significantly overexpressed TOPO-IIα compared with their primary tumor counterparts, which conferred a novel sensitivity to doxorubicin (DOX) chemotherapy upon the recurrent tumors. This was exploited in vivo using combination therapies to cure mice, which would otherwise have relapsed, after suboptimal primary therapy in both models. Our data show that recurrent tumors-across histologies and primary treatments-express distinct antigens compared with the primary tumor which can be identified using the VSV-cDNA library technology. These results suggest that it may be possible to design a few common second-line therapies against a variety of tumor recurrences, in some cases using agents with no obvious activity against the primary tumor.

Chromatin regulator PRC2 is a key regulator of epigenetic plasticity in glioblastoma

Tumor cell plasticity contributes to functional and morphologic heterogeneity. To uncover the underlying mechanisms of this plasticity, we examined glioma stem-like cells (GSC) where we found that the biologic interconversion between GSCs and differentiated non-GSCs is functionally plastic and accompanied by gain or loss of polycomb repressive complex 2 (PRC2), a complex that modifies chromatin structure. PRC2 mediates lysine 27 trimethylation on histone H3 and in GSC it affected pluripotency or development-associated genes (e.g., Nanog, Wnt1, and BMP5) together with alterations in the subcellular localization of EZH2, a catalytic component of PRC2. Intriguingly, exogenous expression of EZH2-dNLS, which lacks nuclear localization sequence, impaired the repression of Nanog expression under differentiation conditions. RNA interference (RNAi)-mediated attenuation or pharmacologic inhibition of EZH2 had little to no effect on apoptosis or bromodeoxyuridine incorporation in GSCs, but it disrupted morphologic interconversion and impaired GSC integration into the brain tissue, thereby improving survival of GSC-bearing mice. Pathologic analysis of human glioma specimens revealed that the number of tumor cells with nuclear EZH2 is larger around tumor vessels and the invasive front, suggesting that nuclear EZH2 may help reprogram tumor cells in close proximity to this microenvironment. Our results indicate that epigenetic regulation by PRC2 is a key mediator of tumor cell plasticity, which is required for the adaptation of glioblastoma cells to their microenvironment. Thus, PRC2-targeted therapy may reduce tumor cell plasticity and tumor heterogeneity, offering a new paradigm for glioma treatment.

T cell immunotherapy for melanoma from bedside to bench to barn and back: how conceptual advances in experimental mouse models can be translated into clinical benefit for patients

A solid scientific basis now supports the concept that cytotoxic T lymphocytes can specifically recognize and destroy melanoma cells. Over the last decades, clinicians and basic scientists have joined forces to advance our concepts of melanoma immunobiology. This has catalyzed the rational development of therapeutic approaches to enforce melanoma-specific T cell responses. Preclinical studies in experimental mouse models paved the way for their successful translation into clinical benefit for patients with metastatic melanoma. A more thorough understanding of how melanomas develop resistance to T cell immunotherapy is necessary to extend this success. This requires a continued interdisciplinary effort of melanoma biologists and immunologists that closely connects clinical observations with in vitro investigations and appropriate in vivo mouse models: From bedside to bench to barn and back.

Plasticity of tumour and immune cells: a source of heterogeneity and a cause for therapy resistance?

Immunotherapies, signal transduction inhibitors and chemotherapies can successfully achieve remissions in advanced stage cancer patients, but durable responses are rare. Using malignant melanoma as a paradigm, we propose that therapy-induced injury to tumour tissue and the resultant inflammation can activate protective and regenerative responses that represent a shared resistance mechanism to different treatments. Inflammation-driven phenotypic plasticity alters the antigenic landscape of tumour cells, rewires oncogenic signalling networks, protects against cell death and reprogrammes immune cell functions. We propose that the successful combination of cancer treatments to tackle resistance requires an interdisciplinary understanding of these resistance mechanisms, supported by mathematical models.

Response of CD44+/CD24-/low breast cancer stem/progenitor cells to tamoxifen‑ and doxorubicin‑induced autophagy

The cancer stem cell hypothesis emphasizes that cancers are driven by cells having stem cell properties, and it is believed that cancer stem cells (CSCs) may be responsible for resistance against therapeutic approaches and for recurrent tumors. Since the biology of the normal breast requires large numbers of stem cells, it has been thought that breast stem cells play an important role in initiating breast cancer. A better characterization of breast CSCs appears to be an essential step to improve the understanding of the biology of breast cancer and its management. The scope of this study was to isolate breast CSCs from a breast cancer cell line (MCF-7) using cell surface markers, and to test whether these cells have any resistance to autophagic cell death mechanisms mediated by commonly used chemotherapies and hormonal therapies such as doxorubicin (adriamycin) and tamoxifen (anti-estrogen), respectively. For this purpose, the CD44+/CD24-/low MCF-7 breast cancer stem/progenitor cell population was isolated and treated with doxorubicin or tamoxifen and evaluated for their response to growth, autophagy and apoptosis. Our findings suggest that CD44+/CD24-/low cells were less sensitive to doxorubicin, but did not demonstrate a significant difference towards tamoxifen in regards to the induction of autophagy.

Dynamic transcription factor networks in epithelial-mesenchymal transition in breast cancer models

The epithelial-mesenchymal transition (EMT) is a complex change in cell differentiation that allows breast carcinoma cells to acquire invasive properties. EMT involves a cascade of regulatory changes that destabilize the epithelial phenotype and allow mesenchymal features to manifest. As transcription factors (TFs) are upstream effectors of the genome-wide expression changes that result in phenotypic change, understanding the sequential changes in TF activity during EMT provides rich information on the mechanism of this process. Because molecular interactions will vary as cells progress from an epithelial to a mesenchymal differentiation program, dynamic networks are needed to capture the changing context of molecular processes. In this study we applied an emerging high-throughput, dynamic TF activity array to define TF activity network changes in three cell-based models of EMT in breast cancer based on HMLE Twist ER and MCF-7 mammary epithelial cells. The TF array distinguished conserved from model-specific TF activity changes in the three models. Time-dependent data was used to identify pairs of TF activities with significant positive or negative correlation, indicative of interdependent TF activity throughout the six-day study period. Dynamic TF activity patterns were clustered into groups of TFs that change along a time course of gene expression changes and acquisition of invasive capacity. Time-dependent TF activity data was combined with prior knowledge of TF interactions to construct dynamic models of TF activity networks as epithelial cells acquire invasive characteristics. These analyses show EMT from a unique and targetable vantage and may ultimately contribute to diagnosis and therapy.

AXL induces epithelial-to-mesenchymal transition and regulates the function of breast cancer stem cells

Despite significant progress in the treatment of breast cancer particularly through the use of targeted therapy, relapse and chemo-resistance remain a major hindrance to the fight to minimize the burden of the disease. It is becoming increasingly clear that a rare subpopulation of cells known as cancer stem cells (CSC), able to be generated through epithelial to mesenchymal transition (EMT) and capable of tumor initiation and self-renewal, contributes to treatment resistance and metastases. This means that a more effective therapy should target both the chemoresistant CSCs and the proliferating epithelial cells that give rise to them in order to reverse EMT and attenuate their conversion to CSCs. Here, we demonstrate a novel function of AXL in acting upstream to induce EMT in normal and immortalized human mammary epithelial cells in an apparent positive feedback loop mechanism and regulate breast CSC (BCSC) self-renewal and chemoresistance. Downregulation of AXL using MP470 (amuvatinib) reversed EMT in mesenchymal normal human mammary epithelial cells and murine BCSCs attenuating self-renewal and restored chemosensitivity of the BCSCs. AXL expression was also found to be associated with expression of stem cell genes, regulation of metastases genes, increased tumorigenicity, and was important for BCSC invasion and migration. Inactivation of AXL also led to downregulation of NFκB pathway and reduced tumor formation in vivo. Together, our data suggest that targeted therapy against AXL, in combination with systemic therapies, has the potential to improve response to anti-cancer therapies and to reduce breast cancer recurrence and metastases.

Sox2 expression predicts poor survival of hepatocellular carcinoma patients and it promotes liver cancer cell invasion by activating Slug

Sox2 is a major transcription factor essential to the stemness characteristics and is associated with various types of cancers. In this study, we investigated the expressions and functional roles of Sox2 in hepatocellular carcinoma (HCC). Our data show that high level of Sox2 expression correlates with metastasis and low survival rate in HCC. HCC cells overexpressing Sox2 are characterized by active epithelial-mesenchymal transition and exhibit increased ability of transwell invasion, soft agar colonization, and sphere formation. We also found Sox2 expression was correlated with the transcription activity of SLUG promoter region. These results present novel mechanistic insight into an important role of Sox2 in HCC and suggest a potential application of Sox2 in HCC prognosis and treatment.

Phosphosulindac (OXT-328) selectively targets breast cancer stem cells in vitro and in human breast cancer xenografts

Pharmacological targeting of breast cancer stem cells (CSCs) is highly promising for the treatment of breast cancer, as the small population of CSCs appears responsible for tumor initiation and progression and also for resistance to conventional treatment. Here we report that the novel phosphosulindac (OXT-328, PS) selectively and effectively eliminates breast CSCs both in vitro and in vivo. PS reduced cell proliferation and induced apoptosis in various breast CSCs. Breast CSCs are resistant to conventional cancer drugs but are sensitive to PS. Long-term treatment of mixtures of cultured breast CSCs and breast cancer cells with PS preferentially eliminated the CSCs. PS impaired the ability of CSCs to form mammospheres and markedly suppressed the expression of CSC-related genes. More importantly, PS prevented by half (p = .06) the formation of tumors initiated by CSCs in immunodeficient mice, and inhibited by 83% (p < .05) the growth of already formed breast cancer xenografts, reducing the proportion of CSCs in them. PS suppressed the Wnt/β-catenin pathway by stimulating the degradation of β-catenin and its relocalization to the cell membrane and also blocked the epithelial-mesenchymal transition and the generation of breast CSCs. These results indicate that PS has a strong inhibitory effect against breast cancer, acting, at least in part, by targeting CSCs through a signaling mechanism involving Wnt signaling.

Molecular alterations in metaplastic breast carcinoma

Metaplastic carcinoma of the breast is a rare and heterogeneous subtype of breast carcinoma with a generally poor outcome, and few therapeutic options once disease recurs or progresses. Metaplastic carcinomas of the breast are usually of a larger size at diagnosis, with less frequent nodal metastasis compared with invasive ductal carcinoma no special type, and lack hormone and HER2 receptor expression. Recent research has revealed some potentially actionable genetic changes in a subset of these rare tumours. However, ongoing efforts to further characterise the genetic basis and the molecular alterations underlying the distinctive morphological and clinical characteristics of these tumours are needed in order to identify new targets for treatment. This review will describe the theories of pathogenesis of metaplastic breast carcinoma, and highlight genetic changes and potential therapeutic targets in this generally poor prognosis malignancy.

Stacking the DEK: from chromatin topology to cancer stem cells

Stem cells are essential for development and tissue maintenance and display molecular markers and functions distinct from those of differentiated cell types in a given tissue. Malignant cells that exhibit stem cell-like activities have been detected in many types of cancers and have been implicated in cancer recurrence and drug resistance. Normal stem cells and cancer stem cells have striking commonalities, including shared cell surface markers and signal transduction pathways responsible for regulating quiescence vs. proliferation, self-renewal, pluripotency and differentiation. As the search continues for markers that distinguish between stem cells, progenitor cells and cancer stem cells, growing evidence suggests that a unique chromatin-associated protein called DEK may confer stem cell-like qualities. Here, we briefly describe current knowledge regarding stem and progenitor cells. We then focus on new findings that implicate DEK as a regulator of stem and progenitor cell qualities, potentially through its unusual functions in the regulation of local or global chromatin organization.

Nicotine promotes acquisition of stem cell and epithelial-to-mesenchymal properties in head and neck squamous cell carcinoma

The ability of nicotine to enhance the malignancy of cancer cells is known; however, the possibility that nicotine could regulate a cancer stem cell phenotype remains to be well-established. In this study we sought to determine whether long-term exposure to nicotine could promote cancer stem cell-like properties in two head and neck squamous cell carcinoma cell lines, UMSCC-10B and HN-1. Nicotine treatment induced epithelial-to-mesenchymal transition (EMT) in both cell lines by repressing E-cadherin expression, and led to the induction of stem cell markers Oct-4, Nanog, CD44 and BMI-1, which was reversed upon ectopic re-expression of E-cadherin. Nicotine-treated cells formed spheres at a higher efficiency than non-treated cells, formed larger tumors when injected into mice, and formed tumors with 4-fold greater efficiency compared to control cells when injected at limiting doses. Consistent with previous literature, nicotine-treated cells demonstrated a greater capacity for survival and also a higher tendency to invade. Comparison of microRNA profiles between nicotine and control cells revealed the upregulation of miR-9, a repressor of E-cadherin, and the downregulation of miR-101, a repressor of EZH2. Taken together, these results suggest that nicotine may play a critical role in the development of tobacco-induced cancers by regulating cancer stem cell characteristics, and that these effects are likely mediated through EMT-promoting, microRNA-mediated pathways. Further characterization of such pathways remains a promising avenue for the understanding and treatment of tobacco-related cancers.

Herbal Compound "Songyou Yin" Renders Hepatocellular Carcinoma Sensitive to Oxaliplatin through Inhibition of Stemness

We investigated the effect of Chinese herbal compound Song-you Yin on HCC stemness. MHCC97H and Hep3B cell lines were pretreated with SYY for 4 weeks, and their chemosensitivity to oxaliplatin was evaluated. The expression of CSC-related markers, cell invasion and migration, and colony formation were also examined. SYY-treated orthotopic nude mouse models of human HCC were developed to explore the effect of oxaliplatin on tumor growth, metastasis, and survival. The CSC-related molecular changes in vivo were also evaluated. The result showed that MHCC97H and Hep3B cells pretreated with SYY showed significantly increased chemosensitivity to oxaliplatin and the downregulation of CSC-related markers CD90, CD24, and EPCAM. SYY also attenuated cell motility, invasion, and colony formation in MHCC97H and Hep3B cell lines. The reduced tumorigenicity and pulmonary metastasis were observed in SYY-pretreated cell lines. Combination treatment with oxaliplatin and SYY significantly reduced tumor volume and pulmonary metastasis and prolonged survival compared with oxaliplatin treatment alone. Immunohistochemical analysis showed reduced expression of CD90, ABCG2, ALDH, CD44, EPCAM, vimentin, and MMP-9 and increased the expression of E-cadherin, in HCC cells following combination treatment. These data clearly demonstrate that SYY renders hepatocellular carcinoma sensitive to oxaliplatin through the inhibition of stemness.

Grhl2 determines the epithelial phenotype of breast cancers and promotes tumor progression

Until now the essential transcription factor that determines the epithelial phenotype of breast cancer has not been identified and its role in epithelial-to-mesenchymal transition (EMT) and tumor progression remain unclear. Here, by analyzing large expression profiles of human breast cancer cells, we found an extraordinary correlation between the expression of Grainyhead transcription factor Grhl2 and epithelial marker E-cadherin. Knockdown of Grhl2 expression by shRNA in human mammary epithelial cell MCF10A leads to down-regulation of E-cadherin and EMT. Grhl2 is down-regulated in disseminated cancer cells that have undergone EMT, and over-expression of Grhl2 is sufficient to induce epithelial gene expression. Large clinical datasets reveal that expression of Grhl2 is significantly associated with poor relapse free survival and increased risk of metastasis in breast cancer patients. In mouse models, over-expression of Grhl2 significantly promotes tumor growth and metastasis. Further testing of several Grhl2 regulated genes leads to the same conclusions that the tumorigenic and metastatic potentials of tumor cells are linked to epithelial phenotype but not mesenchymal phenotype. In conclusion, our findings indicate that Grhl2 plays an essential role in the determination of epithelial phenotype of breast cancers, EMT and tumor progression.

Cancer stem cells, the epithelial to mesenchymal transition (EMT) and radioresistance: potential role of hypoxia

Numerous studies have demonstrated the presence of cancer stem cells (CSCs) within solid tumors. Although the precursor of these cells is not clearly established, recent studies suggest that the phenotype of CSCs may be quite plastic and associated with the epithelial-to-mesenchymal transition (EMT). In patients, the presence of EMT and CSCs has been implicated in increased resistance to radiotherapy. Hypoxia, a negative prognostic factor for treatment success, is a potent driver of a multitude of molecular signalling pathways that allow cells to survive and thrive in the hostile tumor microenvironment and can induce EMT. Hypoxia also provides tumor cells with cues for maintenance of a stem-like state and may help to drive the linkage between EMT and CSCs. Understanding the biology of CSCs, the EMT phenotype and their implications in therapeutic relapse may provide crucial new approaches in the development of improved therapeutic strategies.

Signatures of tumor-immune interactions as biomarkers for breast cancer prognosis

Breast cancer mortality is usually due to distant recurrence of cancer at an advanced stage of the disease rather than from primary cancer. Therefore, prediction of breast cancer recurrence at the time of diagnosis could lead to advances in personalized treatment of cancer patients in order to prevent risk of recurrence. Two prognostic biomarkers that are currently being used in clinical practice are a 70-gene MammaPrint signature and a 21-gene Oncotype DX panel. These assays generate relative risks of recurrence, but they do not provide a 'yes' or 'no' answer about recurrence in a given patient. These tests include genes that are involved in the cell cycle, invasion, metastasis and angiogenesis related to breast cancer. Emerging evidence suggests that a signature of genes involved in tumor-immune interactions may provide a more accurate prognostic tool. This paper reviews recent advances in the discovery of prognostic biomarkers for breast cancer patients.

Phenotype-dependent effects of EpCAM expression on growth and invasion of human breast cancer cell lines

Background

The epithelial cell adhesion molecule (EpCAM) has been shown to be overexpressed in breast cancer and stem cells and has emerged as an attractive target for immunotherapy of breast cancer patients. This study analyzes the effects of EpCAM on breast cancer cell lines with epithelial or mesenchymal phenotype.

Methods

For this purpose, shRNA-mediated knockdown of EpCAM gene expression was performed in EpCAM^high breast cancer cell lines with epithelial phenotype (MCF-7, T47D and SkBR3). Moreover, EpCAM^low breast carcinoma cell lines with mesenchymal phenotype (MDA-MB-231, Hs578t) and inducible overexpression of EpCAM were used to study effects on proliferation, migration and in vivo growth.

Results

In comparison to non-specific silencing controls (n/s-crtl) knockdown of EpCAM (E#2) in EpCAM^high cell lines resulted in reduced cell proliferation under serum-reduced culture conditions. Moreover, DNA synthesis under 3D culture conditions in collagen was significantly reduced. Xenografts of MCF-7 and T47D cells with knockdown of EpCAM formed smaller tumors that were less invasive. EpCAM^low cell lines with tetracycline-inducible overexpression of EpCAM showed no increased cell proliferation or migration under serum-reduced growth conditions. MDA-MB-231 xenografts with EpCAM overexpression showed reduced invasion into host tissue and more infiltrates of chicken granulocytes.

Conclusions

The role of EpCAM in breast cancer strongly depends on the epithelial or mesenchymal phenotype of tumor cells. Cancer cells with epithelial phenotype need EpCAM as a growth- and invasion-promoting factor, whereas tumor cells with a mesenchymal phenotype are independent of EpCAM in invasion processes and tumor progression. These findings might have clinical implications for EpCAM-based targeting strategies in patients with invasive breast cancer.

In vivo tumorigenesis was observed after injection of in vitro expanded neural crest stem cells isolated from adult bone marrow

Bone marrow stromal cells are adult multipotent cells that represent an attractive tool in cellular therapy strategies. Several studies have reported that in vitro passaging of mesenchymal stem cells alters the functional and biological properties of those cells, leading to the accumulation of genetic aberrations. Recent studies described bone marrow stromal cells (BMSC) as mixed populations of cells including mesenchymal (MSC) and neural crest stem cells (NCSC). Here, we report the transformation of NCSC into tumorigenic cells, after in vitro long-term passaging. Indeed, the characterization of 6 neural crest-derived clones revealed the presence of one tumorigenic clone. Transcriptomic analyses of this clone highlighted, among others, numerous cell cycle checkpoint modifications and chromosome 11q down-regulation (suggesting a deletion of chromosome 11q) compared with the other clones. Moreover, unsupervised analysis such as a dendrogram generated after agglomerative hierarchical clustering comparing several transcriptomic data showed important similarities between the tumorigenic neural crest-derived clone and mammary tumor cell lines. Altogether, it appeared that NCSC isolated from adult bone marrow represents a potential danger for cellular therapy, and consequently, we recommend that phenotypic, functional and genetic assays should be performed on bone marrow mesenchymal and neural crest stem cells before in vivo use, to demonstrate whether their biological properties, after ex vivo expansion, remain suitable for clinical application.

Functional heterogeneity within the CD44 high human breast cancer stem cell-like compartment reveals a gene signature predictive of distant metastasis

The CD44(hi) compartment in human breast cancer is enriched in tumor-initiating cells; however, the functional heterogeneity within this subpopulation remains poorly defined. We used a triple-negative breast cancer cell line with a known bilineage phenotype to isolate and clone CD44(hi) single cells that exhibited mesenchymal/basal B and luminal/basal A features, respectively. Herein, we demonstrate in this and other triple-negative breast cancer cell lines that, rather than CD44(hi)/CD24(-) mesenchymal-like basal B cells, the CD44(hi)/CD24(lo) epithelioid basal A cells retained classic cancer stem cell features, such as tumor-initiating capacity in vivo, mammosphere formation and resistance to standard chemotherapy. These results complement previous findings using oncogene-transformed normal mammary cells showing that only cell clones with a mesenchymal phenotype exhibit cancer stem cell features. Further, we performed comparative quantitative proteomic and gene array analyses of these cells and identified potential novel markers of breast cancer cells with tumor-initiating features, such as lipolysis-stimulated lipoprotein receptor (LSR), RAB25, S100A14 and mucin 1 (MUC1), as well as a novel 31-gene signature capable of predicting distant metastasis in cohorts of estrogen receptor-negative human breast cancers. These findings strongly favor functional heterogeneity in the breast cancer cell compartment and hold promise for further refinements of prognostic marker profiling. Our work confirms that, in addition to cancer stem cells with mesenchymal-like morphology, those tumor-initiating cells with epithelial-like morphology should also be the focus of drug development.

EMT in carcinoma progression and dissemination: facts, unanswered questions, and clinical considerations

Over the past decade, much effort has been made to understand how cancers metastasize. In deciphering the metastatic process, a vast amount of work has focused on the role of the epithelial to mesenchymal transition (EMT), which, in experimental models, confers tumor cells with invasive and metastatic abilities, resistance to therapies, as well as cancer stem cell phenotype-properties that have a major impact on cancer prognosis. Searching "EMT and cancer" in PubMed retrieves thousands of original research articles, yet, we haven't answered the most basic question in the field: has EMT any relevance in human tumors?

Dichotomy effects of Akt signaling in breast cancer

BACKGROUND

The oncogenic roles contributed by the Akt/PKB kinase family remain controversial and presumably depend on cell context, but are perceived to be modulated by an interplay and net balance between various isoforms. This study is intended to decipher whether distinct Akt kinase isoforms exert either redundant or unique functions in regulating neoplastic features of breast cancer cells, including epithelial-mesenchymal transition (EMT), cell motility, and stem/progenitor cell expansion.

RESULTS

We demonstrate that overactivation of Akt signaling in nonmalignant MCF10A cells and in primary cultures of normal human mammary epithelial tissue results in previously unreported inhibitory effects on EMT, cell motility and stem/progenitor cell expansion. Importantly, this effect is largely redundant and independent of Akt isoform types. However, using a series of isogenic cell lines derived from MCF-10A cells but exhibiting varying stages of progressive tumorigenesis, we observe that this inhibition of neoplastic behavior can be reversed in epithelial cells that have advanced to a highly malignant state. In contrast to the tumor suppressive properties of Akt, activated Akt signaling in MCF10A cells can rescue cell viability upon treatment with cytotoxic agents. This feature is regarded as tumor-promoting.

CONCLUSION

We demonstrate that Akt signaling conveys novel dichotomy effects in which its oncogenic properties contributes mainly to sustaining cell viability, as opposed to the its tumor suppressing effects, which are mediated by repressing EMT, cell motility, and stem/progenitor cell expansion. While the former exerts a tumor-enhancing effect, the latter merely acts as a safeguard by restraining epithelial cells at the primary sites until metastatic spread can be moved forward, a process that is presumably dictated by the permissive tumor microenvironment or additional oncogenic insults.

Adaptive immune responses associated with breast cancer relapse

The generation, survival, and differentiation of breast cancer stem cells (BCSC) in immunocompetent hosts remain elusive. Some investigators have shown that BCSC can be induced from epithelial tumor cells by the pathologic epithelial to mesenchymal transition (EMT). Emerging evidence suggests that the induction of EMT among epithelial tumor cells originates from signals produced by the non-tumor cells that constitute the tumor microenvironment, including the immune effectors that infiltrate the tumors. Thus, this suggests that the immune system not only has anti-tumor function, but also paradoxically immunoedits tumors, facilitating tumor escape and progression. Indeed, many studies in human breast cancers show both positive and negative associations between the infiltration of various immune effectors (e.g., CD4 and CD8 T cells) and the propensity to relapse with metastatic disease. These observations suggest that distinct types of immune effector cells may induce or inhibit tumor relapse. This review focuses on recent advances in identifying components of the immune system that may directly induce tumor escape and relapse. We propose that levels of interferon (IFN)-γ production or levels of the expression of IFN-γ receptor α on tumor cells may determine whether tumor inhibitory or relapse-promoting effect of IFN-γ may prevail.

An in vivo model of epithelial to mesenchymal transition reveals a mitogenic switch

The epithelial to mesenchymal transition (EMT) is a process by which differentiated epithelial cells transition to a mesenchymal phenotype. EMT enables the escape of epithelial cells from the rigid structural constraints of the tissue architecture to a phenotype more amenable to cell migration and, therefore, invasion and metastasis. We characterized an in vivo model of EMT and discovered that marked changes in mitogenic signaling occurred during this process. DNA microarray analysis revealed that the expression of a number of genes varied significantly between post-EMT and pre-EMT breast cancer cells. Post-EMT cancer cells upregulated mRNA encoding c-Met and the PDGF and LPA receptors, and acquired increased responsiveness to HGF, PDGF, and LPA. This rendered the post-EMT cells responsive to the growth inhibitory effects of HGF, PDGF, and LPA receptor inhibitors/antagonists. Furthermore, post-EMT cells exhibited decreased basal Raf and Erk phosphorylation, and in comparison to pre-EMT cells, their proliferation was poorly inhibited by a MEK inhibitor. These studies suggest that therapies need to be designed to target both pre-EMT and post-EMT cancer cells and that signaling changes in post-EMT cells may allow them to take advantage of paracrine signaling from the stroma in vivo.

Immune microenvironment in tumor progression: characteristics and challenges for therapy

The tumor microenvironment plays a critical role in cancer development, progression, and control. The molecular and cellular nature of the tumor immune microenvironment influences disease outcome by altering the balance of suppressive versus cytotoxic responses in the vicinity of the tumor. Recent developments in systems biology have improved our understanding of the complex interactions between tumors and their immunological microenvironment in various human cancers. Effective tumor surveillance by the host immune system protects against disease, but chronic inflammation and tumor “immunoediting” have also been implicated in disease development and progression. Accordingly, reactivation and maintenance of appropriate antitumor responses within the tumor microenvironment correlate with a good prognosis in cancer patients. Improved understanding of the factors that shape the tumor microenvironment will be critical for the development of effective future strategies for disease management. The manipulation of these microenvironmental factors is already emerging as a promising tool for novel cancer treatments. In this paper, we summarize the various roles of the tumor microenvironment in cancer, focusing on immunological mediators of tumor progression and control, as well as the significant challenges for future therapies.

The three M's: melanoma, microphthalmia-associated transcription factor and microRNA

Studies examining intratumor heterogeneity have indicated that several cancer types, including melanoma, can display phenotypic plasticity, corresponding to their capacity to undergo transient reversible cellular changes. Conceptual models constructed to explain the process of cancer propagation differ in their treatment of intratumor heterogeneity. Recent observations of reversible phenotypic heterogeneity in melanoma have led to the proposal of a novel 'phenotypic plasticity' model of cancer propagation. Microphthalmia-associated transcription factor (MITF), the melanocyte 'lineage-specific' transcription factor, has emerged as one of the central players in melanoma phenotypic plasticity. Here we discuss the conceptual models suggested to explain the relations between MITF and melanoma plasticity, in addition to the complex regulatory roles that MITF plays in melanocytes and melanoma development. Finally, we provide an in-depth literature survey of microRNAs (miRNAs) involved in MITF activity, melanoma propagation and metastasis, in addition to their potential use as agents of personalized therapy.

Inflammation linking EMT and cancer stem cells

Similar to actors changing costumes during a performance, cancer cells undergo many rapid changes during the process of tumor metastasis, including epithelial-mesenchymal transition (EMT), acquisition of cancer stem cells (CSCs) properties, and mesenchymal-epithelial transition (MET). Such changes allow the tumor to compete with the normal microenvironment to overcome anti-tumorigenic pressures. Then, once tissue homeostasis is lost, the altered microenvironment, like that accompanying inflammation, can itself become a potent tumor promoter. This review will discuss the changes that cancer cells undergo in converting from EMT to CSCs in an inflammation microenvironment, to understand the mechanisms behind invasion and metastasis and provide insights into prevention of metastasis.

Metformin: an emerging new therapeutic option for targeting cancer stem cells and metastasis

Metastasis is an intricate process by which a small number of cancer cells from the primary tumor site undergo numerous alterations, which enables them to form secondary tumors at another and often multiple sites in the host. Transition of a cancer cell from epithelial to mesenchymal phenotype is thought to be the first step in the progression of metastasis. Recently, the recognition of cancer stem cells has added to the perplexity in understanding metastasis, as studies suggest cancer stem cells to be the originators of metastasis. All current and investigative drugs have been unable to prevent or reverse metastasis, as a result of which most metastatic cancers are incurable. A potential drug that can be considered is metformin, an oral hypoglycemic drug. In this review we discuss the potential of metformin in targeting both epithelial to mesenchymal transition and cancer stem cells in combating cancer metastases.

EMT and stem cell-like properties associated with HIF-2α are involved in arsenite-induced transformation of human bronchial epithelial cells

BACKGROUND

Arsenic is well-established as a human carcinogen, but the molecular mechanisms leading to arsenic-induced carcinogenesis are complex and elusive. It is not been determined if the epithelial-mesenchymal transition (EMT) and stem cell-like properties contribute in causing to carcinogen-induced malignant transformation and subsequent tumor formation.

METHODS

To investigate the molecular mechanisms underlying EMT and the emergence of cancer stem cell-like properties during neoplastic transformation of human bronchial epithelial (HBE) cells induced by chronic exposure to arsenite. HBE cells were continuously exposed to arsenite. Spheroid formation assays and analyses of side populations (SPs) were performed to confirm that arsenite induces the acquired EMT and cancer stem cell-like phenotype. Treated HBE cells were molecularly characterized by RT-PCR, Western blots, immunofluorescence, Southwestern assays, reporter assays, and chromatin immunoprecipitation.

RESULTS

With chronic exposure to arsenite, HBE cells undergo an EMT and then acquire a malignant cancer stem cell-like phenotype. Twist1 and Bmi1 are involved in arsenite-induced EMT. The process is directly regulated by HIF-2α. The self-renewal genes, Oct4, Bmi1, and ALDH1, are necessary for arsenite-mediated maintenance of stem cells.

CONCLUSIONS

EMT, regulated by HIF-2α, and the development of a cancer stem cell-like phenotype are associated with arsenite-induced transformation of HBE cells.

EMT inducers catalyze malignant transformation of mammary epithelial cells and drive tumorigenesis towards claudin-low tumors in transgenic mice

The epithelial-mesenchymal transition (EMT) is an embryonic transdifferentiation process consisting of conversion of polarized epithelial cells to motile mesenchymal ones. EMT–inducing transcription factors are aberrantly expressed in multiple tumor types and are known to favor the metastatic dissemination process. Supporting oncogenic activity within primary lesions, the TWIST and ZEB proteins can prevent cells from undergoing oncogene-induced senescence and apoptosis by abolishing both p53- and RB-dependent pathways. Here we show that they also downregulate PP2A phosphatase activity and efficiently cooperate with an oncogenic version of H-RAS in malignant transformation of human mammary epithelial cells. Thus, by down-regulating crucial tumor suppressor functions, EMT inducers make cells particularly prone to malignant conversion. Importantly, by analyzing transformed cells generated in vitro and by characterizing novel transgenic mouse models, we further demonstrate that cooperation between an EMT inducer and an active form of RAS is sufficient to trigger transformation of mammary epithelial cells into malignant cells exhibiting all the characteristic features of claudin-low tumors, including low expression of tight and adherens junction genes, EMT traits, and stem cell–like characteristics. Claudin-low tumors are believed to be the most primitive breast malignancies, having arisen through transformation of an early epithelial precursor with inherent stemness properties and metaplastic features. Challenging this prevailing view, we propose that these aggressive tumors arise from cells committed to luminal differentiation, through a process driven by EMT inducers and combining malignant transformation and transdifferentiation.

The epithelial-mesenchymal transition (EMT) is essential to germ layer formation and cell migration in the early vertebrate embryo. EMT is aberrantly reactivated under pathological conditions, including fibrotic disease and cancer progression. In the latter process, EMT is known to promote invasion and metastatic dissemination of tumor cells. EMT is orchestrated by a variety of embryonic transcription factors called EMT inducers. Among these, the TWIST and ZEB proteins are known to be frequently reactivated during tumor development. We here report in vitro and in vivo observations demonstrating that activation of these factors fosters cell transformation and primary tumor growth by alleviating key oncosuppressive mechanisms, thereby minimizing the number of events required for acquisition of malignant properties. In a model of breast cancer, cooperation between a single EMT inducer and a single mitogenic oncoprotein is sufficient to transform mammary epithelial cells into malignant cells and to drive the development of aggressive and undifferentiated tumors. Overall, these data underscore the oncogenic role of embryonic transcription factors in initiating the development of poor-prognosis neoplasms by promoting both cell transformation and dedifferentiation.

Snail overexpression induces an epithelial to mesenchymal transition and cancer stem cell-like properties in SCC9 cells

Local invasiveness and distant metastasis are critical factors that contribute to oral squamous cell carcinoma-related deaths. Increasing evidence has shown that the epithelial to mesenchymal transition (EMT) is involved in cancer progression and is associated with the 'stemness' of cancer cells. Snail is a transcriptional factor that can induce EMT and preserve stem-cell function, which may induce resistance to radio- and chemotherapies in the cells. In the present study, SCC9 cells were transfected with an empty vector or a vector encoding human Snail (SCC9-S). Overexpression of Snail induced SCC9 cells to undergo EMT, in which the cells presented a fibroblast-like appearance, downregulated the epithelial markers E-cadherin and β-catenin, upregulated the mesenchymal marker vimentin, and associated with highly invasive and metastatic properties. Furthermore, the induction of EMT promoted cancer stem cell (CSC)-like characteristics in the SCC9-S cells, such as low proliferation, self-renewal, and CSC-like markers expression. These results indicate that overexpression of Snail induces EMT and promotes CSC-like traits in the SCC9 cells. Further understanding the role of Snail in cancer progression may reveal new targets for the prevention or therapy of oral cancers.

Breast cancer stem cells: obstacles to therapy

Only a fraction of the cells in a breast tumour are able to seed new tumour growth. These so-called breast cancer stem cells (bCSCs) are characterised by a number of discrete functional properties, some of which impact on therapeutic strategies aimed at eliminating these cells from tumours. Here we discuss how recent experimental evidence indicates that phenotypic plasticity is a central feature of tumour cell heterogeneity and drug resistance, traits that must be overcome in order to efficiently target bCSCs as a therapy for breast cancer. We propose that a better understanding of this fundamental property of breast cancer stem cells, over and above their identification in tumours, is a priority for improvement of patient survival.

Selection of Mesenchymal-Like Metastatic Cells in Primary Tumors - An in silico Investigation

In order to metastasize, cancer cells must undergo phenotypic transition from an anchorage-dependent form to a motile form via a process referred to as epithelial to mesenchymal transition. It is currently unclear whether metastatic cells emerge late during tumor progression by successive accumulation of mutations, or whether they derive from distinct cell populations already present during the early stages of tumorigenesis. Similarly, the selective pressures that drive metastasis are poorly understood. Selection of cancer cells with increased proliferative capacity and enhanced survival characteristics may explain how some transformations promote a metastatic phenotype. However, it is difficult to explain how cancer cells that disseminate can emerge due to such selective pressure, since these cells usually remain dormant for prolonged periods of time. In the current study, we have used in silico modeling and simulation to investigate the hypothesis that mesenchymal-like cancer cells evolve during the early stages of primary tumor development, and that these cells exhibit survival and proliferative advantages within the tumor microenvironment. In an agent-based tumor microenvironment model, cancer cell agents with distinct sets of attributes governing nutrient consumption, proliferation, apoptosis, random motility, and cell adhesion were allowed to compete for space and nutrients. These simulation data indicated that mesenchymal-like cancer cells displaying high motility and low adhesion proliferate more rapidly and display a survival advantage over epithelial-like cancer cells. Furthermore, the presence of mesenchymal-like cells within the primary tumor influences the macroscopic properties, emergent morphology, and growth rate of tumors.

MiR-21 regulates epithelial-mesenchymal transition phenotype and hypoxia-inducible factor-1α expression in third-sphere forming breast cancer stem cell-like cells

Cancer stem cells (CSCs) are predicted to be critical drivers of tumor progression due to their "stemness", but the molecular mechanism of CSCs in regulating metastasis remains to be elucidated. Epithelial-mesenchymal transition (EMT), hypoxia-inducible factor (HIF)-1α, and miR-21, all of which contribute to cell migration for metastasis, are interrelated with CSCs. In the present study, third-sphere forming (3-S) CSC-like cells, which showed elevated CSC surface markers (ALDH1(+) and CD44(+)/CD24(-/low)) and sphereforming capacity as well as migration and invasion capacities, were cultured and isolated from breast cancer MCF-7 parental cells, to evaluate the role of miR-21 in regulating the CSC-like cell biological features, especially EMT. EMT, which was assessed by overexpression of mesenchymal cell markers (N-cadherin, Vimentin, alpha-smooth muscle actin [α-SMA]) and suppression of epithelial cell marker (E-cadherin), was induced in 3-S CSC-like cells. Moreover, both of HIF-1α and miR-21 were upregulated in the CSC-like cells. Interestingly, antagonism of miR-21 by antagomir led to reversal of EMT, downexpression of HIF-1α, as well as suppression of invasion and migration, which indicates a key role of miR-21 involved in regulate CSC-associated features. In conclusion, we demonstrated that the formation of CSC-like cells undergoing process of EMT-like associated with overexpression of HIF-1α, both of which are regulated by miR-21.

Vaccines targeting cancer stem cells: are they within reach?

Increased appreciation of intraclonal heterogeneity of tumors in the past decade has led to the resurgence of the cancer stem cell hypothesis. This hypothesis also has potential implications for immunologic approaches targeting cancer, and it has been suggested that vaccines targeting cancer stem cells may be essential for durable antitumor immunity. Recent studies have provided novel insights into the nature of antigenic targets expressed on putative cancer stem cells and the capacity of both the innate and the adaptive immune system to target these cells, as well as the associated challenges. While the phenotypic properties of cancer stem cells may be plastic, their stemness and capacity for self-renewal may depend on a limited set of genes. Several of these genes overlap with those regulating stemness in embryonal stem cells and are also emerging as potential oncogenes in some cancers. Immunologic approaches targeting stemness-associated pathways in cancer may provide an important strategy for the prevention of diverse cancers, including those occurring in the context of regenerative therapies.

Sphere formation reverses the metastatic and cancer stem cell phenotype of the murine mammary tumour 4T1, independently of the putative cancer stem cell marker Sca-1

Breast cancer stem cells (BCSCs) initiate and sustain breast cancers, and several putative markers have been proposed to prospectively isolate BCSC from the non-cancer stem cell population. The candidate BCSC marker Sca-1 is a GPI-linked membrane protein expressed on activated lymphocytes, hematopoietic stem cells and mammary stem cells. Sca-1+ cells were purified from the murine mammary tumour cell line 4T1. However, this did not enrich for a stem-like, tumour initiating or metastatic cell population in vitro or in vivo. Sphere formation, which induced high levels of Sca-1, reduced BCSC gene expression with near complete loss of spontaneous metastasis from sphere-derived tumours. This was associated with decreased expression of TGFB2 and reduced activation of the TGFβ signalling pathway in spheres. Both TGFB2 expression in vitro and spontaneous metastasis in vivo could be restored upon re-differentiation of sphere cells by exposure to serum, and this occurred with retention of the majority of Sca-1 expression. We conclude that while putative BCSC, including spheres, can have high Sca-1 expression, Sca-1 itself is not a marker of BCSC in established 4T1 tumours or the cell line.

Leptin-induced epithelial-mesenchymal transition in breast cancer cells requires β-catenin activation via Akt/GSK3- and MTA1/Wnt1 protein-dependent pathways

Perturbations in the adipocytokine profile, especially higher levels of leptin, are a major cause of breast tumor progression and metastasis; the underlying mechanisms, however, are not well understood. In particular, it remains elusive whether leptin is involved in epithelial-mesenchymal transition (EMT). Here, we provide molecular evidence that leptin induces breast cancer cells to undergo a transition from epithelial to spindle-like mesenchymal morphology. Investigating the downstream mediator(s) that may direct leptin-induced EMT, we found functional interactions between leptin, metastasis-associated protein 1 (MTA1), and Wnt1 signaling components. Leptin increases accumulation and nuclear translocation of β-catenin leading to increased promoter recruitment. Silencing of β-catenin or treatment with the small molecule inhibitor, ICG-001, inhibits leptin-induced EMT, invasion, and tumorsphere formation. Mechanistically, leptin stimulates phosphorylation of glycogen synthase kinase 3β (GSK3β) via Akt activation resulting in a substantial decrease in the formation of the GSK3β-LKB1-Axin complex that leads to increased accumulation of β-catenin. Leptin treatment also increases Wnt1 expression that contributes to GSK3β phosphorylation. Inhibition of Wnt1 abrogates leptin-stimulated GSK3β phosphorylation. We also discovered that leptin increases the expression of an important modifier of Wnt1 signaling, MTA1, which is integral to leptin-mediated regulation of the Wnt/β-catenin pathway as silencing of MTA1 inhibits leptin-induced Wnt1 expression, GSK3β phosphorylation, and β-catenin activation. Furthermore, analysis of leptin-treated breast tumors shows increased expression of Wnt1, pGSK3β, and vimentin along with higher nuclear accumulation of β-catenin and reduced E-cadherin expression providing in vivo evidence for a previously unrecognized cross-talk between leptin and MTA1/Wnt signaling in epithelial-mesenchymal transition of breast cancer cells.

Dickkopf-1 inhibits epithelial-mesenchymal transition of colon cancer cells and contributes to colon cancer suppression

This study aimed to determine the expression pattern of dickkopf-1 (Dkk1), a potent inhibitor of Wnt signaling, in colon cancer and to assess the function and mechanism of Dkk1 in tumor progression in vitro and in vivo. We detected the protein expression of Dkk1 and some epithelial-mesenchymal transition (EMT)-associated markers (E-cadherin, vimentin and β-catenin) in 217 tissue samples of human colon cancer, upregulated Dkk1 expression in HCT116 colon cancer cells, and established a nude mouse xenograft model. Dkk1 protein overexpression was inversely related to tumor grade and the presence of metastasis and recurrence of colon cancer. Notably, the expression of Dkk1 was concomitant with reduced immunohistochemical features of EMT (e.g. increased expression of epithelial marker E-cadherin, decreased expression of mesenchymal marker vimentin, and cytoplasmic distribution of β-catenin). Furthermore, Dkk1 overexpression resulted in restoration of the epithelial phenotype, decreased expression of EMT transcription factors Snail and Twist, and decreased expression of markers suggestive of intestinal stem cells (e.g. cluster of differentiation 133 [CD133] and leucine-rich-repeat-containing G-protein-coupled receptor 5 [Lgr5]). Functional analysis showed overexpression of Dkk1 reduced proliferation, migration, and invasion of colon cancer cells. Moreover, upregulation of Dkk1 led to decreased tumor-initiating ability and suppressed colon tumor growth in nude mice. Our findings indicate that Dkk1 can suppress the progression of colon cancer, possibly through EMT inhibition, and could therefore serve as a target for tumor therapy.

Epithelial-mesenchymal transition: general principles and pathological relevance with special emphasis on the role of matrix metalloproteinases

Epithelial-mesenchymal transition (EMT) is a physiological process in which epithelial cells acquire the motile and invasive characteristics of mesenchymal cells. Although EMT in embryonic development is a coordinated, organized process involving interaction between many different cells and tissue types, aspects of the EMT program can be inappropriately activated in response to microenvironmental alterations and aberrant stimuli, and this can contribute to disease conditions including tissue fibrosis and cancer progression. Here we will outline how EMT functions in normal development, how it could be activated in pathologic conditions-especially by matrix metalloproteinases-and how it may be targeted for therapeutic benefit.