Mesenchymal cells reactivate Snail1 expression to drive three-dimensional invasion programs

Dual delivery gene-activated scaffold directs fibroblast activity and keratinocyte epithelization

Fibroblasts are the most abundant cell type in dermal skin and keratinocytes are the most abundant cell type in the epidermis; both play a crucial role in wound remodeling and maturation. We aim to assess the functionality of a novel dual gene activated scaffold (GAS) on human adult dermal fibroblasts (hDFs) and see how the secretome produced could affect human dermal microvascular endothelial cells (HDMVECs) and human epidermal keratinocyte (hEKs) growth and epithelization. Our GAS is a collagen chondroitin sulfate scaffold loaded with pro-angiogenic stromal derived factor (SDF-1α) and/or an anti-aging β-Klotho plasmids. hDFs were grown on GAS for two weeks and compared to gene-free scaffolds. GAS produced a significantly better healing outcome in the fibroblasts than in the gene-free scaffold group. Among the GAS groups, the dual GAS induced the most potent pro-regenerative maturation in fibroblasts with a downregulation in proliferation (twofold, p < 0.05), fibrotic remodeling regulators TGF-β1 (1.43-fold, p < 0.01) and CTGF (1.4-fold, p < 0.05), fibrotic cellular protein α-SMA (twofold, p < 0.05), and fibronectin matrix deposition (twofold, p < 0.05). The dual GAS secretome also showed enhancements of paracrine keratinocyte pro-epithelializing ability (1.3-fold, p < 0.05); basement membrane regeneration through laminin (6.4-fold, p < 0.005) and collagen IV (8.7-fold, p < 0.005) deposition. Our findings demonstrate enhanced responses in dual GAS containing hDFs by proangiogenic SDF-1α and β-Klotho anti-fibrotic rejuvenating activities. This was demonstrated by activating hDFs on dual GAS to become anti-fibrotic in nature while eliciting wound repair basement membrane proteins; enhancing a proangiogenic HDMVECs paracrine signaling and greater epithelisation of hEKs.

Helicobacter pylori-activated fibroblasts as a silent partner in gastric cancer development

The discovery of Helicobacter pylori (Hp) infection of gastric mucosa leading to active chronic gastritis, gastroduodenal ulcers, and MALT lymphoma laid the groundwork for understanding of the general relationship between chronic infection, inflammation, and cancer. Nevertheless, this sequence of events is still far from full understanding with new players and mediators being constantly identified. Originally, the Hp virulence factors affecting mainly gastric epithelium were proposed to contribute considerably to gastric inflammation, ulceration, and cancer. Furthermore, it has been shown that Hp possesses the ability to penetrate the mucus layer and directly interact with stroma components including fibroblasts and myofibroblasts. These cells, which are the source of biophysical and biochemical signals providing the proper balance between cell proliferation and differentiation within gastric epithelial stem cell compartment, when exposed to Hp, can convert into cancer-associated fibroblast (CAF) phenotype. The crosstalk between fibroblasts and myofibroblasts with gastric epithelial cells including stem/progenitor cell niche involves several pathways mediated by non-coding RNAs, Wnt, BMP, TGF-β, and Notch signaling ligands. The current review concentrates on the consequences of Hp-induced increase in gastric fibroblast and myofibroblast number, and their activation towards CAFs with the emphasis to the altered communication between mesenchymal and epithelial cell compartment, which may lead to inflammation, epithelial stem cell overproliferation, disturbed differentiation, and gradual gastric cancer development. Thus, Hp-activated fibroblasts may constitute the target for anti-cancer treatment and, importantly, for the pharmacotherapies diminishing their activation particularly at the early stages of Hp infection.

Microenvironmental Snail1-induced immunosuppression promotes melanoma growth

Melanoma is an aggressive form of skin cancer due to its high metastatic abilities and resistance to therapies. Melanoma cells reside in a heterogeneous tumour microenvironment that acts as a crucial regulator of its progression. Snail1 is an epithelial-to-mesenchymal transition transcription factor expressed during development and reactivated in pathological situations including fibrosis and cancer. In this work, we show that Snail1 is activated in the melanoma microenvironment, particularly in fibroblasts. Analysis of mouse models that allow stromal Snail1 depletion and therapeutic Snail1 blockade indicate that targeting Snail1 in the tumour microenvironment decreases melanoma growth and lung metastatic burden, extending mice survival. Transcriptomic analysis of melanoma-associated fibroblasts and analysis of the tumours indicate that stromal Snail1 induces melanoma growth by promoting an immunosuppressive microenvironment and a decrease in anti-tumour immunity. This study unveils a novel role of Snail1 in melanoma biology and supports its potential as a therapeutic target.

Role of epithelial-mesenchymal transition factor SNAI1 and its targets in ovarian cancer aggressiveness

Ovarian cancer remains the most lethal gynecologic malignancy in the USA. For over twenty years, epithelial-mesenchymal transition (EMT) has been characterized extensively in development and disease. The dysregulation of this process in cancer has been identified as a mechanism by which epithelial tumors become more aggressive, allowing them to survive and invade distant tissues. This occurs in part due to the increased expression of the EMT transcription factor, SNAI1 (Snail). In the case of epithelial ovarian cancer, Snail has been shown to contribute to cancer invasion, stemness, chemoresistance, and metabolic changes. Thus, in this review, we focus on summarizing current findings on the role of EMT (specifically, factors downstream of Snail) in determining ovarian cancer aggressiveness.

SNAI1-expressing fibroblasts and derived-extracellular matrix as mediators of drug resistance in colorectal cancer patients

Resistance to antitumor treatments is one of the most important problems faced by clinicians in the management of colorectal cancer (CRC) patients. Cancer-Associated Fibroblasts (CAFs) are the main producers and remodelers of the extracellular matrix (ECM), which is directly involved in drug resistance mechanisms. Primary Normal Fibroblasts (NFs) and CAFs and cell lines (fibroblasts and tumor cells), were used to generate ECM and to identify its role in the oxaliplatin and cetuximab chemoresistance processes of CRC cells mediated by SNAI1-expressing fibroblasts. Matrices generated by Snai1 KO MEFs (Knockout Mouse Embryonic Fibroblasts) confer less resistance on oxaliplatin and cetuximab than wild-type MEF-derived matrices. Similarly, matrices derived from CAFs cause greater survival of colorectal cancer cells than NF-derived matrices, in a similar way to Snai1 expression levels. In addition, Snail1 expression in fibroblasts regulates drug resistance and metabolism gene expression in tumor cells mediated by ECM. Finally, a series of 531 patients (TCGA) with CRC was used to assess the role of SNAI1 expression in patients' prognosis indicating an association between tumor SNAI1 expression and overall survival in colon cancer patients but not in rectal cancer patients. SNAI1 expression in CRC cancer patients, together with in vitro experimentation, suggests the possible use of SNAI1 expression in tumor-associated fibroblasts as a predictive biomarker of response to oxaliplatin and cetuximab treatments in patients with CRC.

Matrix Metalloproteinases Shape the Tumor Microenvironment in Cancer Progression

Cancer progression with uncontrolled tumor growth, local invasion, and metastasis depends largely on the proteolytic activity of numerous matrix metalloproteinases (MMPs), which affect tissue integrity, immune cell recruitment, and tissue turnover by degrading extracellular matrix (ECM) components and by releasing matrikines, cell surface-bound cytokines, growth factors, or their receptors. Among the MMPs, MMP-14 is the driving force behind extracellular matrix and tissue destruction during cancer invasion and metastasis. MMP-14 also influences both intercellular as well as cell-matrix communication by regulating the activity of many plasma membrane-anchored and extracellular proteins. Cancer cells and other cells of the tumor stroma, embedded in a common extracellular matrix, interact with their matrix by means of various adhesive structures, of which particularly invadopodia are capable to remodel the matrix through spatially and temporally finely tuned proteolysis. As a deeper understanding of the underlying functional mechanisms is beneficial for the development of new prognostic and predictive markers and for targeted therapies, this review examined the current knowledge of the interplay of the various MMPs in the cancer context on the protein, subcellular, and cellular level with a focus on MMP14.

Role of fibroblast specific protein 1 expression in the progression of adriamycin-induced glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a commonly occurring cause of steroid-resistant nephrotic syndrome and frequently progresses to renal failure. Podocyte epithelial-mesenchymal transition (EMT) is thought to induce podocyte detachment in glomerular diseases, and severe degeneration and shedding of glomerular podocytes plays a major role in the progression of FSGS. We showed that fibroblast specific protein 1 (FSP1), an EMT marker, is strongly expressed in podocytes of FSGS patients, but the significance of podocyte expression of FSP1 to the pathophysiology of FSGS remained unclear. Here, we investigated FSP1 expression in podocytes from mice with adriamycin (ADR)-induced nephropathy, a murine model of FSGS. The number of FSP1-positive (FSP1+) podocytes was increased in ADR-treated mice and positively correlated with the degree of proteinuria and glomerulosclerosis in ADR-treated mice. ADR-induced FSGS and the attendant proteinuria were significantly ameliorated in FSP1 knockout mice as compared to wild type mice. These findings indicate that podocyte expression of FSP1 plays a crucial role in the pathogenesis of FSGS, which makes FSP1 a potential target for treatment of FSGS.

Emerging roles of MT-MMPs in embryonic development

Membrane-type matrix metalloproteinases (MT-MMPs) are cell membrane-tethered proteinases that belong to the family of the MMPs. Apart from their roles in degradation of the extracellular milieu, MT-MMPs are able to activate through proteolytic processing at the cell surface distinct molecules such as receptors, growth factors, cytokines, adhesion molecules, and other pericellular proteins. Although most of the information regarding these enzymes comes from cancer studies, our current knowledge about their contribution in distinct developmental processes occurring in the embryo is limited. In this review, we want to summarize the involvement of MT-MMPs in distinct processes during embryonic morphogenesis, including cell migration and proliferation, epithelial-mesenchymal transition, cell polarity and branching, axon growth and navigation, synapse formation, and angiogenesis. We also considered information about MT-MMP functions from studies assessed in pathological conditions and compared these data with those relevant for embryonic development.

Snail1 expression in endothelial cells controls growth, angiogenesis and differentiation of breast tumors

Snail1 is a transcriptional factor required for epithelial to mesenchymal transition and activation of cancer-associated fibroblasts (CAF). Apart from that, tumor endothelial cells also express Snail1. Here, we have unraveled the role of Snail1 in this tissue in a tumorigenic context. Methods: We generated transgenic mice with an endothelial-specific and inducible Snail1 depletion. This murine line was crossed with MMTV-PyMT mice that develop mammary gland tumors and the consequence of Snail1 depletion in the endothelium were investigated. We also interfere Snail1 expression in cultured endothelial cells. Results: Specific Snail1 depletion in the endothelium of adult mice does not promote an overt phenotype; however, it delays the formation of mammary gland tumors in MMTV-PyMT mice. These effects are associated to the inability of Snail1-deficient endothelial cells to undergo angiogenesis and to enhance CAF activation in a paracrine manner. Moreover, tumors generated in mice with endothelium-specific Snail1 depletion are less advanced and show a papillary phenotype. Similar changes on onset and tumor morphology are observed by pretreatment of MMTV-PyMT mice with the angiogenic inhibitor Bevacizumab. Human breast papillary carcinomas exhibit a lower angiogenesis and present lower staining of Snail1, both in endothelial and stromal cells, compared with other breast neoplasms. Furthermore, human breast tumors datasets show a strong correlation between Snail1 expression and high angiogenesis. Conclusion: These findings show a novel role for Snail1 in endothelial cell activation and demonstrate that these cells impact not only on angiogenesis, but also on tumor onset and phenotype.

Functional Hierarchy and Cooperation of EMT Master Transcription Factors in Breast Cancer Metastasis

Several master transcription factors (TF) can activate the epithelial-to-mesenchymal transition (EMT). However, their individual and combinatorial contributions to EMT in breast cancer are not defined. We show that overexpression of EMT-TFs individually in epithelial cells upregulated endogenous SNAI2, ZEB1/2, TCF4, and TWIST1/2 as a result of positive feedback mediated in part by suppression of their negative regulator miRNAs miR200s/203/205. We identified TCF4 as a potential new target of miR200s. Expression of ZEB1/2 strongly correlated with the mesenchymal phenotype in breast cancer cells, with the CD24^-/CD44⁺ stemness profile, and with lower expression of core epithelial genes in human breast tumors. Knockdown of EMT-TFs identified the key role of ZEB1 and its functional cooperation with other EMT-TFs in the maintenance of the mesenchymal state. Inducible ZEB1+2 knockdown in xenograft models inhibited pulmonary metastasis, emphasizing their critical role in dissemination from primary site and in extravasation. However, ZEB1+2 depletion one-week after intravenous injection did not inhibit lung colonization, suggesting that ZEB1/2 and EMT are not essential for macrometastatic outgrowth. These results provide strong evidence that EMT is orchestrated by coordinated expression of several EMT-TFs and establish ZEB1 as a key master regulator of EMT and metastasis in breast cancer. IMPLICATIONS: The EMT program is orchestrated by coordinated expression of multiple EMT transcription factors, whereas ZEB1 integrates the EMT master regulatory network and plays the major role in promoting EMT and metastasis.

Role of Endothelial and Mesenchymal Cell Transitions in Heart Failure and Recovery Thereafter

Background: Mechanisms of myocardial recovery are not well elucidated.

Methods: 3-month-old C57/BL6 mice were treated with Angiotensin-II infusion and N (w)-nitro-L-arginine methyl ester in drinking water to induce HF at 5 weeks. These agents were discontinued, and animals studied with echocardiographic, histological and genetic assessment every 2 weeks until week 19. mRNA was extracted from these samples and human pre-post LVAD samples.

Results: Histologic and echo characteristics showed progressive worsening of cardiac function by week 5 and normalization by week 19 accompanied by normalization of the transcriptional profile. Expression of 1,350 genes were upregulated and 3,050 genes down regulated in HF compared to controls; during recovery, this altered gene expression was largely reversed. We focused on genes whose expression was altered during HF but reverted to control levels by Week 19. A gene ontology (GO) analysis of this cohort of genes implicated pathways involved in EndoMT and MEndoT. The cohort of genes that were differentially regulated in heart failure recovery in the murine model, were similarly regulated in human myocardial samples obtained pre- and post-placement of a left ventricular assist device (LVAD). Human end stage HF myocardial samples showed cells with dual expressed VE-Cadherin and FSP-1 consistent with cell fate transition. Furthermore, we observed a reduction in fibrosis, and an increase in endothelial cell density, in myocardial samples pre- and post-LVAD.

Conclusions: Cell fate transitions between endothelial and mesenchymal types contribute to the pathophysiology of heart failure followed by recovery.

Glutamine-Directed Migration of Cancer-Activated Fibroblasts Facilitates Epithelial Tumor Invasion

Tumors are complex tissues composed of transformed epithelial cells as well as cancer-activated fibroblasts (CAF) that facilitate epithelial tumor cell invasion. We show here that CAFs and other mesenchymal cells rely much more on glutamine than epithelial tumor cells; consequently, they are more sensitive to inhibition of glutaminase. Glutamine dependence drove CAF migration toward this amino acid when cultured in low glutamine conditions. CAFs also invaded a Matrigel matrix following a glutamine concentration gradient and enhanced the invasion of tumor cells when both cells were cocultured. Accordingly, glutamine directed invasion of xenografted tumors in immunocompromised mice. Stimulation of glutamine-driven epithelial tumor invasion by fibroblasts required previous CAF activation, which involved the TGFβ/Snail1 signaling axis. CAFs moving toward Gln presented a polarized Akt2 distribution that was modulated by the Gln-dependent activity of TRAF6 and p62 in the migrating front, and depletion of these proteins prevented Akt2 polarization and Gln-driven CAF invasion. Our results demonstrate that glutamine deprivation promotes CAF migration and invasion, which in turn facilitates the movement of tumor epithelial cells toward nutrient-rich territories. These results provide a novel molecular mechanism for how metabolic stress enhances invasion and metastasis. SIGNIFICANCE: Cancer-associated fibroblasts migrate and invade toward free glutamine and facilitate invasion of tumor epithelial cells, accounting for their movement away from the hostile conditions of the tumor towards nutrient-rich adjacent tissues. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/2/438/F1.large.jpg.

Endothelial to mesenchymal transition (EndMT) and vascular remodeling in pulmonary hypertension and idiopathic pulmonary fibrosis

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, and irreversible fibrotic disease associated with respiratory failure. The disease remains idiopathic, but repeated alveolar epithelium injury, disruption of alveolar-capillary integrity, abnormal vascular repair, and pulmonary vascular remodeling are considered possible pathogenic mechanisms. Also, the development of comorbidities such as pulmonary hypertension (PH) could further impact disease outcome, quality of life and survival rates in IPF.

AREAS COVERED

The current review provides a comprehensive literature survey of the mechanisms involved in the development and manifestations of IPF and their links to PH pathology. This review also provides the current understanding of molecular mechanisms that link the two pathologies and will specifically decipher the role of endothelial to mesenchymal transition (EndMT) along with the possible triggers of EndMT. The possibility of targeting EndMT as a therapeutic option in IPF is discussed.

EXPERT OPINION

With a steady increase in prevalence and mortality, IPF is no longer considered a rare disease. Thus, it is of utmost importance and urgency that the underlying profibrotic pathways and mechanisms are fully understood, to enable the development of novel therapeutic strategies.

Kidney allograft fibrosis: what we learned from latest translational research studies

To add new molecular and pathogenetic insights into the biological machinery associated to kidney allograft fibrosis is a major research target in nephrology and organ transplant translational medicine. Interstitial fibrosis associated to tubular atrophy (IF/TA) is, in fact, an inevitable and progressive process that occurs in almost every type of chronic allograft injury (particularly in grafts from expanded criteria donors) characterized by profound remodeling and excessive production/deposition of fibrillar extracellular matrix (ECM) with a great clinical impact. IF/TA is detectable in more than 50% of kidney allografts at 2 years. However, although well studied, the complete cellular/biological network associated with IF/TA is only partially evaluated. In the last few years, then, thanks to the introduction of new biomolecular technologies, inflammation in scarred/fibrotic parenchyma areas (recently acknowledged by the BANFF classification) has been recognized as a pivotal element able to accelerate the onset and development of the allograft chronic damage. Therefore, in this review, we focused on some new pathogenetic elements involved in graft fibrosis (including epithelial/endothelial to mesenchymal transition, oxidative stress, activation of Wnt and Hedgehog signaling pathways, fatty acids oxidation and cellular senescence) that, in our opinion, could become in future good candidates as potential biomarkers and therapeutic targets.

Slug, a Cancer-Related Transcription Factor, is Involved in Vascular Smooth Muscle Cell Transdifferentiation Induced by Platelet-Derived Growth Factor-BB During Atherosclerosis

Background Heart attacks and stroke often result from occlusive thrombi following the rupture of vulnerable atherosclerotic plaques. Vascular smooth muscle cells (VSMCs) play a pivotal role in plaque vulnerability because of their switch towards a proinflammatory/macrophage-like phenotype when in the context of atherosclerosis. The prometastatic transcription factor Slug/Snail2 is a critical regulator of cell phenotypic transition. Here, we aimed to investigate the role of Slug in the transdifferentiation process of VSMCs occurring during atherogenesis. Methods and Results In rat and human primary aortic smooth muscle cells, Slug protein expression is strongly and rapidly increased by platelet-derived growth factor-BB (PDGF-BB). PDGF-BB increases Slug protein without affecting mRNA levels indicating that this growth factor stabilizes Slug protein. Immunocytochemistry and subcellular fractionation experiments reveal that PDGF-BB triggers a rapid accumulation of Slug in VSMC nuclei. Using pharmacological tools, we show that the PDGF-BB-dependent mechanism of Slug stabilization in VSMCs involves the extracellular signal-regulated kinase 1/2 pathway. Immunohistochemistry experiments on type V and type VI atherosclerotic lesions of human carotids show smooth muscle-specific myosin heavy chain-/Slug-positive cells surrounding the prothrombotic lipid core. In VSMCs, Slug siRNAs inhibit prostaglandin E2 secretion and prevent the inhibition of cholesterol efflux gene expression mediated by PDGF-BB, known to be involved in plaque vulnerability and/or thrombogenicity. Conclusions Our results highlight, for the first time, a role of Slug in aortic smooth muscle cell transdifferentiation and enable us to consider Slug as an actor playing a role in the atherosclerotic plaque progression towards a life-threatening phenotype. This also argues for common features between acute cardiovascular events and cancer.

Controversies around epithelial-mesenchymal plasticity in cancer metastasis

Experimental evidence accumulated over decades has implicated epithelial-mesenchymal plasticity (EMP), which collectively encompasses epithelial-mesenchymal transition and the reverse process of mesenchymal-epithelial transition, in tumour metastasis, cancer stem cell generation and maintenance, and therapeutic resistance. However, the dynamic nature of EMP processes, the apparent need to reverse mesenchymal changes for the development of macrometastases and the likelihood that only minor cancer cell subpopulations exhibit EMP at any one time have made such evidence difficult to accrue in the clinical setting. In this Perspectives article, we outline the existing preclinical and clinical evidence for EMP and reflect on recent controversies, including the failure of initial lineage-tracing experiments to confirm a major role for EMP in dissemination, and discuss accumulating data suggesting that epithelial features and/or a hybrid epithelial-mesenchymal phenotype are important in metastasis. We also highlight strategies to address the complexities of therapeutically targeting the EMP process that give consideration to its spatially and temporally divergent roles in metastasis, with the view that this will yield a potent and broad class of therapeutic agents.

Overexpression of SLFN5 induced the epithelial-mesenchymal transition in human lung cancer cell line A549 through β-catenin/Snail/E-cadherin pathway

Lung cancer is a disease with increasing morbidity worldwide in recent years. Approaches such as chemotherapy and biological targeting for its treatment are urgently needed. Epithelial-mesenchymal transition (EMT) is an important initiation stage for tumor cells to acquire invasive and metastatic abilities. Increasing findings have shown that human schlafen family member 5 (SLFN5) plays a key role in malignant tumors. However, the role of SLFN5 in lung cancer cells is not completely elucidated yet. In this study, overexpression or knockdown of SLFN5 gene were induced by lentiviral transfection in human lung cancer cell line A549, then the EMT of A549 was detected by green fluorescent protein labeling method, the migrative and invasive abilities were evaluated via transwell and wound-healing tests in vitro and chick chorioallantoic membrane inoculation in vivo, and the possible mechanism was studied by quantitative real-time PCR and Western blotting. Our results demonstrated that overexpression of SLFN5 promoted the morphology transformation of A549 from epithelial to mesenchymal, as well as migration and invasion. However, knockdown of SLFN5 resulted in the opposite results. Moreover, with the development of EMT after SLFN5 was overexpressed, A549 exhibited enhanced translocation of β-catenin from membrane to cytoplasm or nucleus, with higher level of EMT-related transcription factor Snail, and lower expression of adhesin E-cadherin. Together these results suggest that SLFN5 may act as a synergist in lung cancer cell tumorigenesis and progression, providing a potential target for developing drugs for lung cancer therapy in future.

MT1-MMP-dependent cell migration: proteolytic and non-proteolytic mechanisms

Membrane-type 1 matrix metalloproteinase (MT1-MMP) is a type I transmembrane proteinase that belongs to the matrix metalloproteinase (MMP) family. It is a potent modifier of cellular microenvironment and promotes cell migration and invasion of a wide variety of cell types both in physiological and pathological conditions. It promotes cell migration by degrading extracellular matrix on the cell surface and creates a migration path, by modifying cell adhesion property by shedding cell adhesion molecules to increase cell motility, and by altering cellular metabolism. Thus, MT1-MMP is a multifunctional cell motility enhancer. In this review, we will discuss the current understanding of the proteolytic and non-proteolytic mechanism of MT1-MMP-dependent cell migration.

SLFN5 suppresses cancer cell migration and invasion by inhibiting MT1-MMP expression via AKT/GSK-3β/β-catenin pathway

Human SLFN5 inhibits invasions of IFNα-sensitive renal clear-cell carcinoma and melanoma cells. However, whether this inhibition is confined to these IFNα-sensitive cancers is unclear. Here we show that SLFN5 expressions on both mRNA and protein levels are significantly higher in non/low-invasive cancer cell lines (breast cancer cell line MCF7, colorectal cancer cell line HCT116 and lung cancer cell line A549) than in highly-invasive cancer cell lines (fibrosarcoma cell line HT1080 and renal clear cell cancer cell line 786-0). SLFN5 knockdown in non/low-invasive cancer cell lines enhanced MT1-MMP expression and increased migration and invasion in vitro, and in vivo. Furthermore, SLFN5 overexpression in HT1080 and 786-0 inhibited MT1-MMP expression and repressed migration and invasion. MT1-MMP is instrumental in SLFN5-controlled inhibition of cancer cell migration and invasion, as shown by MT1-MMP-knockdown and -overexpression analyses. SLFN5 knockdown activated AKT/GSK-3β/β-catenin pathway by promotion AKT phosphorylation and subsequent GSK-3β phosphorylation, further β-catenin translocation into nucleus as un-phosphorylated protein at Ser33, 37 and 45 and Thr41 sites. This is the first study to report that SLFN5 inhibits cancer migration and invasiveness in several common cancer cell lines by repressing MT1-MMP expression via the AKT/GSK-3β/β-catenin signalling pathway, suggesting that SLFN5 plays wide inhibitory roles in various cancers.

Endothelial cell activation on 3D-matrices derived from PDGF-BB-stimulated fibroblasts is mediated by Snail1

Carcinomas, such as colon cancer, initiate their invasion by rescuing the innate plasticity of both epithelial cells and stromal cells. Although Snail is a transcriptional factor involved in the Epithelial-Mesenchymal Transition, in recent years, many studies have also identified the major role of Snail in the activation of Cancer-Associated Fibroblast (CAF) cells and the remodeling of the extracellular matrix. In CAFs, Platelet-derived growth factor (PDGF) receptor signaling is a major functional determinant. High expression of both SNAI1 and PDGF receptors is associated with poor prognosis in cancer patients, but the mechanism(s) that underlie these connections are not understood. In this study, we demonstrate that PDGF-activated fibroblasts stimulate extracellular matrix (ECM) fiber remodeling and deposition. Furthermore, we describe how SNAI1, through the FAK pathway, is a necessary factor for ECM fiber organization. The parallel-oriented fibers are used by endothelial cells as “tracks”, facilitating their activation and the creation of tubular structures mimicking in vivo capillary formation. Accordingly, Snail1 expression in fibroblasts was required for the co-adjuvant effect of these cells on matrix remodeling and neoangiogenesis when co-xenografted in nude mice. Finally, in tumor samples from colorectal cancer patients a direct association between stromal SNAI1 expression and the endothelial marker CD34 was observed. In summary, our results advance the understanding of PDGF/SNAI1-activated CAFs in matrix remodeling and angiogenesis stimulation.

Insulin/Snail1 axis ameliorates fatty liver disease by epigenetically suppressing lipogenesis

Insulin stimulates lipogenesis but insulin resistance is also associated with increased hepatic lipogenesis in obesity. However, the underlying mechanism remains poorly characterized. Here, we show a noncanonical insulin-Snail1 pathway that suppresses lipogenesis. Insulin robustly upregulates zinc-finger protein Snail1 in a PI 3-kinase-dependent manner. In obesity, the hepatic insulin-Snail1 cascade is impaired due to insulin resistance. Hepatocyte-specific deletion of Snail1 enhances insulin-stimulated lipogenesis in hepatocytes, exacerbates dietary NAFLD in mice, and attenuates NAFLD-associated insulin resistance. Liver-specific overexpression of Snail1 has the opposite effect. Mechanistically, Snail1 binds to the fatty acid synthase promoter and recruits HDAC1/2 to induce deacetylation of H3K9 and H3K27, thereby repressing fatty acid synthase promoter activity. Our data suggest that insulin pathways bifurcate into canonical (lipogenic) and noncanonical (anti-lipogenesis by Snail1) two arms. The noncanonical arm counterbalances the canonical arm through Snail1-elicited epigenetic suppression of lipogenic genes. Impairment in the insulin-Snail1 arm may contribute to NAFLD in obesity.

SNAIL is a key regulator of alveolar rhabdomyosarcoma tumor growth and differentiation through repression of MYF5 and MYOD function

Rhabdomyosarcoma (RMS) is a mesenchymal tumor of soft tissue in children that originates from a myogenic differentiation defect. Expression of SNAIL transcription factor is elevated in the alveolar subtype of RMS (ARMS), characterized by a low myogenic differentiation status and high aggressiveness. In RMS patients SNAIL level increases with higher stage. Moreover, SNAIL level negatively correlates with MYF5 expression. The differentiation of human ARMS cells diminishes SNAIL level. SNAIL silencing in ARMS cells inhibits proliferation and induces differentiation in vitro, and thereby completely abolishes the growth of human ARMS xenotransplants in vivo. SNAIL silencing induces myogenic differentiation by upregulation of myogenic factors and muscle-specific microRNAs, such as miR-206. SNAIL binds to the MYF5 promoter suppressing its expression. SNAIL displaces MYOD from E-box sequences (CANNTG) that are associated with genes expressed during differentiation and G/C rich in their central dinucleotides. SNAIL silencing allows the re-expression of MYF5 and canonical MYOD binding, promoting ARMS cell myogenic differentiation. In differentiating ARMS cells SNAIL forms repressive complex with histone deacetylates 1 and 2 (HDAC1/2) and regulates their expression. Accordingly, in human myoblasts SNAIL silencing induces differentiation by upregulation of myogenic factors. Our data clearly point to SNAIL as a key regulator of myogenic differentiation and a new promising target for future ARMS therapies.

Hic-5 expression is a major indicator of cancer cell morphology, migration, and plasticity in three-dimensional matrices

The focal adhesion proteins Hic-5 and paxillin have been previously identified as key regulators of MDA-MB-231 breast cancer cell migration and morphologic mesenchymal-amoeboid plasticity in three-dimensional (3D) extracellular matrices (ECMs). However, their respective roles in other cancer cell types have not been evaluated. Herein, utilizing 3D cell-derived matrices and fibronectin-coated one-dimensional substrates, we show that across a variety of cancer cell lines, the level of Hic-5 expression serves as the major indicator of the cells primary morphology, plasticity, and in vitro invasiveness. Domain mapping studies reveal sites critical to the functions of both Hic-5 and paxillin in regulating phenotype, while ectopic expression of Hic-5 in cell lines with low endogenous levels of the protein is sufficient to induce a Rac1-dependent mesenchymal phenotype and, in turn, increase amoeboid-mesenchymal plasticity and invasion. We show that the activity of vinculin, when coupled to the expression of Hic-5 is required for the mesenchymal morphology in the 3D ECM. Taken together, our results identify Hic-5 as a critical modulator of tumor cell phenotype that could be utilized in predicting tumor cell migratory and invasive behavior in vivo.

SNAIL1 action in tumor cells influences macrophage polarization and metastasis in breast cancer through altered GM-CSF secretion

The EMT inducer SNAIL1 regulates breast cancer metastasis and its expression in human primary breast tumor predicts for poor outcomes. During tumor progression SNAIL1 has multiple effects in tumor cells that can impact metastasis. An inflammatory tumor microenvironment also impacts metastasis and recently SNAIL1 has been implicated as modulating the secretion of cytokines that can influence the tumor immune infiltrate. Using a spontaneous genetic model of breast cancer metastasis and syngeneic orthotopic transplant experiments we show that the action of SNAIL1 in primary breast tumor cells is required for breast tumor growth and metastasis. It does so, in part, by regulating production of GM-CSF, IL1α, IL-6, and TNFα by breast cancer cells. The SNAIL1-dependent tumor cell secretome modulates the primary tumor-associated macrophage (TAM) polarization. GM-CSF alone modulates TAM polarization and impacts breast cancer metastasis in vivo. This study highlights another role for breast tumor SNAIL1 in cancer progression to metastasis—modulation of the immune microenvironment of primary breast tumors.

A right-handed signalling pathway drives heart looping in vertebrates

The majority of animals show external bilateral symmetry, precluding the observation of multiple internal left-right (L/R) asymmetries that are fundamental for organ packaging and function1,2. In vertebrates, left identity is mediated by the left-specific Nodal-Pitx2 axis that is repressed on the right-hand side by the epithelial-mesenchymal transition (EMT) inducer Snail13,4. Despite some existing evidence3,5, it remains unclear whether an equivalent instructive pathway provides right-hand specific information to the embryo. Here we show that in zebrafish, BMP mediates the L/R asymmetric activation of another EMT inducer, Prrx1a, in the lateral plate mesoderm (LPM) with higher levels on the right. Prrx1a drives L/R differential cell movements towards the midline leading to a leftward displacement of the cardiac posterior pole through an actomyosin-dependent mechanism. Downregulation of Prrx1a prevents heart looping and leads to mesocardia. Two parallel and mutually repressed pathways, respectively driven by Nodal and BMP on the left and right LPM, converge on the asymmetric activation of Pitx2 and Prrx1, two transcription factors that integrate left and right information to govern heart morphogenesis. This mechanism is conserved in the chicken embryo and, in the mouse, Snail1 fulfills the role played by Prrx1 in fish and chick. Thus, a differential L/R EMT produces asymmetric cell movements and forces, more prominent from the right, that drive heart laterality in vertebrates.

EGFR is involved in dermatofibrosarcoma protuberans progression to high grade sarcoma

Dermatofibrosarcoma protuberans (DFSP), amounting to 6% of all soft tissue sarcomas, has a slow growth rate, contrasting with a likelihood for local recurrence and a 10-20% evolution to higher-grade sarcoma, or "transformed DFSP" (DFSP-T). At molecular level, the characteristic COL1A1-PDGFB rearrangement, leading to sustained PDGFR signaling, is not linked to the evolutive potential. Here, we studied EGFR, another tyrosine kinase receptor, using laser-microdissection to select the different histologic components of DFSP (DFSP center, DFSP infiltrative periphery, DFSP-T higher-grade sarcoma), in 22 patients followed over 3 to 156 months. EGFR protein and mRNA were expressed in 13/22 patients with DFSP or DFSP-T, and increased with tumor progression, both in microdissected areas of higher-grade sarcomas and in microdissected areas of local extension. No cancer-associated EGFR gene mutation or copy-number variation, nor any KRAS, BRAF, NRAS hotspot mutations were found in any microdissected area. Among epithelial-mesenchymal transition factors tested, SNAIL 1/2 had the same expression pattern as EGFR while ZEB1/2 or TWIST1/2 did not. Using a proteome profiler phospho-kinase array on 3 DFSP and 3 DFSP-T cryopreserved tissue samples, EGFR phosphorylation was detected in each case. Among EGFR downstream pathways, we found positive correlations between phosphorylation levels of EGFR and STAT5a/b (r = 0.87, p < 0.05) and TOR (r = 0.95, p < 0.01), but not ERK in the MAPK pathway (r = -0.18, p > 0.70). We thus demonstrated that in DFSP evolution to high grade sarcoma, EGFR and SNAIL were involved, with EGFR activation and signaling through TOR and STAT5a/b downstream effectors, which could lead on to new therapies for advanced DFSP.

Ezrin contributes to cervical cancer progression through induction of epithelial-mesenchymal transition

Cervical cancer is the third most common cancer in females worldwide. The treatment options for advanced cervical cancer are limited, leading to high mortality. Ezrin is a membrane-cytoskeleton-binding protein recently reported to act as a tumor promoter, and we previously indicated that the aberrant localization and overexpression of Ezrin could be an independent effective biomarker for prognostic evaluation of cervical cancers. In this study, we identified Ezrin as a regulator of epithelial-mesenchymal transition (EMT) and metastasis in cervical cancer. Ezrin knock-down inhibited anchorage-independent growth, cell migration, and invasion of cervical cancer cell lines in vitro and in vivo. EMT was inhibited in Ezrin-depleted cells, with up-regulation of E-cadherin and Cytokeratin-18 (CK-18) and down-regulation of mesenchymal markers. Ezrin knock-down also induced Akt phosphorylation. These results implicate Ezrin as an EMT regulator and tumor promoter in cervical cancer, and down-regulation of Ezrin suppressed cervical cancer progression, possibly via the phosphoinositide 3-kinase/Akt pathway. Furthermore, the expression pattern of Ezrin protein was closely related with the lymphovascular invasion status of cervical cancer by immunohistochemistry, and the survival analysis revealed that the cervical cancer patients with the perinuclear Ezrin expression pattern had longer survival time than those with the cytoplasmic Ezrin expression pattern. Ezrin thus represents a promising target for the development of novel and effective strategies aimed at preventing the progression of cervical cancer.

Hesperetin alleviates renal interstitial fibrosis by inhibiting tubular epithelial-mesenchymal transition in vivo and in vitro

Hesperetin (HES) is a flavonoid that has been reported to exert protective effects against cardiac remodeling, lung fibrosis and hepatic fibrosis. However, reports on the effects and potential mechanisms of HES in renal fibrosis are limited. In the present study, a unilateral ureteric obstruction (UUO) mouse model and a transforming growth factor (TGF)-β1-activated normal rat kidney (NRK)-52E cell model were established. HES was subsequently administered to these models to evaluate its anti-fibrotic effects and potential underlying mechanisms of action. The results demonstrated that HES reduced obstruction-induced renal injury and deposition of the extracellular matrix components collagen-I and fibronectin in UUO mouse kidneys (P<0.05). Furthermore, HES treatment significantly suppressed EMT, as evidenced by decreased expression of α-smooth muscle actin and E-cadherin, (P<0.05). Additionally, HES inhibited the hedgehog signaling pathway in UUO mice and TGF-β1-treated NRK-52E cells. The present findings indicate that HES treatment may inhibit EMT and renal fibrosis in vivo and in vitro by antagonizing the hedgehog signaling pathway.

EMT: Present and future in clinical oncology

Epithelial/mesenchymal transition (EMT) has emerged as a key regulator of metastasis by facilitating tumor cell invasion and dissemination to distant organs. Recent evidences support that the reverse mesenchymal/epithelial transition (MET) is required for metastatic outgrowth; moreover, the existence of hybrid epithelial/mesenchymal (E/M) phenotypes is increasingly being reported in different tumor contexts. The accumulated data strongly support that plasticity between epithelial and mesenchymal states underlies the dissemination and metastatic potential of carcinoma cells. However, the translation into the clinics of EMT and epithelial plasticity processes presents enormous challenges and still remains a controversial issue. In this review, we will evaluate current evidences for translational applicability of EMT and depict an overview of the most recent EMT in vivo models, EMT marker analyses in human samples as well as potential EMT therapeutic approaches and ongoing clinical trials. We foresee that standardized analyses of EMT markers in solid and liquid tumor biopsies in addition to innovative tools targeting the E/M states will become promising strategies for future translation to the clinical setting.

Epithelial-to-mesenchymal transition transcription factors in cancer-associated fibroblasts

Beyond inducing epithelial‐to‐mesenchymal transcription (EMT), transcriptional factors of the Snail, ZEB and Twist families (EMT‐TFs) control global plasticity programmes affecting cell stemness and fate. Literature addressing the reactivation of these factors in adult tumour cells is very extensive, as they enable cancer cell plasticity and fuel both tumour initiation and metastatic spread. Incipient data reveal that EMT‐TFs are also expressed in fibroblasts, providing these with additional properties. Here, I will review recent reports on the expression of EMT‐TFs in cancer‐associated fibroblasts (CAFs). The new model suggests that EMT‐TFs can be envisioned as essential metastasis and chemoresistance‐promoting molecules, thereby enabling coordinated plasticity programmes in parenchyma and stroma–tumour compartments.

β-lapachone suppresses tumour progression by inhibiting epithelial-to-mesenchymal transition in NQO1-positive breast cancers

NQO1 is a FAD-binding protein that can form homodimers and reduce quinones to hydroquinones, and a growing body of evidence currently suggests that NQO1 is dramatically elevated in solid cancers. Here, we demonstrated that NQO1 was elevated in breast cancer and that its expression level was positively correlated with invasion and reduced disease free survival (DFS) and overall survival (OS) rates. Next, we found that β-lapachone exerted significant anti-proliferation and anti-metastasis effects in breast cancer cell lines due to its effects on NQO1 expression. Moreover, we revealed that the anti-cancer effects of β-lapachone were mediated by the inactivation of the Akt/mTOR pathway. In conclusion, these results demonstrated that NQO1 could be a useful prognostic biomarker for patients with breast cancer, and its bioactivatable drug, β-lapachone represented a promising new development and an effective strategy for indicating the progression of NQO1-positive breast cancers.

HMEC-1 adopt the mixed amoeboid-mesenchymal migration type during EndMT

The contribution of endothelial cells to scar and fibrotic tissue formation is undisputedly connected to their ability to undergo the endothelial-to-mesenchymal transition (EndMT) towards fibroblast phenotype-resembling cells. The migration model of fibroblasts and fibroblast-resembling cells is still not fully understood. It may be either a Rho/ROCK-independent, an integrin- and MMP-correlated ECM degradation-dependent, a mesenchymal model or Rho/ROCK-dependent, integrin adhesion- and MMP activity-independent, an amoeboid model. Here, we hypothesized that microvascular endothelial cells (HMEC-1) undergoing EndMT adopt an intermediate state of drifting migration model between the mesenchymal and amoeboid protrusive types in the early stages of fibrosis. We characterized the response of HMEC-1 to TGF-β2, a well-known mediator of EndMT within the microvasculature. We observed that TGF-β2 induces up to an intermediate mesenchymal phenotype in HMEC-1. In parallel, MMP-2 is upregulated and is responsible for most proteolytic activity. Interestingly, the migration of HMEC-1 undergoing EndMT is dependent on both ECM degradation and invadosome formation associated with MMP-2 proteolytic activity and Rho/ROCK cytoskeleton contraction. In conclusion, the transition from mesenchymal towards amoeboid movement highlights a molecular plasticity mechanism in endothelial cell migration in skin fibrosis.

Snail reprograms glucose metabolism by repressing phosphofructokinase PFKP allowing cancer cell survival under metabolic stress

Dynamic regulation of glucose flux between aerobic glycolysis and the pentose phosphate pathway (PPP) during epithelial–mesenchymal transition (EMT) is not well-understood. Here we show that Snail (SNAI1), a key transcriptional repressor of EMT, regulates glucose flux toward PPP, allowing cancer cell survival under metabolic stress. Mechanistically, Snail regulates glycolytic activity via repression of phosphofructokinase, platelet (PFKP), a major isoform of cancer-specific phosphofructokinase-1 (PFK-1), an enzyme involving the first rate-limiting step of glycolysis. The suppression of PFKP switches the glucose flux towards PPP, generating NADPH with increased metabolites of oxidative PPP. Functionally, dynamic regulation of PFKP significantly potentiates cancer cell survival under metabolic stress and increases metastatic capacities in vivo. Further, knockdown of PFKP rescues metabolic reprogramming and cell death induced by loss of Snail. Thus, the Snail-PFKP axis plays an important role in cancer cell survival via regulation of glucose flux between glycolysis and PPP.

Cancer cell survival under metabolic stress is a critical step for metastasis. Here, the authors show that under glucose deprivation, Snail, a key regulator of the metastatic process, promotes survival by diverting glucose to the pentose phosphate pathway through repression of phosphofructokinase PFKP.

Snail/Slug-YAP/TAZ complexes cooperatively regulate mesenchymal stem cell function and bone formation

Snail and Slug are zinc-finger transcription factors that play key roles in directing the epithelial-mesenchymal transition (EMT) programs associated with normal development as well as disease progression. More recent work suggests that these EMT-associated transcription factors also modulate the function of both embryonic and adult stem cells. Interestingly, YAP and TAZ, the co-transcriptional effectors of the Hippo pathway, likewise play an important role in stem cell self-renewal and lineage commitment. While direct intersections between the Snail/Slug and Hippo pathways have not been described previously, we recently described an unexpected cooperative interaction between Snail/Slug and YAP/TAZ that controls the self-renewal and differentiation properties of bone marrow-derived mesenchymal stem cells (MSCs), a cell population critical to bone development. Additional studies revealed that both Snail and Slug are able to form binary complexes with either YAP or TAZ that, together, control YAP/TAZ transcriptional activity and function throughout mouse development. Given the more recent observations that MSC-like cell populations are found in association throughout the vasculature where they participate in tissue regeneration, fibrosis and cancer, the Snail/Slug-YAP/TAZ axis is well-positioned to regulate global stem cell function in health and disease.

Adipose Snail1 Regulates Lipolysis and Lipid Partitioning by Suppressing Adipose Triacylglycerol Lipase Expression

Lipolysis provides metabolic fuel; however, aberrant adipose lipolysis results in ectopic lipid accumulation and lipotoxicity. While adipose triacylglycerol lipase (ATGL) catalyzes the first step of lipolysis, its regulation is not fully understood. Here, we demonstrate that adipocyte Snail1 suppresses both ATGL expression and lipolysis. Adipose Snail1 levels are higher in fed mice than in fasted mice and higher in obese mice as opposed to lean mice. Insulin increases Snail1 levels in both murine and human adipocytes, wherein Snail1 binds to the ATGL promoter to repress its expression. Importantly, adipocyte-specific deletion of Snail1 increases adipose ATGL expression and lipolysis, resulting in decreased fat mass and increased liver fat content in mice fed either a normal chow diet or a high-fat diet. Thus, we have identified a Snail1-ATGL axis that regulates adipose lipolysis and fatty acid release, thereby governing lipid partitioning between adipose and non-adipose tissues.

Snail1 is required for the maintenance of the pancreatic acinar phenotype

The Snail1 transcriptional factor is required for correct embryonic development, yet its expression in adult animals is very limited and its functional roles are not evident. We have now conditionally inactivated Snail1 in adult mice and analyzed the phenotype of these animals. Snail1 ablation rapidly altered pancreas structure: one month after Snail1 depletion, acinar cells were markedly depleted, and pancreas accumulated adipose tissue. Snail1 expression was not detected in the epithelium but was in pancreatic mesenchymal cells (PMCs). Snail1 ablation in cultured PMCs downregulated the expression of several β-catenin/Tcf-4 target genes, modified the secretome of these cells and decreased their ability to maintain acinar markers in cultured pancreas cells. Finally, Snail1 deficiency modified the phenotype of pancreatic tumors generated in transgenic mice expressing c-myc under the control of the elastase promoter. Specifically, Snail1 depletion did not significantly alter the size of the tumors but accelerated acinar-ductal metaplasia. These results demonstrate that Snail1 is expressed in PMCs and plays a pivotal role in maintaining acinar cells within the pancreas in normal and pathological conditions.

Snail1-dependent p53 repression regulates expansion and activity of tumour-initiating cells in breast cancer

The zinc-finger transcription factor Snail1 is inappropriately expressed in breast cancer and associated with poor prognosis. While interrogating human databases, we uncovered marked decreases in relapse-free survival of breast cancer patients expressing high Snail1 levels in tandem with wild-type, but not mutant, p53. Using a Snail1 conditional knockout model of mouse breast cancer that maintains wild-type p53, we find that Snail1 plays an essential role in tumour progression by controlling the expansion and activity of tumour-initiating cells in preneoplastic glands and established tumours, whereas it is not required for normal mammary development. Growth and survival of preneoplastic as well as neoplastic mammary epithelial cells is dependent on the formation of a Snail1/HDAC1/p53 tri-molecular complex that deacetylates active p53, thereby promoting its proteasomal degradation. Our findings identify Snail1 as a molecular bypass that suppresses the anti-proliferative and pro-apoptotic effects exerted by wild-type p53 in breast cancer.

Action of SNAIL1 in Cardiac Myofibroblasts Is Important for Cardiac Fibrosis following Hypoxic Injury

Hypoxic injury to the heart results in cardiac fibrosis that leads to cardiac dysfunction and heart failure. SNAIL1 is a zinc finger transcription factor implicated in fibrosis following organ injury and cancer. To determine if the action of SNAIL1 contributed to cardiac fibrosis following hypoxic injury, we used an endogenous SNAIL1 bioluminescence reporter mice, and SNAIL1 knockout mouse models. Here we report that SNAIL1 expression is upregulated in the infarcted heart, especially in the myofibroblasts. Utilizing primary cardiac fibroblasts in ex vivo cultures we find that pro-fibrotic factors and collagen I increase SNAIL1 protein level. SNAIL1 is required in cardiac fibroblasts for the adoption of myofibroblast fate, collagen I expression and expression of fibrosis-related genes. Taken together this data suggests that SNAIL1 expression is induced in the cardiac fibroblasts after hypoxic injury and contributes to myofibroblast phenotype and a fibrotic scar formation. Resultant collagen deposition in the scar can maintain elevated SNAIL1 expression in the myofibroblasts and help propagate fibrosis.

The hallmarks of CAFs in cancer invasion

The ability of cancer cells to move out of the primary tumor and disseminate through the circulation to form metastases is one of the main contributors to poor patient outcome. The tumor microenvironment provides a niche that supports cancer cell invasion and proliferation. Carcinoma-associated fibroblasts (CAFs) are a highly enriched cell population in the tumor microenvironment that plays an important role in cancer invasion. However, it remains unclear whether CAFs directly stimulate cancer cell invasion or they remodel the extracellular matrix to make it more permissive for invasion. Here we discuss paracrine communication between cancer cells and CAFs that promotes tumor invasion but also stimulates CAFs to remodel the matrix increasing cancer dissemination.

Snail1-Dependent Activation of Cancer-Associated Fibroblast Controls Epithelial Tumor Cell Invasion and Metastasis

Snail1 transcriptional factor is essential for triggering epithelial-to-mesenchymal transition (EMT) and inducing tumor cell invasion. We report here an EMT-independent action of Snail1 on tumor invasion, as it is required for the activation of cancer-associated fibroblasts (CAF). Snail1 expression in fibroblasts requires signals derived from tumor cells, such as TGFβ; reciprocally, in fibroblasts, Snail1 organizes a complex program that stimulates invasion of epithelial cells independent of the expression of Snail1 in these cells. Epithelial cell invasion is stimulated by the secretion by fibroblast of diffusible signaling molecules, such as prostaglandin E₂ The capability of human or murine CAFs to promote tumor invasion is dependent on Snail1 expression. Inducible Snail1 depletion in mice decreases the invasion of breast tumors; moreover, epithelial tumor cells coxenografted with Snail1-depleted fibroblasts originated tumors with lower invasion than those transplanted with control fibroblasts. Therefore, these results demonstrate that the role of Snail1 in tumor invasion is not limited to EMT, but it is also dependent on its activity in stromal fibroblasts, where it orchestrates the cross-talk with epithelial tumor cells. Cancer Res; 76(21); 6205-17. ©2016 AACR.

Snail/Slug binding interactions with YAP/TAZ control skeletal stem cell self-renewal and differentiation

Bone marrow-derived skeletal stem/stromal cell (SSC) self-renewal and function are critical to skeletal development, homeostasis and repair. Nevertheless, the mechanisms controlling SSC behavior, particularly bone formation, remain ill-defined. Using knockout mouse models that target the zinc-finger transcription factors, Snail, Slug or Snail and Slug combined, a regulatory axis has been uncovered wherein Snail and Slug cooperatively control SSC self-renewal, osteoblastogenesis and bone formation. Mechanistically, Snail/Slug regulate SSC function by forming complexes with the transcriptional co-activators, YAP and TAZ, in tandem with the inhibition of the Hippo pathway-dependent regulation of YAP/TAZ signaling cascades. In turn, the Snail/Slug-YAP/TAZ axis activates a series of YAP/TAZ/TEAD and Runx2 downstream targets that control SSC homeostasis and osteogenesis. Together, these results demonstrate that SSCs mobilize Snail/Slug-YAP/TAZ complexes to control stem cell function.

Snail levels control the migration mechanism of mesenchymal tumor cells

Cancer cells use two major types of movement: Mesenchymal, which is typical of cells of mesenchymal origin and depends on matrix metalloproteinase (MMP) activity, and amoeboid, which is characteristic of cells with a rounded shape and relies on the activity of Rho-associated kinase (ROCK). The present authors previously demonstrated that, during neoplastic transformation, telomerase-immortalized human fibroblasts (cen3tel cells) acquired a ROCK-dependent/MMP independent mechanism of invasion, mediated by the downregulation of the ROCK cellular inhibitor Round (Rnd)3/RhoE. In the present study, cen3tel transformation was also demonstrated to be paralleled by downregulation of Snail, a major determinant of the mesenchymal movement. To test whether Snail levels could determine the type of movement adopted by mesenchymal tumor cells, Snail was ectopically expressed in tumorigenic cells. It was observed that ectopic Snail did not increase the levels of typical mesenchymal markers, but induced cells to adopt an MMP-dependent mechanism of invasion. In cells expressing ectopic Snail, invasion became sensitive to the MMP inhibitor Ro 28-2653 and insensitive to the ROCK inhibitor Y27632, suggesting that, once induced by Snail, the mesenchymal movement prevails over the amoeboid one. Snail-expressing cells had a more aggressive behavior in vivo, and exhibited increased tumor growth rate and metastatic ability. These results confirm the high plasticity of cancer cells, which can adopt different types of movement in response to changes in the expression of specific genes. Furthermore, the present findings indicate that Rnd3 and Snail are possible regulators of the type of invasion mechanism adopted by mesenchymal tumor cells.

Mechanical signals regulate and activate SNAIL1 protein to control the fibrogenic response of cancer-associated fibroblasts

Increased deposition of collagen in extracellular matrix (ECM) leads to increased tissue stiffness and occurs in breast tumors. When present, this increases tumor invasion and metastasis. Precisely how this deposition is regulated and maintained in tumors is unclear. Much has been learnt about mechanical signal transduction in cells, but transcriptional responses and the pathophysiological consequences are just becoming appreciated. Here, we show that the SNAIL1 (also known as SNAI1) protein level increases and accumulates in nuclei of breast tumor cells and cancer-associated fibroblasts (CAFs) following exposure to stiff ECM in culture and in vivo SNAIL1 is required for the fibrogenic response of CAFs when exposed to a stiff matrix. ECM stiffness induces ROCK activity, which stabilizes SNAIL1 protein indirectly by increasing intracellular tension, integrin clustering and integrin signaling to ERK2 (also known as MAPK1). Increased ERK2 activity leads to nuclear accumulation of SNAIL1, and, thus, avoidance of cytosolic proteasome degradation. SNAIL1 also influences the level and activity of YAP1 in CAFs exposed to a stiff matrix. This work describes a mechanism whereby increased tumor fibrosis can perpetuate activation of CAFs to sustain tumor fibrosis and promote tumor metastasis through regulation of SNAIL1 protein level and activity.

Membrane type 1-matrix metalloproteinase induces epithelial-to-mesenchymal transition in esophageal squamous cell carcinoma: Observations from clinical and in vitro analyses

Membrane type 1-matrix metalloproteinase (MT1-MMP) is associated with enhanced tumorigenicity in many cancers. A recent study has revealed that MT1-MMP induces epithelial-to-mesenchymal transition (EMT) in prostate and breast cancer cells. However, its role in esophageal squamous cell carcinoma (ESCC) has not been studied. Here, we investigated the role of MT1-MMP in the dissemination of ESCC. Expression of MT1-MMP was detected by immunohistochemistry and tissue microarray in 88 Kazakh ESCC patients. Western blotting was performed to detect endogenous and overexpressed exogenous MT1-MMP in the Eca109 and Eca9706 cell lines, respectively. Transwell assay was used to estimate MT1-MMP-induced invasion and metastasis. EMT-associated proteins were detected by immunohistochemistry and western blotting. The associations between the expression of MT1-MMP and EMT-associated proteins with clinicopathologic parameters were analyzed. Overexpression of MT1-MMP was confirmed in Kazakh ESCC patients. MT1-MMP levels were found to be correlated with the depth of tumor infiltration. MT1-MMP induced EMT in ESCC both in vivo and in vitro, N-cadherin and Vimentin expression was upregulated upon MT1-MMP transfection into cells. However, E-cadherin was found to be downregulated. MT1-MMP-induced EMT led to increase migration and invasion in ESCC cell lines. In conclusion, our results suggest that MT1-MMP promotes ESCC invasion and metastasis.

Glioma-associated oncogene homolog 1 promotes epithelial-mesenchymal transition in human renal tubular epithelial cell

Sonic hedgehog (Shh) signaling critically regulates embryogenesis and tissue homeostasis. Here, we investigated the role of Shh signaling in mediating epithelial-mesenchymal transition (EMT) in human renal tubular epithelial cells HKC-8. Our RT-PCR assays demonstrated that TGF-β1 induced time-dependent changes in the mRNA transcript levels of Shh, with a steady rise from one hour post TGF-β1 treatment and a peak at four hours post TGF-β1 treatment. Furthermore, TGF-β1 induced a time-dependent increase in the mRNA transcript levels of Gli1. Pre-treatment with 2 or 5 µM cyclopamine significantly attenuated TGF-β1-induced rise in the mRNA transcript levels of Gli1, but failed to attenuate TGF-β1-induced rise in Shh mRNA transcript levels. Additionally, immunoblotting assays and immunofluorescence staining demonstrated that inhibition of Shh signaling by cyclopamine significantly attenuated TGF-β1-induced increase in the mRNA transcript levels of α-SMA, collagen I, and fibronectin. Gli1 overexpression induced Snail1 expression. Moreover, Gli(-/-) mice that had undergone unilateral ureteral obstruction for seven days showed significant reduction in the mRNA transcript levels of Snail1 compared to the wildtype controls. In conclusion, the current study provides novel insight into the regulation of EMT by the Shh/Gli1 signaling pathway, suggesting a critical role of Shh/Gli1 signaling in EMT of human renal tubular epithelial cells.

The emerging role of Snail1 in the tumor stroma

The transcription factor Snail1 leads to the epithelial-mesenchymal transition by repressing the adherent and tight junctions in epithelial cells. This process is related to an increase of cell migratory and mesenchymal properties during both embryonic development and tumor progression. Although Snail1 expression is very limited in adult animals, emerging evidence has placed Snail at the forefront of medical science. As a transcriptional repressor, Snail1 confers cancer stem cell-like traits on tumor cells and promotes drug resistance, tumor recurrence and metastasis. In this review, we summarize recent reports that suggest the pro-tumorigenic roles of Snail1 expression in tumor stroma. The crosstalk between tumor and stromal cells mediated by Snail1 regulates paracrine communication, pro-tumorigenic abilities of cancer cells, extracellular matrix characteristics and mesenchymal differentiation in cancer stem cells and cancer-associated fibroblasts. Therefore, understanding the regulation and functional roles of Snail1 in the tumor microenvironment will provide us with new therapies for treating metastatic disease.

Snail Is a Critical Mediator of Invadosome Formation and Joint Degradation in Arthritis

Progressive cartilage destruction, mediated by invasive fibroblast-like synoviocytes, is a central feature in the pathogenesis of rheumatoid arthritis (RA). Members of the Snail family of transcription factors are required for cell migration and invasion, but their role in joint destruction remains unknown. Herein, we demonstrate that Snail is essential for the formation of extracellular matrix-degrading invadosomal structures by synovial cells from collagen-induced arthritis (CIA) rats and RA patients. Mechanistically, Snail induces extracellular matrix degradation in synovial cells by repressing PTEN, resulting in increased phosphorylation of platelet-derived growth factor receptor and activation of the phosphatidylinositol 3-kinase/AKT pathway. Of significance, Snail is overexpressed in synovial cells and tissues of CIA rats and RA patients, whereas knockdown of Snail in CIA joints prevents cartilage invasion and joint damage. Furthermore, Snail expression is associated with an epithelial-mesenchymal transition gene signature characteristic of transglutaminase 2/transforming growth factor-β activation. Transforming growth factor-β and transglutaminase 2 stimulate Snail-dependent invadosome formation in rat and human synoviocytes. Our results identify the Snail-PTEN platelet-derived growth factor receptor/phosphatidylinositol 3-kinase axis as a novel regulator of the prodestructive invadosome-forming phenotype of synovial cells. New therapies for RA target inflammation, and are only partly effective in preventing joint damage. Blocking Snail and/or its associated gene expression program may provide an additional tool to improve the efficacy of treatments to prevent joint destruction.

Snail1-dependent control of embryonic stem cell pluripotency and lineage commitment

Embryonic stem cells (ESCs) exhibit the dual properties of self-renewal and pluripotency as well as the ability to undergo differentiation that gives rise to all three germ layers. Wnt family members can both promote ESC maintenance and trigger differentiation while also controlling the expression of Snail1, a zinc-finger transcriptional repressor. Snail1 has been linked to events ranging from cell cycle regulation and cell survival to epithelial-mesenchymal transition (EMT) and gastrulation, but its role in self-renewal, pluripotency or lineage commitment in ESCs remains undefined. Here we demonstrate using isogenic pairs of conditional knockout mouse ESCs, that Snail1 exerts Wnt- and EMT independent control over the stem cell transcriptome without affecting self-renewal or pluripotency-associated functions. By contrast, during ESC differentiation, an endogenous Wnt-mediated burst in Snail1 expression regulates neuroectodermal fate while playing a required role in epiblast stem cell exit and the consequent lineage fate decisions that define mesoderm commitment.