Reversibility of the Snail-induced epithelial-mesenchymal transition revealed by the Cre-loxP system

Adherens junction regulates cryptic lamellipodia formation for epithelial cell migration

Collective migration of epithelial cells plays crucial roles in various biological processes such as cancer invasion. In migrating epithelial sheets, leader cells form lamellipodia to advance, and follower cells also form similar motile apparatus at cell-cell boundaries, which are called cryptic lamellipodia (c-lamellipodia). Using adenocarcinoma-derived epithelial cells, we investigated how c-lamellipodia form and found that they sporadically grew from around E-cadherin-based adherens junctions (AJs). WAVE and Arp2/3 complexes were localized along the AJs, and silencing them not only interfered with c-lamellipodia formation but also prevented follower cells from trailing the leaders. Disruption of AJs by removing αE-catenin resulted in uncontrolled c-lamellipodia growth, and this was brought about by myosin II activation and the resultant contraction of AJ-associated actomyosin cables. Additional observations indicated that c-lamellipodia tended to grow at mechanically weak sites of the junction. We conclude that AJs not only tie cells together but also support c-lamellipodia formation by recruiting actin regulators, enabling epithelial cells to undergo ordered collective migration.

Endothelial-to-Mesenchymal Transition (EndoMT): Roles in Tumorigenesis, Metastatic Extravasation and Therapy Resistance

Cancer cells evolve in a very complex tumor microenvironment, composed of several cell types, among which the endothelial cells are the major actors of the tumor angiogenesis. Today, these cells are also characterized for their plasticity, as endothelial cells have demonstrated their potential to modify their phenotype to differentiate into mesenchymal cells through the endothelial-to-mesenchymal transition (EndoMT). This cellular plasticity is mediated by various stimuli including transforming growth factor-β (TGF-β) and is modulated dependently of experimental conditions. Recently, emerging evidences have shown that EndoMT is involved in the development and dissemination of cancer and also in cancer cell to escape from therapeutic treatment. In this review, we summarize current updates on EndoMT and its main induction pathways. In addition, we discuss the role of EndoMT in tumorigenesis, metastasis, and its potential implication in cancer therapy resistance.

Molecular pathways in the development and treatment of oesophageal cancer

The molecular pathways involved in the development and treatment of oesophageal cancer are complex. Recent large-scale genome sequencing studies have delivered novel insights into aetiology and possible targeted treatments. Oesophageal squamous cell carcinoma (OSCC) and adenocarcinoma (OAC) are distinct entities. At the molecular level OSCC is more similar to squamous cell cancers in other organs than OAC. Whilst considerable heterogeneity exists in both tumour types new data suggests that driver gene events and mutational signatures may be able to categorise tumours into potentially actionable subtypes. Taken together these findings not only suggest new avenues for treatments in a cancer type with appalling outcomes, but also a new era of molecular rather than purely anatomical classification and staging of oesophageal cancer.

miRNA-520f Reverses Epithelial-to-Mesenchymal Transition by Targeting ADAM9 and TGFBR2

Reversing epithelial-to-mesenchymal transition (EMT) in cancer cells has been widely considered as an approach to combat cancer progression and therapeutic resistance, but a limited number of broadly comprehensive investigations of miRNAs involved in this process have been conducted. In this study, we screened a library of 1120 miRNA for their ability to transcriptionally activate the E-cadherin gene CDH1 in a promoter reporter assay as a measure of EMT reversal. By this approach, we defined miR-520f as a novel EMT-reversing miRNA. miR-520f expression was sufficient to restore endogenous levels of E-cadherin in cancer cell lines exhibiting strong or intermediate mesenchymal phenotypes. In parallel, miR-520f inhibited invasive behavior in multiple cancer cell systems and reduced metastasis in an experimental mouse model of lung metastasis. Mechanistically, miR-520f inhibited tumor cell invasion by directly targeting ADAM9, the TGFβ receptor TGFBR2 and the EMT inducers ZEB1, ZEB2, and the snail transcriptional repressor SNAI2, each crucial factors in mediating EMT. Collectively, our results show that miR-520f exerts anti-invasive and antimetastatic effects in vitro and in vivo, warranting further study in clinical settings. Cancer Res; 77(8); 2008-17. ©2017 AACR.

Developmental pathways associated with cancer metastasis: Notch, Wnt, and Hedgehog

Master developmental pathways, such as Notch, Wnt, and Hedgehog, are signaling systems that control proliferation, cell death, motility, migration, and stemness. These systems are not only commonly activated in many solid tumors, where they drive or contribute to cancer initiation, but also in primary and metastatic tumor development. The reactivation of developmental pathways in cancer stroma favors the development of cancer stem cells and allows their maintenance, indicating these signaling pathways as particularly attractive targets for efficient anticancer therapies, especially in advanced primary tumors and metastatic cancers. Metastasis is the worst feature of cancer development. This feature results from a cascade of events emerging from the hijacking of epithelial-mesenchymal transition, angiogenesis, migration, and invasion by transforming cells and is associated with poor survival, drug resistance, and tumor relapse. In the present review, we summarize and discuss experimental data suggesting pivotal roles for developmental pathways in cancer development and metastasis, considering the therapeutic potential. Emerging targeted antimetastatic therapies based on Notch, Wnt, and Hedgehog pathways are also discussed.

Hypoxia induced the differentiation of Tbx18-positive epicardial cells to CoSMCs

Understanding the origin and differentiation mechanism of coronary vascular smooth muscle cells (CoSMCs) is very important to cardiovascular biology. The early cardiovascular system is formed in a hypoxic microenvironment, and Tbx18-positive epicardial cells are a source of CoSMCs. However, the effects of hypoxia on the differentiation of Tbx18-positive epicardial cells to CoSMCs and the primary regulatory mechanism are insufficiently understood. Using Tbx18:Cre/R26R^EYFP/LacZ fate-tracing mice, we cultured highly purified Tbx18-positive epicardial cells. We further showed that hypoxia induced Tbx18-positive epicardial cells to differentiate into CoSMCs and promoted the epithelial-mesenchymal transition (EMT) process of the cells in vitro. The induction of differentiation was primarily achieved via the hypoxia inducible factor-1α (HIF-1α)-mediated effects exerted on Snail. Using a cell migration assay, we showed that hypoxia enhanced the motility of Tbx18-positive epicardial cells. By constructing a hypoxic model of the embryonic epicardium in vivo, we showed that hypoxia led to premature in situ differentiation of Tbx18-positive epicardial cells to CoSMCs. Furthermore, hypoxia was sufficient to induce Snail expression in Tbx18-positive epicardial cells in vivo. Our study suggests that hypoxia intervention was sufficient to induce the differentiation of Tbx18-positive epicardial cells to CoSMCs. Furthermore, this differentiation was achieved primarily via HIF-1α-mediated regulation of Snail.

Role of Snail in regulation of intestinal epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is involved in many pathological processes such as tissue fibrosis, tumor occurrence and metastasis, which has become one of current research focuses. The transcription factor Snail is a C₂H₂-type zinc finger protein and has a crucial regulatory role in EMT through the transcription inhibition region, which is composed of SNAG domain and C-terminal binding protein, to inhibit the expression of genes. Recently, numerous studies have confirmed that Snail can promote EMT through the tumor necrosis factor α (TNF-α)-nuclear factor κB (NF-κB)- Snail pathway and transforming growth factor β1 (TGF-β1)-Smads-Snail pathway. This article aims to summarize the regulatory role of Snail in mediating intestinal EMT via the above two

pathways.

Mining the epigenetic landscape of tissue polarity in search of new targets for cancer therapy

The epigenetic nature of cancer encourages the development of inhibitors of epigenetic pathways. Yet, the clinical use for solid tumors of approved epigenetic drugs is meager. We argue that this situation might improve upon understanding the coinfluence between epigenetic pathways and tissue architecture. We present emerging information on the epigenetic control of the polarity axis, a central feature of epithelial architecture created by the orderly distribution of multiprotein complexes at cell-cell and cell-extracellular matrix contacts and altered upon cancer onset (with apical polarity loss), invasive progression (with basolateral polarity loss) and metastatic development (with basoapical polarity imbalance). This information combined with the impact of polarity-related proteins on epigenetic mechanisms of cancer enables us to envision how to guide the choice of drugs specific for distinct epigenetic modifiers, in order to halt cancer development and counter the consequences of polarity alterations.

E-cadherin cytoplasmic domain inhibits cell surface localization of endogenous cadherins and fusion of C2C12 myoblasts

Myoblast fusion is a highly regulated process that is essential for skeletal muscle formation during muscle development and regeneration in mammals. Much remains to be elucidated about the molecular mechanism of myoblast fusion although cadherins, which are Ca(2+)-dependent cell-cell adhesion molecules, are thought to play a critical role in this process. Mouse myoblasts lacking either N-cadherin or M-cadherin can still fuse to form myotubes, indicating that they have no specific function in this process and may be functionally replaced by either M-cadherin or N-cadherin, respectively. In this study, we show that expressing the E-cadherin cytoplasmic domain ectopically in C2C12 myoblasts inhibits cell surface localization of endogenous M-cadherin and N-cadherin, as well as cell-cell fusion. This domain, however, does not inhibit myoblast differentiation according to microarray-based gene expression analysis. In contrast, expressing a dominant-negative β-catenin mutant ectopically, which suppresses Wnt/β-catenin signaling, did not inhibit cell-cell fusion. Therefore, the E-cadherin cytoplasmic domain inhibits cell-cell fusion by inhibiting cell surface localization of endogenous cadherins and not by inhibiting Wnt/β-catenin signaling.

The ectopic expression of Snail in MDBK cells does not induce epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT), a key process in the tumor metastatic cascade, is characterized by the loss of cell-cell junctions and cell polarity, as well as by the acquisition of migratory and invasive properties. However, the precise molecular events that initiate this complex EMT process are poorly understood. Snail expression induces EMT in Madin-Darby canine kidney (MDCK) cells and the human epidermoid carcinoma cell line, A431. Snail is a zinc finger transcription factor and triggers EMT by suppressing E-cadherin expression. In the present study, to broaden our knowledge of Snail-induced EMT, we generated stable Snail transfectants using Madin-Darby bovine kidney (MDBK) cells. Contrary to the MDCK or A431 cells examined in our previous studies, the MDBK cells transfected with the Snail construct maintained an epithelial morphology and showed no sign of reduced cell-cell adhesiveness compared to the control cells. Consistent with these observations, the down-regulation of epithelial marker proteins, e.g. E-cadherin and desmoglein, and the upregulation of mesenchymal marker proteins, e.g., N-cadherin and fibronectin, were not detected. Furthermore, the E-cadherin promoter was not methylated. Therefore, in the MDBK cells, the ectopic expression of Snail failed to induce EMT. As previously demonstrated, in MDCK cells, Snail expression is accompanied by the increased expression of other EMT-inducing transcription factors, e.g., Slug and zinc finger E-box-binding homeobox 1 (ZEB1). However, the MDBK cells transfected with the Snail construct did not exhibit an increased expression of these factors. Thus, it is possible that the failure to upregulate other EMT-related transcription factors may explain the lack of Snail-mediated induction of EMT in MDBK cells.

The role of EMT and MET in cancer dissemination

Metastatic cancer cells are lethal. Understanding the molecular mechanisms that bolster the conversion from benign to malignant progression is key for treating these heterogeneous and resistant neoplasms. The epithelial-mesenchymal transition (EMT) is a conserved cellular program that alters cell shape, adhesion and movement. The shift to a more mesenchymal-like phenotype can promote tumor cell intravasation of surrounding blood vessels and emigration to a new organ, yet may not be necessary for extravasation or colonization into that environment. Lymphatic dissemination, on the other hand, may not require EMT. This review presents emerging data on the modes by which tumor cells promote EMT/MET via microRNA and prepare the pre-metastatic niche via exosomes.