162 Cell SnapShot: The Epithelial-Mesenchymal Transition 145 Jonathan P. Sleeman3,4 and Jean Paul Thiery2,3 , April1, 2011©2011Elsevier Inc. DOI 10.1016/j.cell.2011.03.029 1IMCB and Experimental Therapeutics Centre, Biopolis A*STAR, 138673 Singapore; 2Cancer Science Institute, 117456 Singapore 3University of Heidelberg, Medical Faculty Mannheim, D-68167 Mannheim, Germany; 4Karlsruhe Institute of Technology, Postfach 3640, 76021 Karlsruhe, Germany EPITHELIAL JAG2 MESENCHYMAL IL-6 Hedgehog Growth Other EMT-inducing pathways factors ILEI Endothelin-A receptor-PI3K Smoothened Patched BMPs NOTCH TNF-α-NF-κB, Akt Hyaluronic acid Microtentacles COX2-PGE2 IL-6R RTK BMPR1 AMF Tight junction BMPR2 Actin PTH(rP)R Claudin ZO3 Bile acids Claudin ZO1 Nicotine ZO3 ER Occludin ZO2 UV irradiation Occludin ZO1 SCF Balanced RhoA ZO2 STAT3 PI3K Ras TβRI Smad2/3 TGF-β Axl-Gas6 activities Par6 TβRI TβRII P Par6 Cdc42 Par3 Smurf1 P Par3 aPKC Stabilized actin LIV1 AKT MAPK aPKC JAM Other EMT-associated effects cytoskeleton Rac1 Snail1/2 JAM Dissociation of P tight junctions Resistance to senescence Ub Resistance to apoptosis DAB2 PAK1 RhoA Focal Therapy resistance Proteasome adhesion Stemness IQGAP formation Adherens junction P F-actin β-cat Rap1 Nectin Ub Glu-tubulin Afadin ILK Clip170 CSL Endocytosis FAK Dynein/ CK1E EB1 E-cadherin P degradation Loss of dynactin X Vinculin Examples of down- complex β-cat α-Actinin desmosomes β-cat α-cat Focal regulated genes Ninein adhesion DDR1 formation Tubulin tyrosine ligase NF-κB AKT Claudins Par6 Par3 Occludins p120-Cat FAK Hakai ZO1/ZO3 Collective Gli1 Loss of gap RhoE cell NF-κB MTA3 GSK3β β-cat c-src Crumbs3 junctions migration P Desmoplakin Apicobasal p190 Adherens Connexin43 microtubules Rho DAP21P GSK3β junction E-cadherin Cytoskeleton GAP remodeling Dishevelled disassembly Nectin-1 Frizzled VE-cadherin RhoA miR-200 miR-205 Myosin Wnt Cytokeratins Membrane Collagen I, II A light ROCK LRP5/6 Cdc42 rufes chain P Twist Snail1/2 Zeb1/2 β-cat PDGF Cytokeratin Rac1 N-cad Desmocollin P Desmosome Plakoglobin GSC α-cat Desmoplakin Examples of up- p190 p53 FOXQ1 Rho LoxL2 E2.2 c-src Increased regulated genes GAP β-cat Desmoglein KLF8 RTK TGF-β TβRI Six1 p120-Cat E47 p120-Cat signaling Vimentin RhoA See online version for legend and references. SMA PDGFR miR-200 miR-205 N-cadherin Afadin NCAM Nectin Fibronectin Snail1/2 Zeb1/2 Gap junction Laminins Upregulated genes E-cadherin and other miR-661 (see box B) downregulated genes MMPs B (see box A) FAK p130 FAK CAS HIF 1/2 P Fyn Pyk2 p190 Collagen 1 Rho Rac1 GAP p120-Cat DDR1 E-cadherin Kaiso p120-Cat NCAM E-cadherin Cdc42 Transcription degradation Focal adhesion RhoA assembly and turnover FOXA1/2 Reactive Filopodia oxygen Rac1b MMPs Lamellipodia species Migration Invasion Hypoxia ECM remodelling Integrin Plectin α6β4 BASEMENT MEMBRANE Laminin 5 Basement membrane degradation SnapShot: The Epithelial-Mesenchymal Transition Jonathan P. Sleeman3,4 and Jean Paul Thiery1,2 1IMCB and Experimental Therapeutics Centre, Biopolis A*STAR, 138673 Singapore 2Cancer Science Institute, 117456 Singapore 3University of Heidelberg, Medical Faculty Mannheim, D-68167 Mannheim, Germany 4Karlsruhe Institute of Technology, Postfach 3640, 76021 Karlsruhe, Germany This SnapShot portrays important regulatory pathways and major cellular events that are activated during the transition from an epithelial to a mesenchymal morphology during development and disease. The cell on the left represents the epithelial state, whereas the central cell depicts transcriptional regulatory networks that orchestrate the process of epithelial-to-mesenchymal transition (EMT). The cell on the right illustrates some of the consequences of the activity of these networks that endow formerly epithelial cells with mesenchymal characteristics. Note that this overview does not take into account cell-type-specific regulation of EMT, and that not all illustrated mechanisms are obligate for EMT to occur. The temporal regulation of the EMT process is also not considered in this SnapShot. The Epithelial Phenotype Polarized epithelial cells are typified by tight junctions, adherens junctions, desmosomes, and gap junctions. Junctional complexes not only act as mediators of polarized cell-cell contacts but also serve as anchor points for the actin cytoskeleton. Adherens junctions can additionally anchor apicobasal microtubule arrays, and through E-cadherin-DDR1 interactions are also involved in collective cell migration. Organization of the actin cytoskeleton, microtubule arrays, and cell-cell junctions is tightly coordinated in a mechanism that probably involves IQGAP, but the details remain to be investigated. Balanced regulation of the activities of RhoA (stress fibers), Cdc42 (filopodia), and Rac1 (lamellipodia) stabilizes the actin cytoskeleton and maintains the epithelial phenotype. Epithelial cells are tethered to the underlying basement membrane, for example through integrins. The repression of EMT-inducing transcriptional regulators (for example, through microRNAs), as well the activity of positively acting factors such as FOXA1/2, ensures that expression of key junctional proteins such as E-cadherin is maintained. Suppression of GSK3β also helps to maintain the epithelial phenotype. Transcriptional Activation of EMT A variety of extracellular stimuli have the potential to induce EMT. A complex network of positively and negatively acting signal transduction mechanisms converge on the nucleus to downregulate genes required for the epithelial phenotype and to upregulate genes that specify mesenchymal characteristics. GSK3β and NF-κB play central roles in coordinating these pathways. Members of the Snail family of transcriptional regulators, namely Snail1 and Snail2, have emerged as a key regulatory node. The zinc finger transcription factors Zeb1 and Zeb2 also make a pivotal contribution to this regulation. EMT-inducing signals promote their expression, regulate their stability, and/or alter their subcellular location. Loss of Epithelial and Acquisition of Mesenchymal Characteristics Key targets of the pathways that induce EMT include the adherens junction components E-cadherin and β-catenin. In addition to being transcriptionally downregulated and epigenetically switched off, E-cadherin can be proteolytically cleaved and targeted to endosomes for degradation. Proteosomal degradation of β-catenin destabilizes adherens junctions, whereas loss of E-cadherin can increase the free pool of β-catenin that can then enter the nucleus and modulate transcription. An important consequence of EMT- inducing transcriptional modulation as well as other pro-EMT processes is the loss of the junctional complexes that typify polarized epithelial cells. Enhanced activation of the GTPases Cdc42 and Rac1 and suppression of RhoA favor the formation of lamellipodia and filopodia, migration, and invasion. A variety of mechanisms promote the assembly and turnover of focal adhesions. Extensive cytoskeleton remodeling occurs, including switching from a predominantly cytokeratin to a vimentin-rich intermediate filament net- work. Detyrosination of tubulin promotes microtentacle formation. Proteolytic enzymes are produced that together with increased expression of extracellular matrix components serve to remodel the microenvironment surrounding the cells. Other properties endowed on cells undergoing EMT include resistance to apoptosis, senescence, and therapeutics and the acquisition of stemness characteristics. 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