EMT: Epithelial Mesenchimal Transition

Transcription

1 EMT: Epithelial Mesenchimal Transition A phenotypic change that is characteristic of some developing tissues and certain forms of cancer. This is a multistep, key process in embryonic development and metastasis formation during which static epithelial cells lose cell to cell junctions and, as consequence, they lose apicalbasal polarity to become migratory mesenkimallike cells.

2 Epithelial-Mesenchimal Transition(EMT) Morphological changes from a monolayer of regular form to dispersed cells more like fibroblasts E P IT E LI O M ES E N C H I M A Changes in gene expression of junctional proteins Functional changes with the conversion of resident cells to mobile cells that can invade the extracellular matrix

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5 Cadherin-containing junctions connect cells to one another

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7 Outline of Wnt/{beta}-catenin signaling Cadigan, K. M. et al. J Cell Sci 2006;119:

8 SFRP: secreted frizzled-related protein-1

9 EMT, cellule staminali tumorali e progressione tumorale EMT has a double role in metastasis formation Mesenchimal cells, which are mobile, can leave the primary cancer and move to a new site EMT appears to generate cancer stem cells which, being able to re-generate, allow metastasis forma;on

10 Meccanismi di attivazione dell EMT 1. Vie di segnalazione TGFβ Notch wnt 2. Ipoxia 3. Genetic and epigenetic control Metilation Transcriptional control micrornas

11 SFRP: secreted frizzled-related protein-1

12 Genetic control At least 6 transcriptionl factors control EMT: 1) FOX C1/C2 2) SNAI 1 3) SNAI 2 They repress directly the expression of E-CADERIN 4) ZEB2 5) ZEB 1 6) TWIST 1

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14 TGF beta is the main factor involved in the EMT. There are about 30 members of the TGF family in humans. The target genes can range from few in pluripotent ES cells to hundreds in differentiated cells. However, an old mystery has endured: how does the context determine the cellular response to TGFβ? Solving this question is key to understanding TGFβ biology and its many malfunctions.

15 7 type I And 5 type II Receptors. Both Serin-threonin kinase Type II phophorilates Type I that propagates The signal

16 Contact with Integrins activates TGF-beta While the SMADs play a key role in the trnscriptional response TGFβ-induced, some mechanisms SMAD-independent regulate other cell pathways such as polarity, migration, and cytoskeleton rearrangments through a pathway smad-independent: type II receptor phosphorilates Par6, important for cell polarity, that recruits the ubiqutin-ligase SMURF1 that degrades RHOA, thus determining the breakup of the tight junctions.

17 TGFbeta inhibits cell cycle through INK4 In epithelial cells, TGFbeta induces the expression of CDKN2B, the cdk4 inhibitor p15ink4b. This is due to the binding of a SMAD4-SMAD3-FOXO to the promoter and dissociation of the repressor complex. The binding of the SMAD/FOXO complexes recruits a DNA excision repair complex that demethylates the promoter, leading to the INK expression.

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19 Snail can also activate transcription

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21 EMT GENETC control EPIGENETIC Control E-cadherin down-regulation

22 mirnas and EMT Donwregulation mir 200 family e mir 205 (targets: ZEB1 e ZEB2) Decremento E-caderina ed incremento vimentina Upregulation mir 10b (targets: HOXD10 e RHOC) Incremento del processo metastatico e d invasione Upregulation mir 335 (targets: COL1A1, MERTK, PLCB1, PTPRN2, TNC e SOX4) Decremento del processo metastatico e d invasione

23 The MIRs have a role in the EMT and in the MET

24 MicroRNA e EMT I mirnas agiscono a vari livelli sia nella EMT che nella MET - Componenti dell architettura cell mir-9 E-caderina - Componenti multipli dell EMT mir-138 Rock, Rho, Zeb - Fattori di trascrizione mir-34 SNAIL (feeedback)

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26 Copyright 2012 Elsevier Inc. Terms and Conditions Figure 1

27 Ù A direct molecular link between EMT and stemness was demonstrated by seminal findings that EMT activators, such as Twist1, can co-induce EMT and stemness properties (Mani et al., 2008; Morel et al., 2008). But why do metastases re-differentiate? Invasive, de-differentiated cancer cells were shown to be growth arrested, and proliferation was detected in re-differentiated metastasis, leading to the proposal that EMT must be reversed in order to allow growth and colonization (Brabletz et al., 2001). This is supported by the fact that EMT-inducing transcription factors can directly inhibit proliferation (Thiery et al., 2009). Although many clinical reports fostered the concept of transient EMT-MET switches in metastasis, there are only a few experimental proofs. Two papers in this issue of Cancer Cell support the role of an EMT in dissemination and the need of a MET for efficient metastasis. Moreover, the authors demonstrated that downregulation of Twist1 in metastases was associated with increased proliferation and reversal of an EMT-associated growth arrest. In summary, this study clearly supports the role of an EMT in dissemination and the necessity of a subsequent MET for colonization and macrometastasis. Twist1 down-regulation was shown to be important to overcome EMT-associated growth arrest, but reactivation of proliferation is likely not the only reason for a MET in metastasis. Recently, it was shown that, while re-differentiation induced by expression of mir-200 is required for metastatic colonization in a xenograft model, mir-200 also directly targets SEC23A, which stimulates the secretion of metastasis-suppressive proteins (Korpal et al., 2011).