1. Signal Transduction Pathways of EMT Induced by WNT-GSK3-Snail Cascade
Signal Transduction Pathways of EMT Induced by WNT-GSK3-Snail Cascade
Lab of Molecular genetics
Donguk Kim

2. Epithelial to Mesenchymal Transition Summary
Contents
WNT Signaling
Snail
Epithelial to Mesenchymal Transition
Summary

3. WNT Signaling
Pathway
Dev Cell Jul;17(1):9-26

4. Axin Complex assembly for β-catenin degradation
WNT Signaling
Axin Complex assembly for β-catenin degradation
Dev Cell Jul;17(1):9-26
J Cell Sci 2007 120: 

5. APC(Adenomatous polyposis coli)
WNT Signaling
APC(Adenomatous polyposis coli)
Adenomatous polyposis coli (APC) also known as deleted in polyposis 2.5 (DP2.5) is a protein that in humans is encoded by the APC gene.[1] The APC protein is a negative regulator that controls beta-catenin concentrations and interacts with E-cadherin, which are involved in cell adhesion. Mutations in the APC gene may result in colorectal cancer.[2]
APC is classified as a tumor suppressor gene. Tumor suppressor genes prevent the uncontrolled growth of cells that may result in cancerous tumors. The protein made by the APC gene plays a critical role in several cellular processes that determine whether a cell may develop into a tumor. The APC protein helps control how often a cell divides, how it attaches to other cells within a tissue, how the cell polarizes and the morphogenesis of the 3D structures,[3] or whether a cell moves within or away from a tissue. This protein also helps ensure that the chromosome number in cells produced through cell division is correct. The APC protein accomplishes these tasks mainly through association with other proteins, especially those that are involved in cell attachment and signaling. The activity of one protein in particular, beta-catenin, is controlled by the APC protein (see: Wnt signaling pathway). Regulation of beta-catenin prevents genes that stimulate cell division from being turned on too often and prevents cell overgrowth.
The human APC gene is located on the long (q) arm of chromosome 5 in band q22.2 The APC gene has been shown to contain an internal ribosome entry site. APC orthologs[4] have also been identified in all mammals for which complete genome data are available.
Nature Reviews Cancer 1, 55-67 (October 2001)
APC is an enormous protein that has multiple roles in the cell.
In the Wnt pathway, it binds to b-catenin and is necessary for its down-regulation.
APC also interacts directly with Axin.

6. β-catenin WNT Signaling
β-catenin is regulated and destroyed by the β-catenin destruction complex.
β-catenin (armadillo in Drosophila) is the key mediator of the Wnt signal.
In cells not exposed to the signal, β-catenin levels are kept low through interactions with the protein kinase zw3/GSK-3, CK1a, APC and Axin (Behrens, 1998Itoh 1998., Hamada, 1999.) β-catenin is degraded, after phosphorylation by GSK-3 and CK1 alpha (Yanagawa 2002, Liu 2002, Amit 2002), through the ubiquitinpathway (Aberle 1997.), involving interactions with Slimb/bTrCP (Jiang 1998, Marikawa 1998,; reviewed in Maniatis 1999)
In a current model, Wnt signaling initially leads to a complex between Dsh, GBP/Frat1, Axin and Zw3/GSK, which may be the regulatory step in the inactivation of Zw3/GSK (Salic, 2000; Farr 2000). The DIX domain in Axin is similar to the NH2 terminus in Dsh, and promotes interactions between Dsh and Axin (Hsu 1999,Smalley, 1999). As a consequence, GSK does not phosphorylate β-catenin anymore, releasing it from the Axin complex and accumulation (Salic, 2000).The stabilized β-catenin then enters the nucleus to interact with TCF. β-catenin can convert TCF into a transcriptional activator of the same genes that are repressed by TCF alone (reviewed in Nusse, 1999). Two other key players in this complex are Legless (Bcl9) and Pygopos (Kramps 2002, Thompson 2002, Parker 2002). In mammalian cells and in the Zebrafish, Bcl9-2 regulates binding of β-catenin to the adhesion complex or its presence in the nucleus, by interacting with the tyrosine phosphorylated form of β-catenin (Brembeck, 2004).
Activating mutations in the human β-catenin gene have been found in human colon cancer and melanomas (Morin et al, 1997) These mutations alter specific β-catenin residues important for GSK3 phosphorylation and stability. There is a separate list of mutations.
Vertebrates have two Armadillo/β-catenin homologs, β-catenin and plakoglobin (also called gamma-catenin). It is not clear whether plakoglobin is mutated in cancer, although overexpression of mutant forms can transform cells (Kolligs, 2000) . Both plakoglobin and β-catenin bind to cadherins to establish cell adhesion.
There are three β-catenin genes in C. elegans. Interestingly, one of them (HMP-2) is dedicated to adhesion only, whereas BAR-1 and WRM-1 act in Wnt signaling(Korswagen 2000 Natarajan 2001) Schneider et al (2003) postulate that a single, β-catenin gene fulfilled both adhesion and signaling functions in the last common ancestor of metazoans some 700 million years ago.

7. WNT Signaling
GSK-3
Oncotarget May 30;5(10):

8. Snail stability and degradation is modulated by GSK3
Nature Reviews Molecular Cell Biology 15, (2014)
Snail is a zinc finger transcription factor that induces epithelial-to-mesenchymal transition(EMT).
GSK3 phosphorylates Snail at two motifs; phosphorylation of the first motif facilitates the nuclear export of Snail, and the second motif enables the ubiquitin-mediated degradation of Snail.

9. Snail genes are a convergence point in EMT induction
Epithelial-mesenchymal transition (EMT) occurs when epithelial cells lose their epithelial cell characteristics, including dissolution of cell-cell junctions, i.e. tight junctions (black), adherens junctions (blue) and desmosomes (green), and loss of apical-basolateral polarity, and acquire a mesenchymal phenotype, characterized by actin reorganization and stress fiber formation (red), migration and invasion.
Development 2005 132: 

10. Epithelial to Mesenchymal Transition(EMT)
Drivers and mediators of EMT
Epithelial-mesenchymal transition (EMT) occurs when epithelial cells lose their epithelial cell characteristics, including dissolution of cell-cell junctions, i.e. tight junctions (black), adherens junctions (blue) and desmosomes (green), and loss of apical-basolateral polarity, and acquire a mesenchymal phenotype, characterized by actin reorganization and stress fiber formation (red), migration and invasion.
Cell Aug 6;118(3):277-9

11. Epithelial to Mesenchymal Transition(EMT)
The characteristics of epithelial and mesenchymal cell
Epithelial-mesenchymal transition (EMT) occurs when epithelial cells lose their epithelial cell characteristics, including dissolution of cell-cell junctions, i.e. tight junctions (black), adherens junctions (blue) and desmosomes (green), and loss of apical-basolateral polarity, and acquire a mesenchymal phenotype, characterized by actin reorganization and stress fiber formation (red), migration and invasion.
EMT occurs when epithelial cells lose their epithelial cell characteristics.
During EMT, epithelial cells gain mesenchymal features which include changes in the expression of epithelial and mesenchymal markers.
The cells acquire a migratory behavior, allowing them to move away from their epithelial cell community and to integrate into surrounding tissue, even at remote locations.

12. Epithelial to Mesenchymal Transition(EMT)
Phenotype of epithelial to mesenchymal transition
SCp2 murine mammary cells (a) were treated with matrix metalloproteinase-3(MMP3) to induce EMT (b).
Eph4 V12-transformed murine mammary cells (c) were treated with transforming-growth factor-β to induce EMT (d).
EMT in rat bladder carcinoma NBT-II cells (e, f).
Epithelial-mesenchymal transition (EMT) occurs when epithelial cells lose their epithelial cell characteristics, including dissolution of cell-cell junctions, i.e. tight junctions (black), adherens junctions (blue) and desmosomes (green), and loss of apical-basolateral polarity, and acquire a mesenchymal phenotype, characterized by actin reorganization and stress fiber formation (red), migration and invasion.
Nature Reviews Molecular Cell Biology 7,   (February 2006)

13. Epithelial to Mesenchymal Transition(EMT)
The cycle of epithelial-cell plasticity
In tumour cells, epithelial to mesenchymal transition (EMT)-inducing transcription factors (EMT-TFs) may primarily redefine the epithelial status of the cell, potentially — but not necessarily — assigning stem cell (SC) characteristics to dedifferentiated tumour cells, or they may redefine resident genetically altered stem cells to be cancer stem cells (CSCs). The dissemination of tumour cells from the solid tumour and subsequent migration after breakdown of the basement membrane (BM) — the classical view of the role of EMT in cancer — can only be achieved when all component pathways of the network are activated and fully parallels the process that is seen in development: if the cancer cell has acquired the necessary genetic aberrations and receives the appropriate signals at the tumour–host interface, the cell is ready to move towards metastasis. At this point, the active contribution of the EMT-associated programme is probably to give survival signals and to maintain the mesenchymal status of the metastasizing cell. It is likely that EMT also has a role in parallel progression, in which tumour cells escape early and metastasis progresses in parallel to the primary tumour. EMT features may further promote resistance during tumour therapy, leading to recurrence and a poor prognosis. The degree of EMT during the different steps in cancer progression probably depends on the imbalance of several associated regulatory networks with activated oncogenic pathways. MET, mesenchymal to epithelial transition
Nature Reviews Molecular Cell Biology 7,   (February 2006)

14. Epithelial to Mesenchymal Transition(EMT)
Cellular events during EMT
In tumour cells, epithelial to mesenchymal transition (EMT)-inducing transcription factors (EMT-TFs) may primarily redefine the epithelial status of the cell, potentially — but not necessarily — assigning stem cell (SC) characteristics to dedifferentiated tumour cells, or they may redefine resident genetically altered stem cells to be cancer stem cells (CSCs). The dissemination of tumour cells from the solid tumour and subsequent migration after breakdown of the basement membrane (BM) — the classical view of the role of EMT in cancer — can only be achieved when all component pathways of the network are activated and fully parallels the process that is seen in development: if the cancer cell has acquired the necessary genetic aberrations and receives the appropriate signals at the tumour–host interface, the cell is ready to move towards metastasis. At this point, the active contribution of the EMT-associated programme is probably to give survival signals and to maintain the mesenchymal status of the metastasizing cell. It is likely that EMT also has a role in parallel progression, in which tumour cells escape early and metastasis progresses in parallel to the primary tumour. EMT features may further promote resistance during tumour therapy, leading to recurrence and a poor prognosis. The degree of EMT during the different steps in cancer progression probably depends on the imbalance of several associated regulatory networks with activated oncogenic pathways. MET, mesenchymal to epithelial transition
Nature Reviews Molecular Cell Biology 15, (2014)

15. Epithelial to Mesenchymal Transition(EMT)
Role of EMT during cancer progression
In tumour cells, epithelial to mesenchymal transition (EMT)-inducing transcription factors (EMT-TFs) may primarily redefine the epithelial status of the cell, potentially — but not necessarily — assigning stem cell (SC) characteristics to dedifferentiated tumour cells, or they may redefine resident genetically altered stem cells to be cancer stem cells (CSCs). The dissemination of tumour cells from the solid tumour and subsequent migration after breakdown of the basement membrane (BM) — the classical view of the role of EMT in cancer — can only be achieved when all component pathways of the network are activated and fully parallels the process that is seen in development: if the cancer cell has acquired the necessary genetic aberrations and receives the appropriate signals at the tumour–host interface, the cell is ready to move towards metastasis. At this point, the active contribution of the EMT-associated programme is probably to give survival signals and to maintain the mesenchymal status of the metastasizing cell. It is likely that EMT also has a role in parallel progression, in which tumour cells escape early and metastasis progresses in parallel to the primary tumour. EMT features may further promote resistance during tumour therapy, leading to recurrence and a poor prognosis. The degree of EMT during the different steps in cancer progression probably depends on the imbalance of several associated regulatory networks with activated oncogenic pathways. MET, mesenchymal to epithelial transition
Nature Reviews Cancer 13, 97-110 (February 2013)

16. Summary
Dual regulation of Snail by GSK3 mediated phosphorylation in control of epithelial to mesenchymal transition
Nature Cell Biology 6, (2004)
Nature Reviews Molecular Cell Biology 7,   (February 2006)
Wnt signals inhibit GSK3, resulting in activation of Snail and repression of E-cadherin, thus inducing an EMT.

17. Reference Nature Cell Biology 6, 931 - 940 (2004)
Nature Reviews Molecular Cell Biology 7,   (February 2006)
Nature Reviews Cancer 13, 97-110 (February 2013)
Nature Reviews Molecular Cell Biology 15, (2014)
Cell Aug 6;118(3):277-9
Development 2005 132: 
Oncotarget May 30;5(10):
Nature Reviews Cancer 1, 55-67 (October 2001)
Dev Cell Jul;17(1):9-26
J Cell Sci 2007 120: