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Epithelial-mesenchymal transition or transformation (EMT) is a program of development of biological cells characterized by loss of cell adhesion, repression of E-cadherin expression, and increased cell mobility. EMT is essential for numerous developmental processes including mesoderm formation and neural tube formation.

Several oncogenic pathways (peptide growth factors, Src, Ras, Ets, integrin, Wnt/beta-catenin and Notch) induce EMT. In particular, Ras-MAPK has been shown to activate two related transcription factors known as Snail and Slug. Both of these proteins are transcriptional repressors of E-cadherin and their expression induces EMT. Recently, activation of the phosphatidylinositol 3' kinase (PI3K)/AKT axis is emerging as a central feature of EMT.

Twist, another transcription factor, has also been shown to induce EMT, and is also implicated in the regulation of metastasis. Expression of FOXC2, an important player during embryonic development has been shown to induce EMT and regulate metastasis. Moreover, expression of FOXC2 is induced when epithelial cells undergo EMT by Snail, Twist, Goosecoid, and TGF-beta 1.

EMT can be induced by type I collagen, mediated by integrin α1β2. As cells assume a more mesenchymal phenotype, expression of molecules such as osteopontin and type 1 collagen are increased.^[1]

Initiation of metastasis involves invasion, which has many phenotypic similarities to EMT, including a loss of cell-cell adhesion mediated by E-cadherin repression and an increase in cell mobility. Loss of certain genes (e.g. Hedgehog family) has been shown to activate integrin, Wnt, and possibly other signaling pathways, leading to alterations in cell-cell adhesion.

EMT is a characteristic feature of cells undergoing proliferation. Cells expanding in-vitro, like beta cells- and epithelial phenotype, of the pancreas, assume mesenchymal phenotype. Similarly cultured hepatocytes and kidney tubular epithelial cells undergo dedifferentiation in a process similar to an EMT event. In-vivo (via KO or under cancer-inducing scenarios), EMT has been shown to occur in proliferating cells (e.g. stomach epithelium) when pathways known to be involved with EMT are altered.

Nicotine may contribute to EMT^[2]. Molecular factors that participate in EMT-related processes include also Hedgehog, nuclear factor-kappaB and Activating Transcription Factor 2^[3][4][5].

See also

Mesenchymal-epithelial transition

Sources

• Vernon, A., and LaBonne, C. (2004). "Tumor metastasis: a new twist on epithelial-mesenchymal transitions". Current Biology 14: 719–21. doi:10.1016/j.cub.2004.08.048. PMID 15341765. 

• Yang, J., Mani, S., Donaher, J., Ramaswamy, S., Itzkyson, R., Come, C., Savagner, P., Gitelman, I., Richardson, A., and Weinberg, R. (2004). "Twist, a master regulator of morphogenesis, plays an essential role in tumor metastasis". Cell 117: 927–39. doi:10.1016/j.cell.2004.06.006. PMID 15210113. .

• Sendurai A. Mani, Jing Yang, Mary Brooks, Gunda Schwaninger, Alicia Zhou, Naoyuki Miura, Jeffery L. Kutok, Kimberly Hartwell, Andrea L. Richardson, and Robert A. Weinberg (2007). "Mesenchyme Forkhead 1 (FOXC2) plays a key role in metastasis and is associated with aggressive basal-like breast cancers.". Proceedings of the National Academy of Sciences 104 (24): 10069–74. doi:10.1073/pnas.0703900104. PMID 17537911. 

• Mani SA, Guo W, Liao MJ, Eaton EN, Ayyanan A, Zhou AY, Brooks M, Reinhard F, Zhang CC, Shipitsin M, Campbell LL, Polyak K, Brisken C, Yang J, Weinberg RA. (2008). "The epithelial-mesenchymal transition generates cells with properties of stem cells". Cell 133: 704–15.. doi:10.1016/j.cell.2008.03.027.  PMID 18485877

References

1. Dasgupta P, Rizwani W, Pillai S, Kinkade R, Kovacs M, Rastogi S, Banerjee S, Carless M, Kim E, Coppola D, Haura E, Chellappan S.Nicotine induces cell proliferation, invasion and epithelial-mesenchymal transition in a variety of human cancer cell lines.Int J Cancer. 2008 Oct 9.

2. Vlahopoulos SA, Logotheti S, Mikas D, Giarika A, Gorgoulis V, Zoumpourlis V.The role of ATF-2 in oncogenesis.Bioessays. 2008 Apr;30(4):314-27. Review.

3. Huber MA, Beug H, Wirth T.Epithelial-mesenchymal transition: NF-kappaB takes center stage.Cell Cycle. 2004 Dec;3(12):1477-80. Epub 2004 Dec 4.

4. Katoh Y, Katoh M.Hedgehog signaling, epithelial-to-mesenchymal transition and miRNA (review).Int J Mol Med. 2008 Sep;22(3):271-5.