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Birchmeier/Macmillan
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Cells come unglued and transition to a more motile phenotype with the help of an E3 ligase, according to new results from Walter Birchmeier and colleagues (Max-Delbrück-Center for Molecular Medicine, Berlin, Germany).8 s# t0 U+ t9 C' u4 B3 j
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Birchmeier's study focused on cadherins, adhesion molecules that act as anchors via a catenin link to the actin cytoskeleton. During embryogenesis and carcinoma progression, disruption of cadherin-mediated adhesion between epithelial cells helps them make the transition to a more mobile, mesenchymal phenotype. This transition involves endocytosis of cadherin and catenin molecules following phosphorylation by tyrosine kinases such as Src or c-Met.
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U) p# X( o' T+ C$ zIn the new study, Birchmeier identified a cadherin-binding protein, Hakai, that promotes endocytosis of the cadherin complex, leading to disruption of cell adhesion. Hakai binds to E-cadherin, the prototypical member of the cadherin family, in a phosphorylation-dependent manner. It also competes with other adhesion molecules, such as p120ctn, for E-cadherin binding.
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1 E% i) D5 m) L" b& y9 e' ^/ e& Q4 }Birchmeier says that "Hakai smelled of degradation," as it has sequence similarity to c-Cbl, an E3 ligase that ubiquitinates phosphorylated tyrosine kinase receptors and prompts their internalization and degradation. Hakai, which is Japanese for destruction, increases ubiquitination of the E-cadherin complex, particularly when E-cadherin is phosphorylated by Src or in response to growth factors.0 b# q, A, e9 L" B7 S9 I
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Disruption of cell adhesion by Hakai causes cell scattering, similar to that observed during the transition to a mesenchymal phenotype. Birchmeier now plans to test whether Hakai's motility-promoting properties are used by tumor cells to trigger invasion and metastasis.Reference:" k! d% j2 [8 v7 A4 Z
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Fujita, Y., et al., 2002. Nat. Cell Biol. 10.1038/ncb758.(Overexpression of Hakai (right) increase) |
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发表于 2009-3-6 00:18
发表于 2015-6-6 09:01
