Ozawa Masayuki
Department of Biochemistry and Molecular Biology, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima 890-8544, Japan.
J Biol Chem. 2003 Nov 14;278(46):46014-20. doi: 10.1074/jbc.M307778200. Epub 2003 Sep 2.
Cadherins are transmembrane glycoproteins that function as Ca2+-dependent cell-cell adhesion molecules and are linked to the actin cytoskeleton via catenins. Previously, we showed that, although E-cadherin lacking its cytoplasmic tail is active in aggregation assays, partially truncated E-cadherin lacking the carboxyl-terminal catenin-binding site is not. Contrary to this observation, a similar N-cadherin construct is found to be functional. Chimeric constructs, in which the membrane-proximal region of the partially truncated E-cadherin was replaced by that of N-cadherin, are active in aggregation assays. N-cadherin constructs in the opposite manner are nonfunctional. Although deletion of the membrane-proximal region, which eliminates the binding site for p120, results in activation of the nonfunctional E-cadherin mutant polypeptides, amino acid substitutions in the membrane-proximal region, which uncouple p120 binding, do not. The p120 uncoupling could not activate a full-length E-cadherin construct, which was beta-catenin-uncoupled by amino acid substitutions in the catenin-binding site. These results indicate that the membrane-proximal region determines the activity of these cadherin constructs but that p120 does not seem directly involved in the modulation of E-cadherin activity.
钙黏蛋白是跨膜糖蛋白，作为钙离子依赖的细胞间黏附分子发挥作用，并通过连环蛋白与肌动蛋白细胞骨架相连。此前，我们发现，虽然缺乏细胞质尾巴的E-钙黏蛋白在聚集试验中具有活性，但缺乏羧基末端连环蛋白结合位点的部分截短的E-钙黏蛋白则没有活性。与这一观察结果相反，类似的N-钙黏蛋白构建体被发现具有功能。将部分截短的E-钙黏蛋白的膜近端区域替换为N-钙黏蛋白的膜近端区域的嵌合构建体在聚集试验中具有活性。以相反方式构建的N-钙黏蛋白构建体则无功能。虽然缺失消除了p120结合位点的膜近端区域会导致无功能的E-钙黏蛋白突变多肽激活，但在膜近端区域进行氨基酸替换以解除p120结合则不会激活。解除p120结合无法激活全长E-钙黏蛋白构建体，该构建体通过在连环蛋白结合位点进行氨基酸替换而与β-连环蛋白解偶联。这些结果表明，膜近端区域决定了这些钙黏蛋白构建体的活性，但p120似乎并不直接参与E-钙黏蛋白活性的调节。
