Braga V M, Del Maschio A, Machesky L, Dejana E
MRC-Laboratory for Molecular Cell Biology, University College London, WC1E 6BT, London, United Kingdom.
Mol Biol Cell. 1999 Jan;10(1):9-22. doi: 10.1091/mbc.10.1.9.
Cadherins are cell-cell adhesion receptors whose adhesive function requires their association with the actin cytoskeleton via proteins called catenins. The small guanosine triphosphatases (GTPases), Rho and Rac, are intracellular proteins that regulate the formation of distinct actin structures in different cell types. In keratinocytes and in other epithelial cells, Rho and Rac activities are required for E-cadherin function. Here we show that the regulation of cadherin adhesiveness by the small GTPases is influenced by the maturation status of the junction and the cellular context. E-cadherin localization was disrupted in mature keratinocyte junctions after inhibition of Rho and Rac. However, an incubation of 2 h was required after GTPase inhibition, when compared with newly established E-cadherin contacts (30 min). Regarding other cadherin receptors, P-cadherin was effectively removed from mature keratinocytes junctions by blocking Rho or Rac. In contrast, VE-cadherin localization at endothelial junctions was independent of Rho/Rac activity. We demontrate that the insensitivity of VE-cadherin to inhibition of Rho and Rac was not due to the maturation status of endothelial junction, but rather the cellular background: when transfected into CHO cells, the localization of VE-cadherin was perturbed by inhibition of Rho proteins. Our results suggest that the same stimuli may have different activity in regulating the paracellular activity in endothelial and epithelial cells. In addition, we uncovered possible roles for the small GTPases during the establishment of E-cadherin-dependent contacts. In keratinocytes, Rac activation by itself cannot promote accumulation of actin at the cell periphery in the absence of cadherin-dependent contacts. Moreover, neither Rho nor Rac activation was sufficient to redistribute cadherin molecules to cell borders, indicating that redistribution results mostly from the homophilic binding of the receptors. Our results point out the complexity of the regulation of cadherin-mediated adhesion by the small GTPases, Rho and Rac.
钙黏蛋白是细胞间黏附受体，其黏附功能需要通过称为连环蛋白的蛋白质与肌动蛋白细胞骨架结合。小GTP酶（GTPases）Rho和Rac是细胞内蛋白质，可调节不同细胞类型中不同肌动蛋白结构的形成。在角质形成细胞和其他上皮细胞中，Rho和Rac活性是E-钙黏蛋白功能所必需的。在这里，我们表明小GTP酶对钙黏蛋白黏附性的调节受连接的成熟状态和细胞环境的影响。在抑制Rho和Rac后，成熟角质形成细胞连接中的E-钙黏蛋白定位被破坏。然而，与新建立的E-钙黏蛋白接触（30分钟）相比，GTP酶抑制后需要2小时的孵育时间。关于其他钙黏蛋白受体，通过阻断Rho或Rac可有效从成熟角质形成细胞连接中去除P-钙黏蛋白。相反，VE-钙黏蛋白在内皮连接中的定位与Rho/Rac活性无关。我们证明VE-钙黏蛋白对Rho和Rac抑制的不敏感性不是由于内皮连接的成熟状态，而是由于细胞背景：当转染到CHO细胞中时，VE-钙黏蛋白的定位会因Rho蛋白的抑制而受到干扰。我们的结果表明，相同的刺激在调节内皮细胞和上皮细胞的细胞旁活性方面可能具有不同的活性。此外，我们发现了小GTP酶在建立E-钙黏蛋白依赖性接触过程中的可能作用。在角质形成细胞中，在没有钙黏蛋白依赖性接触的情况下，Rac自身激活不能促进肌动蛋白在细胞周边的积累。此外，Rho和Rac的激活都不足以将钙黏蛋白分子重新分布到细胞边界，这表明重新分布主要是由受体的同源结合引起的。我们的结果指出了小GTP酶Rho和Rac对钙黏蛋白介导的黏附调节的复杂性。
