Yamamura Rie, Nishimura Noriyuki, Nakatsuji Hiroyoshi, Arase Seiji, Sasaki Takuya
Department of Biochemistry, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima 770-8503, Japan.
Mol Biol Cell. 2008 Mar;19(3):971-83. doi: 10.1091/mbc.e07-06-0551. Epub 2007 Dec 19.
The assembly of tight junctions (TJs) and adherens junctions (AJs) is regulated by the transport of integral TJ and AJ proteins to and/or from the plasma membrane (PM) and it is tightly coordinated in epithelial cells. We previously reported that Rab13 and a junctional Rab13-binding protein (JRAB)/molecule interacting with CasL-like 2 (MICAL-L2) mediated the endocytic recycling of an integral TJ protein occludin and the formation of functional TJs. Here, we investigated the role of Rab13 and JRAB/MICAL-L2 in the transport of other integral TJ and AJ proteins claudin-1 and E-cadherin to the PM by using a Ca(2+)-switch model. Although knockdown of Rab13 specifically suppressed claudin-1 and occludin but not E-cadherin transport, knockdown of JRAB/MICAL-L2 and expression of its Rab13-binding domain (JRAB/MICAL-L2-C) inhibited claudin-1, occludin, and E-cadherin transport. We then identified Rab8 as another JRAB/MICAL-L2-C-binding protein. Knockdown of Rab8 inhibited the Rab13-independent transport of E-cadherin to the PM. Rab8 and Rab13 competed with each other for the binding to JRAB/MICAL-L2 and functionally associated with JRAB/MICAL-L2 at the perinuclear recycling/storage compartments and PM, respectively. These results suggest that the interaction of JRAB/MICAL-L2 with Rab8 and Rab13 coordinates the assembly of AJs and TJs.
紧密连接（TJs）和黏着连接（AJs）的组装受整合型TJ和AJ蛋白在质膜（PM）内外转运的调控，且在上皮细胞中这种调控是紧密协调的。我们之前报道过，Rab13和一种连接性Rab13结合蛋白（JRAB）/与CasL样分子2相互作用的分子（MICAL-L2）介导了整合型TJ蛋白闭合蛋白的内吞再循环以及功能性TJs的形成。在此，我们利用Ca(2+)转换模型研究了Rab13和JRAB/MICAL-L2在其他整合型TJ和AJ蛋白（紧密连接蛋白-1和E-钙黏蛋白）向PM转运中的作用。虽然敲低Rab13特异性抑制了紧密连接蛋白-1和闭合蛋白的转运，但未抑制E-钙黏蛋白的转运，而敲低JRAB/MICAL-L2及其Rab13结合结构域（JRAB/MICAL-L2-C）的表达则抑制了紧密连接蛋白-1、闭合蛋白和E-钙黏蛋白的转运。随后我们鉴定出Rab8是另一种JRAB/MICAL-L2-C结合蛋白。敲低Rab8抑制了E-钙黏蛋白向PM的不依赖Rab13的转运。Rab8和Rab13相互竞争与JRAB/MICAL-L2的结合，并且分别在核周再循环/储存区室和PM与JRAB/MICAL-L2在功能上相关联。这些结果表明，JRAB/MICAL-L2与Rab8和Rab13的相互作用协调了AJs和TJs的组装。
