Division of Cell Biology, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe 650-0017, Japan.
J Cell Sci. 2011 Feb 15;124(Pt 4):548-55. doi: 10.1242/jcs.072058. Epub 2011 Jan 18.
Epithelial cell contacts consist of not only bicellular contacts but also tricellular contacts, where the corners of three cells meet. At tricellular contacts, tight junctions (TJs) generate specialized structures termed tricellular TJs (tTJs) to seal the intercellular space. Tricellulin is the only known molecular component of tTJs and is involved in the formation of tTJs, as well as in the normal epithelial barrier function. However, the detailed molecular mechanism of how tTJs are formed and maintained remains elusive. Using a localization-based expression cloning method, we identified a novel tTJ-associated protein known as lipolysis-stimulated lipoprotein receptor (LSR). Upon LSR knockdown in epithelial cells, tTJ formation was affected and the epithelial barrier function was diminished. Tricellulin accumulation at the tricellular contacts was also diminished in these cells. By contrast, LSR still accumulated at the tricellular contacts upon tricellulin knockdown. Analyses of deletion mutants revealed that the cytoplasmic domain of LSR was responsible for the recruitment of tricellulin. On the basis of these observations, we propose that LSR defines tricellular contacts in epithelial cellular sheets by acting as a landmark to recruit tricellulin for tTJ formation.
上皮细胞连接不仅包括双细胞连接，还包括三个细胞角接触形成的三细胞连接。在三细胞连接中，紧密连接（TJ）形成特化结构，称为三细胞 TJ（tTJ），以封闭细胞间隙。桥粒芯糖蛋白是 tTJ 的唯一已知分子组成部分，参与 tTJ 的形成以及上皮正常屏障功能。然而，tTJ 形成和维持的详细分子机制仍不清楚。我们使用基于定位的表达克隆方法，鉴定了一种新型的 tTJ 相关蛋白，称为脂肪酶刺激脂蛋白受体（LSR）。在上皮细胞中敲低 LSR 后，tTJ 的形成受到影响，上皮屏障功能减弱。这些细胞中，桥粒芯糖蛋白在三细胞连接处的积累也减少。相比之下，在敲低桥粒芯糖蛋白后，LSR 仍在三细胞连接处积累。缺失突变体分析表明，LSR 的细胞质结构域负责招募桥粒芯糖蛋白。基于这些观察结果，我们提出 LSR 通过作为招募桥粒芯糖蛋白形成 tTJ 的标志物，在上皮细胞层中定义三细胞连接。
