Lin Ya-Huei, Currinn Heather, Pocha Shirin Meher, Rothnie Alice, Wassmer Thomas, Knust Elisabeth
Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany.
School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK.
J Cell Sci. 2015 Dec 15;128(24):4538-49. doi: 10.1242/jcs.174573. Epub 2015 Nov 2.
Maintenance of epithelial polarity depends on the correct localization and levels of polarity determinants. The evolutionarily conserved transmembrane protein Crumbs is crucial for the size and identity of the apical membrane, yet little is known about the molecular mechanisms controlling the amount of Crumbs at the surface. Here, we show that Crumbs levels on the apical membrane depend on a well-balanced state of endocytosis and stabilization. The adaptor protein 2 (AP-2) complex binds to a motif in the cytoplasmic tail of Crumbs that overlaps with the binding site of Stardust, a protein known to stabilize Crumbs on the surface. Preventing endocytosis by mutation of AP-2 causes expansion of the Crumbs-positive plasma membrane domain and polarity defects, which can be partially rescued by removing one copy of crumbs. Strikingly, knocking down both AP-2 and Stardust leads to the retention of Crumbs on the membrane. This study provides evidence for a molecular mechanism, based on stabilization and endocytosis, to adjust surface levels of Crumbs, which are essential for maintaining epithelial polarity.
上皮极性的维持取决于极性决定因子的正确定位和水平。进化上保守的跨膜蛋白Crumb对顶端膜的大小和特性至关重要，但对于控制表面Crumb数量的分子机制却知之甚少。在这里，我们表明顶端膜上的Crumb水平取决于内吞作用和稳定性的良好平衡状态。衔接蛋白2（AP-2）复合物与Crumb胞质尾部的一个基序结合，该基序与星尘蛋白的结合位点重叠，星尘蛋白是一种已知能在表面稳定Crumb的蛋白质。通过AP-2突变阻止内吞作用会导致Crumb阳性质膜结构域扩张和极性缺陷，去除一个拷贝的crumbs可部分挽救这种缺陷。引人注目的是，敲低AP-2和星尘蛋白都会导致Crumb保留在膜上。这项研究为一种基于稳定性和内吞作用来调节Crumb表面水平的分子机制提供了证据，而Crumb表面水平对于维持上皮极性至关重要。
