Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA.
Dev Cell. 2012 Jun 12;22(6):1299-312. doi: 10.1016/j.devcel.2012.04.005. Epub 2012 May 31.
Notch signaling induced by cell surface ligands is critical to development and maintenance of many eukaryotic organisms. Notch and its ligands are integral membrane proteins that facilitate direct cell-cell interactions to activate Notch proteolysis and release the intracellular domain that directs Notch-specific cellular responses. Genetic studies suggest that Notch ligands require endocytosis, ubiquitylation, and epsin endocytic adaptors to activate signaling, but the exact role of ligand endocytosis remains unresolved. Here we characterize a molecularly distinct mode of clathrin-mediated endocytosis requiring ligand ubiquitylation, epsins, and actin for ligand cells to activate signaling in Notch cells. Using a cell-bead optical tweezers system, we obtained evidence for cell-mediated mechanical force dependent on this distinct mode of ligand endocytosis. We propose that the mechanical pulling force produced by endocytosis of Notch-bound ligand drives conformational changes in Notch that permit activating proteolysis.
细胞表面配体诱导的 Notch 信号对于许多真核生物的发育和维持至关重要。Notch 和其配体是整合膜蛋白，它们促进直接的细胞间相互作用，以激活 Notch 蛋白水解并释放指导 Notch 特异性细胞反应的细胞内结构域。遗传研究表明，Notch 配体需要内吞作用、泛素化和衔接蛋白 epsin 来激活信号，但配体内吞的确切作用仍未解决。在这里，我们描述了一种分子上不同的网格蛋白介导的内吞作用模式，该模式需要配体泛素化、衔接蛋白 epsin 和肌动蛋白，以使配体细胞在 Notch 细胞中激活信号。使用细胞珠光镊系统，我们获得了证据表明，这种配体内吞的独特模式依赖于细胞介导的机械力。我们提出，由 Notch 结合配体的内吞作用产生的机械拉力驱动 Notch 构象变化，从而允许激活蛋白水解。
