Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.
Development. 2010 Jun;137(11):1825-32. doi: 10.1242/dev.045484.
Evidence indicates that endosomal entry promotes signaling by the Notch receptor, but the mechanisms involved are not clear. In a search for factors that regulate Notch activation in endosomes, we isolated mutants in Drosophila genes that encode subunits of the vacuolar ATPase (V-ATPase) proton pump. Cells lacking V-ATPase function display impaired acidification of the endosomal compartment and a correlated failure to degrade endocytic cargoes. V-ATPase mutant cells internalize Notch and accumulate it in the lysosome, but surprisingly also show a substantial loss of both physiological and ectopic Notch activation in endosomes. V-ATPase activity is required in signal-receiving cells for Notch signaling downstream of ligand activation but upstream of gamma-secretase-dependent S3 cleavage. These data indicate that V-ATPase, probably via acidification of early endosomes, promotes not only the degradation of Notch in the lysosome but also the activation of Notch signaling in endosomes. The results also suggest that the ionic properties of the endosomal lumen might regulate Notch cleavage, providing a rationale for physiological as well as pathological endocytic control of Notch activity.
有证据表明，内体进入可促进 Notch 受体的信号转导，但涉及的机制尚不清楚。在寻找调节 Notch 在内涵体中激活的因素时，我们分离了果蝇基因编码液泡 ATP 酶（V-ATPase）质子泵亚基的突变体。缺乏 V-ATPase 功能的细胞显示内涵体酸化受损，并且相关的内吞货物降解失败。V-ATPase 突变体细胞内化 Notch 并将其积累在溶酶体中，但令人惊讶的是，它们在内涵体中也表现出生理和异位 Notch 激活的大量丧失。在配体激活下游的信号接收细胞中，V-ATPase 活性是 Notch 信号转导所必需的，但在 γ-分泌酶依赖性 S3 切割的上游。这些数据表明，V-ATPase 可能通过早期内涵体的酸化，不仅促进了溶酶体中 Notch 的降解，而且促进了内涵体中 Notch 信号转导的激活。这些结果还表明，内涵体腔的离子特性可能调节 Notch 切割，为生理和病理内吞控制 Notch 活性提供了依据。
