Schroeter E H, Kisslinger J A, Kopan R
Department of Molecular Biology and Pharmacology, Washington University, St Louis, Missouri 63110, USA.
Nature. 1998 May 28;393(6683):382-6. doi: 10.1038/30756.
Notch proteins are ligand-activated transmembrane receptors involved in cell-fate selection throughout development. No known enzymatic activity is contained within Notch and the molecular mechanism by which it transduces signals across the cell membrane is poorly understood. In many instances, Notch activation results in transcriptional changes in the nucleus through an association with members of the CSL family of DNA-binding proteins (where CSL stands for CBF1, Su(H), Lag-1). As Notch is located in the plasma membrane and CSL is a nuclear protein, two models have been proposed to explain how they interact. The first suggests that the two interact transiently at the membrane. The second postulates that Notch is cleaved by a protease, enabling the cleaved fragment to enter the nucleus. Here we show that signalling by a constitutively active membrane-bound Notch-1 protein requires the proteolytic release of the Notch intracellular domain (NICD), which interacts preferentially with CSL. Very small amounts of NICD are active, explaining why it is hard to detect in the nucleus in vivo. We also show that it is ligand binding that induces release of NICD.
Notch蛋白是配体激活的跨膜受体，在整个发育过程中参与细胞命运的选择。Notch蛋白本身不具有已知的酶活性，其跨细胞膜转导信号的分子机制也鲜为人知。在许多情况下，Notch激活通过与DNA结合蛋白CSL家族成员的结合（CSL代表CBF1、Su(H)、Lag-1）导致细胞核内的转录变化。由于Notch位于质膜上，而CSL是一种核蛋白，因此提出了两种模型来解释它们如何相互作用。第一种模型认为两者在膜上短暂相互作用。第二种模型假定Notch被蛋白酶切割，使切割后的片段能够进入细胞核。在此我们表明，组成型活性膜结合Notch-1蛋白的信号传导需要Notch细胞内结构域（NICD）的蛋白水解释放，该结构域优先与CSL相互作用。极少量的NICD具有活性，这解释了为什么在体内细胞核中很难检测到它。我们还表明，是配体结合诱导了NICD的释放。
