Notch subunit heterodimerization and prevention of ligand-independent proteolytic activation depend, respectively, on a novel domain and the LNR repeats
Notch subunit heterodimerization and prevention of ligand-independent proteolytic activation depend, respectively, on a novel domain and the LNR repeats
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DOI：
10.1128/mcb.24.21.9265-9273.2004
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发表时间：
2004-11-01
影响因子：
5.3
通讯作者：
Blacklow, SC
中科院分区：
文献类型：
--
作者：
Sanchez-Irizarry, C;Carpenter, AC;Blacklow, SC
Notch蛋白是一种跨膜受体，参与调节后生动物形态发生的高度保守的信号通路。新合成的Notch受体在转运到细胞表面的过程中被蛋白水解性切割，形成由非共价结合的胞外(N-EC)和跨膜(N-TM)亚单位组成的异二聚体成熟受体。配体结合通过诱导两个连续的蛋白水解性切割来激活Notch，分别由金属蛋白酶和伽马分泌酶催化，允许N-TM的胞内部分移位到细胞核并激活靶基因的转录。先前的工作表明，N-EC的存在阻止了N-TM的非配体依赖的激活，但涉及的机制尚不清楚。在这里，我们定义了N-EC C末端的两个区域的作用，这两个区域通过不同的机制参与维持静息Notch受体的完整性。第一个区域是N-EC的疏水的、以前未被描述的部分，足以与N-TM的胞外部分形成稳定的复合物。第二个区域由三个Lin12/Notch重复序列组成，它不是异源二聚所必需的，而是保护N-TM免受金属蛋白水解酶的非配体切割。总之，N-EC的这两个相邻区域施加了关键的限制，阻止了Notch受体的过早激活。
Notch proteins are transmembrane receptors that participate in a highly conserved signaling pathway that regulates morphogenesis in metazoans. Newly synthesized Notch receptors are proteolytically cleaved during transit to the cell surface, creating heterodimeric mature receptors comprising noncovalently associated extracellular (N-EC) and transmembrane (N-TM) Subunits. Ligand binding activates Notch by inducing two successive proteolytic cleavages, catalyzed by metalloproteases and gamma-secretase, respectively, that permit the intracellular portion of N-TM to translocate to the nucleus and activate transcription of target genes. Prior work has shown that the presence of N-EC prevents ligand-independent activation of N-TM, but the mechanisms involved are poorly understood. Here, we define the roles of two regions at the C-terminal end of N-EC that participate in maintaining the integrity of resting Notch receptors through distinct mechanisms. The first region, a hydrophobic, previously uncharacterized portion of N-EC, is sufficient to form stable complexes with the extraceltular portion of N-TM. The second region, consisting of the three Lin12/Notch repeats, is not needed for heterodimerization but acts to protect N-TM from ligand-independent cleavage by metalloproteases. Together, these two contiguous regions of N-EC impose crucial restraints that prevent premature Notch receptor activation.