Adolf-Butenandt-Institute, Biochemistry, Ludwig-Maximilians-University, 80336 Munich, Germany.
J Neurosci. 2013 May 1;33(18):7856-69. doi: 10.1523/JNEUROSCI.3372-12.2013.
Proteolytic shedding of cell surface proteins generates paracrine signals involved in numerous signaling pathways. Neuregulin 1 (NRG1) type III is involved in myelination of the peripheral nervous system, for which it requires proteolytic activation by proteases of the ADAM family and BACE1. These proteases are major therapeutic targets for the prevention of Alzheimer's disease because they are also involved in the proteolytic generation of the neurotoxic amyloid β-peptide. Identification and functional investigation of their physiological substrates is therefore of greatest importance in preventing unwanted side effects. Here we investigated proteolytic processing of NRG1 type III and demonstrate that the ectodomain can be cleaved by three different sheddases, namely ADAM10, ADAM17, and BACE1. Surprisingly, we not only found cleavage by ADAM10, ADAM17, and BACE1 C-terminal to the epidermal growth factor (EGF)-like domain, which is believed to play a pivotal role in signaling, but also additional cleavage sites for ADAM17 and BACE1 N-terminal to that domain. Proteolytic processing at N- and C-terminal sites of the EGF-like domain results in the secretion of this domain from NRG1 type III. The soluble EGF-like domain is functionally active and stimulates ErbB3 signaling in tissue culture assays. Moreover, the soluble EGF-like domain is capable of rescuing hypomyelination in a zebrafish mutant lacking BACE1. Our data suggest that NRG1 type III-dependent myelination is not only controlled by membrane-retained NRG1 type III, but also in a paracrine manner via proteolytic liberation of the EGF-like domain.
细胞表面蛋白的蛋白水解脱落产生旁分泌信号，参与许多信号通路。神经调节蛋白 1（NRG1）III 型参与周围神经系统的髓鞘形成，为此它需要 ADAM 家族和 BACE1 的蛋白酶进行蛋白水解激活。这些蛋白酶是预防阿尔茨海默病的主要治疗靶点，因为它们还参与神经毒性淀粉样β肽的蛋白水解产生。因此，鉴定和功能研究其生理底物对于预防不必要的副作用至关重要。在这里，我们研究了 NRG1 III 型的蛋白水解加工，并证明其外显域可以被三种不同的脱落酶切割，即 ADAM10、ADAM17 和 BACE1。令人惊讶的是，我们不仅发现 ADAM10、ADAM17 和 BACE1 在表皮生长因子（EGF）样结构域的 C 端切割，这被认为在信号转导中起关键作用，而且还发现了 ADAM17 和 BACE1 在该结构域的 N 端的额外切割位点。EGF 样结构域的 N 和 C 端位点的蛋白水解加工导致 NRG1 III 型的该结构域从 NRG1 III 中分泌出来。可溶性 EGF 样结构域具有功能活性，并在组织培养测定中刺激 ErbB3 信号。此外，可溶性 EGF 样结构域能够挽救缺乏 BACE1 的斑马鱼突变体中的低髓鞘形成。我们的数据表明，NRG1 III 型依赖的髓鞘形成不仅受膜保留的 NRG1 III 型控制，而且还通过 EGF 样结构域的蛋白水解释放以旁分泌方式控制。
