Saadipour Khalil, MacLean Michael, Pirkle Sean, Ali Solav, Lopez-Redondo Maria-Luisa, Stokes David L, Chao Moses V
From the Departments of Cell Biology, Physiology & Neuroscience, and Psychiatry, Skirball Institute of Biomolecular Medicine, New York University Langone Medical Center, New York, New York 10016
From the Departments of Cell Biology, Physiology & Neuroscience, and Psychiatry, Skirball Institute of Biomolecular Medicine, New York University Langone Medical Center, New York, New York 10016.
J Biol Chem. 2017 Oct 6;292(40):16594-16604. doi: 10.1074/jbc.M117.788729. Epub 2017 Aug 17.
The function of protein products generated from intramembraneous cleavage by the γ-secretase complex is not well defined. The γ-secretase complex is responsible for the cleavage of several transmembrane proteins, most notably the amyloid precursor protein that results in Aβ, a transmembrane (TM) peptide. Another protein that undergoes very similar γ-secretase cleavage is the p75 neurotrophin receptor. However, the fate of the cleaved p75 TM domain is unknown. p75 neurotrophin receptor is highly expressed during early neuronal development and regulates survival and process formation of neurons. Here, we report that the p75 TM can stimulate the phosphorylation of TrkB (tyrosine kinase receptor B). phosphorylation experiments indicated that a peptide representing p75 TM increases TrkB phosphorylation in a dose- and time-dependent manner. Moreover, mutagenesis analyses revealed that a valine residue at position 264 in the rat p75 neurotrophin receptor is necessary for the ability of p75 TM to induce TrkB phosphorylation. Because this residue is just before the γ-secretase cleavage site, we then investigated whether the p75(αγ) peptide, which is a product of both α- and γ-cleavage events, could also induce TrkB phosphorylation. Experiments using TM domains from other receptors, EGFR and FGFR1, failed to stimulate TrkB phosphorylation. Co-immunoprecipitation and biochemical fractionation data suggested that p75 TM stimulates TrkB phosphorylation at the cell membrane. Altogether, our results suggest that TrkB activation by p75(αγ) peptide may be enhanced in situations where the levels of the p75 receptor are increased, such as during brain injury, Alzheimer's disease, and epilepsy.
γ-分泌酶复合物通过膜内裂解产生的蛋白质产物的功能尚未明确界定。γ-分泌酶复合物负责切割几种跨膜蛋白，最显著的是淀粉样前体蛋白，其切割产物为Aβ，一种跨膜（TM）肽。另一种经历非常相似的γ-分泌酶切割的蛋白是p75神经营养因子受体。然而，切割后的p75 TM结构域的去向尚不清楚。p75神经营养因子受体在神经元早期发育过程中高度表达，并调节神经元的存活和突起形成。在此，我们报告p75 TM可以刺激TrkB（酪氨酸激酶受体B）的磷酸化。磷酸化实验表明，代表p75 TM的肽以剂量和时间依赖性方式增加TrkB磷酸化。此外，诱变分析显示，大鼠p75神经营养因子受体第264位的缬氨酸残基是p75 TM诱导TrkB磷酸化能力所必需的。由于该残基恰好在γ-分泌酶切割位点之前，我们随后研究了作为α-和γ-切割事件产物的p75(αγ)肽是否也能诱导TrkB磷酸化。使用来自其他受体（表皮生长因子受体和纤维母细胞生长因子受体1）的TM结构域进行的实验未能刺激TrkB磷酸化。免疫共沉淀和生化分级分离数据表明，p75 TM在细胞膜上刺激TrkB磷酸化。总之，我们的结果表明，在p75受体水平升高的情况下，如脑损伤、阿尔茨海默病和癫痫期间，p75(αγ)肽对TrkB的激活作用可能会增强。
