ROLE OF PS1/Y-SECRETASE IN THE ANGIOGENIC PROPERTIES OF EPHRINB/EphB

阿尔茨海默病（Alzheimer's disease，AD）是一种以严重的神经血管功能障碍为特征的神经退行性疾病。越来越多的证据表明脑微血管异常与AD的神经病理学发生有关。早老素1（PS1）是AD神经病理学中的重要蛋白质。这种蛋白质的突变与许多常染色体显性形式的AD病例有关。PS1控制γ-分泌酶切割几种I型跨膜蛋白，产生具有信号传导和基因表达功能的细胞质肽。我们最近发现，PS1/γ-分泌酶切割ephrinB蛋白，并促进EphB诱导的Src磷酸化。由于ephrinB和Src在血管生成中起关键作用，因此PS1/γ-分泌酶可能调节ephrinB介导的血管生成。在这里，我们表明，γ-分泌酶促进血管生成反应的内皮细胞EphB的Src依赖性的方式和产品的γ-分泌酶切割ephrinB（ephrinB/CTF 2胞质肽），其生产是由EphB受体刺激。这表明PSI/γ-分泌酶可能调节EphB诱导的细胞凋亡。 通过切割肝配蛋白B并通过这种切割激活Src来促进血管生成。为了阐明PS1/γ-分泌酶促进EphB诱导的Src激活的机制，我们分析了ephrinB/CTF 2肽与Src调节复合物的关联。该复合物由衔接蛋白PAG/Cbp和调节激酶Csk组成，其调节Src的自磷酸化和活化。我们发现ephrinB/CTF 2与PAG/Cbp形成特异性复合物，影响其酪氨酸残基的磷酸化及其与Csk激酶的结合，并且PAG/Cbp在两种体外血管生成测定中介导EphB诱导的内皮细胞的血管生成反应。我们的数据表明，PS1/γ-分泌酶通过切割ephrinB，产生ephrinB/CTF 2肽，其与Src调节机制相互作用，促进Src激活和细胞发芽，从而促进EphB诱导的血管生成。因此，PS1/γ-分泌酶可能调节脑血管的发育和完整性，和PS1突变中发现的家族性AD可能会损害它。我们建议检查PSI/γ-分泌酶在EphB/ephrinB介导的血管生成的作用。

Alzheimer's disease (AD) is a neurodegenerative disease characterized by severe neurovascular disfunction. Increasing evidence implicates cerebral microvasculature abnormalities in the genesis of AD neuropathology. Presenilin 1 (PS1) is a protein of central importance to the neuropathology of AD. Mutations in this protein are linked to many cases of autosomal dominant forms of AD. PS1 controls the y-secretase cleavage of several type I transmembrane proteins producing cytoplasmic peptides with signaling and gene expression functions. We recently showed that PS1/y-secretase cleaves ephrinB proteins and promotes the EphB-induced phosphorylation of Src. Since both ephrinB and Src play a critical role in angiogenesis it is possible that PS1/y-secretase may regulate ephrinB-mediated angiogenesis. Here we show that y-secretase promotes the angiogenic response of endothelial cells to EphB in a Src-dependent manner and so does the product of y-secretase cleavage of ephrinB (ephrinB/CTF2 cytoplasmic peptide), whose production is stimulated by EphB receptor. This suggests that PSI/y-secretase may regulate the EphB-induced angiogenesis by cleaving ephrinB and activating Src via this cleavage. To elucidate the mechanism by which PS1/y-secretase promotes the EphB-induced Src activation we analyze the association of ephrinB/CTF2 peptide with the Src regulatory complex. This complex consists of the adaptor protein PAG/Cbp and the regulatory kinase Csk, which regulate the autophosphorylation and activation of Src. We found that ephrinB/CTF2 forms specific complexes with PAG/Cbp affecting its phosphorylation on tyrosine residues and its association with Csk kinase and that PAG/Cbp mediates the EphB-induced angiogenic response of endothelial cells in two in vitro angiogenesis assays. Our data suggest that PS1/y-secretase promotes EphBinduced angiogenesis by cleaving ephrinB, producing ephrinB/CTF2 peptide, which interacts with the Src regulatory machinery promoting Src activation and cell sprouting. Thus PS1/y-secretase may regulate development and integrity of the brain vasculature, and PS1 mutations found in Familial AD may impair it. We propose to examine the role of PSI/y-secretase in the EphB/ephrinB-mediated angiogenesis.