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

阿尔茨海默病(AD)是一种以严重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神经病理的发生有关。早老素1(PS1)是阿尔茨海默病(AD)神经病理中的一种重要蛋白。该蛋白的突变与许多常染色体显性类型的AD有关。PS1控制几种I型跨膜蛋白的γ-分泌酶的裂解，产生具有信号和基因表达功能的细胞质多肽。我们最近发现PS1/y-分泌酶可以裂解EphinB蛋白，并促进EphB诱导的Src的磷酸化。由于eaffinB和Src在血管生成中都起着关键作用，因此PS1/y-分泌酶可能调节eaffinB介导的血管生成。在这里，我们发现，Y-分泌酶以一种依赖于Src的方式促进内皮细胞对EphB的血管生成反应，同时也促进了由EphB受体刺激的EphB的Y-分泌酶裂解产物(ewitinB/CTF2细胞质多肽)的产生。提示PSI/y-分泌酶可能对EphB诱导的 通过裂解肾上腺素B和通过这种裂解激活Src的血管生成。为了阐明PS1/y-分泌酶促进EphB诱导的Src激活的机制，我们分析了ewitinB/CTF2多肽与Src调节复合体的关系。该复合体由适配蛋白PAG/CBP和调节蛋白CSK组成，调节Src的自磷酸化和激活。在两种体外血管生成实验中，我们发现EphinB/CTF2与PAG/CBP形成特异的复合体，影响其酪氨酸残基的磷酸化及其与CSK激酶的结合，PAG/CBP介导了EphB诱导的内皮细胞血管生成反应。我们的研究结果表明，PS1/y-分泌酶通过裂解EphB，产生eaffinB/CTF2多肽来促进EphB诱导的血管生成，该多肽与Src调节机制相互作用，促进Src的激活和细胞的萌发。因此，PS1/y-分泌酶可能调节脑血管系统的发育和完整性，而在家族性AD中发现的PS1突变可能会损害它。我们建议研究PSI/y-分泌酶在EphB/ewitinB介导的血管生成中的作用。

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.