Mechanisms of beta-APP Processing in the Brain

我们基于其他系统中细胞间相互作用的先例提出了一个假设，该细胞间相互作用对单个跨膜蛋白和七个跨膜整合蛋白之间的发育至关重要，即一种或多种形式的β-淀粉样前体蛋白（Beta-APP）和早老素1或2（PS-1或2）通常可能是细胞间分泌物信号系统的组分（1）。我们已经表明，B-APP和PS-1和2是在细胞表面表达，β-APP和早老素细胞间相互作用，这种相互作用的结果在信号转导，最后，我们的假设最关键的测试：AB是产生作为结果的β-APP与PS-1或PS-2的跨细胞结合。在本申请中，我们扩展了我们的原始假设，提出β-APP和PS的细胞间结合也是β-APP在α位点切割所需的。PS-1似乎不仅调节不同的γ-分泌酶活性，还调节诱导型α-分泌酶活性（2）。到目前为止，还没有详细的机制来说明这是如何发生的。我们认为，在β-APP与PS-1或PS-2的细胞-细胞相互作用后，ABeta可能通过内吞途径产生，或者，细胞表面机制运作，β-APP被α-分泌酶切割，排除ABeta的形成。然后β-APP的α-切割胞外域脱落，可能触发细胞-细胞去粘附，如对肝配蛋白所述（3）。因此，该模型提出，要发生α-裂解，β-APP必须首先与PS-1或PS-2发生细胞间相互作用。我们的具体目标是：1.研究β-APP的切割和胞外域脱落是否需要β-APP与PS-1或PS-2结合介导的特异性细胞间相互作用，并研究可溶性β-APP产生与ABeta产生的定量关系。2.研究β-APP与PS细胞间结合后细胞-细胞接触区域的事件，以激活β-APP的α-分泌酶蛋白水解和接触细胞的可能分离。3.研究β-APP：PS细胞间结合诱导的生化信号是否是β-APP α裂解所必需的。

We had proposed a hypothesis based on precedents in other systems of an intercellular interaction crucial to development between single membrane spanning and seven membrane spanning integral proteins, that one or more forms of the Beta-amyloid precursor protein (Beta-APP) and Presenilin 1 or 2 (PS-1 or 2) may normally be components of an intercellular juxtacrine signaling system (1). We have shown that B-APP and PS-1 and 2 are expressible at the cell surface, that Beta-APP and the presenilins interact intercellularly, that this interaction results in signaling and finally, the most critical test of our hypothesis: that AB is produced as a result of the transcellular binding of Beta-APP with PS-1 or PS-2. In this application we are extending our original hypothesis to propose that intercellular binding of Beta-APP and PS is also required for the cleavage of Beta-APP at the alpha-site. PS-1 appears to regulate not only distinct gamma-secretase activities, but inducible alpha-secretase activity as well (2). No detailed mechanisms have so far been described as to how this might happen. We propose that after cell-cell interaction of Beta-APP with PS-1 or PS-2, either ABeta may be produced via an endocytic pathway, or alternatively, a cell-surface mechanism operates and Beta-APP is cleaved by alpha-secretase, precluding the formation of ABeta. The alpha-cleaved ectodomain of Beta-APP is then shed, possibly triggering a cell-cell de-adhesion, as has been described for the ephrins (3). Therefore, this model proposes that for alpha-cleavage to occur, Beta-APP must first interact intercellularly with PS-1 or PS-2. Our specific aims are: 1. To investigate whether or-cleavage of Beta-APP and ectodomain shedding requires the prior specific cell-cell interaction mediated by the binding of Beta-APP with either PS-1 or PS-2 and to investigate the quantitative relationship of soluble Beta-APP production to ABeta production. 2. To investigate events at regions of cell-cell contact following the intercellular binding of Beta-APP with PS for the activation of alpha-secretase proteolysis of Beta-APP and the possible detachment of the contacting cells. 3. To investigate whether the biochemical signals that are induced by Beta-APP:PS intercellular binding are required for the alpha cleavage of Beta-APP.