Mechanisms of beta-APP Processing in the Brain

我们根据其他系统中的先例提出了一个假设，即β-淀粉样前体蛋白(Beta-APP)和早老素1或2(PS-1或2)的一种或多种形式通常可能是细胞间旁分泌信号系统(1)的组成部分。我们已经证明了B-APP和PS-1和PS-2在细胞表面是可表达的，β-APP和早老素在细胞间相互作用，这种相互作用导致了信号传递，最后，对我们的假设最关键的检验：AB是由于Beta-APP与PS-1或PS-2跨细胞结合的结果。在本申请中，我们扩展了我们最初的假设，提出β-APP和PS的细胞间结合也是β-APP在α-位点切割所必需的。PS-1似乎不仅调节不同的伽马分泌酶活性，而且还调节诱导的α分泌酶活性(2)。到目前为止，还没有关于这可能如何发生的详细机制的描述。我们认为，在β-APP与PS-1或PS-2的细胞-细胞相互作用后，ABeta可能是通过内吞途径产生的，或者是细胞-表面机制作用，β-APP被α-分泌酶切割，从而阻止ABeta的形成。然后，β-APP的α-裂解胞外结构域被剥离，可能触发细胞-细胞间的去黏附，就像已经描述的ephins(3)一样。因此，这个模型提出，为了发生α-切割，β-APP必须首先与PS-1或PS-2进行细胞间相互作用。我们的具体目标是：1.研究β-APP的裂解和胞外结构域的脱落是否需要事先通过β-APP与PS-1或PS-2的结合而介导的细胞-细胞之间的特异性相互作用，以及可溶性β-APP的产生与ABeta的产生之间的定量关系。2.研究β-APP与PS细胞间结合后细胞-细胞接触区发生的事件，以激活β-APP的α-分泌酶蛋白分解，以及可能的接触细胞的脱落。3.探讨β-APP：PS细胞间结合诱导的生化信号是否为β-APP的α-裂解所必需。

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.