Koo E H, Squazzo S L
Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts 02115.
J Biol Chem. 1994 Jul 1;269(26):17386-9.
Amyloid beta-protein (A beta), the 40-43-amino acid polypeptide that is the principal constituent of senile plaques found in Alzheimer's disease, is constitutively produced and released into medium of cultured cells by an unclear mechanism. In this study, we report that one route of A beta generation involves the internalization of cell surface amyloid precursor protein (beta PP) via the coated pit-mediated endocytic pathway. Radiolabeled A beta can be recovered in medium following selective cell surface radioiodination, indicating that cell surface beta PP is a direct precursor to A beta. In addition, deletion of the cytoplasmic domains of beta PP or depletion of potassium in medium, both of which resulted in reduced beta PP internalization, significantly diminished A beta release. Moreover, pulse-chase experiments after surface radioiodination showed that the kinetics of beta PP secretion and A beta release was different, with the latter occurring at a significantly slower rate. We therefore hypothesize that the internalization of cell surface beta PP via coated pit-mediated endocytosis is one pathway leading to A beta generation and release into medium.
淀粉样β蛋白（Aβ）是一种由40 - 43个氨基酸组成的多肽，是阿尔茨海默病中发现的老年斑的主要成分，其通过一种不明机制持续产生并释放到培养细胞的培养基中。在本研究中，我们报告Aβ产生的一条途径涉及细胞表面淀粉样前体蛋白（βPP）通过被膜小窝介导的内吞途径内化。在选择性细胞表面放射性碘化后，放射性标记的Aβ可在培养基中回收，这表明细胞表面βPP是Aβ的直接前体。此外，βPP胞质结构域的缺失或培养基中钾的耗尽，这两者均导致βPP内化减少，显著减少了Aβ的释放。而且，表面放射性碘化后的脉冲追踪实验表明，βPP分泌和Aβ释放的动力学不同，后者的发生速率明显较慢。因此，我们推测细胞表面βPP通过被膜小窝介导的内吞作用内化是导致Aβ产生并释放到培养基中的一条途径。
