Yamazaki T, Koo E H, Selkoe D J
Department of Neurology, Harvard Medical School, Boston, MA 02115, USA.
J Cell Sci. 1996 May;109 ( Pt 5):999-1008. doi: 10.1242/jcs.109.5.999.
Amyloid beta-protein (A beta) is a proteolytic fragment of the amyloid beta-protein precursor (beta PP). Progressive cerebral deposition of A beta is an early and invariant feature of Alzheimer's disease. The cellular trafficking of beta PP is of particular interest because understanding the production of A beta requires a comprehensive elucidation of the metabolic pathways of this protein. In addition, beta PP is a type I integral membrane glycoprotein that belongs to a class of molecules with both full length and secreted products. Recent evidence suggests that beta PP can be processed in an endosomal/lysosomal pathway. In the latter organelles, a number of beta PP carboxy-terminal derivatives are found, but the precise pathway and kinetics of beta PP trafficking from the cell surface remain unclear. To address these questions, we visualized directly the beta PP internalization pathway by following the localization and distribution of beta PP monoclonal antibodies added to intact beta PP-transfected Chinese hamster ovary cells. Using immunofluorescence and immunoelectron microscopy, beta PP was shown to be rapidly internalized via coated pits and vesicles, after which the molecules were transported to endosomes, prelysosomes, and lysosomes. Using a modified immunodetection protocol, we demonstrated the rapid recycling of endocytosed beta PP to the cell surface and its ultimate targeting to lysosomes. Because we recently found that endocytosis of cell surface beta PP is one route for the constitutive production of A beta, the recycling pathway for cell surface beta PP demonstrated here is a probable route for production of the critical A beta fragment.
淀粉样β蛋白（Aβ）是淀粉样β蛋白前体（βPP）的蛋白水解片段。Aβ在大脑中的进行性沉积是阿尔茨海默病的早期且不变的特征。βPP的细胞运输特别令人感兴趣，因为了解Aβ的产生需要全面阐明该蛋白的代谢途径。此外，βPP是一种I型整合膜糖蛋白，属于一类既有全长产物又有分泌产物的分子。最近的证据表明，βPP可以在内体/溶酶体途径中进行加工。在后者的细胞器中，发现了许多βPP的羧基末端衍生物，但βPP从细胞表面运输的精确途径和动力学仍不清楚。为了解决这些问题，我们通过追踪添加到完整的βPP转染的中国仓鼠卵巢细胞中的βPP单克隆抗体的定位和分布，直接观察了βPP的内化途径。使用免疫荧光和免疫电子显微镜，显示βPP通过有被小窝和小泡迅速内化，之后分子被运输到内体、前溶酶体和溶酶体。使用改良的免疫检测方案，我们证明了内吞的βPP迅速循环到细胞表面并最终靶向溶酶体。因为我们最近发现细胞表面βPP的内吞作用是Aβ组成型产生的一条途径，这里展示的细胞表面βPP的循环途径可能是关键Aβ片段产生的途径。
