Haass C, Hung A Y, Schlossmacher M G, Oltersdorf T, Teplow D B, Selkoe D J
Department of Neurology and Program in Neuroscience, Harvard Medical School, Brigham and Women's Hospital, Boston, Massachusetts 02115.
Ann N Y Acad Sci. 1993 Sep 24;695:109-16. doi: 10.1111/j.1749-6632.1993.tb23037.x.
Alzheimer's disease is characterized by the extracellular deposition in the brain and its blood vessels of insoluble aggregates of the amyloid beta peptide (A beta). This peptide is derived from a large integral membrane protein, the beta-amyloid precursor protein (beta APP), by proteolytic processing. The A beta has previously been found only in the brains of patients with Alzheimer's disease or advanced aging. We describe here the finding that A beta is produced continuously by normal processing in tissue culture cells. A beta and closely related peptides were identified in the media of cells transfected with cDNAs coding for beta APP in a variety of cell lines and primary tissue cultured cells. The identity of these peptides was confirmed by epitope mapping and radiosequencing. Peptides of a molecular weight of approximately 3 and approximately 4 kDa are described. The 4 kDa range contains mostly the A beta and two related peptides starting N-terminal to the beginning of A beta. In the 3 kDa range, the majority of peptides start at the secretase site; in addition, two longer peptides were found starting at amino acid F(4) and E(11) of the A beta sequence. To identify the processing pathways which lead to the secretion of these peptides, we used a variety of drugs known to interfere with certain cell biological pathways. We conclude that lysosomes may not play a predominant role in the formation of 3 and 4 kDa peptides. We show that an acidic environment is necessary to create the N-terminus of the A beta and postulate that alternative secretory cleavage might result in the formation of the N-terminus of A beta and related peptides. This cleavage takes place either in the late Golgi, at the cell-surface or in early endosomes, but not in lysosomes. The N-terminus of most of the 3 kDa peptides is created by secretory cleavage on the cell surface or within late Golgi.
阿尔茨海默病的特征是大脑及其血管中存在淀粉样β肽（Aβ）的不溶性聚集体的细胞外沉积。这种肽是由一种大型整合膜蛋白β淀粉样前体蛋白（βAPP）经蛋白水解加工产生的。此前仅在阿尔茨海默病患者或老龄患者的大脑中发现Aβ。我们在此描述了在组织培养细胞中通过正常加工持续产生Aβ的这一发现。在多种细胞系和原代组织培养细胞中，用编码βAPP的cDNA转染的细胞培养基中鉴定出了Aβ及密切相关的肽。通过表位作图和放射性测序证实了这些肽的身份。描述了分子量约为3 kDa和约4 kDa的肽。4 kDa范围内的肽大多为Aβ以及从Aβ起始N端开始的两种相关肽。在3 kDa范围内，大多数肽从分泌酶位点开始；此外，还发现了两种更长的肽从Aβ序列的氨基酸F(4)和E(11)开始。为了确定导致这些肽分泌的加工途径，我们使用了多种已知会干扰某些细胞生物学途径的药物。我们得出结论，溶酶体可能在3 kDa和4 kDa肽的形成过程中不发挥主要作用。我们表明酸性环境对于形成Aβ的N端是必要的，并推测替代性分泌性切割可能导致Aβ及相关肽的N端形成。这种切割发生在晚期高尔基体、细胞表面或早期内体中，但不在溶酶体中。大多数3 kDa肽的N端是通过细胞表面或晚期高尔基体中的分泌性切割形成的。
