Golde T E, Cai X D, Shoji M, Younkin S G
Division of Neuropathology, Case Western Reserve University, Cleveland, Ohio 44106.
Ann N Y Acad Sci. 1993 Sep 24;695:103-8. doi: 10.1111/j.1749-6632.1993.tb23036.x.
The approximately 4 kD (39-43 amino acid) polypeptide (amyloid beta protein, A beta) deposited as amyloid in Alzheimer's disease (AD) is derived from a set of 695-770 residue precursor proteins collectively referred to as the amyloid beta-protein precursor (beta APP). Using immunoblotting techniques, metabolic labeling, and sequencing we have analyzed beta APP derivatives in medium conditioned by: (1) human mononuclear leukemic (K562) cells expressing a model beta AP-bearing carboxyl-terminal beta APP derivative (2) human neuroblastoma (M17) cells transfected with constructs expressing full length beta APP and (3) M17 cells expressing only endogenous beta APP. In each case, we observed the release of a approximately 4 kD beta APP derivative essentially identical to the A beta found in AD amyloid. A similar, if not identical, beta APP fragment was readily detected in CSF from both Alzheimer's disease patients and controls. These observations indicate that the A beta is produced and released by normal processing of the beta APP. To determine if the production of A beta or A beta-tearing COOH-terminal beta APP derivatives is altered in cells expressing the mutant beta APPs linked to familial AD, we have compared M17 cells expressing wild type beta APP with those expressing mutant beta APPs (beta APP delta I or beta APP delta NL). After continuous metabolic labeling for 8 hours, cells expressing the beta APP delta NL mutant showed a 5-fold increase in the relative amount of an approximately 11.4 kD A beta-bearing carboxyl-terminal beta APP derivative, and they released 6-fold more 4 kD A beta into the medium. These observations provide strong evidence that: (1) the pathway producing A beta in cultured cells is highly relevant to AD and (2) the beta APP delta NL mutant causes AD because its processing is altered in a way that releases increased amounts of A beta.
在阿尔茨海默病（AD）中作为淀粉样蛋白沉积的约4 kD（39 - 43个氨基酸）多肽（β淀粉样蛋白，Aβ）源自一组695 - 770个残基的前体蛋白，统称为β淀粉样蛋白前体（βAPP）。我们使用免疫印迹技术、代谢标记和测序分析了在以下条件下培养的培养基中的βAPP衍生物：（1）表达携带模型βAP的羧基末端βAPP衍生物的人单核白血病（K562）细胞；（2）用表达全长βAPP的构建体转染的人神经母细胞瘤（M17）细胞；（3）仅表达内源性βAPP的M17细胞。在每种情况下，我们都观察到释放出一种约4 kD的βAPP衍生物，其与在AD淀粉样蛋白中发现的Aβ基本相同。在阿尔茨海默病患者和对照的脑脊液中很容易检测到类似（如果不是相同）的βAPP片段。这些观察结果表明Aβ是通过βAPP的正常加工产生和释放的。为了确定在表达与家族性AD相关的突变βAPP的细胞中Aβ或Aβ切割的COOH末端βAPP衍生物的产生是否改变，我们将表达野生型βAPP的M17细胞与表达突变βAPP（βAPPΔI或βAPPΔNL）的细胞进行了比较。在连续代谢标记8小时后，表达βAPPΔNL突变体的细胞显示出一种约11.4 kD的携带Aβ的羧基末端βAPP衍生物的相对量增加了5倍，并且它们向培养基中释放的4 kD Aβ多了6倍。这些观察结果提供了强有力的证据表明：（1）在培养细胞中产生Aβ的途径与AD高度相关；（2）βAPPΔNL突变体导致AD是因为其加工方式发生改变，从而释放出更多量的Aβ。
