INTRACELLULAR ACCUMULATION AND RESISTANCE TO DEGRADATION OF THE ALZHEIMER AMYLOID A4/BETA-PROTEIN
INTRACELLULAR ACCUMULATION AND RESISTANCE TO DEGRADATION OF THE ALZHEIMER AMYLOID A4/BETA-PROTEIN
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DOI：
10.1073/pnas.89.16.7437
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发表时间：
1992-08-15
影响因子：
11.1
通讯作者：
GLABE, CG
中科院分区：
文献类型：
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作者：
KNAUER, MF;SOREGHAN, B;GLABE, CG
A4 或 β 蛋白是一种肽，构成阿尔茨海默病老年斑的主要蛋白质成分。 A4/β 蛋白源自较大的跨膜淀粉样前体蛋白 (APP)。导致淀粉样蛋白积累的假定的异常加工事件在很大程度上是未知的。在这里，我们报道了一种 42 残基合成肽 beta-1-42，对应于 A4/β-蛋白的较长形式之一，在培养的人皮肤成纤维细胞中积累，并且稳定至少 3 天。该肽似乎在细胞内积累，因为它在阻止内吞作用的条件下不会积累，并且积累与获得对胰蛋白酶消化去除的抗性有关。这种细胞内积累还与通过 SDS/聚丙烯酰胺凝胶电泳测定的肽聚集能力相关。在低浓度的 β-1-42 肽（有利于非聚集状态）下，没有观察到积累。 C 末端截短的较短肽类似物（28 或 39 个残基）缺乏在 SDS 凝胶中聚集的能力，因此无法积累。细胞内积累的β-1-42肽处于聚集状态，并包含在与晚期内体或次级溶酶体的分布重叠的致密细胞器区室中。透化细胞中内化肽的免疫荧光表明它包含在颗粒沉积物中，这与晚期内涵体或次级溶酶体中的定位一致。序列分析表明，一些内化肽进行了 N 末端修剪。这些结果表明聚集的A4/β-蛋白可能抵抗降解，并且表明A4/β-蛋白可能至少部分地由APP的内体或溶酶体加工产生。我们的结果还表明，如果 APP 的这一部分选择性地抵抗蛋白水解，则相对非特异性的蛋白水解可能足以产生 A4/β 蛋白。
The A4 or beta-protein is a peptide that constitutes the major protein component of senile plaques in Alzheimer disease. The A4/beta-protein is derived from a larger, transmembrane amyloid precursor protein (APP). The putative abnormal processing events leading to amyloid accumulation are largely unknown. Here we report that a 42-residue synthetic peptide, beta-1-42, corresponding to one of the longer forms of the A4/beta-protein, accumulates in cultured human skin fibroblasts and is stable for at least 3 days. The peptide appears to accumulate intracellularly, since it does not accumulate under conditions that prevent endocytosis and accumulation is correlated with the acquisition of resistance to removal by trypsin digestion. This intracellular accumulation is also correlated with the ability of the peptide to aggregate as determined by SDS/polyacrylamide gel electrophoresis. At low concentrations of the beta-1-42 peptide, which favor the nonaggregated state, no accumulation is observed. Shorter peptide analogs (28 or 39 residues) that are truncated at the C terminus, which lack the ability to aggregate in SDS gels, fail to accumulate. The accumulated intracellular beta-1-42 peptide is in an aggregated state and is contained in a dense organellar compartment that overlaps the distribution of late endosomes or secondary lysosomes. Immunofluorescence of the internalized peptide in permeabilized cells reveals that it is contained in granular deposits, consistent with localization in late endosomes or secondary lysosomes. Sequence analysis indicates that some of the internalized peptide is subject to N-terminal trimming. These results suggest that the aggregated A4/beta-protein may be resistant to degradation and suggest that the A4/beta-protein may arise, at least in part, by endosomal or lysosomal processing of APP. Our results also suggest that relatively nonspecific proteolysis may be sufficient to generate the A4/beta-protein if this part of APP is selectively resistant to proteolysis.