Graduate Program in Pathobiology and Molecular Medicine, Department of Pathology and cell Biology, Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University Medical Center, New York, NY 10032, USA.
J Biol Chem. 2011 Apr 8;286(14):12602-16. doi: 10.1074/jbc.M110.170217. Epub 2011 Jan 18.
BACE1 (β-site β-amyloid precursor protein (APP)-cleaving enzyme 1) mediates the first proteolytic cleavage of APP, leading to amyloid β-peptide (Aβ) production. It has been reported that BACE1 intracellular trafficking, in particular endosome-to-TGN sorting, is mediated by adaptor complexes, such as retromer and Golgi-localized γ-ear-containing ARF-binding proteins (GGAs). Here we investigated whether sortilin, a Vps10p domain-sorting receptor believed to participate in retromer-mediated transport of select membrane cargoes, contributes to the subcellular trafficking and activity of BACE1. Our initial studies revealed increased levels of sortilin in post-mortem brain tissue of AD patients and that overexpression of sortilin leads to increased BACE1-mediated cleavage of APP in cultured cells. In contrast, RNAi suppression of sortilin results in decreased BACE1-mediated cleavage of APP. We also found that sortilin interacts with BACE1 and that a sortilin construct lacking its cytoplasmic domain, which contains putative retromer sorting motifs, remains bound to BACE1. However, expression of this truncated sortilin redistributes BACE1 from the trans-Golgi network to the endosomes and substantially reduces the retrograde trafficking of BACE1. Site-directed mutagenesis and chimera experiments reveal that the cytoplasmic tail of sortilin, but not those from other VPS10p domain receptors (e.g. SorCs1b and SorLA), plays a unique role in BACE1 trafficking. Our studies suggest a new function for sortilin as a modulator of BACE1 retrograde trafficking and subsequent generation of Aβ.
BACE1（β-位淀粉样前体蛋白（APP）裂解酶 1）介导 APP 的首次蛋白水解裂解，导致淀粉样 β-肽（Aβ）的产生。据报道，BACE1 的细胞内运输，特别是内体到 TGN 的分拣，是由衔接复合物介导的，如逆行蛋白复合物和高尔基定位 γ -ear 含 ARF 结合蛋白（GGAs）。在这里，我们研究了分选连接蛋白（sortilin）是否参与 BACE1 的亚细胞运输和活性，分选连接蛋白是一种 Vps10p 结构域分拣受体，被认为参与了选择膜货物的逆行蛋白复合物介导的运输。我们的初步研究表明，AD 患者死后大脑组织中分选连接蛋白的水平增加，并且分选连接蛋白的过表达导致培养细胞中 BACE1 介导的 APP 裂解增加。相比之下，分选连接蛋白的 RNAi 抑制导致 BACE1 介导的 APP 裂解减少。我们还发现分选连接蛋白与 BACE1 相互作用，并且缺乏其包含潜在逆行蛋白分拣基序的细胞质结构域的分选连接蛋白构建体仍然与 BACE1 结合。然而，这种截断的分选连接蛋白的表达将 BACE1 从反式高尔基体网络重新分布到内体，并大大减少 BACE1 的逆行运输。定点突变和嵌合体实验表明，分选连接蛋白的细胞质尾巴，而不是其他 VPS10p 结构域受体（例如 SorCs1b 和 SorLA）的细胞质尾巴，在 BACE1 运输中发挥独特作用。我们的研究表明，分选连接蛋白作为 BACE1 逆行运输和随后 Aβ 生成的调节剂具有新的功能。
