Endocytosis of the amyloid precursor protein (APP) is critical for generation of β-amyloid, aggregating in Alzheimer's disease. APP endocytosis depending on the intracellular NPTY motif is well investigated, whereas involvement of the YTSI (also termed BaSS) motif remains controversial. Here, we show that APP lacking the YTSI motif (ΔYTSI) displays reduced localization to early endosomes and decreased internalization rates, similar to APP ΔNPTY. Additionally, we show that the YTSI-binding protein, PAT1a interacts with the Rab5 activator RME-6, as shown by several independent assays. Interestingly, knockdown of RME-6 decreased APP endocytosis, whereas overexpression increased the same. Similarly, APP ΔNPTY endocytosis was affected by PAT1a and RME-6 overexpression, whereas APP ΔYTSI internalization remained unchanged. Moreover, we could show that RME-6 mediated increase of APP endocytosis can be diminished upon knocking down PAT1a. Together, our data identify RME-6 as a novel player in APP endocytosis, involving the YTSI-binding protein PAT1a.

淀粉样前体蛋白 (APP) 的内吞作用对于 β-淀粉样蛋白的生成至关重要，β-淀粉样蛋白在阿尔茨海默病中聚集。依赖于细胞内 NPTY 基序的 APP 内吞作用已得到充分研究，而 YTSI（也称为 BaSS）基序的参与仍存在争议。在这里，我们发现缺乏 YTSI 基序 (ΔYTSI) 的 APP 显示出早期内体定位减少和内化率降低，与 APP ΔNPTY 类似。此外，我们还发现 YTSI 结合蛋白 PAT1a 与 Rab5 激活剂 RME-6 相互作用，如多项独立测定所示。有趣的是，敲除 RME-6 会减少 APP 内吞作用，而过表达则会增加同样的作用。同样，APP ΔNPTY 内吞作用受到 PAT1a 和 RME-6 过表达的影响，而 APP ΔYTSI 内化保持不变。此外，我们可以证明，敲除 PAT1a 后，RME-6 介导的 APP 内吞作用的增加可以减弱。总之，我们的数据表明 RME-6 是 APP 内吞作用的新参与者，涉及 YTSI 结合蛋白 PAT1a。