von Arnim Christine A F, Kinoshita Ayae, Peltan Ithan D, Tangredi Michelle M, Herl Lauren, Lee Bonny M, Spoelgen Robert, Hshieh Tammy T, Ranganathan Sripriya, Battey Frances D, Liu Chun-Xiang, Bacskai Brian J, Sever Sanja, Irizarry Michael C, Strickland Dudley K, Hyman Bradley T
Alzheimer Disease Research Laboratory, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA.
J Biol Chem. 2005 May 6;280(18):17777-85. doi: 10.1074/jbc.M414248200. Epub 2005 Mar 4.
BACE is a transmembrane protease with beta-secretase activity that cleaves the amyloid precursor protein (APP). After BACE cleavage, APP becomes a substrate for gamma-secretase, leading to release of amyloid-beta peptide (Abeta), which accumulates in senile plaques in Alzheimer disease. APP and BACE are co-internalized from the cell surface to early endosomes. APP is also known to interact at the cell surface and be internalized by the low density lipoprotein receptor-related protein (LRP), a multifunctional endocytic and signaling receptor. Using a new fluorescence resonance energy transfer (FRET)-based assay of protein proximity, fluorescence lifetime imaging (FLIM), and co-immunoprecipitation we demonstrate that the light chain of LRP interacts with BACE on the cell surface in association with lipid rafts. Surprisingly, the BACE-LRP interaction leads to an increase in LRP C-terminal fragment, release of secreted LRP in the media and subsequent release of the LRP intracellular domain from the membrane. Taken together, these data suggest that there is a close interaction between BACE and LRP on the cell surface, and that LRP is a novel BACE substrate.
β-分泌酶（BACE）是一种具有β-分泌酶活性的跨膜蛋白酶，可切割淀粉样前体蛋白（APP）。BACE切割后，APP成为γ-分泌酶的底物，导致淀粉样β肽（Aβ）释放，其在阿尔茨海默病的老年斑中积累。APP和BACE从细胞表面共同内化至早期内体。已知APP也在细胞表面相互作用，并被低密度脂蛋白受体相关蛋白（LRP）内化，LRP是一种多功能的内吞和信号受体。利用基于荧光共振能量转移（FRET）的蛋白质接近度检测、荧光寿命成像（FLIM）和免疫共沉淀，我们证明LRP的轻链在细胞表面与BACE相互作用并与脂筏相关联。令人惊讶的是，BACE-LRP相互作用导致LRP C末端片段增加、培养基中分泌型LRP释放以及随后LRP细胞内结构域从膜上释放。综上所述，这些数据表明BACE和LRP在细胞表面存在密切相互作用，并且LRP是一种新型的BACE底物。
