Borg J P, Yang Y, De Taddéo-Borg M, Margolis B, Turner R S
Howard Hughes Medical Institute, University of Michigan Medical Center, Ann Arbor, Michigan 48109, USA.
J Biol Chem. 1998 Jun 12;273(24):14761-6. doi: 10.1074/jbc.273.24.14761.
Constitutive amyloid precursor protein (APP) metabolism results in the generation of soluble APP (APPs) and Abeta peptides, including Abeta40 and Abeta42-the major component of amyloid plaques in Alzheimer's disease brain. The phosphotyrosine binding (PTB) domain of X11 binds to a peptide containing a YENPTY motif found in the carboxyl terminus of APP. We have cloned the full-length X11 gene now referred to as X11alpha. Coexpression of X11alpha with APP results in comparatively greater levels of cellular APP and less APPs, Abeta40, and Abeta42 recovered in conditioned medium of transiently transfected HEK 293 cells. These effects are impaired by a single missense mutation of either APP (Y682G within the YENPTY motif) or X11alpha (F608V within the PTB domain), which diminishes their interaction, thus demonstrating specificity. The inhibitory effect of X11alpha on Abeta40 and Abeta42 secretion is amplified by coexpression with the Swedish mutation of APP (K595N/M596L), which promotes its amyloidogenic processing. Pulse-chase analysis demonstrates that X11alpha prolongs the half-life of APP from approximately 2 h to approximately 4 h. The effects of X11alpha on cellular APP and APPs recovery were confirmed in a 293 cell line stably transfected with APP. The specific binding of the PTB domain of X11alpha to the YENPTY motif-containing peptide of APP appears to slow cellular APP processing and thus reduces recovery of its soluble fragments APPs, Abeta40, and Abeta42 in conditioned medium of transfected HEK 293 cells. X11alpha may be involved in APP trafficking and metabolism in neurons and thus may be implicated in amyloidogenesis in normal aging and Alzheimer's disease brain.
组成型淀粉样前体蛋白（APP）代谢会产生可溶性APP（APPs）和β淀粉样肽，包括β淀粉样蛋白40（Aβ40）和β淀粉样蛋白42（Aβ42），它们是阿尔茨海默病大脑中淀粉样斑块的主要成分。X11的磷酸酪氨酸结合（PTB）结构域与APP羧基末端含YENPTY基序的肽段结合。我们现已克隆出全长X11基因，现称为X11α。X11α与APP共表达时，在瞬时转染的HEK 293细胞的条件培养基中，细胞内APP水平相对更高，而回收的APPs、Aβ40和Aβ42则更少。APP（YENPTY基序内的Y682G）或X11α（PTB结构域内的F608V）的单个错义突变会损害这些效应，减弱它们之间的相互作用，从而证明了特异性。与APP的瑞典突变（K595N/M596L）共表达可增强X11α对Aβ40和Aβ42分泌的抑制作用，该突变会促进APP的淀粉样生成加工。脉冲追踪分析表明，X11α可将APP的半衰期从约2小时延长至约4小时。在稳定转染APP的293细胞系中证实了X11α对细胞内APP和APPs回收的影响。X11α的PTB结构域与含APP的YENPTY基序肽段的特异性结合似乎减缓了细胞内APP的加工过程，从而减少了转染的HEK 293细胞条件培养基中其可溶性片段APPs、Aβ40和Aβ42的回收。X11α可能参与神经元中APP的转运和代谢，因此可能与正常衰老和阿尔茨海默病大脑中的淀粉样蛋白生成有关。
