The Journal of Neuroscience 2001 Nov 1; 21(21):8354-8361

Demonstration by Fluorescence Resonance Energy Transfer of Two Sites of Interaction between the Low-Density Lipoprotein Receptor-Related Protein and the Amyloid Precursor Protein: Role of the Intracellular Adapter Protein Fe65

Ayae Kinoshita, Christa M. Whelan, Carolyn J. Smith, Irena Mikhailenko, G. William Reback, Dudley K. Strickland, and Bradley T. Hyman.

Amyoid-beta, the major constituent of senile plaques in Alh\zheimer's disease, is derived from the amyloid precursor protein (APP) by proteolysis. Kunitz protease inhibitor (KPI) containing forms of APP (APP751/770) interact with a multifunctional endocytic receptor, the low-density lipoprotein receptor-related protein (LRP), which modulates its proteolytic processing affecting production of amyloid-beta. We used fluorescence resonance energy transfer (FRET) using labeled LRP and APP in H4 cell line to examine the subcellular localization and the molecular domains inbolved in the APP-LRP interaction. KPI-containing forms of APP (APP770) demonstrated FRET with LRP that was sensitive to the LRP inhibitor receptor-associated protein (RAP), suggesting an interaction between the extracellular domains of APP770 and LRP. APP695 also interacts with LRP to lesser degree (as measure by extracellular domain probes), and this ectodomain interaction is not altered by RAP. By using C-terminally tagged LRP and APP, we domonstrate a second site of interaction between the C termini of both APP695 and APP770 and the C terminus of LRP, and that the interactions at these regions are not sensitive to RAP. We next examined the possibility that the C-termini APP-LRP interaction was mediated by Fe65, and adaptor protein that interacts with the cytoplasmic tail of LRP and APP. FRET studies confirmed a close proximity between the amino Fe65 phosphotyrosine binding (PTB) domain and LRP cytoplasmic domain and between the carboxyl Fe65 PTB domain and the APP cytoplasmic domain. These findings demonstrate that LRP interaction with APP occurs via both extracellular and intracellular protein interaction domains.