FE65 Constitutes the Functional Link between the Low-Density Lipoprotein Receptor-Related Protein and the Amyloid Precursor Protein

Abstract

Increasing evidence has implicated the low density lipoprotein receptor-related protein (LRP) and the adaptor protein FE65 in Alzheimer's disease pathogenesis. We have shown previously that LRP mediates ␤-amyloid precursor protein (APP) processing and affects amyloid ␤-protein and APP secretion and APP-c-terminal fragment generation. Furthermore, LRP mediates APP processing through its intracellular domain. Here, we set out to examine whether this interaction is of direct or indirect nature. Specifically, we asked whether adaptor proteins such as FE65 influence the LRP-mediated effect on APP processing by forming a protein complex. In coimmunoprecipitation experiments, we confirmed the postulated APP-FE65 and the LRP-FE65 interaction. However, we also showed an LRP-FE65-APP trimeric complex using pull-down techniques. Because FE65 alters APP processing, we investigated whether this effect is LRP dependent. Indeed, FE65 was only able to increase APP secretion in the presence of LRP. In the absence of LRP, APP secretion was unchanged compared with the LRP knock-out phenotype. Using RNA short interference techniques against FE65, we demonstrated that a reduction in FE65 protein mimics the LRP knock-out phenotype on APP processing. These results clearly demonstrate that FE65 acts as a functional linker between APP and LRP.

SorLA Complement-type Repeat Domains Protect the Amyloid Precursor Protein against Processing

“…As mentioned by Spoelgen et al (36), the cytosolic tails of SorLA and APP most likely associate with adaptor proteins that mediate the interaction, and the array of available LRP1 and LRP1B are examples of receptor proteins that also bind to APP via their CR-domains (55)(56)(57)(58). The physiological function of these interactions is not fully understood, but the current model suggests that these receptors bind APP at the cell surface and release APP in the endosome to regulate its internalization (57)(58)(59)(60)(61). Based on our previous work, we have proposed a model in which SorLA does not contribute to APP endocytosis but instead associates with APP in intracellular vesicles (10,22,23).…”

Loss of γ-Secretase Function Impairs Endocytosis of Lipoprotein Particles and Membrane Cholesterol Homeostasis

“…The constructs encoding APP C99-EGFP (Kaether et al, 2006), Fe65-myc (Pietrzik et al, 2004), and ARH (Noviello et al, 2003) have been described earlier. APP C99-EGFP represents the ␥-secretase substrate derived from APP by ␤-secretase cleavage.…”

Trafficking and Proteolytic Processing of APP

“…Fe65 is capable of interacting with APP and LRP (a multifunctional endocytosis receptor containing two NPXY motifs) via distinct protein interaction domains (Trommsdorff et al 1998). Lack of LRP expression causes reduced APP internalization and Ab secretion (Ulery et al 2000;Pietrzik et al 2002;Cam et al 2005), leading to the conclusion that endocytosis of LRP is coupled to APP internalization and processing, and Fe65 acts as a functional linker between APP and LRP in modulating endocytic APP trafficking (Pietrzik et al 2004). In addition, Ran-binding protein 9 promotes APP interaction with APP and facilitates APP internalization in a Fe65-independent manner (Lakshmana et al 2009).…”