FE65 as a link between VLDLR and APP to regulate their trafficking and processing

We found that FE65 interacted with VLDLR using GST pull-down and co-immunoprecipitation assays in COS7 cells and in brain lysates. This interaction occurs via the PTB1 domain of FE65. Co-transfection with FE65 and full length VLDLR increased secreted VLDLR (sVLDLR); however, the levels of VLDLR C-terminal fragment (CTF) were undetectable as a result of proteasomal degradation. Additionally, FE65 increased cell surface levels of VLDLR. Moreover, we identified a novel complex between VLDLR and APP, which altered trafficking and processing of both proteins. Furthermore, immunoprecipitation results demonstrated that the presence of FE65 increased the interaction between APP and VLDLR in vitro and in vivo.These data suggest that FE65 can regulate VLDLR trafficking and processing. Additionally, the interaction between VLDLR and APP altered both protein's trafficking and processing. Finally, our data suggest that FE65 serves as a link between VLDLR and APP. This novel interaction adds to a growing body of literature indicating trimeric complexes with various ApoE Receptors and APP.FE65 and FE65-like (FE65L or FE65L1) proteins are cytoplasmic adaptor proteins that possess two phosphotyrosine binding domains (PTB1 and PTB2) and one WW binding domain. FE65 is primarily found in the CNS and is highly expressed in neurons of the hippocampus, cerebellum, thalamus, and brainstem nuclei in the adult mouse brain [1]. Several studies have shown that FE65 can form a stable, transcriptionally active complex with AICD (APP intracellular domain) in heterologous gene reporter systems [2-8], although the full range of gene targets is still unknown. FE65 is functionally linked to cellular motility and morphology and actin dynamics through binding of its WW domain to the actin-binding protein Mena [9,10]. Interestingly, FE65 and FE65L double knockout mice exhibit defects similar to triple APP knockout (APP tKO): lissencephaly and selected axonal projection defects [11].The PTB2 domain of FE