Retromer Binds the FANSHY Sorting Motif in SorLA to Regulate Amyloid Precursor Protein Sorting and Processing

Abstract

sorLA is a sorting receptor for amyloid precursor protein (APP) genetically linked to Alzheimer's disease (AD). Retromer, an adaptor complex in the endosome-to-Golgi retrieval pathway, has been implicated in APP transport because retromer deficiency leads to aberrant APP sorting and processing and levels of retromer proteins are altered in AD. Here we report that sorLA and retromer functionally interact in neurons to control trafficking and amyloidogenic processing of APP. We have identified a sequence (FANSHY) in the cytoplasmic domain of sorLA that is recognized by the VPS26 subunit of the retromer complex. Accordingly, we characterized the interaction between the retromer complex and sorLA and determined the role of retromer on sorLA-dependent sorting and processing of APP. Mutations in the VPS26 binding site resulted in receptor redistribution to the endosomal network, similar to the situation seen in cells with VPS26 knockdown. The sorLA mutant retained APP-binding activity but, as opposed to the wild-type receptor, misdirected APP into a distinct non-Golgi compartment, resulting in increased amyloid processing. In conclusion, our data provide a molecular link between reduced retromer expression and increased amyloidogenesis as seen in patients with sporadic AD.

A mechanism for retromer endosomal coat complex assembly with cargo

“…Thus, recognition of cargo by this region of retromer would anchor the two ends of the retromer complex to the membrane, and this arrangement likely underlies the substantially increased association of retromer with the membrane. Cargo binding activity has also been reported for the VPS26 subunit of retromer, which binds to the opposite end of VPS35 (31), raising the possibility that recognition of different cargos may drive distinct retromer coat assembly pathways.…”

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

“…Transfected Cell Lines-SH-SY5Y cells were cultured and transfected with FuGENE (Roche Diagnostics) or HiFect (Amaxa) as described previously (23). Stably transfected clones were maintained by adding 300 g/ml Zeocin (Invitrogen).…”

“…Surface Protein Determination-Biotinylation of cell surface proteins in SH-SY5Y cells stably expressing SorLA-WT/variants was performed as described previously (23).…”

“…Significance was evaluated using two-tailed t tests. Surface levels of APP and SorLA were determined by biotinylation experiments as described previously using membraneimpermeable, EZ-linked sulfo-NHS-S-biotin (Pierce) and streptavidin beads (GE Healthcare) (23).…”

“…SorLA binds directly to APP and slows down its cellular transport out of the Golgi; thus, less of the precursor protein enters secretase-containing compartments, decreasing the processing of APP to both nonamyloidogenic (sAPP␣) and amyloidogenic (A␤) products (10,11,(21)(22)(23). This function is dependent on receptor localization to the Golgi, establishing a direct link to the trafficking pathway from endosomes to the trans-Golgi network/Golgi, a pathway suspected to be altered in sporadic AD (2,24,25).…”