The adaptor protein PICK1 targets the sorting receptor SorLA

Abstract

SorLA is a member of the Vps10p-domain (Vps10p-D) receptor family of type-I transmembrane proteins conveying neuronal endosomal sorting. The extracellular/luminal moiety of SorLA has a unique mosaic domain composition and interacts with a large number of different and partially unrelated ligands, including the amyloid precursor protein as well as amyloid-β. Several studies support a strong association of SorLA with sporadic and familial forms of Alzheimer’s disease (AD). Although SorLA seems to be an important factor in AD, the large number of different ligands suggests a role as a neuronal multifunctional receptor with additional intracellular sorting capacities. Therefore, understanding the determinants of SorLA’s subcellular targeting might be pertinent for understanding neuronal endosomal sorting mechanisms in general. A number of cytosolic adaptor proteins have already been demonstrated to determine intracellular trafficking of SorLA. Most of these adaptors and several ligands of the extracellular/luminal moiety are shared with the Vps10p-D receptor Sortilin. Although SorLA and Sortilin show both a predominant intracellular and endosomal localization, they are targeted to different endosomal compartments. Thus, independent adaptor proteins may convey their differential endosomal targeting. Here, we hypothesized that Sortilin and SorLA interact with the cytosolic adaptors PSD95 and PICK1 which have been shown to bind the Vps10p-D receptor SorCS3. We observed only an interaction for SorLA and PICK1 in mammalian-two-hybrid, pull-down and cellular recruitment experiments. We demonstrate by mutational analysis that the C-terminal minimal PDZ domain binding motif VIA of SorLA mediates the interaction. Moreover, we show co-localization of SorLA and PICK1 at vesicular structures in primary neurons. Although the physiological role of the interaction between PICK1 and SorLA remains unsolved, our study suggests that PICK1 partakes in regulating SorLA’s intracellular itinerary.

Internally tagged Vps10p-domain receptors reveal uptake of the neurotrophin BDNF

“…Between these two fragments, the amplified cDNA of tdTomato or mVenus was inserted respectively. For lentiviral expression, these constructs were then also cloned into the L21 vector ( 50 ). We generated first a SorCS3-tagged construct starting the C-terminal fragment following the fluorophore with S 1123 , but this was retained in the ER in different cell types.…”

“…Accordingly, cDNA encoding GFP was cloned to the 3′-ends of the respective cDNAs encoding BDNF ( 89 ), TrkB, Vps35, or β-1.4-GT and cloned into an L21C-M2 destination vector. GFP-Rab5 ( 90 ), tdTomato-GGA2, and tdTomato-PICK1 ( 50 ) have been described before. mCherry-Rab9a was purchased from Addgene (Plasmid #78592) ( 91 ).…”

“…The assumption that Vps10p-D receptors convey intracellular sorting is based on the interaction of their cytoplasmic domains with various adaptor proteins involved in endosomal targeting ( 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ). Moreover, studies employing knockout models revealed altered localization or mistargeting of interacting proteins ( 24 , 49 , 52 , 53 , 54 , 55 , 56 , 57 ), and the expression of chimeric receptor constructs demonstrated internalization and intracellular targeting of ligands or rescued specific phenotypes in knockout models ( 6 , 33 , 43 , 46 , 47 , 48 ).…”

“…Notably, already small C-terminal peptide tags, such as a myc tag, impede GGA interaction ( 64 ). GGAs are known functional Sortilin and SorLA interactors ( 48 , 49 , 64 , 66 , 67 ), the PDZ-domain protein PICK1 targets SorLA and SorCS3 ( 44 , 50 ) and additional yet unidentified C-terminal interactors are most likely. Therefore, C-terminal tagging probably leads to aberrant subcellular targeting of Vps10p-D receptors.…”

Finding memo: versatile interactions of the VPS10p-Domain receptors in Alzheimer’s disease

“…Recently, the heat shock protein 12A (HSP12A) was identified as a novel adaptor molecule able to selectively target the cytoplasmic domain of SorLA in an ATP-dependent fashion, affecting its internalization and subcellular localization [182]. Also, the last three amino acids "VIA" at the C terminus of SorLA mediates binding to Protein Interacting with C Kinase-1 (PICK1), a protein known to promote transport of different cargos to endosomes including postsynaptic AMPA glutamate receptor (AMPAR) [183].…”