Institute for Molecular and Cellular Cognition, Center for Molecular Neurobiology Hamburg, University Medical Center Hamburg-Eppendorf, Falkenried 94, 20251, Hamburg, Germany.
Mol Brain. 2022 Feb 19;15(1):18. doi: 10.1186/s13041-022-00903-0.
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.
SorLA 是 Vps10p 结构域 (Vps10p-D) 受体家族的一员，属于Ⅰ型跨膜蛋白，负责神经元内体分拣。 SorLA 的细胞外/腔部分具有独特的镶嵌结构域组成，并与大量不同且部分不相关的配体相互作用，包括淀粉样前体蛋白和淀粉样β。多项研究支持 SorLA 与散发性和家族性阿尔茨海默病 (AD) 之间存在强烈关联。尽管 SorLA 似乎是 AD 的一个重要因素，但大量不同的配体表明其作为神经元多功能受体具有额外的细胞内分拣能力。因此，了解 SorLA 亚细胞靶向的决定因素可能与理解一般神经元内体分拣机制有关。已经证明许多细胞溶质衔接蛋白决定 SorLA 的细胞内运输。这些衔接蛋白中的大多数以及细胞外/腔部分的一些配体与 Vps10p-D 受体 Sortilin 共享。尽管 SorLA 和 Sortilin 都具有主要的细胞内和内体定位，但它们被靶向到不同的内体隔室。因此，独立的衔接蛋白可能传递其不同的内体靶向。在这里，我们假设 SorLA 与 PSD95 和 PICK1 这两种细胞溶质衔接蛋白相互作用，因为它们已经显示出与 Vps10p-D 受体 SorCS3 结合。我们仅在哺乳动物双杂交、下拉和细胞募集实验中观察到 SorLA 与 PICK1 的相互作用。通过突变分析，我们证明 SorLA 的 C 端最小 PDZ 结构域结合基序 VIA 介导了这种相互作用。此外，我们在原代神经元中显示 SorLA 和 PICK1 在囊泡结构上的共定位。尽管 PICK1 和 SorLA 之间相互作用的生理作用仍未解决，但我们的研究表明 PICK1 参与调节 SorLA 的细胞内行程。
