Departamento de Biología Celular y Molecular, Facultad de Ciencias Biológicas, Millenium Nucleus for Renerative Biology (MINREB), Pontificia Universidad Católica de Chile, Santiago, Chile.
Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America.
PLoS One. 2014 Apr 4;9(4):e93672. doi: 10.1371/journal.pone.0093672. eCollection 2014.
ApoER2 is a member of the low density-lipoprotein receptor (LDL-R) family. As a receptor for reelin, ApoER2 participates in neuronal migration during development as well as synaptic plasticity and survival in the adult brain. A previous yeast two-hybrid screen showed that ApoER2 is a binding partner of sorting nexin 17 (SNX17) - a cytosolic adaptor protein that regulates the trafficking of several membrane proteins in the endosomal pathway, including LRP1, P-selectin and integrins. However, no further studies have been performed to investigate the role of SNX17 in ApoER2 trafficking and function. In this study, we present evidence based on GST pull-down and inmunoprecipitation assays that the cytoplasmic NPxY endocytosis motif of ApoER2 interacts with the FERM domain of SNX17. SNX17 stimulates ApoER2 recycling in different cell lines including neurons without affecting its endocytic rate and also facilitates the transport of ApoER2 from the early endosomes to the recycling endosomes. The reduction of SNX17 was associated with accumulation of an ApoER2 carboxy-terminal fragment (CTF). In addition, in SNX17 knockdown cells, constitutive ApoER2 degradation was not modified, whereas reelin-induced ApoER2 degradation was increased, implying that SNX17 is a regulator of the receptor's half-life. Finally, in SNX17 silenced hippocampal and cortical neurons, we underscored a positive role of this endosomal protein in the development of the dendritic tree and reelin signaling. Overall, these results establish the role of SNX17 in ApoER2 trafficking and function and aid in identifying new links between endocytic trafficking and receptor signaling.
载脂蛋白 E 受体 2（ApoER2）是低密度脂蛋白受体（LDL-R）家族的成员。作为 Reelin 的受体，ApoER2 参与了发育过程中的神经元迁移以及成年大脑中的突触可塑性和存活。先前的酵母双杂交筛选表明，ApoER2 是分选连接蛋白 17（SNX17）的结合伴侣 - 一种细胞溶质衔接蛋白，可调节内体途径中几种膜蛋白的转运，包括 LRP1、P 选择素和整合素。然而，没有进一步的研究来研究 SNX17 在 ApoER2 转运和功能中的作用。在这项研究中，我们基于 GST 下拉和免疫沉淀实验提供了证据，表明 ApoER2 的细胞质 NPxY 内吞基序与 SNX17 的 FERM 结构域相互作用。SNX17 刺激包括神经元在内的不同细胞系中的 ApoER2 回收，而不影响其内吞率，并且还促进 ApoER2 从早期内体到回收内体的转运。SNX17 的减少与 ApoER2 羧基末端片段（CTF）的积累有关。此外，在 SNX17 敲低的细胞中，组成型 ApoER2 降解没有改变，而 Reelin 诱导的 ApoER2 降解增加，表明 SNX17 是受体半衰期的调节剂。最后，在 SNX17 沉默的海马和皮质神经元中，我们强调了这种内体蛋白在树突发育和 Reelin 信号中的积极作用。总之，这些结果确立了 SNX17 在 ApoER2 转运和功能中的作用，并有助于确定内吞转运和受体信号之间的新联系。
