Sorting Nexin 17 Regulates ApoER2 Recycling and Reelin Signaling

Abstract

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.

Neurotrophins regulate ApoER2 proteolysis through activation of the Trk signaling pathway

“…PC12-ApoER2 cells that were incubated with DAPT accumulated the ApoER2 17 kDa CTF, as has been previously described in other cell types, which supports the constitutive proteolytic processing of ApoER2 [4, 64, 71] (Figure 3B). PC12-ApoER2 cells that were incubated with NGF for 2 h showed a significant increase in the CTF level (Figure 3B,C).…”

“…Cortical neurons were prepared and cultured essentially as described [71]. Cerebral cortexes from 18-day-old embryos were washed two times with cold Hank’s medium and digested with Hank’s 0.5% trypsin-EDTA (Invitrogen) for 18 min at 37°C.…”

News on the molecular regulation and function of hepatic low-density lipoprotein receptor and LDLR-related protein 1

“…For example, high expression of the endosome-associated protein Sortin nexin 17 (SNX17) enhances LDL uptake due to increased endocytosis of LDLR [33]. SNX17 also facilitates the recycling of LRP1 and ApoER2 [34,35], but whether SNX17 acts in conjunction with the CCC and WASH complexes, and whether these two complexes are also required for endosomal sorting of LRP1 or other members of the LDLR family has yet to be determined.…”

The life cycle of the low-density lipoprotein receptor

“…ARH, autosomal recessive hypercholesterolemia; Dab2, disabled-2; ESCRT, endosomal-sorting complex required for transport machinery; IDOL, inducible degrader of the LDL receptor; LDLR, LDL receptor; PCSK9, proprotein convertase subtilisin/kexin type 9; SNX17, sorting nexin 17; Ub, ubiquitin. two, without changing the number of receptors on the cell surface [27,28]. This suggests that interaction of SNX17 with the LDLR does not influence degradation of the receptor by directing it to the lysosome, but rather accelerates its movement through the early endocytic compartment [27].…”