The lysosomal trafficking of sphingolipid activator proteins (SAPs) is mediated by sortilin

Abstract

Most soluble lysosomal proteins bind the mannose 6-phosphate receptor (M6P-R) to be sorted to the lysosomes. However, the lysosomes of I-cell disease (ICD) patients, a condition resulting from a mutation in the phosphotransferase that adds mannose 6-phosphate to hydrolases, have near normal levels of several lysosomal proteins, including the sphingolipid activator proteins (SAPs), GM2AP and prosaposin. We tested the hypothesis that SAPs are targeted to the lysosomal compartment via the sortilin receptor. To test this hypothesis, a dominant-negative construct of sortilin and a sortilin small interfering RNA (siRNA) were introduced into COS-7 cells. Our results showed that both the truncated sortilin and the sortilin siRNA block the traffic of GM2AP and prosaposin to the lysosomal compartment. This observation was confirmed by a co-immunoprecipitation, which demonstrated that GM2AP and prosaposin are interactive partners of sortilin. Furthermore, a dominant-negative mutant GGA prevented the trafficking of prosaposin and GM2AP to lysosomes. In conclusion, our results show that the trafficking of SAPs is dependent on sortilin, demonstrating a novel lysosomal trafficking.

WNK4 Enhances the Degradation of NCC through a Sortilin-Mediated Lysosomal Pathway

“…The pEGFP-sortilin WT and its truncated sortilin lacking cytoplasmic tail (pEGFP-sortilin TRU), a dominant negative mutant, were provided by Dr. Carlos R. Morales (McGill University, Hamilton, Ontario, Canada). 27 All constructs, shown in Figure 1, were confirmed by sequence analysis. These constructs have been successfully expressed in African green monkey kidney cells (Cos-7) and confirmed by Western blot analysis.…”

“…Sortilin is a newly identified lysosomal targeting receptor that is involved in the alternative sorting of the lysosomal sphingolipid activator protein prosaposin 27,28 and the GM2 activator protein. 28,29 It is a homolog of the yeast vacuolar sorting receptor Vps10p and belongs to the type I Vps10p superfamily.…”

BACE1 Retrograde Trafficking Is Uniquely Regulated by the Cytoplasmic Domain of Sortilin

“…Sortilin has been widely implicated in protein delivery to the lysosome. Interestingly, some studies of sortilin lysosomal trafficking have been shown to involve GGA adaptor proteins (27,28). It is possible that directly, or indirectly, sortilin interacts with the CTFs and promotes their degradation in the lysosome.…”

“…It has been demonstrated that the sortilin cytoplasmic domain can convey Golgi localization and Golgi-endosome transport. Such a sorting and trafficking role for sortilin can be attributed to two motifs, a tyrosine-based YSVL motif and an acidic clusterdileucine motif, both appearing to contribute to the endocytosis and intracellular trafficking of sortilin (27)(28)(29)(30). These motifs are likewise found within the CI-MPR (the functional equivalent of Vps10p), which is responsible for transporting lysosomal enzymes from the Golgi to the lysosome and subsequently undergoes retrograde transport via retromer (31)(32)(33).…”

La sortiline : une protéine associée à de multiples fonctions

“…En effet, l'extrémité cytoplasmique de la sortiline interagit avec le domaine VHS de la protéine de tri cytosolique GGA2 (Golgilocalizing, γ-adaptin ear homology domain, ADP-ribosylation factor-binding protein) [9]. Cette interaction permet en outre à la sortiline de contribuer à l'adressage des SAP (sphingolipid activator proteins) dans les lysosomes [10]. La sortiline, en tant que protéine «cargo», ferait partie intégrante d'une machinerie intracellulaire, située principalement au niveau du réseau transgolgien, qui servirait à l'adressage de multiples protéines vers les lysosomes et autres compartiments vésicu-laires (Figure 2).…”