Sortilin and prosaposin localize to detergent-resistant membrane microdomains.
Most soluble lysosomal hydrolases are sorted in the trans-Golgi network (TGN) and delivered to the lysosomes by the mannose 6-phosphate receptor (M6PR). However, the non-enzymic sphingolipid activator protein (SAP), prosaposin, as well as certain soluble lysosomal hydrolases, is sorted and trafficked to the lysosomes by sortilin. Based on previous results demonstrating that prosaposin requires sphingomyelin to be targeted to the lysosomes, we hypothesized that sortilin and its ligands are found in detergent-resistant membranes (DRMs). To test this hypothesis we have analyzed DRM fractions and demonstrated the presence of sortilin and its ligand, prosaposin. Our results showed that both the M6PR and its cargo, cathepsin B, were also present in DRMs. Cathepsin H has previously been demonstrated to interact with sortilin, while cathepsin D interacts with both sortilin and the M6PR. Both of these soluble lysosomal proteins were also found in DRM fractions. Using sortilin shRNA we have showed that prosaposin is localized to DRM fractions only in the presence of sortilin. These observations suggest that in addition to interacting with the same adaptor proteins, such as GGAs, AP-1 and retromer, both sortilin and the M6PR localize to similar membrane platforms, and that prosaposin must interact with sortilin to be recruited to DRMs.
Canuel
Maryssa
M
Department of Anatomy and Cell Biology, McGill University, 3640 University Street, Montreal, Quebec, Canada, H3A 2B2.
Bhattacharyya
Nihar
N
Balbis
Alejandro
A
Yuan
Libin
L
Morales
Carlos R
CR
D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002522:Chlorocebus aethiops; D006056:Golgi Apparatus; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D047468:Immunoprecipitation; D008247:Lysosomes; D021962:Membrane Microdomains / Q000378:metabolism*; D018613:Microscopy, Confocal; D011485:Protein Binding / Q000502:physiology; D054730:Protein Interaction Domains and Motifs / Q000502:physiology; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D034622:RNA Interference; D017527:Receptor, IGF Type 2 / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D049231:Saposins / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D000099183:Sortilin
D033942:Adaptor Proteins, Vesicular Transport; D049452:Green Fluorescent Proteins; D011498:Protein Precursors; D017527:Receptor, IGF Type 2; D011993:Recombinant Fusion Proteins; D049231:Saposins; D000099183:Sortilin