title: Calnuc Function in Endosomal Sorting of Lysosomal Receptors.
abstract: Calnuc is a ubiquitous Ca(2+)-binding protein present on the trans-Golgi network (TGN) and endosomes. However, the precise role of Calnuc in these organelles is poorly characterized. We previously highlighted the role of Calnuc in the transport of LRP9, a new member of a low-density lipoprotein (LDL) receptor subfamily that cycles between the TGN and endosomes. The objective of this study was to explore the role of Calnuc in the endocytic sorting of mannose-6-phosphate receptor (MPR) and Sortilin, two well-characterized lysosomal receptors that transit between the TGN and endosomes. Using biochemical and microscopy assays, we showed that Calnuc depletion [by small interfering RNA (siRNA)] causes the misdelivery to and degradation in lysosomes of cationic-independent mannose-6-phosphate receptor (CI-MPR) and Sortilin due to a defect in the endosomal recruitment of retromers, which are key components of the endosome-to-Golgi retrieval machinery. Indeed, we demonstrated that Calnuc depletion impairs the activation and membrane association of Rab7, a small G protein required for the endosomal recruitment of retromers. Overall, our data indicate a novel role for Calnuc in the endosome-to-TGN retrograde transport of lysosomal receptors through the regulation of Rab7 activity and the recruitment of retromers to endosomes.
authors.affiliation: Department of Pharmacology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC, Canada.
authors.forename: Heidi
authors.initials: H
authors.lastname: Larkin
authors.affiliation: Centre de recherche de l'Hôpital Maisonneuve-Rosemont, Université de Montréal, Montréal, H1T 2M, Canada.
authors.forename: Santiago
authors.initials: S
authors.lastname: Costantino
authors.affiliation: Cambridge Institute for Medical Research, Department of Clinical Biochemistry, Wellcome Trust/MRC Building, Addenbrookes Hospital, University of Cambridge, Cambridge, CB2 0XY, UK.
authors.forename: Matthew N J
authors.initials: MN
authors.lastname: Seaman
authors.affiliation: Department of Pharmacology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC, Canada.
authors.forename: Christine
authors.initials: C
authors.lastname: Lavoie
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism*; D000818:Animals; D019556:COS Cells; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D000080866:Nucleobindins; D021381:Protein Transport; D017527:Receptor, IGF Type 2 / Q000378:metabolism*; D021601:trans-Golgi Network / Q000378:metabolism; D000099183:Sortilin
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D002135:Calcium-Binding Proteins; D004268:DNA-Binding Proteins; D009419:Nerve Tissue Proteins; D000080866:Nucleobindins; D017527:Receptor, IGF Type 2; D000099183:Sortilin
keywords: Calnuc; Rab7; Sortilin; endosomal sorting; lysosomal receptor; lysosome; mannose-6-phosphate receptor; nucleobindin; retromers