title: Intracellular trafficking of LRP9 is dependent on two acidic cluster/dileucine motifs.
abstract: LDL receptor-related protein 9 (LRP9) is a distant member of the low-density lipoprotein receptor (LDLR) superfamily. To date, there are no reports on the cellular distribution of LRP9 or the signals responsible for its localization. Here, we investigated the intracellular localization and trafficking of LRP9. Using confocal microscopy, we demonstrated that LRP9 was not present at the plasma membrane but co-localized with various markers of the trans-Golgi network (TGN) and endosomes. This co-localization was dependent on the presence of two acidic cluster/dileucine (DXXLL) motifs in the cytoplasmic tail of LRP9, which interact with GGA proteins, clathrin adaptors involved in transport between the TGN and endosomes. LRP9 is the first example of a transmembrane protein with an internal GGA-binding sequence in addition to the usual C-terminal motif. An inactivating mutation (LL --> AA) in both DXXLL motifs, which completely inhibited the interaction of LRP9 with GGA proteins, led to an intracellular redistribution of LRP9 from the TGN to early endosomes and the cell surface, indicating that the two DXXLL motifs are essential sorting determinants of LRP9. In conclusion, our results suggest that LRP9 cycles between the TGN, endosomes and the plasma membrane through a GGA dependent-trafficking mechanism.
authors.affiliation: Department of Pharmacology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3001-12e Avenue Nord, Sherbrooke, QC, Canada, J1H 5N4.
authors.forename: Rémi
authors.initials: R
authors.lastname: Boucher
authors.forename: Heidi
authors.initials: H
authors.lastname: Larkin
authors.forename: Julie
authors.initials: J
authors.lastname: Brodeur
authors.forename: Hugo
authors.initials: H
authors.lastname: Gagnon
authors.forename: Caroline
authors.initials: C
authors.lastname: Thériault
authors.forename: Christine
authors.initials: C
authors.lastname: Lavoie
mesh_terms: D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism*; D020816:Amino Acid Motifs; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism*; D026502:LDL-Receptor Related Proteins / Q000235:genetics / Q000378:metabolism*; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D014162:Transfection; D021601:trans-Golgi Network / Q000378:metabolism*
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; C407306:GGA adaptor proteins; D026502:LDL-Receptor Related Proteins; D026503:Low Density Lipoprotein Receptor-Related Protein-1; C538941:Lrp10 protein, mouse; D026901:Membrane Transport Proteins; D050505:Mutant Proteins; D020727:ADP-Ribosylation Factors