title: Lrp1/LDL Receptor Play Critical Roles in Mannose 6-Phosphate-Independent Lysosomal Enzyme Targeting.
abstract: Most lysosomal enzymes require mannose 6-phosphate (M6P) residues for efficient receptor-mediated lysosomal targeting. Although the lack of M6P residues results in missorting and hypersecretion, selected lysosomal enzymes reach normal levels in lysosomes of various cell types, suggesting the existence of M6P-independent transport routes. Here, we quantify the lysosomal proteome in M6P-deficient mouse fibroblasts (PT(ki)) using Stable Isotope Labeling by Amino acids in Cell culture (SILAC)-based comparative mass spectrometry, and find unchanged amounts of 20% of lysosomal enzymes, including cathepsins D and B (Ctsd and Ctsb). Examination of fibroblasts from a new mouse line lacking both M6P and sortilin, a candidate for M6P-independent transport of lysosomal enzymes, revealed that sortilin does not act as cargo receptor for Ctsb and Ctsd. Using fibroblast lines deficient for endocytic lipoprotein receptors, we could demonstrate that both LDL receptor and Lrp1 mediate the internalization of non-phosphorylated Ctsb and Ctsd. Furthermore, the presence of Lrp1 inhibitor increased the secretion of Ctsd from PT(ki) cells. These findings establish Lrp1 and LDL receptors in M6P-independent secretion-recapture targeting mechanism for lysosomal enzymes.
authors: Department for Biochemistry, Children's Hospital, University Medical Center Hamburg-Eppendorf, D-20246, Hamburg, Germany.
authors: Sandra
authors: S
authors: Markmann
authors: Institute of Biochemistry and Molecular Biology, University of Bonn, Nussallee 11, D-53115, Bonn, Germany.
authors: Melanie
authors: M
authors: Thelen
authors: Research Department Cell and Gene Therapy, Clinic for Stem Cell Transplantation, University Medical Center Hamburg-Eppendorf, D-20246, Hamburg, Germany.
authors: Kerstin
authors: K
authors: Cornils
authors: Center for Molecular Neurobiology Hamburg, ZMNH, University Medical Center Hamburg-Eppendorf, 20246, Hamburg, Germany.
authors: Michaela
authors: M
authors: Schweizer
authors: Institute of Biochemistry and Molecular Biology, University of Bonn, Nussallee 11, D-53115, Bonn, Germany.
authors: Nahal
authors: N
authors: Brocke-Ahmadinejad
authors: Max Delbrück Center for Molecular Medicine, 13125, Berlin-Buch, Germany.
authors: Thomas
authors: T
authors: Willnow
authors: Department of Biochemistry and Molecular Cell Biology, University Medical Center Hamburg-Eppendorf, D-20246, Hamburg, Germany.
authors: Joerg
authors: J
authors: Heeren
authors: Institute of Biochemistry and Molecular Biology, University of Bonn, Nussallee 11, D-53115, Bonn, Germany.
authors: Volkmar
authors: V
authors: Gieselmann
authors: Department for Biochemistry, Children's Hospital, University Medical Center Hamburg-Eppendorf, D-20246, Hamburg, Germany.
authors: Thomas
authors: T
authors: Braulke
authors: Department for Biochemistry, Children's Hospital, University Medical Center Hamburg-Eppendorf, D-20246, Hamburg, Germany.
authors: Katrin
authors: K
authors: Kollmann
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism; D000818:Animals; D002403:Cathepsins / Q000378:metabolism; D002478:Cells, Cultured; D005347:Fibroblasts / Q000378:metabolism; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008247:Lysosomes / Q000378:metabolism*; D008360:Mannosephosphates / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D021381:Protein Transport; D011973:Receptors, LDL / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000099183:Sortilin
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D002403:Cathepsins; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008360:Mannosephosphates; D011973:Receptors, LDL; D025521:Tumor Suppressor Proteins; D000099183:Sortilin; C486645:Lrp1 protein, mouse; C027693:mannose-6-phosphate
keywords: low-density lipoprotein-related receptor; lysosomal storage disorder; lysosomal targeting; mannose 6-phosphate; receptor-mediated endocytosis; sortilin