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Lrp1/ LDL Receptor Play Critical Roles in Mannose 6‐Phosphate‐Independent Lysosomal Enzyme Targeting
Author(s) -
Markmann Sandra,
Thelen Melanie,
Cornils Kerstin,
Schweizer Michaela,
BrockeAhmadinejad Nahal,
Willnow Thomas,
Heeren Joerg,
Gieselmann Volkmar,
Braulke Thomas,
Kollmann Katrin
Publication year - 2015
Publication title -
traffic
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.677
H-Index - 130
eISSN - 1600-0854
pISSN - 1398-9219
DOI - 10.1111/tra.12284
Subject(s) - mannose 6 phosphate , mannose 6 phosphate receptor , biology , internalization , stable isotope labeling by amino acids in cell culture , lrp1 , lysosome , cathepsin d , ldl receptor , endocytic cycle , receptor , microbiology and biotechnology , cathepsin , endosome , biochemistry , endocytosis , enzyme , proteomics , lipoprotein , growth factor , cholesterol , gene
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.