title: Site-1 protease-activated formation of lysosomal targeting motifs is independent of the lipogenic transcription control.
abstract: Site-1 protease (S1P) cleaves membrane-bound lipogenic sterol regulatory element-binding proteins (SREBPs) and the α/β-subunit precursor protein of the N-acetylglucosamine-1-phosphotransferase forming mannose 6-phosphate (M6P) targeting markers on lysosomal enzymes. The translocation of SREBPs from the endoplasmic reticulum (ER) to the Golgi-resident S1P depends on the intracellular sterol content, but it is unknown whether the ER exit of the α/β-subunit precursor is regulated. Here, we investigated the effect of cholesterol depletion (atorvastatin treatment) and elevation (LDL overload) on ER-Golgi transport, S1P-mediated cleavage of the α/β-subunit precursor, and the subsequent targeting of lysosomal enzymes along the biosynthetic and endocytic pathway to lysosomes. The data showed that the proteolytic cleavage of the α/β-subunit precursor into mature and enzymatically active subunits does not depend on the cholesterol content. In either treatment, lysosomal enzymes are normally decorated with M6P residues, allowing the proper sorting to lysosomes. In addition, we found that, in fibroblasts of mucolipidosis type II mice and Niemann-Pick type C patients characterized by aberrant cholesterol accumulation, the proteolytic cleavage of the α/β-subunit precursor was not impaired. We conclude that S1P substrate-dependent regulatory mechanisms for lipid synthesis and biogenesis of lysosomes are different.
authors.affiliation: Biochemistry Section, Children's Hospital, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
authors.forename: Sarah
authors.initials: S
authors.lastname: Klünder
authors.affiliation: Department of Biochemistry and Molecular Cell Biology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Heeren
authors.affiliation: Biochemistry Section, Children's Hospital, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Markmann
authors.affiliation: Biochemistry Section, Children's Hospital, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
authors.forename: René
authors.initials: R
authors.lastname: Santer
authors.affiliation: Biochemistry Section, Children's Hospital, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Braulke
authors.affiliation: Biochemistry Section, Children's Hospital, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Pohl
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004789:Enzyme Activation; D005347:Fibroblasts / Q000166:cytology; D005786:Gene Expression Regulation; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D050155:Lipogenesis / Q000235:genetics*; D008247:Lysosomes / Q000378:metabolism*; D051379:Mice; D043484:Proprotein Convertases / Q000737:chemistry / Q000378:metabolism*; D021381:Protein Transport; D059748:Proteolysis; D011973:Receptors, LDL / Q000378:metabolism; D012697:Serine Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic; D017855:Transferases (Other Substituted Phosphate Groups) / Q000378:metabolism
chemical_list: D011973:Receptors, LDL; D017855:Transferases (Other Substituted Phosphate Groups); C505859:alpha-beta GlcNAc-1-phosphotransferase, human; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; C115575:membrane-bound transcription factor peptidase, site 1
keywords: Golgi apparatus; LDL receptor; Niemann-Pick type C1 disease; cholesterol; endocytosis; lysosome; mannose 6-phosphate; mucolipidosis type II; statins