title: Membranous complexes characteristic of melanocytes derived from patients with Hermansky-Pudlak syndrome type 1 are macroautophagosomal entities of the lysosomal compartment.
abstract: Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder resulting from mutations in a family of genes required for efficient transport of lysosomal-related proteins from the trans-Golgi network to a target organelle. To date, there are several genetically distinct forms of HPS. Many forms of HPS exhibit aberrant trafficking of melanosome-targeted proteins resulting in incomplete melanosome biogenesis responsible for oculocutaneous albinism observed in patients. In HPS-1, melanosome-targeted proteins are localized to characteristic membranous complexes, which have morphologic similarities to macroautophagosomes. In this report, we evaluated the hypothesis that HPS-1-specific membranous complexes comprise a component of the lysosomal compartment of melanocytes. Using indirect immunofluorescence, an increase in co-localization of misrouted tyrosinase with cathepsin-L, a lysosomal cysteine protease, occurred in HPS-1 melanocytes. In addition, ribophorin II, an integral endoplasmic reticulum protein that is also a component of macroautophagosomes, and LC3, a specific marker of macrophagosomes, demonstrated localization to membranous complexes in HPS-1 melanocytes. At the electron microscopic level, the membranous complexes exhibited acid phosphatase activity and localization of exogenously supplied horseradish peroxidase (HRP)-conjugated gold particles, indicating incorporation of lysosomal and endosomal components to membranous complexes, respectively. These results confirm that membranous complexes of HPS-1 melanocytes are macroautophagosomal representatives of the lysosomal compartment.
authors.affiliation: Department of Dermatology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA.
authors.forename: Justin W
authors.initials: JW
authors.lastname: Smith
authors.forename: Amy
authors.initials: A
authors.lastname: Koshoffer
authors.forename: Randal E
authors.initials: RE
authors.lastname: Morris
authors.forename: Raymond E
authors.initials: RE
authors.lastname: Boissy
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism; D001343:Autophagy; D001706:Biopsy; D056668:Cathepsin L; D002403:Cathepsins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D003546:Cysteine Endopeptidases / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D006046:Gold / Q000737:chemistry; D022861:Hermanski-Pudlak Syndrome / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D008247:Lysosomes / Q000378:metabolism*; D008544:Melanocytes / Q000378:metabolism* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D014442:Monophenol Monooxygenase / Q000378:metabolism; D010588:Phagosomes / Q000378:metabolism*; D021381:Protein Transport; D012867:Skin / Q000378:metabolism
chemical_list: C477012:MAP1LC3A protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; C034241:ribophorin; D006046:Gold; D014442:Monophenol Monooxygenase; D000135:Acid Phosphatase; D002403:Cathepsins; D003546:Cysteine Endopeptidases; C534281:CTSL protein, human; D056668:Cathepsin L