title: ESCRT-I function is required for Tyrp1 transport from early endosomes to the melanosome limiting membrane.
abstract: Melanosomes are lysosome-related organelles that coexist with lysosomes within melanocytes. The pathways by which melanosomal proteins are diverted from endocytic organelles toward melanosomes are incompletely defined. In melanocytes from mouse models of Hermansky-Pudlak syndrome that lack BLOC-1, melanosomal proteins such as tyrosinase-related protein 1 (Tyrp1) accumulate in early endosomes. Whether this accumulation represents an anomalous pathway or an arrested normal intermediate in melanosome protein trafficking is not clear. Here, we show that early endosomes are requisite intermediates in the trafficking of Tyrp1 from the Golgi to late stage melanosomes in normal melanocytic cells. Kinetic analyses show that very little newly synthesized Tyrp1 traverses the cell surface and that internalized Tyrp1 is inefficiently sorted to melanosomes. Nevertheless, nearly all Tyrp1 traverse early endosomes since it becomes trapped within enlarged, modified endosomes upon overexpression of Hrs. Although Tyrp1 localization is not affected by Hrs depletion, depletion of the ESCRT-I component, Tsg101, or inhibition of ESCRT function by dominant-negative approaches results in a dramatic redistribution of Tyrp1 to aberrant endosomal membranes that are largely distinct from those harboring traditional ESCRT-dependent, ubiquitylated cargoes such as MART-1. The lysosomal protein content of some of these membranes and the lack of Tyrp1 recycling to the plasma membrane in Tsg101-depleted cells suggests that ESCRT-I functions downstream of BLOC-1. Our data delineate a novel pathway for Tyrp1 trafficking and illustrate a requirement for ESCRT-I function in controlling protein sorting from vacuolar endosomes to the limiting membrane of a lysosome-related organelle.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Steven T
authors.initials: ST
authors.lastname: Truschel
authors.forename: Sabrina
authors.initials: S
authors.lastname: Simoes
authors.forename: Subba Rao Gangi
authors.initials: SR
authors.lastname: Setty
authors.forename: Dawn C
authors.initials: DC
authors.lastname: Harper
authors.forename: Danièle
authors.initials: D
authors.lastname: Tenza
authors.forename: Penelope C
authors.initials: PC
authors.lastname: Thomas
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Herman
authors.forename: Sara D
authors.initials: SD
authors.lastname: Sackett
authors.forename: David C
authors.initials: DC
authors.lastname: Cowan
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Theos
authors.forename: Graça
authors.initials: G
authors.lastname: Raposo
authors.forename: Michael S
authors.initials: MS
authors.lastname: Marks
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics / Q000502:physiology*; D011992:Endosomes / Q000378:metabolism*; D022861:Hermanski-Pudlak Syndrome / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D037102:Lectins / Q000378:metabolism; D008543:Melanins / Q000096:biosynthesis; D008544:Melanocytes / Q000378:metabolism; D020460:Melanosomes / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D010088:Oxidoreductases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics; D021381:Protein Transport; D014157:Transcription Factors / Q000235:genetics; D014162:Transfection; D000099177:Tsg101 Protein
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D047908:Intracellular Signaling Peptides and Proteins; D037102:Lectins; D008543:Melanins; D008562:Membrane Glycoproteins; D010088:Oxidoreductases; D010750:Phosphoproteins; D014157:Transcription Factors; D000099177:Tsg101 Protein; C513476:Bloc1s6 protein, mouse; C096164:hepatocyte growth factor-regulated tyrosine kinase substrate; C079621:Tyrp1 protein, mouse