title: AP-3 mediates tyrosinase but not TRP-1 trafficking in human melanocytes.
abstract: Patients with Hermansky-Pudlak syndrome type 2 (HPS-2) have mutations in the beta 3A subunit of adaptor complex-3 (AP-3) and functional deficiency of this complex. AP-3 serves as a coat protein in the formation of new vesicles, including, apparently, the platelet's dense body and the melanocyte's melanosome. We used HPS-2 melanocytes in culture to determine the role of AP-3 in the trafficking of the melanogenic proteins tyrosinase and tyrosinase-related protein-1 (TRP-1). TRP-1 displayed a typical melanosomal pattern in both normal and HPS-2 melanocytes. In contrast, tyrosinase exhibited a melanosomal (i.e., perinuclear and dendritic) pattern in normal cells but only a perinuclear pattern in the HPS-2 melanocytes. In addition, tyrosinase exhibited a normal pattern of expression in HPS-2 melanocytes transfected with a cDNA encoding the beta 3A subunit of the AP-3 complex. This suggests a role for AP-3 in the normal trafficking of tyrosinase to premelanosomes, consistent with the presence of a dileucine recognition signal in the C-terminal portion of the tyrosinase molecule. In the AP-3-deficient cells, tyrosinase was also present in structures resembling late endosomes or multivesicular bodies; these vesicles contained exvaginations devoid of tyrosinase. This suggests that, under normal circumstances, AP-3 may act on multivesicular bodies to form tyrosinase-containing vesicles destined to fuse with premelanosomes. Finally, our studies demonstrate that tyrosinase and TRP-1 use different mechanisms to reach their premelanosomal destination.
authors.affiliation: Section on Human Biochemical Genetics, Heritable Disorders Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: M
authors.initials: M
authors.lastname: Huizing
authors.forename: R
authors.initials: R
authors.lastname: Sarangarajan
authors.forename: E
authors.initials: E
authors.lastname: Strovel
authors.forename: Y
authors.initials: Y
authors.lastname: Zhao
authors.forename: W A
authors.initials: WA
authors.lastname: Gahl
authors.forename: R E
authors.initials: RE
authors.lastname: Boissy
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport; D015703:Antigens, CD / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D022861:Hermanski-Pudlak Syndrome / Q000378:metabolism*; D006801:Humans; D008544:Melanocytes / Q000378:metabolism*; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D034041:Monomeric Clathrin Assembly Proteins; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D010088:Oxidoreductases; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D060149:Tetraspanin 30
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D015703:Antigens, CD; C554586:CD63 protein, human; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D034041:Monomeric Clathrin Assembly Proteins; D010980:Platelet Membrane Glycoproteins; D011506:Proteins; D060149:Tetraspanin 30; C439023:clathrin assembly protein AP180; D010088:Oxidoreductases; C489799:TYRP1 protein, human; C064056:tyrosinase-related protein-1; D014442:Monophenol Monooxygenase