title: The etiology of oculocutaneous albinism (OCA) type II: the pink protein modulates the processing and transport of tyrosinase.
abstract: Oculocutaneous albinism (OCA) is caused by reduced or deficient melanin pigmentation in the skin, hair, and eyes. OCA has different phenotypes resulting from mutations in distinct pigmentation genes involved in melanogenesis. OCA type 2 (OCA2), the most common form of OCA, is an autosomal recessive disorder caused by mutations in the P gene, the function(s) of which is controversial. In order to elucidate the mechanism(s) involved in OCA2, our group used several antibodies specific for various melanosomal proteins (tyrosinase, Tyrp1, Dct, Pmel17 and HMB45), including a specific set of polyclonal antibodies against the p protein. We used confocal immunohistochemistry to compare the processing and distribution of those melanosomal proteins in wild type (melan-a) and in p mutant (melan-p1) melanocytes. Our results indicate that the melanin content of melan-p1 melanocytes was less than 50% that of wild type melan-a melanocytes. In contrast, the tyrosinase activities were similar in extracts of wild type and p mutant melanocytes. Confocal microscopy studies and pulse-chase analyses showed altered processing and sorting of tyrosinase, which is released from melan-p1 cells to the medium. Processing and sorting of Tyrp1 was also altered to some extent. However, Dct and Pmel17 expression and subcellular localization were similar in melan-a and in melan-p1 melanocytes. In melan-a cells, the p protein showed mainly a perinuclear pattern with some staining in the cytoplasm where some co-localization with HMB45 antibody was observed. These findings suggest that the p protein plays a major role in modulating the intracellular transport of tyrosinase and a minor role for Tyrp1, but is not critically involved in the transport of Dct and Pmel17. This study provides a basis to understand the relationship of the p protein with tyrosinase function and melanin synthesis, and also provides a rational approach to unveil the consequences of P gene mutations in the pathogenesis of OCA2.
authors.affiliation: Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Kazutomo
authors.initials: K
authors.lastname: Toyofuku
authors.forename: Julio C
authors.initials: JC
authors.lastname: Valencia
authors.forename: Tsuneto
authors.initials: T
authors.lastname: Kushimoto
authors.forename: Gertrude-E
authors.initials: GE
authors.lastname: Costin
authors.forename: Victoria M
authors.initials: VM
authors.lastname: Virador
authors.forename: Wilfred D
authors.initials: WD
authors.lastname: Vieira
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Ferrans
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Hearing
mesh_terms: D016115:Albinism, Oculocutaneous / Q000209:etiology* / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D033862:Iron-Binding Proteins; D008544:Melanocytes / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D026901:Membrane Transport Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D014442:Monophenol Monooxygenase / Q000235:genetics* / Q000378:metabolism*; D009154:Mutation; D010088:Oxidoreductases; D011233:Precipitin Tests; D021381:Protein Transport; D011506:Proteins / Q000378:metabolism; D013997:Time Factors; D058951:gp100 Melanoma Antigen; D000099236:Solute Carrier Family 11, Member 2
chemical_list: D002352:Carrier Proteins; D027682:Cation Transport Proteins; D033862:Iron-Binding Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D014442:Monophenol Monooxygenase; D010088:Oxidoreductases; D011506:Proteins; D058951:gp100 Melanoma Antigen; D000099236:Solute Carrier Family 11, Member 2; C489600:OCA2 protein, human; C548637:PMEL protein, human; C548642:Pmel protein, mouse; C489799:TYRP1 protein, human; C079621:Tyrp1 protein, mouse