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Published online 19 February 2001. doi:10.1083/jcb.152.4.795
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© The Rockefeller University Press, 0021-9525/2001//795 $5.00
The Journal of Cell Biology, Volume 152, Number 4, , 2001 795-808

Original Article

Rab27a Regulates the Peripheral Distribution of Melanosomes in Melanocytes



Alistair N. Humea, Lucy M. Collinsonb, Andrzej Rapaka, Anita Q. Gomesa, Colin R. Hopkinsb, and Miguel C. Seabraa

a Cell and Molecular Biology Section, Division of Biomedical Sciences
b Department of Biochemistry, Imperial College of Science, Technology and Medicine, London SW7 2AZ, United Kingdom
Cell and Molecular Biology Section, Division of Biomedical Sciences, Imperial College School of Medicine, Sir Alexander Fleming Building, London SW7 2AZ, UK.44-20-7594-301544-20-7594-3024

m.seabra{at}ic.ac.uk

Rab GTPases are regulators of intracellular membrane traffic. We report a possible function of Rab27a, a protein implicated in several diseases, including Griscelli syndrome, choroideremia, and the Hermansky-Pudlak syndrome mouse model, gunmetal. We studied endogenous Rab27a and overexpressed enhanced GFP-Rab27a fusion protein in several cultured melanocyte and melanoma-derived cell lines. In pigmented cells, we observed that Rab27a decorates melanosomes, whereas in nonpigmented cells Rab27a colocalizes with melanosome-resident proteins. When dominant interfering Rab27a mutants were expressed in pigmented cells, we observed a redistribution of pigment granules with perinuclear clustering. This phenotype is similar to that observed by others in melanocytes derived from the ashen and dilute mutant mice, which bear mutations in the Rab27a and MyoVa loci, respectively. We also found that myosinVa coimmunoprecipitates with Rab27a in extracts from melanocytes and that both Rab27a and myosinVa colocalize on the cytoplasmic face of peripheral melanosomes in wild-type melanocytes. However, the amount of myosinVa in melanosomes from Rab27a-deficient ashen melanocytes is greatly reduced. These results, together with recent data implicating myosinVa in the peripheral capture of melanosomes, suggest that Rab27a is necessary for the recruitment of myosinVa, so allowing the peripheral retention of melanosomes in melanocytes.

Key Words: Rab27a • GTP-binding proteins • vesicular transport • melanosome • myosinVa

© 2001 The Rockefeller University Press

The online version of this article contains supplemental material.

Abbreviations used in this paper: CHM, choroideremia; EGFP, enhanced green fluorescent protein; gm, gunmetal; HPS, Hermansky-Pudlak syndrome; LAMP, lysosome-associated membrane protein; REP, Rab escort protein; RGGT, Rab geranylgeranyl transferase; TRP-1, tyrosinase-related protein 1.


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