title: The leaden gene product is required with Rab27a to recruit myosin Va to melanosomes in melanocytes.
abstract: The function of lysosome-related organelles such as melanosomes in melanocytes, and lytic granules in cytotoxic T lymphocytes is disrupted in Griscelli syndrome and related diseases. Griscelli syndrome results from loss of function mutations in either the RAB27A (type 1 Griscelli syndrome) or MYO5A (type 2 Griscelli syndrome) genes. Melanocytes from Griscelli syndrome patients and respective murine models ashen (Rab27a mutant), dilute (myosin Va mutant), and leaden exhibit perinuclear clustering of melanosomes. Recent work suggests that Rab27a is required to recruit myosin Va to melanosomes, thereby tethering melanosomes to the peripheral actin network and promoting melanosome retention at the tips of melanocytic dendrites. Here, we characterize the function of the leaden gene product. We show that Rab27a, but not myosin Va, can be localized to melanosomes in leaden melanocytes, suggesting that the leaden gene product acts downstream of, or in parallel to, Rab27a in melanocytes to promote recruitment of myosin Va to melanosomes. We also observed reduced levels of myosin Va protein in leaden and ashen melanocytes, suggesting that myosin Va stability is influenced by the leaden and ashen gene products. In leaden cytotoxic T lymphocytes, we observed that lytic granules polarize towards the immunological synapse and kill target cells normally. However, in contrast to melanocytes, we found that neither the leaden gene product (melanophilin) nor myosin Va was detectable in cytotoxic T lymphocytes. These results suggest that Rab27a interacts with different classes of effector proteins in melanocytes and cytotoxic T lymphocytes.
authors.affiliation: Cell and Molecular Biology, Division of Biomedical Sciences, Faculty of Medicine, Imperial College, London SW7 2AZ, UK.
authors.forename: Alistair N
authors.initials: AN
authors.lastname: Hume
authors.forename: Lucy M
authors.initials: LM
authors.lastname: Collinson
authors.forename: Colin R
authors.initials: CR
authors.lastname: Hopkins
authors.forename: Molly
authors.initials: M
authors.lastname: Strom
authors.forename: Duarte C
authors.initials: DC
authors.lastname: Barral
authors.forename: Giovanna
authors.initials: G
authors.lastname: Bossi
authors.forename: Gillian M
authors.initials: GM
authors.lastname: Griffiths
authors.forename: Miguel C
authors.initials: MC
authors.lastname: Seabra
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D015151:Immunoblotting; D008544:Melanocytes / Q000378:metabolism*; D020460:Melanosomes / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009154:Mutation; D024701:Myosin Type V / Q000378:metabolism*; D014176:Protein Biosynthesis; D011506:Proteins / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013154:Spleen / Q000166:cytology; D013577:Syndrome; D013602:T-Lymphocytes, Cytotoxic / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000378:metabolism*; D000075745:rab27 GTP-Binding Proteins
chemical_list: D011506:Proteins; D000075745:rab27 GTP-Binding Proteins; D024701:Myosin Type V; C512962:Rab27a protein, mouse; D020691:rab GTP-Binding Proteins