title: Rab27b association with melanosomes: dominant negative mutants disrupt melanosomal movement.
abstract: The movement of melanosomes from post-Golgi compartments to the periphery of melanocytes is known to be regulated by factors including myosin Va and at least one Rab protein, Rab27a. Mutations in the genes encoding either protein in the mouse result in a hypopigmented phenotype mimicking the human disease Griscelli syndrome. Rab27b and Rab27a share 72% identity and they belong to the same melanocyte/platelet subfamily of Rab proteins. Rab27a orchestrates the transport of melanosomes by recruitment of the actin motor, myosin Va, onto melanosomes. By contrast, the function of Rab27b has remained elusive. In this study, we found that Rab27b mRNA is present in melanocytes and demonstrated the intrinsic GTPase activity of Rab27b protein. We explored the function of Rab27b by overexpression of two dominant negative mutants as well as the wild-type Rab27b in melan-a melanocytes. Green-fluorescent-protein-tagged Rab27b colocalizes with the melanosome marker tyrosinase-related protein 1 and with myosin Va at the cell periphery, whereas Rab27b mutants do not decorate melanosomes, and melanosomes in these mutant transfected cells redistribute from cell periphery to the perinuclear region. Furthermore, transient overexpression of the dominant negative forms of Rab27b caused diminution in both numbers and length of dendrites of melan-a cells. Our results suggest that Rab27b may regulate the outward movement of melanosomes and the formation or maintenance of dendritic extensions in melanocytes.
authors.affiliation: Department of Cell Biology, New York University School of Medicine, New York, New York 10016, USA.
authors.forename: Yanru
authors.initials: Y
authors.lastname: Chen
authors.forename: Preminda
authors.initials: P
authors.lastname: Samaraweera
authors.forename: Tung-Tien
authors.initials: TT
authors.lastname: Sun
authors.forename: Gert
authors.initials: G
authors.lastname: Kreibich
authors.forename: Seth J
authors.initials: SJ
authors.lastname: Orlow
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003712:Dendrites / Q000737:chemistry / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D006160:Guanosine Triphosphate / Q000378:metabolism; D008544:Melanocytes / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D020460:Melanosomes / Q000737:chemistry / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D016297:Mutagenesis, Site-Directed / Q000502:physiology; D017354:Point Mutation / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D020691:rab GTP-Binding Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D000075745:rab27 GTP-Binding Proteins
chemical_list: D012333:RNA, Messenger; D000075745:rab27 GTP-Binding Proteins; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; C512958:Rab27b protein, mouse; C512962:Rab27a protein, mouse; D020691:rab GTP-Binding Proteins