title: The recycling endosome protein Rab17 regulates melanocytic filopodia formation and melanosome trafficking.
abstract: Rab GTPases including Rab27a, Rab38 and Rab32 function in melanosome maturation or trafficking in melanocytes. A screen to identify additional Rabs involved in these processes revealed the localization of GFP-Rab17 on recycling endosomes (REs) and melanosomes in melanocytic cells. Rab17 mRNA expression is regulated by microphthalmia transcription factor (MITF), a characteristic of known pigmentation genes. Rab17 siRNA knockdown in melanoma cells quantitatively increased melanosome concentration at the cell periphery. Rab17 knockdown did not inhibit melanosome maturation nor movement, but it caused accumulation of melanin inside cells. Double knockdown of Rab17 and Rab27a indicated that Rab17 acts on melanosomes downstream of Rab27a. Filopodia are known to play a role in melanosome transfer, and in Rab17 knockdown cells filopodia formation was inhibited. Furthermore, we show that stimulation of melanoma cells with α-melanocyte-stimulating hormone induces filopodia formation, supporting a role for filopodia in melanosome release. Cell stimulation also caused redistribution of REs to the periphery, and knockdown of additional RE-associated Rabs 11a and 11b produced a similar accumulation of melanosomes and melanin to that seen after loss of Rab17. Our findings reveal new functions for RE and Rab17 in pigmentation through a distal step in the process of melanosome release via filopodia.
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane 4072 QLD, Australia.
authors.forename: Kimberley A
authors.initials: KA
authors.lastname: Beaumont
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Hamilton
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Moores
authors.forename: Darren L
authors.initials: DL
authors.lastname: Brown
authors.forename: Norihiko
authors.initials: N
authors.lastname: Ohbayashi
authors.forename: Oliver
authors.initials: O
authors.lastname: Cairncross
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Cook
authors.forename: Aaron G
authors.initials: AG
authors.lastname: Smith
authors.forename: Ryo
authors.initials: R
authors.lastname: Misaki
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Fukuda
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Taguchi
authors.forename: Richard A
authors.initials: RA
authors.lastname: Sturm
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Stow
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D045744:Cell Line, Tumor; D011992:Endosomes / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006801:Humans; D008543:Melanins / Q000378:metabolism; D008544:Melanocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D020460:Melanosomes / Q000378:metabolism*; D051379:Mice; D051739:Microphthalmia-Associated Transcription Factor / Q000235:genetics / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism* / Q000648:ultrastructure; D034741:RNA, Small Interfering / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D000521:alpha-MSH / Q000494:pharmacology; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000099193:rab11 GTP-Binding Proteins
chemical_list: D015415:Biomarkers; D008543:Melanins; D051739:Microphthalmia-Associated Transcription Factor; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; D000521:alpha-MSH; D020691:rab GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins; C081073:rab17 protein, epithelial