title: Rab9A is required for delivery of cargo from recycling endosomes to melanosomes.
abstract: Melanosomes are a type of lysosome-related organelle that is commonly defective in Hermansky-Pudlak syndrome. Biogenesis of melanosomes is regulated by BLOC-1, -2, -3, or AP-1, -3 complexes, which mediate cargo transport from recycling endosomes to melanosomes. Although several Rab GTPases have been shown to regulate these trafficking steps, the precise role of Rab9A remains unknown. Here, we found that a cohort of Rab9A associates with the melanosomes and its knockdown in melanocytes results in hypopigmented melanosomes due to mistargeting of melanosomal proteins to lysosomes. In addition, the Rab9A-depletion phenotype resembles Rab38/32-inactivated or BLOC-3-deficient melanocytes, suggesting that Rab9A works in line with BLOC-3 and Rab38/32 during melanosome cargo transport. Furthermore, silencing of Rab9A, Rab38/32 or its effector VARP, or BLOC-3-deficiency in melanocytes decreased the length of STX13-positive recycling endosomal tubules and targeted the SNARE to lysosomes. This result indicates a defect in directing recycling endosomal tubules to melanosomes. Thus, Rab9A and its co-regulatory GTPases control STX13-mediated cargo delivery to maturing melanosomes.
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India.
authors.forename: Sarmistha
authors.initials: S
authors.lastname: Mahanty
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India.
authors.forename: Keerthana
authors.initials: K
authors.lastname: Ravichandran
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India.
authors.forename: Praneeth
authors.initials: P
authors.lastname: Chitirala
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India.
authors.forename: Jyothi
authors.initials: J
authors.lastname: Prabha
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India.
authors.forename: Riddhi Atul
authors.initials: RA
authors.lastname: Jani
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India.
authors.forename: Subba Rao Gangi
authors.initials: SR
authors.lastname: Setty
mesh_terms: D000818:Animals; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D008247:Lysosomes / Q000378:metabolism; D008544:Melanocytes / Q000378:metabolism; D020460:Melanosomes / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D010858:Pigmentation; D021381:Protein Transport; D034741:RNA, Small Interfering / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D034741:RNA, Small Interfering; C498786:Rab38 protein, mouse; C544263:rab9 protein, mouse; D020691:rab GTP-Binding Proteins
keywords: AP-3; BLOC-1; BLOC-2; BLOC-3; HPS; Rab38/Rab32; Rab9A