title: RUTBC1 Functions as a GTPase-activating Protein for Rab32/38 and Regulates Melanogenic Enzyme Trafficking in Melanocytes.
abstract: Two cell type-specific Rab proteins, Rab32 and Rab38 (Rab32/38), have been proposed as regulating the trafficking of melanogenic enzymes, including tyrosinase and tyrosinase-related protein 1 (Tyrp1), to melanosomes in melanocytes. Like other GTPases, Rab32/38 function as switch molecules that cycle between a GDP-bound inactive form and a GTP-bound active form; the cycle is thought to be regulated by an activating enzyme, guanine nucleotide exchange factor (GEF), and an inactivating enzyme, GTPase-activating protein (GAP), which stimulates the GTPase activity of Rab32/38. Although BLOC-3 has already been identified as a Rab32/38-specific GEF that regulates the trafficking of tyrosinase and Tyrp1, no physiological GAP for Rab32/38 in melanocytes has ever been identified, and it has remained unclear whether Rab32/38 is involved in the trafficking of dopachrome tautomerase, another melanogenic enzyme, in mouse melanocytes. In this study we investigated RUTBC1, which was originally characterized as a Rab9-binding protein and GAP for Rab32 and Rab33B in vitro, and the results demonstrated that RUTBC1 functions as a physiological GAP for Rab32/38 in the trafficking of all three melanogenic enzymes in mouse melanocytes. The results of this study also demonstrated the involvement of Rab9A in the regulation of the RUTBC1 localization and in the trafficking of all three melanogenic enzymes. We discovered that either excess activation or inactivation of Rab32/38 achieved by manipulating RUTBC1 inhibits the trafficking of all three melanogenic enzymes. These results collectively indicate that proper spatiotemporal regulation of Rab32/38 is essential for the trafficking of all three melanogenic enzymes in mouse melanocytes.
authors.affiliation: From the Laboratory of Membrane Trafficking Mechanisms, Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai, Miyagi 980-8578, Japan and.
authors.forename: Soujiro
authors.initials: S
authors.lastname: Marubashi
authors.affiliation: From the Laboratory of Membrane Trafficking Mechanisms, Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai, Miyagi 980-8578, Japan and.
authors.forename: Hikaru
authors.initials: H
authors.lastname: Shimada
authors.affiliation: From the Laboratory of Membrane Trafficking Mechanisms, Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai, Miyagi 980-8578, Japan and nori@m.tohoku.ac.jp.
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Fukuda
authors.affiliation: From the Laboratory of Membrane Trafficking Mechanisms, Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai, Miyagi 980-8578, Japan and the Department of Physiological Chemistry, Faculty of Medicine and Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan nohbayashi@md.tsukuba.ac.jp.
authors.forename: Norihiko
authors.initials: N
authors.lastname: Ohbayashi
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation; D020662:Guanine Nucleotide Exchange Factors; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019746:Intramolecular Oxidoreductases / Q000378:metabolism; D008544:Melanocytes / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D020460:Melanosomes / Q000201:enzymology* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D014442:Monophenol Monooxygenase / Q000378:metabolism; D009154:Mutation; D010088:Oxidoreductases / Q000378:metabolism; D021381:Protein Transport; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C507980:Hps4 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; C523295:SGSM2 protein, human; D033921:Vesicular Transport Proteins; D010088:Oxidoreductases; C079621:Tyrp1 protein, mouse; D014442:Monophenol Monooxygenase; C478766:Rab32 protein, mouse; C498786:Rab38 protein, mouse; C544263:rab9 protein, mouse; D020691:rab GTP-Binding Proteins; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase
keywords: GTPase-activating protein (GAP); Rab; melanogenesis; membrane trafficking; organelle