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The Rab21-GEF activity of Varp, but not its Rab32/38 effector function, is required for dendrite formation in melanocytes

Vacuolar protein sorting 9 (VPS9)–ankyrin-repeat protein (Varp) has recently been identified as an effector molecule for two small GTPases—Rab32 and Rab38—in the transport of a melanogenic enzyme tyrosinase-related protein 1 (Tyrp1) to melanosomes in melanocytes. Although Varp contains a Rab21–guani...

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Autores principales: Ohbayashi, Norihiko, Yatsu, Ayaka, Tamura, Kanako, Fukuda, Mitsunori
Formato: Online Artículo Texto
Lenguaje:English
Publicado: The American Society for Cell Biology 2012
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3279394/
https://www.ncbi.nlm.nih.gov/pubmed/22171327
http://dx.doi.org/10.1091/mbc.E11-04-0324
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author Ohbayashi, Norihiko
Yatsu, Ayaka
Tamura, Kanako
Fukuda, Mitsunori
author_facet Ohbayashi, Norihiko
Yatsu, Ayaka
Tamura, Kanako
Fukuda, Mitsunori
author_sort Ohbayashi, Norihiko
collection PubMed
description Vacuolar protein sorting 9 (VPS9)–ankyrin-repeat protein (Varp) has recently been identified as an effector molecule for two small GTPases—Rab32 and Rab38—in the transport of a melanogenic enzyme tyrosinase-related protein 1 (Tyrp1) to melanosomes in melanocytes. Although Varp contains a Rab21–guanine nucleotide exchange factor (GEF) domain (i.e., VPS9 domain), since Rab21-GEF activity is not required for Tyrp1 transport, nothing is known about the physiological significance of the Rab21-GEF activity in melanocytes. Here we show by knockdown-rescue experiments that the Rab21-GEF activity of Varp, but not its Rab32/38 effector function, is required for forskolin-induced dendrite formation of cultured melanocytes. We found that Varp-deficient cells are unable to extend dendrites in response to forskolin stimulation and that reexpression of wild-type Varp or a Rab32/38-binding–deficient mutant Varp(Q509A/Y550A) in Varp-deficient cells completely restores their ability to form dendrites. By contrast, VPS9 mutants (D310A and Y350A) and a vesicle-associated membrane protein 7 (VAMP7)-binding–deficient mutant were unable to support forskolin-induced dendrite formation in Varp-deficient cells. These findings indicate that the Rab21-GEF activity and Rab32/38 binding activity of Varp are required for different melanocyte functions, that is, Rab21 activation by the VPS9 domain is required for dendrite formation, and the Rab32/38 effector function of the ankyrin repeat 1 domain is required for Tyrp1 transport to melanosomes, although VAMP7-binding ability is required for both functions.
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spelling pubmed-32793942012-04-30 The Rab21-GEF activity of Varp, but not its Rab32/38 effector function, is required for dendrite formation in melanocytes Ohbayashi, Norihiko Yatsu, Ayaka Tamura, Kanako Fukuda, Mitsunori Mol Biol Cell Articles Vacuolar protein sorting 9 (VPS9)–ankyrin-repeat protein (Varp) has recently been identified as an effector molecule for two small GTPases—Rab32 and Rab38—in the transport of a melanogenic enzyme tyrosinase-related protein 1 (Tyrp1) to melanosomes in melanocytes. Although Varp contains a Rab21–guanine nucleotide exchange factor (GEF) domain (i.e., VPS9 domain), since Rab21-GEF activity is not required for Tyrp1 transport, nothing is known about the physiological significance of the Rab21-GEF activity in melanocytes. Here we show by knockdown-rescue experiments that the Rab21-GEF activity of Varp, but not its Rab32/38 effector function, is required for forskolin-induced dendrite formation of cultured melanocytes. We found that Varp-deficient cells are unable to extend dendrites in response to forskolin stimulation and that reexpression of wild-type Varp or a Rab32/38-binding–deficient mutant Varp(Q509A/Y550A) in Varp-deficient cells completely restores their ability to form dendrites. By contrast, VPS9 mutants (D310A and Y350A) and a vesicle-associated membrane protein 7 (VAMP7)-binding–deficient mutant were unable to support forskolin-induced dendrite formation in Varp-deficient cells. These findings indicate that the Rab21-GEF activity and Rab32/38 binding activity of Varp are required for different melanocyte functions, that is, Rab21 activation by the VPS9 domain is required for dendrite formation, and the Rab32/38 effector function of the ankyrin repeat 1 domain is required for Tyrp1 transport to melanosomes, although VAMP7-binding ability is required for both functions. The American Society for Cell Biology 2012-02-15 /pmc/articles/PMC3279394/ /pubmed/22171327 http://dx.doi.org/10.1091/mbc.E11-04-0324 Text en © 2012 Ohbayashi et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0). “ASCB®,” “The American Society for Cell Biology®,” and “Molecular Biology of the Cell®” are registered trademarks of The American Society of Cell Biology.
spellingShingle Articles
Ohbayashi, Norihiko
Yatsu, Ayaka
Tamura, Kanako
Fukuda, Mitsunori
The Rab21-GEF activity of Varp, but not its Rab32/38 effector function, is required for dendrite formation in melanocytes
title The Rab21-GEF activity of Varp, but not its Rab32/38 effector function, is required for dendrite formation in melanocytes
title_full The Rab21-GEF activity of Varp, but not its Rab32/38 effector function, is required for dendrite formation in melanocytes
title_fullStr The Rab21-GEF activity of Varp, but not its Rab32/38 effector function, is required for dendrite formation in melanocytes
title_full_unstemmed The Rab21-GEF activity of Varp, but not its Rab32/38 effector function, is required for dendrite formation in melanocytes
title_short The Rab21-GEF activity of Varp, but not its Rab32/38 effector function, is required for dendrite formation in melanocytes
title_sort rab21-gef activity of varp, but not its rab32/38 effector function, is required for dendrite formation in melanocytes
topic Articles
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3279394/
https://www.ncbi.nlm.nih.gov/pubmed/22171327
http://dx.doi.org/10.1091/mbc.E11-04-0324
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