title: A Varp-Binding Protein, RACK1, Regulates Dendrite Outgrowth through Stabilization of Varp Protein in Mouse Melanocytes.
abstract: Varp (VPS9-ankyrin repeat protein) in melanocytes is thought to function as a key player in the pigmentation of mammals. Varp regulates two different melanocyte functions: (i) transport of melanogenic enzymes to melanosomes by functioning as a Rab32/38 effector and (ii) promotion of dendrite outgrowth by functioning as a Rab21-guanine nucleotide exchange factor. The Varp protein level has recently been shown to be negatively regulated by proteasomal degradation through interaction of the ankyrin repeat 2 (ANKR2) domain of Varp with Rab40C. However, the molecular mechanisms by which Varp escapes from Rab40C and retains its own expression level remain completely unknown. Here, we identified RACK1 (receptor of activated protein kinase C 1) as a Varp-ANKR2 binding partner and investigated its involvement in Varp stabilization in mouse melanocytes. The results showed that knockdown of endogenous RACK1 in melanocytes caused dramatic reduction of the Varp protein level and inhibition of dendrite outgrowth, and intriguingly, overexpression of RACK1 inhibited the interaction between Varp and Rab40C and counteracted the negative effect of Rab40C on dendrite outgrowth. These findings indicated that RACK1 competes with Rab40C for binding to the ANKR2 domain of Varp and regulates dendrite outgrowth through stabilization of Varp in mouse melanocytes.
authors.affiliation: 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.
authors.forename: Soujiro
authors.initials: S
authors.lastname: Marubashi
authors.affiliation: 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; 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. Electronic address: nohbayashi@md.tsukuba.ac.jp.
authors.forename: Norihiko
authors.initials: N
authors.lastname: Ohbayashi
authors.affiliation: 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. Electronic address: nori@m.tohoku.ac.jp.
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Fukuda
mesh_terms: D000818:Animals; D017487:Ankyrins / Q000378:metabolism; D019556:COS Cells; D002522:Chlorocebus aethiops; D003712:Dendrites / Q000378:metabolism*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D008544:Melanocytes / Q000166:cytology / Q000378:metabolism*; D020460:Melanosomes / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D009479:Neuropeptides / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D000072417:Protein Domains; D000075370:Receptors for Activated C Kinase; D020798:Two-Hybrid System Techniques
chemical_list: C486007:Ankra2 protein, mouse; D017487:Ankyrins; D020662:Guanine Nucleotide Exchange Factors; D008562:Membrane Glycoproteins; D009479:Neuropeptides; C090294:RACK1 protein, mouse; D000075370:Receptors for Activated C Kinase; C512038:VPS9-ankyrin-repeat protein, mouse; D049452:Green Fluorescent Proteins; D046988:Proteasome Endopeptidase Complex