title: The Rab5 activator ALS2/alsin acts as a novel Rac1 effector through Rac1-activated endocytosis.
abstract: Mutations in the ALS2 gene cause a number of recessive motor neuron diseases, indicating that the ALS2 protein (ALS2/alsin) is vital for motor neurons. ALS2 acts as a guanine nucleotide exchange factor (GEF) for Rab5 (Rab5GEF) and is involved in endosome dynamics. However, the spatiotemporal regulation of the ALS2-mediated Rab5 activation is unclear. Here we identified an upstream activator for ALS2 and showed a functional significance of the ALS2 activation in endosome dynamics. ALS2 preferentially interacts with activated Rac1. In the cells activated Rac1 recruits cytoplasmic ALS2 to membrane ruffles and subsequently to nascent macropinosomes via Rac1-activated macropinocytosis. At later endocytic stages macropinosomal ALS2 augments fusion of the ALS2-localized macropinosomes with the transferrin-positive endosomes, depending on the ALS2-associated Rab5GEF activity. These results indicate that Rac1 promotes the ALS2 membranous localization, thereby rendering ALS2 active via Rac1-activated endocytosis. Thus, ALS2 is a novel Rac1 effector and is involved in Rac1-activated macropinocytosis. All together, loss of ALS2 may perturb macropinocytosis and/or the following membrane trafficking, which gives rise to neuronal dysfunction in the ALS2-linked motor neuron diseases.
authors.affiliation: Department of Molecular Life Sciences, Tokai University School of Medicine, Isehara, Kanagawa 259-1193, Japan.
authors.forename: Ryota
authors.initials: R
authors.lastname: Kunita
authors.forename: Asako
authors.initials: A
authors.lastname: Otomo
authors.forename: Hikaru
authors.initials: H
authors.lastname: Mizumura
authors.forename: Kyoko
authors.initials: K
authors.lastname: Suzuki-Utsunomiya
authors.forename: Shinji
authors.initials: S
authors.lastname: Hadano
authors.forename: Joh-E
authors.initials: JE
authors.lastname: Ikeda
mesh_terms: D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D002522:Chlorocebus aethiops; D011992:Endosomes / Q000235:genetics / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D016472:Motor Neuron Disease / Q000235:genetics / Q000378:metabolism; D009046:Motor Neurons / Q000378:metabolism*; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism*; D010873:Pinocytosis / Q000502:physiology*; D021381:Protein Transport / Q000502:physiology; D020696:rab5 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020744:rac GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein
chemical_list: C512358:Als2 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D009479:Neuropeptides; C484602:Rac1 protein, mouse; D020696:rab5 GTP-Binding Proteins; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein