title: Negative guidance factor-induced macropinocytosis in the growth cone plays a critical role in repulsive axon turning.
abstract: Macropinocytosis is a type of poorly characterized fluid-phase endocytosis that results in formation of relatively large vesicles. We report that Sonic hedgehog (Shh) protein induces macropinocytosis in the axons through activation of a noncanonical signaling pathway, including Rho GTPase and nonmuscle myosin II. Macropinocytosis induced by Shh is independent of clathrin-mediated endocytosis but dependent on dynamin, myosin II, and Rho GTPase activities. Inhibitors of macropinocytosis also abolished the negative effects of Shh on axonal growth, including growth cone collapse and chemorepulsive axon turning but not turning per se. Conversely, activation of myosin II or treatment of phorbol ester induces macropinocytosis in the axons and elicits growth cone collapse and repulsive axon turning. Furthermore, macropinocytosis is also induced by ephrin-A2, and inhibition of dynamin abolished repulsive axon turning induced by ephrin-A2. Macropinocytosis can be induced ex vivo by high Shh, correlating with axon retraction. These results demonstrate that macropinocytosis-mediated membrane trafficking is an important cellular mechanism involved in axon chemorepulsion induced by negative guidance factors.
authors.affiliation: Department of Medicine and Cell Biology, Program in Neuroscience, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA.
authors.forename: Adrianne L
authors.initials: AL
authors.lastname: Kolpak
authors.forename: Jun
authors.initials: J
authors.lastname: Jiang
authors.forename: Daorong
authors.initials: D
authors.lastname: Guo
authors.forename: Clive
authors.initials: C
authors.lastname: Standley
authors.forename: Karl
authors.initials: K
authors.lastname: Bellve
authors.forename: Kevin
authors.initials: K
authors.lastname: Fogarty
authors.forename: Zheng-Zheng
authors.initials: ZZ
authors.lastname: Bao
mesh_terms: D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002642:Chick Embryo; D003911:Dextrans / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics; D020439:Growth Cones / Q000187:drug effects / Q000502:physiology*; D053823:Hedgehog Proteins / Q000494:pharmacology; D066298:In Vitro Techniques; D024462:Myosin Type II / Q000378:metabolism; D010873:Pinocytosis / Q000187:drug effects / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000166:cytology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D014168:Transferrin / Q000378:metabolism; D014704:Veratrum Alkaloids / Q000494:pharmacology; D020741:rho GTP-Binding Proteins / Q000378:metabolism
chemical_list: D003911:Dextrans; D004791:Enzyme Inhibitors; D053823:Hedgehog Proteins; D014168:Transferrin; D014704:Veratrum Alkaloids; D049452:Green Fluorescent Proteins; D024462:Myosin Type II; D020741:rho GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate; C000541:cyclopamine