title: The MAP kinase pathway is upstream of the activation of GSK3beta that enables it to phosphorylate MAP1B and contributes to the stimulation of axon growth.
abstract: In pheochromocytoma 12 (PC12) cells and sympathetic neurons, nerve growth factor (NGF) engagement with the tropomyosin-related tyrosine kinase (TrkA) receptor activates the serine/threonine kinase glycogen synthase kinase 3beta (GSK3beta), enabling it to phosphorylate the microtubule-associated protein 1B (MAP1B). GSK3beta phosphorylation of MAP1B acts as a molecular switch to regulate microtubule dynamics in growing axons, and hence the rate of axon growth. An important question relates to the identification of the upstream pathway linking the activation of GSK3beta with TrkA engagement. TrkA can utilise a number of intracellular signalling pathways, including the mitogen-activated protein kinase (MAPK) pathway and the phosphatidylinositol-3 kinase (PI3K) pathway. We now show, using pharmacological inhibitor studies of PC12 cells and sympathetic neurons in culture and in vitro kinase and activation assays, that the MAPK pathway, and not the PI3K pathway, links NGF engagement with the TrkA receptor to GSK3beta activation in PC12 cells and sympathetic neurons. We also show that activated GSK3beta is a small fraction of the total GSK3beta present in developing brain and that it is not part of a multiprotein complex. Thus, NGF drives increased neurite growth rates partly by coupling the MAPK pathway to the activation of GSK3beta and thereby phosphorylation of MAP1B.
authors.affiliation: The MRC Centre for Developmental Neurobiology, New Hunt's House, Guy's Campus, King's College London, London SE1 1UL, UK.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Goold
authors.forename: Phillip R
authors.initials: PR
authors.lastname: Gordon-Weeks
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000166:cytology / Q000196:embryology* / Q000254:growth & development*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D020439:Growth Cones / Q000201:enzymology* / Q000648:ultrastructure; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D008869:Microtubule-Associated Proteins / Q000187:drug effects / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D020932:Nerve Growth Factor / Q000378:metabolism; D016716:PC12 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D020917:Receptor, trkA / Q000378:metabolism; D017783:Superior Cervical Ganglion
chemical_list: D004791:Enzyme Inhibitors; D038362:Glycogen Synthase Kinase 3; D000071679:Glycogen Synthase Kinase 3 beta; D008869:Microtubule-Associated Proteins; D048052:Mitogen-Activated Protein Kinase 3; D020932:Nerve Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D020917:Receptor, trkA; C085284:microtubule-associated protein 1B; C000605508:Gsk3b protein, rat