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

Mol Cell Neurosci. 2005 Mar;28(3):524-34. doi: 10.1016/j.mcn.2004.11.005.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Animals, Newborn
  • Brain / cytology
  • Brain / embryology*
  • Brain / growth & development*
  • Cell Differentiation / drug effects
  • Cell Differentiation / physiology
  • Cells, Cultured
  • Enzyme Inhibitors / pharmacology
  • Glycogen Synthase Kinase 3 / metabolism*
  • Glycogen Synthase Kinase 3 beta
  • Growth Cones / enzymology*
  • Growth Cones / ultrastructure
  • MAP Kinase Signaling System / drug effects
  • MAP Kinase Signaling System / physiology*
  • Microtubule-Associated Proteins / drug effects
  • Microtubule-Associated Proteins / metabolism*
  • Mitogen-Activated Protein Kinase 3 / antagonists & inhibitors
  • Mitogen-Activated Protein Kinase 3 / metabolism
  • Nerve Growth Factor / metabolism
  • PC12 Cells
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphoinositide-3 Kinase Inhibitors
  • Phosphorylation / drug effects
  • Rats
  • Rats, Wistar
  • Receptor, trkA / metabolism
  • Superior Cervical Ganglion


  • Enzyme Inhibitors
  • Microtubule-Associated Proteins
  • Phosphoinositide-3 Kinase Inhibitors
  • microtubule-associated protein 1B
  • Nerve Growth Factor
  • Receptor, trkA
  • Glycogen Synthase Kinase 3 beta
  • Gsk3b protein, rat
  • Mitogen-Activated Protein Kinase 3
  • Glycogen Synthase Kinase 3