PIP3 Is Involved in Neuronal Polarization and Axon Formation

J Neurochem. 2004 Apr;89(1):109-18. doi: 10.1046/j.1471-4159.2004.02302.x.

Abstract

Recent experiments in various cell types such as mammalian neutrophils and Dictyostelium discoideum amoebae point to a key role for the lipid product of PI 3-kinase, PIP(3), in determining internal polarity. In neurons, as a consequence of the elongation of one neurite, the axon is specified and the cell acquires its polarity. To test the hypothesis that PI 3-kinase and PIP(3) may play a role in neuronal polarity, and especially in axon specification, we observed localization of PIP(3) visualized by Akt-PH-GFP in developing hippocampal neurons. We found that PIP(3) accumulates in the tip of the growing processes. This accumulation is inhibited by addition of PI 3-kinase inhibitors. Those inhibitors, consistently with a role of PIP(3) in process formation and elongation, delay the transition from stage 1 neurons to stage 3 neurons, and both axon formation and elongation. Moreover, when the immature neurite contacts a bead coated with laminin, a substrate known to induce axon specification, PIP(3) accumulates in its growth cone followed by a rapid elongation of the neurite. In such conditions, the addition of PI 3-kinase inhibitors inhibits both PIP(3) accumulation and future axon elongation. These results suggest that PIP(3) is involved in axon specification, possibly by stimulating neurite outgrowth. In addition, when a second neurite contacted the beads, this neurite rapidly elongates whereas the elongation of the first laminin-contacting neurite stops, consistently with the hypothesis of a negative feedback mechanism from the growing future axon to the other neurites.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Axons / physiology*
  • Cell Polarity / physiology*
  • Cells, Cultured
  • Green Fluorescent Proteins
  • Hippocampus / cytology
  • Laminin / metabolism
  • Luminescent Proteins / genetics
  • Neurites / physiology
  • Neurons / cytology
  • Neurons / metabolism
  • Neurons / physiology*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphatidylinositol Phosphates / metabolism*
  • Protein Structure, Tertiary / genetics
  • Protein-Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins c-akt
  • Rats
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism

Substances

  • Laminin
  • Luminescent Proteins
  • Phosphatidylinositol Phosphates
  • Proto-Oncogene Proteins
  • Recombinant Fusion Proteins
  • phosphatidylinositol 3,4,5-triphosphate
  • Green Fluorescent Proteins
  • Phosphatidylinositol 3-Kinases
  • Akt1 protein, rat
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt