Neuronal IP3 3-kinase is an F-actin-bundling protein: role in dendritic targeting and regulation of spine morphology

Mol Biol Cell. 2009 Dec;20(24):5166-80. doi: 10.1091/mbc.e09-01-0083.


The actin microstructure in dendritic spines is involved in synaptic plasticity. Inositol trisphosphate 3-kinase A (ITPKA) terminates Ins(1,4,5)P(3) signals emanating from spines and also binds filamentous actin (F-actin) through its amino terminal region (amino acids 1-66, N66). Here we investigated how ITPKA, independent of its kinase activity, regulates dendritic spine F-actin microstructure. We show that the N66 region of the protein mediates F-actin bundling. An N66 fusion protein bundled F-actin in vitro, and the bundling involved N66 dimerization. By mutagenesis we identified a point mutation in a predicted helical region that eliminated both F-actin binding and bundling, rendering the enzyme cytosolic. A fusion protein containing a minimal helical region (amino acids 9-52, N9-52) bound F-actin in vitro and in cells, but had lower affinity. In hippocampal neurons, GFP-tagged N66 expression was highly polarized, with targeting of the enzyme predominantly to spines. By contrast, N9-52-GFP expression occurred in actin-rich structures in dendrites and growth cones. Expression of N66-GFP tripled the length of dendritic protrusions, induced longer dendritic spine necks, and induced polarized actin motility in time-lapse assays. These results suggest that, in addition to its ability to regulate intracellular Ca(2+) via Ins(1,4,5)P(3) metabolism, ITPKA regulates structural plasticity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acids / metabolism
  • Animals
  • Axons / enzymology
  • Cell Line, Tumor
  • Cytosol / enzymology
  • Dendritic Spines / enzymology*
  • Fluorescence Recovery After Photobleaching
  • Growth Cones / enzymology
  • Microfilament Proteins / chemistry
  • Microfilament Proteins / metabolism*
  • Models, Molecular
  • Molecular Sequence Data
  • Mutant Proteins / chemistry
  • Mutant Proteins / metabolism
  • Phosphotransferases (Alcohol Group Acceptor) / chemistry
  • Phosphotransferases (Alcohol Group Acceptor) / metabolism*
  • Point Mutation / genetics
  • Protein Binding
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Protein Transport
  • Rabbits
  • Rats
  • Synapses / enzymology


  • Amino Acids
  • Microfilament Proteins
  • Mutant Proteins
  • actin filament bundling proteins
  • Phosphotransferases (Alcohol Group Acceptor)
  • Inositol 1,4,5-trisphosphate 3-kinase