Neuronal IP3 3-kinase is an F-actin-bundling protein: role in dendritic targeting and regulation of spine morphology.
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.
Johnson
Hong W
HW
Department of Pharmacology, Uniformed Services University, Bethesda, MD 20814, USA.
Schell
Michael J
MJ
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000201:enzymology; D045744:Cell Line, Tumor; D003600:Cytosol / Q000201:enzymology; D049229:Dendritic Spines / Q000201:enzymology*; D036681:Fluorescence Recovery After Photobleaching; D020439:Growth Cones / Q000201:enzymology; D008840:Microfilament Proteins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry / Q000378:metabolism*; D017354:Point Mutation / Q000235:genetics; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011817:Rabbits; D051381:Rats; D013569:Synapses / Q000201:enzymology
D000596:Amino Acids; D008840:Microfilament Proteins; D050505:Mutant Proteins; C052523:actin filament bundling proteins; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase