title: Interaction of Cupidin/Homer2 with two actin cytoskeletal regulators, Cdc42 small GTPase and Drebrin, in dendritic spines.
abstract: BACKGROUND
  Homer is a postsynaptic scaffold protein that links various synaptic signaling proteins, including the type I metabotropic glutamate receptor subunits 1alpha and 5, the inositol 1,4,5-trisphosphate receptor, Shank and Cdc42 small GTPase. Overexpression of Homer induces changes in dendritic spine morphology in cultured hippocampal neurons. However, the molecular basis underpinning Homer-mediated spine morphogenesis remains unclear. In this study, we aimed to elucidate the structural and functional properties of the interaction between Cupidin/Homer2 and two actin-cytoskeletal regulators, Cdc42 small GTPase and Drebrin.
  
  
  RESULTS
  Cupidin/Homer2 interacted with activated Cdc42 small GTPase via the Cdc42-binding domain that resides around amino acid residues 191-283, within the C-terminal coiled-coil domain. We generated a Cupidin deletion mutant lacking amino acids 191-230 (CPDDelta191-230), which showed decrease Cdc42-binding ability but maintained self-multimerization ability. Cupidin suppressed Cdc42-induced filopodia-like protrusion formation in HeLa cells, whereas CPDDelta191-230 failed to do so. In cultured hippocampal neurons, Cupidin was targeted to dendritic spines, whereas CPDDelta191-230 was distributed in dendritic shafts as well as spines. Overexpression of CPDDelta191-230 decreased the number of synapses and reduced the amplitudes of miniature excitatory postsynaptic currents in hippocampal neurons. Cupidin interacted with a dendritic spine F-actin-binding protein, Drebrin, which possesses two Homer ligand motifs, via the N-terminal EVH-1 domain. CPDDelta191-230 overexpression decreased Drebrin clustering in the dendritic spines of hippocampal neurons.
  
  
  CONCLUSIONS
  These results indicate that Cupidin/Homer2 interacts with the dendritic spine actin regulators Cdc42 and Drebrin via its C-terminal and N-terminal domains, respectively, and that it may be involved in spine morphology and synaptic properties.
authors.affiliation: Laboratory for Molecular Neurogenesis, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan. f1966@cc.nagasaki-u.ac.jp
authors.forename: Yoko
authors.initials: Y
authors.lastname: Shiraishi-Yamaguchi
authors.forename: Yumi
authors.initials: Y
authors.lastname: Sato
authors.forename: Rieko
authors.initials: R
authors.lastname: Sakai
authors.forename: Akihiro
authors.initials: A
authors.lastname: Mizutani
authors.forename: Thomas
authors.initials: T
authors.lastname: Knöpfel
authors.forename: Nozomu
authors.initials: N
authors.lastname: Mori
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Mikoshiba
authors.forename: Teiichi
authors.initials: T
authors.lastname: Furuichi
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism; D049229:Dendritic Spines / Q000502:physiology*; D015870:Gene Expression; D006367:HeLa Cells; D006624:Hippocampus / Q000502:physiology; D000072233:Homer Scaffolding Proteins; D006801:Humans; D055369:Miniature Postsynaptic Potentials / Q000502:physiology; D009154:Mutation; D009479:Neuropeptides / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000502:physiology; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; D002352:Carrier Proteins; D000072233:Homer Scaffolding Proteins; C000606626:Homer2 protein, rat; D009479:Neuropeptides; C053386:drebrins; D020764:cdc42 GTP-Binding Protein