Interaction of Cupidin/Homer2 with two actin cytoskeletal regulators, Cdc42 small GTPase and Drebrin, in dendritic spines.
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.
Shiraishi-Yamaguchi
Yoko
Y
Laboratory for Molecular Neurogenesis, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan. f1966@cc.nagasaki-u.ac.jp
Sato
Yumi
Y
Sakai
Rieko
R
Mizutani
Akihiro
A
Knöpfel
Thomas
T
Mori
Nozomu
N
Mikoshiba
Katsuhiko
K
Furuichi
Teiichi
T
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*
D000199:Actins; D002352:Carrier Proteins; D000072233:Homer Scaffolding Proteins; C000606626:Homer2 protein, rat; D009479:Neuropeptides; C053386:drebrins; D020764:cdc42 GTP-Binding Protein