Abstract
BackgroundHomer is a postsynaptic scaffold protein that links various synaptic signaling proteins, including the type I metabotropic glutamate receptor subunits 1α 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.ResultsCupidin/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 (CPDΔ191–230), which showed decrease Cdc42-binding ability but maintained self-multimerization ability. Cupidin suppressed Cdc42-induced filopodia-like protrusion formation in HeLa cells, whereas CPDΔ191–230 failed to do so. In cultured hippocampal neurons, Cupidin was targeted to dendritic spines, whereas CPDΔ191–230 was distributed in dendritic shafts as well as spines. Overexpression of CPDΔ191–230 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. CPDΔ191–230 overexpression decreased Drebrin clustering in the dendritic spines of hippocampal neurons.ConclusionThese 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.
Highlights
Homer is a postsynaptic scaffold protein that links various synaptic signaling proteins, including the type I metabotropic glutamate receptor subunits 1α and 5, the inositol 1,4,5trisphosphate receptor, Shank and Cdc42 small GTPase
Cupidin interacts with activated Cdc42 via the C-terminal coiled-coil region Cupidin/Homer2 is comprised of an N-terminal Ena/VASP homology 1 (EVH1) domain, a C-terminal coiled-coil (CC) motif and two Leu zipper motifs A and B (LZA and LZB, respectively) (Fig. 1)
Cupidin/Homer2 interacts with activated Cdc42 via the Cdc42-binding domain within the C-terminal coiled-coil domain, which may play a role in the suppression of Cdc42-induced filopodia-like protrusion formation in HeLa cells and the formation of mushroom-type spines in hippocampal neurons
Summary
Homer is a postsynaptic scaffold protein that links various synaptic signaling proteins, including the type I metabotropic glutamate receptor subunits 1α and 5, the inositol 1,4,5trisphosphate receptor, Shank and Cdc small GTPase. We aimed to elucidate the structural and functional properties of the interaction between Cupidin/Homer and two actin-cytoskeletal regulators, Cdc small GTPase and Drebrin. Postsynaptic Homer scaffolds interact with a variety of PPxxF (ProPro-x-x-Phe) ligand motif-containing signaling molecules, including the type I metabotropic glutamate receptor subunits 1α and 5 (mGluR1α/5), the inositol 1,4,5trisphosphate receptor (InsP3R) and Shank, via its N-terminal Ena/VASP homology 1 (EVH1) domain [1,2,4,5,8,9], and forms a tetramer by self-assembly via its C-terminal coiled-coil (CC) and Leu zipper (LZ) motifs [4,8,10]. The results of these studies suggest that Homer family proteins are involved in the regulation and/or plasticity of spine morphology by interacting with two dendritic F-actin regulators, Cdc and Drebrin. Little is known about the molecular basis underpinning the involvement of Homer proteins in actin cytoskeleton-based regulation of spine morphology
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