title: Key role of the postsynaptic density scaffold proteins Shank and Homer in the functional architecture of Ca2+ homeostasis at dendritic spines in hippocampal neurons.
abstract: A key aspect of postsynaptic function, also important for plasticity, is the segregation within dendritic spines of Ca2+ rises attributable to release from intracellular stores. Previous studies have shown that overexpression in hippocampal neurons of two postsynaptic density (PSD) scaffold proteins, Shank1B and Homer1b, induces spine maturation, including translocation of the intracellular Ca2+ channel inositol trisphosphate receptor (IP3R). The structural and functional significance of these processes remained undefined. Here, we show that in its relocation, IP3R is accompanied by other endoplasmic reticulum (ER) proteins: the Ca2+ pump sarcoendoplasmic reticulum calcium ATPase, the lumenal Ca2+-binding protein calreticulin, the ER lumen-addressed green fluorescent protein, and, to a lesser extent, the membrane chaperone calbindin. The specificity of these translocations was demonstrated by their inhibition by both a Shank1 fragment and the dominant-negative Homer1a. Activation in Shank1B-transfected neurons of the metabotropic glutamatergic receptors 1/5 (mGluRs1/5), which induce IP3 generation with ensuing Ca2+ release from the stores, triggered considerable increases in Ca2+-dependent responses: activation of the big K+ channel, which was revealed by patch clamping, and extracellular signal-regulated protein kinase (ERK) phosphorylation. The interaction of Shank1B and Homer1b appears as the molecular mechanism linking mGluRs1/5, strategically located in the spines, to IP3R with the integration of entire ER cisternas in the PSD and with consequences on both local Ca2+ homeostasis and overall neuronal signaling.
authors.affiliation: Cellular and Molecular Pharmacology Section, Institute of Neuroscience, Consiglio Nazionale delle Ricerche, and Department of Pharmacology, University of Milan, 20129 Milan, Italy. c.sala@in.cnr.it
authors.forename: Carlo
authors.initials: C
authors.lastname: Sala
authors.forename: Gautier
authors.initials: G
authors.lastname: Roussignol
authors.forename: Jacopo
authors.initials: J
authors.lastname: Meldolesi
authors.forename: Laurent
authors.initials: L
authors.lastname: Fagni
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000502:physiology*; D000818:Animals; D064026:Calbindins; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D037282:Calreticulin / Q000378:metabolism; D002352:Carrier Proteins / Q000502:physiology*; D002478:Cells, Cultured; D049229:Dendritic Spines / Q000378:metabolism*; D004622:Embryo, Mammalian; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology*; D006706:Homeostasis / Q000502:physiology*; D000072233:Homer Scaffolding Proteins; D007150:Immunohistochemistry / Q000379:methods; D008564:Membrane Potentials / Q000502:physiology / Q000528:radiation effects; D008734:Methoxyhydroxyphenylglycol / Q000031:analogs & derivatives / Q000494:pharmacology; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009419:Nerve Tissue Proteins; D009474:Neurons / Q000166:cytology*; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D014162:Transfection / Q000379:methods
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D064026:Calbindins; D037282:Calreticulin; D002352:Carrier Proteins; D000072233:Homer Scaffolding Proteins; D009419:Nerve Tissue Proteins; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D064030:S100 Calcium Binding Protein G; C120531:Shank1 protein, rat; D049452:Green Fluorescent Proteins; D008734:Methoxyhydroxyphenylglycol; D048052:Mitogen-Activated Protein Kinase 3; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium; C010117:3,4-dihydroxyphenylglycol