title: Postsynaptic density scaffold SAP102 regulates cortical synapse development through EphB and PAK signaling pathway.
abstract: Membrane-associated guanylate kinases (MAGUKs), including SAP102, PSD-95, PSD-93, and SAP97, are scaffolding proteins for ionotropic glutamate receptors at excitatory synapses. MAGUKs play critical roles in synaptic plasticity; however, details of signaling roles for each MAGUK remain largely unknown. Here we report that SAP102 regulates cortical synapse development through the EphB and PAK signaling pathways. Using lentivirus-delivered shRNAs, we found that SAP102 and PSD-95, but not PSD-93, are necessary for excitatory synapse formation and synaptic AMPA receptor (AMPAR) localization in developing mouse cortical neurons. SAP102 knockdown (KD) increased numbers of elongated dendritic filopodia, which is often observed in mouse models and human patients with mental retardation. Further analysis revealed that SAP102 coimmunoprecipitated the receptor tyrosine kinase EphB2 and RacGEF Kalirin-7 in neonatal cortex, and SAP102 KD reduced surface expression and dendritic localization of EphB. Moreover, SAP102 KD prevented reorganization of actin filaments, synapse formation, and synaptic AMPAR trafficking in response to EphB activation triggered by its ligand ephrinB. Last, p21-activated kinases (PAKs) were downregulated in SAP102 KD neurons. These results demonstrate that SAP102 has unique roles in cortical synapse development by mediating EphB and its downstream PAK signaling pathway. Both SAP102 and PAKs are associated with X-linked mental retardation in humans; thus, synapse formation mediated by EphB/SAP102/PAK signaling in the early postnatal brain may be crucial for cognitive development.
authors.affiliation: McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. ymurata@mit.edu
authors.forename: Yasunobu
authors.initials: Y
authors.lastname: Murata
authors.forename: Martha
authors.initials: M
authors.lastname: Constantine-Paton
mesh_terms: D000367:Age Factors; D000704:Analysis of Variance; D000818:Animals; D019921:Biotinylation; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000076122:Disks Large Homolog 4 Protein; D004622:Embryo, Mammalian; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D005822:Genetic Vectors / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D016086:Lentivirus / Q000235:genetics; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000502:physiology / Q000648:ultrastructure; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism*; D057907:Post-Synaptic Density / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D036081:Receptors, Eph Family / Q000235:genetics / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D013569:Synapses / Q000502:physiology*; D013574:Synaptosomes / Q000378:metabolism; D014162:Transfection; D014793:Visual Cortex / Q000166:cytology / Q000254:growth & development / Q000378:metabolism
chemical_list: D000076122:Disks Large Homolog 4 Protein; C101195:Dlg3 protein, rat; C501449:Dlg4 protein, rat; D020662:Guanine Nucleotide Exchange Factors; D047908:Intracellular Signaling Peptides and Proteins; C102365:Kalrn protein, rat; D008565:Membrane Proteins; C121001:NR2B NMDA receptor; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; D034741:RNA, Small Interfering; D016194:Receptors, N-Methyl-D-Aspartate; D049452:Green Fluorescent Proteins; D036081:Receptors, Eph Family; D017868:Cyclic AMP-Dependent Protein Kinases