title: Homer interactions are necessary for metabotropic glutamate receptor-induced long-term depression and translational activation.
abstract: Group I metabotropic glutamate receptors (mGluRs) induce a form of long-term synaptic depression (mGluR-LTD) in area CA1 of the hippocampus that requires rapid protein synthesis. Although much is known about the mechanisms underlying mGluR-LTD, it is unclear how mGluRs couple to the effectors necessary for translation initiation. A clue comes from work in the mouse model of Fragile X syndrome [Fmr1 knock-out (KO) mice], where group 1 mGluR stimulation of protein synthesis is absent and mGluRs are less associated with the postsynaptic scaffolding protein Homer (Giuffrida et al., 2005). Here, we examined the role of Homer interactions in mGluR-LTD and mGluR signaling to protein synthesis machinery in wild-type and Fmr1 KO animals. A peptide that mimics the C-terminal tail of mGluR5 (mGluR5ct), shown previously to disrupt Homer interactions with mGluRs, blocks mGluR-LTD and mGluR-signaling to protein synthesis initiation in wild-type animals. Disruption of mGluR-Homer interactions selectively blocks mGluR activation of the phosphoinositide 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR), but not ERK (extracellular signal-regulated kinase), pathway and translation of a 5' terminal oligopyrimidine tract containing mRNA, Elongation factor 1alpha. In Fmr1 KO mice, mGluR-LTD is insensitive to disruption of Homer interactions and mGluR activation of PI3K-mTOR is lost. Our results find specific roles for Homer in mGluR signaling and plasticity and suggest that reduced mGluR-Homer interactions in Fmr1 KO mice lead to a deficit in mGluR stimulation of translation initiation.
authors.affiliation: Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Ronesi
authors.forename: Kimberly M
authors.initials: KM
authors.lastname: Huber
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002352:Carrier Proteins / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics; D005786:Gene Expression Regulation / Q000502:physiology*; D006624:Hippocampus / Q000166:cytology; D000072233:Homer Scaffolding Proteins; D066298:In Vitro Techniques; D036881:Long-Term Synaptic Depression / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D008734:Methoxyhydroxyphenylglycol / Q000031:analogs & derivatives / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009474:Neurons / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018408:Patch-Clamp Techniques / Q000379:methods; D010455:Peptides / Q000494:pharmacology; D014176:Protein Biosynthesis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects
chemical_list: D002352:Carrier Proteins; D051860:Fragile X Messenger Ribonucleoprotein 1; D000072233:Homer Scaffolding Proteins; D008734:Methoxyhydroxyphenylglycol; D010455:Peptides; D018094:Receptors, Metabotropic Glutamate; C497684:Fmr1 protein, mouse; C010117:3,4-dihydroxyphenylglycol