title: Excess phosphoinositide 3-kinase subunit synthesis and activity as a novel therapeutic target in fragile X syndrome.
abstract: Fragile X syndrome (FXS) is an inherited neurologic disease caused by loss of fragile X mental retardation protein (FMRP), which is hypothesized to mediate negative regulation of mRNA translation at synapses. A prominent feature of FXS animal models is exaggerated signaling through group 1 metabotropic glutamate receptors (gp1 mGluRs), and therapeutic strategies to treat FXS are targeted mainly at gp1 mGluRs. Recent studies, however, indicate that a variety of receptor-mediated signal transduction pathways are dysregulated in FXS, suggesting that FMRP acts on a common downstream signaling molecule. Here, we show that deficiency of FMRP results in excess activity of phosphoinositide 3-kinase (PI3K), a downstream signaling molecule of many cell surface receptors. In Fmr1 knock-out neurons, excess synaptic PI3K activity can be reduced by perturbation of gp1 mGluR-mediated signaling. Remarkably, increased PI3K activity was also observed in FMRP-deficient non-neuronal cells in the absence of gp1 mGluRs. Here, we show that FMRP regulates the synthesis and synaptic localization of p110beta, the catalytic subunit of PI3K. In wild type, gp1 mGluR activation induces p110beta translation, p110beta protein expression, and PI3K activity. In contrast, both p110beta protein synthesis and PI3K activity are elevated and insensitive to gp1 mGluR stimulation in Fmr1 knock-out. This suggests that dysregulated PI3K signaling may underlie the synaptic impairments in FXS. In support of this hypothesis, we show that PI3K antagonists rescue three FXS-associated phenotypes: dysregulated synaptic protein synthesis, excess AMPA receptor internalization, and increased spine density. Targeting excessive PI3K activity might thus be a potent therapeutic strategy for FXS.
authors: Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
authors: Christina
authors: C
authors: Gross
authors: Mika
authors: M
authors: Nakamoto
authors: Xiaodi
authors: X
authors: Yao
authors: Chi-Bun
authors: CB
authors: Chan
authors: So Y
authors: SY
authors: Yim
authors: Keqiang
authors: K
authors: Ye
authors: Stephen T
authors: ST
authors: Warren
authors: Gary J
authors: GJ
authors: Bassell
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002478:Cells, Cultured; D058534:Class I Phosphatidylinositol 3-Kinases; D003712:Dendrites / Q000378:metabolism; D004195:Disease Models, Animal; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology / Q000627:therapeutic use*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics; D005600:Fragile X Syndrome / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000235:genetics; D006624:Hippocampus / Q000166:cytology; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D008164:Luminescent Proteins / Q000235:genetics; D008734:Methoxyhydroxyphenylglycol / Q000031:analogs & derivatives / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D009474:Neurons / Q000378:metabolism / Q000648:ultrastructure; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D018091:Receptors, AMPA / Q000378:metabolism; D013569:Synapses / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D014162:Transfection / Q000379:methods; D000097573:Red Fluorescent Protein
chemical_list: D058534:Class I Phosphatidylinositol 3-Kinases; D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D051860:Fragile X Messenger Ribonucleoprotein 1; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D008734:Methoxyhydroxyphenylglycol; D019869:Phosphatidylinositol 3-Kinases; D021122:Protein Subunits; D012333:RNA, Messenger; D018091:Receptors, AMPA; D000097573:Red Fluorescent Protein; C497684:Fmr1 protein, mouse; C485184:enhanced green fluorescent protein; C509622:1-phosphatidylinositol 3-kinase p110 subunit, mouse; C010117:3,4-dihydroxyphenylglycol