title: FMRP interferes with the Rac1 pathway and controls actin cytoskeleton dynamics in murine fibroblasts.
abstract: Fragile X syndrome, the most common form of inherited mental retardation, is caused by absence of FMRP, an RNA-binding protein implicated in regulation of mRNA translation and/or transport. We have previously shown that dFMR1, the Drosophila ortholog of FMRP, is genetically linked to the dRac1 GTPase, a key player in actin cytoskeleton remodeling. Here, we demonstrate that FMRP and the Rac1 pathway are connected in a model of murine fibroblasts. We show that Rac1 activation induces relocalization of four FMRP partners to actin ring areas. Moreover, Rac1-induced actin remodeling is altered in fibroblasts lacking FMRP or carrying a point-mutation in the KH1 or in the KH2 RNA-binding domain. In absence of wild-type FMRP, we found that phospho-ADF/Cofilin (P-Cofilin) level, a major mediator of Rac1 signaling, is lowered, whereas the level of protein phosphatase 2A catalytic subunit (PP2Ac), a P-Cofilin phosphatase, is increased. We show that FMRP binds with high affinity to the 5'-UTR of pp2acbeta mRNA and is thus a likely negative regulator of its translation. The molecular mechanism unraveled here points to a role for FMRP in modulation of actin dynamics, which is a key process in morphogenesis of dendritic spines, synaptic structures abnormally developed in Fragile X syndrome patient's brain.
authors.affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP/Collège de France.
authors.forename: Marie
authors.initials: M
authors.lastname: Castets
authors.forename: Céline
authors.initials: C
authors.lastname: Schaeffer
authors.forename: Elias
authors.initials: E
authors.lastname: Bechara
authors.forename: Annette
authors.initials: A
authors.lastname: Schenck
authors.forename: Edward W
authors.initials: EW
authors.lastname: Khandjian
authors.forename: Sylvie
authors.initials: S
authors.lastname: Luche
authors.forename: Hervé
authors.initials: H
authors.lastname: Moine
authors.forename: Thierry
authors.initials: T
authors.lastname: Rabilloud
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Mandel
authors.forename: Barbara
authors.initials: B
authors.lastname: Bardoni
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D003599:Cytoskeleton / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism*; D051860:Fragile X Messenger Ribonucleoprotein 1; D005600:Fragile X Syndrome / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D000199:Actins; D051860:Fragile X Messenger Ribonucleoprotein 1; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; D020830:rac1 GTP-Binding Protein; C497683:FMR1 protein, human; C497684:Fmr1 protein, mouse