title: Subcellular fractionation and localization studies reveal a direct interaction of the fragile X mental retardation protein (FMRP) with nucleolin.
abstract: Fragile X mental Retardation Protein (FMRP) is a well-known regulator of local translation of its mRNA targets in neurons. However, despite its ubiquitous expression, the role of FMRP remains ill-defined in other cell types. In this study we investigated the subcellular distribution of FMRP and its protein complexes in HeLa cells using confocal imaging as well as detergent-free fractionation and size exclusion protocols. We found FMRP localized exclusively to solid compartments, including cytosolic heavy and light membranes, mitochondria, nuclear membrane and nucleoli. Interestingly, FMRP was associated with nucleolin in both a high molecular weight ribosomal and translation-associated complex (≥6 MDa) in the cytosol, and a low molecular weight complex (∼200 kDa) in the nucleoli. Consistently, we identified two functional nucleolar localization signals (NoLSs) in FMRP that are responsible for a strong nucleolar colocalization of the C-terminus of FMRP with nucleolin, and a direct interaction of the N-terminus of FMRP with the arginine-glycine-glycine (RGG) domain of nucleolin. Taken together, we propose a novel mechanism by which a transient nucleolar localization of FMRP underlies a strong nucleocytoplasmic translocation, most likely in a complex with nucleolin and possibly ribosomes, in order to regulate translation of its target mRNAs.
authors.affiliation: Institute of Biochemistry and Molecular Biology II, Medical Faculty of the Heinrich-Heine-University, Düsseldorf, Germany.
authors.forename: Mohamed S
authors.initials: MS
authors.lastname: Taha
authors.affiliation: Institute of Biochemistry and Molecular Biology II, Medical Faculty of the Heinrich-Heine-University, Düsseldorf, Germany.
authors.forename: Kazem
authors.initials: K
authors.lastname: Nouri
authors.affiliation: Laboratory of Chemical Biology and Institute of Complex Molecular Systems, Department of Biomedical Engineering, Technische Universiteit Eindhoven, Eindhoven, the Netherlands.
authors.forename: Lech G
authors.initials: LG
authors.lastname: Milroy
authors.affiliation: Institute of Biochemistry and Molecular Biology II, Medical Faculty of the Heinrich-Heine-University, Düsseldorf, Germany.
authors.forename: Jens M
authors.initials: JM
authors.lastname: Moll
authors.affiliation: Department of Physical Chemistry I, Ruhr University Bochum, Bochum, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Herrmann
authors.affiliation: Laboratory of Chemical Biology and Institute of Complex Molecular Systems, Department of Biomedical Engineering, Technische Universiteit Eindhoven, Eindhoven, the Netherlands.
authors.forename: Luc
authors.initials: L
authors.lastname: Brunsveld
authors.affiliation: Institute of Biochemistry and Molecular Biology II, Medical Faculty of the Heinrich-Heine-University, Düsseldorf, Germany.
authors.forename: Roland P
authors.initials: RP
authors.lastname: Piekorz
authors.affiliation: Institute of Biochemistry and Molecular Biology II, Medical Faculty of the Heinrich-Heine-University, Düsseldorf, Germany.
authors.forename: Mohammad R
authors.initials: MR
authors.lastname: Ahmadian
mesh_terms: D002458:Cell Fractionation; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000032:analysis / Q000378:metabolism*; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D019913:Nuclear Localization Signals; D010750:Phosphoproteins / Q000032:analysis / Q000378:metabolism*; D021381:Protein Transport; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000032:analysis / Q000378:metabolism*; D000097796:Nucleolin
chemical_list: D051860:Fragile X Messenger Ribonucleoprotein 1; D019913:Nuclear Localization Signals; D010750:Phosphoproteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D000097796:Nucleolin