The nuclear microspherule protein 58 is a novel RNA-binding protein that interacts with fragile X mental retardation protein in polyribosomal mRNPs from neurons.
The fragile X syndrome, the leading cause of inherited mental retardation, is due to the inactivation of the fragile mental retardation 1 gene (FMR1) and the subsequent absence of its gene product FMRP. This RNA-binding protein is thought to control mRNA translation and its absence in fragile X cells leads to alteration in protein synthesis. In neurons, FMRP is thought to repress specific mRNAs during their transport as silent ribonucleoparticles (mRNPs) from the cell body to the distant synapses which are the sites of local synthesis of neuro-specific proteins. The mechanism by which FMRP sorts out its different mRNAs targets might be tuned by the intervention of different proteins. Using a yeast two-hybrid system, we identified MicroSpherule Protein 58 (MSP58) as a novel FMRP-cellular partner. In cell cultures, we found that MSP58 is predominantly present in the nucleus where it interacts with the nuclear isoform of FMRP. However, in neurons but not in glial cells, MSP58 is also present in the cytoplasmic compartment, as well as in neurites, where it co-localizes with FMRP. Biochemical evidence is given that MSP58 is associated with polyribosomal poly(A)+ mRNPs. We also show that MSP58, similar to FMRP, is present on polyribosomes prepared from synaptoneurosomes and that it behaves as an RNA-binding protein with a high affinity to the G-quartet structure. We propose that this novel cellular partner for FMRP escorts FMRP-containing mRNP from the nucleus and nucleolus to the somato-dendritic compartment where it might participate in neuronal translation regulation.
Unité de Recherche en Génétique Humaine et Moléculaire, Centre de recherche Hôpital Saint-François d'Assise, le CHUQ, Québec, Canada G1L 3L5.
Laetitia
L
Davidovic
Elias
E
Bechara
Maud
M
Gravel
Xavier H
XH
Jaglin
Sandra
S
Tremblay
Attila
A
Sik
Barbara
B
Bardoni
Edouard W
EW
Khandjian
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002466:Cell Nucleolus / Q000378:metabolism; D002522:Chlorocebus aethiops; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012261:Ribonucleoproteins / Q000378:metabolism*
D051860:Fragile X Messenger Ribonucleoprotein 1; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; C113292:MCRS1 protein, human; C026452:messenger ribonucleoprotein