title: Defining the role of the CGGBP1 protein in FMR1 gene expression.
abstract: Fragile X syndrome is the most common heritable form of intellectual disability and is caused by the expansion over 200 repeats and subsequent methylation of the CGG triplets at the 5' UTR of the FMR1 gene, leading to its silencing. The epigenetic and molecular mechanisms responsible for FMR1 gene silencing are not fully clarified. To identify structure-specific proteins that could recruit components of the silencing machinery we investigated the role of CGGBP1 in FMR1 gene transcription. CGGBP1 is a highly conserved protein that binds specifically to unmethylated CGG tracts. Its role on FMR1 transcription is yet to be defined. Sequencing analysis and expression studies through quantitative PCR of CGGBP1 were performed in cell lines with different allele expansions: wild type, premutation, methylated full mutation and unmethylated full mutation, demonstrating no differences between them. ChIP assays clearly demonstrated that CGGBP1 binds to unmethylated CGG triplets of the FMR1 gene, but not to methylated CGGs. We also observed that CGGBP1 binding to the FMR1 locus was restored after pharmacological demethylation, with 5-azadC, of alleles, carriers of methylated full mutation, suggesting a possible role for CGGBP1 in FMR1 expression. CGGBP1 silencing with shRNAs (reaching ~98% of CGGBP1-mRNA depletion) did not affect FMR1 transcription and CGG expansion stability in expanded alleles. Although the strong binding to the CGG tract could suggest a relevant role of CGGBP1 on FMR1 gene expression, our results demonstrate that CGGBP1 has no direct effect on FMR1 transcription and CGG repeat stability.
authors: Istituto di Genetica Medica, Università Cattolica, Rome, Italy.
authors: Martina
authors: M
authors: Goracci
authors: Istituto di Genetica Medica, Università Cattolica, Rome, Italy.
authors: Stella
authors: S
authors: Lanni
authors: Istituto di Genetica Medica, Università Cattolica, Rome, Italy.
authors: Giorgia
authors: http://orcid.org/0000-0001-6528-1841
authors: G
authors: Mancano
authors: Istituto di Genetica Medica, Università Cattolica, Rome, Italy.
authors: Federica
authors: F
authors: Palumbo
authors: Istituto di Genetica Medica, Università Cattolica, Rome, Italy.
authors: Pietro
authors: P
authors: Chiurazzi
authors: Istituto di Genetica Medica, Università Cattolica, Rome, Italy.
authors: Giovanni
authors: G
authors: Neri
authors: Istituto di Genetica Medica, Università Cattolica, Rome, Italy.
authors: Elisabetta
authors: E
authors: Tabolacci
mesh_terms: D020121:5' Untranslated Regions; D002460:Cell Line; D019175:DNA Methylation; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D011485:Protein Binding
chemical_list: D020121:5' Untranslated Regions; D004268:DNA-Binding Proteins; D051860:Fragile X Messenger Ribonucleoprotein 1; C106905:CGGBP1 protein, human; C497683:FMR1 protein, human