title: Regulation of BCL-X splicing reveals a role for the polypyrimidine tract binding protein (PTBP1/hnRNP I) in alternative 5' splice site selection.
abstract: Alternative splicing (AS) modulates many physiological and pathological processes. For instance, AS of the BCL-X gene balances cell survival and apoptosis in development and cancer. Herein, we identified the polypyrimidine tract binding protein (PTBP1) as a direct regulator of BCL-X AS. Overexpression of PTBP1 promotes selection of the distal 5' splice site in BCL-X exon 2, generating the pro-apoptotic BCL-Xs splice variant. Conversely, depletion of PTBP1 enhanced splicing of the anti-apoptotic BCL-XL variant. In vivo cross-linking experiments and site-directed mutagenesis restricted the PTBP1 binding site to a polypyrimidine tract located between the two alternative 5' splice sites. Binding of PTBP1 to this site was required for its effect on splicing. Notably, a similar function of PTBP1 in the selection of alternative 5' splice sites was confirmed using the USP5 gene as additional model. Mechanistically, PTBP1 displaces SRSF1 binding from the proximal 5' splice site, thus repressing its selection. Our study provides a novel mechanism of alternative 5' splice site selection by PTBP1 and indicates that the presence of a PTBP1 binding site between two alternative 5' splice sites promotes selection of the distal one, while repressing the proximal site by competing for binding of a positive regulator.
authors.affiliation: Department of Biomedicine and Prevention, University of Rome Tor Vergata, 00133 Rome, Italy Laboratory of Neuroembryology, Fondazione Santa Lucia, 00143 Rome, Italy.
authors.forename: Pamela
authors.initials: P
authors.lastname: Bielli
authors.affiliation: Department of Biomedicine and Prevention, University of Rome Tor Vergata, 00133 Rome, Italy Laboratory of Neuroembryology, Fondazione Santa Lucia, 00143 Rome, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Bordi
authors.affiliation: Department of Biomedicine and Prevention, University of Rome Tor Vergata, 00133 Rome, Italy Laboratory of Neuroembryology, Fondazione Santa Lucia, 00143 Rome, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Di Biasio
authors.affiliation: Department of Biomedicine and Prevention, University of Rome Tor Vergata, 00133 Rome, Italy Laboratory of Neuroembryology, Fondazione Santa Lucia, 00143 Rome, Italy claudio.sette@uniroma2.it.
authors.forename: Claudio
authors.initials: C
authors.lastname: Sette
mesh_terms: D017398:Alternative Splicing; D045744:Cell Line, Tumor; D005091:Exons; D057809:HEK293 Cells; D006367:HeLa Cells; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000378:metabolism*; D006801:Humans; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D038941:Polypyrimidine Tract-Binding Protein / Q000378:metabolism*; D022821:RNA Splice Sites; D016601:RNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D000068103:Serine-Arginine Splicing Factors; D051020:bcl-X Protein / Q000235:genetics*
chemical_list: D034441:Heterogeneous-Nuclear Ribonucleoproteins; D009687:Nuclear Proteins; C450006:PTBP1 protein, human; D022821:RNA Splice Sites; D016601:RNA-Binding Proteins; D051020:bcl-X Protein; D038941:Polypyrimidine Tract-Binding Protein; D000068103:Serine-Arginine Splicing Factors