Generation of functionally distinct isoforms of PTBP3 by alternative splicing and translation initiation.
Polypyrimidine tract binding protein (PTBP1) is a widely expressed RNA binding protein that acts as a regulator of alternative splicing and of cytoplasmic mRNA functions. Vertebrates contain two closely-related paralogs with >75% amino acid sequence identity. Early replacement of PTBP1 by PTBP2 during neuronal differentiation causes a concerted set of splicing changes. By comparison, very little is known about the molecular functions or physiological roles of PTBP3, although its expression and conservation throughout the vertebrates suggest a role in haematopoietic cells. To begin to understand its functions we have characterized the mRNA and protein isoform repertoire of PTBP3. Combinatorial alternative splicing events at the 5' end of the gene allow for the generation of eight mRNA and three major protein isoforms. Individual mRNAs generate up to three protein isoforms via alternative translation initiation by re-initiation and leaky scanning using downstream AUG codons. The N-terminally truncated PTBP3 isoforms lack nuclear localization signals and/or most of the RRM1 domain and vary in their RNA binding properties and nuclear/cytoplasmic distribution, suggesting that PTBP3 may have major post-transcriptional cytoplasmic roles. Our findings set the stage for understanding the non-redundant physiological roles of PTBP3.
Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK.
Lit-Yeen
LY
Tan
Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK.
Peter
P
Whitfield
Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK.
Miriam
M
Llorian
Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK Laboratory of Lymphocyte Signalling and Development, The Babraham Institute, Babraham Research Campus, CB22 3AT, UK.
Elisa
E
Monzon-Casanova
Laboratory of Lymphocyte Signalling and Development, The Babraham Institute, Babraham Research Campus, CB22 3AT, UK.
Manuel D
MD
Diaz-Munoz
Laboratory of Lymphocyte Signalling and Development, The Babraham Institute, Babraham Research Campus, CB22 3AT, UK.
Martin
M
Turner
Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK cwjs1@cam.ac.uk.
Christopher W J
CW
Smith
D017398:Alternative Splicing; D000818:Animals; D002478:Cells, Cultured; D018387:Codon, Initiator; D006801:Humans; D020014:K562 Cells; D008810:Mice, Inbred C57BL; D010442:Peptide Chain Initiation, Translational; D038941:Polypyrimidine Tract-Binding Protein / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D012313:RNA / Q000378:metabolism
D018387:Codon, Initiator; C118823:PTBP3 protein, human; D020033:Protein Isoforms; D038941:Polypyrimidine Tract-Binding Protein; D012313:RNA