Polypyrimidine tract binding protein antagonizes exon definition.
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ABSTRACT:
SUBMITTER: Wagner EJ
PROVIDER: S-EPMC100250 | biostudies-literature | 2001 May
REPOSITORIES: biostudies-literature
Publications
Polypyrimidine tract binding protein antagonizes exon definition.
Wagner E J EJ Garcia-Blanco M A MA
Molecular and cellular biology 20010501 10
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Project description:Polypyrimidine tract binding protein (PTB) is known to silence the splicing of many alternative exons. However, exons repressed by PTB are affected by other RNA regulatory elements and proteins. This makes it difficult to dissect the structure of the pre-mRNP complexes that silence splicing, and to understand the role of PTB in this process. We determined the minimal requirements for PTB-mediated splicing repression. We find that the minimal sequence for high affinity binding by PTB is relatively large, containing multiple polypyrimidine elements. Analytical ultracentrifugation and proteolysis mapping of RNA cross-links on the PTB protein indicate that most PTB exists as a monomer, and that a polypyrimidine element extends across multiple PTB domains. The high affinity site is bound initially by a PTB monomer and at higher concentrations by additional PTB molecules. Significantly, this site is not sufficient for splicing repression when placed in the 3' splice site of a strong test exon. Efficient repression requires a second binding site within the exon itself or downstream from it. This second site enhances formation of a multimeric PTB complex, even if it does not bind well to PTB on its own. These experiments show that PTB can be sufficient to repress splicing of an otherwise constitutive exon, without binding sites for additional regulatory proteins and without competing with U2AF binding. The minimal complex mediating splicing repression by PTB requires two binding sites bound by an oligomeric PTB complex.
| S-EPMC1370756 | biostudies-literature
Project description:The polypyrimidine tract binding protein (PTB) binds pre-mRNAs to alter splice-site choice. We characterized a series of spliceosomal complexes that assemble on a pre-mRNA under conditions of either PTB-mediated splicing repression or its absence. In the absence of repression, exon definition complexes that were assembled downstream of the regulated exon could progress to pre-spliceosomal A complexes and functional spliceosomes. Under PTB-mediated repression, assembly was arrested at an A-like complex that was unable to transition to spliceosomal complexes. Trans-splicing experiments indicated that, even when the U1 and U2 small nuclear ribonucleoprotein particles (snRNPs) are properly bound to the upstream and downstream exons, the presence of PTB prevents the interaction of the two exon complexes. Proteomic analyses of these complexes provide a new description of exon definition complexes, and indicate that splicing regulators can act on the transition between the exon definition complex and an intron-defined spliceosome.
| S-EPMC2546704 | biostudies-literature
Project description:The Nova paraneoplastic antigens are neuron-specific RNA binding proteins that participate in the control of alternative splicing. We have used the yeast two-hybrid system to isolate Nova interacting proteins and identify an RNA binding protein that is closely related to the polypyrimidine tract-binding protein (PTB). The expression of this protein, brPTB, is enriched in the brain, where it is expressed in glia and neurons. brPTB interacts with Nova proteins in cell lines and colocalizes with Nova within neuronal nuclei. We previously found that Nova binds to a pyrimidine-rich RNA element present upstream of an alternatively spliced exon, E3A, in glycine receptor alpha2 (GlyRalpha2) pre-mRNA, and this binding is implicated in Nova-dependent regulation of splicing. Cotransfection assays with a GlyRalpha2 minigene demonstrate that brPTB antagonizes the action of Nova to increase utilization of GlyRalpha2 E3A. brPTB binds to a 90-nt GlyRalpha2 RNA adjacent to the Nova binding site, but with an affinity that is more than 10-fold lower than Nova. When a putative binding site for brPTB on the GlyRalpha2 RNA is mutated, binding is abolished and the inhibitory effect on Nova-dependent exon selection disappears. These results suggest that brPTB is a tissue-restricted RNA binding protein that interacts with and inhibits the ability of Nova to activate exon selection in neurons.
| S-EPMC18606 | biostudies-literature
Project description:The polypyrimidine tract binding (PTB) protein is a potent regulator of alternative mRNA splicing. It also participates in other essential cellular functions, including translation initiation and polyadenylation. Several published reports have suggested that the protein forms a dimer in solution, a feature that has been widely incorporated into mechanistic models of protein function. However, recent studies have provided indications that full-length PTB is a monomer. Here we present new biophysical and biochemical evidence supporting the monomeric status of the protein. By use of blue-native polyacrylamide gel electrophoresis and size-exclusion chromatography, PTB was observed as a single molecular species under native reducing environments, though in oxidizing conditions, a larger protein species was also detected. Further analyses of wild-type and mutant PTB molecules with SDS-PAGE and time-of-flight electrospray ionization mass spectroscopy confirmed these observations. They also identified the single reduced species as monomeric PTB and the higher-molecular-weight nonreduced species as disulphide-linked PTB dimer mediated by Cys23. Our results indicate that the use of oxidizing environments in previous studies is likely to have contributed to the mis-assignment of PTB as a dimer. Although purified PTB may form disulphide-linked dimers under these conditions, in the reducing intracellular environment the protein will be monomeric. These findings have implications for the construction of models of PTB function in regulating mRNA metabolism.
| S-EPMC1370869 | biostudies-literature
Project description:Alternative splicing of 3'-terminal exons plays a critical role in gene expression by producing mRNA with distinct 3'-untranslated regions that regulate their fate and their expression. The Xenopus alpha-tropomyosin pre-mRNA possesses a composite internal/3'-terminal exon (exon 9A9') that is differentially processed depending on the embryonic tissue. Exon 9A9' is repressed in non-muscle tissue by the polypyrimidine tract binding protein, whereas it is selected as a 3'-terminal or internal exon in myotomal cells and adult striated muscles, respectively. We report here the identification of an intronic regulatory element, designated the upstream terminal exon enhancer (UTE), that is required for the specific usage of exon 9A9' as a 3'-terminal exon in the myotome. We demonstrate that polypyrimidine tract binding protein prevents the activity of UTE in non-muscle cells, whereas a subclass of serine/arginine rich (SR) proteins promotes the selection of exon 9A9' in a UTE-dependent way. Morpholino-targeted blocking of UTE in the embryo strongly reduced the inclusion of exon 9A9' as a 3'-terminal exon in the endogenous mRNA, demonstrating the function of UTE under physiological circumstances. This strategy allowed us to reveal a splicing pathway that generates a mRNA with no in frame stop codon and whose steady-state level is translation-dependent. This result suggests that a non-stop decay mechanism participates in the strict control of the 3'-end processing of the alpha-tropomyosin pre-mRNA.
| S-EPMC2781652 | biostudies-literature
Project description:Tethered hydroxyl-radical probing has been used to determine the orientation of binding of polypyrimidine tract-binding protein (PTB) to the poliovirus type 1 (Mahoney) (PV-1(M)) internal ribosome entry site/segment (IRES)-the question of which RNA-binding domain (RBD) binds to which sites on the IRES. The results show that under conditions in which PTB strongly stimulates IRES activity, a single PTB is binding to the IRES, a finding which was confirmed by mass spectrometry of PTB/IRES complexes. RBDs1 and 2 interact with the basal part of the Domain V irregular stem loop, very close to the binding site of eIF4G, and RBDs3 and 4 interact with the single-stranded regions flanking Domain V. The binding of PTB is subtly altered in the presence of the central domain (p50) of eIF4G, and p50 binding is likewise modified if PTB is present. This suggests that PTB stimulates PV-1(M) IRES activity by inducing eIF4G to bind in the optimal position and orientation to promote internal ribosome entry, which, in PV-1(M), is at an AUG triplet 30 nt downstream of the base of Domain V.
| S-EPMC2982756 | biostudies-literature
Project description:The heterogeneous nuclear ribonucleoprotein particle (hnRNP) proteins play important roles in mRNA processing in eukaryotes, but little is known about how they are regulated by cellular signaling pathways. The polypyrimidine-tract binding protein (PTB, or hnRNP I) is an important regulator of alternative pre-mRNA splicing, of viral RNA translation, and of mRNA localization. Here we show that the nucleo-cytoplasmic transport of PTB is regulated by the 3',5'-cAMP-dependent protein kinase (PKA). PKA directly phosphorylates PTB on conserved Ser-16, and PKA activation in PC12 cells induces Ser-16 phosphorylation. PTB carrying a Ser-16 to alanine mutation accumulates normally in the nucleus. However, export of this mutant protein from the nucleus is greatly reduced in heterokaryon shuttling assays. Conversely, hyperphosphorylation of PTB by coexpression with the catalytic subunit of PKA results in the accumulation of PTB in the cytoplasm. This accumulation is again specifically blocked by the S16A mutation. Similarly, in Xenopus oocytes, the phospho-Ser-16-PTB is restricted to the cytoplasm, whereas the non-Ser-16-phosphorylated PTB is nuclear. Thus, direct PKA phosphorylation of PTB at Ser-16 modulates the nucleo-cytoplasmic distribution of PTB. This phosphorylation likely plays a role in the cytoplasmic function of PTB.
| S-EPMC166389 | biostudies-literature
Project description:AimsThe activation of cardiac fibroblasts (CFs) leads to overproduction of collagens and subsequently cardiac fibrosis. However, the regulatory mechanism of CF function in the process of cardiac fibrosis remains unclear. This work investigated the function of polypyrimidine tract binding protein 1 (PTBP1)/nuclear receptor NR4A1 (Nur77)/fatty acid-binding protein 5 (FABP5) axis in myocardial fibrosis.Methods and resultsCardiac fibrosis was induced in mice suffered left anterior descending ligation. In parallel, neonatal mouse CFs were isolated and stimulated with transforming growth factor-β1 (TGF-β1). Cardiac fibrosis was evaluated by Masson's trichrome staining. Expression of PTBP1, Nur77, FABP5, collagen I, and collagen III was measured by quantitative real-time PCR and western blotting. Proliferation of CFs was assessed by 5-ethynyl-2'-deoxyuridine assay. Molecular interaction was validated by RNA-binding protein immunoprecipitation, chromatin immunoprecipitation, and dual luciferase reporter assay. PTBP1 was up-regulated (P < 0.05), whereas Nur77 (P < 0.05) and FABP5 (P < 0.05) were down-regulated in the fibrotic hearts of mice and TGF-β1-exposed CFs. PTBP1 overexpression facilitated proliferation (P < 0.05) and collagen I (P < 0.05) and collagen III (P < 0.05) expression of CFs after stimulation with TGF-β1. PTBP1 reduced Nur77 stability (P < 0.05) to inhibit Nur77 expression (P < 0.05) in CFs. Nur77 bound to FABP5 promoter to promote the transcription (P < 0.05) and expression (P < 0.05) of FABP5. Silencing of Nur77 or FABP5 abolished the inhibitory effect of PTBP1 knockdown on proliferation (P < 0.05) and collagen I (P < 0.05) and collagen III (P < 0.05) expression of CFs in vitro. PTBP1 depletion ameliorated cardiac fibrosis (P < 0.05), α-smooth muscle actin (P < 0.05), and collagen I (P < 0.05) expression in myocardial infarction mice through regulating Nur77/FABP5 pathway (P < 0.05) in vivo.ConclusionsPTBP1 contributed to cardiac fibrosis via promoting CF proliferation and collagen deposition through Nur77 mRNA decay and subsequent transcription inhibition of FABP5. Our findings suggest that PTBP1/Nur77/FABP5 axis may be potential targets for cardiac fibrosis therapy.
| S-EPMC10192252 | biostudies-literature
Project description:Purpose : Splicing factors regulate splice site choices in pre-mRNA and determine final exon set in mRNA. To understand mechanisms of splicing regulation, it is important to identify and characterize exon targets of splicing factors. Recently, development of RNA-seq technology enables researchers to investigate exon splicing profiles as well as gene expression profiles in transcriptome-wide. The goal of this study is to investigate transcriptome changes by splicing factors, Polypyrimidine Tract Binding proteins (PTB). In this study, we analyzed exon and gene expression changes followed by Ptbp1 knock down. Methods : The knockdown experiment was performed in mouse neuroblastoma (N2A) cells. Total RNA was collected from cells and further treated with DNase I to avoid DNA contamination. RNA-seq libraries were constructed in a strand specific way using dUTP and Uracil-Specific Excision Reagent enzyme. The libraries were subjected to 100bp paired-end sequencing (Illumina HiSeq2000 platform). Poly(A)-mRNA and exon profiles of N2A mouse blastoma cells in two samples: shRNA transfection control, single knock down of ptbp1. RNA-seq libraries were generated in strand specific way using dUTP and USER enzyme and sequenced using Illumina HiSeq2000.
2013-12-01 | E-GEOD-45119 | biostudies-arrayexpress
Project description:Purpose : Splicing factors regulate splice site choices in pre-mRNA and determine final exon set in mRNA. To understand mechanisms of splicing regulation, it is important to identify and characterize exon targets of splicing factors. Recently, development of RNA-seq technology enables researchers to investigate exon splicing profiles as well as gene expression profiles in transcriptome-wide. The goal of this study is to investigate transcriptome changes by splicing factors, Polypyrimidine Tract Binding proteins (PTB). In this study, we analyzed exon and gene expression changes followed by Ptbp1 knock down. Methods : The knockdown experiment was performed in mouse neuroblastoma (N2A) cells. Total RNA was collected from cells and further treated with DNase I to avoid DNA contamination. RNA-seq libraries were constructed in a strand specific way using dUTP and Uracil-Specific Excision Reagent enzyme. The libraries were subjected to 100bp paired-end sequencing (Illumina HiSeq2000 platform).
2013-12-01 | GSE45119 | GEO