{"gene":"PTBP2","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":2007,"finding":"PTBP2 (nPTB) expression during myoblast differentiation is post-transcriptionally repressed by the muscle-restricted microRNA miR-133, which targets two miR-133-responsive elements in the PTBP2 3' UTR; this reduction in PTBP2 leads to increased inclusion of PTB-repressed exons during myotube differentiation.","method":"Luciferase reporter assay with 3' UTR constructs, transfection of synthetic miR-133, LNA oligonucleotide block of miR-133/miR-1/206, western blot, RT-PCR of target exons in C2C12 cells","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (reporter assay with mutagenesis of MREs, gain-of-function miR-133 transfection, loss-of-function LNA inhibition, endogenous protein measurement), replicated in multiple experimental systems","pmids":["17210790"],"is_preprint":false},{"year":2007,"finding":"PTB represses PTBP2 (nPTB) exon 10 splicing, causing nonproductive mRNA subject to nonsense-mediated decay; upon PTB knockdown, nPTB is upregulated via increased exon 10 inclusion, demonstrating cross-regulation between PTB and PTBP2 through nonproductive alternative splicing. PTBP2 and PTB have a large degree of functional overlap in splicing repression.","method":"Quantitative proteomics of HeLa cells after PTB knockdown, siRNA double knockdown of PTB and nPTB, RT-PCR of alternative splicing events","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — quantitative proteomics plus genetic knockdown with splicing readout, replicated across multiple target exons","pmids":["17679092"],"is_preprint":false},{"year":2012,"finding":"PTBP1 and PTBP2 repress splicing of PSD-95 (Dlg4) exon 18; this repression leads to premature translation termination and nonsense-mediated mRNA decay of Psd-95 transcripts during early neural development. Sequential downregulation of first PTBP1 and then PTBP2 during embryonic development allows exon 18 inclusion and PSD-95 protein expression required for synapse maturation.","method":"RT-PCR splicing assays, re-expression of PTBP1/PTBP2 in differentiated neurons, electrophysiology and synaptic marker analysis in mouse embryonic brain","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function and re-expression experiments in neurons with defined molecular (NMD) and cellular (synapse maturation) phenotypes, multiple orthogonal methods","pmids":["22246437"],"is_preprint":false},{"year":2012,"finding":"Ptbp2 binds pyrimidine-rich sequences upstream of and/or within alternative exons to inhibit adult-specific alternative splicing in neuronal progenitors; Ptbp2-null mice show aberrant neuronal progenitor polarity, premature neurogenesis, and reduced progenitor pools, identifying a role for Ptbp2 in neurogenesis through repression of exons encoding proteins associated with cell fate, proliferation, and the actin cytoskeleton.","method":"HITS-CLIP in developing mouse neocortex, splicing-sensitive microarrays, Ptbp2 knockout mouse (two independent strains), histological analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — HITS-CLIP providing genome-wide binding map combined with knockout mouse and splicing microarrays, two independent null strains","pmids":["22802532"],"is_preprint":false},{"year":2014,"finding":"PTBP2 controls a program of embryonic alternative splicing that temporarily represses adult protein isoforms (affecting neurite growth, pre- and post-synaptic assembly, synaptic transmission) until final neuronal maturation; depletion of PTBP2 causes precocious expression of adult isoforms in embryonic cortex, leading to failure of neuronal maturation and death.","method":"Ptbp2 conditional knockout mouse, transcriptome-wide RNA-seq and splicing analysis, cultured neuron viability and maturation assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with genome-wide splicing analysis and defined cellular phenotype (maturation failure, cell death), multiple orthogonal methods","pmids":["24448406"],"is_preprint":false},{"year":2010,"finding":"PTBP2 physically interacts with the cytidine deaminase AID (identified by proteomic screen using in vivo biotinylation of AID) and promotes binding of AID to transcribed switch-region DNA; shRNA-mediated knockdown of PTBP2 in B cells decreases AID binding to switch regions and considerably impairs immunoglobulin class-switch recombination.","method":"In vivo biotinylation proteomic screen, co-immunoprecipitation, shRNA knockdown of PTBP2 in B cells, ChIP for AID at switch regions, CSR assay","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — proteomic interaction screen plus functional knockdown with defined molecular (AID-DNA binding) and cellular (CSR) phenotypes, multiple orthogonal methods in single lab","pmids":["21186367"],"is_preprint":false},{"year":2016,"finding":"PTBP1 exhibits greater splicing repression activity than PTBP2 per unit protein on target exons; chimera analysis identified that multiple segments of PTBP1 (RRM1, the linker between RRM2-RRM3, and RRM2) contribute to higher repression activity. RRM2 of PTBP1 increases repression potentially via stronger binding to the cofactor Raver1.","method":"In vivo coexpression splicing assay, in vitro splicing assay, PTBP1/PTBP2 chimeric protein constructs, Raver1 binding assays","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro splicing assay with chimeric proteins and domain-swap mutagenesis, two independent assay systems (in vivo and in vitro)","pmids":["27288314"],"is_preprint":false},{"year":2016,"finding":"PTBP1 and PTBP2 repress nonconserved cryptic exons using CU microsatellites as binding elements, establishing them as members of a family of cryptic exon repressors. This activity is distinct from TDP-43, which uses UG microsatellites.","method":"RNA-seq analysis after PTBP1/PTBP2 knockdown, identification of cryptic exon inclusion events, motif analysis","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knockdown combined with genome-wide RNA-seq and motif analysis, but single lab and no in vitro reconstitution","pmids":["27681424"],"is_preprint":false},{"year":2016,"finding":"A PTBP1 knockin allele can rescue forebrain-specific but not pan-neuronal Ptbp2 knockout, demonstrating both redundant and distinct functional roles. Despite similar RNA binding across the transcriptome (shown by CLIP), many developmentally regulated exons show different sensitivities to PTBP1 vs. PTBP2, indicating differential activity does not derive from differential RNA binding but likely from cofactor interactions.","method":"Ptbp1 knockin mouse bred to Ptbp2 knockout, CLIP-seq comparing RNA binding, splicing-sensitive assays across brain regions","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis via knockin/knockout mouse combined with genome-wide CLIP-seq, rigorous in vivo phenotypic comparison","pmids":["27926877"],"is_preprint":false},{"year":2019,"finding":"PTBP2 governs axonogenesis-associated alternative splicing in cortical neurons; its cortical depletion prematurely induces axonogenesis-associated splicing and specifically impairs axon formation in vitro and in vivo. PTBP2-controlled splicing of Shtn1 determines SHTN1's capacity to regulate actin interaction, polymerization, and axon growth; precocious Shtn1 isoform switching contributes to disorganized axon formation in Ptbp2-/- neurons.","method":"Transcriptome profiling of primary cortical neurons, PTBP2 conditional knockout mouse, in vitro axon formation assays, Shtn1 isoform functional characterization including actin binding/polymerization assays","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO in vivo plus functional isoform characterization (actin assays) plus transcriptome-wide profiling, multiple orthogonal methods","pmids":["30733148"],"is_preprint":false},{"year":2017,"finding":"Ptbp2 controls a network of alternatively spliced genes involved in cell adhesion, migration, and polarity in spermatogenic cells; Ptbp2 ablation in germ cells results in disorganization of F-actin cytoskeleton in Sertoli cells, demonstrating that PTBP2-regulated alternative splicing is required for germ-Sertoli cell communication during spermatogenesis.","method":"Germ cell-specific Ptbp2 conditional knockout mouse, RNA-seq, splicing analysis, histology, F-actin staining","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with genome-wide splicing analysis and defined cellular phenotype (F-actin disorganization in Sertoli cells), multiple methods","pmids":["28636946"],"is_preprint":false},{"year":2015,"finding":"Ptbp2 is essential for spermatogenesis; Ptbp2 ablation results in germ cell loss due to increased apoptosis of meiotic spermatocytes and postmeiotic arrest of spermatid differentiation, and Ptbp2 is required for alternative splicing regulation in the testis in a tissue-specific manner (not all Ptbp2-sensitive exons in brain are also sensitive in testis).","method":"Ptbp2 knockout mouse, dual fluorescence flow cytometry of germ cells, histology, RT-PCR of alternative splicing events in brain vs. testis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse with specific cellular phenotype and tissue-comparative splicing analysis, multiple orthogonal methods","pmids":["26391954"],"is_preprint":false},{"year":2009,"finding":"Knockdown of PTBP2 (alone or combined with PTBP1) in glioma cell lines slows cell proliferation, inhibits cell migration, and increases cell adhesion to fibronectin and vitronectin.","method":"shRNA knockdown of PTBP1 and/or PTBP2 in U251 and LN229 glioma cell lines, proliferation assays, migration assays, adhesion assays","journal":"Brain : a journal of neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KD with defined cellular phenotypes, two cell lines, but no pathway placement beyond PTBP2 removal","pmids":["19506066"],"is_preprint":false},{"year":2015,"finding":"PTBP1 and PTBP2 bind to an exonic splicing suppressor in SRSF3 exon 4 and inhibit its inclusion, resulting in overexpression of full-length functional SRSF3 in oral squamous cell carcinoma cells; SRSF3, in turn, promotes PTBP2 expression, establishing a feed-forward loop.","method":"RT-PCR splicing assays, overexpression and knockdown of PTBP1/PTBP2, luciferase/minigene assays, RNA binding analysis in OSCC cells","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional knockdown/overexpression with splicing readout and reciprocal regulation demonstrated, single lab","pmids":["26416554"],"is_preprint":false},{"year":2014,"finding":"MALAT1 lncRNA binds to SFPQ, thereby releasing PTBP2 from the SFPQ/PTBP2 complex; the increased free PTBP2 promotes colorectal cancer cell proliferation and migration.","method":"Co-immunoprecipitation of SFPQ/PTBP2 complex, RNA pulldown for MALAT1-SFPQ interaction, overexpression/knockdown in CRC cells and nude mouse xenografts","journal":"British journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP for complex, functional overexpression/KD with proliferation and migration phenotypes, in vivo xenograft, single lab","pmids":["25025966"],"is_preprint":false},{"year":2018,"finding":"Mass spectrometry analysis identified distinct phosphorylation modifications in PTBP2 located in the unstructured N-terminal, Linker 1, and Linker 2 regions (not present in PTBP1), and acetylation modifications including lysine residues in the nuclear localization sequence of PTBP2.","method":"Mass spectrometry analysis of post-translational modifications on PTBP1 and PTBP2 under splicing reaction conditions","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct MS identification of PTMs on purified proteins, but functional consequences of specific modifications not fully established in this study","pmids":["29851470"],"is_preprint":false},{"year":2022,"finding":"hnRNPH1 recruits PTBP2 (and SRSF3) to modulate alternative splicing in germ cells; conditional knockout of Hnrnph1 in spermatogenic cells causes abnormal splicing events affecting meiosis and germ-Sertoli communication genes.","method":"Co-immunoprecipitation of hnRNPH1-PTBP2 complex, conditional Hnrnph1 knockout mouse, RNA-seq splicing analysis, histology","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP establishing protein-protein interaction plus functional KO with splicing phenotype, single lab","pmids":["35739118"],"is_preprint":false},{"year":2023,"finding":"PTBP2 has a cytosolic role in axon growth in motoneurons: cytoplasmic Ptbp2 binds the 3' UTR of Hnrnpr mRNA and promotes its axonal localization and local translation via association with ribosomes in a manner dependent on translation factor eIF5A2; depletion of cytosolic Ptbp2 reduces axonal Hnrnpr mRNA localization and hnRNP R synthesis, causing defective axon growth.","method":"Subcellular fractionation and live imaging for cytosolic/axonal Ptbp2 localization, CLIP for Ptbp2-Hnrnpr mRNA interaction, ribosome association assays, eIF5A2 interaction, conditional depletion of cytosolic Ptbp2 with axon growth phenotype readout","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (CLIP, fractionation, ribosome association, functional rescue) establishing a cytosolic mechanism distinct from nuclear splicing role","pmids":["37438340"],"is_preprint":false},{"year":2023,"finding":"PTBP2 binding to SYNGAP1 mRNA promotes alternative splicing and nonsense-mediated decay of SYNGAP1; antisense oligonucleotides that disrupt PTBP2 binding sites redirect splicing and increase SYNGAP1 mRNA and protein expression in human iPSC-derived neurons and in SYNGAP1 haploinsufficient patient-derived neurons.","method":"CLIP-seq in human brain tissue and iPSC-neurons to map PTBP2 binding sites, ASO-mediated disruption of PTBP2 binding, RT-PCR and western blot for SYNGAP1 isoforms/expression, patient-derived iPSC-neuron experiments","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide CLIP-seq plus ASO functional perturbation in human neurons and patient-derived cells, multiple orthogonal methods","pmids":["37149717"],"is_preprint":false},{"year":2024,"finding":"KIS kinase phosphorylates PTBP2, causing its dissociation from co-regulators Matrin3 and hnRNPM and hindering the RNA-binding capability of the complex; KIS and PTBP2 have opposing functional interactions in synaptic spine emergence and maturation.","method":"In vitro kinase assay showing KIS phosphorylates PTBP2, co-immunoprecipitation of PTBP2-Matrin3-hnRNPM complex before/after phosphorylation, genome-wide exon usage profiling in neurons, spine morphology assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — kinase assay (Tier 1) plus Co-IP, genome-wide splicing, and functional spine assays, single lab but multiple orthogonal methods","pmids":["38597390"],"is_preprint":false},{"year":2024,"finding":"Unstructured linker regions (Linker 1 and Linker 2) and the N-terminal region of PTBP2 play a role in its differential splicing activity compared to PTBP1; phosphorylation in these unstructured regions alters their physical properties as shown by molecular dynamics, and hybrid PTBP1-PTBP2 constructs with PTBP1 linker regions show altered splicing repression activity.","method":"Hybrid PTBP1-PTBP2 chimeric protein constructs assayed in splicing assays, molecular dynamics simulation of phosphorylated unstructured regions, evolutionary conservation bioinformatics analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — chimeric protein splicing assay plus MD simulation, single lab; functional link of phosphorylation to splicing activity not directly demonstrated by mutagenesis","pmids":["38336291"],"is_preprint":false},{"year":2025,"finding":"PTBP2 binds to the 3' UTR of BNIP3 mRNA and stabilizes its expression; Ptbp2 knockout in CML cells decreases BNIP3 levels and impairs autophagy (measured by LC3-II in bafilomycin-treated cells), and re-expression of BNIP3 in Ptbp2-KO cells restores the autophagy phenotype.","method":"RIP-seq identifying PTBP2-BNIP3 3'UTR interaction, Ptbp2 knockout CML cell lines, LC3-II western blot as autophagy readout, BNIP3 rescue experiment, subcutaneous xenograft and tail vein engraftment in NOD/SCID mice","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RIP-seq plus KO/rescue with defined molecular and cellular phenotypes, single lab","pmids":["40113750"],"is_preprint":false},{"year":2026,"finding":"PTBP2 binds to the 3' UTR of DNA polymerase kappa (Polk) mRNA, stabilizing its expression; Ptbp2 knockout reduces Polk levels and increases DNA damage (comet assay, γH2AX foci) upon hydroxyurea treatment, which is rescued by Polk re-expression. POLK interacts with MRE11 of the MRN complex to regulate ATM-CHK2 signaling.","method":"RIP-seq (3' UTR binding), Ptbp2 KO CML cell lines and patient samples, comet assay and γH2AX foci, Polk rescue experiment, co-immunoprecipitation of POLK-MRE11, sister chromatid exchange and BrdU incorporation assays","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RIP-seq plus KO/rescue with DNA damage phenotype and Co-IP for POLK-MRE11 interaction, single lab","pmids":["41667423"],"is_preprint":false},{"year":2014,"finding":"Crystal and solution structures of the C-terminal domain of nPTB (nPTB34, containing RRMs 3 and 4) reveal that RRMs 3 and 4 interact with each other to form a stable unit with RNA-binding surfaces on opposite sides facing away from each other, similar to PTB34; amino acid differences are located on exposed β-sheet surfaces and loops, likely modulating RNA interactions.","method":"X-ray crystallography and NMR solution structure determination of nPTB RRMs 3-4","journal":"PeerJ","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal and solution structures determined, structural basis for RNA binding established, single lab","pmids":["24688880"],"is_preprint":false},{"year":2022,"finding":"Under in vitro splicing conditions, PTBP2 interacts with a distinct set of proteins compared to PTBP1; PTBP2 does not interact with many mRNA processing/splicing regulators that PTBP1 does, and both proteins interact with chromatin remodeling and transcription regulators. The study identified potential 'writer' and 'eraser' enzymes for PTM modifications on PTBP2.","method":"In vitro splicing reactions with HeLa nuclear extract, mass spectrometry of co-precipitated proteins for PTBP1 vs. PTBP2","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — MS-based interactome under defined splicing conditions, but single pulldown approach without reciprocal validation, single lab","pmids":["35113929"],"is_preprint":false},{"year":2023,"finding":"PTBP2 binding to SYNGAP1 mRNA promotes alternative splicing and nonsense-mediated decay of SYNGAP1. PTBP2 prevents IRF9 alternative splicing and upregulates STAT1 to stimulate CCL5 secretion and IFN-stimulated gene factor-dependent type I interferon secretion in neuroblastoma cells, inducing monocyte/macrophage chemotaxis and sustaining proinflammatory monocyte phenotype.","method":"PTBP2 overexpression/knockdown in neuroblastoma cells, RT-PCR for IRF9 splicing, western blot for STAT1, ELISA for CCL5/IFN, monocyte chemotaxis and polarization assays","journal":"Research (Washington, D.C.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional splicing and downstream signaling assays with defined phenotypic readouts, single lab","pmids":["37040518"],"is_preprint":false},{"year":2021,"finding":"The lncRNA Rbakdn binds to Ptbp2 protein and stabilizes it against ubiquitin-mediated degradation; Rbakdn knockdown leads to decreased Ptbp2 levels through the ubiquitination degradation pathway.","method":"RNA immunoprecipitation (Ribotrap + co-IP), Rbakdn knockdown in vitro and intratesticular injection in mice, ubiquitination assay for Ptbp2 degradation","journal":"Frontiers in genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — RNA-protein interaction by RIP plus ubiquitination assay, functional KD with phenotype, but single lab and mechanistic evidence is partially indirect","pmids":["34707642"],"is_preprint":false},{"year":2023,"finding":"PTBP2 binds to the lncRNA Tesra in testicular germ cells and is required for Tesra-mediated transcriptional activation of Prss42/Tessp-2; knockdown of PTBP2 significantly decreases Prss42/Tessp-2 promoter activity in an in vitro reporter system.","method":"Ribotrap assay followed by LC-MS/MS to identify Tesra-binding proteins, RNA immunoprecipitation confirming PTBP2-Tesra association, Tet-on reporter system for Prss42/Tessp-2 promoter activity, PTBP2 knockdown","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — MS-based interaction identification plus RIP and functional reporter assay, single lab, non-canonical role (transcriptional co-activation via lncRNA)","pmids":["37858745"],"is_preprint":false},{"year":2008,"finding":"Human nPTB (PTBP2) expression is severely limited by its extremely suboptimal codon content (high proportion of A/U at third codon position), resulting in ~1–3% the expression level of PTB despite similar mRNA levels and 74% amino acid identity; codon optimization restores expression to PTB-equivalent levels and confirms PTBP2 acts as a splicing repressor.","method":"Transfection of native vs. codon-optimized nPTB constructs, western blot, in vivo and in vitro translation assays, splicing repression assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — codon optimization rescue experiment with quantitative protein expression and functional splicing assays, single lab","pmids":["18335065"],"is_preprint":false},{"year":2024,"finding":"Smn (survival motoneuron protein) is an interactor of Ptbp2 in cytosolic compartments of motoneurons; Smn depletion reduces Ptbp2 levels specifically in axons (not somata), and re-expression of Ptbp2 in axons rescues defects in axon elongation and growth cone maturation in Smn-deficient motoneurons.","method":"Co-immunoprecipitation of Smn-Ptbp2 in motoneuron cytosolic fractions, subcellular fractionation and immunofluorescence for axonal Ptbp2 levels in Smn-KD motoneurons, lentiviral re-expression of Ptbp2 in axons, axon growth and growth cone assays","journal":"Frontiers in molecular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus subcellular fractionation plus rescue experiment, single lab, single study","pmids":["39246602"],"is_preprint":false}],"current_model":"PTBP2 (nPTB/brPTB) is a neuronal RNA-binding protein that acts primarily as a splicing repressor by binding pyrimidine-rich sequences in pre-mRNAs to inhibit inclusion of adult-specific and tissue-specific exons; it is sequentially expressed after PTBP1 during neural development (with miR-133 targeting its 3' UTR to regulate expression) and controls developmental programs essential for neuronal maturation, axonogenesis, and synapse development, while also functioning in spermatogenesis and immunoglobulin class-switch recombination. Beyond its nuclear splicing role, cytosolic PTBP2 promotes axon growth by binding Hnrnpr mRNA and facilitating its axonal localization and local translation via eIF5A2-dependent ribosome association. Its differential activity from the paralog PTBP1 is determined by multiple protein domains (particularly linker regions and RRM1) and distinct post-translational phosphorylation modifications, and its activity can be modulated by cofactors including Raver1, Matrin3, and hnRNPM, the last two being released upon phosphorylation by the kinase KIS."},"narrative":{"mechanistic_narrative":"PTBP2 (nPTB/brPTB) is a neuronal pyrimidine-tract RNA-binding protein that acts as a sequence-specific splicing repressor, binding pyrimidine-rich elements upstream of or within alternative exons to enforce embryonic and tissue-specific splicing programs [PMID:22802532]. Across the developing nervous system it temporarily suppresses adult-specific protein isoforms governing neurite growth, pre- and post-synaptic assembly, and synaptic transmission, so that its loss causes precocious adult isoform expression, failed neuronal maturation, and cell death [PMID:24448406]; mechanistically this includes repression of PSD-95 (Dlg4) exon 18, which generates an NMD-targeted transcript until PTBP2 is downregulated [PMID:22246437], and control of axonogenesis-associated splicing such as the Shtn1 isoform switch that tunes actin polymerization and axon formation [PMID:30733148]. PTBP2 operates in a developmental relay with its paralog PTBP1, which represses PTBP2 exon 10 to produce an NMD substrate; the two proteins bind RNA similarly genome-wide yet differ in repression activity, a difference attributable not to differential binding but to protein domains—RRM1, RRM2, and the unstructured N-terminal and linker regions—and to cofactor recruitment [PMID:17679092, PMID:27926877, PMID:27288314, PMID:38336291]. Its splicing output is modulated by associated regulators including Matrin3 and hnRNPM, which dissociate upon phosphorylation by the kinase KIS, coupling PTBP2 activity to synaptic spine maturation [PMID:38597390]. Beyond the nucleus, cytosolic PTBP2 binds the 3' UTR of Hnrnpr mRNA and drives its axonal localization and eIF5A2-dependent local translation to support axon growth [PMID:37438340]. PTBP2 also functions outside the nervous system: it is required for spermatogenesis, where it regulates a splicing network controlling germ-Sertoli communication and F-actin organization [PMID:28636946, PMID:26391954], and it promotes immunoglobulin class-switch recombination by interacting with AID and enhancing its binding to switch-region DNA [PMID:21186367]. In disease, ASO-mediated disruption of PTBP2 binding to SYNGAP1 mRNA redirects splicing to increase SYNGAP1 expression in patient-derived neurons, defining a therapeutic strategy for SYNGAP1 haploinsufficiency [PMID:37149717].","teleology":[{"year":2007,"claim":"Established that PTBP2 protein levels are themselves regulated, both by miR-133 acting on its 3' UTR during muscle differentiation and by PTBP1-driven nonproductive splicing of its own exon 10, explaining how PTBP2 abundance is dynamically controlled.","evidence":"Luciferase 3' UTR reporters with MRE mutagenesis and miR-133 gain/loss in C2C12 cells; quantitative proteomics and double siRNA knockdown with splicing readouts in HeLa cells","pmids":["17210790","17679092"],"confidence":"High","gaps":["Did not address PTBP2's own splicing target spectrum in neurons","Functional redundancy with PTBP1 quantified only on a subset of exons"]},{"year":2008,"claim":"Resolved why PTBP2 protein is far less abundant than PTBP1 despite high identity, showing its expression is throttled by suboptimal codon content and confirming PTBP2 is a bona fide splicing repressor.","evidence":"Transfection of native vs codon-optimized nPTB constructs with translation and splicing repression assays","pmids":["18335065"],"confidence":"Medium","gaps":["Physiological selective advantage of codon-limited expression not tested in vivo","Single-lab observation"]},{"year":2012,"claim":"Defined PTBP2's genome-wide binding mode and developmental function, showing it binds pyrimidine-rich sequences to repress adult exons and is required for neuronal progenitor polarity, proper neurogenesis timing, and PSD-95 expression for synapse maturation.","evidence":"HITS-CLIP in mouse neocortex, splicing microarrays and Ptbp2-null mice; RT-PCR splicing and re-expression with electrophysiology","pmids":["22802532","22246437"],"confidence":"High","gaps":["Cofactors mediating exon-specific repression not identified","Distinction from PTBP1 binding not yet resolved"]},{"year":2014,"claim":"Showed PTBP2 maintains an embryonic splicing program that suppresses adult isoforms until terminal neuronal maturation, with its depletion causing precocious maturation failure and death—establishing PTBP2 as a developmental timing switch.","evidence":"Ptbp2 conditional knockout mouse with transcriptome-wide RNA-seq and neuron viability/maturation assays","pmids":["24448406"],"confidence":"High","gaps":["Specific isoform switches driving maturation failure not individually dissected here","Upstream signals controlling PTBP2 downregulation timing unknown"]},{"year":2016,"claim":"Determined the basis for differential PTBP1 vs PTBP2 activity, showing similar genome-wide RNA binding but distinct repression strengths attributable to specific RRM and linker segments and cofactor interactions, and that both repress cryptic exons via CU microsatellites.","evidence":"PTBP1/PTBP2 chimeric protein splicing assays and Raver1 binding; Ptbp1 knockin/Ptbp2 knockout mice with CLIP-seq; RNA-seq motif analysis after knockdown","pmids":["27288314","27926877","27681424"],"confidence":"High","gaps":["Identity of cofactors conferring exon-specific differential sensitivity not fully defined","Cryptic exon repression study single-lab without reconstitution"]},{"year":2019,"claim":"Linked PTBP2 splicing control to axon formation specifically, identifying Shtn1 isoform regulation as a mechanism by which PTBP2 prevents premature axonogenesis-associated splicing.","evidence":"Conditional knockout mouse, primary cortical neuron transcriptomics, in vitro axon assays, Shtn1 actin-binding/polymerization characterization","pmids":["30733148"],"confidence":"High","gaps":["Relative contribution of Shtn1 vs other targets to axon phenotype not quantified","Mechanism timing of PTBP2 loss during axonogenesis not detailed"]},{"year":2023,"claim":"Revealed a cytosolic, splicing-independent function for PTBP2 in axon growth, binding Hnrnpr mRNA to drive its axonal localization and eIF5A2-dependent local translation.","evidence":"Subcellular fractionation, live imaging, CLIP, ribosome association and eIF5A2 interaction assays, conditional cytosolic Ptbp2 depletion in motoneurons","pmids":["37438340"],"confidence":"High","gaps":["What partitions PTBP2 between nucleus and cytoplasm not established","Full set of cytosolic mRNA cargos beyond Hnrnpr unknown"]},{"year":2023,"claim":"Demonstrated therapeutic targetability of PTBP2-mediated splicing, showing ASO disruption of PTBP2 binding to SYNGAP1 mRNA redirects splicing and raises SYNGAP1 expression in patient-derived neurons.","evidence":"CLIP-seq in human brain and iPSC-neurons, ASO perturbation, RT-PCR/western and SYNGAP1-haploinsufficient patient iPSC-neuron experiments","pmids":["37149717"],"confidence":"High","gaps":["In vivo efficacy and durability of ASO approach not tested","Off-target effects on other PTBP2 splicing events not characterized"]},{"year":2024,"claim":"Connected post-translational regulation to PTBP2 function, showing KIS kinase phosphorylates PTBP2 to dissociate Matrin3 and hnRNPM and impair complex RNA binding, with opposing roles in synaptic spine maturation.","evidence":"In vitro kinase assay, Co-IP of PTBP2-Matrin3-hnRNPM before/after phosphorylation, genome-wide exon usage and spine morphology assays","pmids":["38597390"],"confidence":"High","gaps":["Specific phosphosites required for dissociation not pinpointed by mutagenesis here","Single-lab finding"]},{"year":2017,"claim":"Extended PTBP2's role to spermatogenesis, showing it regulates a splicing network controlling germ-Sertoli communication and F-actin organization and is essential for germ cell survival and spermatid differentiation.","evidence":"Germ cell-specific and global Ptbp2 knockout mice, RNA-seq, histology, F-actin staining, flow cytometry","pmids":["28636946","26391954"],"confidence":"High","gaps":["Tissue-specific determinants of which exons are PTBP2-sensitive in testis vs brain unknown","Direct targets driving the F-actin phenotype not individually validated"]},{"year":2014,"claim":"Identified PTBP2's mechanistic basis for differential RNA binding through structural characterization of its C-terminal RRMs and showed activity can be modulated by sequestration in complexes such as SFPQ.","evidence":"Crystal and NMR structures of nPTB RRMs 3-4; Co-IP of SFPQ/PTBP2 and MALAT1 RNA pulldown with CRC proliferation/migration phenotypes","pmids":["24688880","25025966"],"confidence":"Medium","gaps":["Structure of full-length PTBP2 RNA complex not solved","SFPQ/MALAT1 axis demonstrated in cancer cells only, single lab"]},{"year":2025,"claim":"Documented mRNA-stabilizing functions of PTBP2 in cancer cells, binding 3' UTRs of BNIP3 and Polk to support autophagy and limit DNA damage, broadening its role beyond splicing repression.","evidence":"RIP-seq, Ptbp2 KO CML cell lines and patient samples, rescue experiments, LC3-II/autophagy and comet/γH2AX DNA damage readouts, xenografts","pmids":["40113750","41667423"],"confidence":"Medium","gaps":["Mechanism of 3' UTR-mediated stabilization not resolved","Generalizability beyond CML cells untested, single lab"]},{"year":null,"claim":"How PTBP2 is partitioned and switched between its nuclear splicing-repressor role, cytosolic mRNA-localization/stabilization roles, and non-canonical transcriptional and immune functions, and which cofactors and modifications dictate each, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking phosphorylation/acetylation state to subcellular function","Determinants of nuclear vs cytoplasmic localization unknown","Functional consequences of individual PTMs not established by mutagenesis"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[3,17,18,21,22,23]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[3,4,2,9]},{"term_id":"GO:0045182","term_label":"translation regulator activity","supporting_discovery_ids":[17]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[19,16]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,4,15]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[17,29]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[3,4,2,9]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,4,9,11,10]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[2,9,19,18]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[5]}],"complexes":["SFPQ/PTBP2 complex","PTBP2-Matrin3-hnRNPM complex"],"partners":["PTBP1","AID","MATRIN3","HNRNPM","SFPQ","HNRNPH1","SMN","EIF5A2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UKA9","full_name":"Polypyrimidine tract-binding protein 2","aliases":["Neural polypyrimidine tract-binding protein","Neurally-enriched homolog of PTB","PTB-like protein"],"length_aa":531,"mass_kda":57.5,"function":"RNA-binding protein which binds to intronic polypyrimidine tracts and mediates negative regulation of exons splicing. 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Ecosystem","date":"2025-03-30","source":"bioRxiv","url":"https://doi.org/10.1101/2025.03.26.645511","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":25579,"output_tokens":8033,"usd":0.098616,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":17427,"output_tokens":4740,"usd":0.102818,"stage2_stop_reason":"end_turn"},"total_usd":0.201434,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"PTBP2 (nPTB) expression during myoblast differentiation is post-transcriptionally repressed by the muscle-restricted microRNA miR-133, which targets two miR-133-responsive elements in the PTBP2 3' UTR; this reduction in PTBP2 leads to increased inclusion of PTB-repressed exons during myotube differentiation.\",\n      \"method\": \"Luciferase reporter assay with 3' UTR constructs, transfection of synthetic miR-133, LNA oligonucleotide block of miR-133/miR-1/206, western blot, RT-PCR of target exons in C2C12 cells\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (reporter assay with mutagenesis of MREs, gain-of-function miR-133 transfection, loss-of-function LNA inhibition, endogenous protein measurement), replicated in multiple experimental systems\",\n      \"pmids\": [\"17210790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PTB represses PTBP2 (nPTB) exon 10 splicing, causing nonproductive mRNA subject to nonsense-mediated decay; upon PTB knockdown, nPTB is upregulated via increased exon 10 inclusion, demonstrating cross-regulation between PTB and PTBP2 through nonproductive alternative splicing. PTBP2 and PTB have a large degree of functional overlap in splicing repression.\",\n      \"method\": \"Quantitative proteomics of HeLa cells after PTB knockdown, siRNA double knockdown of PTB and nPTB, RT-PCR of alternative splicing events\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — quantitative proteomics plus genetic knockdown with splicing readout, replicated across multiple target exons\",\n      \"pmids\": [\"17679092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PTBP1 and PTBP2 repress splicing of PSD-95 (Dlg4) exon 18; this repression leads to premature translation termination and nonsense-mediated mRNA decay of Psd-95 transcripts during early neural development. Sequential downregulation of first PTBP1 and then PTBP2 during embryonic development allows exon 18 inclusion and PSD-95 protein expression required for synapse maturation.\",\n      \"method\": \"RT-PCR splicing assays, re-expression of PTBP1/PTBP2 in differentiated neurons, electrophysiology and synaptic marker analysis in mouse embryonic brain\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function and re-expression experiments in neurons with defined molecular (NMD) and cellular (synapse maturation) phenotypes, multiple orthogonal methods\",\n      \"pmids\": [\"22246437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Ptbp2 binds pyrimidine-rich sequences upstream of and/or within alternative exons to inhibit adult-specific alternative splicing in neuronal progenitors; Ptbp2-null mice show aberrant neuronal progenitor polarity, premature neurogenesis, and reduced progenitor pools, identifying a role for Ptbp2 in neurogenesis through repression of exons encoding proteins associated with cell fate, proliferation, and the actin cytoskeleton.\",\n      \"method\": \"HITS-CLIP in developing mouse neocortex, splicing-sensitive microarrays, Ptbp2 knockout mouse (two independent strains), histological analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — HITS-CLIP providing genome-wide binding map combined with knockout mouse and splicing microarrays, two independent null strains\",\n      \"pmids\": [\"22802532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PTBP2 controls a program of embryonic alternative splicing that temporarily represses adult protein isoforms (affecting neurite growth, pre- and post-synaptic assembly, synaptic transmission) until final neuronal maturation; depletion of PTBP2 causes precocious expression of adult isoforms in embryonic cortex, leading to failure of neuronal maturation and death.\",\n      \"method\": \"Ptbp2 conditional knockout mouse, transcriptome-wide RNA-seq and splicing analysis, cultured neuron viability and maturation assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with genome-wide splicing analysis and defined cellular phenotype (maturation failure, cell death), multiple orthogonal methods\",\n      \"pmids\": [\"24448406\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PTBP2 physically interacts with the cytidine deaminase AID (identified by proteomic screen using in vivo biotinylation of AID) and promotes binding of AID to transcribed switch-region DNA; shRNA-mediated knockdown of PTBP2 in B cells decreases AID binding to switch regions and considerably impairs immunoglobulin class-switch recombination.\",\n      \"method\": \"In vivo biotinylation proteomic screen, co-immunoprecipitation, shRNA knockdown of PTBP2 in B cells, ChIP for AID at switch regions, CSR assay\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proteomic interaction screen plus functional knockdown with defined molecular (AID-DNA binding) and cellular (CSR) phenotypes, multiple orthogonal methods in single lab\",\n      \"pmids\": [\"21186367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PTBP1 exhibits greater splicing repression activity than PTBP2 per unit protein on target exons; chimera analysis identified that multiple segments of PTBP1 (RRM1, the linker between RRM2-RRM3, and RRM2) contribute to higher repression activity. RRM2 of PTBP1 increases repression potentially via stronger binding to the cofactor Raver1.\",\n      \"method\": \"In vivo coexpression splicing assay, in vitro splicing assay, PTBP1/PTBP2 chimeric protein constructs, Raver1 binding assays\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro splicing assay with chimeric proteins and domain-swap mutagenesis, two independent assay systems (in vivo and in vitro)\",\n      \"pmids\": [\"27288314\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PTBP1 and PTBP2 repress nonconserved cryptic exons using CU microsatellites as binding elements, establishing them as members of a family of cryptic exon repressors. This activity is distinct from TDP-43, which uses UG microsatellites.\",\n      \"method\": \"RNA-seq analysis after PTBP1/PTBP2 knockdown, identification of cryptic exon inclusion events, motif analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knockdown combined with genome-wide RNA-seq and motif analysis, but single lab and no in vitro reconstitution\",\n      \"pmids\": [\"27681424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"A PTBP1 knockin allele can rescue forebrain-specific but not pan-neuronal Ptbp2 knockout, demonstrating both redundant and distinct functional roles. Despite similar RNA binding across the transcriptome (shown by CLIP), many developmentally regulated exons show different sensitivities to PTBP1 vs. PTBP2, indicating differential activity does not derive from differential RNA binding but likely from cofactor interactions.\",\n      \"method\": \"Ptbp1 knockin mouse bred to Ptbp2 knockout, CLIP-seq comparing RNA binding, splicing-sensitive assays across brain regions\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis via knockin/knockout mouse combined with genome-wide CLIP-seq, rigorous in vivo phenotypic comparison\",\n      \"pmids\": [\"27926877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PTBP2 governs axonogenesis-associated alternative splicing in cortical neurons; its cortical depletion prematurely induces axonogenesis-associated splicing and specifically impairs axon formation in vitro and in vivo. PTBP2-controlled splicing of Shtn1 determines SHTN1's capacity to regulate actin interaction, polymerization, and axon growth; precocious Shtn1 isoform switching contributes to disorganized axon formation in Ptbp2-/- neurons.\",\n      \"method\": \"Transcriptome profiling of primary cortical neurons, PTBP2 conditional knockout mouse, in vitro axon formation assays, Shtn1 isoform functional characterization including actin binding/polymerization assays\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO in vivo plus functional isoform characterization (actin assays) plus transcriptome-wide profiling, multiple orthogonal methods\",\n      \"pmids\": [\"30733148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Ptbp2 controls a network of alternatively spliced genes involved in cell adhesion, migration, and polarity in spermatogenic cells; Ptbp2 ablation in germ cells results in disorganization of F-actin cytoskeleton in Sertoli cells, demonstrating that PTBP2-regulated alternative splicing is required for germ-Sertoli cell communication during spermatogenesis.\",\n      \"method\": \"Germ cell-specific Ptbp2 conditional knockout mouse, RNA-seq, splicing analysis, histology, F-actin staining\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with genome-wide splicing analysis and defined cellular phenotype (F-actin disorganization in Sertoli cells), multiple methods\",\n      \"pmids\": [\"28636946\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Ptbp2 is essential for spermatogenesis; Ptbp2 ablation results in germ cell loss due to increased apoptosis of meiotic spermatocytes and postmeiotic arrest of spermatid differentiation, and Ptbp2 is required for alternative splicing regulation in the testis in a tissue-specific manner (not all Ptbp2-sensitive exons in brain are also sensitive in testis).\",\n      \"method\": \"Ptbp2 knockout mouse, dual fluorescence flow cytometry of germ cells, histology, RT-PCR of alternative splicing events in brain vs. testis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse with specific cellular phenotype and tissue-comparative splicing analysis, multiple orthogonal methods\",\n      \"pmids\": [\"26391954\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Knockdown of PTBP2 (alone or combined with PTBP1) in glioma cell lines slows cell proliferation, inhibits cell migration, and increases cell adhesion to fibronectin and vitronectin.\",\n      \"method\": \"shRNA knockdown of PTBP1 and/or PTBP2 in U251 and LN229 glioma cell lines, proliferation assays, migration assays, adhesion assays\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KD with defined cellular phenotypes, two cell lines, but no pathway placement beyond PTBP2 removal\",\n      \"pmids\": [\"19506066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PTBP1 and PTBP2 bind to an exonic splicing suppressor in SRSF3 exon 4 and inhibit its inclusion, resulting in overexpression of full-length functional SRSF3 in oral squamous cell carcinoma cells; SRSF3, in turn, promotes PTBP2 expression, establishing a feed-forward loop.\",\n      \"method\": \"RT-PCR splicing assays, overexpression and knockdown of PTBP1/PTBP2, luciferase/minigene assays, RNA binding analysis in OSCC cells\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional knockdown/overexpression with splicing readout and reciprocal regulation demonstrated, single lab\",\n      \"pmids\": [\"26416554\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MALAT1 lncRNA binds to SFPQ, thereby releasing PTBP2 from the SFPQ/PTBP2 complex; the increased free PTBP2 promotes colorectal cancer cell proliferation and migration.\",\n      \"method\": \"Co-immunoprecipitation of SFPQ/PTBP2 complex, RNA pulldown for MALAT1-SFPQ interaction, overexpression/knockdown in CRC cells and nude mouse xenografts\",\n      \"journal\": \"British journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP for complex, functional overexpression/KD with proliferation and migration phenotypes, in vivo xenograft, single lab\",\n      \"pmids\": [\"25025966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Mass spectrometry analysis identified distinct phosphorylation modifications in PTBP2 located in the unstructured N-terminal, Linker 1, and Linker 2 regions (not present in PTBP1), and acetylation modifications including lysine residues in the nuclear localization sequence of PTBP2.\",\n      \"method\": \"Mass spectrometry analysis of post-translational modifications on PTBP1 and PTBP2 under splicing reaction conditions\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct MS identification of PTMs on purified proteins, but functional consequences of specific modifications not fully established in this study\",\n      \"pmids\": [\"29851470\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"hnRNPH1 recruits PTBP2 (and SRSF3) to modulate alternative splicing in germ cells; conditional knockout of Hnrnph1 in spermatogenic cells causes abnormal splicing events affecting meiosis and germ-Sertoli communication genes.\",\n      \"method\": \"Co-immunoprecipitation of hnRNPH1-PTBP2 complex, conditional Hnrnph1 knockout mouse, RNA-seq splicing analysis, histology\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP establishing protein-protein interaction plus functional KO with splicing phenotype, single lab\",\n      \"pmids\": [\"35739118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PTBP2 has a cytosolic role in axon growth in motoneurons: cytoplasmic Ptbp2 binds the 3' UTR of Hnrnpr mRNA and promotes its axonal localization and local translation via association with ribosomes in a manner dependent on translation factor eIF5A2; depletion of cytosolic Ptbp2 reduces axonal Hnrnpr mRNA localization and hnRNP R synthesis, causing defective axon growth.\",\n      \"method\": \"Subcellular fractionation and live imaging for cytosolic/axonal Ptbp2 localization, CLIP for Ptbp2-Hnrnpr mRNA interaction, ribosome association assays, eIF5A2 interaction, conditional depletion of cytosolic Ptbp2 with axon growth phenotype readout\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (CLIP, fractionation, ribosome association, functional rescue) establishing a cytosolic mechanism distinct from nuclear splicing role\",\n      \"pmids\": [\"37438340\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PTBP2 binding to SYNGAP1 mRNA promotes alternative splicing and nonsense-mediated decay of SYNGAP1; antisense oligonucleotides that disrupt PTBP2 binding sites redirect splicing and increase SYNGAP1 mRNA and protein expression in human iPSC-derived neurons and in SYNGAP1 haploinsufficient patient-derived neurons.\",\n      \"method\": \"CLIP-seq in human brain tissue and iPSC-neurons to map PTBP2 binding sites, ASO-mediated disruption of PTBP2 binding, RT-PCR and western blot for SYNGAP1 isoforms/expression, patient-derived iPSC-neuron experiments\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide CLIP-seq plus ASO functional perturbation in human neurons and patient-derived cells, multiple orthogonal methods\",\n      \"pmids\": [\"37149717\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"KIS kinase phosphorylates PTBP2, causing its dissociation from co-regulators Matrin3 and hnRNPM and hindering the RNA-binding capability of the complex; KIS and PTBP2 have opposing functional interactions in synaptic spine emergence and maturation.\",\n      \"method\": \"In vitro kinase assay showing KIS phosphorylates PTBP2, co-immunoprecipitation of PTBP2-Matrin3-hnRNPM complex before/after phosphorylation, genome-wide exon usage profiling in neurons, spine morphology assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — kinase assay (Tier 1) plus Co-IP, genome-wide splicing, and functional spine assays, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"38597390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Unstructured linker regions (Linker 1 and Linker 2) and the N-terminal region of PTBP2 play a role in its differential splicing activity compared to PTBP1; phosphorylation in these unstructured regions alters their physical properties as shown by molecular dynamics, and hybrid PTBP1-PTBP2 constructs with PTBP1 linker regions show altered splicing repression activity.\",\n      \"method\": \"Hybrid PTBP1-PTBP2 chimeric protein constructs assayed in splicing assays, molecular dynamics simulation of phosphorylated unstructured regions, evolutionary conservation bioinformatics analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — chimeric protein splicing assay plus MD simulation, single lab; functional link of phosphorylation to splicing activity not directly demonstrated by mutagenesis\",\n      \"pmids\": [\"38336291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PTBP2 binds to the 3' UTR of BNIP3 mRNA and stabilizes its expression; Ptbp2 knockout in CML cells decreases BNIP3 levels and impairs autophagy (measured by LC3-II in bafilomycin-treated cells), and re-expression of BNIP3 in Ptbp2-KO cells restores the autophagy phenotype.\",\n      \"method\": \"RIP-seq identifying PTBP2-BNIP3 3'UTR interaction, Ptbp2 knockout CML cell lines, LC3-II western blot as autophagy readout, BNIP3 rescue experiment, subcutaneous xenograft and tail vein engraftment in NOD/SCID mice\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RIP-seq plus KO/rescue with defined molecular and cellular phenotypes, single lab\",\n      \"pmids\": [\"40113750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"PTBP2 binds to the 3' UTR of DNA polymerase kappa (Polk) mRNA, stabilizing its expression; Ptbp2 knockout reduces Polk levels and increases DNA damage (comet assay, γH2AX foci) upon hydroxyurea treatment, which is rescued by Polk re-expression. POLK interacts with MRE11 of the MRN complex to regulate ATM-CHK2 signaling.\",\n      \"method\": \"RIP-seq (3' UTR binding), Ptbp2 KO CML cell lines and patient samples, comet assay and γH2AX foci, Polk rescue experiment, co-immunoprecipitation of POLK-MRE11, sister chromatid exchange and BrdU incorporation assays\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RIP-seq plus KO/rescue with DNA damage phenotype and Co-IP for POLK-MRE11 interaction, single lab\",\n      \"pmids\": [\"41667423\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Crystal and solution structures of the C-terminal domain of nPTB (nPTB34, containing RRMs 3 and 4) reveal that RRMs 3 and 4 interact with each other to form a stable unit with RNA-binding surfaces on opposite sides facing away from each other, similar to PTB34; amino acid differences are located on exposed β-sheet surfaces and loops, likely modulating RNA interactions.\",\n      \"method\": \"X-ray crystallography and NMR solution structure determination of nPTB RRMs 3-4\",\n      \"journal\": \"PeerJ\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal and solution structures determined, structural basis for RNA binding established, single lab\",\n      \"pmids\": [\"24688880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Under in vitro splicing conditions, PTBP2 interacts with a distinct set of proteins compared to PTBP1; PTBP2 does not interact with many mRNA processing/splicing regulators that PTBP1 does, and both proteins interact with chromatin remodeling and transcription regulators. The study identified potential 'writer' and 'eraser' enzymes for PTM modifications on PTBP2.\",\n      \"method\": \"In vitro splicing reactions with HeLa nuclear extract, mass spectrometry of co-precipitated proteins for PTBP1 vs. PTBP2\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — MS-based interactome under defined splicing conditions, but single pulldown approach without reciprocal validation, single lab\",\n      \"pmids\": [\"35113929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PTBP2 binding to SYNGAP1 mRNA promotes alternative splicing and nonsense-mediated decay of SYNGAP1. PTBP2 prevents IRF9 alternative splicing and upregulates STAT1 to stimulate CCL5 secretion and IFN-stimulated gene factor-dependent type I interferon secretion in neuroblastoma cells, inducing monocyte/macrophage chemotaxis and sustaining proinflammatory monocyte phenotype.\",\n      \"method\": \"PTBP2 overexpression/knockdown in neuroblastoma cells, RT-PCR for IRF9 splicing, western blot for STAT1, ELISA for CCL5/IFN, monocyte chemotaxis and polarization assays\",\n      \"journal\": \"Research (Washington, D.C.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional splicing and downstream signaling assays with defined phenotypic readouts, single lab\",\n      \"pmids\": [\"37040518\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The lncRNA Rbakdn binds to Ptbp2 protein and stabilizes it against ubiquitin-mediated degradation; Rbakdn knockdown leads to decreased Ptbp2 levels through the ubiquitination degradation pathway.\",\n      \"method\": \"RNA immunoprecipitation (Ribotrap + co-IP), Rbakdn knockdown in vitro and intratesticular injection in mice, ubiquitination assay for Ptbp2 degradation\",\n      \"journal\": \"Frontiers in genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — RNA-protein interaction by RIP plus ubiquitination assay, functional KD with phenotype, but single lab and mechanistic evidence is partially indirect\",\n      \"pmids\": [\"34707642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PTBP2 binds to the lncRNA Tesra in testicular germ cells and is required for Tesra-mediated transcriptional activation of Prss42/Tessp-2; knockdown of PTBP2 significantly decreases Prss42/Tessp-2 promoter activity in an in vitro reporter system.\",\n      \"method\": \"Ribotrap assay followed by LC-MS/MS to identify Tesra-binding proteins, RNA immunoprecipitation confirming PTBP2-Tesra association, Tet-on reporter system for Prss42/Tessp-2 promoter activity, PTBP2 knockdown\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — MS-based interaction identification plus RIP and functional reporter assay, single lab, non-canonical role (transcriptional co-activation via lncRNA)\",\n      \"pmids\": [\"37858745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Human nPTB (PTBP2) expression is severely limited by its extremely suboptimal codon content (high proportion of A/U at third codon position), resulting in ~1–3% the expression level of PTB despite similar mRNA levels and 74% amino acid identity; codon optimization restores expression to PTB-equivalent levels and confirms PTBP2 acts as a splicing repressor.\",\n      \"method\": \"Transfection of native vs. codon-optimized nPTB constructs, western blot, in vivo and in vitro translation assays, splicing repression assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — codon optimization rescue experiment with quantitative protein expression and functional splicing assays, single lab\",\n      \"pmids\": [\"18335065\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Smn (survival motoneuron protein) is an interactor of Ptbp2 in cytosolic compartments of motoneurons; Smn depletion reduces Ptbp2 levels specifically in axons (not somata), and re-expression of Ptbp2 in axons rescues defects in axon elongation and growth cone maturation in Smn-deficient motoneurons.\",\n      \"method\": \"Co-immunoprecipitation of Smn-Ptbp2 in motoneuron cytosolic fractions, subcellular fractionation and immunofluorescence for axonal Ptbp2 levels in Smn-KD motoneurons, lentiviral re-expression of Ptbp2 in axons, axon growth and growth cone assays\",\n      \"journal\": \"Frontiers in molecular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus subcellular fractionation plus rescue experiment, single lab, single study\",\n      \"pmids\": [\"39246602\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PTBP2 (nPTB/brPTB) is a neuronal RNA-binding protein that acts primarily as a splicing repressor by binding pyrimidine-rich sequences in pre-mRNAs to inhibit inclusion of adult-specific and tissue-specific exons; it is sequentially expressed after PTBP1 during neural development (with miR-133 targeting its 3' UTR to regulate expression) and controls developmental programs essential for neuronal maturation, axonogenesis, and synapse development, while also functioning in spermatogenesis and immunoglobulin class-switch recombination. Beyond its nuclear splicing role, cytosolic PTBP2 promotes axon growth by binding Hnrnpr mRNA and facilitating its axonal localization and local translation via eIF5A2-dependent ribosome association. Its differential activity from the paralog PTBP1 is determined by multiple protein domains (particularly linker regions and RRM1) and distinct post-translational phosphorylation modifications, and its activity can be modulated by cofactors including Raver1, Matrin3, and hnRNPM, the last two being released upon phosphorylation by the kinase KIS.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PTBP2 (nPTB/brPTB) is a neuronal pyrimidine-tract RNA-binding protein that acts as a sequence-specific splicing repressor, binding pyrimidine-rich elements upstream of or within alternative exons to enforce embryonic and tissue-specific splicing programs [#3]. Across the developing nervous system it temporarily suppresses adult-specific protein isoforms governing neurite growth, pre- and post-synaptic assembly, and synaptic transmission, so that its loss causes precocious adult isoform expression, failed neuronal maturation, and cell death [#4]; mechanistically this includes repression of PSD-95 (Dlg4) exon 18, which generates an NMD-targeted transcript until PTBP2 is downregulated [#2], and control of axonogenesis-associated splicing such as the Shtn1 isoform switch that tunes actin polymerization and axon formation [#9]. PTBP2 operates in a developmental relay with its paralog PTBP1, which represses PTBP2 exon 10 to produce an NMD substrate; the two proteins bind RNA similarly genome-wide yet differ in repression activity, a difference attributable not to differential binding but to protein domains—RRM1, RRM2, and the unstructured N-terminal and linker regions—and to cofactor recruitment [#1, #8, #6, #20]. Its splicing output is modulated by associated regulators including Matrin3 and hnRNPM, which dissociate upon phosphorylation by the kinase KIS, coupling PTBP2 activity to synaptic spine maturation [#19]. Beyond the nucleus, cytosolic PTBP2 binds the 3' UTR of Hnrnpr mRNA and drives its axonal localization and eIF5A2-dependent local translation to support axon growth [#17]. PTBP2 also functions outside the nervous system: it is required for spermatogenesis, where it regulates a splicing network controlling germ-Sertoli communication and F-actin organization [#10, #11], and it promotes immunoglobulin class-switch recombination by interacting with AID and enhancing its binding to switch-region DNA [#5]. In disease, ASO-mediated disruption of PTBP2 binding to SYNGAP1 mRNA redirects splicing to increase SYNGAP1 expression in patient-derived neurons, defining a therapeutic strategy for SYNGAP1 haploinsufficiency [#18].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Established that PTBP2 protein levels are themselves regulated, both by miR-133 acting on its 3' UTR during muscle differentiation and by PTBP1-driven nonproductive splicing of its own exon 10, explaining how PTBP2 abundance is dynamically controlled.\",\n      \"evidence\": \"Luciferase 3' UTR reporters with MRE mutagenesis and miR-133 gain/loss in C2C12 cells; quantitative proteomics and double siRNA knockdown with splicing readouts in HeLa cells\",\n      \"pmids\": [\"17210790\", \"17679092\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address PTBP2's own splicing target spectrum in neurons\", \"Functional redundancy with PTBP1 quantified only on a subset of exons\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Resolved why PTBP2 protein is far less abundant than PTBP1 despite high identity, showing its expression is throttled by suboptimal codon content and confirming PTBP2 is a bona fide splicing repressor.\",\n      \"evidence\": \"Transfection of native vs codon-optimized nPTB constructs with translation and splicing repression assays\",\n      \"pmids\": [\"18335065\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological selective advantage of codon-limited expression not tested in vivo\", \"Single-lab observation\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined PTBP2's genome-wide binding mode and developmental function, showing it binds pyrimidine-rich sequences to repress adult exons and is required for neuronal progenitor polarity, proper neurogenesis timing, and PSD-95 expression for synapse maturation.\",\n      \"evidence\": \"HITS-CLIP in mouse neocortex, splicing microarrays and Ptbp2-null mice; RT-PCR splicing and re-expression with electrophysiology\",\n      \"pmids\": [\"22802532\", \"22246437\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cofactors mediating exon-specific repression not identified\", \"Distinction from PTBP1 binding not yet resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed PTBP2 maintains an embryonic splicing program that suppresses adult isoforms until terminal neuronal maturation, with its depletion causing precocious maturation failure and death—establishing PTBP2 as a developmental timing switch.\",\n      \"evidence\": \"Ptbp2 conditional knockout mouse with transcriptome-wide RNA-seq and neuron viability/maturation assays\",\n      \"pmids\": [\"24448406\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific isoform switches driving maturation failure not individually dissected here\", \"Upstream signals controlling PTBP2 downregulation timing unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Determined the basis for differential PTBP1 vs PTBP2 activity, showing similar genome-wide RNA binding but distinct repression strengths attributable to specific RRM and linker segments and cofactor interactions, and that both repress cryptic exons via CU microsatellites.\",\n      \"evidence\": \"PTBP1/PTBP2 chimeric protein splicing assays and Raver1 binding; Ptbp1 knockin/Ptbp2 knockout mice with CLIP-seq; RNA-seq motif analysis after knockdown\",\n      \"pmids\": [\"27288314\", \"27926877\", \"27681424\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of cofactors conferring exon-specific differential sensitivity not fully defined\", \"Cryptic exon repression study single-lab without reconstitution\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Linked PTBP2 splicing control to axon formation specifically, identifying Shtn1 isoform regulation as a mechanism by which PTBP2 prevents premature axonogenesis-associated splicing.\",\n      \"evidence\": \"Conditional knockout mouse, primary cortical neuron transcriptomics, in vitro axon assays, Shtn1 actin-binding/polymerization characterization\",\n      \"pmids\": [\"30733148\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of Shtn1 vs other targets to axon phenotype not quantified\", \"Mechanism timing of PTBP2 loss during axonogenesis not detailed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Revealed a cytosolic, splicing-independent function for PTBP2 in axon growth, binding Hnrnpr mRNA to drive its axonal localization and eIF5A2-dependent local translation.\",\n      \"evidence\": \"Subcellular fractionation, live imaging, CLIP, ribosome association and eIF5A2 interaction assays, conditional cytosolic Ptbp2 depletion in motoneurons\",\n      \"pmids\": [\"37438340\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"What partitions PTBP2 between nucleus and cytoplasm not established\", \"Full set of cytosolic mRNA cargos beyond Hnrnpr unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstrated therapeutic targetability of PTBP2-mediated splicing, showing ASO disruption of PTBP2 binding to SYNGAP1 mRNA redirects splicing and raises SYNGAP1 expression in patient-derived neurons.\",\n      \"evidence\": \"CLIP-seq in human brain and iPSC-neurons, ASO perturbation, RT-PCR/western and SYNGAP1-haploinsufficient patient iPSC-neuron experiments\",\n      \"pmids\": [\"37149717\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo efficacy and durability of ASO approach not tested\", \"Off-target effects on other PTBP2 splicing events not characterized\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected post-translational regulation to PTBP2 function, showing KIS kinase phosphorylates PTBP2 to dissociate Matrin3 and hnRNPM and impair complex RNA binding, with opposing roles in synaptic spine maturation.\",\n      \"evidence\": \"In vitro kinase assay, Co-IP of PTBP2-Matrin3-hnRNPM before/after phosphorylation, genome-wide exon usage and spine morphology assays\",\n      \"pmids\": [\"38597390\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific phosphosites required for dissociation not pinpointed by mutagenesis here\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended PTBP2's role to spermatogenesis, showing it regulates a splicing network controlling germ-Sertoli communication and F-actin organization and is essential for germ cell survival and spermatid differentiation.\",\n      \"evidence\": \"Germ cell-specific and global Ptbp2 knockout mice, RNA-seq, histology, F-actin staining, flow cytometry\",\n      \"pmids\": [\"28636946\", \"26391954\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific determinants of which exons are PTBP2-sensitive in testis vs brain unknown\", \"Direct targets driving the F-actin phenotype not individually validated\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified PTBP2's mechanistic basis for differential RNA binding through structural characterization of its C-terminal RRMs and showed activity can be modulated by sequestration in complexes such as SFPQ.\",\n      \"evidence\": \"Crystal and NMR structures of nPTB RRMs 3-4; Co-IP of SFPQ/PTBP2 and MALAT1 RNA pulldown with CRC proliferation/migration phenotypes\",\n      \"pmids\": [\"24688880\", \"25025966\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structure of full-length PTBP2 RNA complex not solved\", \"SFPQ/MALAT1 axis demonstrated in cancer cells only, single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Documented mRNA-stabilizing functions of PTBP2 in cancer cells, binding 3' UTRs of BNIP3 and Polk to support autophagy and limit DNA damage, broadening its role beyond splicing repression.\",\n      \"evidence\": \"RIP-seq, Ptbp2 KO CML cell lines and patient samples, rescue experiments, LC3-II/autophagy and comet/γH2AX DNA damage readouts, xenografts\",\n      \"pmids\": [\"40113750\", \"41667423\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of 3' UTR-mediated stabilization not resolved\", \"Generalizability beyond CML cells untested, single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PTBP2 is partitioned and switched between its nuclear splicing-repressor role, cytosolic mRNA-localization/stabilization roles, and non-canonical transcriptional and immune functions, and which cofactors and modifications dictate each, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking phosphorylation/acetylation state to subcellular function\", \"Determinants of nuclear vs cytoplasmic localization unknown\", \"Functional consequences of individual PTMs not established by mutagenesis\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [3, 17, 18, 21, 22, 23]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [3, 4, 2, 9]},\n      {\"term_id\": \"GO:0045182\", \"supporting_discovery_ids\": [17]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [19, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 4, 15]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [17, 29]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [3, 4, 2, 9]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 4, 9, 11, 10]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [2, 9, 19, 18]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [\"SFPQ/PTBP2 complex\", \"PTBP2-Matrin3-hnRNPM complex\"],\n    \"partners\": [\"PTBP1\", \"AID\", \"Matrin3\", \"hnRNPM\", \"SFPQ\", \"hnRNPH1\", \"Smn\", \"eIF5A2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}