{"gene":"PABPC4","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":1995,"finding":"iPABP (PABPC4) was identified as an inducible poly(A)-binding protein predominantly localized to the cytoplasm, with expression upregulated following T-cell activation. Unlike constitutively expressed PABP, iPABP mRNA levels are rapidly induced upon T-cell activation and are highly expressed in heart and skeletal muscle tissue.","method":"Molecular cloning, Northern blot, subcellular fractionation/immunofluorescence","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct cloning, localization by fractionation, expression characterization in multiple tissues; single lab but orthogonal methods","pmids":["8524242"],"is_preprint":false},{"year":1997,"finding":"APP-1 (PABPC4) was identified as an activated-platelet protein expressed on the platelet surface upon stimulation by thrombin, A23187, or ADP. Recombinant APP-1 protein specifically binds poly(A)-Sepharose, demonstrating poly(A) RNA-binding activity mediated through four RNA recognition motif domains.","method":"Expression cloning with monoclonal antibody, poly(A)-Sepharose binding assay, Northern analysis","journal":"European journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro binding assay with recombinant protein, monoclonal antibody-based expression cloning; single lab, two orthogonal methods","pmids":["9030741"],"is_preprint":false},{"year":2004,"finding":"iPABP (PABPC4) binds AU-rich RNA with high affinity and shows less discrimination between AU-rich and poly(A) RNA than PABP1 (affinities differing by only twofold), suggesting PABPC4 may interact with RNA regions beyond the poly(A) tail in cells.","method":"In vitro RNA binding affinity measurements (electrophoretic mobility shift / filter binding), recombinant protein","journal":"European journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro binding assay with quantitative Kd measurements; single lab but rigorous biochemical characterization","pmids":["14717712"],"is_preprint":false},{"year":2005,"finding":"Tob anti-proliferative protein physically associates with the C-terminal region of iPABP (PABPC4), and this interaction abrogates iPABP-enhanced translation of IL-2 mRNA in vitro. iPABP enhances translation of IL-2 mRNA in a manner requiring the 3'UTR and poly(A) sequences. Tob was co-immunoprecipitated with iPABP in human T cells after anergic stimulation.","method":"Co-immunoprecipitation, GST pull-down, in vitro translation assay","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of translational enhancement and Tob-mediated abrogation, reciprocal Co-IP in T cells, GST pull-down identifying C-terminal binding region; multiple orthogonal methods in single study","pmids":["15676026"],"is_preprint":false},{"year":2010,"finding":"PABPC4 (and PABPC1) are required for the posttranscriptional stabilization of hTERT mRNA and telomerase activity in HPV16 E6-expressing keratinocytes. Overexpression of PABPC4 increased hTERT mRNA levels and telomerase activity, while knockdown decreased them. This effect was dependent on the PAM2 motif of the NFX1-123 co-factor, which bridges HPV16 E6 and PABPCs. Knockdown had no effect in HPV-negative C33A cells.","method":"siRNA knockdown, overexpression, qRT-PCR, telomerase activity assay (TRAP)","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function and gain-of-function with defined molecular readout (hTERT mRNA, telomerase activity); single lab, multiple orthogonal manipulations","pmids":["20943973"],"is_preprint":false},{"year":2014,"finding":"PABPC4 is expressed in erythroid cells and stabilizes a subset of erythroid mRNAs containing AU-rich motifs in their 3'UTRs, particularly when poly(A) tails are critically shortened. Selective depletion of PABPC4 in an erythroblast cell line inhibits terminal erythroid maturation with corresponding alterations in erythroid gene expression.","method":"RNA co-immunoprecipitation, siRNA knockdown, mRNA stability assays, motif analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function with defined cellular phenotype (impaired terminal erythroid maturation), RNA-binding characterization with AU-rich motif identification, multiple orthogonal methods in single study","pmids":["24469397"],"is_preprint":false},{"year":2018,"finding":"miR-192-5p suppresses PABPC4 expression, and suppression of miR-192-5p in HCC cells significantly increased PABPC4 levels and multiple cancer stem cell (CSC) populations and CSC-related features. The circuit from hypermethylation of the mir-192 promoter to increased PABPC4 was identified as a shared regulatory pathway in CSC+ HCC.","method":"miRNA overexpression/suppression, luciferase reporter, loss-of-function, functional CSC assays","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional experiments linking miR-192-5p to PABPC4 and CSC phenotype, but mechanism downstream of PABPC4 elevation is not fully resolved at molecular level; single lab","pmids":["30530815"],"is_preprint":false},{"year":2020,"finding":"The lncRNA RP11-286H15.1 binds to PABPC4 (nucleotides 620-750) and promotes its ubiquitination, reducing the stability of TRIM37 and CDC27 mRNAs, thereby repressing HCC progression.","method":"RNA pulldown, RNA immunoprecipitation (RIP), ubiquitination assay, FISH, Western blot","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding of lncRNA to PABPC4 demonstrated by pulldown and RIP with downstream mRNA stability readout; single lab, multiple orthogonal methods","pmids":["33259899"],"is_preprint":false},{"year":2021,"finding":"PABPC4 broadly inhibits coronavirus replication by interacting with the nucleocapsid (N) protein from eight CoVs across four genera, recruiting E3 ubiquitin ligase MARCH8/MARCHF8 to ubiquitinate the N protein, which is then recognized by cargo receptor NDP52/CALCOCO2 and delivered to autolysosomes for degradation via selective autophagy.","method":"Co-immunoprecipitation, overexpression/knockdown, viral replication assays, ubiquitination assay, autophagy inhibitor experiments","journal":"Microbiology spectrum","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP demonstrating interaction with N proteins from 8 CoVs, ubiquitination assay, cargo receptor identification, functional viral replication readout; multiple orthogonal methods and broad mechanistic dissection","pmids":["34612687"],"is_preprint":false},{"year":2021,"finding":"PABPC4 is identified as a substrate of the E3 ubiquitin ligase TRIM25 by a substrate-trapping approach. Knockdown of PABPC4 diminished TRIM25-mediated antiviral activity against alphaviruses, indicating PABPC4 ubiquitination by TRIM25 contributes to antiviral defense.","method":"TRIM25 catalytic mutant (R54P) substrate trapping, proteomics, siRNA knockdown, viral infection assay","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — substrate trapping with catalytic mutant and functional knockdown validation; single lab, multiple orthogonal methods","pmids":["36067236"],"is_preprint":false},{"year":2021,"finding":"TDP-43 LLPS ablation increased its association with PABPC4, RPS6, RPL7, and other translational factors in mouse brain neurons, resulting in globally enhanced protein synthesis. Physical interaction between LLPS-deficient TDP-43 and PABPC4 (along with other translational factors) requires a specific TDP-43 motif, deletion of which abolishes the translational impact.","method":"Co-immunoprecipitation, mouse knock-in model, metabolic labeling of protein synthesis, mutant TDP-43","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP from brain tissue, in vivo mouse model, motif deletion; single lab with in vivo genetic evidence","pmids":["34427634"],"is_preprint":false},{"year":2023,"finding":"PABPC4 interacts with nuclear receptor corepressor NCoR1, and silencing of PABPC4 increases ubiquitination and consequent degradation of NCoR1, leading to derepression of PPAR-regulated genes, increased oxygen consumption, mitochondria content, and reduced lactate production in C2C12 and MEF cells. PABPC4 protein content is markedly reduced under conditions that induce mitochondrial function/biogenesis.","method":"Co-immunoprecipitation, siRNA knockdown, ubiquitination assay, Seahorse oxygen consumption, gene expression analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — Co-IP identifying NCoR1 as binding partner, mechanistic dissection through ubiquitination assay and functional metabolic readouts, multiple orthogonal methods in single study","pmids":["37059182"],"is_preprint":false},{"year":2021,"finding":"PABPC4 was identified as the most enriched binding partner of circFAM134B via RNA pulldown and mass spectrometry. PABPC4 functions as an antagonist of nonsense-mediated mRNA decay (NMD), and circFAM134B acts as a sponge that competitively sequesters PABPC4, thereby releasing FAM134B mRNA to NMD-mediated decay.","method":"RNA pulldown, mass spectrometry, RNA immunoprecipitation (RIP), luciferase reporter, NMD reporter gene assay","journal":"Cell cycle","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding identified by pulldown/MS, functional NMD reporter assays; single lab, multiple orthogonal methods","pmids":["37603831"],"is_preprint":false},{"year":2021,"finding":"LncRNA Lnc-PCIR blocks PABPC4 proteasome-dependent ubiquitination degradation, and the resulting stabilized PABPC4 increases TAB3 mRNA stability in triple-negative breast cancer cells, activating the TNF-α/NF-κB pathway.","method":"RNA pulldown, RIP, Western blot, siRNA knockdown, mRNA stability assay","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct PABPC4-lncRNA interaction demonstrated by pulldown/RIP with mRNA stability and pathway readout; single lab","pmids":["34012913"],"is_preprint":false},{"year":2018,"finding":"PABPC4 interacts with LIX1L (a putative RNA-binding protein) as identified by MALDI-TOF/TOF mass spectrometry and RNA immunoprecipitation-sequencing in HEK-293 cells.","method":"Mass spectrometry, RNA immunoprecipitation-sequencing","journal":"Scientific reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — interactome-level identification without specific functional follow-up on the PABPC4-LIX1L interaction; single method for this specific interaction","pmids":["26310847"],"is_preprint":false},{"year":2021,"finding":"Sheep SERP1 and PABPC4 were identified as host target proteins of Orf virus ORF047 (L1R) by yeast two-hybrid screening, with interaction confirmed by Co-IP, suggesting PABPC4 involvement in viral mRNA translation and replication.","method":"Yeast two-hybrid, Co-immunoprecipitation","journal":"Virology journal","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP confirmation of yeast two-hybrid hit, no functional mechanistic follow-up on PABPC4 role","pmids":["33499896"],"is_preprint":false},{"year":2024,"finding":"PABPC4 is identified by RBPmap bioinformatics and functionally confirmed by siRNA depletion to be responsible for repressive activity of the HPV-1a late 3'UTR in keratinocytes, demonstrating a role for PABPC4 in papillomavirus late gene expression regulation.","method":"siRNA depletion, reporter gene assay, bioinformatics prediction","journal":"Biomedical reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — siRNA knockdown with reporter readout, single method for the specific functional claim, single lab","pmids":["39006509"],"is_preprint":false},{"year":2025,"finding":"PABPC4 inhibits SADS-CoV replication by targeting and degrading the N protein via selective autophagy. PABPC4 recruits MARCHF8 (E3 ubiquitin ligase) to ubiquitinate the N protein, which is then degraded via NDP52/CALCOCO2 cargo receptor, replicating the mechanism established for other coronaviruses.","method":"Co-immunoprecipitation, overexpression/knockdown, ubiquitination assay, viral replication assay","journal":"Veterinary sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway confirmed using Co-IP, ubiquitination assay, and functional viral readout, replicating prior coronavirus findings; single lab","pmids":["40266995"],"is_preprint":false},{"year":2025,"finding":"PABPC1 and PABPC4 are required for global mRNA stabilization during prolonged mitotic arrest. Depletion of PABPC1&4 disrupts poly(A)-tail length maintenance during mitosis and compromises the maintenance of mitotic arrest, demonstrating that mitotic transcriptome buffering is PABPC-dependent.","method":"siRNA depletion, poly(A)-tail length profiling, mitotic arrest assays, mRNA half-life measurements","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with poly(A) tail profiling and mitotic phenotype; preprint, single lab, multiple orthogonal methods","pmids":["41641701"],"is_preprint":false},{"year":2025,"finding":"PABPC4 (together with PABPC1) is required for Pumilio (PUM1/2)-mediated mRNA repression. PUMs physically associate with PABPC4, and in its absence, PUM target mRNAs bypass PUM-mediated control. Increasing PABPC concentration inhibits PUM activity in a concentration-dependent manner by protecting poly(A) from CCR4-NOT deadenylation.","method":"Co-immunoprecipitation, siRNA knockdown, mRNA stability assays, transcriptome analysis","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and loss-of-function with defined molecular readout; peer-reviewed, single lab, multiple orthogonal methods","pmids":["41641701"],"is_preprint":false},{"year":2025,"finding":"In Pabpc4 knockout mice, loss of PABPC4 is not lethal but affects birth weight, post-natal growth trajectories, survival, and red blood cell parameters (microcytic RBCs, altered RBC distribution width). The microcytic anemia phenotype is not red blood cell intrinsic, as shown by conditional genetic approaches.","method":"Knockout mouse generation, conditional genetics, haematological analysis, growth measurement","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo knockout with defined phenotypic readouts and conditional genetics to test cell-autonomy; preprint, single lab, multiple orthogonal approaches","pmids":[],"is_preprint":true},{"year":2023,"finding":"PABPC4 binds LINC00493 mRNA and facilitates its transfer to ribosomes for translation of the microprotein SMIM26 in renal cell carcinoma cells.","method":"RNA immunoprecipitation (RIP), ribosome fractionation, functional validation","journal":"EMBO reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — RIP demonstrates association but mechanistic detail of how PABPC4 facilitates LINC00493 translation is limited; single lab, indirect functional evidence","pmids":["37009826"],"is_preprint":false}],"current_model":"PABPC4 (iPABP/APP-1) is a cytoplasmic poly(A)-binding protein with four RNA recognition motifs that binds poly(A) tails and AU-rich RNA elements to regulate mRNA stability and translation; it enhances translation of specific mRNAs (e.g., IL-2) through its C-terminal domain (antagonized by Tob), protects subsets of deadenylated mRNAs from decay (including erythroid mRNAs and during mitotic arrest in a PABPC1/4-dependent manner), facilitates Pumilio-mediated mRNA repression via CCR4-NOT deadenylation, interacts with NCoR1 to regulate mitochondrial gene expression and metabolic phenotype, and exerts antiviral activity by recruiting the E3 ubiquitin ligase MARCHF8 to ubiquitinate coronavirus nucleocapsid proteins for selective autophagy-mediated degradation via the NDP52 cargo receptor."},"narrative":{"mechanistic_narrative":"PABPC4 (iPABP/APP-1) is a cytoplasmic poly(A)-binding protein with four RNA recognition motifs that regulates mRNA stability and translation, functioning broadly in poly(A)-tail protection and selective transcript control [PMID:9030741, PMID:14717712]. First identified as an inducible poly(A)-binding protein upregulated upon T-cell activation and abundant in heart and skeletal muscle [PMID:8524242], it binds both poly(A) and AU-rich RNA, discriminating between them only weakly and thereby engaging RNA regions beyond the poly(A) tail [PMID:14717712]. Through its C-terminal region PABPC4 enhances translation of IL-2 mRNA in a 3'UTR- and poly(A)-dependent manner, an activity abrogated when the antiproliferative protein Tob binds the same C-terminal region [PMID:15676026]. It stabilizes subsets of mRNAs bearing AU-rich 3'UTR motifs—including erythroid transcripts when poly(A) tails are critically shortened, where its depletion blocks terminal erythroid maturation [PMID:24469397]—and, redundantly with PABPC1, maintains poly(A)-tail length and global transcriptome stability during prolonged mitotic arrest [PMID:41641701]. PABPC4 protects poly(A) from CCR4-NOT deadenylation in a concentration-dependent manner, an activity required for Pumilio (PUM1/2)-mediated repression of target mRNAs [PMID:41641701]. Beyond translational control, PABPC4 binds the nuclear receptor corepressor NCoR1 and limits its ubiquitin-dependent degradation, thereby restraining PPAR-regulated mitochondrial gene expression and oxidative metabolism [PMID:37059182]. PABPC4 also exerts antiviral activity by interacting with coronavirus nucleocapsid proteins across multiple genera and recruiting the E3 ubiquitin ligase MARCHF8 to ubiquitinate them for NDP52/CALCOCO2-dependent selective autophagic degradation [PMID:34612687, PMID:40266995]. Knockout mice are viable but show altered growth, survival, and microcytic red blood cell parameters that are not red-cell intrinsic.","teleology":[{"year":1995,"claim":"Established PABPC4 as a distinct, inducible cytoplasmic poly(A)-binding protein rather than a constitutive housekeeping factor, raising the question of activity-dependent mRNA regulation.","evidence":"Molecular cloning, Northern blot, and subcellular fractionation/immunofluorescence in T cells and tissues","pmids":["8524242"],"confidence":"Medium","gaps":["No molecular target mRNAs identified at this stage","Inducibility mechanism not resolved"]},{"year":1997,"claim":"Confirmed that the protein binds poly(A) RNA through its four RRM domains, defining its biochemical activity.","evidence":"Expression cloning with monoclonal antibody and poly(A)-Sepharose binding of recombinant protein","pmids":["9030741"],"confidence":"Medium","gaps":["Surface expression on platelets not mechanistically explained","No in-cell RNA targets defined"]},{"year":2004,"claim":"Showed PABPC4 binds AU-rich RNA nearly as well as poly(A), implying it engages internal mRNA elements and not only the poly(A) tail.","evidence":"Quantitative in vitro RNA-binding affinity measurements with recombinant protein","pmids":["14717712"],"confidence":"Medium","gaps":["No cellular AU-rich targets identified in this study","Functional consequence of AU-rich binding untested"]},{"year":2005,"claim":"Defined a translational-enhancer function for PABPC4 on IL-2 mRNA and identified Tob as a C-terminal-binding regulator that switches off this activity.","evidence":"Co-IP in T cells, GST pull-down mapping the C-terminal region, and in vitro translation assays","pmids":["15676026"],"confidence":"High","gaps":["Generality beyond IL-2 mRNA not established","Structural basis of Tob/C-terminal interaction unresolved"]},{"year":2010,"claim":"Linked PABPC4 to posttranscriptional stabilization of hTERT mRNA in HPV16 E6 keratinocytes via the NFX1-123 PAM2 bridge, extending its role to viral oncogenesis.","evidence":"siRNA knockdown, overexpression, qRT-PCR, and telomerase (TRAP) assays","pmids":["20943973"],"confidence":"Medium","gaps":["Direct PABPC4 binding to hTERT mRNA not shown","Redundancy with PABPC1 not dissected"]},{"year":2014,"claim":"Demonstrated PABPC4 selectively stabilizes AU-rich erythroid mRNAs when poly(A) tails shorten, with a defined developmental phenotype upon depletion.","evidence":"RNA co-IP, siRNA knockdown, mRNA stability assays, and motif analysis in erythroblasts","pmids":["24469397"],"confidence":"High","gaps":["Mechanism of selective protection at short poly(A) unresolved","In vivo erythroid requirement not yet tested at this stage"]},{"year":2018,"claim":"Connected PABPC4 to cancer stem cell biology via a miR-192-5p/promoter-methylation circuit in hepatocellular carcinoma.","evidence":"miRNA overexpression/suppression, luciferase reporters, and functional CSC assays","pmids":["30530815"],"confidence":"Medium","gaps":["Molecular events downstream of PABPC4 elevation not resolved","Direct PABPC4 mRNA targets in CSCs unknown"]},{"year":2021,"claim":"Identified a broad antiviral mechanism whereby PABPC4 bridges coronavirus N proteins to MARCHF8-mediated ubiquitination and NDP52-dependent autophagic degradation.","evidence":"Co-IP across N proteins of eight CoVs, ubiquitination assays, autophagy inhibitor experiments, and viral replication readouts","pmids":["34612687"],"confidence":"High","gaps":["Determinants of N-protein recognition not mapped","Whether RNA binding is required for antiviral activity unknown"]},{"year":2021,"claim":"Showed PABPC4 is itself a regulated substrate of E3 ligases (TRIM25) and that this ubiquitination contributes to antiviral defense against alphaviruses.","evidence":"TRIM25 catalytic-mutant substrate trapping, proteomics, siRNA knockdown, and viral infection assays","pmids":["36067236"],"confidence":"Medium","gaps":["Functional consequence of PABPC4 ubiquitination on its RNA activity unresolved","Ubiquitination sites not mapped"]},{"year":2021,"claim":"Placed PABPC4 within neuronal translational control as an interactor of LLPS-deficient TDP-43 that contributes to enhanced global protein synthesis.","evidence":"Co-IP from brain tissue, mouse knock-in model, metabolic labeling, and motif-deletion mutants","pmids":["34427634"],"confidence":"Medium","gaps":["Direct vs indirect PABPC4-TDP-43 contact unclear","PABPC4-specific contribution within the multiprotein complex not isolated"]},{"year":2021,"claim":"Established PABPC4 as a target of multiple regulatory lncRNAs that tune its abundance and downstream mRNA fates in cancer.","evidence":"RNA pulldown, RIP, ubiquitination and mRNA-stability assays for RP11-286H15.1, Lnc-PCIR, and circFAM134B","pmids":["33259899","34012913","37603831"],"confidence":"Medium","gaps":["Whether these lncRNAs share a common PABPC4 interaction surface unknown","NMD-antagonist role mechanistically incomplete"]},{"year":2023,"claim":"Uncovered a non-RNA-stability role: PABPC4 binds NCoR1 and protects it from degradation, thereby restraining PPAR-driven mitochondrial biogenesis and oxidative metabolism.","evidence":"Co-IP, siRNA knockdown, ubiquitination assays, Seahorse oxygen consumption, and gene-expression analysis in C2C12/MEF cells","pmids":["37059182"],"confidence":"High","gaps":["How an RNA-binding protein stabilizes a corepressor mechanistically unclear","In vivo metabolic relevance not tested in this study"]},{"year":2025,"claim":"Defined PABPC4 (with PABPC1) as required for poly(A)-tail maintenance and global transcriptome buffering during prolonged mitotic arrest.","evidence":"siRNA depletion, poly(A)-tail length profiling, and mRNA half-life measurements (preprint)","pmids":["41641701"],"confidence":"Medium","gaps":["Relative contributions of PABPC4 vs PABPC1 not separated","Preprint, awaits peer review"]},{"year":2025,"claim":"Showed PABPC4 is required for Pumilio-mediated repression by concentration-dependent protection of poly(A) from CCR4-NOT deadenylation, integrating it into a defined repression pathway.","evidence":"Co-IP with PUM1/2, siRNA knockdown, mRNA stability assays, and transcriptome analysis","pmids":["41641701"],"confidence":"Medium","gaps":["Direct vs PUM-bridged poly(A) protection not fully resolved","Selectivity of PABPC4 vs PABPC1 in this context unclear"]},{"year":2025,"claim":"Provided in vivo genetic evidence that PABPC4 is non-essential for viability but influences growth, survival, and red-cell parameters non-cell-autonomously.","evidence":"Knockout and conditional mouse genetics with haematological and growth analysis (preprint)","pmids":[],"confidence":"Medium","gaps":["Tissue source of the non-intrinsic microcytic phenotype unidentified","Preprint, awaits peer review"]},{"year":null,"claim":"How PABPC4 achieves transcript selectivity and how its RNA-binding activity is mechanistically coupled to its protein-stabilizing and antiviral functions remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of PABPC4 on selected mRNAs or with NCoR1/N proteins","Functional separation of PABPC4 from PABPC1 across contexts incomplete","Determinants of AU-rich vs poly(A) target choice in cells unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[1,2,5]},{"term_id":"GO:0045182","term_label":"translation regulator activity","supporting_discovery_ids":[3]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[19]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[11]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[5,18,19]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[8,9,17]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[8,17]}],"complexes":[],"partners":["TOB1","NCOR1","MARCHF8","CALCOCO2","TRIM25","PUM1","PUM2","PABPC1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q13310","full_name":"Polyadenylate-binding protein 4","aliases":["Activated-platelet protein 1","APP-1","Inducible poly(A)-binding protein","iPABP"],"length_aa":644,"mass_kda":70.8,"function":"Binds the poly(A) tail of mRNA (PubMed:8524242). Binds to SMIM26 mRNA and plays a role in its post-transcriptional regulation (PubMed:37009826). May be involved in cytoplasmic regulatory processes of mRNA metabolism. Can probably bind to cytoplasmic RNA sequences other than poly(A) in vivo (By similarity)","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q13310/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PABPC4","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000090621","cell_line_id":"CID001762","localizations":[{"compartment":"cytoplasmic","grade":3}],"interactors":[{"gene":"PAIP1","stoichiometry":10.0},{"gene":"CTCF","stoichiometry":4.0},{"gene":"DDX6","stoichiometry":4.0},{"gene":"EIF3B","stoichiometry":4.0},{"gene":"EMC9","stoichiometry":4.0},{"gene":"GSPT1","stoichiometry":4.0},{"gene":"RPL4","stoichiometry":4.0},{"gene":"ATG13","stoichiometry":0.2},{"gene":"ATG4B","stoichiometry":0.2},{"gene":"ATXN2L","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001762","total_profiled":1310},"omim":[{"mim_id":"604679","title":"POLYADENYLATE-BINDING PROTEIN, CYTOPLASMIC, 1; PABPC1","url":"https://www.omim.org/entry/604679"},{"mim_id":"603407","title":"POLYADENYLATE-BINDING PROTEIN, CYTOPLASMIC, 4; PABPC4","url":"https://www.omim.org/entry/603407"},{"mim_id":"300407","title":"POLYADENYLATE-BINDING PROTEIN, CYTOPLASMIC, 5; PABPC5","url":"https://www.omim.org/entry/300407"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Cytosol","reliability":"Enhanced"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"pancreas","ntpm":338.9},{"tissue":"skeletal 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Unlike constitutively expressed PABP, iPABP mRNA levels are rapidly induced upon T-cell activation and are highly expressed in heart and skeletal muscle tissue.\",\n      \"method\": \"Molecular cloning, Northern blot, subcellular fractionation/immunofluorescence\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct cloning, localization by fractionation, expression characterization in multiple tissues; single lab but orthogonal methods\",\n      \"pmids\": [\"8524242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"APP-1 (PABPC4) was identified as an activated-platelet protein expressed on the platelet surface upon stimulation by thrombin, A23187, or ADP. Recombinant APP-1 protein specifically binds poly(A)-Sepharose, demonstrating poly(A) RNA-binding activity mediated through four RNA recognition motif domains.\",\n      \"method\": \"Expression cloning with monoclonal antibody, poly(A)-Sepharose binding assay, Northern analysis\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro binding assay with recombinant protein, monoclonal antibody-based expression cloning; single lab, two orthogonal methods\",\n      \"pmids\": [\"9030741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"iPABP (PABPC4) binds AU-rich RNA with high affinity and shows less discrimination between AU-rich and poly(A) RNA than PABP1 (affinities differing by only twofold), suggesting PABPC4 may interact with RNA regions beyond the poly(A) tail in cells.\",\n      \"method\": \"In vitro RNA binding affinity measurements (electrophoretic mobility shift / filter binding), recombinant protein\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro binding assay with quantitative Kd measurements; single lab but rigorous biochemical characterization\",\n      \"pmids\": [\"14717712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Tob anti-proliferative protein physically associates with the C-terminal region of iPABP (PABPC4), and this interaction abrogates iPABP-enhanced translation of IL-2 mRNA in vitro. iPABP enhances translation of IL-2 mRNA in a manner requiring the 3'UTR and poly(A) sequences. Tob was co-immunoprecipitated with iPABP in human T cells after anergic stimulation.\",\n      \"method\": \"Co-immunoprecipitation, GST pull-down, in vitro translation assay\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of translational enhancement and Tob-mediated abrogation, reciprocal Co-IP in T cells, GST pull-down identifying C-terminal binding region; multiple orthogonal methods in single study\",\n      \"pmids\": [\"15676026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PABPC4 (and PABPC1) are required for the posttranscriptional stabilization of hTERT mRNA and telomerase activity in HPV16 E6-expressing keratinocytes. Overexpression of PABPC4 increased hTERT mRNA levels and telomerase activity, while knockdown decreased them. This effect was dependent on the PAM2 motif of the NFX1-123 co-factor, which bridges HPV16 E6 and PABPCs. Knockdown had no effect in HPV-negative C33A cells.\",\n      \"method\": \"siRNA knockdown, overexpression, qRT-PCR, telomerase activity assay (TRAP)\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function and gain-of-function with defined molecular readout (hTERT mRNA, telomerase activity); single lab, multiple orthogonal manipulations\",\n      \"pmids\": [\"20943973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PABPC4 is expressed in erythroid cells and stabilizes a subset of erythroid mRNAs containing AU-rich motifs in their 3'UTRs, particularly when poly(A) tails are critically shortened. Selective depletion of PABPC4 in an erythroblast cell line inhibits terminal erythroid maturation with corresponding alterations in erythroid gene expression.\",\n      \"method\": \"RNA co-immunoprecipitation, siRNA knockdown, mRNA stability assays, motif analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function with defined cellular phenotype (impaired terminal erythroid maturation), RNA-binding characterization with AU-rich motif identification, multiple orthogonal methods in single study\",\n      \"pmids\": [\"24469397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"miR-192-5p suppresses PABPC4 expression, and suppression of miR-192-5p in HCC cells significantly increased PABPC4 levels and multiple cancer stem cell (CSC) populations and CSC-related features. The circuit from hypermethylation of the mir-192 promoter to increased PABPC4 was identified as a shared regulatory pathway in CSC+ HCC.\",\n      \"method\": \"miRNA overexpression/suppression, luciferase reporter, loss-of-function, functional CSC assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional experiments linking miR-192-5p to PABPC4 and CSC phenotype, but mechanism downstream of PABPC4 elevation is not fully resolved at molecular level; single lab\",\n      \"pmids\": [\"30530815\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The lncRNA RP11-286H15.1 binds to PABPC4 (nucleotides 620-750) and promotes its ubiquitination, reducing the stability of TRIM37 and CDC27 mRNAs, thereby repressing HCC progression.\",\n      \"method\": \"RNA pulldown, RNA immunoprecipitation (RIP), ubiquitination assay, FISH, Western blot\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding of lncRNA to PABPC4 demonstrated by pulldown and RIP with downstream mRNA stability readout; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"33259899\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PABPC4 broadly inhibits coronavirus replication by interacting with the nucleocapsid (N) protein from eight CoVs across four genera, recruiting E3 ubiquitin ligase MARCH8/MARCHF8 to ubiquitinate the N protein, which is then recognized by cargo receptor NDP52/CALCOCO2 and delivered to autolysosomes for degradation via selective autophagy.\",\n      \"method\": \"Co-immunoprecipitation, overexpression/knockdown, viral replication assays, ubiquitination assay, autophagy inhibitor experiments\",\n      \"journal\": \"Microbiology spectrum\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP demonstrating interaction with N proteins from 8 CoVs, ubiquitination assay, cargo receptor identification, functional viral replication readout; multiple orthogonal methods and broad mechanistic dissection\",\n      \"pmids\": [\"34612687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PABPC4 is identified as a substrate of the E3 ubiquitin ligase TRIM25 by a substrate-trapping approach. Knockdown of PABPC4 diminished TRIM25-mediated antiviral activity against alphaviruses, indicating PABPC4 ubiquitination by TRIM25 contributes to antiviral defense.\",\n      \"method\": \"TRIM25 catalytic mutant (R54P) substrate trapping, proteomics, siRNA knockdown, viral infection assay\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — substrate trapping with catalytic mutant and functional knockdown validation; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"36067236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TDP-43 LLPS ablation increased its association with PABPC4, RPS6, RPL7, and other translational factors in mouse brain neurons, resulting in globally enhanced protein synthesis. Physical interaction between LLPS-deficient TDP-43 and PABPC4 (along with other translational factors) requires a specific TDP-43 motif, deletion of which abolishes the translational impact.\",\n      \"method\": \"Co-immunoprecipitation, mouse knock-in model, metabolic labeling of protein synthesis, mutant TDP-43\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP from brain tissue, in vivo mouse model, motif deletion; single lab with in vivo genetic evidence\",\n      \"pmids\": [\"34427634\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PABPC4 interacts with nuclear receptor corepressor NCoR1, and silencing of PABPC4 increases ubiquitination and consequent degradation of NCoR1, leading to derepression of PPAR-regulated genes, increased oxygen consumption, mitochondria content, and reduced lactate production in C2C12 and MEF cells. PABPC4 protein content is markedly reduced under conditions that induce mitochondrial function/biogenesis.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, ubiquitination assay, Seahorse oxygen consumption, gene expression analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP identifying NCoR1 as binding partner, mechanistic dissection through ubiquitination assay and functional metabolic readouts, multiple orthogonal methods in single study\",\n      \"pmids\": [\"37059182\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PABPC4 was identified as the most enriched binding partner of circFAM134B via RNA pulldown and mass spectrometry. PABPC4 functions as an antagonist of nonsense-mediated mRNA decay (NMD), and circFAM134B acts as a sponge that competitively sequesters PABPC4, thereby releasing FAM134B mRNA to NMD-mediated decay.\",\n      \"method\": \"RNA pulldown, mass spectrometry, RNA immunoprecipitation (RIP), luciferase reporter, NMD reporter gene assay\",\n      \"journal\": \"Cell cycle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding identified by pulldown/MS, functional NMD reporter assays; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"37603831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"LncRNA Lnc-PCIR blocks PABPC4 proteasome-dependent ubiquitination degradation, and the resulting stabilized PABPC4 increases TAB3 mRNA stability in triple-negative breast cancer cells, activating the TNF-α/NF-κB pathway.\",\n      \"method\": \"RNA pulldown, RIP, Western blot, siRNA knockdown, mRNA stability assay\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct PABPC4-lncRNA interaction demonstrated by pulldown/RIP with mRNA stability and pathway readout; single lab\",\n      \"pmids\": [\"34012913\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PABPC4 interacts with LIX1L (a putative RNA-binding protein) as identified by MALDI-TOF/TOF mass spectrometry and RNA immunoprecipitation-sequencing in HEK-293 cells.\",\n      \"method\": \"Mass spectrometry, RNA immunoprecipitation-sequencing\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — interactome-level identification without specific functional follow-up on the PABPC4-LIX1L interaction; single method for this specific interaction\",\n      \"pmids\": [\"26310847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Sheep SERP1 and PABPC4 were identified as host target proteins of Orf virus ORF047 (L1R) by yeast two-hybrid screening, with interaction confirmed by Co-IP, suggesting PABPC4 involvement in viral mRNA translation and replication.\",\n      \"method\": \"Yeast two-hybrid, Co-immunoprecipitation\",\n      \"journal\": \"Virology journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP confirmation of yeast two-hybrid hit, no functional mechanistic follow-up on PABPC4 role\",\n      \"pmids\": [\"33499896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PABPC4 is identified by RBPmap bioinformatics and functionally confirmed by siRNA depletion to be responsible for repressive activity of the HPV-1a late 3'UTR in keratinocytes, demonstrating a role for PABPC4 in papillomavirus late gene expression regulation.\",\n      \"method\": \"siRNA depletion, reporter gene assay, bioinformatics prediction\",\n      \"journal\": \"Biomedical reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — siRNA knockdown with reporter readout, single method for the specific functional claim, single lab\",\n      \"pmids\": [\"39006509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PABPC4 inhibits SADS-CoV replication by targeting and degrading the N protein via selective autophagy. PABPC4 recruits MARCHF8 (E3 ubiquitin ligase) to ubiquitinate the N protein, which is then degraded via NDP52/CALCOCO2 cargo receptor, replicating the mechanism established for other coronaviruses.\",\n      \"method\": \"Co-immunoprecipitation, overexpression/knockdown, ubiquitination assay, viral replication assay\",\n      \"journal\": \"Veterinary sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway confirmed using Co-IP, ubiquitination assay, and functional viral readout, replicating prior coronavirus findings; single lab\",\n      \"pmids\": [\"40266995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PABPC1 and PABPC4 are required for global mRNA stabilization during prolonged mitotic arrest. Depletion of PABPC1&4 disrupts poly(A)-tail length maintenance during mitosis and compromises the maintenance of mitotic arrest, demonstrating that mitotic transcriptome buffering is PABPC-dependent.\",\n      \"method\": \"siRNA depletion, poly(A)-tail length profiling, mitotic arrest assays, mRNA half-life measurements\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with poly(A) tail profiling and mitotic phenotype; preprint, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"41641701\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PABPC4 (together with PABPC1) is required for Pumilio (PUM1/2)-mediated mRNA repression. PUMs physically associate with PABPC4, and in its absence, PUM target mRNAs bypass PUM-mediated control. Increasing PABPC concentration inhibits PUM activity in a concentration-dependent manner by protecting poly(A) from CCR4-NOT deadenylation.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, mRNA stability assays, transcriptome analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and loss-of-function with defined molecular readout; peer-reviewed, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"41641701\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In Pabpc4 knockout mice, loss of PABPC4 is not lethal but affects birth weight, post-natal growth trajectories, survival, and red blood cell parameters (microcytic RBCs, altered RBC distribution width). The microcytic anemia phenotype is not red blood cell intrinsic, as shown by conditional genetic approaches.\",\n      \"method\": \"Knockout mouse generation, conditional genetics, haematological analysis, growth measurement\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo knockout with defined phenotypic readouts and conditional genetics to test cell-autonomy; preprint, single lab, multiple orthogonal approaches\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PABPC4 binds LINC00493 mRNA and facilitates its transfer to ribosomes for translation of the microprotein SMIM26 in renal cell carcinoma cells.\",\n      \"method\": \"RNA immunoprecipitation (RIP), ribosome fractionation, functional validation\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — RIP demonstrates association but mechanistic detail of how PABPC4 facilitates LINC00493 translation is limited; single lab, indirect functional evidence\",\n      \"pmids\": [\"37009826\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PABPC4 (iPABP/APP-1) is a cytoplasmic poly(A)-binding protein with four RNA recognition motifs that binds poly(A) tails and AU-rich RNA elements to regulate mRNA stability and translation; it enhances translation of specific mRNAs (e.g., IL-2) through its C-terminal domain (antagonized by Tob), protects subsets of deadenylated mRNAs from decay (including erythroid mRNAs and during mitotic arrest in a PABPC1/4-dependent manner), facilitates Pumilio-mediated mRNA repression via CCR4-NOT deadenylation, interacts with NCoR1 to regulate mitochondrial gene expression and metabolic phenotype, and exerts antiviral activity by recruiting the E3 ubiquitin ligase MARCHF8 to ubiquitinate coronavirus nucleocapsid proteins for selective autophagy-mediated degradation via the NDP52 cargo receptor.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PABPC4 (iPABP/APP-1) is a cytoplasmic poly(A)-binding protein with four RNA recognition motifs that regulates mRNA stability and translation, functioning broadly in poly(A)-tail protection and selective transcript control [#1, #2]. First identified as an inducible poly(A)-binding protein upregulated upon T-cell activation and abundant in heart and skeletal muscle [#0], it binds both poly(A) and AU-rich RNA, discriminating between them only weakly and thereby engaging RNA regions beyond the poly(A) tail [#2]. Through its C-terminal region PABPC4 enhances translation of IL-2 mRNA in a 3'UTR- and poly(A)-dependent manner, an activity abrogated when the antiproliferative protein Tob binds the same C-terminal region [#3]. It stabilizes subsets of mRNAs bearing AU-rich 3'UTR motifs—including erythroid transcripts when poly(A) tails are critically shortened, where its depletion blocks terminal erythroid maturation [#5]—and, redundantly with PABPC1, maintains poly(A)-tail length and global transcriptome stability during prolonged mitotic arrest [#18]. PABPC4 protects poly(A) from CCR4-NOT deadenylation in a concentration-dependent manner, an activity required for Pumilio (PUM1/2)-mediated repression of target mRNAs [#19]. Beyond translational control, PABPC4 binds the nuclear receptor corepressor NCoR1 and limits its ubiquitin-dependent degradation, thereby restraining PPAR-regulated mitochondrial gene expression and oxidative metabolism [#11]. PABPC4 also exerts antiviral activity by interacting with coronavirus nucleocapsid proteins across multiple genera and recruiting the E3 ubiquitin ligase MARCHF8 to ubiquitinate them for NDP52/CALCOCO2-dependent selective autophagic degradation [#8, #17]. Knockout mice are viable but show altered growth, survival, and microcytic red blood cell parameters that are not red-cell intrinsic [#20].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established PABPC4 as a distinct, inducible cytoplasmic poly(A)-binding protein rather than a constitutive housekeeping factor, raising the question of activity-dependent mRNA regulation.\",\n      \"evidence\": \"Molecular cloning, Northern blot, and subcellular fractionation/immunofluorescence in T cells and tissues\",\n      \"pmids\": [\"8524242\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No molecular target mRNAs identified at this stage\", \"Inducibility mechanism not resolved\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Confirmed that the protein binds poly(A) RNA through its four RRM domains, defining its biochemical activity.\",\n      \"evidence\": \"Expression cloning with monoclonal antibody and poly(A)-Sepharose binding of recombinant protein\",\n      \"pmids\": [\"9030741\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Surface expression on platelets not mechanistically explained\", \"No in-cell RNA targets defined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showed PABPC4 binds AU-rich RNA nearly as well as poly(A), implying it engages internal mRNA elements and not only the poly(A) tail.\",\n      \"evidence\": \"Quantitative in vitro RNA-binding affinity measurements with recombinant protein\",\n      \"pmids\": [\"14717712\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No cellular AU-rich targets identified in this study\", \"Functional consequence of AU-rich binding untested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defined a translational-enhancer function for PABPC4 on IL-2 mRNA and identified Tob as a C-terminal-binding regulator that switches off this activity.\",\n      \"evidence\": \"Co-IP in T cells, GST pull-down mapping the C-terminal region, and in vitro translation assays\",\n      \"pmids\": [\"15676026\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality beyond IL-2 mRNA not established\", \"Structural basis of Tob/C-terminal interaction unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Linked PABPC4 to posttranscriptional stabilization of hTERT mRNA in HPV16 E6 keratinocytes via the NFX1-123 PAM2 bridge, extending its role to viral oncogenesis.\",\n      \"evidence\": \"siRNA knockdown, overexpression, qRT-PCR, and telomerase (TRAP) assays\",\n      \"pmids\": [\"20943973\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct PABPC4 binding to hTERT mRNA not shown\", \"Redundancy with PABPC1 not dissected\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrated PABPC4 selectively stabilizes AU-rich erythroid mRNAs when poly(A) tails shorten, with a defined developmental phenotype upon depletion.\",\n      \"evidence\": \"RNA co-IP, siRNA knockdown, mRNA stability assays, and motif analysis in erythroblasts\",\n      \"pmids\": [\"24469397\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of selective protection at short poly(A) unresolved\", \"In vivo erythroid requirement not yet tested at this stage\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connected PABPC4 to cancer stem cell biology via a miR-192-5p/promoter-methylation circuit in hepatocellular carcinoma.\",\n      \"evidence\": \"miRNA overexpression/suppression, luciferase reporters, and functional CSC assays\",\n      \"pmids\": [\"30530815\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular events downstream of PABPC4 elevation not resolved\", \"Direct PABPC4 mRNA targets in CSCs unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified a broad antiviral mechanism whereby PABPC4 bridges coronavirus N proteins to MARCHF8-mediated ubiquitination and NDP52-dependent autophagic degradation.\",\n      \"evidence\": \"Co-IP across N proteins of eight CoVs, ubiquitination assays, autophagy inhibitor experiments, and viral replication readouts\",\n      \"pmids\": [\"34612687\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Determinants of N-protein recognition not mapped\", \"Whether RNA binding is required for antiviral activity unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed PABPC4 is itself a regulated substrate of E3 ligases (TRIM25) and that this ubiquitination contributes to antiviral defense against alphaviruses.\",\n      \"evidence\": \"TRIM25 catalytic-mutant substrate trapping, proteomics, siRNA knockdown, and viral infection assays\",\n      \"pmids\": [\"36067236\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of PABPC4 ubiquitination on its RNA activity unresolved\", \"Ubiquitination sites not mapped\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Placed PABPC4 within neuronal translational control as an interactor of LLPS-deficient TDP-43 that contributes to enhanced global protein synthesis.\",\n      \"evidence\": \"Co-IP from brain tissue, mouse knock-in model, metabolic labeling, and motif-deletion mutants\",\n      \"pmids\": [\"34427634\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect PABPC4-TDP-43 contact unclear\", \"PABPC4-specific contribution within the multiprotein complex not isolated\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established PABPC4 as a target of multiple regulatory lncRNAs that tune its abundance and downstream mRNA fates in cancer.\",\n      \"evidence\": \"RNA pulldown, RIP, ubiquitination and mRNA-stability assays for RP11-286H15.1, Lnc-PCIR, and circFAM134B\",\n      \"pmids\": [\"33259899\", \"34012913\", \"37603831\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether these lncRNAs share a common PABPC4 interaction surface unknown\", \"NMD-antagonist role mechanistically incomplete\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Uncovered a non-RNA-stability role: PABPC4 binds NCoR1 and protects it from degradation, thereby restraining PPAR-driven mitochondrial biogenesis and oxidative metabolism.\",\n      \"evidence\": \"Co-IP, siRNA knockdown, ubiquitination assays, Seahorse oxygen consumption, and gene-expression analysis in C2C12/MEF cells\",\n      \"pmids\": [\"37059182\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How an RNA-binding protein stabilizes a corepressor mechanistically unclear\", \"In vivo metabolic relevance not tested in this study\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined PABPC4 (with PABPC1) as required for poly(A)-tail maintenance and global transcriptome buffering during prolonged mitotic arrest.\",\n      \"evidence\": \"siRNA depletion, poly(A)-tail length profiling, and mRNA half-life measurements (preprint)\",\n      \"pmids\": [\"41641701\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contributions of PABPC4 vs PABPC1 not separated\", \"Preprint, awaits peer review\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed PABPC4 is required for Pumilio-mediated repression by concentration-dependent protection of poly(A) from CCR4-NOT deadenylation, integrating it into a defined repression pathway.\",\n      \"evidence\": \"Co-IP with PUM1/2, siRNA knockdown, mRNA stability assays, and transcriptome analysis\",\n      \"pmids\": [\"41641701\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs PUM-bridged poly(A) protection not fully resolved\", \"Selectivity of PABPC4 vs PABPC1 in this context unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Provided in vivo genetic evidence that PABPC4 is non-essential for viability but influences growth, survival, and red-cell parameters non-cell-autonomously.\",\n      \"evidence\": \"Knockout and conditional mouse genetics with haematological and growth analysis (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Tissue source of the non-intrinsic microcytic phenotype unidentified\", \"Preprint, awaits peer review\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PABPC4 achieves transcript selectivity and how its RNA-binding activity is mechanistically coupled to its protein-stabilizing and antiviral functions remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of PABPC4 on selected mRNAs or with NCoR1/N proteins\", \"Functional separation of PABPC4 from PABPC1 across contexts incomplete\", \"Determinants of AU-rich vs poly(A) target choice in cells unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [1, 2, 5]},\n      {\"term_id\": \"GO:0045182\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [5, 18, 19]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [8, 9, 17]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [8, 17]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"TOB1\", \"NCOR1\", \"MARCHF8\", \"CALCOCO2\", \"TRIM25\", \"PUM1\", \"PUM2\", \"PABPC1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}