{"gene":"PCID2","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":2014,"finding":"BRCA2 associates with PCID2 (a TREX-2 subunit) in the cell; depletion of PCID2 (along with other TREX-2 subunits GANP and DSS1) causes genome instability as measured by γ-H2AX/53BP1 foci accumulation and comet assay, but does not induce R-loop accumulation (detected by EGFP-RNase H1 hybrid-binding domain and S9.6 antibody), placing TREX-2/PCID2 in a pathway that prevents DNA damage independently of R-loop suppression.","method":"Co-immunoprecipitation (BRCA2-PCID2 association); siRNA depletion with γ-H2AX/53BP1 foci and single-cell electrophoresis; R-loop detection by EGFP-RNase H1 and S9.6 antibody","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP plus multiple orthogonal functional readouts (foci, comet assay, R-loop detection), published in high-impact journal","pmids":["24896180"],"is_preprint":false},{"year":2017,"finding":"Pcid2 interacts with ZNHIT1 in multipotent progenitors to block SRCAP chromatin remodelling activity, thereby preventing deposition of histone variant H2A.Z and transcription factor PU.1 at key lymphoid fate regulator genes, and restricting lymphoid lineage commitment; Pcid2 deletion causes skewed lymphoid lineage specification.","method":"Co-immunoprecipitation (Pcid2-ZNHIT1 interaction); conditional Pcid2 knockout in haematopoietic system; H2A.Z and PU.1 chromatin localization assays; Znhit1 deletion epistasis","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, conditional KO with defined cellular phenotype, epistasis with Znhit1, multiple orthogonal methods","pmids":["29138493"],"is_preprint":false},{"year":2014,"finding":"Pcid2 is present in the CBP/p300-EID1 complex in embryonic stem cells. Pcid2 binds EID1 to impede its association with MDM2 (an E3 ligase that mediates K48-linked ubiquitination and proteasomal degradation of EID1), thereby stabilizing EID1 and sustaining its inhibition of CBP/p300 HAT activity, leading to suppression of developmental gene expression and maintenance of pluripotency.","method":"Co-immunoprecipitation (Pcid2-EID1, Pcid2-CBP/p300-EID1 complex); siRNA/knockdown; ubiquitination assays; Pcid2 knockout causing embryonic lethality before blastocyst stage","journal":"Stem Cells","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP of multi-protein complex, ubiquitination assay, KO phenotype, multiple orthogonal methods in single study","pmids":["24167073"],"is_preprint":false},{"year":2010,"finding":"Pcid2 selectively regulates MAD2 mRNA export; siRNA knockdown of Pcid2 reduces MAD2 protein expression (but not MAD1, BUBR1, cyclin A, cyclin B1, or CDK1), causing cell-cycle abnormalities (polyploidy) and increased apoptosis phenocopying MAD2 knockdown. Cd19-cre conditional deletion of Pcid2 causes mature B cell deficiency.","method":"siRNA knockdown with real-time RT-PCR and in situ RNA hybridization for MAD2 mRNA; flow cytometry for cell cycle/apoptosis; conditional knockout (Cd19-cre)","journal":"Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined phenotype, selective mRNA export demonstrated, single lab","pmids":["20870947"],"is_preprint":false},{"year":2021,"finding":"Drosophila PCID2 is present in the cytoplasm and directly interacts with NudC protein, which maintains PCID2 cytoplasmic stability. Cytoplasmic PCID2 associates with mRNA and microtubules. PCID2 knockdown blocks nuclear mRNA export and also impairs general cytoplasmic mRNA transport, indicating a dual role in nuclear export and subsequent cytoplasmic mRNA trafficking.","method":"Subcellular fractionation/immunofluorescence for cytoplasmic localization; co-immunoprecipitation (PCID2-NudC); RNA immunoprecipitation (mRNA association); co-localization with microtubules; siRNA knockdown with mRNA localization assays","journal":"RNA Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple Co-IP and localization experiments with functional KD readout, single lab, Drosophila ortholog","pmids":["33602059"],"is_preprint":false},{"year":2013,"finding":"Human PCID2 localizes to the centrosome in a subset of HeLa cells throughout the cell cycle, and this centrosomal localization is dependent on centrin 2. PCID2 (but not ENY2) is involved in nuclear protein export: siRNA knockdown of PCID2 delays (but does not block) nuclear protein export. Co-depletion of centrin 2 and PCID2 blocks rather than delays nuclear protein export.","method":"Immunofluorescence co-staining with centrosome markers and cyclins; siRNA knockdown; nuclear protein export assay; epistasis by co-depletion","journal":"Experimental Cell Research","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — direct localization with functional consequence, epistasis experiment, single lab, multiple orthogonal methods","pmids":["24291146"],"is_preprint":false},{"year":2021,"finding":"PCID2 binds PML (promyelocytic leukemia protein, a tumor suppressor) as shown by co-immunoprecipitation and mass spectrometry. PCID2 promotes poly-ubiquitination and degradation of PML, which in turn activates canonical Wnt/β-catenin signaling and represses the ARF-p53 pathway in colorectal cancer cells.","method":"Co-immunoprecipitation and mass spectrometry; ubiquitination assay; gain/loss-of-function in cell lines and xenograft mouse models; Western blotting for pathway activation","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP/MS identification of binding partner, ubiquitination assay, in vivo xenograft, single lab","pmids":["34625711"],"is_preprint":false},{"year":2024,"finding":"PCID2 binds the latent HIV-1 LTR promoter and represses transcription initiation. PCID2 depletion remodels the chromatin landscape at the HIV-1 promoter and causes latency reversal. Immunoprecipitation-mass spectrometry identified PCID2-interacting proteins as negative viral RNA splicing regulators; PCID2 depletion leads to over-splicing of intron-containing viral RNA. PCID2 acts within a TREX2 sub-complex (PCID2-DSS1-MCM3AP) to block transcription and dysregulate viral RNA processing.","method":"ChIP (PCID2 at HIV-1 LTR); siRNA depletion with chromatin remodeling analysis; IP-mass spectrometry; viral RNA splicing assays; latency reversal assays in cell lines and primary cells from people with HIV","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP, IP-MS, functional depletion with multiple orthogonal readouts, single lab","pmids":["38384833"],"is_preprint":false},{"year":2023,"finding":"The C-terminal region of the WH domain of Drosophila PCID2 specifically binds the 3′-noncoding region of ras2 RNA (shown by EMSA). An additional RNA-binding region (M region) in the N-terminal part of the PCI domain binds RNA nonspecifically. Point mutations of conserved residues in the M region abolish PCID2-RNA interaction; deletion of the C-terminal domain only partly decreases it, indicating both regions are required for full RNA binding.","method":"Electrophoretic mobility shift assay (EMSA); deletion and point mutagenesis of PCID2 domains","journal":"Current Issues in Molecular Biology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct in vitro binding assay with mutagenesis, Drosophila ortholog, single lab","pmids":["37504273"],"is_preprint":false},{"year":2023,"finding":"Deletion of the C-terminal sequence of Drosophila PCID2 decreases its interaction with RNA and impairs mRNA export from the nucleus to the cytoplasm in D. melanogaster cells.","method":"PCID2 C-terminal deletion constructs; mRNA export assays in D. melanogaster cells","journal":"Doklady Biochemistry and Biophysics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single method (deletion + export assay), Drosophila ortholog, single lab, brief report","pmids":["38066318"],"is_preprint":false},{"year":2024,"finding":"Point mutations of conserved amino acids in the M region of Drosophila PCID2 disrupt its interaction with cellular RNAs and cause defective export of polyA-containing mRNAs from the nucleus to the cytoplasm in Drosophila cells.","method":"Point mutagenesis in M domain; RNA-binding assays; polyA mRNA export assays in Drosophila cells","journal":"Doklady Biological Sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single functional assay, brief report, Drosophila ortholog","pmids":["39128950"],"is_preprint":false},{"year":2025,"finding":"The M-PCID2 and C-PCID2 RNA-binding regions of Drosophila PCID2 competitively bind ras2 fr4_2 mRNA, with M-PCID2 binding more efficiently and displacing C-PCID2. Point mutations in M-PCID2 that disrupt full-length PCID2-RNA interaction paradoxically increase M-PCID2 fragment affinity for RNA, suggesting that additional factors are required to transition from nonspecific to specific binding in the intact complex.","method":"EMSA with isolated M-PCID2 and C-PCID2 fragments and point mutants; competition binding assays","journal":"Doklady Biochemistry and Biophysics","confidence":"Low","confidence_rationale":"Tier 1 / Weak — direct in vitro binding/competition assay but single lab, Drosophila ortholog, brief report","pmids":["41083631"],"is_preprint":false},{"year":2025,"finding":"The N-terminal region of Drosophila PCID2 interacts with its C-terminal (C-PCID2) region via distinct surfaces that do not overlap with the RNA-binding surface of C-PCID2, indicating an intramolecular interaction that may modulate TREX-2 function without blocking RNA binding.","method":"In vitro protein interaction assays between isolated PCID2 domain fragments","journal":"Doklady Biochemistry and Biophysics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single in vitro assay, Drosophila ortholog, brief report","pmids":["41083629"],"is_preprint":false},{"year":2015,"finding":"Molecular dynamics simulations of PCID2 in complex with the intrinsically disordered protein DSS1 show that DSS1 binding reduces conformational variation of PCID2 (particularly helices IV and VIII), promotes coil formation between helix III and IV, and induces a short anti-parallel β-sheet. Decomposition of binding free energy indicates electrostatic and hydrophobic interactions (including a seven-residue hydrophobic core in DSS1) are key for DSS1-PCID2 recognition.","method":"Molecular dynamics simulation (3 × 500 ns); binding free energy decomposition","journal":"Journal of Molecular Modeling","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational only, no experimental validation in this paper","pmids":["25914122"],"is_preprint":false},{"year":2026,"finding":"PCID2 acts as a scaffold for mutually exclusive SAC3(PCI-fold)-based subcomplexes with GANP, LENG8, and SAC3D1 within the TREX2 system. The GANP-PCID2-SEM1 subcomplex localizes at the nuclear envelope and mediates canonical mRNA export, while the LENG8-PCID2-SEM1 subcomplex localizes to nuclear speckles and interacts with mRNA processing factors to influence polyadenylation site usage. The two SAC3-containing subcomplexes have distinct and alternative localizations and functions.","method":"Interactome mapping (IP-MS); depletion experiments with RNA-seq; subcellular localization by immunofluorescence; transcriptomic analysis of polyadenylation site usage","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — IP-MS interactome with functional depletion and transcriptomic readout, multiple orthogonal methods, preprint not yet peer-reviewed","pmids":["42039562"],"is_preprint":true},{"year":2025,"finding":"LENG8 binds PCID2 and SEM1 to form the REX (Repressor of EXport) complex, which acts as a dominant negative factor for TREX-2-mediated mRNA export and causes nuclear RNA retention. The LENG8-PCID2-SEM1 trimer is structurally and functionally equivalent to the GANP-PCID2-SEM1 trimer of TREX-2. LENG8 depletion leads to leakage of misprocessed mRNAs and noncoding RNAs into the cytoplasm; LENG8 also promotes RNA degradation by recruiting PAXT and the nuclear RNA exosome.","method":"Co-immunoprecipitation (LENG8-PCID2-SEM1 complex); structural analysis; siRNA depletion with RNA-seq; mRNA export/retention assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, structural equivalence analysis, depletion with transcriptomic readout, preprint not yet peer-reviewed","pmids":["bio_10.1101_2025.08.14.670437"],"is_preprint":true},{"year":2025,"finding":"The LENG8-PCID2-SEM1 (LENG8-PS) trimer is structurally and functionally equivalent to the central GANP-PCID2-SEM1 (GANP-PS) trimer of TREX-2. The LENG8-PS module is part of the PAXT connection and releases polyadenylated RNAs from UAP56 for nuclear exosome-mediated decay, while the NPC-associated TREX-2 (GANP-PS) releases RNAs for export. Mutagenesis and transcriptomic data show that competing actions of PAXT (with LENG8-PS) and TREX-2 (with GANP-PS) govern nuclear fate of polyadenylated RNPs.","method":"Structural analysis; mutagenesis; transcriptomics; biochemical reconstitution of competing complexes","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — structural and mutagenesis data combined with transcriptomics, preprint not yet peer-reviewed, novel findings","pmids":["bio_10.1101_2025.09.16.676470"],"is_preprint":true},{"year":2026,"finding":"PCID2 is required for spermatogonial differentiation; conditional knockout (Stra8-Cre) causes male infertility, germ cell apoptosis, developmental arrest at type A to type B spermatogonia transition, and failure of meiosis initiation. IP-MS and co-IP show PCID2 interacts with splicing factors SNRPG, hnRNPH1, and SF3B1 in germ cells to modulate alternative splicing of Prpf3, Nek3, Dvl2, and Slc30a9.","method":"Conditional knockout (Stra8-Cre); single-cell transcriptomics; IP-MS and co-IP; RNA-seq with splice analysis; RT-PCR validation","journal":"Cellular and Molecular Life Sciences","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with defined spermatogenesis phenotype, IP-MS and co-IP identification of splicing factor partners, RNA-seq splicing analysis, multiple orthogonal methods","pmids":["41526677"],"is_preprint":false}],"current_model":"PCID2 is a scaffold subunit of the TREX-2 mRNA transcription-export complex that directly binds mRNA via two PCI-domain regions (M and C regions) and assembles mutually exclusive subcomplexes with GANP, LENG8, or SAC3D1 to mediate either nuclear mRNA export (with GANP-PCID2-SEM1 at the nuclear pore) or RNA nuclear retention/decay (with LENG8-PCID2-SEM1 in nuclear speckles/PAXT); beyond RNA export, PCID2 prevents genome instability by associating with BRCA2, sustains embryonic stem cell pluripotency by stabilizing EID1 and inhibiting CBP/p300, controls haematopoietic lymphoid lineage commitment by suppressing SRCAP-mediated H2A.Z deposition through ZNHIT1, regulates MAD2 mRNA export for B cell survival, interacts with splicing factors (SNRPG, hnRNPH1, SF3B1) to control alternative splicing in spermatogonia, and can promote tumor progression by driving poly-ubiquitination and degradation of PML to activate Wnt/β-catenin signaling."},"narrative":{"mechanistic_narrative":"PCID2 is a PCI-domain scaffold subunit of the TREX-2 mRNA transcription–export system that couples nuclear RNA processing to the decision between mRNA export and nuclear retention/decay [PMID:42039562, PMID:bio_10.1101_2025.08.14.670437]. Within TREX-2, PCID2 nucleates mutually exclusive SAC3-fold subcomplexes: a GANP–PCID2–SEM1 trimer at the nuclear envelope that drives canonical mRNA export, and a LENG8–PCID2–SEM1 (REX/PAXT-linked) trimer in nuclear speckles that acts as a dominant-negative for export, retains misprocessed mRNAs and noncoding RNAs, and recruits PAXT and the nuclear exosome for degradation, with the two modules competing to govern polyadenylation site usage and the nuclear fate of polyadenylated RNPs [PMID:42039562, PMID:bio_10.1101_2025.08.14.670437, PMID:bio_10.1101_2025.09.16.676470]. PCID2 binds RNA directly through two regions of its PCI/WH architecture — a nonspecific M region and a sequence-specific C-terminal region — both required for full RNA binding and for nuclear mRNA export [PMID:37504273, PMID:38066318, PMID:39128950]. Selective export control is illustrated by PCID2-dependent MAD2 mRNA export required for mature B cell survival [PMID:20870947], and by its interaction with splicing factors SNRPG, hnRNPH1, and SF3B1 to modulate alternative splicing during spermatogonial differentiation, where its loss causes male infertility and arrest at the type A–to–type B spermatogonia transition [PMID:41526677]. Beyond RNA metabolism, PCID2 associates with BRCA2 and prevents genome instability independently of R-loop suppression [PMID:24896180]; in embryonic stem cells it binds EID1 to block its MDM2-mediated degradation, sustaining EID1 inhibition of CBP/p300 and maintaining pluripotency [PMID:24167073]; in haematopoietic progenitors it partners with ZNHIT1 to restrict SRCAP-mediated H2A.Z deposition and limit lymphoid lineage commitment [PMID:29138493]; and it can promote tumor progression by driving poly-ubiquitination and degradation of PML to activate Wnt/β-catenin signaling [PMID:34625711].","teleology":[{"year":2010,"claim":"Established that PCID2 does not export mRNA bulk-indiscriminately but selectively governs export of specific transcripts with a physiological consequence, linking it to mitotic checkpoint integrity and lymphocyte survival.","evidence":"siRNA knockdown with RT-PCR and in situ hybridization for MAD2 mRNA, flow cytometry, and Cd19-cre conditional knockout in mouse B cells","pmids":["20870947"],"confidence":"Medium","gaps":["Mechanism of transcript selectivity not defined","Whether selectivity is intrinsic to PCID2 or contributed by partner subunits unresolved"]},{"year":2013,"claim":"Showed PCID2 has functions beyond mRNA export, localizing to the centrosome (centrin 2-dependent) and contributing to nuclear protein export.","evidence":"Immunofluorescence with centrosome markers, siRNA knockdown, nuclear protein export assay, and centrin 2 co-depletion epistasis in HeLa cells","pmids":["24291146"],"confidence":"Medium","gaps":["Significance of centrosomal localization unknown","Molecular basis of nuclear protein export role not defined"]},{"year":2014,"claim":"Connected PCID2/TREX-2 to genome stability via physical association with BRCA2, distinguishing this DNA-damage-preventing role from R-loop suppression.","evidence":"Co-immunoprecipitation, siRNA depletion with γ-H2AX/53BP1 foci and comet assay, and R-loop detection by RNase H1 and S9.6 antibody","pmids":["24896180"],"confidence":"High","gaps":["Direct mechanism linking PCID2-BRCA2 to damage prevention not defined","Whether the effect is export-dependent unresolved"]},{"year":2014,"claim":"Defined a chromatin/pluripotency role: PCID2 stabilizes EID1 by blocking MDM2-mediated degradation, sustaining repression of CBP/p300 and developmental gene programs.","evidence":"Co-IP of the CBP/p300-EID1 complex, ubiquitination assays, knockdown, and Pcid2 knockout causing pre-blastocyst embryonic lethality","pmids":["24167073"],"confidence":"High","gaps":["Relationship between this nuclear role and TREX-2 export function unclear","How PCID2 occludes the MDM2-EID1 interface not structurally defined"]},{"year":2017,"claim":"Extended PCID2's chromatin influence to lineage decisions by showing it partners ZNHIT1 to block SRCAP-driven H2A.Z deposition and restrain lymphoid commitment.","evidence":"Co-IP, conditional haematopoietic knockout, H2A.Z/PU.1 chromatin localization assays, and Znhit1 deletion epistasis in mouse","pmids":["29138493"],"confidence":"High","gaps":["Whether this is independent of TREX-2 export not resolved","Direct biochemical inhibition of SRCAP not reconstituted"]},{"year":2021,"claim":"Identified a tumor-promoting axis in which PCID2 drives PML poly-ubiquitination and degradation to activate Wnt/β-catenin and repress ARF-p53.","evidence":"Co-IP/mass spectrometry, ubiquitination assays, gain/loss-of-function in cell lines, and xenograft mouse models","pmids":["34625711"],"confidence":"Medium","gaps":["Direct E3 ligase activity vs. adaptor role for PML degradation unresolved","Single-lab finding"]},{"year":2021,"claim":"Demonstrated a cytoplasmic function: PCID2 stability and mRNA/microtubule association in the cytoplasm depend on NudC, implying roles beyond the nuclear export step.","evidence":"Subcellular fractionation/immunofluorescence, Co-IP, RNA immunoprecipitation, microtubule co-localization, and knockdown mRNA localization assays in Drosophila","pmids":["33602059"],"confidence":"Medium","gaps":["Conservation of cytoplasmic role in mammals untested","Mechanism of cytoplasmic mRNA transport not defined"]},{"year":2023,"claim":"Mapped the RNA-binding architecture of PCID2 to two cooperating regions (nonspecific M region and sequence-specific C-terminal WH region) both required for full RNA engagement and export.","evidence":"EMSA with deletion and point mutagenesis of PCID2 domains, plus C-terminal deletion mRNA export assays in Drosophila cells","pmids":["37504273","38066318"],"confidence":"Medium","gaps":["Drosophila ortholog; mammalian RNA-binding mode not confirmed","Structural basis of sequence specificity not solved"]},{"year":2025,"claim":"Refined the RNA-binding model by showing M and C regions compete for the same RNA and that point mutations and an intramolecular N–C interaction modulate the switch from nonspecific to specific binding, implying regulation by additional factors.","evidence":"EMSA and competition assays with isolated M-PCID2 and C-PCID2 fragments and point mutants; in vitro inter-domain interaction assays (Drosophila)","pmids":["39128950","41083631","41083629"],"confidence":"Low","gaps":["Single lab, Drosophila ortholog, brief reports","Identity of factors driving specific binding unknown","No full-length structural validation"]},{"year":2024,"claim":"Revealed a chromatin-level role of PCID2 at the HIV-1 LTR, where it represses transcription initiation and viral RNA over-splicing within a PCID2-DSS1-MCM3AP TREX2 subcomplex.","evidence":"ChIP, siRNA depletion with chromatin analysis, IP-mass spectrometry, viral splicing and latency reversal assays in cell lines and primary cells","pmids":["38384833"],"confidence":"Medium","gaps":["Generality to host promoters not tested","Direct vs. indirect transcriptional repression unresolved"]},{"year":2026,"claim":"Unified PCID2 as a scaffold for mutually exclusive SAC3-fold subcomplexes (GANP, LENG8, SAC3D1) that partition between export at the nuclear envelope and PAXT/exosome-linked retention/decay in speckles, and showed PCID2-dependent splicing control in spermatogenesis.","evidence":"IP-MS interactome and depletion with RNA-seq, immunofluorescence, and polyadenylation analysis; Co-IP and structural equivalence of LENG8-PS vs GANP-PS trimers (preprints); Stra8-Cre conditional KO with single-cell transcriptomics and splice analysis identifying SNRPG/hnRNPH1/SF3B1 partners","pmids":["42039562","bio_10.1101_2025.08.14.670437","bio_10.1101_2025.09.16.676470","41526677"],"confidence":"Medium","gaps":["Key subcomplex partitioning data are preprints awaiting peer review","How subcomplex choice is regulated in a given cell type unknown","Mechanism coupling splicing-factor binding to fate decision undefined"]},{"year":null,"claim":"How PCID2's many activities — RNA export, nuclear retention/decay, chromatin regulation, genome stability, and protein degradation — are coordinated and which are intrinsic versus partner-imposed remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No integrated model linking export-independent roles to the TREX-2 scaffold","Regulation of subcomplex selection in vivo undefined","Mammalian structural mechanism of dual RNA-binding regions unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[4,8,9,10,11]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[14,15,16]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[14,15]}],"localization":[{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[14]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[14,15]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[5]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[3,14,15,16]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[7]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[1,2]}],"complexes":["TREX-2 (GANP-PCID2-SEM1)","REX/LENG8-PCID2-SEM1 (PAXT-linked)","CBP/p300-EID1 complex"],"partners":["GANP","LENG8","SEM1/DSS1","BRCA2","EID1","ZNHIT1","PML","SF3B1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5JVF3","full_name":"PCI domain-containing protein 2","aliases":["CSN12-like protein"],"length_aa":399,"mass_kda":46.0,"function":"Required for B-cell survival through the regulation of the expression of cell-cycle checkpoint MAD2L1 protein during B cell differentiation (By similarity). As a component of the TREX-2 complex, involved in the export of mRNAs to the cytoplasm through the nuclear pores (PubMed:22307388). Binds and stabilizes BRCA2 and is thus involved in the control of R-loop-associated DNA damage and transcription-associated genomic instability (PubMed:24896180). Blocks the activity of the SRCAP chromatin remodeling complex by interacting with SRCAP complex member ZNHIT1 and inhibiting its interaction with the complex (By similarity). This prevents the deposition of histone variant H2AZ1/H2A.Z at the nucleosomes of key lymphoid fate regulator genes which suppresses their expression and restricts lymphoid lineage commitment (By similarity)","subcellular_location":"Cytoplasm; Nucleus, nuclear pore complex","url":"https://www.uniprot.org/uniprotkb/Q5JVF3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/PCID2","classification":"Common Essential","n_dependent_lines":1168,"n_total_lines":1208,"dependency_fraction":0.9668874172185431},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"DDX39B","stoichiometry":0.2},{"gene":"SEM1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/PCID2","total_profiled":1310},"omim":[{"mim_id":"613713","title":"PCI DOMAIN-CONTAINING PROTEIN 2; PCID2","url":"https://www.omim.org/entry/613713"},{"mim_id":"603137","title":"CULLIN 4A; CUL4A","url":"https://www.omim.org/entry/603137"},{"mim_id":"601467","title":"MITOTIC ARREST-DEFICIENT 2 LIKE 1; MAD2L1","url":"https://www.omim.org/entry/601467"},{"mim_id":"600185","title":"BRCA2 DNA REPAIR-ASSOCIATED PROTEIN; BRCA2","url":"https://www.omim.org/entry/600185"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Nucleoli","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PCID2"},"hgnc":{"alias_symbol":["FLJ11305"],"prev_symbol":[]},"alphafold":{"accession":"Q5JVF3","domains":[{"cath_id":"1.10.10.10","chopping":"316-396","consensus_level":"medium","plddt":95.5972,"start":316,"end":396},{"cath_id":"1.25.40","chopping":"1-181","consensus_level":"medium","plddt":95.313,"start":1,"end":181}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5JVF3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5JVF3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5JVF3-F1-predicted_aligned_error_v6.png","plddt_mean":95.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PCID2","jax_strain_url":"https://www.jax.org/strain/search?query=PCID2"},"sequence":{"accession":"Q5JVF3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5JVF3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5JVF3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5JVF3"}},"corpus_meta":[{"pmid":"24896180","id":"PMC_24896180","title":"BRCA2 prevents R-loop accumulation and associates with TREX-2 mRNA export factor PCID2.","date":"2014","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/24896180","citation_count":441,"is_preprint":false},{"pmid":"29138493","id":"PMC_29138493","title":"Suppression of SRCAP chromatin remodelling complex and restriction of lymphoid lineage commitment by Pcid2.","date":"2017","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/29138493","citation_count":32,"is_preprint":false},{"pmid":"24167073","id":"PMC_24167073","title":"Pcid2 inactivates developmental genes in human and mouse embryonic stem cells to sustain their pluripotency by modulation of EID1 stability.","date":"2014","source":"Stem cells (Dayton, Ohio)","url":"https://pubmed.ncbi.nlm.nih.gov/24167073","citation_count":19,"is_preprint":false},{"pmid":"20870947","id":"PMC_20870947","title":"Critical role of Pcid2 in B cell survival through the regulation of MAD2 expression.","date":"2010","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/20870947","citation_count":18,"is_preprint":false},{"pmid":"33602059","id":"PMC_33602059","title":"PCID2, a subunit of the Drosophila TREX-2 nuclear export complex, is essential for both mRNA nuclear export and its subsequent cytoplasmic trafficking.","date":"2021","source":"RNA biology","url":"https://pubmed.ncbi.nlm.nih.gov/33602059","citation_count":14,"is_preprint":false},{"pmid":"24291146","id":"PMC_24291146","title":"Human TREX2 components PCID2 and centrin 2, but not ENY2, have distinct functions in protein export and co-localize to the centrosome.","date":"2013","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/24291146","citation_count":13,"is_preprint":false},{"pmid":"34625711","id":"PMC_34625711","title":"A novel amplification gene PCI domain containing 2 (PCID2) promotes colorectal cancer through directly degrading a tumor suppressor promyelocytic leukemia (PML).","date":"2021","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/34625711","citation_count":12,"is_preprint":false},{"pmid":"34031538","id":"PMC_34031538","title":"Increased chemosensitivity via BRCA2-independent DNA damage in DSS1- and PCID2-depleted breast carcinomas.","date":"2021","source":"Laboratory investigation; a journal of technical methods and pathology","url":"https://pubmed.ncbi.nlm.nih.gov/34031538","citation_count":11,"is_preprint":false},{"pmid":"38384833","id":"PMC_38384833","title":"PCID2 dysregulates transcription and viral RNA processing to promote HIV-1 latency.","date":"2024","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/38384833","citation_count":6,"is_preprint":false},{"pmid":"38066318","id":"PMC_38066318","title":"Interaction of mRNA with the C-Terminal Domain of PCID2, a Subunit of the TREX-2 Complex, Is Required for Its Export from the Nucleus to the Cytoplasm in Drosophila melanogaster.","date":"2023","source":"Doklady. Biochemistry and biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/38066318","citation_count":5,"is_preprint":false},{"pmid":"37504273","id":"PMC_37504273","title":"PCID2 Subunit of the Drosophila TREX-2 Complex Has Two RNA-Binding Regions.","date":"2023","source":"Current issues in molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/37504273","citation_count":4,"is_preprint":false},{"pmid":"25914122","id":"PMC_25914122","title":"Conformational stability of PCID2 upon DSS1 binding with molecular dynamics simulation.","date":"2015","source":"Journal of molecular modeling","url":"https://pubmed.ncbi.nlm.nih.gov/25914122","citation_count":1,"is_preprint":false},{"pmid":"39128950","id":"PMC_39128950","title":"Point Mutations in the M Domain of PCID2 Impair Its Function in mRNA Export in Drosophila melanogaster.","date":"2024","source":"Doklady biological sciences : proceedings of the Academy of Sciences of the USSR, Biological sciences sections","url":"https://pubmed.ncbi.nlm.nih.gov/39128950","citation_count":1,"is_preprint":false},{"pmid":"41526677","id":"PMC_41526677","title":"PCID2 is essential for spermatogonial differentiation by regulating alternative splicing.","date":"2026","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/41526677","citation_count":0,"is_preprint":false},{"pmid":"41083631","id":"PMC_41083631","title":"Two RNA-Binding Regions of PCID2, a Subunit of the TREX-2 mRNA Nuclear Export Complex, Competitively Interact with the 3' Noncoding Region of ras2 mRNA.","date":"2025","source":"Doklady. Biochemistry and biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/41083631","citation_count":0,"is_preprint":false},{"pmid":"41083629","id":"PMC_41083629","title":"Interdomain Interactions of the PCID2 Protein, One of the Subunits of the TREX-2 mRNA Export Complex in Drosophila melanogaster.","date":"2025","source":"Doklady. Biochemistry and biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/41083629","citation_count":0,"is_preprint":false},{"pmid":"42039562","id":"PMC_42039562","title":"TREX2 component PCID2 scaffolds alternative SAC3-based subcomplexes with distinct RNA processing and export function.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/42039562","citation_count":0,"is_preprint":false},{"pmid":"41394136","id":"PMC_41394136","title":"A natural PCID2-Targeting compound suppresses hepatocellular carcinoma progression: evidence from structure-based discovery and biological evaluation.","date":"2025","source":"Frontiers in pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/41394136","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.09.16.676470","title":"Molecular basis of polyadenylated RNA fate determination in the nucleus","date":"2025-09-16","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.16.676470","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.08.14.670437","title":"LENG8 mediates RNA nuclear retention and degradation in eukaryotes","date":"2025-08-16","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.14.670437","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11273,"output_tokens":5235,"usd":0.056172,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13375,"output_tokens":4532,"usd":0.090088,"stage2_stop_reason":"end_turn"},"total_usd":0.14626,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2014,\n      \"finding\": \"BRCA2 associates with PCID2 (a TREX-2 subunit) in the cell; depletion of PCID2 (along with other TREX-2 subunits GANP and DSS1) causes genome instability as measured by γ-H2AX/53BP1 foci accumulation and comet assay, but does not induce R-loop accumulation (detected by EGFP-RNase H1 hybrid-binding domain and S9.6 antibody), placing TREX-2/PCID2 in a pathway that prevents DNA damage independently of R-loop suppression.\",\n      \"method\": \"Co-immunoprecipitation (BRCA2-PCID2 association); siRNA depletion with γ-H2AX/53BP1 foci and single-cell electrophoresis; R-loop detection by EGFP-RNase H1 and S9.6 antibody\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP plus multiple orthogonal functional readouts (foci, comet assay, R-loop detection), published in high-impact journal\",\n      \"pmids\": [\"24896180\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Pcid2 interacts with ZNHIT1 in multipotent progenitors to block SRCAP chromatin remodelling activity, thereby preventing deposition of histone variant H2A.Z and transcription factor PU.1 at key lymphoid fate regulator genes, and restricting lymphoid lineage commitment; Pcid2 deletion causes skewed lymphoid lineage specification.\",\n      \"method\": \"Co-immunoprecipitation (Pcid2-ZNHIT1 interaction); conditional Pcid2 knockout in haematopoietic system; H2A.Z and PU.1 chromatin localization assays; Znhit1 deletion epistasis\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, conditional KO with defined cellular phenotype, epistasis with Znhit1, multiple orthogonal methods\",\n      \"pmids\": [\"29138493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Pcid2 is present in the CBP/p300-EID1 complex in embryonic stem cells. Pcid2 binds EID1 to impede its association with MDM2 (an E3 ligase that mediates K48-linked ubiquitination and proteasomal degradation of EID1), thereby stabilizing EID1 and sustaining its inhibition of CBP/p300 HAT activity, leading to suppression of developmental gene expression and maintenance of pluripotency.\",\n      \"method\": \"Co-immunoprecipitation (Pcid2-EID1, Pcid2-CBP/p300-EID1 complex); siRNA/knockdown; ubiquitination assays; Pcid2 knockout causing embryonic lethality before blastocyst stage\",\n      \"journal\": \"Stem Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP of multi-protein complex, ubiquitination assay, KO phenotype, multiple orthogonal methods in single study\",\n      \"pmids\": [\"24167073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Pcid2 selectively regulates MAD2 mRNA export; siRNA knockdown of Pcid2 reduces MAD2 protein expression (but not MAD1, BUBR1, cyclin A, cyclin B1, or CDK1), causing cell-cycle abnormalities (polyploidy) and increased apoptosis phenocopying MAD2 knockdown. Cd19-cre conditional deletion of Pcid2 causes mature B cell deficiency.\",\n      \"method\": \"siRNA knockdown with real-time RT-PCR and in situ RNA hybridization for MAD2 mRNA; flow cytometry for cell cycle/apoptosis; conditional knockout (Cd19-cre)\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined phenotype, selective mRNA export demonstrated, single lab\",\n      \"pmids\": [\"20870947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Drosophila PCID2 is present in the cytoplasm and directly interacts with NudC protein, which maintains PCID2 cytoplasmic stability. Cytoplasmic PCID2 associates with mRNA and microtubules. PCID2 knockdown blocks nuclear mRNA export and also impairs general cytoplasmic mRNA transport, indicating a dual role in nuclear export and subsequent cytoplasmic mRNA trafficking.\",\n      \"method\": \"Subcellular fractionation/immunofluorescence for cytoplasmic localization; co-immunoprecipitation (PCID2-NudC); RNA immunoprecipitation (mRNA association); co-localization with microtubules; siRNA knockdown with mRNA localization assays\",\n      \"journal\": \"RNA Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple Co-IP and localization experiments with functional KD readout, single lab, Drosophila ortholog\",\n      \"pmids\": [\"33602059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Human PCID2 localizes to the centrosome in a subset of HeLa cells throughout the cell cycle, and this centrosomal localization is dependent on centrin 2. PCID2 (but not ENY2) is involved in nuclear protein export: siRNA knockdown of PCID2 delays (but does not block) nuclear protein export. Co-depletion of centrin 2 and PCID2 blocks rather than delays nuclear protein export.\",\n      \"method\": \"Immunofluorescence co-staining with centrosome markers and cyclins; siRNA knockdown; nuclear protein export assay; epistasis by co-depletion\",\n      \"journal\": \"Experimental Cell Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — direct localization with functional consequence, epistasis experiment, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"24291146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PCID2 binds PML (promyelocytic leukemia protein, a tumor suppressor) as shown by co-immunoprecipitation and mass spectrometry. PCID2 promotes poly-ubiquitination and degradation of PML, which in turn activates canonical Wnt/β-catenin signaling and represses the ARF-p53 pathway in colorectal cancer cells.\",\n      \"method\": \"Co-immunoprecipitation and mass spectrometry; ubiquitination assay; gain/loss-of-function in cell lines and xenograft mouse models; Western blotting for pathway activation\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP/MS identification of binding partner, ubiquitination assay, in vivo xenograft, single lab\",\n      \"pmids\": [\"34625711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PCID2 binds the latent HIV-1 LTR promoter and represses transcription initiation. PCID2 depletion remodels the chromatin landscape at the HIV-1 promoter and causes latency reversal. Immunoprecipitation-mass spectrometry identified PCID2-interacting proteins as negative viral RNA splicing regulators; PCID2 depletion leads to over-splicing of intron-containing viral RNA. PCID2 acts within a TREX2 sub-complex (PCID2-DSS1-MCM3AP) to block transcription and dysregulate viral RNA processing.\",\n      \"method\": \"ChIP (PCID2 at HIV-1 LTR); siRNA depletion with chromatin remodeling analysis; IP-mass spectrometry; viral RNA splicing assays; latency reversal assays in cell lines and primary cells from people with HIV\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP, IP-MS, functional depletion with multiple orthogonal readouts, single lab\",\n      \"pmids\": [\"38384833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The C-terminal region of the WH domain of Drosophila PCID2 specifically binds the 3′-noncoding region of ras2 RNA (shown by EMSA). An additional RNA-binding region (M region) in the N-terminal part of the PCI domain binds RNA nonspecifically. Point mutations of conserved residues in the M region abolish PCID2-RNA interaction; deletion of the C-terminal domain only partly decreases it, indicating both regions are required for full RNA binding.\",\n      \"method\": \"Electrophoretic mobility shift assay (EMSA); deletion and point mutagenesis of PCID2 domains\",\n      \"journal\": \"Current Issues in Molecular Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro binding assay with mutagenesis, Drosophila ortholog, single lab\",\n      \"pmids\": [\"37504273\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Deletion of the C-terminal sequence of Drosophila PCID2 decreases its interaction with RNA and impairs mRNA export from the nucleus to the cytoplasm in D. melanogaster cells.\",\n      \"method\": \"PCID2 C-terminal deletion constructs; mRNA export assays in D. melanogaster cells\",\n      \"journal\": \"Doklady Biochemistry and Biophysics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single method (deletion + export assay), Drosophila ortholog, single lab, brief report\",\n      \"pmids\": [\"38066318\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Point mutations of conserved amino acids in the M region of Drosophila PCID2 disrupt its interaction with cellular RNAs and cause defective export of polyA-containing mRNAs from the nucleus to the cytoplasm in Drosophila cells.\",\n      \"method\": \"Point mutagenesis in M domain; RNA-binding assays; polyA mRNA export assays in Drosophila cells\",\n      \"journal\": \"Doklady Biological Sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single functional assay, brief report, Drosophila ortholog\",\n      \"pmids\": [\"39128950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The M-PCID2 and C-PCID2 RNA-binding regions of Drosophila PCID2 competitively bind ras2 fr4_2 mRNA, with M-PCID2 binding more efficiently and displacing C-PCID2. Point mutations in M-PCID2 that disrupt full-length PCID2-RNA interaction paradoxically increase M-PCID2 fragment affinity for RNA, suggesting that additional factors are required to transition from nonspecific to specific binding in the intact complex.\",\n      \"method\": \"EMSA with isolated M-PCID2 and C-PCID2 fragments and point mutants; competition binding assays\",\n      \"journal\": \"Doklady Biochemistry and Biophysics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct in vitro binding/competition assay but single lab, Drosophila ortholog, brief report\",\n      \"pmids\": [\"41083631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The N-terminal region of Drosophila PCID2 interacts with its C-terminal (C-PCID2) region via distinct surfaces that do not overlap with the RNA-binding surface of C-PCID2, indicating an intramolecular interaction that may modulate TREX-2 function without blocking RNA binding.\",\n      \"method\": \"In vitro protein interaction assays between isolated PCID2 domain fragments\",\n      \"journal\": \"Doklady Biochemistry and Biophysics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single in vitro assay, Drosophila ortholog, brief report\",\n      \"pmids\": [\"41083629\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Molecular dynamics simulations of PCID2 in complex with the intrinsically disordered protein DSS1 show that DSS1 binding reduces conformational variation of PCID2 (particularly helices IV and VIII), promotes coil formation between helix III and IV, and induces a short anti-parallel β-sheet. Decomposition of binding free energy indicates electrostatic and hydrophobic interactions (including a seven-residue hydrophobic core in DSS1) are key for DSS1-PCID2 recognition.\",\n      \"method\": \"Molecular dynamics simulation (3 × 500 ns); binding free energy decomposition\",\n      \"journal\": \"Journal of Molecular Modeling\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational only, no experimental validation in this paper\",\n      \"pmids\": [\"25914122\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"PCID2 acts as a scaffold for mutually exclusive SAC3(PCI-fold)-based subcomplexes with GANP, LENG8, and SAC3D1 within the TREX2 system. The GANP-PCID2-SEM1 subcomplex localizes at the nuclear envelope and mediates canonical mRNA export, while the LENG8-PCID2-SEM1 subcomplex localizes to nuclear speckles and interacts with mRNA processing factors to influence polyadenylation site usage. The two SAC3-containing subcomplexes have distinct and alternative localizations and functions.\",\n      \"method\": \"Interactome mapping (IP-MS); depletion experiments with RNA-seq; subcellular localization by immunofluorescence; transcriptomic analysis of polyadenylation site usage\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — IP-MS interactome with functional depletion and transcriptomic readout, multiple orthogonal methods, preprint not yet peer-reviewed\",\n      \"pmids\": [\"42039562\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LENG8 binds PCID2 and SEM1 to form the REX (Repressor of EXport) complex, which acts as a dominant negative factor for TREX-2-mediated mRNA export and causes nuclear RNA retention. The LENG8-PCID2-SEM1 trimer is structurally and functionally equivalent to the GANP-PCID2-SEM1 trimer of TREX-2. LENG8 depletion leads to leakage of misprocessed mRNAs and noncoding RNAs into the cytoplasm; LENG8 also promotes RNA degradation by recruiting PAXT and the nuclear RNA exosome.\",\n      \"method\": \"Co-immunoprecipitation (LENG8-PCID2-SEM1 complex); structural analysis; siRNA depletion with RNA-seq; mRNA export/retention assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, structural equivalence analysis, depletion with transcriptomic readout, preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.08.14.670437\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The LENG8-PCID2-SEM1 (LENG8-PS) trimer is structurally and functionally equivalent to the central GANP-PCID2-SEM1 (GANP-PS) trimer of TREX-2. The LENG8-PS module is part of the PAXT connection and releases polyadenylated RNAs from UAP56 for nuclear exosome-mediated decay, while the NPC-associated TREX-2 (GANP-PS) releases RNAs for export. Mutagenesis and transcriptomic data show that competing actions of PAXT (with LENG8-PS) and TREX-2 (with GANP-PS) govern nuclear fate of polyadenylated RNPs.\",\n      \"method\": \"Structural analysis; mutagenesis; transcriptomics; biochemical reconstitution of competing complexes\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — structural and mutagenesis data combined with transcriptomics, preprint not yet peer-reviewed, novel findings\",\n      \"pmids\": [\"bio_10.1101_2025.09.16.676470\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"PCID2 is required for spermatogonial differentiation; conditional knockout (Stra8-Cre) causes male infertility, germ cell apoptosis, developmental arrest at type A to type B spermatogonia transition, and failure of meiosis initiation. IP-MS and co-IP show PCID2 interacts with splicing factors SNRPG, hnRNPH1, and SF3B1 in germ cells to modulate alternative splicing of Prpf3, Nek3, Dvl2, and Slc30a9.\",\n      \"method\": \"Conditional knockout (Stra8-Cre); single-cell transcriptomics; IP-MS and co-IP; RNA-seq with splice analysis; RT-PCR validation\",\n      \"journal\": \"Cellular and Molecular Life Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with defined spermatogenesis phenotype, IP-MS and co-IP identification of splicing factor partners, RNA-seq splicing analysis, multiple orthogonal methods\",\n      \"pmids\": [\"41526677\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PCID2 is a scaffold subunit of the TREX-2 mRNA transcription-export complex that directly binds mRNA via two PCI-domain regions (M and C regions) and assembles mutually exclusive subcomplexes with GANP, LENG8, or SAC3D1 to mediate either nuclear mRNA export (with GANP-PCID2-SEM1 at the nuclear pore) or RNA nuclear retention/decay (with LENG8-PCID2-SEM1 in nuclear speckles/PAXT); beyond RNA export, PCID2 prevents genome instability by associating with BRCA2, sustains embryonic stem cell pluripotency by stabilizing EID1 and inhibiting CBP/p300, controls haematopoietic lymphoid lineage commitment by suppressing SRCAP-mediated H2A.Z deposition through ZNHIT1, regulates MAD2 mRNA export for B cell survival, interacts with splicing factors (SNRPG, hnRNPH1, SF3B1) to control alternative splicing in spermatogonia, and can promote tumor progression by driving poly-ubiquitination and degradation of PML to activate Wnt/β-catenin signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PCID2 is a PCI-domain scaffold subunit of the TREX-2 mRNA transcription–export system that couples nuclear RNA processing to the decision between mRNA export and nuclear retention/decay [#14, #15]. Within TREX-2, PCID2 nucleates mutually exclusive SAC3-fold subcomplexes: a GANP–PCID2–SEM1 trimer at the nuclear envelope that drives canonical mRNA export, and a LENG8–PCID2–SEM1 (REX/PAXT-linked) trimer in nuclear speckles that acts as a dominant-negative for export, retains misprocessed mRNAs and noncoding RNAs, and recruits PAXT and the nuclear exosome for degradation, with the two modules competing to govern polyadenylation site usage and the nuclear fate of polyadenylated RNPs [#14, #15, #16]. PCID2 binds RNA directly through two regions of its PCI/WH architecture — a nonspecific M region and a sequence-specific C-terminal region — both required for full RNA binding and for nuclear mRNA export [#8, #9, #10]. Selective export control is illustrated by PCID2-dependent MAD2 mRNA export required for mature B cell survival [#3], and by its interaction with splicing factors SNRPG, hnRNPH1, and SF3B1 to modulate alternative splicing during spermatogonial differentiation, where its loss causes male infertility and arrest at the type A–to–type B spermatogonia transition [#17]. Beyond RNA metabolism, PCID2 associates with BRCA2 and prevents genome instability independently of R-loop suppression [#0]; in embryonic stem cells it binds EID1 to block its MDM2-mediated degradation, sustaining EID1 inhibition of CBP/p300 and maintaining pluripotency [#2]; in haematopoietic progenitors it partners with ZNHIT1 to restrict SRCAP-mediated H2A.Z deposition and limit lymphoid lineage commitment [#1]; and it can promote tumor progression by driving poly-ubiquitination and degradation of PML to activate Wnt/β-catenin signaling [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 2010,\n      \"claim\": \"Established that PCID2 does not export mRNA bulk-indiscriminately but selectively governs export of specific transcripts with a physiological consequence, linking it to mitotic checkpoint integrity and lymphocyte survival.\",\n      \"evidence\": \"siRNA knockdown with RT-PCR and in situ hybridization for MAD2 mRNA, flow cytometry, and Cd19-cre conditional knockout in mouse B cells\",\n      \"pmids\": [\"20870947\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Mechanism of transcript selectivity not defined\", \"Whether selectivity is intrinsic to PCID2 or contributed by partner subunits unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showed PCID2 has functions beyond mRNA export, localizing to the centrosome (centrin 2-dependent) and contributing to nuclear protein export.\",\n      \"evidence\": \"Immunofluorescence with centrosome markers, siRNA knockdown, nuclear protein export assay, and centrin 2 co-depletion epistasis in HeLa cells\",\n      \"pmids\": [\"24291146\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Significance of centrosomal localization unknown\", \"Molecular basis of nuclear protein export role not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Connected PCID2/TREX-2 to genome stability via physical association with BRCA2, distinguishing this DNA-damage-preventing role from R-loop suppression.\",\n      \"evidence\": \"Co-immunoprecipitation, siRNA depletion with γ-H2AX/53BP1 foci and comet assay, and R-loop detection by RNase H1 and S9.6 antibody\",\n      \"pmids\": [\"24896180\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct mechanism linking PCID2-BRCA2 to damage prevention not defined\", \"Whether the effect is export-dependent unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined a chromatin/pluripotency role: PCID2 stabilizes EID1 by blocking MDM2-mediated degradation, sustaining repression of CBP/p300 and developmental gene programs.\",\n      \"evidence\": \"Co-IP of the CBP/p300-EID1 complex, ubiquitination assays, knockdown, and Pcid2 knockout causing pre-blastocyst embryonic lethality\",\n      \"pmids\": [\"24167073\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Relationship between this nuclear role and TREX-2 export function unclear\", \"How PCID2 occludes the MDM2-EID1 interface not structurally defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended PCID2's chromatin influence to lineage decisions by showing it partners ZNHIT1 to block SRCAP-driven H2A.Z deposition and restrain lymphoid commitment.\",\n      \"evidence\": \"Co-IP, conditional haematopoietic knockout, H2A.Z/PU.1 chromatin localization assays, and Znhit1 deletion epistasis in mouse\",\n      \"pmids\": [\"29138493\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Whether this is independent of TREX-2 export not resolved\", \"Direct biochemical inhibition of SRCAP not reconstituted\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified a tumor-promoting axis in which PCID2 drives PML poly-ubiquitination and degradation to activate Wnt/β-catenin and repress ARF-p53.\",\n      \"evidence\": \"Co-IP/mass spectrometry, ubiquitination assays, gain/loss-of-function in cell lines, and xenograft mouse models\",\n      \"pmids\": [\"34625711\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct E3 ligase activity vs. adaptor role for PML degradation unresolved\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrated a cytoplasmic function: PCID2 stability and mRNA/microtubule association in the cytoplasm depend on NudC, implying roles beyond the nuclear export step.\",\n      \"evidence\": \"Subcellular fractionation/immunofluorescence, Co-IP, RNA immunoprecipitation, microtubule co-localization, and knockdown mRNA localization assays in Drosophila\",\n      \"pmids\": [\"33602059\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Conservation of cytoplasmic role in mammals untested\", \"Mechanism of cytoplasmic mRNA transport not defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Mapped the RNA-binding architecture of PCID2 to two cooperating regions (nonspecific M region and sequence-specific C-terminal WH region) both required for full RNA engagement and export.\",\n      \"evidence\": \"EMSA with deletion and point mutagenesis of PCID2 domains, plus C-terminal deletion mRNA export assays in Drosophila cells\",\n      \"pmids\": [\"37504273\", \"38066318\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Drosophila ortholog; mammalian RNA-binding mode not confirmed\", \"Structural basis of sequence specificity not solved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Refined the RNA-binding model by showing M and C regions compete for the same RNA and that point mutations and an intramolecular N–C interaction modulate the switch from nonspecific to specific binding, implying regulation by additional factors.\",\n      \"evidence\": \"EMSA and competition assays with isolated M-PCID2 and C-PCID2 fragments and point mutants; in vitro inter-domain interaction assays (Drosophila)\",\n      \"pmids\": [\"39128950\", \"41083631\", \"41083629\"],\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Single lab, Drosophila ortholog, brief reports\", \"Identity of factors driving specific binding unknown\", \"No full-length structural validation\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed a chromatin-level role of PCID2 at the HIV-1 LTR, where it represses transcription initiation and viral RNA over-splicing within a PCID2-DSS1-MCM3AP TREX2 subcomplex.\",\n      \"evidence\": \"ChIP, siRNA depletion with chromatin analysis, IP-mass spectrometry, viral splicing and latency reversal assays in cell lines and primary cells\",\n      \"pmids\": [\"38384833\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Generality to host promoters not tested\", \"Direct vs. indirect transcriptional repression unresolved\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Unified PCID2 as a scaffold for mutually exclusive SAC3-fold subcomplexes (GANP, LENG8, SAC3D1) that partition between export at the nuclear envelope and PAXT/exosome-linked retention/decay in speckles, and showed PCID2-dependent splicing control in spermatogenesis.\",\n      \"evidence\": \"IP-MS interactome and depletion with RNA-seq, immunofluorescence, and polyadenylation analysis; Co-IP and structural equivalence of LENG8-PS vs GANP-PS trimers (preprints); Stra8-Cre conditional KO with single-cell transcriptomics and splice analysis identifying SNRPG/hnRNPH1/SF3B1 partners\",\n      \"pmids\": [\"42039562\", \"bio_10.1101_2025.08.14.670437\", \"bio_10.1101_2025.09.16.676470\", \"41526677\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Key subcomplex partitioning data are preprints awaiting peer review\", \"How subcomplex choice is regulated in a given cell type unknown\", \"Mechanism coupling splicing-factor binding to fate decision undefined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PCID2's many activities — RNA export, nuclear retention/decay, chromatin regulation, genome stability, and protein degradation — are coordinated and which are intrinsic versus partner-imposed remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No integrated model linking export-independent roles to the TREX-2 scaffold\", \"Regulation of subcomplex selection in vivo undefined\", \"Mammalian structural mechanism of dual RNA-binding regions unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [4, 8, 9, 10, 11]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [14, 15, 16]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [14, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [14]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [14, 15]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [3, 14, 15, 16]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"complexes\": [\n      \"TREX-2 (GANP-PCID2-SEM1)\",\n      \"REX/LENG8-PCID2-SEM1 (PAXT-linked)\",\n      \"CBP/p300-EID1 complex\"\n    ],\n    \"partners\": [\n      \"GANP\",\n      \"LENG8\",\n      \"SEM1/DSS1\",\n      \"BRCA2\",\n      \"EID1\",\n      \"ZNHIT1\",\n      \"PML\",\n      \"SF3B1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}