{"gene":"POLQ","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2003,"finding":"POLQ encodes a 2592-amino acid protein with an N-terminal ATPase-helicase domain, a central spacer domain, and a C-terminal family A DNA polymerase domain. Purified full-length human POLQ displays DNA polymerase activity on nicked double-stranded DNA and singly primed templates (resistant to aphidicolin, inhibited by dideoxynucleotides) and a single-stranded DNA-dependent ATPase activity.","method":"Baculovirus expression and purification of full-length human POLQ; in vitro polymerase and ATPase assays; domain analysis by sequence","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro biochemical reconstitution of both polymerase and ATPase activities with purified protein, replicated in subsequent studies","pmids":["14576298"],"is_preprint":false},{"year":2010,"finding":"The DNA polymerase (pol) domain of POLQ is sufficient for highly efficient bypass of abasic sites, independent of the helicase-like or central domains. Three unique sequence insertions (not found in other A-family polymerases) are required for lesion bypass: insertion 1 increases processivity but does not affect TLS; insertions 2 and 3 are essential for activity on undamaged DNA and completely required for bypass of abasic sites and thymine glycol lesions.","method":"In vitro polymerase assay with purified recombinant POLQ pol domain deletion constructs lacking each insertion element individually; translesion synthesis assays on abasic site and thymine glycol templates","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic mutagenesis of insertion elements combined with in vitro biochemical assays; multiple orthogonal deletions tested","pmids":["21050863"],"is_preprint":false},{"year":2007,"finding":"POLQ (pol theta) can extend DNA from mismatched termini (A:G, A:T, A:C mismatches) with less discrimination than E. coli pol I, and can extend from primers placed opposite a (6-4) photoproduct. When combined with DNA polymerase iota (which inserts opposite the lesion), POLQ enables complete bypass of a (6-4) photoproduct, acting as an extender polymerase.","method":"In vitro primer extension assays with purified POLQ on templates containing mismatches, cyclobutane pyrimidine dimers, and (6-4) photoproducts; two-polymerase reconstitution with pol iota + POLQ","journal":"DNA repair","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with defined substrates and two-polymerase bypass assay, single lab","pmids":["17920341"],"is_preprint":false},{"year":2006,"finding":"POLQ participates in base excision repair (BER) of oxidative DNA damage and has an overlapping function with POLbeta. POLQ-deficient DT40 cells are hypersensitive to H2O2-induced oxidative base damage; this is synergistically enhanced by concurrent POLbeta deletion. Cell extracts from POLQ-null cells show reduced BER activity. POLQ accumulates rapidly at sites of base damage, similar to POLbeta.","method":"Gene disruption in chicken DT40 cells (POLQ, POLbeta, polq/polb double mutants); cell survival assays; in vitro BER activity assays on cell extracts; live-cell imaging of POLQ accumulation at laser-induced damage sites","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis via double knockouts, biochemical BER assay, and direct localization experiment; multiple orthogonal methods","pmids":["17018297"],"is_preprint":false},{"year":2014,"finding":"POLQ mediates an alternative end-joining (alt-EJ) pathway for DNA double-strand break repair that is Ku70-independent and requires POLQ's DNA polymerase activity. POLQ promotes end joining of DNA ends with long 3' single-stranded overhangs by its unique ability to extend DNA from minimally paired primers, generating insertions of base pairs at joins with microhomology to switch-region sequences. Loss of POLQ leads to increased Myc/IgH chromosome translocations, showing POLQ suppresses genomic instability at DSBs.","method":"Polq-null murine cell lines; cell-based DNA break end-joining assay with long 3' ssDNA overhang substrates; immunoglobulin class switch recombination assays; Ku70-independent assay; biochemical assays with purified human POLQ; chromosomal translocation analysis by PCR","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — combines purified protein biochemistry, cell-based repair assays, genetic null cells, and chromosomal translocation analysis; multiple orthogonal methods","pmids":["25275444"],"is_preprint":false},{"year":2004,"finding":"The chaos1 missense mutation in mouse Polq causes spontaneous and induced chromosome instability (increased micronucleated erythrocytes). Chaos1 is confirmed as a Polq allele by BAC complementation and failed complementation with a Polq-null allele. Double homozygosity with Atm deficiency is synthetically lethal (90% neonatal death), with survivors showing synergistic growth retardation and chromosome instability, indicating that POLQ and ATM operate in distinct but partially compensatory DSB repair pathways.","method":"Mouse genetics: BAC complementation, allelic complementation test with gene-targeted Polq null; double-mutant (Polq/Atm) phenotypic analysis; micronucleus assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic complementation and epistasis with Atm null; two independent genetic approaches confirming gene identity; replicated across multiple analyses","pmids":["15542845"],"is_preprint":false},{"year":2011,"finding":"POLQ's non-polymerase domains retain significant function in tolerance to DSB-inducing agents (etoposide, gamma-irradiation): POLQ-null B cells are more sensitive than POLQ-polymerase-inactive (pol domain deleted) cells to these agents, while both are equally sensitive to agents repaired by the polymerase domain (MMC, cisplatin, UV). Class switch recombination is unaffected by loss of either form of POLQ.","method":"Gene targeting in CH12F3 B cells to generate POLQ-null and POLQ-polymerase-inactive lines; clonogenic survival assays with multiple DNA-damaging agents; class switch recombination assay","journal":"Genes to cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic comparison of two distinct POLQ mutant cell lines with multiple damage agents; single lab","pmids":["21883722"],"is_preprint":false},{"year":2016,"finding":"In zebrafish embryos, POLQ-mediated alternative end joining (alt-EJ) is the essential and dominant pathway for repair of DSBs during early vertebrate development. Polq-mutant embryos cannot repair CRISPR/Cas9- or ionizing radiation-induced DSBs, fail to survive mutagenesis, and show dramatic differences in mutation profiles compared to wild-type.","method":"Zebrafish polq genetic mutants; CRISPR/Cas9-induced DSBs; ionizing radiation; survival assays; mutation spectrum analysis","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic null in vertebrate model with defined DSB induction; single lab, two orthogonal DSB-inducing methods","pmids":["27149851"],"is_preprint":false},{"year":2017,"finding":"POLQ substantially contributes to random integration of foreign DNA in human cells via a mechanism independent of NHEJ. Dual loss of POLQ and LIG4 (essential for NHEJ) abolishes random integration entirely, revealing that POLQ-mediated end joining is the sole homology-independent repair route for foreign DNA integration when NHEJ is absent.","method":"POLQ and LIG4 double-knockout human cells; gene targeting frequency assays; random integration frequency measurement","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean human cell double knockout with quantitative integration assays; single lab","pmids":["28695890"],"is_preprint":false},{"year":2019,"finding":"POLQ is required for MMEJ repair of DSBs generated by both endonucleases (I-SceI, Cas9) and Cas9 nickase-derived single-strand breaks that collapse at replication forks. POLQ deficiency causes sensitivity to topoisomerase inhibitors and ATR inhibitors that induce replication stress and fork collapse, placing POLQ in the response to replication-associated DSBs.","method":"POLQ-deficient human cancer cell lines; I-SceI and Cas9/Cas9-nickase DSB repair assays; clonogenic survival with topoisomerase inhibitors and ATR inhibitors","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined genetic loss-of-function with specific mechanistic assays; single lab, multiple repair substrates","pmids":["30655289"],"is_preprint":false},{"year":2019,"finding":"POLQ and RAD52 operate in distinct backup DSB repair pathways with different microhomology requirements: POLQ is important for repair events using 6 nt (but not ≥18 nt) flanking microhomologies and for oligonucleotide microhomology-templated (12–20 nt) repair events requiring nascent DNA synthesis, whereas RAD52 is important for longer (≥50 nt) repeat-mediated repair. Combined disruption of both causes additive hypersensitivity to cisplatin and synthetic reduction in replication fork restart velocity.","method":"Human U2OS cells with POLQ mutations (upstream of pol domain), RAD52 knockout, and combined disruption; defined DSB repair substrate assays; fork restart assay; clonogenic survival","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis with defined repair substrates distinguishing microhomology lengths; single lab, multiple orthogonal assays","pmids":["31381562"],"is_preprint":false},{"year":2022,"finding":"POLQ seals post-replicative ssDNA gaps in BRCA1/2-deficient cells or upon PARP inhibitor treatment. Biochemically, the POLQ helicase activity promotes RPA displacement from ssDNA gaps while the polymerase activity fills in the gaps. POLQ also performs microhomology-mediated gap skipping (MMGS), generating deletions during gap repair that resemble genomic scars in POLQ-overexpressing cancers.","method":"POLQ-deficient cell lines with BRCA1/2 loss or PARP inhibitor treatment; ssDNA gap accumulation assay; biochemical reconstitution of RPA displacement and gap fill-in with POLQ helicase and polymerase domain activities; genomic scar analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — biochemical reconstitution of both helicase and polymerase activities in gap sealing, combined with genetic experiments and genomic scar analysis; multiple orthogonal methods","pmids":["36455556"],"is_preprint":false},{"year":2020,"finding":"POLQ promotes end joining in cis at DSBs, limiting breaks available for interhomolog recombination (IHR) in trans. Depletion of POLQ causes a dramatic increase in IHR and in copy-neutral loss of heterozygosity (cnLOH) at CRISPR-Cas9-targeted DSBs in human cells.","method":"POLQ depletion in human cells; CRISPR-Cas9 targeted DSBs at both homologs; quantitative IHR and cnLOH frequency assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined genetic depletion with quantitative recombination assays; single lab","pmids":["32873648"],"is_preprint":false},{"year":2008,"finding":"In C. elegans, polq-1 functions in a distinct ICL repair pathway that is dependent on brc-1 (CeBRCA1), separate from the Fanconi anemia-dependent pathway used by hel-308. Epistasis analysis places polq-1 and hel-308 in different DNA repair pathways.","method":"C. elegans polq-1 and hel-308 mutants; survival assays after ICL agent treatment; genetic epistasis analysis with Fanconi anemia pathway mutants and brc-1","journal":"DNA repair","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in C. elegans model organism with multiple pathway mutants; single lab","pmids":["18472307"],"is_preprint":false},{"year":2024,"finding":"POLQ-mediated end-joining (TMEJ) is the primary mechanism generating structural variants (SVs) at common fragile sites (CFSs) in human cells under replication stress. SV junction formation increases 5-fold after G2-to-M-phase transition; neither SV formation nor CFS expression depend on mitotic DNA synthesis (MiDAS). POLQ inhibition reduces SV formation, placing POLQ as the principal driver of nonrecurrent SV formation at CFSs.","method":"Error-minimized capture sequencing of CFS DNA from human cell lines after aphidicolin treatment; DNA repair pathway inhibition (POLQ and others); cell cycle fractionation; analysis of tens of thousands of de novo SV junctions","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — large-scale sequencing combined with pharmacological inhibition and cell-cycle analysis; single lab","pmids":["39505880"],"is_preprint":false},{"year":2023,"finding":"POLQ inhibition in HR-deficient BRCA2-deficient pancreatic cancer cells is synthetically lethal and activates cGAS-STING signaling by enhancing cytosolic micronuclei formation, leading to increased CD8+ T cell infiltration in vivo.","method":"POLQ knockdown in human and murine HR-deficient PDAC models; synthetic lethality assay with BRCA1/2 and ATM mutations; micronuclei quantification; cGAS-STING signaling assay; in vivo syngeneic tumor model with CD8+ T cell quantification","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined genetic knockdown with mechanistic immune signaling readout and in vivo validation; single lab","pmids":["36976649"],"is_preprint":false},{"year":2023,"finding":"In mouse embryonic stem cells, the RNA-binding protein DPPA5A promotes cryptic exon (CE) inclusion in Polq pre-mRNA, disrupting normal POLθ protein expression and suppressing MMEJ activity. Depletion of DPPA5A decreases CE inclusion in Polq, restores POLθ expression, and stimulates MMEJ activity.","method":"DPPA5A depletion in mouse ESCs; RT-PCR for CE inclusion in Polq; Western blot for POLθ protein; MMEJ activity assays; enforced DPPA5A expression in NIH3T3 cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic depletion and overexpression with mechanistic splicing and activity readouts; single lab, two cell types","pmids":["37459543"],"is_preprint":false},{"year":2025,"finding":"HPV16 E6 oncoprotein stabilizes POLQ protein by activating the E3 ubiquitin ligase UBE3A/E6AP, which ubiquitinates and degrades RAD23A — a shuttle protein required for delivering polyubiquitinated POLQ to the proteasome. Loss of RAD23A phenocopies HPV16 E6 expression, leading to POLQ stabilization and increased MMEJ activity. This E6-UBE3A-RAD23A-POLQ axis promotes viral genome integration.","method":"Co-expression of HPV16 E6 in cells; Western blot for POLQ and RAD23A protein levels; UBE3A knockdown/knockout; RAD23A knockdown; MMEJ activity assays; viral integration assays; ubiquitination assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway dissection with multiple genetic perturbations; preprint, single lab","pmids":["41357977"],"is_preprint":true},{"year":2025,"finding":"SMARCB1 (a core BAF/SWI-SNF subunit) is required for maintaining POLQ protein levels by facilitating nuclear export of POLQ mRNA through interaction with the nuclear pore complex. Loss of SMARCB1 reduces POLQ protein, impairs MMEJ, and forces a compensatory hyper-dependence on the FA/BRCA pathway.","method":"SMARCB1-deficient rhabdoid tumor cell lines; Western blot for POLQ protein; POLQ mRNA nuclear export assay; nuclear pore complex interaction; MMEJ activity assay; synthetic lethality with FA/BRCA pathway inhibition","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, single lab, nuclear export mechanism inferred from interaction data without full mechanistic reconstitution","pmids":["bio_10.1101_2025.11.20.689563"],"is_preprint":true},{"year":2025,"finding":"EWSR1 is a splicing factor that promotes accurate splicing of POLQ pre-mRNA. The EWS-FLI1 fusion oncoprotein, or loss of EWSR1, causes exon 25 skipping of the POLQ transcript, decreased POLθ protein expression, and impaired MMEJ activity in Ewing sarcoma cells. Knockdown of EWS-FLI1 restores POLθ expression and increases MMEJ activity.","method":"Ewing sarcoma cell lines with EWS-FLI1 expression or EWSR1 loss; RT-PCR for POLQ exon 25 skipping; Western blot for POLθ; MMEJ activity assay; EWS-FLI1 knockdown rescue experiments; POLQ mitotic foci quantification","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function and rescue experiments defining splicing mechanism; preprint, single lab, multiple orthogonal methods","pmids":["bio_10.1101_2025.05.06.651696"],"is_preprint":true},{"year":2025,"finding":"POLQ variant forms (patient-derived melanoma variants) show decreased efficiency during bypass and extension of cyclobutane pyrimidine dimers (CPDs) compared to wild-type, but two of three tested variants nonetheless protect against UV-induced cell death, dissociating lesion bypass efficiency from cell survival.","method":"In vitro primer extension assays with purified recombinant POLQ variants on CPD-containing templates; cell survival assays after UV irradiation with POLQ variant expression","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 1 / Weak — in vitro biochemical assay with purified proteins is rigorous, but preprint, single lab, limited variants tested","pmids":["41357977"],"is_preprint":true}],"current_model":"POLQ (DNA polymerase theta) is a large multidomain protein with an N-terminal DNA-dependent ATPase/helicase domain and a C-terminal family A DNA polymerase domain; the polymerase domain harbors three unique insertion elements (insertions 2 and 3 essential for lesion bypass) that allow it to extend DNA from minimally paired primers and bypass abasic sites and thymine glycol lesions, while the helicase domain displaces RPA from ssDNA gaps; together, these activities define POLQ as the central effector of theta-mediated end joining (TMEJ/alt-EJ), a Ku-independent pathway that joins DSBs using short (≥6 nt) microhomologies, seals post-replicative ssDNA gaps in BRCA-deficient cells via microhomology-mediated gap skipping, contributes to BER of oxidative damage redundantly with POLbeta, suppresses chromosome translocations and interhomolog recombination by promoting cis end-joining, and drives the somatic mutation scars and structural variants prevalent in HR-deficient cancers."},"narrative":{"mechanistic_narrative":"POLQ (DNA polymerase theta) is the central effector of theta-mediated/alternative end joining (TMEJ/alt-EJ), a Ku-independent double-strand break (DSB) repair pathway that joins ends through short microhomologies [PMID:25275444]. It is a large multidomain enzyme combining an N-terminal single-stranded-DNA-dependent ATPase/helicase domain with a C-terminal family A DNA polymerase domain, and purified full-length protein displays both polymerase activity on primed and nicked templates and ssDNA-dependent ATPase activity [PMID:14576298]. The polymerase domain is intrinsically lesion-tolerant: three unique sequence insertions absent from other A-family polymerases (insertions 2 and 3 being essential) enable synthesis on undamaged DNA and bypass of abasic sites and thymine glycol [PMID:21050863], and POLQ extends from mismatched primers and from primers opposite a (6-4) photoproduct, acting as an extender polymerase in concert with pol iota [PMID:17920341]. In end joining, POLQ uniquely extends DNA from minimally paired 3' overhangs, generating templated insertions at microhomology junctions, and its polymerase activity drives repair of breaks bearing ~6 nt microhomologies in a pathway distinct from RAD52-dependent long-repeat repair [PMID:25275444, PMID:31381562]. The two enzymatic domains cooperate beyond DSBs: the helicase activity displaces RPA from post-replicative ssDNA gaps while the polymerase fills them, and microhomology-mediated gap skipping generates characteristic deletion scars in BRCA1/2-deficient or PARP-inhibited cells [PMID:36455556]. POLQ also contributes redundantly with POLbeta to base excision repair of oxidative damage [PMID:17018297], suppresses chromosome translocations and interhomolog recombination by promoting end joining in cis [PMID:25275444, PMID:32873648], and is the principal driver of structural variants at common fragile sites under replication stress [PMID:39505880]. POLQ loss is synthetically lethal in HR-deficient cancers, where its inhibition activates cGAS-STING signaling and CD8+ T-cell infiltration [PMID:36976649], and POLQ protein abundance and MMEJ activity are tuned by transcript splicing and protein-stability control by factors including DPPA5A and EWSR1 [PMID:37459543, PMID:bio_10.1101_2025.05.06.651696].","teleology":[{"year":2003,"claim":"Established the basic enzymatic identity of POLQ, answering whether the predicted dual-domain protein is biochemically active.","evidence":"Baculovirus expression of full-length human POLQ with in vitro polymerase and ATPase assays plus sequence-based domain analysis","pmids":["14576298"],"confidence":"High","gaps":["Did not define a cellular pathway for either activity","No functional role for the helicase/ATPase domain established"]},{"year":2004,"claim":"Linked POLQ to genome stability in vivo and to DSB repair pathway architecture by showing genetic interaction with ATM.","evidence":"Mouse chaos1 missense allele characterized by BAC and allelic complementation; Polq/Atm double-mutant phenotyping and micronucleus assays","pmids":["15542845"],"confidence":"High","gaps":["Molecular mechanism of chromosome instability not defined","Did not identify the repair pathway POLQ acts in"]},{"year":2006,"claim":"Defined a base excision repair role for POLQ redundant with POLbeta, answering which damage types depend on POLQ.","evidence":"DT40 single and double knockouts, in vitro BER assays on extracts, and live-cell imaging of POLQ recruitment to laser damage","pmids":["17018297"],"confidence":"High","gaps":["Precise BER step performed by POLQ not resolved","Relationship between BER role and DSB role unclear"]},{"year":2007,"claim":"Showed POLQ functions as a lesion-tolerant extender polymerase, explaining how it copes with mismatched and damaged termini.","evidence":"In vitro primer extension on mismatch, CPD and (6-4) photoproduct templates and two-polymerase reconstitution with pol iota","pmids":["17920341"],"confidence":"High","gaps":["In vivo relevance of (6-4) bypass not established","Partner insertases in cells not identified"]},{"year":2010,"claim":"Identified the structural basis of POLQ's lesion bypass by mapping three unique insertion elements required for activity.","evidence":"Systematic deletion mutagenesis of pol-domain insertions with in vitro TLS assays on abasic and thymine glycol templates","pmids":["21050863"],"confidence":"High","gaps":["No crystal structure of the active insertions","Contribution of insertions to end joining not tested here"]},{"year":2011,"claim":"Separated functions of POLQ's polymerase and non-polymerase domains, showing the helicase-like region has independent activity in DSB-agent tolerance.","evidence":"POLQ-null versus pol-domain-deleted CH12F3 B cells with clonogenic survival across multiple damaging agents and CSR assays","pmids":["21883722"],"confidence":"Medium","gaps":["Biochemical function of the non-polymerase domain in survival undefined","Single cell-line system"]},{"year":2014,"claim":"Defined POLQ as the effector of Ku-independent alt-EJ that uses minimally paired primers and suppresses translocations, establishing the core TMEJ mechanism.","evidence":"Polq-null murine cells, long-3'-overhang end-joining substrates, CSR and Ku70-independent assays, purified-protein biochemistry, and translocation PCR","pmids":["25275444"],"confidence":"High","gaps":["End resection factors feeding POLQ not defined","Ligase used to seal POLQ-extended ends not identified here"]},{"year":2016,"claim":"Showed alt-EJ via POLQ is the dominant DSB repair route in early vertebrate development, establishing physiological importance.","evidence":"Zebrafish polq mutants with CRISPR/Cas9- and irradiation-induced DSBs, survival and mutation-spectrum analysis","pmids":["27149851"],"confidence":"Medium","gaps":["Developmental-stage specificity of dependence not mechanistically explained","Single model organism"]},{"year":2017,"claim":"Demonstrated POLQ mediates homology-independent foreign-DNA integration as the sole route when NHEJ is absent.","evidence":"POLQ/LIG4 double-knockout human cells with random integration and gene targeting frequency assays","pmids":["28695890"],"confidence":"Medium","gaps":["Mechanism of capturing exogenous DNA ends not detailed","Single lab"]},{"year":2019,"claim":"Connected POLQ to replication-associated breaks and distinguished its microhomology preference from RAD52's, refining pathway boundaries.","evidence":"POLQ-deficient and RAD52-knockout human cells with defined-microhomology DSB substrates, fork-restart assays, and survival with TOP/ATR inhibitors","pmids":["30655289","31381562"],"confidence":"Medium","gaps":["How POLQ is recruited specifically to collapsed forks unclear","Determinants of microhomology length selection not molecularly defined"]},{"year":2020,"claim":"Showed POLQ enforces cis end-joining to suppress interhomolog recombination and copy-neutral LOH, explaining its anti-recombinogenic role.","evidence":"POLQ depletion with CRISPR-Cas9 DSBs on both homologs and quantitative IHR/cnLOH assays in human cells","pmids":["32873648"],"confidence":"Medium","gaps":["Mechanism restricting break mobility not defined","Depletion rather than clean genetic null"]},{"year":2022,"claim":"Defined a post-replicative ssDNA gap-sealing function in BRCA-deficient cells, reconstituting cooperation between the helicase (RPA displacement) and polymerase (gap fill-in) activities.","evidence":"POLQ-deficient cells with BRCA1/2 loss or PARP inhibition, gap-accumulation assays, biochemical reconstitution of both domain activities, and genomic-scar analysis","pmids":["36455556"],"confidence":"High","gaps":["Trigger directing POLQ to gaps versus DSBs unclear","MMGS choice between fill-in and skipping not regulated mechanistically"]},{"year":2023,"claim":"Showed POLQ inhibition in HR-deficient tumors is synthetically lethal and engages cGAS-STING-driven anti-tumor immunity, providing therapeutic mechanism.","evidence":"POLQ knockdown in HR-deficient PDAC models, synthetic-lethality and micronuclei assays, cGAS-STING readouts, and in vivo CD8+ T-cell quantification","pmids":["36976649"],"confidence":"Medium","gaps":["Source of immunogenic cytosolic DNA not fully traced to POLQ activity","Single tumor type"]},{"year":2023,"claim":"Revealed transcript-level control of POLQ via DPPA5A-driven cryptic exon inclusion that suppresses POLθ expression and MMEJ.","evidence":"DPPA5A depletion and overexpression in mouse ESCs and NIH3T3 with RT-PCR, Western blot, and MMEJ assays","pmids":["37459543"],"confidence":"Medium","gaps":["Direct binding of DPPA5A to Polq pre-mRNA not shown here","Human relevance untested"]},{"year":2024,"claim":"Established POLQ as the principal driver of nonrecurrent structural variants at common fragile sites under replication stress.","evidence":"Error-minimized capture sequencing of CFS DNA after aphidicolin, pathway inhibition, and cell-cycle fractionation in human cells","pmids":["39505880"],"confidence":"Medium","gaps":["Why SV formation peaks after G2-to-M not mechanistically explained","Pharmacological rather than genetic POLQ loss"]},{"year":2025,"claim":"Identified multiple convergent mechanisms controlling POLQ protein stability and splicing accuracy in cancer contexts (HPV16 E6/UBE3A/RAD23A, EWSR1/EWS-FLI1, SMARCB1).","evidence":"HPV16 E6 and UBE3A/RAD23A perturbations, EWSR1/EWS-FLI1 splicing assays, and SMARCB1-deficient cell analyses with MMEJ readouts (preprints)","pmids":["41357977","bio_10.1101_2025.05.06.651696","bio_10.1101_2025.11.20.689563"],"confidence":"Medium","gaps":["Mechanisms are preprint-stage and single-lab","Nuclear-export mechanism for POLQ mRNA inferred without reconstitution","Generality across tumor types untested"]},{"year":null,"claim":"How POLQ is recruited to and selects among its substrates (DSB ends, post-replicative gaps, fragile sites) and which factors hand off ends to and seal POLQ-extended products remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of full-length POLQ engaging a substrate","Recruitment and substrate-choice determinants undefined","Ligation partner sealing POLQ-extended junctions not identified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140097","term_label":"catalytic activity, acting on DNA","supporting_discovery_ids":[0,1,2,11]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[0,11]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0,2]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,11]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,18]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[3,4,11]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[14,15]}],"complexes":[],"partners":["POLB","RAD52","RAD23A","UBE3A","DPPA5A","EWSR1","SMARCB1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O75417","full_name":"DNA polymerase theta","aliases":["DNA polymerase eta"],"length_aa":2590,"mass_kda":289.6,"function":"Low-fidelity DNA polymerase with a helicase activity that promotes microhomology-mediated end-joining (MMEJ), an alternative non-homologous end-joining (NHEJ) machinery required to repair double-strand breaks in DNA during mitosis (PubMed:14576298, PubMed:18503084, PubMed:24648516, PubMed:25642963, PubMed:25643323, PubMed:25775267, PubMed:26636256, PubMed:27311885, PubMed:27591252, PubMed:30655289, PubMed:31562312, PubMed:32873648, PubMed:34140467, PubMed:34179826, PubMed:36455556, PubMed:37440612, PubMed:37674080). MMEJ is an error-prone repair pathway that produces deletions of sequences from the strand being repaired and promotes genomic rearrangements, such as telomere fusions, some of them leading to cellular transformation (PubMed:25642963, PubMed:25643323, PubMed:25775267, PubMed:27311885, PubMed:27591252, PubMed:31562312, PubMed:32873648). MMEJ is required during mitosis to repair persistent double-strand breaks that originate in S-phase (PubMed:37440612, PubMed:37674080). Although error-prone, MMEJ protects against chromosomal instability and tumorigenesis (By similarity). The polymerase acts by binding directly the 2 ends of resected double-strand breaks, allowing microhomologous sequences in the overhangs to form base pairs (PubMed:25643323, PubMed:25775267, PubMed:27311885, PubMed:27591252). It then extends each strand from the base-paired region using the opposing overhang as a template (PubMed:25643323, PubMed:25775267, PubMed:27311885, PubMed:27591252). Requires partially resected DNA containing 2 to 6 base pairs of microhomology to perform MMEJ (PubMed:25643323, PubMed:25775267, PubMed:27311885, PubMed:27591252). The polymerase lacks proofreading activity and is highly promiscuous: unlike most polymerases, promotes extension of ssDNA and partial ssDNA (pssDNA) substrates (PubMed:18503084, PubMed:21050863, PubMed:22135286). When the ends of a break do not contain terminal microhomology must identify embedded complementary sequences through a scanning step (PubMed:32234782). Also acts as a DNA helicase, promoting dissociation of the replication protein A complex (RPA/RP-A), composed of RPA1, RPA2 and RPA3, from resected double-strand breaks to allow their annealing and subsequent joining by MMEJ (PubMed:36455556). Removal of RPA/RP-A complex proteins prevents RAD51 accumulation at resected ends, thereby inhibiting homology-recombination repair (HR) pathway (PubMed:25642963, PubMed:28695890). Also shows RNA-directed DNA polymerase activity to mediate DNA repair in vitro; however this activity needs additional evidence in vivo (PubMed:34117057). May also have lyase activity (PubMed:19188258). Involved in somatic hypermutation of immunoglobulin genes, a process that requires the activity of DNA polymerases to ultimately introduce mutations at both A/T and C/G base pairs (By similarity). POLQ-mediated end joining activity is involved in random integration of exogenous DNA hampers (PubMed:28695890)","subcellular_location":"Nucleus; Chromosome","url":"https://www.uniprot.org/uniprotkb/O75417/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/POLQ","classification":"Not Classified","n_dependent_lines":328,"n_total_lines":1208,"dependency_fraction":0.271523178807947},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"HSPA4","stoichiometry":0.2},{"gene":"RBM25","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/POLQ","total_profiled":1310},"omim":[{"mim_id":"610887","title":"POLYMERASE, DNA, NU; POLN","url":"https://www.omim.org/entry/610887"},{"mim_id":"606769","title":"HELICASE, POLQ-LIKE; HELQ","url":"https://www.omim.org/entry/606769"},{"mim_id":"605650","title":"POLYMERASE, DNA, KAPPA; POLK","url":"https://www.omim.org/entry/605650"},{"mim_id":"604419","title":"POLYMERASE, DNA, THETA; POLQ","url":"https://www.omim.org/entry/604419"},{"mim_id":"179617","title":"RAD51 RECOMBINASE; RAD51","url":"https://www.omim.org/entry/179617"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Golgi apparatus","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"bone marrow","ntpm":5.6},{"tissue":"lymphoid tissue","ntpm":4.2}],"url":"https://www.proteinatlas.org/search/POLQ"},"hgnc":{"alias_symbol":["POLH"],"prev_symbol":[]},"alphafold":{"accession":"O75417","domains":[{"cath_id":"3.40.50.300","chopping":"64-247_256-290","consensus_level":"medium","plddt":84.808,"start":64,"end":290},{"cath_id":"3.40.50.300","chopping":"293-367_381-510","consensus_level":"high","plddt":86.1517,"start":293,"end":510},{"cath_id":"1.10.10.10","chopping":"520-565_579-623","consensus_level":"medium","plddt":79.1803,"start":520,"end":623},{"cath_id":"1.10.3380.30","chopping":"628-789","consensus_level":"medium","plddt":86.1575,"start":628,"end":789},{"cath_id":"-","chopping":"792-896","consensus_level":"medium","plddt":78.8562,"start":792,"end":896},{"cath_id":"3.30.420.10","chopping":"1826-1860_1888-1922_1933-2068","consensus_level":"medium","plddt":80.6595,"start":1826,"end":2068},{"cath_id":"1.20.1060.10","chopping":"2093-2145_2179-2222","consensus_level":"medium","plddt":81.9104,"start":2093,"end":2222}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75417","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75417-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75417-F1-predicted_aligned_error_v6.png","plddt_mean":59.34},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=POLQ","jax_strain_url":"https://www.jax.org/strain/search?query=POLQ"},"sequence":{"accession":"O75417","fasta_url":"https://rest.uniprot.org/uniprotkb/O75417.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75417/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75417"}},"corpus_meta":[{"pmid":"25275444","id":"PMC_25275444","title":"Mechanism 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\"finding\": \"POLQ encodes a 2592-amino acid protein with an N-terminal ATPase-helicase domain, a central spacer domain, and a C-terminal family A DNA polymerase domain. Purified full-length human POLQ displays DNA polymerase activity on nicked double-stranded DNA and singly primed templates (resistant to aphidicolin, inhibited by dideoxynucleotides) and a single-stranded DNA-dependent ATPase activity.\",\n      \"method\": \"Baculovirus expression and purification of full-length human POLQ; in vitro polymerase and ATPase assays; domain analysis by sequence\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro biochemical reconstitution of both polymerase and ATPase activities with purified protein, replicated in subsequent studies\",\n      \"pmids\": [\"14576298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The DNA polymerase (pol) domain of POLQ is sufficient for highly efficient bypass of abasic sites, independent of the helicase-like or central domains. Three unique sequence insertions (not found in other A-family polymerases) are required for lesion bypass: insertion 1 increases processivity but does not affect TLS; insertions 2 and 3 are essential for activity on undamaged DNA and completely required for bypass of abasic sites and thymine glycol lesions.\",\n      \"method\": \"In vitro polymerase assay with purified recombinant POLQ pol domain deletion constructs lacking each insertion element individually; translesion synthesis assays on abasic site and thymine glycol templates\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic mutagenesis of insertion elements combined with in vitro biochemical assays; multiple orthogonal deletions tested\",\n      \"pmids\": [\"21050863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"POLQ (pol theta) can extend DNA from mismatched termini (A:G, A:T, A:C mismatches) with less discrimination than E. coli pol I, and can extend from primers placed opposite a (6-4) photoproduct. When combined with DNA polymerase iota (which inserts opposite the lesion), POLQ enables complete bypass of a (6-4) photoproduct, acting as an extender polymerase.\",\n      \"method\": \"In vitro primer extension assays with purified POLQ on templates containing mismatches, cyclobutane pyrimidine dimers, and (6-4) photoproducts; two-polymerase reconstitution with pol iota + POLQ\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with defined substrates and two-polymerase bypass assay, single lab\",\n      \"pmids\": [\"17920341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"POLQ participates in base excision repair (BER) of oxidative DNA damage and has an overlapping function with POLbeta. POLQ-deficient DT40 cells are hypersensitive to H2O2-induced oxidative base damage; this is synergistically enhanced by concurrent POLbeta deletion. Cell extracts from POLQ-null cells show reduced BER activity. POLQ accumulates rapidly at sites of base damage, similar to POLbeta.\",\n      \"method\": \"Gene disruption in chicken DT40 cells (POLQ, POLbeta, polq/polb double mutants); cell survival assays; in vitro BER activity assays on cell extracts; live-cell imaging of POLQ accumulation at laser-induced damage sites\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis via double knockouts, biochemical BER assay, and direct localization experiment; multiple orthogonal methods\",\n      \"pmids\": [\"17018297\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"POLQ mediates an alternative end-joining (alt-EJ) pathway for DNA double-strand break repair that is Ku70-independent and requires POLQ's DNA polymerase activity. POLQ promotes end joining of DNA ends with long 3' single-stranded overhangs by its unique ability to extend DNA from minimally paired primers, generating insertions of base pairs at joins with microhomology to switch-region sequences. Loss of POLQ leads to increased Myc/IgH chromosome translocations, showing POLQ suppresses genomic instability at DSBs.\",\n      \"method\": \"Polq-null murine cell lines; cell-based DNA break end-joining assay with long 3' ssDNA overhang substrates; immunoglobulin class switch recombination assays; Ku70-independent assay; biochemical assays with purified human POLQ; chromosomal translocation analysis by PCR\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — combines purified protein biochemistry, cell-based repair assays, genetic null cells, and chromosomal translocation analysis; multiple orthogonal methods\",\n      \"pmids\": [\"25275444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The chaos1 missense mutation in mouse Polq causes spontaneous and induced chromosome instability (increased micronucleated erythrocytes). Chaos1 is confirmed as a Polq allele by BAC complementation and failed complementation with a Polq-null allele. Double homozygosity with Atm deficiency is synthetically lethal (90% neonatal death), with survivors showing synergistic growth retardation and chromosome instability, indicating that POLQ and ATM operate in distinct but partially compensatory DSB repair pathways.\",\n      \"method\": \"Mouse genetics: BAC complementation, allelic complementation test with gene-targeted Polq null; double-mutant (Polq/Atm) phenotypic analysis; micronucleus assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic complementation and epistasis with Atm null; two independent genetic approaches confirming gene identity; replicated across multiple analyses\",\n      \"pmids\": [\"15542845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"POLQ's non-polymerase domains retain significant function in tolerance to DSB-inducing agents (etoposide, gamma-irradiation): POLQ-null B cells are more sensitive than POLQ-polymerase-inactive (pol domain deleted) cells to these agents, while both are equally sensitive to agents repaired by the polymerase domain (MMC, cisplatin, UV). Class switch recombination is unaffected by loss of either form of POLQ.\",\n      \"method\": \"Gene targeting in CH12F3 B cells to generate POLQ-null and POLQ-polymerase-inactive lines; clonogenic survival assays with multiple DNA-damaging agents; class switch recombination assay\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic comparison of two distinct POLQ mutant cell lines with multiple damage agents; single lab\",\n      \"pmids\": [\"21883722\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In zebrafish embryos, POLQ-mediated alternative end joining (alt-EJ) is the essential and dominant pathway for repair of DSBs during early vertebrate development. Polq-mutant embryos cannot repair CRISPR/Cas9- or ionizing radiation-induced DSBs, fail to survive mutagenesis, and show dramatic differences in mutation profiles compared to wild-type.\",\n      \"method\": \"Zebrafish polq genetic mutants; CRISPR/Cas9-induced DSBs; ionizing radiation; survival assays; mutation spectrum analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic null in vertebrate model with defined DSB induction; single lab, two orthogonal DSB-inducing methods\",\n      \"pmids\": [\"27149851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"POLQ substantially contributes to random integration of foreign DNA in human cells via a mechanism independent of NHEJ. Dual loss of POLQ and LIG4 (essential for NHEJ) abolishes random integration entirely, revealing that POLQ-mediated end joining is the sole homology-independent repair route for foreign DNA integration when NHEJ is absent.\",\n      \"method\": \"POLQ and LIG4 double-knockout human cells; gene targeting frequency assays; random integration frequency measurement\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean human cell double knockout with quantitative integration assays; single lab\",\n      \"pmids\": [\"28695890\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"POLQ is required for MMEJ repair of DSBs generated by both endonucleases (I-SceI, Cas9) and Cas9 nickase-derived single-strand breaks that collapse at replication forks. POLQ deficiency causes sensitivity to topoisomerase inhibitors and ATR inhibitors that induce replication stress and fork collapse, placing POLQ in the response to replication-associated DSBs.\",\n      \"method\": \"POLQ-deficient human cancer cell lines; I-SceI and Cas9/Cas9-nickase DSB repair assays; clonogenic survival with topoisomerase inhibitors and ATR inhibitors\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined genetic loss-of-function with specific mechanistic assays; single lab, multiple repair substrates\",\n      \"pmids\": [\"30655289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"POLQ and RAD52 operate in distinct backup DSB repair pathways with different microhomology requirements: POLQ is important for repair events using 6 nt (but not ≥18 nt) flanking microhomologies and for oligonucleotide microhomology-templated (12–20 nt) repair events requiring nascent DNA synthesis, whereas RAD52 is important for longer (≥50 nt) repeat-mediated repair. Combined disruption of both causes additive hypersensitivity to cisplatin and synthetic reduction in replication fork restart velocity.\",\n      \"method\": \"Human U2OS cells with POLQ mutations (upstream of pol domain), RAD52 knockout, and combined disruption; defined DSB repair substrate assays; fork restart assay; clonogenic survival\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis with defined repair substrates distinguishing microhomology lengths; single lab, multiple orthogonal assays\",\n      \"pmids\": [\"31381562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"POLQ seals post-replicative ssDNA gaps in BRCA1/2-deficient cells or upon PARP inhibitor treatment. Biochemically, the POLQ helicase activity promotes RPA displacement from ssDNA gaps while the polymerase activity fills in the gaps. POLQ also performs microhomology-mediated gap skipping (MMGS), generating deletions during gap repair that resemble genomic scars in POLQ-overexpressing cancers.\",\n      \"method\": \"POLQ-deficient cell lines with BRCA1/2 loss or PARP inhibitor treatment; ssDNA gap accumulation assay; biochemical reconstitution of RPA displacement and gap fill-in with POLQ helicase and polymerase domain activities; genomic scar analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — biochemical reconstitution of both helicase and polymerase activities in gap sealing, combined with genetic experiments and genomic scar analysis; multiple orthogonal methods\",\n      \"pmids\": [\"36455556\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"POLQ promotes end joining in cis at DSBs, limiting breaks available for interhomolog recombination (IHR) in trans. Depletion of POLQ causes a dramatic increase in IHR and in copy-neutral loss of heterozygosity (cnLOH) at CRISPR-Cas9-targeted DSBs in human cells.\",\n      \"method\": \"POLQ depletion in human cells; CRISPR-Cas9 targeted DSBs at both homologs; quantitative IHR and cnLOH frequency assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined genetic depletion with quantitative recombination assays; single lab\",\n      \"pmids\": [\"32873648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In C. elegans, polq-1 functions in a distinct ICL repair pathway that is dependent on brc-1 (CeBRCA1), separate from the Fanconi anemia-dependent pathway used by hel-308. Epistasis analysis places polq-1 and hel-308 in different DNA repair pathways.\",\n      \"method\": \"C. elegans polq-1 and hel-308 mutants; survival assays after ICL agent treatment; genetic epistasis analysis with Fanconi anemia pathway mutants and brc-1\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in C. elegans model organism with multiple pathway mutants; single lab\",\n      \"pmids\": [\"18472307\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"POLQ-mediated end-joining (TMEJ) is the primary mechanism generating structural variants (SVs) at common fragile sites (CFSs) in human cells under replication stress. SV junction formation increases 5-fold after G2-to-M-phase transition; neither SV formation nor CFS expression depend on mitotic DNA synthesis (MiDAS). POLQ inhibition reduces SV formation, placing POLQ as the principal driver of nonrecurrent SV formation at CFSs.\",\n      \"method\": \"Error-minimized capture sequencing of CFS DNA from human cell lines after aphidicolin treatment; DNA repair pathway inhibition (POLQ and others); cell cycle fractionation; analysis of tens of thousands of de novo SV junctions\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — large-scale sequencing combined with pharmacological inhibition and cell-cycle analysis; single lab\",\n      \"pmids\": [\"39505880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"POLQ inhibition in HR-deficient BRCA2-deficient pancreatic cancer cells is synthetically lethal and activates cGAS-STING signaling by enhancing cytosolic micronuclei formation, leading to increased CD8+ T cell infiltration in vivo.\",\n      \"method\": \"POLQ knockdown in human and murine HR-deficient PDAC models; synthetic lethality assay with BRCA1/2 and ATM mutations; micronuclei quantification; cGAS-STING signaling assay; in vivo syngeneic tumor model with CD8+ T cell quantification\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined genetic knockdown with mechanistic immune signaling readout and in vivo validation; single lab\",\n      \"pmids\": [\"36976649\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In mouse embryonic stem cells, the RNA-binding protein DPPA5A promotes cryptic exon (CE) inclusion in Polq pre-mRNA, disrupting normal POLθ protein expression and suppressing MMEJ activity. Depletion of DPPA5A decreases CE inclusion in Polq, restores POLθ expression, and stimulates MMEJ activity.\",\n      \"method\": \"DPPA5A depletion in mouse ESCs; RT-PCR for CE inclusion in Polq; Western blot for POLθ protein; MMEJ activity assays; enforced DPPA5A expression in NIH3T3 cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic depletion and overexpression with mechanistic splicing and activity readouts; single lab, two cell types\",\n      \"pmids\": [\"37459543\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HPV16 E6 oncoprotein stabilizes POLQ protein by activating the E3 ubiquitin ligase UBE3A/E6AP, which ubiquitinates and degrades RAD23A — a shuttle protein required for delivering polyubiquitinated POLQ to the proteasome. Loss of RAD23A phenocopies HPV16 E6 expression, leading to POLQ stabilization and increased MMEJ activity. This E6-UBE3A-RAD23A-POLQ axis promotes viral genome integration.\",\n      \"method\": \"Co-expression of HPV16 E6 in cells; Western blot for POLQ and RAD23A protein levels; UBE3A knockdown/knockout; RAD23A knockdown; MMEJ activity assays; viral integration assays; ubiquitination assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway dissection with multiple genetic perturbations; preprint, single lab\",\n      \"pmids\": [\"41357977\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SMARCB1 (a core BAF/SWI-SNF subunit) is required for maintaining POLQ protein levels by facilitating nuclear export of POLQ mRNA through interaction with the nuclear pore complex. Loss of SMARCB1 reduces POLQ protein, impairs MMEJ, and forces a compensatory hyper-dependence on the FA/BRCA pathway.\",\n      \"method\": \"SMARCB1-deficient rhabdoid tumor cell lines; Western blot for POLQ protein; POLQ mRNA nuclear export assay; nuclear pore complex interaction; MMEJ activity assay; synthetic lethality with FA/BRCA pathway inhibition\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, single lab, nuclear export mechanism inferred from interaction data without full mechanistic reconstitution\",\n      \"pmids\": [\"bio_10.1101_2025.11.20.689563\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"EWSR1 is a splicing factor that promotes accurate splicing of POLQ pre-mRNA. The EWS-FLI1 fusion oncoprotein, or loss of EWSR1, causes exon 25 skipping of the POLQ transcript, decreased POLθ protein expression, and impaired MMEJ activity in Ewing sarcoma cells. Knockdown of EWS-FLI1 restores POLθ expression and increases MMEJ activity.\",\n      \"method\": \"Ewing sarcoma cell lines with EWS-FLI1 expression or EWSR1 loss; RT-PCR for POLQ exon 25 skipping; Western blot for POLθ; MMEJ activity assay; EWS-FLI1 knockdown rescue experiments; POLQ mitotic foci quantification\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function and rescue experiments defining splicing mechanism; preprint, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"bio_10.1101_2025.05.06.651696\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"POLQ variant forms (patient-derived melanoma variants) show decreased efficiency during bypass and extension of cyclobutane pyrimidine dimers (CPDs) compared to wild-type, but two of three tested variants nonetheless protect against UV-induced cell death, dissociating lesion bypass efficiency from cell survival.\",\n      \"method\": \"In vitro primer extension assays with purified recombinant POLQ variants on CPD-containing templates; cell survival assays after UV irradiation with POLQ variant expression\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro biochemical assay with purified proteins is rigorous, but preprint, single lab, limited variants tested\",\n      \"pmids\": [\"41357977\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"POLQ (DNA polymerase theta) is a large multidomain protein with an N-terminal DNA-dependent ATPase/helicase domain and a C-terminal family A DNA polymerase domain; the polymerase domain harbors three unique insertion elements (insertions 2 and 3 essential for lesion bypass) that allow it to extend DNA from minimally paired primers and bypass abasic sites and thymine glycol lesions, while the helicase domain displaces RPA from ssDNA gaps; together, these activities define POLQ as the central effector of theta-mediated end joining (TMEJ/alt-EJ), a Ku-independent pathway that joins DSBs using short (≥6 nt) microhomologies, seals post-replicative ssDNA gaps in BRCA-deficient cells via microhomology-mediated gap skipping, contributes to BER of oxidative damage redundantly with POLbeta, suppresses chromosome translocations and interhomolog recombination by promoting cis end-joining, and drives the somatic mutation scars and structural variants prevalent in HR-deficient cancers.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"POLQ (DNA polymerase theta) is the central effector of theta-mediated/alternative end joining (TMEJ/alt-EJ), a Ku-independent double-strand break (DSB) repair pathway that joins ends through short microhomologies [#4]. It is a large multidomain enzyme combining an N-terminal single-stranded-DNA-dependent ATPase/helicase domain with a C-terminal family A DNA polymerase domain, and purified full-length protein displays both polymerase activity on primed and nicked templates and ssDNA-dependent ATPase activity [#0]. The polymerase domain is intrinsically lesion-tolerant: three unique sequence insertions absent from other A-family polymerases (insertions 2 and 3 being essential) enable synthesis on undamaged DNA and bypass of abasic sites and thymine glycol [#1], and POLQ extends from mismatched primers and from primers opposite a (6-4) photoproduct, acting as an extender polymerase in concert with pol iota [#2]. In end joining, POLQ uniquely extends DNA from minimally paired 3' overhangs, generating templated insertions at microhomology junctions, and its polymerase activity drives repair of breaks bearing ~6 nt microhomologies in a pathway distinct from RAD52-dependent long-repeat repair [#4, #10]. The two enzymatic domains cooperate beyond DSBs: the helicase activity displaces RPA from post-replicative ssDNA gaps while the polymerase fills them, and microhomology-mediated gap skipping generates characteristic deletion scars in BRCA1/2-deficient or PARP-inhibited cells [#11]. POLQ also contributes redundantly with POLbeta to base excision repair of oxidative damage [#3], suppresses chromosome translocations and interhomolog recombination by promoting end joining in cis [#4, #12], and is the principal driver of structural variants at common fragile sites under replication stress [#14]. POLQ loss is synthetically lethal in HR-deficient cancers, where its inhibition activates cGAS-STING signaling and CD8+ T-cell infiltration [#15], and POLQ protein abundance and MMEJ activity are tuned by transcript splicing and protein-stability control by factors including DPPA5A and EWSR1 [#16, #19].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established the basic enzymatic identity of POLQ, answering whether the predicted dual-domain protein is biochemically active.\",\n      \"evidence\": \"Baculovirus expression of full-length human POLQ with in vitro polymerase and ATPase assays plus sequence-based domain analysis\",\n      \"pmids\": [\"14576298\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define a cellular pathway for either activity\", \"No functional role for the helicase/ATPase domain established\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Linked POLQ to genome stability in vivo and to DSB repair pathway architecture by showing genetic interaction with ATM.\",\n      \"evidence\": \"Mouse chaos1 missense allele characterized by BAC and allelic complementation; Polq/Atm double-mutant phenotyping and micronucleus assays\",\n      \"pmids\": [\"15542845\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of chromosome instability not defined\", \"Did not identify the repair pathway POLQ acts in\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined a base excision repair role for POLQ redundant with POLbeta, answering which damage types depend on POLQ.\",\n      \"evidence\": \"DT40 single and double knockouts, in vitro BER assays on extracts, and live-cell imaging of POLQ recruitment to laser damage\",\n      \"pmids\": [\"17018297\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise BER step performed by POLQ not resolved\", \"Relationship between BER role and DSB role unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showed POLQ functions as a lesion-tolerant extender polymerase, explaining how it copes with mismatched and damaged termini.\",\n      \"evidence\": \"In vitro primer extension on mismatch, CPD and (6-4) photoproduct templates and two-polymerase reconstitution with pol iota\",\n      \"pmids\": [\"17920341\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of (6-4) bypass not established\", \"Partner insertases in cells not identified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified the structural basis of POLQ's lesion bypass by mapping three unique insertion elements required for activity.\",\n      \"evidence\": \"Systematic deletion mutagenesis of pol-domain insertions with in vitro TLS assays on abasic and thymine glycol templates\",\n      \"pmids\": [\"21050863\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal structure of the active insertions\", \"Contribution of insertions to end joining not tested here\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Separated functions of POLQ's polymerase and non-polymerase domains, showing the helicase-like region has independent activity in DSB-agent tolerance.\",\n      \"evidence\": \"POLQ-null versus pol-domain-deleted CH12F3 B cells with clonogenic survival across multiple damaging agents and CSR assays\",\n      \"pmids\": [\"21883722\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Biochemical function of the non-polymerase domain in survival undefined\", \"Single cell-line system\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined POLQ as the effector of Ku-independent alt-EJ that uses minimally paired primers and suppresses translocations, establishing the core TMEJ mechanism.\",\n      \"evidence\": \"Polq-null murine cells, long-3'-overhang end-joining substrates, CSR and Ku70-independent assays, purified-protein biochemistry, and translocation PCR\",\n      \"pmids\": [\"25275444\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"End resection factors feeding POLQ not defined\", \"Ligase used to seal POLQ-extended ends not identified here\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed alt-EJ via POLQ is the dominant DSB repair route in early vertebrate development, establishing physiological importance.\",\n      \"evidence\": \"Zebrafish polq mutants with CRISPR/Cas9- and irradiation-induced DSBs, survival and mutation-spectrum analysis\",\n      \"pmids\": [\"27149851\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Developmental-stage specificity of dependence not mechanistically explained\", \"Single model organism\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated POLQ mediates homology-independent foreign-DNA integration as the sole route when NHEJ is absent.\",\n      \"evidence\": \"POLQ/LIG4 double-knockout human cells with random integration and gene targeting frequency assays\",\n      \"pmids\": [\"28695890\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of capturing exogenous DNA ends not detailed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Connected POLQ to replication-associated breaks and distinguished its microhomology preference from RAD52's, refining pathway boundaries.\",\n      \"evidence\": \"POLQ-deficient and RAD52-knockout human cells with defined-microhomology DSB substrates, fork-restart assays, and survival with TOP/ATR inhibitors\",\n      \"pmids\": [\"30655289\", \"31381562\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How POLQ is recruited specifically to collapsed forks unclear\", \"Determinants of microhomology length selection not molecularly defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed POLQ enforces cis end-joining to suppress interhomolog recombination and copy-neutral LOH, explaining its anti-recombinogenic role.\",\n      \"evidence\": \"POLQ depletion with CRISPR-Cas9 DSBs on both homologs and quantitative IHR/cnLOH assays in human cells\",\n      \"pmids\": [\"32873648\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism restricting break mobility not defined\", \"Depletion rather than clean genetic null\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined a post-replicative ssDNA gap-sealing function in BRCA-deficient cells, reconstituting cooperation between the helicase (RPA displacement) and polymerase (gap fill-in) activities.\",\n      \"evidence\": \"POLQ-deficient cells with BRCA1/2 loss or PARP inhibition, gap-accumulation assays, biochemical reconstitution of both domain activities, and genomic-scar analysis\",\n      \"pmids\": [\"36455556\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Trigger directing POLQ to gaps versus DSBs unclear\", \"MMGS choice between fill-in and skipping not regulated mechanistically\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed POLQ inhibition in HR-deficient tumors is synthetically lethal and engages cGAS-STING-driven anti-tumor immunity, providing therapeutic mechanism.\",\n      \"evidence\": \"POLQ knockdown in HR-deficient PDAC models, synthetic-lethality and micronuclei assays, cGAS-STING readouts, and in vivo CD8+ T-cell quantification\",\n      \"pmids\": [\"36976649\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Source of immunogenic cytosolic DNA not fully traced to POLQ activity\", \"Single tumor type\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Revealed transcript-level control of POLQ via DPPA5A-driven cryptic exon inclusion that suppresses POLθ expression and MMEJ.\",\n      \"evidence\": \"DPPA5A depletion and overexpression in mouse ESCs and NIH3T3 with RT-PCR, Western blot, and MMEJ assays\",\n      \"pmids\": [\"37459543\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding of DPPA5A to Polq pre-mRNA not shown here\", \"Human relevance untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Established POLQ as the principal driver of nonrecurrent structural variants at common fragile sites under replication stress.\",\n      \"evidence\": \"Error-minimized capture sequencing of CFS DNA after aphidicolin, pathway inhibition, and cell-cycle fractionation in human cells\",\n      \"pmids\": [\"39505880\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Why SV formation peaks after G2-to-M not mechanistically explained\", \"Pharmacological rather than genetic POLQ loss\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified multiple convergent mechanisms controlling POLQ protein stability and splicing accuracy in cancer contexts (HPV16 E6/UBE3A/RAD23A, EWSR1/EWS-FLI1, SMARCB1).\",\n      \"evidence\": \"HPV16 E6 and UBE3A/RAD23A perturbations, EWSR1/EWS-FLI1 splicing assays, and SMARCB1-deficient cell analyses with MMEJ readouts (preprints)\",\n      \"pmids\": [\"41357977\", \"bio_10.1101_2025.05.06.651696\", \"bio_10.1101_2025.11.20.689563\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanisms are preprint-stage and single-lab\", \"Nuclear-export mechanism for POLQ mRNA inferred without reconstitution\", \"Generality across tumor types untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How POLQ is recruited to and selects among its substrates (DSB ends, post-replicative gaps, fragile sites) and which factors hand off ends to and seal POLQ-extended products remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of full-length POLQ engaging a substrate\", \"Recruitment and substrate-choice determinants undefined\", \"Ligation partner sealing POLQ-extended junctions not identified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140097\", \"supporting_discovery_ids\": [0, 1, 2, 11]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [0, 11]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [3, 4, 11]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [14, 15]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"POLB\", \"RAD52\", \"RAD23A\", \"UBE3A\", \"DPPA5A\", \"EWSR1\", \"SMARCB1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}