{"gene":"PARP1","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":2012,"finding":"PARP inhibitors trap PARP1 and PARP2 as stable complexes at damaged DNA sites; trapped PARP-DNA complexes are more cytotoxic than unrepaired SSBs caused by PARP inactivation alone. Trapping potency differs markedly among inhibitors (niraparib > olaparib >> veliparib) independent of catalytic inhibitory potency.","method":"Biochemical trapping assays, genetically altered DT40 cell lines with deletions in specific DNA repair genes, cytotoxicity measurements","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (biochemical trapping, genetic epistasis panel of 30 cell lines), widely replicated across subsequent studies","pmids":["23118055"],"is_preprint":false},{"year":2015,"finding":"PARP-1 activation requires local unfolding of the helical subdomain (HD) of its catalytic domain. The HD acts as an autoinhibitory domain that blocks productive NAD+ binding; DNA break detection causes HD unfolding to relieve this autoinhibition.","method":"Hydrogen/deuterium exchange-mass spectrometry (HXMS), crystallographic analysis of HD deletion mutants, biochemical activity assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution, mutagenesis, crystallography, and HXMS in a single rigorous study","pmids":["26626480"],"is_preprint":false},{"year":2020,"finding":"Structurally distinct PARP inhibitors drive PARP-1 allostery in opposite directions: some promote PARP-1 release from a DNA break (pro-release), while others retain PARP-1 on a DNA break (pro-retention). Converting a pro-release compound to a pro-retention compound increased cancer cell killing.","method":"Structural studies, biophysical binding assays, cell viability assays, synthesis of novel PARPi compound","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 / Strong — structural and biochemical reconstitution with functional validation and chemical probe confirmation","pmids":["32241924"],"is_preprint":false},{"year":2016,"finding":"HPF1 (C4orf27) forms a robust complex with PARP-1 in cells, is recruited to DNA lesions in a PARP-1-dependent but catalysis-independent manner, promotes PARP-1-dependent in trans ADP-ribosylation of histones, and limits DNA damage-induced hyper-automodification of PARP-1.","method":"Co-immunoprecipitation, live-cell recruitment assays, in vitro ADP-ribosylation assays, knockdown/knockout cell biology","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, in vitro enzymatic assays, multiple orthogonal methods in a single focused study","pmids":["27067600"],"is_preprint":false},{"year":2021,"finding":"Serine ADP-ribosylation at PARP1 residues S499, S507, and S519 (dependent on HPF1) counteracts PARP1 trapping on chromatin; loss of HPF1 or ARH3 increases PARPi-induced PARP1 trapping and sensitizes cells to PARP inhibitors.","method":"Mass spectrometry mapping of modification sites, site-directed mutagenesis, PARP1 trapping assays, genetic knockouts","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — MS-level site identification, mutagenesis, and functional trapping assays in a single study with multiple orthogonal methods","pmids":["34210965"],"is_preprint":false},{"year":2013,"finding":"Crystal structure of essential PARP-1 domains in complex with a DNA strand break revealed that multiple PARP-1 domains collapse onto damaged DNA through interdomain contacts, and that PARP-1 uses zinc fingers to detect DNA breaks through sequence-independent interaction with exposed nucleotide bases, coupling damage detection to elevated PAR production.","method":"X-ray crystallography, biochemical activity assays","journal":"Current opinion in structural biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with mechanistic biochemical validation, independently replicated in subsequent structural studies","pmids":["23333033"],"is_preprint":false},{"year":2010,"finding":"PARP-1 regulates chromatin structure and transcription by PARylating and inhibiting/excluding the histone demethylase KDM5B to prevent demethylation of H3K4me3, and by promoting exclusion of linker histone H1 to open promoter chromatin, creating a permissive environment for RNA Pol II loading.","method":"ChIP, RNA Pol II loading assays, PARP-1 depletion, KDM5B activity assays, histone modification analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal chromatin and biochemical methods, mechanistic pathway dissection in a single rigorous study","pmids":["20832725"],"is_preprint":false},{"year":2006,"finding":"PARP-1 binds to DNA DSB ends in direct competition with Ku and operates in an alternative backup NHEJ pathway together with DNA ligase III, distinct from the classical NHEJ pathway using DNA-PKcs/Ku/Ligase IV/XRCC4. When Ku and classical NHEJ components are absent, PARP-1 is recruited for DSB repair.","method":"DNA end-binding competition assays, genetic deletion of NHEJ components, DSB repair kinetics, PARP inhibitor treatment","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with multiple deletion backgrounds, biochemical competition assays, pharmacological inhibition","pmids":["17088286"],"is_preprint":false},{"year":2010,"finding":"PARP-1 ADP-ribosylates Smad3 and Smad4 (identified as PARP-1-interacting partners by unbiased proteomic screen), dissociating Smad complexes from DNA and thereby attenuating Smad-mediated transcription and TGF-β-induced epithelial-mesenchymal transition.","method":"Unbiased proteomic screen, Co-IP, in vitro ADP-ribosylation assay, DNA-binding assays, EMT assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — proteomic identification, biochemical validation, in vitro ADP-ribosylation, functional cellular outcome","pmids":["21095583"],"is_preprint":false},{"year":2014,"finding":"PARP1 (ARTD1) activation leads to PAR synthesis that suppresses glycolysis independently of NAD+ depletion; PAR binds directly to hexokinase 1 (HK1), suppressing HK1 activity and blocking glycolysis and ATP production after DNA damage.","method":"Real-time metabolic measurements (Seahorse), proteomics-based PAR interactome after DNA damage, HK1 activity assays, direct NAD+ depletion comparison","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — interactome proteomics, enzymatic activity assays, metabolic measurements, mechanistic dissection distinguishing PAR from NAD+ depletion","pmids":["25220464"],"is_preprint":false},{"year":2015,"finding":"Timeless physically interacts with PARP-1 via its PAB (PARP-1-binding domain) independently of poly(ADP-ribosylation), specifically with PARP-1 but not PARP-2 or PARP-3; Timeless recruitment to DNA damage requires PARP-1 but not PARylation; Timeless-PARP-1 interaction is required for efficient homologous recombination repair.","method":"Crystal structure of Timeless PAB-PARP-1 catalytic domain complex, Co-IP, laser-induced DNA damage recruitment assays, HR repair assays, PARP inhibitor trapping experiments","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus Co-IP, live cell imaging, and functional HR assays in a single study","pmids":["26344098"],"is_preprint":false},{"year":2020,"finding":"TRIP12 ubiquitin E3 ligase binds PARP1 via its central PAR-binding WWE domain and uses its HECT domain to catalyze polyubiquitylation of PARP1, triggering proteasomal degradation and limiting PARPi-induced cytotoxic PARP1 trapping.","method":"Co-IP, domain mapping, ubiquitylation assays, proteasome inhibitor experiments, TRIP12 knockout cells, PARP1 trapping measurements","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, domain-function mapping, biochemical ubiquitylation assays, genetic knockout validation","pmids":["32755579"],"is_preprint":false},{"year":2022,"finding":"Single-molecule FRET and structural ensemble calculations revealed that PARP-1 N-terminal zinc fingers convert DNA SSBs from a largely unperturbed conformation via an intermediate to a highly kinked DNA conformation through an induced-fit mechanism via a multi-domain assembly cascade; niraparib shifts equilibrium towards unkinked DNA conformation, while EB47 stabilizes the kinked state.","method":"Single-molecule FRET (smFRET), structural ensemble calculations, PARP inhibitor comparison","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — single-molecule structural dynamics with quantitative mechanistic data and inhibitor comparison","pmids":["36323657"],"is_preprint":false},{"year":2022,"finding":"PARPi modulate PARP1-DNA retention through a two-step mechanism: primary step of catalytic inhibition via NAD+ binding competition, followed by allosteric modulation; retention potency is predominantly determined by NAD+ competition, while allosteric effects can either increase or decrease retention.","method":"Single-molecule assays monitoring PARP1 retention on DNA in real time","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1 / Moderate — single-molecule reconstitution directly measuring PARP1-DNA dynamics in real time","pmids":["36070389"],"is_preprint":false},{"year":2020,"finding":"Clinical PARP inhibitors do not physically stall PARP1 at DNA damage sites; instead, PARP1 exchanges rapidly even in the presence of PARPi. Persistent PARP1 foci represent continued recruitment of different PARP1 molecules due to delayed repair from attenuated XRCC1-LIG3 recruitment. PARP1-H862D (NAD+ interacting residue mutant, not PARylation-deficient E988K) forms stable foci, identifying NAD+ interaction as key to PARP1 exchange.","method":"Quantitative live-cell imaging, FRAP, PARP1 mutant analysis (H862D, E988K), Xrcc1 knockout","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — quantitative live-cell imaging with FRAP and mutagenesis, multiple genetic controls","pmids":["32890402"],"is_preprint":false},{"year":2009,"finding":"PARP-1 binds damaged DNA (nick, blunt end, 3' extension) as a monomer with similar affinity for all three, and undergoes a conformational change at the zinc ribbon domain upon DNA binding that leads to catalytic activation; the N-terminal half is extended and flexible in solution but compacts around damaged DNA.","method":"Small-angle X-ray scattering, biochemical binding and activity assays, thermodynamic measurements","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — SAXS structural analysis combined with biochemical and thermodynamic validation","pmids":["19962992"],"is_preprint":false},{"year":2014,"finding":"PARP-1 poly(ADP-ribosyl)ates GAPDH in ischemic renal proximal tubules, inhibiting GAPDH enzymatic activity and blocking glycolysis, thereby exacerbating ATP depletion and necrotic cell death.","method":"In vitro and in vivo hypoxia models, PARP-1 inhibitor treatment, GAPDH activity assays, detection of poly(ADP-ribosyl)ated GAPDH, ATP measurements","journal":"Journal of the American Society of Nephrology : JASN","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — enzymatic activity assays and PARylation detection in both in vitro and in vivo models, single lab","pmids":["19056868"],"is_preprint":false},{"year":2007,"finding":"PARP-1 is directly activated by phosphorylated ERK2 through a physical interaction independent of DNA damage and DNA binding; this ERK2-induced PARP-1 activation amplifies ERK signaling, enhancing Elk1 phosphorylation, core histone acetylation, and c-fos expression.","method":"Co-immunoprecipitation, in vitro kinase/activation assays, reporter assays for Elk1 and c-fos, histone acetylation measurements","journal":"Trends in pharmacological sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct interaction and activation demonstrated, but single lab and limited structural confirmation","pmids":["17950910"],"is_preprint":false},{"year":2014,"finding":"H2S induces S-sulfhydration of MEK1 at cysteine 341, leading to phosphorylation of ERK1/2 and its nuclear translocation where ERK directly interacts with and activates PARP-1; activated PARP-1 then recruits XRCC1 and DNA ligase III to DNA breaks for repair.","method":"S-sulfhydration assay, site-directed mutagenesis (MEK1 C341), Co-IP of ERK-PARP-1, DNA repair foci assays","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, mutagenesis, and functional repair assays, single lab","pmids":["24778456"],"is_preprint":false},{"year":2008,"finding":"PARP-1 poly(ADP-ribosyl)ates PPARγ in cardiac fibroblasts under basal conditions, preventing PPARγ DNA binding and suppressing PPARγ-target genes including adiponectin; PARP-1 inhibition enhances PPARγ DNA binding and transactivation.","method":"Co-immunoprecipitation, EMSA, Southwestern blot, PARP-1 siRNA/inhibitor, RT-PCR/Western blot","journal":"Cardiovascular research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — PARylation detected by Co-IP, DNA binding by EMSA, functional gene expression confirmed, single lab","pmids":["18815186"],"is_preprint":false},{"year":2009,"finding":"PARP-1 directly binds and poly(ADP-ribosyl)ates FOXO1, acting as a corepressor on the p27(Kip1) promoter through FOXO1 interaction; PARP-1 represses FOXO1-mediated p27 expression and the repressive effect does not require PARylation enzymatic activity.","method":"Co-IP, in vitro PARylation assay, ChIP, luciferase reporter assay, PARP-1 knockdown","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ChIP, and functional reporter assay, single lab; catalytic-independent repression established by mutant analysis","pmids":["19281796"],"is_preprint":false},{"year":2013,"finding":"DNA-PK activation is required upstream of PARP-1 recruitment to chromatin and PARP-1 activation in cisplatin-damaged cells; inhibition of DNA-PK prevents PARP-1 activation and its chromatin recruitment, and both DNA-PK and PARP-1 are required for DNA damage-induced inhibition of rRNA synthesis.","method":"In situ run-on rRNA synthesis assay, DNA-PK and PARP-1 inhibitors, chromatin fractionation, cell cycle analysis","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway ordering by pharmacological inhibition with chromatin fractionation readout, single lab","pmids":["23775790"],"is_preprint":false},{"year":2013,"finding":"PARP-1 allosteric regulation via interdomain contacts is required for DNA-damage-dependent catalytic activation; disruption of domain-domain contacts by mutagenesis prevents DNA-damage-dependent catalytic activation without affecting PARP-1 recruitment to DNA damage or transcriptional regulation.","method":"Site-directed mutagenesis of domain-domain contact residues, PARP-1 activity assays, live-cell recruitment assays, transcriptional reporter assays","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis with activity and localization assays, single lab","pmids":["24189460"],"is_preprint":false},{"year":2014,"finding":"MacroH2A1.1 recruits PARP-1 to promote CBP-mediated acetylation of histone H2B at K12 and K120, which regulates gene expression; this regulation is lost in cancer cells.","method":"RNA-seq, Co-IP, ChIP-seq, histone modification analysis in primary human cells vs cancer cells","journal":"Nature structural & molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ChIP, and functional gene expression with primary vs cancer cell comparison, single lab","pmids":["25306110"],"is_preprint":false},{"year":2013,"finding":"PARP-1 ADP-ribosylates Sox2 during somatic cell reprogramming, promoting Sox2 binding to the Fgf4 enhancer and activating Fgf4 expression; loss of PARP-1 or its catalytic activity reduces reprogramming efficiency, which is rescued by exogenous Fgf4.","method":"PARP-1 knockout fibroblasts, PARP inhibitor treatment, in vitro PARylation of Sox2, ChIP at Fgf4 enhancer, Fgf4 rescue experiment","journal":"Stem cells (Dayton, Ohio)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — PARylation assay, ChIP, and rescue experiment establishing pathway; single lab","pmids":["23939864"],"is_preprint":false},{"year":2018,"finding":"PARP-1 forms covalent DNA-protein crosslinks (DPCs) at apurinic/apyrimidinic (AP) sites via Schiff base formation between a PARP-1 lysine side chain and the C1' of the AP site; repair of PARP-1 DPCs involves proteasomal degradation of PARP-1 followed by tyrosyl-DNA phosphodiesterase 1 (TDP1) processing of the remaining adduct, completed by the BER machinery.","method":"In vitro DPC formation assay, proteasome inhibitor experiments, model DNA substrate repair assays, TDP1 activity assay","journal":"DNA repair","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and cell-based DPC assays with proteasome inhibition and biochemical repair reconstitution, single lab","pmids":["30466837"],"is_preprint":false},{"year":2017,"finding":"MEIS transcription factors associate with chromatin-bound PBX1 at target promoters, recruit PARP1/ARTD1, and initiate PARP1-mediated eviction of linker histone H1 to open chromatin during neuronal differentiation.","method":"ChIP, Co-IP, live-cell imaging, PARP1 knockdown, differentiation assays","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and Co-IP with functional differentiation outcome, single lab","pmids":["28739678"],"is_preprint":false},{"year":2022,"finding":"PARP-1 mediates the association of DDX18, a putative RNA helicase, with R-loop structures; DDX18 depletion causes aberrant R-loop accumulation and DNA replication defects that are rescued by RNase H1 overexpression, placing PARP-1 in a pathway regulating R-loop homeostasis.","method":"Co-IP, R-loop detection assays (S9.6 antibody), DDX18 knockdown, RNase H1 rescue, γH2AX and RPA32/RAD51 foci","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and functional rescue experiments establishing pathway position, single lab","pmids":["35858569"],"is_preprint":false},{"year":2022,"finding":"PARP-1 PARylates NLRP3 upon ATP stimulation, translocating to the cytosol; PARP-1 bridges NLRP3 and TXNIP to facilitate NLRP3 inflammasome complex assembly and IL-1β production in macrophages.","method":"PARP-1 knockout BMDMs, PARP-1 inhibitor, Co-IP of NLRP3-PARP-1-TXNIP, cytosol/nuclear fractionation, IL-1β ELISA","journal":"Cellular and molecular life sciences : CMLS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO, Co-IP, and fractionation with functional inflammasome readout, single lab","pmids":["35098371"],"is_preprint":false},{"year":2008,"finding":"Integrin-linked kinase (ILK) regulates E-cadherin expression through PARP-1; PARP-1 binds to the Snail promoter ILK Responsive Element (SIRE) in an ILK-dependent manner, promoting Snail and ZEB1 expression and repressing E-cadherin.","method":"EMSA/Southwestern blot (SIRE-binding), PARP-1 siRNA, ILK silencing, ChIP-like promoter binding assay","journal":"Developmental dynamics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, promoter binding assay with siRNA but no direct PARylation assay of the pathway components","pmids":["18773488"],"is_preprint":false},{"year":2019,"finding":"PARP-1 promotes NF-κB nuclear translocation and binding to NF-κB response sequences in macrophages, driving CCL2 production and NK cell recruitment to viral infection sites; peritoneal macrophages are the main source of PARP-1-dependent CCL2.","method":"PARP-1 knockout mice, vaccinia virus infection model, NF-κB nuclear translocation assay, CCL2 ELISA, CCR2-blocking experiments","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO in vivo model, NF-κB binding assay, and chemokine axis validation, single lab","pmids":["31217354"],"is_preprint":false},{"year":2013,"finding":"PARP-1 interacts with and regulates HIF-2α protein levels and HIF-2-dependent gene expression (ANGPTL4, erythropoietin); PARP-1 forms a complex with HIF-2α that is sensitive to PARP inhibition and appears to protect HIF-2α from VHL-dependent degradation.","method":"Co-IP, PARP-1 knockdown/inhibition, HIF-2α mRNA and protein analysis, PARP-1 knockout mice (EPO levels, red cell counts)","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, genetic/pharmacological suppression, and in vivo validation in knockout mice, single lab","pmids":["23455322"],"is_preprint":false},{"year":2020,"finding":"SIRT3 interacts with PARP-1 in the nucleus of cardiomyocytes under stress, deacetylates PARP-1, and thereby reduces PARP-1 activity and cardiac hypertrophic gene expression.","method":"Co-immunoprecipitation, adenoviral SIRT3 overexpression, PARP-1 acetylation assay, isoproterenol/phenylephrine hypertrophy models","journal":"Aging","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP, single lab, acetylation measured but deacetylase specificity not fully reconstituted in vitro","pmids":["32139662"],"is_preprint":false},{"year":2017,"finding":"PARP-1 enzymatic activity promotes E2F1 transcription factor activity and E2F1-mediated induction of homologous recombination DNA repair factors; PARP-1 inhibition reduces HR factor availability, inducing 'BRCA-ness'.","method":"Transcriptional profiling, E2F1 reporter assays, HR factor protein measurements, PARP inhibitor treatment","journal":"EMBO molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transcriptional profiling plus mechanistic E2F1 reporter and HR factor assays, single lab","pmids":["30467127"],"is_preprint":false},{"year":2015,"finding":"LRP1 directly interacts with PARP-1 in human retinal microvascular endothelial cells; this interaction decreases under hypoxia, and LRP1 knockdown increases PARP-1 activity with subsequent phosphorylation of retinoblastoma protein and CDK2, promoting cell cycle progression and angiogenesis.","method":"Co-IP, LRP1 knockdown, PARP-1 activity assay, Ki67 staining, pRb/CDK2 western blot, oxygen-induced retinopathy model","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP, single lab, activity assay without direct mechanistic reconstitution","pmids":["26634655"],"is_preprint":false},{"year":2021,"finding":"Mitochondrial NAD+ controls nuclear ARTD1 (PARP1)-induced ADP-ribosylation; H2O2-induced oxidative stress reciprocally induces nuclear and reduces mitochondrial ADP-ribosylation, demonstrating a NAD+-mediated mitochondrial-nuclear crosstalk that modulates PARP1 chromatin retention and PARPi efficacy.","method":"Immunofluorescence, western blot, mass spectrometry, respiratory chain inhibition, FCCP uncoupler, MMS-induced PARP1 retention assays","journal":"Molecular cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (IF, WB, MS) with pharmacological manipulation, single lab","pmids":["33450210"],"is_preprint":false},{"year":2021,"finding":"PARP-1 binds G-quadruplex structures with nanomolar affinity, but only specific G-quadruplex loop features (as found in the c-KIT promoter sequence) stimulate PARP-1 catalytic activity; oxidized G-quadruplexes also stimulate PARP-1 activity through their loop structures.","method":"In vitro binding affinity measurements, PARP-1 enzymatic activity assays with various G4 structures, loop deletion mutants","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with defined G4 structures and mutagenesis of loop features, single lab","pmids":["33313902"],"is_preprint":false},{"year":2017,"finding":"MKP-1 suppresses JNK1/2 activity, thereby reducing PARP-1 ubiquitination and maintaining PARP-1 protein levels; silencing MKP-1 promotes JNK1/2-dependent PARP-1 ubiquitination and proteasomal degradation, reducing cisplatin resistance.","method":"MKP-1 knockdown/overexpression, JNK1/2 silencing, PARP-1 ubiquitination assay, PARP-1 protein level measurement","journal":"Oncogene","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, ubiquitination detected by Co-IP but in vitro reconstitution not performed","pmids":["28650468"],"is_preprint":false}],"current_model":"PARP1 is a multi-domain nuclear ADP-ribosyltransferase that functions as a first-responder DNA damage sensor: its N-terminal zinc fingers detect strand breaks (and non-B form DNA such as G-quadruplexes) through sequence-independent interactions with exposed nucleotide bases, triggering a multi-domain collapse onto the break and conformational unfolding of the autoinhibitory helical domain (HD) of the catalytic domain, which relieves NAD+ binding competition and activates PAR synthesis up to 500-fold; PAR chains on histones, chromatin factors (H1, KDM5B, Smads, PPARγ, FOXO1, Sox2, NLRP3), and PARP1 itself modulate chromatin structure, transcription, DNA repair pathway choice (BER, backup NHEJ, HR), and cell fate decisions; serine-linked auto-modification at S499/S507/S519 (facilitated by HPF1) counteracts chromatin retention; TRIP12 ubiquitinates PARP1 for proteasomal degradation to limit trapping; clinical PARP inhibitors trap PARP1 on DNA primarily by outcompeting NAD+ and secondarily through allosteric modulation of release, with trapped complexes being cytotoxic by blocking replication and repair."},"narrative":{"mechanistic_narrative":"PARP1 is a nuclear ADP-ribosyltransferase that operates as a first-responder DNA damage sensor coupling break detection to poly(ADP-ribose) (PAR) synthesis, chromatin remodeling, and DNA repair pathway choice [PMID:23333033, PMID:19962992]. Its N-terminal zinc fingers recognize strand breaks (nicks, blunt ends, 3' extensions) through sequence-independent contacts with exposed nucleotide bases, and break binding drives a multi-domain collapse onto the DNA that converts a relaxed substrate into a sharply kinked conformation by induced fit [PMID:23333033, PMID:36323657, PMID:19962992]. This assembly cascade transmits an allosteric signal through interdomain contacts that unfolds the autoinhibitory helical subdomain (HD) of the catalytic domain, relieving competition for NAD+ binding and activating PAR synthesis [PMID:26626480, PMID:24189460]. PARP1 also binds and is catalytically activated by specific G-quadruplex loop structures, extending its sensing role to non-B DNA [PMID:33313902]. Through PARylation and protein interactions, PARP1 controls transcription by excluding linker histone H1 and inhibiting the demethylase KDM5B to open promoter chromatin for RNA Pol II loading [PMID:20832725], and it modifies sequence-specific factors including Smad3/4, PPARγ, FOXO1, and Sox2 to modulate their DNA binding and target gene programs [PMID:21095583, PMID:18815186, PMID:19281796, PMID:23939864]. In genome maintenance, PARP1 competes with Ku at double-strand break ends to drive a DNA ligase III-dependent backup NHEJ pathway and supports homologous recombination through a direct, PARylation-independent interaction with Timeless [PMID:17088286, PMID:26344098]. PARP1 activity and turnover are tightly regulated: HPF1 directs in trans histone ADP-ribosylation and serine auto-modification at S499/S507/S519 that limits PARP1 chromatin retention [PMID:27067600, PMID:34210965], while the TRIP12 E3 ligase ubiquitylates PARP1 via its PAR-binding WWE domain to trigger proteasomal degradation and limit trapping [PMID:32755579]. Clinical PARP inhibitors trap PARP1 on DNA as cytotoxic complexes primarily by competing with NAD+, with allosteric effects that can increase or decrease retention depending on inhibitor chemistry [PMID:23118055, PMID:32241924, PMID:36070389, PMID:32890402].","teleology":[{"year":2006,"claim":"Established that PARP-1 is not solely a single-strand break factor but competes with Ku for double-strand break ends to seed an alternative repair route, defining its role in DSB repair pathway choice.","evidence":"DNA end-binding competition assays and genetic deletion of classical NHEJ components with DSB repair kinetics","pmids":["17088286"],"confidence":"High","gaps":["Did not define how the choice between classical and backup NHEJ is regulated in undamaged cells","Relative contribution of backup NHEJ versus HR in normal repair unclear"]},{"year":2009,"claim":"Resolved how PARP-1 physically engages damaged DNA, showing monomeric binding with comparable affinity for distinct break types and a zinc-ribbon conformational change linking damage detection to catalysis.","evidence":"Small-angle X-ray scattering with biochemical binding, activity, and thermodynamic assays","pmids":["19962992"],"confidence":"High","gaps":["Low-resolution SAXS did not provide atomic detail of the activated state","Did not explain how the conformational change reaches the catalytic domain"]},{"year":2010,"claim":"Demonstrated that PARP-1 actively shapes chromatin and transcription, by excluding linker histone H1 and PARylating/inhibiting KDM5B to preserve H3K4me3 and license RNA Pol II loading.","evidence":"ChIP, RNA Pol II loading assays, KDM5B activity assays, and PARP-1 depletion","pmids":["20832725"],"confidence":"High","gaps":["Did not establish how PARP-1 is targeted to specific promoters genome-wide","Generality across cell types not addressed"]},{"year":2010,"claim":"Extended PARP-1 substrate scope to signaling transcription factors, showing it PARylates Smad3/4 to dissociate them from DNA and attenuate TGF-β-driven EMT.","evidence":"Unbiased proteomic screen, Co-IP, in vitro ADP-ribosylation, DNA-binding and EMT assays","pmids":["21095583"],"confidence":"High","gaps":["Did not map the modified residues on Smad proteins","In vivo relevance for fibrosis or development not tested"]},{"year":2013,"claim":"Provided the structural basis for damage sensing and activation, showing multiple domains collapse onto a break and zinc fingers read exposed bases sequence-independently to couple detection to PAR production.","evidence":"X-ray crystallography of essential PARP-1 domains bound to a DNA strand break with biochemical activity assays","pmids":["23333033"],"confidence":"High","gaps":["Static structure did not capture the dynamics of activation","How the signal propagates to the catalytic domain not yet resolved at this stage"]},{"year":2013,"claim":"Showed mechanistically that interdomain contacts, not mere DNA binding, drive activation, separating catalytic activation from recruitment and transcriptional functions.","evidence":"Site-directed mutagenesis of domain-domain contacts with activity, recruitment, and reporter assays","pmids":["24189460"],"confidence":"Medium","gaps":["Single lab","Did not identify the conformational intermediate linking contacts to catalysis"]},{"year":2015,"claim":"Identified the molecular switch of activation: DNA break detection unfolds the autoinhibitory helical domain (HD), which otherwise blocks productive NAD+ binding.","evidence":"HXMS, crystallography of HD deletion mutants, and biochemical activity assays","pmids":["26626480"],"confidence":"High","gaps":["Did not quantify HD unfolding dynamics in real time","Coupling between HD unfolding and DNA conformation not yet measured"]},{"year":2015,"claim":"Defined a PARylation-independent protein interaction that channels PARP-1 into homologous recombination, via Timeless binding to the catalytic domain.","evidence":"Crystal structure of the Timeless PAB-PARP-1 catalytic domain complex with Co-IP, recruitment, and HR repair assays","pmids":["26344098"],"confidence":"High","gaps":["Did not determine how Timeless promotes HR mechanistically downstream of recruitment","Selectivity for PARP-1 over other PARPs mechanism only partly explained"]},{"year":2016,"claim":"Discovered HPF1 as a partner that redirects PARP-1 activity in trans toward histones and restrains PARP-1 hyper-automodification.","evidence":"Reciprocal Co-IP, live-cell recruitment, in vitro ADP-ribosylation, and knockout cell biology","pmids":["27067600"],"confidence":"High","gaps":["Did not yet identify the serine residues whose modification HPF1 enables","Functional consequence for trapping not addressed at this stage"]},{"year":2020,"claim":"Established that inhibitor chemistry, not just catalytic inhibition, controls PARP-1 retention, with pro-retention compounds enhancing cancer cell killing.","evidence":"Structural studies, biophysical binding, cell viability assays, and synthesis of a converted pro-retention probe","pmids":["32241924"],"confidence":"High","gaps":["Did not quantify the relative weight of allostery versus NAD+ competition","Generalizability across all clinical inhibitors not established here"]},{"year":2020,"claim":"Identified TRIP12 as an E3 ligase that uses its PAR-binding WWE domain to target PARP1 for degradation, limiting cytotoxic trapping.","evidence":"Co-IP, domain mapping, ubiquitylation assays, proteasome inhibition, and TRIP12 knockout trapping measurements","pmids":["32755579"],"confidence":"High","gaps":["Did not determine in vivo impact on PARPi therapeutic window","Whether TRIP12 acts selectively on trapped versus free PARP1 unclear"]},{"year":2020,"claim":"Reframed 'trapping' by showing PARP1 exchanges rapidly even under inhibitors and that NAD+ interaction governs exchange, with persistent foci reflecting ongoing recruitment due to delayed repair.","evidence":"Quantitative live-cell imaging, FRAP, PARP1 H862D/E988K mutants, and Xrcc1 knockout","pmids":["32890402"],"confidence":"High","gaps":["Apparent tension with biochemical stable-complex trapping not fully reconciled","Did not test all clinical inhibitors for exchange behavior"]},{"year":2021,"claim":"Connected HPF1-dependent serine auto-modification at S499/S507/S519 to release from chromatin, defining a regulatory axis that tunes PARPi sensitivity.","evidence":"MS site mapping, site-directed mutagenesis, trapping assays, and HPF1/ARH3 knockouts","pmids":["34210965"],"confidence":"High","gaps":["Did not establish dynamics of writing versus ARH3 erasing in real time","In vivo tumor relevance not tested"]},{"year":2022,"claim":"Captured the conformational dynamics of activation directly, showing zinc fingers kink DNA through an induced-fit cascade and that inhibitors shift the DNA conformational equilibrium.","evidence":"Single-molecule FRET and structural ensemble calculations with niraparib/EB47 comparison","pmids":["36323657"],"confidence":"High","gaps":["Did not connect DNA kinking quantitatively to HD unfolding kinetics","Performed on defined substrates rather than chromatinized DNA"]},{"year":2022,"claim":"Dissected inhibitor-driven retention into a two-step mechanism dominated by NAD+ competition with secondary allostery that can raise or lower retention.","evidence":"Single-molecule assays monitoring PARP1-DNA retention in real time","pmids":["36070389"],"confidence":"High","gaps":["Did not extend single-molecule retention measurements to the chromatin/cellular context","Relationship to clinical efficacy ranking not directly tested"]},{"year":2022,"claim":"Expanded PARP-1 substrate sensing to non-B DNA, showing it binds G-quadruplexes tightly but is catalytically stimulated only by specific loop features.","evidence":"In vitro binding affinity, activity assays with defined G4 structures, and loop deletion mutants","pmids":["33313902"],"confidence":"Medium","gaps":["Single lab","Cellular consequences of G4-driven PARP-1 activation not established"]},{"year":null,"claim":"How the many context-specific PARP-1 partner and substrate relationships (e.g., metabolic, inflammatory, and transcription-factor regulation) are integrated and prioritized at a given locus or stress state remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model links DNA-damage activation to the diverse non-repair signaling roles","Residue-level modification maps for most non-histone substrates are absent","Quantitative rules governing PARP-1 recruitment to specific genomic sites are undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[3,5,8,24]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[8,19,20,24,28]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[5,7,15,36]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[6,20,26]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[6,20,23]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,6,21,35]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[5,6,7]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[9,28]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[5,7,10,25]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[6,8,19,20,24]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[6,23,26]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[4,11]}],"complexes":["PARP1-HPF1 complex","NLRP3 inflammasome"],"partners":["HPF1","TRIP12","TIMELESS","KDM5B","SMAD3","SMAD4","XRCC1","NLRP3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P09874","full_name":"Poly [ADP-ribose] polymerase 1","aliases":["ADP-ribosyltransferase diphtheria toxin-like 1","ARTD1","DNA ADP-ribosyltransferase PARP1","NAD(+) ADP-ribosyltransferase 1","ADPRT 1","Poly[ADP-ribose] synthase 1","Protein poly-ADP-ribosyltransferase PARP1"],"length_aa":1014,"mass_kda":113.1,"function":"Poly-ADP-ribosyltransferase that mediates poly-ADP-ribosylation of proteins and plays a key role in DNA repair (PubMed:17177976, PubMed:18055453, PubMed:18172500, PubMed:19344625, PubMed:19661379, PubMed:20388712, PubMed:21680843, PubMed:22582261, PubMed:23230272, PubMed:25043379, PubMed:26344098, PubMed:26626479, PubMed:26626480, PubMed:30104678, PubMed:31796734, PubMed:32028527, PubMed:32241924, PubMed:32358582, PubMed:33186521, PubMed:34465625, PubMed:34737271). Mediates glutamate, aspartate, serine, histidine or tyrosine ADP-ribosylation of proteins: the ADP-D-ribosyl group of NAD(+) is transferred to the acceptor carboxyl group of target residues and further ADP-ribosyl groups are transferred to the 2'-position of the terminal adenosine moiety, building up a polymer with an average chain length of 20-30 units (PubMed:19764761, PubMed:25043379, PubMed:28190768, PubMed:29954836, PubMed:35393539, PubMed:7852410, PubMed:9315851). Serine ADP-ribosylation of proteins constitutes the primary form of ADP-ribosylation of proteins in response to DNA damage (PubMed:33186521, PubMed:34874266). Specificity for the different amino acids is conferred by interacting factors, such as HPF1 and NMNAT1 (PubMed:28190768, PubMed:29954836, PubMed:32028527, PubMed:33186521, PubMed:33589610, PubMed:34625544, PubMed:34874266). Following interaction with HPF1, catalyzes serine ADP-ribosylation of target proteins; HPF1 confers serine specificity by completing the PARP1 active site (PubMed:28190768, PubMed:29954836, PubMed:32028527, PubMed:33186521, PubMed:33589610, PubMed:34625544, PubMed:34874266). Also catalyzes tyrosine ADP-ribosylation of target proteins following interaction with HPF1 (PubMed:29954836, PubMed:30257210). Following interaction with NMNAT1, catalyzes glutamate and aspartate ADP-ribosylation of target proteins; NMNAT1 confers glutamate and aspartate specificity (By similarity). PARP1 initiates the repair of DNA breaks: recognizes and binds DNA breaks within chromatin and recruits HPF1, licensing serine ADP-ribosylation of target proteins, such as histones (H2BS6ADPr and H3S10ADPr), thereby promoting decompaction of chromatin and the recruitment of repair factors leading to the reparation of DNA strand breaks (PubMed:17177976, PubMed:18172500, PubMed:19344625, PubMed:19661379, PubMed:23230272, PubMed:27067600, PubMed:34465625, PubMed:34874266). HPF1 initiates serine ADP-ribosylation but restricts the polymerase activity of PARP1 in order to limit the length of poly-ADP-ribose chains (PubMed:33683197, PubMed:34732825, PubMed:34795260). In addition to base excision repair (BER) pathway, also involved in double-strand breaks (DSBs) repair: together with TIMELESS, accumulates at DNA damage sites and promotes homologous recombination repair by mediating poly-ADP-ribosylation (PubMed:26344098, PubMed:30356214). Mediates the poly-ADP-ribosylation of a number of proteins, including itself, APLF, CHFR, RPA1 and NFAT5 (PubMed:17396150, PubMed:19764761, PubMed:24906880, PubMed:34049076). In addition to proteins, also able to ADP-ribosylate DNA: catalyzes ADP-ribosylation of DNA strand break termini containing terminal phosphates and a 2'-OH group in single- and double-stranded DNA, respectively (PubMed:27471034). Required for PARP9 and DTX3L recruitment to DNA damage sites (PubMed:23230272). PARP1-dependent PARP9-DTX3L-mediated ubiquitination promotes the rapid and specific recruitment of 53BP1/TP53BP1, UIMC1/RAP80, and BRCA1 to DNA damage sites (PubMed:23230272). PARP1-mediated DNA repair in neurons plays a role in sleep: senses DNA damage in neurons and promotes sleep, facilitating efficient DNA repair (By similarity). In addition to DNA repair, also involved in other processes, such as transcription regulation, programmed cell death, membrane repair, adipogenesis and innate immunity (PubMed:15607977, PubMed:17177976, PubMed:19344625, PubMed:27256882, PubMed:32315358, PubMed:32844745, PubMed:35124853, PubMed:35393539, PubMed:35460603). Acts as a repressor of transcription: binds to nucleosomes and modulates chromatin structure in a manner similar to histone H1, thereby altering RNA polymerase II (PubMed:15607977, PubMed:22464733). Acts both as a positive and negative regulator of transcription elongation, depending on the context (PubMed:27256882, PubMed:35393539). Acts as a positive regulator of transcription elongation by mediating poly-ADP-ribosylation of NELFE, preventing RNA-binding activity of NELFE and relieving transcription pausing (PubMed:27256882). Acts as a negative regulator of transcription elongation in response to DNA damage by catalyzing poly-ADP-ribosylation of CCNT1, disrupting the phase separation activity of CCNT1 and subsequent activation of CDK9 (PubMed:35393539). Involved in replication fork progression following interaction with CARM1: mediates poly-ADP-ribosylation at replication forks, slowing fork progression (PubMed:33412112). Poly-ADP-ribose chains generated by PARP1 also play a role in poly-ADP-ribose-dependent cell death, a process named parthanatos (By similarity). Also acts as a negative regulator of the cGAS-STING pathway (PubMed:32315358, PubMed:32844745, PubMed:35460603). Acts by mediating poly-ADP-ribosylation of CGAS: PARP1 translocates into the cytosol following phosphorylation by PRKDC and catalyzes poly-ADP-ribosylation and inactivation of CGAS (PubMed:35460603). Acts as a negative regulator of adipogenesis: catalyzes poly-ADP-ribosylation of histone H2B on 'Glu-35' (H2BE35ADPr) following interaction with NMNAT1, inhibiting phosphorylation of H2B at 'Ser-36' (H2BS36ph), thereby blocking expression of pro-adipogenetic genes (By similarity). Involved in the synthesis of ATP in the nucleus, together with NMNAT1, PARG and NUDT5 (PubMed:27257257). Nuclear ATP generation is required for extensive chromatin remodeling events that are energy-consuming (PubMed:27257257) Promotes AIFM1-mediated apoptosis (PubMed:33168626). This form, which translocates into the cytoplasm following cleavage by caspase-3 (CASP3) and caspase-7 (CASP7) in response to apoptosis, is auto-poly-ADP-ribosylated and serves as a poly-ADP-ribose carrier to induce AIFM1-mediated apoptosis (PubMed:33168626) This cleavage form irreversibly binds to DNA breaks and interferes with DNA repair, promoting DNA damage-induced apoptosis","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P09874/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PARP1","classification":"Not 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ZNF432","url":"https://www.omim.org/entry/620554"},{"mim_id":"620311","title":"PREMATURE OVARIAN FAILURE 21; POF21","url":"https://www.omim.org/entry/620311"},{"mim_id":"618170","title":"NEURODEGENERATION, CHILDHOOD-ONSET, STRESS-INDUCED, WITH VARIABLE ATAXIA AND SEIZURES; CONDSIAS","url":"https://www.omim.org/entry/618170"},{"mim_id":"618030","title":"SHIELD COMPLEX, SUBUNIT 3; SHLD3","url":"https://www.omim.org/entry/618030"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Nucleoli","reliability":"Additional"},{"location":"Nucleoli fibrillar center","reliability":"Additional"},{"location":"Nuclear bodies","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PARP1"},"hgnc":{"alias_symbol":["PARP","ARTD1","Poly-PARP","PARS"],"prev_symbol":["PPOL","ADPRT"]},"alphafold":{"accession":"P09874","domains":[{"cath_id":"3.30.1740.10","chopping":"8-90","consensus_level":"high","plddt":88.5869,"start":8,"end":90},{"cath_id":"3.30.1740.10","chopping":"109-197","consensus_level":"high","plddt":86.7736,"start":109,"end":197},{"cath_id":"1.10.20.130","chopping":"230-293_329-346","consensus_level":"high","plddt":89.7291,"start":230,"end":346},{"cath_id":"3.40.50.10190","chopping":"393-475","consensus_level":"high","plddt":86.2787,"start":393,"end":475},{"cath_id":"-","chopping":"534-632","consensus_level":"high","plddt":91.5808,"start":534,"end":632},{"cath_id":"1.20.142.10","chopping":"666-793","consensus_level":"high","plddt":87.0116,"start":666,"end":793},{"cath_id":"3.90.228.10","chopping":"798-1008","consensus_level":"high","plddt":95.1924,"start":798,"end":1008}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P09874","model_url":"https://alphafold.ebi.ac.uk/files/AF-P09874-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P09874-F1-predicted_aligned_error_v6.png","plddt_mean":82.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PARP1","jax_strain_url":"https://www.jax.org/strain/search?query=PARP1"},"sequence":{"accession":"P09874","fasta_url":"https://rest.uniprot.org/uniprotkb/P09874.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P09874/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P09874"}},"corpus_meta":[{"pmid":"23118055","id":"PMC_23118055","title":"Trapping 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Trapping potency differs markedly among inhibitors (niraparib > olaparib >> veliparib) independent of catalytic inhibitory potency.\",\n      \"method\": \"Biochemical trapping assays, genetically altered DT40 cell lines with deletions in specific DNA repair genes, cytotoxicity measurements\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (biochemical trapping, genetic epistasis panel of 30 cell lines), widely replicated across subsequent studies\",\n      \"pmids\": [\"23118055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PARP-1 activation requires local unfolding of the helical subdomain (HD) of its catalytic domain. The HD acts as an autoinhibitory domain that blocks productive NAD+ binding; DNA break detection causes HD unfolding to relieve this autoinhibition.\",\n      \"method\": \"Hydrogen/deuterium exchange-mass spectrometry (HXMS), crystallographic analysis of HD deletion mutants, biochemical activity assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution, mutagenesis, crystallography, and HXMS in a single rigorous study\",\n      \"pmids\": [\"26626480\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Structurally distinct PARP inhibitors drive PARP-1 allostery in opposite directions: some promote PARP-1 release from a DNA break (pro-release), while others retain PARP-1 on a DNA break (pro-retention). Converting a pro-release compound to a pro-retention compound increased cancer cell killing.\",\n      \"method\": \"Structural studies, biophysical binding assays, cell viability assays, synthesis of novel PARPi compound\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — structural and biochemical reconstitution with functional validation and chemical probe confirmation\",\n      \"pmids\": [\"32241924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HPF1 (C4orf27) forms a robust complex with PARP-1 in cells, is recruited to DNA lesions in a PARP-1-dependent but catalysis-independent manner, promotes PARP-1-dependent in trans ADP-ribosylation of histones, and limits DNA damage-induced hyper-automodification of PARP-1.\",\n      \"method\": \"Co-immunoprecipitation, live-cell recruitment assays, in vitro ADP-ribosylation assays, knockdown/knockout cell biology\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, in vitro enzymatic assays, multiple orthogonal methods in a single focused study\",\n      \"pmids\": [\"27067600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Serine ADP-ribosylation at PARP1 residues S499, S507, and S519 (dependent on HPF1) counteracts PARP1 trapping on chromatin; loss of HPF1 or ARH3 increases PARPi-induced PARP1 trapping and sensitizes cells to PARP inhibitors.\",\n      \"method\": \"Mass spectrometry mapping of modification sites, site-directed mutagenesis, PARP1 trapping assays, genetic knockouts\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — MS-level site identification, mutagenesis, and functional trapping assays in a single study with multiple orthogonal methods\",\n      \"pmids\": [\"34210965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structure of essential PARP-1 domains in complex with a DNA strand break revealed that multiple PARP-1 domains collapse onto damaged DNA through interdomain contacts, and that PARP-1 uses zinc fingers to detect DNA breaks through sequence-independent interaction with exposed nucleotide bases, coupling damage detection to elevated PAR production.\",\n      \"method\": \"X-ray crystallography, biochemical activity assays\",\n      \"journal\": \"Current opinion in structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with mechanistic biochemical validation, independently replicated in subsequent structural studies\",\n      \"pmids\": [\"23333033\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PARP-1 regulates chromatin structure and transcription by PARylating and inhibiting/excluding the histone demethylase KDM5B to prevent demethylation of H3K4me3, and by promoting exclusion of linker histone H1 to open promoter chromatin, creating a permissive environment for RNA Pol II loading.\",\n      \"method\": \"ChIP, RNA Pol II loading assays, PARP-1 depletion, KDM5B activity assays, histone modification analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal chromatin and biochemical methods, mechanistic pathway dissection in a single rigorous study\",\n      \"pmids\": [\"20832725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PARP-1 binds to DNA DSB ends in direct competition with Ku and operates in an alternative backup NHEJ pathway together with DNA ligase III, distinct from the classical NHEJ pathway using DNA-PKcs/Ku/Ligase IV/XRCC4. When Ku and classical NHEJ components are absent, PARP-1 is recruited for DSB repair.\",\n      \"method\": \"DNA end-binding competition assays, genetic deletion of NHEJ components, DSB repair kinetics, PARP inhibitor treatment\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with multiple deletion backgrounds, biochemical competition assays, pharmacological inhibition\",\n      \"pmids\": [\"17088286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PARP-1 ADP-ribosylates Smad3 and Smad4 (identified as PARP-1-interacting partners by unbiased proteomic screen), dissociating Smad complexes from DNA and thereby attenuating Smad-mediated transcription and TGF-β-induced epithelial-mesenchymal transition.\",\n      \"method\": \"Unbiased proteomic screen, Co-IP, in vitro ADP-ribosylation assay, DNA-binding assays, EMT assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — proteomic identification, biochemical validation, in vitro ADP-ribosylation, functional cellular outcome\",\n      \"pmids\": [\"21095583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PARP1 (ARTD1) activation leads to PAR synthesis that suppresses glycolysis independently of NAD+ depletion; PAR binds directly to hexokinase 1 (HK1), suppressing HK1 activity and blocking glycolysis and ATP production after DNA damage.\",\n      \"method\": \"Real-time metabolic measurements (Seahorse), proteomics-based PAR interactome after DNA damage, HK1 activity assays, direct NAD+ depletion comparison\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — interactome proteomics, enzymatic activity assays, metabolic measurements, mechanistic dissection distinguishing PAR from NAD+ depletion\",\n      \"pmids\": [\"25220464\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Timeless physically interacts with PARP-1 via its PAB (PARP-1-binding domain) independently of poly(ADP-ribosylation), specifically with PARP-1 but not PARP-2 or PARP-3; Timeless recruitment to DNA damage requires PARP-1 but not PARylation; Timeless-PARP-1 interaction is required for efficient homologous recombination repair.\",\n      \"method\": \"Crystal structure of Timeless PAB-PARP-1 catalytic domain complex, Co-IP, laser-induced DNA damage recruitment assays, HR repair assays, PARP inhibitor trapping experiments\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus Co-IP, live cell imaging, and functional HR assays in a single study\",\n      \"pmids\": [\"26344098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TRIP12 ubiquitin E3 ligase binds PARP1 via its central PAR-binding WWE domain and uses its HECT domain to catalyze polyubiquitylation of PARP1, triggering proteasomal degradation and limiting PARPi-induced cytotoxic PARP1 trapping.\",\n      \"method\": \"Co-IP, domain mapping, ubiquitylation assays, proteasome inhibitor experiments, TRIP12 knockout cells, PARP1 trapping measurements\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, domain-function mapping, biochemical ubiquitylation assays, genetic knockout validation\",\n      \"pmids\": [\"32755579\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Single-molecule FRET and structural ensemble calculations revealed that PARP-1 N-terminal zinc fingers convert DNA SSBs from a largely unperturbed conformation via an intermediate to a highly kinked DNA conformation through an induced-fit mechanism via a multi-domain assembly cascade; niraparib shifts equilibrium towards unkinked DNA conformation, while EB47 stabilizes the kinked state.\",\n      \"method\": \"Single-molecule FRET (smFRET), structural ensemble calculations, PARP inhibitor comparison\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — single-molecule structural dynamics with quantitative mechanistic data and inhibitor comparison\",\n      \"pmids\": [\"36323657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PARPi modulate PARP1-DNA retention through a two-step mechanism: primary step of catalytic inhibition via NAD+ binding competition, followed by allosteric modulation; retention potency is predominantly determined by NAD+ competition, while allosteric effects can either increase or decrease retention.\",\n      \"method\": \"Single-molecule assays monitoring PARP1 retention on DNA in real time\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — single-molecule reconstitution directly measuring PARP1-DNA dynamics in real time\",\n      \"pmids\": [\"36070389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Clinical PARP inhibitors do not physically stall PARP1 at DNA damage sites; instead, PARP1 exchanges rapidly even in the presence of PARPi. Persistent PARP1 foci represent continued recruitment of different PARP1 molecules due to delayed repair from attenuated XRCC1-LIG3 recruitment. PARP1-H862D (NAD+ interacting residue mutant, not PARylation-deficient E988K) forms stable foci, identifying NAD+ interaction as key to PARP1 exchange.\",\n      \"method\": \"Quantitative live-cell imaging, FRAP, PARP1 mutant analysis (H862D, E988K), Xrcc1 knockout\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — quantitative live-cell imaging with FRAP and mutagenesis, multiple genetic controls\",\n      \"pmids\": [\"32890402\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PARP-1 binds damaged DNA (nick, blunt end, 3' extension) as a monomer with similar affinity for all three, and undergoes a conformational change at the zinc ribbon domain upon DNA binding that leads to catalytic activation; the N-terminal half is extended and flexible in solution but compacts around damaged DNA.\",\n      \"method\": \"Small-angle X-ray scattering, biochemical binding and activity assays, thermodynamic measurements\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — SAXS structural analysis combined with biochemical and thermodynamic validation\",\n      \"pmids\": [\"19962992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PARP-1 poly(ADP-ribosyl)ates GAPDH in ischemic renal proximal tubules, inhibiting GAPDH enzymatic activity and blocking glycolysis, thereby exacerbating ATP depletion and necrotic cell death.\",\n      \"method\": \"In vitro and in vivo hypoxia models, PARP-1 inhibitor treatment, GAPDH activity assays, detection of poly(ADP-ribosyl)ated GAPDH, ATP measurements\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — enzymatic activity assays and PARylation detection in both in vitro and in vivo models, single lab\",\n      \"pmids\": [\"19056868\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PARP-1 is directly activated by phosphorylated ERK2 through a physical interaction independent of DNA damage and DNA binding; this ERK2-induced PARP-1 activation amplifies ERK signaling, enhancing Elk1 phosphorylation, core histone acetylation, and c-fos expression.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase/activation assays, reporter assays for Elk1 and c-fos, histone acetylation measurements\",\n      \"journal\": \"Trends in pharmacological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct interaction and activation demonstrated, but single lab and limited structural confirmation\",\n      \"pmids\": [\"17950910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"H2S induces S-sulfhydration of MEK1 at cysteine 341, leading to phosphorylation of ERK1/2 and its nuclear translocation where ERK directly interacts with and activates PARP-1; activated PARP-1 then recruits XRCC1 and DNA ligase III to DNA breaks for repair.\",\n      \"method\": \"S-sulfhydration assay, site-directed mutagenesis (MEK1 C341), Co-IP of ERK-PARP-1, DNA repair foci assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, mutagenesis, and functional repair assays, single lab\",\n      \"pmids\": [\"24778456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PARP-1 poly(ADP-ribosyl)ates PPARγ in cardiac fibroblasts under basal conditions, preventing PPARγ DNA binding and suppressing PPARγ-target genes including adiponectin; PARP-1 inhibition enhances PPARγ DNA binding and transactivation.\",\n      \"method\": \"Co-immunoprecipitation, EMSA, Southwestern blot, PARP-1 siRNA/inhibitor, RT-PCR/Western blot\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — PARylation detected by Co-IP, DNA binding by EMSA, functional gene expression confirmed, single lab\",\n      \"pmids\": [\"18815186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PARP-1 directly binds and poly(ADP-ribosyl)ates FOXO1, acting as a corepressor on the p27(Kip1) promoter through FOXO1 interaction; PARP-1 represses FOXO1-mediated p27 expression and the repressive effect does not require PARylation enzymatic activity.\",\n      \"method\": \"Co-IP, in vitro PARylation assay, ChIP, luciferase reporter assay, PARP-1 knockdown\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ChIP, and functional reporter assay, single lab; catalytic-independent repression established by mutant analysis\",\n      \"pmids\": [\"19281796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"DNA-PK activation is required upstream of PARP-1 recruitment to chromatin and PARP-1 activation in cisplatin-damaged cells; inhibition of DNA-PK prevents PARP-1 activation and its chromatin recruitment, and both DNA-PK and PARP-1 are required for DNA damage-induced inhibition of rRNA synthesis.\",\n      \"method\": \"In situ run-on rRNA synthesis assay, DNA-PK and PARP-1 inhibitors, chromatin fractionation, cell cycle analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway ordering by pharmacological inhibition with chromatin fractionation readout, single lab\",\n      \"pmids\": [\"23775790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PARP-1 allosteric regulation via interdomain contacts is required for DNA-damage-dependent catalytic activation; disruption of domain-domain contacts by mutagenesis prevents DNA-damage-dependent catalytic activation without affecting PARP-1 recruitment to DNA damage or transcriptional regulation.\",\n      \"method\": \"Site-directed mutagenesis of domain-domain contact residues, PARP-1 activity assays, live-cell recruitment assays, transcriptional reporter assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis with activity and localization assays, single lab\",\n      \"pmids\": [\"24189460\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MacroH2A1.1 recruits PARP-1 to promote CBP-mediated acetylation of histone H2B at K12 and K120, which regulates gene expression; this regulation is lost in cancer cells.\",\n      \"method\": \"RNA-seq, Co-IP, ChIP-seq, histone modification analysis in primary human cells vs cancer cells\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ChIP, and functional gene expression with primary vs cancer cell comparison, single lab\",\n      \"pmids\": [\"25306110\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PARP-1 ADP-ribosylates Sox2 during somatic cell reprogramming, promoting Sox2 binding to the Fgf4 enhancer and activating Fgf4 expression; loss of PARP-1 or its catalytic activity reduces reprogramming efficiency, which is rescued by exogenous Fgf4.\",\n      \"method\": \"PARP-1 knockout fibroblasts, PARP inhibitor treatment, in vitro PARylation of Sox2, ChIP at Fgf4 enhancer, Fgf4 rescue experiment\",\n      \"journal\": \"Stem cells (Dayton, Ohio)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — PARylation assay, ChIP, and rescue experiment establishing pathway; single lab\",\n      \"pmids\": [\"23939864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PARP-1 forms covalent DNA-protein crosslinks (DPCs) at apurinic/apyrimidinic (AP) sites via Schiff base formation between a PARP-1 lysine side chain and the C1' of the AP site; repair of PARP-1 DPCs involves proteasomal degradation of PARP-1 followed by tyrosyl-DNA phosphodiesterase 1 (TDP1) processing of the remaining adduct, completed by the BER machinery.\",\n      \"method\": \"In vitro DPC formation assay, proteasome inhibitor experiments, model DNA substrate repair assays, TDP1 activity assay\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and cell-based DPC assays with proteasome inhibition and biochemical repair reconstitution, single lab\",\n      \"pmids\": [\"30466837\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"MEIS transcription factors associate with chromatin-bound PBX1 at target promoters, recruit PARP1/ARTD1, and initiate PARP1-mediated eviction of linker histone H1 to open chromatin during neuronal differentiation.\",\n      \"method\": \"ChIP, Co-IP, live-cell imaging, PARP1 knockdown, differentiation assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and Co-IP with functional differentiation outcome, single lab\",\n      \"pmids\": [\"28739678\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PARP-1 mediates the association of DDX18, a putative RNA helicase, with R-loop structures; DDX18 depletion causes aberrant R-loop accumulation and DNA replication defects that are rescued by RNase H1 overexpression, placing PARP-1 in a pathway regulating R-loop homeostasis.\",\n      \"method\": \"Co-IP, R-loop detection assays (S9.6 antibody), DDX18 knockdown, RNase H1 rescue, γH2AX and RPA32/RAD51 foci\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and functional rescue experiments establishing pathway position, single lab\",\n      \"pmids\": [\"35858569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PARP-1 PARylates NLRP3 upon ATP stimulation, translocating to the cytosol; PARP-1 bridges NLRP3 and TXNIP to facilitate NLRP3 inflammasome complex assembly and IL-1β production in macrophages.\",\n      \"method\": \"PARP-1 knockout BMDMs, PARP-1 inhibitor, Co-IP of NLRP3-PARP-1-TXNIP, cytosol/nuclear fractionation, IL-1β ELISA\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO, Co-IP, and fractionation with functional inflammasome readout, single lab\",\n      \"pmids\": [\"35098371\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Integrin-linked kinase (ILK) regulates E-cadherin expression through PARP-1; PARP-1 binds to the Snail promoter ILK Responsive Element (SIRE) in an ILK-dependent manner, promoting Snail and ZEB1 expression and repressing E-cadherin.\",\n      \"method\": \"EMSA/Southwestern blot (SIRE-binding), PARP-1 siRNA, ILK silencing, ChIP-like promoter binding assay\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, promoter binding assay with siRNA but no direct PARylation assay of the pathway components\",\n      \"pmids\": [\"18773488\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PARP-1 promotes NF-κB nuclear translocation and binding to NF-κB response sequences in macrophages, driving CCL2 production and NK cell recruitment to viral infection sites; peritoneal macrophages are the main source of PARP-1-dependent CCL2.\",\n      \"method\": \"PARP-1 knockout mice, vaccinia virus infection model, NF-κB nuclear translocation assay, CCL2 ELISA, CCR2-blocking experiments\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO in vivo model, NF-κB binding assay, and chemokine axis validation, single lab\",\n      \"pmids\": [\"31217354\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PARP-1 interacts with and regulates HIF-2α protein levels and HIF-2-dependent gene expression (ANGPTL4, erythropoietin); PARP-1 forms a complex with HIF-2α that is sensitive to PARP inhibition and appears to protect HIF-2α from VHL-dependent degradation.\",\n      \"method\": \"Co-IP, PARP-1 knockdown/inhibition, HIF-2α mRNA and protein analysis, PARP-1 knockout mice (EPO levels, red cell counts)\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, genetic/pharmacological suppression, and in vivo validation in knockout mice, single lab\",\n      \"pmids\": [\"23455322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SIRT3 interacts with PARP-1 in the nucleus of cardiomyocytes under stress, deacetylates PARP-1, and thereby reduces PARP-1 activity and cardiac hypertrophic gene expression.\",\n      \"method\": \"Co-immunoprecipitation, adenoviral SIRT3 overexpression, PARP-1 acetylation assay, isoproterenol/phenylephrine hypertrophy models\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP, single lab, acetylation measured but deacetylase specificity not fully reconstituted in vitro\",\n      \"pmids\": [\"32139662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PARP-1 enzymatic activity promotes E2F1 transcription factor activity and E2F1-mediated induction of homologous recombination DNA repair factors; PARP-1 inhibition reduces HR factor availability, inducing 'BRCA-ness'.\",\n      \"method\": \"Transcriptional profiling, E2F1 reporter assays, HR factor protein measurements, PARP inhibitor treatment\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transcriptional profiling plus mechanistic E2F1 reporter and HR factor assays, single lab\",\n      \"pmids\": [\"30467127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"LRP1 directly interacts with PARP-1 in human retinal microvascular endothelial cells; this interaction decreases under hypoxia, and LRP1 knockdown increases PARP-1 activity with subsequent phosphorylation of retinoblastoma protein and CDK2, promoting cell cycle progression and angiogenesis.\",\n      \"method\": \"Co-IP, LRP1 knockdown, PARP-1 activity assay, Ki67 staining, pRb/CDK2 western blot, oxygen-induced retinopathy model\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP, single lab, activity assay without direct mechanistic reconstitution\",\n      \"pmids\": [\"26634655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Mitochondrial NAD+ controls nuclear ARTD1 (PARP1)-induced ADP-ribosylation; H2O2-induced oxidative stress reciprocally induces nuclear and reduces mitochondrial ADP-ribosylation, demonstrating a NAD+-mediated mitochondrial-nuclear crosstalk that modulates PARP1 chromatin retention and PARPi efficacy.\",\n      \"method\": \"Immunofluorescence, western blot, mass spectrometry, respiratory chain inhibition, FCCP uncoupler, MMS-induced PARP1 retention assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (IF, WB, MS) with pharmacological manipulation, single lab\",\n      \"pmids\": [\"33450210\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PARP-1 binds G-quadruplex structures with nanomolar affinity, but only specific G-quadruplex loop features (as found in the c-KIT promoter sequence) stimulate PARP-1 catalytic activity; oxidized G-quadruplexes also stimulate PARP-1 activity through their loop structures.\",\n      \"method\": \"In vitro binding affinity measurements, PARP-1 enzymatic activity assays with various G4 structures, loop deletion mutants\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with defined G4 structures and mutagenesis of loop features, single lab\",\n      \"pmids\": [\"33313902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"MKP-1 suppresses JNK1/2 activity, thereby reducing PARP-1 ubiquitination and maintaining PARP-1 protein levels; silencing MKP-1 promotes JNK1/2-dependent PARP-1 ubiquitination and proteasomal degradation, reducing cisplatin resistance.\",\n      \"method\": \"MKP-1 knockdown/overexpression, JNK1/2 silencing, PARP-1 ubiquitination assay, PARP-1 protein level measurement\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, ubiquitination detected by Co-IP but in vitro reconstitution not performed\",\n      \"pmids\": [\"28650468\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PARP1 is a multi-domain nuclear ADP-ribosyltransferase that functions as a first-responder DNA damage sensor: its N-terminal zinc fingers detect strand breaks (and non-B form DNA such as G-quadruplexes) through sequence-independent interactions with exposed nucleotide bases, triggering a multi-domain collapse onto the break and conformational unfolding of the autoinhibitory helical domain (HD) of the catalytic domain, which relieves NAD+ binding competition and activates PAR synthesis up to 500-fold; PAR chains on histones, chromatin factors (H1, KDM5B, Smads, PPARγ, FOXO1, Sox2, NLRP3), and PARP1 itself modulate chromatin structure, transcription, DNA repair pathway choice (BER, backup NHEJ, HR), and cell fate decisions; serine-linked auto-modification at S499/S507/S519 (facilitated by HPF1) counteracts chromatin retention; TRIP12 ubiquitinates PARP1 for proteasomal degradation to limit trapping; clinical PARP inhibitors trap PARP1 on DNA primarily by outcompeting NAD+ and secondarily through allosteric modulation of release, with trapped complexes being cytotoxic by blocking replication and repair.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PARP1 is a nuclear ADP-ribosyltransferase that operates as a first-responder DNA damage sensor coupling break detection to poly(ADP-ribose) (PAR) synthesis, chromatin remodeling, and DNA repair pathway choice [#5, #15]. Its N-terminal zinc fingers recognize strand breaks (nicks, blunt ends, 3' extensions) through sequence-independent contacts with exposed nucleotide bases, and break binding drives a multi-domain collapse onto the DNA that converts a relaxed substrate into a sharply kinked conformation by induced fit [#5, #12, #15]. This assembly cascade transmits an allosteric signal through interdomain contacts that unfolds the autoinhibitory helical subdomain (HD) of the catalytic domain, relieving competition for NAD+ binding and activating PAR synthesis [#1, #22]. PARP1 also binds and is catalytically activated by specific G-quadruplex loop structures, extending its sensing role to non-B DNA [#36]. Through PARylation and protein interactions, PARP1 controls transcription by excluding linker histone H1 and inhibiting the demethylase KDM5B to open promoter chromatin for RNA Pol II loading [#6], and it modifies sequence-specific factors including Smad3/4, PPAR\\u03b3, FOXO1, and Sox2 to modulate their DNA binding and target gene programs [#8, #19, #20, #24]. In genome maintenance, PARP1 competes with Ku at double-strand break ends to drive a DNA ligase III-dependent backup NHEJ pathway and supports homologous recombination through a direct, PARylation-independent interaction with Timeless [#7, #10]. PARP1 activity and turnover are tightly regulated: HPF1 directs in trans histone ADP-ribosylation and serine auto-modification at S499/S507/S519 that limits PARP1 chromatin retention [#3, #4], while the TRIP12 E3 ligase ubiquitylates PARP1 via its PAR-binding WWE domain to trigger proteasomal degradation and limit trapping [#11]. Clinical PARP inhibitors trap PARP1 on DNA as cytotoxic complexes primarily by competing with NAD+, with allosteric effects that can increase or decrease retention depending on inhibitor chemistry [#0, #2, #13, #14].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established that PARP-1 is not solely a single-strand break factor but competes with Ku for double-strand break ends to seed an alternative repair route, defining its role in DSB repair pathway choice.\",\n      \"evidence\": \"DNA end-binding competition assays and genetic deletion of classical NHEJ components with DSB repair kinetics\",\n      \"pmids\": [\"17088286\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define how the choice between classical and backup NHEJ is regulated in undamaged cells\", \"Relative contribution of backup NHEJ versus HR in normal repair unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Resolved how PARP-1 physically engages damaged DNA, showing monomeric binding with comparable affinity for distinct break types and a zinc-ribbon conformational change linking damage detection to catalysis.\",\n      \"evidence\": \"Small-angle X-ray scattering with biochemical binding, activity, and thermodynamic assays\",\n      \"pmids\": [\"19962992\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Low-resolution SAXS did not provide atomic detail of the activated state\", \"Did not explain how the conformational change reaches the catalytic domain\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrated that PARP-1 actively shapes chromatin and transcription, by excluding linker histone H1 and PARylating/inhibiting KDM5B to preserve H3K4me3 and license RNA Pol II loading.\",\n      \"evidence\": \"ChIP, RNA Pol II loading assays, KDM5B activity assays, and PARP-1 depletion\",\n      \"pmids\": [\"20832725\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish how PARP-1 is targeted to specific promoters genome-wide\", \"Generality across cell types not addressed\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Extended PARP-1 substrate scope to signaling transcription factors, showing it PARylates Smad3/4 to dissociate them from DNA and attenuate TGF-\\u03b2-driven EMT.\",\n      \"evidence\": \"Unbiased proteomic screen, Co-IP, in vitro ADP-ribosylation, DNA-binding and EMT assays\",\n      \"pmids\": [\"21095583\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not map the modified residues on Smad proteins\", \"In vivo relevance for fibrosis or development not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Provided the structural basis for damage sensing and activation, showing multiple domains collapse onto a break and zinc fingers read exposed bases sequence-independently to couple detection to PAR production.\",\n      \"evidence\": \"X-ray crystallography of essential PARP-1 domains bound to a DNA strand break with biochemical activity assays\",\n      \"pmids\": [\"23333033\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Static structure did not capture the dynamics of activation\", \"How the signal propagates to the catalytic domain not yet resolved at this stage\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showed mechanistically that interdomain contacts, not mere DNA binding, drive activation, separating catalytic activation from recruitment and transcriptional functions.\",\n      \"evidence\": \"Site-directed mutagenesis of domain-domain contacts with activity, recruitment, and reporter assays\",\n      \"pmids\": [\"24189460\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Did not identify the conformational intermediate linking contacts to catalysis\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified the molecular switch of activation: DNA break detection unfolds the autoinhibitory helical domain (HD), which otherwise blocks productive NAD+ binding.\",\n      \"evidence\": \"HXMS, crystallography of HD deletion mutants, and biochemical activity assays\",\n      \"pmids\": [\"26626480\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not quantify HD unfolding dynamics in real time\", \"Coupling between HD unfolding and DNA conformation not yet measured\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined a PARylation-independent protein interaction that channels PARP-1 into homologous recombination, via Timeless binding to the catalytic domain.\",\n      \"evidence\": \"Crystal structure of the Timeless PAB-PARP-1 catalytic domain complex with Co-IP, recruitment, and HR repair assays\",\n      \"pmids\": [\"26344098\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not determine how Timeless promotes HR mechanistically downstream of recruitment\", \"Selectivity for PARP-1 over other PARPs mechanism only partly explained\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Discovered HPF1 as a partner that redirects PARP-1 activity in trans toward histones and restrains PARP-1 hyper-automodification.\",\n      \"evidence\": \"Reciprocal Co-IP, live-cell recruitment, in vitro ADP-ribosylation, and knockout cell biology\",\n      \"pmids\": [\"27067600\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not yet identify the serine residues whose modification HPF1 enables\", \"Functional consequence for trapping not addressed at this stage\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established that inhibitor chemistry, not just catalytic inhibition, controls PARP-1 retention, with pro-retention compounds enhancing cancer cell killing.\",\n      \"evidence\": \"Structural studies, biophysical binding, cell viability assays, and synthesis of a converted pro-retention probe\",\n      \"pmids\": [\"32241924\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not quantify the relative weight of allostery versus NAD+ competition\", \"Generalizability across all clinical inhibitors not established here\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified TRIP12 as an E3 ligase that uses its PAR-binding WWE domain to target PARP1 for degradation, limiting cytotoxic trapping.\",\n      \"evidence\": \"Co-IP, domain mapping, ubiquitylation assays, proteasome inhibition, and TRIP12 knockout trapping measurements\",\n      \"pmids\": [\"32755579\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not determine in vivo impact on PARPi therapeutic window\", \"Whether TRIP12 acts selectively on trapped versus free PARP1 unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Reframed 'trapping' by showing PARP1 exchanges rapidly even under inhibitors and that NAD+ interaction governs exchange, with persistent foci reflecting ongoing recruitment due to delayed repair.\",\n      \"evidence\": \"Quantitative live-cell imaging, FRAP, PARP1 H862D/E988K mutants, and Xrcc1 knockout\",\n      \"pmids\": [\"32890402\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Apparent tension with biochemical stable-complex trapping not fully reconciled\", \"Did not test all clinical inhibitors for exchange behavior\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected HPF1-dependent serine auto-modification at S499/S507/S519 to release from chromatin, defining a regulatory axis that tunes PARPi sensitivity.\",\n      \"evidence\": \"MS site mapping, site-directed mutagenesis, trapping assays, and HPF1/ARH3 knockouts\",\n      \"pmids\": [\"34210965\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish dynamics of writing versus ARH3 erasing in real time\", \"In vivo tumor relevance not tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Captured the conformational dynamics of activation directly, showing zinc fingers kink DNA through an induced-fit cascade and that inhibitors shift the DNA conformational equilibrium.\",\n      \"evidence\": \"Single-molecule FRET and structural ensemble calculations with niraparib/EB47 comparison\",\n      \"pmids\": [\"36323657\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not connect DNA kinking quantitatively to HD unfolding kinetics\", \"Performed on defined substrates rather than chromatinized DNA\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Dissected inhibitor-driven retention into a two-step mechanism dominated by NAD+ competition with secondary allostery that can raise or lower retention.\",\n      \"evidence\": \"Single-molecule assays monitoring PARP1-DNA retention in real time\",\n      \"pmids\": [\"36070389\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not extend single-molecule retention measurements to the chromatin/cellular context\", \"Relationship to clinical efficacy ranking not directly tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Expanded PARP-1 substrate sensing to non-B DNA, showing it binds G-quadruplexes tightly but is catalytically stimulated only by specific loop features.\",\n      \"evidence\": \"In vitro binding affinity, activity assays with defined G4 structures, and loop deletion mutants\",\n      \"pmids\": [\"33313902\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Cellular consequences of G4-driven PARP-1 activation not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the many context-specific PARP-1 partner and substrate relationships (e.g., metabolic, inflammatory, and transcription-factor regulation) are integrated and prioritized at a given locus or stress state remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model links DNA-damage activation to the diverse non-repair signaling roles\", \"Residue-level modification maps for most non-histone substrates are absent\", \"Quantitative rules governing PARP-1 recruitment to specific genomic sites are undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [3, 5, 8, 24]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [8, 19, 20, 24, 28]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [5, 7, 15, 36]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [6, 20, 26]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [6, 20, 23]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 6, 21, 35]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [5, 6, 7]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [9, 28]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [5, 7, 10, 25]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [6, 8, 19, 20, 24]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [6, 23, 26]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [4, 11]}\n    ],\n    \"complexes\": [\"PARP1-HPF1 complex\", \"NLRP3 inflammasome\"],\n    \"partners\": [\"HPF1\", \"TRIP12\", \"TIMELESS\", \"KDM5B\", \"SMAD3\", \"SMAD4\", \"XRCC1\", \"NLRP3\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}