{"gene":"CAD","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":1982,"finding":"The CAD gene (encoding carbamoyl-phosphate synthetase, aspartate carbamoyltransferase, and dihydroorotase) was localized by in situ hybridization to the short arm of Syrian hamster chromosome B9; amplification of this gene underlies resistance to PALA (N-phosphonacetyl-L-aspartate), an inhibitor of its aspartate transcarbamylase activity.","method":"In situ hybridization with radiolabeled CAD probes on metaphase chromosomes from wild-type and PALA-resistant cell lines","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — direct chromosomal localization by in situ hybridization, replicated across multiple independent PALA-resistant lines","pmids":["6180304"],"is_preprint":false},{"year":1981,"finding":"A functional CAD gene was cloned from Syrian hamster cells; introduction into CAD-deficient CHO cells by protoplast fusion rescued pyrimidine biosynthesis and conferred PALA resistance, demonstrating that the CAD gene encodes all three enzymatic activities (CPS, ATCase, DHOase) necessary for de novo UMP synthesis.","method":"Cosmid cloning, protoplast fusion into CAD-deficient CHO cells, complementation assay with PALA selection","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — functional complementation with cloned gene, confirmed in multiple independent transformants","pmids":["6277500"],"is_preprint":false},{"year":1982,"finding":"The CAD gene spans ~25 kb and contains ~37 intervening sequences encoding a 7.9 kb mRNA; the coding sequences are small (100–400 bp) and the gene encodes the first three steps of UMP biosynthesis as a single polypeptide.","method":"Electron microscopy of R-loops, hybridization mapping of genomic clones from amplified CAD cell lines","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — direct structural mapping by electron microscopy and hybridization; foundational gene structure paper","pmids":["6125880"],"is_preprint":false},{"year":1983,"finding":"The aspartate transcarbamylase (ATCase) activity of CAD resides in a discrete ~40 kDa domain released by controlled proteolysis; the isolated domain forms a 2–3 subunit oligomer with Km for aspartate of 21 mM and turnover of 4,780 min⁻¹, similar to intact CAD, but with reduced stability, indicating that interactions with other CAD domains stabilize the ATCase domain.","method":"Controlled proteolysis of CAD, purification of the 40 kDa ATCase fragment, kinetic analysis, sedimentation studies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro proteolysis and reconstitution with kinetic characterization; domain isolation and functional analysis","pmids":["6300078"],"is_preprint":false},{"year":1986,"finding":"The dihydroorotase (DHOase) domain of CAD is a ~44 kDa N-terminal fragment released by elastase cleavage; it contains one tightly bound zinc atom essential for catalysis, exists as a homodimer in solution, and the amino terminus of DHOase is identical to that of intact CAD, establishing the domain order as DHO-CPS-ATC.","method":"Controlled elastase proteolysis, purification of DHOase domain, atomic absorption spectrophotometry for zinc, isotopic labeling with ⁶⁵Zn, hydrodynamic analysis (sedimentation, diffusion coefficients), immunoblotting","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct biochemical characterization with multiple orthogonal methods; zinc stoichiometry confirmed by isotope labeling","pmids":["2871022"],"is_preprint":false},{"year":1986,"finding":"CAD gene amplification in single-step PALA-resistant cells involves co-amplification of the CAD gene and at least 65 kb of flanking DNA, with very few novel chromosomal joints, suggesting very large amplicons (~10,000 kb per CAD gene copy) rather than small circular units.","method":"Probing with recombinant phage and cosmids spanning 380 kb of amplified DNA in 33 independent cell lines; Southern blotting for novel joints","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — systematic structural analysis across 33 independent cell lines","pmids":["3023056"],"is_preprint":false},{"year":1985,"finding":"CAD RNA accumulates at equal levels in nucleus and cytoplasm of Syrian hamster cells; nuclear CAD RNA is found in a large ~200S ribonucleoprotein particle distinct from 30S RNP particles, with no detectable higher-molecular-weight precursor forms.","method":"In situ hybridization, subcellular fractionation, sucrose gradient sedimentation, solution and blot hybridization","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization by fractionation and sedimentation; single lab","pmids":["3990684"],"is_preprint":false},{"year":1987,"finding":"CAD gene transcription is rapidly shut off (within 4 hours) during terminal differentiation of HL-60 promyelocytes induced by TPA or retinoic acid/dbcAMP, as demonstrated by nuclear run-off assays, with corresponding loss of CAD mRNA; the CAD protein has a half-life of ~24 hours in differentiating cells.","method":"Nuclear run-off transcription assays, RNA blotting, aspartate transcarbamylase activity assays during HL-60 differentiation","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — direct transcriptional run-off assays establishing transcriptional regulation; kinetic analysis of protein half-life","pmids":["2885743"],"is_preprint":false},{"year":1988,"finding":"Domain mapping by limited proteolysis and antibody probing established the domain order in CAD as GLNase-CPSase-DHOase-ATCase; phosphorylation by cAMP-dependent protein kinase occurs at two sites, with site 1 located at the C-terminal end of the CPSase domain (GLNase/CPSase region), and phosphorylation accelerates proteolytic cleavage and abolishes the protective effect of UTP.","method":"Limited proteolysis with elastase and trypsin, SDS-PAGE, Western blotting with domain-specific antibodies, ³²P-labeling and tryptic peptide mapping with isoelectric focusing","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — domain mapping with multiple proteases and antibodies; phosphorylation site localization by peptide mapping; functional consequence (UTP protection abolished) demonstrated","pmids":["3345746"],"is_preprint":false},{"year":1988,"finding":"CAD is localized predominantly in the cytoplasmic compartment of mammalian cells, excluded from the nucleus, and exhibits a punctate staining pattern suggesting association with subcellular organelles; it is not concentrated near mitochondria, indicating that the DHOase product dihydroorotate diffuses through cytosol rather than being channeled to mitochondrial dihydroorotate dehydrogenase.","method":"Differential centrifugation, immunofluorescence cytochemistry, immunoperoxidase staining in BHK cells and CAD-overproducing BHK 165-23 cells","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — multiple cytochemical methods used; single lab; functional inference (no channeling) supported by lack of mitochondrial colocalization","pmids":["2903106"],"is_preprint":false},{"year":1995,"finding":"An origin of bidirectional DNA replication (OBR) resides within the constitutively expressed CAD transcriptional unit, localized to a 5 kb region near the gene's center; this OBR functions in both single-copy and amplified CAD loci in Syrian and Chinese hamster cells, demonstrating conservation of origin recognition machinery across species.","method":"Nascent strand abundance assay, two-dimensional gel electrophoresis of replication intermediates, analysis of CAD episomes and chromosomally integrated sequences","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — direct biochemical demonstration of replication initiation within expressed gene; multiple approaches including 2D gels","pmids":["7623808"],"is_preprint":false},{"year":1997,"finding":"Myc-Max, but not USF, binding to the E box at +65 of the CAD promoter is essential for G1/S-phase transcriptional activation of CAD; mutations in nucleotides flanking the E box that selectively reduce Myc-Max binding abolish growth-regulated CAD induction without affecting USF binding.","method":"In vivo UV cross-linking and immunoprecipitation (ChIP precursor), promoter mutagenesis with reporter assays, growth synchronization experiments","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — in vivo occupancy assay combined with mutagenesis of the E box element showing functional selectivity of Myc-Max vs. USF","pmids":["9111322"],"is_preprint":false},{"year":2001,"finding":"c-Myc activates transcription of the cad gene by a post-RNA polymerase II recruitment mechanism: RNA Pol II is pre-loaded at the cad promoter in quiescent cells, and c-Myc stimulates CTD hyperphosphorylation (promoter clearance/elongation) by recruiting P-TEFb (cdk9/cyclin T1); direct recruitment of cyclin T1 to the promoter substitutes for c-Myc.","method":"Chromatin immunoprecipitation (ChIP) with antibodies to Pol II CTD (unphosphorylated and hyperphosphorylated), co-immunoprecipitation of c-Myc transactivation domain with cdk9/cyclin T1, activator bypass experiments with Gal4-cyclin T1","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — ChIP demonstrating CTD phosphorylation correlation, co-IP identifying P-TEFb as Myc partner, activator bypass providing epistatic confirmation; multiple orthogonal methods","pmids":["11673469"],"is_preprint":false},{"year":2001,"finding":"High rates of CAD gene amplification (50–100-fold elevated) occur in human cell lines deficient in MLH1 or MSH6 mismatch repair proteins; FISH analysis indicates amplification arises from unequal sister chromatid exchanges and translocations involving chromosome 2, implicating MutSα and MutLα in suppression of gene amplification.","method":"PALA-resistance selection for CAD gene amplification, fluorescence in situ hybridization (FISH), comparison across mismatch repair-deficient vs. proficient cell lines","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — quantitative comparison across isogenic MMR-proficient and deficient lines, FISH for mechanism; strong effect size (50–100-fold)","pmids":["11717437"],"is_preprint":false},{"year":2003,"finding":"The mSin3A/HDAC2 corepressor complex, together with PRMT5 and Brg1-based hSWI/SNF complexes, is directly recruited to the cad promoter to mediate transcriptional repression; PRMT5 preferentially methylates hypoacetylated histones H3 and H4; inactivation of Brg1 or treatment with HDAC inhibitor depsipeptide alters cad repression.","method":"Chromatin immunoprecipitation (ChIP) for Brg1, mSin3A, HDAC2, PRMT5 at cad promoter; histone methylation assays with acetylated vs. hypoacetylated histones; protein-protein interaction studies; reporter assays in cells expressing dominant-negative Brg1","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — ChIP demonstrating direct promoter recruitment, in vitro histone methylation assay, functional perturbation with dominant-negative Brg1 and HDAC inhibitor; multiple orthogonal methods","pmids":["14559996"],"is_preprint":false},{"year":1988,"finding":"Chromosome aberrations (including dicentrics at high frequency in hyperdiploid/polyploid cells containing two copies of the marker chromosome) are associated with CAD gene amplification in Chinese hamster V79 cells; amplified CAD sequences reside in the terminal region of a marker chromosome with elongated q arms (homogeneously staining region).","method":"In situ hybridization with CAD DNA probe, G-banding, cytogenetic analysis of 11 PALA-resistant sublines","journal":"Mutation research","confidence":"Medium","confidence_rationale":"Tier 2 — direct in situ hybridization mapping of amplified sequences; cytogenetic characterization across multiple sublines","pmids":["2896299"],"is_preprint":false},{"year":2005,"finding":"HIF-1α directly binds to a hypoxia response element (HRE) in the cad promoter and transcriptionally represses CAD expression under hypoxia or DFO-induced HIF-1α accumulation; this is demonstrated by promoter-reporter assays with wild-type and mutant HRE constructs and by ChIP showing HIF-1α occupancy at the cad promoter in vivo.","method":"Promoter-reporter assays (luciferase) with HRE deletion/mutation constructs, overexpression of wild-type and dominant-negative HIF-1α, chromatin immunoprecipitation (ChIP) for HIF-1α at cad promoter, RT-PCR of CAD expression under hypoxia","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 — ChIP demonstrating in vivo binding, promoter mutagenesis, dominant-negative rescue; multiple orthogonal methods in a single study","pmids":["16155188"],"is_preprint":false},{"year":2011,"finding":"CAD physically interacts with the androgen receptor (AR) in prostate tumor cells and promotes AR nuclear translocation and transcriptional activity; higher CAD mRNA levels in radical prostatectomy specimens correlate with local tumor extension and cancer relapse.","method":"Immunopurification of AR partners from human tumor xenografts followed by mass spectrometry; co-immunoprecipitation and nuclear translocation assays in C4-2, LNCaP, 22RV1, and PC3 cells; luciferase reporter for AR transcriptional activity","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — mass spectrometry identification followed by co-IP validation and functional nuclear translocation assay; single lab","pmids":["21982950"],"is_preprint":false},{"year":2012,"finding":"CAD physically interacts with NOD2 (identified by immunoprecipitation-coupled mass spectrometry) and acts as a negative regulator of NOD2-dependent NF-κB and p38 MAPK activation and intracellular bacterial killing; CAD overexpression inhibits NOD2 signaling while CAD knockdown or pharmacological inhibition enhances NOD2-dependent antibacterial function.","method":"Immunoprecipitation-coupled mass spectrometry (Co-IP/MS), co-immunoprecipitation in HCT116 cells, NF-κB and p38 reporter assays, Salmonella gentamicin protection assays, siRNA knockdown, CAD inhibitor treatment","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 2 — MS-identified interaction validated by co-IP, functional loss-of-function (siRNA and inhibitor) and gain-of-function with defined signaling and antibacterial readouts; multiple orthogonal methods","pmids":["22387394"],"is_preprint":false},{"year":2014,"finding":"In zebrafish, loss-of-function of cad (carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, dihydroorotase) causes reduced Notch signaling and hyperbranching arteries due to increased endothelial responsiveness to Vegfc/Vegfr3; genetic epistasis places cad upstream of Notch signaling in the regulation of angiogenesis, with CAD's role linked to UDP biosynthesis required for protein glycosylation (a prerequisite for Notch signaling).","method":"Forward genetic screen, positional cloning, Notch reporter transgene assay, genetic epistasis with Vegfc/Vegfr3 pathway mutants, morpholino knockdown","journal":"Developmental dynamics","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis in zebrafish with Notch reporter; ortholog finding with mechanistic pathway placement; single lab","pmids":["25294789"],"is_preprint":false},{"year":2019,"finding":"CAD is a 1.5 MDa particle formed by hexameric association of a 250 kDa polypeptide carrying three enzymatic activities (CPS, ATCase, DHOase); the ATCase domain mediates hexameric and trimeric self-assembly; the fusion of the first three pyrimidine biosynthetic activities into a single multienzymatic particle is unique to animals.","method":"Biochemical and structural characterization review synthesizing limited proteolysis, hydrodynamic studies, electron microscopy, and domain expression data","journal":"Sub-cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 3 — review synthesizing experimental evidence from multiple labs; foundational architecture described","pmids":["31939163"],"is_preprint":false},{"year":2020,"finding":"CAD directly interacts with Ebola virus nucleoprotein NP via the glutaminase (GLN) domain of CAD; NP recruits CAD into viral inclusion bodies, and CAD is required for both viral genome replication and transcription, functioning through its pyrimidine synthesis activity (substrate rescue with uridine/cytidine partially restores viral replication upon CAD knockdown).","method":"siRNA knockdown, co-immunoprecipitation of NP with CAD, co-immunofluorescence colocalization assays, reverse genetics life cycle modelling systems, substrate rescue experiments with uridine/cytidine","journal":"Cells","confidence":"High","confidence_rationale":"Tier 2 — co-IP identifies direct NP-CAD interaction, domain mapping (GLN required), substrate rescue confirms enzymatic function required; multiple orthogonal methods","pmids":["32370067"],"is_preprint":false},{"year":2020,"finding":"A CRISPR/Cas9-generated human CAD-knockout cell line requires uridine for survival; transient transfection with recombinant CAD restores growth in uridine-free medium, enabling a quantitative complementation assay to assess pathogenicity of CAD missense variants; 16 of 34 tested variants were identified as deleterious, confirming CAD deficiency as a uridine-responsive inborn metabolic disorder.","method":"CRISPR/Cas9 knockout of CAD, complementation assay by transient transfection of variant CAD constructs, growth assay in uridine-depleted medium","journal":"Genetics in medicine","confidence":"High","confidence_rationale":"Tier 1 — CRISPR knockout + functional complementation assay with systematic variant testing; clean phenotype and mechanistic readout","pmids":["32461667"],"is_preprint":false},{"year":2021,"finding":"Afatinib, an EGFR tyrosine kinase inhibitor, directly targets CAD and suppresses CD8+ T lymphocyte proliferation by inhibiting de novo pyrimidine biosynthesis; afatinib reduces tumor-infiltrating lymphocyte numbers in mouse tumor models, and sequential (but not simultaneous) combination with anti-PD1 therapy enhances efficacy.","method":"Kinase inhibitor profiling identifying CAD as afatinib target, CD8+ T cell proliferation assays with/without afatinib and CAD inhibitors, flow cytometry of tumor-infiltrating lymphocytes in LLC-bearing mice, combination therapy experiments in MC38 and LLC models","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological identification of CAD as afatinib target with functional proliferation readout; single lab, mechanism confirmed by specific CAD inhibitors","pmids":["33771897"],"is_preprint":false},{"year":2021,"finding":"CAD is a 1.5 MDa hexamer; the dihydroorotase (DHO) domain forms homodimers in solution and crystallizes in space group C222(1) diffracting to 1.75 Å resolution; the ATCase domain forms homotrimers and mediates hexamer formation of intact CAD.","method":"Recombinant expression and purification of CAD DHO and ATCase domains, size exclusion chromatography, X-ray crystallography (synchrotron data collection)","journal":"Protein science","confidence":"High","confidence_rationale":"Tier 1 — direct structural characterization by X-ray crystallography; DHO domain structure at 1.75 Å; ATCase trimer confirmed by solution studies","pmids":["34288185"],"is_preprint":false},{"year":2012,"finding":"The dihydroorotase (DHO) domain of human CAD forms homodimers in solution and yields crystals diffracting to 1.75 Å; X-ray data indicate one molecule per asymmetric unit, providing the first structural data on the isolated DHO domain of human CAD.","method":"Recombinant expression in insect cells, purification, size exclusion chromatography, X-ray crystallography at SLS synchrotron","journal":"Acta crystallographica. Section F","confidence":"Medium","confidence_rationale":"Tier 1 — crystal structure determination; preliminary report without full structure refinement","pmids":["23143245"],"is_preprint":false},{"year":2013,"finding":"The ATCase domain of human CAD forms homotrimers in solution; it crystallizes in space group P6(3)22 (or pseudo-P21 with twinning) and diffracts to 2.1 Å, providing the first structural data on a eukaryotic ATCase and confirming that ATCase-ATCase interactions mediate hexamerization of the full CAD complex.","method":"Recombinant expression in bacteria, purification, size exclusion chromatography, X-ray crystallography with PALA inhibitor, synchrotron data collection","journal":"Acta crystallographica. Section F","confidence":"Medium","confidence_rationale":"Tier 1 — crystal structure determination; preliminary crystallography report; ATCase trimer confirmed; first eukaryotic ATCase structure","pmids":["24316846"],"is_preprint":false},{"year":2022,"finding":"Oncogenic β-catenin transcriptionally upregulates AKT2, which then phosphorylates CAD at S1406 and S1859 to activate de novo pyrimidine synthesis; this β-catenin/AKT2/CAD signaling axis is the major metabolic aberration in β-catenin mutant liver cancer, and its inhibition preferentially suppresses proliferation of β-catenin mutant cells.","method":"Untargeted metabolomics in β-catenin mutant cell lines and mouse livers, phosphorylation site mapping by mass spectrometry, site-directed mutagenesis of S1406 and S1859 in CAD, mouse liver tumor models, pharmacological inhibition of the pathway","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — phosphorylation sites identified by MS and validated by mutagenesis, upstream kinase identified (AKT2), metabolomics readout, in vivo tumor model; multiple orthogonal methods","pmids":["36122209"],"is_preprint":false},{"year":2022,"finding":"CAD is rapidly phosphorylated upon naïve CD8+ T cell activation in an mTORC1-dependent manner and remains phosphorylated in memory T cells; persistent CAD activity drives ongoing de novo pyrimidine synthesis that supports ribosomal RNA synthesis and ribosomal biogenesis required for the rapid recall response; CAD inhibition reduces pre-rRNA levels and ribosomal protein abundance without affecting cytokine mRNA.","method":"Cell synchronization and metabolomics, mTORC1 inhibition (rapamycin), CAD inhibitor treatment, CAD overexpression, pre-rRNA quantification, flow cytometry of cytokine production, measurement of ribosomal protein levels","journal":"Science immunology","confidence":"High","confidence_rationale":"Tier 2 — mTORC1-dependent phosphorylation established, CAD inhibition/overexpression with specific rRNA and ribosome biogenesis readouts; multiple orthogonal methods","pmids":["35622902"],"is_preprint":false},{"year":2023,"finding":"CAD activity is allosterically regulated during the cell cycle via two Animalia-specific loops in the allosteric domain that sense and bind UTP (an allosteric inhibitor); a signal transmission loop (homologous to one in mitochondrial CPS) regulates formation of a substrate channel controlling CAD activity; this allosteric mechanism accounts for cell cycle phase-dependent changes in de novo pyrimidine synthesis.","method":"Cell synchronization and metabolomics to identify cell cycle phase-dependent metabolites, systematic mutational scanning of allosteric domain, structural modelling based on CPS homology, UTP binding assays","journal":"Nature metabolism","confidence":"High","confidence_rationale":"Tier 1 — systematic mutational scanning combined with structural modelling and UTP binding studies; metabolomics-based cell cycle phenotype; mechanistic identification of allosteric loops","pmids":["36747088"],"is_preprint":false},{"year":2023,"finding":"Atomic-resolution crystal structures of eight pathogenic missense variants in the CAD dihydroorotase (DHO) domain reveal that pathogenic variants cluster in the DHO domain and impair CAD activity, stability, or dimerization; molecular dynamics analysis confirms conformational effects of damaging variants; combined functional and structural analysis enables reliable reclassification of CAD variants.","method":"Growth complementation assay in CRISPR CAD-knockout cells, X-ray crystallography of DHO domain variants, molecular dynamics simulations, functional kinetic assays","journal":"Journal of inherited metabolic disease","confidence":"High","confidence_rationale":"Tier 1 — crystal structures of multiple variants combined with functional complementation assay and molecular dynamics; comprehensive structure-function analysis","pmids":["37540500"],"is_preprint":false},{"year":2019,"finding":"A missense mutation p.Tyr452Cys in the carbamoyl-phosphate synthetase 2 domain of CAD, affecting a perfectly conserved tyrosine, causes recessive embryonic lethality in cattle (French Normande breed) with nearly complete penetrance, demonstrating that CAD enzymatic activity is essential for viability during embryonic development.","method":"Genome-wide SNP scanning for homozygous haplotype deficiency in 77,815 cattle, fine mapping and whole-genome sequencing, Sanger sequencing, large-scale genotyping of 33,323 Normande animals","journal":"Journal of dairy science","confidence":"Medium","confidence_rationale":"Tier 3 — genetic association and conservation analysis; embryonic lethality phenotype strong but mechanism inferred from absence of live homozygotes; consistent with known CAD biology","pmids":["31056337"],"is_preprint":false}],"current_model":"CAD (carbamoyl-phosphate synthetase 2, aspartate transcarbamoylase, dihydroorotase) is a ~250 kDa multienzymatic protein that self-assembles into a ~1.5 MDa hexamer and catalyzes the first three rate-limiting steps of de novo pyrimidine nucleotide biosynthesis (CPS→ATCase→DHOase) in the cytoplasm; its activity is allosterically inhibited by UTP through two Animalia-specific loops, and stimulated by AKT2-mediated phosphorylation at S1406/S1859 (downstream of oncogenic β-catenin) and mTORC1-dependent phosphorylation during T cell activation; transcription of the CAD gene is activated at G1/S by Myc-Max recruiting P-TEFb to drive RNA Pol II CTD phosphorylation and elongation, and repressed by HIF-1α occupancy of a promoter HRE and by a Brg1/mSin3A/HDAC2/PRMT5 corepressor complex; CAD physically interacts with the androgen receptor (promoting its nuclear translocation) and with NOD2 (inhibiting its antibacterial signaling), and is hijacked by Ebola virus NP into inclusion bodies via the GLN domain to supply pyrimidines for viral replication."},"narrative":{"teleology":[],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":[],"other_free_text":[]},"mechanistic_narrative":"Insufficient on-target evidence to synthesize a narrative — discovery timeline does not match the canonical CAD protein."},"prefetch_data":{"uniprot":{"accession":"P27708","full_name":"Multifunctional protein CAD","aliases":["Carbamoyl phosphate synthetase 2-aspartate transcarbamylase-dihydroorotase"],"length_aa":2225,"mass_kda":243.0,"function":"Multifunctional protein that encodes the first 3 enzymatic activities of the de novo pyrimidine pathway: carbamoylphosphate synthetase (CPSase; EC 6.3.5.5), aspartate transcarbamylase (ATCase; EC 2.1.3.2) and dihydroorotase (DHOase; EC 3.5.2.3). The CPSase-function is accomplished in 2 steps, by a glutamine-dependent amidotransferase activity (GATase) that binds and cleaves glutamine to produce ammonia, followed by an ammonium-dependent carbamoyl phosphate synthetase, which reacts with the ammonia, hydrogencarbonate and ATP to form carbamoyl phosphate. The endogenously produced carbamoyl phosphate is sequestered and channeled to the ATCase active site. ATCase then catalyzes the formation of carbamoyl-L-aspartate from L-aspartate and carbamoyl phosphate. In the last step, DHOase catalyzes the cyclization of carbamoyl aspartate to dihydroorotate","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P27708/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CAD","classification":"Not Classified","n_dependent_lines":485,"n_total_lines":1208,"dependency_fraction":0.4014900662251656},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000084774","cell_line_id":"CID000996","localizations":[{"compartment":"cytoplasmic","grade":3}],"interactors":[{"gene":"MRTO4","stoichiometry":10.0},{"gene":"CDC37","stoichiometry":0.2},{"gene":"CAPZB","stoichiometry":0.2},{"gene":"FKBP5","stoichiometry":0.2},{"gene":"HMGN5","stoichiometry":0.2},{"gene":"MIF","stoichiometry":0.2},{"gene":"PTGES3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000996","total_profiled":1310},"omim":[{"mim_id":"620291","title":"WD REPEAT-CONTAINING PROTEIN 18; WDR18","url":"https://www.omim.org/entry/620291"},{"mim_id":"620058","title":"FAMILIAL APOLIPOPROTEIN GENE CLUSTER DELETION SYNDROME","url":"https://www.omim.org/entry/620058"},{"mim_id":"619858","title":"AUTOINFLAMMATORY-PANCYTOPENIA SYNDROME; AIPCS","url":"https://www.omim.org/entry/619858"},{"mim_id":"619836","title":"HYPOALPHALIPOPROTEINEMIA, PRIMARY, 2, INTERMEDIATE","url":"https://www.omim.org/entry/619836"},{"mim_id":"618979","title":"HIGH DENSITY LIPOPROTEIN CHOLESTEROL LEVEL QUANTITATIVE TRAIT LOCUS 7; HDLCQ7","url":"https://www.omim.org/entry/618979"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CAD"},"hgnc":{"alias_symbol":["GATD4"],"prev_symbol":[]},"alphafold":{"accession":"O76075","domains":[{"cath_id":"3.10.20.10","chopping":"7-84","consensus_level":"high","plddt":93.8833,"start":7,"end":84},{"cath_id":"-","chopping":"153-307","consensus_level":"high","plddt":95.2195,"start":153,"end":307},{"cath_id":"1.10.287","chopping":"96-128","consensus_level":"high","plddt":91.8948,"start":96,"end":128}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O76075","model_url":"https://alphafold.ebi.ac.uk/files/AF-O76075-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O76075-F1-predicted_aligned_error_v6.png","plddt_mean":92.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CAD","jax_strain_url":"https://www.jax.org/strain/search?query=CAD"},"sequence":{"accession":"O76075","fasta_url":"https://rest.uniprot.org/uniprotkb/O76075.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O76075/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O76075"}},"corpus_meta":[{"pmid":"14559996","id":"PMC_14559996","title":"mSin3A/histone deacetylase 2- and PRMT5-containing Brg1 complex is involved in transcriptional repression of the Myc target gene cad.","date":"2003","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/14559996","citation_count":201,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"15723341","id":"PMC_15723341","title":"Discovery, regulation, and action of the major apoptotic nucleases DFF40/CAD and endonuclease G.","date":"2005","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15723341","citation_count":165,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"11673469","id":"PMC_11673469","title":"c-Myc mediates activation of the cad promoter via a post-RNA polymerase II recruitment mechanism.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11673469","citation_count":162,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"9111322","id":"PMC_9111322","title":"Myc 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non-functional CAD/DFF40 monomer and can disassemble the functional dimer through its middle domain, and caspase cleavage of ICAD/DFF45 leads to self-assembly of CAD/DFF40 into the active dimer.\",\n      \"method\": \"Crystal structure determination, biochemical reconstitution, domain-deletion analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus functional reconstitution and mutagenesis in a single study\",\n      \"pmids\": [\"15149602\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"NMR structure of the CAD domain of CAD/DFF40 reveals an independently folded domain composed of one alpha-helix and five beta-strands with a ubiquitin superfold; this domain binds strongly to the CAD domain of ICAD (Kd ~55 nM), and this protein-protein interaction mediates inhibition of CAD DNase activity and correct folding of CAD.\",\n      \"method\": \"Multi-dimensional NMR spectroscopy, surface plasmon resonance\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure with functional binding validation\",\n      \"pmids\": [\"10764577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Site-directed mutagenesis identified at least four histidine residues in the C-terminal part of CAD as essential for its DNase catalytic activity; ICAD inhibits CAD not by masking the active site but by blocking CAD's ability to bind DNA, indicating steric or electrostatic hindrance.\",\n      \"method\": \"Site-directed mutagenesis, chemical modification, substrate-protection assay, quantitative DNase activity assay\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — active-site mutagenesis combined with chemical modification and mechanistic follow-up\",\n      \"pmids\": [\"11361146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"CAD/DFF40 knockout in chicken DT40 cells demonstrates that CAD is essential for oligonucleosomal DNA fragmentation and complete chromatin condensation/nuclear fragmentation during apoptosis, but is dispensable for high-molecular-weight DNA cleavage and early-stage apoptotic chromatin condensation.\",\n      \"method\": \"Gene knockout (CAD-/- DT40 cells), DNA fragmentation assay, morphological analysis of nuclear disassembly\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple defined cellular phenotypes\",\n      \"pmids\": [\"11577114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"DNA topoisomerase IIα physically binds to CAD, and their association enhances the decatenation activity of Topo IIα in vitro; simultaneous inhibition of Topo IIα and caspases completely abolishes apoptotic chromatin condensation, placing Topo IIα downstream of caspase activation in apoptotic nuclear disassembly.\",\n      \"method\": \"Co-immunoprecipitation, in vitro decatenation assay, pharmacological inhibition with epistasis analysis\",\n      \"journal\": \"Current biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal binding plus in vitro functional assay and epistasis\",\n      \"pmids\": [\"10959840\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"DFF40/CAD is a Mg2+-dependent endonuclease with optimal activity at 50–125 mM K+ (matching apoptotic cytoplasmic K+ concentration); Zn2+ and Cu2+ inhibit the enzyme, Ca2+ does not costimulate it, and high ionic strength causes the enzyme to introduce single-stranded nicks rather than double-strand breaks.\",\n      \"method\": \"In vitro endonuclease assay with defined ionic conditions, native gel analysis of oligomerization\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — detailed in vitro biochemical characterization with multiple conditions\",\n      \"pmids\": [\"11330826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"DFF40/CAD is exclusively specific for double-stranded DNA; single-stranded DNA, RNA, and RNA-DNA hybrids are not cleaved but competitively inhibit cleavage of dsDNA, and RNA degradation in apoptotic cells is not temporally correlated with CAD activation.\",\n      \"method\": \"In vitro nuclease assay with synthetic oligonucleotides, in vivo apoptosis time-course analysis\",\n      \"journal\": \"Apoptosis\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous in vitro substrate-specificity study with multiple substrate types\",\n      \"pmids\": [\"18283539\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Granzyme M directly cleaves ICAD (inhibitor of CAD) to release active CAD nuclease, leading to DNA fragmentation; GzmM also cleaves PARP to prevent DNA repair, establishing a caspase-dependent apoptotic pathway initiated by GzmM in NK cell-mediated cytolysis.\",\n      \"method\": \"Protein transfection of GzmM, cell-based DNA fragmentation assay, in vitro cleavage assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct cleavage demonstrated, single lab\",\n      \"pmids\": [\"16818775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"A novel antiapoptotic protein CIIA binds CAD and inhibits its nuclease activity without affecting caspase-3-mediated ICAD cleavage; CIIA also inhibits ASK1 oligomerization-induced activation, functioning as an endogenous antagonist of both pathways.\",\n      \"method\": \"Co-immunoprecipitation, nuclease activity assay, antisense knockdown, overexpression\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — direct binding and activity assay, single lab with multiple methods\",\n      \"pmids\": [\"14557248\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The Brg1-based hSWI/SNF complex, together with mSin3A, HDAC2, and PRMT5, is directly recruited to the CAD (cad) promoter to mediate transcriptional repression; PRMT5 methylates hypoacetylated histones H3/H4 more efficiently than hyperacetylated forms at this promoter.\",\n      \"method\": \"Chromatin immunoprecipitation, co-purification, in vitro histone methylation assay, dominant-negative Brg1 cells\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP with multiple components plus in vitro methylation, replicated across approaches\",\n      \"pmids\": [\"14559996\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"c-Myc activates cad transcription via a post-RNA polymerase II recruitment mechanism: RNA Pol II is pre-loaded on the cad promoter in quiescent cells, but c-Myc binding correlates with CTD hyperphosphorylation; c-Myc transactivation domain interacts with cdk9 and cyclin T1 (P-TEFb components), and direct recruitment of cyclin T1 to the promoter substitutes for c-Myc.\",\n      \"method\": \"Chromatin immunoprecipitation with phospho-CTD antibody, co-immunoprecipitation, activator-bypass experiment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal ChIP and IP methods, activator-bypass epistasis\",\n      \"pmids\": [\"11673469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"In vivo UV cross-linking and immunoprecipitation showed that Myc, Max, and USF all bind the chromosomal cad E-box (+65); mutations flanking the E-box that selectively reduce Myc-Max binding in vitro abolish G1/S-phase transcriptional activation of cad, establishing Myc-Max (not USF) as the essential activator for cell-cycle-regulated cad expression.\",\n      \"method\": \"In vivo UV cross-linking/immunoprecipitation, E-box mutagenesis, transcriptional activity assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo binding + mutagenesis establishing mechanistic specificity\",\n      \"pmids\": [\"9111322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"HIF-1α directly binds to a hypoxia response element (HRE) in the cad promoter (mapped to a –67/HRE fragment) and represses CAD transcription under hypoxia; dominant-negative HIF-1α abolishes repression, and chromatin immunoprecipitation confirms in vivo HIF-1α occupancy of the cad promoter.\",\n      \"method\": \"Promoter-reporter assay, dominant-negative overexpression, chromatin immunoprecipitation\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple complementary approaches, functional and ChIP validation\",\n      \"pmids\": [\"16155188\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"Controlled elastase cleavage of CAD released a 44 kDa dihydroorotase (DHO) domain at the amino terminus; the isolated domain contains one tightly bound zinc per polypeptide, zinc chelators inhibit DHOase activity, and the domain forms a concentration-dependent dimer-monomer equilibrium.\",\n      \"method\": \"Controlled proteolysis, atomic absorption spectrophotometry, 65Zn radiolabeling, analytical ultracentrifugation, enzyme kinetics\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with multiple orthogonal methods including metal analysis\",\n      \"pmids\": [\"2871022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1983,\n      \"finding\": \"Controlled proteolysis of CAD releases a 40 kDa aspartate transcarbamylase (ATCase) domain as one of the first cleavages; the isolated domain forms an oligomer (2–3 copies), retains kinetics similar to intact CAD, but has a much shorter half-life, indicating that interactions with other CAD domains stabilize the ATCase domain.\",\n      \"method\": \"Controlled proteolysis, enzyme kinetics, sedimentation analysis, stability assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution with kinetic and structural characterization\",\n      \"pmids\": [\"6300078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"Limited proteolysis combined with antibody probing established the domain order in CAD as GLNase-CPSase-DHOase-ATCase; cAMP-dependent protein kinase phosphorylation sites were mapped to near the C-terminal end of the CPSase domain (site 1) and the DHOase-ATCase hinge region; phosphorylation accelerates proteolytic cleavage and abolishes UTP protection.\",\n      \"method\": \"Limited proteolysis, antibody blotting, 32P-labeling, isoelectric focusing of tryptic peptides\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — domain mapping by proteolysis + antibody detection + phosphorylation site identification\",\n      \"pmids\": [\"3345746\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"Immunolocalization and differential centrifugation in hamster cells showed that CAD is localized in the cytoplasmic compartment with a punctate pattern suggesting organelle association, and is almost completely excluded from the nucleus; CAD is not concentrated near mitochondria, indicating that the dihydroorotate intermediate is not channeled to the next pathway enzyme.\",\n      \"method\": \"Immunolocalization (immunofluorescence/immunoelectron microscopy), differential centrifugation, subcellular fractionation\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization by two methods with functional inference, single lab\",\n      \"pmids\": [\"2903106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Oncogenic β-catenin transcriptionally upregulates AKT2, which then phosphorylates CAD on S1406 and S1859 to potentiate de novo pyrimidine synthesis; inhibition of this β-catenin/AKT2/CAD axis selectively suppresses proliferation and tumor formation of β-catenin-mutant cells.\",\n      \"method\": \"Metabolomics, phospho-site mutagenesis, kinase assay, mouse tumor models, shRNA knockdown\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — phospho-site identified by mutagenesis, in vitro kinase assay, replicated in multiple models\",\n      \"pmids\": [\"36122209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CAD activity is allosterically regulated during the cell cycle; systematic mutational scanning and structural modelling identified two Animalia-specific loops in the CAD allosteric domain that sense and bind UTP (an allosteric inhibitor), and a signal transmission loop regulates formation of a substrate channel controlling CAD activity.\",\n      \"method\": \"Metabolomics, cell cycle synchronization, mutational scanning, structural modelling based on mitochondrial CPS homologue\",\n      \"journal\": \"Nature metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutational scanning combined with structural modelling and metabolomics, multiple orthogonal methods\",\n      \"pmids\": [\"36747088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CAD is rapidly phosphorylated upon naïve CD8+ T cell activation in an mTORC1-dependent manner, remains phosphorylated in memory T cells, sustains de novo pyrimidine synthesis, and supports pre-rRNA synthesis for ribosomal biogenesis needed for rapid recall response upon rechallenge.\",\n      \"method\": \"Phospho-flow cytometry, metabolic tracing, CAD inhibition/overexpression, mTORC1 inhibition, ribosomal protein quantification\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods linking phosphorylation to defined functional outcomes\",\n      \"pmids\": [\"35622902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CAD physically interacts with NOD2 (identified by immunoprecipitation-coupled mass spectrometry) and negatively regulates NOD2-dependent NF-κB and p38 MAPK activation and intracellular bacterial killing; CAD inhibitors increase NOD2-dependent antibacterial function.\",\n      \"method\": \"Immunoprecipitation-mass spectrometry, immunoprecipitation, reporter assay, gentamicin protection assay, siRNA knockdown, CAD inhibitors\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — discovery by IP-MS, validated by multiple functional assays\",\n      \"pmids\": [\"22387394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CAD physically interacts with the androgen receptor (AR) in prostate tumor cells; CAD overexpression promotes AR translocation into the nucleus and stimulates AR transcriptional activity, revealing a non-metabolic function for CAD in nuclear receptor signaling.\",\n      \"method\": \"Immunopurification of AR partners in xenografted tumors, co-immunoprecipitation, nuclear translocation assay, transcriptional reporter assay in multiple prostate cell lines\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — binding confirmed by IP, functional outcome by localization and reporter assay, single lab\",\n      \"pmids\": [\"21982950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The EGFR-TKI afatinib directly targets CAD and inhibits its activity, suppressing CD8+ T lymphocyte proliferation by reducing de novo pyrimidine synthesis; this was validated by showing afatinib inhibition is rescued by exogenous uridine.\",\n      \"method\": \"Kinase inhibitor profiling, uridine rescue assay, T cell proliferation assay, tumor models\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional inhibition with mechanistic rescue, single lab\",\n      \"pmids\": [\"33771897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"EBOV nucleoprotein NP directly interacts with CAD and recruits it into inclusion bodies via the glutaminase (GLN) domain of CAD; siRNA knockdown of CAD reduces both viral genome replication and transcription, and substrate rescue experiments show that CAD's pyrimidine synthesis function is required.\",\n      \"method\": \"Co-immunoprecipitation, co-immunofluorescence, siRNA knockdown, reverse genetics life cycle models, substrate rescue\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — binding domain mapped, functional knockdown with rescue, single lab\",\n      \"pmids\": [\"32370067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In zebrafish, cad (carbamoyl-phosphate synthetase 2/aspartate transcarbamylase/dihydroorotase) is required for normal vascular development; cad mutants show reduced lymphatic development and hyperbranching arteries due to reduced Notch signaling; genetic epistasis showed increased Vegfc/Vegfr3 signaling drives excessive artery branching downstream of reduced Notch activity.\",\n      \"method\": \"Forward genetic screen, positional cloning, Notch activity reporter, genetic epistasis with Vegfc/Vegfr3 pathway\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — positional cloning plus epistasis in a vertebrate model\",\n      \"pmids\": [\"25294789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Executioner caspase activation of CAD/DFF40 is essential for TRAIL-induced and vincristine-induced mutagenesis in surviving cells; caspase inhibition or CAD deficiency abolished these mutations, while cisplatin- and temozolomide-induced mutagenesis did not require caspases.\",\n      \"method\": \"CAD-deficient cell lines, caspase inhibitors, mutagenesis assays (drug treatment + colony sequencing)\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with specific mutational readout, pathway placement by epistasis\",\n      \"pmids\": [\"28981092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Crystal data for the DHO domain of human CAD established it forms homodimers in solution; diffraction to 1.75 Å confirmed the domain is amenable to structural determination (space group C222₁).\",\n      \"method\": \"Crystallography, analytical ultracentrifugation\",\n      \"journal\": \"Acta crystallographica Section F\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 1 method but only preliminary crystallographic report, no structure deposited\",\n      \"pmids\": [\"23143245\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The ATCase domain of human CAD forms homotrimers in solution; crystal diffraction to 2.1 Å was obtained, providing the first crystallographic data on a eukaryotic ATCase and confirming that CAD self-assembles into hexamers/trimers through ATCase domain interactions.\",\n      \"method\": \"Crystallography, analytical ultracentrifugation\",\n      \"journal\": \"Acta crystallographica Section F\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 1 method but only preliminary crystallographic report without full structure\",\n      \"pmids\": [\"24316846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"RNA, single-stranded DNA, heparin, and polyglutamic acid inhibit DFF40/CAD by binding to the enzyme and impairing its ability to bind double-stranded DNA; these polyanions are proposed to bind the positively charged surface formed by alpha-4 helices of the DFF40/CAD homodimer.\",\n      \"method\": \"In vitro endonuclease inhibition assay, binding studies\",\n      \"journal\": \"Apoptosis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–3 — in vitro biochemical characterization with structural inference, single lab\",\n      \"pmids\": [\"16699957\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CAD is a ~1.5 MDa hexameric multienzymatic particle (each subunit ~250 kDa) that catalyzes the first three rate-limiting steps of de novo pyrimidine biosynthesis (CPS2-ATCase-DHOase) in the cytoplasm; its ATCase domain mediates hexamerization/trimerization, the DHO domain contains a catalytic zinc, and activity is allosterically inhibited by UTP through Animalia-specific loops; CAD is phosphorylated by PKA at CPSase/DHOase sites and by AKT2 at S1406/S1859 to potentiate nucleotide synthesis; its transcription is activated by Myc-Max (via P-TEFb/CTD kinase recruitment) and repressed by HIF-1α and a Brg1/mSin3A/HDAC2/PRMT5 complex; in apoptosis, caspase-3/7 cleave its inhibitor ICAD/DFF45 to release active CAD/DFF40 homodimer, which cleaves internucleosomal dsDNA in a Mg2+-dependent manner assisted by histone H1, HMGB1/2, and Topo IIα; non-apoptotic roles include interacting with the androgen receptor to promote its nuclear translocation, binding NOD2 to suppress antibacterial signaling, and being recruited by Ebola NP into inclusion bodies to supply pyrimidines for viral replication.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll systematically classify each paper before extracting discoveries.\n\n**Classification:**\n\n- Papers about CAD (carbamoyl-phosphate synthetase 2/aspartate transcarbamylase/dihydroorotase, multifunctional pyrimidine biosynthesis enzyme): KEEP\n- Papers about CAD/DFF40 (caspase-activated DNase): KEEP (same human gene symbol used for this distinct protein — actually this is a different gene: DFFB/DFF40. Let me reconsider.)\n\nWait — CAD the apoptotic nuclease (DFF40/DFFB) is a *different gene* from CAD the pyrimidine biosynthesis enzyme (carbamoyl-phosphate synthetase 2). These are two distinct proteins with the same abbreviation. The corpus clearly contains both. The gene being queried is CAD (pyrimidine biosynthesis), as evidenced by the majority of papers and the HGNC symbol.\n\n- CAD = pyrimidine biosynthesis multienzymatic protein: KEEP\n- DFF40/CAD (caspase-activated DNase, gene DFFB): EXCLUDE (alias collision)\n- Coronary artery disease (CAD): EXCLUDE (disease abbreviation)\n- Computer-aided design (CAD): EXCLUDE\n- Cinnamyl alcohol dehydrogenase (CAD in plants): EXCLUDE (symbol collision, plant)\n- Cis-aconitic acid decarboxylase (CAD in Aspergillus): EXCLUDE (symbol collision, fungal)\n- CAD cell line (Cath.a-differentiated neuronal cell line): EXCLUDE (different entity)\n- CENP-A NAC/CAD kinetochore complex: EXCLUDE (different protein complex)\n- Cad pathway in E. coli (lysine decarboxylase): EXCLUDE (symbol collision, bacterial)\n- Cadmium resistance Cad system in Pseudomonas: EXCLUDE (symbol collision, bacterial)\n\nNow classifying each paper:\n\n[1] mSin3A/PRMT5/Brg1 complex represses cad promoter — KEEP (pyrimidine biosynthesis CAD gene regulation)\n[2] DFF40/CAD apoptotic nuclease — EXCLUDE (alias collision, DFFB gene)\n[3] c-Myc activates cad promoter — KEEP\n[4] Myc vs USF at cad E box — KEEP\n[5] Computer-aided design of Mn(II) complexes — EXCLUDE\n[6] HPLC-CAD (charged aerosol detector) — EXCLUDE\n[7] Crystal structure of CAD/DFF40 — EXCLUDE (DFFB gene)\n[8] CAD/DFF40 in apoptosis (DT40 cells) — EXCLUDE (DFFB gene)\n[9] Syrian hamster CAD gene amplification, chromosomal localization — KEEP\n[10] Cis-aconitic acid decarboxylase CAD gene from Aspergillus — EXCLUDE (symbol collision)\n[11] Treg/Th17 in coronary artery disease CAD — EXCLUDE (disease abbreviation)\n[12] DFF40/CAD endonuclease — EXCLUDE (DFFB gene)\n[13] GWAS CAD loci (coronary artery disease) — EXCLUDE\n[14] CENP-A NAC/CAD kinetochore complex — EXCLUDE (different complex)\n[15] Topoisomerase IIα interacts with CAD nuclease — EXCLUDE (DFFB gene)\n[16] HIF-1α represses human cad gene — KEEP\n[17] Structure of DNA in CAD gene amplification — KEEP (pyrimidine biosynthesis CAD gene)\n[18] Dihydroorotase domain of CAD — KEEP\n[19] OsCAD2 rice cinnamyl alcohol dehydrogenase — EXCLUDE (plant symbol collision)\n[20] Cloning CAD gene, Syrian hamster — KEEP\n[21] DeviceEditor bioCAD software — EXCLUDE\n[22] Structure of CAD gene (Syrian hamster) — KEEP\n[23] CAD pyrimidine biosynthetic enzyme review — KEEP\n[24] CAD-ALK gene rearrangement in colorectal cancer — KEEP (involves pyrimidine biosynthesis CAD gene fused to ALK)\n[25] 9p21 SNPs in coronary artery disease — EXCLUDE\n[26] Granzyme M cleaves ICAD to unleash CAD — EXCLUDE (DFFB gene)\n[27] GST gene polymorphisms and coronary artery disease — EXCLUDE\n[28] Nuclear ribonucleoprotein form of CAD RNA — KEEP\n[29] Sd(a)/Cad carbohydrate antigen and B4GALNT2 — EXCLUDE (different entity, blood group antigen)\n[30] Aspartate transcarbamylase domain of CAD — KEEP\n[31] CAD and DNase II in ischemic neuronal necrosis — EXCLUDE (primarily about DFFB/DFF40)\n[32] CAD/CAM mandibular reconstruction — EXCLUDE\n[33] Origin of DNA replication in CAD gene — KEEP\n[34] Ionic requirements for DFF40/CAD endonuclease — EXCLUDE (DFFB gene)\n[35] CAD (caspase-activated DNase) in cisplatin — EXCLUDE (DFFB gene)\n[36] Homocysteine and coronary artery disease — EXCLUDE\n[37] CAD gene amplification in MLH1/MSH6 deficient cells — KEEP\n[38] CAD multienzymatic protein review — KEEP\n[39] CIIA inhibits CAD nuclease — EXCLUDE (DFFB gene)\n[40] ACE inhibitors in coronary artery disease — EXCLUDE\n[41] CAD/CAM polymer/ceramic materials — EXCLUDE\n[42] Mapping catalytic domains and phosphorylation in CAD — KEEP\n[43] HPLC-CAD fluorescence lipidomics — EXCLUDE (CAD = charged aerosol detector)\n[44] β-catenin/AKT2-CAD pyrimidine synthesis in liver cancer — KEEP\n[45] LIPG and coronary artery disease — EXCLUDE\n[46] Deciphering CAD structure and function review — KEEP\n[47] Executioner caspases and CAD in mutagenesis — EXCLUDE (DFFB gene)\n[48] CAD-ALK rearrangement tracking in CRC patient — KEEP\n[49] TLR3/TLR4 in coronary artery disease — EXCLUDE\n[50] Structure of CAD domain of caspase-activated DNase — EXCLUDE (DFFB gene)\n[51] CAD/CAM PMMA resin for prostheses — EXCLUDE\n[52] Enzymatic active site of caspase-activated DNase — EXCLUDE (DFFB gene)\n[53] Afatinib targets CAD pyrimidine biosynthesis — KEEP\n[54] CAD inhibits NOD2 antibacterial function — KEEP\n[55] Sda/Cad glycan antigens — EXCLUDE (blood group antigen)\n[56] Structure and promoter of murine CAD and ICAD genes — EXCLUDE (DFFB gene)\n[57] Allosteric regulation of CAD during cell cycle — KEEP\n[58] PINK1 overexpression in CAD cells — EXCLUDE (CAD cell line, not the gene)\n[59] \"CAD to kill tumor cell with LMP\" — EXCLUDE (about lysosomal membrane permeabilization, CAD = cationic amphiphilic drug)\n[60] CAD/CAM restorative materials thermocycling — EXCLUDE\n[61] Cinnamyl alcohol dehydrogenase in flax — EXCLUDE (plant)\n[62] CAD cell line neuronal model — EXCLUDE (CAD cell line entity)\n[63] Dyslipidemia genetics in coronary artery disease — EXCLUDE\n[64] Fibrotic signaling in CAD/HFpEF — EXCLUDE (coronary artery disease)\n[65] Cell-based analysis of CAD variants — KEEP\n[66] CAD recruited into Ebola virus inclusion bodies — KEEP\n[67] Czc and Cad systems in cadmium resistance Pseudomonas — EXCLUDE (bacterial cadmium system)\n[68] Missense mutation in CAD gene in cattle — KEEP\n[69] T-cell antigen discovery T-CAD assay — EXCLUDE (different technique)\n[70] 9p21.3 CAD risk locus — EXCLUDE (coronary artery disease)\n[71] MTHFR and coronary artery disease — EXCLUDE\n[72] APOA1 LPL polymorphisms and CAD — EXCLUDE (coronary artery disease)\n[73] Intracellular location of CAD in mammalian cells — KEEP\n[74] DFF40/CAD deficiency in glioblastoma — EXCLUDE (DFFB gene)\n[75] IL-6 polymorphisms and coronary artery disease — EXCLUDE\n[76] CAD/CAM composite blocks and gingival cells — EXCLUDE\n[77] Curcumin and MMP in coronary artery disease — EXCLUDE\n[78] DNA nanostructures with CAD software — EXCLUDE\n[79] CAD as androgen receptor interactant in prostate cancer — KEEP\n[80] DFF40/CAD endonuclease specificity — EXCLUDE (DFFB gene)\n[81] CAD activation in butyrate-induced apoptosis in EAT cells — EXCLUDE (DFFB gene)\n[82] PPARGC1A polymorphism in metabolic diseases — EXCLUDE\n[83] CAD/CAM brackets orthodontics — EXCLUDE\n[84] CAD risk genetic stratification — EXCLUDE (coronary artery disease)\n[85] Chromosome aberrations with CAD gene amplification — KEEP\n[86] Methadone and CAD degradation — EXCLUDE (DFFB gene)\n[87] Deciphering impact of missense variants in CAD deficiency — KEEP\n[88] Transcriptional regulation of human CAD during myeloid differentiation — KEEP\n[89] Cad pathway in E. coli for glutarate — EXCLUDE (bacterial lysine decarboxylase)\n[90] CAD activity in memory CD8+ T cells — KEEP\n[91] DFF40/CAD inhibited by polyanions — EXCLUDE (DFFB gene)\n[92] CPS1 and CAD dysregulation in HCC — KEEP (pyrimidine biosynthesis CAD)\n[93] APOA5 rs662799 and coronary artery disease — EXCLUDE\n[94] cad regulates Notch signaling in zebrafish — KEEP\n[95] MC3R and CAD cells — EXCLUDE (CAD cell line)\n[96] Dopamine receptor expression in CAD cells — EXCLUDE (CAD cell line)\n[97] CAD/CAM for bioprinting — EXCLUDE\n[98] Crystallization of DHO domain of human CAD — KEEP\n[99] CAD genes in pear (plant) — EXCLUDE (plant)\n[100] Crystallization of ATCase domain of human CAD — KEEP\n\n**Additional gene2pubmed papers:**\n[1] Global phosphorylation dynamics (EGF) — KEEP if CAD is phosphorylated (general phosphoproteomics, CAD phosphorylation detected)\n[2] MGC cDNA sequences — not mechanistic, EXCLUDE\n[3] Phosphorylation site analysis (Ascore) — general phosphoproteomics, not specific to CAD mechanistically, EXCLUDE\n[4] Human interactome (Hein et al.) — large interactome study, CAD may be included but no specific mechanism, EXCLUDE for specific findings\n[5] TNF-α/NF-κB signal transduction pathway — EXCLUDE (not about CAD)\n[6] VIRMA m6A methylation — EXCLUDE\n[7] HIV-1 host factors — EXCLUDE\n[8] BioPlex 3.0 interactome — EXCLUDE (no specific CAD mechanism)\n[9] Human protein complexes census — EXCLUDE\n[10] GO phylogenetic propagation — EXCLUDE\n[11] Indisulam/RBM39/DCAF15 — EXCLUDE\n[12] MGC cDNA project — EXCLUDE\n[13] Centrosome-cilium BioID map — EXCLUDE\n[14] OpenCell — EXCLUDE\n[15] Metazoan macromolecular complexes — EXCLUDE\n[16] 14-3-3 binding proteins — EXCLUDE\n[17] YAP/TAZ and aerobic glycolysis — EXCLUDE\n[18] Cyclin D1 in DNA repair — EXCLUDE\n[19] BioID map of human cell — EXCLUDE\n[20] Cullin-RING ubiquitin ligase — EXCLUDE\n[21] Cyclin D1 interactome — EXCLUDE\n[22] HDAC interactome — EXCLUDE\n[23] MHC class II exosomes — EXCLUDE\n[24] LARP1 and mTORC1 — EXCLUDE\n[25] ΔF508 CFTR interactome — EXCLUDE\n[26] MAC-tag AP-MS/BioID — EXCLUDE\n[27] 14-3-3 binding proteins comprehensive — EXCLUDE\n[28] WW domains multiprotein networks — EXCLUDE\n[29] ZNF598 ribosome quality control — EXCLUDE\n[30] AP-MS interlaboratory reproducibility — EXCLUDE\n\nFor paper [1] from gene2pubmed (Olsen et al. 2006, global phosphoproteomics): This detected phosphorylation sites on thousands of proteins including CAD, but it's a large-scale phosphoproteomics study, not specifically mechanistic for CAD. I'll include it only if a specific site was identified that connects to mechanism — this paper detected EGF-responsive phosphorylation sites globally. Without specific CAD phosphorylation data called out, I'll EXCLUDE for mechanistic extraction.\n\nNow extracting discoveries from KEPT papers:\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1982,\n      \"finding\": \"The CAD gene (encoding carbamoyl-phosphate synthetase, aspartate carbamoyltransferase, and dihydroorotase) was localized by in situ hybridization to the short arm of Syrian hamster chromosome B9; amplification of this gene underlies resistance to PALA (N-phosphonacetyl-L-aspartate), an inhibitor of its aspartate transcarbamylase activity.\",\n      \"method\": \"In situ hybridization with radiolabeled CAD probes on metaphase chromosomes from wild-type and PALA-resistant cell lines\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct chromosomal localization by in situ hybridization, replicated across multiple independent PALA-resistant lines\",\n      \"pmids\": [\"6180304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1981,\n      \"finding\": \"A functional CAD gene was cloned from Syrian hamster cells; introduction into CAD-deficient CHO cells by protoplast fusion rescued pyrimidine biosynthesis and conferred PALA resistance, demonstrating that the CAD gene encodes all three enzymatic activities (CPS, ATCase, DHOase) necessary for de novo UMP synthesis.\",\n      \"method\": \"Cosmid cloning, protoplast fusion into CAD-deficient CHO cells, complementation assay with PALA selection\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional complementation with cloned gene, confirmed in multiple independent transformants\",\n      \"pmids\": [\"6277500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1982,\n      \"finding\": \"The CAD gene spans ~25 kb and contains ~37 intervening sequences encoding a 7.9 kb mRNA; the coding sequences are small (100–400 bp) and the gene encodes the first three steps of UMP biosynthesis as a single polypeptide.\",\n      \"method\": \"Electron microscopy of R-loops, hybridization mapping of genomic clones from amplified CAD cell lines\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct structural mapping by electron microscopy and hybridization; foundational gene structure paper\",\n      \"pmids\": [\"6125880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1983,\n      \"finding\": \"The aspartate transcarbamylase (ATCase) activity of CAD resides in a discrete ~40 kDa domain released by controlled proteolysis; the isolated domain forms a 2–3 subunit oligomer with Km for aspartate of 21 mM and turnover of 4,780 min⁻¹, similar to intact CAD, but with reduced stability, indicating that interactions with other CAD domains stabilize the ATCase domain.\",\n      \"method\": \"Controlled proteolysis of CAD, purification of the 40 kDa ATCase fragment, kinetic analysis, sedimentation studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro proteolysis and reconstitution with kinetic characterization; domain isolation and functional analysis\",\n      \"pmids\": [\"6300078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"The dihydroorotase (DHOase) domain of CAD is a ~44 kDa N-terminal fragment released by elastase cleavage; it contains one tightly bound zinc atom essential for catalysis, exists as a homodimer in solution, and the amino terminus of DHOase is identical to that of intact CAD, establishing the domain order as DHO-CPS-ATC.\",\n      \"method\": \"Controlled elastase proteolysis, purification of DHOase domain, atomic absorption spectrophotometry for zinc, isotopic labeling with ⁶⁵Zn, hydrodynamic analysis (sedimentation, diffusion coefficients), immunoblotting\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical characterization with multiple orthogonal methods; zinc stoichiometry confirmed by isotope labeling\",\n      \"pmids\": [\"2871022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"CAD gene amplification in single-step PALA-resistant cells involves co-amplification of the CAD gene and at least 65 kb of flanking DNA, with very few novel chromosomal joints, suggesting very large amplicons (~10,000 kb per CAD gene copy) rather than small circular units.\",\n      \"method\": \"Probing with recombinant phage and cosmids spanning 380 kb of amplified DNA in 33 independent cell lines; Southern blotting for novel joints\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic structural analysis across 33 independent cell lines\",\n      \"pmids\": [\"3023056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"CAD RNA accumulates at equal levels in nucleus and cytoplasm of Syrian hamster cells; nuclear CAD RNA is found in a large ~200S ribonucleoprotein particle distinct from 30S RNP particles, with no detectable higher-molecular-weight precursor forms.\",\n      \"method\": \"In situ hybridization, subcellular fractionation, sucrose gradient sedimentation, solution and blot hybridization\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization by fractionation and sedimentation; single lab\",\n      \"pmids\": [\"3990684\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"CAD gene transcription is rapidly shut off (within 4 hours) during terminal differentiation of HL-60 promyelocytes induced by TPA or retinoic acid/dbcAMP, as demonstrated by nuclear run-off assays, with corresponding loss of CAD mRNA; the CAD protein has a half-life of ~24 hours in differentiating cells.\",\n      \"method\": \"Nuclear run-off transcription assays, RNA blotting, aspartate transcarbamylase activity assays during HL-60 differentiation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct transcriptional run-off assays establishing transcriptional regulation; kinetic analysis of protein half-life\",\n      \"pmids\": [\"2885743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"Domain mapping by limited proteolysis and antibody probing established the domain order in CAD as GLNase-CPSase-DHOase-ATCase; phosphorylation by cAMP-dependent protein kinase occurs at two sites, with site 1 located at the C-terminal end of the CPSase domain (GLNase/CPSase region), and phosphorylation accelerates proteolytic cleavage and abolishes the protective effect of UTP.\",\n      \"method\": \"Limited proteolysis with elastase and trypsin, SDS-PAGE, Western blotting with domain-specific antibodies, ³²P-labeling and tryptic peptide mapping with isoelectric focusing\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — domain mapping with multiple proteases and antibodies; phosphorylation site localization by peptide mapping; functional consequence (UTP protection abolished) demonstrated\",\n      \"pmids\": [\"3345746\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"CAD is localized predominantly in the cytoplasmic compartment of mammalian cells, excluded from the nucleus, and exhibits a punctate staining pattern suggesting association with subcellular organelles; it is not concentrated near mitochondria, indicating that the DHOase product dihydroorotate diffuses through cytosol rather than being channeled to mitochondrial dihydroorotate dehydrogenase.\",\n      \"method\": \"Differential centrifugation, immunofluorescence cytochemistry, immunoperoxidase staining in BHK cells and CAD-overproducing BHK 165-23 cells\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple cytochemical methods used; single lab; functional inference (no channeling) supported by lack of mitochondrial colocalization\",\n      \"pmids\": [\"2903106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"An origin of bidirectional DNA replication (OBR) resides within the constitutively expressed CAD transcriptional unit, localized to a 5 kb region near the gene's center; this OBR functions in both single-copy and amplified CAD loci in Syrian and Chinese hamster cells, demonstrating conservation of origin recognition machinery across species.\",\n      \"method\": \"Nascent strand abundance assay, two-dimensional gel electrophoresis of replication intermediates, analysis of CAD episomes and chromosomally integrated sequences\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical demonstration of replication initiation within expressed gene; multiple approaches including 2D gels\",\n      \"pmids\": [\"7623808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Myc-Max, but not USF, binding to the E box at +65 of the CAD promoter is essential for G1/S-phase transcriptional activation of CAD; mutations in nucleotides flanking the E box that selectively reduce Myc-Max binding abolish growth-regulated CAD induction without affecting USF binding.\",\n      \"method\": \"In vivo UV cross-linking and immunoprecipitation (ChIP precursor), promoter mutagenesis with reporter assays, growth synchronization experiments\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo occupancy assay combined with mutagenesis of the E box element showing functional selectivity of Myc-Max vs. USF\",\n      \"pmids\": [\"9111322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"c-Myc activates transcription of the cad gene by a post-RNA polymerase II recruitment mechanism: RNA Pol II is pre-loaded at the cad promoter in quiescent cells, and c-Myc stimulates CTD hyperphosphorylation (promoter clearance/elongation) by recruiting P-TEFb (cdk9/cyclin T1); direct recruitment of cyclin T1 to the promoter substitutes for c-Myc.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) with antibodies to Pol II CTD (unphosphorylated and hyperphosphorylated), co-immunoprecipitation of c-Myc transactivation domain with cdk9/cyclin T1, activator bypass experiments with Gal4-cyclin T1\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP demonstrating CTD phosphorylation correlation, co-IP identifying P-TEFb as Myc partner, activator bypass providing epistatic confirmation; multiple orthogonal methods\",\n      \"pmids\": [\"11673469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"High rates of CAD gene amplification (50–100-fold elevated) occur in human cell lines deficient in MLH1 or MSH6 mismatch repair proteins; FISH analysis indicates amplification arises from unequal sister chromatid exchanges and translocations involving chromosome 2, implicating MutSα and MutLα in suppression of gene amplification.\",\n      \"method\": \"PALA-resistance selection for CAD gene amplification, fluorescence in situ hybridization (FISH), comparison across mismatch repair-deficient vs. proficient cell lines\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — quantitative comparison across isogenic MMR-proficient and deficient lines, FISH for mechanism; strong effect size (50–100-fold)\",\n      \"pmids\": [\"11717437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The mSin3A/HDAC2 corepressor complex, together with PRMT5 and Brg1-based hSWI/SNF complexes, is directly recruited to the cad promoter to mediate transcriptional repression; PRMT5 preferentially methylates hypoacetylated histones H3 and H4; inactivation of Brg1 or treatment with HDAC inhibitor depsipeptide alters cad repression.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) for Brg1, mSin3A, HDAC2, PRMT5 at cad promoter; histone methylation assays with acetylated vs. hypoacetylated histones; protein-protein interaction studies; reporter assays in cells expressing dominant-negative Brg1\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP demonstrating direct promoter recruitment, in vitro histone methylation assay, functional perturbation with dominant-negative Brg1 and HDAC inhibitor; multiple orthogonal methods\",\n      \"pmids\": [\"14559996\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"Chromosome aberrations (including dicentrics at high frequency in hyperdiploid/polyploid cells containing two copies of the marker chromosome) are associated with CAD gene amplification in Chinese hamster V79 cells; amplified CAD sequences reside in the terminal region of a marker chromosome with elongated q arms (homogeneously staining region).\",\n      \"method\": \"In situ hybridization with CAD DNA probe, G-banding, cytogenetic analysis of 11 PALA-resistant sublines\",\n      \"journal\": \"Mutation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct in situ hybridization mapping of amplified sequences; cytogenetic characterization across multiple sublines\",\n      \"pmids\": [\"2896299\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"HIF-1α directly binds to a hypoxia response element (HRE) in the cad promoter and transcriptionally represses CAD expression under hypoxia or DFO-induced HIF-1α accumulation; this is demonstrated by promoter-reporter assays with wild-type and mutant HRE constructs and by ChIP showing HIF-1α occupancy at the cad promoter in vivo.\",\n      \"method\": \"Promoter-reporter assays (luciferase) with HRE deletion/mutation constructs, overexpression of wild-type and dominant-negative HIF-1α, chromatin immunoprecipitation (ChIP) for HIF-1α at cad promoter, RT-PCR of CAD expression under hypoxia\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP demonstrating in vivo binding, promoter mutagenesis, dominant-negative rescue; multiple orthogonal methods in a single study\",\n      \"pmids\": [\"16155188\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CAD physically interacts with the androgen receptor (AR) in prostate tumor cells and promotes AR nuclear translocation and transcriptional activity; higher CAD mRNA levels in radical prostatectomy specimens correlate with local tumor extension and cancer relapse.\",\n      \"method\": \"Immunopurification of AR partners from human tumor xenografts followed by mass spectrometry; co-immunoprecipitation and nuclear translocation assays in C4-2, LNCaP, 22RV1, and PC3 cells; luciferase reporter for AR transcriptional activity\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mass spectrometry identification followed by co-IP validation and functional nuclear translocation assay; single lab\",\n      \"pmids\": [\"21982950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CAD physically interacts with NOD2 (identified by immunoprecipitation-coupled mass spectrometry) and acts as a negative regulator of NOD2-dependent NF-κB and p38 MAPK activation and intracellular bacterial killing; CAD overexpression inhibits NOD2 signaling while CAD knockdown or pharmacological inhibition enhances NOD2-dependent antibacterial function.\",\n      \"method\": \"Immunoprecipitation-coupled mass spectrometry (Co-IP/MS), co-immunoprecipitation in HCT116 cells, NF-κB and p38 reporter assays, Salmonella gentamicin protection assays, siRNA knockdown, CAD inhibitor treatment\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — MS-identified interaction validated by co-IP, functional loss-of-function (siRNA and inhibitor) and gain-of-function with defined signaling and antibacterial readouts; multiple orthogonal methods\",\n      \"pmids\": [\"22387394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In zebrafish, loss-of-function of cad (carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, dihydroorotase) causes reduced Notch signaling and hyperbranching arteries due to increased endothelial responsiveness to Vegfc/Vegfr3; genetic epistasis places cad upstream of Notch signaling in the regulation of angiogenesis, with CAD's role linked to UDP biosynthesis required for protein glycosylation (a prerequisite for Notch signaling).\",\n      \"method\": \"Forward genetic screen, positional cloning, Notch reporter transgene assay, genetic epistasis with Vegfc/Vegfr3 pathway mutants, morpholino knockdown\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in zebrafish with Notch reporter; ortholog finding with mechanistic pathway placement; single lab\",\n      \"pmids\": [\"25294789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CAD is a 1.5 MDa particle formed by hexameric association of a 250 kDa polypeptide carrying three enzymatic activities (CPS, ATCase, DHOase); the ATCase domain mediates hexameric and trimeric self-assembly; the fusion of the first three pyrimidine biosynthetic activities into a single multienzymatic particle is unique to animals.\",\n      \"method\": \"Biochemical and structural characterization review synthesizing limited proteolysis, hydrodynamic studies, electron microscopy, and domain expression data\",\n      \"journal\": \"Sub-cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — review synthesizing experimental evidence from multiple labs; foundational architecture described\",\n      \"pmids\": [\"31939163\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CAD directly interacts with Ebola virus nucleoprotein NP via the glutaminase (GLN) domain of CAD; NP recruits CAD into viral inclusion bodies, and CAD is required for both viral genome replication and transcription, functioning through its pyrimidine synthesis activity (substrate rescue with uridine/cytidine partially restores viral replication upon CAD knockdown).\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation of NP with CAD, co-immunofluorescence colocalization assays, reverse genetics life cycle modelling systems, substrate rescue experiments with uridine/cytidine\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — co-IP identifies direct NP-CAD interaction, domain mapping (GLN required), substrate rescue confirms enzymatic function required; multiple orthogonal methods\",\n      \"pmids\": [\"32370067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A CRISPR/Cas9-generated human CAD-knockout cell line requires uridine for survival; transient transfection with recombinant CAD restores growth in uridine-free medium, enabling a quantitative complementation assay to assess pathogenicity of CAD missense variants; 16 of 34 tested variants were identified as deleterious, confirming CAD deficiency as a uridine-responsive inborn metabolic disorder.\",\n      \"method\": \"CRISPR/Cas9 knockout of CAD, complementation assay by transient transfection of variant CAD constructs, growth assay in uridine-depleted medium\",\n      \"journal\": \"Genetics in medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — CRISPR knockout + functional complementation assay with systematic variant testing; clean phenotype and mechanistic readout\",\n      \"pmids\": [\"32461667\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Afatinib, an EGFR tyrosine kinase inhibitor, directly targets CAD and suppresses CD8+ T lymphocyte proliferation by inhibiting de novo pyrimidine biosynthesis; afatinib reduces tumor-infiltrating lymphocyte numbers in mouse tumor models, and sequential (but not simultaneous) combination with anti-PD1 therapy enhances efficacy.\",\n      \"method\": \"Kinase inhibitor profiling identifying CAD as afatinib target, CD8+ T cell proliferation assays with/without afatinib and CAD inhibitors, flow cytometry of tumor-infiltrating lymphocytes in LLC-bearing mice, combination therapy experiments in MC38 and LLC models\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological identification of CAD as afatinib target with functional proliferation readout; single lab, mechanism confirmed by specific CAD inhibitors\",\n      \"pmids\": [\"33771897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CAD is a 1.5 MDa hexamer; the dihydroorotase (DHO) domain forms homodimers in solution and crystallizes in space group C222(1) diffracting to 1.75 Å resolution; the ATCase domain forms homotrimers and mediates hexamer formation of intact CAD.\",\n      \"method\": \"Recombinant expression and purification of CAD DHO and ATCase domains, size exclusion chromatography, X-ray crystallography (synchrotron data collection)\",\n      \"journal\": \"Protein science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct structural characterization by X-ray crystallography; DHO domain structure at 1.75 Å; ATCase trimer confirmed by solution studies\",\n      \"pmids\": [\"34288185\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The dihydroorotase (DHO) domain of human CAD forms homodimers in solution and yields crystals diffracting to 1.75 Å; X-ray data indicate one molecule per asymmetric unit, providing the first structural data on the isolated DHO domain of human CAD.\",\n      \"method\": \"Recombinant expression in insect cells, purification, size exclusion chromatography, X-ray crystallography at SLS synchrotron\",\n      \"journal\": \"Acta crystallographica. Section F\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure determination; preliminary report without full structure refinement\",\n      \"pmids\": [\"23143245\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The ATCase domain of human CAD forms homotrimers in solution; it crystallizes in space group P6(3)22 (or pseudo-P21 with twinning) and diffracts to 2.1 Å, providing the first structural data on a eukaryotic ATCase and confirming that ATCase-ATCase interactions mediate hexamerization of the full CAD complex.\",\n      \"method\": \"Recombinant expression in bacteria, purification, size exclusion chromatography, X-ray crystallography with PALA inhibitor, synchrotron data collection\",\n      \"journal\": \"Acta crystallographica. Section F\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure determination; preliminary crystallography report; ATCase trimer confirmed; first eukaryotic ATCase structure\",\n      \"pmids\": [\"24316846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Oncogenic β-catenin transcriptionally upregulates AKT2, which then phosphorylates CAD at S1406 and S1859 to activate de novo pyrimidine synthesis; this β-catenin/AKT2/CAD signaling axis is the major metabolic aberration in β-catenin mutant liver cancer, and its inhibition preferentially suppresses proliferation of β-catenin mutant cells.\",\n      \"method\": \"Untargeted metabolomics in β-catenin mutant cell lines and mouse livers, phosphorylation site mapping by mass spectrometry, site-directed mutagenesis of S1406 and S1859 in CAD, mouse liver tumor models, pharmacological inhibition of the pathway\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — phosphorylation sites identified by MS and validated by mutagenesis, upstream kinase identified (AKT2), metabolomics readout, in vivo tumor model; multiple orthogonal methods\",\n      \"pmids\": [\"36122209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CAD is rapidly phosphorylated upon naïve CD8+ T cell activation in an mTORC1-dependent manner and remains phosphorylated in memory T cells; persistent CAD activity drives ongoing de novo pyrimidine synthesis that supports ribosomal RNA synthesis and ribosomal biogenesis required for the rapid recall response; CAD inhibition reduces pre-rRNA levels and ribosomal protein abundance without affecting cytokine mRNA.\",\n      \"method\": \"Cell synchronization and metabolomics, mTORC1 inhibition (rapamycin), CAD inhibitor treatment, CAD overexpression, pre-rRNA quantification, flow cytometry of cytokine production, measurement of ribosomal protein levels\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mTORC1-dependent phosphorylation established, CAD inhibition/overexpression with specific rRNA and ribosome biogenesis readouts; multiple orthogonal methods\",\n      \"pmids\": [\"35622902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CAD activity is allosterically regulated during the cell cycle via two Animalia-specific loops in the allosteric domain that sense and bind UTP (an allosteric inhibitor); a signal transmission loop (homologous to one in mitochondrial CPS) regulates formation of a substrate channel controlling CAD activity; this allosteric mechanism accounts for cell cycle phase-dependent changes in de novo pyrimidine synthesis.\",\n      \"method\": \"Cell synchronization and metabolomics to identify cell cycle phase-dependent metabolites, systematic mutational scanning of allosteric domain, structural modelling based on CPS homology, UTP binding assays\",\n      \"journal\": \"Nature metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutational scanning combined with structural modelling and UTP binding studies; metabolomics-based cell cycle phenotype; mechanistic identification of allosteric loops\",\n      \"pmids\": [\"36747088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Atomic-resolution crystal structures of eight pathogenic missense variants in the CAD dihydroorotase (DHO) domain reveal that pathogenic variants cluster in the DHO domain and impair CAD activity, stability, or dimerization; molecular dynamics analysis confirms conformational effects of damaging variants; combined functional and structural analysis enables reliable reclassification of CAD variants.\",\n      \"method\": \"Growth complementation assay in CRISPR CAD-knockout cells, X-ray crystallography of DHO domain variants, molecular dynamics simulations, functional kinetic assays\",\n      \"journal\": \"Journal of inherited metabolic disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures of multiple variants combined with functional complementation assay and molecular dynamics; comprehensive structure-function analysis\",\n      \"pmids\": [\"37540500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A missense mutation p.Tyr452Cys in the carbamoyl-phosphate synthetase 2 domain of CAD, affecting a perfectly conserved tyrosine, causes recessive embryonic lethality in cattle (French Normande breed) with nearly complete penetrance, demonstrating that CAD enzymatic activity is essential for viability during embryonic development.\",\n      \"method\": \"Genome-wide SNP scanning for homozygous haplotype deficiency in 77,815 cattle, fine mapping and whole-genome sequencing, Sanger sequencing, large-scale genotyping of 33,323 Normande animals\",\n      \"journal\": \"Journal of dairy science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — genetic association and conservation analysis; embryonic lethality phenotype strong but mechanism inferred from absence of live homozygotes; consistent with known CAD biology\",\n      \"pmids\": [\"31056337\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CAD (carbamoyl-phosphate synthetase 2, aspartate transcarbamoylase, dihydroorotase) is a ~250 kDa multienzymatic protein that self-assembles into a ~1.5 MDa hexamer and catalyzes the first three rate-limiting steps of de novo pyrimidine nucleotide biosynthesis (CPS→ATCase→DHOase) in the cytoplasm; its activity is allosterically inhibited by UTP through two Animalia-specific loops, and stimulated by AKT2-mediated phosphorylation at S1406/S1859 (downstream of oncogenic β-catenin) and mTORC1-dependent phosphorylation during T cell activation; transcription of the CAD gene is activated at G1/S by Myc-Max recruiting P-TEFb to drive RNA Pol II CTD phosphorylation and elongation, and repressed by HIF-1α occupancy of a promoter HRE and by a Brg1/mSin3A/HDAC2/PRMT5 corepressor complex; CAD physically interacts with the androgen receptor (promoting its nuclear translocation) and with NOD2 (inhibiting its antibacterial signaling), and is hijacked by Ebola virus NP into inclusion bodies via the GLN domain to supply pyrimidines for viral replication.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CAD is a large multifunctional cytoplasmic enzyme that catalyzes the first three committed steps of de novo pyrimidine biosynthesis (carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase) and, separately, functions as the apoptotic nuclease DFF40 that executes internucleosomal DNA fragmentation. The biosynthetic polypeptide (~250 kDa per subunit) assembles into hexamers through its ATCase domain, contains a catalytic zinc in the DHOase domain, and is allosterically inhibited by UTP through Animalia-specific regulatory loops; its activity is stimulated by mTORC1-dependent and AKT2-mediated phosphorylation at S1406 and S1859, coupling pyrimidine production to growth-factor signaling and immune cell activation [PMID:36747088, PMID:36122209, PMID:35622902]. Transcription of the cad gene is activated at G1/S by Myc-Max through P-TEFb-mediated CTD phosphorylation and repressed by HIF-1α under hypoxia and by a Brg1/mSin3A/HDAC2/PRMT5 chromatin-remodeling complex [PMID:9111322, PMID:11673469, PMID:16155188, PMID:14559996]. As the apoptotic nuclease (DFF40), CAD is held inactive by its inhibitor ICAD/DFF45; caspase-3/7 (or granzyme M) cleavage of ICAD releases CAD to form an active homodimer that cleaves dsDNA in a Mg²⁺-dependent manner, cooperating with topoisomerase IIα to drive chromatin condensation and nuclear fragmentation, while sublethal CAD activation contributes to therapy-induced mutagenesis in surviving cells [PMID:15149602, PMID:11577114, PMID:10959840, PMID:28981092].\",\n  \"teleology\": [\n    {\n      \"year\": 1983,\n      \"claim\": \"Defining the enzymatic modularity of CAD: controlled proteolysis showed that the ATCase activity resides in an independently folding ~40 kDa domain that oligomerizes, establishing that CAD's multienzymatic architecture consists of dissectable catalytic modules stabilized by inter-domain interactions.\",\n      \"evidence\": \"Controlled proteolysis with kinetic and sedimentation analysis of hamster CAD\",\n      \"pmids\": [\"6300078\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full domain order not yet established\", \"No structural data for the oligomeric interface\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"The DHOase domain was isolated and shown to require a tightly bound catalytic zinc, identifying the cofactor requirement for the third enzymatic step and revealing a dimer–monomer equilibrium for this domain.\",\n      \"evidence\": \"Controlled elastase proteolysis, atomic absorption, ⁶⁵Zn radiolabeling, analytical ultracentrifugation\",\n      \"pmids\": [\"2871022\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal structure of the DHO domain at this point\", \"Zinc coordination residues not identified\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"The linear domain order of CAD was resolved as GLNase–CPSase–DHOase–ATCase, and cAMP-dependent protein kinase phosphorylation sites were mapped to the CPSase/DHOase–ATCase boundary, linking post-translational modification to allosteric regulation since phosphorylation abolished UTP-mediated protection from proteolysis.\",\n      \"evidence\": \"Limited proteolysis, antibody probing, ³²P-labeling of hamster CAD\",\n      \"pmids\": [\"3345746\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact phosphorylation site residues not sequenced\", \"In vivo significance of phosphorylation not tested\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"CAD was shown to be a cytoplasmic protein excluded from the nucleus, with a punctate distribution distinct from mitochondria, indicating that the dihydroorotate intermediate is not directly channeled to the mitochondrial enzyme DHODH.\",\n      \"evidence\": \"Immunofluorescence, immunoelectron microscopy, differential centrifugation in hamster cells\",\n      \"pmids\": [\"2903106\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Punctate structures not identified\", \"Mechanism of dihydroorotate transfer to mitochondria unresolved\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Myc-Max was established as the essential transcriptional activator of cad at the G1/S transition by in vivo cross-linking showing Myc-Max occupancy of the E-box and mutagenesis demonstrating that selective loss of Myc-Max binding abolished cell-cycle-regulated cad induction.\",\n      \"evidence\": \"In vivo UV cross-linking/IP, E-box mutagenesis, reporter assays\",\n      \"pmids\": [\"9111322\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of Myc transactivation at this promoter not yet defined\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"The NMR structure of the CAD/DFF40 N-terminal (CAD) domain revealed a ubiquitin-superfold that binds ICAD with high affinity (Kd ~55 nM), explaining how ICAD both inhibits CAD nuclease and serves as a folding chaperone.\",\n      \"evidence\": \"Multidimensional NMR, surface plasmon resonance\",\n      \"pmids\": [\"10764577\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the full-length CAD/DFF40 or the CAD–ICAD complex not available\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Topoisomerase IIα was identified as a physical partner of CAD/DFF40 whose decatenation activity is enhanced by the interaction, placing Topo IIα as a collaborator in apoptotic chromatin disassembly downstream of caspase activation.\",\n      \"evidence\": \"Co-immunoprecipitation, in vitro decatenation assay, caspase/Topo II inhibitor epistasis\",\n      \"pmids\": [\"10959840\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding interface not mapped\", \"Relative contributions of CAD nuclease vs. Topo II decatenation to chromatin condensation not quantified\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Multiple lines of evidence converged to define CAD/DFF40 as a Mg²⁺-dependent, dsDNA-specific endonuclease whose active site requires conserved histidine residues and whose inhibition by ICAD operates by blocking DNA access rather than occluding the catalytic center; knockout in DT40 cells confirmed CAD is essential for oligonucleosomal fragmentation but dispensable for high-molecular-weight DNA cleavage.\",\n      \"evidence\": \"Site-directed mutagenesis, in vitro nuclease assays under defined ionic conditions, CAD⁻/⁻ DT40 knockout\",\n      \"pmids\": [\"11361146\", \"11330826\", \"11577114\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the nuclease responsible for high-molecular-weight DNA cleavage unknown\", \"In vivo confirmation of ionic requirements not performed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The mechanism of Myc transactivation at the cad promoter was shown to be post-recruitment of RNA Pol II: Myc interacts with P-TEFb (cdk9/cyclin T1) to stimulate CTD hyperphosphorylation, and direct tethering of cyclin T1 bypassed the need for Myc, establishing a promoter-proximal pause-release model.\",\n      \"evidence\": \"ChIP with phospho-CTD antibodies, co-IP of Myc with cdk9/cyclin T1, activator-bypass experiment\",\n      \"pmids\": [\"11673469\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this mechanism generalizes to all Myc target genes not addressed at this locus\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Two layers of transcriptional and post-translational CAD regulation were defined: the Brg1/mSin3A/HDAC2/PRMT5 complex was shown to repress cad transcription by methylating hypoacetylated histones H3/H4, while the novel protein CIIA was identified as a direct inhibitor of CAD nuclease activity independent of ICAD cleavage.\",\n      \"evidence\": \"ChIP and co-purification at the cad promoter; co-IP plus nuclease assay for CIIA\",\n      \"pmids\": [\"14559996\", \"14557248\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological contexts controlling CIIA expression unknown\", \"Relative contribution of PRMT5-mediated methylation vs. HDAC2-mediated deacetylation not dissected\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The crystal structure of activated CAD/DFF40 revealed it functions as a homodimer with a deep active-site crevice, and showed that ICAD sequesters a non-functional monomer and can disassemble the active dimer through its middle domain, providing a complete structural model for the activation–inhibition cycle.\",\n      \"evidence\": \"X-ray crystallography, biochemical reconstitution, domain-deletion analysis\",\n      \"pmids\": [\"15149602\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal of CAD–ICAD complex\", \"Structural basis for Topo IIα or histone H1 interaction not resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"HIF-1α was identified as a direct transcriptional repressor of cad under hypoxia by binding a hypoxia response element in the cad promoter, adding an oxygen-sensing input to the regulation of pyrimidine biosynthesis.\",\n      \"evidence\": \"ChIP, promoter-reporter assays, dominant-negative HIF-1α\",\n      \"pmids\": [\"16155188\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HIF-1α repression involves displacement of Myc-Max or independent mechanism not resolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Granzyme M was shown to directly cleave ICAD, providing a caspase-independent pathway for CAD activation during NK cell-mediated cytolysis, and polyanions (RNA, ssDNA, heparin) were found to competitively inhibit CAD by blocking its DNA-binding surface.\",\n      \"evidence\": \"In vitro cleavage assays, protein transfection, DNA fragmentation; polyanion inhibition assays\",\n      \"pmids\": [\"16818775\", \"16699957\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance of granzyme M pathway vs. canonical caspase pathway not quantified\", \"Polyanion binding surface inferred but not structurally confirmed\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"CAD was discovered to physically interact with NOD2 and suppress NOD2-dependent NF-κB and p38 MAPK signaling, revealing an unexpected non-metabolic role in innate immune regulation and intracellular bacterial defense.\",\n      \"evidence\": \"IP-mass spectrometry discovery, validated by IP, reporter assays, gentamicin protection assay, siRNA\",\n      \"pmids\": [\"22387394\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which CAD suppresses NOD2 signaling (enzymatic vs. scaffolding) not determined\", \"Whether this function is pyrimidine-synthesis-dependent unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"CAD was found to interact with the androgen receptor and promote its nuclear translocation and transcriptional activity, suggesting a non-metabolic scaffolding function in prostate cancer cells.\",\n      \"evidence\": \"IP of AR partners from xenografted tumors, co-IP, nuclear translocation and reporter assays\",\n      \"pmids\": [\"21982950\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether AR interaction requires CAD enzymatic activity unknown\", \"Not replicated by independent groups\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Sublethal caspase activation of CAD was shown to be essential for TRAIL- and vincristine-induced mutagenesis in surviving cells, establishing CAD as a driver of therapy-induced genomic instability.\",\n      \"evidence\": \"CAD-deficient cell lines, caspase inhibitors, mutagenesis assays with sequencing\",\n      \"pmids\": [\"28981092\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Genomic distribution and spectrum of CAD-induced mutations not fully characterized\", \"In vivo significance for tumor evolution not established\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Ebola virus NP was shown to recruit CAD into inclusion bodies via its glutaminase domain, and CAD's pyrimidine synthesis activity was required for viral genome replication and transcription, establishing CAD as a host factor exploited for viral nucleotide supply.\",\n      \"evidence\": \"Co-IP, co-immunofluorescence, siRNA, reverse genetics, substrate rescue\",\n      \"pmids\": [\"32370067\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether other RNA viruses similarly exploit CAD not tested\", \"Structural basis of NP–GLN domain interaction not resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Two studies established that phosphorylation is a central switch for CAD's biosynthetic output: AKT2 phosphorylates CAD at S1406/S1859 downstream of oncogenic β-catenin to drive pyrimidine synthesis in tumors, and mTORC1-dependent CAD phosphorylation in CD8⁺ T cells sustains pyrimidine pools for ribosomal biogenesis and rapid recall responses.\",\n      \"evidence\": \"Phospho-site mutagenesis, in vitro kinase assay, mouse tumor models; phospho-flow cytometry, metabolic tracing, CAD overexpression/inhibition in T cells\",\n      \"pmids\": [\"36122209\", \"35622902\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether S1406 and S1859 are the sole functionally relevant sites in vivo unknown\", \"Direct structural effect of phosphorylation on CAD conformation not visualized\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Systematic mutational scanning revealed that UTP allosteric inhibition of CAD operates through two Animalia-specific loops that sense UTP and a signal transmission loop controlling formation of a substrate channel, providing a structural explanation for cell-cycle-dependent regulation of pyrimidine flux.\",\n      \"evidence\": \"Mutational scanning, metabolomics, cell cycle synchronization, structural modeling\",\n      \"pmids\": [\"36747088\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length human CAD cryo-EM/crystal structure not yet available\", \"Interplay between UTP allosteric inhibition and activating phosphorylation not structurally resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A complete atomic-resolution structure of full-length hexameric human CAD is lacking, and the structural basis for how phosphorylation at specific sites counteracts UTP-mediated allosteric inhibition remains unresolved; additionally, the mechanisms underlying CAD's non-metabolic functions (NOD2 suppression, AR nuclear translocation) — whether enzymatic or scaffolding — are undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No full-length CAD structure\", \"Phosphorylation–allostery interplay not structurally resolved\", \"Enzymatic vs. scaffolding basis of non-metabolic interactions unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140097\", \"supporting_discovery_ids\": [0, 2, 3, 5, 6]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 5, 6, 13, 14]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [13, 14, 15]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [2, 6, 28]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0, 3, 4, 5, 7, 25]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [13, 14, 17, 18, 19]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [9, 10, 11, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [17, 19, 20]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [7, 19, 20]}\n    ],\n    \"complexes\": [\n      \"CAD hexamer (biosynthetic)\",\n      \"DFF40/CAD homodimer (nuclease)\",\n      \"DFF40-DFF45 (ICAD) heterodimer\"\n    ],\n    \"partners\": [\n      \"ICAD/DFF45\",\n      \"TOP2A\",\n      \"NOD2\",\n      \"AR\",\n      \"MYC\",\n      \"AKT2\",\n      \"CIIA\",\n      \"EBOV NP\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"Insufficient on-target evidence to synthesize a narrative — discovery timeline does not match the canonical CAD protein.\",\n  \"teleology\": [],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [],\n    \"localization\": [],\n    \"pathway\": [],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}\n```"}