{"gene":"CPS1","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":2017,"finding":"CPS1 expression in KRAS/LKB1-mutant (KL) lung cancer cells is suppressed by LKB1 through AMPK. CPS1 enables an unconventional pathway of nitrogen flow from ammonia into pyrimidines: silencing CPS1 in KL cells depletes pyrimidines (reducing the pyrimidine-to-purine ratio), compromises S-phase progression, and induces DNA-polymerase stalling and DNA damage. Exogenous pyrimidines reverse the DNA damage and rescue growth, establishing that the role of CPS1 is pyrimidine supply rather than ammonia detoxification in this context.","method":"siRNA silencing, metabolomics, isotope tracing, cell death/growth assays, exogenous pyrimidine rescue, genetic epistasis (KRAS/LKB1 mutant cell lines and patient tumors)","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (metabolomics, isotope tracing, genetic KD, rescue experiments) in human cancer cell lines and mouse xenografts, replicated in patient tumor specimens","pmids":["28538732"],"is_preprint":false},{"year":2011,"finding":"CPS1 expression in human hepatocellular carcinoma cells is silenced by DNA methylation. Two CpG dinucleotides near the transcription start site and a CpG-rich region in the first intron are hypermethylated in HCC cells; site-directed mutagenesis of these CpG dinucleotides reduced CPS1 promoter activity. Treatment with the demethylating agent 5-azacytidine restored CPS1 expression.","method":"Bisulfite sequencing, 5-azacytidine demethylation, promoter-reporter assays with site-directed mutagenesis of CpG sites","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal methods (demethylation rescue + mutagenesis reporter assay), single lab","pmids":["21281797"],"is_preprint":false},{"year":2020,"finding":"Small-molecule inhibitors (including H3B-120) bind to a previously unknown allosteric pocket on CPS1 and block ATP hydrolysis in the first step of carbamoyl phosphate synthesis. These inhibitors are selective for CPS1 over CPS2 and are active in cellular assays, blocking both urea synthesis and pyrimidine biosynthesis.","method":"Biochemical in vitro CPS1 enzymatic assay, structure-based drug design, cellular urea synthesis and pyrimidine pathway assays, selectivity counterscreening against CPS2","journal":"Cell chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic assay with defined mechanism (ATP hydrolysis block at allosteric pocket), structure-based design, cellular functional validation, and selectivity profiling in one rigorous study","pmids":["32017919"],"is_preprint":false},{"year":2019,"finding":"CPS1 is constitutively secreted into bile by hepatocytes, likely as a soluble protein, and is released into blood during acute liver injury. In blood, CPS1 is rapidly sequestered by circulating monocytes, inducing their M2 polarization and homing to the liver independent of CPS1 enzymatic activity. Recombinant CPS1 (but not control transferrin) increases hepatic macrophage numbers and phagocytic activity, and protects mice from Fas-ligand- or acetaminophen-induced liver injury; protection is absent in macrophage-deficient mice.","method":"Mouse/human bile proteomics, sedimentation analysis, recombinant CPS1 administration, monocyte uptake assays, macrophage polarization assays, macrophage-depletion experiments, acetaminophen and FasL liver injury models","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (proteomics, cell biology, genetic macrophage depletion, two injury models, recombinant protein rescue) in a single rigorous study with in vivo validation","pmids":["30979808"],"is_preprint":false},{"year":2022,"finding":"O-GlcNAcylation of CPS1 on specific threonine residues increases the catalytic efficiency of CPS1 for ammonia, thereby enhancing ureagenesis. Pharmacological inhibition of O-GlcNAcase (which removes O-GlcNAc from proteins) reduced systemic ammonia in both genetic (propionic acidemia) and acquired (thioacetamide-induced acute liver failure) mouse models.","method":"Mass spectrometry identification of O-GlcNAcylation sites, enzymatic kinetics of O-GlcNAcylated vs. unmodified CPS1, O-GlcNAcase pharmacological inhibition in two mouse disease models, biochemical ammonia measurements","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — site-specific PTM identified by MS, enzymatic kinetics demonstrating functional consequence, replicated across two independent in vivo disease models","pmids":["36064721"],"is_preprint":false},{"year":2022,"finding":"CPS1 O-GlcNAcylation is increased by high glucose and in aged liver, and inhibits CPS1 enzymatic activity. Liver-specific deletion of OGT (O-GlcNAc transferase) potentiates CPS1 activity and renders it irresponsive to stimulation by prolonged fasting. Calorie restriction reverses CPS1 O-GlcNAcylation. This identifies CPS1 O-GlcNAcylation as a nutrient-sensing regulatory step in the urea cycle during aging.","method":"Liver-specific OGT knockout mice, O-GlcNAc mass spectrometry of aged liver, glucose stimulation assays, calorie restriction experiments, CPS1 activity measurements","journal":"Journal of molecular cell biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — genetic KO model plus pharmacological and dietary interventions, enzymatic activity readout, orthogonal to PMID 36064721 confirming the same PTM-function axis","pmids":["35285892"],"is_preprint":false},{"year":2013,"finding":"Human recombinant CPS1 expressed in baculovirus/insect cells has the same kinetic and molecular properties as natural human CPS1. Glycerol partially substitutes for the essential allosteric activator N-acetyl-L-glutamate (NAG). NAG and its analogue N-carbamoyl-L-glutamate (NCG), together with MgATP, protect CPS1 against proteolytic and thermal inactivation, suggesting a stabilizing/chaperone effect. Site-limited proteolysis confirmed the multidomain architecture of CPS1.","method":"Recombinant protein expression and purification, enzymatic kinetics, thermal stability assays, site-limited proteolysis","journal":"Human mutation","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution of human enzyme with kinetic and stability characterization; multiple orthogonal methods in a single rigorous study","pmids":["23649895"],"is_preprint":false},{"year":2010,"finding":"Using recombinant CPS1 expressed in baculovirus/insect cells, nine clinical CPS1 mutations were shown to affect enzyme solubility, stability, and/or kinetic parameters including NAG affinity; the C-terminal domain mutations were rationalized using the crystal structure of that domain which includes the NAG binding site. This established the functional importance of specific residues, including those at the NAG allosteric site.","method":"Baculovirus/insect cell expression, enzyme purification, kinetic analysis, thermal stability, site-directed mutagenesis, structure-function analysis using C-terminal domain crystal structure","journal":"Human mutation","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution with mutagenesis and structural validation, multiple mutations characterized across orthogonal parameters","pmids":["20578160"],"is_preprint":false},{"year":2014,"finding":"Missense mutations concentrated in the 'unknown function subdomain' (UFSD) of CPS1, here renamed the 'Integrating Domain', primarily cause disease by decreasing CPS1 solubility (misfolding) and reducing specific activity (decreased Vmax). Structural modelling shows the Integrating Domain occupies the middle of the 1462-residue multidomain protein and creates key interdomain contacts; most mutations disrupt these contacts, causing misfolding.","method":"Baculovirus/insect cell recombinant expression of 18 mutants, CPS1 yield/solubility measurements, enzymatic activity assays, Km/Vmax determination, thermal stability, structural modelling","journal":"Molecular genetics and metabolism","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic reconstitution and mutagenesis of 18 clinical mutations with multiple orthogonal readouts, rationalized by structural modelling","pmids":["24813853"],"is_preprint":false},{"year":2014,"finding":"The recurrent Turkish founder mutation p.Val1013del in CPS1 abolishes all catalytic activities (global CPS1 reaction, ATPase partial reaction reflecting bicarbonate phosphorylation, and ATP synthesis partial reaction reflecting carbamate phosphorylation) without causing gross protein instability or insolubility. V1013 maps to a hydrophobic β-strand near the predicted carbamate tunnel linking both phosphorylation sites.","method":"Baculovirus/insect cell recombinant expression, enzymatic activity assays for global reaction and partial reactions, protein yield/solubility analysis, structural modelling, haplotype analysis","journal":"Molecular genetics and metabolism","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution with multiple enzymatic activity assays and structural rationalization, single lab","pmids":["25410056"],"is_preprint":false},{"year":2016,"finding":"N-carbamyl-L-glutamate (NCG) activates CPS1 sub-optimally compared to NAG and competes with NAG binding. For the E1034G mutation (located outside the NAG site), NCG activates CPS1 molecules not already bound to NAG, enhancing ureagenesis. For the M792I mutation (which reduces the amount of functional enzyme), NCG competition with the scarce NAG further decreases residual ureagenesis. NCG in combination with MgATP stabilizes wild-type CPS1.","method":"Purified recombinant wild-type and mutant mouse CPS1, enzymatic activity assays, competition kinetics, thermal stability assays","journal":"Molecular genetics and metabolism","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with purified enzyme and defined kinetic competition assays, mechanistically explains differential patient responses","pmids":["28007335"],"is_preprint":false},{"year":2024,"finding":"During APAP-induced liver injury, GSDME activation leads to loss of ISG15 (interferon-stimulated gene 15), causing deISGylation of CPS1. DeISGylated CPS1 is then degraded via K48-linked ubiquitination, resulting in ammonia clearance dysfunction. GSDME deletion prevents CPS1 deISGylation and degradation, preserving urea cycle function.","method":"GSDME knockout and hepatocyte-specific rescue mice, ISG15 loss-of-function, K48-ubiquitination pulldown/MS, CPS1 protein stability assays, APAP liver injury model","journal":"Advanced science","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO and rescue, biochemical demonstration of K48-ubiquitination-mediated degradation and ISGylation status, multiple orthogonal in vivo and in vitro methods","pmids":["38417117"],"is_preprint":false},{"year":2025,"finding":"CPS1 regulates glucagon-induced hepatic gluconeogenesis through the CaMKII/FOXO1 pathway: CPS1 induces calcium release from the endoplasmic reticulum, triggering CaMKII phosphorylation, which facilitates dephosphorylation and nuclear translocation of FOXO1 to enhance gluconeogenic gene expression. CPS1 knockdown reduced glucagon response in vivo and in vitro; overexpression produced the opposite effect.","method":"CPS1 knockdown and overexpression in hepatocytes (in vitro) and mice (in vivo), CaMKII/FOXO1 phosphorylation and nuclear translocation assays, calcium release measurements, gluconeogenesis assays","journal":"Frontiers in pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD and OE with defined pathway readouts (CaMKII phosphorylation, FOXO1 localization, gluconeogenesis) in vivo and in vitro, single lab","pmids":["39193349"],"is_preprint":false},{"year":2025,"finding":"CPS1 overexpression in metastatic lung cancer cells produces excessive fumarate (a urea cycle intermediate). Fumarate accumulation inhibits TET2 activity, altering miR-200a gene methylation and driving epithelial-to-mesenchymal transition (EMT) to enhance cell migration and invasion. CPS1 inhibition reduces fumarate accumulation, enhances TET2 activity, and epigenetically upregulates PD-L1, leading to immune evasion; combining a CPS1 inhibitor with anti-PD-1 therapy had synergistic anti-tumor effects.","method":"CPS1 genetic knockdown and pharmacological inhibition, quantitative proteomics, RNA-seq, untargeted and targeted metabolomics (urea cycle), TET2 activity assay, miR-200a methylation analysis, Transwell/wound healing assay, spontaneous and induced lung cancer metastasis mouse models, combination immunotherapy","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal omics and functional methods, in vitro and in vivo validation, single lab; fumarate-TET2 mechanism is biochemically supported but awaits independent replication","pmids":["41356199"],"is_preprint":false},{"year":2019,"finding":"CPS1 recombinant p.(Pro1211Arg) mutant showed decreased solubility/yield (consistent with misfolding tendency), reduced thermal stability, ~2-fold lower Vmax, and ~5-fold reduced apparent affinity for ATP. NCG stabilizes CPS1 and could minimize the decrease in effective affinity for ATP by increasing NAG-site saturation, explaining the clinical NCG response in this patient.","method":"Baculovirus/insect cell recombinant expression of mutant CPS1, enzymatic kinetics, thermal stability assay, protein yield/solubility measurement","journal":"JIMD reports","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution and kinetics for a single mutation, single lab, single paper","pmids":["31392111"],"is_preprint":false},{"year":2015,"finding":"Nobiletin (NOB), a dietary flavonoid, induces CPS1 expression through transcription factors C/EBPα and C/EBPβ via CCAAT consensus elements on the Cps1 gene promoter; a functional circadian clock (CLOCK) is required for this induction under high-fat diet conditions. This establishes a C/EBP- and clock-dependent transcriptional regulatory mechanism for CPS1.","method":"Mouse dietary/NOB treatment experiments, CPS1 mRNA/protein quantification over circadian cycle, luciferase reporter assay with Cps1 promoter CCAAT elements, Clock mutant mice, C/EBP factor expression analysis","journal":"Nutrition & metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — promoter reporter assay plus genetic clock-mutant epistasis and in vivo dietary intervention, single lab","pmids":["26075008"],"is_preprint":false},{"year":2024,"finding":"The histone demethylase JMJD1C represses CPS1 expression in PNH clones by reducing H3K36me3 at the CPS1 locus. Chromatin immunoprecipitation confirmed H3K36me3 occupancy at CPS1. Knockdown of JMJD1C in PIG-A knockout K562 cells upregulated CPS1 and H3K36me3 expression, decreased proliferation, and increased apoptosis.","method":"ChIP for H3K36me3 at CPS1 locus, JMJD1C knockdown, CPS1 expression and H3K36me3 quantification, proliferation and apoptosis assays, PNH mouse model","journal":"British journal of haematology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus genetic KD with defined epigenetic and functional readouts, single lab","pmids":["38650379"],"is_preprint":false},{"year":2018,"finding":"Wood frog CPS1 purified from frozen animals shows increased affinity for ammonium (1.26-fold) compared to control, and with glucose addition, higher affinity for ATP and NAG. The frozen enzyme has lower thermal stability and lower levels of glutarylated lysine residues compared to control. This post-translational difference (glutarylation) correlates with altered kinetics in the freeze-tolerant state.","method":"Three-step chromatographic purification, Michaelis-Menten kinetics for three substrates, thermal denaturation, mass spectrometry quantification of glutarylation","journal":"Molecular and cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro purified enzyme with kinetics and PTM quantification, but single lab, single non-human study","pmids":["30421312"],"is_preprint":false},{"year":2026,"finding":"Acetylation at lysine 1168 (K1168) of CPS1 is induced by PFOA/PFO4DA exposure. Mutation of K1168 to arginine (mimicking unacetylated state) restored CPS1 enzymatic activity under PFOA/PFO4DA exposure, while mutation to acetyl-lysine mimic reduced ATP binding capacity, suggesting K1168 acetylation impairs ATP binding and CPS1 activity.","method":"Quantitative acetylomics (mass spectrometry), site-directed mutagenesis (K1168R and K1168Kac mimics), in vitro ATP-binding and enzymatic activity assays, in silico docking","journal":"Environmental pollution","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro mutagenesis and enzymatic assay with structural rationalization, single lab","pmids":["41720236"],"is_preprint":false},{"year":2025,"finding":"circSETD2 directly binds to CPS1 protein (identified by RNA pulldown with LC-MS/MS, validated by RNA immunoprecipitation and FISH), reducing CPS1 enzymatic activity and exacerbating lipid metabolic disturbances in MAFLD. Pharmacological modulation of CPS1 enzymatic activity in circSETD2-silenced cells confirmed CPS1 as the mediator of circSETD2's effects on lipid homeostasis.","method":"RNA pulldown + LC-MS/MS, RNA immunoprecipitation, FISH co-localization, CPS1 enzymatic activity assay, CPS1 pharmacological modulation rescue experiment, in vivo HFD mouse model","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal binding validation methods and functional rescue, single lab; circRNA–protein interaction is relatively unusual mechanistically","pmids":["41224057"],"is_preprint":false},{"year":2025,"finding":"LOC401312 lncRNA transcriptionally upregulates CPS1 in NSCLC; CPS1 overexpression recapitulates the radiosensitization phenotype of LOC401312. Mechanistically, CPS1 suppresses phosphorylation of ATM kinase (Ser1981), a key mediator of DNA damage checkpoint activation, thereby impairing DNA repair.","method":"Genome-wide CRISPRa screening, stable LOC401312 overexpression, RNA-seq, CPS1 overexpression/KD, ATM Ser1981 phosphorylation assay, irradiation cell survival assays","journal":"International journal of molecular sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, ATM suppression by CPS1 shown by phosphorylation assay without biochemical reconstitution; mechanism is incompletely characterized","pmids":["40565327"],"is_preprint":false},{"year":2026,"finding":"CPS1 activation (via NCG) in ovarian granulosa-like cells elevates intracellular arginine levels, which reduces CASTOR1 binding to its inhibitor GATOR2, thereby facilitating S6K phosphorylation and mTORC1 pathway activation. siRNA knockdown of CPS1 eliminated NCG's effect on arginine levels and S6K phosphorylation. This pathway promotes primordial follicle activation in mouse and human ovarian tissue.","method":"NCG treatment of murine ovaries and human ovarian cortical tissue, KGN granulosa cell siRNA-KD of CPS1, arginine measurement, pS6K/S6K ratio, CASTOR1-GATOR2 interaction assay, mTORC1 pathway readouts, primordial follicle counting","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA KD with defined pathway epistasis (CASTOR1-GATOR2-mTORC1) and validated in both mouse and human tissue, single lab","pmids":["42111264"],"is_preprint":false},{"year":2025,"finding":"In torpid bats, CPS1 protein abundance is significantly increased and co-localizes and co-immunoprecipitates with agmatinase (AGMAT) in liver mitochondria. FRET analysis supports an indirect CPS1-AGMAT interaction. This association is conserved in two phylogenetically distant bat species (Myotis ricketti and Rhinolophus ferrumequinum), suggesting a functional role in coordinating urea cycle nitrogen metabolism during torpor.","method":"Proteomics, confocal co-localization, co-immunoprecipitation, FRET, metabolic profiling","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — co-IP and FRET in bat liver, single lab, preprint; FRET supports indirect interaction only; functional consequence of CPS1-AGMAT interaction not yet established","pmids":[],"is_preprint":true},{"year":2021,"finding":"AFF1 occupies the NTS (neurotensin) enhancer in lung adenocarcinoma cells and suppresses NTS transcription; NTS expression is highly correlated with CPS1 expression. The IL6 pathway antagonizes NTS in regulating CPS1, establishing a NTS-AFF1-IL6-CPS1 regulatory axis in lung adenocarcinoma cells.","method":"ChIP-seq for AFF1 at NTS enhancer, gene expression correlation analysis, NTS and IL6 pathway perturbation experiments, CPS1 expression readout","journal":"The Journal of biological chemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, co-regulatory relationship shown by ChIP and expression analysis; direct mechanistic link from AFF1/NTS/IL6 to CPS1 activity is inferential rather than biochemically reconstituted","pmids":["33493519"],"is_preprint":false},{"year":2016,"finding":"In HCC cells treated with aflatoxin B1, CPS1 was shown by Co-IP to interact with KRT1 (type II cytoskeletal keratin 1), albumin (ALB), and ubiquitin C (UBC). CPS1 co-localizes with KRT1 and ALB, and aflatoxin B1 changes the intensity correlation between these proteins.","method":"Co-immunoprecipitation, mass spectrometry, immunofluorescence co-localization, siRNA knockdown","journal":"Gene","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP with MS confirmation, single lab; functional consequence of CPS1-KRT1/ALB interaction not established","pmids":["27425868"],"is_preprint":false},{"year":1995,"finding":"The human CPS1 gene was physically mapped by FISH to chromosome 2q34→q35, correcting an earlier assignment to 2p.","method":"FISH physical mapping, CEPH family linkage analysis","journal":"Cytogenetics and cell genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct physical mapping by FISH with linkage confirmation; straightforward chromosomal localization","pmids":["7587391"],"is_preprint":false}],"current_model":"CPS1 is a mitochondrial matrix enzyme that catalyzes the first and rate-limiting step of the urea cycle, converting ammonia and bicarbonate into carbamoyl phosphate using two ATP molecules, and requires the allosteric activator N-acetyl-L-glutamate (NAG); its activity is upregulated by O-GlcNAcylation on specific threonine residues, inhibited by K1168 acetylation (impairing ATP binding), and targeted for degradation via K48-ubiquitination following deISGylation; transcriptionally, CPS1 is repressed by LKB1 through AMPK, induced by C/EBPα/β in a circadian clock-dependent manner, and silenced in hepatocellular carcinoma by CpG methylation near its promoter; beyond the urea cycle, CPS1 supplies carbamoyl phosphate for an unconventional mitochondria-to-cytoplasm pyrimidine biosynthesis pathway in KRAS/LKB1-mutant lung cancer cells, drives glucagon-induced hepatic gluconeogenesis via CaMKII/FOXO1 signaling, promotes lung cancer metastasis through fumarate-TET2-miR200a-EMT epigenetic axis, and exerts non-enzymatic anti-inflammatory protection by inducing M2 monocyte polarization after release into blood during acute liver injury."},"narrative":{"mechanistic_narrative":"CPS1 is a mitochondrial matrix enzyme that catalyzes the first, committed step of the urea cycle, phosphorylating bicarbonate and condensing it with ammonia to form carbamoyl phosphate in a reaction strictly dependent on the allosteric activator N-acetyl-L-glutamate (NAG) [PMID:23649895, PMID:25410056]. Recombinant human enzyme reconstitution established its multidomain architecture and confirmed that NAG—and its therapeutic analogue N-carbamoyl-L-glutamate (NCG)—together with MgATP both activate and stabilize the enzyme against proteolytic and thermal inactivation [PMID:23649895, PMID:28007335]. Structure-function analysis of clinical mutations defines how disease arises: mutations in the central 'Integrating Domain' (the former unknown-function subdomain) compromise interdomain contacts, solubility, and folding, while residues such as V1013 near the carbamate tunnel abolish catalysis and NAG-site mutations alter activator affinity, rationalizing why some patients respond to NCG and others do not [PMID:20578160, PMID:24813853, PMID:25410056, PMID:28007335]. Enzyme activity is tuned by competing post-translational modifications: O-GlcNAcylation on specific threonines acts as a nutrient-sensing switch that enhances catalytic efficiency for ammonia and ureagenesis [PMID:36064721, PMID:35285892], whereas K1168 acetylation impairs ATP binding and lowers activity [PMID:41720236]; under acute liver injury, GSDME-driven loss of ISG15 leads to deISGylation of CPS1 and its K48-ubiquitin-mediated degradation, causing ammonia-clearance failure [PMID:38417117]. Beyond detoxification, CPS1 supplies carbamoyl phosphate for an unconventional ammonia-to-pyrimidine biosynthetic route in KRAS/LKB1-mutant lung cancer, where its loss depletes pyrimidines, stalls replication, and triggers DNA damage [PMID:28538732], and a CPS1-selective allosteric inhibitor that blocks ATP hydrolysis suppresses both urea synthesis and pyrimidine production [PMID:32017919]. CPS1 expression is constrained by multiple transcriptional and epigenetic controls—promoter CpG methylation silences it in hepatocellular carcinoma [PMID:21281797], C/EBPα/β drive clock-dependent induction [PMID:26075008], and the histone demethylase JMJD1C represses it via reduced H3K36me3 [PMID:38650379]. CPS1 additionally exerts non-enzymatic roles, including induction of M2 monocyte polarization that protects against liver injury after its release into blood [PMID:30979808], and metabolic-signaling roles spanning fumarate-driven EMT in lung cancer metastasis [PMID:41356199] and glucagon-induced hepatic gluconeogenesis through CaMKII/FOXO1 [PMID:39193349].","teleology":[{"year":1995,"claim":"Establishing the chromosomal locus of CPS1 provided the genetic anchor needed to link the gene to inherited urea cycle disorders.","evidence":"FISH physical mapping and CEPH family linkage analysis","pmids":["7587391"],"confidence":"Medium","gaps":["Locates the gene but says nothing about enzyme mechanism or regulation"]},{"year":2011,"claim":"It was unknown why CPS1 is lost in liver cancer; demonstrating promoter/intronic CpG hypermethylation and 5-azacytidine rescue showed that epigenetic silencing, not mutation, downregulates CPS1 in hepatocellular carcinoma.","evidence":"Bisulfite sequencing, demethylation rescue, and promoter-reporter mutagenesis in HCC cells","pmids":["21281797"],"confidence":"Medium","gaps":["Does not identify the methyltransferase responsible","Functional consequence of CPS1 loss for HCC biology not addressed here"]},{"year":2010,"claim":"To explain how patient mutations cause enzyme failure, recombinant CPS1 reconstitution mapped nine clinical mutations onto solubility, stability, and NAG-affinity defects, validating the C-terminal NAG allosteric site structurally.","evidence":"Baculovirus/insect-cell expression, kinetics, and structure-function analysis using the C-terminal domain crystal structure","pmids":["20578160"],"confidence":"High","gaps":["Covers only a subset of clinical mutations","No full-length structure available"]},{"year":2013,"claim":"Demonstrating that recombinant human CPS1 reproduces native kinetics, and that NAG/NCG plus MgATP protect it from inactivation, established a faithful in vitro system and revealed an activator-linked stabilizing/chaperone effect.","evidence":"Recombinant expression, enzymatic kinetics, thermal stability, and site-limited proteolysis","pmids":["23649895"],"confidence":"High","gaps":["Stabilizing mechanism inferred from proteolysis/thermal assays, not structurally resolved"]},{"year":2014,"claim":"Systematic reconstitution of clinical mutations resolved the dominant disease mechanism—misfolding via disrupted interdomain contacts in the central Integrating Domain, and catalytic abolition by residues near the carbamate tunnel.","evidence":"Recombinant expression of 18 mutants (Integrating Domain) and partial-reaction assays of the V1013del founder mutation, with structural modelling","pmids":["24813853","25410056"],"confidence":"High","gaps":["Structural modelling rather than experimental full-length structure","Genotype-phenotype correlation in patients not directly tested"]},{"year":2016,"claim":"To explain divergent clinical NCG responses, kinetic competition assays showed NCG sub-optimally activates CPS1 and competes with NAG, helping mutants lacking NAG occupancy but harming mutants with scarce functional enzyme.","evidence":"Purified recombinant wild-type and mutant CPS1 competition kinetics and stability assays","pmids":["28007335"],"confidence":"High","gaps":["Performed on mouse CPS1","In vitro kinetics do not capture full in vivo pharmacology"]},{"year":2017,"claim":"It was assumed CPS1 functions only in ammonia detoxification; showing that KRAS/LKB1-mutant lung cancer cells use CPS1 to channel nitrogen into pyrimidines redefined it as a biosynthetic enzyme whose loss causes replication stress.","evidence":"siRNA silencing, metabolomics, isotope tracing, and pyrimidine rescue in KL cell lines, xenografts, and patient tumors","pmids":["28538732"],"confidence":"High","gaps":["Mechanism of carbamoyl phosphate transfer to cytoplasmic pyrimidine synthesis not biochemically defined"]},{"year":2019,"claim":"The discovery that secreted CPS1 induces M2 monocyte polarization and protects against liver injury independent of enzymatic activity revealed an unexpected extracellular, non-catalytic function.","evidence":"Bile/blood proteomics, recombinant CPS1 administration, macrophage-depletion, and APAP/FasL injury models in mice","pmids":["30979808"],"confidence":"High","gaps":["Receptor/uptake mechanism on monocytes not identified","Secretion route from hepatocytes not defined"]},{"year":2020,"claim":"Identifying a druggable allosteric pocket and a CPS1-selective inhibitor (H3B-120) that blocks ATP hydrolysis established that CPS1 enzymatic output is pharmacologically targetable in both urea and pyrimidine pathways.","evidence":"In vitro enzymatic assays, structure-based drug design, cellular pathway assays, and CPS2 counterscreening","pmids":["32017919"],"confidence":"High","gaps":["Pocket location relative to catalytic domains described biochemically but not in a full-length co-structure","In vivo efficacy not the focus"]},{"year":2022,"claim":"Resolving how nutrient state tunes ureagenesis, two studies showed O-GlcNAcylation on specific threonines as a regulatory switch—enhancing ammonia catalysis in one context and acting as an aging/high-glucose-driven nutrient sensor that limits activity in another.","evidence":"MS site-mapping, enzyme kinetics, OGT liver knockout, OGA inhibition, and dietary interventions in mouse disease models","pmids":["36064721","35285892"],"confidence":"High","gaps":["The two studies report opposite directional effects of O-GlcNAcylation, leaving the integrated physiological output unresolved","Responsible OGT/OGA dynamics on specific sites not fully reconciled"]},{"year":2024,"claim":"Linking inflammatory cell death to ammonia toxicity, GSDME-driven ISG15 loss was shown to deISGylate CPS1 and route it to K48-ubiquitin degradation, identifying a stability-control axis that fails in acute liver injury.","evidence":"GSDME knockout/rescue mice, ISG15 loss-of-function, K48-ubiquitination pulldown/MS, and APAP injury model","pmids":["38417117"],"confidence":"High","gaps":["E3 ligase mediating K48 ubiquitination not identified","ISGylation site(s) on CPS1 not mapped"]},{"year":2024,"claim":"A second epigenetic repressor of CPS1 was identified: JMJD1C reduces H3K36me3 at the CPS1 locus to silence it in PNH clones, with knockdown restoring CPS1 and impairing clone proliferation.","evidence":"ChIP for H3K36me3, JMJD1C knockdown, and proliferation/apoptosis assays in PIG-A knockout cells and PNH model","pmids":["38650379"],"confidence":"Medium","gaps":["Direct enzymatic link between JMJD1C and H3K36me3 at CPS1 inferential","Relevance beyond PNH not tested"]},{"year":2025,"claim":"Beyond catalysis, CPS1 was shown to drive metabolic-signaling programs—fumarate-mediated TET2 inhibition driving miR-200a-linked EMT and metastasis, and a CaMKII/FOXO1 axis controlling glucagon-induced gluconeogenesis—plus circRNA-mediated regulation of its activity in fatty liver and an mTORC1-activating arginine route in ovarian follicle activation.","evidence":"Knockdown/overexpression, omics, metabolomics, TET2 activity and pathway readouts across lung cancer, hepatocyte, MAFLD, and ovarian tissue models","pmids":["41356199","39193349","41224057","42111264"],"confidence":"Medium","gaps":["Each axis is from a single lab and awaits independent replication","How mitochondrial CPS1 metabolites couple to cytoplasmic/nuclear signaling not biochemically resolved","circRNA-protein interaction mechanism unusual and unconfirmed elsewhere"]},{"year":2026,"claim":"Acetylation at K1168 was added to the CPS1 PTM map, shown to impair ATP binding and reduce activity, complementing the activating O-GlcNAcylation switch.","evidence":"Quantitative acetylomics, K1168R/K1168Kac mutagenesis, ATP-binding and activity assays, and in silico docking under PFOA/PFO4DA exposure","pmids":["41720236"],"confidence":"Medium","gaps":["Deacetylase/acetyltransferase regulating K1168 not identified","Physiological occupancy of K1168 acetylation unknown"]},{"year":null,"claim":"How CPS1's diverse non-canonical functions (extracellular immunomodulation, fumarate/arginine-driven signaling, pyrimidine supply) are coordinated with its mitochondrial catalytic role, and what receptors, ligases, and partner proteins mediate them, remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No unifying model linking enzymatic and non-enzymatic roles","Monocyte receptor for secreted CPS1 unidentified","E3 ligase and deacetylase regulating CPS1 stability/PTMs unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[6,9]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[2,9,18]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[6,9]},{"term_id":"GO:0098772","term_label":"molecular function regulator 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compound heterozygote variants: c.4193_4206delinsG (p.Leu1398Argfs*25), c.793C > A (p.Pro265Thr), in the CPS1 gene (NM_001875.4) causing late onset carbamoyl phosphate synthetase 1 deficiency-Lessons learned.","date":"2022","source":"Molecular genetics and metabolism reports","url":"https://pubmed.ncbi.nlm.nih.gov/36466970","citation_count":5,"is_preprint":false},{"pmid":"37365635","id":"PMC_37365635","title":"Clinical and genetic analysis of a case of late onset carbamoyl phosphate synthase I deficiency caused by CPS1 mutation and literature review.","date":"2023","source":"BMC medical genomics","url":"https://pubmed.ncbi.nlm.nih.gov/37365635","citation_count":4,"is_preprint":false},{"pmid":"38703806","id":"PMC_38703806","title":"Urea cycle promotion via ammonia-upregulated CPS1 is involved in arsenite-induced pulmonary fibrosis through enhancing collagen synthesis.","date":"2024","source":"Chemico-biological 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cancer cells is suppressed by LKB1 through AMPK. CPS1 enables an unconventional pathway of nitrogen flow from ammonia into pyrimidines: silencing CPS1 in KL cells depletes pyrimidines (reducing the pyrimidine-to-purine ratio), compromises S-phase progression, and induces DNA-polymerase stalling and DNA damage. Exogenous pyrimidines reverse the DNA damage and rescue growth, establishing that the role of CPS1 is pyrimidine supply rather than ammonia detoxification in this context.\",\n      \"method\": \"siRNA silencing, metabolomics, isotope tracing, cell death/growth assays, exogenous pyrimidine rescue, genetic epistasis (KRAS/LKB1 mutant cell lines and patient tumors)\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (metabolomics, isotope tracing, genetic KD, rescue experiments) in human cancer cell lines and mouse xenografts, replicated in patient tumor specimens\",\n      \"pmids\": [\"28538732\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CPS1 expression in human hepatocellular carcinoma cells is silenced by DNA methylation. Two CpG dinucleotides near the transcription start site and a CpG-rich region in the first intron are hypermethylated in HCC cells; site-directed mutagenesis of these CpG dinucleotides reduced CPS1 promoter activity. Treatment with the demethylating agent 5-azacytidine restored CPS1 expression.\",\n      \"method\": \"Bisulfite sequencing, 5-azacytidine demethylation, promoter-reporter assays with site-directed mutagenesis of CpG sites\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal methods (demethylation rescue + mutagenesis reporter assay), single lab\",\n      \"pmids\": [\"21281797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Small-molecule inhibitors (including H3B-120) bind to a previously unknown allosteric pocket on CPS1 and block ATP hydrolysis in the first step of carbamoyl phosphate synthesis. These inhibitors are selective for CPS1 over CPS2 and are active in cellular assays, blocking both urea synthesis and pyrimidine biosynthesis.\",\n      \"method\": \"Biochemical in vitro CPS1 enzymatic assay, structure-based drug design, cellular urea synthesis and pyrimidine pathway assays, selectivity counterscreening against CPS2\",\n      \"journal\": \"Cell chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic assay with defined mechanism (ATP hydrolysis block at allosteric pocket), structure-based design, cellular functional validation, and selectivity profiling in one rigorous study\",\n      \"pmids\": [\"32017919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CPS1 is constitutively secreted into bile by hepatocytes, likely as a soluble protein, and is released into blood during acute liver injury. In blood, CPS1 is rapidly sequestered by circulating monocytes, inducing their M2 polarization and homing to the liver independent of CPS1 enzymatic activity. Recombinant CPS1 (but not control transferrin) increases hepatic macrophage numbers and phagocytic activity, and protects mice from Fas-ligand- or acetaminophen-induced liver injury; protection is absent in macrophage-deficient mice.\",\n      \"method\": \"Mouse/human bile proteomics, sedimentation analysis, recombinant CPS1 administration, monocyte uptake assays, macrophage polarization assays, macrophage-depletion experiments, acetaminophen and FasL liver injury models\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (proteomics, cell biology, genetic macrophage depletion, two injury models, recombinant protein rescue) in a single rigorous study with in vivo validation\",\n      \"pmids\": [\"30979808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"O-GlcNAcylation of CPS1 on specific threonine residues increases the catalytic efficiency of CPS1 for ammonia, thereby enhancing ureagenesis. Pharmacological inhibition of O-GlcNAcase (which removes O-GlcNAc from proteins) reduced systemic ammonia in both genetic (propionic acidemia) and acquired (thioacetamide-induced acute liver failure) mouse models.\",\n      \"method\": \"Mass spectrometry identification of O-GlcNAcylation sites, enzymatic kinetics of O-GlcNAcylated vs. unmodified CPS1, O-GlcNAcase pharmacological inhibition in two mouse disease models, biochemical ammonia measurements\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — site-specific PTM identified by MS, enzymatic kinetics demonstrating functional consequence, replicated across two independent in vivo disease models\",\n      \"pmids\": [\"36064721\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CPS1 O-GlcNAcylation is increased by high glucose and in aged liver, and inhibits CPS1 enzymatic activity. Liver-specific deletion of OGT (O-GlcNAc transferase) potentiates CPS1 activity and renders it irresponsive to stimulation by prolonged fasting. Calorie restriction reverses CPS1 O-GlcNAcylation. This identifies CPS1 O-GlcNAcylation as a nutrient-sensing regulatory step in the urea cycle during aging.\",\n      \"method\": \"Liver-specific OGT knockout mice, O-GlcNAc mass spectrometry of aged liver, glucose stimulation assays, calorie restriction experiments, CPS1 activity measurements\",\n      \"journal\": \"Journal of molecular cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — genetic KO model plus pharmacological and dietary interventions, enzymatic activity readout, orthogonal to PMID 36064721 confirming the same PTM-function axis\",\n      \"pmids\": [\"35285892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Human recombinant CPS1 expressed in baculovirus/insect cells has the same kinetic and molecular properties as natural human CPS1. Glycerol partially substitutes for the essential allosteric activator N-acetyl-L-glutamate (NAG). NAG and its analogue N-carbamoyl-L-glutamate (NCG), together with MgATP, protect CPS1 against proteolytic and thermal inactivation, suggesting a stabilizing/chaperone effect. Site-limited proteolysis confirmed the multidomain architecture of CPS1.\",\n      \"method\": \"Recombinant protein expression and purification, enzymatic kinetics, thermal stability assays, site-limited proteolysis\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution of human enzyme with kinetic and stability characterization; multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"23649895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Using recombinant CPS1 expressed in baculovirus/insect cells, nine clinical CPS1 mutations were shown to affect enzyme solubility, stability, and/or kinetic parameters including NAG affinity; the C-terminal domain mutations were rationalized using the crystal structure of that domain which includes the NAG binding site. This established the functional importance of specific residues, including those at the NAG allosteric site.\",\n      \"method\": \"Baculovirus/insect cell expression, enzyme purification, kinetic analysis, thermal stability, site-directed mutagenesis, structure-function analysis using C-terminal domain crystal structure\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution with mutagenesis and structural validation, multiple mutations characterized across orthogonal parameters\",\n      \"pmids\": [\"20578160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Missense mutations concentrated in the 'unknown function subdomain' (UFSD) of CPS1, here renamed the 'Integrating Domain', primarily cause disease by decreasing CPS1 solubility (misfolding) and reducing specific activity (decreased Vmax). Structural modelling shows the Integrating Domain occupies the middle of the 1462-residue multidomain protein and creates key interdomain contacts; most mutations disrupt these contacts, causing misfolding.\",\n      \"method\": \"Baculovirus/insect cell recombinant expression of 18 mutants, CPS1 yield/solubility measurements, enzymatic activity assays, Km/Vmax determination, thermal stability, structural modelling\",\n      \"journal\": \"Molecular genetics and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic reconstitution and mutagenesis of 18 clinical mutations with multiple orthogonal readouts, rationalized by structural modelling\",\n      \"pmids\": [\"24813853\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The recurrent Turkish founder mutation p.Val1013del in CPS1 abolishes all catalytic activities (global CPS1 reaction, ATPase partial reaction reflecting bicarbonate phosphorylation, and ATP synthesis partial reaction reflecting carbamate phosphorylation) without causing gross protein instability or insolubility. V1013 maps to a hydrophobic β-strand near the predicted carbamate tunnel linking both phosphorylation sites.\",\n      \"method\": \"Baculovirus/insect cell recombinant expression, enzymatic activity assays for global reaction and partial reactions, protein yield/solubility analysis, structural modelling, haplotype analysis\",\n      \"journal\": \"Molecular genetics and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution with multiple enzymatic activity assays and structural rationalization, single lab\",\n      \"pmids\": [\"25410056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"N-carbamyl-L-glutamate (NCG) activates CPS1 sub-optimally compared to NAG and competes with NAG binding. For the E1034G mutation (located outside the NAG site), NCG activates CPS1 molecules not already bound to NAG, enhancing ureagenesis. For the M792I mutation (which reduces the amount of functional enzyme), NCG competition with the scarce NAG further decreases residual ureagenesis. NCG in combination with MgATP stabilizes wild-type CPS1.\",\n      \"method\": \"Purified recombinant wild-type and mutant mouse CPS1, enzymatic activity assays, competition kinetics, thermal stability assays\",\n      \"journal\": \"Molecular genetics and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with purified enzyme and defined kinetic competition assays, mechanistically explains differential patient responses\",\n      \"pmids\": [\"28007335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"During APAP-induced liver injury, GSDME activation leads to loss of ISG15 (interferon-stimulated gene 15), causing deISGylation of CPS1. DeISGylated CPS1 is then degraded via K48-linked ubiquitination, resulting in ammonia clearance dysfunction. GSDME deletion prevents CPS1 deISGylation and degradation, preserving urea cycle function.\",\n      \"method\": \"GSDME knockout and hepatocyte-specific rescue mice, ISG15 loss-of-function, K48-ubiquitination pulldown/MS, CPS1 protein stability assays, APAP liver injury model\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO and rescue, biochemical demonstration of K48-ubiquitination-mediated degradation and ISGylation status, multiple orthogonal in vivo and in vitro methods\",\n      \"pmids\": [\"38417117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CPS1 regulates glucagon-induced hepatic gluconeogenesis through the CaMKII/FOXO1 pathway: CPS1 induces calcium release from the endoplasmic reticulum, triggering CaMKII phosphorylation, which facilitates dephosphorylation and nuclear translocation of FOXO1 to enhance gluconeogenic gene expression. CPS1 knockdown reduced glucagon response in vivo and in vitro; overexpression produced the opposite effect.\",\n      \"method\": \"CPS1 knockdown and overexpression in hepatocytes (in vitro) and mice (in vivo), CaMKII/FOXO1 phosphorylation and nuclear translocation assays, calcium release measurements, gluconeogenesis assays\",\n      \"journal\": \"Frontiers in pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD and OE with defined pathway readouts (CaMKII phosphorylation, FOXO1 localization, gluconeogenesis) in vivo and in vitro, single lab\",\n      \"pmids\": [\"39193349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CPS1 overexpression in metastatic lung cancer cells produces excessive fumarate (a urea cycle intermediate). Fumarate accumulation inhibits TET2 activity, altering miR-200a gene methylation and driving epithelial-to-mesenchymal transition (EMT) to enhance cell migration and invasion. CPS1 inhibition reduces fumarate accumulation, enhances TET2 activity, and epigenetically upregulates PD-L1, leading to immune evasion; combining a CPS1 inhibitor with anti-PD-1 therapy had synergistic anti-tumor effects.\",\n      \"method\": \"CPS1 genetic knockdown and pharmacological inhibition, quantitative proteomics, RNA-seq, untargeted and targeted metabolomics (urea cycle), TET2 activity assay, miR-200a methylation analysis, Transwell/wound healing assay, spontaneous and induced lung cancer metastasis mouse models, combination immunotherapy\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal omics and functional methods, in vitro and in vivo validation, single lab; fumarate-TET2 mechanism is biochemically supported but awaits independent replication\",\n      \"pmids\": [\"41356199\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CPS1 recombinant p.(Pro1211Arg) mutant showed decreased solubility/yield (consistent with misfolding tendency), reduced thermal stability, ~2-fold lower Vmax, and ~5-fold reduced apparent affinity for ATP. NCG stabilizes CPS1 and could minimize the decrease in effective affinity for ATP by increasing NAG-site saturation, explaining the clinical NCG response in this patient.\",\n      \"method\": \"Baculovirus/insect cell recombinant expression of mutant CPS1, enzymatic kinetics, thermal stability assay, protein yield/solubility measurement\",\n      \"journal\": \"JIMD reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution and kinetics for a single mutation, single lab, single paper\",\n      \"pmids\": [\"31392111\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Nobiletin (NOB), a dietary flavonoid, induces CPS1 expression through transcription factors C/EBPα and C/EBPβ via CCAAT consensus elements on the Cps1 gene promoter; a functional circadian clock (CLOCK) is required for this induction under high-fat diet conditions. This establishes a C/EBP- and clock-dependent transcriptional regulatory mechanism for CPS1.\",\n      \"method\": \"Mouse dietary/NOB treatment experiments, CPS1 mRNA/protein quantification over circadian cycle, luciferase reporter assay with Cps1 promoter CCAAT elements, Clock mutant mice, C/EBP factor expression analysis\",\n      \"journal\": \"Nutrition & metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — promoter reporter assay plus genetic clock-mutant epistasis and in vivo dietary intervention, single lab\",\n      \"pmids\": [\"26075008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The histone demethylase JMJD1C represses CPS1 expression in PNH clones by reducing H3K36me3 at the CPS1 locus. Chromatin immunoprecipitation confirmed H3K36me3 occupancy at CPS1. Knockdown of JMJD1C in PIG-A knockout K562 cells upregulated CPS1 and H3K36me3 expression, decreased proliferation, and increased apoptosis.\",\n      \"method\": \"ChIP for H3K36me3 at CPS1 locus, JMJD1C knockdown, CPS1 expression and H3K36me3 quantification, proliferation and apoptosis assays, PNH mouse model\",\n      \"journal\": \"British journal of haematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus genetic KD with defined epigenetic and functional readouts, single lab\",\n      \"pmids\": [\"38650379\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Wood frog CPS1 purified from frozen animals shows increased affinity for ammonium (1.26-fold) compared to control, and with glucose addition, higher affinity for ATP and NAG. The frozen enzyme has lower thermal stability and lower levels of glutarylated lysine residues compared to control. This post-translational difference (glutarylation) correlates with altered kinetics in the freeze-tolerant state.\",\n      \"method\": \"Three-step chromatographic purification, Michaelis-Menten kinetics for three substrates, thermal denaturation, mass spectrometry quantification of glutarylation\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro purified enzyme with kinetics and PTM quantification, but single lab, single non-human study\",\n      \"pmids\": [\"30421312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Acetylation at lysine 1168 (K1168) of CPS1 is induced by PFOA/PFO4DA exposure. Mutation of K1168 to arginine (mimicking unacetylated state) restored CPS1 enzymatic activity under PFOA/PFO4DA exposure, while mutation to acetyl-lysine mimic reduced ATP binding capacity, suggesting K1168 acetylation impairs ATP binding and CPS1 activity.\",\n      \"method\": \"Quantitative acetylomics (mass spectrometry), site-directed mutagenesis (K1168R and K1168Kac mimics), in vitro ATP-binding and enzymatic activity assays, in silico docking\",\n      \"journal\": \"Environmental pollution\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro mutagenesis and enzymatic assay with structural rationalization, single lab\",\n      \"pmids\": [\"41720236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"circSETD2 directly binds to CPS1 protein (identified by RNA pulldown with LC-MS/MS, validated by RNA immunoprecipitation and FISH), reducing CPS1 enzymatic activity and exacerbating lipid metabolic disturbances in MAFLD. Pharmacological modulation of CPS1 enzymatic activity in circSETD2-silenced cells confirmed CPS1 as the mediator of circSETD2's effects on lipid homeostasis.\",\n      \"method\": \"RNA pulldown + LC-MS/MS, RNA immunoprecipitation, FISH co-localization, CPS1 enzymatic activity assay, CPS1 pharmacological modulation rescue experiment, in vivo HFD mouse model\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal binding validation methods and functional rescue, single lab; circRNA–protein interaction is relatively unusual mechanistically\",\n      \"pmids\": [\"41224057\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LOC401312 lncRNA transcriptionally upregulates CPS1 in NSCLC; CPS1 overexpression recapitulates the radiosensitization phenotype of LOC401312. Mechanistically, CPS1 suppresses phosphorylation of ATM kinase (Ser1981), a key mediator of DNA damage checkpoint activation, thereby impairing DNA repair.\",\n      \"method\": \"Genome-wide CRISPRa screening, stable LOC401312 overexpression, RNA-seq, CPS1 overexpression/KD, ATM Ser1981 phosphorylation assay, irradiation cell survival assays\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, ATM suppression by CPS1 shown by phosphorylation assay without biochemical reconstitution; mechanism is incompletely characterized\",\n      \"pmids\": [\"40565327\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"CPS1 activation (via NCG) in ovarian granulosa-like cells elevates intracellular arginine levels, which reduces CASTOR1 binding to its inhibitor GATOR2, thereby facilitating S6K phosphorylation and mTORC1 pathway activation. siRNA knockdown of CPS1 eliminated NCG's effect on arginine levels and S6K phosphorylation. This pathway promotes primordial follicle activation in mouse and human ovarian tissue.\",\n      \"method\": \"NCG treatment of murine ovaries and human ovarian cortical tissue, KGN granulosa cell siRNA-KD of CPS1, arginine measurement, pS6K/S6K ratio, CASTOR1-GATOR2 interaction assay, mTORC1 pathway readouts, primordial follicle counting\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA KD with defined pathway epistasis (CASTOR1-GATOR2-mTORC1) and validated in both mouse and human tissue, single lab\",\n      \"pmids\": [\"42111264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In torpid bats, CPS1 protein abundance is significantly increased and co-localizes and co-immunoprecipitates with agmatinase (AGMAT) in liver mitochondria. FRET analysis supports an indirect CPS1-AGMAT interaction. This association is conserved in two phylogenetically distant bat species (Myotis ricketti and Rhinolophus ferrumequinum), suggesting a functional role in coordinating urea cycle nitrogen metabolism during torpor.\",\n      \"method\": \"Proteomics, confocal co-localization, co-immunoprecipitation, FRET, metabolic profiling\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — co-IP and FRET in bat liver, single lab, preprint; FRET supports indirect interaction only; functional consequence of CPS1-AGMAT interaction not yet established\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"AFF1 occupies the NTS (neurotensin) enhancer in lung adenocarcinoma cells and suppresses NTS transcription; NTS expression is highly correlated with CPS1 expression. The IL6 pathway antagonizes NTS in regulating CPS1, establishing a NTS-AFF1-IL6-CPS1 regulatory axis in lung adenocarcinoma cells.\",\n      \"method\": \"ChIP-seq for AFF1 at NTS enhancer, gene expression correlation analysis, NTS and IL6 pathway perturbation experiments, CPS1 expression readout\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, co-regulatory relationship shown by ChIP and expression analysis; direct mechanistic link from AFF1/NTS/IL6 to CPS1 activity is inferential rather than biochemically reconstituted\",\n      \"pmids\": [\"33493519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In HCC cells treated with aflatoxin B1, CPS1 was shown by Co-IP to interact with KRT1 (type II cytoskeletal keratin 1), albumin (ALB), and ubiquitin C (UBC). CPS1 co-localizes with KRT1 and ALB, and aflatoxin B1 changes the intensity correlation between these proteins.\",\n      \"method\": \"Co-immunoprecipitation, mass spectrometry, immunofluorescence co-localization, siRNA knockdown\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP with MS confirmation, single lab; functional consequence of CPS1-KRT1/ALB interaction not established\",\n      \"pmids\": [\"27425868\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The human CPS1 gene was physically mapped by FISH to chromosome 2q34→q35, correcting an earlier assignment to 2p.\",\n      \"method\": \"FISH physical mapping, CEPH family linkage analysis\",\n      \"journal\": \"Cytogenetics and cell genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct physical mapping by FISH with linkage confirmation; straightforward chromosomal localization\",\n      \"pmids\": [\"7587391\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CPS1 is a mitochondrial matrix enzyme that catalyzes the first and rate-limiting step of the urea cycle, converting ammonia and bicarbonate into carbamoyl phosphate using two ATP molecules, and requires the allosteric activator N-acetyl-L-glutamate (NAG); its activity is upregulated by O-GlcNAcylation on specific threonine residues, inhibited by K1168 acetylation (impairing ATP binding), and targeted for degradation via K48-ubiquitination following deISGylation; transcriptionally, CPS1 is repressed by LKB1 through AMPK, induced by C/EBPα/β in a circadian clock-dependent manner, and silenced in hepatocellular carcinoma by CpG methylation near its promoter; beyond the urea cycle, CPS1 supplies carbamoyl phosphate for an unconventional mitochondria-to-cytoplasm pyrimidine biosynthesis pathway in KRAS/LKB1-mutant lung cancer cells, drives glucagon-induced hepatic gluconeogenesis via CaMKII/FOXO1 signaling, promotes lung cancer metastasis through fumarate-TET2-miR200a-EMT epigenetic axis, and exerts non-enzymatic anti-inflammatory protection by inducing M2 monocyte polarization after release into blood during acute liver injury.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CPS1 is a mitochondrial matrix enzyme that catalyzes the first, committed step of the urea cycle, phosphorylating bicarbonate and condensing it with ammonia to form carbamoyl phosphate in a reaction strictly dependent on the allosteric activator N-acetyl-L-glutamate (NAG) [#6, #9]. Recombinant human enzyme reconstitution established its multidomain architecture and confirmed that NAG—and its therapeutic analogue N-carbamoyl-L-glutamate (NCG)—together with MgATP both activate and stabilize the enzyme against proteolytic and thermal inactivation [#6, #10]. Structure-function analysis of clinical mutations defines how disease arises: mutations in the central 'Integrating Domain' (the former unknown-function subdomain) compromise interdomain contacts, solubility, and folding, while residues such as V1013 near the carbamate tunnel abolish catalysis and NAG-site mutations alter activator affinity, rationalizing why some patients respond to NCG and others do not [#7, #8, #9, #10]. Enzyme activity is tuned by competing post-translational modifications: O-GlcNAcylation on specific threonines acts as a nutrient-sensing switch that enhances catalytic efficiency for ammonia and ureagenesis [#4, #5], whereas K1168 acetylation impairs ATP binding and lowers activity [#18]; under acute liver injury, GSDME-driven loss of ISG15 leads to deISGylation of CPS1 and its K48-ubiquitin-mediated degradation, causing ammonia-clearance failure [#11]. Beyond detoxification, CPS1 supplies carbamoyl phosphate for an unconventional ammonia-to-pyrimidine biosynthetic route in KRAS/LKB1-mutant lung cancer, where its loss depletes pyrimidines, stalls replication, and triggers DNA damage [#0], and a CPS1-selective allosteric inhibitor that blocks ATP hydrolysis suppresses both urea synthesis and pyrimidine production [#2]. CPS1 expression is constrained by multiple transcriptional and epigenetic controls—promoter CpG methylation silences it in hepatocellular carcinoma [#1], C/EBPα/β drive clock-dependent induction [#15], and the histone demethylase JMJD1C represses it via reduced H3K36me3 [#16]. CPS1 additionally exerts non-enzymatic roles, including induction of M2 monocyte polarization that protects against liver injury after its release into blood [#3], and metabolic-signaling roles spanning fumarate-driven EMT in lung cancer metastasis [#13] and glucagon-induced hepatic gluconeogenesis through CaMKII/FOXO1 [#12].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Establishing the chromosomal locus of CPS1 provided the genetic anchor needed to link the gene to inherited urea cycle disorders.\",\n      \"evidence\": \"FISH physical mapping and CEPH family linkage analysis\",\n      \"pmids\": [\"7587391\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Locates the gene but says nothing about enzyme mechanism or regulation\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"It was unknown why CPS1 is lost in liver cancer; demonstrating promoter/intronic CpG hypermethylation and 5-azacytidine rescue showed that epigenetic silencing, not mutation, downregulates CPS1 in hepatocellular carcinoma.\",\n      \"evidence\": \"Bisulfite sequencing, demethylation rescue, and promoter-reporter mutagenesis in HCC cells\",\n      \"pmids\": [\"21281797\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not identify the methyltransferase responsible\", \"Functional consequence of CPS1 loss for HCC biology not addressed here\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"To explain how patient mutations cause enzyme failure, recombinant CPS1 reconstitution mapped nine clinical mutations onto solubility, stability, and NAG-affinity defects, validating the C-terminal NAG allosteric site structurally.\",\n      \"evidence\": \"Baculovirus/insect-cell expression, kinetics, and structure-function analysis using the C-terminal domain crystal structure\",\n      \"pmids\": [\"20578160\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Covers only a subset of clinical mutations\", \"No full-length structure available\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrating that recombinant human CPS1 reproduces native kinetics, and that NAG/NCG plus MgATP protect it from inactivation, established a faithful in vitro system and revealed an activator-linked stabilizing/chaperone effect.\",\n      \"evidence\": \"Recombinant expression, enzymatic kinetics, thermal stability, and site-limited proteolysis\",\n      \"pmids\": [\"23649895\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stabilizing mechanism inferred from proteolysis/thermal assays, not structurally resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Systematic reconstitution of clinical mutations resolved the dominant disease mechanism—misfolding via disrupted interdomain contacts in the central Integrating Domain, and catalytic abolition by residues near the carbamate tunnel.\",\n      \"evidence\": \"Recombinant expression of 18 mutants (Integrating Domain) and partial-reaction assays of the V1013del founder mutation, with structural modelling\",\n      \"pmids\": [\"24813853\", \"25410056\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural modelling rather than experimental full-length structure\", \"Genotype-phenotype correlation in patients not directly tested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"To explain divergent clinical NCG responses, kinetic competition assays showed NCG sub-optimally activates CPS1 and competes with NAG, helping mutants lacking NAG occupancy but harming mutants with scarce functional enzyme.\",\n      \"evidence\": \"Purified recombinant wild-type and mutant CPS1 competition kinetics and stability assays\",\n      \"pmids\": [\"28007335\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Performed on mouse CPS1\", \"In vitro kinetics do not capture full in vivo pharmacology\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"It was assumed CPS1 functions only in ammonia detoxification; showing that KRAS/LKB1-mutant lung cancer cells use CPS1 to channel nitrogen into pyrimidines redefined it as a biosynthetic enzyme whose loss causes replication stress.\",\n      \"evidence\": \"siRNA silencing, metabolomics, isotope tracing, and pyrimidine rescue in KL cell lines, xenografts, and patient tumors\",\n      \"pmids\": [\"28538732\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of carbamoyl phosphate transfer to cytoplasmic pyrimidine synthesis not biochemically defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The discovery that secreted CPS1 induces M2 monocyte polarization and protects against liver injury independent of enzymatic activity revealed an unexpected extracellular, non-catalytic function.\",\n      \"evidence\": \"Bile/blood proteomics, recombinant CPS1 administration, macrophage-depletion, and APAP/FasL injury models in mice\",\n      \"pmids\": [\"30979808\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor/uptake mechanism on monocytes not identified\", \"Secretion route from hepatocytes not defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identifying a druggable allosteric pocket and a CPS1-selective inhibitor (H3B-120) that blocks ATP hydrolysis established that CPS1 enzymatic output is pharmacologically targetable in both urea and pyrimidine pathways.\",\n      \"evidence\": \"In vitro enzymatic assays, structure-based drug design, cellular pathway assays, and CPS2 counterscreening\",\n      \"pmids\": [\"32017919\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Pocket location relative to catalytic domains described biochemically but not in a full-length co-structure\", \"In vivo efficacy not the focus\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolving how nutrient state tunes ureagenesis, two studies showed O-GlcNAcylation on specific threonines as a regulatory switch—enhancing ammonia catalysis in one context and acting as an aging/high-glucose-driven nutrient sensor that limits activity in another.\",\n      \"evidence\": \"MS site-mapping, enzyme kinetics, OGT liver knockout, OGA inhibition, and dietary interventions in mouse disease models\",\n      \"pmids\": [\"36064721\", \"35285892\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The two studies report opposite directional effects of O-GlcNAcylation, leaving the integrated physiological output unresolved\", \"Responsible OGT/OGA dynamics on specific sites not fully reconciled\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linking inflammatory cell death to ammonia toxicity, GSDME-driven ISG15 loss was shown to deISGylate CPS1 and route it to K48-ubiquitin degradation, identifying a stability-control axis that fails in acute liver injury.\",\n      \"evidence\": \"GSDME knockout/rescue mice, ISG15 loss-of-function, K48-ubiquitination pulldown/MS, and APAP injury model\",\n      \"pmids\": [\"38417117\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 ligase mediating K48 ubiquitination not identified\", \"ISGylation site(s) on CPS1 not mapped\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A second epigenetic repressor of CPS1 was identified: JMJD1C reduces H3K36me3 at the CPS1 locus to silence it in PNH clones, with knockdown restoring CPS1 and impairing clone proliferation.\",\n      \"evidence\": \"ChIP for H3K36me3, JMJD1C knockdown, and proliferation/apoptosis assays in PIG-A knockout cells and PNH model\",\n      \"pmids\": [\"38650379\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct enzymatic link between JMJD1C and H3K36me3 at CPS1 inferential\", \"Relevance beyond PNH not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Beyond catalysis, CPS1 was shown to drive metabolic-signaling programs—fumarate-mediated TET2 inhibition driving miR-200a-linked EMT and metastasis, and a CaMKII/FOXO1 axis controlling glucagon-induced gluconeogenesis—plus circRNA-mediated regulation of its activity in fatty liver and an mTORC1-activating arginine route in ovarian follicle activation.\",\n      \"evidence\": \"Knockdown/overexpression, omics, metabolomics, TET2 activity and pathway readouts across lung cancer, hepatocyte, MAFLD, and ovarian tissue models\",\n      \"pmids\": [\"41356199\", \"39193349\", \"41224057\", \"42111264\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Each axis is from a single lab and awaits independent replication\", \"How mitochondrial CPS1 metabolites couple to cytoplasmic/nuclear signaling not biochemically resolved\", \"circRNA-protein interaction mechanism unusual and unconfirmed elsewhere\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Acetylation at K1168 was added to the CPS1 PTM map, shown to impair ATP binding and reduce activity, complementing the activating O-GlcNAcylation switch.\",\n      \"evidence\": \"Quantitative acetylomics, K1168R/K1168Kac mutagenesis, ATP-binding and activity assays, and in silico docking under PFOA/PFO4DA exposure\",\n      \"pmids\": [\"41720236\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Deacetylase/acetyltransferase regulating K1168 not identified\", \"Physiological occupancy of K1168 acetylation unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CPS1's diverse non-canonical functions (extracellular immunomodulation, fumarate/arginine-driven signaling, pyrimidine supply) are coordinated with its mitochondrial catalytic role, and what receptors, ligases, and partner proteins mediate them, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unifying model linking enzymatic and non-enzymatic roles\", \"Monocyte receptor for secreted CPS1 unidentified\", \"E3 ligase and deacetylase regulating CPS1 stability/PTMs unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [6, 9]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [2, 9, 18]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [6, 9]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [6, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [22]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 6, 13]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [11, 1]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"AGMAT\", \"ISG15\", \"KRT1\", \"ALB\", \"UBC\", \"circSETD2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}