{"gene":"PCYT1A","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":2018,"finding":"PCYT1A (CCTα), the rate-limiting enzyme of PC synthesis, is intranuclear under basal conditions and re-locates to the inner nuclear membrane in response to membrane phospholipid packing defects (stored curvature elastic stress), a mechanism conserved in yeast, fly, and mammalian cells. Nuclear localization signal mutants can compensate for loss of endogenous PCYT1A in yeast and fly photoreceptors.","method":"Live-cell imaging, lipidomic analysis, data-driven modeling, nuclear localization signal mutagenesis, genetic rescue experiments in yeast and Drosophila","journal":"Developmental Cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (imaging, lipidomics, modeling, mutagenesis) across three model systems (yeast, fly, mammalian cells) in a single study with functional validation","pmids":["29754800"],"is_preprint":false},{"year":2005,"finding":"CCTα (encoded by Pcyt1a) catalyzes the rate-controlling step in CDP-choline pathway PC biosynthesis; Pcyt1a-/- knockout mice fail to form blastocysts and die by embryonic day 3.5, demonstrating that CCTα is essential for early embryonic development. Heterozygous mice show reduced lung PtdCho mass but no change in liver PtdCho, and CCTbeta is not upregulated to compensate in adult tissues.","method":"Cre-lox conditional gene deletion, in situ hybridization, enzymatic activity assays, real-time PCR, radiolabeled choline incorporation into isolated hepatocytes, phospholipid mass measurements","journal":"Molecular and Cellular Biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — complete genetic knockout with multiple orthogonal biochemical readouts in a rigorous mouse model study","pmids":["15798219"],"is_preprint":false},{"year":1997,"finding":"The murine PCYT1A (Ctpct) gene spans ~26 kb and comprises 9 exons whose boundaries align with distinct functional protein domains: exon 2 encodes the nuclear localization signal, exons 4–7 the catalytic domain, exon 8 the α-helical membrane-binding domain, and exon 9 the C-terminal phosphorylation domain. Two transcriptional start sites were identified 35 nt apart; the promoter lacks TATA/CAAT boxes and contains GC-rich regions with Sp1, AP1, AP2, AP3, Y1, and TFIIIA binding sites in two clusters.","method":"Genomic cloning and sequencing, 5'-RACE PCR, exon-intron mapping, promoter analysis","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — complete structural characterization of gene with direct experimental mapping of functional domains to exon boundaries","pmids":["9148929"],"is_preprint":false},{"year":1999,"finding":"Transcription of the murine PCYT1A (Ctpct) gene is regulated by Sp1, AP1, and an unknown transcription factor binding to positive regulatory elements between -130 and -52 bp and basal elements between -52 and +38 bp upstream of the transcription start site.","method":"Promoter deletion constructs linked to luciferase reporter, transient transfection, DNase I protection assays, electromobility-shift assays (EMSA), co-transfection in Sp1-deficient Drosophila cells","journal":"Biochimica et Biophysica Acta","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal methods (reporter assays, DNase I footprinting, EMSA, Sp1-deficient cell rescue) in a single study","pmids":["10216289"],"is_preprint":false},{"year":2009,"finding":"CCTα nuclear import in lung epithelia is triggered by extracellular Ca2+ and requires binding to 14-3-3ζ. Helix G of 14-3-3ζ interacts with a phosphoserine motif in the CCTα C-terminal domain (residues 328–343). 14-3-3ζ is both sufficient and required for CCTα nuclear import and for maintaining phosphatidylcholine synthesis and cell viability during Pseudomonas aeruginosa infection.","method":"Co-immunoprecipitation, siRNA knockdown, overexpression, nuclear fractionation, Ca2+ manipulation, cell viability assays, infection model","journal":"FASEB Journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal binding, functional rescue, and loss-of-function data converge on the same mechanistic conclusion in a single study","pmids":["20007511"],"is_preprint":false},{"year":2011,"finding":"CCTα and nuclear lamins cooperate to form an intranuclear membrane network (nucleoplasmic reticulum, NR); lipid activation of CCTα drives its translocation to the nuclear envelope and NR expansion by membrane deformation. However, depletion of lamin A/C or lamin B1 alone had no effect on PC synthesis, and overall nuclear envelope structure has minimal impact on CCT activity and PC synthesis. In HGPS fibroblasts, CCTα mislocalized to the cytoplasm/nuclear envelope with a 2-fold reduction in PC synthesis attributable to reduced choline transporter activity rather than CCTα activity itself.","method":"RNAi silencing of lamins, expression of progerin (HGPS mutant lamin A), CCTα localization imaging, choline radiolabeling, subcellular fractionation","journal":"Biochimica et Biophysica Acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple methods (RNAi, imaging, metabolic labeling) in a single lab; some findings are negative (lamin depletion does not affect PC synthesis)","pmids":["21504799"],"is_preprint":false},{"year":2005,"finding":"Farnesol (FOH) and oleyl alcohol first transiently activate CCTα and PtdCho synthesis (accompanied by DAG depletion), then promote caspase-mediated cleavage and nuclear export of CCTα leading to PtdCho synthesis inhibition and apoptosis. Stable overexpression of CCTα confers partial resistance to FOH-induced apoptosis; restoration of PtdCho synthesis by oleate or DiC8 also protects.","method":"Radioactive PtdCho synthesis assays, caspase inhibitors, CCTα overexpression in MT58 cells, DAG mass measurements, nuclear export imaging","journal":"Biochemical Journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal biochemical and cell-biological methods in a single lab study","pmids":["16097951"],"is_preprint":false},{"year":2015,"finding":"Palmitate-induced cisternal ER expansion in RAW 264.7 macrophages depends on XBP-1-driven upregulation of CCTα mRNA expression, leading to increased phospholipid synthesis and ER membrane expansion. Downregulation of XBP-1 or CCTα attenuates palmitate-induced phospholipid accumulation and ER expansion.","method":"siRNA knockdown of XBP-1 and CCTα, ER stress inhibitors (4-PBA, TUDCA), transmission electron microscopy, RT-PCR, phospholipid staining","journal":"Lipids in Health and Disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with structural and molecular readouts, single lab, multiple orthogonal approaches","pmids":["26174230"],"is_preprint":false},{"year":2020,"finding":"Nuclear lipid droplets (nLDs) form on the inner nuclear membrane via PML-containing lipid-associated PML structures (LAPS). CCTα is recruited to nLDs via its α-helical M-domain (not correlated with its activator DAG). PML knockout reduces nLDs with associated CCTα by 40–50%, inhibits Lipin1 and DAG recruitment, and reduces phosphatidylcholine and triacylglycerol synthesis.","method":"PML knockout cells, high-resolution immunofluorescence imaging, lipid mass measurements, domain mutant overexpression","journal":"Life Science Alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout with functional lipid metabolic readout and imaging, single lab study","pmids":["32461215"],"is_preprint":false},{"year":2014,"finding":"Homozygous loss-of-function mutations in PCYT1A, encoding the enzyme that converts phosphocholine to CDP-choline in the phosphatidylcholine biosynthesis pathway, cause spondylometaphyseal dysplasia with cone-rod dystrophy (SMD-CRD) in humans, establishing PCYT1A enzymatic activity as essential for normal skeletal and retinal development.","method":"Whole-exome sequencing, clinical phenotyping of affected individuals from two Brazilian families, identification of two homozygous PCYT1A mutations","journal":"American Journal of Human Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human genetics linking specific loss-of-function mutations to defined pathology, single study with two independent families","pmids":["24387991"],"is_preprint":false},{"year":2017,"finding":"Mutations in PCYT1A can cause isolated retinal dystrophy without skeletal or metabolic involvement, expanding the phenotypic spectrum of PCYT1A loss-of-function beyond SMD-CRD and lipodystrophy.","method":"Next-generation sequencing, clinical evaluation (whole-skeleton X-ray, metabolic assessment, liver ultrasound) of three patients from two Italian families","journal":"European Journal of Human Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human genetics with careful clinical exclusion of alternative phenotypes, two independent families, single lab","pmids":["28272537"],"is_preprint":false},{"year":2018,"finding":"Disease-linked missense mutations in the PCYT1A catalytic domain (e.g., V142M, P150A) produce aggregated, non-refolding enzymes; other catalytic domain mutations destabilize folding (lower unfolding transition temperatures) and impair substrate Km values. A linker mutation (R223S) impairs enzyme kinetics. A single-amino-acid deletion in the autoinhibitory helix (E280del) increases constitutive (lipid-independent) activity ~4-fold and enhances the response to anionic lipid vesicles ~4-fold.","method":"Expression of WT and mutant CCTs in COS-1 cells, protein purification, denaturation/refolding assays, differential scanning fluorimetry (Tm measurements), enzyme kinetics, lipid activation assays with anionic vesicles","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assays with mutagenesis and biophysical stability measurements, multiple variants characterized","pmids":["30559292"],"is_preprint":false},{"year":2020,"finding":"PCYT1A knockdown in lung adenocarcinoma cells enhances cell proliferation and migration by activating mTORC1 signaling; these effects are abolished by rapamycin treatment or RAPTOR depletion, placing PCYT1A upstream as a negative regulator of mTORC1.","method":"siRNA knockdown, rapamycin treatment, RAPTOR depletion, cell proliferation and migration assays, Western blotting for mTORC1 pathway components","journal":"Biochemical and Biophysical Research Communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis established by pharmacological and genetic inhibition of mTORC1 rescuing the PCYT1A-KD phenotype, single lab","pmids":["32703435"],"is_preprint":false},{"year":1993,"finding":"The murine CTP:phosphocholine cytidylyltransferase gene (Ctpct/PCYT1A) is located on mouse chromosome 16 between the Smst and Stf-1 genes.","method":"Southern blot hybridization of interspecific backcross progeny DNA, genomic cloning and sequencing of murine cDNA","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct experimental chromosomal mapping, single study","pmids":["8307580"],"is_preprint":false},{"year":2024,"finding":"In cancer-associated fibroblasts (CAFs), FAK inhibitor treatment elevates intracellular Ca2+, promoting formation of an AKT2/CCTα complex, leading to phosphorylation of CCTα at Ser315/319/323 by AKT2, which enhances stromal phosphatidylcholine (PC) production; secreted PCs then activate the JAK2/STAT3 pathway in tumor cells, mediating FAK inhibitor resistance in esophageal squamous cell carcinoma.","method":"Phosphoproteomics, untargeted metabolomics/lipidomics, co-immunoprecipitation of AKT2/CCTα complex, Ca2+ manipulation, FAK inhibitor treatment, JAK2/STAT3 pathway analysis, clinical sample validation","journal":"Signal Transduction and Targeted Therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multi-omics plus co-IP and functional rescue, single lab, multiple orthogonal methods","pmids":["38280862"],"is_preprint":false},{"year":2006,"finding":"A SNP in PCYT1A (rs939883 genotype AA) is associated with approximately 2-fold increased risk of spina bifida in a California population, suggesting that PCYT1A function in choline/phosphatidylcholine metabolism may influence neural tube closure.","method":"Fluorescence-based allelic discrimination (SNP genotyping) in 103 spina bifida cases and 338 controls","journal":"BMC Medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single genotyping study, no mechanistic experiment on the protein itself, association only","pmids":["17184542"],"is_preprint":false}],"current_model":"PCYT1A encodes CCTα, the rate-limiting enzyme of the CDP-choline pathway for phosphatidylcholine (PC) biosynthesis; the protein is normally nucleoplasmic and translocates to the inner nuclear membrane in response to membrane phospholipid packing defects (stored curvature elastic stress), a conserved mechanism across yeast, fly, and mammals, where its α-helical M-domain mediates lipid-dependent membrane binding and activation, its nuclear import is regulated by Ca2+-triggered 14-3-3ζ binding to a C-terminal phosphoserine motif, its autoinhibitory helix suppresses constitutive activity, disease-linked catalytic domain mutations destabilize folding and impair kinetics, and its activity is coupled to mTORC1 suppression and to AKT2-mediated phosphorylation at Ser315/319/323 in fibroblasts, with complete loss-of-function causing early embryonic lethality in mice and, in humans, spondylometaphyseal dysplasia with cone-rod dystrophy, isolated retinal dystrophy, or lipodystrophy depending on the specific mutation."},"narrative":{"mechanistic_narrative":"PCYT1A encodes CCTα, the rate-limiting enzyme of the CDP-choline pathway that converts phosphocholine to CDP-choline for phosphatidylcholine (PC) biosynthesis, and is essential for early development—complete loss in mice prevents blastocyst formation and causes embryonic lethality by E3.5 [PMID:15798219]. The enzyme is amphitropic: it resides in the nucleoplasm under basal conditions and translocates to the inner nuclear membrane in response to membrane phospholipid packing defects (stored curvature elastic stress), a mechanism conserved across yeast, fly, and mammalian cells, with its α-helical M-domain mediating lipid-dependent membrane binding [PMID:29754800, PMID:32461215]. This membrane-sensing activity couples CCTα to membrane biogenesis programs, including expansion of the nucleoplasmic reticulum together with nuclear lamins [PMID:21504799], recruitment to PML-dependent nuclear lipid droplets via the M-domain [PMID:32461215], and XBP-1-driven ER membrane expansion under lipid stress [PMID:26174230]. Its localization and activity are tightly regulated: Ca2+-triggered binding of 14-3-3ζ to a C-terminal phosphoserine motif drives nuclear import and sustains PC synthesis and cell viability during infection [PMID:20007511], an autoinhibitory helix suppresses constitutive lipid-independent activity [PMID:30559292], and the enzyme acts as a negative regulator of mTORC1 signaling [PMID:32703435]. In disease, homozygous loss-of-function mutations cause spondylometaphyseal dysplasia with cone-rod dystrophy and, depending on the specific allele, isolated retinal dystrophy [PMID:24387991, PMID:28272537]; catalytic-domain missense mutations act by destabilizing folding and impairing kinetics, while an autoinhibitory-helix deletion produces a constitutively hyperactive enzyme [PMID:30559292].","teleology":[{"year":1993,"claim":"Establishing the chromosomal location of the murine gene provided the genomic foundation for subsequent structural and functional dissection of CCTα.","evidence":"interspecific backcross Southern blot mapping and cDNA cloning in mouse","pmids":["8307580"],"confidence":"Medium","gaps":["No protein function or regulation addressed","Human locus not mapped here"]},{"year":1997,"claim":"Resolving the gene's exon-intron architecture revealed that functional protein modules map cleanly to distinct exons, framing CCTα as a multi-domain enzyme with separable localization, catalytic, membrane-binding, and phosphorylation functions.","evidence":"genomic cloning, 5'-RACE, exon-intron mapping and promoter analysis of murine Ctpct","pmids":["9148929"],"confidence":"High","gaps":["Domain functions inferred from exon boundaries, not yet tested biochemically","Promoter element function not yet validated"]},{"year":1999,"claim":"Identifying Sp1/AP1-dependent promoter elements answered how PCYT1A transcription is driven, linking enzyme abundance to defined regulatory regions.","evidence":"promoter deletion-luciferase reporters, DNase I footprinting, EMSA, and Sp1-deficient Drosophila cell rescue","pmids":["10216289"],"confidence":"High","gaps":["Physiological signals controlling these factors not defined","An unidentified transcription factor remains uncharacterized"]},{"year":2005,"claim":"Genetic knockout settled whether CCTα is dispensable, showing it is absolutely required for early embryogenesis and that the β isoform does not compensate in adult tissues.","evidence":"Cre-lox deletion in mice with enzymatic, radiolabeling, and phospholipid mass readouts","pmids":["15798219"],"confidence":"High","gaps":["Tissue-specific requirements beyond lung not dissected","Mechanism of lethality (which PC-dependent process fails first) not resolved"]},{"year":2005,"claim":"Lipid-mediator experiments connected CCTα activity to cell-fate decisions, showing biphasic activation then caspase cleavage/nuclear export drives apoptosis.","evidence":"PtdCho synthesis assays, caspase inhibitors, CCTα overexpression and DAG measurements in MT58 cells","pmids":["16097951"],"confidence":"Medium","gaps":["Caspase cleavage site and in vivo relevance not established","Link between PC synthesis and apoptosis execution remains correlative"]},{"year":2009,"claim":"Identifying Ca2+-triggered 14-3-3ζ binding to a C-terminal phosphoserine motif answered how CCTα nuclear import is signal-regulated and tied it to survival during bacterial infection.","evidence":"Co-IP, siRNA, overexpression, nuclear fractionation and infection-model viability assays in lung epithelia","pmids":["20007511"],"confidence":"High","gaps":["Kinase generating the phosphoserine motif not identified here","Generality beyond lung epithelia untested"]},{"year":2011,"claim":"Testing the role of nuclear architecture clarified that CCTα drives intranuclear membrane (nucleoplasmic reticulum) expansion via membrane deformation, while bulk nuclear envelope structure has minimal impact on its activity.","evidence":"lamin RNAi, progerin expression, CCTα imaging and choline radiolabeling in fibroblasts","pmids":["21504799"],"confidence":"Medium","gaps":["Several negative results (lamin depletion did not change PC synthesis)","HGPS PC deficit attributed to choline transport, not CCTα itself"]},{"year":2014,"claim":"Human genetics established PCYT1A as a disease gene, linking loss-of-function mutations causally to spondylometaphyseal dysplasia with cone-rod dystrophy and demonstrating PC synthesis is essential for skeletal and retinal development.","evidence":"whole-exome sequencing and phenotyping of two Brazilian families","pmids":["24387991"],"confidence":"Medium","gaps":["Tissue-specific basis for skeletal/retinal vulnerability unexplained","Genotype-phenotype mechanism not yet biochemically dissected"]},{"year":2015,"claim":"Linking XBP-1 to CCTα upregulation answered how lipid-stress signaling expands the ER, positioning CCTα as an effector of membrane biogenesis under saturated-fat load.","evidence":"siRNA of XBP-1/CCTα, ER stress inhibitors, TEM and phospholipid staining in macrophages","pmids":["26174230"],"confidence":"Medium","gaps":["Direct transcriptional control of PCYT1A by XBP-1 not proven","In vivo significance not addressed"]},{"year":2017,"claim":"Identifying patients with isolated retinal dystrophy expanded the PCYT1A phenotypic spectrum, showing mutation-dependent variability in which tissues are affected.","evidence":"next-generation sequencing with skeletal and metabolic exclusion in two Italian families","pmids":["28272537"],"confidence":"Medium","gaps":["Molecular basis for phenotypic restriction to retina unknown","Small patient number"]},{"year":2018,"claim":"Combining structural and biochemical analysis explained disease mechanism at the protein level: catalytic-domain mutations destabilize folding/kinetics while an autoinhibitory-helix deletion causes constitutive hyperactivation.","evidence":"expression of WT/mutant CCTs, purification, DSF Tm measurements, kinetics and anionic-vesicle activation assays","pmids":["30559292"],"confidence":"High","gaps":["No full-length structure of the activated enzyme","Cellular consequences of hyperactive E280del not tested in vivo"]},{"year":2020,"claim":"Two studies extended CCTα beyond canonical metabolism: it is recruited to PML-dependent nuclear lipid droplets via its M-domain and acts as a negative regulator of mTORC1 in lung cancer cells.","evidence":"PML knockout imaging and lipid mass assays; siRNA knockdown with rapamycin/RAPTOR epistasis in adenocarcinoma cells","pmids":["32461215","32703435"],"confidence":"Medium","gaps":["Molecular link between CCTα/PC and mTORC1 not defined","Whether nLD recruitment and mTORC1 regulation are connected unknown"]},{"year":2024,"claim":"Defining an AKT2/CCTα phosphorylation axis explained how stromal PC production is signal-controlled and drives drug resistance, identifying Ser315/319/323 as AKT2 targets that boost secreted PC and JAK2/STAT3 signaling.","evidence":"phosphoproteomics, lipidomics, AKT2/CCTα co-IP, Ca2+ manipulation and FAK-inhibitor treatment in cancer-associated fibroblasts","pmids":["38280862"],"confidence":"Medium","gaps":["Direct demonstration that phosphorylation activates catalysis not isolated from localization","Generality beyond esophageal squamous carcinoma untested"]},{"year":null,"claim":"How specific PCYT1A alleles produce tissue-restricted disease (skeletal vs retinal vs lipodystrophy) and how CCTα activity is mechanistically coupled to mTORC1 remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No molecular explanation for genotype-tissue specificity","Biochemical link from PC synthesis to mTORC1 suppression undefined","No high-resolution structure of the membrane-activated full-length enzyme"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,9,11]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,8,11]}],"localization":[{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[0,5]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[0,4]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[7]},{"term_id":"GO:0005811","term_label":"lipid droplet","supporting_discovery_ids":[8]}],"pathway":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[1]}],"complexes":[],"partners":["YWHAZ","AKT2","PML"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P49585","full_name":"Choline-phosphate cytidylyltransferase A","aliases":["CCT-alpha","CTP:phosphocholine cytidylyltransferase A","CCT A","CT A","Phosphorylcholine transferase A"],"length_aa":367,"mass_kda":41.7,"function":"Catalyzes the key rate-limiting step in the CDP-choline pathway for phosphatidylcholine biosynthesis","subcellular_location":"Cytoplasm, cytosol; Membrane; Endoplasmic reticulum membrane; Nucleus","url":"https://www.uniprot.org/uniprotkb/P49585/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PCYT1A","classification":"Not Classified","n_dependent_lines":656,"n_total_lines":1208,"dependency_fraction":0.543046357615894},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PCYT1A","total_profiled":1310},"omim":[{"mim_id":"620680","title":"LIPODYSTROPHY, CONGENITAL GENERALIZED, TYPE 5; CGL5","url":"https://www.omim.org/entry/620680"},{"mim_id":"608940","title":"SPONDYLOMETAPHYSEAL DYSPLASIA WITH CONE-ROD DYSTROPHY; SMDCRD","url":"https://www.omim.org/entry/608940"},{"mim_id":"608594","title":"LIPODYSTROPHY, CONGENITAL GENERALIZED, TYPE 1; CGL1","url":"https://www.omim.org/entry/608594"},{"mim_id":"300948","title":"PHOSPHATE CYTIDYLYLTRANSFERASE 1, CHOLINE, BETA ISOFORM; PCYT1B","url":"https://www.omim.org/entry/300948"},{"mim_id":"123695","title":"PHOSPHATE CYTIDYLYLTRANSFERASE 1, CHOLINE, ALPHA ISOFORM; PCYT1A","url":"https://www.omim.org/entry/123695"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PCYT1A"},"hgnc":{"alias_symbol":["CT","CTPCT","CCTalpha"],"prev_symbol":["PCYT1"]},"alphafold":{"accession":"P49585","domains":[{"cath_id":"3.40.50.620","chopping":"47-199","consensus_level":"high","plddt":95.7628,"start":47,"end":199}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P49585","model_url":"https://alphafold.ebi.ac.uk/files/AF-P49585-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P49585-F1-predicted_aligned_error_v6.png","plddt_mean":76.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PCYT1A","jax_strain_url":"https://www.jax.org/strain/search?query=PCYT1A"},"sequence":{"accession":"P49585","fasta_url":"https://rest.uniprot.org/uniprotkb/P49585.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P49585/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P49585"}},"corpus_meta":[{"pmid":"19719775","id":"PMC_19719775","title":"Cancer/testis 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Nuclear localization signal mutants can compensate for loss of endogenous PCYT1A in yeast and fly photoreceptors.\",\n      \"method\": \"Live-cell imaging, lipidomic analysis, data-driven modeling, nuclear localization signal mutagenesis, genetic rescue experiments in yeast and Drosophila\",\n      \"journal\": \"Developmental Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (imaging, lipidomics, modeling, mutagenesis) across three model systems (yeast, fly, mammalian cells) in a single study with functional validation\",\n      \"pmids\": [\"29754800\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CCTα (encoded by Pcyt1a) catalyzes the rate-controlling step in CDP-choline pathway PC biosynthesis; Pcyt1a-/- knockout mice fail to form blastocysts and die by embryonic day 3.5, demonstrating that CCTα is essential for early embryonic development. Heterozygous mice show reduced lung PtdCho mass but no change in liver PtdCho, and CCTbeta is not upregulated to compensate in adult tissues.\",\n      \"method\": \"Cre-lox conditional gene deletion, in situ hybridization, enzymatic activity assays, real-time PCR, radiolabeled choline incorporation into isolated hepatocytes, phospholipid mass measurements\",\n      \"journal\": \"Molecular and Cellular Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — complete genetic knockout with multiple orthogonal biochemical readouts in a rigorous mouse model study\",\n      \"pmids\": [\"15798219\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The murine PCYT1A (Ctpct) gene spans ~26 kb and comprises 9 exons whose boundaries align with distinct functional protein domains: exon 2 encodes the nuclear localization signal, exons 4–7 the catalytic domain, exon 8 the α-helical membrane-binding domain, and exon 9 the C-terminal phosphorylation domain. Two transcriptional start sites were identified 35 nt apart; the promoter lacks TATA/CAAT boxes and contains GC-rich regions with Sp1, AP1, AP2, AP3, Y1, and TFIIIA binding sites in two clusters.\",\n      \"method\": \"Genomic cloning and sequencing, 5'-RACE PCR, exon-intron mapping, promoter analysis\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — complete structural characterization of gene with direct experimental mapping of functional domains to exon boundaries\",\n      \"pmids\": [\"9148929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Transcription of the murine PCYT1A (Ctpct) gene is regulated by Sp1, AP1, and an unknown transcription factor binding to positive regulatory elements between -130 and -52 bp and basal elements between -52 and +38 bp upstream of the transcription start site.\",\n      \"method\": \"Promoter deletion constructs linked to luciferase reporter, transient transfection, DNase I protection assays, electromobility-shift assays (EMSA), co-transfection in Sp1-deficient Drosophila cells\",\n      \"journal\": \"Biochimica et Biophysica Acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal methods (reporter assays, DNase I footprinting, EMSA, Sp1-deficient cell rescue) in a single study\",\n      \"pmids\": [\"10216289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CCTα nuclear import in lung epithelia is triggered by extracellular Ca2+ and requires binding to 14-3-3ζ. Helix G of 14-3-3ζ interacts with a phosphoserine motif in the CCTα C-terminal domain (residues 328–343). 14-3-3ζ is both sufficient and required for CCTα nuclear import and for maintaining phosphatidylcholine synthesis and cell viability during Pseudomonas aeruginosa infection.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, overexpression, nuclear fractionation, Ca2+ manipulation, cell viability assays, infection model\",\n      \"journal\": \"FASEB Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal binding, functional rescue, and loss-of-function data converge on the same mechanistic conclusion in a single study\",\n      \"pmids\": [\"20007511\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CCTα and nuclear lamins cooperate to form an intranuclear membrane network (nucleoplasmic reticulum, NR); lipid activation of CCTα drives its translocation to the nuclear envelope and NR expansion by membrane deformation. However, depletion of lamin A/C or lamin B1 alone had no effect on PC synthesis, and overall nuclear envelope structure has minimal impact on CCT activity and PC synthesis. In HGPS fibroblasts, CCTα mislocalized to the cytoplasm/nuclear envelope with a 2-fold reduction in PC synthesis attributable to reduced choline transporter activity rather than CCTα activity itself.\",\n      \"method\": \"RNAi silencing of lamins, expression of progerin (HGPS mutant lamin A), CCTα localization imaging, choline radiolabeling, subcellular fractionation\",\n      \"journal\": \"Biochimica et Biophysica Acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple methods (RNAi, imaging, metabolic labeling) in a single lab; some findings are negative (lamin depletion does not affect PC synthesis)\",\n      \"pmids\": [\"21504799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Farnesol (FOH) and oleyl alcohol first transiently activate CCTα and PtdCho synthesis (accompanied by DAG depletion), then promote caspase-mediated cleavage and nuclear export of CCTα leading to PtdCho synthesis inhibition and apoptosis. Stable overexpression of CCTα confers partial resistance to FOH-induced apoptosis; restoration of PtdCho synthesis by oleate or DiC8 also protects.\",\n      \"method\": \"Radioactive PtdCho synthesis assays, caspase inhibitors, CCTα overexpression in MT58 cells, DAG mass measurements, nuclear export imaging\",\n      \"journal\": \"Biochemical Journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal biochemical and cell-biological methods in a single lab study\",\n      \"pmids\": [\"16097951\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Palmitate-induced cisternal ER expansion in RAW 264.7 macrophages depends on XBP-1-driven upregulation of CCTα mRNA expression, leading to increased phospholipid synthesis and ER membrane expansion. Downregulation of XBP-1 or CCTα attenuates palmitate-induced phospholipid accumulation and ER expansion.\",\n      \"method\": \"siRNA knockdown of XBP-1 and CCTα, ER stress inhibitors (4-PBA, TUDCA), transmission electron microscopy, RT-PCR, phospholipid staining\",\n      \"journal\": \"Lipids in Health and Disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with structural and molecular readouts, single lab, multiple orthogonal approaches\",\n      \"pmids\": [\"26174230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Nuclear lipid droplets (nLDs) form on the inner nuclear membrane via PML-containing lipid-associated PML structures (LAPS). CCTα is recruited to nLDs via its α-helical M-domain (not correlated with its activator DAG). PML knockout reduces nLDs with associated CCTα by 40–50%, inhibits Lipin1 and DAG recruitment, and reduces phosphatidylcholine and triacylglycerol synthesis.\",\n      \"method\": \"PML knockout cells, high-resolution immunofluorescence imaging, lipid mass measurements, domain mutant overexpression\",\n      \"journal\": \"Life Science Alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout with functional lipid metabolic readout and imaging, single lab study\",\n      \"pmids\": [\"32461215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Homozygous loss-of-function mutations in PCYT1A, encoding the enzyme that converts phosphocholine to CDP-choline in the phosphatidylcholine biosynthesis pathway, cause spondylometaphyseal dysplasia with cone-rod dystrophy (SMD-CRD) in humans, establishing PCYT1A enzymatic activity as essential for normal skeletal and retinal development.\",\n      \"method\": \"Whole-exome sequencing, clinical phenotyping of affected individuals from two Brazilian families, identification of two homozygous PCYT1A mutations\",\n      \"journal\": \"American Journal of Human Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human genetics linking specific loss-of-function mutations to defined pathology, single study with two independent families\",\n      \"pmids\": [\"24387991\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Mutations in PCYT1A can cause isolated retinal dystrophy without skeletal or metabolic involvement, expanding the phenotypic spectrum of PCYT1A loss-of-function beyond SMD-CRD and lipodystrophy.\",\n      \"method\": \"Next-generation sequencing, clinical evaluation (whole-skeleton X-ray, metabolic assessment, liver ultrasound) of three patients from two Italian families\",\n      \"journal\": \"European Journal of Human Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human genetics with careful clinical exclusion of alternative phenotypes, two independent families, single lab\",\n      \"pmids\": [\"28272537\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Disease-linked missense mutations in the PCYT1A catalytic domain (e.g., V142M, P150A) produce aggregated, non-refolding enzymes; other catalytic domain mutations destabilize folding (lower unfolding transition temperatures) and impair substrate Km values. A linker mutation (R223S) impairs enzyme kinetics. A single-amino-acid deletion in the autoinhibitory helix (E280del) increases constitutive (lipid-independent) activity ~4-fold and enhances the response to anionic lipid vesicles ~4-fold.\",\n      \"method\": \"Expression of WT and mutant CCTs in COS-1 cells, protein purification, denaturation/refolding assays, differential scanning fluorimetry (Tm measurements), enzyme kinetics, lipid activation assays with anionic vesicles\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assays with mutagenesis and biophysical stability measurements, multiple variants characterized\",\n      \"pmids\": [\"30559292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PCYT1A knockdown in lung adenocarcinoma cells enhances cell proliferation and migration by activating mTORC1 signaling; these effects are abolished by rapamycin treatment or RAPTOR depletion, placing PCYT1A upstream as a negative regulator of mTORC1.\",\n      \"method\": \"siRNA knockdown, rapamycin treatment, RAPTOR depletion, cell proliferation and migration assays, Western blotting for mTORC1 pathway components\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis established by pharmacological and genetic inhibition of mTORC1 rescuing the PCYT1A-KD phenotype, single lab\",\n      \"pmids\": [\"32703435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"The murine CTP:phosphocholine cytidylyltransferase gene (Ctpct/PCYT1A) is located on mouse chromosome 16 between the Smst and Stf-1 genes.\",\n      \"method\": \"Southern blot hybridization of interspecific backcross progeny DNA, genomic cloning and sequencing of murine cDNA\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct experimental chromosomal mapping, single study\",\n      \"pmids\": [\"8307580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In cancer-associated fibroblasts (CAFs), FAK inhibitor treatment elevates intracellular Ca2+, promoting formation of an AKT2/CCTα complex, leading to phosphorylation of CCTα at Ser315/319/323 by AKT2, which enhances stromal phosphatidylcholine (PC) production; secreted PCs then activate the JAK2/STAT3 pathway in tumor cells, mediating FAK inhibitor resistance in esophageal squamous cell carcinoma.\",\n      \"method\": \"Phosphoproteomics, untargeted metabolomics/lipidomics, co-immunoprecipitation of AKT2/CCTα complex, Ca2+ manipulation, FAK inhibitor treatment, JAK2/STAT3 pathway analysis, clinical sample validation\",\n      \"journal\": \"Signal Transduction and Targeted Therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multi-omics plus co-IP and functional rescue, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"38280862\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"A SNP in PCYT1A (rs939883 genotype AA) is associated with approximately 2-fold increased risk of spina bifida in a California population, suggesting that PCYT1A function in choline/phosphatidylcholine metabolism may influence neural tube closure.\",\n      \"method\": \"Fluorescence-based allelic discrimination (SNP genotyping) in 103 spina bifida cases and 338 controls\",\n      \"journal\": \"BMC Medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single genotyping study, no mechanistic experiment on the protein itself, association only\",\n      \"pmids\": [\"17184542\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PCYT1A encodes CCTα, the rate-limiting enzyme of the CDP-choline pathway for phosphatidylcholine (PC) biosynthesis; the protein is normally nucleoplasmic and translocates to the inner nuclear membrane in response to membrane phospholipid packing defects (stored curvature elastic stress), a conserved mechanism across yeast, fly, and mammals, where its α-helical M-domain mediates lipid-dependent membrane binding and activation, its nuclear import is regulated by Ca2+-triggered 14-3-3ζ binding to a C-terminal phosphoserine motif, its autoinhibitory helix suppresses constitutive activity, disease-linked catalytic domain mutations destabilize folding and impair kinetics, and its activity is coupled to mTORC1 suppression and to AKT2-mediated phosphorylation at Ser315/319/323 in fibroblasts, with complete loss-of-function causing early embryonic lethality in mice and, in humans, spondylometaphyseal dysplasia with cone-rod dystrophy, isolated retinal dystrophy, or lipodystrophy depending on the specific mutation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PCYT1A encodes CCTα, the rate-limiting enzyme of the CDP-choline pathway that converts phosphocholine to CDP-choline for phosphatidylcholine (PC) biosynthesis, and is essential for early development—complete loss in mice prevents blastocyst formation and causes embryonic lethality by E3.5 [#1]. The enzyme is amphitropic: it resides in the nucleoplasm under basal conditions and translocates to the inner nuclear membrane in response to membrane phospholipid packing defects (stored curvature elastic stress), a mechanism conserved across yeast, fly, and mammalian cells, with its α-helical M-domain mediating lipid-dependent membrane binding [#0, #8]. This membrane-sensing activity couples CCTα to membrane biogenesis programs, including expansion of the nucleoplasmic reticulum together with nuclear lamins [#5], recruitment to PML-dependent nuclear lipid droplets via the M-domain [#8], and XBP-1-driven ER membrane expansion under lipid stress [#7]. Its localization and activity are tightly regulated: Ca2+-triggered binding of 14-3-3ζ to a C-terminal phosphoserine motif drives nuclear import and sustains PC synthesis and cell viability during infection [#4], an autoinhibitory helix suppresses constitutive lipid-independent activity [#11], and the enzyme acts as a negative regulator of mTORC1 signaling [#12]. In disease, homozygous loss-of-function mutations cause spondylometaphyseal dysplasia with cone-rod dystrophy and, depending on the specific allele, isolated retinal dystrophy [#9, #10]; catalytic-domain missense mutations act by destabilizing folding and impairing kinetics, while an autoinhibitory-helix deletion produces a constitutively hyperactive enzyme [#11].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Establishing the chromosomal location of the murine gene provided the genomic foundation for subsequent structural and functional dissection of CCTα.\",\n      \"evidence\": \"interspecific backcross Southern blot mapping and cDNA cloning in mouse\",\n      \"pmids\": [\"8307580\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No protein function or regulation addressed\", \"Human locus not mapped here\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Resolving the gene's exon-intron architecture revealed that functional protein modules map cleanly to distinct exons, framing CCTα as a multi-domain enzyme with separable localization, catalytic, membrane-binding, and phosphorylation functions.\",\n      \"evidence\": \"genomic cloning, 5'-RACE, exon-intron mapping and promoter analysis of murine Ctpct\",\n      \"pmids\": [\"9148929\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Domain functions inferred from exon boundaries, not yet tested biochemically\", \"Promoter element function not yet validated\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identifying Sp1/AP1-dependent promoter elements answered how PCYT1A transcription is driven, linking enzyme abundance to defined regulatory regions.\",\n      \"evidence\": \"promoter deletion-luciferase reporters, DNase I footprinting, EMSA, and Sp1-deficient Drosophila cell rescue\",\n      \"pmids\": [\"10216289\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological signals controlling these factors not defined\", \"An unidentified transcription factor remains uncharacterized\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Genetic knockout settled whether CCTα is dispensable, showing it is absolutely required for early embryogenesis and that the β isoform does not compensate in adult tissues.\",\n      \"evidence\": \"Cre-lox deletion in mice with enzymatic, radiolabeling, and phospholipid mass readouts\",\n      \"pmids\": [\"15798219\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific requirements beyond lung not dissected\", \"Mechanism of lethality (which PC-dependent process fails first) not resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Lipid-mediator experiments connected CCTα activity to cell-fate decisions, showing biphasic activation then caspase cleavage/nuclear export drives apoptosis.\",\n      \"evidence\": \"PtdCho synthesis assays, caspase inhibitors, CCTα overexpression and DAG measurements in MT58 cells\",\n      \"pmids\": [\"16097951\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Caspase cleavage site and in vivo relevance not established\", \"Link between PC synthesis and apoptosis execution remains correlative\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying Ca2+-triggered 14-3-3ζ binding to a C-terminal phosphoserine motif answered how CCTα nuclear import is signal-regulated and tied it to survival during bacterial infection.\",\n      \"evidence\": \"Co-IP, siRNA, overexpression, nuclear fractionation and infection-model viability assays in lung epithelia\",\n      \"pmids\": [\"20007511\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase generating the phosphoserine motif not identified here\", \"Generality beyond lung epithelia untested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Testing the role of nuclear architecture clarified that CCTα drives intranuclear membrane (nucleoplasmic reticulum) expansion via membrane deformation, while bulk nuclear envelope structure has minimal impact on its activity.\",\n      \"evidence\": \"lamin RNAi, progerin expression, CCTα imaging and choline radiolabeling in fibroblasts\",\n      \"pmids\": [\"21504799\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Several negative results (lamin depletion did not change PC synthesis)\", \"HGPS PC deficit attributed to choline transport, not CCTα itself\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Human genetics established PCYT1A as a disease gene, linking loss-of-function mutations causally to spondylometaphyseal dysplasia with cone-rod dystrophy and demonstrating PC synthesis is essential for skeletal and retinal development.\",\n      \"evidence\": \"whole-exome sequencing and phenotyping of two Brazilian families\",\n      \"pmids\": [\"24387991\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Tissue-specific basis for skeletal/retinal vulnerability unexplained\", \"Genotype-phenotype mechanism not yet biochemically dissected\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Linking XBP-1 to CCTα upregulation answered how lipid-stress signaling expands the ER, positioning CCTα as an effector of membrane biogenesis under saturated-fat load.\",\n      \"evidence\": \"siRNA of XBP-1/CCTα, ER stress inhibitors, TEM and phospholipid staining in macrophages\",\n      \"pmids\": [\"26174230\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct transcriptional control of PCYT1A by XBP-1 not proven\", \"In vivo significance not addressed\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identifying patients with isolated retinal dystrophy expanded the PCYT1A phenotypic spectrum, showing mutation-dependent variability in which tissues are affected.\",\n      \"evidence\": \"next-generation sequencing with skeletal and metabolic exclusion in two Italian families\",\n      \"pmids\": [\"28272537\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis for phenotypic restriction to retina unknown\", \"Small patient number\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Combining structural and biochemical analysis explained disease mechanism at the protein level: catalytic-domain mutations destabilize folding/kinetics while an autoinhibitory-helix deletion causes constitutive hyperactivation.\",\n      \"evidence\": \"expression of WT/mutant CCTs, purification, DSF Tm measurements, kinetics and anionic-vesicle activation assays\",\n      \"pmids\": [\"30559292\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length structure of the activated enzyme\", \"Cellular consequences of hyperactive E280del not tested in vivo\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Two studies extended CCTα beyond canonical metabolism: it is recruited to PML-dependent nuclear lipid droplets via its M-domain and acts as a negative regulator of mTORC1 in lung cancer cells.\",\n      \"evidence\": \"PML knockout imaging and lipid mass assays; siRNA knockdown with rapamycin/RAPTOR epistasis in adenocarcinoma cells\",\n      \"pmids\": [\"32461215\", \"32703435\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular link between CCTα/PC and mTORC1 not defined\", \"Whether nLD recruitment and mTORC1 regulation are connected unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defining an AKT2/CCTα phosphorylation axis explained how stromal PC production is signal-controlled and drives drug resistance, identifying Ser315/319/323 as AKT2 targets that boost secreted PC and JAK2/STAT3 signaling.\",\n      \"evidence\": \"phosphoproteomics, lipidomics, AKT2/CCTα co-IP, Ca2+ manipulation and FAK-inhibitor treatment in cancer-associated fibroblasts\",\n      \"pmids\": [\"38280862\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct demonstration that phosphorylation activates catalysis not isolated from localization\", \"Generality beyond esophageal squamous carcinoma untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How specific PCYT1A alleles produce tissue-restricted disease (skeletal vs retinal vs lipodystrophy) and how CCTα activity is mechanistically coupled to mTORC1 remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No molecular explanation for genotype-tissue specificity\", \"Biochemical link from PC synthesis to mTORC1 suppression undefined\", \"No high-resolution structure of the membrane-activated full-length enzyme\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 9, 11]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 8, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"YWHAZ\", \"AKT2\", \"PML\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":5,"faith_total":5,"faith_pct":100.0}}