{"gene":"CYB5A","run_date":"2026-04-28T17:28:53","timeline":{"discoveries":[{"year":2010,"finding":"CYB5A is required for androstenedione production in human adrenal H295R cells; siRNA knockdown of CYB5A significantly inhibited androstenedione production, and CYB5A co-localizes with HSD3B2 in hybrid ZF/ZR border cells of the human adrenal cortex.","method":"siRNA knockdown in H295R cells with androstenedione measurement; co-immunolocalization in human adrenal tissue","journal":"The Journal of steroid biochemistry and molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD with defined biochemical phenotype, supported by immunolocalization; single lab","pmids":["21185375"],"is_preprint":false},{"year":2015,"finding":"A CYB5A intronic SNP (rs1790834) doubles CYB5A mRNA expression and results in a 2–3 fold activation of steroid 17,20-lyase (CYP17A1) activity, demonstrating that CYB5A is a critical cofactor for 17,20-lyase activity and androgen synthesis.","method":"Radiolabeled steroid conversion assays in synovial fibroblasts; quantitative RT-PCR; immunohistochemistry; GWAS association study","journal":"Arthritis research & therapy","confidence":"Medium","confidence_rationale":"Tier 2 — functional steroid conversion assay with expression data; single lab but multiple orthogonal methods","pmids":["25890314"],"is_preprint":false},{"year":2005,"finding":"A SNP in the 5' UTR of porcine CYB5A (G→T at -8 upstream of ATG) reduces CYB5A enzymatic activity and is associated with lower androstenone levels in fat, linking CYB5A activity directly to 16-androstene (androstenone) biosynthesis.","method":"Functional activity assay comparing CYB5A activity between genotypes; genotyping of 229 testis samples","journal":"Mammalian genome","confidence":"Medium","confidence_rationale":"Tier 2 — direct functional activity assay linked to metabolite levels; single lab","pmids":["16104384"],"is_preprint":false},{"year":2019,"finding":"Specific surface residues of porcine CYB5A are involved in binding to CYP17A1; mutations at these residues (including N62S, N21K, L28V, R52M) alter the production of DHEA and 16-androstene steroids, with N62S increasing both 16A and DHEA production when combined with wild-type CYP17A1.","method":"Site-directed mutagenesis of CYB5A and CYP17A1; expression in HEK293 cells with radiolabeled pregnenolone substrate; HPLC metabolite quantification","journal":"The Journal of steroid biochemistry and molecular biology","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with in vitro reconstitution assay and quantitative metabolite analysis","pmids":["31509771"],"is_preprint":false},{"year":2019,"finding":"A homozygous loss-of-function CYB5A mutation (p.Tyr35Ter) causes isolated 17,20-lyase deficiency with methemoglobinemia in humans, confirming that CYB5A is required for CYP17A1 17,20-lyase activity in vivo.","method":"Human genetic case study; hormonal studies confirming isolated 17,20-lyase deficiency; DNA sequencing","journal":"Journal of the Endocrine Society","confidence":"Medium","confidence_rationale":"Tier 2 — human loss-of-function variant with defined biochemical phenotype; clinical case study","pmids":["32051920"],"is_preprint":false},{"year":2024,"finding":"CYB5A (microsomal) and CYB5B (mitochondrial) compensate for each other in sterol C4-demethylation during cholesterol biosynthesis; knockout of CYB5B alone in HeLa cells blocks cholesterol biosynthesis causing T-MAS accumulation, and combined knockdown of both CYB5A and CYB5B in liver-specific Cyb5b KO mice leads to marked T-MAS/dihydro-T-MAS accumulation, inhibiting the SREBP pathway and activating the PPARγ pathway.","method":"CRISPR knockout in HeLa cells; liver-specific Cyb5b KO mice with shRNA knockdown of Cyb5a; sterol profiling; SREBP and PPARγ pathway analysis","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1–2 — genetic KO/KD in two orthogonal systems (cells and mice) with sterol metabolomics and pathway readouts","pmids":["39489939"],"is_preprint":false},{"year":2014,"finding":"CYB5A inhibits oncogenic phenotypes in pancreatic cancer cells through induction of autophagy, and its downstream pathway involves TRAF6.","method":"In vitro and in vivo studies with CYB5A loss-of-function; autophagy readouts; pathway analysis involving TRAF6","journal":"Autophagy","confidence":"Low","confidence_rationale":"Tier 3 — single lab, limited mechanistic detail in abstract, no mutagenesis or reconstitution","pmids":["24448000"],"is_preprint":false},{"year":2025,"finding":"CYB5A promotes osteogenic differentiation of MC3T3-E1 cells by stimulating autophagy via activation of ULK1 and reduction of mTOR phosphorylation (AKT/mTOR/ULK1 pathway); CYB5A overexpression increases LC3-II/LC3-I ratio and decreases P62, and autophagy inhibitors/activators confirmed this pathway mediates CYB5A's effect on osteogenesis.","method":"Overexpression and siRNA knockdown in MC3T3-E1 cells; Western blotting for LC3-II/I, P62, mTOR phosphorylation, ULK1; autophagy inhibitor/activator pharmacological validation","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2–3 — KD and OE with pathway readouts and pharmacological validation; single lab","pmids":["40246926"],"is_preprint":false},{"year":2012,"finding":"CYB5A (cytochrome b5) functions to detoxify sulfonamide hydroxylamine metabolites, with CYB5A activity serving as part of a reductive detoxification pathway for aromatic amine intermediates.","method":"Candidate gene sequencing; genotyping of CYB5A polymorphisms in sulfonamide hypersensitivity cases vs controls","journal":"Pharmacogenetics and genomics","confidence":"Low","confidence_rationale":"Tier 3 — association study with no direct in vitro enzymatic demonstration of detoxification in this paper","pmids":["22850190"],"is_preprint":false},{"year":2014,"finding":"Promoter SNPs in porcine CYB5A affect transcription factor (MAZ) binding and alter CYB5A expression levels, as demonstrated by EMSA and reporter assays, with haplotype B showing higher CYB5A expression than haplotype A.","method":"Electrophoretic mobility shift assay (EMSA); in vitro cell transfection with luciferase reporter assay; quantitative PCR from liver tissues; in silico transcription factor prediction","journal":"Animal genetics","confidence":"Medium","confidence_rationale":"Tier 2 — EMSA and reporter assay directly demonstrate mechanistic effect of SNP on transcription factor binding and expression","pmids":["25516134"],"is_preprint":false},{"year":2022,"finding":"An alternative CYB5A transcript (CYB5Aalt) with a novel transcription start site and non-canonical exon usage is expressed in aneuploid B-cell precursor ALL; overexpression of CYB5Aalt in NALM-6 cells downregulates pathways related to wild-type CYB5A functions, decreases wild-type CYB5A expression, and increases resistance to BCL2-mediated apoptosis.","method":"RNA sequencing; stable overexpression of CYB5Aalt in NALM-6 cells; differential expression and GSEA analysis; cell death/viability assays","journal":"BMC genomic data","confidence":"Medium","confidence_rationale":"Tier 2 — functional overexpression with transcriptomic and cell death readouts; single lab","pmids":["35436854"],"is_preprint":false}],"current_model":"CYB5A (microsomal cytochrome b5) functions primarily as an allosteric/electron-transfer cofactor that directly stimulates CYP17A1 17,20-lyase activity to drive androgen (DHEA, androstenedione) and 16-androstene biosynthesis, with specific surface residues mediating its interaction with CYP17A1; it also compensates with mitochondrial CYB5B for sterol C4-demethylation in cholesterol biosynthesis, modulating SREBP and PPARγ pathways via accumulation of dimethyl sterol intermediates, and additionally participates in autophagy-mediated cellular processes (osteogenic differentiation, tumor suppression) through the AKT/mTOR/ULK1 pathway."},"narrative":{"teleology":[{"year":2005,"claim":"A naturally occurring 5′ UTR polymorphism in porcine CYB5A directly reduced CYB5A enzymatic activity and lowered androstenone levels in fat, establishing CYB5A as a functional determinant of 16-androstene steroid biosynthesis.","evidence":"Functional activity assay comparing CYB5A activity between genotypes in 229 porcine testis samples","pmids":["16104384"],"confidence":"Medium","gaps":["Mechanism by which CYB5A stimulates 16-androstene synthesis not defined at residue level","No human data provided"]},{"year":2010,"claim":"siRNA knockdown in human adrenal cells demonstrated that CYB5A is required for androstenedione production, connecting CYB5A's cofactor role specifically to human adrenal androgen output.","evidence":"siRNA knockdown in H295R cells with androstenedione measurement; co-immunolocalization in human adrenal cortex","pmids":["21185375"],"confidence":"Medium","gaps":["Whether CYB5A directly transfers electrons to CYP17A1 versus acts allosterically was not resolved","Single cell line system"]},{"year":2014,"claim":"Promoter SNPs in porcine CYB5A were shown to alter transcription factor (MAZ) binding and expression levels, revealing transcriptional regulatory mechanisms controlling CYB5A abundance.","evidence":"EMSA and luciferase reporter assays in transfected cells with quantitative PCR from liver tissues","pmids":["25516134"],"confidence":"Medium","gaps":["Whether MAZ-dependent regulation operates in human CYB5A promoter unknown","Downstream metabolic consequences of expression differences not measured"]},{"year":2014,"claim":"CYB5A was linked to autophagy induction and tumor suppression in pancreatic cancer, broadening its known functions beyond electron transfer to include signaling through TRAF6.","evidence":"In vitro and in vivo loss-of-function studies with autophagy readouts and TRAF6 pathway analysis","pmids":["24448000"],"confidence":"Low","gaps":["Limited mechanistic detail; no reconstitution or mutagenesis to establish direct CYB5A–TRAF6 interaction","Single lab with no independent confirmation","How an ER-anchored electron carrier triggers autophagy is unexplained"]},{"year":2015,"claim":"A human intronic CYB5A SNP that doubles mRNA expression was shown to produce 2–3 fold activation of CYP17A1 17,20-lyase activity, quantitatively linking CYB5A expression levels to androgen synthetic capacity.","evidence":"Radiolabeled steroid conversion assays in synovial fibroblasts; qRT-PCR; immunohistochemistry","pmids":["25890314"],"confidence":"Medium","gaps":["Studied in synovial fibroblasts rather than adrenal or gonadal tissue","Allosteric versus electron-transfer mechanism not distinguished"]},{"year":2019,"claim":"Site-directed mutagenesis of specific CYB5A surface residues (N62S, N21K, L28V, R52M) altered DHEA and 16-androstene production when co-expressed with CYP17A1, identifying the molecular interface that governs CYB5A's stimulation of 17,20-lyase activity.","evidence":"Mutagenesis of CYB5A and CYP17A1 expressed in HEK293 cells; radiolabeled pregnenolone conversion; HPLC metabolite quantification","pmids":["31509771"],"confidence":"High","gaps":["No crystal structure of the CYB5A–CYP17A1 complex to confirm binding mode","Whether the same residues are critical in human versus porcine CYB5A not tested"]},{"year":2019,"claim":"A homozygous nonsense CYB5A mutation (p.Tyr35Ter) in a human patient caused isolated 17,20-lyase deficiency with methemoglobinemia, providing in vivo genetic proof that CYB5A is essential for CYP17A1 lyase activity and methemoglobin reduction.","evidence":"Human genetic case study with hormonal profiling and DNA sequencing","pmids":["32051920"],"confidence":"Medium","gaps":["Single family; full phenotypic spectrum of CYB5A deficiency not delineated","No functional rescue experiment performed"]},{"year":2022,"claim":"An alternative CYB5A transcript (CYB5Aalt) expressed in aneuploid B-ALL was found to downregulate canonical CYB5A functions and increase resistance to BCL2-mediated apoptosis, revealing that alternative CYB5A isoforms can act as dominant-negative regulators.","evidence":"RNA-seq discovery; stable CYB5Aalt overexpression in NALM-6 cells with transcriptomic and cell death assays","pmids":["35436854"],"confidence":"Medium","gaps":["Protein product of CYB5Aalt not biochemically characterized","Whether CYB5Aalt is recurrently expressed in other cancers unknown"]},{"year":2024,"claim":"Combined loss of CYB5A and CYB5B was shown to block sterol C4-demethylation, causing T-MAS accumulation that suppresses SREBP and activates PPARγ, establishing functional redundancy between the two cytochrome b5 paralogs in cholesterol biosynthesis.","evidence":"CRISPR knockout in HeLa cells; liver-specific Cyb5b KO mice with shRNA knockdown of Cyb5a; sterol profiling and pathway analysis","pmids":["39489939"],"confidence":"High","gaps":["Which C4-demethylation enzyme(s) CYB5A directly donates electrons to was not identified","Tissue-specific relative contributions of CYB5A vs CYB5B not fully resolved"]},{"year":2025,"claim":"CYB5A was shown to promote osteogenic differentiation by activating autophagy through the AKT/mTOR/ULK1 axis, providing a defined signaling pathway for CYB5A's autophagy-stimulating function first noted in cancer cells.","evidence":"Overexpression and siRNA knockdown in MC3T3-E1 cells; Western blotting for autophagy markers; pharmacological autophagy modulators","pmids":["40246926"],"confidence":"Medium","gaps":["How an ER-membrane electron carrier engages AKT/mTOR signaling is mechanistically unexplained","Single cell line (osteoblast precursor); generalizability unclear"]},{"year":null,"claim":"The structural basis of CYB5A interaction with CYP17A1 and the C4-demethylation machinery, the mechanism by which CYB5A activates autophagy signaling, and the physiological significance of the alternative CYB5Aalt isoform remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal or cryo-EM structure of CYB5A–CYP17A1 complex","Electron-transfer versus allosteric mechanism for 17,20-lyase stimulation not resolved","Molecular link between CYB5A and AKT/mTOR unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[0,2,3,5]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[3,5]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,5]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,2,3,5]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[6,7]}],"complexes":[],"partners":["CYP17A1","CYB5B","TRAF6","HSD3B2"],"other_free_text":[]},"mechanistic_narrative":"CYB5A (microsomal cytochrome b5) is an electron-transfer cofactor central to androgen biosynthesis and cholesterol pathway regulation. It stimulates CYP17A1 17,20-lyase activity to drive production of DHEA, androstenedione, and 16-androstene steroids, with specific surface residues (including N62, N21, L28, R52) mediating the CYB5A–CYP17A1 interaction [PMID:31509771, PMID:21185375, PMID:25890314]; homozygous loss-of-function mutations in CYB5A cause isolated 17,20-lyase deficiency with methemoglobinemia in humans [PMID:32051920]. CYB5A and its mitochondrial paralog CYB5B compensate for each other in sterol C4-demethylation during cholesterol biosynthesis, and their combined loss causes accumulation of dimethyl sterol intermediates (T-MAS), suppressing the SREBP pathway and activating PPARγ signaling [PMID:39489939]. CYB5A also promotes autophagy through the AKT/mTOR/ULK1 axis, a function linked to osteogenic differentiation and suppression of oncogenic phenotypes in pancreatic cancer [PMID:40246926, PMID:24448000]."},"prefetch_data":{"uniprot":{"accession":"P00167","full_name":"Cytochrome b5","aliases":["Microsomal cytochrome b5 type A","MCB5"],"length_aa":134,"mass_kda":15.3,"function":"Cytochrome b5 is a membrane-bound hemoprotein functioning as an electron carrier for several membrane-bound oxygenases","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P00167/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CYB5A","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"RTN4","stoichiometry":4.0},{"gene":"BCAP31","stoichiometry":0.2},{"gene":"CANX","stoichiometry":0.2},{"gene":"COPB2","stoichiometry":0.2},{"gene":"DDOST","stoichiometry":0.2},{"gene":"EMC4","stoichiometry":0.2},{"gene":"OST4","stoichiometry":0.2},{"gene":"RER1","stoichiometry":0.2},{"gene":"RPN1","stoichiometry":0.2},{"gene":"RPN2","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CYB5A","total_profiled":1310},"omim":[{"mim_id":"615341","title":"CYTOCHROME P450, FAMILY 4, SUBFAMILY A, POLYPEPTIDE 22; CYP4A22","url":"https://www.omim.org/entry/615341"},{"mim_id":"613218","title":"CYTOCHROME b5, TYPE A (MICROSOMAL); CYB5A","url":"https://www.omim.org/entry/613218"},{"mim_id":"613213","title":"CYTOCHROME b5 REDUCTASE 3; CYB5R3","url":"https://www.omim.org/entry/613213"},{"mim_id":"611964","title":"CYTOCHROME b5, TYPE B (OUTER MITOCHONDRIAL MEMBRANE); CYB5B","url":"https://www.omim.org/entry/611964"},{"mim_id":"608343","title":"CYTOCHROME b5 REDUCTASE 4; CYB5R4","url":"https://www.omim.org/entry/608343"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Vesicles","reliability":"Enhanced"},{"location":"Cytosol","reliability":"Enhanced"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"kidney","ntpm":828.0},{"tissue":"liver","ntpm":2306.7}],"url":"https://www.proteinatlas.org/search/CYB5A"},"hgnc":{"alias_symbol":["MCB5"],"prev_symbol":["CYB5"]},"alphafold":{"accession":"P00167","domains":[{"cath_id":"3.10.120.10","chopping":"10-97","consensus_level":"high","plddt":89.1457,"start":10,"end":97}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P00167","model_url":"https://alphafold.ebi.ac.uk/files/AF-P00167-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P00167-F1-predicted_aligned_error_v6.png","plddt_mean":80.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CYB5A","jax_strain_url":"https://www.jax.org/strain/search?query=CYB5A"},"sequence":{"accession":"P00167","fasta_url":"https://rest.uniprot.org/uniprotkb/P00167.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P00167/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P00167"}},"corpus_meta":[{"pmid":"21185375","id":"PMC_21185375","title":"Human adrenal cells that express both 3β-hydroxysteroid dehydrogenase type 2 (HSD3B2) and cytochrome b5 (CYB5A) contribute to adrenal androstenedione production.","date":"2010","source":"The Journal of steroid biochemistry and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/21185375","citation_count":28,"is_preprint":false},{"pmid":"25890314","id":"PMC_25890314","title":"CYB5A polymorphism increases androgens and reduces risk of rheumatoid arthritis in women.","date":"2015","source":"Arthritis research & therapy","url":"https://pubmed.ncbi.nlm.nih.gov/25890314","citation_count":24,"is_preprint":false},{"pmid":"24832628","id":"PMC_24832628","title":"3βHSD and CYB5A double positive adrenocortical cells during adrenal development/aging.","date":"2014","source":"Endocrine research","url":"https://pubmed.ncbi.nlm.nih.gov/24832628","citation_count":20,"is_preprint":false},{"pmid":"16104384","id":"PMC_16104384","title":"A novel polymorphism in the 5' untranslated region of the porcine cytochrome b5 (CYB5) gene is associated with decreased fat androstenone level.","date":"2005","source":"Mammalian genome : official journal of the International Mammalian Genome Society","url":"https://pubmed.ncbi.nlm.nih.gov/16104384","citation_count":20,"is_preprint":false},{"pmid":"22850190","id":"PMC_22850190","title":"Evaluation of polymorphisms in the sulfonamide detoxification genes NAT2, CYB5A, and CYB5R3 in patients with sulfonamide hypersensitivity.","date":"2012","source":"Pharmacogenetics and genomics","url":"https://pubmed.ncbi.nlm.nih.gov/22850190","citation_count":15,"is_preprint":false},{"pmid":"25516134","id":"PMC_25516134","title":"Differential expression of CYB5A in Chinese and European pig breeds due to genetic variations in the promoter region.","date":"2014","source":"Animal genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25516134","citation_count":13,"is_preprint":false},{"pmid":"25225034","id":"PMC_25225034","title":"Polymorphisms in the carcinogen detoxification genes CYB5A and CYB5R3 and breast cancer risk in African American women.","date":"2014","source":"Cancer causes & control : CCC","url":"https://pubmed.ncbi.nlm.nih.gov/25225034","citation_count":13,"is_preprint":false},{"pmid":"24448000","id":"PMC_24448000","title":"CYB5A and autophagy-mediated cell death in pancreatic cancer.","date":"2014","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/24448000","citation_count":12,"is_preprint":false},{"pmid":"32051920","id":"PMC_32051920","title":"Isolated 17,20-Lyase Deficiency in a CYB5A Mutated Female With Normal Sexual Development and Fertility.","date":"2019","source":"Journal of the Endocrine Society","url":"https://pubmed.ncbi.nlm.nih.gov/32051920","citation_count":11,"is_preprint":false},{"pmid":"15328107","id":"PMC_15328107","title":"Disruption of the Candida albicans CYB5 gene results in increased azole sensitivity.","date":"2004","source":"Antimicrobial agents and chemotherapy","url":"https://pubmed.ncbi.nlm.nih.gov/15328107","citation_count":10,"is_preprint":false},{"pmid":"31509771","id":"PMC_31509771","title":"Effect of mutations in porcine CYB5A and CYP17A1 on the metabolism of pregnenolone.","date":"2019","source":"The Journal of steroid biochemistry and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/31509771","citation_count":8,"is_preprint":false},{"pmid":"22816446","id":"PMC_22816446","title":"Evaluation of polymorphisms in the sulfonamide detoxification genes CYB5A and CYB5R3 in dogs with sulfonamide hypersensitivity.","date":"2012","source":"Journal of veterinary internal medicine","url":"https://pubmed.ncbi.nlm.nih.gov/22816446","citation_count":7,"is_preprint":false},{"pmid":"35043601","id":"PMC_35043601","title":"Functional variants in cytochrome b5 type A (CYB5A) are enriched in Southwest American Indian individuals and associate with obesity.","date":"2022","source":"Obesity (Silver Spring, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/35043601","citation_count":6,"is_preprint":false},{"pmid":"27136898","id":"PMC_27136898","title":"2,3,7,8 Tetrachlorodibenzo-p-dioxin-induced RNA abundance changes identify Ackr3, Col18a1, Cyb5a and Glud1 as candidate mediators of toxicity.","date":"2016","source":"Archives of toxicology","url":"https://pubmed.ncbi.nlm.nih.gov/27136898","citation_count":6,"is_preprint":false},{"pmid":"22445012","id":"PMC_22445012","title":"Effect of polymorphism in the porcine cytochrome b5 ( CYB5A) gene on androstenone and skatole concentrations and sexual development in Swedish pig populations.","date":"2008","source":"Animal : an international journal of animal bioscience","url":"https://pubmed.ncbi.nlm.nih.gov/22445012","citation_count":6,"is_preprint":false},{"pmid":"39489939","id":"PMC_39489939","title":"Defects in CYB5A and CYB5B impact sterol-C4 oxidation in cholesterol biosynthesis and demonstrate regulatory roles of dimethyl sterols.","date":"2024","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/39489939","citation_count":5,"is_preprint":false},{"pmid":"40246926","id":"PMC_40246926","title":"CYB5A promotes osteogenic differentiation of MC3T3-E1 cells through autophagy mediated by the AKT/mTOR/ULK1 signaling pathway.","date":"2025","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/40246926","citation_count":5,"is_preprint":false},{"pmid":"33626548","id":"PMC_33626548","title":"Isolated 17, 20 Lyase Deficiency Secondary to a Novel CYB5A Variant: Comparison of Steroid Metabolomic Findings with Published Cases Provides Diagnostic Guidelines and Greater Insight into Its Biological Role.","date":"2021","source":"Hormone research in paediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/33626548","citation_count":4,"is_preprint":false},{"pmid":"34160668","id":"PMC_34160668","title":"Lack of association between CYB5A gene rs1790834 polymorphism and the response to leflunomide in women with rheumatoid arthritis.","date":"2021","source":"European journal of clinical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/34160668","citation_count":3,"is_preprint":false},{"pmid":"40123165","id":"PMC_40123165","title":"Two families, two pathways: a case series of 46, XY DSD with 17α-hydroxylase deficiency and isolated 17,20-lyase deficiency due to novel CYB5A variant.","date":"2025","source":"Journal of pediatric endocrinology & metabolism : JPEM","url":"https://pubmed.ncbi.nlm.nih.gov/40123165","citation_count":2,"is_preprint":false},{"pmid":"37289314","id":"PMC_37289314","title":"The association between CYB5A gene rs1790834 polymorphism and clinical improvement after 6 months of leflunomide treatment in women with rheumatoid arthritis.","date":"2023","source":"Clinical rheumatology","url":"https://pubmed.ncbi.nlm.nih.gov/37289314","citation_count":1,"is_preprint":false},{"pmid":"35436854","id":"PMC_35436854","title":"An alternative CYB5A transcript is expressed in aneuploid ALL and enriched in relapse.","date":"2022","source":"BMC genomic data","url":"https://pubmed.ncbi.nlm.nih.gov/35436854","citation_count":1,"is_preprint":false},{"pmid":"27524697","id":"PMC_27524697","title":"Development of CYB5-fusion monitoring system for efficient periplasmic expression of multimeric proteins in Escherichia coli.","date":"2016","source":"Protein expression and purification","url":"https://pubmed.ncbi.nlm.nih.gov/27524697","citation_count":1,"is_preprint":false},{"pmid":"41052660","id":"PMC_41052660","title":"Haplotype-based association of CYB5A gene polymorphisms (rs1790834 and rs1790858) with polycystic ovary syndrome in a south Indian cohort.","date":"2025","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/41052660","citation_count":0,"is_preprint":false},{"pmid":"41891695","id":"PMC_41891695","title":"The azole-resistance phenotype of a Nakaseomyces glabratus clinical strain encoding a wild-type PDR1 allele involves the efflux pumps Aus1 and Pdh1 and Cyb5, an alternative reductase required for ergosterol biosynthesis.","date":"2026","source":"Microbiology spectrum","url":"https://pubmed.ncbi.nlm.nih.gov/41891695","citation_count":0,"is_preprint":false},{"pmid":"41453937","id":"PMC_41453937","title":"Micro RNA miR-726-3p targets CYB5A in Hen ovaries to modulate granulosa cell proliferation and differentiation.","date":"2025","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/41453937","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15631,"output_tokens":2688,"usd":0.043606},"stage2":{"model":"claude-opus-4-6","input_tokens":6038,"output_tokens":2657,"usd":0.144923},"total_usd":0.188529,"stage1_batch_id":"msgbatch_011kfMfE81o6CTcyhVUqumuW","stage2_batch_id":"msgbatch_01DTputS6WNkH745x1nVSoBo","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"CYB5A is required for androstenedione production in human adrenal H295R cells; siRNA knockdown of CYB5A significantly inhibited androstenedione production, and CYB5A co-localizes with HSD3B2 in hybrid ZF/ZR border cells of the human adrenal cortex.\",\n      \"method\": \"siRNA knockdown in H295R cells with androstenedione measurement; co-immunolocalization in human adrenal tissue\",\n      \"journal\": \"The Journal of steroid biochemistry and molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined biochemical phenotype, supported by immunolocalization; single lab\",\n      \"pmids\": [\"21185375\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"A CYB5A intronic SNP (rs1790834) doubles CYB5A mRNA expression and results in a 2–3 fold activation of steroid 17,20-lyase (CYP17A1) activity, demonstrating that CYB5A is a critical cofactor for 17,20-lyase activity and androgen synthesis.\",\n      \"method\": \"Radiolabeled steroid conversion assays in synovial fibroblasts; quantitative RT-PCR; immunohistochemistry; GWAS association study\",\n      \"journal\": \"Arthritis research & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional steroid conversion assay with expression data; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"25890314\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"A SNP in the 5' UTR of porcine CYB5A (G→T at -8 upstream of ATG) reduces CYB5A enzymatic activity and is associated with lower androstenone levels in fat, linking CYB5A activity directly to 16-androstene (androstenone) biosynthesis.\",\n      \"method\": \"Functional activity assay comparing CYB5A activity between genotypes; genotyping of 229 testis samples\",\n      \"journal\": \"Mammalian genome\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct functional activity assay linked to metabolite levels; single lab\",\n      \"pmids\": [\"16104384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Specific surface residues of porcine CYB5A are involved in binding to CYP17A1; mutations at these residues (including N62S, N21K, L28V, R52M) alter the production of DHEA and 16-androstene steroids, with N62S increasing both 16A and DHEA production when combined with wild-type CYP17A1.\",\n      \"method\": \"Site-directed mutagenesis of CYB5A and CYP17A1; expression in HEK293 cells with radiolabeled pregnenolone substrate; HPLC metabolite quantification\",\n      \"journal\": \"The Journal of steroid biochemistry and molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with in vitro reconstitution assay and quantitative metabolite analysis\",\n      \"pmids\": [\"31509771\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A homozygous loss-of-function CYB5A mutation (p.Tyr35Ter) causes isolated 17,20-lyase deficiency with methemoglobinemia in humans, confirming that CYB5A is required for CYP17A1 17,20-lyase activity in vivo.\",\n      \"method\": \"Human genetic case study; hormonal studies confirming isolated 17,20-lyase deficiency; DNA sequencing\",\n      \"journal\": \"Journal of the Endocrine Society\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — human loss-of-function variant with defined biochemical phenotype; clinical case study\",\n      \"pmids\": [\"32051920\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CYB5A (microsomal) and CYB5B (mitochondrial) compensate for each other in sterol C4-demethylation during cholesterol biosynthesis; knockout of CYB5B alone in HeLa cells blocks cholesterol biosynthesis causing T-MAS accumulation, and combined knockdown of both CYB5A and CYB5B in liver-specific Cyb5b KO mice leads to marked T-MAS/dihydro-T-MAS accumulation, inhibiting the SREBP pathway and activating the PPARγ pathway.\",\n      \"method\": \"CRISPR knockout in HeLa cells; liver-specific Cyb5b KO mice with shRNA knockdown of Cyb5a; sterol profiling; SREBP and PPARγ pathway analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — genetic KO/KD in two orthogonal systems (cells and mice) with sterol metabolomics and pathway readouts\",\n      \"pmids\": [\"39489939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CYB5A inhibits oncogenic phenotypes in pancreatic cancer cells through induction of autophagy, and its downstream pathway involves TRAF6.\",\n      \"method\": \"In vitro and in vivo studies with CYB5A loss-of-function; autophagy readouts; pathway analysis involving TRAF6\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, limited mechanistic detail in abstract, no mutagenesis or reconstitution\",\n      \"pmids\": [\"24448000\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CYB5A promotes osteogenic differentiation of MC3T3-E1 cells by stimulating autophagy via activation of ULK1 and reduction of mTOR phosphorylation (AKT/mTOR/ULK1 pathway); CYB5A overexpression increases LC3-II/LC3-I ratio and decreases P62, and autophagy inhibitors/activators confirmed this pathway mediates CYB5A's effect on osteogenesis.\",\n      \"method\": \"Overexpression and siRNA knockdown in MC3T3-E1 cells; Western blotting for LC3-II/I, P62, mTOR phosphorylation, ULK1; autophagy inhibitor/activator pharmacological validation\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — KD and OE with pathway readouts and pharmacological validation; single lab\",\n      \"pmids\": [\"40246926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CYB5A (cytochrome b5) functions to detoxify sulfonamide hydroxylamine metabolites, with CYB5A activity serving as part of a reductive detoxification pathway for aromatic amine intermediates.\",\n      \"method\": \"Candidate gene sequencing; genotyping of CYB5A polymorphisms in sulfonamide hypersensitivity cases vs controls\",\n      \"journal\": \"Pharmacogenetics and genomics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — association study with no direct in vitro enzymatic demonstration of detoxification in this paper\",\n      \"pmids\": [\"22850190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Promoter SNPs in porcine CYB5A affect transcription factor (MAZ) binding and alter CYB5A expression levels, as demonstrated by EMSA and reporter assays, with haplotype B showing higher CYB5A expression than haplotype A.\",\n      \"method\": \"Electrophoretic mobility shift assay (EMSA); in vitro cell transfection with luciferase reporter assay; quantitative PCR from liver tissues; in silico transcription factor prediction\",\n      \"journal\": \"Animal genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — EMSA and reporter assay directly demonstrate mechanistic effect of SNP on transcription factor binding and expression\",\n      \"pmids\": [\"25516134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"An alternative CYB5A transcript (CYB5Aalt) with a novel transcription start site and non-canonical exon usage is expressed in aneuploid B-cell precursor ALL; overexpression of CYB5Aalt in NALM-6 cells downregulates pathways related to wild-type CYB5A functions, decreases wild-type CYB5A expression, and increases resistance to BCL2-mediated apoptosis.\",\n      \"method\": \"RNA sequencing; stable overexpression of CYB5Aalt in NALM-6 cells; differential expression and GSEA analysis; cell death/viability assays\",\n      \"journal\": \"BMC genomic data\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional overexpression with transcriptomic and cell death readouts; single lab\",\n      \"pmids\": [\"35436854\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CYB5A (microsomal cytochrome b5) functions primarily as an allosteric/electron-transfer cofactor that directly stimulates CYP17A1 17,20-lyase activity to drive androgen (DHEA, androstenedione) and 16-androstene biosynthesis, with specific surface residues mediating its interaction with CYP17A1; it also compensates with mitochondrial CYB5B for sterol C4-demethylation in cholesterol biosynthesis, modulating SREBP and PPARγ pathways via accumulation of dimethyl sterol intermediates, and additionally participates in autophagy-mediated cellular processes (osteogenic differentiation, tumor suppression) through the AKT/mTOR/ULK1 pathway.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CYB5A (microsomal cytochrome b5) is an electron-transfer cofactor central to androgen biosynthesis and cholesterol pathway regulation. It stimulates CYP17A1 17,20-lyase activity to drive production of DHEA, androstenedione, and 16-androstene steroids, with specific surface residues (including N62, N21, L28, R52) mediating the CYB5A–CYP17A1 interaction [PMID:31509771, PMID:21185375, PMID:25890314]; homozygous loss-of-function mutations in CYB5A cause isolated 17,20-lyase deficiency with methemoglobinemia in humans [PMID:32051920]. CYB5A and its mitochondrial paralog CYB5B compensate for each other in sterol C4-demethylation during cholesterol biosynthesis, and their combined loss causes accumulation of dimethyl sterol intermediates (T-MAS), suppressing the SREBP pathway and activating PPARγ signaling [PMID:39489939]. CYB5A also promotes autophagy through the AKT/mTOR/ULK1 axis, a function linked to osteogenic differentiation and suppression of oncogenic phenotypes in pancreatic cancer [PMID:40246926, PMID:24448000].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"A naturally occurring 5′ UTR polymorphism in porcine CYB5A directly reduced CYB5A enzymatic activity and lowered androstenone levels in fat, establishing CYB5A as a functional determinant of 16-androstene steroid biosynthesis.\",\n      \"evidence\": \"Functional activity assay comparing CYB5A activity between genotypes in 229 porcine testis samples\",\n      \"pmids\": [\"16104384\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which CYB5A stimulates 16-androstene synthesis not defined at residue level\", \"No human data provided\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"siRNA knockdown in human adrenal cells demonstrated that CYB5A is required for androstenedione production, connecting CYB5A's cofactor role specifically to human adrenal androgen output.\",\n      \"evidence\": \"siRNA knockdown in H295R cells with androstenedione measurement; co-immunolocalization in human adrenal cortex\",\n      \"pmids\": [\"21185375\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CYB5A directly transfers electrons to CYP17A1 versus acts allosterically was not resolved\", \"Single cell line system\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Promoter SNPs in porcine CYB5A were shown to alter transcription factor (MAZ) binding and expression levels, revealing transcriptional regulatory mechanisms controlling CYB5A abundance.\",\n      \"evidence\": \"EMSA and luciferase reporter assays in transfected cells with quantitative PCR from liver tissues\",\n      \"pmids\": [\"25516134\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether MAZ-dependent regulation operates in human CYB5A promoter unknown\", \"Downstream metabolic consequences of expression differences not measured\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"CYB5A was linked to autophagy induction and tumor suppression in pancreatic cancer, broadening its known functions beyond electron transfer to include signaling through TRAF6.\",\n      \"evidence\": \"In vitro and in vivo loss-of-function studies with autophagy readouts and TRAF6 pathway analysis\",\n      \"pmids\": [\"24448000\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Limited mechanistic detail; no reconstitution or mutagenesis to establish direct CYB5A–TRAF6 interaction\", \"Single lab with no independent confirmation\", \"How an ER-anchored electron carrier triggers autophagy is unexplained\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"A human intronic CYB5A SNP that doubles mRNA expression was shown to produce 2–3 fold activation of CYP17A1 17,20-lyase activity, quantitatively linking CYB5A expression levels to androgen synthetic capacity.\",\n      \"evidence\": \"Radiolabeled steroid conversion assays in synovial fibroblasts; qRT-PCR; immunohistochemistry\",\n      \"pmids\": [\"25890314\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Studied in synovial fibroblasts rather than adrenal or gonadal tissue\", \"Allosteric versus electron-transfer mechanism not distinguished\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Site-directed mutagenesis of specific CYB5A surface residues (N62S, N21K, L28V, R52M) altered DHEA and 16-androstene production when co-expressed with CYP17A1, identifying the molecular interface that governs CYB5A's stimulation of 17,20-lyase activity.\",\n      \"evidence\": \"Mutagenesis of CYB5A and CYP17A1 expressed in HEK293 cells; radiolabeled pregnenolone conversion; HPLC metabolite quantification\",\n      \"pmids\": [\"31509771\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal structure of the CYB5A–CYP17A1 complex to confirm binding mode\", \"Whether the same residues are critical in human versus porcine CYB5A not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"A homozygous nonsense CYB5A mutation (p.Tyr35Ter) in a human patient caused isolated 17,20-lyase deficiency with methemoglobinemia, providing in vivo genetic proof that CYB5A is essential for CYP17A1 lyase activity and methemoglobin reduction.\",\n      \"evidence\": \"Human genetic case study with hormonal profiling and DNA sequencing\",\n      \"pmids\": [\"32051920\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single family; full phenotypic spectrum of CYB5A deficiency not delineated\", \"No functional rescue experiment performed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"An alternative CYB5A transcript (CYB5Aalt) expressed in aneuploid B-ALL was found to downregulate canonical CYB5A functions and increase resistance to BCL2-mediated apoptosis, revealing that alternative CYB5A isoforms can act as dominant-negative regulators.\",\n      \"evidence\": \"RNA-seq discovery; stable CYB5Aalt overexpression in NALM-6 cells with transcriptomic and cell death assays\",\n      \"pmids\": [\"35436854\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Protein product of CYB5Aalt not biochemically characterized\", \"Whether CYB5Aalt is recurrently expressed in other cancers unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Combined loss of CYB5A and CYB5B was shown to block sterol C4-demethylation, causing T-MAS accumulation that suppresses SREBP and activates PPARγ, establishing functional redundancy between the two cytochrome b5 paralogs in cholesterol biosynthesis.\",\n      \"evidence\": \"CRISPR knockout in HeLa cells; liver-specific Cyb5b KO mice with shRNA knockdown of Cyb5a; sterol profiling and pathway analysis\",\n      \"pmids\": [\"39489939\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which C4-demethylation enzyme(s) CYB5A directly donates electrons to was not identified\", \"Tissue-specific relative contributions of CYB5A vs CYB5B not fully resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"CYB5A was shown to promote osteogenic differentiation by activating autophagy through the AKT/mTOR/ULK1 axis, providing a defined signaling pathway for CYB5A's autophagy-stimulating function first noted in cancer cells.\",\n      \"evidence\": \"Overexpression and siRNA knockdown in MC3T3-E1 cells; Western blotting for autophagy markers; pharmacological autophagy modulators\",\n      \"pmids\": [\"40246926\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How an ER-membrane electron carrier engages AKT/mTOR signaling is mechanistically unexplained\", \"Single cell line (osteoblast precursor); generalizability unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis of CYB5A interaction with CYP17A1 and the C4-demethylation machinery, the mechanism by which CYB5A activates autophagy signaling, and the physiological significance of the alternative CYB5Aalt isoform remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal or cryo-EM structure of CYB5A–CYP17A1 complex\", \"Electron-transfer versus allosteric mechanism for 17,20-lyase stimulation not resolved\", \"Molecular link between CYB5A and AKT/mTOR unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [0, 2, 3, 5]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [3, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1, 2, 3, 5]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [6, 7]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CYP17A1\",\n      \"CYB5B\",\n      \"TRAF6\",\n      \"HSD3B2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}