{"gene":"RFXAP","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":1997,"finding":"RFXAP is a novel subunit of the RFX DNA-binding complex; mutations in RFXAP abolish RFX complex DNA-binding activity and MHC class II gene expression, defining complementation group D of MHC-II deficiency. Transfection with wild-type RFXAP fully restores endogenous MHC-II gene expression.","method":"Complementation assays, transfection rescue, and identification of mutations in patient cell lines","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — reciprocal complementation, mutation identification, in vivo rescue; independently replicated in NEJM same year","pmids":["9118943","9287230"],"is_preprint":false},{"year":2001,"finding":"Only a short C-terminal segment of RFXAP is essential for HLA-DR expression, while optimal HLA-DQ and HLA-DP expression requires a larger C-terminal segment. This differential requirement is due to isotype-specific differences in promoter occupancy and CIITA recruitment in vivo.","method":"Domain deletion analysis, in vivo ChIP/promoter occupancy assays, transfection rescue in RFXAP-deficient cell lines","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (functional rescue, in vivo promoter occupancy, CIITA recruitment) in a single rigorous study","pmids":["11486010"],"is_preprint":false},{"year":2005,"finding":"Conserved hydrophobic and other C-terminal residues (not the glutamine-rich tract) of RFXAP are required for coordinate MHC-II isotype expression; mutation of potential phosphorylation sites abolishes RFXAP activity. Certain RFXAP mutants form transcriptionally inefficient complexes with isotype-specific promoter factors.","method":"Comparative genomic analysis, site-directed mutagenesis, complementation/rescue assays, ChIP (CIITA recruitment), chimeric reporter gene assays","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis combined with in vivo ChIP and reporter assays in a single study with multiple orthogonal methods","pmids":["16337482"],"is_preprint":false},{"year":2008,"finding":"RFX5 DNA-binding activity is autoinhibited by domains flanking its DNA-binding domain; both RFXAP and RFXB are required to relieve this autoinhibition. A single RFX complex (containing RFX5, RFXAP, and RFXB) binds to the proximal regulatory region of the MHC-II promoter.","method":"Electrophoretic mobility shift assays (EMSA) characterizing DNA binding of RFX5 alone and in complex with RFXAP and RFXB","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with defined recombinant components and rigorous EMSA analysis","pmids":["18723135"],"is_preprint":false},{"year":2008,"finding":"A homozygous 75 bp insertion in the 5'-UTR of RFXAP impairs RFXAP promoter activity, abolishes RFXAP mRNA and protein expression, and reduces RNA polymerase II recruitment to RFXAP chromatin, representing a novel transcriptional silencing mechanism for MHC-II deficiency.","method":"Sequencing, promoter activity assays, ChIP (RNA Pol II), mRNA/protein expression analysis in patient cells","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods but single patient/lab study","pmids":["18336911"],"is_preprint":false},{"year":2009,"finding":"The C-terminal domain of RFXAP (RFXAP-C) is intrinsically disordered but folds upon interaction with the N-terminal dimerization domain of RFX5 (RFX5-N). This folded RFX5(N)2–RFXAP(C) complex then binds RFXB with high affinity, defining a hierarchical assembly pathway for the RFX complex.","method":"NMR spectroscopy, circular dichroism spectroscopy, isothermal titration calorimetry","journal":"Proteins","confidence":"High","confidence_rationale":"Tier 1 — multiple biophysical methods (NMR, CD, ITC) establishing folding-upon-binding mechanism","pmids":["19274739"],"is_preprint":false},{"year":2010,"finding":"The solution structure of the RFX5(N)2–RFXAP(C) complex was determined: two RFX5-N helices form an antiparallel coiled coil ('staple'), and RFXAP-C adopts two α-helices in a V-shape that packs within the staple. Leucine residues in RFX5-N (62-LYLYLQL-68) contribute to both the RFX5 dimer interface and the RFX5–RFXAP interface, and are critical for MHC-II expression in vivo.","method":"Solution NMR (15N- and 13C-edited), in vivo functional validation of leucine mutants","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — high-resolution NMR structure with in vivo mutagenesis validation","pmids":["20732328"],"is_preprint":false},{"year":2009,"finding":"An 11-base deletion in RFXAP causing a frameshift at amino acid 234 and loss of C-terminal residues is responsible for coordinate MHC-II loss in the DLBCL cell line OCI-Ly2; stable transfection of wild-type RFXAP restores MHC-II expression.","method":"Sequencing of RFXAP cDNA, stable transfection rescue in DLBCL cell line","journal":"Immunogenetics","confidence":"Medium","confidence_rationale":"Tier 2 — mutation identification with functional rescue, single lab","pmids":["20024540"],"is_preprint":false},{"year":2015,"finding":"Pancreatic cancer-derived exosomes transfer miR-212-3p to dendritic cells, where it directly targets and inhibits RFXAP mRNA expression, leading to decreased MHC-II surface expression and induction of immune tolerance in dendritic cells.","method":"Exosome transfer experiments, bioinformatics target prediction, luciferase reporter validation of miR-212-3p targeting RFXAP 3'UTR, qRT-PCR, western blot","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2–3 — luciferase reporter plus functional assays, but single lab; mechanism of miR-212-3p suppression of RFXAP confirmed by multiple methods","pmids":["26337469"],"is_preprint":false},{"year":2020,"finding":"RFXAP directly transcriptionally activates KDM4A (a histone H3K36 demethylase) in pancreatic cancer cells; RFXAP overexpression upregulates KDM4A, reduces H3K36 trimethylation, impairs DNA repair, and enhances fisetin-induced DNA damage, while RFXAP knockdown reverses these effects.","method":"ChIP-seq (RFXAP binding at KDM4A promoter), dual-luciferase reporter assay, RFXAP overexpression/silencing, immunofluorescence for DNA damage markers, xenograft model","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP-seq and reporter assay establish direct transcriptional regulation; multiple functional readouts in single lab","pmids":["33093461"],"is_preprint":false}],"current_model":"RFXAP is an essential subunit of the trimeric RFX complex (with RFX5 and RFXB) that binds X-box elements in MHC class II gene promoters; its intrinsically disordered C-terminal domain folds upon binding to the RFX5 N-terminal dimerization domain (forming an antiparallel coiled-coil staple), enabling subsequent high-affinity RFXB recruitment and relief of RFX5 autoinhibition, while RFXAP's C-terminal conserved residues (including phosphorylatable sites) mediate isotype-specific CIITA recruitment and coordinate HLA-DR, -DQ, and -DP expression; additionally, RFXAP can transcriptionally activate KDM4A to modulate H3K36 methylation and DNA damage responses, and its expression is post-transcriptionally regulated by miR-212-3p."},"narrative":{"teleology":[{"year":1997,"claim":"Identification of RFXAP as the gene defective in complementation group D of MHC class II deficiency established that a previously unknown RFX complex subunit is essential for MHC-II expression and RFX DNA-binding activity.","evidence":"Complementation cloning, mutation identification in patient cell lines, and transfection rescue restoring MHC-II expression","pmids":["9118943","9287230"],"confidence":"High","gaps":["No structural information on RFXAP or its mode of incorporation into the RFX complex","Mechanism by which RFXAP contributes to DNA binding unknown","Relationship between RFXAP domains and function unresolved"]},{"year":2001,"claim":"Domain mapping revealed that only the C-terminal segment of RFXAP is required for HLA-DR expression, while larger C-terminal regions are needed for HLA-DQ and -DP, demonstrating that RFXAP mediates isotype-specific promoter occupancy and CIITA recruitment.","evidence":"Deletion analysis with transfection rescue and in vivo ChIP/promoter occupancy assays in RFXAP-deficient cells","pmids":["11486010"],"confidence":"High","gaps":["Identity of specific residues responsible for isotype selectivity not yet determined","Mechanism of differential CIITA recruitment unclear"]},{"year":2005,"claim":"Site-directed mutagenesis pinpointed conserved hydrophobic residues and potential phosphorylation sites in the RFXAP C-terminus as essential for coordinate MHC-II expression and efficient CIITA recruitment, resolving which sequence features underlie isotype-specific transcription.","evidence":"Comparative genomics, site-directed mutagenesis, complementation rescue, ChIP for CIITA, chimeric reporter assays","pmids":["16337482"],"confidence":"High","gaps":["Kinase(s) responsible for RFXAP phosphorylation not identified","Whether phosphorylation regulates RFXAP in vivo remains untested"]},{"year":2008,"claim":"Biochemical reconstitution demonstrated that RFX5 DNA-binding activity is autoinhibited and that both RFXAP and RFXB are required to relieve autoinhibition, establishing the functional logic of the trimeric RFX complex.","evidence":"EMSA with recombinant RFX5 alone and in complex with RFXAP and RFXB","pmids":["18723135"],"confidence":"High","gaps":["Structural basis of autoinhibition relief not resolved","Stoichiometry of the full complex on DNA not determined"]},{"year":2009,"claim":"Biophysical studies revealed that the RFXAP C-terminal domain is intrinsically disordered but undergoes coupled folding-and-binding upon interacting with the RFX5 N-terminal dimer, and that this pre-formed subcomplex then recruits RFXB with high affinity, defining a hierarchical assembly pathway.","evidence":"NMR, circular dichroism, and isothermal titration calorimetry on recombinant domains","pmids":["19274739"],"confidence":"High","gaps":["Full-length complex structure not available","Whether the hierarchical assembly occurs on or off DNA in cells unknown"]},{"year":2010,"claim":"The solution NMR structure of the RFX5(N)₂–RFXAP(C) complex showed RFXAP-C adopting a V-shaped two-helix fold packed within an antiparallel coiled-coil staple formed by RFX5-N, with leucine residues at the interface critical for MHC-II expression in vivo.","evidence":"Solution NMR structure determination (¹⁵N/¹³C-edited) with in vivo validation of leucine point mutants","pmids":["20732328"],"confidence":"High","gaps":["Structure of the full trimeric complex with RFXB not determined","How the structural interface connects to CIITA recruitment is unresolved"]},{"year":2015,"claim":"Discovery that pancreatic cancer exosomes deliver miR-212-3p to dendritic cells to directly suppress RFXAP mRNA revealed a post-transcriptional mechanism by which tumors downregulate MHC-II expression for immune evasion.","evidence":"Exosome transfer assays, luciferase reporter validation of miR-212-3p targeting the RFXAP 3′-UTR, qRT-PCR and western blot in dendritic cells","pmids":["26337469"],"confidence":"Medium","gaps":["Single lab study; independent replication lacking","In vivo relevance of miR-212-3p-mediated RFXAP suppression in patient tumors not established"]},{"year":2020,"claim":"Identification of KDM4A as a direct transcriptional target of RFXAP expanded its functional scope beyond MHC-II regulation to chromatin remodeling and DNA damage responses.","evidence":"ChIP-seq showing RFXAP binding at the KDM4A promoter, dual-luciferase reporter assay, RFXAP overexpression/knockdown affecting H3K36me3 levels and DNA damage markers in pancreatic cancer cells and xenografts","pmids":["33093461"],"confidence":"Medium","gaps":["Whether RFXAP acts at KDM4A as part of the canonical RFX complex or independently is unknown","Genome-wide identification of RFXAP transcriptional targets beyond MHC-II and KDM4A not performed"]},{"year":null,"claim":"A complete structural model of the full trimeric RFX–DNA complex, the identity of kinases phosphorylating RFXAP, and the genome-wide spectrum of RFXAP transcriptional targets remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No full-length trimeric RFX complex structure on DNA","Kinase(s) for RFXAP phosphorylation unidentified","Genome-wide RFXAP target gene repertoire undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,1,2,9]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0,3]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,1,3,9]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,1,2,9]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1,7]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[9]}],"complexes":["RFX complex (RFX5/RFXAP/RFXB)"],"partners":["RFX5","RFXB","CIITA","KDM4A"],"other_free_text":[]},"mechanistic_narrative":"RFXAP is an essential subunit of the trimeric RFX transcription factor complex (with RFX5 and RFXB) that binds X-box elements in MHC class II gene promoters and is required for MHC class II gene expression [PMID:9118943, PMID:18723135]. Its intrinsically disordered C-terminal domain folds upon binding the RFX5 N-terminal dimerization domain, forming a V-shaped α-helical structure packed within an antiparallel coiled-coil staple, which then enables high-affinity recruitment of RFXB and relief of RFX5 autoinhibition [PMID:19274739, PMID:20732328, PMID:18723135]. Conserved hydrophobic and phosphorylatable C-terminal residues mediate isotype-specific CIITA recruitment, differentially coordinating HLA-DR, -DQ, and -DP expression [PMID:11486010, PMID:16337482]. Loss-of-function mutations in RFXAP cause MHC class II deficiency (bare lymphocyte syndrome complementation group D), and RFXAP also directly activates transcription of the histone demethylase KDM4A, linking the RFX complex to chromatin remodeling and DNA damage responses [PMID:9118943, PMID:33093461]."},"prefetch_data":{"uniprot":{"accession":"O00287","full_name":"Regulatory factor X-associated protein","aliases":["RFX DNA-binding complex 36 kDa subunit"],"length_aa":272,"mass_kda":28.2,"function":"Part of the RFX complex that binds to the X-box of MHC II promoters","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/O00287/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RFXAP","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/RFXAP","total_profiled":1310},"omim":[{"mim_id":"620817","title":"MHC CLASS II DEFICIENCY 4; MHC2D4","url":"https://www.omim.org/entry/620817"},{"mim_id":"620815","title":"MHC CLASS II DEFICIENCY 2; MHC2D2","url":"https://www.omim.org/entry/620815"},{"mim_id":"603200","title":"REGULATORY FACTOR X, ANKYRIN REPEAT-CONTAINING; RFXANK","url":"https://www.omim.org/entry/603200"},{"mim_id":"601863","title":"REGULATORY FACTOR X, 5; RFX5","url":"https://www.omim.org/entry/601863"},{"mim_id":"601861","title":"REGULATORY FACTOR X-ASSOCIATED PROTEIN; RFXAP","url":"https://www.omim.org/entry/601861"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nuclear speckles","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RFXAP"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"O00287","domains":[{"cath_id":"-","chopping":"229-263","consensus_level":"medium","plddt":95.654,"start":229,"end":263}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O00287","model_url":"https://alphafold.ebi.ac.uk/files/AF-O00287-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O00287-F1-predicted_aligned_error_v6.png","plddt_mean":63.97},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RFXAP","jax_strain_url":"https://www.jax.org/strain/search?query=RFXAP"},"sequence":{"accession":"O00287","fasta_url":"https://rest.uniprot.org/uniprotkb/O00287.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O00287/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O00287"}},"corpus_meta":[{"pmid":"26337469","id":"PMC_26337469","title":"Pancreatic cancer-derived exosomes transfer miRNAs to dendritic cells and inhibit RFXAP expression via miR-212-3p.","date":"2015","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/26337469","citation_count":245,"is_preprint":false},{"pmid":"9118943","id":"PMC_9118943","title":"RFXAP, a novel subunit of the RFX DNA binding complex is mutated in MHC class II deficiency.","date":"1997","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/9118943","citation_count":186,"is_preprint":false},{"pmid":"9287230","id":"PMC_9287230","title":"Mutation of RFXAP, a regulator of MHC class II genes, in primary MHC class II deficiency.","date":"1997","source":"The New England journal of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/9287230","citation_count":53,"is_preprint":false},{"pmid":"33093461","id":"PMC_33093461","title":"Fisetin inhibits proliferation of pancreatic adenocarcinoma by inducing DNA damage via RFXAP/KDM4A-dependent histone H3K36 demethylation.","date":"2020","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/33093461","citation_count":42,"is_preprint":false},{"pmid":"11486010","id":"PMC_11486010","title":"Expression of the three human major histocompatibility complex class II isotypes exhibits a differential dependence on the transcription factor RFXAP.","date":"2001","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/11486010","citation_count":27,"is_preprint":false},{"pmid":"18723135","id":"PMC_18723135","title":"Assembly of the RFX complex on the MHCII promoter: role of RFXAP and RFXB in relieving autoinhibition of RFX5.","date":"2008","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/18723135","citation_count":20,"is_preprint":false},{"pmid":"29467893","id":"PMC_29467893","title":"IFN-γ induces the upregulation of RFXAP via inhibition of miR-212-3p in pancreatic cancer cells: A novel mechanism for IFN-γ response.","date":"2018","source":"Oncology letters","url":"https://pubmed.ncbi.nlm.nih.gov/29467893","citation_count":19,"is_preprint":false},{"pmid":"16337482","id":"PMC_16337482","title":"Conserved residues of the bare lymphocyte syndrome transcription factor RFXAP determine coordinate MHC class II expression.","date":"2005","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/16337482","citation_count":14,"is_preprint":false},{"pmid":"18336911","id":"PMC_18336911","title":"Transcriptional silencing of RFXAP in MHC class II-deficiency.","date":"2008","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/18336911","citation_count":8,"is_preprint":false},{"pmid":"20732328","id":"PMC_20732328","title":"Solution structure of the heterotrimeric complex between the interaction domains of RFX5 and RFXAP from the RFX gene regulatory complex.","date":"2010","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/20732328","citation_count":7,"is_preprint":false},{"pmid":"22390233","id":"PMC_22390233","title":"Type III bare lymphocyte syndrome associated with a novel RFXAP mutation: a case report.","date":"2012","source":"International journal of immunogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/22390233","citation_count":7,"is_preprint":false},{"pmid":"19274739","id":"PMC_19274739","title":"Formation of the RFX gene regulatory complex induces folding of the interaction domain of RFXAP.","date":"2009","source":"Proteins","url":"https://pubmed.ncbi.nlm.nih.gov/19274739","citation_count":6,"is_preprint":false},{"pmid":"20024540","id":"PMC_20024540","title":"Coordinate loss of MHC class II expression in the diffuse large B cell lymphoma cell line OCI-Ly2 is due to a novel mutation in RFX-AP.","date":"2009","source":"Immunogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/20024540","citation_count":5,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7299,"output_tokens":2480,"usd":0.029548},"stage2":{"model":"claude-opus-4-6","input_tokens":5806,"output_tokens":2327,"usd":0.130807},"total_usd":0.160355,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"RFXAP is a novel subunit of the RFX DNA-binding complex; mutations in RFXAP abolish RFX complex DNA-binding activity and MHC class II gene expression, defining complementation group D of MHC-II deficiency. Transfection with wild-type RFXAP fully restores endogenous MHC-II gene expression.\",\n      \"method\": \"Complementation assays, transfection rescue, and identification of mutations in patient cell lines\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal complementation, mutation identification, in vivo rescue; independently replicated in NEJM same year\",\n      \"pmids\": [\"9118943\", \"9287230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Only a short C-terminal segment of RFXAP is essential for HLA-DR expression, while optimal HLA-DQ and HLA-DP expression requires a larger C-terminal segment. This differential requirement is due to isotype-specific differences in promoter occupancy and CIITA recruitment in vivo.\",\n      \"method\": \"Domain deletion analysis, in vivo ChIP/promoter occupancy assays, transfection rescue in RFXAP-deficient cell lines\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (functional rescue, in vivo promoter occupancy, CIITA recruitment) in a single rigorous study\",\n      \"pmids\": [\"11486010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Conserved hydrophobic and other C-terminal residues (not the glutamine-rich tract) of RFXAP are required for coordinate MHC-II isotype expression; mutation of potential phosphorylation sites abolishes RFXAP activity. Certain RFXAP mutants form transcriptionally inefficient complexes with isotype-specific promoter factors.\",\n      \"method\": \"Comparative genomic analysis, site-directed mutagenesis, complementation/rescue assays, ChIP (CIITA recruitment), chimeric reporter gene assays\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis combined with in vivo ChIP and reporter assays in a single study with multiple orthogonal methods\",\n      \"pmids\": [\"16337482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"RFX5 DNA-binding activity is autoinhibited by domains flanking its DNA-binding domain; both RFXAP and RFXB are required to relieve this autoinhibition. A single RFX complex (containing RFX5, RFXAP, and RFXB) binds to the proximal regulatory region of the MHC-II promoter.\",\n      \"method\": \"Electrophoretic mobility shift assays (EMSA) characterizing DNA binding of RFX5 alone and in complex with RFXAP and RFXB\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with defined recombinant components and rigorous EMSA analysis\",\n      \"pmids\": [\"18723135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A homozygous 75 bp insertion in the 5'-UTR of RFXAP impairs RFXAP promoter activity, abolishes RFXAP mRNA and protein expression, and reduces RNA polymerase II recruitment to RFXAP chromatin, representing a novel transcriptional silencing mechanism for MHC-II deficiency.\",\n      \"method\": \"Sequencing, promoter activity assays, ChIP (RNA Pol II), mRNA/protein expression analysis in patient cells\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods but single patient/lab study\",\n      \"pmids\": [\"18336911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The C-terminal domain of RFXAP (RFXAP-C) is intrinsically disordered but folds upon interaction with the N-terminal dimerization domain of RFX5 (RFX5-N). This folded RFX5(N)2–RFXAP(C) complex then binds RFXB with high affinity, defining a hierarchical assembly pathway for the RFX complex.\",\n      \"method\": \"NMR spectroscopy, circular dichroism spectroscopy, isothermal titration calorimetry\",\n      \"journal\": \"Proteins\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple biophysical methods (NMR, CD, ITC) establishing folding-upon-binding mechanism\",\n      \"pmids\": [\"19274739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The solution structure of the RFX5(N)2–RFXAP(C) complex was determined: two RFX5-N helices form an antiparallel coiled coil ('staple'), and RFXAP-C adopts two α-helices in a V-shape that packs within the staple. Leucine residues in RFX5-N (62-LYLYLQL-68) contribute to both the RFX5 dimer interface and the RFX5–RFXAP interface, and are critical for MHC-II expression in vivo.\",\n      \"method\": \"Solution NMR (15N- and 13C-edited), in vivo functional validation of leucine mutants\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution NMR structure with in vivo mutagenesis validation\",\n      \"pmids\": [\"20732328\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"An 11-base deletion in RFXAP causing a frameshift at amino acid 234 and loss of C-terminal residues is responsible for coordinate MHC-II loss in the DLBCL cell line OCI-Ly2; stable transfection of wild-type RFXAP restores MHC-II expression.\",\n      \"method\": \"Sequencing of RFXAP cDNA, stable transfection rescue in DLBCL cell line\",\n      \"journal\": \"Immunogenetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mutation identification with functional rescue, single lab\",\n      \"pmids\": [\"20024540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Pancreatic cancer-derived exosomes transfer miR-212-3p to dendritic cells, where it directly targets and inhibits RFXAP mRNA expression, leading to decreased MHC-II surface expression and induction of immune tolerance in dendritic cells.\",\n      \"method\": \"Exosome transfer experiments, bioinformatics target prediction, luciferase reporter validation of miR-212-3p targeting RFXAP 3'UTR, qRT-PCR, western blot\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — luciferase reporter plus functional assays, but single lab; mechanism of miR-212-3p suppression of RFXAP confirmed by multiple methods\",\n      \"pmids\": [\"26337469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RFXAP directly transcriptionally activates KDM4A (a histone H3K36 demethylase) in pancreatic cancer cells; RFXAP overexpression upregulates KDM4A, reduces H3K36 trimethylation, impairs DNA repair, and enhances fisetin-induced DNA damage, while RFXAP knockdown reverses these effects.\",\n      \"method\": \"ChIP-seq (RFXAP binding at KDM4A promoter), dual-luciferase reporter assay, RFXAP overexpression/silencing, immunofluorescence for DNA damage markers, xenograft model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-seq and reporter assay establish direct transcriptional regulation; multiple functional readouts in single lab\",\n      \"pmids\": [\"33093461\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RFXAP is an essential subunit of the trimeric RFX complex (with RFX5 and RFXB) that binds X-box elements in MHC class II gene promoters; its intrinsically disordered C-terminal domain folds upon binding to the RFX5 N-terminal dimerization domain (forming an antiparallel coiled-coil staple), enabling subsequent high-affinity RFXB recruitment and relief of RFX5 autoinhibition, while RFXAP's C-terminal conserved residues (including phosphorylatable sites) mediate isotype-specific CIITA recruitment and coordinate HLA-DR, -DQ, and -DP expression; additionally, RFXAP can transcriptionally activate KDM4A to modulate H3K36 methylation and DNA damage responses, and its expression is post-transcriptionally regulated by miR-212-3p.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"RFXAP is an essential subunit of the trimeric RFX transcription factor complex (with RFX5 and RFXB) that binds X-box elements in MHC class II gene promoters and is required for MHC class II gene expression [PMID:9118943, PMID:18723135]. Its intrinsically disordered C-terminal domain folds upon binding the RFX5 N-terminal dimerization domain, forming a V-shaped α-helical structure packed within an antiparallel coiled-coil staple, which then enables high-affinity recruitment of RFXB and relief of RFX5 autoinhibition [PMID:19274739, PMID:20732328, PMID:18723135]. Conserved hydrophobic and phosphorylatable C-terminal residues mediate isotype-specific CIITA recruitment, differentially coordinating HLA-DR, -DQ, and -DP expression [PMID:11486010, PMID:16337482]. Loss-of-function mutations in RFXAP cause MHC class II deficiency (bare lymphocyte syndrome complementation group D), and RFXAP also directly activates transcription of the histone demethylase KDM4A, linking the RFX complex to chromatin remodeling and DNA damage responses [PMID:9118943, PMID:33093461].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Identification of RFXAP as the gene defective in complementation group D of MHC class II deficiency established that a previously unknown RFX complex subunit is essential for MHC-II expression and RFX DNA-binding activity.\",\n      \"evidence\": \"Complementation cloning, mutation identification in patient cell lines, and transfection rescue restoring MHC-II expression\",\n      \"pmids\": [\"9118943\", \"9287230\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural information on RFXAP or its mode of incorporation into the RFX complex\", \"Mechanism by which RFXAP contributes to DNA binding unknown\", \"Relationship between RFXAP domains and function unresolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Domain mapping revealed that only the C-terminal segment of RFXAP is required for HLA-DR expression, while larger C-terminal regions are needed for HLA-DQ and -DP, demonstrating that RFXAP mediates isotype-specific promoter occupancy and CIITA recruitment.\",\n      \"evidence\": \"Deletion analysis with transfection rescue and in vivo ChIP/promoter occupancy assays in RFXAP-deficient cells\",\n      \"pmids\": [\"11486010\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of specific residues responsible for isotype selectivity not yet determined\", \"Mechanism of differential CIITA recruitment unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Site-directed mutagenesis pinpointed conserved hydrophobic residues and potential phosphorylation sites in the RFXAP C-terminus as essential for coordinate MHC-II expression and efficient CIITA recruitment, resolving which sequence features underlie isotype-specific transcription.\",\n      \"evidence\": \"Comparative genomics, site-directed mutagenesis, complementation rescue, ChIP for CIITA, chimeric reporter assays\",\n      \"pmids\": [\"16337482\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase(s) responsible for RFXAP phosphorylation not identified\", \"Whether phosphorylation regulates RFXAP in vivo remains untested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Biochemical reconstitution demonstrated that RFX5 DNA-binding activity is autoinhibited and that both RFXAP and RFXB are required to relieve autoinhibition, establishing the functional logic of the trimeric RFX complex.\",\n      \"evidence\": \"EMSA with recombinant RFX5 alone and in complex with RFXAP and RFXB\",\n      \"pmids\": [\"18723135\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of autoinhibition relief not resolved\", \"Stoichiometry of the full complex on DNA not determined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Biophysical studies revealed that the RFXAP C-terminal domain is intrinsically disordered but undergoes coupled folding-and-binding upon interacting with the RFX5 N-terminal dimer, and that this pre-formed subcomplex then recruits RFXB with high affinity, defining a hierarchical assembly pathway.\",\n      \"evidence\": \"NMR, circular dichroism, and isothermal titration calorimetry on recombinant domains\",\n      \"pmids\": [\"19274739\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length complex structure not available\", \"Whether the hierarchical assembly occurs on or off DNA in cells unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"The solution NMR structure of the RFX5(N)₂–RFXAP(C) complex showed RFXAP-C adopting a V-shaped two-helix fold packed within an antiparallel coiled-coil staple formed by RFX5-N, with leucine residues at the interface critical for MHC-II expression in vivo.\",\n      \"evidence\": \"Solution NMR structure determination (¹⁵N/¹³C-edited) with in vivo validation of leucine point mutants\",\n      \"pmids\": [\"20732328\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the full trimeric complex with RFXB not determined\", \"How the structural interface connects to CIITA recruitment is unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Discovery that pancreatic cancer exosomes deliver miR-212-3p to dendritic cells to directly suppress RFXAP mRNA revealed a post-transcriptional mechanism by which tumors downregulate MHC-II expression for immune evasion.\",\n      \"evidence\": \"Exosome transfer assays, luciferase reporter validation of miR-212-3p targeting the RFXAP 3′-UTR, qRT-PCR and western blot in dendritic cells\",\n      \"pmids\": [\"26337469\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab study; independent replication lacking\", \"In vivo relevance of miR-212-3p-mediated RFXAP suppression in patient tumors not established\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identification of KDM4A as a direct transcriptional target of RFXAP expanded its functional scope beyond MHC-II regulation to chromatin remodeling and DNA damage responses.\",\n      \"evidence\": \"ChIP-seq showing RFXAP binding at the KDM4A promoter, dual-luciferase reporter assay, RFXAP overexpression/knockdown affecting H3K36me3 levels and DNA damage markers in pancreatic cancer cells and xenografts\",\n      \"pmids\": [\"33093461\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether RFXAP acts at KDM4A as part of the canonical RFX complex or independently is unknown\", \"Genome-wide identification of RFXAP transcriptional targets beyond MHC-II and KDM4A not performed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A complete structural model of the full trimeric RFX–DNA complex, the identity of kinases phosphorylating RFXAP, and the genome-wide spectrum of RFXAP transcriptional targets remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length trimeric RFX complex structure on DNA\", \"Kinase(s) for RFXAP phosphorylation unidentified\", \"Genome-wide RFXAP target gene repertoire undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 1, 2, 9]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 1, 3, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 1, 2, 9]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 7]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"complexes\": [\n      \"RFX complex (RFX5/RFXAP/RFXB)\"\n    ],\n    \"partners\": [\n      \"RFX5\",\n      \"RFXB\",\n      \"CIITA\",\n      \"KDM4A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}