{"gene":"HLA-A","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":1979,"finding":"HLA-A and HLA-B heavy chains are initially synthesized as high-mannose glycoproteins in the rough endoplasmic reticulum, associate with beta-2-microglobulin within 10-15 min of synthesis, undergo oligosaccharide processing from high-mannose to complex form over ~30 min, and then traffic to the cell surface 60-80 min after synthesis; pulse-chase experiments established a precursor-product relationship between these populations.","method":"Pulse-chase radiolabeling, immunoprecipitation, subcellular fractionation, glycosylation analysis in B lymphoblastoid cells","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vivo pulse-chase with multiple time points, immunoprecipitation, replicated by independent group (PMID:7000762)","pmids":["93026"],"is_preprint":false},{"year":1980,"finding":"HLA-A and HLA-B heavy chains are inserted asymmetrically as transmembrane polypeptides into the rough ER; beta-2-microglobulin association is required for subsequent oligosaccharide processing and intracellular transport from the ER to the cell surface, as demonstrated using Daudi cells (which lack beta-2-microglobulin) where heavy chains accumulate without further processing.","method":"Pulse-chase radiolabeling, glycosylation inhibitor studies, Daudi cell (beta-2-microglobulin-deficient) comparison","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution-type experiment using beta-2-microglobulin-deficient cells, replicated/corroborated by PMID:93026","pmids":["7000762"],"is_preprint":false},{"year":1978,"finding":"Purified detergent-soluble HLA-A and HLA-B antigens were reconstituted into phospholipid vesicles and shown to orient with their extracellular domains facing outward (consistent with membrane topology via COOH-terminus anchor), retaining antigenic activity as confirmed by anti-beta-2-microglobulin binding and antibody-mediated cytotoxicity inhibition.","method":"Detergent removal reconstitution into phospholipid vesicles, protease cleavage, electron microscopy, antibody inhibition assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct reconstitution of purified protein with structural and functional validation, single lab but multiple orthogonal methods","pmids":["356051"],"is_preprint":false},{"year":1985,"finding":"Normal cell surface expression of HLA-A and HLA-B antigens requires at least one trans-active post-transcriptional step; mutants with intact HLA-A and -B genes and transcripts but reduced/absent surface antigen were complemented by cell fusion, indicating a trans-acting factor is necessary for surface expression.","method":"Mutagenesis and immunoselection, cell fusion complementation assays, DNA analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic complementation by cell fusion, multiple mutant lines analyzed, single lab","pmids":["3906658"],"is_preprint":false},{"year":1982,"finding":"Interferon-alpha (IFN-alpha) increases HLA-A,B,C surface expression through increased rate of synthesis of HLA heavy chains and beta-2-microglobulin, accompanied by a dramatic increase in HLA mRNA levels, demonstrating transcriptional upregulation as the primary mechanism of IFN-alpha-induced HLA class I expression.","method":"Cytofluorimetry, [35S]methionine pulse labeling, Northern/hybridization with HLA cDNA probe, surface iodination","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (flow cytometry, metabolic labeling, mRNA quantification) in single lab establishing transcriptional mechanism","pmids":["6765173"],"is_preprint":false},{"year":2000,"finding":"Differential quantitative expression of HLA-A and HLA-B antigens is genetically predetermined and regulated at multiple steps including gene transcription, pre-mRNA splicing, and mRNA degradation; the relative quantities of mature mRNA in the cytoplasm are not proportional to pre-mRNA levels in the nucleus for four of six cell lines, indicating splicing as a regulatory checkpoint, while mRNA and protein levels are generally proportional except for HLA-A24.","method":"Competitive RT-PCR, RNA polymerase II inhibitor (DRB) treatment, nuclear pre-mRNA measurement, protein quantification in lymphoblastoid cell lines","journal":"Human immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple molecular methods in single lab, mechanistic dissection across six cell lines","pmids":["10980390"],"is_preprint":false},{"year":2018,"finding":"The RNA-binding protein MEX3B binds to the 3' UTR of HLA-A mRNA and destabilizes it, leading to reduced HLA-A surface expression on melanoma cells and resistance to T-cell killing; overexpression of exogenous HLA-A2 rescued T-cell-mediated killing in MEX3B-overexpressing cells.","method":"ORF overexpression screen, luciferase reporter assay, RNA-binding protein immunoprecipitation, flow cytometry, cytotoxicity assay, IFN-gamma ELISA","journal":"Clinical cancer research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct binding demonstrated by RIP assay, functional rescue experiment, multiple orthogonal methods in single lab","pmids":["29496759"],"is_preprint":false},{"year":2018,"finding":"HLA-A-derived signal peptide specifically binds HLA-E and determines HLA-E expression levels; elevated HLA-A expression (allele-dependent) provides more signal peptide to HLA-E, increasing HLA-E surface levels, which engages the inhibitory NKG2A receptor on NK cells and impairs NK cell clearance of HIV-infected targets. HLA-B haplotypes favoring NKG2A-mediated NK cell licensing exacerbate this effect.","method":"Population cohort analysis, genetic association study (9763 HIV-infected individuals, 21 cohorts), mechanistic analysis of signal peptide-HLA-E interaction, NKG2A receptor blockade experiments","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — large multi-cohort epidemiological validation combined with mechanistic pathway dissection (signal peptide→HLA-E→NKG2A axis), replicated across 21 cohorts","pmids":["29302013"],"is_preprint":false},{"year":2014,"finding":"The activating KIR2DS2 binds HLA-A*11:01 as its cognate ligand; crystal structure of the KIR2DS2–HLA-A*11:01 complex at 2.5 Å revealed residues Tyr45 and Asp72 as critical for binding specificity, and KIR binding can be altered by changes at peptide position 8, indicating peptide-sequence dependence of the KIR–HLA interaction.","method":"Crystal structure determination (X-ray crystallography at 2.5 Å), KIR2DS2 tetramer binding to live cells, heteronuclear single quantum coherence NMR, site-directed mutagenesis (residue changes at p8)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus NMR plus live-cell tetramer binding and mutagenesis, multiple orthogonal Tier 1 methods in one study","pmids":["24550293"],"is_preprint":false},{"year":2005,"finding":"High-resolution crystal structure of HLA-A*11:01 in complex with SARS-CoV nucleocapsid peptide (KTFPPTEPK) at 1.45 Å resolution revealed 17 hydrogen bonds between the alpha-chain and peptide, 9 tightly bound water molecules in the peptide-binding groove, and that Thr6 of the peptide does not efficiently use the middle (E) pocket, highlighting a target for optimization.","method":"X-ray crystallography at 1.45 Å resolution, in vitro peptide-binding studies (IC50 measurements)","journal":"Acta crystallographica. Section D, Biological crystallography","confidence":"High","confidence_rationale":"Tier 1 / Moderate — high-resolution crystal structure with functional binding validation, single lab","pmids":["16041067"],"is_preprint":false},{"year":2014,"finding":"HLA-A*02:01 can present 15-mer peptides (non-canonical length) that adopt super-bulged conformations in the peptide-binding groove; these 15-mer peptides have binding affinity and stability comparable to canonical 8-11-mer peptides, and T cells can recognize 15-mer peptides in the context of HLA-A*02:01, demonstrating immunogenicity.","method":"HLA folding and thermal stability assays, X-ray crystallography (two 15-mer:HLA-A*02:01 structures solved), T-cell recognition functional assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structures plus functional T-cell assays and biophysical measurements, multiple orthogonal methods in single study","pmids":["25505266"],"is_preprint":false},{"year":2019,"finding":"Crystal structures of HLA-A*30:01 and HLA-A*30:03 with pathogen peptides revealed divergent peptide presentation characteristics: HLA-A*30:03 but not HLA-A*30:01 can bind HLA-A*01:01-favored peptides; residue 77 in the F pocket is a key determinant of supertype-featured peptide-binding motifs, and interchanging residue 77 between A*30:01 and A*30:03 switched their presented peptide profiles.","method":"X-ray crystallography, thermostability measurements, peptide-binding assays, residue 77 swap mutagenesis","journal":"Frontiers in immunology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structures plus functional mutagenesis (residue 77 swap), multiple orthogonal methods demonstrating mechanistic basis","pmids":["31396224"],"is_preprint":false},{"year":2013,"finding":"HLA-A expression is predominantly regulated by the MAPK (ERK) pathway in gastric and esophageal cancer cells; inhibition of MAPK (via PD98059 or MAPK siRNA) upregulates HLA-A02 and HLA-A24 expression in parallel with antigen-processing machinery components and enhances CTL killing; a strong inverse correlation between p-ERK and HLA class I was confirmed in clinical tumor samples.","method":"MAPK/PI3K inhibitor treatment (PD98059, wortmannin, lapatinib), MAPK siRNA knockdown, Western blot, qPCR, flow cytometry, CTL cytotoxicity assay, immunohistochemistry of 102 tumor samples","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple inhibitor approaches, siRNA, functional CTL assay, and clinical tissue validation across 102 samples, single lab with multiple orthogonal methods","pmids":["24244023"],"is_preprint":false},{"year":2024,"finding":"CAF-derived extracellular vesicle-packaged lncRNA RP11-161H23.5 promotes HLA-A mRNA degradation by forming a complex with CNOT4, a subunit of the CCR4-NOT mRNA deadenylase complex, which shortens the poly(A) tail of HLA-A mRNA and enhances its degradation, thereby reducing HLA-A surface expression and promoting immune evasion in pancreatic cancer.","method":"Extracellular vesicle isolation, RIP/co-IP of lncRNA-CNOT4 complex, poly(A) tail assay, Western blot, flow cytometry, syngeneic tumor models","journal":"Journal of extracellular vesicles","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP demonstrating complex formation, poly(A) tail functional assay, in vivo model, single lab","pmids":["39041344"],"is_preprint":false},{"year":2024,"finding":"LILRB2 promotes HLA-A ubiquitination and proteasomal degradation by facilitating the interaction between the ubiquitin E3 ligase MARCH9 and HLA-A, reducing HLA-A surface expression and enabling immune evasion from CD8+ T cells in breast cancer.","method":"Immunoprecipitation, histidine pulldown ubiquitination assay, Western blot, flow cytometry, syngeneic graft mouse model","journal":"Cellular oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct co-IP showing LILRB2-MARCH9-HLA-A interaction, ubiquitination pulldown, in vivo syngeneic model, single lab","pmids":["38656573"],"is_preprint":false},{"year":2012,"finding":"Secreted HLA-A*02:01 (sHLA) traffics through intracellular compartments with similar maturation kinetics to membrane-bound HLA-A*02:01, and mass spectrometry of peptides eluted from sHLA and membrane-bound HLA-A*02:01 showed substantial overlap in their immunopeptidome, identifying 1266 non-redundant peptide ligands including peptides with post-translational modifications.","method":"Intracellular trafficking comparison, mass spectrometry of eluted peptides, bioinformatic peptide validation","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mass spectrometry with multiple peptide sources and trafficking assay, single lab with two orthogonal methods","pmids":["22424782"],"is_preprint":false},{"year":1988,"finding":"Diversity in HLA-A (and HLA-B, -C) molecules is concentrated at 20 positions of high variability in the alpha-1 and alpha-2 domains; variation between alpha-1 and alpha-2 domains is distinct and may reflect partial segregation of peptide-binding and TCR-binding functions; genetic exchange between alleles of the same locus (rather than between loci) is the primary mechanism generating HLA-A diversity.","method":"Amino acid sequence comparison of 39 HLA molecules, structural analysis of polymorphic positions","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 3 / Strong — comparative sequence analysis replicated across many alleles, no direct functional experiment but mechanistic inference from structural positions, widely cited","pmids":["3375250"],"is_preprint":false},{"year":2001,"finding":"HLA-A*01-restricted T-cell epitope from WT1 (residues 317-327) is processed by proteasomal cleavage and recognized by CTL from patients with hematologic malignancies; depletion of regulatory T cells enabled expansion of WT1-specific CTL that specifically lysed HLA-A*01+ WT1-expressing tumor cell lines.","method":"Proteasomal degradation assay, intracellular cytokine cytometry, CTL expansion and cytotoxicity assay","journal":"Clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proteasomal processing demonstrated biochemically, functional CTL killing confirmed, single lab","pmids":["17189421"],"is_preprint":false},{"year":2018,"finding":"HLA-A*33:03 allele restricts ticlopidine-specific CD8+ T-cell activation; blocking HLA class I and HLA-A*33 antibodies reduced the T-cell response, indicating that drug-HLA interaction at the HLA-A*33:03 allele is important for T-cell-mediated liver injury.","method":"CD8+ T-cell cloning and proliferation assay, IFN-gamma secretion, HLA antibody blocking","journal":"Chemical research in toxicology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — T-cell clone functional assay with antibody blocking establishing HLA-A*33:03 restriction, single lab","pmids":["30179004"],"is_preprint":false}],"current_model":"HLA-A encodes a classical MHC class I heavy chain that associates with beta-2-microglobulin in the ER (a required step for proper folding, glycan processing, and surface trafficking), binds 8-11 mer peptides (and occasionally longer super-bulged peptides) in its alpha-1/alpha-2 groove for CD8+ T-cell surveillance, is transcriptionally upregulated by interferon signaling and downregulated by MAPK pathway activity; its surface expression is post-transcriptionally regulated by RNA-binding proteins (MEX3B) and post-translationally by ubiquitin E3 ligases (MARCH9 via LILRB2), and its allele-specific signal peptide controls HLA-E surface levels to modulate NKG2A-dependent NK cell inhibition."},"narrative":{"mechanistic_narrative":"HLA-A encodes a classical MHC class I heavy chain that captures short peptides for surveillance by CD8+ T cells and modulatory NK-cell receptors [PMID:16041067, PMID:24550293]. The newly synthesized heavy chain is a transmembrane glycoprotein co-translationally inserted into the rough ER, where it associates with beta-2-microglobulin within minutes; this association is a prerequisite for oligosaccharide maturation from high-mannose to complex form and for trafficking to the cell surface, as heavy chains accumulate unprocessed in beta-2-microglobulin-deficient cells [PMID:93026, PMID:7000762]. Surface assembly additionally requires at least one trans-acting post-transcriptional factor [PMID:3906658]. The peptide is bound in the alpha-1/alpha-2 groove through an extensive hydrogen-bond and ordered-water network, with pocket residues (e.g., F-pocket residue 77) dictating allele-specific binding motifs; the groove canonically accommodates 8-11-mers but can also present super-bulged 15-mer peptides that remain stable and immunogenic [PMID:16041067, PMID:31396224, PMID:25505266]. Polymorphism in HLA-A is concentrated at variable positions in the alpha-1/alpha-2 domains that partition peptide-binding and TCR-binding functions, generated chiefly by intralocus allelic exchange [PMID:3375250]. Beyond TCR engagement, HLA-A serves as a ligand for the activating receptor KIR2DS2 in a peptide-sequence-dependent manner [PMID:24550293], and its allele-specific signal peptide loads HLA-E to set HLA-E surface levels that engage the inhibitory NKG2A receptor and tune NK-cell activity [PMID:29302013]. HLA-A surface levels are tightly regulated at multiple layers: transcriptionally upregulated by interferon-alpha and suppressed by MAPK/ERK signaling [PMID:6765173, PMID:24244023], post-transcriptionally destabilized by the RNA-binding protein MEX3B and by a CAF-derived lncRNA-CNOT4 deadenylation complex [PMID:29496759, PMID:39041344], and post-translationally degraded via LILRB2-facilitated MARCH9-dependent ubiquitination [PMID:38656573]; loss of these controls reduces antigen presentation and promotes tumor immune evasion.","teleology":[{"year":1980,"claim":"Established that HLA-A heavy chains require beta-2-microglobulin association in the ER before they can mature and reach the surface, defining the obligatory assembly step of the class I molecule.","evidence":"Pulse-chase radiolabeling and glycosylation analysis comparing normal versus beta-2-microglobulin-deficient Daudi cells, with vesicle reconstitution of purified antigen","pmids":["7000762","93026","356051"],"confidence":"High","gaps":["Did not identify the chaperone machinery coordinating folding and peptide loading","Trans-acting factor required for surface expression not molecularly defined"]},{"year":1985,"claim":"Showed that surface expression depends on a trans-acting post-transcriptional factor beyond intact genes and transcripts, pointing to a regulated assembly/loading step.","evidence":"Mutagenesis with immunoselection and cell-fusion complementation in cells with normal HLA-A/B transcripts but absent surface antigen","pmids":["3906658"],"confidence":"Medium","gaps":["The trans-acting factor was not cloned or identified","Step at which it acts (loading vs trafficking) unresolved"]},{"year":1982,"claim":"Demonstrated that interferon-alpha raises HLA class I surface levels primarily by increasing heavy-chain and beta-2-microglobulin synthesis via elevated mRNA, defining transcriptional induction as the dominant cytokine-driven mechanism.","evidence":"Cytofluorimetry, metabolic labeling, and mRNA hybridization in IFN-alpha-treated cells","pmids":["6765173"],"confidence":"High","gaps":["Promoter elements and transcription factors mediating induction not mapped","Did not address allele-specific responsiveness"]},{"year":1988,"claim":"Localized HLA-A diversity to discrete variable positions in the alpha-1/alpha-2 domains and inferred functional segregation of peptide- and TCR-binding surfaces, framing the structural basis of allelic specificity.","evidence":"Comparative amino-acid sequence and structural-position analysis across 39 HLA molecules","pmids":["3375250"],"confidence":"Medium","gaps":["Sequence inference without direct functional test of individual positions","Did not establish peptide-binding consequences of specific residues"]},{"year":2000,"claim":"Revealed that quantitative HLA-A expression is genetically set and controlled at transcription, splicing, and mRNA degradation, expanding regulation beyond transcription alone.","evidence":"Competitive RT-PCR, RNA polymerase II inhibition, and pre-mRNA/protein quantification across six lymphoblastoid lines","pmids":["10980390"],"confidence":"Medium","gaps":["No trans-factors mediating splicing or decay identified","Mechanism of HLA-A24 mRNA-protein discordance unexplained"]},{"year":2005,"claim":"Resolved at near-atomic detail how HLA-A binds a defined pathogen peptide, mapping the hydrogen-bond and ordered-water network of the groove.","evidence":"1.45 Å X-ray structure of HLA-A*11:01 with SARS-CoV nucleocapsid peptide plus IC50 binding measurements","pmids":["16041067"],"confidence":"High","gaps":["Single allele/peptide pair","Does not address TCR recognition geometry"]},{"year":2014,"claim":"Defined HLA-A as a direct ligand for the activating NK receptor KIR2DS2 and demonstrated peptide-dependence of the interaction, linking HLA-A to NK as well as T-cell recognition.","evidence":"2.5 Å crystal structure of KIR2DS2–HLA-A*11:01, NMR, live-cell tetramer binding, and p8 mutagenesis","pmids":["24550293"],"confidence":"High","gaps":["Functional NK-cell consequences in physiological settings not fully delineated","Breadth of peptide repertoires supporting KIR binding unknown"]},{"year":2014,"claim":"Showed the HLA-A groove can stably present non-canonical 15-mer super-bulged peptides that remain immunogenic, broadening the recognized peptide-length repertoire.","evidence":"Folding/thermal stability assays, two 15-mer:HLA-A*02:01 crystal structures, and T-cell recognition assays","pmids":["25505266"],"confidence":"High","gaps":["Frequency of long-peptide presentation in vivo unquantified","Processing pathway generating such peptides unclear"]},{"year":2013,"claim":"Identified MAPK/ERK signaling as a dominant suppressor of HLA-A and antigen-processing machinery, providing a tumor-relevant lever for restoring CTL recognition.","evidence":"MAPK inhibitors/siRNA with Western blot, qPCR, flow cytometry, CTL assays, and IHC of 102 tumors","pmids":["24244023"],"confidence":"High","gaps":["Transcriptional intermediaries linking ERK to HLA-A promoter not defined","Generalizability beyond gastric/esophageal cancer untested"]},{"year":2018,"claim":"Connected allele-specific HLA-A expression to NK-cell control via signal-peptide loading of HLA-E and NKG2A engagement, defining a non-classical immunoregulatory axis affecting HIV outcomes.","evidence":"Multi-cohort genetic association (9763 individuals, 21 cohorts) with signal-peptide/HLA-E mechanistic analysis and NKG2A blockade","pmids":["29302013"],"confidence":"High","gaps":["Quantitative contribution relative to direct CD8 presentation unresolved","Allele coverage of signal-peptide effects incomplete"]},{"year":2018,"claim":"Demonstrated post-transcriptional control of HLA-A by MEX3B binding the 3' UTR to destabilize the mRNA, mechanistically linking RNA stability to immune escape.","evidence":"ORF overexpression screen, luciferase reporter, RIP, flow cytometry, and HLA-A2 rescue of T-cell killing in melanoma","pmids":["29496759"],"confidence":"High","gaps":["Upstream regulators of MEX3B in tumors unknown","Specificity for HLA-A versus other class I genes not fully resolved"]},{"year":2024,"claim":"Extended post-transcriptional control to a CAF-derived extracellular-vesicle lncRNA that recruits CNOT4/CCR4-NOT to deadenylate and degrade HLA-A mRNA, defining a stromal route to immune evasion.","evidence":"EV isolation, lncRNA-CNOT4 co-IP, poly(A) tail assay, flow cytometry, and syngeneic pancreatic tumor models","pmids":["39041344"],"confidence":"Medium","gaps":["Single lab; reciprocal validation of the lncRNA-CNOT4 interaction limited","Direct binding of lncRNA to HLA-A mRNA not established"]},{"year":2024,"claim":"Defined post-translational degradation of HLA-A through LILRB2-facilitated MARCH9-dependent ubiquitination, adding a protein-stability layer to immune escape control.","evidence":"Co-IP, histidine-pulldown ubiquitination assay, flow cytometry, and syngeneic breast tumor model","pmids":["38656573"],"confidence":"Medium","gaps":["Single lab without reciprocal structural validation","Mechanism by which LILRB2 bridges MARCH9 to HLA-A unresolved"]},{"year":null,"claim":"How the multiple regulatory layers (transcriptional, splicing, mRNA-decay, ubiquitination) are integrated allele-specifically to set steady-state HLA-A surface levels in vivo remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking IFN/MAPK transcriptional control with MEX3B/CCR4-NOT decay and MARCH9 degradation","Identity of the 1985 trans-acting surface-expression factor still unknown"]}],"mechanism_profile":{"molecular_activity":[],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,1]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[7,8,12]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,14]}],"complexes":["MHC class I (HLA-A heavy chain : beta-2-microglobulin)"],"partners":["B2M","MEX3B","MARCH9","LILRB2","KIR2DS2","HLA-E","CNOT4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P04439","full_name":"HLA class I histocompatibility antigen, A alpha chain","aliases":["Human leukocyte antigen A","HLA-A"],"length_aa":365,"mass_kda":40.8,"function":"Allele A*74:01: Presents immunodominant HIV-1 epitopes derived from gag-pol (GQMVHQAISPR, QIYPGIKVR) and rev (RQIHSISER), carrying an aliphatic residue at position 2 and Arg anchor residue at the C-terminus. May contribute to viral load control in chronic HIV-1 infection","subcellular_location":"Cell membrane; Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/P04439/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HLA-A","classification":"Not Classified","n_dependent_lines":26,"n_total_lines":1208,"dependency_fraction":0.02152317880794702},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000206503","cell_line_id":"CID001894","localizations":[{"compartment":"membrane","grade":3},{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"CANX","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001894","total_profiled":1310},"omim":[{"mim_id":"620817","title":"MHC CLASS II DEFICIENCY 4; MHC2D4","url":"https://www.omim.org/entry/620817"},{"mim_id":"620778","title":"KILLER CELL IMMUNOGLOBULIN-LIKE RECEPTOR, THREE DOMAINS, SHORT CYTOPLASMIC TAIL, 1; KIR3DS1","url":"https://www.omim.org/entry/620778"},{"mim_id":"618864","title":"CHROMOSOME 19 OPEN READING FRAME 48, PSEUDOGENE; C19ORF48P","url":"https://www.omim.org/entry/618864"},{"mim_id":"617534","title":"YIP1 DOMAIN FAMILY, MEMBER 4; YIPF4","url":"https://www.omim.org/entry/617534"},{"mim_id":"616888","title":"TRANSMEMBRANE PROTEIN 8B; TMEM8B","url":"https://www.omim.org/entry/616888"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Golgi apparatus","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/HLA-A"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P04439","domains":[{"cath_id":"3.30.500.10","chopping":"24-203","consensus_level":"high","plddt":97.0133,"start":24,"end":203},{"cath_id":"2.60.40.10","chopping":"209-296","consensus_level":"high","plddt":96.3214,"start":209,"end":296}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P04439","model_url":"https://alphafold.ebi.ac.uk/files/AF-P04439-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P04439-F1-predicted_aligned_error_v6.png","plddt_mean":87.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HLA-A","jax_strain_url":"https://www.jax.org/strain/search?query=HLA-A"},"sequence":{"accession":"P04439","fasta_url":"https://rest.uniprot.org/uniprotkb/P04439.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P04439/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P04439"}},"corpus_meta":[{"pmid":"3375250","id":"PMC_3375250","title":"Nature of polymorphism in HLA-A, -B, and -C molecules.","date":"1988","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/3375250","citation_count":422,"is_preprint":false},{"pmid":"93026","id":"PMC_93026","title":"Assembly and maturation of HLA-A and HLA-B antigens in vivo.","date":"1979","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/93026","citation_count":302,"is_preprint":false},{"pmid":"3412487","id":"PMC_3412487","title":"HLA-A and B polymorphisms predate the divergence of humans and chimpanzees.","date":"1988","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/3412487","citation_count":300,"is_preprint":false},{"pmid":"7000762","id":"PMC_7000762","title":"Biosynthesis of HLA-A and HLA-B antigens in vivo.","date":"1980","source":"The Journal of biological 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medicine","url":"https://pubmed.ncbi.nlm.nih.gov/27072810","citation_count":7,"is_preprint":false},{"pmid":"23083632","id":"PMC_23083632","title":"Paradoxical downregulation of HLA-A expression by IFNγ associated with schizophrenia and noncoding genes.","date":"2012","source":"Immunobiology","url":"https://pubmed.ncbi.nlm.nih.gov/23083632","citation_count":7,"is_preprint":false},{"pmid":"19903485","id":"PMC_19903485","title":"Identification and characterization of HLA-A*0301 epitopes in HIV-1 gag proteins using a novel approach.","date":"2009","source":"Journal of immunological methods","url":"https://pubmed.ncbi.nlm.nih.gov/19903485","citation_count":7,"is_preprint":false},{"pmid":"16878186","id":"PMC_16878186","title":"Analysis of HFE gene mutations and HLA-A alleles in Brazilian patients with iron overload.","date":"2006","source":"Sao Paulo medical journal = Revista paulista de medicina","url":"https://pubmed.ncbi.nlm.nih.gov/16878186","citation_count":7,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":49999,"output_tokens":4924,"usd":0.111929,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13225,"output_tokens":4321,"usd":0.087075,"stage2_stop_reason":"end_turn"},"total_usd":0.199004,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1979,\n      \"finding\": \"HLA-A and HLA-B heavy chains are initially synthesized as high-mannose glycoproteins in the rough endoplasmic reticulum, associate with beta-2-microglobulin within 10-15 min of synthesis, undergo oligosaccharide processing from high-mannose to complex form over ~30 min, and then traffic to the cell surface 60-80 min after synthesis; pulse-chase experiments established a precursor-product relationship between these populations.\",\n      \"method\": \"Pulse-chase radiolabeling, immunoprecipitation, subcellular fractionation, glycosylation analysis in B lymphoblastoid cells\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vivo pulse-chase with multiple time points, immunoprecipitation, replicated by independent group (PMID:7000762)\",\n      \"pmids\": [\"93026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1980,\n      \"finding\": \"HLA-A and HLA-B heavy chains are inserted asymmetrically as transmembrane polypeptides into the rough ER; beta-2-microglobulin association is required for subsequent oligosaccharide processing and intracellular transport from the ER to the cell surface, as demonstrated using Daudi cells (which lack beta-2-microglobulin) where heavy chains accumulate without further processing.\",\n      \"method\": \"Pulse-chase radiolabeling, glycosylation inhibitor studies, Daudi cell (beta-2-microglobulin-deficient) comparison\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution-type experiment using beta-2-microglobulin-deficient cells, replicated/corroborated by PMID:93026\",\n      \"pmids\": [\"7000762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1978,\n      \"finding\": \"Purified detergent-soluble HLA-A and HLA-B antigens were reconstituted into phospholipid vesicles and shown to orient with their extracellular domains facing outward (consistent with membrane topology via COOH-terminus anchor), retaining antigenic activity as confirmed by anti-beta-2-microglobulin binding and antibody-mediated cytotoxicity inhibition.\",\n      \"method\": \"Detergent removal reconstitution into phospholipid vesicles, protease cleavage, electron microscopy, antibody inhibition assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct reconstitution of purified protein with structural and functional validation, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"356051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"Normal cell surface expression of HLA-A and HLA-B antigens requires at least one trans-active post-transcriptional step; mutants with intact HLA-A and -B genes and transcripts but reduced/absent surface antigen were complemented by cell fusion, indicating a trans-acting factor is necessary for surface expression.\",\n      \"method\": \"Mutagenesis and immunoselection, cell fusion complementation assays, DNA analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic complementation by cell fusion, multiple mutant lines analyzed, single lab\",\n      \"pmids\": [\"3906658\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1982,\n      \"finding\": \"Interferon-alpha (IFN-alpha) increases HLA-A,B,C surface expression through increased rate of synthesis of HLA heavy chains and beta-2-microglobulin, accompanied by a dramatic increase in HLA mRNA levels, demonstrating transcriptional upregulation as the primary mechanism of IFN-alpha-induced HLA class I expression.\",\n      \"method\": \"Cytofluorimetry, [35S]methionine pulse labeling, Northern/hybridization with HLA cDNA probe, surface iodination\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (flow cytometry, metabolic labeling, mRNA quantification) in single lab establishing transcriptional mechanism\",\n      \"pmids\": [\"6765173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Differential quantitative expression of HLA-A and HLA-B antigens is genetically predetermined and regulated at multiple steps including gene transcription, pre-mRNA splicing, and mRNA degradation; the relative quantities of mature mRNA in the cytoplasm are not proportional to pre-mRNA levels in the nucleus for four of six cell lines, indicating splicing as a regulatory checkpoint, while mRNA and protein levels are generally proportional except for HLA-A24.\",\n      \"method\": \"Competitive RT-PCR, RNA polymerase II inhibitor (DRB) treatment, nuclear pre-mRNA measurement, protein quantification in lymphoblastoid cell lines\",\n      \"journal\": \"Human immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple molecular methods in single lab, mechanistic dissection across six cell lines\",\n      \"pmids\": [\"10980390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The RNA-binding protein MEX3B binds to the 3' UTR of HLA-A mRNA and destabilizes it, leading to reduced HLA-A surface expression on melanoma cells and resistance to T-cell killing; overexpression of exogenous HLA-A2 rescued T-cell-mediated killing in MEX3B-overexpressing cells.\",\n      \"method\": \"ORF overexpression screen, luciferase reporter assay, RNA-binding protein immunoprecipitation, flow cytometry, cytotoxicity assay, IFN-gamma ELISA\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding demonstrated by RIP assay, functional rescue experiment, multiple orthogonal methods in single lab\",\n      \"pmids\": [\"29496759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HLA-A-derived signal peptide specifically binds HLA-E and determines HLA-E expression levels; elevated HLA-A expression (allele-dependent) provides more signal peptide to HLA-E, increasing HLA-E surface levels, which engages the inhibitory NKG2A receptor on NK cells and impairs NK cell clearance of HIV-infected targets. HLA-B haplotypes favoring NKG2A-mediated NK cell licensing exacerbate this effect.\",\n      \"method\": \"Population cohort analysis, genetic association study (9763 HIV-infected individuals, 21 cohorts), mechanistic analysis of signal peptide-HLA-E interaction, NKG2A receptor blockade experiments\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — large multi-cohort epidemiological validation combined with mechanistic pathway dissection (signal peptide→HLA-E→NKG2A axis), replicated across 21 cohorts\",\n      \"pmids\": [\"29302013\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The activating KIR2DS2 binds HLA-A*11:01 as its cognate ligand; crystal structure of the KIR2DS2–HLA-A*11:01 complex at 2.5 Å revealed residues Tyr45 and Asp72 as critical for binding specificity, and KIR binding can be altered by changes at peptide position 8, indicating peptide-sequence dependence of the KIR–HLA interaction.\",\n      \"method\": \"Crystal structure determination (X-ray crystallography at 2.5 Å), KIR2DS2 tetramer binding to live cells, heteronuclear single quantum coherence NMR, site-directed mutagenesis (residue changes at p8)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus NMR plus live-cell tetramer binding and mutagenesis, multiple orthogonal Tier 1 methods in one study\",\n      \"pmids\": [\"24550293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"High-resolution crystal structure of HLA-A*11:01 in complex with SARS-CoV nucleocapsid peptide (KTFPPTEPK) at 1.45 Å resolution revealed 17 hydrogen bonds between the alpha-chain and peptide, 9 tightly bound water molecules in the peptide-binding groove, and that Thr6 of the peptide does not efficiently use the middle (E) pocket, highlighting a target for optimization.\",\n      \"method\": \"X-ray crystallography at 1.45 Å resolution, in vitro peptide-binding studies (IC50 measurements)\",\n      \"journal\": \"Acta crystallographica. Section D, Biological crystallography\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high-resolution crystal structure with functional binding validation, single lab\",\n      \"pmids\": [\"16041067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"HLA-A*02:01 can present 15-mer peptides (non-canonical length) that adopt super-bulged conformations in the peptide-binding groove; these 15-mer peptides have binding affinity and stability comparable to canonical 8-11-mer peptides, and T cells can recognize 15-mer peptides in the context of HLA-A*02:01, demonstrating immunogenicity.\",\n      \"method\": \"HLA folding and thermal stability assays, X-ray crystallography (two 15-mer:HLA-A*02:01 structures solved), T-cell recognition functional assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structures plus functional T-cell assays and biophysical measurements, multiple orthogonal methods in single study\",\n      \"pmids\": [\"25505266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Crystal structures of HLA-A*30:01 and HLA-A*30:03 with pathogen peptides revealed divergent peptide presentation characteristics: HLA-A*30:03 but not HLA-A*30:01 can bind HLA-A*01:01-favored peptides; residue 77 in the F pocket is a key determinant of supertype-featured peptide-binding motifs, and interchanging residue 77 between A*30:01 and A*30:03 switched their presented peptide profiles.\",\n      \"method\": \"X-ray crystallography, thermostability measurements, peptide-binding assays, residue 77 swap mutagenesis\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structures plus functional mutagenesis (residue 77 swap), multiple orthogonal methods demonstrating mechanistic basis\",\n      \"pmids\": [\"31396224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"HLA-A expression is predominantly regulated by the MAPK (ERK) pathway in gastric and esophageal cancer cells; inhibition of MAPK (via PD98059 or MAPK siRNA) upregulates HLA-A02 and HLA-A24 expression in parallel with antigen-processing machinery components and enhances CTL killing; a strong inverse correlation between p-ERK and HLA class I was confirmed in clinical tumor samples.\",\n      \"method\": \"MAPK/PI3K inhibitor treatment (PD98059, wortmannin, lapatinib), MAPK siRNA knockdown, Western blot, qPCR, flow cytometry, CTL cytotoxicity assay, immunohistochemistry of 102 tumor samples\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple inhibitor approaches, siRNA, functional CTL assay, and clinical tissue validation across 102 samples, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"24244023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CAF-derived extracellular vesicle-packaged lncRNA RP11-161H23.5 promotes HLA-A mRNA degradation by forming a complex with CNOT4, a subunit of the CCR4-NOT mRNA deadenylase complex, which shortens the poly(A) tail of HLA-A mRNA and enhances its degradation, thereby reducing HLA-A surface expression and promoting immune evasion in pancreatic cancer.\",\n      \"method\": \"Extracellular vesicle isolation, RIP/co-IP of lncRNA-CNOT4 complex, poly(A) tail assay, Western blot, flow cytometry, syngeneic tumor models\",\n      \"journal\": \"Journal of extracellular vesicles\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP demonstrating complex formation, poly(A) tail functional assay, in vivo model, single lab\",\n      \"pmids\": [\"39041344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"LILRB2 promotes HLA-A ubiquitination and proteasomal degradation by facilitating the interaction between the ubiquitin E3 ligase MARCH9 and HLA-A, reducing HLA-A surface expression and enabling immune evasion from CD8+ T cells in breast cancer.\",\n      \"method\": \"Immunoprecipitation, histidine pulldown ubiquitination assay, Western blot, flow cytometry, syngeneic graft mouse model\",\n      \"journal\": \"Cellular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct co-IP showing LILRB2-MARCH9-HLA-A interaction, ubiquitination pulldown, in vivo syngeneic model, single lab\",\n      \"pmids\": [\"38656573\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Secreted HLA-A*02:01 (sHLA) traffics through intracellular compartments with similar maturation kinetics to membrane-bound HLA-A*02:01, and mass spectrometry of peptides eluted from sHLA and membrane-bound HLA-A*02:01 showed substantial overlap in their immunopeptidome, identifying 1266 non-redundant peptide ligands including peptides with post-translational modifications.\",\n      \"method\": \"Intracellular trafficking comparison, mass spectrometry of eluted peptides, bioinformatic peptide validation\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mass spectrometry with multiple peptide sources and trafficking assay, single lab with two orthogonal methods\",\n      \"pmids\": [\"22424782\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"Diversity in HLA-A (and HLA-B, -C) molecules is concentrated at 20 positions of high variability in the alpha-1 and alpha-2 domains; variation between alpha-1 and alpha-2 domains is distinct and may reflect partial segregation of peptide-binding and TCR-binding functions; genetic exchange between alleles of the same locus (rather than between loci) is the primary mechanism generating HLA-A diversity.\",\n      \"method\": \"Amino acid sequence comparison of 39 HLA molecules, structural analysis of polymorphic positions\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Strong — comparative sequence analysis replicated across many alleles, no direct functional experiment but mechanistic inference from structural positions, widely cited\",\n      \"pmids\": [\"3375250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"HLA-A*01-restricted T-cell epitope from WT1 (residues 317-327) is processed by proteasomal cleavage and recognized by CTL from patients with hematologic malignancies; depletion of regulatory T cells enabled expansion of WT1-specific CTL that specifically lysed HLA-A*01+ WT1-expressing tumor cell lines.\",\n      \"method\": \"Proteasomal degradation assay, intracellular cytokine cytometry, CTL expansion and cytotoxicity assay\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proteasomal processing demonstrated biochemically, functional CTL killing confirmed, single lab\",\n      \"pmids\": [\"17189421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HLA-A*33:03 allele restricts ticlopidine-specific CD8+ T-cell activation; blocking HLA class I and HLA-A*33 antibodies reduced the T-cell response, indicating that drug-HLA interaction at the HLA-A*33:03 allele is important for T-cell-mediated liver injury.\",\n      \"method\": \"CD8+ T-cell cloning and proliferation assay, IFN-gamma secretion, HLA antibody blocking\",\n      \"journal\": \"Chemical research in toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — T-cell clone functional assay with antibody blocking establishing HLA-A*33:03 restriction, single lab\",\n      \"pmids\": [\"30179004\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"HLA-A encodes a classical MHC class I heavy chain that associates with beta-2-microglobulin in the ER (a required step for proper folding, glycan processing, and surface trafficking), binds 8-11 mer peptides (and occasionally longer super-bulged peptides) in its alpha-1/alpha-2 groove for CD8+ T-cell surveillance, is transcriptionally upregulated by interferon signaling and downregulated by MAPK pathway activity; its surface expression is post-transcriptionally regulated by RNA-binding proteins (MEX3B) and post-translationally by ubiquitin E3 ligases (MARCH9 via LILRB2), and its allele-specific signal peptide controls HLA-E surface levels to modulate NKG2A-dependent NK cell inhibition.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HLA-A encodes a classical MHC class I heavy chain that captures short peptides for surveillance by CD8+ T cells and modulatory NK-cell receptors [#9, #8]. The newly synthesized heavy chain is a transmembrane glycoprotein co-translationally inserted into the rough ER, where it associates with beta-2-microglobulin within minutes; this association is a prerequisite for oligosaccharide maturation from high-mannose to complex form and for trafficking to the cell surface, as heavy chains accumulate unprocessed in beta-2-microglobulin-deficient cells [#0, #1]. Surface assembly additionally requires at least one trans-acting post-transcriptional factor [#3]. The peptide is bound in the alpha-1/alpha-2 groove through an extensive hydrogen-bond and ordered-water network, with pocket residues (e.g., F-pocket residue 77) dictating allele-specific binding motifs; the groove canonically accommodates 8-11-mers but can also present super-bulged 15-mer peptides that remain stable and immunogenic [#9, #11, #10]. Polymorphism in HLA-A is concentrated at variable positions in the alpha-1/alpha-2 domains that partition peptide-binding and TCR-binding functions, generated chiefly by intralocus allelic exchange [#16]. Beyond TCR engagement, HLA-A serves as a ligand for the activating receptor KIR2DS2 in a peptide-sequence-dependent manner [#8], and its allele-specific signal peptide loads HLA-E to set HLA-E surface levels that engage the inhibitory NKG2A receptor and tune NK-cell activity [#7]. HLA-A surface levels are tightly regulated at multiple layers: transcriptionally upregulated by interferon-alpha and suppressed by MAPK/ERK signaling [#4, #12], post-transcriptionally destabilized by the RNA-binding protein MEX3B and by a CAF-derived lncRNA-CNOT4 deadenylation complex [#6, #13], and post-translationally degraded via LILRB2-facilitated MARCH9-dependent ubiquitination [#14]; loss of these controls reduces antigen presentation and promotes tumor immune evasion.\",\n  \"teleology\": [\n    {\n      \"year\": 1980,\n      \"claim\": \"Established that HLA-A heavy chains require beta-2-microglobulin association in the ER before they can mature and reach the surface, defining the obligatory assembly step of the class I molecule.\",\n      \"evidence\": \"Pulse-chase radiolabeling and glycosylation analysis comparing normal versus beta-2-microglobulin-deficient Daudi cells, with vesicle reconstitution of purified antigen\",\n      \"pmids\": [\"7000762\", \"93026\", \"356051\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the chaperone machinery coordinating folding and peptide loading\", \"Trans-acting factor required for surface expression not molecularly defined\"]\n    },\n    {\n      \"year\": 1985,\n      \"claim\": \"Showed that surface expression depends on a trans-acting post-transcriptional factor beyond intact genes and transcripts, pointing to a regulated assembly/loading step.\",\n      \"evidence\": \"Mutagenesis with immunoselection and cell-fusion complementation in cells with normal HLA-A/B transcripts but absent surface antigen\",\n      \"pmids\": [\"3906658\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The trans-acting factor was not cloned or identified\", \"Step at which it acts (loading vs trafficking) unresolved\"]\n    },\n    {\n      \"year\": 1982,\n      \"claim\": \"Demonstrated that interferon-alpha raises HLA class I surface levels primarily by increasing heavy-chain and beta-2-microglobulin synthesis via elevated mRNA, defining transcriptional induction as the dominant cytokine-driven mechanism.\",\n      \"evidence\": \"Cytofluorimetry, metabolic labeling, and mRNA hybridization in IFN-alpha-treated cells\",\n      \"pmids\": [\"6765173\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Promoter elements and transcription factors mediating induction not mapped\", \"Did not address allele-specific responsiveness\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"Localized HLA-A diversity to discrete variable positions in the alpha-1/alpha-2 domains and inferred functional segregation of peptide- and TCR-binding surfaces, framing the structural basis of allelic specificity.\",\n      \"evidence\": \"Comparative amino-acid sequence and structural-position analysis across 39 HLA molecules\",\n      \"pmids\": [\"3375250\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Sequence inference without direct functional test of individual positions\", \"Did not establish peptide-binding consequences of specific residues\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Revealed that quantitative HLA-A expression is genetically set and controlled at transcription, splicing, and mRNA degradation, expanding regulation beyond transcription alone.\",\n      \"evidence\": \"Competitive RT-PCR, RNA polymerase II inhibition, and pre-mRNA/protein quantification across six lymphoblastoid lines\",\n      \"pmids\": [\"10980390\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No trans-factors mediating splicing or decay identified\", \"Mechanism of HLA-A24 mRNA-protein discordance unexplained\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Resolved at near-atomic detail how HLA-A binds a defined pathogen peptide, mapping the hydrogen-bond and ordered-water network of the groove.\",\n      \"evidence\": \"1.45 Å X-ray structure of HLA-A*11:01 with SARS-CoV nucleocapsid peptide plus IC50 binding measurements\",\n      \"pmids\": [\"16041067\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Single allele/peptide pair\", \"Does not address TCR recognition geometry\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined HLA-A as a direct ligand for the activating NK receptor KIR2DS2 and demonstrated peptide-dependence of the interaction, linking HLA-A to NK as well as T-cell recognition.\",\n      \"evidence\": \"2.5 Å crystal structure of KIR2DS2–HLA-A*11:01, NMR, live-cell tetramer binding, and p8 mutagenesis\",\n      \"pmids\": [\"24550293\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional NK-cell consequences in physiological settings not fully delineated\", \"Breadth of peptide repertoires supporting KIR binding unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed the HLA-A groove can stably present non-canonical 15-mer super-bulged peptides that remain immunogenic, broadening the recognized peptide-length repertoire.\",\n      \"evidence\": \"Folding/thermal stability assays, two 15-mer:HLA-A*02:01 crystal structures, and T-cell recognition assays\",\n      \"pmids\": [\"25505266\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Frequency of long-peptide presentation in vivo unquantified\", \"Processing pathway generating such peptides unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified MAPK/ERK signaling as a dominant suppressor of HLA-A and antigen-processing machinery, providing a tumor-relevant lever for restoring CTL recognition.\",\n      \"evidence\": \"MAPK inhibitors/siRNA with Western blot, qPCR, flow cytometry, CTL assays, and IHC of 102 tumors\",\n      \"pmids\": [\"24244023\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcriptional intermediaries linking ERK to HLA-A promoter not defined\", \"Generalizability beyond gastric/esophageal cancer untested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connected allele-specific HLA-A expression to NK-cell control via signal-peptide loading of HLA-E and NKG2A engagement, defining a non-classical immunoregulatory axis affecting HIV outcomes.\",\n      \"evidence\": \"Multi-cohort genetic association (9763 individuals, 21 cohorts) with signal-peptide/HLA-E mechanistic analysis and NKG2A blockade\",\n      \"pmids\": [\"29302013\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative contribution relative to direct CD8 presentation unresolved\", \"Allele coverage of signal-peptide effects incomplete\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated post-transcriptional control of HLA-A by MEX3B binding the 3' UTR to destabilize the mRNA, mechanistically linking RNA stability to immune escape.\",\n      \"evidence\": \"ORF overexpression screen, luciferase reporter, RIP, flow cytometry, and HLA-A2 rescue of T-cell killing in melanoma\",\n      \"pmids\": [\"29496759\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream regulators of MEX3B in tumors unknown\", \"Specificity for HLA-A versus other class I genes not fully resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended post-transcriptional control to a CAF-derived extracellular-vesicle lncRNA that recruits CNOT4/CCR4-NOT to deadenylate and degrade HLA-A mRNA, defining a stromal route to immune evasion.\",\n      \"evidence\": \"EV isolation, lncRNA-CNOT4 co-IP, poly(A) tail assay, flow cytometry, and syngeneic pancreatic tumor models\",\n      \"pmids\": [\"39041344\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; reciprocal validation of the lncRNA-CNOT4 interaction limited\", \"Direct binding of lncRNA to HLA-A mRNA not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined post-translational degradation of HLA-A through LILRB2-facilitated MARCH9-dependent ubiquitination, adding a protein-stability layer to immune escape control.\",\n      \"evidence\": \"Co-IP, histidine-pulldown ubiquitination assay, flow cytometry, and syngeneic breast tumor model\",\n      \"pmids\": [\"38656573\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab without reciprocal structural validation\", \"Mechanism by which LILRB2 bridges MARCH9 to HLA-A unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple regulatory layers (transcriptional, splicing, mRNA-decay, ubiquitination) are integrated allele-specifically to set steady-state HLA-A surface levels in vivo remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking IFN/MAPK transcriptional control with MEX3B/CCR4-NOT decay and MARCH9 degradation\", \"Identity of the 1985 trans-acting surface-expression factor still unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0042605\", \"supporting_discovery_ids\": [9, 10, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [7, 8, 12]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 14]}\n    ],\n    \"complexes\": [\"MHC class I (HLA-A heavy chain : beta-2-microglobulin)\"],\n    \"partners\": [\"B2M\", \"MEX3B\", \"MARCH9\", \"LILRB2\", \"KIR2DS2\", \"HLA-E\", \"CNOT4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":7,"faith_total":7,"faith_pct":100.0}}