{"gene":"AHRR","run_date":"2026-06-09T22:02:42","timeline":{"discoveries":[{"year":2017,"finding":"Crystal structure of the AhRR-ARNT heterodimer determined by X-ray crystallography revealed an asymmetric intertwined domain organization. The structure showed that the bHLH-PAS-A region of AhRR-ARNT is similar to AhR-ARNT, but the PAS-B domain of ARNT adopts a distinct arrangement in the AhRR complex. The structure demonstrated that AhRR competitively represses AhR binding to both ARNT and target DNA, and suggested an additional AhRR-ARNT-specific repression mechanism.","method":"X-ray crystallography of AhRR-ARNT heterodimer complex","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with functional interpretation and domain-level mutagenesis context; single rigorous study with structural validation","pmids":["28904176"],"is_preprint":false},{"year":2003,"finding":"Heterodimeric bHLH-PAS domains from AhRR and ARNT were co-expressed in E. coli, and the purified AhRR-ARNT heterodimer exhibited full DNA-binding activity at xenobiotic response element (XRE) sequences. Methylation of the two CpG sites within the XRE core sequence reduced binding affinity of both AhR-ARNT and AhRR-ARNT heterodimers, with 5-methylcytosine at the AhR recognition site showing greater inhibitory effect than at the Arnt recognition site.","method":"Recombinant co-expression in E. coli, EMSA/DNA-binding activity assay, methylation interference assay","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted heterodimer in vitro, direct DNA-binding assay, methylation interference, single lab with multiple orthogonal methods","pmids":["12944374"],"is_preprint":false},{"year":2012,"finding":"In soft tissue angiofibroma, a recurrent chromosomal translocation t(5;8)(p15;q13) generates an in-frame AHRR/NCOA2 fusion transcript in which the C-terminal repressor domain of AHRR is replaced by the two activation domains of NCOA2. The AHRR/NCOA2 fusion protein retains the N-terminal bHLH-PAS domain of AHRR (responsible for XRE recognition and ARNT heterodimerization) but lacks the repressor domain. Global gene expression analysis confirmed upregulation of canonical AHR target genes including CYP1A1 and toll-like receptor genes in tumors bearing this fusion.","method":"Cytogenetic analysis, FISH, RT-PCR for fusion transcripts, global gene expression analysis","journal":"Genes, chromosomes & cancer","confidence":"High","confidence_rationale":"Tier 2 / Strong — fusion gene identified by FISH and RT-PCR, functional consequence (AHR target gene upregulation) confirmed by expression analysis; replicated across multiple tumor cases","pmids":["22337624"],"is_preprint":false},{"year":2017,"finding":"Genome-wide ChIP-Seq in MCF-7 human breast cancer cells treated with TCDD identified 2811 AHRR-bound chromatin regions, of which 974 (35%) overlapped with AHR-bound regions and 994 were unique to AHRR. AHRR-bound regions mapped preferentially closer to promoters compared to AHR-bound regions. The AHR response element (AHRE) motif was enriched in both shared and unique AHRR-bound regions. Unique AHRR-bound regions were validated by ChIP-qPCR and shown to regulate gene expression by luciferase reporter assay, supporting context- and gene-specific repression by AHRR.","method":"ChIP-Seq, ChIP-qPCR, luciferase reporter assay in MCF-7 cells","journal":"Archives of toxicology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genome-wide binding profiling with orthogonal ChIP-qPCR validation and functional reporter assays; single lab with multiple methods","pmids":["28681081"],"is_preprint":false},{"year":2013,"finding":"Tristetraprolin (TTP), an AU-rich element (ARE)-binding protein, suppresses AHRR expression post-transcriptionally by binding directly to AREs in the AHRR 3'UTR, destabilizing AHRR mRNA. TTP overexpression decreased AHRR mRNA stability and protein levels, while TTP siRNA knockdown increased AHRR expression. RNA EMSA confirmed direct TTP binding to the AHRR 3'UTR. Point mutations in AREs abolished TTP-mediated destabilization.","method":"TTP overexpression and siRNA knockdown, mRNA stability assay, RNA EMSA, ARE point mutagenesis","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct binding demonstrated by RNA EMSA, functional rescue by ARE mutagenesis, gain- and loss-of-function, single lab with multiple orthogonal methods","pmids":["23583445"],"is_preprint":false},{"year":2016,"finding":"Transgenic mice overexpressing AhRR (AhRR Tg) showed significantly attenuated TCDD-induced expression of inflammatory cytokines IL-1β, CXCL2, and CXCL3 in white adipose tissue compared to wild-type mice. AhRR Tg male mice were protected from high-dose TCDD-induced lethality, with reduced inflammatory response and lower levels of TCDD-induced alanine aminotransferase and hepatic triglycerides, identifying AhRR as a regulator of specific inflammatory cytokines and a protector against acute TCDD toxicity in vivo.","method":"AhRR transgenic mice, TCDD treatment, cytokine expression analysis, flow cytometry for immune cell infiltration, hepatotoxicity markers","journal":"Environmental health perspectives","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vivo transgenic overexpression model with multiple functional readouts (cytokines, survival, liver damage markers); single lab with orthogonal methods","pmids":["26862745"],"is_preprint":false},{"year":2017,"finding":"LINC00305, a long non-coding RNA, interacted with lipocalin-1 interacting membrane receptor (LIMR), enhanced the LIMR–AHRR protein interaction, and promoted nuclear localization of AHRR in THP-1 monocytes. This LINC00305-mediated LIMR–AHRR cooperation activated NF-κB, inducing inflammatory cytokine expression. AHRR was required for LINC00305-mediated NF-κB activation, as NF-κB activation occurred exclusively in the presence of both LIMR and AHRR.","method":"Co-immunoprecipitation, overexpression studies, siRNA knockdown of AHRR/LIMR, immunofluorescence for nuclear localization, NF-κB reporter assay in THP-1 cells","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal interaction demonstrated by Co-IP and functional rescue, nuclear localization confirmed by immunofluorescence; however, the mechanistic role described is for AHRR as a co-factor in NF-κB activation, a non-canonical function supported by single lab","pmids":["28393844"],"is_preprint":false},{"year":2006,"finding":"Stable overexpression of AhRR in human breast cancer MCF-7 cells (MCFRR4 line) resulted in slower cell growth compared to parental MCF-7 cells, with decreased mRNA levels of cell cycle-related genes E2F, cyclin E1, and PCNA, and the estrogen-responsive gene cathepsin D. Cyclin D1 mRNA was enhanced, while Rb, p27Kip1, c-myc, and hsp27 were unaffected.","method":"Stable transfection/overexpression of AhRR in MCF-7 cells, cell proliferation assay (MTS), RT-PCR for cell cycle and estrogen-responsive genes","journal":"Biological & pharmaceutical bulletin","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — overexpression with defined phenotypic readout and gene expression analysis; no pathway placement by epistasis, single lab","pmids":["16755028"],"is_preprint":false},{"year":2006,"finding":"AhRR mRNA tissue distribution in C57BL/6 mice showed constitutively high expression in heart and brain, with low levels in other tissues. In AhR-deficient mice, AhRR mRNA levels were 2–3 orders of magnitude lower than in wild-type, demonstrating that baseline AhRR expression is dependent on AhR signaling. Treatment with benzo(a)pyrene induced AhRR expression in liver, spleen, lung, and ovary, but not in brain and heart.","method":"Quantitative RT-PCR in wild-type and AhR-/- mouse tissues, B(a)P treatment with dose-response","journal":"Archives of toxicology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — AhR knockout genetic epistasis establishes AhR-dependent regulation of basal AHRR expression; replicated across multiple tissues, single lab","pmids":["16205913"],"is_preprint":false},{"year":2020,"finding":"In AhRR-reporter mice, AhRR expression in intestinal immune cells was driven primarily by dietary AhR ligands (indole-3-carbinol) and was independent of microbial metabolites. Comparison of AhRR-deficient, AhR-deficient, and wild-type mice revealed both AhR-dependent and AhR-independent alterations in gut microbiota composition following I3C supplementation. AhRR-deficient mice, when deprived of dietary AhR ligands, showed enhanced susceptibility to DSS-induced colitis.","method":"AhRR-reporter mice, AhRR-knockout and AhR-knockout mouse models, dietary supplementation experiments, DSS colitis model, microbiota profiling","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout models with defined functional phenotype (colitis susceptibility); multiple genotypes tested, single lab","pmids":["32366032"],"is_preprint":false},{"year":2022,"finding":"CRISPR/Cas9-induced AHRR knockout in human bronchial epithelial 16HBE cells resulted in lower baseline proliferation rate, stronger cigarette smoke extract (CSE)-induced decrease in mitochondrial membrane potential, and higher CSE-induced late apoptosis/necroptosis compared to control cells, indicating that AHRR expression protects airway epithelial cells from cigarette smoke-induced mitochondrial dysfunction and cell death.","method":"CRISPR/Cas9 AHRR knockout in 16HBE cells, proliferation assay, mitochondrial membrane potential measurement, apoptosis/necroptosis assay with CSE treatment","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean CRISPR knockout with multiple defined functional readouts; single lab, single cell line","pmids":["36359818"],"is_preprint":false},{"year":2022,"finding":"AHRR induced HIF-1β (ARNT) expression in head and neck cancer (HNC) cells; increased ARNT interacted with EPAS1 (HIF-2α), enhancing transcription of VEGFD and promoting lymphangiogenesis. In AHRR wild-type transgenic mice, tumors developed with greater frequency than in AHRR-null mice. Hypoxia-induced VEGFD protein levels were genotype-dependent (Ahrr +/+, +/-, -/-), while upstream PI3K-pathway activation (Akt phosphorylation) was similar across genotypes.","method":"AHRR transgenic and knockout mouse models, Western blot for VEGFD and Akt phosphorylation, co-immunoprecipitation of ARNT-EPAS1","journal":"American journal of cancer research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, limited methodological detail in abstract, mechanistic pathway placement is inferred from mouse genotype comparisons without full mechanistic reconstitution","pmids":["35261785"],"is_preprint":false},{"year":2025,"finding":"FTO (m6A eraser) knockdown in A549 cells significantly decreased AHRR expression, while METTL3 (m6A writer) or ALKBH5 (m6A eraser) knockdown did not affect AHRR expression. FTO knockdown enhanced CYP1A1 induction by AhR agonist TCDD, and this enhancement was associated with decreased AHRR levels, suggesting that m6A modification (removed by FTO) suppresses AHRR expression and that AHRR levels modulate AhR-mediated CYP1A1 induction.","method":"siRNA knockdown of m6A regulatory enzymes (METTL3, ALKBH5, FTO) in A549 cells, RT-PCR for AHRR and ARNT mRNA, CYP1A1 induction assay","journal":"Toxicology letters","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, mechanistic inference from indirect knockdown experiments, m6A modification of AHRR mRNA itself not directly mapped","pmids":["40118351"],"is_preprint":false},{"year":2012,"finding":"In human skin fibroblasts, repression of CYP1 enzyme activity was found NOT to be causally related to AhRR expression. Despite prior hypotheses, AhRR was expressed at only moderate levels, and some fibroblast strains could induce CYP1A1 mRNA. Enhancement of CYP1A1 mRNA by trichostatin A (an inhibitor of AhRR-recruited histone deacetylases) failed to induce measurable CYP1 activity. AhRR-deficient mouse embryonic fibroblasts showed impressive CYP1A1 mRNA induction but no biologically relevant CYP1 enzyme activity.","method":"Primary human skin fibroblast cultures (n=25), AhRR-knockout mouse embryonic fibroblasts, CYP1 enzyme activity assays, mRNA quantification, trichostatin A treatment","journal":"The Journal of investigative dermatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout model plus pharmacological intervention with direct enzyme activity measurements; single lab, multiple orthogonal approaches; negative finding explicitly established","pmids":["22951721"],"is_preprint":false}],"current_model":"AHRR (AhRR) is a bHLH-PAS transcription factor that forms a heterodimer with ARNT and competes with AhR for ARNT binding and XRE (xenobiotic response element) occupancy, thereby repressing AhR-driven gene transcription; its crystal structure revealed that it blocks AhR-ARNT interaction through both competitive ARNT sequestration and an AhRR-ARNT-specific repression mechanism, its expression is itself AhR-dependent and induced by AhR ligands, its mRNA is post-transcriptionally regulated by the ARE-binding protein tristetraprolin, and in vivo it suppresses specific inflammatory cytokines (IL-1β, CXCL2/3), protects airway epithelium from cigarette smoke-induced mitochondrial dysfunction and cell death, and contributes to intestinal immune homeostasis."},"narrative":{"mechanistic_narrative":"AHRR (AhRR) is a bHLH-PAS transcription factor that heterodimerizes with ARNT to repress AhR-driven xenobiotic gene transcription, acting within a feedback loop in which its own expression is dependent on AhR signaling and induced by AhR ligands [PMID:16205913]. The reconstituted AhRR-ARNT heterodimer binds xenobiotic response element (XRE/AHRE) sequences with full DNA-binding activity, and binding of both AhR-ARNT and AhRR-ARNT is sensitive to CpG methylation within the XRE core [PMID:12944374]. The crystal structure of the AhRR-ARNT complex shows an asymmetric, intertwined domain organization in which the ARNT PAS-B domain adopts a distinct arrangement, establishing that AhRR represses AhR both by competitive sequestration of ARNT and target DNA and through an additional AhRR-ARNT-specific repression mechanism [PMID:28904176]. Genome-wide ChIP-Seq shows AHRR occupies thousands of chromatin regions, many shared with AHR and enriched near promoters but also a large set of unique sites, consistent with context- and gene-specific repression [PMID:28681081]. AHRR expression is constrained post-transcriptionally: the ARE-binding protein tristetraprolin binds the AHRR 3'UTR and destabilizes its mRNA [PMID:23583445]. Physiologically, AHRR restrains specific inflammatory cytokines (IL-1β, CXCL2, CXCL3) and protects against acute TCDD toxicity in vivo [PMID:26862745], contributes to intestinal immune homeostasis with susceptibility to DSS-colitis when dietary AhR ligands are absent [PMID:32366032], and protects airway epithelial cells from cigarette-smoke-induced mitochondrial dysfunction and death [PMID:36359818]. A recurrent t(5;8) translocation generates an AHRR/NCOA2 fusion in soft tissue angiofibroma that retains the AHRR bHLH-PAS domain but replaces its repressor domain with NCOA2 activation domains, converting it to an activator and upregulating AHR target genes such as CYP1A1 [PMID:22337624].","teleology":[{"year":2003,"claim":"Established that AhRR is a bona fide ARNT-partnering, XRE-binding factor by reconstituting the heterodimer and demonstrating direct, methylation-sensitive DNA binding.","evidence":"Recombinant co-expression of AhRR-ARNT bHLH-PAS domains in E. coli with EMSA and methylation interference","pmids":["12944374"],"confidence":"High","gaps":["Did not resolve how AhRR-ARNT binding differs structurally from AhR-ARNT","Genome-wide binding repertoire not addressed"]},{"year":2006,"claim":"Defined the AhR-AhRR feedback architecture by showing baseline AhRR expression is AhR-dependent and ligand-inducible in a tissue-specific manner.","evidence":"qRT-PCR in wild-type and AhR-/- mouse tissues with benzo(a)pyrene dose-response","pmids":["16205913"],"confidence":"Medium","gaps":["Constitutive high expression in heart and brain unexplained","Functional consequence of tissue-restricted induction not tested"]},{"year":2006,"claim":"First linked AhRR overexpression to altered proliferation and cell-cycle gene expression in breast cancer cells, hinting at roles beyond xenobiotic repression.","evidence":"Stable AhRR overexpression in MCF-7 with proliferation assays and RT-PCR of cell cycle/estrogen-responsive genes","pmids":["16755028"],"confidence":"Medium","gaps":["Mechanism connecting AhRR to E2F/cyclin E1/PCNA repression not established","No epistasis placement"]},{"year":2012,"claim":"Demonstrated the functional importance of the AHRR repressor domain in disease by identifying an AHRR/NCOA2 fusion that converts AHRR into an activator of AHR targets.","evidence":"Cytogenetics, FISH, RT-PCR and global expression analysis of soft tissue angiofibromas","pmids":["22337624"],"confidence":"High","gaps":["Direct transforming activity of fusion not reconstituted","Tumor-initiating mechanism beyond target-gene upregulation unknown"]},{"year":2012,"claim":"Challenged the assumption that AhRR is the principal repressor of CYP1 enzyme activity in fibroblasts via a negative genetic result.","evidence":"Primary human skin fibroblasts and AhRR-knockout MEFs with CYP1 enzyme activity assays and trichostatin A treatment","pmids":["22951721"],"confidence":"Medium","gaps":["Does not generalize beyond fibroblast systems","Alternative repressors of CYP1 activity not identified"]},{"year":2013,"claim":"Identified post-transcriptional control of AHRR levels through ARE-mediated mRNA destabilization by tristetraprolin.","evidence":"TTP gain/loss-of-function, mRNA stability assay, RNA EMSA, and ARE point mutagenesis","pmids":["23583445"],"confidence":"High","gaps":["Physiological signals controlling TTP-AHRR axis not defined","In vivo relevance not tested"]},{"year":2016,"claim":"Provided in vivo evidence that AhRR suppresses specific inflammatory cytokines and protects against acute TCDD toxicity.","evidence":"AhRR transgenic mice with TCDD challenge, cytokine profiling, survival, and hepatotoxicity markers","pmids":["26862745"],"confidence":"High","gaps":["Cell-type origin of cytokine suppression not resolved","Whether effect is purely AhR-repression-dependent unclear"]},{"year":2017,"claim":"Resolved the structural basis of AhRR repression, showing both competitive ARNT/DNA sequestration and an AhRR-specific repression mechanism.","evidence":"X-ray crystallography of the AhRR-ARNT heterodimer","pmids":["28904176"],"confidence":"High","gaps":["AhRR-ARNT-specific repression mechanism not mechanistically dissected","Full-length protein and coregulator interfaces not in structure"]},{"year":2017,"claim":"Mapped the genome-wide AHRR binding landscape, revealing extensive AHR-shared and AHRR-unique promoter-proximal sites consistent with gene-specific repression.","evidence":"ChIP-Seq, ChIP-qPCR, and luciferase reporters in TCDD-treated MCF-7 cells","pmids":["28681081"],"confidence":"High","gaps":["Functional output of AHRR-unique sites largely uncharacterized","Coregulator recruitment at unique sites unknown"]},{"year":2017,"claim":"Described a non-canonical role for AHRR as a cytoplasmic/nuclear co-factor in NF-κB-driven inflammation via LINC00305 and LIMR.","evidence":"Co-IP, overexpression/siRNA, immunofluorescence, and NF-κB reporter assays in THP-1 monocytes","pmids":["28393844"],"confidence":"Medium","gaps":["Single-lab observation of non-canonical pro-inflammatory function","Reconciliation with AHRR's anti-inflammatory role in vivo not addressed"]},{"year":2020,"claim":"Showed AHRR contributes to intestinal immune homeostasis, with dietary AhR-ligand-driven expression and colitis susceptibility upon ligand deprivation.","evidence":"AhRR-reporter, AhRR-knockout and AhR-knockout mice with dietary I3C, DSS-colitis, and microbiota profiling","pmids":["32366032"],"confidence":"Medium","gaps":["Immune cell subset mediating protection not pinpointed","Mechanism linking AHRR to microbiota shifts unclear"]},{"year":2022,"claim":"Demonstrated that AHRR protects airway epithelial cells from cigarette-smoke-induced mitochondrial dysfunction and death.","evidence":"CRISPR/Cas9 AHRR knockout in 16HBE cells with proliferation, mitochondrial membrane potential, and apoptosis/necroptosis assays","pmids":["36359818"],"confidence":"Medium","gaps":["Single cell line; in vivo airway relevance not tested","Molecular link between AHRR and mitochondrial protection unknown"]},{"year":2022,"claim":"Proposed a pro-tumorigenic AHRR function in head and neck cancer through ARNT/EPAS1-driven VEGFD induction and lymphangiogenesis.","evidence":"AHRR transgenic and knockout mice with Western blot and ARNT-EPAS1 Co-IP","pmids":["35261785"],"confidence":"Low","gaps":["Low-confidence single study with limited mechanistic detail","Direct transcriptional control of VEGFD by AHRR not established"]},{"year":2025,"claim":"Implicated m6A/FTO regulation in setting AHRR expression and thereby AhR-mediated CYP1A1 induction.","evidence":"siRNA knockdown of METTL3/ALKBH5/FTO in A549 cells with RT-PCR and CYP1A1 induction assays","pmids":["40118351"],"confidence":"Low","gaps":["m6A modification of AHRR mRNA not directly mapped","Inference rests on indirect knockdown effects"]},{"year":null,"claim":"How AHRR's canonical anti-inflammatory transcriptional repression is reconciled with its reported pro-inflammatory and pro-tumorigenic context-dependent functions remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["Coregulators recruited at AHRR-unique binding sites unknown","Mechanistic basis of cytoprotective and context-specific roles undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,1,2,3]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[1,3]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,6]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,3]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[5,9]}],"complexes":["AhRR-ARNT heterodimer"],"partners":["ARNT","AHR","NCOA2","ZBTB7B","LIMR","EPAS1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"A9YTQ3","full_name":"Aryl hydrocarbon receptor repressor","aliases":["Class E basic helix-loop-helix protein 77","bHLHe77"],"length_aa":697,"mass_kda":75.8,"function":"Mediates dioxin toxicity and is involved in regulation of cell growth and differentiation. Represses the transcription activity of AHR by competing with AHR for heterodimer formation with ARNT and subsequently binding to the xenobiotic response element (XRE) sequence present in the promoter regulatory region of a variety of genes. Represses CYP1A1 by binding the XRE sequence and recruiting ANKRA2, HDAC4 and/or HDAC5. Autoregulates its expression by associating with its own XRE site Represses AHR transcription activity (PubMed:19380484). Also represses transcription mediated by HIF1A and EPAS1/HIF2A but does not repress NR1I2/PXR or ESR1 transcriptional activities (PubMed:19380484) Does not repress AHR transcription activity","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/A9YTQ3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/AHRR","classification":"Not Classified","n_dependent_lines":9,"n_total_lines":1208,"dependency_fraction":0.0074503311258278145},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/AHRR","total_profiled":1310},"omim":[{"mim_id":"617489","title":"LONG INTERGENIC NONCODING RNA 305; LINC00305","url":"https://www.omim.org/entry/617489"},{"mim_id":"610007","title":"LIMB REGION 1 HOMOLOG-LIKE; LMBR1L","url":"https://www.omim.org/entry/610007"},{"mim_id":"606517","title":"ARYLHYDROCARBON RECEPTOR REPRESSOR; AHRR","url":"https://www.omim.org/entry/606517"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"testis","ntpm":22.8}],"url":"https://www.proteinatlas.org/search/AHRR"},"hgnc":{"alias_symbol":["KIAA1234","bHLHe77"],"prev_symbol":["AHH","AHHR"]},"alphafold":{"accession":"A9YTQ3","domains":[{"cath_id":"3.30.450.20","chopping":"119-186_194-280","consensus_level":"medium","plddt":86.5919,"start":119,"end":280},{"cath_id":"1.10.20","chopping":"47-91","consensus_level":"medium","plddt":93.1251,"start":47,"end":91}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/A9YTQ3","model_url":"https://alphafold.ebi.ac.uk/files/AF-A9YTQ3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-A9YTQ3-F1-predicted_aligned_error_v6.png","plddt_mean":52.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=AHRR","jax_strain_url":"https://www.jax.org/strain/search?query=AHRR"},"sequence":{"accession":"A9YTQ3","fasta_url":"https://rest.uniprot.org/uniprotkb/A9YTQ3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/A9YTQ3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/A9YTQ3"}},"corpus_meta":[{"pmid":"22232023","id":"PMC_22232023","title":"Coordinated changes in AHRR methylation in lymphoblasts and pulmonary macrophages from smokers.","date":"2012","source":"American journal of medical genetics. 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pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/1802352","citation_count":5,"is_preprint":false},{"pmid":"26339380","id":"PMC_26339380","title":"MCI extraction from Turkish galls played protective roles against X-ray-induced damage in AHH-1 cells.","date":"2015","source":"International journal of clinical and experimental pathology","url":"https://pubmed.ncbi.nlm.nih.gov/26339380","citation_count":5,"is_preprint":false},{"pmid":"25918796","id":"PMC_25918796","title":"Protective activity of C-geranylflavonoid analogs from Paulownia tomentosa against DNA damage in 137Cs irradiated AHH-1 cells.","date":"2014","source":"Natural product communications","url":"https://pubmed.ncbi.nlm.nih.gov/25918796","citation_count":5,"is_preprint":false},{"pmid":"3435181","id":"PMC_3435181","title":"Epidermal cell growth-dependent arylhydrocarbon-hydroxylase (AHH) activity in vitro.","date":"1987","source":"Archives of dermatological research","url":"https://pubmed.ncbi.nlm.nih.gov/3435181","citation_count":5,"is_preprint":false},{"pmid":"38528596","id":"PMC_38528596","title":"A validated restriction enzyme ddPCR cg05575921 (AHRR) assay to accurately assess smoking exposure.","date":"2024","source":"Clinical epigenetics","url":"https://pubmed.ncbi.nlm.nih.gov/38528596","citation_count":4,"is_preprint":false},{"pmid":"37755881","id":"PMC_37755881","title":"AHRR Hypomethylation mediates the association between maternal smoking and metabolic profiles in children.","date":"2023","source":"Hepatology communications","url":"https://pubmed.ncbi.nlm.nih.gov/37755881","citation_count":4,"is_preprint":false},{"pmid":"37150141","id":"PMC_37150141","title":"Development and validation of a simple general population lung cancer risk model including AHRR-methylation.","date":"2023","source":"Lung cancer (Amsterdam, Netherlands)","url":"https://pubmed.ncbi.nlm.nih.gov/37150141","citation_count":4,"is_preprint":false},{"pmid":"28962422","id":"PMC_28962422","title":"1,4-benzoquinone-induced STAT-3 hypomethylation in AHH-1 cells: Role of oxidative stress.","date":"2015","source":"Toxicology reports","url":"https://pubmed.ncbi.nlm.nih.gov/28962422","citation_count":4,"is_preprint":false},{"pmid":"30506768","id":"PMC_30506768","title":"Association of the human aryl hydrocarbon receptor repressor (AhRR)-c.565C>G transversion with male infertility: A case-control study from Iran.","date":"2018","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/30506768","citation_count":4,"is_preprint":false},{"pmid":"7523883","id":"PMC_7523883","title":"Induction of mutations at the hypoxanthine phosphoribosyl transferase (HPRT) locus in AHH-1 human lymphoblastoid cells.","date":"1994","source":"Mutation research","url":"https://pubmed.ncbi.nlm.nih.gov/7523883","citation_count":4,"is_preprint":false},{"pmid":"8625943","id":"PMC_8625943","title":"Cell cycle traverse in AHH-1 tk +/- human lymphoblastoid cells exposed to the chromosomal mutagen, m-amsa.","date":"1996","source":"Environmental and molecular mutagenesis","url":"https://pubmed.ncbi.nlm.nih.gov/8625943","citation_count":4,"is_preprint":false},{"pmid":"32801256","id":"PMC_32801256","title":"Expression analysis of aryl hydrocarbon receptor repressor (AHRR) gene in gallbladder cancer.","date":"2021","source":"Saudi journal of gastroenterology : official journal of the Saudi Gastroenterology Association","url":"https://pubmed.ncbi.nlm.nih.gov/32801256","citation_count":3,"is_preprint":false},{"pmid":"36093686","id":"PMC_36093686","title":"AhRR methylation contributes to disease progression in urothelial bladder cancer.","date":"2022","source":"Cancer biomarkers : section A of Disease markers","url":"https://pubmed.ncbi.nlm.nih.gov/36093686","citation_count":3,"is_preprint":false},{"pmid":"28485216","id":"PMC_28485216","title":"Influence of AHRR Pro189Ala polymorphism on kidney functions.","date":"2017","source":"Bioscience, biotechnology, and biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28485216","citation_count":3,"is_preprint":false},{"pmid":"35261785","id":"PMC_35261785","title":"AHRR contributes to inflammatory lymphangiogenesis by activating the EPAS1/VEGFD signaling axis in head and neck cancer.","date":"2022","source":"American journal of cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/35261785","citation_count":3,"is_preprint":false},{"pmid":"36060023","id":"PMC_36060023","title":"Arthroscopic Excision of Intra-articular AHRR-NCOA2- positive Angiofibroma of Soft Tissue of the Knee: A Case Report.","date":"2022","source":"Cancer diagnosis & prognosis","url":"https://pubmed.ncbi.nlm.nih.gov/36060023","citation_count":3,"is_preprint":false},{"pmid":"6685642","id":"PMC_6685642","title":"The effect of cigarette smoke on aryl-hydrocarbon hydroxylase (AHH) activity of the human kidney.","date":"1983","source":"European journal of cancer & clinical oncology","url":"https://pubmed.ncbi.nlm.nih.gov/6685642","citation_count":3,"is_preprint":false},{"pmid":"39030724","id":"PMC_39030724","title":"The enigmatic AHRR: beyond aryl hydrocarbon receptor repression.","date":"2024","source":"Journal of leukocyte biology","url":"https://pubmed.ncbi.nlm.nih.gov/39030724","citation_count":2,"is_preprint":false},{"pmid":"40118351","id":"PMC_40118351","title":"Cigarette smoking modulates m6A modification, affecting the induction of CYP1A1 mRNA by regulating human ARNT and AHRR in A549 cells.","date":"2025","source":"Toxicology letters","url":"https://pubmed.ncbi.nlm.nih.gov/40118351","citation_count":2,"is_preprint":false},{"pmid":"38103810","id":"PMC_38103810","title":"Aromatic Hydrocarbon Receptor Repressor (AHRR) is a biomarker of ambient air pollution exposure and Coronary Artery Disease (CAD).","date":"2023","source":"Environmental toxicology and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/38103810","citation_count":2,"is_preprint":false},{"pmid":"38990298","id":"PMC_38990298","title":"Aryl hydrocarbon receptor repressor ( AHRR ) methylation predicts risk of vascular disease: A cohort study of the general population.","date":"2024","source":"International journal of surgery (London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/38990298","citation_count":2,"is_preprint":false},{"pmid":"34504427","id":"PMC_34504427","title":"Cell-Penetrating Peptides Predicted From CASC3, AKIP1, and AHRR Proteins.","date":"2021","source":"Frontiers in pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/34504427","citation_count":1,"is_preprint":false},{"pmid":"38051301","id":"PMC_38051301","title":"The Influence of Smoking and Occupational Risk Factors on DNA Methylation in the AHRR and F2RL3 Genes.","date":"2024","source":"Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology","url":"https://pubmed.ncbi.nlm.nih.gov/38051301","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":54820,"output_tokens":4345,"usd":0.114818,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12336,"output_tokens":4169,"usd":0.082952,"stage2_stop_reason":"end_turn"},"total_usd":0.19777,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2017,\n      \"finding\": \"Crystal structure of the AhRR-ARNT heterodimer determined by X-ray crystallography revealed an asymmetric intertwined domain organization. The structure showed that the bHLH-PAS-A region of AhRR-ARNT is similar to AhR-ARNT, but the PAS-B domain of ARNT adopts a distinct arrangement in the AhRR complex. The structure demonstrated that AhRR competitively represses AhR binding to both ARNT and target DNA, and suggested an additional AhRR-ARNT-specific repression mechanism.\",\n      \"method\": \"X-ray crystallography of AhRR-ARNT heterodimer complex\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with functional interpretation and domain-level mutagenesis context; single rigorous study with structural validation\",\n      \"pmids\": [\"28904176\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Heterodimeric bHLH-PAS domains from AhRR and ARNT were co-expressed in E. coli, and the purified AhRR-ARNT heterodimer exhibited full DNA-binding activity at xenobiotic response element (XRE) sequences. Methylation of the two CpG sites within the XRE core sequence reduced binding affinity of both AhR-ARNT and AhRR-ARNT heterodimers, with 5-methylcytosine at the AhR recognition site showing greater inhibitory effect than at the Arnt recognition site.\",\n      \"method\": \"Recombinant co-expression in E. coli, EMSA/DNA-binding activity assay, methylation interference assay\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted heterodimer in vitro, direct DNA-binding assay, methylation interference, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"12944374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In soft tissue angiofibroma, a recurrent chromosomal translocation t(5;8)(p15;q13) generates an in-frame AHRR/NCOA2 fusion transcript in which the C-terminal repressor domain of AHRR is replaced by the two activation domains of NCOA2. The AHRR/NCOA2 fusion protein retains the N-terminal bHLH-PAS domain of AHRR (responsible for XRE recognition and ARNT heterodimerization) but lacks the repressor domain. Global gene expression analysis confirmed upregulation of canonical AHR target genes including CYP1A1 and toll-like receptor genes in tumors bearing this fusion.\",\n      \"method\": \"Cytogenetic analysis, FISH, RT-PCR for fusion transcripts, global gene expression analysis\",\n      \"journal\": \"Genes, chromosomes & cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — fusion gene identified by FISH and RT-PCR, functional consequence (AHR target gene upregulation) confirmed by expression analysis; replicated across multiple tumor cases\",\n      \"pmids\": [\"22337624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Genome-wide ChIP-Seq in MCF-7 human breast cancer cells treated with TCDD identified 2811 AHRR-bound chromatin regions, of which 974 (35%) overlapped with AHR-bound regions and 994 were unique to AHRR. AHRR-bound regions mapped preferentially closer to promoters compared to AHR-bound regions. The AHR response element (AHRE) motif was enriched in both shared and unique AHRR-bound regions. Unique AHRR-bound regions were validated by ChIP-qPCR and shown to regulate gene expression by luciferase reporter assay, supporting context- and gene-specific repression by AHRR.\",\n      \"method\": \"ChIP-Seq, ChIP-qPCR, luciferase reporter assay in MCF-7 cells\",\n      \"journal\": \"Archives of toxicology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome-wide binding profiling with orthogonal ChIP-qPCR validation and functional reporter assays; single lab with multiple methods\",\n      \"pmids\": [\"28681081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Tristetraprolin (TTP), an AU-rich element (ARE)-binding protein, suppresses AHRR expression post-transcriptionally by binding directly to AREs in the AHRR 3'UTR, destabilizing AHRR mRNA. TTP overexpression decreased AHRR mRNA stability and protein levels, while TTP siRNA knockdown increased AHRR expression. RNA EMSA confirmed direct TTP binding to the AHRR 3'UTR. Point mutations in AREs abolished TTP-mediated destabilization.\",\n      \"method\": \"TTP overexpression and siRNA knockdown, mRNA stability assay, RNA EMSA, ARE point mutagenesis\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding demonstrated by RNA EMSA, functional rescue by ARE mutagenesis, gain- and loss-of-function, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"23583445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Transgenic mice overexpressing AhRR (AhRR Tg) showed significantly attenuated TCDD-induced expression of inflammatory cytokines IL-1β, CXCL2, and CXCL3 in white adipose tissue compared to wild-type mice. AhRR Tg male mice were protected from high-dose TCDD-induced lethality, with reduced inflammatory response and lower levels of TCDD-induced alanine aminotransferase and hepatic triglycerides, identifying AhRR as a regulator of specific inflammatory cytokines and a protector against acute TCDD toxicity in vivo.\",\n      \"method\": \"AhRR transgenic mice, TCDD treatment, cytokine expression analysis, flow cytometry for immune cell infiltration, hepatotoxicity markers\",\n      \"journal\": \"Environmental health perspectives\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo transgenic overexpression model with multiple functional readouts (cytokines, survival, liver damage markers); single lab with orthogonal methods\",\n      \"pmids\": [\"26862745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"LINC00305, a long non-coding RNA, interacted with lipocalin-1 interacting membrane receptor (LIMR), enhanced the LIMR–AHRR protein interaction, and promoted nuclear localization of AHRR in THP-1 monocytes. This LINC00305-mediated LIMR–AHRR cooperation activated NF-κB, inducing inflammatory cytokine expression. AHRR was required for LINC00305-mediated NF-κB activation, as NF-κB activation occurred exclusively in the presence of both LIMR and AHRR.\",\n      \"method\": \"Co-immunoprecipitation, overexpression studies, siRNA knockdown of AHRR/LIMR, immunofluorescence for nuclear localization, NF-κB reporter assay in THP-1 cells\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal interaction demonstrated by Co-IP and functional rescue, nuclear localization confirmed by immunofluorescence; however, the mechanistic role described is for AHRR as a co-factor in NF-κB activation, a non-canonical function supported by single lab\",\n      \"pmids\": [\"28393844\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Stable overexpression of AhRR in human breast cancer MCF-7 cells (MCFRR4 line) resulted in slower cell growth compared to parental MCF-7 cells, with decreased mRNA levels of cell cycle-related genes E2F, cyclin E1, and PCNA, and the estrogen-responsive gene cathepsin D. Cyclin D1 mRNA was enhanced, while Rb, p27Kip1, c-myc, and hsp27 were unaffected.\",\n      \"method\": \"Stable transfection/overexpression of AhRR in MCF-7 cells, cell proliferation assay (MTS), RT-PCR for cell cycle and estrogen-responsive genes\",\n      \"journal\": \"Biological & pharmaceutical bulletin\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — overexpression with defined phenotypic readout and gene expression analysis; no pathway placement by epistasis, single lab\",\n      \"pmids\": [\"16755028\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"AhRR mRNA tissue distribution in C57BL/6 mice showed constitutively high expression in heart and brain, with low levels in other tissues. In AhR-deficient mice, AhRR mRNA levels were 2–3 orders of magnitude lower than in wild-type, demonstrating that baseline AhRR expression is dependent on AhR signaling. Treatment with benzo(a)pyrene induced AhRR expression in liver, spleen, lung, and ovary, but not in brain and heart.\",\n      \"method\": \"Quantitative RT-PCR in wild-type and AhR-/- mouse tissues, B(a)P treatment with dose-response\",\n      \"journal\": \"Archives of toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — AhR knockout genetic epistasis establishes AhR-dependent regulation of basal AHRR expression; replicated across multiple tissues, single lab\",\n      \"pmids\": [\"16205913\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In AhRR-reporter mice, AhRR expression in intestinal immune cells was driven primarily by dietary AhR ligands (indole-3-carbinol) and was independent of microbial metabolites. Comparison of AhRR-deficient, AhR-deficient, and wild-type mice revealed both AhR-dependent and AhR-independent alterations in gut microbiota composition following I3C supplementation. AhRR-deficient mice, when deprived of dietary AhR ligands, showed enhanced susceptibility to DSS-induced colitis.\",\n      \"method\": \"AhRR-reporter mice, AhRR-knockout and AhR-knockout mouse models, dietary supplementation experiments, DSS colitis model, microbiota profiling\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout models with defined functional phenotype (colitis susceptibility); multiple genotypes tested, single lab\",\n      \"pmids\": [\"32366032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CRISPR/Cas9-induced AHRR knockout in human bronchial epithelial 16HBE cells resulted in lower baseline proliferation rate, stronger cigarette smoke extract (CSE)-induced decrease in mitochondrial membrane potential, and higher CSE-induced late apoptosis/necroptosis compared to control cells, indicating that AHRR expression protects airway epithelial cells from cigarette smoke-induced mitochondrial dysfunction and cell death.\",\n      \"method\": \"CRISPR/Cas9 AHRR knockout in 16HBE cells, proliferation assay, mitochondrial membrane potential measurement, apoptosis/necroptosis assay with CSE treatment\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean CRISPR knockout with multiple defined functional readouts; single lab, single cell line\",\n      \"pmids\": [\"36359818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"AHRR induced HIF-1β (ARNT) expression in head and neck cancer (HNC) cells; increased ARNT interacted with EPAS1 (HIF-2α), enhancing transcription of VEGFD and promoting lymphangiogenesis. In AHRR wild-type transgenic mice, tumors developed with greater frequency than in AHRR-null mice. Hypoxia-induced VEGFD protein levels were genotype-dependent (Ahrr +/+, +/-, -/-), while upstream PI3K-pathway activation (Akt phosphorylation) was similar across genotypes.\",\n      \"method\": \"AHRR transgenic and knockout mouse models, Western blot for VEGFD and Akt phosphorylation, co-immunoprecipitation of ARNT-EPAS1\",\n      \"journal\": \"American journal of cancer research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, limited methodological detail in abstract, mechanistic pathway placement is inferred from mouse genotype comparisons without full mechanistic reconstitution\",\n      \"pmids\": [\"35261785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FTO (m6A eraser) knockdown in A549 cells significantly decreased AHRR expression, while METTL3 (m6A writer) or ALKBH5 (m6A eraser) knockdown did not affect AHRR expression. FTO knockdown enhanced CYP1A1 induction by AhR agonist TCDD, and this enhancement was associated with decreased AHRR levels, suggesting that m6A modification (removed by FTO) suppresses AHRR expression and that AHRR levels modulate AhR-mediated CYP1A1 induction.\",\n      \"method\": \"siRNA knockdown of m6A regulatory enzymes (METTL3, ALKBH5, FTO) in A549 cells, RT-PCR for AHRR and ARNT mRNA, CYP1A1 induction assay\",\n      \"journal\": \"Toxicology letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, mechanistic inference from indirect knockdown experiments, m6A modification of AHRR mRNA itself not directly mapped\",\n      \"pmids\": [\"40118351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In human skin fibroblasts, repression of CYP1 enzyme activity was found NOT to be causally related to AhRR expression. Despite prior hypotheses, AhRR was expressed at only moderate levels, and some fibroblast strains could induce CYP1A1 mRNA. Enhancement of CYP1A1 mRNA by trichostatin A (an inhibitor of AhRR-recruited histone deacetylases) failed to induce measurable CYP1 activity. AhRR-deficient mouse embryonic fibroblasts showed impressive CYP1A1 mRNA induction but no biologically relevant CYP1 enzyme activity.\",\n      \"method\": \"Primary human skin fibroblast cultures (n=25), AhRR-knockout mouse embryonic fibroblasts, CYP1 enzyme activity assays, mRNA quantification, trichostatin A treatment\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout model plus pharmacological intervention with direct enzyme activity measurements; single lab, multiple orthogonal approaches; negative finding explicitly established\",\n      \"pmids\": [\"22951721\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"AHRR (AhRR) is a bHLH-PAS transcription factor that forms a heterodimer with ARNT and competes with AhR for ARNT binding and XRE (xenobiotic response element) occupancy, thereby repressing AhR-driven gene transcription; its crystal structure revealed that it blocks AhR-ARNT interaction through both competitive ARNT sequestration and an AhRR-ARNT-specific repression mechanism, its expression is itself AhR-dependent and induced by AhR ligands, its mRNA is post-transcriptionally regulated by the ARE-binding protein tristetraprolin, and in vivo it suppresses specific inflammatory cytokines (IL-1β, CXCL2/3), protects airway epithelium from cigarette smoke-induced mitochondrial dysfunction and cell death, and contributes to intestinal immune homeostasis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"AHRR (AhRR) is a bHLH-PAS transcription factor that heterodimerizes with ARNT to repress AhR-driven xenobiotic gene transcription, acting within a feedback loop in which its own expression is dependent on AhR signaling and induced by AhR ligands [#8]. The reconstituted AhRR-ARNT heterodimer binds xenobiotic response element (XRE/AHRE) sequences with full DNA-binding activity, and binding of both AhR-ARNT and AhRR-ARNT is sensitive to CpG methylation within the XRE core [#1]. The crystal structure of the AhRR-ARNT complex shows an asymmetric, intertwined domain organization in which the ARNT PAS-B domain adopts a distinct arrangement, establishing that AhRR represses AhR both by competitive sequestration of ARNT and target DNA and through an additional AhRR-ARNT-specific repression mechanism [#0]. Genome-wide ChIP-Seq shows AHRR occupies thousands of chromatin regions, many shared with AHR and enriched near promoters but also a large set of unique sites, consistent with context- and gene-specific repression [#3]. AHRR expression is constrained post-transcriptionally: the ARE-binding protein tristetraprolin binds the AHRR 3'UTR and destabilizes its mRNA [#4]. Physiologically, AHRR restrains specific inflammatory cytokines (IL-1β, CXCL2, CXCL3) and protects against acute TCDD toxicity in vivo [#5], contributes to intestinal immune homeostasis with susceptibility to DSS-colitis when dietary AhR ligands are absent [#9], and protects airway epithelial cells from cigarette-smoke-induced mitochondrial dysfunction and death [#10]. A recurrent t(5;8) translocation generates an AHRR/NCOA2 fusion in soft tissue angiofibroma that retains the AHRR bHLH-PAS domain but replaces its repressor domain with NCOA2 activation domains, converting it to an activator and upregulating AHR target genes such as CYP1A1 [#2].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established that AhRR is a bona fide ARNT-partnering, XRE-binding factor by reconstituting the heterodimer and demonstrating direct, methylation-sensitive DNA binding.\",\n      \"evidence\": \"Recombinant co-expression of AhRR-ARNT bHLH-PAS domains in E. coli with EMSA and methylation interference\",\n      \"pmids\": [\"12944374\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve how AhRR-ARNT binding differs structurally from AhR-ARNT\", \"Genome-wide binding repertoire not addressed\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined the AhR-AhRR feedback architecture by showing baseline AhRR expression is AhR-dependent and ligand-inducible in a tissue-specific manner.\",\n      \"evidence\": \"qRT-PCR in wild-type and AhR-/- mouse tissues with benzo(a)pyrene dose-response\",\n      \"pmids\": [\"16205913\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Constitutive high expression in heart and brain unexplained\", \"Functional consequence of tissue-restricted induction not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"First linked AhRR overexpression to altered proliferation and cell-cycle gene expression in breast cancer cells, hinting at roles beyond xenobiotic repression.\",\n      \"evidence\": \"Stable AhRR overexpression in MCF-7 with proliferation assays and RT-PCR of cell cycle/estrogen-responsive genes\",\n      \"pmids\": [\"16755028\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism connecting AhRR to E2F/cyclin E1/PCNA repression not established\", \"No epistasis placement\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstrated the functional importance of the AHRR repressor domain in disease by identifying an AHRR/NCOA2 fusion that converts AHRR into an activator of AHR targets.\",\n      \"evidence\": \"Cytogenetics, FISH, RT-PCR and global expression analysis of soft tissue angiofibromas\",\n      \"pmids\": [\"22337624\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct transforming activity of fusion not reconstituted\", \"Tumor-initiating mechanism beyond target-gene upregulation unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Challenged the assumption that AhRR is the principal repressor of CYP1 enzyme activity in fibroblasts via a negative genetic result.\",\n      \"evidence\": \"Primary human skin fibroblasts and AhRR-knockout MEFs with CYP1 enzyme activity assays and trichostatin A treatment\",\n      \"pmids\": [\"22951721\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not generalize beyond fibroblast systems\", \"Alternative repressors of CYP1 activity not identified\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified post-transcriptional control of AHRR levels through ARE-mediated mRNA destabilization by tristetraprolin.\",\n      \"evidence\": \"TTP gain/loss-of-function, mRNA stability assay, RNA EMSA, and ARE point mutagenesis\",\n      \"pmids\": [\"23583445\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological signals controlling TTP-AHRR axis not defined\", \"In vivo relevance not tested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Provided in vivo evidence that AhRR suppresses specific inflammatory cytokines and protects against acute TCDD toxicity.\",\n      \"evidence\": \"AhRR transgenic mice with TCDD challenge, cytokine profiling, survival, and hepatotoxicity markers\",\n      \"pmids\": [\"26862745\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-type origin of cytokine suppression not resolved\", \"Whether effect is purely AhR-repression-dependent unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Resolved the structural basis of AhRR repression, showing both competitive ARNT/DNA sequestration and an AhRR-specific repression mechanism.\",\n      \"evidence\": \"X-ray crystallography of the AhRR-ARNT heterodimer\",\n      \"pmids\": [\"28904176\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"AhRR-ARNT-specific repression mechanism not mechanistically dissected\", \"Full-length protein and coregulator interfaces not in structure\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Mapped the genome-wide AHRR binding landscape, revealing extensive AHR-shared and AHRR-unique promoter-proximal sites consistent with gene-specific repression.\",\n      \"evidence\": \"ChIP-Seq, ChIP-qPCR, and luciferase reporters in TCDD-treated MCF-7 cells\",\n      \"pmids\": [\"28681081\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional output of AHRR-unique sites largely uncharacterized\", \"Coregulator recruitment at unique sites unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Described a non-canonical role for AHRR as a cytoplasmic/nuclear co-factor in NF-κB-driven inflammation via LINC00305 and LIMR.\",\n      \"evidence\": \"Co-IP, overexpression/siRNA, immunofluorescence, and NF-κB reporter assays in THP-1 monocytes\",\n      \"pmids\": [\"28393844\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab observation of non-canonical pro-inflammatory function\", \"Reconciliation with AHRR's anti-inflammatory role in vivo not addressed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed AHRR contributes to intestinal immune homeostasis, with dietary AhR-ligand-driven expression and colitis susceptibility upon ligand deprivation.\",\n      \"evidence\": \"AhRR-reporter, AhRR-knockout and AhR-knockout mice with dietary I3C, DSS-colitis, and microbiota profiling\",\n      \"pmids\": [\"32366032\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Immune cell subset mediating protection not pinpointed\", \"Mechanism linking AHRR to microbiota shifts unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated that AHRR protects airway epithelial cells from cigarette-smoke-induced mitochondrial dysfunction and death.\",\n      \"evidence\": \"CRISPR/Cas9 AHRR knockout in 16HBE cells with proliferation, mitochondrial membrane potential, and apoptosis/necroptosis assays\",\n      \"pmids\": [\"36359818\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single cell line; in vivo airway relevance not tested\", \"Molecular link between AHRR and mitochondrial protection unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Proposed a pro-tumorigenic AHRR function in head and neck cancer through ARNT/EPAS1-driven VEGFD induction and lymphangiogenesis.\",\n      \"evidence\": \"AHRR transgenic and knockout mice with Western blot and ARNT-EPAS1 Co-IP\",\n      \"pmids\": [\"35261785\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Low-confidence single study with limited mechanistic detail\", \"Direct transcriptional control of VEGFD by AHRR not established\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Implicated m6A/FTO regulation in setting AHRR expression and thereby AhR-mediated CYP1A1 induction.\",\n      \"evidence\": \"siRNA knockdown of METTL3/ALKBH5/FTO in A549 cells with RT-PCR and CYP1A1 induction assays\",\n      \"pmids\": [\"40118351\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"m6A modification of AHRR mRNA not directly mapped\", \"Inference rests on indirect knockdown effects\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How AHRR's canonical anti-inflammatory transcriptional repression is reconciled with its reported pro-inflammatory and pro-tumorigenic context-dependent functions remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Coregulators recruited at AHRR-unique binding sites unknown\", \"Mechanistic basis of cytoprotective and context-specific roles undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [5, 9]}\n    ],\n    \"complexes\": [\"AhRR-ARNT heterodimer\"],\n    \"partners\": [\"ARNT\", \"AHR\", \"NCOA2\", \"ZBTB7B\", \"LIMR\", \"EPAS1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}