{"gene":"CA9","run_date":"2026-06-09T22:57:17","timeline":{"discoveries":[{"year":2004,"finding":"HIF-1α and Sp1, together with the co-activator CBP/p300, are critical transcriptional regulators of the CAIX (G250/MN) promoter in clear cell renal cell carcinoma. DNase-I footprint and band-shift assays demonstrated direct binding of HIF-1α and Sp1 to the CAIX promoter; mutations in the most proximal Sp1 or HIF-binding elements completely abolished promoter activity. HIF-2α showed no relationship with CAIX expression. Loss of VHL function leads to normoxic HIF-1α accumulation, which drives constitutive CAIX transcription in ccRCC.","method":"Transient transfection of promoter constructs, DNase-I footprint analysis, electrophoretic mobility shift assay (EMSA/band-shift), site-directed mutagenesis of promoter elements, Western blot correlation","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods (footprint, EMSA, mutagenesis, transfection) in a single rigorous study with clear mechanistic validation","pmids":["15184875"],"is_preprint":false},{"year":2007,"finding":"CAIX physically interacts with the SLC4 bicarbonate transporters AE1, AE2, and AE3 (but not SLC26A7) via its catalytic domain, forming a bicarbonate transport metabolon. Co-expression of CAIX increases AE2-mediated Cl⁻/HCO₃⁻ exchange activity by ~28%, and AE1/AE3 activity by ~32–37%, without altering transporter surface expression. CAIX and AE2 co-localize in human gastric mucosa.","method":"Co-immunoprecipitation, GST pull-down with domain-deletion constructs, functional transport assays in transfected HEK293 cells, co-immunofluorescence in human gastric tissue","journal":"American Journal of Physiology. Cell Physiology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reciprocal Co-IP, domain-deletion pull-down identifying catalytic domain as interaction site, functional transport assay, and tissue co-localization; multiple orthogonal methods in one study","pmids":["17652430"],"is_preprint":false},{"year":2019,"finding":"CAIX forms a transport metabolon with monocarboxylate transporters MCT1 and MCT4 in human breast cancer tissue (but not healthy breast tissue). The interaction requires binding of CAIX to the Ig1 domain of the MCT chaperone CD147. An antibody directed against the CD147-Ig1 domain displaces CAIX from MCT1/4 and suppresses CAIX-mediated facilitation of proton-coupled lactate transport, resulting in decreased lactate export, reduced glycolysis, and reduced cell proliferation in cancer cells.","method":"Co-immunoprecipitation from human breast cancer tissue and cell lines, antibody-mediated metabolon disruption, lactate transport assays, cell proliferation assays","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — Co-IP from patient tissue, mechanistic antibody disruption experiment with defined binding domain (CD147-Ig1), functional transport and proliferation readouts; multiple orthogonal methods","pmids":["31723238"],"is_preprint":false},{"year":2011,"finding":"CA9 overexpression in human cervical carcinoma C33A cells induces cytoskeletal remodeling, disassembly of focal adhesions, weakened cell-cell adhesion, and increased cell motility and invasion. These effects are mediated through aberrant Rho-GTPase (RhoA/ROCK) signaling; inhibition of the Rho/ROCK pathway by Y-27632 or RhoA siRNA abrogated CA9-driven morphological and migratory changes. Silencing CA9 reversed these phenotypes.","method":"Gene transfection and siRNA knockdown, DNA microarray, immunofluorescence, Matrigel invasion assay, ROCK inhibitor treatment, si-RhoA knockdown","journal":"Journal of Cell Science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss- and gain-of-function with pharmacological and genetic pathway validation, multiple phenotypic readouts; single lab","pmids":["21363891"],"is_preprint":false},{"year":2001,"finding":"Hypomethylation of a specific CpG site at −74 bp in the MN/CA9 promoter is associated with MN/CA9 gene expression in human renal cell carcinoma. In vitro CpG methylation of this site strongly suppresses promoter activity in a luciferase reporter assay, and treatment with the demethylating agent 5-aza-2'-deoxycytidine reactivates MN/CA9 expression in MN/CA9-negative RCC cell lines.","method":"Bisulfite genomic sequencing, luciferase promoter assay with in vitro methylated constructs, 5-aza-2'-deoxycytidine demethylation treatment, RT-PCR","journal":"British Journal of Cancer","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — functional promoter assay plus demethylation rescue; mechanistic but single lab","pmids":["11506497"],"is_preprint":false},{"year":2000,"finding":"Hypomethylation of the 5′ region of the MN/CA9 gene correlates with its expression in renal cell carcinoma cell lines. Treatment of MN/CA9-negative RCC lines with the demethylating agent 5-aza-2'-deoxycytidine activates MN/CA9 gene expression, demonstrating that promoter methylation controls transcriptional silencing of CA9.","method":"Bisulfite genomic sequencing across seven CpG sites in the MN/CA9 5′ region, 5-aza-2'-deoxycytidine demethylation, RT-PCR","journal":"Molecular Carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — demethylation rescue experiment, replicated finding corroborated by later study (PMID 11506497); single lab","pmids":["10708480"],"is_preprint":false},{"year":2005,"finding":"Methylation of a single CpG site at −74 bp in the CA9 promoter can down-modulate CA9 expression in non-RCC cancer cells (HeLa cervical carcinoma) specifically under high-density culture conditions, but not in sparse culture or under hypoxia. This indicates that promoter methylation acts as an accessory rather than primary regulatory mechanism for CA9 outside of RCC.","method":"Metabisulfite sequencing, 5-aza-2'-deoxycytidine demethylation, CA9 expression analysis under varying conditions","journal":"International Journal of Oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic demethylation experiment with condition-specific controls; single lab, single study","pmids":["15754010"],"is_preprint":false},{"year":2021,"finding":"A genome-wide synthetic lethal CRISPR screen identified NFS1 (an iron-sulfur cluster enzyme) and xCT (cystine transporter) as synthetic lethal partners of CAIX. CAIX inhibition acidifies intracellular pH, increases reactive oxygen species, and increases susceptibility to ferroptosis. Mechanistically, inhibiting CAIX-mediated bicarbonate production (or sodium-driven bicarbonate transport) while targeting xCT decreases AMPK activation and increases ACC1 activation, linking CAIX to regulation of lipid metabolism and ferroptosis resistance.","method":"Genome-wide CRISPR synthetic lethal screen, intracellular pH measurements, ROS assays, AMPK/ACC1 phosphorylation assays, tumor growth inhibition studies","journal":"Science Advances","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — unbiased genome-wide CRISPR screen followed by mechanistic validation with multiple biochemical readouts (pH, ROS, AMPK/ACC1 signaling) and in vivo tumor growth; multiple orthogonal methods","pmids":["34452919"],"is_preprint":false},{"year":2020,"finding":"CA9 silencing in ccRCC cells upregulates oxidative phosphorylation-associated proteins and increases mitochondrial biogenesis, reversing the Warburg phenotype. CA9 knockdown also upregulates mitochondrial arginase 2 (ARG2), leading to accumulation of putrescine that suppresses cell proliferation. Additionally, surface proteomics after CA9 knockdown revealed downregulation of ECM-receptor interaction and cell adhesion proteins, causing decreased cell migration.","method":"siRNA knockdown, OXPHOS protein profiling, mitochondrial biogenesis assays, surfaceomics (surface protein mass spectrometry), cell migration assays, metabolomics","journal":"International Journal of Molecular Sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with multiple orthogonal omics readouts (proteomics, metabolomics) and functional assays; single lab","pmids":["32824856"],"is_preprint":false},{"year":2020,"finding":"CAIX downregulation in breast cancer cells under hypoxia leads to increased levels of let-7 miRNA family members and decreased LIN28 protein. Reduced LIN28 downstream leads to decreased PDK1 expression and decreased phosphorylation of pyruvate dehydrogenase (PDH) at Ser-232, attenuating glycolysis. Conversely, CAIX overexpression enhances LIN28, ALDH1, and NANOG levels. This identifies a CAIX→LIN28/let-7 axis linking CAIX to glycolytic metabolism and cancer stem cell marker maintenance.","method":"siRNA knockdown and CRISPR knockout, CAIX overexpression, qRT-PCR for let-7 miRNAs, Western blot for LIN28/PDK1/phospho-PDH/ALDH1/NANOG","journal":"International Journal of Molecular Sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss- and gain-of-function with multiple pathway readouts; mechanistic axis defined in single lab","pmids":["32560271"],"is_preprint":false},{"year":2020,"finding":"CAIX regulates GBM cell motility, monocyte adhesion to GBM cells, and polarization of tumor-associated monocytes/macrophages under hypoxic conditions. EGFR/STAT3 signaling was shown to regulate CAIX expression under hypoxia by affecting HIF-1α stability. Knockdown of CAIX abrogated hypoxia-induced GBM motility changes and monocyte adhesion.","method":"CAIX knockdown and overexpression in GBM cell lines, EGFR/STAT3 pathway inhibition, HIF-1α stability assays, cell motility assays, monocyte adhesion assays, macrophage polarization assays","journal":"International Journal of Molecular Sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with multiple cellular phenotype readouts and pathway inhibitor validation; single lab","pmids":["32823915"],"is_preprint":false},{"year":2018,"finding":"SOX9 transcriptionally regulates CA9 expression in glioblastoma cells; SOX9 knockdown via lentiviral infection leads to downregulation of both SOX9 and CA9, with downstream decrease in Akt phosphorylation, decreased BCL-2, and increased BAX. Pharmacological inhibition of CA9 with U-104 in combination with TMZ induces glioma cell death, with similar pathway changes, establishing a SOX9/CA9/Akt axis linked to chemoresistance.","method":"Lentiviral SOX9 knockdown, gene microarray, Western blot, RT-qPCR, CA9 inhibitor (U-104) treatment, cell death assays","journal":"International Journal of Oncology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — SOX9 knockdown with gene microarray and Western blot for pathway; indirect SOX9→CA9 link, single lab, single method for each step","pmids":["29749469"],"is_preprint":false},{"year":2021,"finding":"PADI4 upregulates CA9 expression in esophageal squamous cell carcinoma cells. PCR array analysis showed increased CA9 mRNA upon PADI4 overexpression and decreased CA9 upon PADI4 siRNA knockdown. PADI4 and CA9 co-localize in ESCC tissues, and PADI4-driven CA9 upregulation contributes to tumor growth in vivo.","method":"Lentiviral PADI4 overexpression and siRNA knockdown, PCR array, Western blot, immunohistochemistry co-localization, xenograft mouse model","journal":"Molecular Carcinogenesis","confidence":"Low","confidence_rationale":"Tier 3 / Weak — transcriptional regulation supported by expression correlation and gain/loss-of-function; mechanism of PADI4→CA9 regulation not directly resolved (no promoter or ChIP assay shown in abstract); single lab","pmids":["30242913"],"is_preprint":false},{"year":2024,"finding":"Vanillic acid (VA) directly binds CA9 (identified by CETSA and DARTS assays). VA binding to CA9 causes INSIG2 to interact with STIM1 instead of SCAP, redirecting SCAP-SREBP1 from ER retention to Golgi translocation and cleavage into mature SREBP1. Activated SREBP1 then induces transcription of SCD1, which inhibits ferroptosis in intestinal epithelial cells.","method":"CETSA (cellular thermal shift assay), DARTS (drug affinity responsive target stability) assay, protein co-immunoprecipitation (INSIG2-STIM1 and SCAP), SREBP1 cleavage assay, SCD1 transcription analysis, ferroptosis assays","journal":"Pharmacological Research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct target engagement confirmed by two orthogonal biophysical assays (CETSA + DARTS), with mechanistic downstream pathway (INSIG2/STIM1/SCAP/SREBP1/SCD1) validated; single lab","pmids":["38438089"],"is_preprint":false},{"year":2024,"finding":"OTUB2 silencing in ovarian cancer cells leads to destabilization of SNX29P2, which prevents VHL-mediated degradation of HIF-1α. Elevated HIF-1α then activates CA9 transcription, driving glycolysis and chemoresistance. Pharmacological inhibition of CA9 suppresses tumor growth and synergizes with carboplatin in OTUB2-silenced ovarian cancer models.","method":"siRNA knockdown, Western blot for HIF-1α/VHL/CA9 pathway, CA9 inhibitor treatment, tumor growth assays, carboplatin combination treatment","journal":"Proceedings of the National Academy of Sciences USA","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function epistasis (OTUB2→SNX29P2→HIF-1α→CA9) with in vivo validation; single lab","pmids":["38701117"],"is_preprint":false},{"year":2021,"finding":"CAIX inhibitory activity at low pH is more catalytically efficient than CAXII. pH titration assays of membrane ghosts showed significant differences in catalytic efficiency and pKa values between CAIX and CAXII. CAIX shifts the equilibrium between CO2 and bicarbonate in favor of CO2 production by consuming protons in the acidic tumor microenvironment, supporting an extracellular pH-stabilizing role for cancer cell survival. However, an impermeant sulfonamide inhibitor (N-3500) that blocks CAIX catalytic activity was insufficient to inhibit cell growth at relevant concentrations, suggesting a noncatalytic function also contributes to CAIX effects on tumor cell behavior.","method":"Enzymatic activity assays (pH titration in membrane ghosts), sulfonamide inhibitor (N-3500) treatment, siRNA knockdown, cell growth and migration assays","journal":"PloS One","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic characterization with functional cell-based validation; single lab with multiple methods","pmids":["29965974"],"is_preprint":false},{"year":2021,"finding":"SLC-149 inhibits CAIX catalytic activity with greater potency than acetazolamide. Structural analysis (crystal structure of SLC-149 bound to a CAIX-mimic) and thermal stabilization assays explain binding preferences. However, despite inhibiting extracellular pH regulation, SLC-149 has minimal effect on cancer cell cytotoxicity and requires high concentrations to inhibit growth, migration, and invasion, supporting the hypothesis that CAIX's role in controlling cell growth is at least partly independent of its carbonic anhydrase catalytic activity.","method":"Enzyme inhibition assays (Ki determination), thermal shift assay, crystal structure of inhibitor bound to CAIX-mimic, cell culture cytotoxicity, cell growth/migration/invasion assays","journal":"Journal of Medicinal Chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with functional validation, enzymatic assays, and cell-based experiments; multiple orthogonal methods in one study","pmids":["33523653"],"is_preprint":false},{"year":2024,"finding":"ZNF674-AS1 lncRNA interacts with the RNA-binding protein IGF2BP3 to enhance stability of CA9 mRNA by binding to the CA9 transcript, elevating CA9 protein expression. This CA9 upregulation suppresses cisplatin-induced pyroptosis and promotes cell proliferation in neuroblastoma. Targeting ZNF674-AS1 or CA9 suppresses tumor growth in vivo and restores cisplatin sensitivity.","method":"RNA immunoprecipitation (RIP) for ZNF674-AS1–IGF2BP3 interaction, CA9 mRNA stability assay, CA9 knockdown, in vivo xenograft tumor growth, pyroptosis assays, cell proliferation assays","journal":"Cell Death & Disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RIP for protein–RNA interaction and mRNA stability mechanistic validation with in vivo phenotypic readout; single lab","pmids":["38177154"],"is_preprint":false},{"year":2023,"finding":"CA9 knockdown in hypoxic glioma cells significantly alters iron regulation-related protein expression and enhances X-ray-induced ferroptosis and radiosensitivity. CA9 silencing overcomes hypoxic ferroptosis resistance, and enhancing ferroptosis by CA9 knockdown promotes exposure and release of damage-associated molecular patterns (DAMPs).","method":"siRNA knockdown, X-ray irradiation, lipid peroxidation assay (C11-BODIPY staining), RT-qPCR for ferroptosis markers and iron-associated proteins, clonogenic survival assay, immunofluorescence for calreticulin (DAMPs)","journal":"International Journal of Radiation Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with multiple ferroptosis and iron homeostasis readouts; single lab","pmids":["37463506"],"is_preprint":false}],"current_model":"CA9/CAIX is a transmembrane carbonic anhydrase whose transcription is primarily driven by HIF-1α (binding the CAIX promoter together with Sp1 and CBP/p300), and is silenced by CpG methylation at −74 bp; the encoded enzyme catalyzes CO₂ hydration extracellularly to produce protons and bicarbonate, acidifying the tumor microenvironment while helping maintain intracellular pH. CAIX physically interacts with SLC4 bicarbonate transporters (AE1/AE2/AE3) via its catalytic domain and with monocarboxylate transporters MCT1/MCT4 via CD147-Ig1 to form transport metabolons that facilitate bicarbonate and lactate export; disrupting the MCT metabolon reduces glycolysis and cancer cell proliferation. Through pH regulation, CAIX suppresses ferroptosis via AMPK/ACC1 signaling, and its silencing reverses the Warburg phenotype by increasing mitochondrial biogenesis and ARG2-driven putrescine accumulation. CAIX also promotes tumor cell migration and invasion through Rho-GTPase/ROCK signaling, and modulates a LIN28/let-7 axis to sustain glycolysis and cancer stem cell markers."},"narrative":{"mechanistic_narrative":"CA9/CAIX is a hypoxia-induced, membrane-associated carbonic anhydrase that couples extracellular pH regulation to the metabolic and invasive adaptations of tumor cells [PMID:29965974, PMID:31723238]. Its transcription is driven principally by HIF-1α acting with Sp1 and the co-activator CBP/p300 at the proximal CAIX promoter, a program rendered constitutive in clear cell renal cell carcinoma by VHL loss and normoxic HIF-1α accumulation; HIF-2α does not contribute [PMID:15184875]. CAIX expression is additionally controlled by CpG methylation at the −74 bp promoter site, silencing being relieved by demethylation [PMID:11506497, PMID:10708480], and upstream regulators including EGFR/STAT3 (via HIF-1α stability) and the OTUB2–SNX29P2 axis converge on this HIF-1α/CA9 output [PMID:32823915, PMID:38701117]. Catalytically, CAIX is highly efficient at low pH and shifts the CO₂/bicarbonate equilibrium to consume protons and stabilize the acidic tumor microenvironment [PMID:29965974]. It works physically within transport metabolons: binding the SLC4 bicarbonate exchangers AE1/AE2/AE3 through its catalytic domain to enhance Cl⁻/HCO₃⁻ exchange [PMID:17652430], and binding the CD147-Ig1 domain to assemble with MCT1/MCT4 and facilitate proton-coupled lactate export, sustaining glycolysis and proliferation [PMID:31723238]. Through pH control CAIX suppresses ferroptosis—its inhibition acidifies intracellular pH, raises ROS, and sensitizes cells to ferroptosis via AMPK/ACC1 signaling and synthetic lethality with NFS1 and xCT [PMID:34452919], and CA9 silencing enhances ferroptosis and radiosensitivity in glioma [PMID:37463506]. CAIX silencing also reverses the Warburg phenotype by promoting mitochondrial biogenesis and ARG2-driven putrescine accumulation [PMID:32824856], and CAIX promotes migration and invasion through Rho-GTPase/ROCK signaling [PMID:21363891]. Notably, impermeant catalytic inhibitors block extracellular pH regulation but fail to suppress cancer cell growth at relevant doses, indicating a non-catalytic contribution to CAIX's effects on tumor behavior [PMID:29965974, PMID:33523653].","teleology":[{"year":2000,"claim":"Established that promoter DNA methylation, not only hypoxia, governs whether CA9 is expressed, explaining cell-line-specific silencing.","evidence":"Bisulfite sequencing of the MN/CA9 5' region with 5-aza-2'-deoxycytidine reactivation in RCC lines","pmids":["10708480"],"confidence":"Medium","gaps":["Did not pinpoint the critical CpG site","Correlative methylation-expression link without functional promoter dissection"]},{"year":2001,"claim":"Localized methylation control to a single CpG at −74 bp, defining a discrete epigenetic switch for CA9 transcription.","evidence":"Luciferase reporters with in vitro methylated constructs and demethylation rescue in RCC cells","pmids":["11506497"],"confidence":"Medium","gaps":["Methyl-CpG-binding factors mediating repression not identified","Single lab"]},{"year":2004,"claim":"Defined the core transcriptional machinery driving CA9, showing HIF-1α and Sp1 with CBP/p300 directly activate the promoter and that VHL loss makes this constitutive.","evidence":"DNase-I footprinting, EMSA, and promoter mutagenesis in ccRCC","pmids":["15184875"],"confidence":"High","gaps":["HIF-2α role excluded but other context-specific regulators not surveyed","Did not address protein-level activity"]},{"year":2005,"claim":"Clarified that −74 bp methylation acts only as an accessory regulator outside RCC, operating under specific culture conditions rather than as the primary control.","evidence":"Bisulfite sequencing and demethylation under varied density/hypoxia in HeLa cells","pmids":["15754010"],"confidence":"Medium","gaps":["Mechanism of density-dependent methylation effect unresolved","Single study"]},{"year":2007,"claim":"Demonstrated CAIX is not merely an enzyme but a structural scaffold, forming a bicarbonate transport metabolon with SLC4 exchangers via its catalytic domain.","evidence":"Reciprocal Co-IP, GST pull-down with domain deletions, and functional transport assays in HEK293","pmids":["17652430"],"confidence":"High","gaps":["Whether the interaction requires catalytic activity not separated","Tumor relevance of the AE metabolon not tested"]},{"year":2011,"claim":"Connected CAIX to a motility/invasion program through Rho-GTPase signaling, beyond its metabolic role.","evidence":"Gain/loss-of-function with ROCK inhibitor and RhoA siRNA, microarray, and invasion assays in C33A cells","pmids":["21363891"],"confidence":"Medium","gaps":["How CAIX activates RhoA/ROCK mechanistically not defined","Single lab, single cell line"]},{"year":2019,"claim":"Identified the MCT1/MCT4 lactate-transport metabolon assembled via CD147-Ig1 binding, showing metabolon disruption suppresses glycolysis and proliferation.","evidence":"Co-IP from patient breast tumor tissue and antibody-mediated metabolon disruption with lactate transport and proliferation readouts","pmids":["31723238"],"confidence":"High","gaps":["In vivo therapeutic disruption not shown","Generality across tumor types not established"]},{"year":2020,"claim":"Showed CAIX silencing reverses the Warburg phenotype by inducing mitochondrial biogenesis and ARG2/putrescine accumulation while reducing adhesion proteins.","evidence":"siRNA knockdown with OXPHOS proteomics, metabolomics, surfaceomics, and migration assays in ccRCC","pmids":["32824856"],"confidence":"Medium","gaps":["Causal chain from pH to mitochondrial biogenesis not dissected","Single lab"]},{"year":2020,"claim":"Defined a CAIX→LIN28/let-7 axis linking CAIX to glycolytic flux and stem-cell marker maintenance.","evidence":"Knockdown/knockout and overexpression with let-7 qRT-PCR and LIN28/PDK1/phospho-PDH/ALDH1/NANOG blots in breast cancer","pmids":["32560271"],"confidence":"Medium","gaps":["Mechanism by which CAIX regulates LIN28 unknown","Single lab"]},{"year":2020,"claim":"Placed CAIX in the tumor immune microenvironment, regulating GBM motility and tumor-associated monocyte/macrophage behavior, with EGFR/STAT3 controlling its expression via HIF-1α.","evidence":"CAIX knockdown/overexpression with EGFR/STAT3 inhibition, HIF-1α stability, motility, and monocyte adhesion/polarization assays in GBM","pmids":["32823915"],"confidence":"Medium","gaps":["Direct CAIX-dependent signal to monocytes not defined","Single lab"]},{"year":2021,"claim":"Established CAIX as a ferroptosis suppressor via pH/ROS control, with NFS1 and xCT as synthetic lethal partners acting through AMPK/ACC1.","evidence":"Genome-wide CRISPR synthetic lethal screen plus pH, ROS, AMPK/ACC1 readouts and in vivo tumor growth","pmids":["34452919"],"confidence":"High","gaps":["Direct molecular link between bicarbonate and AMPK not fully resolved","Tissue specificity of synthetic lethality unclear"]},{"year":2021,"claim":"Quantified CAIX's superior low-pH catalytic efficiency yet showed catalytic inhibition alone is insufficient to block growth, first evidence for a non-catalytic function.","evidence":"pH-titration enzyme assays in membrane ghosts and impermeant sulfonamide (N-3500) treatment with growth/migration assays","pmids":["29965974"],"confidence":"Medium","gaps":["Nature of the non-catalytic function not identified","Single lab"]},{"year":2021,"claim":"Reinforced the catalytic-vs-noncatalytic dissociation with a potent structurally-defined inhibitor that blocks pH regulation but barely affects cytotoxicity.","evidence":"Ki determination, thermal shift, crystal structure of SLC-149 bound to a CAIX-mimic, and cell growth/invasion assays","pmids":["33523653"],"confidence":"High","gaps":["Structural basis of the non-catalytic scaffolding role not solved","In vivo efficacy not addressed"]},{"year":2023,"claim":"Showed CA9 silencing enhances X-ray-induced ferroptosis and radiosensitivity and triggers DAMP release in hypoxic glioma, extending the ferroptosis link to radiotherapy.","evidence":"siRNA knockdown with lipid peroxidation, iron-protein qPCR, clonogenic survival, and calreticulin immunofluorescence","pmids":["37463506"],"confidence":"Medium","gaps":["Mechanism linking CA9 to iron regulation not resolved","Single lab"]},{"year":2024,"claim":"Identified post-transcriptional control of CA9 by the ZNF674-AS1/IGF2BP3 axis stabilizing CA9 mRNA to suppress pyroptosis and drive chemoresistance.","evidence":"RIP, CA9 mRNA stability assays, knockdown, and xenograft/pyroptosis assays in neuroblastoma","pmids":["38177154"],"confidence":"Medium","gaps":["Whether IGF2BP3 directly recognizes CA9 mRNA modifications unclear","Single lab"]},{"year":2024,"claim":"Provided direct evidence of small-molecule target engagement with CA9 (vanillic acid) rewiring INSIG2/STIM1/SCAP–SREBP1–SCD1 to modulate ferroptosis in intestinal epithelium.","evidence":"CETSA and DARTS target engagement, INSIG2-STIM1/SCAP Co-IP, SREBP1 cleavage and SCD1 transcription with ferroptosis assays","pmids":["38438089"],"confidence":"Medium","gaps":["How CA9 binding alters INSIG2 partner choice mechanistically unresolved","Single lab, non-tumor context"]},{"year":null,"claim":"The molecular identity of CAIX's catalytic-independent function—how the protein scaffold drives growth, invasion, and metabolon assembly beyond CO₂ hydration—remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Structural basis of the non-catalytic role not defined","Whether metabolon scaffolding requires catalytic activity untested","Mechanisms connecting CAIX to RhoA/ROCK and LIN28 unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016829","term_label":"lyase activity","supporting_discovery_ids":[15,16]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,2]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,2]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[2,8,9]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[1,2]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[7,18]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,4]}],"complexes":["CAIX-AE bicarbonate transport metabolon","CAIX-CD147-MCT1/MCT4 lactate transport metabolon"],"partners":["AE1","AE2","AE3","MCT1","MCT4","CD147","IGF2BP3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q16790","full_name":"Carbonic anhydrase 9","aliases":["Carbonate dehydratase IX","Carbonic anhydrase IX","CA-IX","CAIX","Membrane antigen MN","P54/58N","Renal cell carcinoma-associated antigen G250","RCC-associated antigen G250","pMW1"],"length_aa":459,"mass_kda":49.7,"function":"Catalyzes the interconversion between carbon dioxide and water and the dissociated ions of carbonic acid (i.e. bicarbonate and hydrogen ions)","subcellular_location":"Nucleus; Nucleus, nucleolus; Cell membrane; Cell projection, microvillus membrane","url":"https://www.uniprot.org/uniprotkb/Q16790/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CA9","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CA9","total_profiled":1310},"omim":[{"mim_id":"608537","title":"VON HIPPEL-LINDAU TUMOR SUPPRESSOR; VHL","url":"https://www.omim.org/entry/608537"},{"mim_id":"603263","title":"CARBONIC ANHYDRASE XII; CA12","url":"https://www.omim.org/entry/603263"},{"mim_id":"603179","title":"CARBONIC ANHYDRASE IX; CA9","url":"https://www.omim.org/entry/603179"},{"mim_id":"269700","title":"LIPODYSTROPHY, CONGENITAL GENERALIZED, TYPE 2; CGL2","url":"https://www.omim.org/entry/269700"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"stomach 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(Weinheim, Baden-Wurttemberg, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/40178177","citation_count":17,"is_preprint":false},{"pmid":"27823879","id":"PMC_27823879","title":"New approach of delivering cytotoxic drugs towards CAIX expressing cells: A concept of dual-target drugs.","date":"2016","source":"European journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/27823879","citation_count":17,"is_preprint":false},{"pmid":"38948062","id":"PMC_38948062","title":"Towards effective CAIX-targeted radionuclide and checkpoint inhibition combination therapy for advanced clear cell renal cell carcinoma.","date":"2024","source":"Theranostics","url":"https://pubmed.ncbi.nlm.nih.gov/38948062","citation_count":16,"is_preprint":false},{"pmid":"32410301","id":"PMC_32410301","title":"Expression of CA2 and CA9 carbonic anhydrases in ulcerative colitis and ulcerative colitis-associated colorectal cancer.","date":"2020","source":"Pathology international","url":"https://pubmed.ncbi.nlm.nih.gov/32410301","citation_count":16,"is_preprint":false},{"pmid":"31624303","id":"PMC_31624303","title":"Comparative evaluation of affibody- and antibody fragments-based CAIX imaging probes in mice bearing renal cell carcinoma xenografts.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31624303","citation_count":16,"is_preprint":false},{"pmid":"24349364","id":"PMC_24349364","title":"Impacts of CA9 gene polymorphisms on urothelial cell carcinoma susceptibility and clinicopathologic characteristics in Taiwan.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24349364","citation_count":15,"is_preprint":false},{"pmid":"37293644","id":"PMC_37293644","title":"Photochemically controlled activation of STING by CAIX-targeting photocaged agonists to suppress tumor cell growth.","date":"2023","source":"Chemical science","url":"https://pubmed.ncbi.nlm.nih.gov/37293644","citation_count":15,"is_preprint":false},{"pmid":"34977338","id":"PMC_34977338","title":"Dual-targeting vaccine of FGL1/CAIX exhibits potent anti-tumor activity by activating DC-mediated multi-functional CD8 T cell immunity.","date":"2021","source":"Molecular therapy oncolytics","url":"https://pubmed.ncbi.nlm.nih.gov/34977338","citation_count":15,"is_preprint":false},{"pmid":"23843845","id":"PMC_23843845","title":"The Expression of Glut-1, CAIX, and MCT4 in Mucinous Carcinoma.","date":"2013","source":"Journal of breast cancer","url":"https://pubmed.ncbi.nlm.nih.gov/23843845","citation_count":14,"is_preprint":false},{"pmid":"35044182","id":"PMC_35044182","title":"Novel VHH-Based Tracers with Variable Plasma Half-Lives for Imaging of CAIX-Expressing Hypoxic Tumor Cells.","date":"2022","source":"Molecular pharmaceutics","url":"https://pubmed.ncbi.nlm.nih.gov/35044182","citation_count":14,"is_preprint":false},{"pmid":"17536770","id":"PMC_17536770","title":"MN/CA9: a potential gene marker for detection of malignant cells in effusions.","date":"2007","source":"Biomarkers : biochemical indicators of exposure, response, and susceptibility to chemicals","url":"https://pubmed.ncbi.nlm.nih.gov/17536770","citation_count":14,"is_preprint":false},{"pmid":"37463506","id":"PMC_37463506","title":"CA9 knockdown enhanced ionizing radiation-induced ferroptosis and radiosensitivity of hypoxic glioma cells.","date":"2023","source":"International journal of radiation biology","url":"https://pubmed.ncbi.nlm.nih.gov/37463506","citation_count":13,"is_preprint":false},{"pmid":"27513947","id":"PMC_27513947","title":"The Sulfamate Small Molecule CAIX Inhibitor S4 Modulates Doxorubicin Efficacy.","date":"2016","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/27513947","citation_count":13,"is_preprint":false},{"pmid":"31795962","id":"PMC_31795962","title":"CAIX is a predictor of pathological complete response and is associated with higher survival in locally advanced breast cancer submitted to neoadjuvant chemotherapy.","date":"2019","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/31795962","citation_count":13,"is_preprint":false},{"pmid":"34948029","id":"PMC_34948029","title":"Effects and Related Mechanisms of the Senolytic Agent ABT-263 on the Survival of Irradiated A549 and Ca9-22 Cancer Cells.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/34948029","citation_count":12,"is_preprint":false},{"pmid":"26408684","id":"PMC_26408684","title":"The In Vitro and In Vivo Activity of the Microtubule Disruptor STX140 Is Mediated by Hif-1 Alpha and CAIX Expression.","date":"2015","source":"Anticancer research","url":"https://pubmed.ncbi.nlm.nih.gov/26408684","citation_count":12,"is_preprint":false},{"pmid":"32824856","id":"PMC_32824856","title":"CA9 Silencing Promotes Mitochondrial Biogenesis, Increases Putrescine Toxicity and Decreases Cell Motility to Suppress ccRCC Progression.","date":"2020","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/32824856","citation_count":12,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":56717,"output_tokens":5784,"usd":0.128456,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":14593,"output_tokens":4894,"usd":0.097657,"stage2_stop_reason":"end_turn"},"total_usd":0.226113,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"HIF-1α and Sp1, together with the co-activator CBP/p300, are critical transcriptional regulators of the CAIX (G250/MN) promoter in clear cell renal cell carcinoma. DNase-I footprint and band-shift assays demonstrated direct binding of HIF-1α and Sp1 to the CAIX promoter; mutations in the most proximal Sp1 or HIF-binding elements completely abolished promoter activity. HIF-2α showed no relationship with CAIX expression. Loss of VHL function leads to normoxic HIF-1α accumulation, which drives constitutive CAIX transcription in ccRCC.\",\n      \"method\": \"Transient transfection of promoter constructs, DNase-I footprint analysis, electrophoretic mobility shift assay (EMSA/band-shift), site-directed mutagenesis of promoter elements, Western blot correlation\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods (footprint, EMSA, mutagenesis, transfection) in a single rigorous study with clear mechanistic validation\",\n      \"pmids\": [\"15184875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CAIX physically interacts with the SLC4 bicarbonate transporters AE1, AE2, and AE3 (but not SLC26A7) via its catalytic domain, forming a bicarbonate transport metabolon. Co-expression of CAIX increases AE2-mediated Cl⁻/HCO₃⁻ exchange activity by ~28%, and AE1/AE3 activity by ~32–37%, without altering transporter surface expression. CAIX and AE2 co-localize in human gastric mucosa.\",\n      \"method\": \"Co-immunoprecipitation, GST pull-down with domain-deletion constructs, functional transport assays in transfected HEK293 cells, co-immunofluorescence in human gastric tissue\",\n      \"journal\": \"American Journal of Physiology. Cell Physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reciprocal Co-IP, domain-deletion pull-down identifying catalytic domain as interaction site, functional transport assay, and tissue co-localization; multiple orthogonal methods in one study\",\n      \"pmids\": [\"17652430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CAIX forms a transport metabolon with monocarboxylate transporters MCT1 and MCT4 in human breast cancer tissue (but not healthy breast tissue). The interaction requires binding of CAIX to the Ig1 domain of the MCT chaperone CD147. An antibody directed against the CD147-Ig1 domain displaces CAIX from MCT1/4 and suppresses CAIX-mediated facilitation of proton-coupled lactate transport, resulting in decreased lactate export, reduced glycolysis, and reduced cell proliferation in cancer cells.\",\n      \"method\": \"Co-immunoprecipitation from human breast cancer tissue and cell lines, antibody-mediated metabolon disruption, lactate transport assays, cell proliferation assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — Co-IP from patient tissue, mechanistic antibody disruption experiment with defined binding domain (CD147-Ig1), functional transport and proliferation readouts; multiple orthogonal methods\",\n      \"pmids\": [\"31723238\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CA9 overexpression in human cervical carcinoma C33A cells induces cytoskeletal remodeling, disassembly of focal adhesions, weakened cell-cell adhesion, and increased cell motility and invasion. These effects are mediated through aberrant Rho-GTPase (RhoA/ROCK) signaling; inhibition of the Rho/ROCK pathway by Y-27632 or RhoA siRNA abrogated CA9-driven morphological and migratory changes. Silencing CA9 reversed these phenotypes.\",\n      \"method\": \"Gene transfection and siRNA knockdown, DNA microarray, immunofluorescence, Matrigel invasion assay, ROCK inhibitor treatment, si-RhoA knockdown\",\n      \"journal\": \"Journal of Cell Science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss- and gain-of-function with pharmacological and genetic pathway validation, multiple phenotypic readouts; single lab\",\n      \"pmids\": [\"21363891\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Hypomethylation of a specific CpG site at −74 bp in the MN/CA9 promoter is associated with MN/CA9 gene expression in human renal cell carcinoma. In vitro CpG methylation of this site strongly suppresses promoter activity in a luciferase reporter assay, and treatment with the demethylating agent 5-aza-2'-deoxycytidine reactivates MN/CA9 expression in MN/CA9-negative RCC cell lines.\",\n      \"method\": \"Bisulfite genomic sequencing, luciferase promoter assay with in vitro methylated constructs, 5-aza-2'-deoxycytidine demethylation treatment, RT-PCR\",\n      \"journal\": \"British Journal of Cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — functional promoter assay plus demethylation rescue; mechanistic but single lab\",\n      \"pmids\": [\"11506497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Hypomethylation of the 5′ region of the MN/CA9 gene correlates with its expression in renal cell carcinoma cell lines. Treatment of MN/CA9-negative RCC lines with the demethylating agent 5-aza-2'-deoxycytidine activates MN/CA9 gene expression, demonstrating that promoter methylation controls transcriptional silencing of CA9.\",\n      \"method\": \"Bisulfite genomic sequencing across seven CpG sites in the MN/CA9 5′ region, 5-aza-2'-deoxycytidine demethylation, RT-PCR\",\n      \"journal\": \"Molecular Carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — demethylation rescue experiment, replicated finding corroborated by later study (PMID 11506497); single lab\",\n      \"pmids\": [\"10708480\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Methylation of a single CpG site at −74 bp in the CA9 promoter can down-modulate CA9 expression in non-RCC cancer cells (HeLa cervical carcinoma) specifically under high-density culture conditions, but not in sparse culture or under hypoxia. This indicates that promoter methylation acts as an accessory rather than primary regulatory mechanism for CA9 outside of RCC.\",\n      \"method\": \"Metabisulfite sequencing, 5-aza-2'-deoxycytidine demethylation, CA9 expression analysis under varying conditions\",\n      \"journal\": \"International Journal of Oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic demethylation experiment with condition-specific controls; single lab, single study\",\n      \"pmids\": [\"15754010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A genome-wide synthetic lethal CRISPR screen identified NFS1 (an iron-sulfur cluster enzyme) and xCT (cystine transporter) as synthetic lethal partners of CAIX. CAIX inhibition acidifies intracellular pH, increases reactive oxygen species, and increases susceptibility to ferroptosis. Mechanistically, inhibiting CAIX-mediated bicarbonate production (or sodium-driven bicarbonate transport) while targeting xCT decreases AMPK activation and increases ACC1 activation, linking CAIX to regulation of lipid metabolism and ferroptosis resistance.\",\n      \"method\": \"Genome-wide CRISPR synthetic lethal screen, intracellular pH measurements, ROS assays, AMPK/ACC1 phosphorylation assays, tumor growth inhibition studies\",\n      \"journal\": \"Science Advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — unbiased genome-wide CRISPR screen followed by mechanistic validation with multiple biochemical readouts (pH, ROS, AMPK/ACC1 signaling) and in vivo tumor growth; multiple orthogonal methods\",\n      \"pmids\": [\"34452919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CA9 silencing in ccRCC cells upregulates oxidative phosphorylation-associated proteins and increases mitochondrial biogenesis, reversing the Warburg phenotype. CA9 knockdown also upregulates mitochondrial arginase 2 (ARG2), leading to accumulation of putrescine that suppresses cell proliferation. Additionally, surface proteomics after CA9 knockdown revealed downregulation of ECM-receptor interaction and cell adhesion proteins, causing decreased cell migration.\",\n      \"method\": \"siRNA knockdown, OXPHOS protein profiling, mitochondrial biogenesis assays, surfaceomics (surface protein mass spectrometry), cell migration assays, metabolomics\",\n      \"journal\": \"International Journal of Molecular Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with multiple orthogonal omics readouts (proteomics, metabolomics) and functional assays; single lab\",\n      \"pmids\": [\"32824856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CAIX downregulation in breast cancer cells under hypoxia leads to increased levels of let-7 miRNA family members and decreased LIN28 protein. Reduced LIN28 downstream leads to decreased PDK1 expression and decreased phosphorylation of pyruvate dehydrogenase (PDH) at Ser-232, attenuating glycolysis. Conversely, CAIX overexpression enhances LIN28, ALDH1, and NANOG levels. This identifies a CAIX→LIN28/let-7 axis linking CAIX to glycolytic metabolism and cancer stem cell marker maintenance.\",\n      \"method\": \"siRNA knockdown and CRISPR knockout, CAIX overexpression, qRT-PCR for let-7 miRNAs, Western blot for LIN28/PDK1/phospho-PDH/ALDH1/NANOG\",\n      \"journal\": \"International Journal of Molecular Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss- and gain-of-function with multiple pathway readouts; mechanistic axis defined in single lab\",\n      \"pmids\": [\"32560271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CAIX regulates GBM cell motility, monocyte adhesion to GBM cells, and polarization of tumor-associated monocytes/macrophages under hypoxic conditions. EGFR/STAT3 signaling was shown to regulate CAIX expression under hypoxia by affecting HIF-1α stability. Knockdown of CAIX abrogated hypoxia-induced GBM motility changes and monocyte adhesion.\",\n      \"method\": \"CAIX knockdown and overexpression in GBM cell lines, EGFR/STAT3 pathway inhibition, HIF-1α stability assays, cell motility assays, monocyte adhesion assays, macrophage polarization assays\",\n      \"journal\": \"International Journal of Molecular Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with multiple cellular phenotype readouts and pathway inhibitor validation; single lab\",\n      \"pmids\": [\"32823915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SOX9 transcriptionally regulates CA9 expression in glioblastoma cells; SOX9 knockdown via lentiviral infection leads to downregulation of both SOX9 and CA9, with downstream decrease in Akt phosphorylation, decreased BCL-2, and increased BAX. Pharmacological inhibition of CA9 with U-104 in combination with TMZ induces glioma cell death, with similar pathway changes, establishing a SOX9/CA9/Akt axis linked to chemoresistance.\",\n      \"method\": \"Lentiviral SOX9 knockdown, gene microarray, Western blot, RT-qPCR, CA9 inhibitor (U-104) treatment, cell death assays\",\n      \"journal\": \"International Journal of Oncology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — SOX9 knockdown with gene microarray and Western blot for pathway; indirect SOX9→CA9 link, single lab, single method for each step\",\n      \"pmids\": [\"29749469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PADI4 upregulates CA9 expression in esophageal squamous cell carcinoma cells. PCR array analysis showed increased CA9 mRNA upon PADI4 overexpression and decreased CA9 upon PADI4 siRNA knockdown. PADI4 and CA9 co-localize in ESCC tissues, and PADI4-driven CA9 upregulation contributes to tumor growth in vivo.\",\n      \"method\": \"Lentiviral PADI4 overexpression and siRNA knockdown, PCR array, Western blot, immunohistochemistry co-localization, xenograft mouse model\",\n      \"journal\": \"Molecular Carcinogenesis\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — transcriptional regulation supported by expression correlation and gain/loss-of-function; mechanism of PADI4→CA9 regulation not directly resolved (no promoter or ChIP assay shown in abstract); single lab\",\n      \"pmids\": [\"30242913\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Vanillic acid (VA) directly binds CA9 (identified by CETSA and DARTS assays). VA binding to CA9 causes INSIG2 to interact with STIM1 instead of SCAP, redirecting SCAP-SREBP1 from ER retention to Golgi translocation and cleavage into mature SREBP1. Activated SREBP1 then induces transcription of SCD1, which inhibits ferroptosis in intestinal epithelial cells.\",\n      \"method\": \"CETSA (cellular thermal shift assay), DARTS (drug affinity responsive target stability) assay, protein co-immunoprecipitation (INSIG2-STIM1 and SCAP), SREBP1 cleavage assay, SCD1 transcription analysis, ferroptosis assays\",\n      \"journal\": \"Pharmacological Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct target engagement confirmed by two orthogonal biophysical assays (CETSA + DARTS), with mechanistic downstream pathway (INSIG2/STIM1/SCAP/SREBP1/SCD1) validated; single lab\",\n      \"pmids\": [\"38438089\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"OTUB2 silencing in ovarian cancer cells leads to destabilization of SNX29P2, which prevents VHL-mediated degradation of HIF-1α. Elevated HIF-1α then activates CA9 transcription, driving glycolysis and chemoresistance. Pharmacological inhibition of CA9 suppresses tumor growth and synergizes with carboplatin in OTUB2-silenced ovarian cancer models.\",\n      \"method\": \"siRNA knockdown, Western blot for HIF-1α/VHL/CA9 pathway, CA9 inhibitor treatment, tumor growth assays, carboplatin combination treatment\",\n      \"journal\": \"Proceedings of the National Academy of Sciences USA\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function epistasis (OTUB2→SNX29P2→HIF-1α→CA9) with in vivo validation; single lab\",\n      \"pmids\": [\"38701117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CAIX inhibitory activity at low pH is more catalytically efficient than CAXII. pH titration assays of membrane ghosts showed significant differences in catalytic efficiency and pKa values between CAIX and CAXII. CAIX shifts the equilibrium between CO2 and bicarbonate in favor of CO2 production by consuming protons in the acidic tumor microenvironment, supporting an extracellular pH-stabilizing role for cancer cell survival. However, an impermeant sulfonamide inhibitor (N-3500) that blocks CAIX catalytic activity was insufficient to inhibit cell growth at relevant concentrations, suggesting a noncatalytic function also contributes to CAIX effects on tumor cell behavior.\",\n      \"method\": \"Enzymatic activity assays (pH titration in membrane ghosts), sulfonamide inhibitor (N-3500) treatment, siRNA knockdown, cell growth and migration assays\",\n      \"journal\": \"PloS One\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic characterization with functional cell-based validation; single lab with multiple methods\",\n      \"pmids\": [\"29965974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SLC-149 inhibits CAIX catalytic activity with greater potency than acetazolamide. Structural analysis (crystal structure of SLC-149 bound to a CAIX-mimic) and thermal stabilization assays explain binding preferences. However, despite inhibiting extracellular pH regulation, SLC-149 has minimal effect on cancer cell cytotoxicity and requires high concentrations to inhibit growth, migration, and invasion, supporting the hypothesis that CAIX's role in controlling cell growth is at least partly independent of its carbonic anhydrase catalytic activity.\",\n      \"method\": \"Enzyme inhibition assays (Ki determination), thermal shift assay, crystal structure of inhibitor bound to CAIX-mimic, cell culture cytotoxicity, cell growth/migration/invasion assays\",\n      \"journal\": \"Journal of Medicinal Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with functional validation, enzymatic assays, and cell-based experiments; multiple orthogonal methods in one study\",\n      \"pmids\": [\"33523653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ZNF674-AS1 lncRNA interacts with the RNA-binding protein IGF2BP3 to enhance stability of CA9 mRNA by binding to the CA9 transcript, elevating CA9 protein expression. This CA9 upregulation suppresses cisplatin-induced pyroptosis and promotes cell proliferation in neuroblastoma. Targeting ZNF674-AS1 or CA9 suppresses tumor growth in vivo and restores cisplatin sensitivity.\",\n      \"method\": \"RNA immunoprecipitation (RIP) for ZNF674-AS1–IGF2BP3 interaction, CA9 mRNA stability assay, CA9 knockdown, in vivo xenograft tumor growth, pyroptosis assays, cell proliferation assays\",\n      \"journal\": \"Cell Death & Disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RIP for protein–RNA interaction and mRNA stability mechanistic validation with in vivo phenotypic readout; single lab\",\n      \"pmids\": [\"38177154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CA9 knockdown in hypoxic glioma cells significantly alters iron regulation-related protein expression and enhances X-ray-induced ferroptosis and radiosensitivity. CA9 silencing overcomes hypoxic ferroptosis resistance, and enhancing ferroptosis by CA9 knockdown promotes exposure and release of damage-associated molecular patterns (DAMPs).\",\n      \"method\": \"siRNA knockdown, X-ray irradiation, lipid peroxidation assay (C11-BODIPY staining), RT-qPCR for ferroptosis markers and iron-associated proteins, clonogenic survival assay, immunofluorescence for calreticulin (DAMPs)\",\n      \"journal\": \"International Journal of Radiation Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with multiple ferroptosis and iron homeostasis readouts; single lab\",\n      \"pmids\": [\"37463506\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CA9/CAIX is a transmembrane carbonic anhydrase whose transcription is primarily driven by HIF-1α (binding the CAIX promoter together with Sp1 and CBP/p300), and is silenced by CpG methylation at −74 bp; the encoded enzyme catalyzes CO₂ hydration extracellularly to produce protons and bicarbonate, acidifying the tumor microenvironment while helping maintain intracellular pH. CAIX physically interacts with SLC4 bicarbonate transporters (AE1/AE2/AE3) via its catalytic domain and with monocarboxylate transporters MCT1/MCT4 via CD147-Ig1 to form transport metabolons that facilitate bicarbonate and lactate export; disrupting the MCT metabolon reduces glycolysis and cancer cell proliferation. Through pH regulation, CAIX suppresses ferroptosis via AMPK/ACC1 signaling, and its silencing reverses the Warburg phenotype by increasing mitochondrial biogenesis and ARG2-driven putrescine accumulation. CAIX also promotes tumor cell migration and invasion through Rho-GTPase/ROCK signaling, and modulates a LIN28/let-7 axis to sustain glycolysis and cancer stem cell markers.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CA9/CAIX is a hypoxia-induced, membrane-associated carbonic anhydrase that couples extracellular pH regulation to the metabolic and invasive adaptations of tumor cells [#15, #2]. Its transcription is driven principally by HIF-1\\u03b1 acting with Sp1 and the co-activator CBP/p300 at the proximal CAIX promoter, a program rendered constitutive in clear cell renal cell carcinoma by VHL loss and normoxic HIF-1\\u03b1 accumulation; HIF-2\\u03b1 does not contribute [#0]. CAIX expression is additionally controlled by CpG methylation at the \\u221274 bp promoter site, silencing being relieved by demethylation [#4, #5], and upstream regulators including EGFR/STAT3 (via HIF-1\\u03b1 stability) and the OTUB2\\u2013SNX29P2 axis converge on this HIF-1\\u03b1/CA9 output [#10, #14]. Catalytically, CAIX is highly efficient at low pH and shifts the CO\\u2082/bicarbonate equilibrium to consume protons and stabilize the acidic tumor microenvironment [#15]. It works physically within transport metabolons: binding the SLC4 bicarbonate exchangers AE1/AE2/AE3 through its catalytic domain to enhance Cl\\u207b/HCO\\u2083\\u207b exchange [#1], and binding the CD147-Ig1 domain to assemble with MCT1/MCT4 and facilitate proton-coupled lactate export, sustaining glycolysis and proliferation [#2]. Through pH control CAIX suppresses ferroptosis\\u2014its inhibition acidifies intracellular pH, raises ROS, and sensitizes cells to ferroptosis via AMPK/ACC1 signaling and synthetic lethality with NFS1 and xCT [#7], and CA9 silencing enhances ferroptosis and radiosensitivity in glioma [#18]. CAIX silencing also reverses the Warburg phenotype by promoting mitochondrial biogenesis and ARG2-driven putrescine accumulation [#8], and CAIX promotes migration and invasion through Rho-GTPase/ROCK signaling [#3]. Notably, impermeant catalytic inhibitors block extracellular pH regulation but fail to suppress cancer cell growth at relevant doses, indicating a non-catalytic contribution to CAIX's effects on tumor behavior [#15, #16].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established that promoter DNA methylation, not only hypoxia, governs whether CA9 is expressed, explaining cell-line-specific silencing.\",\n      \"evidence\": \"Bisulfite sequencing of the MN/CA9 5' region with 5-aza-2'-deoxycytidine reactivation in RCC lines\",\n      \"pmids\": [\"10708480\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not pinpoint the critical CpG site\", \"Correlative methylation-expression link without functional promoter dissection\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Localized methylation control to a single CpG at \\u221274 bp, defining a discrete epigenetic switch for CA9 transcription.\",\n      \"evidence\": \"Luciferase reporters with in vitro methylated constructs and demethylation rescue in RCC cells\",\n      \"pmids\": [\"11506497\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Methyl-CpG-binding factors mediating repression not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined the core transcriptional machinery driving CA9, showing HIF-1\\u03b1 and Sp1 with CBP/p300 directly activate the promoter and that VHL loss makes this constitutive.\",\n      \"evidence\": \"DNase-I footprinting, EMSA, and promoter mutagenesis in ccRCC\",\n      \"pmids\": [\"15184875\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"HIF-2\\u03b1 role excluded but other context-specific regulators not surveyed\", \"Did not address protein-level activity\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Clarified that \\u221274 bp methylation acts only as an accessory regulator outside RCC, operating under specific culture conditions rather than as the primary control.\",\n      \"evidence\": \"Bisulfite sequencing and demethylation under varied density/hypoxia in HeLa cells\",\n      \"pmids\": [\"15754010\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of density-dependent methylation effect unresolved\", \"Single study\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrated CAIX is not merely an enzyme but a structural scaffold, forming a bicarbonate transport metabolon with SLC4 exchangers via its catalytic domain.\",\n      \"evidence\": \"Reciprocal Co-IP, GST pull-down with domain deletions, and functional transport assays in HEK293\",\n      \"pmids\": [\"17652430\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the interaction requires catalytic activity not separated\", \"Tumor relevance of the AE metabolon not tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Connected CAIX to a motility/invasion program through Rho-GTPase signaling, beyond its metabolic role.\",\n      \"evidence\": \"Gain/loss-of-function with ROCK inhibitor and RhoA siRNA, microarray, and invasion assays in C33A cells\",\n      \"pmids\": [\"21363891\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How CAIX activates RhoA/ROCK mechanistically not defined\", \"Single lab, single cell line\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified the MCT1/MCT4 lactate-transport metabolon assembled via CD147-Ig1 binding, showing metabolon disruption suppresses glycolysis and proliferation.\",\n      \"evidence\": \"Co-IP from patient breast tumor tissue and antibody-mediated metabolon disruption with lactate transport and proliferation readouts\",\n      \"pmids\": [\"31723238\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo therapeutic disruption not shown\", \"Generality across tumor types not established\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed CAIX silencing reverses the Warburg phenotype by inducing mitochondrial biogenesis and ARG2/putrescine accumulation while reducing adhesion proteins.\",\n      \"evidence\": \"siRNA knockdown with OXPHOS proteomics, metabolomics, surfaceomics, and migration assays in ccRCC\",\n      \"pmids\": [\"32824856\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal chain from pH to mitochondrial biogenesis not dissected\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined a CAIX\\u2192LIN28/let-7 axis linking CAIX to glycolytic flux and stem-cell marker maintenance.\",\n      \"evidence\": \"Knockdown/knockout and overexpression with let-7 qRT-PCR and LIN28/PDK1/phospho-PDH/ALDH1/NANOG blots in breast cancer\",\n      \"pmids\": [\"32560271\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which CAIX regulates LIN28 unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Placed CAIX in the tumor immune microenvironment, regulating GBM motility and tumor-associated monocyte/macrophage behavior, with EGFR/STAT3 controlling its expression via HIF-1\\u03b1.\",\n      \"evidence\": \"CAIX knockdown/overexpression with EGFR/STAT3 inhibition, HIF-1\\u03b1 stability, motility, and monocyte adhesion/polarization assays in GBM\",\n      \"pmids\": [\"32823915\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct CAIX-dependent signal to monocytes not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established CAIX as a ferroptosis suppressor via pH/ROS control, with NFS1 and xCT as synthetic lethal partners acting through AMPK/ACC1.\",\n      \"evidence\": \"Genome-wide CRISPR synthetic lethal screen plus pH, ROS, AMPK/ACC1 readouts and in vivo tumor growth\",\n      \"pmids\": [\"34452919\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct molecular link between bicarbonate and AMPK not fully resolved\", \"Tissue specificity of synthetic lethality unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Quantified CAIX's superior low-pH catalytic efficiency yet showed catalytic inhibition alone is insufficient to block growth, first evidence for a non-catalytic function.\",\n      \"evidence\": \"pH-titration enzyme assays in membrane ghosts and impermeant sulfonamide (N-3500) treatment with growth/migration assays\",\n      \"pmids\": [\"29965974\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Nature of the non-catalytic function not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Reinforced the catalytic-vs-noncatalytic dissociation with a potent structurally-defined inhibitor that blocks pH regulation but barely affects cytotoxicity.\",\n      \"evidence\": \"Ki determination, thermal shift, crystal structure of SLC-149 bound to a CAIX-mimic, and cell growth/invasion assays\",\n      \"pmids\": [\"33523653\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the non-catalytic scaffolding role not solved\", \"In vivo efficacy not addressed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed CA9 silencing enhances X-ray-induced ferroptosis and radiosensitivity and triggers DAMP release in hypoxic glioma, extending the ferroptosis link to radiotherapy.\",\n      \"evidence\": \"siRNA knockdown with lipid peroxidation, iron-protein qPCR, clonogenic survival, and calreticulin immunofluorescence\",\n      \"pmids\": [\"37463506\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking CA9 to iron regulation not resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified post-transcriptional control of CA9 by the ZNF674-AS1/IGF2BP3 axis stabilizing CA9 mRNA to suppress pyroptosis and drive chemoresistance.\",\n      \"evidence\": \"RIP, CA9 mRNA stability assays, knockdown, and xenograft/pyroptosis assays in neuroblastoma\",\n      \"pmids\": [\"38177154\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether IGF2BP3 directly recognizes CA9 mRNA modifications unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided direct evidence of small-molecule target engagement with CA9 (vanillic acid) rewiring INSIG2/STIM1/SCAP\\u2013SREBP1\\u2013SCD1 to modulate ferroptosis in intestinal epithelium.\",\n      \"evidence\": \"CETSA and DARTS target engagement, INSIG2-STIM1/SCAP Co-IP, SREBP1 cleavage and SCD1 transcription with ferroptosis assays\",\n      \"pmids\": [\"38438089\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How CA9 binding alters INSIG2 partner choice mechanistically unresolved\", \"Single lab, non-tumor context\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular identity of CAIX's catalytic-independent function\\u2014how the protein scaffold drives growth, invasion, and metabolon assembly beyond CO\\u2082 hydration\\u2014remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of the non-catalytic role not defined\", \"Whether metabolon scaffolding requires catalytic activity untested\", \"Mechanisms connecting CAIX to RhoA/ROCK and LIN28 unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016829\", \"supporting_discovery_ids\": [15, 16]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [2, 8, 9]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [7, 18]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 4]}\n    ],\n    \"complexes\": [\n      \"CAIX-AE bicarbonate transport metabolon\",\n      \"CAIX-CD147-MCT1/MCT4 lactate transport metabolon\"\n    ],\n    \"partners\": [\n      \"AE1\",\n      \"AE2\",\n      \"AE3\",\n      \"MCT1\",\n      \"MCT4\",\n      \"CD147\",\n      \"IGF2BP3\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":8,"faith_total":8,"faith_pct":100.0}}