{"gene":"AQP5","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":1998,"finding":"AQP5 protein is selectively localized to the apical membrane of corneal epithelial surface cells, apical membranes of acinar cells in lacrimal gland, microvilli of serous salivary gland intracellular secretory canaliculi, and apical membranes of type I pulmonary epithelial cells, consistent with a role in water transport at these sites.","method":"Immunohistochemistry and immunoelectron microscopy with affinity-purified anti-AQP5 antibody; RNase protection assay","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — direct localization by immunoelectron microscopy with functional tissue context, replicated across multiple organs and labs","pmids":["9755069"],"is_preprint":false},{"year":1999,"finding":"AQP5 in salivary gland acinar cells is restricted to apical membranes including intercellular secretory canaliculi; upon isoproterenol (β-adrenergic) stimulation, apical AQP5 staining in parotid acinar cells shifts to a clustered dot pattern, suggesting stimulus-dependent redistribution.","method":"Immunofluorescence microscopy; anti-AQP5 antibody raised and validated","journal":"Cell and tissue research","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization with functional stimulus, single lab","pmids":["10022971"],"is_preprint":false},{"year":1999,"finding":"AQP5 trafficking to the plasma membrane in salivary gland cells is triggered by an increase in intracellular Ca2+ (induced by thapsigargin or calcium ionophore A-23187), and requires intact microtubules but not microfilaments, implicating vesicle-cytoskeleton interaction in AQP5 membrane targeting.","method":"Confocal laser microscopy of AQP5-transfected HSG cells; pharmacologic inhibition with colchicine/vinblastine (microtubule inhibitors) and cytochalasin B (microfilament inhibitor)","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 — live-cell imaging with pharmacologic dissection of cytoskeletal requirements, multiple orthogonal inhibitors","pmids":["10600522"],"is_preprint":false},{"year":2005,"finding":"AQP5 localizes in intracellular lipid rafts in rat parotid interlobular duct cells; activation of M3 muscarinic acetylcholine receptors (mAChR) by cevimeline induces AQP5 trafficking to the apical plasma membrane via intracellular Ca2+ signaling, followed by AQP5 dissociation from lipid rafts to non-raft domains on the apical membrane.","method":"Immunofluorescence/immunoelectron microscopy; detergent solubility assay (Triton X-100); sucrose density gradient flotation; calcium ionophore A-23187 mimicry; co-localization with lipid raft markers flotillin-2 and GM1","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal biochemical and microscopic methods in same study, strong mechanistic dissection","pmids":["16107506"],"is_preprint":false},{"year":2005,"finding":"In rat duodenal Brunner's gland cells, VIP induces AQP5 translocation from secretory granule membranes to the apical membrane in a PKA-dependent (blocked by H-89) but PKC-independent manner, without affecting AQP1 localization.","method":"Immunohistochemistry; in vitro duodenal slice assay with VIP; protein kinase inhibitors H-7, H-89, calphostin C; in vivo VIP injection","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"High","confidence_rationale":"Tier 2 — combined in vitro and in vivo with specific kinase inhibition, multiple concentrations and time points","pmids":["15650134"],"is_preprint":false},{"year":2006,"finding":"AQP5 associates with TRPV4 at the apical membrane of salivary gland acinar cells; the N-terminus of AQP5 is required for TRPV4 activation by hypotonicity (N-terminus-deleted AQP5 suppresses TRPV4 activation); hypotonicity increases co-association and surface expression of AQP5 and TRPV4; both AQP5-null and TRPV4-null acinar cells show greatly reduced Ca2+ entry and loss of regulatory volume decrease (RVD) in response to hypotonicity; actin depolymerization reduces AQP5-TRPV4 co-association and RVD.","method":"Co-immunoprecipitation; AQP5 knockout and TRPV4 knockout mouse acinar cells; N-terminus deletion mutant expression; Ca2+ imaging; cell volume measurements; pharmacological TRPV4 activation/inhibition","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including KO cells, co-IP, deletion mutants, Ca2+ assays; replicated across experimental conditions","pmids":["16571723"],"is_preprint":false},{"year":2007,"finding":"In bronchial epithelial cells, AQP5 Ser156 is phosphorylated by PKA (abolished in S156A mutant); the N185D mutation (disrupting second NPA motif) retains AQP5 in the cytoplasm rather than the apical membrane, whereas S156A does not affect membrane expression, indicating that membrane targeting of AQP5 involves the NPA motif but PKA phosphorylation at Ser156 is not required for apical membrane expression.","method":"Stable transfection in BEAS-2B cells on permeable support; immunofluorescence; site-directed mutagenesis (S156A, N185D); cAMP/PKA pharmacological manipulation (H89, cpt-cAMP)","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — in vitro assay with mutagenesis and pharmacological dissection","pmids":["18042467"],"is_preprint":false},{"year":2008,"finding":"AQP5 promotes cell invasion and epithelial-to-mesenchymal transition (EMT) in lung cells through phosphorylation at Ser156 and subsequent interaction with activated c-Src (phospho-Tyr416); membrane trafficking mutant N185D and phosphorylation-blocking mutant S156A both abolish invasion and c-Src interaction.","method":"In vitro invasion assay; stable transfection in BEAS-2B and NIH3T3 cells; SH3-domain protein array; co-immunoprecipitation with activated c-Src; site-directed mutagenesis (N185D, S156A)","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1-2 — functional assay with mutagenesis, protein array, and co-IP; multiple cell lines","pmids":["18478076"],"is_preprint":false},{"year":2008,"finding":"AQP5 overexpression in CML cells (K562) increases BCR-ABL1 phosphorylation and cell proliferation; siRNA-mediated AQP5 knockdown reduces proliferation, decreases BCR-ABL1 phosphorylation, and increases caspase-9 activity, indicating AQP5 promotes survival/proliferation and suppresses apoptosis in CML cells.","method":"siRNA knockdown; AQP5 overexpression; immunoblotting; flow cytometry; cell proliferation assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2-3 — KD/OE with defined molecular readouts (BCR-ABL1 phosphorylation, caspase-9), single lab","pmids":["18612408"],"is_preprint":false},{"year":2008,"finding":"AQP5 overexpression induces cell proliferation and oncogenic transformation dependent on cAMP-PKA phosphorylation of a cytoplasmic loop consensus site (Ser156); preferential phosphorylation of this site is found in tumor samples.","method":"Ectopic AQP5 expression in vitro and in vivo xenograft; PKA phosphorylation site mutagenesis; immunoblotting of tumor vs. normal samples","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 — functional transformation assay with mutagenesis; single lab","pmids":["18423983"],"is_preprint":false},{"year":2009,"finding":"AQP5 expressed in Xenopus oocytes confers selective CO2 permeability (increased surface pH change and faster time constants with CO2 exposure) compared with water-injected controls, but does not conduct NH3, establishing AQP5 as a CO2-selective gas channel with higher CO2/NH3 selectivity than AQP1 or AQP4.","method":"Xenopus oocyte expression system; surface pH measurement assay; osmotic water permeability (Pf) measurement; comparison with AQP1, AQP4, AmtB, RhAG","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — functional reconstitution in oocytes with quantitative selectivity assay, replicated against multiple controls","pmids":["19273840"],"is_preprint":false},{"year":2009,"finding":"In rat parotid gland, AQP5 dephosphorylation at the PKA consensus motif 152SRRTS promotes translocation to the apical membrane; microtubules but not microfilaments are required for this trafficking event.","method":"GFP-AQP5 chimeric protein expression in MDCK-II cells; PKA inhibitor H-89; site-directed mutagenesis of Ser152; colchicine/cytochalasin B treatment; confocal microscopy","journal":"The journal of medical investigation","confidence":"Medium","confidence_rationale":"Tier 2 — mutagenesis combined with pharmacological cytoskeletal dissection, single lab","pmids":["19262015"],"is_preprint":false},{"year":2010,"finding":"LPS-induced downregulation of AQP5 mRNA in parotid gland is mediated through a transcription factor complex of NF-κB (p65), p-c-Jun, and c-Fos acting on NF-κB-responsive elements in the AQP5 promoter; this is blocked by inhibitors of IκB kinase, 26S proteasome, ERK1/2, JNK, and p38 MAPK; co-immunoprecipitation revealed physical association of NF-κB, p-c-Jun, and c-Fos.","method":"In vivo LPS injection in C3H/HeN and TLR4-mutant C3H/HeJ mice; tissue culture with kinase inhibitors; co-immunoprecipitation; EMSA/protein-binding assay on AQP5 promoter sequences","journal":"The American journal of pathology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including genetic model (TLR4 mutant), pharmacological inhibitors, co-IP, and promoter binding assay","pmids":["20522648"],"is_preprint":false},{"year":2010,"finding":"Parasympathetic denervation (chorda tympani) decreases AQP5 protein in submandibular gland via lysosomal degradation (enhanced by autophagosomes/lysosomes, reversed by chloroquine); cathepsins B and L are implicated as degrading enzymes; M3 mAChR agonist cevimeline recovers AQP5 protein levels post-denervation.","method":"Chorda tympani denervation in rat; autophagosome marker LC3B-II western blot; TUNEL apoptosis assay; lysosomal fraction in vitro degradation assay; protease inhibitor experiments; immunohistochemistry for AQP5/Lamp2/LC3B co-localization","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (co-localization, in vitro degradation, inhibitor rescue) in same study","pmids":["20689061"],"is_preprint":false},{"year":2012,"finding":"Caveolin-1 is required for agonist-stimulated AQP5 translocation to the apical membrane of salivary gland acinar cells; in Cav1-/- mice, AQP5 apical localization is disrupted and agonist-induced surface expression of AQP5 (which requires Ca2+ influx via TRPC1 channels) is abrogated; adenoviral re-expression of Cav1 restores AQP5 apical targeting and fluid secretion.","method":"Cav1 knockout mice; adenoviral Cav1 re-expression; Ca2+ imaging; immunofluorescence for AQP5 apical localization; surface biotinylation assay; fluid secretion measurement","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — KO with defined cellular phenotype, rescue experiment, multiple readouts","pmids":["23203809"],"is_preprint":false},{"year":2013,"finding":"AQP5 is a transcriptional target repressed by histone H3K79 methyltransferase Dot1a; in Dot1l-deficient kidney cells, AQP5 is upregulated and colocalizes with AQP2; AQP5 directly interacts with AQP2 (co-immunoprecipitation) and impairs AQP2 surface localization, with the AQP5/AQP2 complex partially residing in the ER/Golgi.","method":"cDNA array; real-time RT-qPCR; luciferase reporter assay; cell surface biotinylation; co-immunoprecipitation; co-localization microscopy; ChIP showing Dot1a/H3diMe-K79 occupancy at AQP5 promoter","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including ChIP, co-IP, reporter assay, and surface biotinylation in same study","pmids":["23326416"],"is_preprint":false},{"year":2013,"finding":"Missense mutations in AQP5 cause autosomal-dominant diffuse nonepidermolytic palmoplantar keratoderma; protein structure analysis suggests these variants affect normal channel regulation; immunofluorescence shows mutant AQP5 is trafficked normally to the plasma membrane in stratum granulosum, suggesting the mutations likely produce open/dysregulated channels rather than trafficking defects.","method":"Exome sequencing; protein structure analysis; immunofluorescence of patient skin biopsies","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2-3 — genetic disease linkage with localization data, but no functional channel assay in this study","pmids":["23830519"],"is_preprint":false},{"year":2013,"finding":"Hypoxia and hypoxia mimetic cobalt decrease AQP5 expression (~70%) in mouse lung; HIF-1α is a key mediator (dominant-negative HIF-1α and siRNA block the effect); proteasome inhibitors abolish both hypoxia-induced and cobalt-induced AQP5 decrease at both protein and mRNA levels, indicating the proteasome pathway stabilizes HIF-1α and/or unidentified transcription factors that regulate AQP5 transcription.","method":"Mouse hypoxia exposure; MLE-12 cell line; cobalt treatment; HIF-1α dominant-negative mutants and siRNA; proteasome inhibitors lactacystin and PI-III; hnRNA quantification by real-time PCR","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1-2 — multiple genetic and pharmacological perturbations with transcriptional readout including hnRNA measurement","pmids":["23469202"],"is_preprint":false},{"year":2015,"finding":"Activation of muscarinic receptors in rat parotid acinar cells induces AQP5 translocation to the nucleus, apical plasma membrane, and lateral plasma membrane; AQP5 presence in the nuclear membrane coincides with nuclear shrinkage, suggesting AQP5 facilitates water transport across the nuclear membrane.","method":"Immunoconfocal and immunoelectron microscopy; western blot of nuclear fractions; detergent solubility and sucrose density flotation; atropine (mAChR antagonist) pretreatment","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization with antagonist controls and nuclear fractionation, single lab","pmids":["25603543"],"is_preprint":false},{"year":2017,"finding":"AQP5 forms functional water channels in rodent lens fiber cells; AQP5 membrane insertion in cortical fiber cells modulates water permeability (PH2O); species-specific differences in AQP5 subcellular distribution (membranous in mouse, cytoplasmic in rat) correlate with Hg2+-sensitive PH2O contributions; organ culture promotes AQP5 membrane insertion in rat lens cortical fiber cells with corresponding increase in Hg2+-sensitive PH2O.","method":"Fluorescence dye dilution assay for PH2O; HgCl2 inhibition; immunolabeling of lens sections and fiber membrane vesicles; organ culture","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 1-2 — direct functional water permeability assay with pharmacological inhibition and matched subcellular localization data","pmids":["29118028"],"is_preprint":false},{"year":2017,"finding":"GATA6 and Sp1 activate AQP5 transcription via histone H3 acetylation; HDAC3 represses AQP5 by binding Sp1 and reducing H3 acetylation at the AQP5 promoter; p300 histone acetyltransferase cooperates with GATA6/Sp1 to activate AQP5; HDAC inhibitor SAHA increases AQP5 expression and H3 acetylation at the Aqp5 promoter.","method":"HDAC3 overexpression/knockdown; GATA6/p300 knockdown/overexpression; luciferase reporter assay; ChIP for H3/H4 acetylation; co-immunoprecipitation of GATA6/Sp1/p300/HDAC3 interactions; SAHA treatment","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1-2 — ChIP, co-IP, reporter assay, and genetic perturbations in same study with multiple orthogonal methods","pmids":["28615712"],"is_preprint":false},{"year":2017,"finding":"In hyperosmolarity-treated human corneal epithelial cells, AQP5 upregulation mediates JNK1/2 MAPK activation, proinflammatory cytokine expression (IL-1β, IL-6, IL-8, TNF-α, caspase-1), and cell death; siRNA knockdown of AQP5 or JNK1/2 inhibition with SP600125 reduces these effects, placing AQP5 upstream of JNK1/2 signaling in hyperosmotic corneal injury.","method":"siRNA AQP5 gene silencing; SP600125 JNK1/2 inhibitor; real-time RT-PCR; western blot for AQP5 and p-JNK1/2; TUNEL assay; step increases in osmolarity up to 550 mOsm","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA knockdown with pathway inhibitor; single lab but two orthogonal interventions","pmids":["28680052"],"is_preprint":false},{"year":2017,"finding":"AQP5 downregulation in HCC cells suppresses EMT and tumor metastasis partly via inactivation of the NF-κB signaling pathway, altering expression of E-cadherin, α-catenin, N-cadherin, and vimentin.","method":"AQP5 knockdown in HCC cell lines; in vitro invasion assay; in vivo metastasis model; western blot for EMT markers and NF-κB pathway components","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2-3 — KD with defined molecular and in vivo phenotype, single lab","pmids":["28619511"],"is_preprint":false},{"year":2021,"finding":"Prolactin-inducible protein (PIP) physically interacts with AQP5 via the AQP5 C-terminus (one PIP molecule per AQP5 tetramer); PIP knockout in mice and PIP misexpression in Sjögren's syndrome patients correlate with altered AQP5 distribution at the acinar apical membrane, indicating PIP regulates AQP5 localization in salivary glands.","method":"Co-immunoprecipitation in vitro and in vivo (mouse and human salivary glands); PIP knockout mice; structural binding analysis (C-terminus deletion); immunofluorescence of human minor salivary glands from SS patients","journal":"Cells","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP in multiple systems, KO mouse localization data, domain mapping; multiple orthogonal approaches","pmids":["34440877"],"is_preprint":false},{"year":2021,"finding":"AQP5 knockout in mouse lens leads to mild lens opacity at ~6 months; mechanistically, AQP5 loss downregulates miR-124-3p.1, which normally suppresses vimentin (a dual luciferase reporter confirmed vimentin as direct miR-124-3p.1 target); AQP5 knockout and AQP5-L51P mutation increase vimentin expression, contributing to lens opacity; miR-124-3p.1 agomir reduces lens opacity and vimentin in both WT and KO mice.","method":"CRISPR/Cas9 AQP5 knockout mice; whole exome sequencing; dual luciferase reporter assay; qRT-PCR; western blot; immunofluorescence; miR-124-3p.1 agomir organ culture","journal":"Experimental eye research","confidence":"High","confidence_rationale":"Tier 1-2 — KO mouse phenotype, dual luciferase target validation, miRNA rescue; multiple orthogonal methods","pmids":["33582182"],"is_preprint":false},{"year":2024,"finding":"In Sjögren's syndrome salivary gland epithelial cells, reduced GPX4 expression leads to lipid ROS accumulation, which activates STAT4 phosphorylation and nuclear translocation; nuclear pSTAT4 binds the AQP5 promoter (confirmed by ChIP) and inhibits AQP5 transcription, reducing salivary secretion; GPX4 overexpression reverses this and restores AQP5 expression.","method":"GPX4 overexpression/knockdown in SGECs; ChIP assay confirming pSTAT4 binding at AQP5 promoter; lipid ROS inhibitor ferrostatin-1 in vitro and in vivo; SS mouse model; immunohistochemistry; western blot; bioinformatics of SS patient GSE databases","journal":"Free radical biology & medicine","confidence":"High","confidence_rationale":"Tier 1-2 — ChIP for direct promoter binding, genetic perturbations, pharmacological rescue, in vivo model; multiple orthogonal methods","pmids":["38574973"],"is_preprint":false},{"year":2022,"finding":"AQP5 recruits E3 ubiquitin ligase TRIM21 to the key autophagy protein ULK1, inducing K63-mediated ubiquitination of ULK1 and activating autophagy (LC3I/LC3II conversion) in gastric cancer stem cells; this autophagy activation is required for AQP5-driven cancer stem cell biological functions.","method":"Transcriptome sequencing; proteomic detection; mass spectrometry; co-immunoprecipitation; ubiquitination assay; sphere formation and tumorigenesis assays","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2-3 — co-IP/MS identification of TRIM21, functional autophagy assay; single lab","pmids":["36372898"],"is_preprint":false}],"current_model":"AQP5 is a regulated apical membrane water (and CO2-selective gas) channel whose trafficking to secretory epithelial apical membranes requires microtubule-dependent vesicle transport and is controlled by intracellular Ca2+ signaling downstream of M3 muscarinic receptors, with lipid raft association/dissociation, PKA phosphorylation at Ser156 (which modulates constitutive expression and lateral diffusion but is not strictly required for membrane targeting), and caveolin-1-dependent TRPC1 Ca2+ influx all contributing to regulated surface delivery; AQP5 partners with TRPV4 (via its N-terminus) to enable hypotonic volume sensing and regulatory volume decrease, interacts with AQP2 to impair its membrane localization, and with PIP to control its own apical targeting; its transcription is activated by GATA6/Sp1/p300-mediated H3 acetylation, repressed by Dot1a-dependent H3K79 methylation and by NF-κB/AP-1 complexes (induced by LPS), and suppressed under hypoxia via HIF-1α and proteasome-dependent mechanisms; in cancer contexts AQP5 promotes invasion, EMT, and stemness through phospho-Ser156-dependent c-Src interaction, NF-κB-driven EMT, and TRIM21-mediated K63-ubiquitination of ULK1 to activate autophagy."},"narrative":{"teleology":[{"year":1998,"claim":"Establishing where AQP5 acts: immunolocalization resolved AQP5 to apical membranes of corneal, lacrimal, salivary, and type I lung epithelial cells, defining it as an apical water channel of diverse secretory epithelia.","evidence":"Immunohistochemistry and immunoelectron microscopy with affinity-purified antibody across multiple tissues","pmids":["9755069"],"confidence":"High","gaps":["No functional water permeability measurement in these tissues at this stage","Mechanism of apical targeting unknown"]},{"year":1999,"claim":"Defining the trafficking mechanism: Ca²⁺ elevation was shown to drive AQP5 translocation to the plasma membrane via a microtubule-dependent, microfilament-independent route, establishing regulated vesicular insertion as the basis for AQP5 surface delivery.","evidence":"Confocal microscopy of AQP5-transfected HSG cells with thapsigargin/ionophore stimulation and pharmacological cytoskeletal disruption","pmids":["10600522","10022971"],"confidence":"High","gaps":["Identity of motor proteins and vesicle carriers unknown","Whether Ca²⁺ acts directly on vesicle fusion or via an intermediate kinase unclear"]},{"year":2005,"claim":"Resolving the receptor-to-membrane pathway: M3 muscarinic receptor activation and PKA signaling were shown to control AQP5 apical insertion, with lipid raft association/dissociation serving as a membrane-organizing step during trafficking.","evidence":"Detergent solubility/flotation assays and immunoEM in parotid gland (M3 agonist cevimeline); PKA inhibitor H-89 in duodenal Brunner's gland VIP-stimulated slices","pmids":["16107506","15650134"],"confidence":"High","gaps":["Whether PKA phosphorylates AQP5 directly versus raft components not resolved","PKA site identity not yet mapped"]},{"year":2006,"claim":"Linking AQP5 to volume sensing: AQP5 was shown to physically associate with TRPV4 via its N-terminus at the apical membrane, and both AQP5-null and TRPV4-null cells lost Ca²⁺ entry and regulatory volume decrease upon hypotonicity, establishing AQP5 as a co-sensor for osmotic stress rather than a passive pore.","evidence":"Co-immunoprecipitation, AQP5/TRPV4 knockout acinar cells, N-terminal deletion mutant, Ca²⁺ imaging, and cell volume assays","pmids":["16571723"],"confidence":"High","gaps":["Structural basis of N-terminus–TRPV4 interaction unresolved","Whether AQP5–TRPV4 coupling operates in non-salivary tissues unknown"]},{"year":2007,"claim":"Dissecting the PKA phosphorylation site: Ser156 was confirmed as the PKA substrate but S156A did not block membrane targeting, while the NPA-motif mutant N185D retained AQP5 in the cytoplasm, separating channel maturation/folding requirements from kinase-dependent regulation.","evidence":"Site-directed mutagenesis (S156A, N185D) in stably transfected BEAS-2B cells on permeable support with cAMP/PKA pharmacological manipulation","pmids":["18042467"],"confidence":"High","gaps":["What downstream process Ser156 phosphorylation controls if not trafficking","Whether N185D causes global misfolding versus specific NPA-dependent retention"]},{"year":2008,"claim":"Establishing an oncogenic signaling role: phospho-Ser156 was required for AQP5 to interact with activated c-Src and promote cell invasion, proliferation, and EMT, revealing a non-channel, signaling-scaffold function.","evidence":"Invasion assays, SH3-domain protein array, co-IP with phospho-Src in BEAS-2B/NIH3T3; overexpression/siRNA in K562 CML cells","pmids":["18478076","18423983","18612408"],"confidence":"Medium","gaps":["Whether AQP5–c-Src interaction requires water channel activity unknown","Generalizability of CML BCR-ABL1 connection not independently replicated"]},{"year":2009,"claim":"Expanding substrate selectivity: functional reconstitution in oocytes demonstrated AQP5 conducts CO₂ with high selectivity over NH₃, extending its physiological role beyond water to gas transport.","evidence":"Xenopus oocyte expression with surface pH measurement and osmotic water permeability comparison to AQP1/AQP4","pmids":["19273840"],"confidence":"High","gaps":["Physiological relevance of CO₂ transport via AQP5 in vivo not established","Molecular determinants of CO₂ vs. NH₃ selectivity not mapped"]},{"year":2010,"claim":"Defining transcriptional repression: LPS was shown to downregulate AQP5 transcription via a physical NF-κB(p65)/p-c-Jun/c-Fos complex binding the AQP5 promoter, and parasympathetic denervation was shown to degrade AQP5 protein through lysosomal/autophagic pathways involving cathepsins B and L.","evidence":"TLR4-mutant mice, EMSA/co-IP on AQP5 promoter; chorda tympani denervation with lysosomal co-localization and protease inhibitor rescue","pmids":["20522648","20689061"],"confidence":"High","gaps":["Whether NF-κB directly binds DNA or acts through AP-1 composite elements not fully resolved","Whether autophagy-mediated AQP5 degradation is a general regulatory mechanism beyond denervation"]},{"year":2012,"claim":"Identifying the Ca²⁺ entry gateway: caveolin-1 was required for agonist-induced AQP5 apical translocation because it enables TRPC1-mediated Ca²⁺ influx; Cav1 knockout ablated the response and adenoviral rescue restored it.","evidence":"Cav1 knockout mice, adenoviral Cav1 re-expression, Ca²⁺ imaging, surface biotinylation, fluid secretion measurement in salivary glands","pmids":["23203809"],"confidence":"High","gaps":["Whether Cav1 scaffolds AQP5 vesicles directly or acts solely through TRPC1-Ca²⁺ unclear","Role of other TRP channels not excluded"]},{"year":2013,"claim":"Resolving chromatin-level control and a disease link: Dot1a-mediated H3K79 methylation was shown to repress AQP5 transcription (with derepression causing AQP5–AQP2 hetero-interaction that impairs AQP2 surface expression in kidney), and missense AQP5 mutations were identified as the cause of autosomal-dominant palmoplantar keratoderma.","evidence":"ChIP for H3K79me at AQP5 promoter, co-IP of AQP5–AQP2, surface biotinylation in Dot1l-deficient cells; exome sequencing of keratoderma families with immunofluorescence of patient skin","pmids":["23326416","23830519"],"confidence":"High","gaps":["Whether AQP5–AQP2 interaction is physiological or only pathological upon AQP5 overexpression","Functional channel assay for keratoderma mutants not performed"]},{"year":2017,"claim":"Building the epigenetic activation model and identifying tissue-specific channel function: GATA6/Sp1/p300 were shown to activate AQP5 via H3 acetylation opposed by HDAC3, and AQP5 was demonstrated to form functional water channels in lens fiber cells with species-specific membrane insertion.","evidence":"ChIP for H3 acetylation, co-IP of GATA6/Sp1/p300/HDAC3, luciferase reporter in salivary cells; fluorescence dye dilution water permeability assay with HgCl₂ inhibition in mouse and rat lens","pmids":["28615712","29118028"],"confidence":"High","gaps":["Signals that switch HDAC3 occupancy at the AQP5 promoter unidentified","Whether GATA6/Sp1 axis operates in non-salivary AQP5-expressing tissues unknown"]},{"year":2021,"claim":"Identifying PIP as an apical-targeting partner and AQP5's role in lens clarity via miR-124-3p.1: PIP was shown to interact with the AQP5 C-terminus to regulate apical localization in salivary glands (with altered distribution in Sjögren's syndrome), and AQP5 knockout in lens caused opacity through miR-124-3p.1 downregulation and vimentin upregulation.","evidence":"Reciprocal co-IP, PIP knockout mice, domain mapping; CRISPR AQP5 KO mice, dual luciferase reporter for miR-124-3p.1–vimentin, agomir rescue in organ culture","pmids":["34440877","33582182"],"confidence":"High","gaps":["Mechanism by which AQP5 regulates miR-124-3p.1 expression entirely unknown","PIP–AQP5 structural interface not resolved at atomic level"]},{"year":2022,"claim":"Revealing a non-channel autophagy-scaffold function in cancer: AQP5 was shown to recruit E3 ligase TRIM21 to ULK1, inducing K63-ubiquitination that activates autophagy and sustains gastric cancer stemness.","evidence":"Co-IP/mass spectrometry, ubiquitination assay, sphere formation and tumorigenesis assays in gastric cancer stem cells","pmids":["36372898"],"confidence":"Medium","gaps":["Whether AQP5–TRIM21–ULK1 axis operates in non-cancer contexts unknown","Domain on AQP5 mediating TRIM21 recruitment not mapped","Single-lab finding awaits independent replication"]},{"year":2024,"claim":"Connecting lipid peroxidation to AQP5 silencing in Sjögren's syndrome: GPX4 deficiency was shown to cause lipid ROS accumulation that activates STAT4 phosphorylation, and pSTAT4 directly binds and represses the AQP5 promoter, reducing salivary secretion.","evidence":"ChIP confirming pSTAT4 at AQP5 promoter; GPX4 OE/KD, ferrostatin-1 rescue in SGECs and SS mouse model","pmids":["38574973"],"confidence":"High","gaps":["Whether pSTAT4-mediated AQP5 repression operates outside Sjögren's disease context","Whether other aquaporins are similarly regulated by this lipid ROS–STAT4 axis"]},{"year":null,"claim":"Key unresolved questions include the structural basis of AQP5's non-channel scaffolding interactions (c-Src, TRPV4, TRIM21), whether CO₂ transport by AQP5 is physiologically significant in vivo, and how the multiple transcriptional inputs (GATA6/Sp1, Dot1a, NF-κB, HIF-1α, pSTAT4) are integrated in different tissues.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of AQP5 in complex with any signaling partner","In vivo relevance of CO₂ selectivity not tested","No systems-level model integrating the diverse transcriptional and post-translational regulatory inputs"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,2,10,19]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[5,7,26]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,2,3,6,14,16,19,23]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[2,3,4]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[18]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,2,10,19]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,5,7,14,21]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[13,26]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[12,15,17,20,25]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[15,20]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[2,3,4,6,11,14,23]}],"complexes":[],"partners":["TRPV4","AQP2","PIP","SRC","TRIM21","CAV1","ULK1"],"other_free_text":[]},"mechanistic_narrative":"AQP5 is a regulated water and CO2-selective gas channel expressed at apical membranes of secretory and barrier epithelia, where it mediates transcellular water transport and participates in cell volume sensing [PMID:9755069, PMID:19273840]. Its trafficking from intracellular vesicles to the apical plasma membrane requires microtubule-dependent transport and is triggered by intracellular Ca²⁺ signaling downstream of muscarinic M3 receptors; this process involves lipid raft dissociation, caveolin-1-dependent TRPC1 Ca²⁺ influx, and regulation by PKA phosphorylation at Ser156 and by the interacting partner PIP, while AQP5 also partners with TRPV4 via its N-terminus to enable hypotonic regulatory volume decrease [PMID:10600522, PMID:16107506, PMID:23203809, PMID:16571723, PMID:34440877]. Transcription of AQP5 is activated by a GATA6/Sp1/p300 histone acetylation axis, repressed by Dot1a-mediated H3K79 methylation, suppressed under hypoxia through HIF-1α, downregulated by LPS-induced NF-κB/AP-1 complexes, and inhibited by lipid ROS-driven pSTAT4 promoter binding in Sjögren's syndrome [PMID:28615712, PMID:23326416, PMID:23469202, PMID:20522648, PMID:38574973]. Missense mutations in AQP5 cause autosomal-dominant diffuse nonepidermolytic palmoplantar keratoderma, and in cancer contexts AQP5 promotes invasion and stemness through phospho-Ser156-dependent c-Src interaction, NF-κB-driven EMT, and TRIM21-mediated K63-ubiquitination of ULK1 to activate autophagy [PMID:23830519, PMID:18478076, PMID:28619511, PMID:36372898]."},"prefetch_data":{"uniprot":{"accession":"P55064","full_name":"Aquaporin-5","aliases":[],"length_aa":265,"mass_kda":28.3,"function":"Aquaporins form homotetrameric transmembrane channels, with each monomer independently mediating water transport across the plasma membrane along its osmotic gradient (PubMed:18768791, PubMed:8621489). Plays an important role in fluid secretion in salivary glands (By similarity). Required for TRPV4 activation by hypotonicity. Together with TRPV4, controls regulatory volume decrease in salivary epithelial cells (PubMed:16571723). Seems to play a redundant role in water transport in the eye, lung and in sweat glands (By similarity)","subcellular_location":"Apical cell membrane; Cell membrane; Cytoplasmic vesicle membrane","url":"https://www.uniprot.org/uniprotkb/P55064/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/AQP5","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/AQP5","total_profiled":1310},"omim":[{"mim_id":"615598","title":"PALMOPLANTAR KERATODERMA, NAGASHIMA TYPE; PPKN","url":"https://www.omim.org/entry/615598"},{"mim_id":"605427","title":"TRANSIENT RECEPTOR POTENTIAL CATION CHANNEL, SUBFAMILY V, MEMBER 4; TRPV4","url":"https://www.omim.org/entry/605427"},{"mim_id":"602974","title":"AQUAPORIN 7; AQP7","url":"https://www.omim.org/entry/602974"},{"mim_id":"601383","title":"AQUAPORIN 6; AQP6","url":"https://www.omim.org/entry/601383"},{"mim_id":"600962","title":"PALMOPLANTAR KERATODERMA, NONEPIDERMOLYTIC; NEPPK","url":"https://www.omim.org/entry/600962"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"salivary gland","ntpm":586.3},{"tissue":"testis","ntpm":211.1}],"url":"https://www.proteinatlas.org/search/AQP5"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P55064","domains":[{"cath_id":"1.20.1080.10","chopping":"1-228","consensus_level":"medium","plddt":97.4179,"start":1,"end":228}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P55064","model_url":"https://alphafold.ebi.ac.uk/files/AF-P55064-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P55064-F1-predicted_aligned_error_v6.png","plddt_mean":94.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=AQP5","jax_strain_url":"https://www.jax.org/strain/search?query=AQP5"},"sequence":{"accession":"P55064","fasta_url":"https://rest.uniprot.org/uniprotkb/P55064.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P55064/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P55064"}},"corpus_meta":[{"pmid":"19273840","id":"PMC_19273840","title":"Relative CO2/NH3 selectivities of AQP1, AQP4, AQP5, AmtB, and RhAG.","date":"2009","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/19273840","citation_count":207,"is_preprint":false},{"pmid":"16571723","id":"PMC_16571723","title":"A role for AQP5 in activation of TRPV4 by hypotonicity: concerted involvement of AQP5 and TRPV4 in regulation of cell volume recovery.","date":"2006","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16571723","citation_count":193,"is_preprint":false},{"pmid":"10615063","id":"PMC_10615063","title":"Decreased expression of aquaporin (AQP)1 and AQP5 in mouse lung after acute viral infection.","date":"2000","source":"American journal of respiratory cell and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/10615063","citation_count":183,"is_preprint":false},{"pmid":"10022971","id":"PMC_10022971","title":"Aquaporin-5 (AQP5), a water channel protein, in the rat salivary and lacrimal glands: immunolocalization and effect of secretory stimulation.","date":"1999","source":"Cell and tissue research","url":"https://pubmed.ncbi.nlm.nih.gov/10022971","citation_count":160,"is_preprint":false},{"pmid":"12801959","id":"PMC_12801959","title":"Distribution of aquaporin water channels AQP1 and AQP5 in the ductal system of the human pancreas.","date":"2003","source":"Gut","url":"https://pubmed.ncbi.nlm.nih.gov/12801959","citation_count":136,"is_preprint":false},{"pmid":"9755069","id":"PMC_9755069","title":"Localization and expression of AQP5 in cornea, serous salivary glands, and pulmonary epithelial cells.","date":"1998","source":"The American journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/9755069","citation_count":135,"is_preprint":false},{"pmid":"18478076","id":"PMC_18478076","title":"Expression of aquaporin 5 (AQP5) promotes tumor invasion in human non small cell lung cancer.","date":"2008","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/18478076","citation_count":128,"is_preprint":false},{"pmid":"32025032","id":"PMC_32025032","title":"AQP5 enriches for stem cells and cancer origins in the distal stomach.","date":"2020","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/32025032","citation_count":109,"is_preprint":false},{"pmid":"16107506","id":"PMC_16107506","title":"Identification of AQP5 in lipid rafts and its translocation to apical membranes by activation of M3 mAChRs in interlobular ducts of rat parotid gland.","date":"2005","source":"American journal of physiology. 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Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal biochemical and microscopic methods in same study, strong mechanistic dissection\",\n      \"pmids\": [\"16107506\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In rat duodenal Brunner's gland cells, VIP induces AQP5 translocation from secretory granule membranes to the apical membrane in a PKA-dependent (blocked by H-89) but PKC-independent manner, without affecting AQP1 localization.\",\n      \"method\": \"Immunohistochemistry; in vitro duodenal slice assay with VIP; protein kinase inhibitors H-7, H-89, calphostin C; in vivo VIP injection\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — combined in vitro and in vivo with specific kinase inhibition, multiple concentrations and time points\",\n      \"pmids\": [\"15650134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"AQP5 associates with TRPV4 at the apical membrane of salivary gland acinar cells; the N-terminus of AQP5 is required for TRPV4 activation by hypotonicity (N-terminus-deleted AQP5 suppresses TRPV4 activation); hypotonicity increases co-association and surface expression of AQP5 and TRPV4; both AQP5-null and TRPV4-null acinar cells show greatly reduced Ca2+ entry and loss of regulatory volume decrease (RVD) in response to hypotonicity; actin depolymerization reduces AQP5-TRPV4 co-association and RVD.\",\n      \"method\": \"Co-immunoprecipitation; AQP5 knockout and TRPV4 knockout mouse acinar cells; N-terminus deletion mutant expression; Ca2+ imaging; cell volume measurements; pharmacological TRPV4 activation/inhibition\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including KO cells, co-IP, deletion mutants, Ca2+ assays; replicated across experimental conditions\",\n      \"pmids\": [\"16571723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In bronchial epithelial cells, AQP5 Ser156 is phosphorylated by PKA (abolished in S156A mutant); the N185D mutation (disrupting second NPA motif) retains AQP5 in the cytoplasm rather than the apical membrane, whereas S156A does not affect membrane expression, indicating that membrane targeting of AQP5 involves the NPA motif but PKA phosphorylation at Ser156 is not required for apical membrane expression.\",\n      \"method\": \"Stable transfection in BEAS-2B cells on permeable support; immunofluorescence; site-directed mutagenesis (S156A, N185D); cAMP/PKA pharmacological manipulation (H89, cpt-cAMP)\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro assay with mutagenesis and pharmacological dissection\",\n      \"pmids\": [\"18042467\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"AQP5 promotes cell invasion and epithelial-to-mesenchymal transition (EMT) in lung cells through phosphorylation at Ser156 and subsequent interaction with activated c-Src (phospho-Tyr416); membrane trafficking mutant N185D and phosphorylation-blocking mutant S156A both abolish invasion and c-Src interaction.\",\n      \"method\": \"In vitro invasion assay; stable transfection in BEAS-2B and NIH3T3 cells; SH3-domain protein array; co-immunoprecipitation with activated c-Src; site-directed mutagenesis (N185D, S156A)\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — functional assay with mutagenesis, protein array, and co-IP; multiple cell lines\",\n      \"pmids\": [\"18478076\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"AQP5 overexpression in CML cells (K562) increases BCR-ABL1 phosphorylation and cell proliferation; siRNA-mediated AQP5 knockdown reduces proliferation, decreases BCR-ABL1 phosphorylation, and increases caspase-9 activity, indicating AQP5 promotes survival/proliferation and suppresses apoptosis in CML cells.\",\n      \"method\": \"siRNA knockdown; AQP5 overexpression; immunoblotting; flow cytometry; cell proliferation assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — KD/OE with defined molecular readouts (BCR-ABL1 phosphorylation, caspase-9), single lab\",\n      \"pmids\": [\"18612408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"AQP5 overexpression induces cell proliferation and oncogenic transformation dependent on cAMP-PKA phosphorylation of a cytoplasmic loop consensus site (Ser156); preferential phosphorylation of this site is found in tumor samples.\",\n      \"method\": \"Ectopic AQP5 expression in vitro and in vivo xenograft; PKA phosphorylation site mutagenesis; immunoblotting of tumor vs. normal samples\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional transformation assay with mutagenesis; single lab\",\n      \"pmids\": [\"18423983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"AQP5 expressed in Xenopus oocytes confers selective CO2 permeability (increased surface pH change and faster time constants with CO2 exposure) compared with water-injected controls, but does not conduct NH3, establishing AQP5 as a CO2-selective gas channel with higher CO2/NH3 selectivity than AQP1 or AQP4.\",\n      \"method\": \"Xenopus oocyte expression system; surface pH measurement assay; osmotic water permeability (Pf) measurement; comparison with AQP1, AQP4, AmtB, RhAG\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional reconstitution in oocytes with quantitative selectivity assay, replicated against multiple controls\",\n      \"pmids\": [\"19273840\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In rat parotid gland, AQP5 dephosphorylation at the PKA consensus motif 152SRRTS promotes translocation to the apical membrane; microtubules but not microfilaments are required for this trafficking event.\",\n      \"method\": \"GFP-AQP5 chimeric protein expression in MDCK-II cells; PKA inhibitor H-89; site-directed mutagenesis of Ser152; colchicine/cytochalasin B treatment; confocal microscopy\",\n      \"journal\": \"The journal of medical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis combined with pharmacological cytoskeletal dissection, single lab\",\n      \"pmids\": [\"19262015\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"LPS-induced downregulation of AQP5 mRNA in parotid gland is mediated through a transcription factor complex of NF-κB (p65), p-c-Jun, and c-Fos acting on NF-κB-responsive elements in the AQP5 promoter; this is blocked by inhibitors of IκB kinase, 26S proteasome, ERK1/2, JNK, and p38 MAPK; co-immunoprecipitation revealed physical association of NF-κB, p-c-Jun, and c-Fos.\",\n      \"method\": \"In vivo LPS injection in C3H/HeN and TLR4-mutant C3H/HeJ mice; tissue culture with kinase inhibitors; co-immunoprecipitation; EMSA/protein-binding assay on AQP5 promoter sequences\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including genetic model (TLR4 mutant), pharmacological inhibitors, co-IP, and promoter binding assay\",\n      \"pmids\": [\"20522648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Parasympathetic denervation (chorda tympani) decreases AQP5 protein in submandibular gland via lysosomal degradation (enhanced by autophagosomes/lysosomes, reversed by chloroquine); cathepsins B and L are implicated as degrading enzymes; M3 mAChR agonist cevimeline recovers AQP5 protein levels post-denervation.\",\n      \"method\": \"Chorda tympani denervation in rat; autophagosome marker LC3B-II western blot; TUNEL apoptosis assay; lysosomal fraction in vitro degradation assay; protease inhibitor experiments; immunohistochemistry for AQP5/Lamp2/LC3B co-localization\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (co-localization, in vitro degradation, inhibitor rescue) in same study\",\n      \"pmids\": [\"20689061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Caveolin-1 is required for agonist-stimulated AQP5 translocation to the apical membrane of salivary gland acinar cells; in Cav1-/- mice, AQP5 apical localization is disrupted and agonist-induced surface expression of AQP5 (which requires Ca2+ influx via TRPC1 channels) is abrogated; adenoviral re-expression of Cav1 restores AQP5 apical targeting and fluid secretion.\",\n      \"method\": \"Cav1 knockout mice; adenoviral Cav1 re-expression; Ca2+ imaging; immunofluorescence for AQP5 apical localization; surface biotinylation assay; fluid secretion measurement\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO with defined cellular phenotype, rescue experiment, multiple readouts\",\n      \"pmids\": [\"23203809\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"AQP5 is a transcriptional target repressed by histone H3K79 methyltransferase Dot1a; in Dot1l-deficient kidney cells, AQP5 is upregulated and colocalizes with AQP2; AQP5 directly interacts with AQP2 (co-immunoprecipitation) and impairs AQP2 surface localization, with the AQP5/AQP2 complex partially residing in the ER/Golgi.\",\n      \"method\": \"cDNA array; real-time RT-qPCR; luciferase reporter assay; cell surface biotinylation; co-immunoprecipitation; co-localization microscopy; ChIP showing Dot1a/H3diMe-K79 occupancy at AQP5 promoter\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including ChIP, co-IP, reporter assay, and surface biotinylation in same study\",\n      \"pmids\": [\"23326416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Missense mutations in AQP5 cause autosomal-dominant diffuse nonepidermolytic palmoplantar keratoderma; protein structure analysis suggests these variants affect normal channel regulation; immunofluorescence shows mutant AQP5 is trafficked normally to the plasma membrane in stratum granulosum, suggesting the mutations likely produce open/dysregulated channels rather than trafficking defects.\",\n      \"method\": \"Exome sequencing; protein structure analysis; immunofluorescence of patient skin biopsies\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — genetic disease linkage with localization data, but no functional channel assay in this study\",\n      \"pmids\": [\"23830519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Hypoxia and hypoxia mimetic cobalt decrease AQP5 expression (~70%) in mouse lung; HIF-1α is a key mediator (dominant-negative HIF-1α and siRNA block the effect); proteasome inhibitors abolish both hypoxia-induced and cobalt-induced AQP5 decrease at both protein and mRNA levels, indicating the proteasome pathway stabilizes HIF-1α and/or unidentified transcription factors that regulate AQP5 transcription.\",\n      \"method\": \"Mouse hypoxia exposure; MLE-12 cell line; cobalt treatment; HIF-1α dominant-negative mutants and siRNA; proteasome inhibitors lactacystin and PI-III; hnRNA quantification by real-time PCR\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple genetic and pharmacological perturbations with transcriptional readout including hnRNA measurement\",\n      \"pmids\": [\"23469202\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Activation of muscarinic receptors in rat parotid acinar cells induces AQP5 translocation to the nucleus, apical plasma membrane, and lateral plasma membrane; AQP5 presence in the nuclear membrane coincides with nuclear shrinkage, suggesting AQP5 facilitates water transport across the nuclear membrane.\",\n      \"method\": \"Immunoconfocal and immunoelectron microscopy; western blot of nuclear fractions; detergent solubility and sucrose density flotation; atropine (mAChR antagonist) pretreatment\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with antagonist controls and nuclear fractionation, single lab\",\n      \"pmids\": [\"25603543\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"AQP5 forms functional water channels in rodent lens fiber cells; AQP5 membrane insertion in cortical fiber cells modulates water permeability (PH2O); species-specific differences in AQP5 subcellular distribution (membranous in mouse, cytoplasmic in rat) correlate with Hg2+-sensitive PH2O contributions; organ culture promotes AQP5 membrane insertion in rat lens cortical fiber cells with corresponding increase in Hg2+-sensitive PH2O.\",\n      \"method\": \"Fluorescence dye dilution assay for PH2O; HgCl2 inhibition; immunolabeling of lens sections and fiber membrane vesicles; organ culture\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct functional water permeability assay with pharmacological inhibition and matched subcellular localization data\",\n      \"pmids\": [\"29118028\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GATA6 and Sp1 activate AQP5 transcription via histone H3 acetylation; HDAC3 represses AQP5 by binding Sp1 and reducing H3 acetylation at the AQP5 promoter; p300 histone acetyltransferase cooperates with GATA6/Sp1 to activate AQP5; HDAC inhibitor SAHA increases AQP5 expression and H3 acetylation at the Aqp5 promoter.\",\n      \"method\": \"HDAC3 overexpression/knockdown; GATA6/p300 knockdown/overexpression; luciferase reporter assay; ChIP for H3/H4 acetylation; co-immunoprecipitation of GATA6/Sp1/p300/HDAC3 interactions; SAHA treatment\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP, co-IP, reporter assay, and genetic perturbations in same study with multiple orthogonal methods\",\n      \"pmids\": [\"28615712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In hyperosmolarity-treated human corneal epithelial cells, AQP5 upregulation mediates JNK1/2 MAPK activation, proinflammatory cytokine expression (IL-1β, IL-6, IL-8, TNF-α, caspase-1), and cell death; siRNA knockdown of AQP5 or JNK1/2 inhibition with SP600125 reduces these effects, placing AQP5 upstream of JNK1/2 signaling in hyperosmotic corneal injury.\",\n      \"method\": \"siRNA AQP5 gene silencing; SP600125 JNK1/2 inhibitor; real-time RT-PCR; western blot for AQP5 and p-JNK1/2; TUNEL assay; step increases in osmolarity up to 550 mOsm\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown with pathway inhibitor; single lab but two orthogonal interventions\",\n      \"pmids\": [\"28680052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"AQP5 downregulation in HCC cells suppresses EMT and tumor metastasis partly via inactivation of the NF-κB signaling pathway, altering expression of E-cadherin, α-catenin, N-cadherin, and vimentin.\",\n      \"method\": \"AQP5 knockdown in HCC cell lines; in vitro invasion assay; in vivo metastasis model; western blot for EMT markers and NF-κB pathway components\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — KD with defined molecular and in vivo phenotype, single lab\",\n      \"pmids\": [\"28619511\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Prolactin-inducible protein (PIP) physically interacts with AQP5 via the AQP5 C-terminus (one PIP molecule per AQP5 tetramer); PIP knockout in mice and PIP misexpression in Sjögren's syndrome patients correlate with altered AQP5 distribution at the acinar apical membrane, indicating PIP regulates AQP5 localization in salivary glands.\",\n      \"method\": \"Co-immunoprecipitation in vitro and in vivo (mouse and human salivary glands); PIP knockout mice; structural binding analysis (C-terminus deletion); immunofluorescence of human minor salivary glands from SS patients\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP in multiple systems, KO mouse localization data, domain mapping; multiple orthogonal approaches\",\n      \"pmids\": [\"34440877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"AQP5 knockout in mouse lens leads to mild lens opacity at ~6 months; mechanistically, AQP5 loss downregulates miR-124-3p.1, which normally suppresses vimentin (a dual luciferase reporter confirmed vimentin as direct miR-124-3p.1 target); AQP5 knockout and AQP5-L51P mutation increase vimentin expression, contributing to lens opacity; miR-124-3p.1 agomir reduces lens opacity and vimentin in both WT and KO mice.\",\n      \"method\": \"CRISPR/Cas9 AQP5 knockout mice; whole exome sequencing; dual luciferase reporter assay; qRT-PCR; western blot; immunofluorescence; miR-124-3p.1 agomir organ culture\",\n      \"journal\": \"Experimental eye research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — KO mouse phenotype, dual luciferase target validation, miRNA rescue; multiple orthogonal methods\",\n      \"pmids\": [\"33582182\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In Sjögren's syndrome salivary gland epithelial cells, reduced GPX4 expression leads to lipid ROS accumulation, which activates STAT4 phosphorylation and nuclear translocation; nuclear pSTAT4 binds the AQP5 promoter (confirmed by ChIP) and inhibits AQP5 transcription, reducing salivary secretion; GPX4 overexpression reverses this and restores AQP5 expression.\",\n      \"method\": \"GPX4 overexpression/knockdown in SGECs; ChIP assay confirming pSTAT4 binding at AQP5 promoter; lipid ROS inhibitor ferrostatin-1 in vitro and in vivo; SS mouse model; immunohistochemistry; western blot; bioinformatics of SS patient GSE databases\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP for direct promoter binding, genetic perturbations, pharmacological rescue, in vivo model; multiple orthogonal methods\",\n      \"pmids\": [\"38574973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"AQP5 recruits E3 ubiquitin ligase TRIM21 to the key autophagy protein ULK1, inducing K63-mediated ubiquitination of ULK1 and activating autophagy (LC3I/LC3II conversion) in gastric cancer stem cells; this autophagy activation is required for AQP5-driven cancer stem cell biological functions.\",\n      \"method\": \"Transcriptome sequencing; proteomic detection; mass spectrometry; co-immunoprecipitation; ubiquitination assay; sphere formation and tumorigenesis assays\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP/MS identification of TRIM21, functional autophagy assay; single lab\",\n      \"pmids\": [\"36372898\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"AQP5 is a regulated apical membrane water (and CO2-selective gas) channel whose trafficking to secretory epithelial apical membranes requires microtubule-dependent vesicle transport and is controlled by intracellular Ca2+ signaling downstream of M3 muscarinic receptors, with lipid raft association/dissociation, PKA phosphorylation at Ser156 (which modulates constitutive expression and lateral diffusion but is not strictly required for membrane targeting), and caveolin-1-dependent TRPC1 Ca2+ influx all contributing to regulated surface delivery; AQP5 partners with TRPV4 (via its N-terminus) to enable hypotonic volume sensing and regulatory volume decrease, interacts with AQP2 to impair its membrane localization, and with PIP to control its own apical targeting; its transcription is activated by GATA6/Sp1/p300-mediated H3 acetylation, repressed by Dot1a-dependent H3K79 methylation and by NF-κB/AP-1 complexes (induced by LPS), and suppressed under hypoxia via HIF-1α and proteasome-dependent mechanisms; in cancer contexts AQP5 promotes invasion, EMT, and stemness through phospho-Ser156-dependent c-Src interaction, NF-κB-driven EMT, and TRIM21-mediated K63-ubiquitination of ULK1 to activate autophagy.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"AQP5 is a regulated water and CO2-selective gas channel expressed at apical membranes of secretory and barrier epithelia, where it mediates transcellular water transport and participates in cell volume sensing [PMID:9755069, PMID:19273840]. Its trafficking from intracellular vesicles to the apical plasma membrane requires microtubule-dependent transport and is triggered by intracellular Ca²⁺ signaling downstream of muscarinic M3 receptors; this process involves lipid raft dissociation, caveolin-1-dependent TRPC1 Ca²⁺ influx, and regulation by PKA phosphorylation at Ser156 and by the interacting partner PIP, while AQP5 also partners with TRPV4 via its N-terminus to enable hypotonic regulatory volume decrease [PMID:10600522, PMID:16107506, PMID:23203809, PMID:16571723, PMID:34440877]. Transcription of AQP5 is activated by a GATA6/Sp1/p300 histone acetylation axis, repressed by Dot1a-mediated H3K79 methylation, suppressed under hypoxia through HIF-1α, downregulated by LPS-induced NF-κB/AP-1 complexes, and inhibited by lipid ROS-driven pSTAT4 promoter binding in Sjögren's syndrome [PMID:28615712, PMID:23326416, PMID:23469202, PMID:20522648, PMID:38574973]. Missense mutations in AQP5 cause autosomal-dominant diffuse nonepidermolytic palmoplantar keratoderma, and in cancer contexts AQP5 promotes invasion and stemness through phospho-Ser156-dependent c-Src interaction, NF-κB-driven EMT, and TRIM21-mediated K63-ubiquitination of ULK1 to activate autophagy [PMID:23830519, PMID:18478076, PMID:28619511, PMID:36372898].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing where AQP5 acts: immunolocalization resolved AQP5 to apical membranes of corneal, lacrimal, salivary, and type I lung epithelial cells, defining it as an apical water channel of diverse secretory epithelia.\",\n      \"evidence\": \"Immunohistochemistry and immunoelectron microscopy with affinity-purified antibody across multiple tissues\",\n      \"pmids\": [\"9755069\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No functional water permeability measurement in these tissues at this stage\", \"Mechanism of apical targeting unknown\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defining the trafficking mechanism: Ca²⁺ elevation was shown to drive AQP5 translocation to the plasma membrane via a microtubule-dependent, microfilament-independent route, establishing regulated vesicular insertion as the basis for AQP5 surface delivery.\",\n      \"evidence\": \"Confocal microscopy of AQP5-transfected HSG cells with thapsigargin/ionophore stimulation and pharmacological cytoskeletal disruption\",\n      \"pmids\": [\"10600522\", \"10022971\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of motor proteins and vesicle carriers unknown\", \"Whether Ca²⁺ acts directly on vesicle fusion or via an intermediate kinase unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Resolving the receptor-to-membrane pathway: M3 muscarinic receptor activation and PKA signaling were shown to control AQP5 apical insertion, with lipid raft association/dissociation serving as a membrane-organizing step during trafficking.\",\n      \"evidence\": \"Detergent solubility/flotation assays and immunoEM in parotid gland (M3 agonist cevimeline); PKA inhibitor H-89 in duodenal Brunner's gland VIP-stimulated slices\",\n      \"pmids\": [\"16107506\", \"15650134\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PKA phosphorylates AQP5 directly versus raft components not resolved\", \"PKA site identity not yet mapped\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Linking AQP5 to volume sensing: AQP5 was shown to physically associate with TRPV4 via its N-terminus at the apical membrane, and both AQP5-null and TRPV4-null cells lost Ca²⁺ entry and regulatory volume decrease upon hypotonicity, establishing AQP5 as a co-sensor for osmotic stress rather than a passive pore.\",\n      \"evidence\": \"Co-immunoprecipitation, AQP5/TRPV4 knockout acinar cells, N-terminal deletion mutant, Ca²⁺ imaging, and cell volume assays\",\n      \"pmids\": [\"16571723\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of N-terminus–TRPV4 interaction unresolved\", \"Whether AQP5–TRPV4 coupling operates in non-salivary tissues unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Dissecting the PKA phosphorylation site: Ser156 was confirmed as the PKA substrate but S156A did not block membrane targeting, while the NPA-motif mutant N185D retained AQP5 in the cytoplasm, separating channel maturation/folding requirements from kinase-dependent regulation.\",\n      \"evidence\": \"Site-directed mutagenesis (S156A, N185D) in stably transfected BEAS-2B cells on permeable support with cAMP/PKA pharmacological manipulation\",\n      \"pmids\": [\"18042467\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"What downstream process Ser156 phosphorylation controls if not trafficking\", \"Whether N185D causes global misfolding versus specific NPA-dependent retention\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Establishing an oncogenic signaling role: phospho-Ser156 was required for AQP5 to interact with activated c-Src and promote cell invasion, proliferation, and EMT, revealing a non-channel, signaling-scaffold function.\",\n      \"evidence\": \"Invasion assays, SH3-domain protein array, co-IP with phospho-Src in BEAS-2B/NIH3T3; overexpression/siRNA in K562 CML cells\",\n      \"pmids\": [\"18478076\", \"18423983\", \"18612408\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether AQP5–c-Src interaction requires water channel activity unknown\", \"Generalizability of CML BCR-ABL1 connection not independently replicated\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Expanding substrate selectivity: functional reconstitution in oocytes demonstrated AQP5 conducts CO₂ with high selectivity over NH₃, extending its physiological role beyond water to gas transport.\",\n      \"evidence\": \"Xenopus oocyte expression with surface pH measurement and osmotic water permeability comparison to AQP1/AQP4\",\n      \"pmids\": [\"19273840\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of CO₂ transport via AQP5 in vivo not established\", \"Molecular determinants of CO₂ vs. NH₃ selectivity not mapped\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defining transcriptional repression: LPS was shown to downregulate AQP5 transcription via a physical NF-κB(p65)/p-c-Jun/c-Fos complex binding the AQP5 promoter, and parasympathetic denervation was shown to degrade AQP5 protein through lysosomal/autophagic pathways involving cathepsins B and L.\",\n      \"evidence\": \"TLR4-mutant mice, EMSA/co-IP on AQP5 promoter; chorda tympani denervation with lysosomal co-localization and protease inhibitor rescue\",\n      \"pmids\": [\"20522648\", \"20689061\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether NF-κB directly binds DNA or acts through AP-1 composite elements not fully resolved\", \"Whether autophagy-mediated AQP5 degradation is a general regulatory mechanism beyond denervation\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identifying the Ca²⁺ entry gateway: caveolin-1 was required for agonist-induced AQP5 apical translocation because it enables TRPC1-mediated Ca²⁺ influx; Cav1 knockout ablated the response and adenoviral rescue restored it.\",\n      \"evidence\": \"Cav1 knockout mice, adenoviral Cav1 re-expression, Ca²⁺ imaging, surface biotinylation, fluid secretion measurement in salivary glands\",\n      \"pmids\": [\"23203809\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Cav1 scaffolds AQP5 vesicles directly or acts solely through TRPC1-Ca²⁺ unclear\", \"Role of other TRP channels not excluded\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Resolving chromatin-level control and a disease link: Dot1a-mediated H3K79 methylation was shown to repress AQP5 transcription (with derepression causing AQP5–AQP2 hetero-interaction that impairs AQP2 surface expression in kidney), and missense AQP5 mutations were identified as the cause of autosomal-dominant palmoplantar keratoderma.\",\n      \"evidence\": \"ChIP for H3K79me at AQP5 promoter, co-IP of AQP5–AQP2, surface biotinylation in Dot1l-deficient cells; exome sequencing of keratoderma families with immunofluorescence of patient skin\",\n      \"pmids\": [\"23326416\", \"23830519\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether AQP5–AQP2 interaction is physiological or only pathological upon AQP5 overexpression\", \"Functional channel assay for keratoderma mutants not performed\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Building the epigenetic activation model and identifying tissue-specific channel function: GATA6/Sp1/p300 were shown to activate AQP5 via H3 acetylation opposed by HDAC3, and AQP5 was demonstrated to form functional water channels in lens fiber cells with species-specific membrane insertion.\",\n      \"evidence\": \"ChIP for H3 acetylation, co-IP of GATA6/Sp1/p300/HDAC3, luciferase reporter in salivary cells; fluorescence dye dilution water permeability assay with HgCl₂ inhibition in mouse and rat lens\",\n      \"pmids\": [\"28615712\", \"29118028\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signals that switch HDAC3 occupancy at the AQP5 promoter unidentified\", \"Whether GATA6/Sp1 axis operates in non-salivary AQP5-expressing tissues unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identifying PIP as an apical-targeting partner and AQP5's role in lens clarity via miR-124-3p.1: PIP was shown to interact with the AQP5 C-terminus to regulate apical localization in salivary glands (with altered distribution in Sjögren's syndrome), and AQP5 knockout in lens caused opacity through miR-124-3p.1 downregulation and vimentin upregulation.\",\n      \"evidence\": \"Reciprocal co-IP, PIP knockout mice, domain mapping; CRISPR AQP5 KO mice, dual luciferase reporter for miR-124-3p.1–vimentin, agomir rescue in organ culture\",\n      \"pmids\": [\"34440877\", \"33582182\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which AQP5 regulates miR-124-3p.1 expression entirely unknown\", \"PIP–AQP5 structural interface not resolved at atomic level\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealing a non-channel autophagy-scaffold function in cancer: AQP5 was shown to recruit E3 ligase TRIM21 to ULK1, inducing K63-ubiquitination that activates autophagy and sustains gastric cancer stemness.\",\n      \"evidence\": \"Co-IP/mass spectrometry, ubiquitination assay, sphere formation and tumorigenesis assays in gastric cancer stem cells\",\n      \"pmids\": [\"36372898\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether AQP5–TRIM21–ULK1 axis operates in non-cancer contexts unknown\", \"Domain on AQP5 mediating TRIM21 recruitment not mapped\", \"Single-lab finding awaits independent replication\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connecting lipid peroxidation to AQP5 silencing in Sjögren's syndrome: GPX4 deficiency was shown to cause lipid ROS accumulation that activates STAT4 phosphorylation, and pSTAT4 directly binds and represses the AQP5 promoter, reducing salivary secretion.\",\n      \"evidence\": \"ChIP confirming pSTAT4 at AQP5 promoter; GPX4 OE/KD, ferrostatin-1 rescue in SGECs and SS mouse model\",\n      \"pmids\": [\"38574973\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether pSTAT4-mediated AQP5 repression operates outside Sjögren's disease context\", \"Whether other aquaporins are similarly regulated by this lipid ROS–STAT4 axis\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of AQP5's non-channel scaffolding interactions (c-Src, TRPV4, TRIM21), whether CO₂ transport by AQP5 is physiologically significant in vivo, and how the multiple transcriptional inputs (GATA6/Sp1, Dot1a, NF-κB, HIF-1α, pSTAT4) are integrated in different tissues.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of AQP5 in complex with any signaling partner\", \"In vivo relevance of CO₂ selectivity not tested\", \"No systems-level model integrating the diverse transcriptional and post-translational regulatory inputs\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 2, 10, 19]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [5, 7, 26]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 2, 3, 6, 14, 16, 19, 23]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [2, 3, 4]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 2, 10, 19]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 5, 7, 14, 21]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [13, 26]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [12, 15, 17, 20, 25]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [15, 20]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [2, 3, 4, 6, 11, 14, 23]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"TRPV4\",\n      \"AQP2\",\n      \"PIP\",\n      \"SRC\",\n      \"TRIM21\",\n      \"CAV1\",\n      \"ULK1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}