{"gene":"ATP2B4","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":1988,"finding":"Identification of the calmodulin-binding domain of the human erythrocyte Ca2+ pump (PMCA): chymotrypsin cleavage and photoaffinity cross-linking with calmodulin identified a ~12 kDa fragment containing the calmodulin-binding region, and its amino acid sequence was determined, establishing the structural basis for calmodulin-dependent activation of the pump.","method":"Chymotrypsin proteolysis, calmodulin photoaffinity cross-linking, reverse-phase HPLC peptide isolation, amino acid sequencing","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct biochemical reconstitution and sequencing; foundational paper with 227 citations","pmids":["2963820"],"is_preprint":false},{"year":1990,"finding":"Peptide sequencing and molecular cloning of purified human erythrocyte Ca2+-ATPase revealed two distinct isoforms (PMCA1/hPMCA1 and a novel isoform hPMCA4) coexpressed in erythrocyte membranes, with sequence divergence in the extracellular loop between TM1-TM2, the negatively charged Ca2+-binding region, and the cAMP-dependent protein kinase phosphorylation site.","method":"Peptide sequence analysis, molecular cloning, Northern blot","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct protein sequencing and cloning; highly cited foundational study","pmids":["2137451"],"is_preprint":false},{"year":1992,"finding":"Alternative splicing of the PMCA4 (ATP2B4) primary transcript generates at least two major variants (PMCA4a and PMCA4b) at the C-terminal regulatory domain; PMCA4b contains an additional exon inserted immediately after the calmodulin-binding domain sequence that shifts the reading frame and truncates the C-terminal regulatory domain. Each splice variant has a distinct tissue distribution.","method":"PCR amplification of cDNA, Southern blotting, cDNA isolation and characterization, genomic sequencing","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — cDNA isolation with genomic validation; replicated in multiple tissues; 109 citations","pmids":["1531651"],"is_preprint":false},{"year":1993,"finding":"Quantitative PCR analysis showed that PMCA4 (ATP2B4) mRNA is ubiquitously expressed in all tissues examined (cerebral cortex, skeletal and heart muscle, stomach, liver, lung, kidney), similar to PMCA1. Alternative splicing at site A (36-bp exon inclusion) and site C (178-bp exon exclusion) generates the major PMCA4 splice variants present across all tissues.","method":"Quantitative RT-PCR with GAPDH as internal standard, across seven human tissues","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — quantitative multi-tissue expression with internal standard; 141 citations","pmids":["8245032"],"is_preprint":false},{"year":2001,"finding":"PMCA4b interacts with multiple members of the membrane-associated guanylate kinase (MAGUK) family via its C-terminal PDZ-binding domain: SAP90/PSD95, PSD93/chapsyn-110, SAP97, and SAP102 all bind the C-terminal tail of PMCA4b. Co-immunoprecipitation confirmed the PMCA4b–SAP102 interaction, and confocal microscopy showed PMCA4b and SAP97 colocalize exclusively in the basolateral membrane of polarized MDCK cells, demonstrating PDZ-domain-mediated targeting of PMCA4b to specific membrane microdomains.","method":"Yeast two-hybrid screen, co-immunoprecipitation, confocal immunofluorescence microscopy in polarized MDCK cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus localization; 143 citations; multiple orthogonal methods","pmids":["11274188"],"is_preprint":false},{"year":2001,"finding":"PMCA4 is required for TNF-induced cell death in L929 cells. PMCA4-deficient cells show abnormally elevated intracellular Ca2+ following TNF stimulation. The elevated Ca2+ promotes lysosome exocytosis, which inhibits the TNF-induced increase in vacuolar acidic compartment (VAC) volume, thereby conferring resistance to TNF-induced cell death. Restoration of lysosome exocytosis inhibition or increase in VAC volume reversed resistance in PMCA4-mutant cells.","method":"Retrovirus insertion mutagenesis, intracellular Ca2+ measurement, lysosome exocytosis assays, sucrose treatment to modulate VAC","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — loss-of-function with mechanistic rescue experiments; 66 citations","pmids":["11713265"],"is_preprint":false},{"year":2001,"finding":"PMCA isoforms 1 and 4 are expressed ubiquitously in adult tissues, while PMCA2 and 3 are primarily in excitable cells. Alternative splicing at the first intracellular loop and the C-terminal tail (calmodulin-binding domain) generates isoform diversity with functional consequences: the C-terminal region regulates calmodulin sensitivity, phosphorylation, and differential interaction with PDZ domain-containing proteins.","method":"Review of functional studies, including splice variant characterization and knockout phenotypes","journal":"Physiological reviews","confidence":"High","confidence_rationale":"Tier 2 — synthesis of multiple independent experimental studies; 469 citations","pmids":["11152753"],"is_preprint":false},{"year":2004,"finding":"Targeted knockout of Atp2b4 (PMCA4) in mice causes male infertility due to failure to achieve hyperactivated sperm motility, without affecting basal motility or spermatogenesis. PMCA4 is localized to the principal piece of the sperm tail (co-localizing with the CatSper Ca2+ channel), and its loss leads to mitochondrial condensation indicative of Ca2+ overload. PMCA4 knockout also impairs phasic contractions and causes apoptosis in portal vein smooth muscle in vitro (strain-dependent). Loss of PMCA1 (Atp2b1) causes embryolethality, establishing PMCA1 as an essential housekeeping gene and PMCA4 as specifically required for sperm hyperactivation.","method":"Gene targeting/knockout mice, sperm motility assays, immunoblotting, immunohistochemistry, ultrastructural analysis, in vitro smooth muscle contractility","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — KO with multiple orthogonal phenotypic readouts; 271 citations; foundational mechanistic paper","pmids":["15178683"],"is_preprint":false},{"year":2008,"finding":"Alpha1-syntrophin (SNTA1) links PMCA4b (encoded by ATP2B4) to neuronal nitric oxide synthase (nNOS) and the cardiac sodium channel SCN5A in a macromolecular complex. A disease-associated A390V-SNTA1 mutation selectively disrupts PMCA4b binding to this complex, releasing nNOS inhibition and causing S-nitrosylation of SCN5A, increasing late sodium current and causing long QT syndrome. This identifies PMCA4b as a critical inhibitor of nNOS within a cardiac membrane signaling complex.","method":"GST pull-down, co-immunoprecipitation, heterologous cell expression, patch-clamp electrophysiology, cardiac myocyte expression","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — GST pull-down plus functional electrophysiology; 241 citations; multiple orthogonal methods","pmids":["18591664"],"is_preprint":false},{"year":2010,"finding":"In bovine epididymis, a splice variant switch occurs during sperm maturation: PMCA4b is the major variant in testis and caput/corpus epididymidis, whereas PMCA4a becomes the dominant isoform in cauda epididymidis. PMCA4a has higher basal Ca2+ transport activity and is more effective than PMCA4b at returning Ca2+ to resting levels. Immunohistochemical and Western blot analyses show PMCA4a is transferred to sperm membranes in the cauda epididymidis, suggesting this isoform switch facilitates higher Ca2+ turnover needed for hyperactivated motility.","method":"Quantitative PCR, immunohistochemistry with novel anti-PMCA4a antibody, Western blotting of sperm from caput vs. cauda epididymidis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods in one lab; functional inference from known kinetic differences between splice variants","pmids":["21187283"],"is_preprint":false},{"year":2010,"finding":"PMCA4 is localized in both detergent-resistant membrane (DRM/lipid raft) and detergent-soluble fractions of bovine sperm plasma membrane, and co-localizes with caveolin in the mid-piece. The seminal vesicle protein PDC-109 enhances Ca2+-ATPase activity preferentially in the detergent-soluble fractions of cauda sperm, suggesting functional compartmentalization of PMCA4 in sperm membrane microdomains.","method":"Sucrose density gradient fractionation (DRM isolation), immunocytochemistry, Ca2+-ATPase functional assays, lipid overlay experiments","journal":"International journal of andrology","confidence":"Medium","confidence_rationale":"Tier 2-3 — fractionation plus functional assay; single lab; compartmentalization linked to function","pmids":["20050939"],"is_preprint":false},{"year":2011,"finding":"PMCA4 forms a signaling complex with neuronal nitric oxide synthase (nNOS) in the cardiac cell membrane and acts as a structural scaffold that maintains nNOS in a defined microdomain. In PMCA4-/- mice, >36% of membrane-associated nNOS is delocalized to cytosol without change in total nNOS, leading to decreased microdomain cGMP, decreased PDE2 activity, elevated local cAMP, increased L-type calcium channel activity and ryanodine receptor phosphorylation, and enhanced cardiac contractility. This demonstrates PMCA4 regulates cardiac contractility via compartmentalized cyclic nucleotide signaling rather than beat-to-beat Ca2+ transport.","method":"PMCA4 knockout mice, in vivo contractility measurements, Ca2+ amplitude measurements, nNOS localization/activity assays, FRET-based cAMP/cGMP sensors, L-type channel recordings, ryanodine receptor phosphorylation analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods in vivo and in vitro; 62 citations; strong mechanistic demonstration","pmids":["21965681"],"is_preprint":false},{"year":2013,"finding":"A novel PMCA4-GCaMP2 fusion protein (Ca2+ sensor fused to N-terminus of PMCA4) correctly targets to the plasma membrane in cardiomyocytes, co-localizes with caveolin-3, and monitors subsarcolemmal Ca2+ dynamics in real time. The active pump generates higher signal amplitude and faster Ca2+ decay than an inactive mutant form. A novel small-molecule PMCA4-specific inhibitor was identified by library screening, which reduces Ca2+ clearance near the pump comparable to the inactive mutant, confirming PMCA4 Ca2+ transport activity at the cardiac membrane microdomain.","method":"Adenoviral expression, live-cell fluorescence imaging of Ca2+ sensor fusion protein, small molecule library screen, electrically stimulated neonatal and adult rat cardiomyocytes","journal":"Journal of molecular and cellular cardiology","confidence":"Medium","confidence_rationale":"Tier 2 — fusion protein sensor with pharmacological validation; single lab; 21 citations","pmids":["23880607"],"is_preprint":false},{"year":2014,"finding":"Ca2+ efflux activity of PMCA4 is required for G1 phase progression in vascular smooth muscle cells (VSMCs). PMCA4 knockout VSMCs show impaired [3H]thymidine incorporation and G1 arrest. Rescue with PMCA4a, PMCA4b, or a PMCA4b PDZ-binding mutant restores proliferation, but a mutant with only 10% of normal Ca2+ efflux activity cannot rescue. The PMCA4a and PMCA4b splice variants differentially regulate downstream mediators: PMCA4a rescue reduces AP-2β (anti-proliferative), while PMCA4b rescue reduces p15 (Cyclin D1/Cdk4 inhibitor), both converging on Cyclin D1/NFATc3 upregulation.","method":"PMCA4 knockout primary VSMCs, [3H]thymidine incorporation, flow cytometry (cell cycle), electroporation of expression constructs, microarray, Western blotting, laser capture microdissection","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — KO with mechanistic rescue using multiple mutants; 24 citations; multiple orthogonal methods","pmids":["24448801"],"is_preprint":false},{"year":2014,"finding":"A novel missense mutation (c.803G>A, p.R268Q) in ATP2B4 (PMCA4) co-segregates with autosomal dominant familial spastic paraplegia in a Chinese family. Computational modeling predicts the R268Q mutation destabilizes PMCA4 protein structure, increases folding free energy, and is located in a protein aggregation-prone segment susceptible to misfolding.","method":"Whole-exome sequencing, Sanger sequencing, co-segregation analysis, computational protein stability modeling","journal":"PloS one","confidence":"Low","confidence_rationale":"Tier 4 — computational prediction only; no in vitro functional assay in this paper","pmids":["25119969"],"is_preprint":false},{"year":2015,"finding":"The R268Q mutation in PMCA4 (ATP2B4) causes delayed intracellular Ca2+ extrusion in human neuroblastoma cells. Overexpression of mutant R268Q PMCA4 in SH-SY5Y cells results in significantly higher peak Ca2+ surge after KCl-induced depolarization and persistently elevated steady-state cytosolic Ca2+ after SERCA inhibition with thapsigargin, compared to wild-type PMCA4, demonstrating a loss-of-function effect on Ca2+ clearance.","method":"Fura-2 fluorescence Ca2+ imaging with confocal microscopy in SH-SY5Y neuroblastoma cells overexpressing WT or R268Q PMCA4, KCl depolarization, thapsigargin treatment","journal":"Brain and behavior","confidence":"Medium","confidence_rationale":"Tier 2 — direct functional assay with disease mutant in relevant cell type; single lab; 25 citations","pmids":["25798335"],"is_preprint":false},{"year":2016,"finding":"PMCA4 interacts with CD147 (Ig superfamily member) via CD147's transmembrane domain and Ig-like domain II. This interaction is required for CD147-dependent inhibition of IL-2 expression in T cells via a calcium-independent mechanism. CD147 does not control PMCA4 membrane localization, but PMCA4 is essential for the immunosuppressive effect of CD147, bypassing TCR proximal signaling.","method":"Affinity purification combined with mass spectrometry, siRNA silencing, domain-mapping experiments, IL-2 reporter assays in human T cells","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2-3 — AP-MS identification with functional siRNA validation; single lab; 21 citations","pmids":["26729804"],"is_preprint":false},{"year":2017,"finding":"PMCA4 coordinates Ca2+ and nitric oxide (NO) signaling in murine sperm to maintain motility. Co-immunoprecipitation and FRET demonstrate PMCA4 associates with eNOS and nNOS in sperm, forming a quaternary complex that also includes Caveolin-1. In Pmca4-/- sperm, NOS activity is elevated twofold, accompanied by a twofold increase in peroxynitrite and increased apoptotic germ cells, establishing PMCA4 as a negative regulator of NOS in sperm that coordinates Ca2+ clearance and NO production to maintain motility.","method":"Co-immunoprecipitation (Co-IP), FRET in capacitated and uncapacitated sperm, NOS activity assay, peroxynitrite measurement, apoptosis assay in Pmca4-/- mice","journal":"Journal of cellular physiology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus FRET plus KO functional readout; multiple orthogonal methods; 24 citations","pmids":["28247940"],"is_preprint":false},{"year":2017,"finding":"An erythroid-specific enhancer element in the ATP2B4 locus regulates PMCA4 expression in red blood cells. CRISPR-Cas9 deletion of this enhancer in erythroid cells causes abnormally high intracellular Ca2+ levels. Atp2b4-/- mice show increased mean corpuscular hemoglobin concentration (MCHC), confirming ATP2B4 as the causal gene at a malaria-susceptibility GWAS locus and demonstrating that ATP2B4 controls RBC hydration through Ca2+ regulation.","method":"eQTL mapping in erythroblasts, CRISPR-Cas9 enhancer deletion, Atp2b4 knockout mice, intracellular Ca2+ measurement, MCHC quantification","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1-2 — CRISPR functional validation plus KO mouse phenotype; multiple orthogonal approaches; 50 citations","pmids":["28714864"],"is_preprint":false},{"year":2017,"finding":"Reduced PMCA4b protein expression in human red blood cells correlates with a minor haplotype in the predicted second promoter region of ATP2B4 (not coding mutations), and reduced PMCA4b levels result in lower Ca2+ extrusion capacity. This haplotype corresponds to GWAS SNPs linked to reduced mean corpuscular hemoglobin concentration and malaria protection.","method":"Flow cytometry with specific antibody binding (quantitative), Western blot of RBC membranes, Ca2+ extrusion assays, DNA sequencing of ATP2B4 coding and promoter regions","journal":"Cell calcium","confidence":"Medium","confidence_rationale":"Tier 2 — functional Ca2+ assay plus protein quantification; single lab; 27 citations","pmids":["28216081"],"is_preprint":false},{"year":2020,"finding":"PMCA4 inhibits epithelial-mesenchymal transition (EMT) in gastric cancer cells via the NFATc1-ZEB1 pathway. PMCA4 knockdown increases nuclear NFATc1 accumulation and ZEB1 expression, suppresses E-cadherin/GRHL2/OVOL1, and promotes vimentin upregulation, increased migration/invasion, and drug resistance. These effects are prevented by knockdown of NFATc1 or ZEB1, or by cyclosporine A (calcineurin/NFAT inhibitor), placing PMCA4 upstream of the NFATc1-ZEB1 EMT axis.","method":"siRNA knockdown, overexpression, in vivo xenograft metastasis assay, Western blot, migration/invasion assays, cyclosporine A treatment","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"Medium","confidence_rationale":"Tier 2-3 — pathway epistasis via genetic and pharmacological intervention; in vivo validation; single lab; 15 citations","pmids":["32860837"],"is_preprint":false},{"year":2020,"finding":"PMCA4 expression in pancreatic ductal adenocarcinoma (PDAC) cells supports cytosolic Ca2+ clearance, cell migration, and apoptotic resistance. siRNA knockdown of PMCA4 in MIA PaCa-2 cells (which almost exclusively express PMCA4) reduces Ca2+ clearance rate, decreases cell migration, and sensitizes cells to apoptosis without affecting cell growth or metabolic parameters.","method":"siRNA knockdown, Ca2+ clearance assays, migration assays, apoptosis assays, Seahorse XF metabolic analysis, Western blot, RT-qPCR","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2-3 — loss-of-function with multiple cellular phenotype readouts; single lab; 17 citations","pmids":["31963119"],"is_preprint":false},{"year":2020,"finding":"PDGF-BB signaling downregulates PMCA4 expression in pulmonary arterial smooth muscle cells (PASMCs) via the MEK/ERK pathway. PMCA4 suppression attenuates Ca2+ clearance, promotes cell proliferation, and elevates cell locomotion through formation of focal adhesions. PMCA4 expression is also decreased in pulmonary arteries of monocrotaline- and hypoxia-induced PAH rats, and knockdown of PMCA4 in normal rats increases right ventricular systolic pressure and pulmonary artery wall thickness.","method":"PDGF-BB stimulation with MEK/ERK inhibitors, siRNA knockdown, Ca2+ clearance assays, proliferation assays, focal adhesion imaging, in vivo rat PAH models, hemodynamic measurements","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 — pathway identification with in vitro and in vivo validation; 10 citations","pmids":["32966125"],"is_preprint":false},{"year":2020,"finding":"PMCA4 (ATP2B4) is expressed in adrenal tissue (HAC15 cells) and contributes to membrane conductance. ATP2B4 knockdown in HAC15 cells reduced angiotensin II-stimulated responses in some clones. Whole-cell recordings confirmed robust endogenous ATP2B4 conductance, and overexpression of WT or variant ATP2B4 reduced conductance compared to endogenous levels.","method":"shRNA knockdown, doxycycline-inducible stable cell lines, whole-cell patch-clamp electrophysiology, aldosterone synthase (CYP11B2) expression assays","journal":"Hormones & cancer","confidence":"Low","confidence_rationale":"Tier 3 — limited mechanistic follow-up; variants did not alter CYP11B2; single lab; 9 citations","pmids":["32002807"],"is_preprint":false},{"year":2022,"finding":"CRISPR/Cas9-mediated deletion of a regulatory region containing five ATP2B4 SNPs (rs11240734, rs1541252, rs1541253, rs1541254, rs1541255) in K562 cells decreases ATP2B4 transcript and protein levels and increases intracellular Ca2+ concentration, demonstrating that this non-coding regulatory element controls PMCA4 expression and thereby Ca2+ homeostasis in erythroid cells.","method":"CRISPR/Cas9 regulatory region deletion, RT-qPCR, Western blot, intracellular Ca2+ measurement in K562 cells, SNP association analysis","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — CRISPR functional deletion with molecular and functional readouts; 20 citations","pmids":["35563239"],"is_preprint":false},{"year":2022,"finding":"Multiple myeloma-derived exosomal miR-4261 is transferred into red blood cells and downregulates ATP2B4 expression by directly targeting its mRNA (confirmed by dual-luciferase assay), reducing PMCA4 protein levels and causing calcium overload in RBCs.","method":"Transwell exosome transfer assay, dual-luciferase reporter assay, flow cytometry, Western blot, atomic absorption spectroscopy for Ca2+","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct target validation by luciferase assay plus functional Ca2+ readout; single lab; 6 citations","pmids":["36091107"],"is_preprint":false},{"year":2023,"finding":"RBCs from homozygous carriers of the minor ATP2B4 haplotype (rs1541252 C/C) show significantly reduced PMCA4b protein surface expression and markedly slower rates of Ca2+ expulsion (calcium t½ = 4.7 min vs 1.9 min for wildtype). P. falciparum growth (both laboratory strain and field isolates) is decreased in RBCs from homozygotes, and PMCA4b inhibition with aurintricarboxylic acid (IC50=122 µM) also inhibits parasite growth, supporting Ca2+ channel blockade as the protective mechanism.","method":"Recall-by-genotype study design, flow cytometry (PMCA4b surface expression), Ca2+ expulsion kinetics, in vitro P. falciparum growth assays with field isolates, pharmacological PMCA4b inhibition","journal":"Malaria journal","confidence":"Medium","confidence_rationale":"Tier 2 — human genetics linked to direct functional Ca2+ and parasite growth assays; single study; 4 citations","pmids":["36604655"],"is_preprint":false},{"year":2024,"finding":"ATP2B4 (encoding PMCA4) is an essential gene for EGF-induced macropinocytosis in A431 cells. ATP2B4 knockout inhibits ruffle closure and macropinosome formation without affecting ruffle formation. PMCA4 Ca2+ pump activity itself (independent of C-terminal PDZ-binding interactions) is required, as it regulates EGF-stimulated Ca2+ oscillations during macropinocytosis. Both intracellular and extracellular Ca2+ are required for this process.","method":"CRISPR/Cas9 ATP2B4 knockout, fluid-phase uptake assays, live-cell imaging of ruffle formation and closure, Ca2+ oscillation measurement, expression of PMCA4 mutant lacking PDZ-binding motif","journal":"Genes to cells","confidence":"Medium","confidence_rationale":"Tier 2 — KO plus mechanistic rescue with pump-activity mutant; 3 citations","pmids":["38597132"],"is_preprint":false},{"year":2024,"finding":"GATA1 binds to the erythroid-specific ATP2B4 promoter in a sequence-specific manner. Using a native holdup (nHU) assay, the short isoform GATA1s (lacking N-terminal transactivation domain) binds this promoter with increased affinity relative to full-length GATA1, while the disease-associated R307C mutation reduces binding affinity. These binding differences translate into altered functional activity at the ATP2B4 erythroid promoter.","method":"Native holdup (nHU) assay for quantitative DNA-protein interaction analysis, luciferase reporter assay for functional validation","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 — novel assay in preprint; single lab; not yet peer-reviewed","pmids":[],"is_preprint":true},{"year":2025,"finding":"Pooled CRISPR screens in erythroid cells identified ATP2B4 as a regulator of red blood cell density, confirming its role in RBC biology as established by prior GWAS and functional studies.","method":"Pooled CRISPR perturbation screen with density gradient separation in erythroid cell line","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 — CRISPR screen in preprint; ATP2B4 confirmed but not mechanistically elaborated beyond known Ca2+ role","pmids":[],"is_preprint":true},{"year":2025,"finding":"In C6 glioma cells, PMCA4 localizes to lipid raft microdomains and interacts with GAT3 (GABA transporter 3). Knockdown of PMCA4 increases resting Ca2+ and Ca2+ accumulation in lipid rafts following GABA stimulation, impairing glioma cell migration and invasion. Long-term GABA stimulation disrupts the PMCA4/GAT3 complex and overloads lipid rafts with Ca2+. PMCA4 interacts with calmodulin (a key PMCA4 regulator) and participates in GAT3/CaMKII-dependent CREB phosphorylation at Ser133 required for glioma invasiveness.","method":"siRNA knockdown, lipid raft fractionation, Ca2+ imaging, migration and invasion assays, Co-IP, CREB phosphorylation analysis","journal":"Cell calcium","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple methods with mechanistic pathway placement; single lab; 0 citations (very recent)","pmids":["40580687"],"is_preprint":false},{"year":2026,"finding":"FOXM1 inhibitor RCM-1 downregulates ATP2B4 expression in rhabdomyosarcoma (RMS) cells. ATP2B4 knockdown decreases RMS cell proliferation, migration, and colony formation, increases apoptosis, and reduces tumor growth in animal models. ATP2B4 overexpression decreases apoptosis. RCM-1 combined with venetoclax (Bcl-2 inhibitor) uniquely decreases ATP2B4 expression and sensitizes RMS cells to apoptosis.","method":"siRNA knockdown, overexpression, in vivo tumor growth assay, RNA-sequencing, apoptosis assays, colony formation, migration assays","journal":"International journal of oncology","confidence":"Medium","confidence_rationale":"Tier 2-3 — loss-of-function and gain-of-function with in vivo validation; mechanistic link to FOXM1-ATP2B4 axis; 0 citations","pmids":["41789627"],"is_preprint":false},{"year":2026,"finding":"Sodium pentachlorophenol (PCP-Na) reduces ATP2B4 protein expression in mouse testes, preventing normal Ca2+ efflux, causing intracellular Ca2+ accumulation and Ca2+ overload. This Ca2+ overload drives oxidative stress (ROS increase) and inflammation, and is correlated with reduced testosterone levels. siRNA knockdown of ATP2B4 in vitro recapitulates the Ca2+ accumulation, confirming ATP2B4 as the upstream key protein in this signaling axis.","method":"ATP2B4 siRNA transfection in vitro, NAC and BAPTA-AM inhibitor treatment, Ca2+ measurement, ROS assay, testosterone assay, Western blot","journal":"Pesticide biochemistry and physiology","confidence":"Low","confidence_rationale":"Tier 3 — siRNA knockdown with functional readout; limited mechanistic depth; 0 citations","pmids":["41831900"],"is_preprint":false},{"year":2026,"finding":"In multiple myeloma, miR-4261 targets and downregulates YWHAE (14-3-3ε), CAST (calpastatin), and GPX1, which are regulators of PMCA4 function in erythrocytes. Downregulation of these three proteins impairs PMCA4 function, leading to Ca2+ overload and oxidative stress in RBCs. Dual-luciferase assays confirmed direct miR-4261 binding to YWHAE, CAST, and GPX1 mRNAs.","method":"Dual-luciferase reporter assays, qRT-PCR, Western blot, ROS/H2O2/GSH measurement, atomic absorption spectroscopy for Ca2+, targeted drug (calpain-1 and PMCA4 inhibitors) treatment","journal":"Indian journal of pathology & microbiology","confidence":"Low","confidence_rationale":"Tier 3 — indirect regulation of PMCA4 via three intermediate proteins; 0 citations","pmids":["41983776"],"is_preprint":false}],"current_model":"ATP2B4 encodes PMCA4, a ubiquitously expressed plasma membrane Ca2+-ATPase that extrudes Ca2+ from the cytosol; it is alternatively spliced at two regulatory sites to generate isoforms (PMCA4a/b) with distinct calmodulin-sensitivity and tissue distributions. PMCA4 is essential for sperm hyperactivated motility and male fertility, acts as a structural scaffold for nNOS in cardiac and sperm membrane microdomains to regulate nitric oxide signaling and cyclic nucleotide compartmentalization, interacts via its C-terminal PDZ-binding domain with MAGUK family proteins (SAP97, PSD95, SAP102) for membrane targeting, controls RBC hydration and Ca2+ homeostasis via an erythroid-specific enhancer, promotes G1 cell cycle progression in vascular smooth muscle cells through Ca2+ efflux activity, regulates TNF-induced cell death via lysosomal exocytosis, inhibits EMT in gastric cancer via the NFATc1-ZEB1 pathway, and is required for EGF-induced macropinocytosis through Ca2+ oscillation regulation."},"narrative":{"teleology":[{"year":1988,"claim":"Identification of the calmodulin-binding domain of the erythrocyte Ca²⁺ pump established the structural basis for calmodulin-dependent activation of PMCA, answering how pump activity is allosterically regulated.","evidence":"Chymotrypsin proteolysis and calmodulin photoaffinity cross-linking of purified human erythrocyte PMCA, with peptide sequencing","pmids":["2963820"],"confidence":"High","gaps":["Full three-dimensional structure of calmodulin–PMCA complex not resolved","Isoform-specific calmodulin affinity differences not yet addressed"]},{"year":1992,"claim":"Cloning of PMCA4 as a distinct isoform and discovery of alternative splicing at the C-terminal regulatory domain (generating PMCA4a and PMCA4b) resolved how a single gene produces functionally distinct pump variants with different calmodulin sensitivities and tissue distributions.","evidence":"Molecular cloning, peptide sequencing of erythrocyte Ca²⁺-ATPase revealing two isoforms (PMCA1/PMCA4); PCR-based cDNA characterization and genomic sequencing showing splice site C usage across tissues","pmids":["2137451","1531651","8245032"],"confidence":"High","gaps":["Functional consequences of splice variants not yet tested in cellular Ca²⁺ clearance assays","Regulation of splice-site choice unknown"]},{"year":2001,"claim":"Discovery that PMCA4b's C-terminal PDZ-binding motif interacts with MAGUK scaffolds (SAP97, PSD95, SAP102) and directs basolateral membrane targeting in polarized cells established how PMCA4 is positioned in specific membrane microdomains.","evidence":"Yeast two-hybrid screen, co-immunoprecipitation, confocal imaging in polarized MDCK cells","pmids":["11274188"],"confidence":"High","gaps":["Whether PDZ-mediated targeting is required for PMCA4 physiological function in vivo not tested","Identity of all relevant PDZ partners in different tissues incomplete"]},{"year":2001,"claim":"Loss-of-function mutagenesis revealed PMCA4 is required for TNF-induced cell death by maintaining low cytosolic Ca²⁺ that prevents premature lysosomal exocytosis, uncovering a role for PMCA4 in regulated cell death beyond simple Ca²⁺ homeostasis.","evidence":"Retroviral insertion mutagenesis in L929 cells with lysosome exocytosis assays and Ca²⁺ measurement; phenotypic rescue by restoring vacuolar acidic compartment volume","pmids":["11713265"],"confidence":"High","gaps":["Generalizability to other cell types and death receptor pathways not established","Whether PMCA4 pump activity or scaffold function is the key determinant unclear"]},{"year":2004,"claim":"Pmca4-knockout mice revealed PMCA4 is essential for sperm hyperactivated motility and male fertility but dispensable for spermatogenesis, establishing the first organism-level physiological role for PMCA4.","evidence":"Gene-targeted knockout mice; sperm motility assays, immunohistochemistry showing PMCA4 in sperm principal piece, ultrastructural Ca²⁺ overload evidence","pmids":["15178683"],"confidence":"High","gaps":["Molecular mechanism linking Ca²⁺ overload to motility failure not fully dissected","Contribution of individual splice variants (4a vs 4b) to sperm function not resolved"]},{"year":2008,"claim":"Discovery that PMCA4b scaffolds nNOS within a cardiac SNTA1–SCN5A complex, and that disruption of this interaction causes unrestrained nNOS activity leading to long QT syndrome, revealed PMCA4's scaffold function as distinct from its pump activity.","evidence":"GST pull-down, co-immunoprecipitation, patch-clamp electrophysiology in heterologous cells and cardiomyocytes; disease-associated SNTA1 A390V mutation disrupting PMCA4b binding","pmids":["18591664"],"confidence":"High","gaps":["Direct structural interface between PMCA4b and nNOS not resolved","Whether PMCA4 pump activity also contributes to cardiac nNOS regulation not separated from scaffold role"]},{"year":2011,"claim":"In vivo cardiac studies in Pmca4-knockout mice demonstrated that PMCA4 controls contractility not through beat-to-beat Ca²⁺ transport but by scaffolding nNOS to maintain compartmentalized cGMP/cAMP signaling, resolving a long-standing question about PMCA4's cardiac function.","evidence":"PMCA4 KO mice with in vivo contractility, FRET-based cAMP/cGMP sensors, nNOS localization assays, L-type Ca²⁺ channel recordings, RyR phosphorylation analysis","pmids":["21965681"],"confidence":"High","gaps":["Whether PMCA4 scaffold function similarly dominates in non-cardiac tissues not established","Structural basis for nNOS anchoring to PMCA4 remains unresolved"]},{"year":2014,"claim":"Rescue experiments in Pmca4-KO vascular smooth muscle cells showed that Ca²⁺ efflux activity (not PDZ-binding) is required for G1 cell-cycle progression, with PMCA4a and PMCA4b converging on cyclin D1 upregulation through distinct intermediates, demonstrating splice-variant-specific signaling downstream of Ca²⁺ clearance.","evidence":"PMCA4 KO primary VSMCs, [³H]thymidine incorporation, flow cytometry, rescue with WT, splice variant, and pump-dead mutant constructs, microarray","pmids":["24448801"],"confidence":"High","gaps":["In vivo relevance to vascular remodeling not confirmed","How reduced Ca²⁺ leads to different transcriptional responses depending on splice variant is unclear"]},{"year":2017,"claim":"PMCA4 was shown to form a quaternary complex with eNOS, nNOS, and Caveolin-1 in sperm, with Pmca4-KO leading to elevated NOS activity and peroxynitrite-driven germ cell apoptosis—unifying the Ca²⁺ clearance and NO-scaffolding functions in the context of male fertility.","evidence":"Reciprocal co-immunoprecipitation, FRET in sperm, NOS activity and peroxynitrite measurement in Pmca4⁻/⁻ mice","pmids":["28247940"],"confidence":"High","gaps":["Whether pharmacological NOS inhibition can rescue Pmca4-KO infertility not tested","Stoichiometry and structural arrangement of the quaternary complex unknown"]},{"year":2017,"claim":"CRISPR deletion of an erythroid-specific enhancer and analysis of Atp2b4-KO mice established that ATP2B4 is the causal gene at a malaria GWAS locus, controlling RBC Ca²⁺ homeostasis and hydration (MCHC), with reduced PMCA4b surface expression slowing Ca²⁺ clearance and impairing P. falciparum growth.","evidence":"eQTL mapping, CRISPR enhancer deletion in erythroid cells, Atp2b4-KO mice (MCHC phenotype), recall-by-genotype functional Ca²⁺ assays, in vitro parasite growth with field isolates and pharmacological PMCA4b inhibition","pmids":["28714864","28216081","36604655"],"confidence":"High","gaps":["Precise mechanism by which altered RBC Ca²⁺ impairs parasite development unknown","Whether other RBC membrane properties beyond Ca²⁺/hydration contribute to protection not resolved"]},{"year":2020,"claim":"Multiple studies extended PMCA4's role to cancer cell biology: PMCA4 inhibits EMT via the NFATc1–ZEB1 axis in gastric cancer, supports migration and apoptotic resistance in pancreatic cancer, and its downregulation by PDGF-BB/MEK/ERK drives proliferation of pulmonary arterial smooth muscle cells, establishing PMCA4 as a context-dependent modulator of proliferation, migration, and cell death.","evidence":"siRNA/overexpression with in vivo xenograft (gastric cancer), PMCA4 knockdown in MIA PaCa-2 cells (pancreatic cancer), PDGF-BB stimulation with MEK/ERK inhibitors and in vivo PAH rat models","pmids":["32860837","31963119","32966125"],"confidence":"Medium","gaps":["Cancer phenotypes studied in single cell lines each; generalizability uncertain","Whether PMCA4's scaffold vs. pump function drives these cancer phenotypes not distinguished","Patient-level clinical significance of PMCA4 expression changes not established"]},{"year":2024,"claim":"CRISPR knockout demonstrated ATP2B4 is required for EGF-induced macropinocytosis via its Ca²⁺ pump activity (not PDZ interactions), regulating ruffle closure through Ca²⁺ oscillations—revealing a new cellular process dependent on PMCA4.","evidence":"CRISPR/Cas9 ATP2B4 KO in A431 cells, live-cell imaging of ruffles, Ca²⁺ oscillation measurement, rescue with PDZ-binding-domain mutant","pmids":["38597132"],"confidence":"Medium","gaps":["Whether this function generalizes beyond EGF-stimulated A431 cells is untested","Downstream effectors linking Ca²⁺ oscillations to ruffle closure not identified"]},{"year":null,"claim":"Key unresolved questions include the high-resolution structure of PMCA4 with its regulatory and scaffolding domains, how pump vs. scaffold functions are differentially deployed across tissues, and whether PMCA4 variants or inhibitors can be therapeutically exploited for malaria protection, cancer, or cardiovascular disease.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of full-length PMCA4 available","Relative contribution of pump vs. scaffold function not systematically dissected across physiological contexts","No clinical trials targeting PMCA4"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[0,1,7,11,12,13,18,27]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[8,11,17]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,7,10,11,12,17,26,30]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,11,13,20,22]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[13]},{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[7,9,17]},{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[11]}],"complexes":["SNTA1-nNOS-SCN5A complex","Caveolin-1-eNOS-nNOS complex (sperm)"],"partners":["NOS1","NOS3","SNTA1","CAV1","DLG1","DLG4","BSG","SLC6A11"],"other_free_text":[]},"mechanistic_narrative":"ATP2B4 encodes PMCA4, a ubiquitously expressed P-type Ca²⁺-ATPase that extrudes cytosolic Ca²⁺ across the plasma membrane and is regulated by calmodulin binding to a C-terminal domain subject to alternative splicing (PMCA4a/4b variants with distinct calmodulin sensitivity and tissue distributions) [PMID:2963820, PMID:1531651, PMID:8245032]. Beyond its ion-transport function, PMCA4 acts as a structural scaffold that anchors nNOS in membrane microdomains to compartmentalize NO/cGMP/cAMP signaling in cardiomyocytes and sperm, thereby regulating cardiac contractility and sperm hyperactivated motility; accordingly, Pmca4-knockout mice are male-infertile and exhibit enhanced cardiac contractility with delocalized nNOS [PMID:15178683, PMID:21965681, PMID:28247940]. PMCA4 controls red blood cell hydration through an erythroid-specific enhancer whose common variants reduce PMCA4b surface expression, slow Ca²⁺ clearance, and confer protection against P. falciparum malaria [PMID:28714864, PMID:36604655]. In proliferating cells, PMCA4 Ca²⁺ efflux activity promotes G1-phase progression in vascular smooth muscle via cyclin D1/NFAT signaling, inhibits epithelial–mesenchymal transition in gastric cancer through the NFATc1–ZEB1 axis, and is required for EGF-induced macropinocytosis through regulation of Ca²⁺ oscillations [PMID:24448801, PMID:32860837, PMID:38597132]."},"prefetch_data":{"uniprot":{"accession":"P23634","full_name":"Plasma membrane calcium-transporting ATPase 4","aliases":["Matrix-remodeling-associated protein 1","Plasma membrane calcium ATPase isoform 4","Plasma membrane calcium pump isoform 4"],"length_aa":1241,"mass_kda":137.9,"function":"Calcium/calmodulin-regulated and magnesium-dependent enzyme that catalyzes the hydrolysis of ATP coupled with the transport of calcium out of the cell (PubMed:8530416). By regulating sperm cell calcium homeostasis, may play a role in sperm motility (By similarity)","subcellular_location":"Cell membrane; Cell projection, cilium, flagellum membrane","url":"https://www.uniprot.org/uniprotkb/P23634/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ATP2B4","classification":"Not Classified","n_dependent_lines":39,"n_total_lines":1208,"dependency_fraction":0.03228476821192053},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CALM1","stoichiometry":0.2},{"gene":"CALM2","stoichiometry":0.2},{"gene":"CALM3","stoichiometry":0.2},{"gene":"XPO6","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/ATP2B4","total_profiled":1310},"omim":[{"mim_id":"611162","title":"MALARIA, SUSCEPTIBILITY TO","url":"https://www.omim.org/entry/611162"},{"mim_id":"601017","title":"SYNTROPHIN, ALPHA-1; SNTA1","url":"https://www.omim.org/entry/601017"},{"mim_id":"300014","title":"ATPase, Ca(2+)-TRANSPORTING, PLASMA MEMBRANE, 3; ATP2B3","url":"https://www.omim.org/entry/300014"},{"mim_id":"108733","title":"ATPase, Ca(2+)-TRANSPORTING, PLASMA MEMBRANE, 2; ATP2B2","url":"https://www.omim.org/entry/108733"},{"mim_id":"108732","title":"ATPase, Ca(2+)-TRANSPORTING, PLASMA MEMBRANE, 4; ATP2B4","url":"https://www.omim.org/entry/108732"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Primary cilium","reliability":"Supported"},{"location":"Mitochondria","reliability":"Additional"},{"location":"Basal body","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"smooth 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PMCA4-null male mice are infertile with Ca2+ overload (mitochondrial condensation) in sperm tails despite normal spermatogenesis and mating behavior.\",\n      \"method\": \"Knockout mouse (Pmca4-/- null mutation), immunoblotting, immunohistochemistry, sperm motility analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype, replicated localization by IHC/immunoblot, multiple orthogonal methods\",\n      \"pmids\": [\"15178683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PMCA1 (ATP2B1) has an essential housekeeping/developmental function, as homozygous loss causes embryolethality, whereas PMCA4 (ATP2B4) loss is not embryolethal, demonstrating distinct in vivo functional roles for the two isoforms.\",\n      \"method\": \"Knockout mouse (Atp2b1 and Atp2b4 null mutations), embryonic viability assessment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined lethal vs. viable phenotype, direct genetic epistasis\",\n      \"pmids\": [\"15178683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PMCA4 (ATP2B4) is required for TNF-induced cell death in L929 cells; PMCA4-deficient cells exhibit abnormally elevated intracellular Ca2+, which promotes lysosome exocytosis and inhibits TNF-induced increase in acidic compartment volume (VAC), conferring resistance to TNF-induced death.\",\n      \"method\": \"Retrovirus insertion-mediated mutagenesis, intracellular Ca2+ measurement, lysosome exocytosis assays, pharmacological rescue\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with defined cellular phenotype and mechanistic pathway placement using multiple orthogonal methods\",\n      \"pmids\": [\"11713265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PMCA4 (ATP2B4) acts as a structural scaffold that tethers neuronal nitric oxide synthase (nNOS) to a subsarcolemmal microdomain in cardiomyocytes; loss of PMCA4 delocalizes >36% of membrane-associated nNOS to the cytosol, reduces microdomain cGMP, elevates local cAMP via decreased PDE2 activity, increases L-type Ca2+ channel activity and ryanodine receptor phosphorylation, and increases cardiac contractility in vivo.\",\n      \"method\": \"PMCA4 knockout mice, FRET-based cAMP/cGMP sensors, nNOS activity assay, L-type Ca2+ channel recordings, ryanodine receptor phosphorylation, in vivo contractility measurement\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods in single study with in vivo validation and FRET-based sensor readouts\",\n      \"pmids\": [\"21965681\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ATP2B4 is the main calcium ATPase of red blood cells; Atp2b4-/- mice exhibit increased mean corpuscular hemoglobin concentration (MCHC), and CRISPR-Cas9 deletion of an erythroid-specific enhancer of ATP2B4 causes abnormally high intracellular Ca2+ levels in erythroid cells, confirming ATP2B4 as the causal gene at a GWAS locus for MCHC and malaria susceptibility.\",\n      \"method\": \"Atp2b4 knockout mouse, CRISPR-Cas9 enhancer deletion, eQTL mapping in erythroblasts, intracellular Ca2+ measurement\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — CRISPR functional genomics plus KO mouse with orthogonal phenotypic readouts\",\n      \"pmids\": [\"28714864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"ATP2B4 primary transcripts are alternatively spliced at the region encoding the regulatory/calmodulin-binding domain, generating at least PMCA4a and PMCA4b isoforms with distinct tissue distributions; PMCA4b contains an extra exon that shifts the reading frame, removing a large portion of the C-terminal regulatory domain.\",\n      \"method\": \"PCR amplification of cDNA, Southern blotting, genomic sequencing of intron-exon boundaries, cDNA characterization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct sequencing and genomic structural characterization with functional domain implications\",\n      \"pmids\": [\"1531651\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PMCA4 (ATP2B4) forms a quaternary complex with eNOS, nNOS, and Caveolin1 in sperm; PMCA4 negatively regulates NOS activity in a Ca2+-dependent manner. In Pmca4-/- sperm, NOS activity is elevated 2-fold, peroxynitrite levels are doubled, and apoptotic germ cells are increased, establishing PMCA4 as a coordinator of Ca2+ and NO signaling for sperm motility.\",\n      \"method\": \"Co-immunoprecipitation, FRET (efficiency measurements <10 nm), NOS activity assay, peroxynitrite measurement, Pmca4-/- mouse\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus FRET plus KO mouse with defined biochemical phenotype\",\n      \"pmids\": [\"28247940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Ca2+ efflux activity of PMCA4 (ATP2B4) is required for G1-phase progression in vascular smooth muscle cells (VSMCs); PMCA4-KO VSMCs show impaired [3H]thymidine incorporation and G1 arrest, reversed by PMCA4a or PMCA4b but not by a mutant with only 10% normal Ca2+ efflux activity. PMCA4a and PMCA4b differentially regulate downstream mediators (AP-2β vs. p15/Cyclin D1/NFATc3).\",\n      \"method\": \"PMCA4 knockout mouse-derived VSMCs, [3H]thymidine incorporation, electroporation of expression constructs, microarray, Western blot, laser capture microdissection\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cell-cycle phenotype, rescue by WT vs. mutant constructs, multiple orthogonal approaches\",\n      \"pmids\": [\"24448801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CD147 interacts with PMCA4 (ATP2B4) via its transmembrane domain and Ig-like domain II; this interaction is required for CD147-dependent inhibition of IL-2 expression in T cells via a calcium-independent mechanism. PMCA4 silencing does not affect TCR proximal signaling but is essential for CD147-mediated immunosuppression.\",\n      \"method\": \"CD147 silencing in human T cells, affinity purification combined with mass spectrometry, domain-specific interaction mapping, IL-2 measurement\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MS-identified interaction with functional siRNA validation, single lab\",\n      \"pmids\": [\"26729804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The R268Q missense mutation in PMCA4 (ATP2B4), associated with familial spastic paraplegia, causes delayed intracellular Ca2+ extrusion; cells overexpressing R268Q mutant show significantly higher Ca2+ surge after KCl-induced depolarization and elevated steady-state cytosolic Ca2+ after SERCA inhibition compared to wild-type PMCA4-overexpressing cells.\",\n      \"method\": \"Fura-2 fluorescent Ca2+ imaging in SH-SY5Y neuroblastoma cells overexpressing WT or R268Q PMCA4, KCl depolarization, thapsigargin treatment\",\n      \"journal\": \"Brain and behavior\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct functional assay with mutagenesis in human neuronal cell line, single lab\",\n      \"pmids\": [\"25798335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"A PMCA4-GCaMP2 fusion protein correctly targets to the plasma membrane of cardiomyocytes, co-localizes with caveolin-3, and reports Ca2+ dynamics in the vicinity of the pump during electrical stimulation; active PMCA4-GCaMP2 shows higher signal amplitude and faster decay than a catalytically inactive mutant, and responds to β-adrenergic stimulation only when PMCA4 is active.\",\n      \"method\": \"Adenoviral expression, live-cell Ca2+ imaging (GCaMP2 fluorescence), immunofluorescence co-localization, pharmacological inhibition, electrical stimulation of neonatal and adult rat cardiomyocytes\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with functional consequence, active vs. inactive mutant comparison, single lab\",\n      \"pmids\": [\"23880607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PMCA4 (ATP2B4) splice variants switch during sperm maturation in bovine epididymis: PMCA4b predominates in testis and caput/corpus epididymidis, while PMCA4a (which has higher basal Ca2+ efflux activity and different calmodulin-binding mechanism) becomes the major isoform in cauda epididymidis and is transferred to sperm membranes there.\",\n      \"method\": \"Quantitative PCR, immunohistochemistry with isoform-specific antibody, Western blotting of testis/epididymis/sperm fractions\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with fractionation and isoform-specific antibodies, functional implication via known isoform properties\",\n      \"pmids\": [\"21187283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PMCA4 (ATP2B4) knockdown in MIA PaCa-2 pancreatic cancer cells reduces cytosolic Ca2+ clearance, impairs cell migration, and sensitizes cells to apoptosis, without affecting cell growth or major metabolic parameters.\",\n      \"method\": \"siRNA knockdown, Ca2+ clearance assay, migration assay, apoptosis assay, Seahorse XF metabolic analysis\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined cellular phenotypes and multiple orthogonal readouts, single lab\",\n      \"pmids\": [\"31963119\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PDGF-BB suppresses PMCA4 (ATP2B4) expression in pulmonary arterial smooth muscle cells via the MEK/ERK pathway; reduced PMCA4 impairs cytosolic Ca2+ clearance, promotes cell proliferation and migration via focal adhesion formation, and in vivo knockdown of PMCA4 increases right ventricular systolic pressure and pulmonary artery wall thickness in rats.\",\n      \"method\": \"PDGF-BB stimulation with MEK/ERK inhibitors, siRNA knockdown, Ca2+ imaging, cell proliferation/migration assays, focal adhesion analysis, in vivo rat model (monocrotaline/hypoxia-induced PAH), RVSP measurement\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway epistasis with inhibitors plus in vivo validation, single lab\",\n      \"pmids\": [\"32966125\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PMCA4 (ATP2B4) inhibition in gastric cancer cells promotes epithelial-mesenchymal transition (EMT) via increased nuclear accumulation of NFATc1 and upregulation of ZEB1; EMT induced by PMCA4 knockdown is prevented by knockdown of NFATc1 or ZEB1, or by cyclosporine A (calcineurin/NFAT inhibitor). PMCA4 overexpression reduces in vivo lung metastasis.\",\n      \"method\": \"siRNA knockdown, overexpression, NFATc1/ZEB1 knockdown epistasis, cyclosporine A treatment, in vivo metastasis assay in nude mice\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis between PMCA4, NFATc1, and ZEB1 with in vivo validation, single lab\",\n      \"pmids\": [\"32860837\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CRISPR/Cas9-mediated deletion of an ATP2B4 regulatory region (containing malaria-associated SNPs rs11240734, rs1541252–rs1541255) decreases ATP2B4 transcript and protein levels and increases intracellular Ca2+ concentration in K562 cells, demonstrating that this regulatory element functionally controls ATP2B4 expression and erythrocyte Ca2+ homeostasis.\",\n      \"method\": \"CRISPR/Cas9 deletion, RT-PCR, Western blot, intracellular Ca2+ measurement, luciferase reporter assays\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — CRISPR functional genomics with direct molecular readouts, single lab\",\n      \"pmids\": [\"35563239\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ATP2B4 (PMCA4) is required for EGF-induced macropinocytosis in A431 cells; ATP2B4-KO inhibits ruffle closure and macropinosome formation (without affecting ruffle formation) and reduces EGF-stimulated Ca2+ oscillations. This function depends on PMCA4's Ca2+ pump activity rather than PDZ domain-binding interactions with other proteins.\",\n      \"method\": \"ATP2B4 knockout (CRISPR), live-cell imaging, Ca2+ oscillation measurement, rescue with pump-active vs. PDZ-motif-deleted constructs\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype, mechanistic dissection with domain mutants, single lab\",\n      \"pmids\": [\"38597132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A minor haplotype in the predicted second promoter region of ATP2B4 (not in the coding sequence) is associated with significantly reduced PMCA4b protein expression in human erythrocytes and decreased Ca2+ extrusion capacity, without compensatory upregulation of other PMCA isoforms.\",\n      \"method\": \"Flow cytometry with specific antibody (quantitative), Western blot of RBC membranes, sequencing of ATP2B4 coding regions, haplotype analysis\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — quantitative protein measurement with functional Ca2+ extrusion assay in human RBCs, single lab\",\n      \"pmids\": [\"28216081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PMCA4 is present in both detergent-resistant membrane (DRM/lipid raft) and detergent-soluble fractions of bovine sperm; capacitation does not alter PMCA4 localization between fractions. PDC-109 (seminal vesicle major protein) enhances Ca2+-ATPase activity preferentially in detergent-soluble fractions, suggesting functional compartmentalization of PMCA4 in sperm membrane microdomains.\",\n      \"method\": \"Membrane fractionation (DRM vs. detergent-soluble), immunocytochemistry, Ca2+-ATPase activity assay, lipid overlay experiment\",\n      \"journal\": \"International journal of andrology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct fractionation with functional enzymatic assay, single lab\",\n      \"pmids\": [\"20050939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In C6 glioma cells, PMCA4 interacts with GAT3 within lipid raft microdomains to regulate compartmentalized Ca2+ dynamics; PMCA4 knockdown increases resting Ca2+ and Ca2+ accumulation in lipid rafts after GABA stimulation, impairing glioma cell migration and invasion. GAT3 also interacts with calmodulin (a PMCA4 regulator), and long-term GABA treatment disrupts the PMCA4/GAT3 complex, promoting Ca2+ overload in rafts and decreasing invasiveness via CaMKII-dependent CREB phosphorylation.\",\n      \"method\": \"PMCA4 knockdown, co-immunoprecipitation, Ca2+ imaging in lipid rafts, migration/invasion assays, CaMKII/CREB phosphorylation analysis\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP/pulldown with partial mechanistic follow-up, single lab\",\n      \"pmids\": [\"40580687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Exosomal miR-4261 from multiple myeloma cells is transferred to red blood cells and downregulates ATP2B4 expression (confirmed by dual-luciferase reporter assay), reducing PMCA4 protein levels and causing intracellular Ca2+ overload in RBCs.\",\n      \"method\": \"Dual-luciferase reporter assay (miR-4261 targeting ATP2B4 3'UTR), Western blot, flow cytometry, Transwell transfer assay, atomic absorption spectroscopy\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct luciferase validation of miRNA-target relationship plus functional Ca2+ readout, single lab\",\n      \"pmids\": [\"36091107\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ATP2B4 encodes PMCA4, a plasma membrane Ca2+-ATPase that extrudes Ca2+ from the cytosol; it is required for hyperactivated sperm motility and male fertility (localized to the sperm tail principal piece), acts as a structural scaffold anchoring nNOS to subsarcolemmal microdomains to regulate cardiac contractility via compartmentalized cGMP/cAMP signaling, controls Ca2+-dependent G1-phase cell cycle progression in vascular smooth muscle cells, mediates Ca2+-efflux-dependent macropinocytosis, regulates TNF-induced cell death via lysosome exocytosis, and serves as the primary Ca2+ efflux pump in erythrocytes whose expression level determines red blood cell hydration and malaria susceptibility.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries only from KEEP papers.\n\n**Classification:**\n- Papers about ATP2B4 (PMCA4): KEEP\n- Papers about ATP2B2 (PMCA2): EXCLUDE (alias collision - different gene)\n- Papers about ATP2B3 (PMCA3): EXCLUDE\n- Papers about general PMCA family without ATP2B4-specific findings: EXCLUDE/limited\n- lncRNA ATP2B2-IT2: EXCLUDE (alt-locus product)\n- General proteomics/interactome papers: EXCLUDE unless ATP2B4-specific finding\n\n**KEEP:** [1], [2] (has ATP2B4/PMCA4b splicing data), [3], [4], [5], [12] (general PMCA review with ATP2B4-specific splice info), [13] (general review), [14] (PMCA4 in familial spastic paraplegia), [15], [16], [17], [18], [19], [20], [21] (calmodulin binding domain - erythrocyte PMCA, relevant to PMCA4), [23] (GWAS identifying ATP2B4), [26] (erythrocyte PMCA isoforms - identifies PMCA4), [27], [28], [29] (PDZ domain interactions with PMCA4b), [30] (SAP interactions with PMCA4b - from gene2pubmed), [31], [32], [34], [35], [36], [39], [43], [44], [45] (gene fusion - limited mechanistic info), [52], [54], [55], [56], [57] (preprint - ATP2B4 in RBC density), [59] (preprint - GATA1 binding to ATP2B4 promoter), [60] (preprint - PMCA4b in malaria/artemisinin)\n\n**EXCLUDE:** [6],[7],[8],[9],[10],[11],[25],[30 (ATP2B2)],[33],[37],[40],[41],[42],[47] (ATP2B2), [48] (lncRNA ATP2B2-IT2), [49] (ATP2B2), [51] (ATP2B2), [53] (ATP2B2), [58] (ATP2B2 focused), [61] (Atp2b2 in proteomics), [62] (Atp2b2 hair cells)\n\nFrom gene2pubmed: [20] (SNTA1/nNOS/PMCA4b complex - KEEP), [21] (calmodulin binding domain - KEEP), [26] (erythrocyte PMCA isoforms - KEEP), [29] (PDZ interactions PMCA4b - KEEP), [30] (quantitative splicing - KEEP for PMCA4)\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1988,\n      \"finding\": \"Identification of the calmodulin-binding domain of the human erythrocyte Ca2+ pump (PMCA): chymotrypsin cleavage and photoaffinity cross-linking with calmodulin identified a ~12 kDa fragment containing the calmodulin-binding region, and its amino acid sequence was determined, establishing the structural basis for calmodulin-dependent activation of the pump.\",\n      \"method\": \"Chymotrypsin proteolysis, calmodulin photoaffinity cross-linking, reverse-phase HPLC peptide isolation, amino acid sequencing\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical reconstitution and sequencing; foundational paper with 227 citations\",\n      \"pmids\": [\"2963820\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"Peptide sequencing and molecular cloning of purified human erythrocyte Ca2+-ATPase revealed two distinct isoforms (PMCA1/hPMCA1 and a novel isoform hPMCA4) coexpressed in erythrocyte membranes, with sequence divergence in the extracellular loop between TM1-TM2, the negatively charged Ca2+-binding region, and the cAMP-dependent protein kinase phosphorylation site.\",\n      \"method\": \"Peptide sequence analysis, molecular cloning, Northern blot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct protein sequencing and cloning; highly cited foundational study\",\n      \"pmids\": [\"2137451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Alternative splicing of the PMCA4 (ATP2B4) primary transcript generates at least two major variants (PMCA4a and PMCA4b) at the C-terminal regulatory domain; PMCA4b contains an additional exon inserted immediately after the calmodulin-binding domain sequence that shifts the reading frame and truncates the C-terminal regulatory domain. Each splice variant has a distinct tissue distribution.\",\n      \"method\": \"PCR amplification of cDNA, Southern blotting, cDNA isolation and characterization, genomic sequencing\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cDNA isolation with genomic validation; replicated in multiple tissues; 109 citations\",\n      \"pmids\": [\"1531651\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Quantitative PCR analysis showed that PMCA4 (ATP2B4) mRNA is ubiquitously expressed in all tissues examined (cerebral cortex, skeletal and heart muscle, stomach, liver, lung, kidney), similar to PMCA1. Alternative splicing at site A (36-bp exon inclusion) and site C (178-bp exon exclusion) generates the major PMCA4 splice variants present across all tissues.\",\n      \"method\": \"Quantitative RT-PCR with GAPDH as internal standard, across seven human tissues\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — quantitative multi-tissue expression with internal standard; 141 citations\",\n      \"pmids\": [\"8245032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PMCA4b interacts with multiple members of the membrane-associated guanylate kinase (MAGUK) family via its C-terminal PDZ-binding domain: SAP90/PSD95, PSD93/chapsyn-110, SAP97, and SAP102 all bind the C-terminal tail of PMCA4b. Co-immunoprecipitation confirmed the PMCA4b–SAP102 interaction, and confocal microscopy showed PMCA4b and SAP97 colocalize exclusively in the basolateral membrane of polarized MDCK cells, demonstrating PDZ-domain-mediated targeting of PMCA4b to specific membrane microdomains.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, confocal immunofluorescence microscopy in polarized MDCK cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus localization; 143 citations; multiple orthogonal methods\",\n      \"pmids\": [\"11274188\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PMCA4 is required for TNF-induced cell death in L929 cells. PMCA4-deficient cells show abnormally elevated intracellular Ca2+ following TNF stimulation. The elevated Ca2+ promotes lysosome exocytosis, which inhibits the TNF-induced increase in vacuolar acidic compartment (VAC) volume, thereby conferring resistance to TNF-induced cell death. Restoration of lysosome exocytosis inhibition or increase in VAC volume reversed resistance in PMCA4-mutant cells.\",\n      \"method\": \"Retrovirus insertion mutagenesis, intracellular Ca2+ measurement, lysosome exocytosis assays, sucrose treatment to modulate VAC\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with mechanistic rescue experiments; 66 citations\",\n      \"pmids\": [\"11713265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PMCA isoforms 1 and 4 are expressed ubiquitously in adult tissues, while PMCA2 and 3 are primarily in excitable cells. Alternative splicing at the first intracellular loop and the C-terminal tail (calmodulin-binding domain) generates isoform diversity with functional consequences: the C-terminal region regulates calmodulin sensitivity, phosphorylation, and differential interaction with PDZ domain-containing proteins.\",\n      \"method\": \"Review of functional studies, including splice variant characterization and knockout phenotypes\",\n      \"journal\": \"Physiological reviews\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — synthesis of multiple independent experimental studies; 469 citations\",\n      \"pmids\": [\"11152753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Targeted knockout of Atp2b4 (PMCA4) in mice causes male infertility due to failure to achieve hyperactivated sperm motility, without affecting basal motility or spermatogenesis. PMCA4 is localized to the principal piece of the sperm tail (co-localizing with the CatSper Ca2+ channel), and its loss leads to mitochondrial condensation indicative of Ca2+ overload. PMCA4 knockout also impairs phasic contractions and causes apoptosis in portal vein smooth muscle in vitro (strain-dependent). Loss of PMCA1 (Atp2b1) causes embryolethality, establishing PMCA1 as an essential housekeeping gene and PMCA4 as specifically required for sperm hyperactivation.\",\n      \"method\": \"Gene targeting/knockout mice, sperm motility assays, immunoblotting, immunohistochemistry, ultrastructural analysis, in vitro smooth muscle contractility\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — KO with multiple orthogonal phenotypic readouts; 271 citations; foundational mechanistic paper\",\n      \"pmids\": [\"15178683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Alpha1-syntrophin (SNTA1) links PMCA4b (encoded by ATP2B4) to neuronal nitric oxide synthase (nNOS) and the cardiac sodium channel SCN5A in a macromolecular complex. A disease-associated A390V-SNTA1 mutation selectively disrupts PMCA4b binding to this complex, releasing nNOS inhibition and causing S-nitrosylation of SCN5A, increasing late sodium current and causing long QT syndrome. This identifies PMCA4b as a critical inhibitor of nNOS within a cardiac membrane signaling complex.\",\n      \"method\": \"GST pull-down, co-immunoprecipitation, heterologous cell expression, patch-clamp electrophysiology, cardiac myocyte expression\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — GST pull-down plus functional electrophysiology; 241 citations; multiple orthogonal methods\",\n      \"pmids\": [\"18591664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In bovine epididymis, a splice variant switch occurs during sperm maturation: PMCA4b is the major variant in testis and caput/corpus epididymidis, whereas PMCA4a becomes the dominant isoform in cauda epididymidis. PMCA4a has higher basal Ca2+ transport activity and is more effective than PMCA4b at returning Ca2+ to resting levels. Immunohistochemical and Western blot analyses show PMCA4a is transferred to sperm membranes in the cauda epididymidis, suggesting this isoform switch facilitates higher Ca2+ turnover needed for hyperactivated motility.\",\n      \"method\": \"Quantitative PCR, immunohistochemistry with novel anti-PMCA4a antibody, Western blotting of sperm from caput vs. cauda epididymidis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods in one lab; functional inference from known kinetic differences between splice variants\",\n      \"pmids\": [\"21187283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PMCA4 is localized in both detergent-resistant membrane (DRM/lipid raft) and detergent-soluble fractions of bovine sperm plasma membrane, and co-localizes with caveolin in the mid-piece. The seminal vesicle protein PDC-109 enhances Ca2+-ATPase activity preferentially in the detergent-soluble fractions of cauda sperm, suggesting functional compartmentalization of PMCA4 in sperm membrane microdomains.\",\n      \"method\": \"Sucrose density gradient fractionation (DRM isolation), immunocytochemistry, Ca2+-ATPase functional assays, lipid overlay experiments\",\n      \"journal\": \"International journal of andrology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — fractionation plus functional assay; single lab; compartmentalization linked to function\",\n      \"pmids\": [\"20050939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PMCA4 forms a signaling complex with neuronal nitric oxide synthase (nNOS) in the cardiac cell membrane and acts as a structural scaffold that maintains nNOS in a defined microdomain. In PMCA4-/- mice, >36% of membrane-associated nNOS is delocalized to cytosol without change in total nNOS, leading to decreased microdomain cGMP, decreased PDE2 activity, elevated local cAMP, increased L-type calcium channel activity and ryanodine receptor phosphorylation, and enhanced cardiac contractility. This demonstrates PMCA4 regulates cardiac contractility via compartmentalized cyclic nucleotide signaling rather than beat-to-beat Ca2+ transport.\",\n      \"method\": \"PMCA4 knockout mice, in vivo contractility measurements, Ca2+ amplitude measurements, nNOS localization/activity assays, FRET-based cAMP/cGMP sensors, L-type channel recordings, ryanodine receptor phosphorylation analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods in vivo and in vitro; 62 citations; strong mechanistic demonstration\",\n      \"pmids\": [\"21965681\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"A novel PMCA4-GCaMP2 fusion protein (Ca2+ sensor fused to N-terminus of PMCA4) correctly targets to the plasma membrane in cardiomyocytes, co-localizes with caveolin-3, and monitors subsarcolemmal Ca2+ dynamics in real time. The active pump generates higher signal amplitude and faster Ca2+ decay than an inactive mutant form. A novel small-molecule PMCA4-specific inhibitor was identified by library screening, which reduces Ca2+ clearance near the pump comparable to the inactive mutant, confirming PMCA4 Ca2+ transport activity at the cardiac membrane microdomain.\",\n      \"method\": \"Adenoviral expression, live-cell fluorescence imaging of Ca2+ sensor fusion protein, small molecule library screen, electrically stimulated neonatal and adult rat cardiomyocytes\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — fusion protein sensor with pharmacological validation; single lab; 21 citations\",\n      \"pmids\": [\"23880607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Ca2+ efflux activity of PMCA4 is required for G1 phase progression in vascular smooth muscle cells (VSMCs). PMCA4 knockout VSMCs show impaired [3H]thymidine incorporation and G1 arrest. Rescue with PMCA4a, PMCA4b, or a PMCA4b PDZ-binding mutant restores proliferation, but a mutant with only 10% of normal Ca2+ efflux activity cannot rescue. The PMCA4a and PMCA4b splice variants differentially regulate downstream mediators: PMCA4a rescue reduces AP-2β (anti-proliferative), while PMCA4b rescue reduces p15 (Cyclin D1/Cdk4 inhibitor), both converging on Cyclin D1/NFATc3 upregulation.\",\n      \"method\": \"PMCA4 knockout primary VSMCs, [3H]thymidine incorporation, flow cytometry (cell cycle), electroporation of expression constructs, microarray, Western blotting, laser capture microdissection\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — KO with mechanistic rescue using multiple mutants; 24 citations; multiple orthogonal methods\",\n      \"pmids\": [\"24448801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A novel missense mutation (c.803G>A, p.R268Q) in ATP2B4 (PMCA4) co-segregates with autosomal dominant familial spastic paraplegia in a Chinese family. Computational modeling predicts the R268Q mutation destabilizes PMCA4 protein structure, increases folding free energy, and is located in a protein aggregation-prone segment susceptible to misfolding.\",\n      \"method\": \"Whole-exome sequencing, Sanger sequencing, co-segregation analysis, computational protein stability modeling\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational prediction only; no in vitro functional assay in this paper\",\n      \"pmids\": [\"25119969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The R268Q mutation in PMCA4 (ATP2B4) causes delayed intracellular Ca2+ extrusion in human neuroblastoma cells. Overexpression of mutant R268Q PMCA4 in SH-SY5Y cells results in significantly higher peak Ca2+ surge after KCl-induced depolarization and persistently elevated steady-state cytosolic Ca2+ after SERCA inhibition with thapsigargin, compared to wild-type PMCA4, demonstrating a loss-of-function effect on Ca2+ clearance.\",\n      \"method\": \"Fura-2 fluorescence Ca2+ imaging with confocal microscopy in SH-SY5Y neuroblastoma cells overexpressing WT or R268Q PMCA4, KCl depolarization, thapsigargin treatment\",\n      \"journal\": \"Brain and behavior\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct functional assay with disease mutant in relevant cell type; single lab; 25 citations\",\n      \"pmids\": [\"25798335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PMCA4 interacts with CD147 (Ig superfamily member) via CD147's transmembrane domain and Ig-like domain II. This interaction is required for CD147-dependent inhibition of IL-2 expression in T cells via a calcium-independent mechanism. CD147 does not control PMCA4 membrane localization, but PMCA4 is essential for the immunosuppressive effect of CD147, bypassing TCR proximal signaling.\",\n      \"method\": \"Affinity purification combined with mass spectrometry, siRNA silencing, domain-mapping experiments, IL-2 reporter assays in human T cells\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — AP-MS identification with functional siRNA validation; single lab; 21 citations\",\n      \"pmids\": [\"26729804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PMCA4 coordinates Ca2+ and nitric oxide (NO) signaling in murine sperm to maintain motility. Co-immunoprecipitation and FRET demonstrate PMCA4 associates with eNOS and nNOS in sperm, forming a quaternary complex that also includes Caveolin-1. In Pmca4-/- sperm, NOS activity is elevated twofold, accompanied by a twofold increase in peroxynitrite and increased apoptotic germ cells, establishing PMCA4 as a negative regulator of NOS in sperm that coordinates Ca2+ clearance and NO production to maintain motility.\",\n      \"method\": \"Co-immunoprecipitation (Co-IP), FRET in capacitated and uncapacitated sperm, NOS activity assay, peroxynitrite measurement, apoptosis assay in Pmca4-/- mice\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus FRET plus KO functional readout; multiple orthogonal methods; 24 citations\",\n      \"pmids\": [\"28247940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"An erythroid-specific enhancer element in the ATP2B4 locus regulates PMCA4 expression in red blood cells. CRISPR-Cas9 deletion of this enhancer in erythroid cells causes abnormally high intracellular Ca2+ levels. Atp2b4-/- mice show increased mean corpuscular hemoglobin concentration (MCHC), confirming ATP2B4 as the causal gene at a malaria-susceptibility GWAS locus and demonstrating that ATP2B4 controls RBC hydration through Ca2+ regulation.\",\n      \"method\": \"eQTL mapping in erythroblasts, CRISPR-Cas9 enhancer deletion, Atp2b4 knockout mice, intracellular Ca2+ measurement, MCHC quantification\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — CRISPR functional validation plus KO mouse phenotype; multiple orthogonal approaches; 50 citations\",\n      \"pmids\": [\"28714864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Reduced PMCA4b protein expression in human red blood cells correlates with a minor haplotype in the predicted second promoter region of ATP2B4 (not coding mutations), and reduced PMCA4b levels result in lower Ca2+ extrusion capacity. This haplotype corresponds to GWAS SNPs linked to reduced mean corpuscular hemoglobin concentration and malaria protection.\",\n      \"method\": \"Flow cytometry with specific antibody binding (quantitative), Western blot of RBC membranes, Ca2+ extrusion assays, DNA sequencing of ATP2B4 coding and promoter regions\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional Ca2+ assay plus protein quantification; single lab; 27 citations\",\n      \"pmids\": [\"28216081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PMCA4 inhibits epithelial-mesenchymal transition (EMT) in gastric cancer cells via the NFATc1-ZEB1 pathway. PMCA4 knockdown increases nuclear NFATc1 accumulation and ZEB1 expression, suppresses E-cadherin/GRHL2/OVOL1, and promotes vimentin upregulation, increased migration/invasion, and drug resistance. These effects are prevented by knockdown of NFATc1 or ZEB1, or by cyclosporine A (calcineurin/NFAT inhibitor), placing PMCA4 upstream of the NFATc1-ZEB1 EMT axis.\",\n      \"method\": \"siRNA knockdown, overexpression, in vivo xenograft metastasis assay, Western blot, migration/invasion assays, cyclosporine A treatment\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — pathway epistasis via genetic and pharmacological intervention; in vivo validation; single lab; 15 citations\",\n      \"pmids\": [\"32860837\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PMCA4 expression in pancreatic ductal adenocarcinoma (PDAC) cells supports cytosolic Ca2+ clearance, cell migration, and apoptotic resistance. siRNA knockdown of PMCA4 in MIA PaCa-2 cells (which almost exclusively express PMCA4) reduces Ca2+ clearance rate, decreases cell migration, and sensitizes cells to apoptosis without affecting cell growth or metabolic parameters.\",\n      \"method\": \"siRNA knockdown, Ca2+ clearance assays, migration assays, apoptosis assays, Seahorse XF metabolic analysis, Western blot, RT-qPCR\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — loss-of-function with multiple cellular phenotype readouts; single lab; 17 citations\",\n      \"pmids\": [\"31963119\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PDGF-BB signaling downregulates PMCA4 expression in pulmonary arterial smooth muscle cells (PASMCs) via the MEK/ERK pathway. PMCA4 suppression attenuates Ca2+ clearance, promotes cell proliferation, and elevates cell locomotion through formation of focal adhesions. PMCA4 expression is also decreased in pulmonary arteries of monocrotaline- and hypoxia-induced PAH rats, and knockdown of PMCA4 in normal rats increases right ventricular systolic pressure and pulmonary artery wall thickness.\",\n      \"method\": \"PDGF-BB stimulation with MEK/ERK inhibitors, siRNA knockdown, Ca2+ clearance assays, proliferation assays, focal adhesion imaging, in vivo rat PAH models, hemodynamic measurements\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway identification with in vitro and in vivo validation; 10 citations\",\n      \"pmids\": [\"32966125\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PMCA4 (ATP2B4) is expressed in adrenal tissue (HAC15 cells) and contributes to membrane conductance. ATP2B4 knockdown in HAC15 cells reduced angiotensin II-stimulated responses in some clones. Whole-cell recordings confirmed robust endogenous ATP2B4 conductance, and overexpression of WT or variant ATP2B4 reduced conductance compared to endogenous levels.\",\n      \"method\": \"shRNA knockdown, doxycycline-inducible stable cell lines, whole-cell patch-clamp electrophysiology, aldosterone synthase (CYP11B2) expression assays\",\n      \"journal\": \"Hormones & cancer\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — limited mechanistic follow-up; variants did not alter CYP11B2; single lab; 9 citations\",\n      \"pmids\": [\"32002807\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CRISPR/Cas9-mediated deletion of a regulatory region containing five ATP2B4 SNPs (rs11240734, rs1541252, rs1541253, rs1541254, rs1541255) in K562 cells decreases ATP2B4 transcript and protein levels and increases intracellular Ca2+ concentration, demonstrating that this non-coding regulatory element controls PMCA4 expression and thereby Ca2+ homeostasis in erythroid cells.\",\n      \"method\": \"CRISPR/Cas9 regulatory region deletion, RT-qPCR, Western blot, intracellular Ca2+ measurement in K562 cells, SNP association analysis\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — CRISPR functional deletion with molecular and functional readouts; 20 citations\",\n      \"pmids\": [\"35563239\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Multiple myeloma-derived exosomal miR-4261 is transferred into red blood cells and downregulates ATP2B4 expression by directly targeting its mRNA (confirmed by dual-luciferase assay), reducing PMCA4 protein levels and causing calcium overload in RBCs.\",\n      \"method\": \"Transwell exosome transfer assay, dual-luciferase reporter assay, flow cytometry, Western blot, atomic absorption spectroscopy for Ca2+\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct target validation by luciferase assay plus functional Ca2+ readout; single lab; 6 citations\",\n      \"pmids\": [\"36091107\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"RBCs from homozygous carriers of the minor ATP2B4 haplotype (rs1541252 C/C) show significantly reduced PMCA4b protein surface expression and markedly slower rates of Ca2+ expulsion (calcium t½ = 4.7 min vs 1.9 min for wildtype). P. falciparum growth (both laboratory strain and field isolates) is decreased in RBCs from homozygotes, and PMCA4b inhibition with aurintricarboxylic acid (IC50=122 µM) also inhibits parasite growth, supporting Ca2+ channel blockade as the protective mechanism.\",\n      \"method\": \"Recall-by-genotype study design, flow cytometry (PMCA4b surface expression), Ca2+ expulsion kinetics, in vitro P. falciparum growth assays with field isolates, pharmacological PMCA4b inhibition\",\n      \"journal\": \"Malaria journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — human genetics linked to direct functional Ca2+ and parasite growth assays; single study; 4 citations\",\n      \"pmids\": [\"36604655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ATP2B4 (encoding PMCA4) is an essential gene for EGF-induced macropinocytosis in A431 cells. ATP2B4 knockout inhibits ruffle closure and macropinosome formation without affecting ruffle formation. PMCA4 Ca2+ pump activity itself (independent of C-terminal PDZ-binding interactions) is required, as it regulates EGF-stimulated Ca2+ oscillations during macropinocytosis. Both intracellular and extracellular Ca2+ are required for this process.\",\n      \"method\": \"CRISPR/Cas9 ATP2B4 knockout, fluid-phase uptake assays, live-cell imaging of ruffle formation and closure, Ca2+ oscillation measurement, expression of PMCA4 mutant lacking PDZ-binding motif\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO plus mechanistic rescue with pump-activity mutant; 3 citations\",\n      \"pmids\": [\"38597132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GATA1 binds to the erythroid-specific ATP2B4 promoter in a sequence-specific manner. Using a native holdup (nHU) assay, the short isoform GATA1s (lacking N-terminal transactivation domain) binds this promoter with increased affinity relative to full-length GATA1, while the disease-associated R307C mutation reduces binding affinity. These binding differences translate into altered functional activity at the ATP2B4 erythroid promoter.\",\n      \"method\": \"Native holdup (nHU) assay for quantitative DNA-protein interaction analysis, luciferase reporter assay for functional validation\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — novel assay in preprint; single lab; not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Pooled CRISPR screens in erythroid cells identified ATP2B4 as a regulator of red blood cell density, confirming its role in RBC biology as established by prior GWAS and functional studies.\",\n      \"method\": \"Pooled CRISPR perturbation screen with density gradient separation in erythroid cell line\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — CRISPR screen in preprint; ATP2B4 confirmed but not mechanistically elaborated beyond known Ca2+ role\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In C6 glioma cells, PMCA4 localizes to lipid raft microdomains and interacts with GAT3 (GABA transporter 3). Knockdown of PMCA4 increases resting Ca2+ and Ca2+ accumulation in lipid rafts following GABA stimulation, impairing glioma cell migration and invasion. Long-term GABA stimulation disrupts the PMCA4/GAT3 complex and overloads lipid rafts with Ca2+. PMCA4 interacts with calmodulin (a key PMCA4 regulator) and participates in GAT3/CaMKII-dependent CREB phosphorylation at Ser133 required for glioma invasiveness.\",\n      \"method\": \"siRNA knockdown, lipid raft fractionation, Ca2+ imaging, migration and invasion assays, Co-IP, CREB phosphorylation analysis\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple methods with mechanistic pathway placement; single lab; 0 citations (very recent)\",\n      \"pmids\": [\"40580687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"FOXM1 inhibitor RCM-1 downregulates ATP2B4 expression in rhabdomyosarcoma (RMS) cells. ATP2B4 knockdown decreases RMS cell proliferation, migration, and colony formation, increases apoptosis, and reduces tumor growth in animal models. ATP2B4 overexpression decreases apoptosis. RCM-1 combined with venetoclax (Bcl-2 inhibitor) uniquely decreases ATP2B4 expression and sensitizes RMS cells to apoptosis.\",\n      \"method\": \"siRNA knockdown, overexpression, in vivo tumor growth assay, RNA-sequencing, apoptosis assays, colony formation, migration assays\",\n      \"journal\": \"International journal of oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — loss-of-function and gain-of-function with in vivo validation; mechanistic link to FOXM1-ATP2B4 axis; 0 citations\",\n      \"pmids\": [\"41789627\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Sodium pentachlorophenol (PCP-Na) reduces ATP2B4 protein expression in mouse testes, preventing normal Ca2+ efflux, causing intracellular Ca2+ accumulation and Ca2+ overload. This Ca2+ overload drives oxidative stress (ROS increase) and inflammation, and is correlated with reduced testosterone levels. siRNA knockdown of ATP2B4 in vitro recapitulates the Ca2+ accumulation, confirming ATP2B4 as the upstream key protein in this signaling axis.\",\n      \"method\": \"ATP2B4 siRNA transfection in vitro, NAC and BAPTA-AM inhibitor treatment, Ca2+ measurement, ROS assay, testosterone assay, Western blot\",\n      \"journal\": \"Pesticide biochemistry and physiology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — siRNA knockdown with functional readout; limited mechanistic depth; 0 citations\",\n      \"pmids\": [\"41831900\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In multiple myeloma, miR-4261 targets and downregulates YWHAE (14-3-3ε), CAST (calpastatin), and GPX1, which are regulators of PMCA4 function in erythrocytes. Downregulation of these three proteins impairs PMCA4 function, leading to Ca2+ overload and oxidative stress in RBCs. Dual-luciferase assays confirmed direct miR-4261 binding to YWHAE, CAST, and GPX1 mRNAs.\",\n      \"method\": \"Dual-luciferase reporter assays, qRT-PCR, Western blot, ROS/H2O2/GSH measurement, atomic absorption spectroscopy for Ca2+, targeted drug (calpain-1 and PMCA4 inhibitors) treatment\",\n      \"journal\": \"Indian journal of pathology & microbiology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — indirect regulation of PMCA4 via three intermediate proteins; 0 citations\",\n      \"pmids\": [\"41983776\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ATP2B4 encodes PMCA4, a ubiquitously expressed plasma membrane Ca2+-ATPase that extrudes Ca2+ from the cytosol; it is alternatively spliced at two regulatory sites to generate isoforms (PMCA4a/b) with distinct calmodulin-sensitivity and tissue distributions. PMCA4 is essential for sperm hyperactivated motility and male fertility, acts as a structural scaffold for nNOS in cardiac and sperm membrane microdomains to regulate nitric oxide signaling and cyclic nucleotide compartmentalization, interacts via its C-terminal PDZ-binding domain with MAGUK family proteins (SAP97, PSD95, SAP102) for membrane targeting, controls RBC hydration and Ca2+ homeostasis via an erythroid-specific enhancer, promotes G1 cell cycle progression in vascular smooth muscle cells through Ca2+ efflux activity, regulates TNF-induced cell death via lysosomal exocytosis, inhibits EMT in gastric cancer via the NFATc1-ZEB1 pathway, and is required for EGF-induced macropinocytosis through Ca2+ oscillation regulation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ATP2B4 encodes PMCA4, a plasma membrane Ca²⁺-ATPase that extrudes cytosolic Ca²⁺ and functions both as an ion pump and as a signaling scaffold in diverse cell types. Alternative splicing generates PMCA4a and PMCA4b isoforms with distinct calmodulin-binding properties and tissue distributions, with isoform switching occurring during sperm maturation [PMID:1531651, PMID:21187283]. PMCA4 is required for hyperactivated sperm motility and male fertility, as knockout mice exhibit sperm Ca²⁺ overload and infertility despite normal spermatogenesis [PMID:15178683]; in cardiomyocytes it tethers nNOS to subsarcolemmal microdomains to regulate compartmentalized cGMP/cAMP signaling and contractility [PMID:21965681]; in erythrocytes it is the principal Ca²⁺ efflux pump controlling red blood cell hydration and malaria susceptibility [PMID:28714864, PMID:28216081]; and its Ca²⁺ pump activity drives G1-phase cell cycle progression in vascular smooth muscle cells, EGF-induced macropinocytosis, and TNF-induced cell death via lysosome exocytosis [PMID:24448801, PMID:38597132, PMID:11713265]. The R268Q missense mutation in ATP2B4 impairs Ca²⁺ extrusion and is associated with familial spastic paraplegia [PMID:25798335].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Establishing that ATP2B4 transcripts are alternatively spliced at the calmodulin-binding/regulatory domain revealed that a single gene produces functionally distinct PMCA4a and PMCA4b isoforms with different tissue distributions, setting the framework for understanding isoform-specific roles.\",\n      \"evidence\": \"PCR amplification of cDNA, Southern blotting, and genomic sequencing of intron-exon boundaries in human tissues\",\n      \"pmids\": [\"1531651\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequences of each splice variant on Ca²⁺ transport kinetics were not directly measured\", \"Regulatory mechanisms controlling splice-site selection were not addressed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstrating that PMCA4 loss renders cells resistant to TNF-induced death by causing Ca²⁺ overload and aberrant lysosome exocytosis established PMCA4 as a regulator of programmed cell death through intracellular Ca²⁺ homeostasis.\",\n      \"evidence\": \"Retrovirus insertion mutagenesis in L929 cells with intracellular Ca²⁺ measurement, lysosome exocytosis assays, and pharmacological rescue\",\n      \"pmids\": [\"11713265\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this TNF-death pathway operates in primary cells or in vivo was not tested\", \"The mechanism linking lysosome exocytosis to death resistance was not fully resolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Generation of Pmca4-null mice established that PMCA4 is dispensable for embryonic development but essential for male fertility, localizing the critical function to Ca²⁺ extrusion in the sperm tail principal piece where CatSper channels operate.\",\n      \"evidence\": \"Knockout mouse with immunohistochemistry, immunoblotting, and sperm motility analysis; comparison with embryolethal Atp2b1 knockouts\",\n      \"pmids\": [\"15178683\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PMCA4 directly interacts with CatSper or merely counterbalances its Ca²⁺ influx was unknown\", \"Contribution of specific PMCA4 splice variants to fertility was not dissected\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Documenting a PMCA4b-to-PMCA4a isoform switch during epididymal sperm maturation, with PMCA4a having higher basal Ca²⁺ efflux, explained how sperm acquire the Ca²⁺ handling capacity needed for hyperactivated motility.\",\n      \"evidence\": \"Quantitative PCR, isoform-specific antibody immunohistochemistry, and Western blotting across bovine testis/epididymis/sperm fractions\",\n      \"pmids\": [\"21187283\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether isoform switching is conserved in human sperm was not confirmed\", \"Mechanism driving the splice switch during epididymal transit was not identified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showing that PMCA4 scaffolds nNOS to subsarcolemmal microdomains in cardiomyocytes, controlling local cGMP/cAMP balance and thereby L-type Ca²⁺ channel activity and contractility, revealed a pump-independent signaling function for PMCA4.\",\n      \"evidence\": \"PMCA4 knockout mice with FRET-based cAMP/cGMP sensors, nNOS activity assays, L-type Ca²⁺ channel recordings, and in vivo contractility measurement\",\n      \"pmids\": [\"21965681\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the PMCA4–nNOS interaction was not resolved\", \"Whether the scaffolding and pumping functions are separable in vivo was not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A PMCA4-GCaMP2 biosensor demonstrated that PMCA4 reports and shapes Ca²⁺ dynamics in its immediate plasma membrane vicinity in cardiomyocytes, responding to β-adrenergic stimulation in a pump-activity-dependent manner.\",\n      \"evidence\": \"Adenoviral expression of active vs. catalytically inactive PMCA4-GCaMP2 fusions in neonatal and adult rat cardiomyocytes with live-cell imaging\",\n      \"pmids\": [\"23880607\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PMCA4 microdomain Ca²⁺ signals feed back to nNOS signaling was not directly tested\", \"Endogenous PMCA4 was overridden by construct overexpression\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Establishing that PMCA4 Ca²⁺ efflux activity is required for G1-phase progression in vascular smooth muscle cells, with PMCA4a and PMCA4b controlling distinct downstream mediators, demonstrated isoform-specific roles in cell proliferation.\",\n      \"evidence\": \"PMCA4 knockout mouse-derived VSMCs with [³H]thymidine incorporation, rescue by WT vs. pump-dead mutants, and microarray profiling\",\n      \"pmids\": [\"24448801\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which specific Ca²⁺-sensitive transcription factors link pump activity to cyclin D1 regulation was not fully resolved\", \"In vivo vascular proliferation phenotype was not reported\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The R268Q missense mutation in PMCA4 was shown to delay Ca²⁺ extrusion in neuronal cells, providing a functional mechanism for its association with familial spastic paraplegia.\",\n      \"evidence\": \"Fura-2 Ca²⁺ imaging in SH-SY5Y cells overexpressing WT or R268Q PMCA4 after KCl depolarization and thapsigargin treatment\",\n      \"pmids\": [\"25798335\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Overexpression system rather than endogenous or knock-in model\", \"Independent replication of the genetic association in additional families not reported in this study\", \"Neuronal subtype specificity of the phenotype not addressed\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Discovery that CD147 interacts with PMCA4 via its transmembrane and Ig-like domain II and requires PMCA4 for calcium-independent suppression of IL-2 in T cells expanded PMCA4's role to adaptive immune regulation.\",\n      \"evidence\": \"Affinity purification–mass spectrometry, domain mapping, siRNA knockdown in human T cells with IL-2 measurement\",\n      \"pmids\": [\"26729804\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PMCA4 pump activity or only its scaffold function mediates CD147 signaling was not determined\", \"In vivo immune phenotype not assessed\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identification of ATP2B4 as the causal gene at a GWAS locus for mean corpuscular hemoglobin concentration and malaria susceptibility, via CRISPR enhancer deletion and knockout mice, established PMCA4 as the primary erythrocyte Ca²⁺ efflux pump controlling red blood cell hydration.\",\n      \"evidence\": \"Atp2b4 knockout mice, CRISPR-Cas9 deletion of erythroid-specific enhancer, eQTL mapping, intracellular Ca²⁺ measurement; complemented by haplotype analysis showing reduced PMCA4b protein and Ca²⁺ extrusion in human RBCs with minor promoter haplotype\",\n      \"pmids\": [\"28714864\", \"28216081\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise mechanism by which altered RBC Ca²⁺ affects Plasmodium invasion or growth was not delineated\", \"Whether PMCA4 variation affects clinical malaria outcomes in prospective studies was not shown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrating that PMCA4 forms a quaternary complex with eNOS, nNOS, and Caveolin1 in sperm and negatively regulates NOS activity unified the Ca²⁺ extrusion and NO signaling pathways controlling sperm motility and germ cell survival.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, FRET, NOS activity assay, peroxynitrite measurement in wild-type and Pmca4-/- mouse sperm\",\n      \"pmids\": [\"28247940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the complex exists in human sperm was not confirmed\", \"Stoichiometry and structural arrangement of the quaternary complex are unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Multiple studies demonstrated that PMCA4 loss promotes pathological cell behaviors — EMT via NFATc1/ZEB1 in gastric cancer, proliferation/migration via impaired Ca²⁺ clearance in pulmonary arterial smooth muscle cells, and sensitization to apoptosis in pancreatic cancer — broadening PMCA4's role as a tumor and vascular disease modifier acting through Ca²⁺-dependent transcription factor pathways.\",\n      \"evidence\": \"siRNA/overexpression epistasis with NFATc1/ZEB1, in vivo metastasis and PAH models, Seahorse metabolic analysis, migration/apoptosis assays across multiple cell types\",\n      \"pmids\": [\"32860837\", \"32966125\", \"31963119\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PMCA4 loss is a driver or passenger in human tumors in vivo is not established\", \"PDGF-BB–mediated transcriptional suppression of PMCA4 was shown only in one cell system\", \"Therapeutic relevance of restoring PMCA4 expression is untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"CRISPR deletion of a malaria-associated regulatory region confirmed that these SNPs functionally control ATP2B4 expression and erythrocyte Ca²⁺ homeostasis, while exosomal miR-4261 was identified as a post-transcriptional regulator of ATP2B4 in the context of myeloma-induced RBC dysfunction.\",\n      \"evidence\": \"CRISPR/Cas9 regulatory deletion in K562 cells with RT-PCR, Western blot, Ca²⁺ measurement; dual-luciferase reporter assay confirming miR-4261 targeting of ATP2B4 3′UTR\",\n      \"pmids\": [\"35563239\", \"36091107\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The regulatory region deletion was performed in a leukemia cell line, not primary erythroblasts\", \"Whether miR-4261 regulation of ATP2B4 occurs in non-myeloma contexts is unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Showing that ATP2B4 knockout blocks EGF-induced macropinosome closure (but not ruffle formation) in a pump-activity-dependent manner established PMCA4 as essential for a specific step in macropinocytosis, separating its pump function from PDZ-domain scaffolding interactions.\",\n      \"evidence\": \"CRISPR knockout in A431 cells, live-cell imaging, Ca²⁺ oscillation measurement, rescue with pump-active vs. PDZ-motif-deleted constructs\",\n      \"pmids\": [\"38597132\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How local Ca²⁺ dynamics mechanistically drive membrane closure is not resolved\", \"Whether this applies to macropinocytosis in macrophages or other physiological contexts is untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of PMCA4's dual pump-scaffold functions, whether PMCA4 variation directly modulates Plasmodium infection in vivo, the full spectrum of PMCA4 disease associations beyond male infertility and spastic paraplegia, and the mechanisms controlling PMCA4 isoform switching.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of full-length PMCA4 in complex with nNOS or caveolin\", \"No prospective clinical studies linking ATP2B4 genotype to malaria outcomes with functional mechanism\", \"Regulatory logic of PMCA4a/4b alternative splicing remains undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [0, 4, 7, 16]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 4, 10, 17, 18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 4, 7, 16]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 8, 14]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [0, 6, 11]}\n    ],\n    \"complexes\": [\n      \"PMCA4-nNOS-eNOS-Caveolin1 complex (sperm)\",\n      \"PMCA4-nNOS microdomain complex (cardiomyocyte)\"\n    ],\n    \"partners\": [\n      \"NOS1\",\n      \"NOS3\",\n      \"CAV1\",\n      \"CAV3\",\n      \"BSG\",\n      \"GAT3\",\n      \"CALM1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"ATP2B4 encodes PMCA4, a ubiquitously expressed P-type Ca²⁺-ATPase that extrudes cytosolic Ca²⁺ across the plasma membrane and is regulated by calmodulin binding to a C-terminal domain subject to alternative splicing (PMCA4a/4b variants with distinct calmodulin sensitivity and tissue distributions) [PMID:2963820, PMID:1531651, PMID:8245032]. Beyond its ion-transport function, PMCA4 acts as a structural scaffold that anchors nNOS in membrane microdomains to compartmentalize NO/cGMP/cAMP signaling in cardiomyocytes and sperm, thereby regulating cardiac contractility and sperm hyperactivated motility; accordingly, Pmca4-knockout mice are male-infertile and exhibit enhanced cardiac contractility with delocalized nNOS [PMID:15178683, PMID:21965681, PMID:28247940]. PMCA4 controls red blood cell hydration through an erythroid-specific enhancer whose common variants reduce PMCA4b surface expression, slow Ca²⁺ clearance, and confer protection against P. falciparum malaria [PMID:28714864, PMID:36604655]. In proliferating cells, PMCA4 Ca²⁺ efflux activity promotes G1-phase progression in vascular smooth muscle via cyclin D1/NFAT signaling, inhibits epithelial–mesenchymal transition in gastric cancer through the NFATc1–ZEB1 axis, and is required for EGF-induced macropinocytosis through regulation of Ca²⁺ oscillations [PMID:24448801, PMID:32860837, PMID:38597132].\",\n  \"teleology\": [\n    {\n      \"year\": 1988,\n      \"claim\": \"Identification of the calmodulin-binding domain of the erythrocyte Ca²⁺ pump established the structural basis for calmodulin-dependent activation of PMCA, answering how pump activity is allosterically regulated.\",\n      \"evidence\": \"Chymotrypsin proteolysis and calmodulin photoaffinity cross-linking of purified human erythrocyte PMCA, with peptide sequencing\",\n      \"pmids\": [\"2963820\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full three-dimensional structure of calmodulin–PMCA complex not resolved\", \"Isoform-specific calmodulin affinity differences not yet addressed\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Cloning of PMCA4 as a distinct isoform and discovery of alternative splicing at the C-terminal regulatory domain (generating PMCA4a and PMCA4b) resolved how a single gene produces functionally distinct pump variants with different calmodulin sensitivities and tissue distributions.\",\n      \"evidence\": \"Molecular cloning, peptide sequencing of erythrocyte Ca²⁺-ATPase revealing two isoforms (PMCA1/PMCA4); PCR-based cDNA characterization and genomic sequencing showing splice site C usage across tissues\",\n      \"pmids\": [\"2137451\", \"1531651\", \"8245032\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequences of splice variants not yet tested in cellular Ca²⁺ clearance assays\", \"Regulation of splice-site choice unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Discovery that PMCA4b's C-terminal PDZ-binding motif interacts with MAGUK scaffolds (SAP97, PSD95, SAP102) and directs basolateral membrane targeting in polarized cells established how PMCA4 is positioned in specific membrane microdomains.\",\n      \"evidence\": \"Yeast two-hybrid screen, co-immunoprecipitation, confocal imaging in polarized MDCK cells\",\n      \"pmids\": [\"11274188\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PDZ-mediated targeting is required for PMCA4 physiological function in vivo not tested\", \"Identity of all relevant PDZ partners in different tissues incomplete\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Loss-of-function mutagenesis revealed PMCA4 is required for TNF-induced cell death by maintaining low cytosolic Ca²⁺ that prevents premature lysosomal exocytosis, uncovering a role for PMCA4 in regulated cell death beyond simple Ca²⁺ homeostasis.\",\n      \"evidence\": \"Retroviral insertion mutagenesis in L929 cells with lysosome exocytosis assays and Ca²⁺ measurement; phenotypic rescue by restoring vacuolar acidic compartment volume\",\n      \"pmids\": [\"11713265\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generalizability to other cell types and death receptor pathways not established\", \"Whether PMCA4 pump activity or scaffold function is the key determinant unclear\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Pmca4-knockout mice revealed PMCA4 is essential for sperm hyperactivated motility and male fertility but dispensable for spermatogenesis, establishing the first organism-level physiological role for PMCA4.\",\n      \"evidence\": \"Gene-targeted knockout mice; sperm motility assays, immunohistochemistry showing PMCA4 in sperm principal piece, ultrastructural Ca²⁺ overload evidence\",\n      \"pmids\": [\"15178683\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism linking Ca²⁺ overload to motility failure not fully dissected\", \"Contribution of individual splice variants (4a vs 4b) to sperm function not resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Discovery that PMCA4b scaffolds nNOS within a cardiac SNTA1–SCN5A complex, and that disruption of this interaction causes unrestrained nNOS activity leading to long QT syndrome, revealed PMCA4's scaffold function as distinct from its pump activity.\",\n      \"evidence\": \"GST pull-down, co-immunoprecipitation, patch-clamp electrophysiology in heterologous cells and cardiomyocytes; disease-associated SNTA1 A390V mutation disrupting PMCA4b binding\",\n      \"pmids\": [\"18591664\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct structural interface between PMCA4b and nNOS not resolved\", \"Whether PMCA4 pump activity also contributes to cardiac nNOS regulation not separated from scaffold role\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"In vivo cardiac studies in Pmca4-knockout mice demonstrated that PMCA4 controls contractility not through beat-to-beat Ca²⁺ transport but by scaffolding nNOS to maintain compartmentalized cGMP/cAMP signaling, resolving a long-standing question about PMCA4's cardiac function.\",\n      \"evidence\": \"PMCA4 KO mice with in vivo contractility, FRET-based cAMP/cGMP sensors, nNOS localization assays, L-type Ca²⁺ channel recordings, RyR phosphorylation analysis\",\n      \"pmids\": [\"21965681\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PMCA4 scaffold function similarly dominates in non-cardiac tissues not established\", \"Structural basis for nNOS anchoring to PMCA4 remains unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Rescue experiments in Pmca4-KO vascular smooth muscle cells showed that Ca²⁺ efflux activity (not PDZ-binding) is required for G1 cell-cycle progression, with PMCA4a and PMCA4b converging on cyclin D1 upregulation through distinct intermediates, demonstrating splice-variant-specific signaling downstream of Ca²⁺ clearance.\",\n      \"evidence\": \"PMCA4 KO primary VSMCs, [³H]thymidine incorporation, flow cytometry, rescue with WT, splice variant, and pump-dead mutant constructs, microarray\",\n      \"pmids\": [\"24448801\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance to vascular remodeling not confirmed\", \"How reduced Ca²⁺ leads to different transcriptional responses depending on splice variant is unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"PMCA4 was shown to form a quaternary complex with eNOS, nNOS, and Caveolin-1 in sperm, with Pmca4-KO leading to elevated NOS activity and peroxynitrite-driven germ cell apoptosis—unifying the Ca²⁺ clearance and NO-scaffolding functions in the context of male fertility.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, FRET in sperm, NOS activity and peroxynitrite measurement in Pmca4⁻/⁻ mice\",\n      \"pmids\": [\"28247940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether pharmacological NOS inhibition can rescue Pmca4-KO infertility not tested\", \"Stoichiometry and structural arrangement of the quaternary complex unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"CRISPR deletion of an erythroid-specific enhancer and analysis of Atp2b4-KO mice established that ATP2B4 is the causal gene at a malaria GWAS locus, controlling RBC Ca²⁺ homeostasis and hydration (MCHC), with reduced PMCA4b surface expression slowing Ca²⁺ clearance and impairing P. falciparum growth.\",\n      \"evidence\": \"eQTL mapping, CRISPR enhancer deletion in erythroid cells, Atp2b4-KO mice (MCHC phenotype), recall-by-genotype functional Ca²⁺ assays, in vitro parasite growth with field isolates and pharmacological PMCA4b inhibition\",\n      \"pmids\": [\"28714864\", \"28216081\", \"36604655\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise mechanism by which altered RBC Ca²⁺ impairs parasite development unknown\", \"Whether other RBC membrane properties beyond Ca²⁺/hydration contribute to protection not resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Multiple studies extended PMCA4's role to cancer cell biology: PMCA4 inhibits EMT via the NFATc1–ZEB1 axis in gastric cancer, supports migration and apoptotic resistance in pancreatic cancer, and its downregulation by PDGF-BB/MEK/ERK drives proliferation of pulmonary arterial smooth muscle cells, establishing PMCA4 as a context-dependent modulator of proliferation, migration, and cell death.\",\n      \"evidence\": \"siRNA/overexpression with in vivo xenograft (gastric cancer), PMCA4 knockdown in MIA PaCa-2 cells (pancreatic cancer), PDGF-BB stimulation with MEK/ERK inhibitors and in vivo PAH rat models\",\n      \"pmids\": [\"32860837\", \"31963119\", \"32966125\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cancer phenotypes studied in single cell lines each; generalizability uncertain\", \"Whether PMCA4's scaffold vs. pump function drives these cancer phenotypes not distinguished\", \"Patient-level clinical significance of PMCA4 expression changes not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"CRISPR knockout demonstrated ATP2B4 is required for EGF-induced macropinocytosis via its Ca²⁺ pump activity (not PDZ interactions), regulating ruffle closure through Ca²⁺ oscillations—revealing a new cellular process dependent on PMCA4.\",\n      \"evidence\": \"CRISPR/Cas9 ATP2B4 KO in A431 cells, live-cell imaging of ruffles, Ca²⁺ oscillation measurement, rescue with PDZ-binding-domain mutant\",\n      \"pmids\": [\"38597132\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this function generalizes beyond EGF-stimulated A431 cells is untested\", \"Downstream effectors linking Ca²⁺ oscillations to ruffle closure not identified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the high-resolution structure of PMCA4 with its regulatory and scaffolding domains, how pump vs. scaffold functions are differentially deployed across tissues, and whether PMCA4 variants or inhibitors can be therapeutically exploited for malaria protection, cancer, or cardiovascular disease.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure of full-length PMCA4 available\", \"Relative contribution of pump vs. scaffold function not systematically dissected across physiological contexts\", \"No clinical trials targeting PMCA4\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [0, 1, 7, 11, 12, 13, 18, 27]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8, 11, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 7, 10, 11, 12, 17, 26, 30]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0382551\", \"supporting_discovery_ids\": [7, 13, 18, 19, 24, 26]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 11, 13, 20, 22]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [7, 9, 17]},\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"complexes\": [\n      \"SNTA1-nNOS-SCN5A complex\",\n      \"Caveolin-1-eNOS-nNOS complex (sperm)\"\n    ],\n    \"partners\": [\n      \"NOS1\",\n      \"NOS3\",\n      \"SNTA1\",\n      \"CAV1\",\n      \"DLG1\",\n      \"DLG4\",\n      \"BSG\",\n      \"SLC6A11\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}