{"gene":"PIK3C2A","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2000,"finding":"PI3K-C2α is constitutively associated with phospholipid membranes and co-purifies with clathrin-coated vesicles (CCVs). Its perinuclear localization co-distributes with γ-adaptin (AP-1) and TGN-46, placing it at the trans-Golgi network. Brefeldin A treatment disrupted this localization, demonstrating dependence on ARF GTPase activity. Neither the PX nor C2 C-terminal domains were required for membrane association or TGN localization.","method":"Differential centrifugation, Western blot, immunofluorescence dual-label, brefeldin A treatment, deletion mutant expression","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (fractionation, immunofluorescence, domain mutants) in a single study with clear functional-localization linkage","pmids":["10766823"],"is_preprint":false},{"year":1998,"finding":"MCP-1 stimulates lipid kinase activity in PI3K-C2α immunoprecipitates with kinetics paralleling intracellular PI(3,4,5)P3 accumulation. This activation is inhibited by pertussis toxin but not by wortmannin, distinguishing PI3K-C2α activation from the class IA p85/p110 isoform and identifying PI3K-C2α as the likely source of MCP-1-induced D-3 phosphoinositide production in vivo.","method":"Immunoprecipitation lipid kinase assay, pharmacological inhibition (wortmannin, pertussis toxin), PI lipid profiling","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal IP kinase assay with pharmacological dissection, single lab, two orthogonal readouts","pmids":["9748276"],"is_preprint":false},{"year":2010,"finding":"In response to insulin, PI3K-C2α generates PI(3,4)P2 (not PI(3)P), which selectively activates PKBα/Akt1. PI3K-C2α and PKBα/Akt1 co-distribute with insulin receptor isoform B in the same plasma membrane microdomains. Knockdown of PI3K-C2α impaired glucose-stimulated insulin secretion in pancreatic β-cells, at least partly through reduced glucokinase expression and increased AS160 activity.","method":"siRNA knockdown, pharmacological inhibitors, PI-lipid profiling, live-cell confocal and TIRF microscopy, transient overexpression","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (lipid profiling, live imaging, KD, OE) in single lab with defined mechanistic pathway","pmids":["20061534"],"is_preprint":false},{"year":2012,"finding":"PI3K-C2α knockdown in endothelial cells decreased PI(3)P-enriched endosomes, impaired endosomal trafficking, blocked VE-cadherin delivery to cell junctions, and prevented junction assembly. It also impaired VEGF receptor internalization and endosomal RhoA activation. Global or endothelial-specific PI3K-C2α knockout caused embryonic lethality with defects in sprouting angiogenesis and vascular maturation. In vivo, endothelial PI3K-C2α deficiency suppressed postischemic and tumor angiogenesis and diminished vascular barrier function.","method":"siRNA knockdown, conditional and global knockout mice, immunofluorescence, in vivo angiogenesis assays, barrier function assays","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic mouse models plus cellular mechanistic dissection across multiple orthogonal assays, replicated across cell and animal systems","pmids":["22983395"],"is_preprint":false},{"year":2015,"finding":"PI3K-C2α knockdown in endothelial cells abolished TGFβ1-induced phosphorylation and nuclear translocation of Smad2/3. PI3K-C2α was required for TGFβ-induced PI(3,4)P2 increases at the plasma membrane and for TGFβ receptor internalization into SARA-containing early endosomes, and for SARA–Smad2/3 complex formation. Dynamin inhibition phenocopied PI3K-C2α knockdown, indicating clathrin-dependent endocytosis is required. EC-specific PI3K-C2α deletion in mice attenuated TGFβ1-induced microvessel formation.","method":"siRNA knockdown, phosphoinositide measurements, immunofluorescence, dynamin inhibitor, EC-specific knockout mice, Matrigel plug assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (KD, pharmacological, in vivo KO) establishing pathway position for TGFβ receptor endocytosis and Smad signaling","pmids":["25614622"],"is_preprint":false},{"year":2015,"finding":"PI3K-C2α heterozygous kinase-dead knock-in in mice caused aberrant platelet morphology (excess barbell-shaped proplatelets), defects in α-granules and membrane structure, increased platelet rigidity, inability to form filopodia, and reduced basal PI(3)P pool. Mislocalization of membrane skeleton proteins controlling plasma membrane–cytoskeleton interactions was observed in affected platelets. These defects led to delayed arterial occlusion and impaired thrombus formation.","method":"Constitutive kinase-dead knock-in mouse, flow cytometry, electron microscopy, PI3P quantification, ex vivo thrombosis assay, in vivo arterial occlusion model","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — kinase-dead genetic mouse model with multiple orthogonal cellular and in vivo functional readouts","pmids":["26109204"],"is_preprint":false},{"year":2015,"finding":"PI3K-C2α knockdown impaired Shigella flexneri dissemination by blocking resolution of protrusions into vacuoles via an intermediate vacuole-like protrusion (VLP). Genetic rescue with RNAi-resistant cDNA (but not kinase-dead PI3K-C2α) restored VLP formation, requiring kinase activity in primary infected cells. PI3K-C2α produced PI(3)P at the protrusion plasma membrane, regulated by host tyrosine kinase signaling and the bacterial T3SS.","method":"siRNA knockdown, time-lapse microscopy, RNAi-resistant rescue constructs, PI(3)P reporter, kinase-dead mutant","journal":"Infection and immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — rescue with kinase-dead vs. WT construct directly establishes kinase requirement; multiple orthogonal methods","pmids":["25667265"],"is_preprint":false},{"year":2015,"finding":"PI3K-C2α knockdown decreased autophagy and caused accumulation of endocytic vesicles at recycling endosomes. Kinase-dead PI3K-C2α failed to rescue autophagy, establishing a requirement for catalytic activity. PI3K-C2α co-localizes with endocytic markers and interacts with ATG9. Double knockdown of PIK3C2A and ATG9A/B phenocopied each other, suggesting a shared pathway connecting endocytic and autophagic trafficking.","method":"siRNA knockdown, confocal microscopy, transferrin labeling, membrane fractionation, co-immunoprecipitation, kinase-dead rescue","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — kinase-dead rescue and co-IP with ATG9 establish mechanistic link; single lab with multiple orthogonal methods","pmids":["28910396"],"is_preprint":false},{"year":2015,"finding":"PI3K-C2α knockdown in pancreatic β-cells rerouted insulin signaling from the IR-B/PI3K-C2α/PKBα metabolic axis to IR-B/Shc/ERK mitogenic signaling, causing a switch from a glucose-responsive differentiated state to a proliferative state, demonstrating cascade-selective insulin resistance within a single cell type.","method":"siRNA knockdown, immunoprecipitation, Western blot, live-cell imaging, glucose-stimulated insulin secretion assays","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — single lab, multiple signaling readouts establishing pathway switch, but no independent replication","pmids":["26387957"],"is_preprint":false},{"year":2016,"finding":"Heterozygous kinase-dead PI3K-C2α knock-in male mice developed early-onset leptin resistance with a defect in leptin signaling in the hypothalamus, correlating with age-dependent obesity, insulin resistance, and glucose intolerance. No metabolic phenotypes were detected in female mice. Importantly, insulin signaling in peripheral insulin target tissues was unaffected in these mice.","method":"Constitutive heterozygous kinase-dead knock-in mice, metabolic phenotyping, glucose tolerance tests, hypothalamic leptin signaling assays","journal":"Diabetologia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic mouse model with defined mechanistic phenotype; single lab, sex-specific effect not independently replicated","pmids":["27138914"],"is_preprint":false},{"year":2017,"finding":"PI3K-C2α acts as a kinase-independent scaffold organizing clathrin and TACC3 into inter-microtubule bridge complexes that crosslink kinetochore fibers (K-fibers) during mitosis. Downregulation of PI3K-C2α caused spindle alterations, delayed anaphase onset, and aneuploidy. Reduced PI3K-C2α expression in breast cancer initially impaired tumor growth but led to evolution of fast-growing clones with mitotic checkpoint defects and increased taxane sensitivity.","method":"siRNA knockdown, live-cell imaging, co-immunoprecipitation (clathrin/TACC3 complex), rescue with kinase-dead vs. WT construct, breast cancer xenograft models","journal":"Cancer cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — kinase-dead rescue distinguishes scaffold from catalytic function; co-IP identifies complex; multiple cellular and in vivo readouts","pmids":["29017056"],"is_preprint":false},{"year":2018,"finding":"PI3K-C2α and PI3K-C2β both localize to clathrin-coated pits and are required for clathrin-mediated (but not clathrin-independent) pinocytosis up to the step of delivery to early endosomes. PI3K-C2β, but not PI3K-C2α, co-localizes with actin filament-associated clathrin-coated structures and is required for actin filament formation at those structures, distinguishing their specific roles.","method":"siRNA knockdown, FITC-dextran uptake assay, transferrin labeling, confocal co-localization, clathrin heavy chain knockdown","journal":"The journal of physiological sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA KD with functional pinocytosis assay and co-localization; single lab, multiple readouts but no rescue","pmids":["30374841"],"is_preprint":false},{"year":2018,"finding":"KSHV nonstructural membrane protein pK15 interacts and co-localizes with PI3K-C2α in perinuclear vesicular structures. PI3K-C2α contributes to pK15-dependent phosphorylation of PLCγ1 and Erk1/2. Depletion of PI3K-C2α in KSHV-infected endothelial cells reduced expression of viral lytic genes K-bZIP and ORF45 and decreased release of infectious virus.","method":"Co-immunoprecipitation with mass spectrometry, immunofluorescence co-localization, siRNA knockdown, Western blot for signaling targets, viral gene expression assays","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP/MS identifies interaction, KD establishes functional role in signaling and viral replication; single lab","pmids":["29950425"],"is_preprint":false},{"year":2019,"finding":"Homozygous loss-of-function mutations in PIK3C2A cause a Mendelian disorder with short stature, cataracts, skeletal abnormalities, and neurological manifestations. Patient-derived fibroblasts lacking PIK3C2A protein showed impaired cilia formation and function and reduced proliferative capacity, establishing PIK3C2A as essential for ciliogenesis and cell proliferation.","method":"Exome sequencing of consanguineous families, patient-derived fibroblast analysis, cilia formation assay, proliferation assay, Western blot","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human genetics with cellular validation in patient fibroblasts; three independent families, but mechanistic depth limited to cilia/proliferation readouts","pmids":["31034465"],"is_preprint":false},{"year":2020,"finding":"PI3K-C2α generates PI(3)P at the primary cilium in response to shear stress (urinary flow) to initiate cilium-dependent autophagy in kidney proximal tubule epithelial cells. This pathway is independent of ULK1 and BECN1, distinguishing it from starvation-induced autophagy driven by PIK3C3/VPS34.","method":"siRNA knockdown of PIK3C2A vs. PIK3C3, PI(3)P reporters, shear stress assay, autophagy markers, confocal microscopy","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — parallel KD of PIK3C2A vs. PIK3C3 with PI(3)P reporter and autophagy assays establishes pathway specificity; single lab","pmids":["32102612"],"is_preprint":false},{"year":2020,"finding":"PI3K-C2α is required for TGFβ receptor endocytosis through sequential phosphoinositide conversions: PI3K-C2α KD abolished TGFβ-induced PI(3,4)P2 increases and also prevented synaptojanin1 recruitment to the plasma membrane, PI(4,5)P2 decreases, and PI(4)P increases. Synaptojanin1 and INPP4B (but not PI3K-C2β, Synj2, or INPP4A) work sequentially with PI3K-C2α. These phosphoinositide conversions are necessary for Smad2/3 activation.","method":"siRNA knockdown of individual PI3K and phosphatase isoforms, phosphoinositide biosensors/quantification, co-localization imaging, Smad2/3 phosphorylation assay","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — isoform-specific KD panel with PI biosensors plus signaling readouts establish ordered pathway; multiple orthogonal methods in single rigorous study","pmids":["31913757"],"is_preprint":false},{"year":2008,"finding":"Crystal structures of the PI3K-C2α PX domain at 2.1 Å and 2.5 Å revealed two conformations of the phosphoinositide-binding loops, with one structure containing a putative ligand in the binding site. This demonstrated that the PX domain undergoes a conformational change associated with ligand binding and clarified the molecular basis for PI specificity.","method":"X-ray crystallography (2.1 Å and 2.5 Å structures of PX domain)","journal":"BMC structural biology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — crystal structures provide direct structural insight; however single study, no functional mutagenesis validation reported","pmids":["18312637"],"is_preprint":false},{"year":2022,"finding":"C/EBPα transcriptionally activates PIK3C2A by binding to a site in its promoter (established by ChIP assay). C/EBPα and PIK3C2A promote autophagy and phenotypic switching (synthetic to contractile) in vascular smooth muscle cells under aortic dissection conditions. PIK3C2A knockdown reversed C/EBPα-driven autophagy activation, MMP upregulation, and VSMC phenotype switching.","method":"ChIP assay, siRNA/plasmid-based gain/loss-of-function, Western blot, aortic ring stretch-stress model, in vivo tail-vein shRNA injection","journal":"Journal of immunology research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP establishes direct transcriptional regulation; functional rescue experiments in multiple contexts; single lab","pmids":["36132983"],"is_preprint":false},{"year":2025,"finding":"Inducible genetic inactivation of PI3K-C2α in adult mice sensitized them to LPS-induced endotoxic shock. Vascular endothelial-specific deletion recapitulated this phenotype. Sensitization was fully rescued by combined deficiency of caspase-8 and RIPK3, placing PI3K-C2α upstream of extrinsic cell death pathway activation in endothelial cells.","method":"Inducible conditional knockout mice, vascular endothelial-specific deletion, LPS challenge model, genetic epistasis (caspase-8/RIPK3 double knockout rescue)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with double-KO rescue definitively places PI3K-C2α in the extrinsic cell death pathway; multiple genetic models","pmids":["40674428"],"is_preprint":false},{"year":2025,"finding":"TTC7A functions as a molecular chaperone for PIK3C2A and is required for its trafficking to the plasma membrane via Rab11a-positive vesicles. PIK3C2A generates PI(3,4)P2 at the apical membrane to specify apical identity during intestinal lumen formation. Defective lumen formation in TTC7A loss-of-function was rescued by exogenous PI(3,4)P2 or small molecules modulating phosphoinositide homeostasis.","method":"Patient-derived organoids, protein trafficking assays, Rab11a co-localization, PI(3,4)P2 reporter, exogenous lipid rescue, pharmacological rescue","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — preprint; multiple orthogonal methods including lipid rescue establish functional pathway, but not yet peer-reviewed","pmids":["bio_10.1101_2025.03.22.644724"],"is_preprint":true}],"current_model":"PI3K-C2α (PIK3C2A) is a class II phosphoinositide 3-kinase that catalyzes production of PI(3)P and PI(3,4)P2 in spatially restricted membrane compartments—including clathrin-coated vesicles, the trans-Golgi network, early endosomes, and the plasma membrane—to regulate clathrin-mediated endocytosis of receptor tyrosine kinases (VEGFR, TGFβR, insulin receptor isoform B) and their downstream signaling (RhoA, Smad2/3, PKBα/Akt1); it also acts as a kinase-independent scaffold organizing clathrin–TACC3 complexes at mitotic kinetochore fibers to ensure genomic stability, generates PI(3)P at the primary cilium to initiate shear-stress-dependent autophagy, and controls endosomal maturation and vesicle recycling, with its inactivation in endothelial cells sensitizing to extrinsic (caspase-8/RIPK3-dependent) cell death."},"narrative":{"mechanistic_narrative":"PIK3C2A (PI3K-C2α) is a class II phosphoinositide 3-kinase that generates spatially restricted pools of PI(3)P and PI(3,4)P2 to couple membrane trafficking with receptor signaling, ciliogenesis, and mitotic fidelity [PMID:10766823, PMID:20061534, PMID:22983395]. It is constitutively membrane-associated and concentrated on clathrin-coated vesicles and the trans-Golgi network in an ARF-dependent manner [PMID:10766823], and together with PI3K-C2β it is required for clathrin-mediated pinocytosis up to delivery to early endosomes [PMID:30374841]. Through this endocytic activity it controls internalization and downstream signaling of multiple receptors: it produces PI(3,4)P2 at plasma membrane microdomains to drive insulin receptor isoform B-dependent PKBα/Akt1 activation in pancreatic β-cells [PMID:20061534, PMID:26387957], and it directs TGFβ receptor uptake into SARA-containing early endosomes—via an ordered phosphoinositide conversion engaging synaptojanin1 and INPP4B—to enable Smad2/3 activation [PMID:25614622, PMID:31913757]. In endothelial cells PI3K-C2α generates PI(3)P-enriched endosomes required for VEGF receptor internalization, endosomal RhoA activation, VE-cadherin delivery, and junction assembly, and its loss causes embryonic lethality with defective angiogenesis and vascular barrier function [PMID:22983395]. Independent of its catalytic activity, PI3K-C2α acts as a scaffold that organizes clathrin and TACC3 into inter-microtubule bridges crosslinking kinetochore fibers, ensuring proper spindle function and genomic stability [PMID:29017056]. It also generates PI(3)P at the primary cilium to initiate a shear-stress-induced, ULK1/BECN1-independent form of autophagy [PMID:32102612], and connects endocytic and autophagic trafficking through interaction with ATG9 [PMID:28910396]. Homozygous loss-of-function mutations in PIK3C2A cause a Mendelian disorder of short stature, cataracts, skeletal abnormalities, and neurological manifestations, with patient fibroblasts showing impaired ciliogenesis and proliferation [PMID:31034465].","teleology":[{"year":1998,"claim":"Established that PI3K-C2α is an agonist-responsive lipid kinase distinct from class IA PI3K, answering whether the enzyme is regulated by physiological stimuli.","evidence":"MCP-1-stimulated IP lipid kinase assay with wortmannin/pertussis toxin dissection","pmids":["9748276"],"confidence":"Medium","gaps":["Direct lipid product specificity in vivo not resolved","Receptor coupling mechanism to the kinase undefined"]},{"year":2000,"claim":"Defined where PI3K-C2α operates by localizing it to clathrin-coated vesicles and the ARF-dependent trans-Golgi network, linking the enzyme to membrane trafficking compartments.","evidence":"Subcellular fractionation, dual-label immunofluorescence, brefeldin A, and deletion mutants","pmids":["10766823"],"confidence":"High","gaps":["Which trafficking step the lipid product controls not shown","Functional consequence of TGN localization untested"]},{"year":2008,"claim":"Provided structural basis for phosphoinositide recognition by resolving PX-domain conformations associated with ligand binding.","evidence":"X-ray crystallography of the PX domain at 2.1 and 2.5 Å","pmids":["18312637"],"confidence":"Medium","gaps":["No functional mutagenesis validating the binding model","Full-length enzyme architecture not determined"]},{"year":2010,"claim":"Identified the lipid product (PI(3,4)P2) and signaling output (PKBα/Akt1) of insulin-stimulated PI3K-C2α, establishing its role in metabolic signaling and insulin secretion.","evidence":"siRNA knockdown, PI-lipid profiling, TIRF/confocal imaging, and insulin secretion assays in β-cells","pmids":["20061534"],"confidence":"High","gaps":["Mechanism linking PI(3,4)P2 to glucokinase and AS160 not detailed","Receptor microdomain organization mechanism unknown"]},{"year":2012,"claim":"Demonstrated an essential endosomal trafficking role in endothelial cells, linking PI3K-C2α-derived PI(3)P to VEGFR internalization, RhoA signaling, junction assembly, and angiogenesis in vivo.","evidence":"siRNA, conditional and global knockout mice, in vivo angiogenesis and barrier assays","pmids":["22983395"],"confidence":"High","gaps":["Direct effector reading the endosomal PI(3)P pool not identified","Distinction between trafficking defect and signaling defect not fully separated"]},{"year":2015,"claim":"Placed PI3K-C2α upstream of TGFβ receptor endocytosis and Smad2/3 signaling, defining its requirement for clathrin/dynamin-dependent uptake into SARA-positive endosomes.","evidence":"siRNA, phosphoinositide measurements, dynamin inhibitor, EC-specific knockout mice, Matrigel assay","pmids":["25614622"],"confidence":"High","gaps":["Order of phosphoinositide conversions not yet resolved at this stage","Direct partners coordinating SARA recruitment unclear"]},{"year":2015,"claim":"Distinguished the requirement for kinase activity by showing kinase-dead PI3K-C2α causes platelet morphology, granule, and cytoskeletal defects affecting thrombus formation.","evidence":"Heterozygous kinase-dead knock-in mice, EM, PI(3)P quantification, thrombosis assays","pmids":["26109204"],"confidence":"High","gaps":["Identity of mislocalized membrane skeleton proteins not mechanistically mapped","Link between basal PI(3)P pool and cytoskeleton coupling undefined"]},{"year":2015,"claim":"Showed kinase-dependent PI(3)P production at protrusion membranes is required for Shigella cell-to-cell spread, extending the enzyme's role to pathogen dissemination.","evidence":"siRNA, RNAi-resistant WT vs kinase-dead rescue, PI(3)P reporter, time-lapse imaging","pmids":["25667265"],"confidence":"High","gaps":["Host effector downstream of PI(3)P at protrusions unknown","Interplay with bacterial T3SS effectors not detailed"]},{"year":2015,"claim":"Connected endocytic and autophagic trafficking by demonstrating kinase-dependent regulation of autophagy and physical interaction with ATG9.","evidence":"siRNA, kinase-dead rescue, transferrin labeling, co-IP with ATG9, double knockdown","pmids":["28910396"],"confidence":"Medium","gaps":["Reciprocal validation of ATG9 interaction limited","Site of PI(3)P production driving autophagy not localized"]},{"year":2015,"claim":"Revealed cascade-selective insulin signaling, where loss of PI3K-C2α reroutes IR-B from the metabolic Akt axis to mitogenic Shc/ERK signaling within a single cell type.","evidence":"siRNA, IP, Western blot, live imaging, glucose-stimulated insulin secretion in β-cells","pmids":["26387957"],"confidence":"Medium","gaps":["Molecular switch directing receptor adaptor choice unknown","Not independently replicated"]},{"year":2016,"claim":"Extended metabolic function in vivo by showing kinase-dead PI3K-C2α causes hypothalamic leptin resistance and sex-specific obesity, distinct from peripheral insulin signaling.","evidence":"Heterozygous kinase-dead knock-in mice, metabolic phenotyping, hypothalamic leptin assays","pmids":["27138914"],"confidence":"Medium","gaps":["Basis of male-specific phenotype unexplained","Direct role in leptin receptor trafficking not shown"]},{"year":2017,"claim":"Defined a kinase-independent scaffold function organizing clathrin-TACC3 bridges at kinetochore fibers to maintain genomic stability, separating structural from catalytic roles.","evidence":"siRNA, live imaging, co-IP, WT vs kinase-dead rescue, breast cancer xenografts","pmids":["29017056"],"confidence":"High","gaps":["How the scaffold is targeted to K-fibers not resolved","Relationship between scaffold and lipid kinase pools unclear"]},{"year":2018,"claim":"Distinguished isoform-specific roles, showing PI3K-C2α and C2β both support clathrin-mediated pinocytosis but only C2β couples to actin-associated clathrin structures.","evidence":"siRNA of each isoform, FITC-dextran uptake, transferrin labeling, co-localization","pmids":["30374841"],"confidence":"Medium","gaps":["No rescue confirming specificity","Mechanistic basis for differential actin coupling unknown"]},{"year":2018,"claim":"Identified a viral cofactor role, where KSHV pK15 recruits PI3K-C2α to drive PLCγ1/Erk signaling and lytic viral gene expression.","evidence":"Co-IP/MS, immunofluorescence, siRNA, signaling and viral gene assays","pmids":["29950425"],"confidence":"Medium","gaps":["Whether kinase activity is required for pK15 signaling untested","Direct vs indirect interaction not resolved"]},{"year":2019,"claim":"Established PIK3C2A as the cause of a human Mendelian disorder, linking loss of function to defective ciliogenesis and proliferation.","evidence":"Exome sequencing of consanguineous families, patient fibroblast cilia and proliferation assays","pmids":["31034465"],"confidence":"Medium","gaps":["Tissue-specific mechanisms behind skeletal/neurological phenotypes not dissected","Lipid product driving ciliogenesis not mapped in patient cells"]},{"year":2020,"claim":"Defined a distinct autophagy pathway in which ciliary PI(3)P from PI3K-C2α initiates shear-stress autophagy independent of ULK1/BECN1 and VPS34.","evidence":"Parallel PIK3C2A vs PIK3C3 knockdown, PI(3)P reporters, shear-stress autophagy assays","pmids":["32102612"],"confidence":"Medium","gaps":["Downstream autophagy machinery reading ciliary PI(3)P unknown","How shear stress activates the enzyme not defined"]},{"year":2020,"claim":"Resolved the ordered phosphoinositide conversion for TGFβ receptor endocytosis, placing PI3K-C2α at the head of a synaptojanin1/INPP4B cascade required for Smad2/3 activation.","evidence":"Isoform/phosphatase-specific siRNA panel, PI biosensors, co-localization, Smad2/3 phosphorylation","pmids":["31913757"],"confidence":"High","gaps":["Spatial recruitment hierarchy of the enzymes not fully mapped","Generality to other receptors untested"]},{"year":2022,"claim":"Identified upstream transcriptional control by C/EBPα and a role in vascular smooth muscle autophagy and phenotypic switching during aortic dissection.","evidence":"ChIP, gain/loss-of-function, aortic ring stretch model, in vivo shRNA","pmids":["36132983"],"confidence":"Medium","gaps":["Whether kinase activity mediates the VSMC phenotype untested","Single lab, mechanism downstream of PIK3C2A in VSMC unclear"]},{"year":2025,"claim":"Placed endothelial PI3K-C2α upstream of extrinsic cell death, showing its inactivation sensitizes to endotoxic shock via caspase-8/RIPK3-dependent death.","evidence":"Inducible and EC-specific knockout mice, LPS challenge, caspase-8/RIPK3 double-KO epistasis rescue","pmids":["40674428"],"confidence":"High","gaps":["Molecular link from lipid signaling to death pathway suppression unknown","Whether kinase or scaffold function is required not resolved"]},{"year":2025,"claim":"Defined TTC7A as a chaperone delivering PIK3C2A to the apical membrane to generate PI(3,4)P2 specifying apical identity during lumen formation.","evidence":"Patient organoids, trafficking and Rab11a co-localization, PI(3,4)P2 reporter, lipid/pharmacological rescue (preprint)","pmids":["bio_10.1101_2025.03.22.644724"],"confidence":"Medium","gaps":["Not peer-reviewed","Direct biochemical TTC7A-PIK3C2A binding details limited"]},{"year":null,"claim":"How PI3K-C2α's distinct PI(3)P and PI(3,4)P2 pools, its kinase-independent scaffold function, and its compartment-specific recruitment are coordinated to produce its diverse physiological roles remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying model linking lipid products to specific effectors across compartments","Mechanism of stimulus-specific enzyme activation undefined","Structural basis of full-length enzyme regulation unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[1,2,3,15]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,16]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[10]}],"localization":[{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,11]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[3,4,7]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,15,19]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[13,14]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,3,11]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,4,15]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[7,14]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[10]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,13]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[18]}],"complexes":["clathrin–TACC3 inter-microtubule bridge"],"partners":["CLTC","TACC3","ATG9A","SARA","SYNJ1","INPP4B","TTC7A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O00443","full_name":"Phosphatidylinositol 4-phosphate 3-kinase C2 domain-containing subunit alpha","aliases":["Phosphoinositide 3-kinase-C2-alpha"],"length_aa":1686,"mass_kda":190.7,"function":"Generates phosphatidylinositol 3-phosphate (PtdIns3P) and phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)P2) that act as second messengers. Has a role in several intracellular trafficking events. Functions in insulin signaling and secretion. Required for translocation of the glucose transporter SLC2A4/GLUT4 to the plasma membrane and glucose uptake in response to insulin-mediated RHOQ activation. Regulates insulin secretion through two different mechanisms: involved in glucose-induced insulin secretion downstream of insulin receptor in a pathway that involves AKT1 activation and TBC1D4/AS160 phosphorylation, and participates in the late step of insulin granule exocytosis probably in insulin granule fusion. Synthesizes PtdIns3P in response to insulin signaling. Functions in clathrin-coated endocytic vesicle formation and distribution. Regulates dynamin-independent endocytosis, probably by recruiting EEA1 to internalizing vesicles. In neurosecretory cells synthesizes PtdIns3P on large dense core vesicles. Participates in calcium induced contraction of vascular smooth muscle by regulating myosin light chain (MLC) phosphorylation through a mechanism involving Rho kinase-dependent phosphorylation of the MLCP-regulatory subunit MYPT1. May play a role in the EGF signaling cascade. May be involved in mitosis and UV-induced damage response. Required for maintenance of normal renal structure and function by supporting normal podocyte function. Involved in the regulation of ciliogenesis and trafficking of ciliary components (PubMed:31034465)","subcellular_location":"Cell membrane; Cytoplasmic vesicle, clathrin-coated vesicle; Nucleus; Cytoplasm; Golgi apparatus, trans-Golgi network","url":"https://www.uniprot.org/uniprotkb/O00443/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PIK3C2A","classification":"Not 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TO","url":"https://www.omim.org/entry/609532"},{"mim_id":"603601","title":"PHOSPHATIDYLINOSITOL 3-KINASE, CLASS 2, ALPHA; PIK3C2A","url":"https://www.omim.org/entry/603601"},{"mim_id":"602838","title":"PHOSPHATIDYLINOSITOL 3-KINASE, CLASS 2, BETA; PIK3C2B","url":"https://www.omim.org/entry/602838"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Vesicles","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PIK3C2A"},"hgnc":{"alias_symbol":["PI3K-C2alpha"],"prev_symbol":[]},"alphafold":{"accession":"O00443","domains":[{"cath_id":"3.10.20.90","chopping":"401-516","consensus_level":"high","plddt":83.9434,"start":401,"end":516},{"cath_id":"-","chopping":"547-608_642-662","consensus_level":"medium","plddt":82.849,"start":547,"end":662},{"cath_id":"2.60.40.150","chopping":"676-772_784-816_831-849","consensus_level":"high","plddt":88.027,"start":676,"end":849},{"cath_id":"3.30.1010.10","chopping":"1040-1141","consensus_level":"medium","plddt":91.9478,"start":1040,"end":1141},{"cath_id":"3.30.1520.10","chopping":"1425-1543","consensus_level":"high","plddt":81.369,"start":1425,"end":1543},{"cath_id":"2.60.40.150","chopping":"1563-1680","consensus_level":"high","plddt":87.454,"start":1563,"end":1680}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O00443","model_url":"https://alphafold.ebi.ac.uk/files/AF-O00443-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O00443-F1-predicted_aligned_error_v6.png","plddt_mean":71.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PIK3C2A","jax_strain_url":"https://www.jax.org/strain/search?query=PIK3C2A"},"sequence":{"accession":"O00443","fasta_url":"https://rest.uniprot.org/uniprotkb/O00443.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O00443/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O00443"}},"corpus_meta":[{"pmid":"22983395","id":"PMC_22983395","title":"Endothelial 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Its perinuclear localization co-distributes with γ-adaptin (AP-1) and TGN-46, placing it at the trans-Golgi network. Brefeldin A treatment disrupted this localization, demonstrating dependence on ARF GTPase activity. Neither the PX nor C2 C-terminal domains were required for membrane association or TGN localization.\",\n      \"method\": \"Differential centrifugation, Western blot, immunofluorescence dual-label, brefeldin A treatment, deletion mutant expression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (fractionation, immunofluorescence, domain mutants) in a single study with clear functional-localization linkage\",\n      \"pmids\": [\"10766823\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"MCP-1 stimulates lipid kinase activity in PI3K-C2α immunoprecipitates with kinetics paralleling intracellular PI(3,4,5)P3 accumulation. This activation is inhibited by pertussis toxin but not by wortmannin, distinguishing PI3K-C2α activation from the class IA p85/p110 isoform and identifying PI3K-C2α as the likely source of MCP-1-induced D-3 phosphoinositide production in vivo.\",\n      \"method\": \"Immunoprecipitation lipid kinase assay, pharmacological inhibition (wortmannin, pertussis toxin), PI lipid profiling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal IP kinase assay with pharmacological dissection, single lab, two orthogonal readouts\",\n      \"pmids\": [\"9748276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In response to insulin, PI3K-C2α generates PI(3,4)P2 (not PI(3)P), which selectively activates PKBα/Akt1. PI3K-C2α and PKBα/Akt1 co-distribute with insulin receptor isoform B in the same plasma membrane microdomains. Knockdown of PI3K-C2α impaired glucose-stimulated insulin secretion in pancreatic β-cells, at least partly through reduced glucokinase expression and increased AS160 activity.\",\n      \"method\": \"siRNA knockdown, pharmacological inhibitors, PI-lipid profiling, live-cell confocal and TIRF microscopy, transient overexpression\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (lipid profiling, live imaging, KD, OE) in single lab with defined mechanistic pathway\",\n      \"pmids\": [\"20061534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PI3K-C2α knockdown in endothelial cells decreased PI(3)P-enriched endosomes, impaired endosomal trafficking, blocked VE-cadherin delivery to cell junctions, and prevented junction assembly. It also impaired VEGF receptor internalization and endosomal RhoA activation. Global or endothelial-specific PI3K-C2α knockout caused embryonic lethality with defects in sprouting angiogenesis and vascular maturation. In vivo, endothelial PI3K-C2α deficiency suppressed postischemic and tumor angiogenesis and diminished vascular barrier function.\",\n      \"method\": \"siRNA knockdown, conditional and global knockout mice, immunofluorescence, in vivo angiogenesis assays, barrier function assays\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic mouse models plus cellular mechanistic dissection across multiple orthogonal assays, replicated across cell and animal systems\",\n      \"pmids\": [\"22983395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PI3K-C2α knockdown in endothelial cells abolished TGFβ1-induced phosphorylation and nuclear translocation of Smad2/3. PI3K-C2α was required for TGFβ-induced PI(3,4)P2 increases at the plasma membrane and for TGFβ receptor internalization into SARA-containing early endosomes, and for SARA–Smad2/3 complex formation. Dynamin inhibition phenocopied PI3K-C2α knockdown, indicating clathrin-dependent endocytosis is required. EC-specific PI3K-C2α deletion in mice attenuated TGFβ1-induced microvessel formation.\",\n      \"method\": \"siRNA knockdown, phosphoinositide measurements, immunofluorescence, dynamin inhibitor, EC-specific knockout mice, Matrigel plug assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (KD, pharmacological, in vivo KO) establishing pathway position for TGFβ receptor endocytosis and Smad signaling\",\n      \"pmids\": [\"25614622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PI3K-C2α heterozygous kinase-dead knock-in in mice caused aberrant platelet morphology (excess barbell-shaped proplatelets), defects in α-granules and membrane structure, increased platelet rigidity, inability to form filopodia, and reduced basal PI(3)P pool. Mislocalization of membrane skeleton proteins controlling plasma membrane–cytoskeleton interactions was observed in affected platelets. These defects led to delayed arterial occlusion and impaired thrombus formation.\",\n      \"method\": \"Constitutive kinase-dead knock-in mouse, flow cytometry, electron microscopy, PI3P quantification, ex vivo thrombosis assay, in vivo arterial occlusion model\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — kinase-dead genetic mouse model with multiple orthogonal cellular and in vivo functional readouts\",\n      \"pmids\": [\"26109204\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PI3K-C2α knockdown impaired Shigella flexneri dissemination by blocking resolution of protrusions into vacuoles via an intermediate vacuole-like protrusion (VLP). Genetic rescue with RNAi-resistant cDNA (but not kinase-dead PI3K-C2α) restored VLP formation, requiring kinase activity in primary infected cells. PI3K-C2α produced PI(3)P at the protrusion plasma membrane, regulated by host tyrosine kinase signaling and the bacterial T3SS.\",\n      \"method\": \"siRNA knockdown, time-lapse microscopy, RNAi-resistant rescue constructs, PI(3)P reporter, kinase-dead mutant\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — rescue with kinase-dead vs. WT construct directly establishes kinase requirement; multiple orthogonal methods\",\n      \"pmids\": [\"25667265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PI3K-C2α knockdown decreased autophagy and caused accumulation of endocytic vesicles at recycling endosomes. Kinase-dead PI3K-C2α failed to rescue autophagy, establishing a requirement for catalytic activity. PI3K-C2α co-localizes with endocytic markers and interacts with ATG9. Double knockdown of PIK3C2A and ATG9A/B phenocopied each other, suggesting a shared pathway connecting endocytic and autophagic trafficking.\",\n      \"method\": \"siRNA knockdown, confocal microscopy, transferrin labeling, membrane fractionation, co-immunoprecipitation, kinase-dead rescue\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — kinase-dead rescue and co-IP with ATG9 establish mechanistic link; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"28910396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PI3K-C2α knockdown in pancreatic β-cells rerouted insulin signaling from the IR-B/PI3K-C2α/PKBα metabolic axis to IR-B/Shc/ERK mitogenic signaling, causing a switch from a glucose-responsive differentiated state to a proliferative state, demonstrating cascade-selective insulin resistance within a single cell type.\",\n      \"method\": \"siRNA knockdown, immunoprecipitation, Western blot, live-cell imaging, glucose-stimulated insulin secretion assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — single lab, multiple signaling readouts establishing pathway switch, but no independent replication\",\n      \"pmids\": [\"26387957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Heterozygous kinase-dead PI3K-C2α knock-in male mice developed early-onset leptin resistance with a defect in leptin signaling in the hypothalamus, correlating with age-dependent obesity, insulin resistance, and glucose intolerance. No metabolic phenotypes were detected in female mice. Importantly, insulin signaling in peripheral insulin target tissues was unaffected in these mice.\",\n      \"method\": \"Constitutive heterozygous kinase-dead knock-in mice, metabolic phenotyping, glucose tolerance tests, hypothalamic leptin signaling assays\",\n      \"journal\": \"Diabetologia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic mouse model with defined mechanistic phenotype; single lab, sex-specific effect not independently replicated\",\n      \"pmids\": [\"27138914\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PI3K-C2α acts as a kinase-independent scaffold organizing clathrin and TACC3 into inter-microtubule bridge complexes that crosslink kinetochore fibers (K-fibers) during mitosis. Downregulation of PI3K-C2α caused spindle alterations, delayed anaphase onset, and aneuploidy. Reduced PI3K-C2α expression in breast cancer initially impaired tumor growth but led to evolution of fast-growing clones with mitotic checkpoint defects and increased taxane sensitivity.\",\n      \"method\": \"siRNA knockdown, live-cell imaging, co-immunoprecipitation (clathrin/TACC3 complex), rescue with kinase-dead vs. WT construct, breast cancer xenograft models\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — kinase-dead rescue distinguishes scaffold from catalytic function; co-IP identifies complex; multiple cellular and in vivo readouts\",\n      \"pmids\": [\"29017056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PI3K-C2α and PI3K-C2β both localize to clathrin-coated pits and are required for clathrin-mediated (but not clathrin-independent) pinocytosis up to the step of delivery to early endosomes. PI3K-C2β, but not PI3K-C2α, co-localizes with actin filament-associated clathrin-coated structures and is required for actin filament formation at those structures, distinguishing their specific roles.\",\n      \"method\": \"siRNA knockdown, FITC-dextran uptake assay, transferrin labeling, confocal co-localization, clathrin heavy chain knockdown\",\n      \"journal\": \"The journal of physiological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA KD with functional pinocytosis assay and co-localization; single lab, multiple readouts but no rescue\",\n      \"pmids\": [\"30374841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"KSHV nonstructural membrane protein pK15 interacts and co-localizes with PI3K-C2α in perinuclear vesicular structures. PI3K-C2α contributes to pK15-dependent phosphorylation of PLCγ1 and Erk1/2. Depletion of PI3K-C2α in KSHV-infected endothelial cells reduced expression of viral lytic genes K-bZIP and ORF45 and decreased release of infectious virus.\",\n      \"method\": \"Co-immunoprecipitation with mass spectrometry, immunofluorescence co-localization, siRNA knockdown, Western blot for signaling targets, viral gene expression assays\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP/MS identifies interaction, KD establishes functional role in signaling and viral replication; single lab\",\n      \"pmids\": [\"29950425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Homozygous loss-of-function mutations in PIK3C2A cause a Mendelian disorder with short stature, cataracts, skeletal abnormalities, and neurological manifestations. Patient-derived fibroblasts lacking PIK3C2A protein showed impaired cilia formation and function and reduced proliferative capacity, establishing PIK3C2A as essential for ciliogenesis and cell proliferation.\",\n      \"method\": \"Exome sequencing of consanguineous families, patient-derived fibroblast analysis, cilia formation assay, proliferation assay, Western blot\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human genetics with cellular validation in patient fibroblasts; three independent families, but mechanistic depth limited to cilia/proliferation readouts\",\n      \"pmids\": [\"31034465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PI3K-C2α generates PI(3)P at the primary cilium in response to shear stress (urinary flow) to initiate cilium-dependent autophagy in kidney proximal tubule epithelial cells. This pathway is independent of ULK1 and BECN1, distinguishing it from starvation-induced autophagy driven by PIK3C3/VPS34.\",\n      \"method\": \"siRNA knockdown of PIK3C2A vs. PIK3C3, PI(3)P reporters, shear stress assay, autophagy markers, confocal microscopy\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — parallel KD of PIK3C2A vs. PIK3C3 with PI(3)P reporter and autophagy assays establishes pathway specificity; single lab\",\n      \"pmids\": [\"32102612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PI3K-C2α is required for TGFβ receptor endocytosis through sequential phosphoinositide conversions: PI3K-C2α KD abolished TGFβ-induced PI(3,4)P2 increases and also prevented synaptojanin1 recruitment to the plasma membrane, PI(4,5)P2 decreases, and PI(4)P increases. Synaptojanin1 and INPP4B (but not PI3K-C2β, Synj2, or INPP4A) work sequentially with PI3K-C2α. These phosphoinositide conversions are necessary for Smad2/3 activation.\",\n      \"method\": \"siRNA knockdown of individual PI3K and phosphatase isoforms, phosphoinositide biosensors/quantification, co-localization imaging, Smad2/3 phosphorylation assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isoform-specific KD panel with PI biosensors plus signaling readouts establish ordered pathway; multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"31913757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Crystal structures of the PI3K-C2α PX domain at 2.1 Å and 2.5 Å revealed two conformations of the phosphoinositide-binding loops, with one structure containing a putative ligand in the binding site. This demonstrated that the PX domain undergoes a conformational change associated with ligand binding and clarified the molecular basis for PI specificity.\",\n      \"method\": \"X-ray crystallography (2.1 Å and 2.5 Å structures of PX domain)\",\n      \"journal\": \"BMC structural biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — crystal structures provide direct structural insight; however single study, no functional mutagenesis validation reported\",\n      \"pmids\": [\"18312637\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"C/EBPα transcriptionally activates PIK3C2A by binding to a site in its promoter (established by ChIP assay). C/EBPα and PIK3C2A promote autophagy and phenotypic switching (synthetic to contractile) in vascular smooth muscle cells under aortic dissection conditions. PIK3C2A knockdown reversed C/EBPα-driven autophagy activation, MMP upregulation, and VSMC phenotype switching.\",\n      \"method\": \"ChIP assay, siRNA/plasmid-based gain/loss-of-function, Western blot, aortic ring stretch-stress model, in vivo tail-vein shRNA injection\",\n      \"journal\": \"Journal of immunology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP establishes direct transcriptional regulation; functional rescue experiments in multiple contexts; single lab\",\n      \"pmids\": [\"36132983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Inducible genetic inactivation of PI3K-C2α in adult mice sensitized them to LPS-induced endotoxic shock. Vascular endothelial-specific deletion recapitulated this phenotype. Sensitization was fully rescued by combined deficiency of caspase-8 and RIPK3, placing PI3K-C2α upstream of extrinsic cell death pathway activation in endothelial cells.\",\n      \"method\": \"Inducible conditional knockout mice, vascular endothelial-specific deletion, LPS challenge model, genetic epistasis (caspase-8/RIPK3 double knockout rescue)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with double-KO rescue definitively places PI3K-C2α in the extrinsic cell death pathway; multiple genetic models\",\n      \"pmids\": [\"40674428\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TTC7A functions as a molecular chaperone for PIK3C2A and is required for its trafficking to the plasma membrane via Rab11a-positive vesicles. PIK3C2A generates PI(3,4)P2 at the apical membrane to specify apical identity during intestinal lumen formation. Defective lumen formation in TTC7A loss-of-function was rescued by exogenous PI(3,4)P2 or small molecules modulating phosphoinositide homeostasis.\",\n      \"method\": \"Patient-derived organoids, protein trafficking assays, Rab11a co-localization, PI(3,4)P2 reporter, exogenous lipid rescue, pharmacological rescue\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — preprint; multiple orthogonal methods including lipid rescue establish functional pathway, but not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.03.22.644724\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"PI3K-C2α (PIK3C2A) is a class II phosphoinositide 3-kinase that catalyzes production of PI(3)P and PI(3,4)P2 in spatially restricted membrane compartments—including clathrin-coated vesicles, the trans-Golgi network, early endosomes, and the plasma membrane—to regulate clathrin-mediated endocytosis of receptor tyrosine kinases (VEGFR, TGFβR, insulin receptor isoform B) and their downstream signaling (RhoA, Smad2/3, PKBα/Akt1); it also acts as a kinase-independent scaffold organizing clathrin–TACC3 complexes at mitotic kinetochore fibers to ensure genomic stability, generates PI(3)P at the primary cilium to initiate shear-stress-dependent autophagy, and controls endosomal maturation and vesicle recycling, with its inactivation in endothelial cells sensitizing to extrinsic (caspase-8/RIPK3-dependent) cell death.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PIK3C2A (PI3K-C2α) is a class II phosphoinositide 3-kinase that generates spatially restricted pools of PI(3)P and PI(3,4)P2 to couple membrane trafficking with receptor signaling, ciliogenesis, and mitotic fidelity [#0, #2, #3]. It is constitutively membrane-associated and concentrated on clathrin-coated vesicles and the trans-Golgi network in an ARF-dependent manner [#0], and together with PI3K-C2β it is required for clathrin-mediated pinocytosis up to delivery to early endosomes [#11]. Through this endocytic activity it controls internalization and downstream signaling of multiple receptors: it produces PI(3,4)P2 at plasma membrane microdomains to drive insulin receptor isoform B-dependent PKBα/Akt1 activation in pancreatic β-cells [#2, #8], and it directs TGFβ receptor uptake into SARA-containing early endosomes—via an ordered phosphoinositide conversion engaging synaptojanin1 and INPP4B—to enable Smad2/3 activation [#4, #15]. In endothelial cells PI3K-C2α generates PI(3)P-enriched endosomes required for VEGF receptor internalization, endosomal RhoA activation, VE-cadherin delivery, and junction assembly, and its loss causes embryonic lethality with defective angiogenesis and vascular barrier function [#3]. Independent of its catalytic activity, PI3K-C2α acts as a scaffold that organizes clathrin and TACC3 into inter-microtubule bridges crosslinking kinetochore fibers, ensuring proper spindle function and genomic stability [#10]. It also generates PI(3)P at the primary cilium to initiate a shear-stress-induced, ULK1/BECN1-independent form of autophagy [#14], and connects endocytic and autophagic trafficking through interaction with ATG9 [#7]. Homozygous loss-of-function mutations in PIK3C2A cause a Mendelian disorder of short stature, cataracts, skeletal abnormalities, and neurological manifestations, with patient fibroblasts showing impaired ciliogenesis and proliferation [#13].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established that PI3K-C2α is an agonist-responsive lipid kinase distinct from class IA PI3K, answering whether the enzyme is regulated by physiological stimuli.\",\n      \"evidence\": \"MCP-1-stimulated IP lipid kinase assay with wortmannin/pertussis toxin dissection\",\n      \"pmids\": [\"9748276\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct lipid product specificity in vivo not resolved\", \"Receptor coupling mechanism to the kinase undefined\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defined where PI3K-C2α operates by localizing it to clathrin-coated vesicles and the ARF-dependent trans-Golgi network, linking the enzyme to membrane trafficking compartments.\",\n      \"evidence\": \"Subcellular fractionation, dual-label immunofluorescence, brefeldin A, and deletion mutants\",\n      \"pmids\": [\"10766823\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which trafficking step the lipid product controls not shown\", \"Functional consequence of TGN localization untested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Provided structural basis for phosphoinositide recognition by resolving PX-domain conformations associated with ligand binding.\",\n      \"evidence\": \"X-ray crystallography of the PX domain at 2.1 and 2.5 Å\",\n      \"pmids\": [\"18312637\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional mutagenesis validating the binding model\", \"Full-length enzyme architecture not determined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified the lipid product (PI(3,4)P2) and signaling output (PKBα/Akt1) of insulin-stimulated PI3K-C2α, establishing its role in metabolic signaling and insulin secretion.\",\n      \"evidence\": \"siRNA knockdown, PI-lipid profiling, TIRF/confocal imaging, and insulin secretion assays in β-cells\",\n      \"pmids\": [\"20061534\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking PI(3,4)P2 to glucokinase and AS160 not detailed\", \"Receptor microdomain organization mechanism unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstrated an essential endosomal trafficking role in endothelial cells, linking PI3K-C2α-derived PI(3)P to VEGFR internalization, RhoA signaling, junction assembly, and angiogenesis in vivo.\",\n      \"evidence\": \"siRNA, conditional and global knockout mice, in vivo angiogenesis and barrier assays\",\n      \"pmids\": [\"22983395\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct effector reading the endosomal PI(3)P pool not identified\", \"Distinction between trafficking defect and signaling defect not fully separated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Placed PI3K-C2α upstream of TGFβ receptor endocytosis and Smad2/3 signaling, defining its requirement for clathrin/dynamin-dependent uptake into SARA-positive endosomes.\",\n      \"evidence\": \"siRNA, phosphoinositide measurements, dynamin inhibitor, EC-specific knockout mice, Matrigel assay\",\n      \"pmids\": [\"25614622\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Order of phosphoinositide conversions not yet resolved at this stage\", \"Direct partners coordinating SARA recruitment unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Distinguished the requirement for kinase activity by showing kinase-dead PI3K-C2α causes platelet morphology, granule, and cytoskeletal defects affecting thrombus formation.\",\n      \"evidence\": \"Heterozygous kinase-dead knock-in mice, EM, PI(3)P quantification, thrombosis assays\",\n      \"pmids\": [\"26109204\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of mislocalized membrane skeleton proteins not mechanistically mapped\", \"Link between basal PI(3)P pool and cytoskeleton coupling undefined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Showed kinase-dependent PI(3)P production at protrusion membranes is required for Shigella cell-to-cell spread, extending the enzyme's role to pathogen dissemination.\",\n      \"evidence\": \"siRNA, RNAi-resistant WT vs kinase-dead rescue, PI(3)P reporter, time-lapse imaging\",\n      \"pmids\": [\"25667265\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Host effector downstream of PI(3)P at protrusions unknown\", \"Interplay with bacterial T3SS effectors not detailed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Connected endocytic and autophagic trafficking by demonstrating kinase-dependent regulation of autophagy and physical interaction with ATG9.\",\n      \"evidence\": \"siRNA, kinase-dead rescue, transferrin labeling, co-IP with ATG9, double knockdown\",\n      \"pmids\": [\"28910396\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reciprocal validation of ATG9 interaction limited\", \"Site of PI(3)P production driving autophagy not localized\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Revealed cascade-selective insulin signaling, where loss of PI3K-C2α reroutes IR-B from the metabolic Akt axis to mitogenic Shc/ERK signaling within a single cell type.\",\n      \"evidence\": \"siRNA, IP, Western blot, live imaging, glucose-stimulated insulin secretion in β-cells\",\n      \"pmids\": [\"26387957\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular switch directing receptor adaptor choice unknown\", \"Not independently replicated\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Extended metabolic function in vivo by showing kinase-dead PI3K-C2α causes hypothalamic leptin resistance and sex-specific obesity, distinct from peripheral insulin signaling.\",\n      \"evidence\": \"Heterozygous kinase-dead knock-in mice, metabolic phenotyping, hypothalamic leptin assays\",\n      \"pmids\": [\"27138914\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Basis of male-specific phenotype unexplained\", \"Direct role in leptin receptor trafficking not shown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined a kinase-independent scaffold function organizing clathrin-TACC3 bridges at kinetochore fibers to maintain genomic stability, separating structural from catalytic roles.\",\n      \"evidence\": \"siRNA, live imaging, co-IP, WT vs kinase-dead rescue, breast cancer xenografts\",\n      \"pmids\": [\"29017056\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the scaffold is targeted to K-fibers not resolved\", \"Relationship between scaffold and lipid kinase pools unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Distinguished isoform-specific roles, showing PI3K-C2α and C2β both support clathrin-mediated pinocytosis but only C2β couples to actin-associated clathrin structures.\",\n      \"evidence\": \"siRNA of each isoform, FITC-dextran uptake, transferrin labeling, co-localization\",\n      \"pmids\": [\"30374841\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No rescue confirming specificity\", \"Mechanistic basis for differential actin coupling unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified a viral cofactor role, where KSHV pK15 recruits PI3K-C2α to drive PLCγ1/Erk signaling and lytic viral gene expression.\",\n      \"evidence\": \"Co-IP/MS, immunofluorescence, siRNA, signaling and viral gene assays\",\n      \"pmids\": [\"29950425\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether kinase activity is required for pK15 signaling untested\", \"Direct vs indirect interaction not resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Established PIK3C2A as the cause of a human Mendelian disorder, linking loss of function to defective ciliogenesis and proliferation.\",\n      \"evidence\": \"Exome sequencing of consanguineous families, patient fibroblast cilia and proliferation assays\",\n      \"pmids\": [\"31034465\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Tissue-specific mechanisms behind skeletal/neurological phenotypes not dissected\", \"Lipid product driving ciliogenesis not mapped in patient cells\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined a distinct autophagy pathway in which ciliary PI(3)P from PI3K-C2α initiates shear-stress autophagy independent of ULK1/BECN1 and VPS34.\",\n      \"evidence\": \"Parallel PIK3C2A vs PIK3C3 knockdown, PI(3)P reporters, shear-stress autophagy assays\",\n      \"pmids\": [\"32102612\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Downstream autophagy machinery reading ciliary PI(3)P unknown\", \"How shear stress activates the enzyme not defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved the ordered phosphoinositide conversion for TGFβ receptor endocytosis, placing PI3K-C2α at the head of a synaptojanin1/INPP4B cascade required for Smad2/3 activation.\",\n      \"evidence\": \"Isoform/phosphatase-specific siRNA panel, PI biosensors, co-localization, Smad2/3 phosphorylation\",\n      \"pmids\": [\"31913757\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Spatial recruitment hierarchy of the enzymes not fully mapped\", \"Generality to other receptors untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified upstream transcriptional control by C/EBPα and a role in vascular smooth muscle autophagy and phenotypic switching during aortic dissection.\",\n      \"evidence\": \"ChIP, gain/loss-of-function, aortic ring stretch model, in vivo shRNA\",\n      \"pmids\": [\"36132983\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether kinase activity mediates the VSMC phenotype untested\", \"Single lab, mechanism downstream of PIK3C2A in VSMC unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Placed endothelial PI3K-C2α upstream of extrinsic cell death, showing its inactivation sensitizes to endotoxic shock via caspase-8/RIPK3-dependent death.\",\n      \"evidence\": \"Inducible and EC-specific knockout mice, LPS challenge, caspase-8/RIPK3 double-KO epistasis rescue\",\n      \"pmids\": [\"40674428\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link from lipid signaling to death pathway suppression unknown\", \"Whether kinase or scaffold function is required not resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined TTC7A as a chaperone delivering PIK3C2A to the apical membrane to generate PI(3,4)P2 specifying apical identity during lumen formation.\",\n      \"evidence\": \"Patient organoids, trafficking and Rab11a co-localization, PI(3,4)P2 reporter, lipid/pharmacological rescue (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.03.22.644724\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Not peer-reviewed\", \"Direct biochemical TTC7A-PIK3C2A binding details limited\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PI3K-C2α's distinct PI(3)P and PI(3,4)P2 pools, its kinase-independent scaffold function, and its compartment-specific recruitment are coordinated to produce its diverse physiological roles remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model linking lipid products to specific effectors across compartments\", \"Mechanism of stimulus-specific enzyme activation undefined\", \"Structural basis of full-length enzyme regulation unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [1, 2, 3, 15]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 16]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 11]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [3, 4, 7]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 15, 19]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [13, 14]},\n      {\"term_id\": \"GO:0005819\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 3, 11]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 4, 15]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [7, 14]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 13]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"complexes\": [\"clathrin–TACC3 inter-microtubule bridge\"],\n    \"partners\": [\"CLTC\", \"TACC3\", \"ATG9A\", \"SARA\", \"SYNJ1\", \"INPP4B\", \"TTC7A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}