{"gene":"PDZK1","run_date":"2026-04-29T11:37:58","timeline":{"discoveries":[{"year":1998,"finding":"PDZK1 was identified as a novel 519-amino acid protein containing four PDZ protein interaction domains, discovered by yeast two-hybrid screening of a human kidney cDNA library using MAP17 as bait. PDZK1 colocalized with MAP17 in the brush border of proximal tubular epithelial cells of the kidney.","method":"Yeast two-hybrid screening, in situ hybridization, co-localization","journal":"Laboratory investigation","confidence":"Medium","confidence_rationale":"Tier 3 — original identification by yeast two-hybrid with localization data, single study","pmids":["9461128"],"is_preprint":false},{"year":2003,"finding":"PDZK1 knockout mice lack overt phenotype but show modulation of selective ion channel expression in the kidney and increased serum cholesterol levels; PDZK1 loss did not significantly redistribute MAP17, cMOAT, or the type IIa Na/Pi cotransporter, suggesting functional compensation by other PDZ proteins.","method":"Homologous recombination knockout mouse, Western blot, serum cholesterol measurement","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined phenotypic readouts in vivo, multiple endpoints measured","pmids":["12556478"],"is_preprint":false},{"year":2003,"finding":"MAP17 interacts specifically with the fourth PDZ domain of PDZK1 (but not with other PDZ proteins in proximal tubular brush borders), and MAP17 acts as an apical anchoring site for PDZK1, as apical localization of PDZK1 is dependent on MAP17 but not vice versa.","method":"Yeast two-hybrid, in vitro binding assays, immunofluorescence, transfection in opossum kidney cells","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 3 — single study with multiple in vitro methods and cell-based localization","pmids":["12837682"],"is_preprint":false},{"year":2003,"finding":"PDZK1 anchors the dual-specific A-kinase anchoring protein D-AKAP2 to the subapical membrane of renal proximal tubular cells via PDZ domain 4 of PDZK1, thereby compartmentalizing PKA activity near NaPi-IIa to enable PTH-mediated regulation.","method":"Yeast two-hybrid, pull-down assays, co-immunoprecipitation from transfected OK cells, immunohistochemistry, real-time PCR","journal":"Kidney international","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal Co-IP plus pull-down with domain mapping, single lab","pmids":["14531807"],"is_preprint":false},{"year":2005,"finding":"PDZK1 is required for normal brush-border expression and function of the Cl-anion exchanger CFEX (SLC26A6/PAT1) in renal proximal tubule; PDZK1 directly binds NHE3 and CFEX via their C-terminal PDZ-interaction sites. Loss of PDZK1 markedly reduced CFEX protein expression and Cl-oxalate exchange activity, while NHE3 brush-border expression was unaffected.","method":"GST pull-down with native brush border membrane proteins, Western blot, immunocytochemistry, brush border membrane vesicle transport assay, microperfused proximal tubule volume absorption, PDZK1-null mice","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro binding assays plus in vivo KO functional readouts, multiple orthogonal methods","pmids":["16141316"],"is_preprint":false},{"year":2005,"finding":"PDZK1 controls hepatic SR-BI protein levels in a posttranscriptional manner; phosphorylation of PDZK1 at Ser-509 by PKA (stimulated by glucagon) is required for PDZK1 to upregulate SR-BI protein expression. Mutation of Ser-509 to Ala abolishes the ability of PDZK1 to upregulate SR-BI.","method":"Metabolic labeling, phosphoamino acid analysis, site-directed mutagenesis, in vitro kinase assay with PKA, cell culture overexpression, phospho-specific antibody, glucagon administration to rats","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay combined with mutagenesis and in vivo hormonal validation","pmids":["16174736"],"is_preprint":false},{"year":2005,"finding":"PDZK1 interacts with organic anion transporter Oatp1a1 via its C-terminal PDZ-interaction site, predominantly at the first and third PDZ domains of PDZK1; PDZK1 is required for basolateral plasma membrane localization of Oatp1a1 in hepatocytes—in PDZK1 knockout liver, Oatp1a1 is retained in intracellular structures, impairing hepatic organic anion transport.","method":"C-terminal peptide affinity isolation, protein mass fingerprinting, co-immunoprecipitation from cotransfected 293T cells and native rat liver membranes, immunofluorescence, radiolabeled substrate plasma disappearance in PDZK1-KO mice","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, domain mapping, in vivo localization and functional transport assay in KO mice","pmids":["15994332"],"is_preprint":false},{"year":2005,"finding":"PDZK1 (CAP70) interacts with the intestinal anion exchanger DRA via the DRA C-terminal PDZ interaction motif, binding at the 2nd and 3rd PDZ domains of PDZK1/CAP70, distinct from CFTR which binds PDZ1, PDZ3, and PDZ4.","method":"Overlay assay with recombinant DRA C-terminus, anti-CAP70 antibody identification, in vitro binding assays, co-immunoprecipitation in transfected HEK cells","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 3 — multiple in vitro binding methods with domain specificity mapping, single lab","pmids":["15766278"],"is_preprint":false},{"year":2005,"finding":"PDZK1 interacts with SSTR5 (somatostatin receptor subtype 5) at the plasma membrane via the PDZ ligand motif at the C-terminus of SSTR5; PDZK1 is required for post-endocytic recycling of SSTR5 back to the plasma membrane after agonist-induced internalization.","method":"Yeast two-hybrid, co-localization studies, receptor recycling assay in transfected cells","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 — yeast two-hybrid and co-localization with functional recycling assay, single lab","pmids":["16012170"],"is_preprint":false},{"year":2006,"finding":"PDZK1 interacts with human PEPT2 (SLC15A2) via PDZ motif of the PEPT2 C-terminus, binding at the 2nd and 3rd PDZ domains of PDZK1; PDZK1 co-expression increases V(max) of glycylsarcosine transport by PEPT2 by increasing PEPT2 surface expression.","method":"Yeast two-hybrid, in vitro binding assay, co-immunoprecipitation (human kidney membrane fraction), surface plasmon resonance for binding affinities, functional transport assay in HEK293 cells","journal":"Kidney international","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including SPR quantification and functional transport assay","pmids":["16738539"],"is_preprint":false},{"year":2006,"finding":"MAP17 interacts with all four NHERF family proteins (including PDZK1/NHERF3) and NaPi-IIa; co-expression of MAP17 with NHERF3 or NHERF4 (but not NHERF1/2) causes internalization of NaPi-IIa, MAP17, and the PDZ protein to the trans-Golgi network via a PKC-dependent mechanism.","method":"Bacterial and mammalian two-hybrid systems, functional studies in opossum kidney (OK) cells, PKC inhibitor/activator treatment, immunofluorescence","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 3 — two-hybrid plus cell imaging and pharmacological intervention, single lab","pmids":["16926447"],"is_preprint":false},{"year":2007,"finding":"PDZK1 is required for cAMP- and Ca2+-dependent inhibition of NHE3 activity in native colonic enterocytes; PDZK1 ablation abolishes forskolin- and ionomycin-mediated inhibition of NHE3 while hyperosmolarity-mediated inhibition remains intact. PDZK1 loss does not alter NHE3 abundance or brush-border localization in colon.","method":"Fluorometric NHE3 transport assay in BCECF-loaded colonic crypts, Western blot, immunohistochemistry, qPCR, PDZK1-null mice","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with specific functional readout (agonist-selective inhibition), multiple methods","pmids":["17395628"],"is_preprint":false},{"year":2007,"finding":"PDZK1 (CAP70) binds to inducible nitric oxide synthase (NOS2) via the four C-terminal amino acids of NOS2, enhancing NOS2 cytochrome c reductase and NO-synthase activities, increasing the population of active NOS2 dimers, and participating in apical targeting of NOS2 in polarized epithelial cells (in combination with N-terminal palmitoylation).","method":"Co-immunoprecipitation, enzyme activity assays, subcellular localization by immunofluorescence in polarized cells","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP with functional enzyme assay, single lab","pmids":["17507652"],"is_preprint":false},{"year":2007,"finding":"PDZK1 ablation in mouse small intestine causes severe defect in electroneutral Na+ absorption and mild reduction of CFTR-mediated anion secretion; NHE3 brush-border expression is unaffected, but NHE3 mRNA is increased, suggesting increased NHE3 turnover due to reduced membrane retention without PDZK1.","method":"Short circuit current measurements, 22Na+ flux assays, qPCR, Western blot, immunohistochemistry in pdzk1-/- mice","journal":"Pflugers Archiv : European journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple transport function measurements, supported by molecular analysis","pmids":["17347851"],"is_preprint":false},{"year":2008,"finding":"PDZK1 is expressed in endothelium and required for HDL/SR-BI-induced Src phosphorylation, endothelial NO synthase (eNOS) activation, and cell migration; PDZK1 is not required for SR-BI abundance, plasma membrane localization, HDL binding, or cholesterol efflux in endothelium. PDZK1-/- mice fail to re-endothelialize after carotid artery injury.","method":"Co-immunoprecipitation (Src-SR-BI interaction), siRNA knockdown, eNOS activity assay, cell migration assay, carotid artery re-endothelialization in PDZK1-/- mice (including liver-specific reconstitution controls), cell surface biotinylation","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal cell biology and in vivo methods with genetic reconstitution controls","pmids":["18174467"],"is_preprint":false},{"year":2008,"finding":"PDZK1 regulates intestinal oligopeptide transporter PEPT1 (Slc15a1) and carnitine transporter OCTN2 (Slc22a5): PDZK1 physically interacts with PEPT1, and loss of PDZK1 reduces apical membrane localization and protein levels of both transporters, delaying GI absorption of their substrates.","method":"Co-immunoprecipitation (PEPT1-PDZK1 from mouse small intestine), immunohistochemistry, Western blot of brush-border membranes, electron microscopy, pharmacokinetic studies in pdzk1-/- mice, functional transport assay in HEK293 cells","journal":"Drug metabolism and disposition","confidence":"High","confidence_rationale":"Tier 2 — Co-IP plus in vivo pharmacokinetics, membrane fractionation, and cell-based functional assays","pmids":["18322073"],"is_preprint":false},{"year":2009,"finding":"PDZK1 undergoes head-to-tail intramolecular association: the C-terminal tail of PDZK1 interacts with its first PDZ domain, inducing a compact conformation. PDZK1 also forms modest homodimers via its third PDZ domain. The tail-PDZ1 intramolecular interaction does not affect binding of PDZ domain ligands of PDZK1 itself, but negatively regulates the interaction of PDZK1's tail with the PDZ domains of EBP50/NHERF1.","method":"In vitro binding assays, co-immunoprecipitation, size exclusion chromatography, limited proteolysis","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — multiple in vitro binding assays with domain mapping, single lab","pmids":["19173579"],"is_preprint":false},{"year":2009,"finding":"PDZK1 (NHERF3) directly binds the NHE3 C-terminus (between amino acids 588-667), co-immunoprecipitates with NHE3 in vivo, co-localizes at the plasma membrane under basal conditions, and reconstitutes Ca2+-dependent inhibition of NHE3 activity by dissociating from NHE3 upon elevated intracellular Ca2+. NHERF3 knockdown reduces basal NHE3 activity and brush border expression in Caco-2BBe cells.","method":"In vitro binding assay, co-immunoprecipitation, confocal microscopy, FRET, fluorometric NHE3 transport assay, shRNA knockdown","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (FRET, Co-IP, functional transport, KD) in two cell systems","pmids":["19535329"],"is_preprint":false},{"year":2009,"finding":"Pdzk1 ablation reduces basal HCO3- secretion in mouse duodenum but not FSK-stimulated secretion, distinguishing PDZK1's role from NHERF1 (obligatory for beta2-AR stimulation) and NHERF2 (mediates LPA inhibition of CFTR). PDZK1 reduction of basal CFTR-mediated secretion indicates a role in tonic CFTR regulation.","method":"Duodenal HCO3- secretion measurements, laser microdissection, qPCR, Nherf/Pdzk1 knockout mouse models","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — clean KO with quantified transport function, genetic epistasis with three PDZ protein knockouts","pmids":["19221439"],"is_preprint":false},{"year":2010,"finding":"PDZK1 binding (via C-terminal PDZ motif) promotes cell surface expression of Oatp1a1, and serine phosphorylation at S634/S635 (upstream of the PDZ motif) negatively regulates surface retention: phosphomimetic oatp1a1 remains intracellular even with PDZK1 co-expression. Extracellular ATP-induced phosphorylation of Oatp1a1 triggers rapid internalization in hepatocytes.","method":"Site-directed mutagenesis, transfection in HEK293T and HuH7 cells, surface biotinylation internalization assay, co-immunoprecipitation, confocal imaging, primary rat hepatocyte experiments","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis combined with quantitative surface biotinylation internalization assays and primary cell validation","pmids":["21183661"],"is_preprint":false},{"year":2010,"finding":"PDZK1 knockdown in hepatoma cells significantly reduces susceptibility to HCV infection; this effect requires more than just the first PDZ domain of PDZK1. PDZK1 facilitates HCV entry indirectly via its interaction with SR-BI, which serves as an HCV entry factor, and this interaction requires the C-terminal PDZ-interacting residue of SR-BI.","method":"Stable shRNA knockdown, PDZK1 overexpression rescue, GFP-SR-BI C-terminus chimera competition, HCV infection assay in Huh-7 cells","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 — shRNA knockdown with rescue, domain-specific competition experiments, single lab","pmids":["20949066"],"is_preprint":false},{"year":2011,"finding":"PDZK1 is required for apical membrane expression of NaPi-2c (but not NaPi-2a) in renal proximal tubule; FRET measurements show both NaPi-2a and NaPi-2c interact with PDZK1, but NaPi-2a shows stronger FRET with NHERF-1. In low-Pi adaptation, NaPi-2c/PDZK1 and NaPi-2a/NHERF-1 interactions increase, explaining differential regulation.","method":"Pdzk1-/- mice on low Pi diets, Western blot, immunofluorescence, FRET in transfected cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — in vivo KO plus quantitative FRET for direct protein-protein interaction, multiple conditions","pmids":["21388960"],"is_preprint":false},{"year":2011,"finding":"PDZK1 physically interacts with BCRP (breast cancer resistance protein) and is required for apical membrane localization of BCRP in mouse small intestine; PDZK1 co-expression in MDCKII/BCRP cells increases basal-to-apical transcellular transport and drug resistance to SN-38.","method":"Pull-down assay, co-immunoprecipitation, immunohistochemistry, Western blot of brush-border membranes, transcellular transport assay, cytotoxicity assay in MDCKII cells, pdzk1-/- mice pharmacokinetics","journal":"Drug metabolism and disposition","confidence":"High","confidence_rationale":"Tier 2 — physical interaction confirmed by Co-IP plus in vivo localization and functional transport assays","pmids":["21816982"],"is_preprint":false},{"year":2012,"finding":"PDZK1 specifically interacts with PLC-β3 (not PLC-β1) and assembles a ternary complex with PLC-β3 and somatostatin receptors (SSTRs), enabling specific activation of PLC-β3 by somatostatin. Disruption of this ternary complex inhibits SST-induced PLC activation, intracellular Ca2+ mobilization, and ERK1/2 phosphorylation.","method":"PDZ protein screen, co-immunoprecipitation, siRNA knockdown of PDZK1 or PLC-β3, Ca2+ mobilization assay, ERK1/2 phosphorylation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — ternary complex demonstrated by Co-IP plus functional signaling assays with selective knockdown controls","pmids":["22528496"],"is_preprint":false},{"year":2013,"finding":"PDZK1 expression in breast cancer cells promotes estrogen-mediated cell proliferation through enhancement of c-Myc expression; PDZK1 interacts with the Src/ER-α/EGFR complex and enhances EGFR-stimulated MEK/ERK1/2 signaling. PDZK1 expression is indirectly regulated by ER-α stimulation, requiring IGF-1R function.","method":"siRNA knockdown, ectopic overexpression, co-immunoprecipitation, proliferation assay, immunoblotting for signaling intermediates, tissue microarrays","journal":"Molecular medicine","confidence":"Medium","confidence_rationale":"Tier 3 — single study with Co-IP and functional proliferation data, mechanistic pathway only partially resolved","pmids":["23821363"],"is_preprint":false},{"year":2014,"finding":"PDZK1 directly interacts with OATP1A2 via its C-terminal PDZ-binding domain and increases OATP1A2 surface expression by decreasing clathrin-dependent (but not caveolin-dependent) internalization, and by enhancing OATP1A2 protein stability, resulting in increased V(max) of estrone-3-sulfate transport.","method":"Co-immunoprecipitation, surface biotinylation, internalization assay with clathrin/caveolin inhibitors, cycloheximide chase for stability, transport functional assay in HEK293 cells","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, mechanistic internalization assay, stability assay, functional transport) in single study","pmids":["24728453"],"is_preprint":false},{"year":2017,"finding":"PDZK1 inhibits SHP-1 phosphorylation at Tyr536 by blocking the association between SHP-1 and PLCβ3, thereby promoting STAT5 phosphorylation and retarding Akt phosphorylation in renal cell carcinoma cells.","method":"PDZK1 overexpression and knockdown models, co-immunoprecipitation, immunoblotting for phosphoproteins, xenograft tumor studies","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP with functional signaling readouts in cell lines and in vivo xenograft, single lab","pmids":["28692056"],"is_preprint":false},{"year":2018,"finding":"HNF4A directly binds the rs1967017 region of the PDZK1 promoter/enhancer and transcriptionally regulates PDZK1 expression; siRNA depletion of HNF4A reduces endogenous PDZK1 in HepG2 cells. The urate-increasing T allele of rs1967017 strengthens the HNF4A binding site, enhancing PDZK1 expression.","method":"siRNA knockdown, luciferase reporter assay, ChIP (HNF4A binding), zebrafish transgenic reporter, eQTL analysis","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP plus functional luciferase and knockdown in human cells, with in vivo zebrafish validation","pmids":["30124855"],"is_preprint":false},{"year":2019,"finding":"PDZK1 directly binds PTEN through its PDZ domains interacting with the PTEN C-terminus, and this interaction inhibits phosphorylation of PTEN at the S380/T382/T383 cluster, thereby enhancing PTEN's capacity to suppress PI3K/AKT signaling and gastric cancer cell proliferation.","method":"Co-immunoprecipitation, GST pull-down, site-directed mutagenesis, PDZK1 knockdown and overexpression, phospho-specific immunoblotting, in vitro and in vivo (xenograft) proliferation assays","journal":"Cancer letters","confidence":"High","confidence_rationale":"Tier 2 — Co-IP and GST pull-down establish direct binding, functional phosphorylation assay with in vivo validation","pmids":["30930234"],"is_preprint":false},{"year":2019,"finding":"PDZK1 interacts with sodium-coupled monocarboxylate transporters SMCT1 (SLC5A8) and SMCT2 (SLC5A12) via their C-terminal PDZ motifs; PDZK1 co-expression enhances nicotinate transport activity in SMCT1-expressing HEK293 cells. PDZK1, SMCT1, and URAT1 assemble into a trimolecular complex in vitro and co-localize in renal proximal tubule in vivo.","method":"Yeast two-hybrid, co-immunoprecipitation, functional transport assay in HEK293 cells, immunohistochemistry","journal":"The journal of physiological sciences","confidence":"Medium","confidence_rationale":"Tier 3 — yeast two-hybrid with Co-IP and functional assay, in vivo localization, single lab","pmids":["30604288"],"is_preprint":false},{"year":2022,"finding":"HDL-mediated protection against macrophage necroptosis requires SR-B1 and PDZK1 in a PI3K/Akt pathway-dependent manner; PDZK1 knockout in bone marrow-derived cells (not liver) increases atherosclerosis and necrotic core formation, which is reversed by restoring PDZK1 in BM-derived cells.","method":"Bone marrow transplantation reconstitution, PDZK1-/- LDLRKO mice, macrophage necroptosis assay, PI3K inhibitor, immunohistochemistry for RIPK3/MLKL","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 2 — BM reconstitution genetic epistasis with cell-specific mechanistic pathway dissection in vivo","pmids":["36353992"],"is_preprint":false},{"year":2024,"finding":"PDZK1 deficiency in chondrocytes impairs mitochondrial function (decreased mtDNA content, increased ROS, accumulation of damaged mitochondria) during mechanical overload by increasing ubiquitination and thereby reducing expression of Hmgcs2; PDZK1 loss exacerbates mechanical overload-induced chondrocyte senescence and cartilage degeneration.","method":"Pdzk1 chondrocyte knockout and AAV-PDZK1 intraarticular injection, mRNA sequencing, ubiquitination assay, mitochondrial function assays (ROS, mtDNA content, mitochondrial morphology), mechanical overload OA model","journal":"Bone research","confidence":"Medium","confidence_rationale":"Tier 2 — KO and rescue with mechanistic pathway (ubiquitination of Hmgcs2) identified by transcriptomics and biochemical assays, single study","pmids":["39019845"],"is_preprint":false}],"current_model":"PDZK1 is a four-PDZ-domain scaffold protein that organizes multiprotein complexes at epithelial apical membranes and in endothelium by directly binding the C-terminal PDZ-interaction motifs of diverse membrane transporters (NHE3, CFEX, Oatp1a1, OATP1A2, PEPT1, PEPT2, OCTN2, BCRP, SMCT1/2, NaPi-2c, SR-BI) and signaling molecules (PLC-β3, NOS2, PTEN, SHP-1); its scaffolding function promotes apical/surface retention, transport activity, and receptor-coupled signal transduction (eNOS activation, somatostatin-PLC-β3 signaling, PTEN-mediated PI3K/AKT suppression), and its activity is regulated by PKA-dependent phosphorylation at Ser-509 as well as by a head-to-tail intramolecular autoinhibitory association."},"narrative":{"teleology":[{"year":1998,"claim":"Identification of PDZK1 as a novel four-PDZ-domain protein in kidney proximal tubule brush border established the gene as a candidate epithelial scaffold.","evidence":"Yeast two-hybrid screen with MAP17 bait in human kidney cDNA library, with in situ hybridization confirming brush-border co-localization","pmids":["9461128"],"confidence":"Medium","gaps":["No functional data on transport or signaling","Interaction partners beyond MAP17 unknown","Expression outside kidney not characterized"]},{"year":2003,"claim":"Generation of PDZK1 knockout mice revealed a mild phenotype (increased serum cholesterol, selective ion channel changes) and showed that many expected client proteins were not redistributed, indicating functional redundancy among PDZ scaffold proteins.","evidence":"Homologous recombination knockout mouse with serum chemistry, Western blot, and immunolocalization of candidate interactors","pmids":["12556478"],"confidence":"High","gaps":["Source of hypercholesterolemia not mechanistically resolved","Identity of compensating PDZ proteins unclear","Tissue-specific contributions not dissected"]},{"year":2003,"claim":"Establishing that MAP17 anchors PDZK1 to the apical membrane (not vice versa) through PDZ domain 4 resolved the hierarchical assembly of the scaffold at the brush border.","evidence":"Yeast two-hybrid, in vitro binding, and immunofluorescence in opossum kidney cells showing PDZK1 apical localization depends on MAP17","pmids":["12837682"],"confidence":"Medium","gaps":["Whether MAP17-independent anchoring exists in other tissues not tested","Structural basis of PDZ4-MAP17 interaction unresolved"]},{"year":2005,"claim":"Demonstration that PDZK1 is required in vivo for CFEX brush-border expression and Cl⁻-oxalate exchange, while NHE3 localization was unaffected, established client-selective scaffolding as PDZK1's primary mechanism for controlling transporter function in kidney.","evidence":"GST pull-down, immunocytochemistry, and brush-border membrane vesicle transport assays in PDZK1-null mice","pmids":["16141316"],"confidence":"High","gaps":["Mechanism of selective client dependence (CFEX yes, NHE3 no) unknown","Whether PDZK1 stabilizes CFEX protein or only retains it at the surface not distinguished"]},{"year":2005,"claim":"Discovery that PKA phosphorylation of PDZK1 at Ser-509 is required for its ability to upregulate SR-BI protein levels provided the first post-translational regulatory mechanism for PDZK1 scaffold activity.","evidence":"In vitro PKA kinase assay, S509A mutagenesis abolishing SR-BI upregulation, glucagon administration in rats validating physiological PKA activation","pmids":["16174736"],"confidence":"High","gaps":["Whether Ser-509 phosphorylation affects PDZK1 interactions with clients other than SR-BI not tested","Structural consequence of phosphorylation on PDZK1 conformation unknown"]},{"year":2005,"claim":"Showing that PDZK1 is required for basolateral membrane localization of Oatp1a1 in hepatocytes extended the scaffold's role beyond apical membranes and into liver organic anion transport.","evidence":"C-terminal peptide affinity isolation, reciprocal Co-IP from rat liver, immunofluorescence and radiolabeled substrate clearance in PDZK1-KO mice","pmids":["15994332"],"confidence":"High","gaps":["Whether PDZK1 similarly controls other hepatic Oatps not determined","Mechanism of PDZK1-dependent basolateral targeting versus apical targeting not distinguished"]},{"year":2007,"claim":"Functional studies in PDZK1-null colon and small intestine demonstrated that PDZK1 is essential for cAMP- and Ca²⁺-dependent regulation of NHE3 and for electroneutral Na⁺ absorption, establishing its role as a signaling scaffold that couples second messengers to transporter regulation.","evidence":"Fluorometric NHE3 transport assay in BCECF-loaded colonic crypts and ²²Na⁺ flux measurements in PDZK1⁻/⁻ small intestine","pmids":["17395628","17347851"],"confidence":"High","gaps":["Identity of the Ca²⁺-sensing component in the PDZK1–NHE3 complex unknown","Whether PDZK1 recruits specific kinases or phosphatases to NHE3 not resolved"]},{"year":2008,"claim":"Discovery that PDZK1 is expressed in endothelium and required for HDL/SR-BI-induced Src activation, eNOS signaling, and vascular repair extended PDZK1's function from epithelial transport to cardiovascular signaling.","evidence":"Co-IP of Src–SR-BI, siRNA knockdown, eNOS activity assay, and carotid artery re-endothelialization in PDZK1⁻/⁻ mice with liver-specific reconstitution controls","pmids":["18174467"],"confidence":"High","gaps":["How PDZK1 couples SR-BI to Src mechanistically not resolved","Whether PDZK1 interacts directly with eNOS in endothelium not tested"]},{"year":2008,"claim":"Extending the client repertoire to intestinal PEPT1 and OCTN2 with in vivo pharmacokinetic consequences showed that PDZK1 is a general determinant of drug and nutrient transporter bioavailability in the gut.","evidence":"Co-IP of PEPT1–PDZK1 from mouse small intestine, brush-border fractionation, and pharmacokinetic absorption studies in PDZK1⁻/⁻ mice","pmids":["18322073"],"confidence":"High","gaps":["Whether PDZK1 loss alters transporter glycosylation or folding not examined","Contribution of other NHERF family members to compensation in gut not quantified"]},{"year":2009,"claim":"Identification of a head-to-tail intramolecular association (C-terminal tail binding PDZ1) revealed an autoinhibitory conformational switch that regulates PDZK1's intermolecular interactions, particularly with NHERF1.","evidence":"In vitro binding assays, size exclusion chromatography, and limited proteolysis showing compact conformation","pmids":["19173579"],"confidence":"Medium","gaps":["Physiological signals that relieve autoinhibition not identified","Whether autoinhibition affects client transporter binding in cells not tested","Structural details of the compact conformation lacking"]},{"year":2012,"claim":"Assembly of a PDZK1–PLC-β3–SSTR ternary signaling complex that specifically transduces somatostatin into Ca²⁺ mobilization and ERK1/2 activation demonstrated that PDZK1 functions as a receptor-to-effector coupling scaffold, not merely a membrane retention factor.","evidence":"Co-IP of ternary complex, siRNA knockdown of PDZK1 or PLC-β3, Ca²⁺ mobilization and ERK phosphorylation assays","pmids":["22528496"],"confidence":"High","gaps":["Whether PDZK1 scaffolds other GPCR–effector pairs unknown","Stoichiometry of the ternary complex not determined"]},{"year":2014,"claim":"Mechanistic dissection showing PDZK1 increases OATP1A2 surface expression by decreasing clathrin-dependent internalization and enhancing protein stability provided the first internalization-pathway-specific explanation for PDZK1's surface retention function.","evidence":"Surface biotinylation internalization assay with clathrin/caveolin inhibitors, cycloheximide chase, and functional transport assay in HEK293 cells","pmids":["24728453"],"confidence":"High","gaps":["Whether clathrin-dependent internalization suppression applies to other PDZK1 clients not tested","Structural basis of how PDZK1 shields the internalization signal unknown"]},{"year":2019,"claim":"Demonstration that PDZK1 binds PTEN and inhibits its inhibitory phosphorylation, thereby enhancing PTEN-mediated suppression of PI3K/AKT, established PDZK1 as a modulator of tumor suppressor activity.","evidence":"Co-IP, GST pull-down, S380/T382/T383 phospho-specific immunoblotting, PDZK1 knockdown/overexpression, and xenograft proliferation assays in gastric cancer cells","pmids":["30930234"],"confidence":"High","gaps":["Whether PDZK1-PTEN interaction occurs in normal epithelium or is cancer-specific not resolved","Identity of kinase whose access to PTEN is blocked by PDZK1 unknown"]},{"year":2022,"claim":"Bone marrow transplantation experiments established that PDZK1 in macrophages—not hepatocytes—mediates HDL/SR-BI protection against necroptosis and atherosclerotic necrotic core formation via PI3K/Akt, revealing a cell-autonomous anti-atherogenic function.","evidence":"Bone marrow reconstitution in PDZK1⁻/⁻ LDLR⁻/⁻ mice, macrophage necroptosis assays, PI3K inhibitor, RIPK3/MLKL immunohistochemistry","pmids":["36353992"],"confidence":"High","gaps":["Whether PDZK1 directly scaffolds PI3K or Akt in macrophages not shown","Molecular partners downstream of SR-BI in macrophage PDZK1 complex not identified"]},{"year":2024,"claim":"PDZK1 deficiency in chondrocytes was linked to mitochondrial dysfunction and senescence through increased ubiquitination and degradation of Hmgcs2, revealing a non-scaffolding role in protein stability and mitochondrial homeostasis.","evidence":"Chondrocyte-specific PDZK1 knockout, AAV rescue, mRNA sequencing, ubiquitination assay, mitochondrial function assays in mechanical overload OA model","pmids":["39019845"],"confidence":"Medium","gaps":["Whether PDZK1 directly binds Hmgcs2 or acts indirectly not determined","Mechanism by which PDZK1 suppresses Hmgcs2 ubiquitination unknown","Relevance to PDZK1's canonical PDZ-scaffolding function unclear"]},{"year":null,"claim":"Major open questions include the structural basis of PDZK1 autoinhibition and its relief by physiological signals, whether the clathrin-internalization-blocking mechanism generalizes across all transporter clients, how PDZK1 couples to PI3K/Akt in macrophages, and the full scope of client selectivity rules distinguishing PDZK1-dependent from PDZK1-independent targets.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of full-length PDZK1 or any client complex","Signal that relieves autoinhibition in vivo not identified","Systematic client dependency rules across tissues not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,6,9,15,17,22,23,25,28,29]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma 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membrane retention, and activity of diverse membrane transporters and signaling effectors. It directly binds the C-terminal PDZ-interaction motifs of transporters including NHE3, CFEX, Oatp1a1, OATP1A2, PEPT1, PEPT2, OCTN2, BCRP, NaPi-2c, and SMCT1/2 to promote their apical or basolateral localization and transport function, and loss of PDZK1 causes mislocalization and reduced activity of specific client proteins in kidney, intestine, and liver [PMID:16141316, PMID:15994332, PMID:18322073, PMID:21816982, PMID:21388960]. Beyond transporter scaffolding, PDZK1 assembles signaling complexes—including a PLC-β3/somatostatin receptor ternary complex for Ca²⁺ mobilization and ERK activation, an SR-BI/Src complex for eNOS activation in endothelium, and a PTEN complex that suppresses PI3K/AKT signaling—and its scaffolding function is regulated by PKA-dependent phosphorylation at Ser-509 and by a head-to-tail intramolecular autoinhibitory association between its C-terminal tail and first PDZ domain [PMID:22528496, PMID:18174467, PMID:30930234, PMID:16174736, PMID:19173579]. PDZK1 knockout mice exhibit increased serum cholesterol, impaired electroneutral Na⁺ absorption, defective endothelial repair after vascular injury, and—in bone marrow–derived macrophages—increased necroptosis and atherosclerotic necrotic core formation dependent on SR-BI/PI3K/Akt signaling [PMID:12556478, PMID:17347851, PMID:18174467, PMID:36353992]."},"prefetch_data":{"uniprot":{"accession":"Q5T2W1","full_name":"Na(+)/H(+) exchange regulatory cofactor NHE-RF3","aliases":["CFTR-associated protein of 70 kDa","Na(+)/H(+) exchanger regulatory factor 3","Na/Pi cotransporter C-terminal-associated protein 1","NaPi-Cap1","PDZ domain-containing protein 1","Sodium-hydrogen exchanger regulatory factor 3"],"length_aa":519,"mass_kda":57.1,"function":"A scaffold protein that connects plasma membrane proteins and regulatory components, regulating their surface expression in epithelial cells apical domains. 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May be involved in the regulation of proximal tubular Na(+)-dependent inorganic phosphate cotransport therefore playing an important role in tubule function (By similarity)","subcellular_location":"Membrane; Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q5T2W1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PDZK1","classification":"Not Classified","n_dependent_lines":186,"n_total_lines":1208,"dependency_fraction":0.15397350993377484},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PDZK1","total_profiled":1310},"omim":[{"mim_id":"611736","title":"GREB1 PROTEIN","url":"https://www.omim.org/entry/611736"},{"mim_id":"607762","title":"KIRRE-LIKE NEPHRIN FAMILY ADHESION MOLECULE 2; KIRREL2","url":"https://www.omim.org/entry/607762"},{"mim_id":"607761","title":"KIRRE-LIKE NEPHRIN FAMILY ADHESION MOLECULE 3; KIRREL3","url":"https://www.omim.org/entry/607761"},{"mim_id":"607428","title":"KIRRE-LIKE NEPHRIN FAMILY ADHESION MOLECULE 1; KIRREL1","url":"https://www.omim.org/entry/607428"},{"mim_id":"607178","title":"PDZK1-INTERACTING PROTEIN 1; PDZK1IP1","url":"https://www.omim.org/entry/607178"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Vesicles","reliability":"Approved"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in 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PDZK1 colocalized with MAP17 in the brush border of proximal tubular epithelial cells of the kidney.\",\n      \"method\": \"Yeast two-hybrid screening, in situ hybridization, co-localization\",\n      \"journal\": \"Laboratory investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — original identification by yeast two-hybrid with localization data, single study\",\n      \"pmids\": [\"9461128\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PDZK1 knockout mice lack overt phenotype but show modulation of selective ion channel expression in the kidney and increased serum cholesterol levels; PDZK1 loss did not significantly redistribute MAP17, cMOAT, or the type IIa Na/Pi cotransporter, suggesting functional compensation by other PDZ proteins.\",\n      \"method\": \"Homologous recombination knockout mouse, Western blot, serum cholesterol measurement\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined phenotypic readouts in vivo, multiple endpoints measured\",\n      \"pmids\": [\"12556478\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"MAP17 interacts specifically with the fourth PDZ domain of PDZK1 (but not with other PDZ proteins in proximal tubular brush borders), and MAP17 acts as an apical anchoring site for PDZK1, as apical localization of PDZK1 is dependent on MAP17 but not vice versa.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assays, immunofluorescence, transfection in opossum kidney cells\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single study with multiple in vitro methods and cell-based localization\",\n      \"pmids\": [\"12837682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PDZK1 anchors the dual-specific A-kinase anchoring protein D-AKAP2 to the subapical membrane of renal proximal tubular cells via PDZ domain 4 of PDZK1, thereby compartmentalizing PKA activity near NaPi-IIa to enable PTH-mediated regulation.\",\n      \"method\": \"Yeast two-hybrid, pull-down assays, co-immunoprecipitation from transfected OK cells, immunohistochemistry, real-time PCR\",\n      \"journal\": \"Kidney international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus pull-down with domain mapping, single lab\",\n      \"pmids\": [\"14531807\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PDZK1 is required for normal brush-border expression and function of the Cl-anion exchanger CFEX (SLC26A6/PAT1) in renal proximal tubule; PDZK1 directly binds NHE3 and CFEX via their C-terminal PDZ-interaction sites. Loss of PDZK1 markedly reduced CFEX protein expression and Cl-oxalate exchange activity, while NHE3 brush-border expression was unaffected.\",\n      \"method\": \"GST pull-down with native brush border membrane proteins, Western blot, immunocytochemistry, brush border membrane vesicle transport assay, microperfused proximal tubule volume absorption, PDZK1-null mice\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro binding assays plus in vivo KO functional readouts, multiple orthogonal methods\",\n      \"pmids\": [\"16141316\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PDZK1 controls hepatic SR-BI protein levels in a posttranscriptional manner; phosphorylation of PDZK1 at Ser-509 by PKA (stimulated by glucagon) is required for PDZK1 to upregulate SR-BI protein expression. Mutation of Ser-509 to Ala abolishes the ability of PDZK1 to upregulate SR-BI.\",\n      \"method\": \"Metabolic labeling, phosphoamino acid analysis, site-directed mutagenesis, in vitro kinase assay with PKA, cell culture overexpression, phospho-specific antibody, glucagon administration to rats\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay combined with mutagenesis and in vivo hormonal validation\",\n      \"pmids\": [\"16174736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PDZK1 interacts with organic anion transporter Oatp1a1 via its C-terminal PDZ-interaction site, predominantly at the first and third PDZ domains of PDZK1; PDZK1 is required for basolateral plasma membrane localization of Oatp1a1 in hepatocytes—in PDZK1 knockout liver, Oatp1a1 is retained in intracellular structures, impairing hepatic organic anion transport.\",\n      \"method\": \"C-terminal peptide affinity isolation, protein mass fingerprinting, co-immunoprecipitation from cotransfected 293T cells and native rat liver membranes, immunofluorescence, radiolabeled substrate plasma disappearance in PDZK1-KO mice\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, domain mapping, in vivo localization and functional transport assay in KO mice\",\n      \"pmids\": [\"15994332\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PDZK1 (CAP70) interacts with the intestinal anion exchanger DRA via the DRA C-terminal PDZ interaction motif, binding at the 2nd and 3rd PDZ domains of PDZK1/CAP70, distinct from CFTR which binds PDZ1, PDZ3, and PDZ4.\",\n      \"method\": \"Overlay assay with recombinant DRA C-terminus, anti-CAP70 antibody identification, in vitro binding assays, co-immunoprecipitation in transfected HEK cells\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — multiple in vitro binding methods with domain specificity mapping, single lab\",\n      \"pmids\": [\"15766278\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PDZK1 interacts with SSTR5 (somatostatin receptor subtype 5) at the plasma membrane via the PDZ ligand motif at the C-terminus of SSTR5; PDZK1 is required for post-endocytic recycling of SSTR5 back to the plasma membrane after agonist-induced internalization.\",\n      \"method\": \"Yeast two-hybrid, co-localization studies, receptor recycling assay in transfected cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — yeast two-hybrid and co-localization with functional recycling assay, single lab\",\n      \"pmids\": [\"16012170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PDZK1 interacts with human PEPT2 (SLC15A2) via PDZ motif of the PEPT2 C-terminus, binding at the 2nd and 3rd PDZ domains of PDZK1; PDZK1 co-expression increases V(max) of glycylsarcosine transport by PEPT2 by increasing PEPT2 surface expression.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assay, co-immunoprecipitation (human kidney membrane fraction), surface plasmon resonance for binding affinities, functional transport assay in HEK293 cells\",\n      \"journal\": \"Kidney international\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including SPR quantification and functional transport assay\",\n      \"pmids\": [\"16738539\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"MAP17 interacts with all four NHERF family proteins (including PDZK1/NHERF3) and NaPi-IIa; co-expression of MAP17 with NHERF3 or NHERF4 (but not NHERF1/2) causes internalization of NaPi-IIa, MAP17, and the PDZ protein to the trans-Golgi network via a PKC-dependent mechanism.\",\n      \"method\": \"Bacterial and mammalian two-hybrid systems, functional studies in opossum kidney (OK) cells, PKC inhibitor/activator treatment, immunofluorescence\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — two-hybrid plus cell imaging and pharmacological intervention, single lab\",\n      \"pmids\": [\"16926447\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PDZK1 is required for cAMP- and Ca2+-dependent inhibition of NHE3 activity in native colonic enterocytes; PDZK1 ablation abolishes forskolin- and ionomycin-mediated inhibition of NHE3 while hyperosmolarity-mediated inhibition remains intact. PDZK1 loss does not alter NHE3 abundance or brush-border localization in colon.\",\n      \"method\": \"Fluorometric NHE3 transport assay in BCECF-loaded colonic crypts, Western blot, immunohistochemistry, qPCR, PDZK1-null mice\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with specific functional readout (agonist-selective inhibition), multiple methods\",\n      \"pmids\": [\"17395628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PDZK1 (CAP70) binds to inducible nitric oxide synthase (NOS2) via the four C-terminal amino acids of NOS2, enhancing NOS2 cytochrome c reductase and NO-synthase activities, increasing the population of active NOS2 dimers, and participating in apical targeting of NOS2 in polarized epithelial cells (in combination with N-terminal palmitoylation).\",\n      \"method\": \"Co-immunoprecipitation, enzyme activity assays, subcellular localization by immunofluorescence in polarized cells\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP with functional enzyme assay, single lab\",\n      \"pmids\": [\"17507652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PDZK1 ablation in mouse small intestine causes severe defect in electroneutral Na+ absorption and mild reduction of CFTR-mediated anion secretion; NHE3 brush-border expression is unaffected, but NHE3 mRNA is increased, suggesting increased NHE3 turnover due to reduced membrane retention without PDZK1.\",\n      \"method\": \"Short circuit current measurements, 22Na+ flux assays, qPCR, Western blot, immunohistochemistry in pdzk1-/- mice\",\n      \"journal\": \"Pflugers Archiv : European journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple transport function measurements, supported by molecular analysis\",\n      \"pmids\": [\"17347851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PDZK1 is expressed in endothelium and required for HDL/SR-BI-induced Src phosphorylation, endothelial NO synthase (eNOS) activation, and cell migration; PDZK1 is not required for SR-BI abundance, plasma membrane localization, HDL binding, or cholesterol efflux in endothelium. PDZK1-/- mice fail to re-endothelialize after carotid artery injury.\",\n      \"method\": \"Co-immunoprecipitation (Src-SR-BI interaction), siRNA knockdown, eNOS activity assay, cell migration assay, carotid artery re-endothelialization in PDZK1-/- mice (including liver-specific reconstitution controls), cell surface biotinylation\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal cell biology and in vivo methods with genetic reconstitution controls\",\n      \"pmids\": [\"18174467\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PDZK1 regulates intestinal oligopeptide transporter PEPT1 (Slc15a1) and carnitine transporter OCTN2 (Slc22a5): PDZK1 physically interacts with PEPT1, and loss of PDZK1 reduces apical membrane localization and protein levels of both transporters, delaying GI absorption of their substrates.\",\n      \"method\": \"Co-immunoprecipitation (PEPT1-PDZK1 from mouse small intestine), immunohistochemistry, Western blot of brush-border membranes, electron microscopy, pharmacokinetic studies in pdzk1-/- mice, functional transport assay in HEK293 cells\",\n      \"journal\": \"Drug metabolism and disposition\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus in vivo pharmacokinetics, membrane fractionation, and cell-based functional assays\",\n      \"pmids\": [\"18322073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PDZK1 undergoes head-to-tail intramolecular association: the C-terminal tail of PDZK1 interacts with its first PDZ domain, inducing a compact conformation. PDZK1 also forms modest homodimers via its third PDZ domain. The tail-PDZ1 intramolecular interaction does not affect binding of PDZ domain ligands of PDZK1 itself, but negatively regulates the interaction of PDZK1's tail with the PDZ domains of EBP50/NHERF1.\",\n      \"method\": \"In vitro binding assays, co-immunoprecipitation, size exclusion chromatography, limited proteolysis\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vitro binding assays with domain mapping, single lab\",\n      \"pmids\": [\"19173579\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PDZK1 (NHERF3) directly binds the NHE3 C-terminus (between amino acids 588-667), co-immunoprecipitates with NHE3 in vivo, co-localizes at the plasma membrane under basal conditions, and reconstitutes Ca2+-dependent inhibition of NHE3 activity by dissociating from NHE3 upon elevated intracellular Ca2+. NHERF3 knockdown reduces basal NHE3 activity and brush border expression in Caco-2BBe cells.\",\n      \"method\": \"In vitro binding assay, co-immunoprecipitation, confocal microscopy, FRET, fluorometric NHE3 transport assay, shRNA knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (FRET, Co-IP, functional transport, KD) in two cell systems\",\n      \"pmids\": [\"19535329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Pdzk1 ablation reduces basal HCO3- secretion in mouse duodenum but not FSK-stimulated secretion, distinguishing PDZK1's role from NHERF1 (obligatory for beta2-AR stimulation) and NHERF2 (mediates LPA inhibition of CFTR). PDZK1 reduction of basal CFTR-mediated secretion indicates a role in tonic CFTR regulation.\",\n      \"method\": \"Duodenal HCO3- secretion measurements, laser microdissection, qPCR, Nherf/Pdzk1 knockout mouse models\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with quantified transport function, genetic epistasis with three PDZ protein knockouts\",\n      \"pmids\": [\"19221439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PDZK1 binding (via C-terminal PDZ motif) promotes cell surface expression of Oatp1a1, and serine phosphorylation at S634/S635 (upstream of the PDZ motif) negatively regulates surface retention: phosphomimetic oatp1a1 remains intracellular even with PDZK1 co-expression. Extracellular ATP-induced phosphorylation of Oatp1a1 triggers rapid internalization in hepatocytes.\",\n      \"method\": \"Site-directed mutagenesis, transfection in HEK293T and HuH7 cells, surface biotinylation internalization assay, co-immunoprecipitation, confocal imaging, primary rat hepatocyte experiments\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis combined with quantitative surface biotinylation internalization assays and primary cell validation\",\n      \"pmids\": [\"21183661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PDZK1 knockdown in hepatoma cells significantly reduces susceptibility to HCV infection; this effect requires more than just the first PDZ domain of PDZK1. PDZK1 facilitates HCV entry indirectly via its interaction with SR-BI, which serves as an HCV entry factor, and this interaction requires the C-terminal PDZ-interacting residue of SR-BI.\",\n      \"method\": \"Stable shRNA knockdown, PDZK1 overexpression rescue, GFP-SR-BI C-terminus chimera competition, HCV infection assay in Huh-7 cells\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — shRNA knockdown with rescue, domain-specific competition experiments, single lab\",\n      \"pmids\": [\"20949066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PDZK1 is required for apical membrane expression of NaPi-2c (but not NaPi-2a) in renal proximal tubule; FRET measurements show both NaPi-2a and NaPi-2c interact with PDZK1, but NaPi-2a shows stronger FRET with NHERF-1. In low-Pi adaptation, NaPi-2c/PDZK1 and NaPi-2a/NHERF-1 interactions increase, explaining differential regulation.\",\n      \"method\": \"Pdzk1-/- mice on low Pi diets, Western blot, immunofluorescence, FRET in transfected cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO plus quantitative FRET for direct protein-protein interaction, multiple conditions\",\n      \"pmids\": [\"21388960\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PDZK1 physically interacts with BCRP (breast cancer resistance protein) and is required for apical membrane localization of BCRP in mouse small intestine; PDZK1 co-expression in MDCKII/BCRP cells increases basal-to-apical transcellular transport and drug resistance to SN-38.\",\n      \"method\": \"Pull-down assay, co-immunoprecipitation, immunohistochemistry, Western blot of brush-border membranes, transcellular transport assay, cytotoxicity assay in MDCKII cells, pdzk1-/- mice pharmacokinetics\",\n      \"journal\": \"Drug metabolism and disposition\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — physical interaction confirmed by Co-IP plus in vivo localization and functional transport assays\",\n      \"pmids\": [\"21816982\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PDZK1 specifically interacts with PLC-β3 (not PLC-β1) and assembles a ternary complex with PLC-β3 and somatostatin receptors (SSTRs), enabling specific activation of PLC-β3 by somatostatin. Disruption of this ternary complex inhibits SST-induced PLC activation, intracellular Ca2+ mobilization, and ERK1/2 phosphorylation.\",\n      \"method\": \"PDZ protein screen, co-immunoprecipitation, siRNA knockdown of PDZK1 or PLC-β3, Ca2+ mobilization assay, ERK1/2 phosphorylation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ternary complex demonstrated by Co-IP plus functional signaling assays with selective knockdown controls\",\n      \"pmids\": [\"22528496\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PDZK1 expression in breast cancer cells promotes estrogen-mediated cell proliferation through enhancement of c-Myc expression; PDZK1 interacts with the Src/ER-α/EGFR complex and enhances EGFR-stimulated MEK/ERK1/2 signaling. PDZK1 expression is indirectly regulated by ER-α stimulation, requiring IGF-1R function.\",\n      \"method\": \"siRNA knockdown, ectopic overexpression, co-immunoprecipitation, proliferation assay, immunoblotting for signaling intermediates, tissue microarrays\",\n      \"journal\": \"Molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single study with Co-IP and functional proliferation data, mechanistic pathway only partially resolved\",\n      \"pmids\": [\"23821363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PDZK1 directly interacts with OATP1A2 via its C-terminal PDZ-binding domain and increases OATP1A2 surface expression by decreasing clathrin-dependent (but not caveolin-dependent) internalization, and by enhancing OATP1A2 protein stability, resulting in increased V(max) of estrone-3-sulfate transport.\",\n      \"method\": \"Co-immunoprecipitation, surface biotinylation, internalization assay with clathrin/caveolin inhibitors, cycloheximide chase for stability, transport functional assay in HEK293 cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, mechanistic internalization assay, stability assay, functional transport) in single study\",\n      \"pmids\": [\"24728453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PDZK1 inhibits SHP-1 phosphorylation at Tyr536 by blocking the association between SHP-1 and PLCβ3, thereby promoting STAT5 phosphorylation and retarding Akt phosphorylation in renal cell carcinoma cells.\",\n      \"method\": \"PDZK1 overexpression and knockdown models, co-immunoprecipitation, immunoblotting for phosphoproteins, xenograft tumor studies\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP with functional signaling readouts in cell lines and in vivo xenograft, single lab\",\n      \"pmids\": [\"28692056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HNF4A directly binds the rs1967017 region of the PDZK1 promoter/enhancer and transcriptionally regulates PDZK1 expression; siRNA depletion of HNF4A reduces endogenous PDZK1 in HepG2 cells. The urate-increasing T allele of rs1967017 strengthens the HNF4A binding site, enhancing PDZK1 expression.\",\n      \"method\": \"siRNA knockdown, luciferase reporter assay, ChIP (HNF4A binding), zebrafish transgenic reporter, eQTL analysis\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP plus functional luciferase and knockdown in human cells, with in vivo zebrafish validation\",\n      \"pmids\": [\"30124855\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PDZK1 directly binds PTEN through its PDZ domains interacting with the PTEN C-terminus, and this interaction inhibits phosphorylation of PTEN at the S380/T382/T383 cluster, thereby enhancing PTEN's capacity to suppress PI3K/AKT signaling and gastric cancer cell proliferation.\",\n      \"method\": \"Co-immunoprecipitation, GST pull-down, site-directed mutagenesis, PDZK1 knockdown and overexpression, phospho-specific immunoblotting, in vitro and in vivo (xenograft) proliferation assays\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and GST pull-down establish direct binding, functional phosphorylation assay with in vivo validation\",\n      \"pmids\": [\"30930234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PDZK1 interacts with sodium-coupled monocarboxylate transporters SMCT1 (SLC5A8) and SMCT2 (SLC5A12) via their C-terminal PDZ motifs; PDZK1 co-expression enhances nicotinate transport activity in SMCT1-expressing HEK293 cells. PDZK1, SMCT1, and URAT1 assemble into a trimolecular complex in vitro and co-localize in renal proximal tubule in vivo.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, functional transport assay in HEK293 cells, immunohistochemistry\",\n      \"journal\": \"The journal of physiological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — yeast two-hybrid with Co-IP and functional assay, in vivo localization, single lab\",\n      \"pmids\": [\"30604288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"HDL-mediated protection against macrophage necroptosis requires SR-B1 and PDZK1 in a PI3K/Akt pathway-dependent manner; PDZK1 knockout in bone marrow-derived cells (not liver) increases atherosclerosis and necrotic core formation, which is reversed by restoring PDZK1 in BM-derived cells.\",\n      \"method\": \"Bone marrow transplantation reconstitution, PDZK1-/- LDLRKO mice, macrophage necroptosis assay, PI3K inhibitor, immunohistochemistry for RIPK3/MLKL\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — BM reconstitution genetic epistasis with cell-specific mechanistic pathway dissection in vivo\",\n      \"pmids\": [\"36353992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PDZK1 deficiency in chondrocytes impairs mitochondrial function (decreased mtDNA content, increased ROS, accumulation of damaged mitochondria) during mechanical overload by increasing ubiquitination and thereby reducing expression of Hmgcs2; PDZK1 loss exacerbates mechanical overload-induced chondrocyte senescence and cartilage degeneration.\",\n      \"method\": \"Pdzk1 chondrocyte knockout and AAV-PDZK1 intraarticular injection, mRNA sequencing, ubiquitination assay, mitochondrial function assays (ROS, mtDNA content, mitochondrial morphology), mechanical overload OA model\",\n      \"journal\": \"Bone research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO and rescue with mechanistic pathway (ubiquitination of Hmgcs2) identified by transcriptomics and biochemical assays, single study\",\n      \"pmids\": [\"39019845\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PDZK1 is a four-PDZ-domain scaffold protein that organizes multiprotein complexes at epithelial apical membranes and in endothelium by directly binding the C-terminal PDZ-interaction motifs of diverse membrane transporters (NHE3, CFEX, Oatp1a1, OATP1A2, PEPT1, PEPT2, OCTN2, BCRP, SMCT1/2, NaPi-2c, SR-BI) and signaling molecules (PLC-β3, NOS2, PTEN, SHP-1); its scaffolding function promotes apical/surface retention, transport activity, and receptor-coupled signal transduction (eNOS activation, somatostatin-PLC-β3 signaling, PTEN-mediated PI3K/AKT suppression), and its activity is regulated by PKA-dependent phosphorylation at Ser-509 as well as by a head-to-tail intramolecular autoinhibitory association.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PDZK1 is a four-PDZ-domain scaffold protein that organizes multiprotein complexes at epithelial apical membranes and in endothelium, controlling the surface expression, membrane retention, and activity of diverse membrane transporters and signaling effectors. It directly binds the C-terminal PDZ-interaction motifs of transporters including NHE3, CFEX, Oatp1a1, OATP1A2, PEPT1, PEPT2, OCTN2, BCRP, NaPi-2c, and SMCT1/2 to promote their apical or basolateral localization and transport function, and loss of PDZK1 causes mislocalization and reduced activity of specific client proteins in kidney, intestine, and liver [PMID:16141316, PMID:15994332, PMID:18322073, PMID:21816982, PMID:21388960]. Beyond transporter scaffolding, PDZK1 assembles signaling complexes—including a PLC-β3/somatostatin receptor ternary complex for Ca²⁺ mobilization and ERK activation, an SR-BI/Src complex for eNOS activation in endothelium, and a PTEN complex that suppresses PI3K/AKT signaling—and its scaffolding function is regulated by PKA-dependent phosphorylation at Ser-509 and by a head-to-tail intramolecular autoinhibitory association between its C-terminal tail and first PDZ domain [PMID:22528496, PMID:18174467, PMID:30930234, PMID:16174736, PMID:19173579]. PDZK1 knockout mice exhibit increased serum cholesterol, impaired electroneutral Na⁺ absorption, defective endothelial repair after vascular injury, and—in bone marrow–derived macrophages—increased necroptosis and atherosclerotic necrotic core formation dependent on SR-BI/PI3K/Akt signaling [PMID:12556478, PMID:17347851, PMID:18174467, PMID:36353992].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Identification of PDZK1 as a novel four-PDZ-domain protein in kidney proximal tubule brush border established the gene as a candidate epithelial scaffold.\",\n      \"evidence\": \"Yeast two-hybrid screen with MAP17 bait in human kidney cDNA library, with in situ hybridization confirming brush-border co-localization\",\n      \"pmids\": [\"9461128\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional data on transport or signaling\", \"Interaction partners beyond MAP17 unknown\", \"Expression outside kidney not characterized\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Generation of PDZK1 knockout mice revealed a mild phenotype (increased serum cholesterol, selective ion channel changes) and showed that many expected client proteins were not redistributed, indicating functional redundancy among PDZ scaffold proteins.\",\n      \"evidence\": \"Homologous recombination knockout mouse with serum chemistry, Western blot, and immunolocalization of candidate interactors\",\n      \"pmids\": [\"12556478\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Source of hypercholesterolemia not mechanistically resolved\", \"Identity of compensating PDZ proteins unclear\", \"Tissue-specific contributions not dissected\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Establishing that MAP17 anchors PDZK1 to the apical membrane (not vice versa) through PDZ domain 4 resolved the hierarchical assembly of the scaffold at the brush border.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro binding, and immunofluorescence in opossum kidney cells showing PDZK1 apical localization depends on MAP17\",\n      \"pmids\": [\"12837682\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether MAP17-independent anchoring exists in other tissues not tested\", \"Structural basis of PDZ4-MAP17 interaction unresolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstration that PDZK1 is required in vivo for CFEX brush-border expression and Cl⁻-oxalate exchange, while NHE3 localization was unaffected, established client-selective scaffolding as PDZK1's primary mechanism for controlling transporter function in kidney.\",\n      \"evidence\": \"GST pull-down, immunocytochemistry, and brush-border membrane vesicle transport assays in PDZK1-null mice\",\n      \"pmids\": [\"16141316\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of selective client dependence (CFEX yes, NHE3 no) unknown\", \"Whether PDZK1 stabilizes CFEX protein or only retains it at the surface not distinguished\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Discovery that PKA phosphorylation of PDZK1 at Ser-509 is required for its ability to upregulate SR-BI protein levels provided the first post-translational regulatory mechanism for PDZK1 scaffold activity.\",\n      \"evidence\": \"In vitro PKA kinase assay, S509A mutagenesis abolishing SR-BI upregulation, glucagon administration in rats validating physiological PKA activation\",\n      \"pmids\": [\"16174736\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Ser-509 phosphorylation affects PDZK1 interactions with clients other than SR-BI not tested\", \"Structural consequence of phosphorylation on PDZK1 conformation unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showing that PDZK1 is required for basolateral membrane localization of Oatp1a1 in hepatocytes extended the scaffold's role beyond apical membranes and into liver organic anion transport.\",\n      \"evidence\": \"C-terminal peptide affinity isolation, reciprocal Co-IP from rat liver, immunofluorescence and radiolabeled substrate clearance in PDZK1-KO mice\",\n      \"pmids\": [\"15994332\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PDZK1 similarly controls other hepatic Oatps not determined\", \"Mechanism of PDZK1-dependent basolateral targeting versus apical targeting not distinguished\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Functional studies in PDZK1-null colon and small intestine demonstrated that PDZK1 is essential for cAMP- and Ca²⁺-dependent regulation of NHE3 and for electroneutral Na⁺ absorption, establishing its role as a signaling scaffold that couples second messengers to transporter regulation.\",\n      \"evidence\": \"Fluorometric NHE3 transport assay in BCECF-loaded colonic crypts and ²²Na⁺ flux measurements in PDZK1⁻/⁻ small intestine\",\n      \"pmids\": [\"17395628\", \"17347851\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the Ca²⁺-sensing component in the PDZK1–NHE3 complex unknown\", \"Whether PDZK1 recruits specific kinases or phosphatases to NHE3 not resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Discovery that PDZK1 is expressed in endothelium and required for HDL/SR-BI-induced Src activation, eNOS signaling, and vascular repair extended PDZK1's function from epithelial transport to cardiovascular signaling.\",\n      \"evidence\": \"Co-IP of Src–SR-BI, siRNA knockdown, eNOS activity assay, and carotid artery re-endothelialization in PDZK1⁻/⁻ mice with liver-specific reconstitution controls\",\n      \"pmids\": [\"18174467\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PDZK1 couples SR-BI to Src mechanistically not resolved\", \"Whether PDZK1 interacts directly with eNOS in endothelium not tested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Extending the client repertoire to intestinal PEPT1 and OCTN2 with in vivo pharmacokinetic consequences showed that PDZK1 is a general determinant of drug and nutrient transporter bioavailability in the gut.\",\n      \"evidence\": \"Co-IP of PEPT1–PDZK1 from mouse small intestine, brush-border fractionation, and pharmacokinetic absorption studies in PDZK1⁻/⁻ mice\",\n      \"pmids\": [\"18322073\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PDZK1 loss alters transporter glycosylation or folding not examined\", \"Contribution of other NHERF family members to compensation in gut not quantified\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identification of a head-to-tail intramolecular association (C-terminal tail binding PDZ1) revealed an autoinhibitory conformational switch that regulates PDZK1's intermolecular interactions, particularly with NHERF1.\",\n      \"evidence\": \"In vitro binding assays, size exclusion chromatography, and limited proteolysis showing compact conformation\",\n      \"pmids\": [\"19173579\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological signals that relieve autoinhibition not identified\", \"Whether autoinhibition affects client transporter binding in cells not tested\", \"Structural details of the compact conformation lacking\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Assembly of a PDZK1–PLC-β3–SSTR ternary signaling complex that specifically transduces somatostatin into Ca²⁺ mobilization and ERK1/2 activation demonstrated that PDZK1 functions as a receptor-to-effector coupling scaffold, not merely a membrane retention factor.\",\n      \"evidence\": \"Co-IP of ternary complex, siRNA knockdown of PDZK1 or PLC-β3, Ca²⁺ mobilization and ERK phosphorylation assays\",\n      \"pmids\": [\"22528496\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PDZK1 scaffolds other GPCR–effector pairs unknown\", \"Stoichiometry of the ternary complex not determined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Mechanistic dissection showing PDZK1 increases OATP1A2 surface expression by decreasing clathrin-dependent internalization and enhancing protein stability provided the first internalization-pathway-specific explanation for PDZK1's surface retention function.\",\n      \"evidence\": \"Surface biotinylation internalization assay with clathrin/caveolin inhibitors, cycloheximide chase, and functional transport assay in HEK293 cells\",\n      \"pmids\": [\"24728453\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether clathrin-dependent internalization suppression applies to other PDZK1 clients not tested\", \"Structural basis of how PDZK1 shields the internalization signal unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstration that PDZK1 binds PTEN and inhibits its inhibitory phosphorylation, thereby enhancing PTEN-mediated suppression of PI3K/AKT, established PDZK1 as a modulator of tumor suppressor activity.\",\n      \"evidence\": \"Co-IP, GST pull-down, S380/T382/T383 phospho-specific immunoblotting, PDZK1 knockdown/overexpression, and xenograft proliferation assays in gastric cancer cells\",\n      \"pmids\": [\"30930234\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PDZK1-PTEN interaction occurs in normal epithelium or is cancer-specific not resolved\", \"Identity of kinase whose access to PTEN is blocked by PDZK1 unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Bone marrow transplantation experiments established that PDZK1 in macrophages—not hepatocytes—mediates HDL/SR-BI protection against necroptosis and atherosclerotic necrotic core formation via PI3K/Akt, revealing a cell-autonomous anti-atherogenic function.\",\n      \"evidence\": \"Bone marrow reconstitution in PDZK1⁻/⁻ LDLR⁻/⁻ mice, macrophage necroptosis assays, PI3K inhibitor, RIPK3/MLKL immunohistochemistry\",\n      \"pmids\": [\"36353992\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PDZK1 directly scaffolds PI3K or Akt in macrophages not shown\", \"Molecular partners downstream of SR-BI in macrophage PDZK1 complex not identified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"PDZK1 deficiency in chondrocytes was linked to mitochondrial dysfunction and senescence through increased ubiquitination and degradation of Hmgcs2, revealing a non-scaffolding role in protein stability and mitochondrial homeostasis.\",\n      \"evidence\": \"Chondrocyte-specific PDZK1 knockout, AAV rescue, mRNA sequencing, ubiquitination assay, mitochondrial function assays in mechanical overload OA model\",\n      \"pmids\": [\"39019845\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PDZK1 directly binds Hmgcs2 or acts indirectly not determined\", \"Mechanism by which PDZK1 suppresses Hmgcs2 ubiquitination unknown\", \"Relevance to PDZK1's canonical PDZ-scaffolding function unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include the structural basis of PDZK1 autoinhibition and its relief by physiological signals, whether the clathrin-internalization-blocking mechanism generalizes across all transporter clients, how PDZK1 couples to PI3K/Akt in macrophages, and the full scope of client selectivity rules distinguishing PDZK1-dependent from PDZK1-independent targets.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of full-length PDZK1 or any client complex\", \"Signal that relieves autoinhibition in vivo not identified\", \"Systematic client dependency rules across tissues not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 6, 9, 15, 17, 22, 23, 25, 28, 29]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 8, 14, 17, 19, 25]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [4, 6, 9, 15, 22, 25, 29]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [4, 6, 9, 15, 22, 25, 29]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 14, 23, 28, 30]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [1, 5, 6]}\n    ],\n    \"complexes\": [\n      \"PDZK1–PLC-β3–SSTR ternary complex\",\n      \"PDZK1–SR-BI–Src endothelial complex\",\n      \"PDZK1–SMCT1–URAT1 trimolecular complex\"\n    ],\n    \"partners\": [\n      \"SLC9A3\",\n      \"SCARB1\",\n      \"PLCB3\",\n      \"SLC26A6\",\n      \"SLCO1A2\",\n      \"ABCG2\",\n      \"PTEN\",\n      \"NOS2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}