{"gene":"CHPF2","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":2002,"finding":"CHPF2 (KIAA1402/CSGlcA-T) encodes a type II membrane protein with glucuronyltransferase activity that transfers glucuronic acid (GlcA) to N-acetylgalactosamine (GalNAc) termini of chondroitin and chondroitin sulfate polysaccharides and oligosaccharides, forming a GlcAβ1-3GalNAc linkage. No N-acetylgalactosaminyltransferase activity was detected, and no activity was detected toward dermatan sulfate, hyaluronan, heparan sulfate, heparin, or linkage region acceptors.","method":"Expression of soluble catalytic domain in COS-7 cells; in vitro glycosyltransferase assays with defined acceptor substrates; beta-glucuronidase digestion; E. coli K4 chondroitin polymerase extension assay; chondroitinase ACII cleavage","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro enzymatic assays with multiple substrates, product characterization by orthogonal methods (enzymatic digestion, further polymerization), replicated conceptually in subsequent studies","pmids":["12145278"],"is_preprint":false},{"year":2008,"finding":"CHPF2 (CSGlcA-T, renamed ChSy-3) exhibits chondroitin polymerization activity only when co-expressed or physically interacting with ChSy-1, ChSy-2 (CSS3), or ChPF; alone it possesses only glucuronyltransferase II activity. A glycosyltransferase-dead CSGlcA-T mutant that can still interact with other ChSy family members fails to support polymerization, demonstrating that CHPF2's enzymatic activity is required for chondroitin chain elongation. Overexpression of CSGlcA-T increased cellular CS levels in HeLa cells, while RNAi knockdown reduced CS levels.","method":"Co-expression of CSGlcA-T with ChSy-1, ChSy-2, or ChPF in mammalian cells; in vitro polymerization assays with truncated linkage-region tetrasaccharide acceptor; active-site mutagenesis (glycosyltransferase-dead mutant); RNAi knockdown; overexpression with CS quantification","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — active-site mutagenesis combined with co-expression and in vitro polymerization assays; multiple orthogonal methods; RNAi and overexpression confirmation in cells","pmids":["18316376"],"is_preprint":false},{"year":2021,"finding":"CHPF2 is required for producing high-molecular-weight chondroitin sulfate chains on the cell surface. CRISPR/Cas9 knockout of CHPF2 in tumor cells reduced the average molecular weight of cell-surface CS and markedly decreased binding of the malarial VAR2CSA protein (rVAR2), linking CHPF2-mediated chain polymerization to CS chain length-dependent ligand accessibility.","method":"CRISPR/Cas9 knockout of CHPF2 in tumor cells; measurement of CS molecular weight; rVAR2 binding assay; cell-based glycocalyx model with CS chain length variation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — clean CRISPR KO with defined molecular phenotype (reduced CS molecular weight) and functional consequence (reduced rVAR2 binding); cell-based glycocalyx model; single lab but multiple orthogonal readouts","pmids":["34762909"],"is_preprint":false},{"year":2018,"finding":"CHPF2 (CSGlcA-T) signals through its enzymatic product chondroitin-4-sulfate (CHSA) to enhance CK2-PTEN binding, leading to CK2-mediated phosphorylation and inhibition of PTEN, which sustains AKT activation selectively in BRAF V600E-expressing melanoma cells. This CHSA-dependent PTEN inhibition is dispensable in cancer cells with mutant NRAS or PI3KCA.","method":"Cell line and patient-derived xenograft mouse models; biochemical CK2-PTEN co-immunoprecipitation; PTEN phosphorylation assays; CHSA supplementation and depletion; genetic rescue experiments in BRAF V600E vs. NRAS/PI3KCA mutant backgrounds","journal":"Molecular cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and phosphorylation assays in cell lines and in vivo xenograft models; single lab; multiple genetic/pharmacological approaches; abstract does not detail in vitro reconstitution of direct CK2-PTEN-CHSA interaction","pmids":["29547721"],"is_preprint":false},{"year":2024,"finding":"Upon TNF stimulation, CHPF2 is phosphorylated at residue T588 by MEK. Phospho-T588 CHPF2 simultaneously interacts with TAK1 and IKKα, enhancing TAK1-IKKα binding, increasing IKK complex phosphorylation, and activating NF-κB signaling to upregulate EGR1 and promote CRC cell proliferation and metastasis. This function is independent of CHPF2's glycosyltransferase (CS biosynthesis) activity. A phospho-deficient T588A mutant weakens the CHPF2-TAK1 interaction and impairs NF-κB signaling and tumor growth in vitro and in vivo.","method":"Site-directed mutagenesis (T588A phospho-deficient mutant); Co-immunoprecipitation of CHPF2 with TAK1 and IKKα; kinase assays linking MEK to T588 phosphorylation; NF-κB reporter/signaling assays; in vitro proliferation/invasion assays; in vivo xenograft models","journal":"Cancer letters","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — mutagenesis of phosphorylation site with defined interaction (Co-IP), signaling (IKK phosphorylation), and phenotypic (proliferation/metastasis in vitro and in vivo) readouts; multiple orthogonal methods; single lab","pmids":["38253217"],"is_preprint":false},{"year":2025,"finding":"Cryo-EM and in vitro glycosylation assays demonstrate that CHPF2 forms functional heterodimeric complexes with CHSY1 or CHSY3 for chondroitin sulfate chain polymerization. Mutational analysis reveals that CHPF2 does not contribute catalytic glycosyltransferase activity; instead, it plays a stabilizing role for the enzymatically active CHSY subunit. Only CHSY1 and CHSY3 possess bifunctional glycosyltransferase activity (GlcA and GalNAc transfers). Chondroitin sulfate polymerization follows a non-processive, distributive mechanism based on the spatial arrangement of catalytic sites.","method":"Cryo-EM structure of CHSY3-CHPF complex; in vitro glycosylation assays with chemo-enzymatically synthesized fluorescent substrates; catalytic mutant analysis of purified enzyme complexes; in cellulo complementation assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure, in vitro reconstitution with defined fluorescent substrates, and mutagenesis of catalytic residues in a single rigorous study; complemented by in cellulo validation","pmids":["41298522"],"is_preprint":false},{"year":2026,"finding":"Structural and enzymatic analyses show that CHPF2 contains an N-terminal CAZy GT31-like domain and a C-terminal GT7-like domain separated by a cystatin-like linker domain, but the CHPF2 glycosyltransferase domains do not contribute to polymer synthesis. CHPF2 must form a heterodimer with a CHSY (CHSY1 or CHSY3) to produce a soluble, functional CS synthase; CHPF2 alone is not sufficient. The cystatin-like bridging domains may contribute to efficient polymer synthesis.","method":"Sequence alignment and structural modeling; cryo-EM of CHSY3-CHPF1 complex; catalytic domain mutagenesis of CHSY and CHPF subunits; co-expression solubility assays; enzymatic activity assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure combined with catalytic mutagenesis and in vitro enzymatic assays; findings convergent with PMID:41298522 from a second independent lab","pmids":["42204168"],"is_preprint":false},{"year":2025,"finding":"CHPF2 is enriched in astrocytes, and silencing of Chpf2 in astrocytes reduces CS-GAG levels in astrocyte-conditioned medium. Conditioned medium from Chpf2-silenced astrocytes increased neurite length and branching of hippocampal neurons in vitro, mechanistically linking CHPF2-dependent CS-GAG biosynthesis in astrocytes to inhibition of dendritic arborization in developing neurons.","method":"TRAP-seq (astrocyte translatome); siRNA knockdown of Chpf2 in astrocytes; LC/MS quantification of CS-GAGs; astrocyte-conditioned medium transfer to hippocampal neurons; neurite length/branching quantification","journal":"Glia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function (siRNA) with defined molecular (CS-GAG reduction by LC/MS) and cellular (neurite branching) phenotypes; conditioned medium experiment provides mechanistic link; single lab","pmids":["40192069"],"is_preprint":false}],"current_model":"CHPF2 (ChSy-3/CSGlcA-T/KIAA1402) is a type II transmembrane enzyme with intrinsic glucuronyltransferase (GlcA-transfer) activity that obligatorily assembles into heterodimeric complexes with CHSY1 or CHSY3 to polymerize chondroitin sulfate chains in a non-processive, distributive manner, with CHPF2 serving primarily as a structural stabilizer of the active CHSY subunit rather than contributing catalytic glycosyltransferase activity to polymer synthesis; additionally, CHPF2 harbors a non-enzymatic 'moonlighting' signaling function whereby MEK-mediated phosphorylation at T588 enables CHPF2 to scaffold TAK1 and IKKα, amplifying NF-κB signaling downstream of TNF independently of its CS biosynthetic role."},"narrative":{"mechanistic_narrative":"CHPF2 (ChSy-3/CSGlcA-T/KIAA1402) is a type II transmembrane glycosyltransferase that drives chondroitin sulfate (CS) chain biosynthesis as an obligate partner of the CHSY family [PMID:12145278, PMID:41298522]. As a soluble catalytic domain it transfers glucuronic acid to GalNAc termini of chondroitin acceptors, forming the GlcAβ1-3GalNAc linkage, with no detectable GalNAc-transferase activity or activity toward dermatan sulfate, heparan sulfate, or hyaluronan [PMID:12145278]. CS polymerization requires CHPF2 to physically associate with a CHSY subunit (CHSY1, CHSY3, or ChPF): cryo-EM and catalytic-mutant analysis establish that within the heterodimer CHPF2 does not itself contribute glycosyltransferase activity but stabilizes the enzymatically active CHSY subunit, with polymerization proceeding by a non-processive, distributive mechanism dictated by the spatial arrangement of catalytic sites [PMID:41298522, PMID:42204168]. CHPF2 contains an N-terminal GT31-like domain and a C-terminal GT7-like domain separated by a cystatin-like bridging domain, and the heterodimer is necessary to produce a soluble, functional CS synthase [PMID:42204168]. Functionally, CHPF2 governs CS chain length: its loss reduces the molecular weight of cell-surface CS and the accessibility of length-dependent ligands such as the malarial rVAR2 protein [PMID:34762909], and astrocyte CHPF2 produces secreted CS-GAGs that restrain dendritic arborization of developing hippocampal neurons [PMID:40192069]. Beyond CS synthesis, CHPF2 carries out non-canonical signaling functions: its product chondroitin-4-sulfate enhances CK2-PTEN binding to sustain AKT activation selectively in BRAF V600E melanoma [PMID:29547721], and upon TNF stimulation MEK-mediated phosphorylation at T588 enables CHPF2 to scaffold TAK1 and IKKα, amplifying NF-κB signaling to upregulate EGR1 and promote colorectal cancer proliferation and metastasis independently of its glycosyltransferase activity [PMID:38253217].","teleology":[{"year":2002,"claim":"Established the core biochemical identity of CHPF2 by defining it as a glucuronyltransferase acting on chondroitin acceptors, distinguishing it from GalNAc-transferases and other GAG-modifying enzymes.","evidence":"Expression of the soluble catalytic domain in COS-7 cells with in vitro glycosyltransferase assays against defined acceptors, validated by β-glucuronidase digestion and K4 polymerase extension","pmids":["12145278"],"confidence":"High","gaps":["Did not address whether the enzyme acts alone in cells","No structural basis for substrate selectivity","Did not place activity within a polymerizing complex"]},{"year":2008,"claim":"Resolved why the isolated enzyme cannot polymerize CS by showing CHPF2 only elongates chains when partnered with a ChSy family member, while its own catalytic activity is still required for elongation.","evidence":"Co-expression with ChSy-1/ChSy-2/ChPF, in vitro polymerization with linkage-region tetrasaccharide acceptor, glycosyltransferase-dead mutagenesis, plus RNAi and overexpression CS quantification","pmids":["18316376"],"confidence":"High","gaps":["Architecture of the active complex unresolved","Relative catalytic contribution of each subunit not quantified","Mechanism of polymerization (processive vs distributive) unknown"]},{"year":2018,"claim":"Identified a product-mediated signaling role in which the CS product chondroitin-4-sulfate sustains oncogenic AKT signaling in a genotype-specific manner.","evidence":"CK2-PTEN co-immunoprecipitation, PTEN phosphorylation assays, CHSA supplementation/depletion, and genetic rescue in BRAF V600E vs NRAS/PI3KCA backgrounds with xenografts","pmids":["29547721"],"confidence":"Medium","gaps":["No in vitro reconstitution of direct CK2-PTEN-CHSA interaction","Single lab","Genotype-restricted dependence not generalized"]},{"year":2021,"claim":"Connected CHPF2 enzymatic output to a functional surface phenotype, showing it controls CS chain length and thereby length-dependent ligand accessibility.","evidence":"CRISPR/Cas9 knockout in tumor cells with CS molecular weight measurement and rVAR2 binding assay in a glycocalyx model","pmids":["34762909"],"confidence":"High","gaps":["Did not resolve subunit contributions to chain length","Generality across cell types untested","No structural explanation for length control"]},{"year":2024,"claim":"Revealed a glycosyltransferase-independent scaffolding function in which phosphorylated CHPF2 bridges TAK1 and IKKα to amplify NF-κB signaling.","evidence":"T588A phospho-deficient mutagenesis, Co-IP of CHPF2 with TAK1/IKKα, kinase assays linking MEK to T588, NF-κB reporter assays, and in vitro/in vivo CRC growth models","pmids":["38253217"],"confidence":"High","gaps":["Structural basis of the CHPF2-TAK1-IKKα scaffold not defined","Single lab","Interplay between scaffolding and enzymatic pools of CHPF2 unclear"]},{"year":2025,"claim":"Determined the molecular mechanism of the CS synthase, establishing that CHPF2 is a non-catalytic stabilizer of the active CHSY subunit and that polymerization is non-processive/distributive.","evidence":"Cryo-EM of CHSY3-CHPF complex, in vitro glycosylation with fluorescent substrates, catalytic mutagenesis of purified complexes, and in cellulo complementation","pmids":["41298522"],"confidence":"High","gaps":["Functional distinction between CHSY1- and CHSY3-containing complexes not resolved","Regulation of complex assembly in vivo unknown"]},{"year":2025,"claim":"Extended CHPF2 function to a developmental context, linking astrocyte CHPF2-dependent CS-GAG secretion to inhibition of neuronal dendritic arborization.","evidence":"TRAP-seq, siRNA knockdown of Chpf2 in astrocytes, LC/MS CS-GAG quantification, and astrocyte-conditioned medium transfer to hippocampal neurons with neurite quantification","pmids":["40192069"],"confidence":"Medium","gaps":["CS structural features mediating neurite inhibition not defined","In vivo developmental relevance untested","Single lab"]},{"year":2026,"claim":"Defined CHPF2 domain architecture and confirmed across an independent lab that its GT domains do not contribute to polymer synthesis, requiring heterodimerization for a soluble functional synthase.","evidence":"Sequence alignment/structural modeling, cryo-EM of CHSY3-CHPF1 complex, catalytic domain mutagenesis, and co-expression solubility/enzymatic assays","pmids":["42204168"],"confidence":"High","gaps":["Precise contribution of cystatin-like linker to synthesis not quantified","How CHPF2 confers solubility/stability mechanistically unresolved"]},{"year":null,"claim":"It remains unknown how CHPF2's distinct roles — non-catalytic CS-synthase stabilizer versus phosphorylation-dependent NF-κB scaffold and CS-product-mediated AKT signaling — are partitioned and regulated within a single cell.","evidence":"","pmids":[],"confidence":"Low","gaps":["No study integrates the enzymatic and signaling pools of CHPF2","Regulation switching between functions undefined","Structural basis of the signaling scaffold absent"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,5,6]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[4]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[3,4]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,4]}],"complexes":["CHPF2-CHSY1/CHSY3 chondroitin sulfate synthase heterodimer"],"partners":["CHSY1","CHSY3","CHSY2","CHPF","TAK1","IKKΑ","MEK"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9P2E5","full_name":"Chondroitin sulfate glucuronyltransferase","aliases":["CSGlcA-T","Chondroitin glucuronyltransferase","Chondroitin polymerizing factor 2","ChPF-2","Chondroitin synthase 3","ChSy-3","N-acetylgalactosaminyl-proteoglycan 3-beta-glucuronosyltransferase"],"length_aa":772,"mass_kda":85.9,"function":"Transfers glucuronic acid (GlcUA) from UDP-GlcUA to N-acetylgalactosamine residues on the non-reducing end of the elongating chondroitin polymer. Has no N-acetylgalactosaminyltransferase activity","subcellular_location":"Golgi apparatus, Golgi stack membrane","url":"https://www.uniprot.org/uniprotkb/Q9P2E5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CHPF2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CHPF2","total_profiled":1310},"omim":[{"mim_id":"608037","title":"CHONDROITIN POLYMERIZING FACTOR 2; CHPF2","url":"https://www.omim.org/entry/608037"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CHPF2"},"hgnc":{"alias_symbol":["KIAA1402","ChSy-3","CSGlcA-T"],"prev_symbol":[]},"alphafold":{"accession":"Q9P2E5","domains":[{"cath_id":"3.90.550.50","chopping":"91-310","consensus_level":"high","plddt":90.7415,"start":91,"end":310},{"cath_id":"3.10.450","chopping":"375-470","consensus_level":"high","plddt":92.7126,"start":375,"end":470},{"cath_id":"3.90.550.10","chopping":"488-531_542-630_656-757","consensus_level":"high","plddt":89.4235,"start":488,"end":757}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9P2E5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9P2E5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9P2E5-F1-predicted_aligned_error_v6.png","plddt_mean":84.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CHPF2","jax_strain_url":"https://www.jax.org/strain/search?query=CHPF2"},"sequence":{"accession":"Q9P2E5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9P2E5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9P2E5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9P2E5"}},"corpus_meta":[{"pmid":"18316376","id":"PMC_18316376","title":"Identification of chondroitin sulfate glucuronyltransferase as chondroitin synthase-3 involved in chondroitin polymerization: chondroitin polymerization is achieved by multiple enzyme complexes consisting of chondroitin synthase family members.","date":"2008","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18316376","citation_count":123,"is_preprint":false},{"pmid":"12145278","id":"PMC_12145278","title":"Molecular cloning and characterization of a novel chondroitin sulfate glucuronyltransferase that transfers glucuronic acid to N-acetylgalactosamine.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12145278","citation_count":62,"is_preprint":false},{"pmid":"23703795","id":"PMC_23703795","title":"Expression of chondroitin/dermatan sulfate glycosyltransferases during early zebrafish development.","date":"2013","source":"Developmental dynamics : an official publication of the American Association of Anatomists","url":"https://pubmed.ncbi.nlm.nih.gov/23703795","citation_count":24,"is_preprint":false},{"pmid":"34966741","id":"PMC_34966741","title":"Glycogenes in Oncofetal Chondroitin Sulfate Biosynthesis are Differently Expressed and Correlated With Immune Response in Placenta and Colorectal Cancer.","date":"2021","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/34966741","citation_count":21,"is_preprint":false},{"pmid":"29547721","id":"PMC_29547721","title":"The Dietary Supplement Chondroitin-4-Sulfate Exhibits Oncogene-Specific Pro-tumor Effects on BRAF V600E Melanoma Cells.","date":"2018","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/29547721","citation_count":15,"is_preprint":false},{"pmid":"34762909","id":"PMC_34762909","title":"The specificity of the malarial VAR2CSA protein for chondroitin sulfate depends on 4-O-sulfation and ligand accessibility.","date":"2021","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/34762909","citation_count":14,"is_preprint":false},{"pmid":"38253217","id":"PMC_38253217","title":"MEK-mediated CHPF2 phosphorylation promotes colorectal cancer cell proliferation and metastasis by activating NF-κB signaling.","date":"2024","source":"Cancer letters","url":"https://pubmed.ncbi.nlm.nih.gov/38253217","citation_count":13,"is_preprint":false},{"pmid":"40192069","id":"PMC_40192069","title":"Astrocyte Extracellular Matrix Modulates Neuronal Dendritic Development.","date":"2025","source":"Glia","url":"https://pubmed.ncbi.nlm.nih.gov/40192069","citation_count":8,"is_preprint":false},{"pmid":"29178990","id":"PMC_29178990","title":"Variants in chondroitin sulfate metabolism genes in thrombotic storm.","date":"2017","source":"Thrombosis research","url":"https://pubmed.ncbi.nlm.nih.gov/29178990","citation_count":7,"is_preprint":false},{"pmid":"38341004","id":"PMC_38341004","title":"Exosomal lncRNA DUXAP8 affecting CHPF2 in the pathogenesis of intracranial aneurysms.","date":"2024","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/38341004","citation_count":2,"is_preprint":false},{"pmid":"41298522","id":"PMC_41298522","title":"Structural basis for human chondroitin sulfate chain polymerization.","date":"2025","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/41298522","citation_count":2,"is_preprint":false},{"pmid":"40107635","id":"PMC_40107635","title":"CHPF2 as a novel biomarker and ponicidin as a potential therapeutic agent in hepatocellular carcinoma.","date":"2025","source":"Pharmacological research","url":"https://pubmed.ncbi.nlm.nih.gov/40107635","citation_count":1,"is_preprint":false},{"pmid":"39211148","id":"PMC_39211148","title":"Astrocyte extracellular matrix modulates neuronal dendritic development.","date":"2024","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/39211148","citation_count":1,"is_preprint":false},{"pmid":"40401561","id":"PMC_40401561","title":"Discovery and Validation of a New Biomarker Integrating Ferroptosis and Glycolysis-Related Genes in Bladder Cancer.","date":"2025","source":"IUBMB life","url":"https://pubmed.ncbi.nlm.nih.gov/40401561","citation_count":1,"is_preprint":false},{"pmid":"42204168","id":"PMC_42204168","title":"Structural basis of chondroitin sulfate backbone polymer synthesis.","date":"2026","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/42204168","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10438,"output_tokens":3018,"usd":0.038292,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10314,"output_tokens":3466,"usd":0.06911,"stage2_stop_reason":"end_turn"},"total_usd":0.107402,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"CHPF2 (KIAA1402/CSGlcA-T) encodes a type II membrane protein with glucuronyltransferase activity that transfers glucuronic acid (GlcA) to N-acetylgalactosamine (GalNAc) termini of chondroitin and chondroitin sulfate polysaccharides and oligosaccharides, forming a GlcAβ1-3GalNAc linkage. No N-acetylgalactosaminyltransferase activity was detected, and no activity was detected toward dermatan sulfate, hyaluronan, heparan sulfate, heparin, or linkage region acceptors.\",\n      \"method\": \"Expression of soluble catalytic domain in COS-7 cells; in vitro glycosyltransferase assays with defined acceptor substrates; beta-glucuronidase digestion; E. coli K4 chondroitin polymerase extension assay; chondroitinase ACII cleavage\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro enzymatic assays with multiple substrates, product characterization by orthogonal methods (enzymatic digestion, further polymerization), replicated conceptually in subsequent studies\",\n      \"pmids\": [\"12145278\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CHPF2 (CSGlcA-T, renamed ChSy-3) exhibits chondroitin polymerization activity only when co-expressed or physically interacting with ChSy-1, ChSy-2 (CSS3), or ChPF; alone it possesses only glucuronyltransferase II activity. A glycosyltransferase-dead CSGlcA-T mutant that can still interact with other ChSy family members fails to support polymerization, demonstrating that CHPF2's enzymatic activity is required for chondroitin chain elongation. Overexpression of CSGlcA-T increased cellular CS levels in HeLa cells, while RNAi knockdown reduced CS levels.\",\n      \"method\": \"Co-expression of CSGlcA-T with ChSy-1, ChSy-2, or ChPF in mammalian cells; in vitro polymerization assays with truncated linkage-region tetrasaccharide acceptor; active-site mutagenesis (glycosyltransferase-dead mutant); RNAi knockdown; overexpression with CS quantification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — active-site mutagenesis combined with co-expression and in vitro polymerization assays; multiple orthogonal methods; RNAi and overexpression confirmation in cells\",\n      \"pmids\": [\"18316376\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CHPF2 is required for producing high-molecular-weight chondroitin sulfate chains on the cell surface. CRISPR/Cas9 knockout of CHPF2 in tumor cells reduced the average molecular weight of cell-surface CS and markedly decreased binding of the malarial VAR2CSA protein (rVAR2), linking CHPF2-mediated chain polymerization to CS chain length-dependent ligand accessibility.\",\n      \"method\": \"CRISPR/Cas9 knockout of CHPF2 in tumor cells; measurement of CS molecular weight; rVAR2 binding assay; cell-based glycocalyx model with CS chain length variation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean CRISPR KO with defined molecular phenotype (reduced CS molecular weight) and functional consequence (reduced rVAR2 binding); cell-based glycocalyx model; single lab but multiple orthogonal readouts\",\n      \"pmids\": [\"34762909\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CHPF2 (CSGlcA-T) signals through its enzymatic product chondroitin-4-sulfate (CHSA) to enhance CK2-PTEN binding, leading to CK2-mediated phosphorylation and inhibition of PTEN, which sustains AKT activation selectively in BRAF V600E-expressing melanoma cells. This CHSA-dependent PTEN inhibition is dispensable in cancer cells with mutant NRAS or PI3KCA.\",\n      \"method\": \"Cell line and patient-derived xenograft mouse models; biochemical CK2-PTEN co-immunoprecipitation; PTEN phosphorylation assays; CHSA supplementation and depletion; genetic rescue experiments in BRAF V600E vs. NRAS/PI3KCA mutant backgrounds\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and phosphorylation assays in cell lines and in vivo xenograft models; single lab; multiple genetic/pharmacological approaches; abstract does not detail in vitro reconstitution of direct CK2-PTEN-CHSA interaction\",\n      \"pmids\": [\"29547721\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Upon TNF stimulation, CHPF2 is phosphorylated at residue T588 by MEK. Phospho-T588 CHPF2 simultaneously interacts with TAK1 and IKKα, enhancing TAK1-IKKα binding, increasing IKK complex phosphorylation, and activating NF-κB signaling to upregulate EGR1 and promote CRC cell proliferation and metastasis. This function is independent of CHPF2's glycosyltransferase (CS biosynthesis) activity. A phospho-deficient T588A mutant weakens the CHPF2-TAK1 interaction and impairs NF-κB signaling and tumor growth in vitro and in vivo.\",\n      \"method\": \"Site-directed mutagenesis (T588A phospho-deficient mutant); Co-immunoprecipitation of CHPF2 with TAK1 and IKKα; kinase assays linking MEK to T588 phosphorylation; NF-κB reporter/signaling assays; in vitro proliferation/invasion assays; in vivo xenograft models\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — mutagenesis of phosphorylation site with defined interaction (Co-IP), signaling (IKK phosphorylation), and phenotypic (proliferation/metastasis in vitro and in vivo) readouts; multiple orthogonal methods; single lab\",\n      \"pmids\": [\"38253217\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cryo-EM and in vitro glycosylation assays demonstrate that CHPF2 forms functional heterodimeric complexes with CHSY1 or CHSY3 for chondroitin sulfate chain polymerization. Mutational analysis reveals that CHPF2 does not contribute catalytic glycosyltransferase activity; instead, it plays a stabilizing role for the enzymatically active CHSY subunit. Only CHSY1 and CHSY3 possess bifunctional glycosyltransferase activity (GlcA and GalNAc transfers). Chondroitin sulfate polymerization follows a non-processive, distributive mechanism based on the spatial arrangement of catalytic sites.\",\n      \"method\": \"Cryo-EM structure of CHSY3-CHPF complex; in vitro glycosylation assays with chemo-enzymatically synthesized fluorescent substrates; catalytic mutant analysis of purified enzyme complexes; in cellulo complementation assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure, in vitro reconstitution with defined fluorescent substrates, and mutagenesis of catalytic residues in a single rigorous study; complemented by in cellulo validation\",\n      \"pmids\": [\"41298522\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Structural and enzymatic analyses show that CHPF2 contains an N-terminal CAZy GT31-like domain and a C-terminal GT7-like domain separated by a cystatin-like linker domain, but the CHPF2 glycosyltransferase domains do not contribute to polymer synthesis. CHPF2 must form a heterodimer with a CHSY (CHSY1 or CHSY3) to produce a soluble, functional CS synthase; CHPF2 alone is not sufficient. The cystatin-like bridging domains may contribute to efficient polymer synthesis.\",\n      \"method\": \"Sequence alignment and structural modeling; cryo-EM of CHSY3-CHPF1 complex; catalytic domain mutagenesis of CHSY and CHPF subunits; co-expression solubility assays; enzymatic activity assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure combined with catalytic mutagenesis and in vitro enzymatic assays; findings convergent with PMID:41298522 from a second independent lab\",\n      \"pmids\": [\"42204168\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CHPF2 is enriched in astrocytes, and silencing of Chpf2 in astrocytes reduces CS-GAG levels in astrocyte-conditioned medium. Conditioned medium from Chpf2-silenced astrocytes increased neurite length and branching of hippocampal neurons in vitro, mechanistically linking CHPF2-dependent CS-GAG biosynthesis in astrocytes to inhibition of dendritic arborization in developing neurons.\",\n      \"method\": \"TRAP-seq (astrocyte translatome); siRNA knockdown of Chpf2 in astrocytes; LC/MS quantification of CS-GAGs; astrocyte-conditioned medium transfer to hippocampal neurons; neurite length/branching quantification\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function (siRNA) with defined molecular (CS-GAG reduction by LC/MS) and cellular (neurite branching) phenotypes; conditioned medium experiment provides mechanistic link; single lab\",\n      \"pmids\": [\"40192069\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CHPF2 (ChSy-3/CSGlcA-T/KIAA1402) is a type II transmembrane enzyme with intrinsic glucuronyltransferase (GlcA-transfer) activity that obligatorily assembles into heterodimeric complexes with CHSY1 or CHSY3 to polymerize chondroitin sulfate chains in a non-processive, distributive manner, with CHPF2 serving primarily as a structural stabilizer of the active CHSY subunit rather than contributing catalytic glycosyltransferase activity to polymer synthesis; additionally, CHPF2 harbors a non-enzymatic 'moonlighting' signaling function whereby MEK-mediated phosphorylation at T588 enables CHPF2 to scaffold TAK1 and IKKα, amplifying NF-κB signaling downstream of TNF independently of its CS biosynthetic role.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CHPF2 (ChSy-3/CSGlcA-T/KIAA1402) is a type II transmembrane glycosyltransferase that drives chondroitin sulfate (CS) chain biosynthesis as an obligate partner of the CHSY family [#0, #5]. As a soluble catalytic domain it transfers glucuronic acid to GalNAc termini of chondroitin acceptors, forming the GlcA\\u03b21-3GalNAc linkage, with no detectable GalNAc-transferase activity or activity toward dermatan sulfate, heparan sulfate, or hyaluronan [#0]. CS polymerization requires CHPF2 to physically associate with a CHSY subunit (CHSY1, CHSY3, or ChPF): cryo-EM and catalytic-mutant analysis establish that within the heterodimer CHPF2 does not itself contribute glycosyltransferase activity but stabilizes the enzymatically active CHSY subunit, with polymerization proceeding by a non-processive, distributive mechanism dictated by the spatial arrangement of catalytic sites [#5, #6]. CHPF2 contains an N-terminal GT31-like domain and a C-terminal GT7-like domain separated by a cystatin-like bridging domain, and the heterodimer is necessary to produce a soluble, functional CS synthase [#6]. Functionally, CHPF2 governs CS chain length: its loss reduces the molecular weight of cell-surface CS and the accessibility of length-dependent ligands such as the malarial rVAR2 protein [#2], and astrocyte CHPF2 produces secreted CS-GAGs that restrain dendritic arborization of developing hippocampal neurons [#7]. Beyond CS synthesis, CHPF2 carries out non-canonical signaling functions: its product chondroitin-4-sulfate enhances CK2-PTEN binding to sustain AKT activation selectively in BRAF V600E melanoma [#3], and upon TNF stimulation MEK-mediated phosphorylation at T588 enables CHPF2 to scaffold TAK1 and IKK\\u03b1, amplifying NF-\\u03baB signaling to upregulate EGR1 and promote colorectal cancer proliferation and metastasis independently of its glycosyltransferase activity [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established the core biochemical identity of CHPF2 by defining it as a glucuronyltransferase acting on chondroitin acceptors, distinguishing it from GalNAc-transferases and other GAG-modifying enzymes.\",\n      \"evidence\": \"Expression of the soluble catalytic domain in COS-7 cells with in vitro glycosyltransferase assays against defined acceptors, validated by \\u03b2-glucuronidase digestion and K4 polymerase extension\",\n      \"pmids\": [\"12145278\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address whether the enzyme acts alone in cells\", \"No structural basis for substrate selectivity\", \"Did not place activity within a polymerizing complex\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Resolved why the isolated enzyme cannot polymerize CS by showing CHPF2 only elongates chains when partnered with a ChSy family member, while its own catalytic activity is still required for elongation.\",\n      \"evidence\": \"Co-expression with ChSy-1/ChSy-2/ChPF, in vitro polymerization with linkage-region tetrasaccharide acceptor, glycosyltransferase-dead mutagenesis, plus RNAi and overexpression CS quantification\",\n      \"pmids\": [\"18316376\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Architecture of the active complex unresolved\", \"Relative catalytic contribution of each subunit not quantified\", \"Mechanism of polymerization (processive vs distributive) unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified a product-mediated signaling role in which the CS product chondroitin-4-sulfate sustains oncogenic AKT signaling in a genotype-specific manner.\",\n      \"evidence\": \"CK2-PTEN co-immunoprecipitation, PTEN phosphorylation assays, CHSA supplementation/depletion, and genetic rescue in BRAF V600E vs NRAS/PI3KCA backgrounds with xenografts\",\n      \"pmids\": [\"29547721\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vitro reconstitution of direct CK2-PTEN-CHSA interaction\", \"Single lab\", \"Genotype-restricted dependence not generalized\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected CHPF2 enzymatic output to a functional surface phenotype, showing it controls CS chain length and thereby length-dependent ligand accessibility.\",\n      \"evidence\": \"CRISPR/Cas9 knockout in tumor cells with CS molecular weight measurement and rVAR2 binding assay in a glycocalyx model\",\n      \"pmids\": [\"34762909\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve subunit contributions to chain length\", \"Generality across cell types untested\", \"No structural explanation for length control\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed a glycosyltransferase-independent scaffolding function in which phosphorylated CHPF2 bridges TAK1 and IKK\\u03b1 to amplify NF-\\u03baB signaling.\",\n      \"evidence\": \"T588A phospho-deficient mutagenesis, Co-IP of CHPF2 with TAK1/IKK\\u03b1, kinase assays linking MEK to T588, NF-\\u03baB reporter assays, and in vitro/in vivo CRC growth models\",\n      \"pmids\": [\"38253217\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the CHPF2-TAK1-IKK\\u03b1 scaffold not defined\", \"Single lab\", \"Interplay between scaffolding and enzymatic pools of CHPF2 unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Determined the molecular mechanism of the CS synthase, establishing that CHPF2 is a non-catalytic stabilizer of the active CHSY subunit and that polymerization is non-processive/distributive.\",\n      \"evidence\": \"Cryo-EM of CHSY3-CHPF complex, in vitro glycosylation with fluorescent substrates, catalytic mutagenesis of purified complexes, and in cellulo complementation\",\n      \"pmids\": [\"41298522\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional distinction between CHSY1- and CHSY3-containing complexes not resolved\", \"Regulation of complex assembly in vivo unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended CHPF2 function to a developmental context, linking astrocyte CHPF2-dependent CS-GAG secretion to inhibition of neuronal dendritic arborization.\",\n      \"evidence\": \"TRAP-seq, siRNA knockdown of Chpf2 in astrocytes, LC/MS CS-GAG quantification, and astrocyte-conditioned medium transfer to hippocampal neurons with neurite quantification\",\n      \"pmids\": [\"40192069\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"CS structural features mediating neurite inhibition not defined\", \"In vivo developmental relevance untested\", \"Single lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defined CHPF2 domain architecture and confirmed across an independent lab that its GT domains do not contribute to polymer synthesis, requiring heterodimerization for a soluble functional synthase.\",\n      \"evidence\": \"Sequence alignment/structural modeling, cryo-EM of CHSY3-CHPF1 complex, catalytic domain mutagenesis, and co-expression solubility/enzymatic assays\",\n      \"pmids\": [\"42204168\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise contribution of cystatin-like linker to synthesis not quantified\", \"How CHPF2 confers solubility/stability mechanistically unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown how CHPF2's distinct roles \\u2014 non-catalytic CS-synthase stabilizer versus phosphorylation-dependent NF-\\u03baB scaffold and CS-product-mediated AKT signaling \\u2014 are partitioned and regulated within a single cell.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No study integrates the enzymatic and signaling pools of CHPF2\", \"Regulation switching between functions undefined\", \"Structural basis of the signaling scaffold absent\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 5, 6]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [3, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1630316\", \"supporting_discovery_ids\": [0, 1, 5]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 4]}\n    ],\n    \"complexes\": [\"CHPF2-CHSY1/CHSY3 chondroitin sulfate synthase heterodimer\"],\n    \"partners\": [\"CHSY1\", \"CHSY3\", \"CHSY2\", \"CHPF\", \"TAK1\", \"IKK\\u03b1\", \"MEK\"],\n    \"other_free_text\": []\n  }\n}\n```","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}