CANT1 is a calcium-dependent nucleoside diphosphatase of the secretory pathway. The full-length protein has an N-terminal type-II membrane anchor and a lumen-facing catalytic domain associated with the endoplasmic reticulum and Golgi; soluble processed forms can be secreted. It preferentially hydrolyzes UDP and also acts on GDP and IDP, with much lower ADP activity. Luminal UDP turnover is thought to support proteoglycan glycosaminoglycan synthesis by removing a glycosyltransferase product and supplying UMP for nucleotide-sugar exchange. Human loss-of-function variants impair glycan production and cause recessive skeletal dysplasias, including Desbuquois dysplasia type 1 and multiple epiphyseal dysplasia 7. Calcium-dependent homodimerization is a biochemical property of the enzyme.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004382 GDP phosphatase activity | IBA GO_REF:0000033 | ACCEPT | Summary: CANT1 has conserved GDP-hydrolyzing nucleotidase activity. Reason: The PTN000989481 IBA agrees with human biochemical characterization and the reviewed GDP-to-GMP reaction. Human Q8WVQ1 is a legitimate experimental descendant supporting the ancestral assertion, not circular support. No phylogenetic loss or conflicting target chemistry is evident; the tree and MSA have not been independently reconstructed. |
| GO:0004382 GDP phosphatase activity | IDA PMID:15248776 Site-directed mutagenesis of human soluble calcium-activated... | ACCEPT | Summary: GDP is a preferred substrate of the human calcium-dependent enzyme. Reason: The mutagenesis study characterizes human hSCAN-1 catalysis, and UniProt assigns its measured GDP reaction to this paper. The independent human cloning study identifies GDP among the favored substrates. Retain the curated activity while distinguishing the read abstract and UniProt evidence from an uninspected kinetic table. |
| GO:0004382 GDP phosphatase activity | IDA PMID:16835225 Calcium-dependent dimerization of human soluble calcium acti... | ACCEPT | Summary: GDP hydrolysis is a measured property of human CANT1. Reason: The dimer-interface work concerns the human nucleotidase; its abstract establishes the assayed enzyme and oligomerization experiments, and UniProt records GDPase measurements for its mutants. This agrees with the earlier human substrate characterization. The full original kinetic table was not accessible, but the activity itself is well supported. |
| GO:0004382 GDP phosphatase activity | IEA GO_REF:0000116 | ACCEPT | Summary: The Rhea GDP phosphatase mapping fits CANT1 chemistry. Reason: RHEA:22156 maps the reviewed GDP plus water to GMP and phosphate reaction. Human substrate characterization supports this reaction, and it is distinct from GDP exchange or GTPase signaling. |
| GO:0005509 calcium ion binding | IDA PMID:16835225 Calcium-dependent dimerization of human soluble calcium acti... | ACCEPT | Summary: Calcium binding is integral to CANT1 structure and catalysis. Reason: The human dimerization study directly reports calcium-dependent changes in oligomeric state and crystallographic analysis; the curated structure features identify bound calcium. The mutagenesis work separately distinguishes the metal-induced conformational change from calcium-supported hydrolysis. This is enzymatic cofactor binding, not a generic calcium-sensor mechanism. |
| GO:0005509 calcium ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: The domain-derived calcium-binding assertion is supported by human experiments. Reason: The InterPro inference is corroborated by direct calcium dependence, conformational studies and structure-based calcium-binding features in the target UniProt record. No function is inferred solely from the family name. |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | KEEP AS NON CORE | Summary: The CANT1βCLRN1 binary interaction is supported as a non-core association. Reason: The exact P58418/CLRN1 interaction joins the GOA IPI row and UniProt IntAct record (three experiments), and the primary HuRI portal indexed result explicitly displays CLRN1βCANT1 in HI-III. The paper describes systematic binary-interaction screens and retesting, but the individual raw experiments and pair-specific orthogonal validation were not inspected. Retain this association without assigning a finer molecular mechanism or transferring CLRN1 function to CANT1. Supporting Evidence: |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | UNDECIDED | Summary: The curated CANT1βFAM209A interaction lacks independently inspected target data. Reason: The exact Q5JX71/FAM209A interaction joins the GOA IPI row and reviewed UniProt IntAct record (three experiments). The HuRI screening framework was read, but finite portal and supplementary-data access did not recover the target-specific primary row. This is not evidence against the curator assertion. Keep the decision uncertain rather than inventing a mechanism or treating database repetition as independent target-level verification. Supporting Evidence: |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-6798745 | KEEP AS NON CORE | Summary: CANT1 is represented as released neutrophil granule cargo. Reason: The human Reactome physical entity R-HSA-6800464 explicitly links Q8WVQ1 to extracellular cargo in the tertiary granule release event. This agrees with secretion of a soluble human enzyme. Retain the contextual location; release as cargo does not establish that CANT1 catalyzes or regulates exocytosis. No new degranulation process is proposed. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-6798749 | KEEP AS NON CORE | Summary: CANT1 is represented as released neutrophil granule cargo. Reason: The human Reactome physical entity R-HSA-6800464 explicitly links Q8WVQ1 to extracellular cargo in the specific granule release event. This agrees with secretion of a soluble human enzyme. Retain the contextual location; release as cargo does not establish that CANT1 catalyzes or regulates exocytosis. No new degranulation process is proposed. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-6800434 | KEEP AS NON CORE | Summary: CANT1 is represented as released neutrophil granule cargo. Reason: The human Reactome physical entity R-HSA-6800464 explicitly links Q8WVQ1 to extracellular cargo in the ficolin-rich granule release event. This agrees with secretion of a soluble human enzyme. Retain the contextual location; release as cargo does not establish that CANT1 catalyzes or regulates exocytosis. No new degranulation process is proposed. |
| GO:0005789 endoplasmic reticulum membrane | EXP PMID:12234496 Cloning, expression, and characterization of a soluble calci... | ACCEPT | Summary: Membrane-associated CANT1 acts in the ER secretory pathway. Reason: The reviewed UniProt entry attributes ER membrane localization and type-II topology to this source, and the combined human enzyme, Golgi and proteoglycan evidence supports the secretory-pathway form. The cached cloning abstract mainly describes the soluble product, so it does not independently expose the localization experiment; this does not contradict the curated ER assertion. |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000120 | ACCEPT | Summary: The combined mapping supports ER membrane localization. Reason: The reviewed human type-II membrane topology and ER localization support the inference, consistent with a lumen-facing nucleotidase supporting secretory-pathway glycan synthesis. The supplied donor identifiers are retained as supplied; no donor-label or assay detail is invented. The human soluble processed form does not imply that the full-length protein lacks an ER membrane anchor. |
| GO:0005794 Golgi apparatus | IDA GO_REF:0000052 | ACCEPT | Summary: Human immunofluorescence supports Golgi localization. Reason: The Human Protein Atlas target page reports Golgi apparatus localization with supported reliability using HPA019639 in U2OS cells. A-431 and U-251MG are listed without staining. The source is an antibody-based localization assay, not transcript expression, and it agrees with the established secretory-pathway nucleotidase role. |
| GO:0005886 plasma membrane | EXP PMID:16835225 Calcium-dependent dimerization of human soluble calcium acti... | UNDECIDED | Summary: Secretory-pathway localization is supported; the specific plasma-membrane experiment remains unresolved. Reason: The PMID:16835225 abstract explicitly places the proposed physiological setting of dimerization in the ER or Golgi. The same group's PMID:18067325 abstract locates the membrane-bound form in the ER and pre-Golgi intermediate membranes, alongside a secreted soluble form. These accessible sources positively support early secretory-pathway localization; the earlier claim that they do not distinguish compartments was incomplete. They do not establish a plasma-membrane pool, but neither is an exhaustive exclusion experiment. The full original PMID:16835225 paper and its target-specific surface-localization assay remain uninspected, so retain UNDECIDED for this curator-attributed experimental assertion rather than reject it from the abstract alone. Supporting Evidence: PMID:18067325 in the endoplasmic reticulum and pre-Golgi intermediate membranes |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | MARK AS OVER ANNOTATED | Summary: The electronic cell-membrane mapping overstates the compartment supported by accessible human evidence. Reason: The UniProt SL-0039 mapping asserts plasma membrane, whereas PMID:18067325 explicitly locates the membrane-bound human form in the ER and pre-Golgi intermediate membranes, and PMID:16835225 discusses the ER/Golgi physiological setting. Human Protein Atlas immunofluorescence independently supports Golgi localization. This positive compartment evidence does not substantiate the electronic assignment to the cell surface. Mark that specific mapping as over-annotated while preserving the original source fields and the separate UNDECIDED experimental assertion; this is not proof that a surface pool cannot exist. Existing ER and Golgi assertions already retain the supported locations, so no duplicate replacement or NEW term is proposed. Supporting Evidence: PMID:18067325 in the endoplasmic reticulum and pre-Golgi intermediate membranes |
| GO:0016020 membrane | IBA GO_REF:0000033 | ACCEPT | Summary: CANT1 has a membrane-associated form. Reason: The IBA is concordant with the human membrane-form experiments and the N-terminal signal-anchor topology. A broad membrane assertion accommodates the secretory-pathway form without claiming that all processed or alternatively spliced products retain the anchor. The target in the descendant source list is valid evidence for ancestral placement. Supporting Evidence: |
| GO:0016020 membrane | IDA PMID:16835225 Calcium-dependent dimerization of human soluble calcium acti... | ACCEPT | Summary: The human full-length enzyme is membrane bound. Reason: The dimerization study explicitly distinguishes its full-length membrane-bound construct from the soluble enzyme. Retain the experimentally supported broad membrane term; the inaccessible detailed localization experiment does not justify narrowing this row to a specific membrane. Supporting Evidence: |
| GO:0017110 nucleoside diphosphate phosphatase activity | EXP PMID:12234496 Cloning, expression, and characterization of a soluble calci... | ACCEPT | Summary: CANT1 hydrolyzes nucleoside diphosphates with strong substrate preferences. Reason: The human cloning and expression study establishes calcium-dependent nucleotide hydrolysis with preferential activity toward UDP and GDP, and no monophosphate hydrolysis. The class-level term accurately describes a multi-substrate nucleotidase; it does not imply equal activity against every diphosphate. Supporting Evidence: PMID:12234496 rather UDP, followed by GDP, UTP, GTP, ADP, and ATP. |
| GO:0017110 nucleoside diphosphate phosphatase activity | EXP PMID:15248776 Site-directed mutagenesis of human soluble calcium-activated... | ACCEPT | Summary: Human CANT1 nucleotidase activity depends on its calcium-responsive catalytic structure. Reason: The mutagenesis study directly characterizes the human enzyme and separates effects on activity, substrate specificity and calcium-induced conformational change. The broad nucleoside diphosphatase assertion is appropriate for the substrate spectrum, while individual substrate-specific source rows remain independently preserved. Supporting Evidence: PMID:15248776 calcium triggers a conformational change in hSCAN-1 necessary for nucleotidase activity. |
| GO:0017110 nucleoside diphosphate phosphatase activity | EXP PMID:16835225 Calcium-dependent dimerization of human soluble calcium acti... | ACCEPT | Summary: The human dimer-interface work retains nucleoside diphosphatase activity. Reason: Human nucleotidase activity is the experimentally established function being examined in the dimerization study and is independently corroborated by the earlier cloning and mutagenesis work. Oligomeric-state effects do not imply a different molecular activity. |
| GO:0017110 nucleoside diphosphate phosphatase activity | IEA GO_REF:0000120 | ACCEPT | Summary: The EC, Rhea and domain mappings describe the correct enzyme class. Reason: The combined sources identify EC 3.6.1.6 and RHEA:36799, consistent with human calcium-dependent diphosphate hydrolysis. The broad class permits the known UDP/GDP/IDP preference without asserting an efficient physiological ATPase or platelet-inhibitory function. |
| GO:0030166 proteoglycan biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: CANT1 participates in proteoglycan biosynthesis through nucleotide turnover. Reason: The IBA agrees with the target experimental annotation and the human patient-cell study. CANT1 supplies catalytic UDP hydrolysis in the proposed ER/Golgi nucleotide-recycling mechanism; it is not merely a substrate consumed during glycan synthesis. The target appearing in the source list is expected experimental grounding, not circularity. The detailed ancestral placement has not been reconstructed. Supporting Evidence: |
| GO:0030166 proteoglycan biosynthetic process | IMP PMID:22539336 Further delineation of CANT1 phenotypic spectrum and demonst... | ACCEPT | Summary: Human CANT1 deficiency impairs glycosaminoglycan chain synthesis. Reason: Two patient fibroblast lines showed significantly reduced GAG synthesis under beta-D-xyloside stimulation. Separately, GAG chain-size chromatography used cultures without xyloside and found shorter chains. Basal synthesis was variable; hyaluronan synthesis and the indirect sulfation measure showed no detected change. Together with CANT1 nucleotide hydrolysis this supports the existing biosynthetic-process assertion. Relief of UDP feedback and UMP-dependent sugar exchange was proposed rather than directly measured in these cells. Supporting Evidence: PMID:22539336 significant reduced GAG synthesis in presence of Ξ²-D-xyloside |
| GO:0032580 Golgi cisterna membrane | IEA GO_REF:0000044 | ACCEPT | Summary: The Golgi membrane assignment fits the membrane-associated nucleotidase. Reason: UniProt maps the type-II full-length protein to Golgi stack membrane, and the independent human HPA assay supports the Golgi apparatus. Retain the cisterna-membrane vocabulary mapping without implying that HPA resolved individual cisternae or that every splice product shares the membrane anchor. |
| GO:0035580 specific granule lumen | TAS Reactome:R-HSA-6798749 | KEEP AS NON CORE | Summary: CANT1 is catalogued in a neutrophil granule compartment. Reason: The official human Reactome entity R-HSA-6799706 identifies Q8WVQ1 in the specific granule lumen within the corresponding cargo set. This target-specific record was checked beyond the generic cached event summary. Retain this contextual location, while recognizing that the underlying proteomic peptide evidence was not reanalysed and cargo localization is not exocytosis machinery. Supporting Evidence: Reactome:R-HSA-6798749 |
| GO:0042803 protein homodimerization activity | IDA PMID:16835225 Calcium-dependent dimerization of human soluble calcium acti... | ACCEPT | Summary: Human CANT1 forms calcium-dependent homodimers. Reason: Analytical ultracentrifugation, cross-linking, mutagenesis and structural analysis establish soluble-enzyme self-association; the full-length membrane form can also form disulfide-linked dimers. The observation supports homodimerization as a property of the nucleotidase, not a second independent core function or constitutive dimerization under every condition. The later interface study shows that monomers are also active, so dimerization is not an absolute prerequisite for catalysis. Supporting Evidence: PMID:16835225 calcium or strontium induce noncovalent dimerization of the soluble human enzyme. |
| GO:0043123 positive regulation of canonical NF-kappaB signal transduction | HMP PMID:12761501 Large-scale identification and characterization of human gen... | UNDECIDED | Summary: The high-throughput NF-kappaB reporter result remains source-specific uncertainty. Reason: The cached abstract describes a human cDNA overexpression screen in HEK293 cells but does not identify the CANT1 clone or its reporter result. UniProt associates this paper with an isoform-2 sequence and a putative activator name; neither substitutes for the inaccessible target result. Do not remove the experimental assertion or convert it into a core signaling mechanism without the full target-specific evidence. Supporting Evidence: |
| GO:0043262 ADP phosphatase activity | IDA PMID:16835225 Calcium-dependent dimerization of human soluble calcium acti... | KEEP AS NON CORE | Summary: CANT1 can hydrolyze ADP, a poor substrate of the wild-type human enzyme. Reason: The human enzyme is experimentally active toward ADP, but its strong UDP/GDP preference and reviewed low ADP activity make this a secondary biochemical capacity. Retain the measured activity without equating the wild-type human enzyme with the efficient platelet-inhibitory insect apyrases or engineered therapeutic variants. |
| GO:0045134 UDP phosphatase activity | IBA GO_REF:0000033 | ACCEPT | Summary: UDP hydrolysis is central to the conserved CANT1 activity. Reason: The PTN000989481 IBA agrees with direct human substrate characterization and the enzyme role in secretory-pathway GAG production. Human Q8WVQ1 in the source list supplies legitimate experimental grounding. No target-specific loss or contradiction of inherited UDPase function is evident. |
| GO:0045134 UDP phosphatase activity | IDA PMID:15248776 Site-directed mutagenesis of human soluble calcium-activated... | ACCEPT | Summary: The human mutagenesis study supports UDPase activity. Reason: CANT1 is a calcium-dependent nucleotidase with UDP as a favored substrate. The cited human mutagenesis work characterizes activity and substrate-specific effects, and the independent cloning study confirms UDP preference. This hydrolysis is distinct from transferring the UDP-bound sugar to a glycan. |
| GO:0045134 UDP phosphatase activity | IEA GO_REF:0000116 | ACCEPT | Summary: The UDP-to-UMP Rhea mapping matches CANT1 catalysis. Reason: RHEA:64876 encodes the reviewed UDP hydrolysis reaction, corroborated by human biochemical studies and the proteoglycan-synthesis phenotype. The enzyme catalyzes nucleotide turnover rather than the glycosyltransferase reaction itself. |
| GO:0070062 extracellular exosome | HDA PMID:23533145 In-depth proteomic analyses of exosomes isolated from expres... | MARK AS OVER ANNOTATED | Summary: Detected in an extracellular-vesicle proteome, but the detection does not establish that this protein is an EV constituent. Reason: ER/Golgi-membrane nucleotidase. Mainly resident in an intracellular compartment that MISEV2018 (PMID:30637094) lists as not enriched in small EVs of plasma-membrane/endosomal origin (category 4), and its own review keeps no experimental cell-surface or plasma-membrane pool; an exosome annotation from a bulk EV proteome is not supported. (Manual re-review for OMICS_EVIDENCE, 2026-10-10; previous action: UNDECIDED.) Supporting Evidence: |
| GO:1904724 tertiary granule lumen | TAS Reactome:R-HSA-6798745 | KEEP AS NON CORE | Summary: CANT1 is catalogued in a neutrophil granule compartment. Reason: The official human Reactome entity R-HSA-6800976 identifies Q8WVQ1 in the tertiary granule lumen within the corresponding cargo set. This target-specific record was checked beyond the generic cached event summary. Retain this contextual location, while recognizing that the underlying proteomic peptide evidence was not reanalysed and cargo localization is not exocytosis machinery. Supporting Evidence: Reactome:R-HSA-6798745 |
| GO:1904813 ficolin-1-rich granule lumen | TAS Reactome:R-HSA-6800434 | KEEP AS NON CORE | Summary: CANT1 is catalogued in a neutrophil granule compartment. Reason: The official human Reactome entity R-HSA-6800998 identifies Q8WVQ1 in the ficolin-1-rich granule lumen within the corresponding cargo set. This target-specific record was checked beyond the generic cached event summary. Retain this contextual location, while recognizing that the underlying proteomic peptide evidence was not reanalysed and cargo localization is not exocytosis machinery. Supporting Evidence: Reactome:R-HSA-6800434 |
| GO:1990003 IDP phosphatase activity | IDA PMID:15248776 Site-directed mutagenesis of human soluble calcium-activated... | ACCEPT | Summary: IDP hydrolysis is part of the characterized human substrate spectrum. Reason: The curated human UniProt reaction records IDP-to-IMP hydrolysis with PMID:15248776 as its experimental source. This is consistent with a diphosphate-preferring enzyme, although the cached abstract does not expose the substrate table. Retain the specific curator-supported chemistry without inventing an in vivo IDP concentration, flux or separate physiological pathway. The later human interface study independently assays IDP hydrolysis. |
| GO:1990003 IDP phosphatase activity | IEA GO_REF:0000116 | ACCEPT | Summary: The IDP phosphatase mapping follows the experimentally curated reaction. Reason: RHEA:35207 maps the human target reaction assigned to the mutagenesis study. It is chemically consistent with the characterized nucleoside-diphosphatase spectrum; the detailed kinetic table remains inaccessible and no stronger physiological IDP role is asserted. Direct IDP assays in the later human interface study corroborate this chemistry. |
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Download this section (compressed HTML)Q: Which endogenous human CANT1 forms reach the cell surface, and how does their activity differ from ER/Golgi and released soluble forms?
Q: How does loss of luminal CANT1 change UDP and UMP concentrations, nucleotide-sugar transport and GAG-chain elongation in human chondrocytes?
Q: Which CANT1 construct produced the NF-kappaB reporter-screen signal, and does physiological CANT1 perturbation reproduce that effect?
Experiment: Measure compartment-resolved nucleotide pools and GAG production in human CANT1-deficient chondrocytes rescued with wild-type or catalytically inactive CANT1, separating catalytic turnover from protein abundance and trafficking.
Experiment: Compare endogenous surface labeling, ER/Golgi localization and secretion for the three CANT1 products while measuring nucleotidase activity, rather than inferring localization from bulk protein expression.
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