SPOCK1

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0031012 extracellular matrix	IBA GO_REF:0000033	ACCEPT	Summary: Testican-1 is a secreted proteoglycan that localizes to and is a structural component of the extracellular matrix. Multiple lines of evidence support this core localization. Reason: IBA annotation is well-supported by experimental evidence. UniProt states "Secreted, extracellular space, extracellular matrix". Multiple proteomics studies (PMID:27068509, PMID:32055794, PMID:33266304) identified testican-1 in ECM preparations using HDA evidence. The protein is described as an ECM proteoglycan in the original characterization (PMID:8389704). This is a core function of testican-1. Supporting Evidence: PMID:8389704 The molecular characterization of a human testicular proteoglycan, the progenitor of a seminal plasma glycosaminoglycan-bearing peptide, was achieved by cDNA cloning. file:human/SPOCK1/SPOCK1-uniprot.txt SUBCELLULAR LOCATION: Secreted, extracellular space, extracellular matrix. file:human/SPOCK1/SPOCK1-deep-research-falcon.md model: Edison Scientific Literature
GO:0008191 metalloendopeptidase inhibitor activity	IBA GO_REF:0000033	ACCEPT	Summary: Testican-1 directly inhibits membrane-type matrix metalloproteinases (MT-MMPs) including MT1-MMP and MT3-MMP, preventing pro-MMP-2 activation. This is a core molecular function. Reason: IBA annotation is supported by experimental evidence from PMID:11751414 showing direct interaction with MT1-MMP and MT3-MMP and inhibition of pro-MMP-2 activation. While this study focused on testican-3, it explicitly states "Expression of testican 1 or testican 3 but not testican 2 also inhibited pro-MMP-2 activation". This metalloproteinase inhibitor activity is a core function of testican-1. Supporting Evidence: PMID:11751414 Expression of testican 1 or testican 3 but not testican 2 also inhibited pro-MMP-2 activation by either MT1-MMP or MT3-MMP.
GO:0010810 regulation of cell-substrate adhesion	IBA GO_REF:0000033	ACCEPT	Summary: Testican-1 regulates cell-substrate adhesion, with experimental evidence showing it inhibits Neuro-2a cell attachment. The IBA term appropriately captures this regulatory function. Reason: IBA annotation is supported by experimental evidence from PMID:12853036 and PMID:8389704. The protein is explicitly described as resembling "modulators of cell social behaviour" and experimental data shows it inhibits neuron attachment (PMID:12853036). This is a core function related to ECM-mediated cell adhesion modulation. Supporting Evidence: PMID:8389704 Testican, a multidomain testicular proteoglycan resembling modulators of cell social behaviour. PMID:12853036 We demonstrate that testican inhibits attachment of Neuro-2a cells and their ability to form neurite extensions.
GO:0005615 extracellular space	IBA GO_REF:0000033	ACCEPT	Summary: Testican-1 is secreted to the extracellular space as confirmed by UniProt and experimental detection in extracellular fluids. Reason: IBA annotation is consistent with the protein being secreted (signal peptide residues 1-21) and detected in extracellular locations including seminal plasma and as part of the ECM. This is a core localization. Supporting Evidence: file:human/SPOCK1/SPOCK1-uniprot.txt SUBCELLULAR LOCATION: Secreted, extracellular space, extracellular matrix. PMID:14511383 Testican-1, a secreted proteoglycan enriched in brain
GO:0005509 calcium ion binding	IBA GO_REF:0000033	ACCEPT	Summary: Testican-1 contains extracellular calcium-binding (EC) domains similar to those in BM-40/SPARC. Direct experimental evidence confirms calcium binding activity. Reason: IBA annotation is supported by both sequence analysis (InterPro IPR019577 SPARC/Testican Ca-binding domain) and experimental evidence from PMID:9323035 demonstrating calcium binding with Kd=68 microM. The EC domain shows structural changes upon calcium depletion. This is a core molecular function. Supporting Evidence: PMID:9323035 The extracellular calcium-binding (EC) module of human testican (115 residues) was obtained in native form by recombinant production in mammalian cell culture and thus shown to represent an independently folding domain. This module showed a large loss in alpha-helix upon calcium depletion. Apparently only one of the two EF hands binds calcium, with a moderate affinity (Kd =68 microM)
GO:0005509 calcium ion binding	IEA GO_REF:0000002	ACCEPT	Summary: Duplicate IEA annotation based on InterPro domain IPR019577. Redundant with IBA and IDA evidence for same term. Reason: This IEA annotation is based on the presence of the SPARC/Testican calcium-binding domain (InterPro IPR019577) and is consistent with experimental evidence. While duplicate, it provides computational confirmation of the calcium-binding function. Supporting Evidence: file:human/SPOCK1/SPOCK1-uniprot.txt InterPro: IPR019577; SPARC/Testican_Ca-bd-dom
GO:0008191 metalloendopeptidase inhibitor activity	IEA GO_REF:0000117	ACCEPT	Summary: Duplicate IEA annotation from ARBA machine learning. Redundant with IBA and IDA evidence for same term. Reason: This IEA annotation provides computational support for the metalloendopeptidase inhibitor activity that is experimentally validated by IBA and IDA evidence. Acceptable as supporting evidence. Supporting Evidence: GO_REF:0000117 Electronic annotation by ARBA machine learning models
GO:0005515 protein binding	IPI PMID:32296183 A reference map of the human binary protein interactome.	REMOVE	Summary: Generic protein binding annotation from binary interactome study. Too vague to be informative about testican-1 function. Reason: The term "protein binding" provides no functional information about testican-1's specific role. While the protein does bind to other proteins (MT-MMPs, cathepsin L, etc.), these interactions are better captured by more specific terms like metalloendopeptidase inhibitor activity and cysteine-type endopeptidase inhibitor activity. PMID:32296183 is a high-throughput interactome study that does not provide specific functional context. Supporting Evidence: PMID:32296183 A reference map of the human binary protein interactome
GO:0005201 extracellular matrix structural constituent	HDA PMID:27068509 Extracellular matrix remodelling in response to venous hyper...	ACCEPT	Summary: Testican-1 functions as a structural component of the ECM, identified in matrisome proteomics studies. This is a core molecular function. Reason: HDA annotation from ECM proteomics study is appropriate. As a proteoglycan with GAG chains that localizes to the ECM, testican-1 contributes to ECM structure. The modular domain architecture and proteoglycan nature support this structural role. Supporting Evidence: file:human/SPOCK1/SPOCK1-uniprot.txt O-glycosylated. Glycosaminoglycan that contains chondroitin sulfate and heparan sulfate. PMID:8389704 Testican is the progenitor of the unique heparan/chondroitin-sulfate-bearing peptide present in human seminal plasma PMID:27068509 Apr 11. Extracellular matrix remodelling in response to venous hypertension: proteomics of human varicose veins.
GO:0031012 extracellular matrix	HDA PMID:27068509 Extracellular matrix remodelling in response to venous hyper...	ACCEPT	Summary: Duplicate HDA annotation for ECM localization from varicose vein ECM proteomics. Redundant with IBA annotation. Reason: This HDA annotation provides independent proteomics evidence for ECM localization from a study on extracellular matrix remodeling in human varicose veins. Multiple independent HDA studies confirm this core localization. Supporting Evidence: PMID:27068509 Apr 11. Extracellular matrix remodelling in response to venous hypertension: proteomics of human varicose veins.
GO:0031012 extracellular matrix	HDA PMID:32055794 3D mapping of native extracellular matrix reveals cellular r...	ACCEPT	Summary: Duplicate HDA annotation for ECM localization from 3D ECM mapping study. Redundant with IBA and other HDA annotations. Reason: Additional proteomics evidence for ECM localization from independent study on 3D mapping of native extracellular matrix. Reinforces core localization. Supporting Evidence: PMID:32055794 3D mapping of native extracellular matrix reveals cellular responses to the microenvironment.
GO:0031012 extracellular matrix	HDA PMID:33266304 Divide-and-Conquer Matrisome Protein (DC-MaP) Strategy: An M...	ACCEPT	Summary: Duplicate HDA annotation for ECM localization from matrisome characterization study. Redundant with IBA and other HDA annotations. Reason: Additional proteomics evidence for ECM localization from Divide-and-Conquer Matrisome Protein (DC-MaP) strategy study. Multiple independent HDA studies provide strong support for this core localization. Supporting Evidence: PMID:33266304 Divide-and-Conquer Matrisome Protein (DC-MaP) Strategy: An MS-Friendly Approach to Proteomic Matrisome Characterization.
GO:0001558 regulation of cell growth	NAS PMID:8389704 Testican, a multidomain testicular proteoglycan resembling m...	KEEP AS NON CORE	Summary: Original paper describes testican-1 as resembling modulators of cell social behavior, but provides no direct experimental evidence for regulation of cell growth. Reason: The annotation is based on NAS (non-traceable author statement) from the original characterization paper. While the multidomain structure suggests potential roles in cell proliferation, this is not a core function based on current evidence. The primary characterized functions are ECM structural roles and protease inhibition. Supporting Evidence: PMID:8389704 Its protein core encompasses several domains encountered in various proteins associated with adhesion, migration and cell proliferation.
GO:0001764 neuron migration	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: ISS annotation based on orthology to mouse testican-1 (Q62288). While testican-1 affects neuron attachment, direct evidence for neuron migration is limited. Reason: ISS annotation transferred from mouse ortholog. While testican-1 clearly affects neuronal cell adhesion and neurite extension (PMID:12853036), migration is a distinct process. This is potentially valid but peripheral to the core ECM structural and protease inhibitor functions. Supporting Evidence: GO_REF:0000024 Manual transfer from mouse ortholog UniProtKB:Q62288
GO:0004867 serine-type endopeptidase inhibitor activity	NAS PMID:14511383 Human proteoglycan testican-1 inhibits the lysosomal cystein...	UNDECIDED	Summary: NAS annotation suggesting serine protease inhibitor activity based on Kazal-like domain presence, but experimental evidence in same paper focused on cysteine protease inhibition. Reason: Kazal-like domains are typically serine protease inhibitors, and testican-1 contains a Kazal-like domain (residues 130-182). However, PMID:14511383 experimentally demonstrated cysteine protease (cathepsin L) inhibition but did not test serine proteases. The NAS evidence is weak without direct experimental validation. Would need experimental testing to confirm. Supporting Evidence: file:human/SPOCK1/SPOCK1-uniprot.txt DOMAIN 130..182 Kazal-like PMID:14511383 Human proteoglycan testican-1 inhibits the lysosomal cysteine protease cathepsin L.
GO:0004869 cysteine-type endopeptidase inhibitor activity	IDA PMID:14511383 Human proteoglycan testican-1 inhibits the lysosomal cystein...	ACCEPT	Summary: Direct experimental demonstration that testican-1 inhibits cathepsin L with Ki=0.7 nM via its thyroglobulin type-1 domain. This is a core molecular function. Reason: Strong IDA evidence from PMID:14511383 showing potent and specific inhibition of cathepsin L (Ki=0.7 nM) but not cathepsin B. The thyroglobulin domain mediates this activity. This is a well-characterized core function of testican-1. Supporting Evidence: PMID:14511383 We demonstrate that purified recombinant human testican-1 is a strong competitive inhibitor of the lysosomal cysteine protease, cathepsin L, with a Ki of 0.7 nM, but it does not inhibit the structurally related lysosomal cysteine protease cathepsin B.
GO:0005509 calcium ion binding	IDA PMID:9323035 Properties of the extracellular calcium binding module of th...	ACCEPT	Summary: Duplicate IDA annotation for calcium binding. Redundant with IBA annotation for same term, both supported by same experimental evidence. Reason: This IDA annotation provides direct experimental evidence for calcium binding (Kd=68 microM) and is the primary experimental reference. Consistent with IBA and IEA annotations for the same function. Supporting Evidence: PMID:9323035 Apparently only one of the two EF hands binds calcium, with a moderate affinity (Kd =68 microM)
GO:0005615 extracellular space	IDA PMID:14511383 Human proteoglycan testican-1 inhibits the lysosomal cystein...	ACCEPT	Summary: Duplicate IDA annotation for extracellular space localization. Redundant with IBA annotation. Reason: IDA evidence from purification and characterization of secreted testican-1 from cell culture medium. Supports IBA annotation for same localization. Supporting Evidence: PMID:14511383 Testican-1, a secreted proteoglycan enriched in brain
GO:0005737 cytoplasm	ISS GO_REF:0000024	REMOVE	Summary: ISS annotation based on mouse ortholog suggesting cytoplasmic localization. Inconsistent with primary secreted localization. Reason: Testican-1 has a signal peptide (residues 1-21) and is characterized as a secreted proteoglycan. UniProt annotation states "Secreted, extracellular space, extracellular matrix" with no mention of cytoplasmic localization. While the protein may transiently pass through the cytoplasm during secretion, cytoplasm is not a functional localization for this protein. This ISS annotation from mouse ortholog appears incorrect. Supporting Evidence: file:human/SPOCK1/SPOCK1-uniprot.txt SIGNAL 1..21; SUBCELLULAR LOCATION: Secreted, extracellular space, extracellular matrix.
GO:0007155 cell adhesion	NAS PMID:8389704 Testican, a multidomain testicular proteoglycan resembling m...	ACCEPT	Summary: NAS annotation for cell adhesion based on structural similarity to cell adhesion modulators. Supported by experimental data on adhesion regulation. Reason: While NAS evidence is weak, the annotation is supported by the protein's domain structure and experimental evidence from PMID:12853036 showing regulation of cell attachment. This is appropriately a general cell adhesion term that encompasses the more specific regulation of cell-substrate adhesion function. Supporting Evidence: PMID:8389704 Testican, a multidomain testicular proteoglycan resembling modulators of cell social behaviour. PMID:12853036 We demonstrate that testican inhibits attachment of Neuro-2a cells
GO:0007399 nervous system development	NAS PMID:9181134 [Cloning of testican/SPOCK in man and mouse. Neuromuscular e...	KEEP AS NON CORE	Summary: NAS annotation for nervous system development based on brain expression and postsynaptic localization. Testican-1 is enriched in brain. Reason: While testican-1 is highly expressed in brain and affects neuron attachment/neurite extension, nervous system development is a broad process term that may be peripheral to the core molecular functions (ECM structure, protease inhibition, adhesion modulation). The NAS evidence is weak but consistent with expression patterns. Supporting Evidence: PMID:9181134 Structural analysis, a main expression in nervous system and preliminary assignment of the human gene in a critical region for neuropathologies, suggest that SPOCK may be of importance in neural development
GO:0008191 metalloendopeptidase inhibitor activity	IDA PMID:11751414 Suppression of membrane-type 1 matrix metalloproteinase (MMP...	ACCEPT	Summary: Duplicate IDA annotation for metalloendopeptidase inhibitor activity. Redundant with IBA annotation. Reason: IDA annotation provides direct experimental evidence for MT-MMP inhibition. This is the primary experimental reference supporting the IBA annotation. Core molecular function. Supporting Evidence: PMID:11751414 Expression of testican 1 or testican 3 but not testican 2 also inhibited pro-MMP-2 activation by either MT1-MMP or MT3-MMP.
GO:0010812 negative regulation of cell-substrate adhesion	IDA PMID:12853036 Testican-1 inhibits attachment of Neuro-2a cells.	ACCEPT	Summary: Direct experimental evidence showing testican-1 inhibits Neuro-2a cell attachment to substrate. More specific than the IBA term for regulation of cell-substrate adhesion. Reason: Strong IDA evidence showing testican-1 inhibits cell attachment when coated on substrate, blocking attachment sites. This negative regulatory function is well-characterized and represents a core activity related to ECM-mediated adhesion modulation. Supporting Evidence: PMID:12853036 We demonstrate that testican inhibits attachment of Neuro-2a cells and their ability to form neurite extensions. Both testican proteoglycan and the core glycoprotein that has been depleted of chondroitin sulfate inhibit cell attachment. Pre-treatment of the culture substratum with testican inhibits Neuro-2a attachment
GO:0010977 negative regulation of neuron projection development	IDA PMID:12853036 Testican-1 inhibits attachment of Neuro-2a cells.	ACCEPT	Summary: Direct experimental evidence showing testican-1 inhibits neurite extension in Neuro-2a cells. Represents a specific neuronal function. Reason: Strong IDA evidence from PMID:12853036 demonstrating inhibition of neurite extensions. This is a well-characterized activity but may be considered non-core as it represents a tissue-specific manifestation of the broader adhesion modulation function. Supporting Evidence: PMID:12853036 We demonstrate that testican inhibits attachment of Neuro-2a cells and their ability to form neurite extensions.
GO:0014069 postsynaptic density	NAS PMID:9181134 [Cloning of testican/SPOCK in man and mouse. Neuromuscular e...	KEEP AS NON CORE	Summary: NAS annotation for postsynaptic density localization based on immunoelectron microscopy showing selective localization in postsynaptic densities. Reason: The annotation is based on immunoelectron microscopy data from PMID:9181134 showing localization to postsynaptic densities of pyramidal neurons and Purkinje cells. However, this is a specialized sub-localization within the broader CNS expression pattern and represents a non-core, tissue-specific localization. Supporting Evidence: PMID:9181134 Immunoelectron microscopy showed the antigen selectively localized in the post-synaptic density of scattered pyramidal neurons and Purkinje cells.
GO:0016528 sarcoplasm	ISS GO_REF:0000024	REMOVE	Summary: ISS annotation for sarcoplasm localization based on mouse ortholog. Inconsistent with secreted nature of protein. Reason: Similar to the cytoplasm annotation, sarcoplasm is inconsistent with testican-1 being a secreted ECM proteoglycan. This ISS annotation from mouse ortholog appears incorrect for a protein with a signal peptide that functions in the extracellular space. Supporting Evidence: file:human/SPOCK1/SPOCK1-uniprot.txt SUBCELLULAR LOCATION: Secreted, extracellular space, extracellular matrix.
GO:0021953 central nervous system neuron differentiation	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: ISS annotation for CNS neuron differentiation based on mouse ortholog. Represents a developmental process. Reason: ISS annotation from mouse ortholog. While testican-1 is highly expressed in brain and affects neuronal cell behavior, neuron differentiation is a broad developmental process that is peripheral to the core ECM structural and protease inhibitor functions. Supporting Evidence: GO_REF:0000024 Manual transfer from mouse ortholog
GO:0022008 neurogenesis	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: ISS annotation for neurogenesis based on mouse ortholog. Very broad developmental process term. Reason: ISS annotation from mouse ortholog. Neurogenesis is an extremely broad process term. While testican-1 affects neuron behavior and is expressed in brain, this broad developmental process is peripheral to core functions. Supporting Evidence: GO_REF:0000024 Manual transfer from mouse ortholog
GO:0031594 neuromuscular junction	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: ISS annotation for neuromuscular junction localization based on mouse ortholog. Specialized tissue-specific localization. Reason: ISS annotation from mouse ortholog suggesting localization to neuromuscular junctions. This is a specialized tissue-specific localization that is peripheral to the core ECM localization. May be valid but represents a minor sub-localization. Supporting Evidence: GO_REF:0000024 Manual transfer from mouse ortholog
GO:0033268 node of Ranvier	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: ISS annotation for node of Ranvier localization based on mouse ortholog. Highly specialized neuronal structure. Reason: ISS annotation from mouse ortholog suggesting localization to nodes of Ranvier. This is a highly specialized sub-localization within myelinated axons that is peripheral to the core ECM function. May be valid but represents a minor tissue-specific localization. Supporting Evidence: GO_REF:0000024 Manual transfer from mouse ortholog
GO:0005518 collagen binding	IBA GO_REF:0000033	NEW	Summary: IBA annotation for collagen binding found in UniProt but not in GOA file. Testican-1 is an ECM proteoglycan that may interact with collagen. Reason: This IBA annotation appears in UniProt (DR GO; GO:0005518; F:collagen binding; IBA:GO_Central) but was not included in the GOA file provided. As an ECM proteoglycan, testican-1 may interact with collagen fibrils, though direct experimental evidence is lacking. PMID:9323035 tested the EC module for collagen binding and found "No clear evidence was obtained for collagen binding", suggesting this IBA annotation may be over-prediction. Requires experimental validation. Supporting Evidence: PMID:9323035 No clear evidence was obtained for collagen binding, indicating that EC modules found in different proteins may not share similar functions.
GO:0050840 extracellular matrix binding	IBA GO_REF:0000033	NEW	Summary: IBA annotation for ECM binding found in UniProt but not in GOA file. As an ECM proteoglycan, testican-1 likely interacts with ECM components. Reason: This IBA annotation appears in UniProt (DR GO; GO:0050840; F:extracellular matrix binding; IBA:GO_Central) but was not in the GOA file. As a proteoglycan with GAG chains that localizes to the ECM and modulates cell-matrix interactions, ECM binding is a reasonable function. However, specific binding partners beyond MT-MMPs have not been well characterized. This represents a core function consistent with the protein's role in ECM organization. Supporting Evidence: file:human/SPOCK1/SPOCK1-uniprot.txt May play a role in cell-cell and cell-matrix interactions.

Gene Description

Existing Annotations Review

Core Functions

Testican-1 functions as a structural component of the extracellular matrix, contributing to ECM organization through its proteoglycan nature with chondroitin sulfate and heparan sulfate GAG chains. Identified in multiple ECM proteomics studies.

Testican-1 directly inhibits membrane-type matrix metalloproteinases (MT1-MMP and MT3-MMP), preventing pro-MMP-2 activation through direct protein-protein interaction.

Testican-1 is a potent competitive inhibitor of cathepsin L (Ki=0.7 nM) via its thyroglobulin type-1 domain. Does not inhibit cathepsin B. Active at both pH 5.5 and pH 7.2, functioning in both intracellular vesicles and extracellular space.

The extracellular calcium-binding (EC) module contains EF-hand motifs and binds calcium with moderate affinity (Kd=68 microM). The module undergoes conformational change upon calcium binding.

Testican-1 binds to extracellular matrix components and modulates cell-matrix interactions, inhibiting neuron attachment to substrate and blocking neurite extension. This function is mediated by both the proteoglycan form and the core protein depleted of chondroitin sulfate.

References

Deep Research

Falcon

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