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Showing SHTN1 — SHOOTIN1 is a alias.

SHTN1

Shootin-1 · UniProt A0MZ66

Length
631 aa
Mass
71.6 kDa
Annotated
2026-06-10
15 papers in source corpus 13 papers cited in narrative 13 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SHTN1 (shootin1) is a clutch-linker protein that converts F-actin retrograde flow into directional traction force at the leading edge of polarizing neurons and migrating cells, thereby driving axon specification, axon guidance, and chemotaxis [PMID:17030985, PMID:18519736, PMID:bio_10.1101_2025.01.13.632873]. Mechanistically, shootin1 mechanically couples actin filament retrograde flow to the cell adhesion molecule L1-CAM, forming an integrin-independent adhesion clutch whose engagement is required for axon outgrowth and for rapid dendritic cell migration; disrupting either the shootin1–actin or shootin1–L1-CAM linkage abolishes force transmission [PMID:18519736, PMID:bio_10.1101_2025.01.13.632873]. Coupling strength is dynamically tuned by phosphorylation: the chemoattractant netrin-1 activates Pak1, which phosphorylates shootin1 to enhance its association with F-actin retrograde flow and with cortactin, an F-actin bridge, increasing traction force and filopodium extension, while PP1-mediated dephosphorylation establishes the asymmetric phospho-shootin1 gradient that orients growth cone turning (PMID:23453953, PMID:26261183, PMID:37044214). Shootin1 is delivered anterogradely to the axonal growth cone by the kinesin KIF20B, and CDKL5 acts as an additional upstream kinase in the polarization pathway (PMID:23864681, PMID:26849555). Its actin-binding activity resides in a noncanonical WH2 domain and a proline-rich region that are held under coiled-coil-dependent autoinhibition in shootin1a and relieved in the shootin1b isoform (PMID:32371045). Beyond cytoskeletal coupling, shootin1 modulates neuroblast fate by dually engaging the LNX1/2 and Itch ubiquitin ligases to activate Notch signaling (PMID:28981589).

Mechanistic history

Synthesis pass · year-by-year structured walk · 13 steps
  1. 2006 High

    Established shootin1 as a polarity determinant whose asymmetric accumulation in a single neurite specifies the axon, answering how a symmetric neuron breaks symmetry.

    Evidence RNAi, overexpression, and transport inhibition with live imaging and PI3K readout in cultured hippocampal neurons

    PMID:17030985

    Open questions at the time
    • Molecular link between shootin1 accumulation and localized PI3K activity unresolved
    • No physical binding partner identified at this stage
  2. 2008 High

    Defined the core clutch mechanism: shootin1 physically couples F-actin retrograde flow to L1-CAM adhesions to transmit force for axon outgrowth.

    Evidence Co-IP of shootin1 with L1-CAM, speckle microscopy of actin coupling, and RNAi axon-length phenotype in rat hippocampal neurons

    PMID:18519736

    Open questions at the time
    • Did not show how coupling is regulated by guidance cues
    • No direct measurement of traction force
  3. 2013 High

    Showed that netrin-1/Pak1 phosphorylation tunes clutch coupling, linking an extracellular guidance signal to mechanical force output.

    Evidence In vitro kinase assay, phosphomimetic/phosphodead mutants, traction force microscopy, and speckle microscopy in hippocampal neurons

    PMID:23453953

    Open questions at the time
    • Phosphorylation sites and their direct effect on actin affinity not fully mapped
    • Counteracting dephosphorylation not yet identified
  4. 2013 High

    Identified KIF20B as the anterograde motor delivering shootin1 to the axon, explaining how the polarity cue is spatially positioned.

    Evidence SPR affinity, reciprocal Co-IP, FRAP after Kif20b knockdown, and in vivo cortical migration epistasis

    PMID:23864681

    Open questions at the time
    • How KIF20B cargo loading is regulated unknown
    • Relationship to diffusive back-flow not detailed
  5. 2015 High

    Identified cortactin as a direct phospho-dependent F-actin bridge, refining how phosphorylation strengthens the actin linkage.

    Evidence Co-IP, phosphomimetic mutants, traction force microscopy, and cortactin RNAi in netrin-1-stimulated neurons

    PMID:26261183

    Open questions at the time
    • Stoichiometry of the shootin1–cortactin–actin assembly unresolved
    • Whether cortactin acts in non-neuronal clutches untested
  6. 2016 Medium

    Placed CDKL5 as an additional upstream kinase in the shootin1 polarization pathway.

    Evidence Yeast two-hybrid, Co-IP, colocalization, phospho-shootin1 western blot after CDKL5 silencing, and double-knockdown epistasis in hippocampal neurons

    PMID:26849555

    Open questions at the time
    • Whether CDKL5 phosphorylates shootin1 directly versus indirectly not resolved
    • Phosphosite not identified
    • Single lab
  7. 2016 Medium

    Discovered the shootin1b splice isoform expressed in peripheral epithelia, broadening shootin1 function beyond neurons to cell-cell contacts.

    Evidence Isoform-specific immunoblot, immunohistochemistry, and colocalization with E-cadherin and cortactin in mouse tissues

    PMID:27177867

    Open questions at the time
    • No functional perturbation of shootin1b performed
    • Role at epithelial junctions not mechanistically tested
  8. 2018 Medium

    Revealed a non-cytoskeletal role: shootin1 activates Notch by dually controlling LNX1/2 and Itch ubiquitin ligases to set neuroblast fate.

    Evidence Co-IP with LNX1/2, Itch, Numb, NICD; ubiquitination assays; in utero electroporation and fate-marker analysis in mouse brain

    PMID:28981589

    Open questions at the time
    • How shootin1 simultaneously coordinates two opposing ligases is unclear
    • Replication absent
    • Connection to its clutch function unknown
  9. 2020 Medium

    Mapped the actin-binding module to a noncanonical WH2/PRR and showed CCD-mediated autoinhibition that differs between isoforms, explaining isoform-specific actin activity.

    Evidence In vitro actin co-sedimentation, native PAGE, and domain/deletion mutagenesis with isoform-specific constructs

    PMID:32371045

    Open questions at the time
    • No structural validation of the autoinhibited state
    • No in-cell functional rescue of the autoinhibition model
  10. 2020 Medium

    Placed shootin1 downstream of Sema6A/PlexinA2 repulsive guidance in vivo, extending its role to retinotectal pathfinding.

    Evidence Zebrafish gain-of-function with PlexinA2 rescue and microarray identifying shtn-1 as Sema6A/PlxnA2-repressed

    PMID:32406957

    Open questions at the time
    • Based on overexpression rather than loss-of-function
    • Molecular link from PlexinA2 to shootin1 not defined
  11. 2023 High

    Identified PP1 as the phosphatase that opposes Pak1, establishing the dephosphorylation arm needed to build the directional phospho-shootin1 gradient for guidance.

    Evidence PP1 overexpression and pharmacological inhibition with spatially resolved phospho-shootin1a imaging and growth cone turning assays

    PMID:37044214

    Open questions at the time
    • PP1 targeting/recruitment to growth cones not defined
    • How gradient is read out into steering not fully resolved
  12. 2025 Medium

    Extended the clutch model to non-neuronal migration, defining an integrin-independent slippery adhesion-clutch tunable by CCL19/laminin and relevant to glioblastoma motility.

    Evidence Traction force microscopy, shootin1/L1 RNAi, and chemotaxis assays in dendritic and glioblastoma cells (preprint)

    PMID:bio_10.1101_2025.01.13.632873

    Open questions at the time
    • Preprint, not yet peer-reviewed
    • Molecular basis of the weak/slippery force regime not detailed
  13. 2025 Medium

    Showed shootin1 coiled-coil oligomerization can drive ligand-independent dimerization in an FGFR2::SHTN1 oncogenic fusion, implicating its self-association in disease.

    Evidence Co-IP, native PAGE, and AlphaFold/HADDOCK modeling with SHTN1 variants in Neuro-2a cells

    PMID:41496852

    Open questions at the time
    • No mutagenesis of the dimerization interface
    • No kinase activity assay confirming constitutive activation
    • Single lab

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the multiple inputs (Pak1, CDKL5, PP1, KIF20B transport, isoform autoinhibition) are integrated in space and time to set clutch coupling, and how the Notch/ubiquitin-ligase role relates to the cytoskeletal clutch, remain unresolved.
  • No unified quantitative model of phospho-regulation versus transport
  • Mechanistic crosstalk between clutch function and Notch signaling unknown
  • Human disease relevance beyond the FGFR2 fusion not established

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0008092 cytoskeletal protein binding 4 GO:0060090 molecular adaptor activity 2 GO:0098631 cell adhesion mediator activity 2
Localization
GO:0005886 plasma membrane 3 GO:0005856 cytoskeleton 2
Pathway
R-HSA-1266738 Developmental Biology 3 R-HSA-162582 Signal Transduction 3 R-HSA-112316 Neuronal System 2
Partners
ACTBCDKL5CTTNITCHKIF20BL1CAMLNX1PAK1

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2006 Shootin1 (SHTN1) is a novel protein that undergoes anterograde transport to axonal growth cones and diffuses back to the soma; its asymmetric accumulation in a single neurite drives axon specification during neuronal polarization. Shootin1 is required for spatially localized phosphoinositide-3-kinase (PI3K) activity in the nascent axon. RNA interference (knockdown), overexpression in cultured hippocampal neurons, live-cell imaging of fluctuating accumulation, inhibition of anterograde transport The Journal of cell biology High 17030985
2008 Shootin1 physically interacts with both actin filament retrograde flow and L1-CAM in axonal growth cones, mechanically coupling F-actin flow to the substrate (the 'clutch' mechanism) to promote L1-dependent axon outgrowth. Disrupting either the shootin1–actin or shootin1–L1-CAM interaction inhibits axon elongation. Co-immunoprecipitation of shootin1 with L1-CAM, speckle microscopy to measure coupling with actin retrograde flow, RNAi knockdown with axon length readout, shootin1 overexpression in cultured rat hippocampal neurons The Journal of cell biology High 18519736
2013 The chemoattractant netrin-1 activates Pak1 kinase, which phosphorylates shootin1a in axonal growth cones. This phosphorylation enhances shootin1's interaction with F-actin retrograde flow, thereby increasing F-actin–substrate coupling efficiency, traction force generation, and filopodium extension for axon outgrowth. In vitro kinase assay (Pak1 phosphorylating shootin1), traction force microscopy, phosphomimetic/phosphodead shootin1 mutants, fluorescence speckle microscopy of actin flow coupling in hippocampal neurons treated with netrin-1 Current biology : CB High 23453953
2013 Shootin1 interacts with KIF20B, a kinesin family member; this interaction (mapped to a 57-aa KIF20B domain) mediates anterograde transport of shootin1 to the developing axon. Kif20b knockdown reduces shootin1 mobilization to the axon tip and PIP3 accumulation in the growth cone. Shootin1 and KIF20B act in the same genetic pathway for neuronal polarization and multipolar-to-bipolar transition during cortical migration. Surface plasmon resonance (affinity ~10⁻⁷ M), co-immunoprecipitation in vivo, FRAP analysis of shootin1 mobility after Kif20b knockdown, in vivo migration assay with shRNA, time-lapse imaging of multipolar cells, epistasis by dominant-negative KIF20B fragment The Journal of neuroscience : the official journal of the Society for Neuroscience High 23864681
2015 Cortactin, an F-actin binding molecule, directly interacts with shootin1 in axonal growth cones. Shootin1 phosphorylation by Pak1 (activated by netrin-1) enhances the shootin1–cortactin interaction, which in turn strengthens the linkage between F-actin retrograde flow and L1-CAM adhesions, increasing traction forces for axon outgrowth. Co-immunoprecipitation (shootin1–cortactin), phosphomimetic shootin1 mutants, traction force microscopy, F-actin flow coupling assay, RNAi knockdown of cortactin in hippocampal neurons with netrin-1 stimulation The Journal of cell biology High 26261183
2016 CDKL5 kinase interacts with shootin1 in vivo (co-immunoprecipitation) and both proteins localize at the distal tip of outgrowing axons. CDKL5 silencing reduces shootin1 phosphorylation, suggesting CDKL5 directly or indirectly phosphorylates shootin1. Epistasis experiments show CDKL5-induced supernumerary axon formation is attenuated by shootin1 knockdown, placing them in the same neuronal polarization pathway. Yeast two-hybrid screening, co-immunoprecipitation in primary hippocampal neurons, immunofluorescence colocalization, RNAi knockdown of CDKL5 with phospho-shootin1 western blot, epistasis by double knockdown PloS one Medium 26849555
2016 A second shootin1 isoform, shootin1b (SHTN1b), generated by alternative splicing, is expressed in peripheral epithelial tissues (lung, liver, intestine, etc.) in addition to brain, where it co-localizes with E-cadherin and cortactin at cell–cell contact sites. Immunoblot with isoform-specific antibody, immunohistochemistry on mouse tissues, immunofluorescence colocalization with E-cadherin and cortactin Cell and tissue research Medium 27177867
2018 Shootin1 activates the Notch signaling pathway through two opposing ubiquitin ligase interactions: (1) it interacts with LNX1/2 E3 ligases to promote poly-ubiquitination and degradation of Numb (a Notch inhibitor), and (2) it interacts with the Itch E3 ligase to impair poly-ubiquitination of the Notch intracellular domain (NICD), thereby stabilizing it. Both activities converge to activate Notch and modulate neuroblast cell fate in the developing brain. Co-immunoprecipitation of shootin1 with LNX1/2, Itch, Numb, and NICD; ubiquitination assays; in utero electroporation with shootin1 constructs; analysis of neuroblast fate markers in developing mouse brain Cerebral cortex (New York, N.Y. : 1991) Medium 28981589
2020 SHTN1 contains a noncanonical WH2 domain and an upstream proline-rich region (PRR) that are sufficient for actin binding. However, shootin1a (SHTN1S) is autoinhibited: an N-terminal coiled-coil domain (CCD) intramolecularly suppresses actin binding. Shootin1b (SHTN1L) relieves this autoinhibition via a C-terminal motif specific to the long isoform, enabling actin interaction. A nuclear localization signal between PRR and WH2 is similarly subject to CCD-dependent autoinhibition. In vitro actin co-sedimentation assay with SHTN1 deletion and domain mutants, native PAGE, domain mapping of WH2 and PRR, isoform-specific construct expression Journal of molecular biology Medium 32371045
2023 Protein phosphatase 1 (PP1) dephosphorylates shootin1a in axonal growth cones. PP1 overexpression abolishes the netrin-1-induced asymmetric localization of phosphorylated shootin1a and blocks growth cone turning toward netrin-1. PP1 inhibition reverses the asymmetric phospho-shootin1a gradient, converting netrin-1-induced attraction to repulsion, demonstrating that PP1-mediated dephosphorylation is required to establish the phospho-shootin1a gradient that directs axon guidance. PP1 overexpression and pharmacological inhibition in hippocampal neurons, immunofluorescence of phospho-shootin1a distribution under netrin-1 gradient, growth cone turning assay The Journal of biological chemistry High 37044214
2020 In zebrafish, overexpression of shootin-1 impairs optic vesicle migration and causes retinotectal pathfinding errors; these phenotypes are rescued by overexpressing PlexinA2, placing shootin-1 downstream of Semaphorin6A/PlexinA2 repulsive guidance signaling. Zebrafish overexpression of shtn-1 and PlxnA2, microarray screen identifying shtn-1 as transcriptionally repressed by Sema6A/PlxnA2, phenotypic rescue assay Developmental dynamics : an official publication of the American Association of Anatomists Medium 32406957
2025 In an FGFR2::SHTN1 oncogenic fusion protein, the coiled-coil domain II (CCD-II) of shootin1 mediates ligand-independent dimerization of FGFR2, resulting in constitutive kinase activation. Shootin1 inherently forms oligomers through its coiled-coil domains, and within the fusion this property drives receptor dimerization. Co-immunoprecipitation, native PAGE, AlphaFold/HADDOCK structural modeling, expression of SHTN1 variants in Neuro-2a cells to assess oligomerization Turkish journal of biology Medium 41496852
2025 Shootin1 and L1-CAM together constitute an integrin-independent 'slippery adhesion-clutch' that transmits weak traction forces (~100-fold weaker than integrin-based forces) from treadmilling actin filaments to the extracellular environment to drive rapid dendritic cell migration. This clutch is polarized and tunable by the chemoattractant CCL19 and the adhesive ligand laminin, mediating chemotaxis. Aberrant shootin1/L1 clutch activity also enhances glioblastoma cell motility. Traction force microscopy, RNAi knockdown of shootin1 and L1 in dendritic cells and glioblastoma cells, chemotaxis assays, live-cell imaging of actin dynamics bioRxivpreprint Medium bio_10.1101_2025.01.13.632873

Source papers

Stage 0 corpus · 15 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2006 Shootin1: A protein involved in the organization of an asymmetric signal for neuronal polarization. The Journal of cell biology 112 17030985
2008 Shootin1 interacts with actin retrograde flow and L1-CAM to promote axon outgrowth. The Journal of cell biology 89 18519736
2013 Conversion of a signal into forces for axon outgrowth through Pak1-mediated shootin1 phosphorylation. Current biology : CB 81 23453953
2015 Shootin1-cortactin interaction mediates signal-force transduction for axon outgrowth. The Journal of cell biology 57 26261183
2013 Shootin1 acts in concert with KIF20B to promote polarization of migrating neurons. The Journal of neuroscience : the official journal of the Society for Neuroscience 44 23864681
2016 CDKL5 and Shootin1 Interact and Concur in Regulating Neuronal Polarization. PloS one 41 26849555
2024 Data-mining-based biomarker evaluation and experimental validation of SHTN1 for bladder cancer. Cancer genetics 26 39260052
2016 Identification of a shootin1 isoform expressed in peripheral tissues. Cell and tissue research 16 27177867
2018 Notch Activation by Shootin1 Opposing Activities on 2 Ubiquitin Ligases. Cerebral cortex (New York, N.Y. : 1991) 11 28981589
2023 Dephosphorylation of neural wiring protein shootin1 by PP1 phosphatase regulates netrin-1-induced axon guidance. The Journal of biological chemistry 9 37044214
2020 Putative Coiled-Coil Domain-Dependent Autoinhibition and Alternative Splicing Determine SHTN1's Actin-Binding Activity. Journal of molecular biology 9 32371045
2015 Rnaset2 inhibits melanocyte outgrowth possibly through interacting with shootin1. Journal of dermatological science 8 26293343
2020 Shootin-1 is required for nervous system development in zebrafish. Developmental dynamics : an official publication of the American Association of Anatomists 3 32406957
2024 Shootin1 Regulates Retinal Ganglion Cell Neurite Development: Insights From an RGC Direct Somatic Cell Reprogramming Model. Investigative ophthalmology & visual science 1 38935030
2025 Exploring Shootin1's oncogenic role within FGFR2 gene fusions. Turkish journal of biology = Turk biyoloji dergisi 0 41496852

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