STON2

STON2 (stonin 2) is a clathrin-mediated endocytic adaptor that ensures the fidelity of synaptic vesicle (SV) protein sorting at presynaptic terminals (PMID:23345427). Genetic deletion in mice causes selective missorting of synaptotagmin 1 (Syt1) to the neuronal surface and an enlarged SV pool, while leaving the overall speed of SV recycling intact — establishing STON2 as a sorting fidelity factor rather than a rate-limiting endocytic component (PMID:23345427). STON2 acts in parallel with the Syt1-associated SV glycoprotein SV2A/B: loss of either alone produces partial Syt1 missorting, whereas combined loss dramatically exacerbates Syt1 depletion and impairs neurotransmission at hippocampal synapses (PMID:26015569). The retrieval of Syt1 depends on a direct STON2–Syt1 interaction controlled by STON2 phosphorylation; schizophrenia-associated STON2 variants (307Pro-851Ala) are dephosphorylated, weakening Syt1 binding and disrupting SV endocytosis, and knockin mice carrying these variants display deficits in synaptic transmission, short-term plasticity, and schizophrenia-like behaviors that are reversed by haloperidol (PMID:38402028). Beyond its synaptic role, STON2 has been linked in cancer cells to a DNMT1/MUC1 epigenetic axis governing stem-like properties (PMID:30518424) and is itself a direct target of multiple microRNAs that regulate proliferation and EMT (PMID:30325582).

1. 2013 High

   Established that STON2 is required for accurate sorting of SV proteins rather than for the speed of vesicle recycling, defining its core function as a fidelity factor in synaptic vesicle protein retrieval.

   Evidence Stn2 knockout mice with live imaging, FM dye assays, and surface immunostaining of SV proteins

   PMID:23345427

   Open questions at the time

   • Did not resolve the direct molecular binding interface mediating Syt1 selectivity
   • Mechanism of the observed up-regulation of bulk endosome SV reformation not defined
2. 2015 High

   Resolved whether STON2 acts alone in Syt1 sorting by showing it operates in parallel with SV2A/B, with the two providing overlapping retrieval activity that converges on neurotransmission efficacy.

   Evidence Single and double genetic knockout/knockdown in mice and neurons, immunostaining, and hippocampal electrophysiology

   PMID:26015569

   Open questions at the time

   • Did not establish whether STON2 and SV2A/B engage Syt1 at distinct sites or compete
   • Structural basis of the redundancy unresolved
3. 2024 High

   Connected STON2 phosphorylation state to the strength of the Syt1 interaction and to human disease, showing dephosphorylated schizophrenia-associated variants impair Syt1 retrieval and cause schizophrenia-like phenotypes reversible by haloperidol.

   Evidence STON2(307Pro851Ala) knockin mouse, co-immunoprecipitation, synaptic electrophysiology, behavioral assays, and pharmacological rescue

   PMID:38402028

   Open questions at the time

   • Identity of the kinase/phosphatase controlling STON2 phosphorylation not defined
   • Mechanism by which haloperidol restores Syt1 sorting not established
4. 2018 Medium

   Extended STON2 function beyond the synapse by placing it upstream of a DNMT1/MUC1 epigenetic axis that controls cancer stem-like properties.

   Evidence siRNA knockdown/overexpression in ovarian cancer cells with RNA-seq, MUC1 promoter pyrosequencing, sphere-forming assays, and xenografts

   PMID:30518424

   Open questions at the time

   • Whether STON2 regulates DNMT1 directly or indirectly not resolved
   • Connection between endocytic adaptor activity and epigenetic regulation unexplained
5. 2018 Medium

   Identified STON2 as a direct miRNA target, with miR-199b-5p suppression of STON2 modulating tumor cell growth, migration, invasion, and EMT.

   Evidence Dual-luciferase reporter validation of miR-199b-5p binding to STON2 3'UTR, overexpression/knockdown in B-CPAP cells, and xenografts

   PMID:30325582

   Open questions at the time

   • Downstream effectors of STON2 in thyroid carcinoma not defined
   • Whether STON2's pro-tumor role uses its endocytic activity unknown
6. 2020 Low

   Positioned STON2 within a competing-endogenous-RNA network as a downstream node of an lncRNA GACAT1/miR-875-3p axis in breast cancer proliferation.

   Evidence Dual-luciferase reporter for miR-875-3p/STON2, qRT-PCR, and overexpression rescue in MCF-7 and BCap-37 cells

   PMID:32194758

   Open questions at the time

   • STON2 is a secondary target in the lncRNA study with limited mechanistic dissection
   • Direct functional role of STON2 in breast cancer not isolated
7. 2022 Low

   Reinforced miRNA regulation of STON2 by showing miR-144-5p directly downregulates STON2 to control thyroid carcinoma proliferation and EMT.

   Evidence Dual-luciferase reporter, qRT-PCR, western blot, and overexpression rescue with xenografts

   PMID:35184686

   Open questions at the time

   • Single lab and mechanistically overlapping with prior miRNA findings
   • Molecular mechanism downstream of STON2 not distinct from earlier reports
8. 2023 Low

   Linked STON2 to lysosomal membrane integrity and Akt-mTOR signaling in oral cancer cells, suggesting a membrane-trafficking role beyond the synapse.

   Evidence STON2 overexpression with TFP inhibitor treatment, western blots for Akt-mTOR, and lysosomal integrity and viability assays

   PMID:36702439

   Open questions at the time

   • Primarily overexpression plus pharmacological inhibitor without dissection of direct vs. indirect effects
   • Whether STON2 physically associates with the lysosomal membrane or mTOR machinery untested

• How STON2's defined presynaptic endocytic adaptor activity relates mechanistically to its reported roles in cancer epigenetics and lysosomal signaling remains unresolved.
• No structural model of the STON2-Syt1 interface
• Kinase/phosphatase regulating STON2 phosphorylation unidentified
• No unifying mechanism connecting synaptic and cancer functions