SH3GL3

SH3GL3 is an SH3- and BAR-domain endophilin-family protein that operates in membrane-trafficking at nerve terminals and acts as a context-dependent regulator of cell growth and invasion in cancer (PMID:9238017, PMID:33524871). At the synapse, its SH3 domain binds synaptojanin and dynamin I, with which it co-precipitates from brain extracts and co-concentrates at nerve terminals, implicating it in synaptic vesicle recycling (PMID:9238017). The same SH3 domain selectively engages the proline-rich region of polyglutamine-expanded huntingtin exon 1, an interaction confirmed in transfected cells and HD brain extract, through which SH3GL3 promotes the formation of insoluble polyglutamine aggregates (PMID:9809064). Its BAR domain mediates a distinct interaction with DYDC1 that supports clathrin-coated vesicle traffic during acrosome biogenesis in spermatogenesis (PMID:19545932). In tumor contexts SH3GL3 has opposing reported roles: in glioblastoma and lung cancer it acts as a tumor suppressor, physically binding STAT3 to block its nuclear translocation and transcriptionally upregulating p21 in an SH3-domain-dependent manner, thereby restraining proliferation, migration, and stem-cell self-renewal (PMID:33168185, PMID:33524871), and its own promoter is silenced by DNMT1 recruited via the lncRNA MIR210HG (PMID:37916731); conversely, in myeloma and glioma it promotes invasion, with overexpression activating FAK/PI3K signaling (PMID:21722156, PMID:27683032).

1. 1997 High

   Established SH3GL3's first molecular partners and a synaptic function by showing its SH3 domain captures the vesicle-trafficking machinery.

   Evidence Yeast two-hybrid from rat brain library plus reciprocal Co-IP from brain extracts and immunolocalization at nerve terminals

   PMID:9238017

   Open questions at the time

   • Direct demonstration that SH3GL3 loss impairs vesicle recycling not shown
   • Functional contribution relative to other endophilin family members not resolved
2. 1998 High

   Linked SH3GL3 to Huntington disease pathology by showing it binds expanded huntingtin and drives aggregate formation, defining the essential interacting domains.

   Evidence Co-IP in transfected COS cells and HD human brain extract, domain-deletion mutagenesis, and in vivo aggregation assay

   PMID:9809064

   Open questions at the time

   • Whether SH3GL3 modifies HD pathology in vivo not established
   • Mechanism by which the interaction nucleates insoluble aggregates not defined
3. 2009 Medium

   Revealed a BAR-domain-mediated function distinct from SH3-domain partnerships, connecting SH3GL3 to acrosome biogenesis via DYDC1.

   Evidence Yeast two-hybrid (BAR domain bait, testis library), RNAi knockdown, and germ cell transplantation

   PMID:19545932

   Open questions at the time

   • BAR-domain–DYDC1 interaction not confirmed by an orthogonal biochemical method
   • Molecular link between DYDC1 binding and clathrin-coated vesicle traffic unresolved
4. 2012 Medium

   Extended SH3GL3 function into cancer by showing it is required for glioma cell invasion.

   Evidence shRNA knockdown with in vitro invasion assay

   PMID:21722156

   Open questions at the time

   • No molecular mechanism for the invasion phenotype
   • Studied as one of several candidates with limited depth
5. 2016 Medium

   Placed SH3GL3 upstream of FAK/PI3K signaling as a pro-invasive, pro-stemness factor in myeloma, contrasting with later tumor-suppressor findings.

   Evidence Gain- and loss-of-function plus FAK/PI3K inhibitor epistasis with migration/invasion assays and Western blot for p-FAK/p-PI3K

   PMID:27683032

   Open questions at the time

   • Whether SH3GL3 directly activates FAK/PI3K or acts indirectly unknown
   • Tissue context driving oncogenic vs tumor-suppressive behavior unexplained
6. 2020 Medium

   Defined SH3GL3 as a tumor suppressor in lung cancer that requires its SH3 domain and transcriptionally upregulates p21.

   Evidence SH3-domain deletion mutants with proliferation/migration, cell cycle, apoptosis assays and qRT-PCR for p21

   PMID:33168185

   Open questions at the time

   • Direct mechanism connecting the SH3 domain to p21 transcription not established
   • Single-lab evidence without in vivo validation
7. 2021 Medium

   Identified a mechanism for tumor suppression: SH3GL3 binds STAT3 and blocks its nuclear translocation in glioblastoma.

   Evidence Co-IP of SH3GL3–STAT3, nuclear localization assay, and constitutively active STAT3-C rescue of growth/migration/self-renewal

   PMID:33524871

   Open questions at the time

   • Domain mediating STAT3 binding not mapped
   • How cytoplasmic sequestration of STAT3 is achieved mechanistically unclear
8. 2023 Medium

   Explained how SH3GL3 is silenced in tumors, showing lncRNA MIR210HG recruits DNMT1 to methylate the SH3GL3 promoter.

   Evidence ChIP for DNMT1 at the SH3GL3 promoter, RIP for MIR210HG–DNMT1, methylation-specific PCR, and knockdown/overexpression functional assays

   PMID:37916731

   Open questions at the time

   • Generality of this silencing axis across tumor types not established
   • Whether promoter methylation is the dominant in vivo regulator unknown

• It remains unresolved what determines whether SH3GL3 acts as a tumor suppressor or a pro-invasive factor, and how its synaptic/trafficking functions relate to its signaling roles in cancer.
• No structural model integrating BAR- and SH3-domain functions
• Context dependence of oncogenic vs tumor-suppressive behavior unexplained
• Physiological relevance of synaptic functions in non-neuronal disease contexts unknown