SH3GL2

SH3GL2 (endophilin A1/SH3p4) is a brain-enriched, nerve-terminal-concentrated SH3-domain adaptor that drives clathrin-mediated endocytosis and synaptic vesicle recycling (PMID:9238017, PMID:10677033). Through its SH3 domain it binds the proline-rich tails of synaptojanin and dynamin I (PMID:9238017), and antibody-mediated disruption at the synapse arrests clathrin-coated pit invagination adjacent to the active zone at an early-to-late endocytosis transition, where it functions as a dynamin partner rather than a clathrin coat component (PMID:10677033). Its adaptor activity extends to receptor internalization: it binds the proline-rich third intracellular loop of the beta1-adrenergic receptor and promotes its agonist-induced internalization (PMID:10535961), and it drives EGFR internalization and degradation, thereby restraining downstream EGFR-dependent MEK/ERK, PI3K/AKT, Src, and STAT3/MMP2 signaling (PMID:20512084, PMID:22968441, PMID:23814487, PMID:28470949). Consistent with this role, loss of SH3GL2 in multiple carcinoma and glioma models elevates active EGFR and pathway output to promote proliferation, invasion, and tumor growth, while re-expression suppresses these behaviors, establishing SH3GL2 as a tumor suppressor acting upstream of EGFR (PMID:23814487, PMID:24736727, PMID:28470949). Beyond endocytosis, calcium influx at the pre-synaptic terminal triggers SH3GL2 redistribution from the plasma membrane to autophagic membranes to initiate autophagosome formation, via a calcium-sensing residue in its flexible region; a Parkinson's disease-risk mutation abolishes this calcium sensing and blocks synaptic autophagy induction (PMID:37067454).

1. 1997 High

   Established SH3GL2 as a nerve-terminal SH3 adaptor by identifying its direct binding partners, answering what molecular machinery it engages.

   Evidence Yeast two-hybrid with synaptojanin proline-rich bait, reciprocal Co-IP from brain extracts, and immunofluorescence localization

   PMID:9238017

   Open questions at the time

   • Functional consequence of dynamin/synaptojanin binding not yet shown
   • Domain-level binding determinants on partners not mapped
2. 1999 High

   Demonstrated a direct functional role in clathrin-coated pit invagination, placing SH3GL2 mechanistically at an endocytic step rather than within the clathrin coat.

   Evidence Antibody microinjection into a tonically stimulated lamprey synapse with EM, plus cell-free biochemical fractionation

   PMID:10677033

   Open questions at the time

   • Precise biophysical contribution to membrane curvature not resolved
   • Relationship to dynamin GTPase cycle not detailed
3. 1999 High

   Extended the adaptor role beyond synaptic vesicles to GPCR internalization with receptor-subtype specificity.

   Evidence GST pull-down with beta1-AR third intracellular loop, two-hybrid, Co-IP and overexpression internalization/cAMP assays in HEK293

   PMID:10535961

   Open questions at the time

   • Endogenous relevance in neurons not tested
   • Basis of beta1- vs beta2-AR selectivity not structurally defined
4. 2010 Medium

   Linked SH3GL2 to EGFR/MEK-ERK control in cancer, positioning it upstream of EGFR signaling.

   Evidence RNAi knockdown in Hep2 cells with MEK inhibitor (U0126) epistasis, proliferation and apoptosis assays

   PMID:20512084

   Open questions at the time

   • Direct effect on EGFR trafficking not shown in this study
   • Single cell line and single lab
5. 2012 Medium

   Showed mechanistically that SH3GL2 drives EGFR internalization and degradation, dampening AKT/STAT3/PI3K output and tumor growth.

   Evidence Stable WT overexpression in three NSCLC lines, internalization assay, Western blot, and mouse xenograft

   PMID:22968441

   Open questions at the time

   • Mechanism connecting EGFR degradation to USP9X and beta-catenin not fully resolved
   • Single lab
6. 2013 High

   Provided reciprocal loss- and gain-of-function evidence that SH3GL2 controls EGFR internalization and Src/STAT3 activation as a tumor suppressor.

   Evidence Stable knockdown and re-expression in urothelial carcinoma lines, internalization and phospho-protein readouts, subrenal capsule xenograft

   PMID:23814487

   Open questions at the time

   • Whether endocytic adaptor activity per se is required for suppression not separated from other roles
7. 2017 Medium

   Tied SH3GL2 loss to STAT3-driven MMP2 secretion and invasion, defining a migration/invasion axis.

   Evidence siRNA knockdown and overexpression in glioma cells, p-STAT3/MMP2 Western blot, zymography, scratch and Transwell assays

   PMID:28470949

   Open questions at the time

   • Direct link between EGFR trafficking and STAT3/MMP2 in this context not established
   • Single lab
8. 2023 Medium

   Revealed a distinct, calcium-triggered role in synaptic autophagy and a disease-relevant defect, answering how SH3GL2 transitions from endocytosis to autophagosome biogenesis.

   Evidence Live FRAP imaging, mutagenesis of a calcium-sensing residue, Drosophila EndoA ortholog model, autophagosome formation assay, and PD-risk variant characterization

   PMID:37067454

   Open questions at the time

   • Mechanism by which the flexible-region residue senses calcium not structurally defined
   • Validation in mammalian neurons of the human variant not shown
   • Single lab

• How the endocytic adaptor function, EGFR-trafficking tumor-suppressor role, and calcium-gated autophagy function are coordinated within a single neuron or cell remains unresolved.
• No structural model unifying SH3-domain binding, curvature, and calcium sensing
• Whether the same pool of protein performs all three roles is unknown
• Endogenous regulation switching between endocytosis and autophagy not defined