SNX16

SNX16 is a phosphatidylinositol 3-phosphate (PI3P)-binding sorting nexin that controls cargo trafficking through the endosomal system (PMID:12813048, PMID:28712807). Its PX domain binds PI3P to associate with membranes, while its coiled-coil domain mediates homo-oligomerization and is required for localization to late endosomal structures; loss of the coiled-coil restricts SNX16 to early endosomes and delays trafficking of internalized EGF (PMID:12813048). SNX16 occupies tubulo-cisternal elements of late endosomes in a microtubule-dependent manner and acts there in tubule formation, cholesterol transport, and trafficking of the tetraspanin CD81 (PMID:21754999). A crystal structure of the PX-CC unit defines a shear-shaped homodimer with a PI3P-binding pocket formed jointly by the PX and CC domains, and reveals that the PPII/α2 loop directly engages E-cadherin cargo to drive its recycling to the cell surface (PMID:28712807). Through this trafficking activity SNX16 governs EGFR signaling: it is required for AngII- and EGF-induced EGFR recycling and transactivation, and cardiac-specific deletion blocks AngII-induced cardiac hypertrophy (PMID:41318855), while in hepatocellular carcinoma cells it sustains phospho-EGFR and downstream AKT signaling (PMID:38849490). Beyond receptor trafficking, SNX16 stabilizes eEF1A2 against ubiquitin-mediated proteasomal degradation to activate c-Myc signaling (PMID:31876369), and modulates cell migration and influenza A virus replication, the latter dependent on residue R144 (PMID:25408875, PMID:35458555).

1. 2003 High

   Established the molecular basis of SNX16 membrane targeting and identified it as an endosomal trafficking regulator, answering how a sorting nexin engages endosomal membranes and influences cargo movement.

   Evidence Phospholipid-binding assays, domain-deletion/dominant-negative mutants, oligomerization and EGF trafficking assays

   PMID:12813048

   Open questions at the time

   • Did not identify specific cargo bound directly by SNX16
   • Did not resolve the structural basis of PI3P recognition or dimerization
2. 2011 Medium

   Refined SNX16 localization to tubulo-cisternal late-endosomal subdomains and linked it to specific functional outputs, addressing where within the late endosome SNX16 acts and what it traffics.

   Evidence Fluorescence microscopy with microtubule disruption, CD81 trafficking and cholesterol transport assays

   PMID:21754999

   Open questions at the time

   • Mechanism coupling SNX16 to microtubules not defined
   • Direct interaction with CD81 or cholesterol machinery not demonstrated
3. 2013 Medium

   Connected SNX16 endosomal positioning to cell behavior, showing cortical Rab5-endosome localization near focal adhesions and a suppressive effect on migration and tumor formation.

   Evidence Microscopy, PI3-kinase/microtubule pharmacology, SNX23 knockdown, migration and soft-agar assays in MCF-7 cells

   PMID:25408875

   Open questions at the time

   • Cargo mediating the anti-migratory effect not identified
   • Reconciliation with pro-tumorigenic roles in other cell types unresolved
4. 2017 High

   Provided the structural mechanism of SNX16, revealing a shear-shaped homodimer with a composite PX-CC PI3P pocket and direct E-cadherin cargo binding via the PPII/α2 loop, answering how SNX16 simultaneously reads lipid and selects cargo.

   Evidence Crystal structure of PX-CC unit, PI3P binding assays, mutagenesis, E-cadherin recycling assay

   PMID:28712807

   Open questions at the time

   • Structure of full-length protein on membranes not determined
   • Whether the same loop binds other cargoes unknown
5. 2020 Medium

   Extended SNX16 function beyond membrane trafficking to protein stability control, showing it shields eEF1A2 from ubiquitin-mediated degradation to activate c-Myc signaling.

   Evidence Co-IP, ubiquitination and proteasome-inhibitor assays, knockdown/overexpression with c-Myc readouts in colorectal cancer cells

   PMID:31876369

   Open questions at the time

   • Direct vs indirect protection of eEF1A2 not distinguished
   • Reciprocal validation and link to SNX16's endosomal role absent
6. 2020 Medium

   Placed SNX16 within a regulatory circuit in trophoblasts, identifying it as a miR-196a-5p target whose suppression restores migration and invasion under hypoxia.

   Evidence Luciferase reporter for miR-196a-5p binding, ChIP, SNX16 knockdown with migration/invasion and MMP readouts

   PMID:32579212

   Open questions at the time

   • Molecular mechanism by which SNX16 inhibits trophoblast migration not defined
   • Cell-type-specific direction of effect unexplained
7. 2022 Medium

   Mapped a single residue (R144) controlling SNX16 expression isoforms and localization, and tied SNX16 to early-stage restriction of influenza A virus.

   Evidence Site-directed R144A mutagenesis, Western blot, microscopy, viral replication assay in A549 cells

   PMID:35458555

   Open questions at the time

   • Step in the IAV replication cycle targeted not pinpointed
   • Mechanistic basis of the two-band phenotype unresolved
8. 2024 Medium

   Positioned SNX16 upstream of EGFR-AKT signaling in cancer, showing knockdown reduces phospho-EGFR and EGFR inhibition reverses SNX16-driven proliferation and invasion.

   Evidence Knockdown/overexpression, phospho-EGFR/AKT immunoblotting, EGFR-inhibitor epistasis in hepatocellular carcinoma cells

   PMID:38849490

   Open questions at the time

   • Whether the effect operates through SNX16-dependent EGFR recycling not directly tested here
   • Direct EGFR-SNX16 interaction not shown
9. 2025 High

   Demonstrated in vivo that SNX16 drives EGFR recycling and transactivation to promote pathological cardiac hypertrophy, integrating its trafficking activity with a physiological disease phenotype.

   Evidence Cardiac-specific knockout mice, endosomal EGFR recycling assay, AZD9291 epistasis, phospho-EGFR/Src immunoblotting

   PMID:41318855

   Open questions at the time

   • Direct molecular contact between SNX16 and the EGFR/recycling machinery not defined
   • Cargo selectivity determining which receptors SNX16 recycles unresolved

• How SNX16's single PI3P-binding endosomal trafficking activity is mechanistically reconciled with its context-dependent roles (anti- vs pro-migratory, eEF1A2 stabilization, antiviral restriction) remains unresolved.
• No unifying model linking endosomal cargo sorting to non-trafficking outputs
• Direct partners for most functional roles not biochemically defined