CLINT1

CLINT1 (epsinR/enthoprotin/Clint) is a peripheral membrane clathrin adaptor that operates at the trans-Golgi network and on clathrin-coated vesicles to couple cargo selection with vesicle formation in TGN-to-endosome traffic (PMID:12429846, PMID:12589059). It engages the core clathrin coat machinery directly, binding the gamma-appendage of AP-1, the clathrin N-terminal domain through an LFDLM motif (residues 423-427), the GGA2 ear domain, and beta2-adaptin, while its ENTH domain associates with PtdIns(4)P-containing membranes; membrane recruitment is ARF-dependent and independent of AP-1 (PMID:12429846, PMID:12589059). Beyond coat assembly, the ENTH domain binds the N-terminal domain of the SNARE vti1b, an interaction conserved to the yeast ortholog Ent3p, which engages multiple SNAREs (Vti1p, Pep12p, Syn8p) and cooperates with them in bidirectional transport between the TGN and the endosome/prevacuole, thereby linking vesicle budding to fusion machinery (PMID:14630930, PMID:20658963). In vivo, Clint1 is required for epidermal homeostasis in zebrafish: loss of function drives epidermal hyperproliferation, IL-1beta induction, leukocyte infiltration, and impaired hemidesmosome formation, phenotypes attributable to deranged endocytic membrane homeostasis and rescued by restoring normal endocytosis (PMID:19570844, PMID:30207308). CLINT1 is phosphorylated by the Numb-associated kinase BIKE at threonine 294, and this modification mediates binding to dengue virus NS3 to promote viral assembly and egress, with CLINT1 co-trafficking with viral particles (PMID:35452674).

1. 2002 High

   Established CLINT1 as a bona fide clathrin-coat adaptor by defining its direct contacts with AP-1, clathrin, and GGA2 and its membrane-binding ENTH domain, answering what molecular machinery it integrates into.

   Evidence GST pulldown/recombinant binding assays, clathrin-coated vesicle fractionation, immunofluorescence colocalization, and liposome binding

   PMID:12429846

   Open questions at the time

   • Functional cargo or trafficking step served by these interactions not yet defined
   • ENTH lipid specificity not yet resolved to a single phosphoinositide
2. 2003 High

   Defined how CLINT1 is recruited to membranes and refined its lipid specificity, showing AP-1-independent, ARF-dependent recruitment via PtdIns(4)P-binding ENTH domain and excluding a requirement in lysosomal enzyme sorting.

   Evidence Reciprocal GST pulldown, protein-lipid overlay, BFA/GTPgammaS perturbation, and RNAi with cathepsin D processing readout

   PMID:12589059

   Open questions at the time

   • The cargo positively sorted by CLINT1 remained unidentified
   • ARF effector linking CLINT1 to membranes not identified
3. 2003 High

   Linked the ENTH domain to fusion machinery by showing direct binding to the SNARE vti1b, conserved to yeast, establishing CLINT1 as a coupler of vesicle budding and SNARE-mediated TGN-to-endosome transport.

   Evidence Yeast two-hybrid, in vitro binding, and yeast vti1/ent3 synthetic-defect genetic epistasis

   PMID:14630930

   Open questions at the time

   • Whether SNARE binding regulates or sequesters vti1b not resolved
   • Structural basis of ENTH-SNARE interface not defined
4. 2010 Medium

   Resolved the modularity of the ENTH-SNARE interaction and directionality of transport, showing the yeast ortholog uses distinct residues to bind multiple SNAREs and that ENTH and C-terminal regions serve anterograde versus retrograde steps.

   Evidence Yeast two-hybrid with interaction-surface mutagenesis, deletion analysis, and GFP-Snc1p retrograde transport assay (Ent3p ortholog)

   PMID:20658963

   Open questions at the time

   • Direct generalization of multi-SNARE binding to mammalian CLINT1 not tested
   • Single-lab ortholog study
5. 2009 High

   Moved CLINT1 from molecular adaptor to physiological regulator by showing it is essential for epidermal homeostasis in vivo, with loss causing psoriasis-like hyperproliferation, inflammation, and hemidesmosome defects.

   Evidence ENU zebrafish mutant, morpholino knockdown, transgenic rescue, genetic interaction with Lgl2, immunofluorescence and EM

   PMID:19570844

   Open questions at the time

   • Molecular link between trafficking defect and hyperproliferation not yet mechanistic
   • Mammalian/human epidermal relevance not tested
6. 2018 Medium

   Connected the in vivo epidermal phenotype to a defined cellular mechanism by showing CLINT1 loss elevates endocytosis and lysosome accumulation, and that inhibiting endocytosis rescues cell size and proliferation.

   Evidence Zebrafish peridermal morpholino knockdown with pharmacological endocytosis inhibition, live imaging, cell-size/proliferation quantification

   PMID:30207308

   Open questions at the time

   • Specific cargo whose mistrafficking drives proliferation not identified
   • Single-lab, morpholino-based perturbation
7. 2022 High

   Identified a regulatory phosphorylation and a pathogen-hijack function, showing BIKE phosphorylates CLINT1 at T294 to enable dengue NS3 binding and promote viral assembly and egress.

   Evidence BFG-Y2H and AP-MS screens, in vitro kinase assay, cell-based PPI assays, and live-cell imaging of CLINT1 co-trafficking with DENV

   PMID:35452674

   Open questions at the time

   • Effect of T294 phosphorylation on canonical AP-1/clathrin/SNARE binding not defined
   • Whether BIKE phosphorylation regulates normal TGN trafficking absent infection not tested

• The specific endogenous cargo molecules sorted by CLINT1 and how its phosphorylation state toggles between coat assembly, SNARE coupling, and viral exploitation remain unresolved.
• No defined physiological cargo for CLINT1-dependent vesicles
• Integration of T294 phosphorylation with AP-1/clathrin/vti1b binding unknown
• No human disease mutation directly tied to CLINT1 in the corpus