CLIC3

CLIC3 is a multifunctional protein that regulates membrane trafficking, ion conductance, and extracellular matrix remodeling to influence cell invasion, proliferation, and senescence. Intracellularly, CLIC3 localizes to late endosomes/lysosomes where it drives recycling of active α5β1 integrin and MT1-MMP to the plasma membrane, enabling cell rear retraction and basement membrane disruption during 3D invasion (PMID:22197222, PMID:25015290). When secreted, CLIC3 functions as a glutathione-dependent oxidoreductase that reduces and activates transglutaminase-2 (TGM2), promoting TGM2-dependent angiogenesis and cancer cell invasiveness (PMID:28198360). At the plasma membrane, CLIC3 conducts outwardly rectifying chloride currents that suppress gastric cancer cell proliferation (PMID:32066374), and during senescence it translocates to the membrane where interaction with ERK7 and chloride efflux drive mitochondrial dysfunction and senescence-associated secretory phenotype expression (PMID:39809890).

1. 2011 High

   Establishing that CLIC3 has a defined intracellular trafficking function—residing on late endosomes/lysosomes and mediating retrograde recycling of active α5β1 integrin to the plasma membrane—answered how integrin recycling is coordinated during 3D cell invasion.

   Evidence Photoactivation, co-localization imaging, siRNA knockdown with 3D organotypic invasion assays in cancer cell lines

   PMID:22197222

   Open questions at the time

   • Whether CLIC3 acts as a channel or adaptor in endosomal recycling is unresolved
   • No structural basis for CLIC3–integrin interaction
   • Mechanism by which CLIC3 selects active versus inactive integrin cargo is unknown
2. 2014 High

   Extending CLIC3's trafficking role beyond integrins to MT1-MMP demonstrated that CLIC3 acts as a general regulator of pro-invasive cargo recycling from late endosomal/lysosomal compartments, not a cargo-specific factor.

   Evidence siRNA knockdown, co-localization imaging, 3D organotypic invasion and basement membrane disruption assays in ER-negative breast cancer cells

   PMID:25015290

   Open questions at the time

   • Whether CLIC3 recognizes a common sorting signal on integrin and MT1-MMP is unknown
   • The role of Rab25 cooperation with CLIC3 in MT1-MMP recycling was not addressed
   • Direct physical interaction between CLIC3 and MT1-MMP was not demonstrated
3. 2017 High

   Revealing that secreted CLIC3 possesses glutathione-dependent oxidoreductase activity that reduces TGM2 established an entirely extracellular enzymatic function distinct from its intracellular trafficking role, linking CLIC3 to angiogenesis and matrix remodeling.

   Evidence Secretome proteomics, in vitro oxidoreductase assay, TGM2 cofactor binding assays, 3D invasion assays, in vivo validation, TGM2 inhibitor rescue

   PMID:28198360

   Open questions at the time

   • The secretion mechanism for CLIC3 (conventional vs. unconventional) is undefined
   • Whether other CLIC family members share extracellular oxidoreductase activity is untested
   • Structural basis of the CLIC3–TGM2 redox interaction is not resolved
4. 2020 Medium

   Direct electrophysiological recording of NPPB-sensitive outwardly rectifying Cl⁻ currents mediated by CLIC3 at the plasma membrane established that CLIC3 genuinely functions as a chloride channel, and linked this conductance to suppression of cell proliferation.

   Evidence Whole-cell patch-clamp electrophysiology, siRNA knockdown and overexpression in gastric cancer cells, proliferation assays

   PMID:32066374

   Open questions at the time

   • Single-lab demonstration; independent replication of channel activity in a reconstituted system is lacking
   • How membrane insertion of CLIC3 is regulated is unknown
   • Relationship between chloride conductance and the anti-proliferative effect is correlative
5. 2024 Medium

   Identification of CLIC3–NAT10 interaction and its suppression of ac4C mRNA modification (reducing p21 mRNA stability) revealed a nuclear/cytoplasmic mechanism by which CLIC3 promotes bladder cancer proliferation, distinct from its trafficking and channel functions.

   Evidence Co-immunoprecipitation, ac4C modification assay, mRNA stability assay, siRNA knockdown, in vitro and in vivo proliferation assays in bladder cancer cells

   PMID:38182571

   Open questions at the time

   • Single-lab finding; independent confirmation of the CLIC3–NAT10 interaction is needed
   • Whether CLIC3 inhibits NAT10 enzymatic activity directly or via sequestration is unclear
   • How the pro-proliferative NAT10 axis relates to the anti-proliferative chloride channel activity is unexplained
6. 2025 Medium

   Demonstrating that CLIC3 translocates to the plasma membrane during senescence and, through ERK7 interaction and chloride efflux, drives mitochondrial dysfunction and SASP expression established CLIC3 as a regulator of cellular senescence.

   Evidence RNA sequencing, membrane fractionation, co-immunoprecipitation with ERK7, intracellular chloride measurement, mitochondrial function assays in fibroblasts

   PMID:39809890

   Open questions at the time

   • Single-lab study; causality between chloride loss and mitochondrial dysfunction needs independent validation
   • Whether the channel activity or a scaffolding function of CLIC3 mediates senescence is not distinguished
   • In vivo relevance of CLIC3-driven senescence is unexamined

• A unified model explaining how CLIC3's channel, trafficking adaptor, oxidoreductase, and NAT10-inhibitory activities are regulated in the same cell—and whether they are mutually exclusive or concurrent—remains unresolved.
• No structure of CLIC3 in a membrane-inserted state exists
• Signals governing CLIC3 partitioning between endosomal, plasma membrane, secreted, and nuclear pools are unknown
• Whether CLIC3's oxidoreductase and channel activities share a catalytic mechanism is untested