LRRC8C

LRRC8C is an auxiliary subunit of volume-regulated anion channels (VRACs) that hetero-oligomerizes with the obligatory LRRC8A subunit (and LRRC8B) in a predominantly 4A:2C hexameric stoichiometry, in which the two LRRC8C subunits confer greater flexibility that destabilizes the closed channel conformation and promotes activation (PMID:36522427, PMID:29853476). The first extracellular loop and pore–cytoplasmic domain boundary of LRRC8C are critical determinants of inactivation kinetics, anion selectivity, voltage gating, and pharmacological inhibitor binding, while oxidation of the N-terminal methionine of LRRC8C mediates redox-dependent channel inhibition (PMID:27325695, PMID:35861288, PMID:41053296). LRRC8A/C channels selectively permeate charged osmolytes such as glutamate/aspartate in astrocytes and bidirectionally transport the immune second messenger 2′3′-cGAMP, thereby activating STING–p53 signaling in T cells and endothelial cells, supporting AKT–eNOS-dependent vasodilation, and enabling innate immune recognition of tumors (PMID:28833202, PMID:33171122, PMID:35105987, PMID:41636028). De novo gain-of-function variants at the LRRC8C pore–cytoplasmic domain boundary cause constitutive channel opening, directly linking LRRC8C gating dysfunction to human disease (PMID:39623139).

1. 2014 Medium

   Establishing that LRRC8C is a physical component of heteromeric LRRC8 complexes answered whether VRAC subunits beyond LRRC8A interact directly, providing the first biochemical evidence for defined heteromeric assembly.

   Evidence Co-immunoprecipitation of LRRC8A, LRRC8B, LRRC8C, and LRRC8D in mammalian cells

   PMID:24782309

   Open questions at the time

   • Single-lab Co-IP without reciprocal validation at the time
   • Stoichiometry and full subunit composition undetermined
   • Functional consequence of heteromeric assembly not yet tested
2. 2015 High

   Demonstrating that LRRC8C-containing channels differ from LRRC8D-containing channels in substrate permeation (cisplatin/taurine excluded from LRRC8C channels) established the principle that auxiliary subunit identity dictates VRAC substrate selectivity.

   Evidence CRISPR/siRNA knockout of individual LRRC8 subunits in HCT116 cells with drug uptake assays and electrophysiology

   PMID:26530471

   Open questions at the time

   • Structural basis for substrate selectivity unknown
   • Native heteromeric composition in tissues not yet defined
3. 2016 High

   Mapping the C-terminal portion of the first extracellular loop (EL1) as the region controlling LRRC8C-dependent inactivation kinetics and anion selectivity answered where in the protein subunit identity encodes channel biophysical properties.

   Evidence Chimeric channels between LRRC8C and LRRC8E with charge-reversal point mutations, validated by patch-clamp electrophysiology

   PMID:27325695

   Open questions at the time

   • Atomic-resolution structural interpretation of EL1 differences not available
   • In vivo relevance of inactivation kinetics not tested
4. 2017 High

   Showing that LRRC8A/C channels are directly inhibited by reactive oxygen species — opposite to LRRC8A/E activation — revealed subunit-specific redox modulation of VRACs and positioned LRRC8C channels as oxidant-sensitive sensors.

   Evidence Whole-cell patch clamp of heterologously expressed LRRC8 heteromers exposed to chloramine-T and tert-butyl hydroperoxide

   PMID:28841766

   Open questions at the time

   • Specific redox-sensitive residue not yet identified
   • Physiological redox conditions for modulation unclear
5. 2017 High

   Establishing that LRRC8A/C/E channels are the primary conduit for swelling-activated glutamate/aspartate release in astrocytes, while LRRC8A/D channels handle uncharged osmolytes, clarified cell-type-specific VRAC function in the brain.

   Evidence Systematic RNAi knockdown of individual LRRC8 subunits in primary rat astrocytes with radiotracer efflux assays

   PMID:28833202

   Open questions at the time

   • Relative contribution of LRRC8C vs. LRRC8E within the same complex unclear
   • In vivo brain phenotype of LRRC8C loss not tested
6. 2018 High

   Domain-swap experiments showing that LRRC8C's EL1 can substitute for LRRC8A's EL1 to reconstitute functional homomeric VRACs, and that intracellular loops determine rectification and voltage sensitivity, delineated the modular architecture governing LRRC8C channel properties.

   Evidence Chimeric LRRC8C/LRRC8A channels expressed in LRRC8-null cells with patch-clamp electrophysiology

   PMID:29853476

   Open questions at the time

   • Structural basis of modular loop function unresolved at atomic level
   • Native pore structure not yet determined
7. 2020 High

   A genome-wide CRISPR screen identified LRRC8C (and LRRC8E) channels as bidirectional transporters of 2′3′-cGAMP, expanding VRAC function from osmolyte transport to innate immune second-messenger signaling.

   Evidence CRISPR screen, genetic KO, cGAMP uptake/efflux assays, and electrophysiology in multiple human cell lines

   PMID:33171122

   Open questions at the time

   • Structural basis for cGAMP permeation through LRRC8C pore not defined
   • Relative contribution in physiological immune contexts not established
8. 2022 High

   The cryo-EM structure of LRRC8A/C at 4:2 stoichiometry revealed that LRRC8C subunits introduce flexibility that destabilizes the closed conformation, providing the first atomic-level explanation for how auxiliary subunits promote channel activation.

   Evidence Cryo-EM structural determination of murine LRRC8A/C heteromeric channels

   PMID:36522427

   Open questions at the time

   • Open-state structure not captured
   • How other LRRC8 family members alter stoichiometry or flexibility unknown
9. 2022 High

   Identifying oxidation of the N-terminal methionine of LRRC8C as the specific residue mediating ROS-dependent channel inhibition resolved the molecular determinant of redox sensitivity first observed in 2017.

   Evidence Site-directed mutagenesis of methionines/cysteines in chimeric and concatemeric LRRC8 channels with patch-clamp electrophysiology

   PMID:35861288

   Open questions at the time

   • Physiological relevance of methionine oxidation in disease not tested in vivo
10. 2022 High

    Lrrc8c knockout mice revealed that LRRC8C is the essential non-LRRC8A subunit for VRAC activity in T cells, where cGAMP import via LRRC8A/C activates STING–p53 signaling to restrain T cell proliferation and cytokine production, connecting channel function to adaptive immunity.

    Evidence Lrrc8c−/− mouse model with electrophysiology, cGAMP transport assays, STING inhibitor epistasis, p53 rescue, and in vivo immune challenge (influenza, EAE)

    PMID:35105987

    Open questions at the time

    • Whether LRRC8C-dependent cGAMP transport is relevant to autoimmune pathology in humans undetermined
    • Redundancy with LRRC8E in other immune cell types not fully explored
11. 2024 High

    Discovery that de novo gain-of-function variants at the pore–cytoplasmic domain boundary of LRRC8C cause constitutive channel opening established LRRC8C as a disease gene and pinpointed this boundary as a critical gating element.

    Evidence Patient genetic analysis, cryo-EM of mutant proteins, and electrophysiology showing constitutive current at isotonic conditions

    PMID:39623139

    Open questions at the time

    • Clinical phenotype and disease penetrance not fully characterized
    • Whether gain-of-function can be pharmacologically corrected unknown
12. 2025 High

    Identifying that LRRC8A/C channels in vascular endothelium support AKT–eNOS signaling, vasodilation, and blood pressure homeostasis — with LRRC8C knockout mice showing exacerbated hypertension — connected VRAC activity to cardiovascular physiology.

    Evidence Epitope-tagged knock-in mice for reciprocal Co-IP, endothelial-specific knockout, patch clamp, pressure myography, angiotensin hypertension model

    PMID:41636028

    Open questions at the time

    • Signal transduction mechanism linking VRAC activity to AKT phosphorylation not defined
    • Relative contribution of LRRC8B vs. LRRC8C in vascular endothelial VRACs unclear
13. 2025 High

    Mapping zafirlukast/pranlukast binding sites to the N-terminal domain and inter-subunit fenestrae of LRRC8A/C channels provided the first pharmacological target sites validated by mutagenesis, establishing a framework for subunit-specific drug design.

    Evidence AlphaFold3 docking and molecular dynamics validated by site-directed mutagenesis of NTD/TM1/TM2 and patch-clamp electrophysiology

    PMID:41053296

    Open questions at the time

    • Co-crystal or cryo-EM structure with bound inhibitor not yet obtained
    • Selectivity over other LRRC8 subunit combinations in vivo untested

• Key unresolved questions include the open-state structure of LRRC8A/C channels, the structural basis for selective cGAMP permeation, the identity of upstream signals coupling cell swelling to channel activation, the in vivo neural consequences of LRRC8C loss in astrocytes, and whether LRRC8C gain-of-function variants define a recognizable clinical syndrome.
• No open-state cryo-EM structure
• Molecular mechanism linking volume change to LRRC8C channel gating unknown
• Astrocyte-specific LRRC8C knockout brain phenotype not reported