LRRC8B

LRRC8B is a complementary, non-obligate subunit of the heterohexameric volume-regulated anion channel (VRAC), assembling with the indispensable LRRC8A subunit and other LRRC8 paralogs (C, D, E) into endogenous channel complexes (PMID:25172945, PMID:31771171). Co-immunoprecipitation of endogenous LRRC8A consistently recovers LRRC8B as a bona fide partner, and cryo-EM of LRRC8A:C heterohexamers defines how complementary subunits assemble through heterotypic leucine-rich-repeat domain interactions and lipid-dependent pore gating (PMID:31771171, PMID:36928458). LRRC8B occupies a structural but non-dominant role: silencing LRRC8B alone does not appreciably alter swelling-activated release of charged or uncharged osmolytes from astrocytes, in contrast to the strong suppression seen with combined LRRC8C/D loss (PMID:28833202). In endothelial cells, LRRC8B is part of a predominant LRRC8A/B/C complex whose subunits are co-dependent for expression, and this mechanoresponsive VRAC regulates AKT-eNOS signaling and vascular tone (PMID:41636028). Beyond its role within VRAC, overexpression and knockdown studies place LRRC8B in the ER membrane as a Ca2+ leak channel, where it lowers ER Ca2+ stores and shapes store-operated Ca2+ entry (PMID:28972132). Constitutive LRRC8B knockout mice show no defect in T or B cell development, indicating it is dispensable for lymphocyte development in vivo (PMID:41419196).

1. 2004 Low

   Before any functional data, the question was whether LRRC8B belonged to a coherent protein family with a shared architecture; sequence analysis established it as a member of the LRRC8 family with extracellular leucine-rich repeats and four transmembrane regions.

   Evidence Sequence analysis and structural prediction of novel LRRC8-like genes

   PMID:15094057

   Open questions at the time

   • Computational prediction only
   • No functional assay on LRRC8B
   • Topology and membrane targeting not experimentally verified
2. 2014 Medium

   The open question of whether LRRC8B physically associates with other family members was answered by showing it co-immunoprecipitates with LRRC8D and localizes to the plasma membrane with a defined topology, establishing it as a candidate transport-complex subunit.

   Evidence Co-immunoprecipitation, localization and topology experiments

   PMID:24782309

   Open questions at the time

   • Single lab
   • Functional consequence of LRRC8B in the complex not shown
   • Stoichiometry undetermined
3. 2014 High

   Establishing the channel context, LRRC8A was shown to be indispensable for VRAC and to require at least one of LRRC8B-E partners, defining LRRC8B as one of the complementary subunits that can complete a functional anion channel.

   Evidence siRNA knockdown and radiotracer osmolyte-release assays in primary rat astrocytes

   PMID:25172945

   Open questions at the time

   • Specific contribution of LRRC8B versus other complementary subunits not resolved
   • No structural model
4. 2017 Medium

   To define LRRC8B's functional weight within VRAC, RNAi dissection showed LRRC8B silencing alone does not impair osmolyte release while LRRC8C/D loss does, placing LRRC8B as a complementary but non-dominant subunit.

   Evidence RNAi knockdown and radiotracer release assays in primary rat astrocytes

   PMID:28833202

   Open questions at the time

   • Negative result for LRRC8B may reflect redundancy
   • Single lab
   • Channel composition in LRRC8B-knockdown cells not characterized
5. 2017 Medium

   A distinct mechanistic role was proposed by overexpression and knockdown experiments indicating LRRC8B can act as an ER Ca2+ leak channel that modulates ER store content and store-operated Ca2+ entry.

   Evidence Overexpression/knockdown in HEK293 cells with intracellular Ca2+ measurements, thapsigargin block and IP3 stimulation

   PMID:28972132

   Open questions at the time

   • Single lab
   • ER localization of an endogenous channel not reconstituted
   • Relationship to plasma-membrane VRAC role unclear
6. 2017 Medium

   Addressing how LRRC8 channels sense redox state, electrophysiology showed subunit-dependent oxidation sensitivity, but LRRC8B-containing heteromers were not specifically tested, leaving its redox behavior undefined.

   Evidence Electrophysiology of tagged LRRC8 heteromers with chloramine-T and tert-butyl hydroperoxide

   PMID:28841766

   Open questions at the time

   • LRRC8B heteromers not assayed for oxidation
   • Cysteine residues responsible not mapped for LRRC8B
7. 2019 Medium

   Whether LRRC8B is part of native channels rather than an overexpression artifact was settled by quantitative immunoblotting and endogenous LRRC8A immunoprecipitation, confirming LRRC8B as a bona fide partner present at generally low, tissue-specific levels.

   Evidence Quantitative immunoblotting with recombinant calibration and IP of endogenous LRRC8A from mouse cells and tissues

   PMID:31771171

   Open questions at the time

   • Single lab
   • Functional output of native LRRC8B-containing complexes not measured
   • Subunit stoichiometry per hexamer unknown
8. 2022 Medium

   Extending tissue context, LRRC8B was shown to co-localize with LRRC8A at proximal-tubule basolateral membranes where LRRC8A/D VRACs mediate organic-compound exit, though LRRC8B's specific functional contribution there was not isolated.

   Evidence Epitope-tagged knock-in mice, immunohistochemistry, conditional/constitutive knockouts, metabolomics

   PMID:35777784

   Open questions at the time

   • No LRRC8B-specific knockout in tubules
   • Co-localization does not establish transport role
9. 2023 High

   The structural basis of how complementary subunits like LRRC8B shape channel architecture was revealed by cryo-EM of LRRC8A:C heterohexamers, showing heterotypic LRR-domain interactions and lipid pore gating as general assembly principles.

   Evidence Single-particle cryo-EM with fiducial tagging and electrophysiology

   PMID:36928458

   Open questions at the time

   • No LRRC8B-containing structure solved
   • LRRC8B-specific pore properties unknown
10. 2025 Medium

    In the vasculature, reciprocal co-IP from knock-in mice defined LRRC8A/B/C as the predominant endothelial heteromer with co-dependent subunit expression, linking LRRC8B-containing VRAC to mechanoresponsive AKT-eNOS signaling and vascular tone.

    Evidence Co-IP from knock-in mice, endothelium-specific knockout/knockdown, electrophysiology, pressure myography, angiotensin hypertension model (one report a preprint)

    PMID:40894750 PMID:41636028

    Open questions at the time

    • LRRC8B-specific functional role not separated from LRRC8A/C
    • Single lab
    • Mechanism coupling channel activity to AKT-eNOS not resolved
11. 2025 Low

    A refined view of LRRC8B's structural role in astrocytes came from RNAi showing that LRRC8B knockdown partially rescues glutamate-analogue release in LRRC8C/D-deficient cells, consistent with a non-determinant structural contribution.

    Evidence RNAi knockdown in primary mouse astrocytes, radiotracer release assays, qPCR, RNA-seq (preprint)

    PMID:40766626

    Open questions at the time

    • Preprint, not peer-reviewed
    • LRRC8B role inferred from double-knockdown rescue
    • Mechanism of rescue unknown
12. 2025 Medium

    Whether LRRC8B is required for immune-cell ontogeny was tested by constitutive knockout, which showed normal T and B cell development and established LRRC8B as dispensable for lymphocyte development in vivo.

    Evidence Constitutive LRRC8B knockout mice analyzed for T and B cell development

    PMID:41419196

    Open questions at the time

    • Negative result; possible redundancy with other paralogs not excluded
    • Other immune or non-immune phenotypes not assessed

• It remains unknown what unique functional contribution LRRC8B makes to native VRAC complexes distinct from other complementary subunits, and how its proposed ER Ca2+-leak role mechanistically relates to its plasma-membrane channel role.
• No LRRC8B-containing channel structure
• No demonstrated LRRC8B-specific permeability property
• Reconciliation of ER versus plasma-membrane functions unresolved