LRRC8B

LRRC8B is a subunit of the volume-regulated anion channel (VRAC) that assembles into heteromeric hexamers with the obligate LRRC8A subunit and other LRRC8 paralogs, contributing to channel composition in a tissue-specific manner. In vascular endothelium, LRRC8B is a core component of the predominant LRRC8A/B/C complex that regulates AKT-eNOS signaling and vascular tone, with co-dependent expression among its subunits (PMID:41636028); in the kidney, LRRC8B co-localizes with LRRC8A and LRRC8D at basolateral membranes of proximal tubules (PMID:35777784). Beyond its plasma membrane VRAC role, LRRC8B localizes to the endoplasmic reticulum where it functions as a Ca²⁺ leak channel, with its overexpression reducing ER Ca²⁺ content and its knockdown slowing ER Ca²⁺ depletion (PMID:28972132). In astrocytes, LRRC8B silencing alone does not affect swelling-activated glutamate release, but co-silencing with LRRC8C or LRRC8D partially rescues activity, indicating a structural or modulatory rather than pore-forming role in certain VRAC populations (PMID:28833202).

1. 2014 High

   Establishing that LRRC8 family members form heteromeric complexes resolved the subunit composition question for VRAC — LRRC8B was identified as a physical interaction partner of LRRC8A, LRRC8C, and LRRC8D through co-immunoprecipitation, and LRRC8A was shown to be an indispensable VRAC component with LRRC8B–E serving as complementary heteromeric partners.

   Evidence Co-immunoprecipitation and topology characterization in mammalian cells; siRNA knockdown of LRRC8A in primary rat astrocytes with radiotracer efflux and HPLC assays

   PMID:24782309 PMID:25172945

   Open questions at the time

   • Stoichiometry and arrangement of heteromeric subunits unknown
   • Whether LRRC8B specifically contributes to channel conductance or selectivity not tested
   • No structural information on any LRRC8 complex
2. 2017 Medium

   Two parallel advances defined distinct roles for LRRC8B: in astrocytes, it was shown to have a structural/modulatory rather than pore-forming role in glutamate-permeable VRACs (silencing LRRC8B alone had no effect but partially rescued activity when LRRC8C/D were depleted); separately, LRRC8B was identified as an ER-resident Ca²⁺ leak channel, with gain- and loss-of-function experiments demonstrating its regulation of ER Ca²⁺ stores.

   Evidence RNAi knockdown in primary rat astrocytes with radiotracer efflux; overexpression and siRNA knockdown in HEK293 cells with Ca²⁺ imaging under thapsigargin, ATP, carbachol, and IP³ stimulation

   PMID:28833202 PMID:28972132

   Open questions at the time

   • ER Ca²⁺ leak function not confirmed by electrophysiology of purified LRRC8B
   • Whether ER and plasma membrane functions reflect distinct LRRC8B-containing complexes is unknown
   • Mechanism by which LRRC8B modulates other subunits' pore properties not resolved
3. 2022 High

   In vivo localization of LRRC8B to basolateral membranes of renal proximal tubules (alongside LRRC8A and LRRC8D) established tissue-specific VRAC subunit expression patterns and linked LRRC8A/D-containing channels to proximal tubular solute transport.

   Evidence Epitope-tagged knock-in mice for localization, conditional and constitutive knockout mice with histology and urine/serum metabolomics

   PMID:35777784

   Open questions at the time

   • No LRRC8B-specific knockout phenotype reported in kidney
   • Functional contribution of LRRC8B versus LRRC8D in renal proximal tubule VRAC not dissected
   • Whether LRRC8B affects substrate selectivity in renal channels is untested
4. 2023 High

   Cryo-EM structures of LRRC8A:C heterohexamers revealed that heterotypic LRR domain interactions displace subunits from the conduction axis and that pore-embedded lipids gate the channel in the closed state, providing the first structural framework for understanding how non-A subunits modulate VRAC architecture and gating.

   Evidence Single-particle cryo-EM with fiducial-tagging, electrophysiology, structure-function analysis

   PMID:36928458

   Open questions at the time

   • No LRRC8A:B structure solved; LRRC8B-specific contributions to pore geometry and gating remain inferred by analogy
   • Whether LRRC8B alters lipid-gating properties is unknown
   • Structural basis for ER versus plasma membrane targeting of LRRC8B not addressed
5. 2025 High

   The identification of a predominant LRRC8A/B/C endothelial complex by reciprocal co-immunoprecipitation from knock-in mice, coupled with functional data showing that depletion of LRRC8A or LRRC8C reduces VRAC currents and impairs AKT-eNOS signaling and vascular tone, established a physiological role for LRRC8B-containing VRACs in vascular regulation.

   Evidence Co-immunoprecipitation from Lrrc8a-3xFlag and Lrrc8c-HA knock-in mouse lung endothelium, endothelium-specific knockout/knockdown, patch-clamp electrophysiology, pressure myography, in vivo angiotensin-induced hypertension model

   PMID:41636028

   Open questions at the time

   • LRRC8B-specific endothelial knockout not performed; its unique contribution beyond stoichiometric assembly is unclear
   • Whether LRRC8B is required for the AKT-eNOS signaling phenotype or is dispensable when LRRC8A/C are present is untested
   • Mechanism connecting VRAC conductance to AKT-eNOS activation not fully delineated

• No cryo-EM structure of an LRRC8B-containing complex exists, and the molecular determinants that direct LRRC8B to the ER (versus the plasma membrane) and confer Ca²⁺ permeability remain unknown.
• No LRRC8A:B heteromer structure
• ER-targeting signals or retention motifs in LRRC8B uncharacterized
• Whether LRRC8B forms homomeric channels or requires LRRC8A for ER Ca²⁺ leak is untested