Sodium channel β1 subunits participate in regulated intramembrane proteolysis-excitation coupling

Abstract

Loss-of-function (LOF) variants in SCN1B, encoding voltage-gated sodium channel β1 subunits, are linked to human diseases with high risk of sudden death, including developmental and epileptic encephalopathy and cardiac arrhythmia. β1 Subunits modulate the cell-surface localization, gating, and kinetics of sodium channel pore-forming α subunits. They also participate in cell-cell and cell-matrix adhesion, resulting in intracellular signal transduction, promotion of cell migration, calcium handling, and regulation of cell morphology. Here, we investigated regulated intramembrane proteolysis (RIP) of β1 by BACE1 and γ-secretase and show that β1 subunits are substrates for sequential RIP by BACE1 and γ-secretase, resulting in the generation of a soluble intracellular domain (ICD) that is translocated to the nucleus. Using RNA sequencing, we identified a subset of genes that are downregulated by β1-ICD overexpression in heterologous cells but upregulated in Scn1b -null cardiac tissue, which lacks β1-ICD signaling, suggesting that the β1-ICD may normally function as a molecular brake on gene transcription in vivo. We propose that human disease variants resulting in SCN1B LOF cause transcriptional dysregulation that contributes to altered excitability. Moreover, these results provide important insights into the mechanism of SCN1B -linked channelopathies, adding RIP-excitation coupling to the multifunctionality of sodium channel β1 subunits.

Subcellular dynamics and functional activity of the cleaved Na+channel β1 subunit intracellular domain

“…Taken together with the available literature (4,31,32,34,39–41), our data suggest that the β1-ICD promotes plasma membrane α subunit expression in breast cancer cells via several mechanisms (Figure 9). The observation that β1STOP-GFP failed to increase Na + current further identifies a requirement for the β1-ICD.…”

“…Therefore, it appears that the mechanisms underlying increased Na + current density, presumably via increased plasma membrane expression, and channel inactivation are distinct. Our data suggest that processing by γ-secretase may play a role in regulating β1 function in breast cancer cells, adding to emerging evidence in other cell systems (39). The important role of γ-secretase activity in cancer progression (42), together with the growing evidence suggesting that β1ICD-mediated cellular changes promote pathologies including epilepsy, cardiac arrhythmia and cancer (39), further highlight the significance of this signalling axis to pathophysiologies associated with abnormal β1 function.…”

“…However, the precise involvement of γ-secretase cleavage on these mechanisms appears complex, given that full-length β1-GFP and β1ICD-GFP both promote Na + current, and that pharmacological inhibition of γ-secretase activity had no effect. Furthermore, the β1-mediated targeting of α subunits to the plasma membrane may be cell type-specific (39). Further work is required to elucidate the context-dependent trafficking mechanisms involved.…”

Scn1b expression in the adult mouse heart modulates Na+ influx in myocytes and reveals a mechanistic link between Na+ entry and diastolic function

“…To obtain mice with conditional and inducible deletion of Scn1b in myocytes, a Scn1b flox/flox /αMHC-MerCreMer (conditional knockout, cKO) mouse line was obtained by intercrossing Scn1b flox/flox animals congenic on the C57Bl/6J background ( 4 , 8 , 9 ) with B6.FVB(129)-A1cf Tg(Myh6-cre/Esr1 * )1Jmk /J mice expressing tamoxifen-inducible Cre recombinase under the α-myosin heavy chain promoter (αMHC-MerCreMer, Jackson Labs, Stock No. 005657) ( 24 , 25 ), backcrossed onto C57BL/6J by the vendor.…”

A single injection of periostin decreases cardiac voltage-gated Na⁺ channel in rat ventricles

“…, Figs. 1B–D , 2B, 2D , 3B ) [ 4 ] or one-way analysis of variance followed by Bonferroni’s post hoc test ( Fig. 3D, 3F ).…”