Phosphorylation of Lamin A/C at serine 22 modulates Na(v)1.5 function

Variants in the LMNA gene, which encodes for Lamin A/C, are associated with cardiac conduction disease (CCD). We previously reported that Lamin A/C variants p.R545H and p.A287Lfs*193, which were identified in CCD patients, decreased peak I (Na) in HEK‐293 cells expressing Na(v)1.5. Decreased peak I (Na) in the cardiac conduction system could account for patients’ atrioventricular block. We found that serine 22 (Ser 22) phosphorylation of Lamin A/C was decreased in the p.R545H variant and hypothesized that lamin phosphorylation modulated Na(v)1.5 activity. To test this hypothesis, we assessed Na(v)1.5 function in HEK‐293 cells co‐transfected with LMNA variants or treated with the small molecule LBL1 (lamin‐binding ligand 1). LBL1 decreased Ser 22 phosphorylation by 65% but did not affect Na(v)1.5 function. To test the complete loss of phosphorylation, we generated a version of LMNA with serine 22 converted to alanine 22 (S22A‐LMNA); and a version of mutant R545H‐LMNA that mimics phosphorylation via serine 22 to aspartic acid 22 substitution (S22D‐R545H‐LMNA). We found that S22A‐LMNA inhibited Lamin‐mediated activation of peak I (Na) by 63% and shifted voltage‐dependency of steady‐state inactivation of Na(v)1.5. Conversely, S22D‐R545H‐LMNA abolished the effects of mutant R545H‐LMNA on voltage‐dependency but not peak I (Na). We conclude that Lamin A/C Ser 22 phosphorylation can modulate Na(v)1.5 function and contributes to the mechanism by which R545H‐LMNA alters Na(v)1.5 function. The differential impact of complete versus partial loss of Ser 22 phosphorylation suggests a threshold of phosphorylation that is required for full Na(v)1.5 modulation. This is the first study to link Lamin A/C phosphorylation to Na(v)1.5 function.