Lateral Membrane-Specific MAGUK CASK Down-Regulates Na_V 1.5 Channel in Cardiac MyocytesNovelty and Significance

Catherine A. Eichel (1) , Adeline Beuriot (1) , Morgan Y.E. Chevalier (2) , Jean-Sébastien Rougier (2) , Florent Louault (1) , Gilles Dilanian (1) , Julien Amour (3, 1) , Alain Coulombe (1) , Hugues Abriel (2) , Stéphane N. Hatem (1, 3) , Elise Balse (1)

1 ICAN - Unité de Recherche sur les Maladies Cardiovasculaires, du Métabolisme et de la Nutrition = Research Unit on Cardiovascular and Metabolic Diseases
2 Department of Clinical Research
3 CHU Pitié-Salpêtrière [AP-HP]

Rationale: Mechanisms underlying membrane protein localization are crucial in the proper function of cardiac myocytes. The main cardiac sodium channel, NaV1.5, carries the sodium current (INa) that provides a rapid depolarizing current during the upstroke of the action potential. Although enriched in the intercalated disc, NaV1.5 is present in different membrane domains in myocytes and interacts with several partners. Objective: To test the hypothesis that the MAGUK (membrane-associated guanylate kinase) protein CASK (calcium/calmodulin-dependent serine protein kinase) interacts with and regulates NaV1.5 in cardiac myocytes. Methods and Results: Immunostaining experiments showed that CASK localizes at lateral membranes of cardiac myocytes, in association with dystrophin. Whole-cell patch clamp showed that CASK-silencing increases INa in vitro. In vivo CASK knockdown similarly increased INa recorded in freshly isolated myocytes. Pull-down experiments revealed that CASK directly interacts with the C-terminus of NaV1.5. CASK silencing reduces syntrophin expression without affecting NaV1.5 and dystrophin expression levels. Total Internal Reflection Fluorescence microscopy and biotinylation assays showed that CASK silencing increased the surface expression of NaV1.5 without changing mRNA levels. Quantification of NaV1.5 expression at the lateral membrane and intercalated disc revealed that the lateral membrane pool only was increased upon CASK silencing. The protein transport inhibitor brefeldin-A prevented INa increase in CASK-silenced myocytes. During atrial dilation/remodeling, CASK expression was reduced but its localization remained unchanged. Conclusion: This study constitutes the first description of an unconventional MAGUK protein, CASK, which directly interacts with NaV1.5 channel and controls its surface expression at the lateral membrane by regulating ion channel trafficking.

Domaines: Cardiologie et système cardiovasculaire; Biochimie, Biologie Moléculaire

Catherine A. Eichel, Adeline Beuriot, Morgan Y.E. Chevalier, Jean-Sébastien Rougier, Florent Louault, et al.. Lateral Membrane-Specific MAGUK CASK Down-Regulates Na_V 1.5 Channel in Cardiac MyocytesNovelty and Significance. Circulation Research, 2016, 119 (4), pp.544-556. ⟨10.1161/CIRCRESAHA.116.309254⟩. ⟨hal-01528973⟩