PDZ-Domain-Binding Motif Regulates Cardiomyocyte Compartment-Specific NaV1.5 Channel Expression and Function
Background—Sodium channel NaV1.5 underlies cardiac excitability and conduction. The last three residues of NaV1.5 (Ser-Ile-Val) constitute a PDZ-domain-binding motif that interacts with PDZ proteins, such as syntrophins and SAP97, at different locations within the cardiomyocyte, thus defining distinct pools of NaV1.5 multi-protein complexes. Here, we explored the in vivo and clinical impact of this motif through characterization of mutant mice and genetic screening of patients.
Methods and Results—To investigate in vivo the regulatory role of this motif, we generated knock-in mice lacking the SIV domain (∆SIV). ∆SIV mice displayed reduced NaV1.5 expression and sodium current (INa), specifically at the lateral myocyte membrane, whereas NaV1.5 expression and INa at the intercalated discs were unaffected. Optical mapping of ∆SIV hearts revealed that ventricular conduction velocity was preferentially decreased in the transversal direction to myocardial fiber orientation, leading to increased anisotropy of ventricular conduction. Internalization of WT and ΔSIV channels was unchanged in HEK293 cells. However, the proteasome inhibitor, MG132 rescued ΔSIV INa, suggesting that the SIV motif is important for regulation of NaV1.5 degradation. A missense mutation within the SIV motif (p.V2016M) was identified in a Brugada syndrome patient. The mutation decreased NaV1.5 cell-surface expression and INa when expressed in HEK293 cells.
Conclusions—Our results demonstrate the in vivo significance of the PDZ-domain-binding motif in correct expression of NaV1.5 at the lateral cardiomyocyte membrane and underline the functional role of lateral NaV1.5 in ventricular conduction. Furthermore, we reveal a clinical relevance of the SIV motif in cardiac disease.
- Received December 3, 2013.
- Revision received March 11, 2014.
- Accepted April 24, 2014.