RATIONALE: Ca(2+) induced Ca(2+) release (CICR) in normal hearts requires close approximation of L-type calcium channels (LTCCs) within the transverse tubules (T-tubules), and Ryanodine receptors (RyR) within the junctional sarcoplasmic reticulum (jSR). CICR is disrupted in cardiac hypertrophy and heart failure, which is associated with loss of T-tubules and disruption of cardiac dyads. In these conditions, LTCCs are redistributed from the T-tubules to disrupt CICR. The molecular mechanism responsible for LTCCs recruitment to and from the T-tubules is not well known. Junctophilin-2 (JPH2) enables close association between T-tubules and the jSR to ensure efficient CICR. JPH2 has a so-called Joining region that is located near domains that interact with T-tubular plasma membrane, where LTCCs are housed. The idea that this Joining region directly interacts with LTCCs and contributes to LTCC recruitment to T-tubules is unknown. OBJECTIVE: To determine if the Joining region in JPH2 recruits LTCCs to T-tubules through direct molecular interaction in cardiomyocytes to enable efficient CICR. METHODS AND RESULTS: Modified abundance of JPH2 and redistribution of LTCC were studied in left ventricular hypertrophy in vivo and in cultured adult Feline and rat ventricular myocytes. Protein-protein interaction studies showed that the Joining region in JPH2 interacts with LTCC-α1C subunit and causes LTCCs distribution to the dyads, where they colocalize with RyRs. A JPH2 with induced mutations in the Joining region (mut(PG1)JPH2) caused T-tubule remodeling and dyad loss, showing that an interaction between LTCC and JPH2 is crucial for T-tubule stabilization. mut(PG1)JPH2 caused asynchronous Ca(2+)-release with impaired excitation-contraction (EC) coupling after β-adrenergic stimulation. The disturbed Ca(2+) regulation in mut(PG1)JPH2 overexpressing myocytes caused Calcium/calmodulin-dependent kinase-II activation and altered myocyte bioenergetics. CONCLUSIONS: The interaction between LTCC and the Joining region in JPH2 facilitates dyad assembly and maintains normal CIRC in cardiomyocytes.
