Abstract
The L-type Ca(2+) channel (Ca(V)1.2) is essential for cardiac excitation-contraction coupling. To contribute to the inward Ca(2+) flux that drives Ca(2+)-induced-Ca(2+)-release, Ca(V)1.2 channels must be expressed on the sarcolemma; thus the regulatory mechanisms that tune Ca(V)1.2 expression to meet contractile demand are an emerging area of research. A ubiquitously expressed protein called 14-3-3 has been proposed to affect Ca(2+) channel trafficking in nonmyocytes; however, whether 14-3-3 has similar effects on Ca(V)1.2 in cardiomyocytes is unknown. 14-3-3 preferentially binds phospho-serine/threonine residues to affect many cellular processes and is known to regulate cardiac ion channels including Na(V)1.5 and the human ether-à-go-go-related gene (hERG) potassium channel. Altered 14-3-3 expression and function have been implicated in cardiac pathologies including hypertrophy. Accordingly, we tested the hypothesis that 14-3-3 interacts with Ca(V)1.2 in a phosphorylation-dependent manner and regulates cardiac Ca(V)1.2 trafficking and recycling. Confocal imaging, proximity ligation assays, superresolution imaging, and coimmunoprecipitation revealed a population of 14-3-3 colocalized and closely associated with Ca(V)1.2. The degree of 14-3-3/Ca(V)1.2 colocalization increased upon stimulation of β-adrenergic receptors with isoproterenol. Notably, only the 14-3-3-associated Ca(V)1.2 population displayed increased cluster size with isoproterenol, revealing a role for 14-3-3 as a nucleation factor that directs Ca(V)1.2 superclustering. Isoproterenol-stimulated augmentation of sarcolemmal Ca(V)1.2 expression, Ca(2+) currents, and Ca(2+) transients in ventricular myocytes were strengthened by 14-3-3 overexpression and attenuated by 14-3-3 inhibition. These data support a model where 14-3-3 interacts with Ca(V)1.2 in a phosphorylation-dependent manner to promote enhanced trafficking/recycling, clustering, and activity during β-adrenergic stimulation.