Aberrant Splicing Promotes Proteasomal Degradation of L-type Ca v 1.2 Calcium Channels by Competitive Binding for Ca_V β Subunits in Cardiac Hypertrophy

Decreased expression and activity of Ca _V1.2 calcium channels has been reported in pressure overload-induced cardiac hypertrophy and heart failure. However, the underlying mechanisms remain unknown. Here we identified in rodents a splice variant of Ca _V1.2 channel, named Ca _V1.2 _e21+22, that contained the pair of mutually exclusive exons 21 and 22. This variant was highly expressed in neonatal hearts. The abundance of this variant was gradually increased by 12.5-folds within 14 days of transverse aortic banding that induced cardiac hypertrophy in adult mouse hearts and was also elevated in left ventricles from patients with dilated cardiomyopathy. Although this variant did not conduct Ca ²⁺ ions, it reduced the cell-surface expression of wild-type Ca _V1.2 channels and consequently decreased the whole-cell Ca ²⁺ influx via the Ca _V1.2 channels. In addition, the Ca _V1.2 _e21+22 variant interacted with Ca _Vβ subunits significantly more than wild-type Ca _V1.2 channels, and competition of Ca _Vβ subunits by Ca _V1.2 _e21+22 consequently enhanced ubiquitination and subsequent proteasomal degradation of the wild-type Ca _V1.2 channels. Our findings show that the resurgence of a specific neonatal splice variant of Ca _V1.2 channels in adult heart under stress may contribute to heart failure.