Two PEST-like motifs regulate Ca2+/calpain-mediated cleavage of the CaVβ3 subunit and provide important determinants for neuronal Ca2+ channel activity

An increase in intracellular Ca2+ due to voltage-gated Ca2+ (Ca-V) channel opening represents an important trigger for a number of second-messenger-mediated effects ranging from neurotransmitter release to gene activation. Ca2+ entry occurs through the principal pore-forming protein but several ancillary subunits are known to more precisely tune ion influx. Among them, the Ca-V beta subunits are perhaps the most important, given that they largely influence the biophysical and pharmacological properties of the channel. Notably, several functional features may be associated with specific structural regions of the Ca-V beta subunits emphasizing the relevance of intramolecular domains in the physiology of these proteins. In the current report, we show that Ca-V beta(3) contains two PEST motifs and undergoes Ca2+-dependent degradation which can be prevented by the specific calpain inhibitor calpeptin. Using mutant constructs lacking the PEST motifs, we present evidence that they are necessary for the cleavage of Ca-V beta(3) by calpain. Furthermore, the deletion of the PEST sequences did not affect the binding of Ca-V beta(3) to the ion-conducting Ca(V)2.2 subunit and, when expressed in human embryonic kidney-293 cells, the PEST motif-deleted Ca-V beta(3) significantly increased whole-cell current density and retarded channel inactivation. Consistent with this observation, calpeptin treatment of human embryonic kidney-293 cells expressing wild-type Ca-V beta(3) resulted in an increase in current amplitude. Together, these findings suggest that calpain-mediated Ca-V beta(3) proteolysis may be an essential process for Ca2+ channel functional regulation.