Calmodulin and Stac3 Enhance Functional Expression of CaV1.1

Abstract

CaV1.1 is a prominent L-type voltage-gated calcium channel (VGCC) that plays an integral role in mediating skeletal muscle excitation-contraction coupling. Unlike other homologous L-type channels (e.g. CaV1.3), in depth biophysical analysis of CaV1.1 is challenging as functional expression of these channels has been generally restricted to cell types with a muscular lineage. Interestingly, in contrast to CaV1.3, the carboxy terminus of CaV1.1 has a low affinity for the calcium binding protein, calmodulin (CaM) suggesting that the loss of CaM pre-association may be responsible for the poor functional expression of CaV1.1 in recombinant systems. Here, we explicitly demonstrate that restoration of CaM to the channel complex enables functional expression of CaV1.1 in HEK293 cells. Further mechanistic analysis shows that CaM substantially enhances surface membrane trafficking of CaV1.1. In conjunction with recent studies that showed Stac3 (SH3 and cysteine rich domain 3) adaptor proteins also enable CaV1.1 currents in recombinant systems (Polster et al (2015) PNAS 112:602), our results argue that multiple cell signaling molecules can evoke similar functional outcomes and points to redundancy in molecular pathways that orchestrate CaV1.1 surface expression. These results also suggest there may be an overlap between channel regulation and trafficking of L-type VGCC with Stac3 and CaM. In all, our findings furnish a convenient platform to probe CaV1.1 function and related pharmacology.