Direct Interaction of CaV{beta} with Actin Up-regulates L-type Calcium Currents in HL-1 Cardiomyocytes [Molecular Biophysics]

December 22nd, 2014 by Stolting, G., Campos de Oliveira, R., Guzman, R. E., Miranda–Laferte, E., Conrad, R., Jordan, N., Schmidt, S., Hendriks, J., Gensch, T., Hidalgo, P.

Expression of the β-subunit (CaVβ) is required for normal function of cardiac L-type calcium channels and its upregulation is associated with heart failure. CaVβ binds to the α1 pore-forming subunit of L-type channels and augments calcium current density by facilitating channel opening and increasing the number of channels in the plasma membrane, by a poorly understood mechanism. Actin, a key component of the intracellular trafficking machinery, interacts with SH3 domains in different proteins. Although CaVβ encompasses a highly conserved SH3 domain, association with actin has not yet been explored. Here, using co-sedimentation assays and FRET experiments we uncover a direct interaction between CaVβ and actin filaments. Consistently, single-molecule localization analysis reveals streak-like structures composed by CaVβ2 that distribute over several micrometers along actin filaments in HL-1 cardiomyocytes. Overexpression of CaVβ2-N3 in HL-1 cells induces an increase in L-type current without altering voltage-dependent activation thus reflecting an increased number of channels in the plasma membrane. CaVβ mediated L-type upregulation and CaVβ/actin association is prevented by disruption of the actin cytoskeleton with cytochalasin D. Our study reveals for the first time an interacting partner of CaVβ that is directly involved in vesicular trafficking. We propose a model in which CaVβ promotes anterograde trafficking of the L-type channels by anchoring them to actin filaments in their itinerary to the plasma membrane.