Ca protein alpha 1D of CaV1.3 regulates intracellular calcium concentration and migration of colon cancer cells through a non-canonical activity.

It is generally accepted that voltage-gated Ca channels, CaV, regulate Ca homeostasis in excitable cells following plasma membrane depolarization. Here, we show that the Ca protein α1D of CaV1.3 channel is overexpressed in colorectal cancer biopsies compared to normal tissues. Gene silencing experiments targeting α1D reduced the migration and the basal cytosolic Ca concentration of HCT116 colon cancer cell line and modified the cytosolic Ca oscillations induced by the sodium/calcium exchanger NCX1/3 working in its reverse mode. Interestingly, NCX1/3 regulated membrane potential of HCT116 cells only when α1D was silenced, and blocking NCX1/3 increased cytosolic Ca concentration and cell migration. However, membrane depolarization did not induce an increase in intracellular Ca. Patch-clamp experiments clearly showed that the inward Ca current was absent. Finally, flow cytometry and immunofluorescence studies showed that α1D protein was localized at the plasma membrane, in cytosol and cell nuclei. Altogether, we uncover a novel signaling pathway showing that α1D is involved in the regulation of Ca homeostasis and cell migration by a mechanism independent of its plasma membrane canonical function but that involved plasma membrane Na/Ca exchanger.