BRAF and NRAS mutated melanoma: Different Ca responses, Na/Ca exchanger expression, and sensitivity to inhibitors.

Calcium is a ubiquitous intracellular second messenger, playing central roles in the regulation of several biological processes. Alterations in Ca homeostasis and signaling are an important feature of tumor cells to acquire proliferative and survival advantages, which include structural and functional changes in storage capacity, channels, and pumps. Here, we investigated the differences in Ca homeostasis in vemurafenib-responsive and non-responsive melanoma cells. Also, the expression of the Na/Ca exchanger (NCX) and the impact of its inhibition were studied. For this, it was used B-RAF and NRAS-mutated human melanoma cells. The intracellular Ca chelator BAPTA-AM decreased the viability of SK-MEL-147 but not of SK-MEL-19 and EGTA sensitized NRAS-mutated cells to vemurafenib. These cells also presented a smaller response to thapsargin and ionomycin regarding the cytosolic Ca levels in relation to SK-MEL-19, which was associated to an increased expression of NCX1, NO basal levels, and sensitivity to NCX inhibitors. These data highlight the differences between B-RAF and NRAS-mutated melanoma cells in response to Ca stimuli and point to the potential combination of clinically used chemotherapeutic drugs, including vemurafenib, with NCX inhibitors as a new therapeutic strategy to the treatment of melanoma.