The plasma membrane Ca2+ pump PMCA4b inhibits the migratory and metastatic activity of BRAF mutant melanoma cells

Oncogenic mutations of BRAF lead to constitutive ERK activity that supports melanoma cell growth and survival. While Ca2+ signaling is a well-known regulator of tumor progression, the crosstalk between Ca2+ signaling and the Ras-BRAF-MEK-ERK pathway is much less explored. Here we show that in BRAF mutant melanoma cells the abundance of the plasma membrane Ca2+ ATPase isoform 4b (PMCA4b, ATP2B4) is low at baseline but markedly elevated by treatment with the mutant BRAF specific inhibitor vemurafenib. In line with these findings gene expression microarray data also shows decreased PMCA4b expression in cutaneous melanoma when compared to benign nevi. The MEK inhibitor selumetinibsimilarly to that of the BRAF-specific inhibitoralso increases PMCA4b levels in both BRAF and NRAS mutant melanoma cells suggesting that the MAPK pathway is involved in the regulation of PMCA4b expression. The increased abundance of PMCA4b in the plasma membrane enhances [Ca2+](i) clearance from cells after Ca2+ entry. Moreover we show that both vemurafenib treatment and PMCA4b overexpression induce marked inhibition of migration of BRAF mutant melanoma cells. Importantly, reduced migration of PMCA4b expressing BRAF mutant cells is associated with a marked decrease in their metastatic potential in vivo. Taken together, our data reveal an important crosstalk between Ca2+ signaling and the MAPK pathway through the regulation of PMCA4b expression and suggest that PMCA4b is a previously unrecognized metastasis suppressor. What's new? New results may give researcher another way to attack metastatic melanoma. Commonly, melanomas have a mutated copy of BRAF, and current therapies focus on these mutants. In search of new target molecules, these authors looked at the calcium ion signaling system, which promotes cell migration and invasion. They found that BRAF-mutant melanoma cells have less of the plasma membrane calcium ion pump molecule PMCA-4b. Treatment with mutant BRAF inhibitor boosts PMCA-4b and slows the migration of cancer cells. Furthermore, PMCA-4b overexpression reduced metastatic potential of cells in vivo. This study is the first to show that PMCA-4b could hinder metastasis.