Transient Ca2+-dependent activation of ERK1 and ERK2 in cytotoxic responses induced by maitotoxin in breast cancer cells.

Treatment of MCF-7 breast cancer cells with the marine toxin maitotoxin (MTX) induces cell death. The cytotoxic effects are clearly detectable within 2-4 h after cell treatment with 10(-10)-10(-9) M concentrations of MTX. The response was found to depend on extracellular Ca2+, inasmuch as cell death was prevented when culture dishes received MTX, following addition of EGTA. MTX caused transient phosphorylation of extracellular signal-regulated kinase isoforms 1 and 2 (ERK1 and ERK2) mitogen-activated protein kinase isoforms in MCF-7 cells, which was maximal 15 min after toxin addition to culture vessels. The effect was dependent on influx of extracellular Ca2+, as it was abolished by EGTA, and was induced by ionophores, such as A23187 and ionomycin. Our findings show that signaling pathways involving Ca2+ ions may cause activation of ERK1 and ERK2 in cell death responses.