Genistein induces Ca 2+-mediated, calpain/caspase-12-dependent apoptosis in breast cancer cells

Abstract

Genistein, a soy-derived isoflavone, has been suggested for breast cancer prevention; however, use of soy products for this purpose remains controversial. Genistein has been reported to regulate growth of tumor cells, although the involved molecular mechanisms are not defined. Here we report that genistein induces apoptosis in breast cancer cells via activation of the Ca 2+-dependent proapoptotic proteases, μ-calpain, and caspase-12. The treatment of MCF-7 breast cancer cells with genistein induced a sustained increase in concentration of intracellular Ca 2+ resulting from depletion of the endoplasmic reticulum Ca 2+ stores. This increase in Ca 2+ was associated with activation of μ-calpain and caspase-12, as evaluated with the calpain and caspase-12 substrates and antibodies to active (cleaved) forms of the enzymes. Selective inhibition of Ca 2+ binding sites of μ-calpain, forced increase of the cytosolic Ca 2+ buffering capacity, and caspase inhibition decreased apoptotic indices in the genistein-treated cells. Our results suggest that Ca 2+-dependent proteases are potential targets for genistein in breast cancer cells and that the cellular Ca 2+ regulatory activity of genistein underlies its apoptotic mechanism.