FIGURE 6.

Doxorubicin-induced calpain activity is enhanced in SPP1-depleted cells. A, MCF7 cells transfected with siControl or siSPP1 were treated without or with doxorubicin (Doxo, 1 μg/ml), and calpain activity was measured at the indicated times with a luminescence assay. *, p < 0.01 as compared with siControl treated with doxorubicin. B, MCF7 cells were treated for 6 h with vehicle, doxorubicin (1 μg/ml), tunicamycin (Tun, 2.5 μm), or both, and calpain activity measured. *, p < 0.01 as compared with vehicle. C, MCF7 cells were co-transfected with siControl, siSPP1, siIRE1α, siATF6, or dnPERK, as indicated, and treated with doxorubicin (1 μg/ml) for 6 h, and calpain activity was measured. Activities were normalized to untreated siControl cells (None) at time 0. *, p < 0.01 as compared with None. Error bars in all panels indicate means ± S.D.