Calcium and calpain as key mediators of apoptosis-like death induced by vitamin D compounds in breast cancer cells.
The active form of vitamin D(3) (1,25(OH)(2)D(3)) induces an increase in the intracellular free calcium ([Ca(2+)](i)) and caspase-independent cell death in human breast cancer cells. Here we show that the treatment of MCF-7 breast cancer cells with 1,25(OH)(2)D(3) or its chemotherapeutic analog, EB 1089, releases Ca(2+) from the endoplasmic reticulum. The increase in [Ca(2+)](i) was associated with the activation of a calcium-dependent cysteine protease, mu-calpain. Interestingly, ectopic expression of a calcium-binding protein, calbindin-D(28k), in MCF-7 cells not only attenuated the elevation in [Ca(2+)](i) and calpain activation, but also reduced death triggered by vitamin D compounds. Similarly, the inhibition of calpain activity by structurally unrelated chemical inhibitors increased the survival of the cells and reduces the amount of annexin V-positive cells. Despite the complete absence of effector caspase activation, transmission electron microscopy of MCF-7 cells treated with 1,25(OH)(2)D(3) or EB 1089 revealed apoptosis-like morphology characterized by the condensed cytoplasm, nuclei, and chromatin. Overall, these results suggest that calpain may take over the role of the major execution protease in apoptosis-like death induced by vitamin D compounds. Thus, these compounds may prove useful in the treatment of tumors resistant to therapeutic agents dependent on the classical caspase cascade.
Mathiasen
Ida Stenfeldt
IS
Apoptosis Laboratory, Danish Cancer Society, Strandboulevarden 49, DK 2100 Copenhagen Ø, Denmark.
Sergeev
Igor N
IN
Bastholm
Lone
L
Elling
Folmer
F
Norman
Anthony W
AW
Jäättelä
Marja
M
D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000473:pathology; D064026:Calbindins; D002117:Calcitriol / Q000031:analogs & derivatives / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology*; D002154:Calpain / Q000502:physiology*; D005260:Female; D006801:Humans; D064030:S100 Calcium Binding Protein G / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D064026:Calbindins; D064030:S100 Calcium Binding Protein G; D019284:Thapsigargin; D002154:Calpain; D002117:Calcitriol; C078903:seocalcitol; D002118:Calcium