title: Calcium and calpain as key mediators of apoptosis-like death induced by vitamin D compounds in breast cancer cells.
abstract: 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.
authors.affiliation: Apoptosis Laboratory, Danish Cancer Society, Strandboulevarden 49, DK 2100 Copenhagen Ø, Denmark.
authors.forename: Ida Stenfeldt
authors.initials: IS
authors.lastname: Mathiasen
authors.forename: Igor N
authors.initials: IN
authors.lastname: Sergeev
authors.forename: Lone
authors.initials: L
authors.lastname: Bastholm
authors.forename: Folmer
authors.initials: F
authors.lastname: Elling
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Norman
authors.forename: Marja
authors.initials: M
authors.lastname: Jäättelä
mesh_terms: 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
chemical_list: D064026:Calbindins; D064030:S100 Calcium Binding Protein G; D019284:Thapsigargin; D002154:Calpain; D002117:Calcitriol; C078903:seocalcitol; D002118:Calcium