Interaction of vitamin D analogs with signaling pathways leading to active cell death in breast cancer cells.
Induction of apoptosis is a feature of the anti-tumor effects of certain vitamin D analogs. The aim of this study was to identify if common effectors are involved in cell death mediated by serum starvation, vitamin D analogs and tumor necrosis factor (TNF) alpha in 3 human breast cancer cell lines: MCF-7, T47-D and Hs578T. Incubation of cells in serum-free medium induced apoptosis as assessed by loss of cell viability and increased DNA fragmentation. Addition of IGF-I (30 ng/ml) protected against loss of cell viability in MCF-7 cells and co-treatment with two synthetic analogs (CB1093 and EB1089, 50 nM for 4 days) prevented these anti-apoptotic effects of IGF-I. Pretreatment of MCF-7 and Hs578T cells with the vitamin D analogs substantially potentiated the cytotoxic effects of TNFalpha. This cytokine was not cytotoxic for T47-D cells but co-incubation with CB1093 led to loss of cell viability. Potentiation by CB1093 of TNFalpha-induced apoptosis in MCF-7 cells was accompanied by increased activation of cytosolic phospholipase A2 and arachidonic acid release, which was partially inhibited by AACOCF3, a specific cPLA2 inhibitor. The broad-spectrum caspase inhibitor z-VAD-fmk prevented TNFalpha but not CB1093 mediated cell death and activation of cPLA2. Serum starvation induced apoptosis was accompanied by cPLA2 activation, which was inhibited by IGF-I and by z-VAD-fmk. However, the ability of these agents to suppress cPLA2 activation was abrogated by co-treatment with CB1093, suggesting a role for arachidonic acid release in the caspase-independent mechanism by which vitamin D analogs prevent the protective effects of IGF-I on breast cancer cell survival.
Pirianov
G
G
Department of Oncology, Gastroenterology, Endocrinology and Metabolism, St George's Hospital Medical School, Cranmer Terrace, SW17 0RE, London, UK.
Colston
K W
KW
D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000473:pathology* / Q000503:physiopathology; D061945:Caspase Inhibitors; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000502:physiology*
D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D014409:Tumor Necrosis Factor-alpha; D014807:Vitamin D; D007334:Insulin-Like Growth Factor I; D010741:Phospholipases A; D054467:Phospholipases A2