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Different mechanisms for suppression of apoptosis by cytokines and calcium mobilizing compounds
1Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.
Abstract:
Overexpression of wild-type p53 in M1 myeloid leukemia cells induces apoptotic cell death that was suppressed by the calcium ionophore A23187 and the calcium ATPase inhibitor thapsigargin (TG). This suppression of apoptosis by A23187 or TG was associated with suppression of caspase activation but not with suppression of wild-type-p53-induced expression of WAF-1, mdm-2, or FAS. In contrast to suppression of apoptosis by the cytokines interleukin 6 (IL-6) and interferon gamma, a protease inhibitor, or an antioxidant, suppression of apoptosis by A23187 or TG required extracellular Ca2+ and was specifically abolished by the calcineurin inhibitor cyclosporin A. IL-6 induced immediate early activation of junB and zif/268 (Egr-1) but A23187 and TG did not. A23187 and TG also suppressed induction of apoptosis by doxorubicin or vincristine in M1 cells that did not express p53 by a cyclosporin A-sensitive mechanism. Suppression of apoptosis by A23187 or TG was not associated with autocrine production of IL-6. Apoptosis induced in IL-6-primed M1 cells after IL-6 withdrawal was not suppressed by A23187 or TG but was suppressed by the cytokines IL-6, IL-3, or interferon gamma. The results indicate that these Ca2+-mobilizing compounds can suppress some pathways of apoptosis suppressed by cytokines but do so by a different mechanism.
Insights
Calcium-mobilizing agents like A23187 and thapsigargin suppress apoptosis in myeloid leukemia cells by inhibiting caspases, but through a distinct mechanism from cytokines. This effect requires extracellular calcium and is blocked by cyclosporin A.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Wild-type p53 overexpression in M1 myeloid leukemia cells triggers apoptosis.
- Apoptotic cell death can be modulated by various external factors, including calcium signaling and cytokines.
Purpose of the Study:
- To investigate the mechanism by which calcium ionophore A23187 and thapsigargin (TG) suppress p53-induced apoptosis in M1 myeloid leukemia cells.
- To compare the apoptotic suppression mechanisms of calcium-mobilizing agents with those of cytokines like IL-6 and interferon gamma.
Main Methods:
- Overexpression of wild-type p53 in M1 myeloid leukemia cells.
- Treatment with calcium ionophore A23187 and thapsigargin (TG).
- Assay of caspase activation, WAF-1, mdm-2, and FAS expression.
- Investigation of the role of extracellular calcium and calcineurin inhibition (cyclosporin A).
- Analysis of immediate early gene activation (junB, zif/268).
- Assessment of apoptosis induced by doxorubicin or vincristine.
Main Results:
- A23187 and TG suppressed p53-induced apoptosis and caspase activation without affecting WAF-1, mdm-2, or FAS expression.
- Suppression by A23187 or TG required extracellular Ca2+ and was sensitive to cyclosporin A, unlike cytokine-mediated suppression.
- A23187 and TG did not induce immediate early gene activation, contrasting with IL-6.
- These agents also suppressed doxorubicin/vincristine-induced apoptosis in a p53-independent, cyclosporin A-sensitive manner.
- Apoptosis after IL-6 withdrawal was not suppressed by A23187 or TG.
Conclusions:
- Calcium-mobilizing agents A23187 and TG suppress apoptosis through a mechanism distinct from cytokines, involving caspase inhibition and dependent on extracellular calcium and calcineurin.
- These findings highlight a novel pathway for apoptosis regulation in myeloid leukemia cells mediated by calcium signaling.