Abstract
It has been previously shown that Walker 256 tumor cells express a high content of the anti-apoptotic protein Bcl-2 which protects mitochondria against the damaging effects of Ca2+. In the present study, we analyze H2O2-induced apoptotic death in two different types of tumor cells: Walker 256 and SCC-25. Treatment with H2O2 (4mM) increased reactive oxygen species generation and the concentration of cytosolic free Ca2+. These alterations preceded apoptosis in both cell lines. In Walker cells, which show a high Bcl-2/Bax ratio, apoptosis was dependent on calcineurin activation and independent of changes in mitochondrial membrane potential (Δ < eqid1 > m), as well as cytochrome c release. In contrast, in SCC-25 cells, which show a lower Bcl-2/Bax ratio, apoptosis was preceded by a decrease in Δ < eqid2 > m, mitochondrial permeability transition, and cytochrome c release. Caspase-3 activation occurred in both cell lines. The data suggest that although the high Bcl-2/Bax ratio protected the mitochondria of Walker cells from oxidative stress, it was not sufficient to prevent apoptosis through calcineurin pathways.
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Abbreviations
- BA:
-
bongkrekic acid
- BAPTA:
-
1,2-bis(2-aminophenoxy) ethane N,N,N′,N′-tetraacetic acid
- CCCP:
-
carbonyl cyanide m-chloro phenyl hydrazone
- [Ca2+]cyt :
-
cytosolic free calcium concentration
- CsA:
-
cyclosporin A
- DHE:
-
dihydroethidium
- DioC6(3):
-
3,3′-dihexyloxacarbocyanine iodide
- ER:
-
endoplasmatic reticulum
- FITC:
-
fluorescein-5-isothiocyanate
- MOMP:
-
mitochondrial outer membrane permeabilization
- MPT:
-
mitochondrial permeability transition
- PI:
-
propidium iodide
- ROS:
-
reactive oxygen species
- SCC:
-
squamous cell carcinoma
- Δ ψm :
-
mitochondrial electrical transmembrane potential
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Zecchin, K.G., Seidinger, A.L.O., Chiaratti, M.R. et al. High Bcl-2/Bax ratio in Walker tumor cells protects mitochondria but does not prevent H2O2-induced apoptosis via calcineurin pathways. J Bioenerg Biomembr 39, 186–194 (2007). https://doi.org/10.1007/s10863-007-9076-z
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DOI: https://doi.org/10.1007/s10863-007-9076-z