Abstract
Apoptosis is a major form of cell death induced by chemotherapeutic drugs. Overexpression of the proto-oncogene bcl-2 can prevent apoptosis in various types of cells. We have constructed a HeLa S3 cell line in which the expression of bcl-2 can be controlled by the concentration of tetracycline in the medium. Using this system, we show that apoptosis induced by various cytostatic treatments could be delayed by the overexpression of bcl-2, as assayed by vital dye exclusion, apoptotic nuclei morphology, DNA histogram shift, and DNA fragmentation. Quantitative analysis revealed a hyperbolic curve when protection from apoptosis was plotted against the amount of Bcl-2. When cells were treated with aphidicolin for 12, 24, or 36 h and then replated in fresh media to assay for colony formation, the majority of cells that did not show apoptotic morphology at the time of drug removal failed to form colonies. Furthermore, Bcl-2 did not increase colony formation after 12–36 h of aphidicolin treatment. Therefore, with aphidicolin treatment, cells were committed to the death program upstream of the point of Bcl-2 action.
Footnotes
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↵1 This work was supported by an anonymous gift and NIH Grant CA16318 to R. T. S.
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↵2 To whom requests for reprints should be addressed, at Stanford University, Department of Biological Sciences, Stanford, CA 94305-5020. Phone: (415) 725-4814; Fax: (415) 723-0155.
- Received February 23, 1995.
- Accepted August 14, 1995.
- ©1995 American Association for Cancer Research.
Volume 55, Issue 21
