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Inhibitory effect of Bcl-2 on p53-mediated transactivation following genotoxic stress
1Laboratory of Biological Chemistry, Division of Basic Sciences, National Cancer Institute, Bethesda, Maryland 20892-4255, USA.
Abstract:
In the cellular response to genotoxic stress, cell cycle checkpoint and apoptosis are considered to be two of the major biological events in maintaining genomic stability. The tumor suppressor p53 has been shown to play critical roles in these stress-induced cellular responses at least in part through the activation of its down-stream genes, such as p21CIP1/WAF1, GADD45 and BAX. In addition, p53 has been found to down-regulate the expression of BCL-2, which is able to block apoptosis induced by both p53-dependent and independent signaling events. In this report, we have found that increased expression of Bcl-2 protein in the human Burkitt's lymphoma WMN cell line suppressed apoptosis induced by different DNA-damaging agents. The induction of p53-regulated genes including GADD45, p21CIP1/WAF1 and BAX by genotoxic stress was substantially reduced in cells expressing high levels of Bcl-2 protein. Furthermore, Bcl-2 protein was shown to specifically suppress the p53-mediated transactivation of p21CIP1/WAF1 and PG13-CAT, which is a typical p53-binding-site reporter construct. Similarly, the inhibitory effect of Bcl-2 protein was seen in a GADD45 promoter reporter construct after treatment with methylmethane sulfonate or UV-radiation. These results indicate that in addition to its apoptosis-suppressing activity, Bcl-2 protein is able to inhibit transactivation of p53-regulated genes, which function in multiple important cellular responses to genotoxic stress, including the control of cell cycle checkpoints, cell growth suppression and DNA repair.
Insights
Bcl-2 protein suppresses apoptosis and inhibits the activation of p53-regulated genes involved in cell cycle control and DNA repair. This finding reveals a novel role for Bcl-2 in maintaining genomic stability under genotoxic stress.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Genomic stability is maintained by cell cycle checkpoints and apoptosis during genotoxic stress.
- The tumor suppressor p53 is crucial for these responses, activating genes like p21CIP1/WAF1, GADD45, and BAX.
- p53 also down-regulates BCL-2, an apoptosis inhibitor.
Purpose of the Study:
- To investigate the effect of increased Bcl-2 protein expression on apoptosis and p53-regulated gene induction.
- To determine if Bcl-2 influences p53-mediated transactivation of downstream genes.
Main Methods:
- Utilized human Burkitt's lymphoma WMN cell line with increased Bcl-2 expression.
- Assessed apoptosis induction by DNA-damaging agents.
- Measured the induction of p53-regulated genes (GADD45, p21CIP1/WAF1, BAX).
- Employed reporter constructs (PG13-CAT, GADD45 promoter) to study p53 transactivation.
Main Results:
- Elevated Bcl-2 protein suppressed apoptosis induced by DNA-damaging agents.
- Induction of GADD45, p21CIP1/WAF1, and BAX by genotoxic stress was significantly reduced in high Bcl-2 cells.
- Bcl-2 specifically inhibited p53-mediated transactivation of p21CIP1/WAF1, PG13-CAT, and GADD45 promoter activity.
Conclusions:
- Bcl-2 protein possesses apoptosis-suppressing activity.
- Bcl-2 inhibits the transactivation of p53-regulated genes involved in cell cycle control, growth suppression, and DNA repair.
- These findings highlight a dual role for Bcl-2 in cellular responses to genotoxic stress.