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DNA damage increases the levels of MDM2 messenger RNA in wtp53 human cells
1Joint Center for Radiation Therapy, Dana-Farber Cancer Institute, Boston, Massachusetts 02115.
Abstract:
Damage to chromosomal DNA increases the levels of the transcriptional regulatory protein p53. We have investigated how the MDM2 protein, which binds to p53 and inactivates its transcriptional activity, may be controlled following DNA damage. Irradiation of human GM2149 fibroblast cells causes an increase in MDM2 mRNA levels within 1 h, and levels remain elevated for at least 8 h. The induction of MDM2 mRNA following irradiation is not blocked by inhibitors of protein synthesis and can be detected after doses of 2-5 Gy. In ataxia telangiectasia cells or cells where p53 is mutated/deleted, MDM2 mRNA levels are not increased after DNA damage. This suggests that p53 is required for transcription of the MDM2 gene following DNA damage.
Insights
DNA damage elevates levels of the tumor suppressor protein p53. This study reveals that p53 is essential for the DNA damage-induced transcription of the MDM2 gene, which regulates p53 activity.
Area of Science:
- Molecular Biology
- Cancer Research
- Cellular Response to DNA Damage
Background:
- Chromosomal DNA damage triggers an increase in the transcriptional regulatory protein p53.
- The MDM2 protein interacts with p53, inhibiting its transcriptional activity.
- Understanding MDM2 regulation post-DNA damage is crucial for comprehending cellular responses.
Purpose of the Study:
- To investigate the control mechanisms of MDM2 protein following DNA damage.
- To determine the role of p53 in the transcriptional regulation of MDM2 after DNA damage.
Main Methods:
- Irradiation of human fibroblast cells (GM2149).
- Measurement of MDM2 mRNA levels over time post-irradiation.
- Assessment of MDM2 mRNA induction in cells with functional p53 versus those with mutated/deleted p53 or ataxia telangiectasia.
- Use of protein synthesis inhibitors to assess the nature of MDM2 induction.
Main Results:
- Irradiation led to a significant increase in MDM2 mRNA levels within 1 hour, sustained for at least 8 hours.
- MDM2 mRNA induction occurred independently of protein synthesis and was detectable at doses of 2-5 Gy.
- Crucially, MDM2 mRNA levels did not increase in ataxia telangiectasia cells or cells with p53 mutations/deletions following DNA damage.
Conclusions:
- The p53 protein is required for the transcriptional upregulation of the MDM2 gene in response to DNA damage.
- This finding elucidates a critical feedback loop in the DNA damage response pathway involving p53 and MDM2.