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Rapid ATM-dependent phosphorylation of MDM2 precedes p53 accumulation in response to DNA damage
R Khosravi1, R Maya, T Gottlieb
1Department of Human Genetics, Sackler School of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel.
Abstract:
The p53 tumor-suppressor protein, a key regulator of cellular responses to genotoxic stress, is stabilized and activated after DNA damage. This process is associated with posttranslational modifications of p53, some of which are mediated by the ATM protein kinase. However, these modifications alone may not account in full for p53 stabilization. p53's stability and activity are negatively regulated by the oncoprotein MDM2, whose gene is activated by p53. Conceivably, p53 function may be modulated by modifications of MDM2 as well. We show here that after treatment of cells with ionizing radiation or a radiomimetic chemical, but not UV radiation, MDM2 is phosphorylated rapidly in an ATM-dependent manner. This phosphorylation is independent of p53 and the DNA-dependent protein kinase. Furthermore, MDM2 is directly phosphorylated by ATM in vitro. These findings suggest that in response to DNA strand breaks, ATM may promote p53 activity and stability by mediating simultaneous phosphorylation of both partners of the p53-MDM2 autoregulatory feedback loop.
Insights
ATM protein kinase phosphorylates MDM2, enhancing p53 tumor suppressor stability and activity after DNA damage. This simultaneous phosphorylation of the p53-MDM2 feedback loop promotes cellular responses to genotoxic stress.
Area of Science:
- Molecular Biology
- Cellular Biology
- Cancer Research
Background:
- The p53 tumor-suppressor protein is crucial for cellular responses to genotoxic stress, undergoing stabilization and activation post-DNA damage.
- Posttranslational modifications, often ATM protein kinase-mediated, contribute to p53 stabilization, but may not fully explain the process.
- p53 stability and activity are negatively regulated by MDM2, an oncoprotein whose gene is p53-activated, suggesting MDM2 modifications could also modulate p53 function.
Purpose of the Study:
- To investigate whether MDM2 undergoes modifications influencing p53 function.
- To determine the role of ATM protein kinase in MDM2 phosphorylation in response to DNA damage.
- To elucidate the mechanism by which ATM influences the p53-MDM2 autoregulatory feedback loop.
Main Methods:
- Treatment of cells with ionizing radiation or a radiomimetic chemical, and UV radiation.
- Assessing MDM2 phosphorylation status.
- Investigating the dependence of MDM2 phosphorylation on ATM, p53, and DNA-dependent protein kinase.
- In vitro phosphorylation assays using purified ATM and MDM2.
Main Results:
- MDM2 is rapidly phosphorylated in an ATM-dependent manner after treatment with ionizing radiation or a radiomimetic chemical, but not UV radiation.
- MDM2 phosphorylation is independent of p53 and DNA-dependent protein kinase.
- ATM directly phosphorylates MDM2 in vitro.
Conclusions:
- ATM kinase promotes p53 activity and stability in response to DNA strand breaks.
- ATM mediates simultaneous phosphorylation of both p53 and MDM2.
- This dual phosphorylation impacts the p53-MDM2 autoregulatory feedback loop, enhancing cellular responses to genotoxic stress.