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Activation of the ATM kinase by ionizing radiation and phosphorylation of p53
C E Canman1, D S Lim, K A Cimprich
1The Johns Hopkins School of Medicine, Oncology Center, Baltimore, MD 21205, USA.
Abstract:
The p53 tumor suppressor protein is activated and phosphorylated on serine-15 in response to various DNA damaging agents. The gene product mutated in ataxia telangiectasia, ATM, acts upstream of p53 in a signal transduction pathway initiated by ionizing radiation. Immunoprecipitated ATM had intrinsic protein kinase activity and phosphorylated p53 on serine-15 in a manganese-dependent manner. Ionizing radiation, but not ultraviolet radiation, rapidly enhanced this p53-directed kinase activity of endogenous ATM. These observations, along with the fact that phosphorylation of p53 on serine-15 in response to ionizing radiation is reduced in ataxia telangiectasia cells, suggest that ATM is a protein kinase that phosphorylates p53 in vivo.
Insights
The ATM gene product phosphorylates the p53 tumor suppressor protein at serine-15, a key step in DNA damage response. This protein kinase activity is enhanced by ionizing radiation, suggesting ATM
Area of Science:
- Molecular Biology
- Cellular Signaling
- Cancer Research
Background:
- p53 is a crucial tumor suppressor protein activated by DNA damage.
- Ataxia telangiectasia is a genetic disorder linked to mutations in the ATM gene.
- DNA damage response pathways involve complex signaling cascades.
Purpose of the Study:
- To investigate the role of ATM (ataxia telangiectasia mutated) in the phosphorylation of p53.
- To determine if ATM possesses intrinsic protein kinase activity towards p53.
- To elucidate the signaling pathway initiated by ionizing radiation involving ATM and p53.
Main Methods:
- Immunoprecipitation of ATM protein.
- In vitro kinase assays using immunoprecipitated ATM.
- Analysis of p53 phosphorylation at serine-15.
- Comparison of ATM activity in normal and ataxia telangiectasia cells.
Main Results:
- Immunoprecipitated ATM demonstrated intrinsic protein kinase activity.
- ATM phosphorylated p53 on serine-15 in a manganese-dependent manner.
- Ionizing radiation, but not UV radiation, rapidly enhanced ATM's p53-directed kinase activity.
- Phosphorylation of p53 on serine-15 was reduced in ataxia telangiectasia cells.
Conclusions:
- ATM functions as a protein kinase that phosphorylates p53 in vivo.
- ATM is a critical component of the signal transduction pathway activated by ionizing radiation.
- The findings provide insight into the molecular mechanisms underlying DNA damage response and cancer predisposition.