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Participation of p53 protein in the cellular response to DNA damage
M B Kastan1, O Onyekwere, D Sidransky
1Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Abstract:
The inhibition of replicative DNA synthesis that follows DNA damage may be critical for avoiding genetic lesions that could contribute to cellular transformation. Exposure of ML-1 myeloblastic leukemia cells to nonlethal doses of the DNA damaging agents, gamma-irradiation or actinomycin D, causes a transient inhibition of replicative DNA synthesis via both G1 and G2 arrests. Levels of p53 protein in ML-1 cells and in proliferating normal bone marrow myeloid progenitor cells increase and decrease in temporal association with the G1 arrest. In contrast, the S-phase arrest of ML-1 cells caused by exposure to the anti-metabolite, cytosine arabinoside, which does not directly damage DNA, is not associated with a significant change in p53 protein levels. Caffeine treatment blocks both the G1 arrest and the induction of p53 protein after gamma-irradiation, thus suggesting that blocking the induction of p53 protein may contribute to the previously observed effects of caffeine on cell cycle changes after DNA damage. Unlike ML-1 cells and normal bone marrow myeloid progenitor cells, hematopoietic cells that either lack p53 gene expression or overexpress a mutant form of the p53 gene do not exhibit a G1 arrest after gamma-irradiation; however, the G2 arrest is unaffected by the status of the p53 gene. These results suggest a role for the wild-type p53 protein in the inhibition of DNA synthesis that follows DNA damage and thus suggest a new mechanism for how the loss of wild-type p53 might contribute to tumorigenesis.
Insights
DNA damage triggers cell cycle arrest to prevent genetic errors. Wild-type p53 protein plays a key role in this process, influencing DNA synthesis inhibition and potentially preventing cancer.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- DNA damage can lead to genetic mutations and cellular transformation.
- Cell cycle regulation is crucial for preventing the propagation of DNA damage.
- The p53 protein is a key regulator involved in DNA damage response.
Purpose of the Study:
- To investigate the role of p53 protein in the inhibition of replicative DNA synthesis following DNA damage.
- To explore the relationship between p53 protein levels and cell cycle arrest (G1 and G2) in response to DNA damaging agents.
- To determine the effect of caffeine on p53 induction and cell cycle arrest after gamma-irradiation.
Main Methods:
- Exposure of ML-1 myeloblastic leukemia cells and normal bone marrow myeloid progenitor cells to DNA damaging agents (gamma-irradiation, actinomycin D, cytosine arabinoside).
- Analysis of p53 protein levels and cell cycle distribution (G1, S, G2 arrests).
- Assessment of caffeine's effects on G1 arrest and p53 induction.
- Comparison of responses in cells with wild-type p53, p53-null, or mutant p53.
Main Results:
- Gamma-irradiation and actinomycin D induced transient inhibition of DNA synthesis via G1 and G2 arrests in ML-1 cells.
- p53 protein levels increased with G1 arrest in ML-1 cells and normal myeloid progenitors after DNA damage.
- Cytosine arabinoside induced S-phase arrest without significant p53 changes.
- Caffeine blocked G1 arrest and p53 induction after gamma-irradiation.
- Cells lacking wild-type p53 did not exhibit G1 arrest after gamma-irradiation, but G2 arrest remained unaffected.
Conclusions:
- Wild-type p53 protein is involved in the G1 cell cycle arrest that inhibits DNA synthesis after DNA damage.
- Loss of wild-type p53 function may contribute to tumorigenesis by bypassing this critical checkpoint.
- p53-independent G2 arrest also occurs in response to DNA damage.