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DNA strand breaks: the DNA template alterations that trigger p53-dependent DNA damage response pathways
1Johns Hopkins Oncology Center, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287.
Molecular and Cellular Biology
|March 1, 1994
Summary
DNA strand breaks are sufficient and likely necessary for inducing the tumor suppressor protein p53 in cells with wild-type p53 alleles when exposed to DNA-damaging agents.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- The tumor suppressor protein p53 regulates cell cycle checkpoints and apoptosis in response to DNA damage.
- The precise mechanism of p53 induction by DNA-damaging agents is not fully understood.
- It remains unclear if DNA template damage is essential for initiating the p53 signaling pathway.
Purpose of the Study:
- To investigate the role of DNA strand breaks in the induction of p53 protein levels.
- To determine if DNA lesions other than strand breaks can trigger p53 elevation.
- To elucidate the signaling pathway leading to p53 activation by DNA-damaging agents.
Main Methods:
- Exposure of human cell lines with wild-type p53 to various DNA-damaging agents (ionizing radiation, bleomycin, topoisomerase inhibitors, PALA, UV light).
- Assessment of p53 protein levels and DNA strand breaks.
- Introduction of nucleases into cells via electroporation to directly induce DNA strand breaks.
- Comparison of p53 induction in normal and excision repair-deficient xeroderma pigmentosum cells.
Main Results:
- Agents inducing rapid DNA strand breaks (ionizing radiation, bleomycin) caused rapid p53 elevations.
- Camptothecin-induced topoisomerase I-DNA complex trapping alone was insufficient; replication-associated strand breaks were required.
- N(phosphonoacetyl)-L-aspartate (PALA) treatment led to delayed p53 increases correlated with DNA strand breaks.
- Electroporation of nucleases directly stimulated rapid p53 elevations, indicating sufficiency of DNA strand breaks.
- UV-induced thymine dimers did not directly induce p53; strand breaks during excision repair did.
Conclusions:
- DNA strand breaks are sufficient to initiate p53-dependent signal transduction.
- DNA strand breaks are likely necessary for p53 induction by DNA-damaging agents in wild-type p53 cells.
- Lesions other than strand breaks do not appear to directly trigger p53 induction.