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Sensitivity and selectivity of the DNA damage sensor responsible for activating p53-dependent G1 arrest
L C Huang1, K C Clarkin, G M Wahl
1Gene Expression Laboratory, The Salk Institute, San Diego, CA 92037, USA.
Abstract:
The tumor suppressor p53 contributes to maintaining genome stability by inducing a cell cycle arrest or apoptosis in response to conditions that generate DNA damage. Nuclear injection of linearized plasmid DNA, circular DNA with a large gap, or single-stranded circular phagemid is sufficient to induce a p53-dependent arrest. Supercoiled and nicked plasmid DNA, and circular DNA with a small gap were ineffective. Titration experiments indicate that the arrest mechanism in normal human fibroblasts can be activated by very few double strand breaks, and only one may be sufficient. Polymerase chain reaction assays showed that end-joining activity is low in serum-arrested human fibroblasts, and that higher joining activity occurs as cells proceed through G1 or into S phase. We propose that the exquisite sensitivity of the p53-dependent G1 arrest is partly due to inefficient repair of certain types of DNA damage in early G1.
Insights
The tumor suppressor p53 induces cell cycle arrest upon DNA damage. This p53-dependent arrest is sensitive to double-strand breaks, potentially due to inefficient DNA repair in early G1.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- The p53 protein is a critical tumor suppressor involved in maintaining genome stability.
- p53 responds to DNA damage by initiating cell cycle arrest or apoptosis.
- Understanding the triggers and mechanisms of p53 activation is crucial for cancer research.
Purpose of the Study:
- To investigate the specific types of DNA damage that activate the p53-dependent cell cycle arrest.
- To determine the sensitivity of the p53 arrest mechanism to the quantity of DNA damage.
- To explore the role of DNA repair efficiency in early G1 phase in p53 activation.
Main Methods:
- Nuclear injection of various forms of plasmid DNA (linearized, gapped, circular, supercoiled) into human fibroblasts.
- Titration experiments to assess the minimum DNA damage required for p53-dependent arrest.
- Polymerase chain reaction (PCR) assays to measure DNA end-joining activity in different cell cycle phases.
Main Results:
- Linearized plasmid DNA, circular DNA with a large gap, and single-stranded circular phagemid induced p53-dependent arrest.
- Supercoiled plasmid DNA, nicked plasmid DNA, and circular DNA with a small gap were ineffective.
- The p53 arrest mechanism is highly sensitive, potentially activated by a single double-strand break.
- DNA end-joining activity was low in serum-arrested fibroblasts and increased during G1 and S phases.
Conclusions:
- The p53-dependent G1 arrest is specifically triggered by certain types of DNA damage, notably double-strand breaks.
- The high sensitivity of this arrest pathway may be linked to inefficient DNA repair mechanisms in early G1.
- These findings provide insights into the intricate regulation of genome stability by the p53 pathway.