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Inhibition of RNA polymerase II as a trigger for the p53 response
1Department of Radiation Oncology, University of Michigan Comprehensive Cancer Center, Ann Arbor 48109-0936, USA.
Abstract:
The mechanisms by which the p53 response is triggered following exposure to DNA-damaging agents have not yet been clearly elucidated. We and others have previously suggested that blockage of RNA polymerase II may be the trigger for induction of the p53 response following exposure to ultraviolet light. Here we report on the correlation between inhibition of mRNA synthesis and the induction of p53, p21WAF1 and apoptosis in diploid human fibroblasts treated with either UV light, cisplatin or the RNA synthesis inhibitors actinomycin D, DRB, H7 and alpha-amanitin. Exposure to ionizing radiation or the proteasome inhibitor LLnL, however, induced p53 and p21WAF1 without affecting mRNA synthesis. Importantly, induction of p53 by the RNA synthesis or proteasome inhibitors did not correlate with the induction of DNA strand breaks. Furthermore, cisplatin-induced accumulation of active p53 in repair-deficient XP-A cells occurred despite the lack of DNA strand break induction. Our results suggest that the induction of the p53 response by certain toxic agents is not triggered by DNA strand breaks but rather, may be linked to inhibition of mRNA synthesis either directly by the poisoning of RNA polymerase II or indirectly by the induction of elongation-blocking DNA lesions.
Insights
The p53 response, crucial for DNA repair, is triggered by inhibited mRNA synthesis, not DNA breaks, in human cells. This finding clarifies how toxic agents activate the p53 pathway.
Area of Science:
- Molecular Biology
- Cellular Biology
- Biochemistry
Background:
- The precise mechanisms initiating the p53 response after DNA damage remain unclear.
- Previous research suggests RNA polymerase II blockage may trigger p53 induction following UV exposure.
Purpose of the Study:
- To investigate the correlation between mRNA synthesis inhibition and p53 pathway activation.
- To determine if DNA strand breaks are the primary trigger for p53 induction.
Main Methods:
- Treatment of human fibroblasts with UV light, cisplatin, and various RNA synthesis inhibitors (actinomycin D, DRB, H7, alpha-amanitin).
- Exposure to ionizing radiation and proteasome inhibitor LLnL.
- Assessment of p53, p21WAF1 induction, apoptosis, mRNA synthesis, and DNA strand breaks.
Main Results:
- Inhibition of mRNA synthesis correlated with p53, p21WAF1 induction, and apoptosis upon treatment with UV light, cisplatin, or RNA synthesis inhibitors.
- Ionizing radiation and LLnL induced p53 and p21WAF1 without affecting mRNA synthesis.
- p53 induction by RNA synthesis or proteasome inhibitors did not correlate with DNA strand breaks.
Conclusions:
- The p53 response to certain toxic agents is likely linked to mRNA synthesis inhibition, not directly to DNA strand breaks.
- Inhibition may occur via direct RNA polymerase II poisoning or through elongation-blocking DNA lesions.