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Nitric oxide-induced p53 accumulation and regulation of inducible nitric oxide synthase expression by wild-type p53
K Forrester1, S Ambs, S E Lupold
1Laboratory of Human Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255, USA.
Abstract:
The tumor suppressor gene product p53 plays an important role in the cellular response to DNA damage from exogenous chemical and physical mutagens. Therefore, we hypothesized that p53 performs a similar role in response to putative endogenous mutagens, such as nitric oxide (NO). We report here that exposure of human cells to NO generated from an NO donor or from overexpression of inducible nitric oxide synthase (NOS2) results in p53 protein accumulation. In addition, expression of wild-type (WT) p53 in a variety of human tumor cell lines, as well as murine fibroblasts, results in down-regulation of NOS2 expression through inhibition of the NOS2 promoter. These data are consistent with the hypothesis of a negative feedback loop in which endogenous NO-induced DNA damage results in WT p53 accumulation and provides a novel mechanism by which p53 safeguards against DNA damage through p53-mediated transrepression of NOS2 gene expression, thus reducing the potential for NO-induced DNA damage.
Insights
The tumor suppressor p53 accumulates in response to nitric oxide (NO), a potential endogenous mutagen. Wild-type p53 then down-regulates NOS2, reducing NO-induced DNA damage and safeguarding cells.
Area of Science:
- Molecular Biology
- Cellular Biology
- Genetics
Background:
- The tumor suppressor p53 is crucial for cellular responses to DNA damage from external mutagens.
- The role of p53 in response to endogenous mutagens like nitric oxide (NO) is not well understood.
Purpose of the Study:
- To investigate the role of p53 in response to endogenous mutagens, specifically nitric oxide (NO).
- To elucidate the regulatory relationship between p53 and inducible nitric oxide synthase (NOS2).
Main Methods:
- Exposure of human cells to nitric oxide (NO) donors or overexpression of inducible nitric oxide synthase (NOS2).
- Analysis of p53 protein accumulation and NOS2 expression levels.
- Investigation of NOS2 promoter activity in response to wild-type (WT) p53 expression.
Main Results:
- Exposure to NO led to p53 protein accumulation in human cells.
- Expression of WT p53 resulted in down-regulation of NOS2 expression.
- WT p53 inhibited the NOS2 promoter, indicating transcriptional regulation.
Conclusions:
- A negative feedback loop exists where endogenous NO-induced DNA damage triggers p53 accumulation.
- p53 safeguards against DNA damage by trans-repressing NOS2 gene expression, thereby reducing NO-induced DNA damage potential.