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Nitric oxide prevents gamma-radiation-induced cell cycle arrest by impairing p53 function in MCF-7 cells
L Chazotte-Aubert1, O Pluquet, P Hainaut
1Unit of Endogenous Cancer Risk Factors, Group of Molecular Carcinogenesis, International Agency for Research on Cancer, 150 Cours Albert Thomas, Lyon cedex 08, 69372, France
Abstract:
We previously reported that nitric oxide (NO) released from S-nitrosoglutathione induces conformational change of the p53 tumor-suppressor protein that impairs its DNA-binding activity in vitro. We now demonstrate that MCF-7 cells preincubated in the presence of 0.5-1 mM S-nitrosoglutathione for 4 h before gamma-irradiation failed to arrest in the G1 phase of the cell cycle, whereas those gamma-irradiated without S-nitrosoglutathione exhibited a normal cell cycle arrest. The S-nitrosoglutathione-treated cells did not express the p53 target gene p21(waf-1) after gamma-irradiation, although p21(waf-1) was strongly expressed in cells irradiated in the absence of S-nitrosoglutathione. These results strongly suggest that NO impairs the function of p53 possibly via conformational change and/or amino acid modifications. On the other hand, cells incubated for 16 h in the presence of 1 mM S-nitrosoglutathione underwent apoptosis with accumulation of the pro-apoptotic protein Bax. This Bax accumulation, however, was shown to occur via a p53-independent pathway.
Insights
Nitric oxide (NO) impairs tumor suppressor p53 function, preventing cell cycle arrest after gamma irradiation. NO also induces apoptosis through a p53-independent pathway involving Bax accumulation.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Nitric oxide (NO) is a signaling molecule with diverse cellular functions.
- The tumor suppressor protein p53 plays a critical role in cell cycle regulation and apoptosis.
- Previous in vitro studies indicated NO impairs p53 DNA-binding activity.
Purpose of the Study:
- To investigate the in vivo effect of NO on p53 function in cancer cells.
- To determine the impact of NO on cell cycle progression and apoptosis following DNA damage.
- To elucidate the mechanisms by which NO affects p53-mediated cellular responses.
Main Methods:
- MCF-7 cells were treated with S-nitrosoglutathione (a NO donor) prior to gamma irradiation.
- Cell cycle progression was analyzed using flow cytometry.
- Expression of p53 target genes (e.g., p21(waf-1)) and apoptotic proteins (e.g., Bax) was assessed.
Main Results:
- S-nitrosoglutathione pre-treatment blocked G1 cell cycle arrest in gamma-irradiated MCF-7 cells.
- p21(waf-1) expression was suppressed in NO-treated cells post-irradiation.
- Long-term NO exposure induced apoptosis via Bax accumulation through a p53-independent mechanism.
Conclusions:
- NO disrupts p53 tumor suppressor function, leading to impaired cell cycle control after DNA damage.
- NO can induce apoptosis independently of p53, suggesting alternative signaling pathways are involved.
- These findings highlight NO's complex role in cancer cell response to genotoxic stress.