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Distinct p53-mediated G1/S checkpoint responses in two NIH3T3 subclone cells following treatment with DNA-damaging
1Clinical Research Institute, National Health Research Institutes, VGH-Taipei, Taiwan, ROC.
Abstract:
N3T3 and P-3T3 cells, originally isolated from a NIH3T3 cell clone on the basis of their negative and positive transformation by v-Abl, v-Src and Bcr-Abl, were previously found to show distinct cyclin activity changes following 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment, which is anti-mitogenic for N-3T3 cells and mitogenic for P-3T3 cells. We have found in this study that, while the G1/S arrest and cell death induced by serum starvation and TPA treatment in N-3T3 cells did not involve p53-mediated checkpoint or apoptosis, N-3T3 and P-3T3 cells evidently responded differently in these aspects of cell cycle regulation to DNA-damaging agents, methylmethane sulfonate (MMS) and gamma-radiation. In N-3T3 cells, DNA damages elicit cell growth arrest at G1/S transition with concomitant accumulation of p53 and p53-inducible Waf1/Cip1 proteins and also signs of apoptosis such as DNA ladder patterns and apoptotic (subgenomic) peak in flow cytograph. Conversely, P-3T3 cells treated with the DNA-damaging agents showed no cell cycle interruption nor accumulation of p53 or Waf1/Cip1. However, both P-3T3 and N-3T3 cells showed the same p53 protein half-life of 40 min or less, the same wild-type p53 DNA sequence and the same co-immunoprecipitable cellular proteins in complexes with p53, suggesting that an alteration in a signal transduction pathway upstream of p53 might account for the evasion of p53-mediated G1 checkpoint in P-3T3 cells.
Insights
N3T3 cells undergo G1/S arrest and apoptosis upon DNA damage via p53, while P-3T3 cells evade this response. This difference in cell cycle regulation suggests an upstream signaling pathway alteration in P-3T3 cells.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- N3T3 and P-3T3 cells exhibit differential responses to 12-O-tetradecanoylphorbol-13-acetate (TPA), affecting cell cycle regulation.
- Previous studies noted distinct cyclin activity changes in N3T3 and P-3T3 cells post-TPA treatment.
Purpose of the Study:
- To investigate the differential responses of N3T3 and P-3T3 cells to DNA-damaging agents.
- To elucidate the role of p53-mediated checkpoints and apoptosis in these cellular responses.
Main Methods:
- Treatment of N3T3 and P-3T3 cells with DNA-damaging agents methylmethane sulfonate (MMS) and gamma-radiation.
- Analysis of cell cycle progression (G1/S arrest), apoptosis markers (DNA laddering, subgenomic peaks), and p53/Waf1/Cip1 protein levels.
- Assessment of p53 protein half-life, DNA sequence, and protein complex formation.
Main Results:
- N3T3 cells experienced G1/S arrest, p53 and Waf1/Cip1 accumulation, and apoptosis following DNA damage.
- P-3T3 cells showed no cell cycle interruption or p53/Waf1/Cip1 accumulation after DNA damage.
- Both cell types had similar p53 protein half-life, wild-type DNA sequence, and complex formation, indicating intact p53 function.
Conclusions:
- N3T3 cells activate p53-dependent G1 checkpoint and apoptosis in response to DNA damage.
- P-3T3 cells evade p53-mediated cell cycle arrest and apoptosis, suggesting a defect in the upstream signaling pathway.
- The distinct cellular responses highlight a critical difference in DNA damage response pathways between N3T3 and P-3T3 cells.