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Evidence for a second cell cycle block at G2/M by p53
N Stewart1, G G Hicks, F Paraskevas
1Manitoba Institute of Cell Biology, Manitoba Cancer Treatment and Research Foundation, Winnipeg, Canada.
Abstract:
Wild type p53 can induce cell cycle arrest at specific points in the cell cycle, in particular G1/S, an ability lost by most p53 mutants. We have previously reported that p53 mutant genes can rescue REF52 cells from ras-induced growth arrest and that over expression of wild type p53 inhibits cell growth in these cells. In this paper we examined whether p53 can also induce cell cycle arrest at the G2/M boundary of the cell cycle. To accomplish this we used the REF52 cell line and the temperature sensitive p53val135 mutant allele. Cells were enriched in the late G1 and early S phases before the temperature shift. REF52 cells expressing mutant-p53val135 alone with an activated H-ras gene arrest primarily at the G1/S and G2/M parts of the cell cycle at the restrictive temperature, as determined by flow cytometry analysis. These results suggest that the anti-proliferative activity of p53 may be involved in regulation of the cell cycle at the G2/M restriction point as well as transit through G1/S and initiation of DNA synthesis.
Insights
Wild type p53 induces cell cycle arrest. Mutant p53, when co-expressed with H-ras, also causes cell cycle arrest at G1/S and G2/M, suggesting p53
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Wild type p53 protein is known to arrest the cell cycle at G1/S.
- Most p53 mutants lose this cell cycle arrest ability.
- Previous studies showed p53 mutants can rescue cells from ras-induced arrest, while wild type p53 inhibits growth.
Purpose of the Study:
- To investigate if p53 can induce cell cycle arrest at the G2/M boundary.
- To analyze the role of p53 in cell cycle regulation at different checkpoints.
Main Methods:
- Utilized the REF52 cell line.
- Employed a temperature-sensitive p53val135 mutant allele.
- Enriched cells in late G1/early S phases before temperature shift.
- Analyzed cell cycle progression using flow cytometry.
Main Results:
- REF52 cells expressing mutant p53val135 and activated H-ras arrested at both G1/S and G2/M phases at the restrictive temperature.
- Flow cytometry confirmed these cell cycle arrest points.
Conclusions:
- p53's anti-proliferative activity is involved in regulating the G2/M checkpoint.
- p53 also plays a role in G1/S transit and DNA synthesis initiation.
- These findings highlight p53's multifaceted role in cell cycle control.