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GM1492 human diploid skin fibroblasts lack the p53-dependent G1 cell-cycle checkpoint
T van Laar1, W T Steegenga, A G Jochemsen
1Laboratory of Molecular Carcinogenesis, Sylvius Laboratories, Leiden University, The Netherlands.
Abstract:
Recently, we reported that GM1492 human diploid skin fibroblasts derived from a Bloom's patient upon UV-C irradiation fail to increase p53 to a detectable level and nevertheless accumulate in the G1-phase of the cell-cycle. Here we show that in GM1492 cells other types of DNA-damaging agents also fail to induce p53 as well as WAF1, a p53-regulated gene product involved in G1 cell-cycle arrest. Furthermore, the p53-dependent G1 cell-cycle checkpoint is indeed defective in these cells: However, induction of GADD45 mRNA still occurs in GM1492 after irradiation with UV-C. Since GADD45 is known to inhibit the entry into S, these data suggest that the observed accumulation of GM1492 cells in G1 after UV-C irradiation occurs at the G1/S boundary and is due to an inhibition of initiation of DNA-replication.
Insights
Bloom
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Bloom's syndrome is a rare genetic disorder.
- DNA damage response pathways are crucial for cell cycle regulation.
- p53 and WAF1 are key regulators of the G1 cell cycle checkpoint.
Purpose of the Study:
- To investigate the DNA damage response in GM1492 cells from a Bloom's patient.
- To determine the role of p53 and WAF1 in cell cycle arrest after DNA damage.
- To elucidate the mechanism of G1 accumulation in GM1492 cells.
Main Methods:
- UV-C irradiation of GM1492 fibroblasts.
- Analysis of p53 and WAF1 protein and mRNA levels.
- Cell cycle analysis using flow cytometry.
- GADD45 mRNA induction assessment.
Main Results:
- GM1492 cells failed to induce p53 and WAF1 after UV-C and other DNA-damaging agents.
- The p53-dependent G1 cell cycle checkpoint was defective in GM1492 cells.
- GADD45 mRNA was induced by UV-C, suggesting G1/S boundary arrest.
Conclusions:
- GM1492 cells exhibit a defective p53-mediated G1 checkpoint.
- UV-C-induced G1 arrest in GM1492 cells is independent of p53 and WAF1.
- The G1 accumulation is likely due to inhibited DNA replication initiation at the G1/S boundary.