The magnitude of methylmercury-induced cytotoxicity and cell cycle arrest is p53-dependent

✍ Scribed by Elizabeth J. Gribble; Sung-Woo Hong; Elaine M. Faustman

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 395 KB
• Volume: 73
• Category: Article
• ISSN: 1542-0752
• DOI: 10.1002/bdra.20104

✦ Synopsis

BACKGROUND: Methylmercury (MeHg), a ubiquitous environmental contaminant, is a known potent teratogen selectively affecting the developing central nervous system. While a definitive mechanism for MeHginduced developmental neurotoxicity remains elusive, in utero exposure has been associated with reduced brain weight and reduction in cell number. This suggests early toxicant interference with critical molecular signaling events controlling cell behavior, i.e., proliferation. METHODS: To examine the role of p53, a major regulator of the G 1 /S and G 2 /M cell cycle checkpoints, in MeHg toxicity, we isolated GD 14 primary embryonal fibroblasts from homozygous wild-type p53 (p53ϩ/ϩ) and homozygous null p53 (p53-/-) mice. Cells were treated at passages 4 -7 for 24 or 48 hr with 0, 1.0, or 2.5 M MeHg and analyzed for effects on viability, cell cycle progression (using BrdU-Hoechst flow cytometric analysis), and apoptosis via annexin V-FITC and propidium iodide (PI) staining. RESULTS: The p53ϩ/ϩ cells are more sensitive than p53-/-cells to MeHginduced cytotoxicity, cell cycle inhibition, and induction of apoptosis: at 24 hr, 2.5 M MeHg reduced p53ϩ/ϩ cell viability to 72.6% Ϯ 3.2%, while p53-/-viability was 94.6% Ϯ 0.4%. The p53-/-cells underwent less necrosis and less apoptosis following MeHg treatment. MeHg (2.5 M) also halted all cycling in the p53ϩ/ϩ cells, while 42.6% Ϯ 7.2% of p53-/-cells were able to reach a new G 0 /G 1 in 48 hr. Time-and dose-dependent accumulation of cells in G 2 /M phase (1.0 and 2.5 M MeHg) was observed independent of the p53 genotype; however, the magnitude of change was p53-dependent. CONCLUSIONS: These studies suggest that MeHginduced cell cycle arrest occurs via both p53-dependent and -independent pathways in our model system; however, cell death resulting from MeHg exposure is highly dependent on p53.