The tumor suppressor protein p53 regulates the sensitivity of embryos to such human teratogens as ionizing radiation, diabetes, and cytostatics. Yet, the molecular mechanisms whereby it fulfills this function remain undefined. We used p53 heterozygous (p53+/−) female mice mated with p53+/− males and then exposed to cyclophosphamide (CP) to test whether caspases 3, 8, and 9 and the transcription factor nuclear factor (NF)-κB may serve as p53 targets. Mice were exposed to CP on day 12 of pregnancy and killed on days 15 and 18 of pregnancy to evaluate CP-induced teratogenic effect. The brain and limbs of embryos harvested 24 h after CP treatment were used to evaluate NF-κB (p65) DNA-binding activity by an ELISA-based method, the activity of the caspases by appropriate colorimetric kits, apoptosis, and cell proliferation by TUNEL, and 5′-bromo-2′-deoxyuridine incorporation respectively. We observed that the activation of caspases 3, 8, and 9 and the suppression of NF-κB DNA binding following CP-induced teratogenic insult took place only in teratologically sensitive organs of p53+/+ but not p53−/− embryos. CP-induced apoptosis and suppression of cell proliferation were also more intensive in the former, and they exhibited a higher incidence of structural anomalies, such as open eyes, digit, limb, and tail anomalies. The analysis of the correlations between the p53 embryonic genotype, the activity of the tested molecules, and the CP-induced dysmorphic events at the cellular and organ level suggests caspases 3, 8, and 9 and NF-κB as components of p53-targeting mechanisms in embryos exposed to the teratogen.
Structure of the p53/RNA polymerase II assembly