Apoptosis in Small Intestinal Epithelial From p53-null Mice: Evidence for a Delayed, p53-independent G2/M-associated Cell Death After Gamma-Irradiation

Oncogene. 1997 Jun 12;14(23):2759-66. doi: 10.1038/sj.onc.1201126.

Abstract

The death of small intestinal epithelial cells has been characterized and quantitated after irradiation of mice rendered homozygously null for the p53 gene. In wild-type animals homozygous for p53 a rapid (4.5 h) elevation of p53 protein was observed in the proliferative compartment of the crypts after 8 Gy of irradiation. Cells underwent cell death by apoptosis in this region. We had reported previously a total repression of apoptosis in small intestinal crypt epithelia 4.5 h after the gamma-irradiation (8 Gy) of p53 homozygously null animals. Thus, while 400 apoptotic cells were observed in 200 half crypts taken from wild-type animals at 4.5 h, this fell to background levels (10-30) in the p53 null animals (Merritt et al., 1994) and did not increase by 12 h. However, we have now found a delayed initiation of a p53-independent apoptosis after 8 Gy of gamma-radiation: at 24 h, approximately 100 apoptotic cells were observed in 200 half crypts. This late wave of apoptosis was not observed after 1 Gy of gamma-radiation. The morphological appearance of this p53-independent apoptosis suggested that death may have arisen as the result of aberrant mitosis. Analysis of the regeneration of crypts 3 days after irradiation of mice with between 11 and 17 Gy showed that there was no significant increase (P=0.135) in the potential of clonogenic cells from the p53 null animals to repopulate the crypts. The data support the idea that a p53-independent apoptotic mechanism permits the engagement of apoptosis, probably by a mitotic catastrophe, after 8 Gy of gamma-irradiation in vivo and that a loss of p53 does not make these epithelial cells radioresistant in vivo to doses of 8 Gy and above. In contrast, irradiation with 1 Gy failed to induce a p53-independent apoptosis in vivo, suggesting that the p53 'sensor' of damage was more sensitive than that engaging the p53-independent mechanism of cell death.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / physiology*
  • Apoptosis / radiation effects
  • Clone Cells
  • DNA Replication
  • G2 Phase
  • Gamma Rays
  • Intestinal Mucosa / cytology*
  • Intestinal Mucosa / ultrastructure
  • Intestine, Small
  • Mice
  • Microscopy, Electron
  • Mitosis
  • Mitotic Index
  • Tumor Suppressor Protein p53 / physiology*

Substances

  • Tumor Suppressor Protein p53