The presence of p53 mutations in human osteosarcomas correlates with high levels of genomic instability

Abstract

The p53 gene is a critical tumor suppressor that is inactivated in a majority of cancers. The central role of p53 in response to stresses such as DNA damage, hypoxia, and oncogene activation underlies this high frequency of negative selection during tumorigenic transformation. Mutations in p53 disrupt checkpoint responses to DNA damage and result in the potential for destabilization of the genome. Consistent with this, p53 mutant cells have been shown to accumulate genomic alterations in cell culture, mouse models, and some human tumors. The relationship between p53 mutation and genomic instability in human osteosarcoma is addressed in this report. Similar to some other primary human tumors, the mutation of p53 correlates significantly with the presence of high levels of genomic instability in osteosarcomas. Surprisingly, osteosarcomas harboring an amplification of the HDM2 oncogene, which inhibits the tumor-suppressive properties of p53, do not display high levels of genomic instability. These results demonstrate that the inactivation of p53 in osteosarcomas directly by mutation versus indirectly by HDM2 amplification may have different cellular consequences with respect to the stability of the genome.

Fig. 1.

Ideogram of CGH-detectable copy-number changes in 34 osteosarcoma tumors. Copy-number gains are depicted by thin gray lines to the right of each chromosome, high-level amplifications (approximately >5-fold) are depicted by thick gray bars, and losses are depicted by thin black lines to the left of each chromosome.

Fig. 2.

Genomic-instability scores. The instability score for each sample is the total number of gains, losses, and high-level amplifications detectable by CGH. The CGH data from 34 high-grade osteosarcoma tumors (Fig. 1 and Table 5) are shown by sample type.

Fig. 3.

p53 mutation, HDM2 amplification, and genomic-instability score. (a) Osteosarcoma tumors with genomic amplification of HDM2 or mutation of p53 are depicted with corresponding genomic-instability scores. (b) P-value determination for p53 status and genomic-instability score. The probability distribution curve depicts the distribution of the mean numbers of genomic changes of 12 p53 mutant tumors of 200,000 randomized trials. The filled area underneath the curve (shown by the arrow) highlights those trials that produced a higher or equal mean number of changes to the actual mean (19.1).

Fig. 4.

Instability scores for osteosarcoma tumor biopsies. p53 mutant and HDM2-amplified osteosarcoma tumor biopsies are depicted with genomic-instability scores.

Fig. 5.

Real-time quantitative PCR analysis of HDM2. The gene copy number for HDM2 for each tumor is shown relative to APP. Error bars represent SD.