p53 gain-of-function cancer mutants induce genetic instability by inactivating ATM

Abstract

Tp53 is the most commonly mutated tumour-suppressor gene in human cancers. In addition to the loss of tumour-suppression function, some missense mutants gain novel oncogenic activities. To elucidate the nature of the gain of function, we introduced the most common p53 cancer mutations (R248W and R273H) independently into the humanized p53 knock-in (HUPKI) allele in mice. Tumour-suppressor functions of p53 are abolished in p53-mutant mice. Several lines of evidence further indicate gain-of-function of p53 mutants in promoting tumorigenesis. p53(R248W) mice rapidly succumb to certain types of cancers not commonly observed in p53(-/-) mice. Interchromosomal translocations, a type of genetic instability rarely observed in p53(-/-) cells, are readily detectable in p53-mutant pre-tumor thymocytes. Although normal in p53(-/-) mouse cells, the G(2)-M checkpoint is impaired in p53-mutant cells after DNA damage. These acquired oncogenic properties of mutant p53 could be explained by the findings that these p53 mutants interact with the nuclease Mre11 and suppress the binding of the Mre11-Rad50-NBS1 (MRN) complex to DNA double-stranded breaks (DSBs), leading to impaired Ataxia-telangiectasia mutated (ATM) activation. Therefore, p53 gain-of-function mutants promote tumorigenesis by a novel mechanism involving active disruption of critical DNA damage-response pathways.

Mutant mouse p53 transgene elevates the chemical induction of tumors that respond to gene silencing with siRNA

“…The mutant p53 could exert its activity over p21 expression in a dominant-negative manner. 12,16,36 We examined p21 expression in the mp53 mouse embryonic fibroblasts after irradiation with 7 Gy. The level of p21 protein in wild-type cells increased with time, reaching a peak 6 h after irradiation, whereas the level of p21 protein in mp53 cells increased only slightly at 3 h and then gradually decreased (Figure 2).…”

“…As the allelic loss of wild-type p53 tends to occur in tumors formed in p53 heterozygous mice with a mutation on one side, [10][11][12] we examined the loss of wild-type p53 alleles in tumors developed in the mp53 mice. As determined by PCR, the wild-type p53 gene was retained in all 20 MCA-induced tumors in the mp53 mice (data not shown).…”

“…Mice carrying p53 mutated at codon135 are highly sensitive to spontaneous 7,8 and chemical tumor induction. 9 Mice carrying p53 mutations analogous to the human Li-Fraumeni syndrome hot spot mutation exhibit a high incidence of spontaneous tumors with a spectrum different from that of p53-null mice, [10][11][12] a high metastatic potential for produced tumors 13 and a high incidence of chemically induced tumors. 14 Especially of note is an approach toward simulating the human context with heterozygous mice containing human p53 and Li-Fraumeni mutant p53 in the genome.…”

“…14 Especially of note is an approach toward simulating the human context with heterozygous mice containing human p53 and Li-Fraumeni mutant p53 in the genome. 12 At the initial step of carcinogenesis caused by p53 mutation, there must exist a heterozygous state of wildtype p53 with mutant p53, resulting in the expression of both types of p53 proteins. Mutant p53 proteins act in a dominant-negative manner by interfering with the activity of wild-type p53 proteins, thus exerting gain-of-function activity.…”

“…Mutant p53 proteins act in a dominant-negative manner by interfering with the activity of wild-type p53 proteins, thus exerting gain-of-function activity. 12,15,16 This activity induces tumor formation by interfering with the ATM-controlled molecular network protecting cells from tumorigenesis. A recent study reported that mutant p53 interferes with the binding of the repair protein complex, Mre11-Rad50-NBS1, to radiation-induced DNA double strand breaks, 12 suggesting an additional role of mutant p53 in DNA repair and tumorigenesis.…”