Chromosome changes caused by alterations of p53 expression.

It has been proposed that p53 tumor-suppressor plays a key role in maintaining genome integrity in mammalian cells. We analyzed karyotype alterations in human and murine cell sublines expressing various exogenous human mutant (His175, Trp248, His273) or wild-type (wt) p53 cDNAs. In human pseudodiploid LIM1215 cells that contain two endogenous wt-p53 gene alleles, p53 mutants caused both an increase in the frequency of chromosome breaks and an emergence of hyperdiploid cells. Murine T12-/- and 10(1) fibroblasts lacking endogenous p53 expression have very unstable karyotypes and show a strong tendency to increase their ploidy levels during growth in culture. Transduction of a wt-p53 construct into p53-deficient cells inhibited an accumulation of highly polyploid cell variants. Transduction of mutant p53 did not show such an effect. Modification of endogenous and exogenous p53 expression by caffeine, which interferes with normal induction of p53 in response to DNA damage, showed no correlation between the induction of chromosome breaks and heteroploidy. We conclude that the caffeine- or mutant p53-induced increase in the frequency of chromosomal breaks in dividing LIM1215 cells is assonated with inactivation of wt-p53 function(s) responsible for control of G1 checkpoint and/or DNA repair, while numerical chromosome changes in these cells may be a result of elimination or modification of a separate p53 function, or due to gain-of-function activities of p53 mutants. p53 modifications may therefore cause chromosome instability by different pathways: (1) through changes in the system(s) preventing proliferation of cells with genomic alterations; and (2) by increasing the probability of events, such as chromosome non-disjunction and/or endoreduplication that can lead to chromosome gains.