THE EFFECT OF DIFFERENT TP53 MUTATIONS ON THE CHROMOSOMAL STABILITY OF A HUMAN COLONIC ADENOMA DERIVED CELL-LINE WITH ENDOGENOUS WILD-TYPE TP53 ACTIVITY, BEFORE AND AFTER DNA-DAMAGE

We examined the effect of loss of wild type TP53 activity on the chrom osomal stability of a human colonic adenoma derived cell line (designa ted AA/Cl) by studying transfected variants which express different TP 53 mutations. Using gross chromosomal aberrations as a measure of inst ability, we studied metaphase spreads of a vector control cell line (A A/PCMV) and variants expressing the 143(Val-Ala) mutation, which retai n endogenous wild type TP53 activity, or the 273(Arg-His) TP53 mutatio n, which acts as a dominant negative. It was found that the proportion of cells with more than 4% aberrations was significantly greater in t he AA/273p53/B cell line (an approximate 5-Fold increase) than in the vector control or the AA/143p53/A cell line. To investigate whether lo ss of TP53 dependent checkpoints also predisposed the cells to accumul ate persistent chromosomal aberrations after DNA damage, cells were ex posed to 5 Gy gamma radiation. Regardless of TP53 status, cells with r adiation induced chromosomal damage were eliminated through a TP53 ind ependent mechanism, suggesting that loss of TP53 activity did not perm it the survival of these cells. In contrast, when exposed to low level gamma radiation (0.2 Gy), decreased wild type TP53 function and/or ex pression of mutant TP53 protein led to increased radioresistance (both in the non-dominant as well as the dominant mutant expressing cell li nes). These findings suggest that loss of TP53 activity and/or acquisi tion of specific TP53 mutations can increase chromosomal instability a nd resistance to low level DNA damage in human colonic adenoma cells. This study emphasises the different biological consequences of individ ual TP53 mutations on the genotype of premalignant colorectal epitheli al cells and subsequent implications for tumorigenic progression. (C) 1997 Wiley-Liss, Inc.