Profile of p53 expression in bladder and oral tumours. Effects of in vitro manipulations of p53 on the behaviour of established human tumour cell lines

In this investigation the profile of p53 and epidermal growth factor receptor (EGFR) expression in tumour tissue biopsies of transitional cell carcinoma of bladder (TCC) and of oral-pharyngeal carcinoma (OP) were compared using an immunocytochemical staining method. In addition, various techniques including sodium dodecyl sulphate-polyacrylamide gel elecrophoresis (SDS-PAGE), colorimetric assay and gene transfection were used to investigate the influence of p53 on the behaviour of human tumour cell lines in vitro. The results showed that: (a) p53 was detectable in more than 45% of cases in both tumour types, although the profile and intensity of expression differed. (b) Concomitant strong expression of EGFR and p53 for TCC and OP was 21% and 38% (P>0.05%), respectively. (c) Treatment of tumour cells by either gamma radiation or by cisplatin resulted in the induction of p53 independent of the origin of the tumour. (d) Susceptibility of two cell lines, one with and one without constitutive expression of p53 showed that the expressing cells were more sensitive to gamma radiation (the percentage inhibition at 250 cGy was 57% versus -15%, P<0.01), and also cisplatin (the percentage inhibition at 1 microgram/ml was 71.0+/-6.0 versus 2.6+/-7.0, P<0.001). (e) Transfection of wild-type TP53 gene into a bladder tumour cell line resulted in a rapid cell apoptosis (by as much as 90%) whereas cells receiving mutated TP53 survived. A similar frequency of TP53 mutation in TCCs and OPs was observed. In addition, the pattern of p53 expression within the squamous type of TCC was similar to that in OPs. If the data from the in vitro studies could be translated into an in vivo setting, one could envisage a situation where the introduction of wild-type TP53 gene by gene transfection into tumour cells (independent of their TP53 gene mutational status), would prove to be beneficial. If the cellular TP53 gene is mutated, then an introduction of the normal TP53 gene would induce cells to undergo apoptosis. Alternatively, if TP53 is wild-type, then the increased levels of p53 expression would enable the cells to become more susceptible to DNA damaging treatments such as cisplatin or gamma radiation.