CLONAL VARIATION OF P53 EXPRESSION AND PROLIFERATIVE PHENOTYPE IN A253 SQUAMOUS CARCINOMA-CELLS

Loss of normal p53 tumor-suppressor gene function is characteristic of the majority of squamous carcinomas. During the course of gene transf er studies in the human squamous carcinoma cell line, A253, which does not express p53 mRNA or protein, we incidentally observed increased l evels of p53 expression in up to 20% of clonal cell lines derived from parental A253 cells. p53-expressing A253 cells (A253-p53) were also i solated by dilutional cloning. Nuclear p53 protein was identified by i mmunohistochemistry in A253-p53 cells in a wild-type pattern, and p53 mRNA (2.5 kb) was demonstrated by northern blot. Mutational analysis o f the p53 gene in A253-p53 cells revealed no evidence for mutations in exons 5-9. A253-p53 cells could be distinguished from native A253 cel ls by prolonged doubling times (2-5 fold) and by a marked reduction of [H-3]-thymidine uptake. Whereas A253 cells were unresponsive to the g rowth-inhibitory effects of TGF-beta, EGF-stimulated A253-p53 cells re sponded to TGF-beta with markedly reduced DNA synthetic rates. A253-p5 3 cells cocultured with A253 demonstrated enhanced cell growth and DNA synthesis rates compared to control A253-p53 cells. Finally, A253-p53 cells show reduced expression of c-fos, fibronectin, thrombospondin a nd parathyroid hormone-related protein (PTHrP) mRNAs. PTHrP measured b y RIA in conditioned medium was approximate to 300 pM for A253 but und etectable for A253-p53. We conclude that the A253 cell line contains a subpopulation of cells which express high levels of ''wild-type-like' ' p53 protein. This results in dramatic changes in gene expression and a slower-growing phenotype in vitro. Copyright (C) 1996 Elsevier Scie nce Inc.