INTRODUCTION OF A MURINE P53 MUTATION CORRESPONDING TO HUMAN CODON-249 INTO A MURINE HEPATOCYTE CELL-LINE RESULTS IN GROWTH ADVANTAGE, BUT NOT IN TRANSFORMATION

The p53 gene is frequently mutated in human tumors; in hepatocellular carcinomas, there is a high frequency of a specific mutation at codon 249 in regions with significant anatoxin exposure, To assess the role of this p53 mutation in the development of hepatocellular carcinoma, a mutant murine p53 gene, p53ser246, which corresponds to human codon 2 49, was transfected into a differentiated, nontransformed hepatocyte c ell line AML12. Expression of p53ser246 in this line resulted in a gro wth advantage when compared with either a control vector (which contai ns a large p53 deletion) or with a different p53 mutant, val135, not f ound in hepatocellular carcinoma, Overall, there was a threefold incre ase in colony formation after transfection with p53ser246 as compared with the control or p53val135 vectors, and the p53ser246 plates develo ped consistently larger colonies. Whereas clones expressing the contro l or p53val135 constructs showed no significant morphological changes, clones expressing p53ser246 showed increased heterogeneity (large mul tinucleated cells and areas of small crowded cells) without focus form ation. In addition, the ser246 mutation imparted a growth advantage in serum-free media, suggesting less dependence on specific factors pres ent in serum, None of the mutant p53 or control lines were capable of growth in soft agar or tumor formation in nude mice, Thus in this mode l, in which endogenous wild-type p53 expression is retained, a high le vel of mutant p53 expression is not sufficient to transform hepatocyte s. Our findings indicate that p53ser246 has effects on hepatocytes tha t may result in a clonal growth advantage and suggest that additional factors are required for the development of hepatocellular carcinoma.