Roles of p53 mutation in cell line establishment and identification of the minimum transactivation and transform...

The mutation of the p53 tumour suppressor gene is the most frequently recognised genetic alteration in human cancer. We recently showed that the frequency of p53 gene mutations in oral squamous cell carcinomas (SCCs) from which cell lines were established (group A) did not significantly differ from that in SCCs from which cell lines could not be established (group B), suggesting that the presence of a p53 mutation by itself is not sufficient. To assess the relevance of p53 mutations to cell line establishment, we determined sequences of the mutated genes, constructed the expression plasmids, and compared biological and biochemical activities. Both groups contained typical mutant type mutations at a similar frequency. However, two mutations in group A had strong transforming activity. One of the mutants, codon 306 Stop mutant with C-terminal truncation, was found to have the transactivation and transform suppression activities similar to wild type. The minimum transactivation and transform suppression domains of p53 were thus determined based on analysis of various C-terminal deletions. Activity disappeared between codons 300 and 282, an interval which contains the C-terminal end of the sequence-specific DNA binding domain, which suggests that the DNA binding domain is essential for the above activities.