More than half of all human cancers are associated with mutations of the TP53 gene. In regard to the functional interaction with the remaining wild-type (WT) p53 allele, p53 mutations are classified into two types, recessive and dominant-negative (DN) mutations. The latter mutant protein has a DN activity over the remaining WT allele. We previously showed that the DN p53 mutant was useful as a predictor of poor outcome or a risk factor for metastatic recurrence in patients with some types of cancers, regardless of the presence or absence of loss of heterozygosity (LOH) of WT p53, suggesting that the DN p53 had 'gain-of-function (GOF)' activity besides the transdominance function. In this study, we investigated GOF activity of two DN p53 mutants which had a point mutation at codon 248 (R248Q and R248W), one of the hot spots, by transfecting them respectively into H1299 cells which originally expressed no p53 protein. Growth activity of the transfectants with the two mutants was not different from that of parent or Mock transfectants. Meanwhile, in vitro invasions of Matrigel and type I collagen gel by R248Q-transfectants were significantly higher than those by R248W-transfectants or the control cells. However, there were no differences in cell motile activities, expressions of extracellular matrix-degradative enzymes such as matrix metalloproteinases, urokinase-type plasminogen activator and heparanase, and their inhibitors, between R248Q-and R248W-transfectants. These findings indicate that the p53 mutants have a different quality in GOF activities even if the mutantions occurred at the same codon. And detailed information of the status of p53, including transdominancy and GOF activity, is expected to be useful for diagnosis and therapeutic strategy fitting the individual patients.TP53 tumor suppressor gene encodes a transcription factor (p53), which forms homotetramer and binds to DNA in a sequence-specific manner to transcribe target genes. It is well known that genotoxic stress induces the stabilization and activation of the p53 protein, resulting in apoptosis, inhibition of cellcycle progression, differentiation, senescence, or accelerated rates of DNA repair (18). More than half of all human cancers are associated with alterations of the TP53 gene (7). Most TP53 alterations are missense mutations, localized in the DNA-binding domain, and abolish the transcriptional activity via p53-responsive element. The residues such as R175, G245, R248, R249, R273 and R282 in the p53 protein are frequently mutated, which called "hot spots" (7). In their functional interactions with the remain-
