SUPPRESSION OF TUMORIGENIC AND METASTATIC POTENTIALS OF HUMAN-MELANOMA CELL-LINES BY MUTATED (143-VAL-ALA) P53

Metastatic melanoma, compared with other cancers, appears to be unusua l because of its low frequency of p53 mutations and prevalence of wild -type p53 protein in advanced malignancy. Here, we examined the effect s of wild-type and mutated p53 (143 Val-Ala) on tumorigenic and metast atic potential of two human melanoma cell lines. The cell line UISO-ME L-4 contains wild-type p53 and is tumorigenic, whereas UISO-MEL-6 lack s p53 and produces lung and liver metastasis upon s.c. injection into athymic mice. Our study showed that UISO-MEL-4 stably transfected with wild-type p53 cDNA driven by cytomegalovirus promoter-enhancer sequen ces expressed high levels of p53 and p21 and formed s.c. tumours in vi vo. Mutated p53 (143 Val-Ala) expression, on the other hand, inhibited tumour growth in 50% of cases and produced significantly slower growi ng non-metastatic tumours. Reduced tumour growth involved necrotic as well as apoptotic cell death. Inhibition of tumour growth was abrogate d by the addition of Matrigel (15 mg ml(-1)). With UISO-MEL-6 cells, s tably transfected with mutant p53, tumour growth was delayed and metas tasis was inhibited. In soft agar colony formation assay, both wild-ty pe and mutant p53 transfectants reduced anchorage-independent colony f ormation in vitro. These data suggest that mutated (143 Val-Ala) p53, which retains DNA binding and some of the transactivation functions of the wild-type p53 protein, suppresses tumorigenic and metastatic pote ntials of human melanoma cell lines in vivo.