P53 MUTATIONS IN MAMMARY-TUMOR CELL-LINES AND CORRESPONDING TUMOR-TISSUES IN THE DOG

Alterations in the p53 gene are frequently observed in a wide variety of human cancers. To elucidate the role of p53 in tumorigenesis of the dog, we analyzed nine mammary tumor cell lines, and the primary or me tastatic tumors used for their establishment, for the presence of geno mic p53 abnormalities. Possible genomic rearrangements were analyzed b y Southern blotting using a canine cDNA probe. More subtle alterations were identified by single strand conformation polymorphism (SSCP) ana lysis for, which we partially characterized the canine p53 gene (codon 109-388 as compared to the human gene). The presence of mutations in SSCP fragments with altered mobility was confirmed by DNA sequencing. Three of the nine cell lines showed a mutated p53 gene. All were misse nse mutations accompanied by loss of the wild type allele. The point m utations, at codon 176 (TGC --> TTC), 236 (TAC --> AAC) and 245 (GGC - -> GCC), were all located in one of the four regions that are frequent ly affected in human cancers. Analysis of the DNA extracted from the t umors of origin demonstrated the presence of two of these point mutati ons. These findings indicate the involvement of the p53 gene in the ge nesis of canine tumors in a way comparable to that of human tumors.