Similar incidence of K-ras mutations in lung carcinomas of FVB/N mice and FVB/N mice carrying a mutant p53 transgene.

Mutated p53 genes are capable of complementing activated ras genes in the transformation of primary rat embryo fibroblasts in vitro. Mutations in both genes have also been found in several human cancers, including lung carcinomas. We generated transgenic mice containing a p53 construct with a missense mutation in exon 5 (ala135val) to study the role of p53 mutations in lung tumorigenesis, and to facilitate identification of other genetic events that might complement p53 mutations in mouse lung carcinogenesis. The p53 transgenic lines exhibited a higher frequency of lethal lung tumors than the parental FVB/N strain. We examined the spontaneously-arising lung carcinomas from mice expressing the mutated p53 transgene for K-ras mutations using single-stranded conformation polymorphism (SSCP) and/or direct sequencing approaches. Fifteen of 29 (52%) carcinomas contained mutations in the K-ras oncogene. Six of 15 of the K-ras mutations were in codon 61 and 9/15 were in codon 12. Subsequent analysis of spontaneous lung carcinomas from mice of the FVB/N parental strain showed that 9/12 (75%) carcinomas examined contained K-ras mutations. Two of these were in codon 12, one in codon 13, and 6 were in codon 61. These results demonstrate that the frequency of ras mutations does not differ between the p53 FVB/N transgenic mice and their parental FVB/N strain but suggest that a high frequency of mutations K-ras can be correlated with lung tumorigenesis in both groups of mice.

Higher frequency of alterations in the p16/CDKN2 gene in squamous cell carcinoma cell lines than in primary tumors of the head and neck.

Sixty-eight primary head and neck squamous cell carcinomas and nine head and neck squamous cell carcinoma cell lines were examined for mutations and homozygous deletions of the p16/CDKN2 gene. Homozygous deletions of the p16/CDKN2 gene were found in three lines, and a mutation was detected in another cell line. In contrast, none of the primary tumors showed homozygous deletions and 11 of 68 tumors had missense or nonsense base changes. Seven tumors contained somatic mutations. Five tumors, including one that also had a somatic mutation, had a probable polymorphism at codon 140 leading to an amino acid change from Ala to Thr. Three of these also contained an apparent polymorphism at codon 98, which did not lead to an amino acid change. The frequency of mutations and deletions detected differs markedly between cell lines (44%) and primary tumors (10%) suggesting that while p16/CDKN2 may play a role in tumorigenesis in some head and neck squamous cell carcinomas, inactivation of p16/CDKN2 probably occurs more frequently in cell lines as a result of adaptation to cell culture.