ACTIVATION OF THE K-RAS GENE BY INSERTION MUTATIONS IN CHEMICALLY-INDUCED RAT RENAL MESENCHYMAL TUMORS

Previously we reported the detection of transforming K-ras sequences i n methyl(methoxymethyl)nitrosamine (DMN-OMe)-induced rat renal mesench ymal tumors by NIH3T3 transfection assays. Subsequent analysis by sele ctive oligonucleotide hybridization revealed a variety of activating p oint mutations in codon 12 of K-ras in most of these tumors and in the ir NIH3T3 transformants, but in some, point mutations could not be det ected by this technique. In the current study, insertion mutations wer e detected in two DMN-OMe-induced tumors from this group with previous ly undefined transforming K-ras alterations. These primary tumors and their NIH3T3 transformants contained K-ras sequences with either a 9 b p or a 12 bp repeat in exon one, both of which included codon 12. No o ther mutations in the entire coding region of the K-ras gene were obse rved. Site-directed mutagenesis studies by others have determined that deletions and insertions near codon 12 can activate the ras gene, but this is the first demonstration of insertional activation of K-ras in a chemically induced rat tumor.