Deep sequencing characterizing mutations in Ras genes in mouse tissues after urethane exposure

Oncogenic mutations in HRAS, NRAS, and KRAS commonly occur in a wide spectrum of human cancers. These mutations are not uniform but instead have a tropism, namely the frequency, RAS isoform, position, and type of mutation are often unique to each cancer. This phenomenon is recapitulated in mice exposed to the environmental carcinogen urethane, which develop KrasQ61L/R-mutant pulmonary tumors. Taking advantage of this system to elucidate the underlying principles of RAS mutation tropism, here we adapted an error-corrected, high-throughput sequencing approach to detect mutations in the murine Kras gene at great sensitivity, capturing the initiating mutation following urethane exposure. Further, by sequencing Kras as well as Hras in this manner, and from different tissues and over time, we find that the specificity of urethane for CAN to CTN mutations, coupled with the sequence and transcription of Kras, to be major influences on the extreme tropism of this carcinogen.