RAS mutation patterns arise from tissue-specific responses to distinct oncogenic signaling

Abstract

Despite multiple possible oncogenic mutations in the proto-oncogene KRAS, unique subsets of these mutations are detected in different cancer types. As KRAS mutations occur early, if not being initiating, these mutational biases are ostensibly a product of how normal cells respond to the encoded oncoprotein. Oncogenic mutations can impact not only the level of active oncoprotein, but also engagement with effectors and other proteins. To separate these two effects, we generated four novel inducible Kras alleles encoded by the biochemically distinct mutations G12D versus Q61R encoded by native (nat) rare versus common (com) codons to produce either low or high protein levels. Each allele induced a distinct transcriptional response in normal cells. At one end of the spectrum, the KrasnatG12D allele induced transcriptional hallmarks suggestive of an expansion of multipotent cells, while at the other end, the KrascomQ61R allele exhibited all the hallmarks of oncogenic stress and inflammation. Further, this dramatic difference in the transcriptomes of normal cells appears to be a product of signaling differences due to increased protein expression as well as the specific mutation. To determine the impact of these distinct responses on RAS mutational patterning in vivo, all four alleles were globally activated, revealing that hematolymphopoietic lesions were sensitive to the level of active oncoprotein, squamous tumors were sensitive to the G12D mutant, while carcinomas were sensitive to both these features. Thus, we identify how specific KRAS mutations uniquely signal to promote the conversion of normal hematopoietic, epithelial, or squamous cells towards a tumorigenic state.