Molecular dynamics driving phenotypic divergence among KRAS mutants in pancreatic tumorigenesis

Inflammation in the pancreas drives acinar-to-ductal metaplasia (ADM), a progenitor-like state that can be hijacked by mutant Kras in the formation of pancreatic cancer (PDAC). How these cell fate decisions vary according to KRAS mutation remains poorly understood. To define mutation-specific lineage reversion and tumor initiation, we implement novel Ptf1a-TdTomato mice and multiple KRAS mutants across an array of genetic, pharmacologic, and inflammatory perturbations in vivo. Whereas KRASG12D co-opts injury to enable lineage reversion, enhancer reprogramming, and tumor initiation, KRASG12R/V can initiate but not sustain dedifferentiated and neoplastic transcriptional and epigenetic programs. We find the KRASG12R/V defects consist of a failure to invoke robust EGFR signaling and activate Rac1/Vav1, with constitutive Akt activation in vivo sufficient to rescue the tumorigenic potential of KRASG12R. As the marked heterogeneity among KRAS variants begins early in tumorigenesis, these data are crucial to understanding mutation-specific oncogenic trajectories and directing the implementation of KRAS-directed therapeutics. SIGNIFICANCEDefining how KRAS mutants drive distinct outcomes in human pancreatic cancer is critical for developing allele-specific therapeutic approaches. This study unveils a hierarchy among KRASG12D, KRASG12V, and KRASG12R to drive tumor initiation, owing to heterogeneous activation of EGFR, PI3K/AKT, and RAC1 signaling, thus revealing mutation-specific evolutionary paths in pancreatic tumorigenesis.