An autochthonous CRISPR activation screening platform for characterizing tissue-specific oncogene selection.

Human adenocarcinomas exhibit tissue-specific mutation and copy-number patterns that suggest diverse selective pressures and distinct oncogene dependencies. Here, we use our FiCASCan platform to test whether in vivo CRISPR activation screening can recapitulate oncogene selection during tumor initiation. Using CRISPRa-competent PPKS mice and intranasal or intraductal delivery of pooled lentivirus, we screen frequently amplified and mutated genes in autochthonous lung and pancreas cancer models. We observe strong selection for Egfr, Myc, Sox2, and Pik3cb activation in lung tumors and near-complete dominance of Myc in pancreatic tumors, revealing striking tissue-specific differences. In our model, Sox2 activation suppresses Nkx2-1 signaling and drives aggressive mucinous lung adenocarcinoma. MYC activation in the pancreas mirrors MYC amplification in human PDAC, including the emergence of an immune-cold microenvironment. Overall, our findings show that in vivo CRISPR activation screening faithfully captures oncogene selection and provides a powerful approach for studying tumor initiation and progression.