Polymerase-Mediated Ultramutagenesis and Carcinogenesis in Mice

Mutations underlie all cancers, and their identification and study is the foundationof cancer biology. We describe a novel approach to mutagenesis and cancer studies based on the DNA polymerase e (POLE) ultramutator phenotype recently described in human cancers, where a single amino acid substitution (most commonly P286R) in the proofreading domain results in error-prone DNA replication. We engineered a conditional Pole P286R allele in mice. Pole P286R/+ embryonic fibroblasts exhibited a striking mutator phenotype and immortalized more efficiently. Pole P286R/+ mice were born at Mendelian ratios but rapidly developed lethal cancers of diverse lineages, yielding the most cancer-prone monoallelic model described to date. Comprehensive whole-genome sequencing analyses showed that the cancers were driven by high base substitution rates in the range of human cancers, overcoming a major limitation ofprevious murine cancer models. These data establish polymerase-mediated ultramutagenesis as an efficient in vivo approach for the generation of diverse animal cancer models that recapitulate the high mutational loads inherent to human cancers.