Human tumors with exonuclease domain mutations in the gene encoding DNA polymerase ε (POLE) have incredibly high mutation burdens. These errors arise in four unique mutation signatures occurring in different relative amounts, the etiologies of which remain poorly understood. We used CRISPR-Cas9 to engineer human cell lines expressing POLE tumor variants, with and without mismatch repair (MMR). Whole-exome sequencing of these cells after defined numbers of population doublings permitted analysis of nascent mutation accumulation. Unlike an exonuclease active site mutant that we previously characterized, POLE cancer mutants readily drive signature mutagenesis in the presence of functional MMR. Comparison of cell line and human patient data suggests that the relative abundance of mutation signatures partitions POLE tumors into distinct subgroups dependent on the nature of the POLE allele, its expression level, and MMR status. These results suggest that different POLE mutants have previously unappreciated differences in replication fidelity and mutagenesis.

编码 DNA 聚合酶 ε (POLE) 的基因中存在核酸外切酶结构域突变的人类肿瘤具有令人难以置信的高突变负担。这些错误出现在以不同相对量发生的四种独特突变特征中，其病因仍知之甚少。我们使用 CRISPR-Cas9 来工程化表达 POLE 肿瘤变体的人类细胞系，有或没有错配修复 (MMR)。在规定数量的群体倍增后对这些细胞进行全外显子组测序，可以分析新生突变的积累。与我们之前表征的核酸外切酶活性位点突变体不同，POLE 癌症突变体在功能性 MMR 存在的情况下很容易驱动特征突变。细胞系和人类患者数据的比较表明，突变特征的相对丰度将 POLE 肿瘤划分为不同的亚组，具体取决于 POLE 等位基因的性质、其表达水平和 MMR 状态。这些结果表明，不同的 POLE 突变体在复制保真度和诱变方面具有先前未被认识到的差异。