Differential effects on tumor progression by APOBEC3A, APOBEC3B, and APOBEC3H Haplotype I in a breast cancer mouse xenograft model.

Introduction: The APOBEC3 family of cytidine deaminases induces somatic mutations that are highly prevalent in cancers, but the functional consequences remain largely unknown. Methods: To determine these consequences, we exposed MCF7 tumorigenic breast epithelial cells to APOBEC3A, APOBEC3B or APOBEC3H Haplotype I. Results: Comparative analysis between cells pre and post -APOBEC3 exposure revealed fewer deamination-dependent γH2AX foci post-APOBEC3 exposure, despite maintaining APOBEC3 protein expression. In a mouse xenograft model, high expressing, but not low expressing APOBEC3A-exposed cells caused increased tumor progression. In contrast, high expressing, but not low expressing APOBEC3B-exposed cells decreased tumor size. APOBEC3H Haplotype I-exposed cells stochastically increased tumor progression independent of expression levels. Consistent with tumor data, RNA-seq showed upregulation of tumor enhancing pathways only in cells that enhanced tumor progression. Discussion: The results indicate that in a breast cancer xenograft model, APOBEC3A and APOBEC3H Haplotype I are more likely to contribute to enhanced tumor progression than APOBEC3B.