Abstract 104: The role of APOBEC3A in ovarian cancer progression
Authors: Devenport Jessica Merritt , Mullen Mary , Fuh Katherine , Green Abby 
Published: June 2023

Abstract
Cancer progression is enabled by the accumulation of somatic mutations and genomic aberrations, leading to metastasis, treatment resistance, and poor clinical outcomes. The analysis of cancer genomes has identified APOBEC3A (A3A) cytidine deaminase activity as a cause of somatic mutagenesis in over 20 tumor types. In particular, A3A mutational signatures are found in a large proportion of ovarian tumors, ranging from 2-26% depending on subtype. Furthermore, genomic analyses of ovarian tumors suggest that A3A mutagenesis occurred during early metastatic progression, indicating the potential for A3A activity to promote clonal evolution. In non-ovarian tumors, A3A activity is associated with metastatic progression through the identification of A3A mutational patterns enriched in or unique to metastatic sites. Therefore, we hypothesized that aberrant A3A activity on OC genomes would increase mutagenesis, promote clonal diversity, and enable tumor progression. To examine the impact of aberrant A3A activity during OC progression, we developed a model system of inducible A3A expression in OC cell lines. We treated cells for 45 days with doxycycline to induce A3A expression (long-term, LT-A3A) and generated three biological replicates by treating individual wells of the parental lines independently. A3A is known to mutate the genome stochastically. Despite this, all versions of LT-A3A cells exhibited similar phenotypes compared to non-treated isogenic controls (NT). LT-A3A cells demonstrated increased colony formation relative to NT cells, indicating improved cell survival. We assessed cellular migration by scratch-wound assays and found that LT-A3A cells exhibited accelerated wound closure rates compared to NT controls, despite similar proliferation rates. In addition, cellular invasion was assessed by spheroid Matrigel invasion assays in which the invasive distance was significantly greater in LT-A3A cells relative to NT controls. By generating cell lines with a catalytically inactive doxycycline-inducible A3A transgene, we determined that the observed A3A-mediated cellular phenotypes were deaminase-dependent. To assess the molecular alterations driving these phenotypic differences, we performed RNA-seq on LT-A3A and NT cell lines. Gene set enrichment analysis of differentially expressed genes identified significant overlap between the Epithelial-Mesenchymal Transition (EMT) and WNT/Beta Catenin, Hedgehog, and TGFβ signaling gene sets. These related signaling pathways converge on the promotion of metastasis and cancer progression. These data suggest that aberrant A3A activity promotes the survival, migration, and invasion of OC cells by altering intracellular signaling pathways that promote EMT. Our ongoing experimental investigation will assess how long-term A3A mutagenesis impacts genomic heterogeneity and how A3A affects tumor behavior in animal models.
Citation Format: Jessica Merritt Devenport, Mary Mullen, Katherine Fuh, Abby Green. The role of APOBEC3A in ovarian cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 104.