Abstract 1485: Hallmarks of APOBEC3 mutagenesis in normal, pre-leukemic, and myeloproliferative neoplasm cell populations

Abstract Changes in gene expression and subsequent editing patterns of APOBEC3 (apolipoprotein B mRNA editing enzyme catalytic polypeptide-like) cytosine deaminases have been shown to be present in solid tumor cancer evolution, however, the context specificity and mechanisms by which APOBEC3 enzymes promote cancer initiation and progression require further elucidation, especially in the hematopoietic niche. Building on advanced sequencing data of healthy, pre-leukemic, and myeloproliferative neoplasm patient samples, we seek to uncover normal and malignant patterns of APOBEC3C overexpression in hematopoietic cells. Overexpression of lentiviral APOBEC3C and an editase-mutated APOBEC3C in normal cord blood, healthy bone marrow, and MPN patient hematopoietic stem/progenitor cells (HSPCs) allows us to study the effects of deaminase dysregulation in hematopoietic cells. In addition to APOBEC3, we are exploring the upregulation of adenosine deaminase acting on RNA1 (ADAR1), as we have previously shown that these two innate immune deaminases are synchronously upregulated in the high-risk myelofibrosis (MF) stem cell population compared to normal aged bone marrow. These overexpression studies show novel differential gene expression changes, RNA hyper-editing sites, and DNA mutation signatures induced by APOBEC3 mutagenesis, which can be cross-referenced to gene expression and mutation signatures seen in hematopoietic malignancies and solid tumor cancers. In addition to mutation patterns, the regulation of LINE-1 elements has been shown to be another important function of APOBEC3 enzymes. In these studies, we examine the effects of APOBEC3 overexpression on repetitive element expression in hematopoietic cell populations and have found that there are strong cell type and context patterns across the APOBEC3 family and between cell types within the hematopoietic system. We will use this comprehensive study of APOBEC3 deregulation to uncover predictive biomarkers of malignant transformation. Citation Format: Jane Marie Isquith, Thomas Whisenant, Jessica Pham, Ludmil Alexandrov, Catriona Jamieson. Hallmarks of APOBEC3 mutagenesis in normal, pre-leukemic, and myeloproliferative neoplasm cell populations abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1485.