title: APOBEC3A damages the cellular genome during DNA replication.
abstract: The human APOBEC3 family of DNA-cytosine deaminases comprises 7 members (A3A-A3H) that act on single-stranded DNA (ssDNA). The APOBEC3 proteins function within the innate immune system by mutating DNA of viral genomes and retroelements to restrict infection and retrotransposition. Recent evidence suggests that APOBEC3 enzymes can also cause damage to the cellular genome. Mutational patterns consistent with APOBEC3 activity have been identified by bioinformatic analysis of tumor genome sequences. These mutational signatures include clusters of base substitutions that are proposed to occur due to APOBEC3 deamination. It has been suggested that transiently exposed ssDNA segments provide substrate for APOBEC3 deamination leading to mutation signatures within the genome. However, the mechanisms that produce single-stranded substrates for APOBEC3 deamination in mammalian cells have not been demonstrated. We investigated ssDNA at replication forks as a substrate for APOBEC3 deamination. We found that APOBEC3A (A3A) expression leads to DNA damage in replicating cells but this is reduced in quiescent cells. Upon A3A expression, cycling cells activate the DNA replication checkpoint and undergo cell cycle arrest. Additionally, we find that replication stress leaves cells vulnerable to A3A-induced DNA damage. We propose a model to explain A3A-induced damage to the cellular genome in which cytosine deamination at replication forks and other ssDNA substrates results in mutations and DNA breaks. This model highlights the risk of mutagenesis by A3A expression in replicating progenitor cells, and supports the emerging hypothesis that APOBEC3 enzymes contribute to genome instability in human tumors.
authors.affiliation: a Division of Oncology , Department of Pediatrics , Children's Hospital of Philadelphia and University of Pennsylvania Perelman School of Medicine , Philadelphia , PA , USA.|b Center for Childhood Cancer Research, Children's Hospital of Philadelphia , Philadelphia , PA , USA.
authors.forename: Abby M
authors.initials: AM
authors.lastname: Green
authors.affiliation: c Faculty of Pharmacy, Université de Montréal , Montréal , QC , Canada.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Landry
authors.affiliation: d Division of Cancer Pathobiology , Department of Pathology and Laboratory Medicine , Children's Hospital of Philadelphia and University of Pennsylvania Perelman School of Medicine , Philadelphia , PA , USA.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Budagyan
authors.affiliation: d Division of Cancer Pathobiology , Department of Pathology and Laboratory Medicine , Children's Hospital of Philadelphia and University of Pennsylvania Perelman School of Medicine , Philadelphia , PA , USA.
authors.forename: Daphne C
authors.initials: DC
authors.lastname: Avgousti
authors.affiliation: e Department of Chemistry , Wayne State University , Detroit , MI , USA.
authors.forename: Sophia
authors.initials: S
authors.lastname: Shalhout
authors.affiliation: e Department of Chemistry , Wayne State University , Detroit , MI , USA.|f Department of Immunology and Microbiology , Wayne State University School of Medicine , Detroit , MI , USA.
authors.forename: Ashok S
authors.initials: AS
authors.lastname: Bhagwat
authors.affiliation: b Center for Childhood Cancer Research, Children's Hospital of Philadelphia , Philadelphia , PA , USA.|d Division of Cancer Pathobiology , Department of Pathology and Laboratory Medicine , Children's Hospital of Philadelphia and University of Pennsylvania Perelman School of Medicine , Philadelphia , PA , USA.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Weitzman
mesh_terms: D059447:Cell Cycle Checkpoints; D002460:Cell Line; D003564:Cytidine Deaminase / Q000378:metabolism*; D004249:DNA Damage; D004261:DNA Replication; D003641:Deamination; D016678:Genome; D006801:Humans; D011506:Proteins / Q000378:metabolism*; D013312:Stress, Physiological
chemical_list: D011506:Proteins; C121399:APOBEC3A protein, human; D003564:Cytidine Deaminase
keywords: APOBEC3; ATR kinase; DNA replication; DNA replication stress; cell cycle checkpoint; cytosine deamination; single-stranded DNA