title: Environmental and chemotherapeutic agents induce breakage at genes involved in leukemia-causing gene rearrangements in human hematopoietic stem/progenitor cells.
abstract: Hematopoietic stem and progenitor cells (HSPCs) give rise to all of the cells that make up the hematopoietic system in the human body, making their stability and resilience especially important. Damage to these cells can severely impact cell development and has the potential to cause diseases, such as leukemia. Leukemia-causing chromosomal rearrangements have largely been studied in the context of radiation exposure and are formed by a multi-step process, including an initial DNA breakage and fusion of the free DNA ends. However, the mechanism for DNA breakage in patients without previous radiation exposure is unclear. Here, we investigate the role of non-cytotoxic levels of environmental factors, benzene, and diethylnitrosamine (DEN), and chemotherapeutic agents, etoposide, and doxorubicin, in generating DNA breakage at the patient breakpoint hotspots of the MLL and CBFB genes in human HSPCs. These conditions represent exposure to chemicals encountered daily or residual doses from chemotherapeutic drugs. Exposure of HSPCs to non-cytotoxic levels of environmental chemicals or chemotherapeutic agents causes DNA breakage at preferential sites in the human genome, including the leukemia-related genes MLL and CBFB. Though benzene, etoposide, and doxorubicin have previously been linked to leukemia formation, this is the first study to demonstrate a role for DEN in the generation of DNA breakage at leukemia-specific sites. These chemical-induced DNA breakpoints coincide with sites of predicted topoisomerase II cleavage. The distribution of breakpoints by exposure to non-cytotoxic levels of chemicals showed a similar pattern to fusion breakpoints in leukemia patients. Our findings demonstrate that HSPCs exposed to non-cytotoxic levels of environmental chemicals and chemotherapeutic agents are prone to topoisomerase II-mediated DNA damage at the leukemia-associated genes MLL and CBFB. These data suggest a role for long-term environmental chemical or residual chemotherapeutic drug exposure in generation of DNA breakage at sites with a propensity to form leukemia-causing gene rearrangements.
authors.affiliation: Department of Cancer Biology, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157-1016, USA. Electronic address: rthys@wakehealth.edu.
authors.forename: Ryan G
authors.initials: RG
authors.lastname: Thys
authors.affiliation: Department of Cancer Biology, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157-1016, USA. Electronic address: clehman@wakehealth.edu.
authors.forename: Christine E
authors.initials: CE
authors.lastname: Lehman
authors.affiliation: Human Longevity, Inc., San Diego, California 92121, USA. Electronic address: Levipierce@gmail.com.
authors.forename: Levi C T
authors.initials: LC
authors.lastname: Pierce
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Virginia, 1340 Jefferson Park Avenue, Charlottesville, VA 22908-0733, USA. Electronic address: yw4b@virginia.edu.
authors.forename: Yuh-Hwa
authors.initials: YH
authors.lastname: Wang
mesh_terms: D001554:Benzene / Q000009:adverse effects; D001854:Bone Marrow Cells / Q000187:drug effects; D019457:Chromosome Breakage / Q000187:drug effects; D050658:Core Binding Factor beta Subunit / Q000235:genetics*; D004249:DNA Damage / Q000187:drug effects* / Q000235:genetics; D004250:DNA Topoisomerases, Type II / Q000235:genetics; D004052:Diethylnitrosamine / Q000009:adverse effects; D004317:Doxorubicin / Q000009:adverse effects; D005047:Etoposide / Q000009:adverse effects; D015321:Gene Rearrangement / Q000187:drug effects; D015894:Genome, Human / Q000187:drug effects; D006412:Hematopoietic Stem Cells / Q000187:drug effects* / Q000473:pathology; D011495:Histone-Lysine N-Methyltransferase / Q000235:genetics*; D006801:Humans; D007938:Leukemia / Q000235:genetics* / Q000473:pathology; D051788:Myeloid-Lymphoid Leukemia Protein / Q000235:genetics*; D061251:Primary Cell Culture
chemical_list: C493692:CBFB protein, human; D050658:Core Binding Factor beta Subunit; C497422:KMT2A protein, human; D051788:Myeloid-Lymphoid Leukemia Protein; D004052:Diethylnitrosamine; D005047:Etoposide; D004317:Doxorubicin; D011495:Histone-Lysine N-Methyltransferase; D004250:DNA Topoisomerases, Type II; D001554:Benzene
keywords: CBFB; Fragile site; Hematopoietic stem cells; Leukemia; MLL; Topoisomerase II