title: DNA cleavage within the MLL breakpoint cluster region is a specific event which occurs as part of higher-order chromatin fragmentation during the initial stages of apoptosis.
abstract: A distinct population of therapy-related acute myeloid leukemia (t-AML) is strongly associated with prior administration of topoisomerase II (topo II) inhibitors. These t-AMLs display distinct cytogenetic alterations, most often disrupting the MLL gene on chromosome 11q23 within a breakpoint cluster region (bcr) of 8.3 kb. We recently identified a unique site within the MLL bcr that is highly susceptible to DNA double-strand cleavage by classic topo II inhibitors (e.g., etoposide and doxorubicin). Here, we report that site-specific cleavage within the MLL bcr can be induced by either catalytic topo II inhibitors, genotoxic chemotherapeutic agents which do not target topo II, or nongenotoxic stimuli of apoptotic cell death, suggesting that this site-specific cleavage is part of a generalized cellular response to an apoptotic stimulus. We also show that site-specific cleavage within the MLL bcr can be linked to the higher-order chromatin fragmentation that occurs during the initial stages of apoptosis, possibly through cleavage of DNA loops at their anchorage sites to the nuclear matrix. In addition, we show that site-specific cleavage is conserved between species, as specific DNA cleavage can also be demonstrated within the murine MLL locus. Lastly, site-specific cleavage during apoptosis can also be identified at the AML1 locus, a locus which is also frequently involved in chromosomal rearrangements present in t-AML patients. In conclusion, these results suggest the potential involvement of higher-order chromatin fragmentation which occurs as a part of a generalized apoptotic response in a mechanism leading to chromosomal translocation of the MLL and AML1 genes and subsequent t-AML.
authors.affiliation: Department of Molecular Medicine, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
authors.forename: M
authors.initials: M
authors.lastname: Stanulla
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.forename: D S
authors.initials: DS
authors.lastname: Chervinsky
authors.forename: S
authors.initials: S
authors.lastname: Thandla
authors.forename: P D
authors.initials: PD
authors.lastname: Aplan
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D050676:Core Binding Factor Alpha 2 Subunit; D053938:DNA Fragmentation / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000235:genetics*; D004791:Enzyme Inhibitors / Q000009:adverse effects; D005047:Etoposide / Q000494:pharmacology; D011495:Histone-Lysine N-Methyltransferase; D006801:Humans; D051379:Mice; D051788:Myeloid-Lymphoid Leukemia Protein; D011518:Proto-Oncogene Proteins; D011519:Proto-Oncogenes; D015183:Restriction Mapping; D013045:Species Specificity; D059005:Topoisomerase II Inhibitors; D014157:Transcription Factors / Q000235:genetics; D014178:Translocation, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D050676:Core Binding Factor Alpha 2 Subunit; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C497422:KMT2A protein, human; D011518:Proto-Oncogene Proteins; C493728:RUNX1 protein, human; C493726:Runx1 protein, mouse; D059005:Topoisomerase II Inhibitors; D014157:Transcription Factors; D051788:Myeloid-Lymphoid Leukemia Protein; D005047:Etoposide; D011495:Histone-Lysine N-Methyltransferase; C497423:Kmt2a protein, mouse