Distribution of 11q23 breakpoints within the MLL breakpoint cluster region in de novo acute leukemia and in treatment-related acute myeloid leukemia: correlation with scaffold attachment regions and topoisomerase II consensus binding sites

Abstract

A major unresolved question for 11q23 translocations involving MLL is the chromosomal mechanism(s) leading to these translocations. We have mapped breakpoints within the 8.3-kb BamHI breakpoint cluster region in 31 patients with acute lymphoblastic leukemia and acute myeloid leukemia (AML) de novo and in 8 t-AML patients. In 23 of 31 leukemia de novo patients, MLL breakpoints mapped to the centromeric half (4.57 kb) of the breakpoint cluster region, whereas those in eight de novo patients mapped to the telomeric half (3.87 kb). In contrast, only two t-AML breakpoints mapped in the centromeric half, whereas six mapped in the telomeric half. The difference in distribution of the leukemia de novo breakpoints is statistically significant (P = .02). A similar difference in distribution of breakpoints between de novo patients and t-AML patients has been reported by others. We identified a low- or weak-affinity scaffold attachment region (SAR) mapping just centromeric to the breakpoint cluster region, and a high-affinity SAR mapping within the telomeric half of the breakpoint cluster region. Using high stringency criteria to define in vitro vertebrate topoisomerase II (topo II) consensus sites, one topo II site mapped adjacent to the telomeric SAR, whereas six mapped within the SAR. Therefore, 74% of leukemia de novo and 25% of t-AML breakpoints map to the centromeric half of the breakpoint cluster region map between the two SARs; in contrast, 26% of the leukemia de novo and 75% of the t-AML patient breakpoints map to the telomeric half of the breakpoint cluster region that contains both the telomeric SAR and the topo II sites. Thus, the chromatin structure of the MLL breakpoint cluster region may be important in determining the distribution of the breakpoints. The data suggest that the mechanism(s) leading to translocations may differ in leukemia de novo and in t-AML.

Taspase1 Facilitates Topoisomerase IIβ-Mediated DNA Double-Strand Breaks Driving Estrogen-Induced Transcription

“…Moreover, Topo II poisons, which are indeed widely spread in cancer therapy, exploit the hazardous potential of Topo II-generated cytotoxic DNA damage, as unrepaired DSBs ideally lead to programmed death of cancer cells. However, following chemotherapy with the Topo II inhibitor etoposide, harmful therapyrelated, secondary leukemia arises in 2-15% of cancer patients, harboring chromosomal rearrangements [77][78][79][80]. This underlines once more that although Taspase1-facilitated transient DSBs catalyzed by Topo II have a high physiological relevance as an initial event for stimulus-provoked transcription, those scheduled DNA breaks also exert a great hazard potential if serious disturbances occur in this pivotal signaling cascade.…”

DNA fragility at the KMT2A / MLL locus: insights from old and new technologies

“…Early apoptotic cleavage has also been proposed as a factor in intron 11/exon 12 cleavage observed in cells and the clustering of t-AL MLL break sites. Data underlying this hypothesis includes relatively low-resolution Southern blot analysis to detect MLL gene cleavage [31,34,37]. Using this approach similar intron 11/exon12 cleavage patterns were observed when cells were treated with TOP2 poisons, non-TOP2 targeting DNA damaging agents, or indeed the pro-apoptotic anti-royalsocietypublishing.org/journal/rsob Open Biol.…”

“…not associated with prior exposure to clastogenic anti-cancer drugs), MLL breakpoints cluster in a broad area towards the centromeric (5 0 ) half of the BCR. However, in t-AL and neonatal acute leukaemias the MLL junction sequences are concentrated in the telomeric (3 0 ) 1 kb of the BCR (figure 2b), suggesting that an additional or alternative mechanism is involved in their formation [2,20,30,31]. Furthermore, nucleotide resolution mapping of translocation break sites from t-AL patients has identified a hot-spot close to the 3 0 -end of intron 11 (figure 2b,c).…”

Targeting Chromatin Complexes in Myeloid Malignancies and Beyond: From Basic Mechanisms to Clinical Innovation

“…In adult mammalian organisms, DOT1L is dispensable for homeostasis of most cell types except hematopoietic stem cells [147,148]. MLL1 (KMT2A), which is the mammalian homologue of Drosophila trithorax, is recurrently affected by chromosomal translocations during the development of acute leukemia, leading to the generation of oncogenic fusion proteins [149][150][151][152]. These MLL1-fusion oncogenes recruit DOT1L directly via the fusion partner (e.g., AF9, AF10, AF17, or ENL) or indirectly to their target genes to establish an active chromatin environment and prevent repression [153][154][155][156][157][158][159][160][161][162].…”