Journal Article

Model for MLL translocations in therapy-related leukemia involving topoisomerase IIβ-mediated DNA strand breaks and gene proximity

Smith, Kayleigh, Austin, Caroline A., Lee, Ka Cheong, Manville, Catriona M., Cowell, Ian G., Rance, Holly Ashlene, Jackson, Graham Hunter, Sondka, Zbyslaw, Adachi, Noritaka, Sidorczuk-Lesthuruge, Malgorzata, Padget, Kay

2012

Overview

Topoisomerase poisons such as the epipodophyllotoxin etoposide are widely used effective cytotoxic anticancer agents. However, they are associated with the development of therapy-related acute myeloid leukemias (t-AMLs), which display characteristic balanced chromosome translocations, most often involving the mixed lineage leukemia (MLL) locus at 11q23. MLL translocation breakpoints in t-AMLs cluster in a DNase I hypersensitive region, which possesses cryptic promoter activity, implicating transcription as well as topoisomerase II activity in the translocation mechanism. We find that 2-3% of MLL alleles undergoing transcription do so in close proximity to one of its recurrent translocation partner genes, AF9 or AF4, consistent with their sharing transcription factories. We show that most etoposide-induced chromosome breaks in the MLL locus and the overall genotoxicity of etoposide are dependent on topoisomerase IIβ, but that topoisomerase lia and -β occupancy and etoposide-induced DNA cleavage data suggest factors other than local topoisomerase II concentration determine specific clustering of MLL translocation breakpoints in t-AML. We propose a model where DNA double-strand breaks (DSBs) introduced by topoisomerase IIβ into pairs of genes undergoing transcription within a common transcription factory become stabilized by antitopoisomerase II drugs such as etoposide, providing the opportunity for illegitimate end joining and translocation.

• Publisher: National Academy of Sciences,National Acad Sciences
• Subject: Biological Sciences / Cell lines / Cell nucleus / Chromatin / Chromatin Immunoprecipitation / Chromosomes / DNA / DNA Breaks, Double-Stranded / DNA Topoisomerases, Type II - metabolism / DNA-Binding Proteins - metabolism / Etoposide / Fluorescence / Genes / Genetic loci / Humans / In Situ Hybridization, Fluorescence / K562 cells / Leukemia / Leukemia, Myeloid, Acute - genetics / Micronucleus Tests / Models, Biological / Myeloid-Lymphoid Leukemia Protein - genetics / Neoplasms, Second Primary - genetics / Poisons / Translocation, Genetic - genetics