Dataset Information

Evidence for direct involvement of epirubicin in the formation of chromosomal translocations in t(15;17) therapy-related acute promyelocytic leukemia.

ABSTRACT: Therapy-related acute promyelocytic leukemia (t-APL) with t(15;17)(q22;q21) involving the PML and RARA genes is associated with exposure to agents targeting topoisomerase II (topoII), particularly mitoxantrone and epirubicin. We previously have shown that mitoxantrone preferentially induces topoII-mediated DNA damage in a "hotspot region" within PML intron 6. To investigate mechanisms underlying epirubicin-associated t-APL, t(15;17) genomic breakpoints were characterized in 6 cases with prior breast cancer. Significant breakpoint clustering was observed in PML and RARA loci (P = .009 and P = .017, respectively), with PML breakpoints lying outside the mitoxantrone-associated hotspot region. Recurrent breakpoints identified in the PML and RARA loci in epirubicin-related t-APL were shown to be preferential sites of topoII-induced DNA damage, enhanced by epirubicin. Although site preferences for DNA damage differed between mitoxantrone and epirubicin, the observation that particular regions of the PML and RARA loci are susceptible to these agents may underlie their respective propensities to induce t-APL.

SUBMITTER: Mays AN

PROVIDER: S-EPMC2808156 | biostudies-literature | 2010 Jan

REPOSITORIES: biostudies-literature

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Evidence for direct involvement of epirubicin in the formation of chromosomal translocations in t(15;17) therapy-related acute promyelocytic leukemia.

Mays Ashley N AN Osheroff Neil N Xiao Yuanyuan Y Wiemels Joseph L JL Felix Carolyn A CA Byl Jo Ann W JA Saravanamuttu Kandeepan K Peniket Andrew A Corser Robert R Chang Cherry C Hoyle Christine C Parker Anne N AN Hasan Syed K SK Lo-Coco Francesco F Solomon Ellen E Grimwade David D

Blood 20091102 2

Therapy-related acute promyelocytic leukemia (t-APL) with t(15;17)(q22;q21) involving the PML and RARA genes is associated with exposure to agents targeting topoisomerase II (topoII), particularly mitoxantrone and epirubicin. We previously have shown that mitoxantrone preferentially induces topoII-mediated DNA damage in a "hotspot region" within PML intron 6. To investigate mechanisms underlying epirubicin-associated t-APL, t(15;17) genomic breakpoints were characterized in 6 cases with prior br ...[more]

PMID: 19884644

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Project description:Genome instability, associated with chromosome breakage syndromes and most human cancers, is still poorly understood. In the yeast Saccharomyces cerevisiae, numerous genes with roles in the preservation of genome integrity have been identified. DNA-damage-checkpoint-deficient yeast cells that lack Sgs1, a RecQ-like DNA helicase related to the human Bloom's-syndrome-associated helicase BLM, show an increased rate of genome instability, and we have previously shown that they accumulate recurring chromosomal translocations between three similar genes, CAN1, LYP1 and ALP1. Here, the chromosomal location, copy number and sequence similarity of the translocation targets ALP1 and LYP1 were altered to gain insight into the formation of complex translocations. Among 844 clones with chromosomal rearrangements, 93 with various types of simple and complex translocations involving CAN1, LYP1 and ALP1 were identified. Breakpoint sequencing and mapping showed that the formation of complex translocation types is strictly dependent on the location of the initiating DNA break and revealed that complex translocations arise via a combination of interchromosomal translocation and template-switching, as well as from unstable dicentric intermediates. Template-switching occurred between sequences on the same chromosome, but was inhibited if the genes were transferred to different chromosomes. Unstable dicentric translocations continuously gave rise to clones with multiple translocations in various combinations, reminiscent of intratumor heterogeneity in human cancers. Base substitutions and evidence of DNA slippage near rearrangement breakpoints revealed that translocation formation can be accompanied by point mutations, and their presence in different translocation types within the same clone provides evidence that some of the different translocation types are derived from each other rather than being formed de novo. These findings provide insight into eukaryotic genome instability, especially the formation of translocations and the sources of intraclonal heterogeneity, both of which are often associated with human cancers.

Project description:A nonrandom chromosomal translocation breakpoint, t(15;17)(q22;q21), is found in almost all patients with acute promyelocytic leukemia (APL). Most of these breakpoints occur within the second intron of the retinoic acid receptor-alpha (RARA) gene. We screened a cDNA library of APL and have identified and sequenced a cDNA transcribed from the t(15;17) translocation breakpoint. The 5' end of cDNA p1715 consists of 503 bp of the RARA exon II sequence. A 1.76-kb cDNA without homology to any known gene available in GenBank was found truncated downstream. This cDNA sequence was assigned to chromosome 15 by dot blot hybridization of the flow cytometry-sorted chromosomes. We designate this fusion cDNA RARA/myl, which is different from myl/RARA reported by de The et al. (H. de The, C. Chomienne, M. Lanotte, L. Degos, and A. Dejean, Nature (London) 347:558-561, 1990). This result demonstrates that the two different types of hybrid mRNA can be transcribed from this breakpoint. We screened a non-APL cDNA library and identified a 2.8-kb myl cDNA. This cDNA is able to encode a polypeptide with a molecular weight of 78,450. Alternative splicing of the myl gene which resulted in myl proteins with different C terminals was found. Southern blot analysis of the genomic DNA isolated from 17 APL patients by using the myl DNA probe demonstrated that the myl gene in 12 samples was rearranged. Northern (RNA) blot analysis of RARA gene expression in two APL RNA samples showed abnormal mRNA species of 4.2 and 3.2 kb in one patient and of 4.8 and 3.8 kb in another patient; these were in addition to the normal mRNA species of 3.7 and 2.7-kb. The myl DNA probe detected a 2.6-kb abnormal mRNA in addition to the normal mRNA species of 3.2, 4.2, and 5.5 kb. Using the polymerase chain reaction, we demonstrated that both RARA/myl and myl/RARA were coexpressed in samples from three different APL patients. From this study, we conclude that the t(15;17) translocation breakpoint results in the transcription of two different fusion transcripts which are expected to be translated into fusion proteins.

Dataset Information

Evidence for direct involvement of epirubicin in the formation of chromosomal translocations in t(15;17) therapy-related acute promyelocytic leukemia.

Publications

Evidence for direct involvement of epirubicin in the formation of chromosomal translocations in t(15;17) therapy-related acute promyelocytic leukemia.

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