Ataxia telangiectasia mutated‐dependent regulation of topoisomerase II alpha expression and sensitivity to topoisomerase II inhibitor

Abstract

Topoisomerase II alpha (TOP2A) has a crucial role in proper chromosome condensation and segregation. Here we report the interaction of TOP2A with ataxia telangiectasia mutated (ATM) and its phosphorylation in an ATM-dependent manner after DNA damage. In vitro kinase assay and site-directed mutagenesis studies revealed that serine 1512 is the target of phosphorylation through ATM. Serine 1512 to Alanine mutation of TOP2A showed increased stability of the protein, retaining TOP2A activity at least with regard to cell survival activity. Ataxia telangiectasiaderived cell lines showed high levels of TOP2A that were associated with hypersensitivity to the TOP2 inhibitor etoposide. These findings suggest that ATM-dependent TOP2A modification is required for proper regulation of TOP2 stability and subsequently of the sensitivity to TOP2 inhibitor. In a lymphoblastoid cell line derived from a patient who developed MLL rearrangement, positive infant leukemia, defective ATM expression, and increased TOP2A expression were shown. It was intriguing that hypersensitivity to TOP2 inhibitor and susceptibility to MLL gene rearrangement were shown by low-dose etoposide exposure in this cell line. Thus, our findings have clinically important implications for the pathogenesis of infantile acute leukemia as well as treatment-associated secondary leukemia following exposure to TOP2 inhibitors. (Cancer Sci 2013; 104: 178-184) A taxia telangiectasia (AT) is an autosomal recessive disorder characterized by a pleiotropic phenotype that includes progressive cerebellar degeneration, immunodeficiency, premature aging, genetic instability, and a high incidence of cancer. Heterozygous carriers also appear to be at increased risk of cancer.(1,2) Cells from AT homozygotes lack multiple cell cycle check points, and this leads to hypersensitivity to double-strand breaks in the DNA. (3,4) DNA topology is controlled and altered by DNA topoisomerases. Topoisomerases are ubiquitous enzymes that resolve topological problems, which arise during the various processes of DNA metabolism including transcription, recombination, replication, and chromosome partitioning during cell division. Topoisomerase I introduces a transient single-strand break into the DNA, passes an intact single strand of DNA through the broken strand, and re-ligates the break. Topoisomerase II (TOP2) makes transient double-strand breaks in one segment of DNA and passes an intact duplex through the broken DNA before resealing the breaks. Human cells express two isoforms of TOP2, topoisomerase II alpha (TOP2A) and topoisomerase II beta (TOP2B). TOP2A is expressed mainly during the S to G 2 ⁄ M phase of the cell cycle and is likely to play a major role in DNA catenation during mitosis. In contrast, TOP2B is expressed constantly throughout the cell cycle. The function of TOP2B is unknown, but the enzyme is speculated to be involved in the metabolism of DNA and ⁄ or RNA. Topoisomerase II alpha is highly phosphorylated, and its enzymatic activity has been postulated to be regulated by ph...

The DNA Damage Response: Implications for Tumor Responses to Radiation and Chemotherapy

“…Consequently, cells can be sensitized to etoposide by inhibitors of DNA-PK (80) and ATM (28). A recent study showed that ATM regulates TOP II expression, and ATM loss results in increased TOP II levels and enhances sensitivity to TOP II inhibition (81). This finding is in accordance with the concept that TOP expression levels correlate with the number of DNA breaks induced by TOP inhibitors.…”

Overexpression of p53 protein is a marker of poor prognosis in Mexican women with breast cancer

“…This group is composed of patients with BC presenting a 65-bp deletion in the p53 gene, thus explaining its protein underexpression. Conversely, p53 mutants could induce TOP2α expression; however, we did not observe any correlation between p53 point mutations (overexpression of p53) and TOP2α protein overexpression (data not shown), suggesting that mechanisms other than p53 mutations are able to induce or regulate TOP2α expression (32,33). The third group included both non-TNBC and TNBC patients carrying a deletion in the TOP2α gene and with baseline expression of the TOP2α and p53 proteins.…”

Dysregulation of the DNA Damage Response and KMT2A Rearrangement in Fetal Liver Hematopoietic Cells

“…Therefore, loss of cell-cycle regulation or defects in the DNA damage response (due to loss or mutation of DNA damage response factors such as ATM, its target genes, or related molecules) may trigger chromosomal translocations following DNA double-strand breaks. ATM-defective cell lines are hypersensitive to etoposide and this is due to high levels of TOP2A expression [ 28 ]. Thus, ATM-dependent regulation of TOP2A might be another factor that influences etoposide sensitivity.…”