Metnase mediates chromosome decatenation in acute leukemia cells

Abstract

After DNA replication, sister chromatids must be untangled, or decatenated, before mitosis so that chromatids do not tear during anaphase. Topoisomerase II␣ (Topo II␣) is the major decatenating enzyme. Topo II␣ inhibitors prevent decatenation, causing cells to arrest during mitosis. Here we report that acute myeloid leukemia cells fail to arrest at the mitotic decatenation checkpoint, and their progression through this checkpoint is regulated by the DNA repair IntroductionDNA double-strand breaks (DSBs) can result from normal cellular events, such as recombination during immune receptor rearrangement, recovery of stalled replication forks, replication of nicked templates, or failed decatenation. 1 Such DSBs can result in translocations or deletions, and this genomic instability can lead to malignancy. Of the normal cell processes producing DSBs, the least well understood is chromosome decatenation. Sister chromatids become intertwined, or catenated, when chromosomes are replicated during DNA synthesis. When decatenation fails, chromatids can tear during anaphase, producing DSBs. Catenation status is actively monitored at 2 points in the cell cycle. One decatenation checkpoint blocks progression from G 2 to M 2 , and another blocks progression from metaphase to anaphase during mitosis. [2][3][4][5][6] These checkpoints are conserved in most organisms, including yeast. 7,8 Previously, it was reported that bladder and lung cancer cells lack decatenation checkpoints and proceed through mitosis even when decatenation is inhibited. 9,10 It is possible that this failure of arrest at the decatenation checkpoints could be a general feature of malignancy, including acute leukemia. The critical decatenating enzyme is Topoisomerase II␣ (Topo II␣). [2][3][4][5][6]11 Topo II␣ inhibitors can trigger decatenation checkpoint arrest in normal cells at either of the 2 decatenation checkpoints. Recently, we identified and characterized a novel DNA repair protein called Metnase (also SETMAR). Metnase has an amino terminal SET histone methylase domain and a carboxy terminal transposase/nuclease domain. We previously reported that Metnase promotes nonhomologous endjoining of DSBs and methylates histone 3 lysine 36. 12 Metnase appears to be localized to DSBs by interaction with Pso4, a poorly characterized DNA repair component. 13 Metnase may promote DSB repair by interacting with DNA ligase IV, the final component of the nonhomologous end-joining pathway. 14 Metnase is present only in primates and exhibits only partial transposase activity. 12,[14][15][16][17][18][19] We also found that Metnase has endonuclease activity specific for supercoiled DNA and improves Topo II␣-mediated decatenation in vitro and in vivo in noncancerous human cells. 16,20 In this study, we hypothesized that Metnase mediates decatenation in acute leukemia cells. If there is a failure of decatenation arrest in acute leukemia cells when Topo II␣ is inhibited, then perhaps Metnase mediated the continued progression of those cells through the decatenation checkpoi...

Methylation of histone H3 lysine 36 enhances DNA repair by nonhomologous end-joining

“…We have found that human cancer cells that express Metnase at high levels display enhanced resistance to treatment with radiation or chemotherapy. Thus targeting Metnase may improve the response to these modalities (30,31). The resistance mediated by Metnase could reflect improved stabilization of the assembly of DSB repair components at DSB sites due to the generation of H3K36me2 at these sites.…”

A Proteomic Strategy Identifies Lysine Methylation of Splicing Factor snRNP70 by the SETMAR Enzyme

“…Resistance to Topoisomerase II Inhibition-SETMAR has been shown to make a small contribution to cell growth in several cell lines, and it contributes to resistance to growth inhibition and cell death when cells are treated with inhibitors of Topo II (8,9). Previous studies characterized the cellular role of SETMAR in DNA damage using SETMAR overexpression or RNAi-mediated depletion (2, 4).…”

“…SETMAR is implicated in the response to or repair of DNA double strand breaks and in non-homologous end joining through the combined activities of the SET and transposase domains (2)(3)(4)(5) and through interactions with factors including topoisomerase II␣ (Topo II␣) and PRPF19 (5-7). SETMAR knockout has been reported to delay recovery from DNA damage in a variety of cell lines and increases sensitivity to inhibitors of Topo II␣ (8,9). However, the molecular mechanism by which SETMAR impacts DNA damage responses is not well understood, and, in particular, the enzymatic function of the SET domain remains enigmatic.…”

Transposable elements and human cancer: A causal relationship?

“…The fusion of the histone methylase SET domain and the transposase domain in the anthropoid lineage to form primate Metnase promotes accurate intrachromosomal NHEJ and thereby suppresses interchromosomal translocations. Metnase may have been selected because it has the function of opposing transposases and thus may play a key role in suppressing translocations that underlie oncogenicity [75][76][77]. Metnase transposase has been remarkably conserved through evolution; however, there is a clustering of substitutions located in alpha helices 4 and 5 within the putative DNA-binding site, consistent with loss of transposition-specific DNA cleavage activity and acquisition of repair-specific DNA cleavage activity [78].…”

“…Metnase is widely expressed, especially in proliferating tissues, and its involvement in cancer cell resistance to Topoisomerase II-α inhibitors has been suggested. Indeed acute leukemia cells as well as breast cancer cells have an attenuated mitotic arrest due to decatenation inhibition by Metnase [76,77]. Therefore Metnase inhibition will restore chemotherapy sensitivity in these cells.…”