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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 IIalpha (Topo IIalpha) is the major decatenating enzyme. Topo IIalpha 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 component Metnase (also termed SETMAR). Metnase contains a SET histone methylase and transposase nuclease domain, and is a component of the nonhomologous end-joining DNA double-strand break repair pathway. Metnase interacts with Topo IIalpha and enhances its decatenation activity. Here we show that multiple types of acute leukemia cells have an attenuated mitotic arrest when decatenation is inhibited and that in an acute myeloid leukemia (AML) cell line this is mediated by Metnase. Of further importance, Metnase permits continued proliferation of these AML cells even in the presence of the clinical Topo IIalpha inhibitor VP-16. In vitro, purified Metnase prevents VP-16 inhibition of Topo IIalpha decatenation of tangled DNA. Thus, Metnase expression levels may predict AML resistance to Topo IIalpha inhibitors, and Metnase is a potential therapeutic target for small molecule interference.

SUBMITTER: Wray J

PROVIDER: S-EPMC2738570 | biostudies-literature | 2009 Aug

REPOSITORIES: biostudies-literature

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Metnase mediates chromosome decatenation in acute leukemia cells.

Wray Justin J Williamson Elizabeth A EA Sheema Sheema S Lee Suk-Hee SH Libby Edward E Willman Cheryl L CL Nickoloff Jac A JA Hromas Robert R

Blood 20090520 9

After DNA replication, sister chromatids must be untangled, or decatenated, before mitosis so that chromatids do not tear during anaphase. Topoisomerase IIalpha (Topo IIalpha) is the major decatenating enzyme. Topo IIalpha 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 component Metnase (also ...[more]

PMID: 19458360

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Project description:IntroductionThe nuclear enzyme topoisomerase IIα (TopoIIα) is able to cleave DNA in a reversible manner, making it a valuable target for agents such as etoposide that trap the enzyme in a covalent bond with the 5' DNA end to which it cleaves. This prevents DNA religation and triggers cell death in cancer cells. However, development of resistance to these agents limits their therapeutic use. In this study, we examined the therapeutic targeting of geminin for improving the therapeutic potential of TopoIIα agents.MethodsHuman mammary epithelial (HME) cells and several breast cancer cell lines were used in this study. Geminin, TopoIIα and cell division cycle 7 (Cdc7) silencing were done using specific small interfering RNA. Transit or stable inducible overexpression of these proteins and casein kinase Iε (CKIε) were also used, as well as several pharmacological inhibitors that target TopoIIα, Cdc7 or CKIε. We manipulated HME cells that expressed H2B-GFP, or did not, to detect chromosome bridges. Immunoprecipitation and direct Western blot analysis were used to detect interactions between these proteins and their total expression, respectively, whereas interactions on chromosomal arms were detected using a trapped in agarose DNA immunostaining assay. TopoIIα phosphorylation by Cdc7 or CKIε was done using an in vitro kinase assay. The TopoGen decatenation kit was used to measure TopoIIα decatenation activity. Finally, a comet assay and metaphase chromosome spread were used to detect chromosome breakage and changes in chromosome condensation or numbers, respectively.ResultsWe found that geminin and TopoIIα interact primarily in G2/M/early G1 cells on chromosomes, that geminin recruits TopoIIα to chromosomal decatenation sites or vice versa and that geminin silencing in HME cells triggers the formation of chromosome bridges by suppressing TopoIIα access to chromosomal arms. CKIε kinase phosphorylates and positively regulates TopoIIα chromosome localization and function. CKIε kinase overexpression or Cdc7 kinase silencing, which we show phosphorylates TopoIIα in vitro, restored DNA decatenation and chromosome segregation in geminin-silenced cells before triggering cell death. In vivo, at normal concentration, geminin recruits the deSUMOylating sentrin-specific proteases SENP1 and SENP2 enzymes to deSUMOylate chromosome-bound TopoIIα and promote its release from chromosomes following completion of DNA decatenation. In cells overexpressing geminin, premature departure of TopoIIα from chromosomes is thought to be due to the fact that geminin recruits more of these deSUMOylating enzymes, or recruits them earlier, to bound TopoIIα. This triggers premature release of TopoIIα from chromosomes, which we propose induces aneuploidy in HME cells, since chromosome breakage generated through this mechanism were not sensed and/or repaired and the cell cycle was not arrested. Expression of mitosis-inducing proteins such as cyclin A and cell division kinase 1 was also increased in these cells because of the overexpression of geminin.ConclusionsTopoIIα recruitment and its chromosome decatenation function require a normal level of geminin. Geminin silencing induces a cytokinetic checkpoint in which Cdc7 phosphorylates TopoIIα and inhibits its chromosomal recruitment and decatenation and/or segregation function. Geminin overexpression prematurely deSUMOylates TopoIIα, triggering its premature departure from chromosomes and leading to chromosomal abnormalities and the formation of aneuploid, drug-resistant cancer cells. On the basis of our findings, we propose that therapeutic targeting of geminin is essential for improving the therapeutic potential of TopoIIα agents.

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Metnase mediates chromosome decatenation in acute leukemia cells.

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Metnase mediates chromosome decatenation in acute leukemia cells.

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