Metnase mediates chromosome decatenation in acute leukemia cells

After DNA replication, sister chromatids must be untangled, or decatenated, before mitosis so that chromatids do not tear during anaphase. Topoisomerase II alpha (Topo II alpha) is the major decatenating enzyme. Topo II alpha 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 II alpha 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 II alpha inhibitor VP-16. In vitro, purified Metnase prevents VP-16 inhibition of Topo II alpha decatenation of tangled DNA. Thus, Metnase expression levels may predict AML resistance to Topo II alpha inhibitors, and Metnase is a potential therapeutic target for small molecule interference. (Blood. 2009;114:1852-1858)