Wednesday, April 2, 2025
4/2/2025
Control of Chromosome Segregation by DNA Topoisomerase II - Title: Control of Chromosome Segregation by DNA Topoisomerase II. Abstract Chromosome segregation errors result in aneuploidy, which causes birth defects and cancer. We have defined a new mitotic Topo II-responsive control (TRC) that delays the cell cycle when Topo II activity is insufficient for accurate chromosome segregation. This TRC mechanism is conserved from yeast to human cells but has not been extensively studied. Activation of the TRC is triggered by stalling of the strand passage reaction of Topo II, when the enzyme becomes trapped on DNA in the Closed Clamp structural conformation. TRC activation requires two distinct modules within the catalytically inert C-terminal domain of TopoII: (i) A cluster of SUMOylation sites, and (ii) The Chromatin Tether domain of Topo II, which interacts with methylated nucleosomes. The central molecular model is that stalled strand passage leads to C-terminal domain SUMOylation that functions as a signal-generating scaffold to halt the cell cycle. The conservation between the human and yeast TRC responses provided unique opportunities to identify TRC components, but gaps remain in our understanding of the mechanism of TRC activation. We aim to determine how the TRC activates Mad2 to inhibit anaphase initiation, which will require determining the identity of the E3 ligase that SUMOylates TopoII as well as the relevant substrates of Aurora B kinase. We will determine how trapped Closed Clamps trigger TopoII SUMOylation and how they are repaired. The role of the ChT domain will be determined and whether interaction with nucleosomes is required for TRC activation. The results of these studies will impact opportunities for translational research because we will identify new potential therapeutic targets. Our findings will also impact the use of widely prescribed therapeutic drugs that target Topo II because we will gain mechanistic insight into cellular responses to Topo II inhibition. The preliminary data and newly developed experimental tools place us in a unique position to determine the conserved mechanism of this scarcely studied mitotic control.
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