In support of the latter assumption, the fact that incubating GST geminin with anti geminin anti body before the reaction BMS-907351 restored TopoIIas ability to decatenate the k DNA. At the moment, we are unable to distinguish between Inhibitors,Modulators,Libraries these possibilities but have future plans to investigate which is valid. Phosphorylation of TopoIIa on S1106 is important in TopoIIa translocation to chromosomes, DNA decatena tion, formation of drug stabilized DNA cleavable com plex and modulation of drug sensitivity. CKI�� is the only known Inhibitors,Modulators,Libraries kinase that targets this site in vitro and in vivo. The facts that CKI�� overexpression restored chromosome decatenation and or segregation that had stalled in the geminin silenced cells and that geminin overexpression upregulated CKI�� expression suggest a positive molecular link by which geminin con trols TopoIIa chromosome localization and function.

The facts that geminin overexpression decreased Cdc7 expression, that Cdc7 silencing restored stalled chromo some decatenation and or segregation in the geminin silenced Inhibitors,Modulators,Libraries cells, that Cdc7 overexpression reduced chromosome breakage and aneuploidy induced by geminin overexpression and that Cdc7 phosphorylated TopoIIa, at least in vitro, sug gest that Cdc7 is a negative molecular link between geminin and TopoIIa chromosome localization and function. It will be important in future studies to inves tigate whether Cdc7 also phosphorylates TopoIIa in vivo and on which sites, what are the upstream kinases and or conditions that activate Cdc7 to phosphorylate TopoIIa and what is their relation to geminin.

TopoIIa SUMOylation is inhibited and or decreased in geminin overexpressing cells. It is possible that geminin overexpression prevents TopoIIa SUMOylation Inhibitors,Modulators,Libraries by decreasing its binding to the SUMOylating complex RanBP2 Ubc9. Alternatively, it is possible that in normal cells, one function of geminin is to bind and or recruit the deSUMOylating enzymes SENP1 and SENP2 to chromo somally bound TopoIIa and to facilitate its deSUMOyla tion and release from chromosomes after chromosome decatenation is completed. In geminin overexpressing cells, this could be accelerated by the fact that geminin recruits more of the enzymes and or recruits them earlier to TopoIIa, thus leading to premature deSUMOylation and release of TopoIIa from chromosomes before the liga tion step.

It is also possible that this is simply the result of a dominant negative effect exerted by overexpressed gemi nin. Whatever the Inhibitors,Modulators,Libraries reason is, this could contribute to the generation of DNA damage and low efficiency of TopoIIa directed selleck bio drugs. At present, we are investigating whether SENP1 and or SENP2 are indeed TopoIIa deSU MOylating enzymes, whether a molecular link between geminin induced TopoIIa phosphorylation, SUMOylation and deSUMOylation exists, and whether using inhibitors of deSUMOylating enzymes in combination with TopoIIa directed drugs could be used to treat breast can cers with high geminin levels.