Playing Polo to deal with DNA damage

Polo kinases (Plks) are fundamental regulators of cell cycle progression in all eukaryotes and are frequently overexpressed in tumors. Through their polo box domain, Plks target multiple substrates, which frequently are previously phosphorylated by CDKs and MAPKs. In response to DNA damage, Plks are temporally inhibited in order to maintain the checkpoint-dependent cell cycle block while their activity is required to silence the checkpoint response and resume cell cycle progression. We recently reported that, in budding yeast, overproduction of the Cdc5 polo kinase overrides the checkpoint signaling induced by double strand DNA breaks (DSBs), preventing the phosphorylation of several Mec1/ATR targets, including Ddc2/ATRIP, the checkpoint mediator Rad9, and the transducer kinase Rad53/CHK2. We started a biochemical screening based on a GST-pull down approach to identify by mass spectrometry the Cdc5 interactors and substrates involved in checkpoint adaptation. Accordingly to previous evidences, it is anticipated that Cdc5 may influence several factors in response to a single irreparable DSB. The screening procedure is on going and I will present the preliminary results obtained with the main promising factors already identified.