The Plk1 Polo Box Domain Mediates a Cell Cycle and DNA Damage Regulated Interaction with Chk2

Abstract

Polo-like kinase 1 (Plk1) regulates multiple processes during mitosis. Chk2 is a tumorsuppressor that participates in DNA damage checkpoint signaling cascades. Plk1phosphorylates, co-localizes with, and interacts with Chk2, suggesting interconnection ofDNA damage checkpoints and mitotic regulation. However, the function of theirassociation is unknown. Here, we show that the interaction between Chk2 and Plk1 is cellcycle-regulated, with a peak in mitosis. DNA damage in G2 and M phases but not in Sphase induces dissociation of Plk1 and Chk2. In vitro, the Plk1 PBD bindsphosphorylated Chk2, and mediates an interaction independent of other eukaryoticproteins. Additionally, a phosphopeptide encompassing phosphoT68 of Chk2 binds Plk1in a PBD-dependent manner, and stimulates Plk1 activity. These results identify potentialmechanisms for interaction and inter-regulation of these two protein kinases.