Plk1-mediated stabilization of 53BP1 suppresses centrosome abnormal amplification

Abstract

Mammalian Plk1 has been studied as an essential factor in regulating mitotic events through the phosphorylation of several Plk1-specific substrates. Here we show that in mitosis 53BP1 binds to the C-terminal polo-box domain of Plk1 and is a substrate for Plk1 in vitro. 53BP1 is hyper-phosphorylated and its level is up-regulated in cells expressing wild type Plk1 (Plk1-WT), but not in cells expressing a kinase-defective mutant (Plk1-KM). Depletion of Plk1 reduces the level of 53BP1 which is restored in cells treated with MG132. In cells expressing Plk1-KM but not in Plk1-WT cells, 53BP1 interacts with Mdm2 suggesting that 53BP1 turnover is regulated by Plk1-mediated phosphorylation. In mitosis, 53BP1 colocalizes with Plk1 to the centrosome and the spindle pole. Down-regulation of 53BP1 by shRNA induces multiple centrioles, multiple spindle poles, and mis-orientation of poles in HeLa cells. The data suggest that the phosphorylation of 53BP1 by Plk1 regulates its stability, and that this biochemical event plays a crucial role in modulating chromosomal amplification which ensures bipolarity in mitosis.