Li Hongchang, Wang Yun, Liu Xiaoqi
Department of Biochemistry and the Cancer Center, Purdue University, 175 S. University Street, West Lafayette, IN 47907, USA.
J Biol Chem. 2008 Mar 7;283(10):6209-21. doi: 10.1074/jbc.M709007200. Epub 2008 Jan 2.
Plk1 (Polo-like kinase 1) has been documented as a critical regulator of many mitotic events. However, increasing evidence supports the notion that Plk1 might also have functions outside of mitosis. Using biochemical fractionation and RNA interference approaches, we found that Plk1 was required for both G(1)/S and G(2)/M phases and that DNA topoisomerase IIalpha (topoIIalpha) was a potential target for Plk1 in both interphase and mitosis. Plk1 phosphorylates Ser(1337) and Ser(1524) of topoIIalpha. Overexpression of an unphosphorylatable topoIIalpha mutant led to S phase arrest, suggesting that Plk1-associated phosphorylation first occurs in S phase. Moreover, overexpression of the unphosphorylatable topoIIalpha mutant activated the ATM/R-dependent DNA damage checkpoint, probably due to reduced catalytic activity of topoIIalpha, and resulted in accumulation of catenated DNA. Finally, we showed that wild type topoIIalpha, but not the unphosphorylatable mutant, was able to rescue topoIIalpha depletion-induced defects in sister chromatid segregation, indicating that Plk1-associated phosphorylation is essential for the functions of topoIIalpha in mitosis.
Polo样激酶1（Plk1）已被证明是许多有丝分裂事件的关键调节因子。然而，越来越多的证据支持Plk1可能在有丝分裂之外也具有功能这一观点。利用生化分级分离和RNA干扰方法，我们发现Plk1在G1/S期和G2/M期均是必需的，并且DNA拓扑异构酶IIα（topoIIα）在间期和有丝分裂期都是Plk1的潜在靶点。Plk1使topoIIα的Ser(1337)和Ser(1524)位点磷酸化。不可磷酸化的topoIIα突变体的过表达导致S期停滞，这表明与Plk1相关的磷酸化首先发生在S期。此外，不可磷酸化的topoIIα突变体的过表达激活了ATM/R依赖性DNA损伤检查点，这可能是由于topoIIα的催化活性降低所致，并导致连环DNA的积累。最后，我们表明野生型topoIIα能够挽救topoIIα缺失诱导的姐妹染色单体分离缺陷，而不可磷酸化的突变体则不能，这表明与Plk1相关的磷酸化对于topoIIα在有丝分裂中的功能至关重要。
