Polo-like kinase 1 phosphorylation of p150^Glued facilitates nuclear envelope breakdown during prophase

Nuclear envelope breakdown (NEBD) is an essential step during the G2/M transition in higher eukaryotic cells. Increasing evidence supports the notion that both microtubules and microtubule-associated motor proteins are critical regulators of NEBD. Although it has been described that p150^Glued, the major component of the dynein/dynactin complex, localizes in the nuclear envelope during prophase, the exact role of p150^Glued and its regulation during NEBD are largely elusive. Polo-like kinase 1 (Plk1), the best characterized Ser/Thr kinase, is involved in mitotic entry in several systems; however, the targets of Plk1 during NEBD are unknown. Herein, we show that in mammalian cells both Plk1 and p150^Glued regulate NEBD and that Plk1 interacts with and phosphoryates p150^Glued during NEBD at prophase. Using various approaches, we showed that Plk1 phosphorylates p150 ^Glued at Ser-179 and that the pS179 epitope is generated at the nuclear envelope of prophase cells. Significantly, Plk1-mediated phosphorylation of p150^Glued at Ser-179 positively regulates its accumulation at the nuclear envelope during prophase. Finally, we found that cells expressing the Plk1-unphosphorylatable mutant (p150^Glued-S179A) arrest at G2, as indicated by reduced NEBD, increased levels of cyclin B and phospho-H3, but a decreased level of Cdc2 kinase activity. Taking these data together, we conclude that Plk1 phosphorylation of p150^Glued might be one major pathway of NEBD regulation.