The. Pik1 By The Interaction Of P53 To Participate In The G <sub> 2 </ Sub> / M Phase Of The Conversion Regulation

During the cell cycle, successful accomplishment of G₂/M transition is a pivotal process to carry out proliferation. Cell itself has the surveillant mechanism at G₂ damage checkpoint, which ensures the successful accomplishment of G₂/M transition. Polo like kinase (Plk1) regulates the G₂/M transition by the positive mechanism while p53 by the negative one. Researches showed that Plk1 paticipated in regulating the activation of p53. So we wanted to find out whether Plkl regulates the G₂/M transition via p53 pathway in this article. Main results are listed below:1. When the synchronized cells released from the G₂ phase, Plkl kinase activity increased. It meant that the cell cycle could transform from G₂ phase to M phase. When those synchronized cells were treated with low dose UV, kinase activity of endogenous Plk1 significantly was down-regulated and its protein level decreased while transactivation of p53 remarkably was up-regulated with its protein level accumulation.2. We comfirmed by immunoprecipitation that Plk1 could physically interact with p53 at the G₂/M transitional phase. The Gal-4 two-hybrid system further indicated that Plk1 directly interacted with the sequence-specific DNA-binding domain of p53. That is to say Plkl might restrain the transactivation of p53 by competitivly binding with the sequence-specific DNA-binding domain of p53. It could be testified by the experiment that over-expression of Plk1 in cultured cells could inhibit the transactivation of p53.3. Over-expression of Plk1 in cultured cells could inhibit the phosphorylation of p53 protein. Over-expression of Plk1 accompanied with Mdm2 could accelerate Mdm2 processing degradation of p53. At the same time, over-expression of Plk1 could inhibit processing nuclear import of p53. These results indicated that Plk1 also leaded to the reduction of stability and transactivation of p53 by inhibiting its phosphorylation, accerating its degradation and preventing its nuclear import.4. Plkl and hNRAGE interacted with the different domains of p53 respectively. Plkl negatively mediated the transactivational activity of p53, while the hNRAGE positivly regulated p53 transactivational activity. When they acted together, their influence to p53 counteracted with each other. hNRAGE did not effect the kinase activity of Plkl. So Plkl and hNRAGE might be the two relatively independent cell signals that regulate the activation of p5 3.As a result, in the G2 damage checkpoint pathway, Plkl regulates the stability and transactivation of p53 by binding to the sequence-specific DNA-binding domain of p53, inhibiting its phosphorylation, promoting its degradation and preventing its nuclear importing. Plkl can paticipate in regulating the G2/M transition via p53 pathway through negatively regulating its transactivational activity.