Flowchart: Preparation: Cdk2
 


Text Box: P27                          

Text Box: P21                                     

 
 

 
 
                                           

Text Box: P53 Text Box: Cdk2  

Text Box: Cdc25                

                                

Text Box: Abl                                                                                      

Text Box: Cdk1 Text Box: Hdac Text Box: E2f-1

 
 

                                                                              

 

 

 

Mitotic entry, a critical decision point for maintaining genetic stability, is governed by the cyclin B/Cyclin dependent kinase 1 (Cdc2) complex. In Xenopus oocytes and early embryos, accumulation of cyclin B activates Cdk1, which then phosphorylates and activates the positive regulator Cdc25 in an autocatalytic feedback loop. However, cyclin B levels do not increase as some human cells approach mitosis, and the key factors regulating Cdk1 activation in human cells are unknown. We report here that reducing cyclin A expression by RNA interference (RNAi) in primary human fibroblasts inhibited activation of Cdc25B and Cdc25C and dephosphorylation of Cdk1 on tyrosine (tyr) 15. These results were reproduced in U2-OS cells by inducing the expression of a dominant-negative (dn) mutant of Cdk2, the principal cyclin A binding partner. Cdk2-dn induction could inhibit Cdc25B activity and foster Cdk1 tyr phosphorylation within the S phase, temporally dissociating these events from Cdk1 activation at mitosis. In contrast, reducing Cdk1 expression delayed mitotic entry without markedly impairing Cdc25B or Cdc25C activity. These results suggest that cyclin A/Cdk2 complexes are key regulators of Cdc25 and Cdk1 activation in human cells. This pathway appears to be commonly deregulated in cancer.Oncogene advance online publication, 9 February 2004; doi:10.1038/sj.onc.1207446

PMID: 14767478 [PubMed - as supplied by publisher]