Phosphorylation of the CCAAT displacement protein (CDP)/Cux transcription factor by cyclin A-cdk1 modulates its DNA binding activity in G(2)

Stable DNA binding by the mammalian CCAAT displacement protein (CDP)/Cux tr anscription factor was previously found to be up-regulated at the G(1)/S tr ansition as the result of two events, dephosphorylation by the Cdc25A phosp hatase and proteolytic processing, to generate an amino-truncated isoform o f 110 kDa. In S phase, CDP/Cux was shown to interact with and repress the c ore promoter of the p21(WAF1) gene. Here we demonstrate that DNA binding by p110 CDP/Cux is down-modulated as cells progress into G(2). Accordingly, c yclin A-Cdk1 was found to bind to CDP/Cux and modulate its DNA binding acti vity in vitro and in vivo. Interaction with CDP/Cux required the presence o f both cyclin A and a cyclin-dependent kinase (Cdk)-activating kinase-activ ated Cdk1 and involved the Cut homeodomain and a downstream Cy motif. Phosp horylation of serines 1237 and 1270 caused inhibition of DNA binding in vit ro. In cotransfection studies, cyclin A-Cdk1 inhibited CDP/ Cux stable DNA binding and prevented repression of the p21(WAF1) reporter. In contrast, mu tant CDP/Cux proteins in which serines 1237 and 1270 were replaced with ala nines were not affected by cyclin A-Cdk1. In summary, our results suggest t hat the phosphorylation of CDP/ Cux by cyclin A-Cdk1 contributes to down-mo dulate CDP/Cux activity as cells progress into the G2 phase of the cell cyc le.