NF-Y binds to both G1- and G2-specific cyclin promoters; a possible role in linking CDK2/Cyclin A to CDK1/Cyclin B

We previously reported that CDK2/Cyclin A can phosphorylate and activate the transcription factor NF-Y. In this study, we investigated a potential regulatory role for NF-Y in the transcription of Cyclin A and other cell cycle regulatory genes. Gel-shift assays demonstrate that NF-Y binds to CCAAT sequences in the Cyclin A promoter, as well as to those in the promoters of cell cycle G2 regulators such as CDC2, Cyclin B and CDC25C. Furthermore, expression of Cyclin A increases NF-Y's affinity for CCAAT sequences in the CDC2 promoter; however, Cyclin A's induction of CDC2 transcription is antagonized by p21, an inhibitor of CDK2/Cyclin A. These results suggest a model wherein NF-Y binds to and activates transcription from the Cyclin A promoter, increasing cellular levels of Cyclin A/CDK2 and potentiating NF-Y's capacity for transcriptional transactivation, and imply a positive feedback loop between NF-Y and Cyclin A/CDK2. Our findings are additionally indicative of a role for Cyclin A in activating Cyclin B/CDK1 through promoting NF-Y dependent transcription of Cyclin B and CDC2; NF-Y mediated crosstalk may therefore help to orchestrate cell-cycle progression.