Activation of FoxM1 during G₂ Requires Cyclin A/Cdk-Dependent Relief of Autorepression by the FoxM1 N-Terminal Domain

Abstract

The Forkhead transcription factor FoxM1 is an important regulator of gene expression during the G(2) phase. Here, we show that FoxM1 transcriptional activity is kept low during G(1)/S through the action of its N-terminal autoinhibitory domain. We found that cyclin A/cdk complexes are required to phosphorylate and activate FoxM1 during G(2) phase. Deletion of the N-terminal autoinhibitory region of FoxM1 generates a mutant of FoxM1 (DeltaN-FoxM1) that is active throughout the cell cycle and no longer depends on cyclin A for its activation. Mutation of two cyclin A/cdk sites in the C-terminal transactivation domain leads to inactivation of full-length FoxM1 but does not affect the transcriptional activity of the DeltaN-FoxM1 mutant. We show that the intramolecular interaction of the N- and C-terminal domains depends on two RXL/LXL motifs in the C terminus of FoxM1. Mutation of these domains leads to a similar gain of function as deletion of the N-terminal repressor domain. Based on these observations we propose a model in which FoxM1 is kept inactive during the G(1)/S transition through the action of the N-terminal autorepressor domain, while phosphorylation by cyclin A/cdk complexes during G(2) results in relief of inhibition by the N terminus, allowing activation of FoxM1-mediated gene transcription.