Laoukili Jamila, Alvarez Monica, Meijer Lars A T, Stahl Marie, Mohammed Shabaz, Kleij Livio, Heck Albert J R, Medema René H
Laboratory of Experimental Oncology, Department of Medical Oncology, University Medical Center, Stratenum 2.118, Universiteitsweg 100, 3584 CG Utrecht, The Netherlands.
Mol Cell Biol. 2008 May;28(9):3076-87. doi: 10.1128/MCB.01710-07. Epub 2008 Feb 19.
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.
叉头转录因子FoxM1是G2期基因表达的重要调节因子。在此，我们表明，通过其N端自抑制结构域的作用，FoxM1转录活性在G1/S期保持较低水平。我们发现，细胞周期蛋白A/细胞周期蛋白依赖性激酶（cdk）复合物在G2期需要磷酸化并激活FoxM1。缺失FoxM1的N端自抑制区域会产生一种FoxM1突变体（ΔN-FoxM1），该突变体在整个细胞周期中都具有活性，并且不再依赖细胞周期蛋白A来激活。C端反式激活结构域中两个细胞周期蛋白A/cdk位点的突变导致全长FoxM1失活，但不影响ΔN-FoxM1突变体的转录活性。我们表明，N端和C端结构域的分子内相互作用取决于FoxM1 C端的两个RXL/LXL基序。这些结构域的突变导致与N端阻遏结构域缺失类似的功能获得。基于这些观察结果，我们提出了一个模型，其中FoxM1在G1/S转换期间通过N端自阻遏结构域的作用保持无活性，而在G2期细胞周期蛋白A/cdk复合物的磷酸化导致N端抑制的解除，从而允许激活FoxM1介导的基因转录。
