Transcriptional induction of cell-cycle regulatory proteins ensures proper timing of subsequent cell-cycle events. Here we show that the Forkhead transcription factor FoxM1 regulates expression of many G2-specific genes and is essential for chromosome stability. Loss of FoxM1 leads to pleiotropic cell-cycle defects, including a delay in G2, chromosome mis-segregation and frequent failure of cytokinesis. We show that transcriptional activation of cyclin B by FoxM1 is essential for timely mitotic entry, whereas CENP-F, another direct target of FoxM1 identified here, is essential for precise functioning of the mitotic spindle checkpoint. Thus, our data uncover a transcriptional cluster regulated by FoxM1 that is essential for proper mitotic progression.

DNA damage triggers multiple checkpoint pathways to arrest cell cycle progression. Less is known about the mechanisms that allow resumption of the cell cycle once checkpoint signaling is silenced. Here we show that while in undamaged cells several redundant pathways can promote the onset of mitosis, this redundancy is lost in cells recovering from a DNA damage-induced arrest. We demonstrate that Plk1 is crucial for mitotic entry following recovery from DNA damage. However, Plk1 is no longer required in cells depleted of Wee1, and we could show that Plk1 is involved in the degradation of Wee1 at the onset of mitosis. Thus, our data show that the cell cycle machinery is reset in response to DNA damage and that cells become critically dependent on Plk1-mediated degradation of Wee1 for their recovery.

Myc synergizes with Ras and PI3-kinase in cell transformation, yet the molecular basis for this behavior is poorly understood. We now show that Myc recruits TFIIH, P-TEFb and Mediator to the cyclin D2 and other target promoters, while the PI3-kinase pathway controls formation of the preinitiation complex and loading of RNA polymerase II. The PI3-kinase pathway involves Aktmediated phosphorylation of FoxO transcription factors. In a nonphosphorylated state, FoxO factors inhibit induction of multiple Myc target genes, Myc-induced cell proliferation and transformation by Myc and Ras. Abrogation of FoxO function enables Myc to activate target genes in the absence of PI3-kinase activity and to induce foci formation in primary cells in the absence of oncogenic Ras. We suggest that the cooperativity between Myc and Ras is at least in part due to the fact that Myc and FoxO proteins control distinct steps in the activation of an overlapping set of critical target genes.

Activation of the DNA damage checkpoint causes a cellcycle arrest through inhibition of cyclin-dependent kinases (cdks). To successfully recover from the arrest, a cell should somehow be maintained in its proper cell-cycle phase. This problem is particularly eminent when a cell arrests in G2, as cdk activity is important to establish a G2 state. Here, we identify the phosphatase Wip1 (PPM1D) as a factor that maintains a cell competent for cell-cycle reentry during an ongoing DNA damage response in G2. We show that Wip1 function is required throughout the arrest, and that Wip1 acts by antagonizing p53-dependent repression of crucial mitotic inducers, such as Cyclin B and Plk1. Our data show that the primary function of Wip1 is to retain cellular competence to divide, rather than to silence the checkpoint to promote recovery. Our findings uncover Wip1 as a first in class recovery competence gene, and suggest that the principal function of Wip1 in cellular transformation is to retain proliferative capacity in the face of oncogene-induced stress.

ERG is a member of the ETS transcription factor family that is highly enriched in endothelial cells (ECs). IntroductionBlood vessel lumenization is a critical step in the development of a functional vascular system during vascular morphogenesis. 1,2 Major mechanisms of lumen formation include cell wrapping, budding, cavitation, cord hollowing, and cell hollowing. 3 Recently, there have been significant advances in our understanding of how endothelial cells (ECs) make lumens and tubes in 3D extracellular matrices. 4,5 We have shown that this process is regulated by the formation of intracellular vacuoles within ECs that aggregate and coalesce. 6 EC lumen and tube expansion occurs through MT1-MMP (membrane type 1-matrix metalloprotease)-dependent proteolysis of 3D collagen matrices. One of the key regulators of lumen formation is the Rho GTPase Cdc42, which was first shown to control this process in ECs and later in epithelial cells. [6][7][8][9] During EC tube formation, Cdc42 activates a signaling cascade that includes PKC⑀, p21 protein-activated kinase Pak2, Pak4, Srcfamily kinases (SFKs) Src, Yes, B-Raf, C-Raf, and ERK1/2. 10 Other Rho GTPases that have recently been evaluated for their role in EC tube formation include RhoA and Rac1. 5 Whereas knockdown of Rac1 with siRNA markedly inhibits EC lumen formation, suppression of RhoA has no effect.The ETS factors are a family of approximately 30 transcription factors that share a highly conserved DNA-binding domain. 11 ETS factors were originally identified as playing a central role in regulating several B-and T-cell-specific genes involved in hematopoiesis. We and others have also demonstrated a critical role for selected ETS family members in the regulation of several vascular specific genes, including Tie1, Tie2, VWF, Robo4, and endothelial nitric oxide synthase. [12][13][14][15][16] Although many ETS factors participate in the regulation of EC-restricted genes, most do not exhibit a vascular-specific expression pattern. However, several recent studies-including those from our own laboratory-have shown that the ETS factor ERG exhibits an EC-restricted expression pattern. [17][18][19][20] Furthermore, it has also been shown that several ECrestricted genes, including VE-cadherin, endoglin, and VWF, are regulated by ERG. [21][22][23] In addition to its function as a regulator of EC-specific gene expression, ERG also plays a developmental role during the differentiation of embryonic stem cells into ECs. 24,25 More recently, ERG has been shown to play a role in endothelial tube formation and angiogenesis. 21 In particular, one of the main downstream targets of ERG identified as playing a role in this process was VE-cadherin. The purpose of this study was to further define the regulatory role of ERG during EC morphogenesis. We found a dramatic inhibitory effect on EC tube and lumen formation in 3D collagen gels as a result of siRNA suppression of ERG. Using quantitative PCR (QPCR) of potential candidate genes we were able to identify the Rho GTPase family member, Rho...