The Forkhead Box m1 transcription factor stimulates the proliferation of tumor cells during development of lung cancer.

The proliferation-specific Forkhead Box m1 (Foxm1 or Foxm1b) transcription factor (previously called HFH-11B, Trident, Win, or MPP2) regulates expression of cell cycle genes essential for progression into DNA replication and mitosis. Expression of Foxm1 is found in a variety of distinct human cancers including hepatocellular carcinomas, intrahepatic cholangiocarcinomas, basal cell carcinomas, ductal breast carcinomas, and anaplastic astrocytomas and glioblastomas. In this study, we show that human Foxm1 protein is abundantly expressed in highly proliferative human non-small cell lung cancers (NSCLC) as well as in mouse lung tumors induced by urethane. To determine the role of Foxm1 during the development of mouse lung tumors, we used IFN-inducible Mx-Cre recombinase transgene to delete mouse Foxm1 fl/fl-targeted allele before inducing lung tumors with urethane. We show that Mx-Cre Foxm1-/- mice exhibit diminished proliferation of lung tumor cells causing a significant reduction in number and size of lung adenomas. Transient transfection experiments with A549 lung adenocarcinoma cells show that depletion of Foxm1 levels by short interfering RNA caused diminished DNA replication and mitosis and reduced anchorage-independent growth of cell colonies on soft agar. Foxm1-depleted A549 cells exhibit reduced expression of cell cycle-promoting cyclin A2 and cyclin B1 genes. These data show that Foxm1 stimulates the proliferation of tumor cells during progression of NSCLC.

The forkhead box M1 transcription factor contributes to the development and growth of mouse colorectal cancer.

BACKGROUND & AIMS: In this study, we used Forkhead Box m1b (Foxm1b) transgenic mice and conditional Foxm1 knock-out mice to examine the role of Foxm1 in colon cancer development and proliferation. METHODS: To induce mouse colorectal cancer, we used a single intraperitoneal injection of azoxymethane (AOM) followed by three 1-week cycles of 2.5% dextran sodium sulfate (DSS) water, each cycle separated by 2 weeks. For these colon tumor studies, we used either Rosa26-Foxm1b transgenic mice that ubiquitously expressed the human Foxm1b complementary DNA or mice in which the Foxm1 fl/fl targeted allele was deleted in colonic epithelial cells using the gut-specific Villin-Cre recombinase transgene (Villin-Cre). Colorectal tumor number and bromodeoxyuridine labeling were determined in Rosa26-Foxm1b mice, Villin-Cre Foxm1-/-, mice and wild-type mice after 12 weeks of AOM/DDS exposure. We also used Foxm1 small interfering RNA-depleted human DLD1 and mouse CT26 colon cancer cell lines to examine DNA replication and anchorage-independent growth. RESULTS: After 12 weeks of treatment with AOM/DSS, Rosa26 Foxm1b transgenic mice showed an increase in the number and size of colorectal tumors compared with wild-type mice. Likewise, a significant reduction in the development and growth of colorectal tumors was found in Villin-Cre Foxm1-/- mice compared with Foxm1 fl/fl mice after AOM/DSS treatment, which was associated with decreased expression of cyclin A2, cyclin B1, survivin, and T-cell factor 4 genes. Moreover, Foxm1-depleted colon cancer cell lines showed reduced DNA replication and anchorage-independent growth. CONCLUSIONS: These studies suggest that Foxm1 is critical for the proliferation and growth of colorectal cancer.

The forkhead box m1 transcription factor is essential for embryonic development of pulmonary vasculature.

Transgenic and gene knock-out studies demonstrated that the mouse Forkhead Box m1 (Foxm1 or Foxm1b) transcription factor (previously called HFH-11B, Trident, Win, or MPP2) is essential for hepatocyte entry into mitosis during liver development, regeneration, and liver cancer. Targeted deletion of Foxm1 gene in mice produces an embryonic lethal phenotype due to severe abnormalities in the development of liver and heart. In this study, we show for the first time that Foxm1(-/-) lungs exhibit severe hypertrophy of arteriolar smooth muscle cells and defects in the formation of peripheral pulmonary capillaries as evidenced by significant reduction in platelet endothelial cell adhesion molecule 1 staining of the distal lung. Consistent with these findings, significant reduction in proliferation of the embryonic Foxm1(-/-) lung mesenchyme was found, yet proliferation levels were normal in the Foxm1-deficient epithelial cells. Severe abnormalities of the lung vasculature in Foxm1(-/-) embryos were associated with diminished expression of the transforming growth factor beta receptor II, a disintegrin and metalloprotease domain 17 (ADAM-17), vascular endothelial growth factor receptors, Polo-like kinase 1, Aurora B kinase, laminin alpha4 (Lama4), and the Forkhead Box f1 transcription factor. Cotransfection studies demonstrated that Foxm1 stimulates transcription of the Lama4 promoter, and this stimulation requires the Foxm1 binding sites located between -1174 and -1145 bp of the mouse Lama4 promoter. In summary, development of mouse lungs depends on the Foxm1 transcription factor, which regulates expression of genes essential for mesenchyme proliferation, extracellular matrix remodeling, and vasculogenesis.

Ubiquitous expression of the forkhead box M1B transgene accelerates proliferation of distinct pulmonary cell types following lung injury.

The delayed early transcription factor Forkhead Box M1B (FoxM1B) is expressed in proliferating cells, but its expression is extinguished in cells undergoing terminal differentiation. Liver regeneration studies with genetically altered mice that either prematurely expressed FoxM1B in hepatocytes or contained a hepatocyte-specific deletion of the Foxm1b allele demonstrated that FoxM1B is critical for regulating the expression of cell cycle genes required for hepatocyte proliferation. Furthermore, preventing the decline in hepatocyte FoxM1B levels during aging was sufficient to increase regenerating hepatocyte proliferation and expression of cell cycle genes to levels found in young regenerating mouse liver. Although these liver regeneration studies demonstrated that FoxM1B is required for hepatocyte proliferation, whether FoxM1B regulates proliferation of cell types other than hepatocytes remains to be determined. Here, we developed a new TG mouse line in which the -800-base pair Rosa26 promoter was used to drive expression of the FoxM1B transgene in all mouse tissues and found that Rosa26-FoxM1B TG mice were healthy, displaying no developmental defects. We used butylated hydroxytoluene (BHT) lung injury to demonstrate that premature expression of the FoxM1B transgene protein accelerated proliferation of different lung cell types, including alveolar type II epithelial cells, bronchial epithelial and smooth muscle cells, and endothelial cells of pulmonary capillaries and arteries. This was associated with the earlier expression of the cell cycle promoting cyclin A2, cyclin E, cyclin B1, cyclin F, and cyclin dependent kinase-1 (Cdk1) genes and diminished protein levels of Cdk inhibitor p21Cip1. Taken together, these results suggest that increasing FoxM1B levels is an effective means to stimulate cellular proliferation during aging and in lung diseases such as emphysema.

Foxf1 haploinsufficiency reduces Notch-2 signaling during mouse lung development.

The forkhead box (Fox) f1 transcription factor is expressed in the mouse splanchnic (visceral) mesoderm, which contributes to development of the liver, gallbladder, lung, and intestinal tract. Pulmonary hemorrhage and peripheral microvascular defects were found in approximately half of the newborn Foxf1(+/-) mice, which expressed low levels of lung Foxf1 mRNA [low-Foxf1(+/-) mice]. Microvascular development was normal in the surviving newborn high-Foxf1(+/-) mice, which compensated for pulmonary Foxf1 haploinsufficiency and expressed wild-type Foxf1 levels. To identify expression of genes regulated by Foxf1, we used Affymetrix microarrays to determine embryonic lung RNAs influenced by Foxf1 haploinsufficiency. Embryonic Foxf1(+/-) lungs exhibited diminished expression of hepatocyte growth factor receptor c-Met, myosin VI, the transcription factors SP-3, BMI-1, ATF-2, and glucocorticoid receptor, and cell cycle inhibitors p53, p21(Cip1), retinoblastoma, and p107. Furthermore, Notch-2 signaling was decreased in embryonic Foxf1(+/-) lungs, as evidenced by significantly reduced levels of the Notch-2 receptor and the Notch-2 downstream target hairy enhancer of split-1. The severity of the Notch-2-signaling defect in 18-day postcoitus Foxf1(+/-) lungs correlated with Foxf1 mRNA levels. Disruption of pulmonary Notch-2 signaling continued in newborn low-Foxf1(+/-) mice, which died of lung hemorrhage and failed to compensate for Foxf1 haploinsufficiency. In contrast, in newborn high-Foxf1(+/-) lungs, Notch-2 signaling was restored to the level found in wild-type mice, which was associated with normal microvascular formation and survival. Foxf1 haploinsufficiency disrupted pulmonary expression of genes in the Notch-2-signaling pathway and resulted in abnormal development of lung microvasculature.

The mouse Forkhead Box m1 transcription factor is essential for hepatoblast mitosis and development of intrahepatic bile ducts and vessels during liver morphogenesis.

Conditional deletion of the mouse Forkhead Box (Fox) m1b targeted allele in adult hepatocytes (Foxm1, previously called HFH-11B, Trident, Win, or MPP2) demonstrated that the Foxm1b transcription factor is essential for hepatocyte mitosis during liver regeneration. To determine the role of Foxm1b in liver development, we have generated Foxm1b -/- mice that deleted the Foxm1b exons encoding the winged helix DNA binding and transcriptional activation domains. Here, we show that all of the Foxm1b -/- embryos died in utero by 18.5 days postcoitum (dpc). Embryonic Foxm1b -/- livers displayed a 75% reduction in the number of hepatoblasts, resulting from diminished DNA replication and a failure to enter mitosis causing a polyploid phenotype. Reduced hepatoblast mitosis was associated with decreased protein levels of the Polo-like kinase 1 and Aurora B kinase, which phosphorylate regulatory proteins essential for orchestrating mitosis and cytokinesis. Diminished proliferation of Foxm1b -/- hepatoblasts contributed to abnormal liver development with significant reduction in the number of large hepatic veins compared to embryonic wild-type (WT) liver. Furthermore, embryonic Foxm1b -/- livers did not develop intrahepatic bile ducts, and these presumptive biliary hepatoblasts failed to express either biliary cytokeratins or nuclear levels of hepatocyte nuclear factor 1beta. These results suggest that Foxm1b is critical for hepatoblast precursor cells to differentiate toward biliary epithelial cell lineage. Finally, we used a hepatoblast-specific Cre recombinase transgene to mediate deletion of the Foxm1b fl/fl allele in the developing liver, and these embryos died in utero and exhibited diminished hepatoblast proliferation with similar abnormalities in liver morphogenesis, suggesting that the defect in liver development contributed to embryonic lethality.

Foxm1b transcription factor is essential for development of hepatocellular carcinomas and is negatively regulated by the p19ARF tumor suppressor.

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related deaths worldwide. Here, we provide evidence that the Forkhead Box (Fox) m1b (Foxm1b or Foxm1) transcription factor is essential for the development of HCC. Conditionally deleted Foxm1b mouse hepatocytes fail to proliferate and are highly resistant to developing HCC in response to a Diethylnitrosamine (DEN)/Phenobarbital (PB) liver tumor-induction protocol. The mechanism of resistance to HCC development is associated with nuclear accumulation of the cell cycle inhibitor p27(Kip1) protein and reduced expression of the Cdk1-activator Cdc25B phosphatase. We showed that the Foxm1b transcription factor is a novel inhibitory target of the p19(ARF) tumor suppressor. Furthermore, we demonstrated that conditional overexpression of Foxm1b protein in osteosarcoma U2OS cells greatly enhances anchorage-independent growth of cell colonies on soft agar. A p19(ARF) 26-44 peptide containing nine D-Arg to enhance cellular uptake of the peptide was sufficient to significantly reduce both Foxm1b transcriptional activity and Foxm1b-induced growth of U2OS cell colonies on soft agar. These results suggest that this (D-Arg)(9)-p19(ARF) 26-44 peptide is a potential therapeutic inhibitor of Foxm1b function during cellular transformation. Our studies demonstrate that the Foxm1b transcription factor is required for proliferative expansion during tumor progression and constitutes a potential new target for therapy of human HCC tumors.