The Forkhead Box m1 Transcription Factor Stimulates the Proliferation of Tumor Cells during Development of Lung Cancer

Abstract

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 nonsmall 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 IFNinducible Mx-Cre recombinase transgene to delete mouse Foxm1 fl/fl-targeted allele before inducing lung tumors with urethane. We show that Mx-Cre Foxm1 À/À 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.

Transgenic expression of the forkhead box M1 transcription factor induces formation of lung tumors

“…Consistent with an important role of Foxm1 in cell cycle progression, increased expression of Foxm1 was found in human lung adenocarcinomas and squamous cell carcinomas (Kim et al, 2006), prostate adenocarcinomas , basal cell carcinomas (Teh et al, 2002), intrahepatic cholangiocarcinomas (Obama et al, 2005), anaplastic astrocytomas and glioblastomas (van den Boom et al, 2003), infiltrating ductal breast carcinomas (Wonsey and Follettie, 2005), as well as in many other solid tumors (Pilarsky et al, 2004). Foxm1 is also overexpressed in hepatocellular carcinomas from patients who respond poorly to treatment (Lee et al, 2004).…”

“…Ubiquitous expression of Foxm1 transgene increases the total number and size of lung tumors induced by MCA/BHT treatment We previously demonstrated that Foxm1 protein is abundantly expressed in highly proliferative human NSCLC as well as in mouse lung tumors induced by urethane (Kim et al, 2006). To determine consequences of Foxm1 overexpression during formation of lung tumors, we used Rosa26-Foxm1 transgenic mice, which contain high levels of Foxm1 protein in all tissues (Kalinichenko et al, 2003).…”

“…Although Cox-2 protein was undetectable in either untreated WT or untreated Rosa26- Decreased Cox-2 expression in Foxm1-deficient lung tumors from Mx-Cre Foxm1 fl/fl mice We have previously demonstrated that treatment of MxCre Foxm1 fl/fl mice with synthetic double-stranded (dsRNA; also known as PolyI:PolyC or PIPC) induced a 75% deletion of Foxm1-floxed allele in the lung during urethane-mediated lung carcinogenesis (Kim et al, 2006). This incomplete Foxm1 deletion resulted in formation of both Foxm1-negative and Foxm1-positive tumors in dsRNA-treated Mx-Cre Foxm1 fl/fl lungs (Kim et al, 2006). Therefore, we examined Cox-2 protein in these two types of Mx-Cre Foxm1 fl/fl lung tumors using immunohistochemical staining with Cox-2 antibody.…”

“…Depletion of Foxm1 in A549 cells caused diminished DNA replication and mitosis, reduced anchorage-independent growth of cell colonies on soft agar and reduced expression of cell cycle-promoting cyclin A2 and cyclin B1 (Kim et al, 2006). Partial deletion of mouse Foxm1-floxed targeted allele in vivo was sufficient to significantly reduce the number and size of lung adenomas induced by urethane (Kim et al, 2006). In this study, to identify new signaling pathways regulated by Foxm1, we used Rosa26-Foxm1 transgenic mice, in which the Rosa26 promoter drives ubiquitous expression of the Foxm1 transgene (Kalinichenko et al, 2003).…”

“…Foxm1 is also overexpressed in hepatocellular carcinomas from patients who respond poorly to treatment (Lee et al, 2004). Depletion of Foxm1 in A549 cells caused diminished DNA replication and mitosis, reduced anchorage-independent growth of cell colonies on soft agar and reduced expression of cell cycle-promoting cyclin A2 and cyclin B1 (Kim et al, 2006). Partial deletion of mouse Foxm1-floxed targeted allele in vivo was sufficient to significantly reduce the number and size of lung adenomas induced by urethane (Kim et al, 2006).…”