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

The forkhead box m1 (Foxm1 or Foxm1b) protein (previously called HFH-11B, Trident, Win or MPP2) is abundantly expressed in human non-small cell lung cancers where it transcriptionally induces expression of genes essential for proliferation of tumor cells. In this study, we used Rosa26-Foxm1 transgenic mice, in which the Rosa26 promoter drives ubiquitous expression of Foxm1 transgene, to identify new signaling pathways regulated by Foxm1. Lung tumors were induced in Rosa26-Foxm1 mice using the 3-methylcholanthrene (MCA)/butylated hydroxytoluene (BHT) lung tumor initiation/promotion protocol. Tumors from MCA/BHT-treated Rosa26-Foxm1 mice displayed a significant increase in the number, size and DNA replication compared to wild-type mice. Elevated tumor formation in Rosa26-Foxm1 transgenic lungs was associated with persistent pulmonary inflammation, macrophage infiltration and increased expression of cyclooxygenase-2 (Cox-2), Cdc25C phosphatase, cyclin E2, chemokine ligands CXCL5, CXCL1 and CCL3, cathepsins and matrix metalloprotease-12. Cell culture experiments with A549 human lung adenocarcinoma cells demonstrated that depletion of Foxm1 by either short interfering RNA transfection or treatment with Foxm1-inhibiting ARF 26-44 peptide significantly reduced Cox-2 expression. In co-transfection experiments, Foxm1 protein-induced Cox-2 promoter activity and directly bound to the -2566/- 2580 bp region of human Cox-2 promoter.