P3.03-14 Downregulation of FOXM1 Inhibits Tumor Proliferation, Colony Formation and Spheroid Formation of Non-Small Cell Lung Cancer

Abstract

Forkhead box protein M1 (FOXM1) is a member of the forkhead superfamily of transcription factors. It plays numerous critical roles in cancer development and progression, such as the regulation of G2/M transitions of cell cycle, anti-apoptosis, DNA damage repair, invasion, and drug resistance. In a pan-cancer meta-analysis of mRNA expression signatures from ∼18,000 human tumors with overall survival outcomes across 39 malignancies, over expression of the FOXM1 was a major predictor of adverse outcomes and appeared anti-correlated with tumor immune cell populations (Nat Med. 2015;21(8):938-945). Thus, we examined the prognostic and biological role of FOXM1 in non-small cell lung cancer (NSCLC). We examined the prognostic impact of FOXM1 expression in lung cancer patients using a genomic database (UTSW – “Lung Cancer Explorer” and KM-Plotter). We also assessed the expression of FOXM1 in NSCLC lines, and human bronchial epithelial cells (HBECs), and assessed the association between FOXM1 and cell cycle related genes in RNA-seq data. We examined the effect of the downregulation of FOXM1 on tumor proliferation and colony formation of lung adenocarcinoma cell lines by short hairpin RNA (Tet-pLKO-FOXM1-shRNA), and the effect of the downregulation of FOXM1 on tumor 3D spheroid formation in spheroid-forming cell lines using Nunclon Sphera. High FOXM1 expression correlated with poor prognosis in NSCLC patients who underwent surgical resection, especially adenocarcinoma. FOXM1 expression in lung cancer cell lines was also much higher than in HBECs. The expression level of FOXM1 was significantly correlated with cell cycle regulator genes such as CCNB1, CCNA2, and PLK1 in both tissue samples (Lung cancer explorer) and cell lines (our data). shRNA mediated reduction of FOXM1 expression significantly inhibited tumor cell proliferation and colony formation of NSCLC cells. Additionally, in the 3D spheroid formation assay, FOXM1 knockdown altered spheroid morphology. FOXM1 was over expressed in NSCLC compared to normal lung epithelial cells, and high tumor FOXM1 expression was prognostic of poor survival in patients with NSCLC who underwent surgical resection, especially in patients with adenocarcinoma. FOXM1 expression correlated with the expression of regulators of the G2/M transition, and functional knockdown studies demonstrate an important role in tumor proliferation, colony formation, and 3D spheroid formation. Overall, our results suggest that FOXM1 has important roles in NSCLC growth, while data from other groups using “CIBERSORT” analyses suggest a possible role for FOXM1 in tumor immune cells infiltration, collectively indicating that FOXM1 is a potential target for the treatment of lung cancer adenocarcinoma.