The m6A demethylase FTO promotes the growth of lung cancer cells by regulating the m6A level of USP7 mRNA

Lung cancer is one of the leading causes of cancer-related death in developed countries. Despite decades of intensive efforts to comate this malignant disease, the prognosis of lung cancer remains unfavorable and is especially poor in advanced non-small cell lung cancer (NSCLC). However, whether and how the m6A demethylase FTO functions in lung cancer cells remain unknown. Here in the present study, we show that FTO plays an oncogenic role in human NSCLC. FTO mRNA and protein levels were overexpressed in human NSCLC tissues and cell lines, which was associated with the reduced m6A content. We next knocked down FTO expression in human lung cancer cell lines with lentivirus-mediated shRNAs and the cellular proliferation assay demonstrated that FTO loss-of-function reduced the proliferation rate of cancer cells. FTO knockdown also inhibited the colony formation ability of lung cancer cells. Importantly, our xenograft experiment showed that FTO knockdown reduced lung cancer cells growth in vivo. Mechanism analysis demonstrated that FTO decreased the m6A level and increased mRNA stability of ubiquitin-specific protease (USP7), which was relied on the demethylase activity of FTO. USP7 mRNA level was overexpressed in human lung cancer tissues and USP7 expression was positively correlated with FTO mRNA level. Genetic knockdown or pharmacological inhibition (P5091 or P22027) of USP7 reduced the proliferation rate of lung cancer cells and decreased the capacity of colony formation of lung cancer cells in vitro, whereas lung cancer cells growth inhibition by FTO knockdown is restored by overexertion of USP7. Collectively, our findings demonstrate that the m6A demethylase FTO promotes the growth of NSCLC cells by increasing the expression of USP7.