Histone Methyltransferase G9a Promotes Invasion of Non-small Cell Lung Cancer Through Enhancing Focaladhesionkinase Activationvia NF-KB Signaling Pathway

Abstract BackgroundOverexpression of euchromatic histone methyltransferase 2 (EHMT2 or G9a) is frequently found in a number of human cancers. Potential roles of G9a in invasion and metastasis are not well understood in non-small cell lung cancer (NSCLC). Here we investigated the effect and underlying mechanisms of G9a, and therapeutic implications of targeting G9a in the invasion of NSCLC. MethodsG9a-associated gene sets were identified by RNAseq analysis. Migration and invasion assays were applied to examine the impact of targeting G9a by siRNA knockdown orits specific inhibitor UNC0638 in NSCLC cells. Rescue experiments were designed to investigate the effect of focal adhesion kinase (FAK) and NF-κB inhibitors on the invasion of NSCLC cells overexpressing G9a. Correlation between the protein level of phosphorylated FAK and G9a was analyzed in NSCLC tissues.ResultsKnockdown and inhibition of G9a drastically suppressed in vitro cellular proliferation, migration, and invasion; while overexpression of G9a significantly enhanced proliferation, migration, and invasion of A549 and H1299 NSCLC cells. Targeting G9a led to a significant decrease in the expression of FAK protein and activation of FAK signaling pathway in both A549 and H1299 cells. Additionally, defactinib, a potent FAK inhibitor, partially abolished the enhanced migration and invasion by overexpression of G9a in these NSCLC cells. Furthermore, G9a was found to boost nuclear factor-kappa B (NF-κB) transcriptional activity in NSCLC cells through partially downregulating inhibitor of κB (IκBα), and an NF-κB inhibitor partially abolished the enhanced FAK activation by overexpressed G9a, which suggests that G9a-enhanced invasion and activation of FAK may be mediated by elevated NF-κB activity. Notably, a strong positive correlation between the immunohistochemical staining of G9a and phosphorylated FAK proteins was identified in H1299 xenografts and 159 cases of NSCLC tissues (R = 0.408).ConclusionsThese data strongly demonstrate that G9a may promote invasion and metastasis of NSCLC cells by enhancing FAK signaling pathway via elevating NF-κB transcriptional activity, indicating potential significance and therapeutic implications of these pathways in the invasion and metastasis of NSCLCs that overexpress G9a protein.