The Function Of NOX1and MicroRNA21for TLR4Signaling To Promote Tumor Metastasis Of Non-small Cell Lung Cancer

BackgroundLung cancer, most of which can be histologically diagnosed as non-small-celllung cancer (NSCLC), is the leading cause of cancer deaths worldwide. Currently, acombined treatment including surgery, chemotherapy, radiotherapy and targetedtherapy is used for the clinical NSCLC patients. However, the outcome of NSCLCpatients still remains poor and the overall5-year survival rate is around15%,dominantly because of the metastasis of NSCLC cells. Therefore, identification ofcritical effectors that were involved in metastasis of NSCLC cells were urgentlyneeded, which might ultimately aid the treatment of NSCLC patients.Germane to tumor metastasis, Toll-like receptor4(TLR4) has long been anextraordinary active subject of investigation. Studies showed that lipopolysaccharide(LPS) stimulation of TLR4could enhance the metastasis of various tumor cells suchas human papillary thyroid carcinoma cells, colorectal cancer cells, breast cancercells and human hepatocellular carcinoma cells. Of interest, stimulation of TLR4with LPS could promote the migration and invasion of lung cancer cells. However,the underlying mechanisms still remain incompletely understood.Reactive oxygen species (ROS) are conventionally thought as cytotoxic andmutagenic, and in high levels they induce cell death, apoptosis and senescence.However, high levels of ROS have been found in a large number of tumors, and thiselevated ROS could contribute to angiogenesis that were important for the metastasisof tumor cells. Given that NADPH oxidases are the only enzymes whose primaryfunction is to generate ROS, these findings indicated a possible role of NADPHoxidases in the metastasis of tumor cells. Indeed, the expression of NADPH oxidaseshas been found in several cancer cells including NSCLC cells. Recent study reportedthat NOX1played a pivotal role in LPS-induced cardiomyocyte apoptosis. TLR4signaling could also enhance the expression of NOX1in macrophages and coloncancer cells. Therefore, we speculated that NOX1might be involved in TLR4signaling enhanced metastasis of NSCLC cells.Objective The aim of this experiment was to study the potential role of ROS in themetastasis of tumor cells in clinical NSCLC by inducing TLR4pathway. Andevaluated the function of NADPH oxidase inhibitor (DPI) in tumor metastasis of lungcancer patients. Analyzedthe microRNA21expression on the activity of NADPHoxidase,and the effect of inhibiting the invasion ability of lung cancer cells wasinhibited.ResultsThe first part: NADPH oxidase1-dependent ROS is crucial for TLR4signalingto promote tumor metastasis of non-small cell lung cancer. Increased ROS wasrequired for enhanced NSCLC metastasis by TLR4signaling. NADPH oxidaseactivity was essential for enhanced NSCLC metastasis by TLR4signaling. NOX1conferred TLR4signaling-enhanced NSCLC metastasis. NOX1regulated theexpression of CXCR4and MMP9in NSCLC. Increased NOX1expression in tumortissues was associated with the TLR4expression and clinical stages in NSCLCpatients. Inhibition of NOX1/ROS alleviated enhanced lung tumor burdens ofNSCLC in mice with LPS-induced acute lung infection.The second part: Inhibition of NADPH oxidase protects against metastasis ofhuman lung cancer by decreasing microRNA-21. NOX inhibition abrogated themetastasis of human lung Cancer. Inhibition of NOX resulted in decreased expressionof microRNA21. Enforced expression of microRNA21abrogated the decreasedmetastasis of human lung cancer induced by NOX inhibition. Reduced expression ofmicroRNA21facilitated the NOX inhibitor to reduce the metastasis of human lungcancer. NOX inhibition led to increased PTEN expression and decreased MMP9expression. microRNA21expression level was correlated inversely with NOXexpression in tumor tissues of lung cancer patients. tumor-burdened mice aftertreatment with DPI the expression of ROS,microRNA21,PTEN and MMP9.Summary and ConclusionsFirstly, NOX1enhanced the ability of NSCLC invasion in the process of TRL4signal pathway. Secondly, the inhibition of NADPH oxidase activity by reducing theexpression of microRNA21can effectively prevent the metastasis of human lung cancer cells. Finally, decreased expression of microRNA21in lung cancer cells inresponse to DPI treatment was responsible for the reduced metastasis of NSCLCcells.