Lymphatic Metastasis of NSCLC Involves Chemotaxis Effects of Lymphatic Endothelial Cells through the CCR7-CCL21 Axis Modulated by TNF-α.

ABSTRACT

Metastasis and recurrence are the main causes of lung adenocarcinoma patients' death. Lymphatic metastasis is the main way of non-small cell lung cancer (NSCLC) metastasis. C-C chemokine receptor type 7 (CCR7) overexpression has been demonstrated to mediate occurrence and progression of NSCLC. Moreover, Chemokine ligand 21 (CCL21) was used to activate CCR7. The CCR7-CCL21 axis is one of the most common "chemokine-receptor" modes of action in the development and metastasis of multiple tumors. However, the role of the CCR7-CCL21 axis in lymphatic metastasis of NSCLC is poorly understood. The study was conducted to investigate the molecular mechanism underlying CCR7-CCL21 axis-mediated lymphatic metastasis of NSCLC A549 cells. Tumor necrosis factor α (TNF-α) could regulate the tumor microenvironment balance by promoting chemokine secretion. Our study demonstrated that TNF-α promoted CCL21 production in human lymphatic endothelial cells (HLEC). Results further showed that TNF-α significantly activated the NF-κB pathway in HLEC. NF-κB pathway inhibition with ammonium pyrrolidinedithiocarbamate (PDTC) caused a significant decrease in CCL21 secretion, suggesting that TNF-α-induced CCL21 secretion in HLEC was through NF-κB pathway. Co-culture of A549 cells and TNF-α-treated HLEC confirmed that the metastasis of A549 cells was enhanced, meanwhile, apoptosis-related proteins were hardly affected. The data proved that a co-culture system prevented cell apoptosis while inducing the lymphatic metastasis of A549 cells. However, the situation was reversed after neutralizing CCL21 expression, suggesting that TNF-α-induced CCL21 secretion in HLEC is involved in A549 cells metastasis. Collectively, our finding demonstrated that NF-κB pathway-controlled CCL21 secretion of HLEC contributing to the lymphatic metastasis of A549 cells via the CCR7-CCL21 axis, validating the CCR7-CCL21 axis as a potential target to inhibit metastasis of NSCLC.