Inhibition of NADPH oxidase 4 attenuates lymphangiogenesis and tumor metastasis in breast cancer

Lymphangiogenesis is thought to contribute to promote tumor cells to enter lymphatic vessels and plant at a secondary site. Endothelial cells are the cornerstone of the generation of new lymphatic vessels. NADPH oxidase 4 (Nox4) is the most abundant one of NADPH oxidases in endothelial cells and the most studied one in relevance with cancer. Our purpose is to analyze the relationship between Nox4 and lymphangiogenesis and find out whether the newborn lymphatic vessels lead to cancer metastasis. We first explored the expression of Nox4 in lymphatic endothelial cells of primary invasive breast tumors and human normal mammary glands using GEO databases and found that Nox4 was upregulated in primary invasive breast tumors samples. In addition, its high expression correlated with lymph node metastasis in breast cancer patients. Nox4 could increase the tube formation and lymphatic vessel sprouting in a three-dimensional setting. In vivo, inhibition of Nox4 in 4T1 tumor-bearing mice could significantly decrease the tumor lymphangiogenesis and metastasis. Nox4 may increase tumor lymphangiogenesis via ROS/ERK/CCL21 pathway and attract CCR7-positive breast cancer cells to entry lymphatic vessels and distant organs. In conclusion, our results show that Nox4 is a factor that promotes lymphangiogenesis and is a potential target of antitumor metastasis.