COX‐2‐Mediated Regulation of VEGF‐C in Association With Lymphangiogenesis and Lymph Node Metastasis in Lung Cancer

The mechanisms underlying the effects of COX‐2 on tumor lymphangiogenesis remain largely undefined. Here, the human lung cancer cell lines A549, 95D, Anip973, and AGZY83‐a with different metastatic capacities were investigated by immunostaining, western blotting, and real‐time RT‐PCR. We observed increased expressions of COX‐2 and VEGF‐C in the three highly metastatic cell lines compared with the less metastatic AGZY83‐a cell line. The COX‐2‐specific inhibitor Celecoxib suppressed VEGF‐C expression whereas the main COX‐2 metabolite PGE₂ elevated VEGF‐C expression in Anip973 and AGZY83‐a cells in positive and negative experiments. To determine the functional link to COX‐2 more specifically and elucidate the mechanistic pathway, we used a siRNA to knock down the high COX‐2 expression in Anip973 cells and transfected a COX‐2 cDNA to enhance the low COX‐2 expression in AGZY83‐a cells, and then treated the cells with EP1/EP4 agonists or antagonists, respectively. The results revealed that the EP1/EP4 agonists significantly increased VEGF‐C production in the COX‐2‐knockdown Anip973 cells. In contrast, the EP1/EP4 antagonists diminished VEGF‐C production in the COX‐2‐overexpressing AGZY83‐a cells. Furthermore, animal models provided evidence that Celecoxib decreased VEGF‐C expression, lymphangiogenesis, and lymph node metastases in Anip973 cells, whereas PGE₂ treatment increased the same factors in the parental AGZY83‐a cells. A positive correlation between COX‐2 and VEGF‐C was also confirmed in vivo. The present data suggest that COX‐2 regulates VEGF‐C expression via the PGE₂ pathway, and that EP1/EP4 receptors are involved in PGE₂‐mediated VEGF‐C production. Thus, COX‐2 may represent a candidate gene for blocking tumor lymphangiogenesis and lymph node metastasis. Anat Rec, 2010. © 2010 Wiley‐Liss, Inc.