Cyclooxygenase (COX)-2, the inducible
isoform of
prostaglandin H synthase, has been implicated in the progression of human
lung adenocarcinoma. However, the mechanism underlying COX-2's effect on
tumor progression remains largely unknown. Lymphangiogenesis, the formation of new lymphatic vessels, has recently received considerable attention and become a new frontier of
tumor metastasis research. Here, we study the interaction between COX-2 and the lymphangiogenic factor,
vascular endothelial growth factor (
VEGF)-C, in human
lung cancer cells and their implication in patient outcomes. We developed an isopropyl-beta-D-thiogalactopyranoside-inducible COX-2 gene expression system in human
lung adenocarcinoma CL1.0 cells. We found that
VEGF-C gene expression but not
VEGF-D was significantly elevated in cells overexpressing COX-2. COX-2-mediated
VEGF-C up-regulation was commonly observed in a broad array of
non-small cell lung cancer cell lines. The use of pharmacological inhibitors or activators and genetic inhibition by EP receptor-
antisense oligonucleotides revealed that
prostaglandin EP(1) receptor but not other
prostaglandin receptors is involved in COX-2-mediated
VEGF-C up-regulation. At the mechanistic level, we found that COX-2 expression or
prostaglandin E(2) (
PGE(2)) treatment could activate the HER-2/Neu
tyrosine kinase receptor through the EP(1) receptor-dependent pathway and that this activation was essential for
VEGF-C induction. The transactivation of HER-2/Neu by
PGE(2) was inhibited by way of blocking the
Src kinase signaling using the specific Src family inhibitor, PP1, or transfection with the mutant dominant negative src plasmid.
Src kinase was involved in not only the HER-2/Neu transactivation but also the following
VEGF-C up-regulation by
PGE(2) treatment. In addition, immunohistochemical staining of 59
lung adenocarcinoma specimens showed that COX-2 level was highly correlated with
VEGF-C, lymphatic vessels density, and other clinicopathological parameters. Taken together, our results provided evidence that COX-2 up-regulated
VEGF-C and promotes lymphangiogenesis in human
lung adenocarcinoma via the EP(1)/Src/HER-2/Neu signaling pathway.