Cyclooxygenase-2 Induces EP1- and HER-2/Neu-Dependent Vascular Endothelial Growth Factor-C Up-Regulation

Abstract

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-␤-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 receptorantisense 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.

COX-2-mediated stimulation of the lymphangiogenic factor VEGF-C in human breast cancer

“…A similar association between COX-2 and VEGF-C was also demonstrated at the protein levels by immunohistochemical studies of squamous cell carcinomas of the head and neck (Kyzas et al, 2005) and oesophagus (Byeon et al, 2004) as well as in non-small cell lung adenocarcinoma (Su et al, 2004). A role of COX-2 in VEGF-C upregulation was suggested in the case of non-small cell lung cancer cells (Su et al, 2004) as well as oesophageal adenocarcinoma cells (von Rahden et al, 2005). To date, however, no information exists regarding whether COX-2 is causally associated with VEGF-C upregulation and thereby lyphangiogenesis in breast cancer, and if so, what is the role of EP receptors on cancer cells in this event.…”

“…Interestingly, a positive association between COX-2 and VEGF-C mRNA expression has been reported in oesophageal adenocarcinoma (von Rahden et al, 2005). A similar association between COX-2 and VEGF-C was also demonstrated at the protein levels by immunohistochemical studies of squamous cell carcinomas of the head and neck (Kyzas et al, 2005) and oesophagus (Byeon et al, 2004) as well as in non-small cell lung adenocarcinoma (Su et al, 2004). A role of COX-2 in VEGF-C upregulation was suggested in the case of non-small cell lung cancer cells (Su et al, 2004) as well as oesophageal adenocarcinoma cells (von Rahden et al, 2005).…”

“…VEGF-C synthesis in other cell types was reported to utilize signalling pathways associated with Her2/neu, Src, and p38 MAP kinases (Tsai et al, 2003;Su et al, 2004). We tested whether the application of the respective kinase inhibitors affected VEGF-C synthesis by MDA-MB-231 breast cancer cells.…”

Cyclooxygenase-2 transactivates the epidermal growth factor receptor through specific E-prostanoid receptors and Tumor Necrosis Factor-α converting enzyme

“…Pai and coworkers demonstrated that PGE 2 transactivated EGFR through release of TGFα [9], while another report [11] showed EGFR transactivation that did not depend on extracellular release of growth factors. Other groups have demonstrated transactivation of ErbB receptors, but they did not address whether or not growth factor release was necessary [24,25]. While these reports concur that PGE 2 can transactivate EGFR, they do not agree on the requirement for metalloproteinase activity.…”

“…In contrast to EP receptors 2-4, we found that over-expressed EP1 did not transactivate EGFR. However, Han and Wu recently demonstrated that an EP1 receptor agonist induced phosphorylation of EGFR and enhanced proliferation and migration of cholangiocarcinoma cells [24], and Su et al showed that PGE 2 transactivated ErbB2 through EP1 [25]. These differing results likely reflect differences between cell lines, opening the possibility that in the correct context, all four EP receptors can transactivate EGFR.…”