Lymphangiogenesis has been shown to promote
lymph node metastasis in
cancers, making it an important target in
cancer therapy.
Vascular endothelial growth factor (
VEGF)-C is upregulated in various
tumors/
cancers and is one of the most potent
growth factors for inducing lymphangiogenesis and promoting
lymph node metastasis (LNM). Likewise,
cyclooxygenase (COX)-2 plays major roles in
carcinogenesis,
tumor growth and
metastasis via multiple mechanisms including inactivation of host antitumor immunity and promotion of
tumor cell migration,
tumor cell invasiveness and
tumor-associated angiogenesis and lymphangiogenesis. We previously demonstrated an association between COX-2 and
VEGF-C in an in vitro model of
lung cancer. However, little is known about the regulation of
VEGF-C by COX-2 in
cervical cancer. In this study, we measured the COX-2 and
VEGF-C expressions by immunohistochemistry in 23 LNM-positive and 20 LNM-negative
cervical cancer specimens. We then examined the correlations among the expressions and the lymphatic microvessel density (LMVD) and ultrastructural changes to the lymphatic vessel walls by
enzyme histochemical staining and electron microscopy. In addition, we used the HeLa
cervical cancer cell line to explore the in vitro regulation of
VEGF-C by COX-2 and its metabolite,
PGE(2), using
siRNA-mediated gene silencing and EP receptor blockade. The LNM-positive specimens exhibited significantly higher
VEGF-C expression, COX-2 expression and LMVD than the LNM-negative specimens. Furthermore, there were strong correlations between the levels of COX-2 expression and the levels of
VEGF-C expression and secretion and a significant positive association between the LMVD and LNM.
siRNA-mediated knockdown of COX-2 expression inhibited
VEGF-C mRNA expression while EP1 and EP4 receptor antagonists reduced the
VEGF-C protein level and
tyrosine phosphorylation of
Src kinase. Moreover, inhibition of
Src kinase with the
tyrosine kinase inhibitor PP1 attenuated
VEGF-C expression. Collectively, our data provide evidence for a clinical association between COX-2 and
VEGF-C expressions in
cervical cancer. EP1 and EP4 receptors may be involved in the COX-2-mediated regulation of
VEGF-C protein and
mRNA expressions. Src may be a downstream mediator of EP1 and EP4 receptors. COX-2 inhibition may diminish LNM by suppressing
VEGF-C-mediated lymphangiogenesis.