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Mortality in cancer patients principally results from metastatic spread of cancer cells to distant organs. Vascular endothelial growth factor C (VEGF-C) binds to VEGF receptor 3 (VEGFR-3/Flt-4), in turn activating lymphangiogenesis. Here we have demonstrated that the expression of Flt-4 receptor not only could be detected on lymphatic vessel endothelium but also on human lung adenocarcinoma epithelial cells. Examination of sixty-five patients with lung adenocarcinoma revealed that patients with the higher expression level of Flt-4 and VEGF-C had poor prognosis, i.e. shorter survival. Treatment with recombinant VEGF-C or transfection with VEGF-C expressing vector strongly induced the tyrosine phosphorylation of Flt-4 as well as promoted migratory and invasive capacity in human lung adenocarcinoma H928 cells. In contrast, interruption of VEGF-C/Flt-4 autocrine loop by using recombinant Flt-4/Fc, which specifically binds VEGF-C and inhibits Flt-4 signaling, or transfection with the mutant Flt-4 expression vector Flt-4ΔTK (deletion of the kinase domain of Flt-4) effectively reduced the invasive activity of A549 cells. By utilizing mini cDNA array, we have found that the contactin-1 (CNTN-1) gene was readily modulated by the VEGF-C/Flt-4 axis. Diminishing the CNTN-1 expression by DNA vector-based small interference RNA (siRNA) significantly abolished VEGF-C/Flt-4 axis-induced cell invasion. Pharmacological or genetic inhibition studies showed that both Src and p38 MAP kinase activation were critical for CNTN-1 induction by VEGF-C/Flt-4 axis. In an in vivo experimental metastasis assay, inhibition of the VEGF-C/Flt-4 axis function by blockage of Flt-4 receptor activation or knockdown of CNTN-1 gene level could significantly impair the metastatic potency of lung adenocarcinoma cells. Taken together, our data suggest that the VEGF-C/Flt-4 axis played an important role in regulating invasive facility of lung adenocarcinoma cells and its function is mediated through up-regulation of CNTN-1 gene via a Src/p38 MARK signaling pathway.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]