Paracrine signaling by VEGF-C promotes non-small cell lung cancer cell metastasis via recruitment of tumor-associated macrophages.

High expression of tumoral vascular endothelial growth factor C (VEGF-C) is correlated with clinical non-small cell lung cancer (NSCLC) metastasis and patient survival. Nevertheless, the comprehensive mechanisms accounting for VEGF-C-mediated cancer progression remain largely unclear. The present study found that VEGF-C expression was upregulated in various NSCLC cell lines. By utilizing transwell migration assay, we found that both recombinant VEGF-C protein and overexpression of VEGF-C in NSCLC cells (A549 and H441 cell lines) could efficiently enhance RAW264.7 cell (murine macrophages) migration. However, recombinant VEGF-C treatment had no effects on both CD206 (an M2 macrophage marker) expression and M1/M2 cytokine profiles of macrophages. Furthermore, additional treatment of recombinant Flt-4/Fc, the specific VEGFR-3 inhibitor or the specific VEGFR-2 inhibitor significantly suppressed macrophage migration compared with A549-CM (conditioned medium) or H441-CM alone group, confirming that NSCLC cells-derived VEGF-C is sufficient to promote macrophage migration. Interestingly, VEGF-C could stimulate the Src/p38 signaling via VEGFR-2/3 axis in macrophages, and inhibition of Src/p38 signaling obviously reversed the enhancement effect of VEGF-C on macrophage migration. Finally, the functional importance of macrophage infiltration induced by tumoral VEGF-C in promoting metastasis was established in a mouse model. In conclusion, our results highlight a novel function of tumoral VEGF-C that paracrinely induces macrophage recruitment, and resultantly promotes NSCLC cell metastasis. Therefore, VEGF-C/VEGFR-2/3 axis may be a promising microenvironmental target against progression of NSCLC.