Sphingosine-1-phosphate induces VEGF-C expression through a MMP-2/FGF-1/FGFR1-dependent pathway in endothelial cells in vitro

Aim: To investigate whether sphingosine-1-phosphate (SIP), a potent angiogenic factor, induced vascular endothelial growth factor-C (VEGF-C) expression in endothelial cells in vitro and to examine its underlying mechanisms. Methods: Human umbilical vein endothelial cells (HUVECs) were examined. VEGF-C mRNA expression in the cells was assessed using real-time PCR. VEGF-C protein and FGFR-I phosphorylation in the cells were measured with ELISA. RNA interference was used to downregulate the expression of matrix metalloproteinase-2 (MMP-2), fibroblast growth factor-1 (FGF-1) and FGF receptor-1 (FGFR-1). Results: Incubation of HUVECs with SIP (1, 5, and 10 mu mol/L) significantly increased VEGF-C expression. The effect was blocked by pretreatment with the MMP inhibitor GM6001 or the FGFR inhibitor SU5402, but not the EGFR inhibitor AGI478. The effect was also blocked in HUVECs that were transfected with FGFR-1 or MMP-2 siRNA. Furthermore, incubation of HUVECs with SIP (5 mu mol/L) significantly increased FGFR-I phosphorylation, which was blocked by GM6001. Moreover, knockdown of FGF-1, not FGF-2, in HUVECs with siRNAs, blocked SIP-induced VEGF-C expression. Conclusion: SIP induces VEGF-C expression through a MMP-2/ FGF-1/FGFR-1-dependent pathway in HUVECs.