Upregulation of neuropilin-1 by basic fibroblast growth factor enhances vascular smooth muscle cell migration in response to VEGF

Neuropilin-1 (NRP-1) is a co-receptor for vascular endothelial growth factor (VEGF). During neovascularization, vascular smooth muscle cells (VSMCs) and pericytes modulate the function of endothelial cells. Factors that mediate NRP-1 in human VSMCs (hVSMCs) remain to be elucidated. We studied various angiogenic cytokines to identify factors that increase NRP-1 expression in hVSMCs. Treatment of hVSMCs with basic fibroblast growth factor (b-FGF) induced expressions of NRP-1 mRNA and protein whereas epidermal growth factor, insulin-like growth factor-1, and interleukin-1β did not. b-FGF induced phosphorylation of Erk-1/2 and JNK. MEK1/2 and nuclear factor kappa B (NF-κB) inhibitors (U0126 and TLCK, respectively) blocked the ability of b-FGF to induce NRP-1 mRNA expression, but inhibition of JNK (SP600125) or PI3-kinase activity (wortmannin) did not. Further, the increase in NRP-1 expression by b-FGF enhanced hVSMCs migration in response to VEGF₁₆₅. This effect was dependent on the binding of VEGF₁₆₅ to VEGFR-2, as blocking antibodies to VEGFR-2, but not VEGFR-1, inhibited VEGF ₁₆₅-induced migration. In conclusion, b-FGF increased NRP-1 expression in hVSMCs that in turn enhance the effect of VEGF₁₆₅ on cell migration. The enhanced migration of hVSMCs was mediated through binding of VEGF₁₆₅ to both NRP-1 and VEGFR-2, as inhibition of VEGFR-2 on these cells blocked the effect of VEGF-mediated cell migration.