Background: 1F6 human melanoma xenografts overexpressing either the 18 kD (18kD) form or all (ALL) forms of human basic fibroblast growth factor (bFGF) demonstrate an abundant number of microvessels and accelerated growth. We now examined whether bFGF mediates vascular endothelial growth factor (VEGF) expression.
Methods: Quantitative RT-PCR was used to determine bFGF and VEGF mRNA, VEGF protein secretion was measured by ELISA and VEGF promoter activation was assessed by a dual luciferase activity assay. Western blot was carried out to detect phosphorylation of bFGF-regulated target proteins.
Results: In 1F6-18kD and 1F6-ALL clones VEGF mRNA was increased 4- to 5-fold and VEGF protein secretion was highly stimulated due to activation of the VEGF promotor. PI-3K, p38 MAPK and ERK1/2 MAPK pathways were activated, while inhibition of PI-3K or p38 resulted in, respectively, 55% and up to 70% reduction of VEGF mRNA overexpression. A concurrent 60% decrease in VEGF protein secretion was mostly apparent upon inhibition of PI-3K. Inhibition of ERK1/2 hardly affected VEGF mRNA or protein secretion. Two unselected human melanoma cell lines with high metastatic potential contained high bFGF and VEGF, while three non- or sporadically metastatic cell lines displayed low bFGF and VEGF.
Conclusion: These data indicate that stimulation of VEGF protein secretion in response to bFGF overexpression may contribute to increased vascularization and enhanced aggressiveness in melanoma.