Fig. 5.

Reciprocal interplay between tumor-derived fibroblast growth factor (FGF) and platelet derived growth factor (PDGF) in promoting tumor angiogenesis. Activation of FGFRs in endothelial cells by tumor-derived FGF-2 leads to switching on the expression of PDGFR-α and PDGFR-β, which acquire responses to PDGF ligand stimulation. PDGF-BB increases sensitization of vascular smooth muscle cells to FGF-2 stimulation by upregulating FGFR-1 expression in these cells. The functional consequence of this reciprocal interaction on the tumor vasculature is manifested by accelerating angiogenic vessel growth. EC, endothelial cell; VSMC, vascular smooth muscle cell.