Endostatin Blocks Vascular Endothelial Growth Factor-mediated Signaling via Direct Interaction with KDR/Flk-1

TLDR

Endostatin, a collagen XVIII fragment, is a potent anti‑angiogenic protein, yet its molecular mechanism remains unclear. The study sought to determine how endostatin modulates VEGF signaling. The authors examined endostatin’s effects on VEGF’s biological and biochemical activities in endothelial cells. Endostatin directly binds KDR/Flk‑1, blocks VEGF‑induced tyrosine phosphorylation of KDR/Flk‑1 and downstream ERK, p38 MAPK, and FAK activation, inhibits VEGF(165) and VEGF(121) binding to KDR/Flk‑1, and does not bind VEGF, indicating that its anti‑angiogenic activity is mediated by direct interaction with KDR/Flk‑1.

Abstract

Endostatin, a fragment of collagen XVIII, is a potent anti-angiogenic protein, but the molecular mechanism of its action is not yet clear. We examined the effects of endostatin on the biological and biochemical activities of vascular endothelial growth factor (VEGF). Endostatin blocked VEGF-induced tyrosine phosphorylation of KDR/Flk-1 and activation of ERK, p38 MAPK, and p125(FAK) in human umbilical vein endothelial cells. Endostatin also inhibited the binding of VEGF(165) to both endothelial cells and purified extracellular domain of KDR/Flk-1. Moreover, the binding of VEGF(121) to KDR/Flk-1 and VEGF(121)-stimulated ERK activation were blocked by endostatin. The direct interaction between endostatin and KDR/Flk-1 was confirmed by affinity chromatography. However, endostatin did not bind to VEGF. Our findings suggest that a direct interaction of endostatin with KDR/Flk-1 may be involved in the inhibitory function of endostatin toward VEGF actions and responsible for its potent anti-angiogenic and anti-tumor activities in vivo.