Molecular Interplay between Endostatin, Integrins, and Heparan Sulfate

Abstract

Endostatin is an endogenous inhibitor of angiogenesis. Although several endothelial cell surface molecules have been reported to interact with endostatin, its molecular mechanism of action is not fully elucidated. We used surface plasmon resonance assays to characterize interactions between endostatin, integrins, and heparin/heparan sulfate. ␣5␤1 and ␣v␤3 integrins form stable complexes with immobilized endostatin (K D ‫؍‬ ϳ1.8 ؋ 10؊8 M, two-state model). Two arginine residues (Arg 27 and Arg 139 ) are crucial for the binding of endostatin to integrins and to heparin/heparan sulfate, suggesting that endostatin would not bind simultaneously to integrins and to heparan sulfate. Experimental data and molecular modeling support endostatin binding to the headpiece of the ␣v␤3 integrin at the interface between the ␤-propeller domain of the ␣v subunit and the ␤A domain of the ␤3 subunit. In addition, we report that ␣5␤1 and ␣v␤3 integrins bind to heparin/heparan sulfate. The ectodomain of the ␣5␤1 integrin binds to haparin with high affinity (K D ‫؍‬ 15.5 nM). The direct binding between integrins and heparin/heparan sulfate might explain why both heparan sulfate and ␣5␤1 integrin are required for the localization of endostatin in endothelial cell lipid rafts.

Heparin promotes platelet responsiveness by potentiating αIIbβ3-mediated outside-in signaling

“…Note that the increase in Akt phosphorylation normally induced by heparin exposure does not take place in platelets expressing signaling-defective ␣IIb␤3. Ig-superfamily member G6b, 42 as well as the cell-surface integrins ␣v␤3 43,44 and ␣5␤1. 44 Whether heparin similarly binds ␣IIb␤3 has been controversial, as Fitzgerald et al purified ␣IIb␤3 from heparin-binding contaminants by allowing it to flow unbound through heparin-Sepharose beads as part of an early chromatographic purification protocol for this integrin, 45 whereas Sobel et al reported that not only could detergent solubilized ␣IIb␤3 specifically bind to and become eluted from this affinity matrix, tritiated heparin became photoaffinity cross-linked to cell surface ␣IIb␤3 in intact platelets.…”

The Cell to Cell Interaction of Breast Cancer Cells Regulates Cancer Invasion via Adam15

“…2G). Alphavbeta3 integrin on D3H2LN cells might bind to heparin sulfate proteglycan within Matrigel (Faye et al, 2009), thus contributing to the adhesion to Matrigel. In sharp contrast, cell migration was significantly inhibited by 8F7, anti-α9β1 or anti-αvβ3 antibody (Fig.…”

Regulation of Angiogenesis in Choroidal Neovascularization of Age Related Macular Degeneration by Endogenous Angioinhibitors

“…Endostatin elicits the anti-proliferative and anti-migratory effects by binding to different EC surface molecules and regulating the signaling cascades (Faye et al, 2009). Recombinant endostatin binds to V integrin as shown in human endothelial cells (Rehn et al, 2001).…”