Agglucetin, a tetrameric C-type lectin-like venom protein, regulates endothelial cell survival and promotes angiogenesis by activating integrin αvβ3 signaling

Agglucetin, a platelet glycoprotein (GP)Ib binding protein from Formosan Agkistrodon acutus (A. acutus) venom, could sustain human umbilical vein endothelial cell (HUVEC) proliferation and HUVEC adhering to immobilized agglucetin showed extensive spreading, which was strongly abrogated by integrin antagonists 7E3 and triflavin. Flow cytometric analyses confirmed the expression of GPIb complex on HUVEC is absent and fluorescein isothiocyanate (FITC)-agglucetin binds to HUVEC in a dose-dependent and saturable manner. Furthermore, native agglucetin specifically and dose-dependently inhibited the binding of FITC-23C6, an anti-αvβ3 monoclonal antibody (mAb), but not antibodies against α2 and α5, toward HUVEC and purified αvβ3 also bound to immobilized agglucetin-β in a dose-dependent manner. Moreover, agglucetin exhibited a pro-angiogenic effect in vitro, as well as the focal adhesion kinase (FAK)-associated signaling molecules responsible for HUVEC activation were initiated by agglucetin. In conclusion, agglucetin, acting as a survival factor, promotes endothelial adhesion and angiogenesis by triggering αvβ3 signaling through FAK/phosphatidylinositol 3-kinase (PI3K)/Akt pathway.