Intracellular Ca2+ signaling in endothelial cells by the angiogenesis inhibitors endostatin and angiostatin

Intracellular signaling mechanisms by the angiogenesis inhibitors endostatin and angiostatin remain poorly understood. We have found that endostatin (2 mu mg/ml) and angiostatin (5 mu mg/ml) elicited transient, approximately threefold increases in intracellular Ca2+ concentration ([Ca2+](i)). Acute exposure to angiostatin or endostatin nearly abolished subsequent endothelial [Ca2+](i) responses to carbachol or to thapsigargin; conversely, thapsigargin attenuated the Ca2+ signal elicited by endostatin. The phospholipase C inhibitor U-73122 and the inositol trisphosphate (IP3) receptor inhibitor xestospongin C both inhibited endostatin-induced elevation in [Ca2+](i), and endostatin rapidly elevated endothelial cell IP3 levels. Pertussis toxin and SB-220025 modestly inhibited the endostatin-induced Ca2+ signal. Removal of extracellular Ca2+ inhibited the endostatin-induced rise in [Ca2+](i), as did a subset of Ca2+-entry inhibitors. Peak Ca2+ responses to endostatin and angiostatin in endothelial cells exceeded those in epithelial cells and were minimal in NIH/3T3 cells. Overnight pretreatment of endothelial cells with endostatin reduced the subsequent acute elevation in [Ca2+](i) in response to vascular endothelial growth factor or to fibroblast growth factor by similar to 70%. Intracellular Ca2+ signaling may initiate or mediate some of the cellular actions of endostatin and angiostatin.