An Inhibitor of the F1 Subunit of ATP Synthase (IF1) Modulates the Activity of Angiostatin on the Endothelial Cell Surface

Abstract

Angiostatin binds to endothelial cell (EC)-surface F 1 -F 0 ATP synthase, leading to inhibition of EC3 migration and proliferation during tumor angiogenesis. This has led to a search for angiostatinmimetics specific for this enzyme. A naturally occurring protein that binds to the F1 subunit of ATP synthase and blocks ATP hydrolysis in mitochondria is Inhibitor of F1 (IF1). The present study explores the effect of IF1 on cell surface ATP synthase. IF1 protein bound to purified F 1 ATP synthase and inhibited F 1 -dependent ATP hydrolysis consistent with its reported activity in studies of mitochondria. While exogenous IF1 did not inhibit ATP production on the surface of EC, it did conserve ATP on the cell surface, particularly at low extracellular pH. IF1 inhibited ATP hydrolysis but not ATP synthesis, in contrast to angiostatin, which inhibited both. In cell-based assays used to model angiogenesis in vitro, IF1 did not inhibit EC differentiation to form tubes and only slightly inhibited cell proliferation compared to angiostatin. From these data, we conclude that inhibition of ATP synthesis is necessary for an anti-angiogenic outcome in cell-based assays. We propose that IF1 is not an angiostatin-mimetic, but it can serve a protective role for EC in the tumor microenvironment. This protection may be overridden in a concentration-dependent manner by angiostatin. In support of this hypothesis, we demonstrate that angiostatin blocks IF1 binding to ATP synthase, and abolishes its ability to conserve ATP. These data suggest that there is a relationship between the binding sites of IF1 and angiostatin on ATP synthase and that IF1 could be employed to modulate angiogenesis.

A Novel Mechanism of γ/δ T-Lymphocyte and Endothelial Activation by Shear Stress

“…In hepatocytes, surface ATPSβ serves as a receptor for ApoA-I or ApoE-enriched high-density lipoprotein 5–7. In ECs, ecto-ATPSβ binds to angiostatin, which suggests that the membrane-bound ATPS is involved in angiogenesis 8–10. Our previous study demonstrated that ECs incubated with cholesterol induced the translocation of ATPSβ from mitochondria to membrane caveolae,11 which suggests that ecto-ATPSβ may be involved in cholesterol efflux from the vessel wall.…”

ATP synthase inhibitory factor 1 (IF1), a novel myokine, regulates glucose metabolism by AMPK and Akt dual pathways

“…F 1 F 0 -ATP synthase is a mitochondrial protein; however, b-F1-ATPase, the F1 catalytic subunit of this enzyme, has been recently found to be present on the plasma membrane of various cell types, such as endothelial cells (25), neuronal cells (26), adipocytes (27), and hepatocytes (28). It is possible that this ecto-F1-ATPase can act as a cell surface receptor to which certain types of ligands can specifically bind.…”

Pigment epithelium‐derived factor binds to cell‐surface F1‐ATP synthase

“…The positive control, piceatannol, was also a potent inhibitor, requiring ≤ 5 min of preincubation time for effective blocking. Other investigators have demonstrated inhibition of extracellular ATP synthesis by pretreatment of HUVECs for 30 min with much higher doses of angiostatin kringles 1–3 (K1–3) (50 μ m [35]) and piceatannol (1–20 μ m [33]; 500 μ m [35]) than those used here. As shown in Fig.…”