Angiostatin is directly cytotoxic to tumor cells at low extracellular pH: a mechanism dependent on cell surface-associated ATP synthase.

Journal Article

Angiostatin, a proteolytic fragment of plasminogen, is a potent angiogenesis inhibitor able to suppress tumor growth and metastasis through inhibition of endothelial cell proliferation and migration. Previously, we showed that angiostatin binds and inhibits F(1)F(o) ATP synthase on the endothelial cell surface and that anti-ATP synthase antibodies reduce endothelial cell proliferation. ATP synthase also occurs on the extracellular surface of a variety of cancer cells, where its function is as yet unknown. Here, we report that ATP synthase is present and active on the tumor cell surface, and angiostatin, or antibody directed against the catalytic beta-subunit of ATP synthase, inhibits the activity of the synthase. We show that tumor cell surface ATP synthase is more active at low extracellular pH (pH(e)). Low pH(e) is a unique characteristic of the tumor microenvironment. Although the mechanism of action of angiostatin has not been fully elucidated, angiostatin treatment in combination with acidosis decreases the intracellular pH (pH(i)) of endothelial cells, leading to cell death. We also find that, at low pH(e), angiostatin and anti-beta-subunit antibody induce intracellular acidification of A549 cells, as well as a direct cytotoxicity that is absent in tumor cells with low levels of extracellular ATP synthase. These results establish angiostatin as an antitumorigenic and antiangiogenic agent through a mechanism implicating tumor cell surface ATP synthase. Furthermore, these data provide evidence that extracellular ATP synthase plays a role in regulating pH(i) in cells challenged by acidosis.

Full Text

Duke Authors

Cited Authors

  • Chi, SL; Pizzo, SV

Published Date

  • January 15, 2006

Published In

Volume / Issue

  • 66 / 2

Start / End Page

  • 875 - 882

PubMed ID

  • 16424020

International Standard Serial Number (ISSN)

  • 0008-5472

Digital Object Identifier (DOI)

  • 10.1158/0008-5472.CAN-05-2806

Language

  • eng

Conference Location

  • United States