Endostatin Binds Tropomyosin
A POTENTIAL MODULATOR OF THE ANTITUMOR ACTIVITY OF ENDOSTATIN*
- Nicholas J. MacDonald,
- Wanda Y. Shivers,
- David L. Narum,
- Stacy M. Plum,
- Jennifer N. Wingard,
- Steven R. Fuhrmann,
- Hong Liang,
- Janel Holland-Linn,
- D. H. Tom Chen and
- B. Kim Lee Sim‡
Abstract
The mechanism of action of Endostatin, an endogenous inhibitor of angiogenesis and tumor growth, remains unknown. We utilized phage-display technology to identify polypeptides that mimic the binding domains of proteins with which Endostatin interacts. A conformed peptide (E37) was identified that shares an epitope with human tropomyosin implicating tropomyosin as an Endostatin-binding protein. We show that recombinant human Endostatin binds tropomyosin in vitro and to tropomyosin-associated microfilaments in a variety of endothelial cell types. The most compelling evidence that tropomyosin modulates the activity of Endostatin was demonstrated when E37 blocked greater than 84% of the tumor-growth inhibitory activity of Endostatin in the B16-BL6 metastatic melanoma model. We conclude that the E37 peptide mimics the Endostatin-binding epitope of tropomyosin and blocks the antitumor activity of Endostatin by competing for Endostatin binding. We postulate that the Endostatin interaction with tropomyosin results in disruption of microfilament integrity leading to inhibition of cell motility, induction of apoptosis, and ultimately inhibition of tumor growth.
Footnotes
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↵* The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: EntreMed, Inc., 9640 Medical Center Dr., Rockville, MD 20850. Tel.: 301-738-2485; Fax: 301-217-9594; E-mail: kims@entremed.com.
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Published, JBC Papers in Press, May 2, 2001, DOI 10.1074/jbc.M100743200
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↵1 The abbreviations used are: rh, recombinant human; rm, recombinant murine; hTM3, human tropomyosin isoform 3; PBS, phosphate-buffered saline; RU, resonance units; AUC, area under curve.
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↵2 H. Liang and B. K. L. Sim, unpublished data.
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↵3 D. L. Narum, S. R. Fuhrmann, B. Nelson, D. Bottaro, D. H. T. Chen, S. M. Plum, and B. K. L. Sim, manuscript in preparation.
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↵4 D. R. Sørensen, T. A. Read, T. Porosol, B. R. Olsen, R. Timpl, T. Sasaki, P. O. Iversen, H. B. Benestad, B. K. L. Sim, and R. Bjerkvig, manuscript in preparation.
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↵5 D. Yang, personal communication.
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- Received January 26, 2001.
- Revision received April 18, 2001.
- The American Society for Biochemistry and Molecular Biology, Inc.
