Heterodimers of Placenta Growth Factor/Vascular Endothelial Growth Factor

doi:10.1074/jbc.271.6.3154

Heterodimers of Placenta Growth Factor/Vascular Endothelial Growth Factor

ENDOTHELIAL ACTIVITY, TUMOR CELL EXPRESSION, AND HIGH AFFINITY BINDING TO Flk-1/KDR (*)

From the (1)Departments of Surgery and
(2)Cell Biology, Harvard Medical School, Boston, Massachusetts 02115 and
(3)R& Systems, Inc., Minneapolis, Minnesota 55413

^§Supported by the International Human Frontier Science Program. To whom correspondence should be addressed. Tel.: 617-355-6382; Fax: 617-355-7043. To whom reprint requests should be addressed:
c/o Judah Folkman, Children's Hospital, Hunewell 103, 300 Longwood Ave., Boston, MA 02115.

Abstract

Here we show that the Escherichia coli expressed monomers of placenta growth factor (PLGF) and vascular endothelial growth factor (VEGF) can be re-folded in vitro to form PLGF/VEGF heterodimers. The purified recombinant PLGF/VEGF heterodimers and VEGF homodimers have potent mitogenic and chemotactic effects on endothelial cells. However, PLGF/VEGF heterodimers display 20-50-fold less mitogenic activity than VEGF homodimers. In contrast, PLGF homodimers have little or no effect in these in vitro assays. We also demonstrate the presence of natural PLGF/VEGF heterodimers in the conditioned media of various human tumor cell lines. While PLGF/VEGF heterodimers bind with high affinity to a soluble Flk-1/KDR receptor, PLGF homodimers fail to bind to this receptor. Cross-linking of I-ligands to human umbilical vein endothelial cells reveals that PLGF/VEGF heterodimers and VEGF homodimers, but not PLGF homodimers, form complexes with membrane receptors. VEGF homodimers and PLGF/VEGF heterodimers stimulate tyrosine phosphorylation of a 220-kDa protein, the expected size for the KDR receptor in human umbilical vein endothelial cells, whereas PLGF homodimers are unable to induce tyrosine phosphorylation of this protein. These data indicate that PLGF may modulate VEGF-induced angiogenesis by the formation of PLGF/VEGF heterodimers in cells producing both factors.

Footnotes

↵^¶ To whom reprint requests may also be addressed.
↵* This study was supported in part by National Institutes of Health Grant PO1-CA-45548. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

VEGF

vascular endothelial growth factor

PLGF

placenta growth factor

PDGF

platelet-derived growth factor

DTT

dithiothreitol

PAGE

polyacrylamide gel electrophoresis

PBS

phosphate-buffered saline

AP

alkaline phosphatase

ELISA

enzyme-linked immunosorbent assay.
↵²Y. Cao, unpublished observation.
↵³Y. Cao, unpublished data.
- Received October 4, 1995.
- Revision received November 10, 1995.