HETERODIMERS OF PLACENTA GROWTH-FACTOR VASCULAR ENDOTHELIAL GROWTH-FACTOR - ENDOTHELIAL ACTIVITY, TUMOR-CELL EXPRESSION, AND HIGH-AFFINITY BINDING TO FLK-1 KDR/

Here we show that the Escherichia coil expressed monomers of placenta growth factor (PLGF)(129) and vascular endothelial growth factor (VEGF )(165) can be refolded in vitro to form PLGF/VEGF heterodimers. The pu rified recombinant PLGF/VEGF heterodimers and VEGF homodimers have pot ent mitogenic and chemotactic effects on endothelial cells. However, P LGF/VEGF heterodimers display 2050-fold less mitogenic activity than V EGF(165) homodimers. In contrast, PLGF(129) homodimers have little or no effect in these in vitro assays. We also demonstrate the presence o f natural PLGF/VEGF heterodimers in the conditioned media of various h uman tumor cell lines. While PLGF/VEGF heterodimers bind with high aff inity to a soluble Flk-1/KDR receptor, PLGF(129) homodimers fail to bi nd to this receptor, Cross-linking of I-125-ligands to human umbilical vein endothelial cells reveals that PLGF/VEGF heterodimers and VEGF(1 65) homodimers, but not PLGF(129) homodimers, form complexes with memb rane receptors. VEGF(165) homodimers and PLGF/VEGF heterodimers stimul ate tyrosine phosphorylation of a 220-kDa protein, the expected size f or the KDR receptor in human umbilical vein endothelial cells, whereas PLGF(129) 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 prod ucing both factors.