Vascular endothelial growth factor is inactivated by binding to alpha 2-macroglobulin and the binding is inhibited by heparin.

Abstract

Vascular endothelial growth factor (VEGF) is a mitogen for cultured endothelial cells, and a potent angiogenic factor in vivo. Incubation of 125I-VEGF with human or bovine serum led to the formation of 125I-VEGF containing complexes that had a molecular mass greater than 300 kDa. These complexes were specifically immunoprecipitated with anti-human alpha 2-macroglobulin (alpha 2M) antibodies. Similar high molecular weight complexes were formed when 125I-VEGF was incubated with commercially available alpha 2M. The 125I-VEGF.alpha 2M complexes were resistant to boiling in the presence of SDS. The formation of 125I-VEGF.alpha 2M complexes was inhibited by iodoacetic acid, indicating that free sulfhydryl groups are required for complex assembly. Tryptic digestion of alpha 2M did not affect its VEGF binding ability. Tryptic digestion of 125I-VEGF.alpha 2M complexes on the other hand, resulted in the degradation of bound 125I-VEGF, indicating that alpha 2M does not protect bound 125I-VEGF from proteolytic digestion. The binding of 125I-VEGF to alpha 2M was partially inhibited by an excess of basic fibroblast growth factor. Other growth factors which bind to alpha 2M, such as platelet-derived growth factor and insulin, did not inhibit the binding of 125I-VEGF. The binding of VEGF to alpha 2M inhibited its receptor binding ability, indicating that alpha 2M may function as a VEGF removal and inactivation factor. Heparin and heparan sulfate, but not other glycosaminoglycans such as chondroitin sulfate, efficiently inhibited the binding of 125I-VEGF to alpha 2M. It is possible that heparin-like molecules released from extracellular matrixes could prevent the inactivation of VEGF by alpha 2M resulting in the potentiation of processes such as tumor angiogenesis.