The Conformation-dependent Interaction of α2-Macroglobulin with Vascular Endothelial Growth Factor

• Published in: The Journal of biological chemistry 2000-09, Vol.275 (35), p.26806
• Main Authors: Gourab Bhattacharjee, Iain R. Asplin, Sean M. Wu, Govind Gawdi, Salvatore V. Pizzo
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M000156200

α 2 -Macroglobulin (α 2 M) is a highly conserved proteinase inhibitor present in human plasma at high concentration (2–4 mg/ml). α 2 M exists in two conformations, a native form and an activated, receptor-recognized form. While α 2 M binds to numerous cytokines and growth factors, in most cases, the nature of the α 2 M interaction with these factors is poorly understood. We examined in detail the interaction between α 2 M and vascular endothelial growth factor (VEGF) and found a novel and unexpected mechanism of interaction as demonstrated by the following observations: 1) the binding of VEGF to α 2 M occurs at a site distinct from the recently characterized growth factor binding site; 2) VEGF binds different forms of α 2 M with distinct spatial arrangement, namely to the interior of methylamine or ammonia-treated α 2 M and to the exterior of native and proteinase-converted α 2 M; and 3) VEGF (molecular mass ∼40 kDa) can access the interior of receptor-recognized α 2 M in the absence of a proteinase trapped within the molecule. VEGF bound to receptor-recognized forms of α 2 M is internalized and degraded by macrophages via the α 2 M receptor, the low density lipoprotein receptor-related protein. Oxidation of both native and receptor-recognized α 2 M results in significant inhibition of VEGF binding. We also examined the biological significance of this interaction by studying the effect of α 2 M on VEGF-induced cell proliferation and VEGF-induced up-regulation of intracellular Ca 2+ levels. We demonstrate that under physiological conditions, α 2 M does not impact the ability of VEGF to induce cell proliferation or up-regulate Ca 2+ .