The conformation-dependent interaction of alpha(2)-macroglobulin with vascular endothelial growth factor - A novel mechanism of alpha(2)-macroglobulin/growth factor binding
G. Bhattacharjee et al., The conformation-dependent interaction of alpha(2)-macroglobulin with vascular endothelial growth factor - A novel mechanism of alpha(2)-macroglobulin/growth factor binding, J BIOL CHEM, 275(35), 2000, pp. 26806-26811
alpha(2)-Macroglobulin (alpha(2)M) is a highly conserved proteinase inhibit
or present in human plasma at high concentration (2-4 mg/ml), alpha(2)M exi
sts in two conformations, a native form and an activated, receptor-recogniz
ed form. While alpha(2)M binds to numerous cytokines and growth factors, in
most cases, the nature of the alpha(2)M interaction with these factors is
poorly understood. We examined in detail the interaction between alpha(2)M
and vascular endothelial growth factor (VEGF) and found a novel and unexpec
ted mechanism of interaction as demonstrated by the following observations:
1) the binding of VEGF to alpha(2)M occurs at a site distinct from the rec
ently characterized growth factor binding site; 2) VEGF binds different for
ms of alpha(2)M with distinct spatial arrangement, namely to the interior o
f methylamine or ammonia-treated alpha(2)M and to the exterior of native an
d proteinase-converted alpha(2)M; and 3) VEGF (molecular mass similar to 40
kDa) can access the interior of receptor-recognized alpha(2)M in the absen
ce of proteinase trapped within the molecule. VEGF bound to receptor-recogn
ized forms of alpha(2)M is internalized VEGF bound to receptor-recognized f
orms of alpha(2)M is internalize and degraded by macrophages via the alpha(
2)M receptor, the low density lipoprotein receptor-related protein, Oxidati
on of both native and receptor-recognized alpha(2)M results in significant
inhibition of VEGF binding. We also examined the biological significance of
this interaction by studying the effect of alpha(2)M On VEGF-induced cell
proliferation and VEGF-induced up-regulation of intracellular Ca2+ levels.
We demonstrate that under physiological conditions, alpha(2)M does not impa
ct the ability of VEGF to induce cell proliferation or up-regulate Ca2+.