Goerges Adrienne L, Nugent Matthew A
Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118, USA.
J Biol Chem. 2004 Jan 16;279(3):2307-15. doi: 10.1074/jbc.M308482200. Epub 2003 Oct 21.
Hypoxia is one of the major signals that induces angiogenesis. Hypoxic conditions lead to reduced extracellular pH. Vascular endothelial growth factor (VEGF) binding to endothelial cells and the extracellular matrix (ECM) increases at acidic pH (7.0-5.5). These interactions are dependent on heparan sulfate proteoglycans, but do not depend on the presence of VEGF receptors. Here we report that VEGF(165) and VEGF(121) binding to fibronectin also increased at acidic pH, and that these interactions are further enhanced by the addition of heparin. These results reveal that the accepted non-heparin-binding isoform of VEGF (VEGF(121)) is converted into a heparin-binding growth factor under acidic conditions. Interestingly, we did not observe increased binding of VEGF to collagen type I at acidic pH in the presence or absence of heparin, indicating that this effect is not a general property of all heparin-binding ECM proteins. The high level of VEGF binding at acidic pH was also rapidly reversed as demonstrated by increased rates of VEGF dissociation from fibronectin and fibronectin-heparin matrices as the pH was raised. The VEGF released from fibronectin retained its ability to stimulate the activation of extracellular-regulated kinase 1/2 in endothelial cells. These results suggest that VEGF may be stored in the extracellular matrix via interactions with fibronectin and heparan sulfate in tissues that are in need of vascularization so that it can aid in directing the dynamic process of growth and migration of new blood vessels.
缺氧是诱导血管生成的主要信号之一。缺氧条件会导致细胞外pH值降低。在酸性pH值（7.0 - 5.5）下，血管内皮生长因子（VEGF）与内皮细胞和细胞外基质（ECM）的结合增加。这些相互作用依赖于硫酸乙酰肝素蛋白聚糖，但不依赖于VEGF受体的存在。在此我们报告，在酸性pH值下，VEGF(165)和VEGF(121)与纤连蛋白的结合也会增加，并且添加肝素会进一步增强这些相互作用。这些结果表明，公认的非肝素结合型VEGF异构体（VEGF(121)）在酸性条件下会转化为肝素结合生长因子。有趣的是，无论有无肝素，我们都未观察到在酸性pH值下VEGF与I型胶原的结合增加，这表明这种效应并非所有肝素结合型ECM蛋白的普遍特性。随着pH值升高，VEGF从纤连蛋白和纤连蛋白 - 肝素基质上的解离速率增加，这表明酸性pH值下高水平的VEGF结合也会迅速逆转。从纤连蛋白释放的VEGF保留了刺激内皮细胞中细胞外调节激酶 1/2活化的能力。这些结果表明，在需要血管化的组织中，VEGF可能通过与纤连蛋白和硫酸乙酰肝素的相互作用而存储在细胞外基质中，从而有助于指导新血管生长和迁移的动态过程。
