Novel Vascular Endothelial Growth Factor Binding Domains of Fibronectin Enhance Vascular Endothelial Growth Factor Biological Activity

Abstract

Abstract-Interactions between integrins and growth factor receptors play a critical role in the development and healing of the vasculature. This study mapped two binding domains on fibronectin (FN) that modulate the activity of the angiogenic factor, vascular endothelial growth factor (VEGF T he growth, repair, and regeneration of blood vessels are complex processes that involve coordinated regulation of endothelial cell proliferation, migration, and differentiation. 1 One of the most important vascular morphogens is vascular endothelial growth factor (VEGF). VEGF has been shown to play a major role in vasculogenesis and angiogenesis by gene deletion studies. 2,3 Targeted disruption of the VEGF receptor Flk-1 (VEGFR-2) in mice resulted in failure of blood-island formation and endothelial differentiation. 4 Flk-1 is also the first endothelial receptor tyrosine kinase to be expressed in the hemangioblast. 5 We and others recently demonstrated that the hematopoietic progenitor cell CD34 ϩ can differentiate into endothelial cells, and that VEGF was one of the critical factors promoting this differentiation. 6,7 Interactions between cells and their extracellular matrix (ECM) play an integral role in blood vessel development. The earliest ECM protein expressed in the embryo during vasculogenesis is fibronectin (FN). 8 Gene deletion studies have demonstrated that both FN and its major integrin receptor, ␣ 5 ␤ 1 , are critical for vasculogenesis and angiogenesis in the developing embryo. 9 -11 Collectively, these observations suggest important roles for FN and its integrin receptor, ␣ 5 ␤ 1 , in vasculogenesis and angiogenesis.In this study, we show that novel VEGF binding domains of FN are required for promoting the specific association of the FN receptor integrin ␣ 5 ␤ 1 with the VEGF receptor, Flk-1. This association between VEGF and FN is required for the full effects of VEGF-induced endothelial cell migration and proliferation. This study demonstrates that FN can profoundly affect VEGF biological activity and consequently the behavior of endothelial cells through their coordinated effects on Flk-1 and ␣ 5 ␤ 1 . Materials and Methods Solid-Phase VEGF Binding AssayECM proteins and FN peptides were purchased from Sigma and Gibco and were purified further by gel filtration and ion exchange chromatography. Microtiter plates were coated with the appropriate ECM proteins (50 L; 10 g/mL) in 100 mmol/L bicarbonate buffer (pH 9) overnight at 4°C.

The interaction of versican with its binding partners

“…Removal of this complex with anti-fibronectin antibody reversed G3's enhancing effects on endothelial cell activities. Our results are in agreement with a recent publication showing that fibronectin binds to VEGF and increases the function of VEGF in endothelial cell migration in culture [72].…”

The VEGF angiogenic switch of fibroblasts is regulated by MMP-7 from cancer cells

“…Fibroblasts synthesize ECM components and paracrine factors, including VEGF and CTGF. These molecules would probably be sequestered in the ECM, because they bind to fibronectin (Wijelath et al, 2002;Chen et al, 2004) and heparin (Ferrara and Henzel, 1989;Brigstock et al, 1997). Furthermore, MMP-7 or other MMPs are upregulated in injured tissues (Parks, 1999), suggesting the potential application of our results in wound healing.…”

Heparin-binding domain of fibrin(ogen) binds growth factors and promotes tissue repair when incorporated within a synthetic matrix

“…For example, many GFs are able to bind the proteoglycan components of the ECM (2). Moreover, it has recently become more evident that ECM proteins such as fibronectin and vitronectin, which do not contain highly negatively charged sugar chains, bind several GFs (3)(4)(5)(6)(7)(8). In addition to sequestration of GF by ECM components, the ECM also can modulate cosignaling between adhesion and GF receptor systems.…”