Anchorage of VEGF to the extracellular matrix conveys differential signaling responses to endothelial cells

Abstract

VEGF can be secreted in multiple isoforms with variable affinity for extracellular proteins and different abilities to induce vascular morphogenesis, but the molecular mechanisms behind these effects remain unclear. Here, we show molecular distinctions between signaling initiated from soluble versus matrix-bound VEGF, which mediates a sustained level of VEGFR2 internalization and clustering. Exposure of endothelial cells to matrix-bound VEGF elicits prolonged activation of VEGFR2 with differential phosphorylation of Y1214, and extended activation kinetics of p38. These events require association of VEGFR2 with β1 integrins. Matrix-bound VEGF also promotes reciprocal responses on β1 integrin by inducing its association with focal adhesions; a response that is absent upon exposure to soluble VEGF. Inactivation of β1 integrin blocks the prolonged phosphorylation of Y1214 and consequent activation of p38. Combined, these results indicate that when in the context of extracellular matrix, activation of VEGFR2 is distinct from that of soluble VEGF in terms of recruitment of receptor partners, phosphorylation kinetics, and activation of downstream effectors.

Characterization of Heparanase-induced Phosphatidylinositol 3-Kinase-AKT Activation and Its Integrin Dependence

“…Two main mechanisms for the cooperation are (i) synergistic signaling from the two receptors by converging pathways, as described for the ERK pathway after EGF stimulation (46,47); and (ii) regulation of growth factor receptors by direct interaction with integrins, e.g. VEGFR2 and ␤1 (48). The mechanism by which the heparanase receptor(s) and integrins cooperate cannot be ascertained until the receptor(s) is identified.…”

Overexpression of VEGF189 in breast cancer cells induces apoptosis via NRP1 under stress conditions

“…41,42 The β1 integrin has previously been involved in VEGF189 signaling. 10,43,44 The inhibition of β1 integrin in several breast cancer cell lines results in higher mortality of cancer cells and is associated with increase in apoptosis. 45,46 The interaction of NRP1 with β1 also modulates cancer cell survival.…”

VEGF-Directed Blood Vessel Patterning: From Cells to Organism

“…This model is reinforced by the finding that tumor expression of a VEGF-A protein that cannot be proteolytically cleaved and released from the matrix results in thin, highly branched vessels, whereas similar expression of a cleaved version of VEGF-A leads to dilated tumor vessels (Lee et al 2005). Recent data also indicate that matrix-bound VEGF stimulates sustained signaling through VEGFR-2 and activation of downstream pathways distinct from those activated by soluble VEGF, suggesting how proliferation and branching might be integrated via a VEGF gradient (Chen et al 2010). Finally, endothelial cells themselves express low levels of VEGF that contribute to vessel homeostasis, and perhaps also to sprouting migration via integrin regulation of VEGFR-2 (Lee et al 2007;da Silva et al 2010).…”