G protein-coupled receptor 124 (GPR124; also called tumor endothelial marker 5, TEM5) is highly expressed in tumor vasculature. While recent studies have revealed a role in vasculogenesis, evidence for GPR124 function in tumor angiogenesis is lacking. Here, we demonstrate that GPR124 is required for VEGF-induced tumor angiogenesis. GPR124 silencing in human endothelial cells inhibited mouse xenograft tumor angiogenic vessel formation and tumor growth. GPR124 regulated VEGF-induced tumor angiogenic processes in vitro including cell-cell interaction, permeability, migration, invasion, and tube formation. Therefore, GPR124 plays a key role in VEGF-induced tumor angiogenesis.

The endothelial cell (EC) outgrowth in both vasculogenesis and angiogenesis starts with remodeling surrounding matrix and proceeds with the crosstalk between cells for the multicelluar vasculature formation. Althought the mechanical plasticity of matrix has been recognized to regulate individual cell behaviors through plastic remodeling, it remains elusive how matrix plasticity impacts cell-to-cell interplay during EC outgrowth and the underlying molecular pathways. Here we developed a collagen-hyaluronic acid based hydrogel platform with tunable plasticity independent of stiffness, by using compositing strategy of dynamic and covalent crosslinks. We show that the increasing plasticity of the hydrogel networks facilitates the matrix remodeling by ECs, thus promoting the process of individual sprouting and branching during vasculogenesis. However, the lagest tubular lumens and the longest invading distance from EC spheoid unexpectedly appear in hydrogels with medium plasticity instead of the highest ones. We unravel that althought the high plasticity of the hydrogels promotes stable integrin cluster of ECs and recruitment of focal adhesion kinase (FAK) with an increase in cell contractility, while the overenhanced contractility downregulates the vascular endothelial calmodulin (VE-CAD) expression and destabilizes the adherens junctions between individual ECs in vasculogenesis (or stalk and tip ECs in angiogenesis). Our results, further validated with mathematical simulations and in vivo angiogenic tests, demonstrate that a balance of matrix plasticity facilitates both cell-matrix binding and cell-to-cell adherens, for promoting vascular assembly and invasion.