Abstract

Vascular endothelial growth factors (VEGFs) bind to membrane receptors on a wide variety of cells to regulate diverse biological responses. The VEGF-A family member promotes vasculogenesis and angiogenesis, processes which are essential for vascular development and physiology. As angiogenesis can be subverted in many disease states, including tumour development and progression, there is much interest in understanding the mechanistic basis for how VEGF-A regulates cell and tissue function. VEGF-A binds with high affinity to two VEGF receptor tyrosine kinases (VEGFR1, VEGFR2) and with lower affinity to co-receptors called neuropilin-1 and neuropilin-2 (NRP1, NRP2). Here, we use a structural viewpoint to summarise our current knowledge of VEGF-VEGFR activation and signal transduction. As targeting VEGF-VEGFR activation holds much therapeutic promise, we examine the structural basis for anti-angiogenic therapy using small-molecule compounds such as tyrosine kinase inhibitors that block VEGFR activation and downstream signalling. This review provides a rational basis towards reconciling VEGF and VEGFR structure and function in developing new therapeutics for a diverse range of ailments.

Highlights

  • Vasculogenesis is the de novo formation of a vascular network whereas angiogenesis is sprouting of new blood vessels from pre-existing ones

  • These ligands bind to VEGFRs which belong to the type IV receptor tyrosine kinase (RTK) family and comprises of VEGFR1 (Flt1), VEGFR2 (KDR, Flk1) and VEGFR3 (Flt4) [7]

  • VEGFE encodes four splice isoforms: vascular endothelial growth factors (VEGFs)-ENZ-2, VEGF-ENZ-7, VEGF-ENZ-10 and VEGF-ED1701, which only bind to VEGFR2 and act as pro-angiogenic factors by promoting pathological angiogenesis in sub-cutaneous lesions infected by the virus [38]

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Summary

Introduction

Vasculogenesis is the de novo formation of a vascular network whereas angiogenesis is sprouting of new blood vessels from pre-existing ones. Both processes are highly dependent on regulation by vascular endothelial growth factors (VEGFs) and their interaction with membrane receptors expressed on different cell types. The VEGF family has complexity with multiple isoforms encoded by each VEGF-related gene, and differences in biological activity between closely related variants [6] These ligands bind to VEGFRs which belong to the type IV receptor tyrosine kinase (RTK) family and comprises of VEGFR1 (Flt1), VEGFR2 (KDR, Flk1) and VEGFR3 (Flt4) [7]. This review focuses on the mechanistic basis for VEGFR activation and function linked to the current portfolio of the drugs that target such molecules

VEGF Ligands and Receptor Diversity
VEGF-A
VEGF-B
VEGF-C and VEGF-D
VEGF-E
VEGF-F
VEGFR1
VEGFR2
VEGFR3
Structural Features of VEGFRs and Their Functions
VEGFR Extracellular Domain
VEGFR Transmembrane Domain
VEGFR Cytoplasmic Domain
Mechanism of TK Activation
VEGFR Signal Transduction
Strategies Employed in Inhibition of VEGFR Function
Protein-Based Therapies
Findings
Conclusions and Future Directions

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