Molecular Pharmacology of VEGF-A Isoforms: Binding and Signalling at VEGFR2

Abstract

Vascular endothelial growth factor-A (VEGF-A) is a key mediator of angiogenesis, signalling via the class IV tyrosine kinase receptor family of VEGF Receptors (VEGFRs). Although VEGF-A ligands bind to both VEGFR1 and VEGFR2, they primarily signal via VEGFR2 leading to endothelial cell proliferation, survival, migration and vascular permeability. Distinct VEGF-A isoforms result from alternative splicing of the Vegfa gene at exon 8, resulting in VEGFxxxa or VEGFxxxb isoforms. Alternative splicing events at exons 5–7, in addition to recently identified posttranslational read-through events, produce VEGF-A isoforms that differ in their bioavailability and interaction with the co-receptor Neuropilin-1. This review explores the molecular pharmacology of VEGF-A isoforms at VEGFR2 in respect to ligand binding and downstream signalling. To understand how VEGF-A isoforms have distinct signalling despite similar affinities for VEGFR2, this review re-evaluates the typical classification of these isoforms relative to the prototypical, “pro-angiogenic” VEGF165a. We also examine the molecular mechanisms underpinning the regulation of VEGF-A isoform signalling and the importance of interactions with other membrane and extracellular matrix proteins. As approved therapeutics targeting the VEGF-A/VEGFR signalling axis largely lack long-term efficacy, understanding these isoform-specific mechanisms could aid future drug discovery efforts targeting VEGF receptor pharmacology.

Comparison of the ligand‐binding properties of fluorescent VEGF‐A isoforms to VEGF receptor 2 in living cells and membrane preparations using NanoBRET

“…Angiogenesis, the growth of new blood vessels from existing vascular networks, is an important physiological process that can be dysregulated in numerous pathologies including cancer and age‐related macular degeneration (Chung & Ferrara, ; Peach, Mignone, et al, ). VEGF‐A is a key mediator of both angiogenesis and vascular permeability, primarily signalling via its cognate receptor VEGF receptor 2 (VEGFR2; Alexander et al, ; Simons, Gordon, & Claesson‐Welsh, ).…”

“…The residues present within each VEGF‐A isoform determine whether they can interact with other membrane proteins (e.g., neuropilin 1; Cébe Suarez et al, ; Parker, Xu, Li, & Vander Kooi, ; Guo & Vander Kooi, ; Peach, Kilpatrick, et al, ) and extracellular matrix components (Krilleke et al, ; Vempati, Popel, & Mac Gabhann, ). This causes isoforms to vary in their bioavailability and signalling outcomes with many isoforms acting as partial agonists relative to VEGF 165 a (Peach, Mignone, et al, ). VEGF‐A isoforms also have distinct expression profiles in health and disease, such as down‐regulation of VEGF 165 b in numerous cancer types (Bates et al, ; Pritchard‐Jones et al, ).…”

“…Alternative mRNA splicing of the Vegfa gene leads to a number of endogenous VEGF-A isoforms of varying length, such as "prototypical" VEGF 165 a or VEGF 121 a, as well as variants (e.g., VEGF 165 b) that have distinct carboxy-terminus substitutions of exon 8a for exon 8b (Peach, Mignone, et al, 2018;Woolard et al, 2004). Additionally, programmed translational readthrough can lead to VEGF-Ax, an isoform containing both exon 8a-and 8b-encoded residues (Eswarappa et al, 2014).…”

Distinct Vegfa isoforms control endothelial cell proliferation through PI3 kinase signalling mediated regulation of cdkn1a/p21

“…This setting allowed us to determine the unique effects of ECM binding Vegfa isoforms on EC behaviors during embryogenesis. Previous studies in developing mice (Ruhrberg et al, 2002; Stalmans et al, 2002), disease settings (Brash et al, 2019; Cheng et al, 1997; Guo et al, 2001; Kazemi et al, 2016) and in cultured ECs (Chen et al, 2010; Delcombel et al, 2013; Fearnley et al, 2016; Herve et al, 2005; Park et al, 1993; Shiying et al, 2017) carefully investigated the effects of the different VEGF isoforms on cellular behaviors (for review see (Peach et al, 2018; Woolard et al, 2009)). Some studies suggested that there are no differences in the ability of various VEGFA isoforms to support EC proliferation (Ruhrberg et al, 2002), while others showed that ECs cultured on ECM derived from cells expressing VEGF189 or VEGF206 proliferated more strongly than those cultured in the presence of VEGF165 (Park et al, 1993).…”

Novel human Ab against vascular endothelial growth factor receptor 2 shows therapeutic potential for leukemia and prostate cancer

“…Several VEGF family members, including VEGF‐A, VEGF‐B, VEGF‐C, VEGF‐D, and PlGF, are known to participate in the regulation of angiogenesis. Vascular endothelial growth factors act by binding with high affinity to receptor tyrosine kinases, VEGFR1‐R3; among these VEGF binding events, VEGF‐A binding to VEGFR2 comprises the main activating signal for angiogenesis . Importantly, VEGF‐A signaling through VEGFR2 is also the key driver for the neovascular growth known to support solid tumor progression .…”