Vascular Endothelial Cell Growth Factor A Acts via Platelet-Derived Growth Factor Receptor α To Promote Viability of Cells Enduring Hypoxia

Abstract

Vascular endothelial cell growth factor A (VEGF) is a biologically and therapeutically important growth factor because it promotes angiogenesis in response to hypoxia, which underlies a wide variety of both physiological and pathological settings. We report here that both VEGF receptor 2 (VEGFR2)-positive and -negative cells depended on VEGF to endure hypoxia. VEGF enhanced the viability of platelet-derived growth factor receptor ␣ (PDGFR␣)-positive and VEGFR2-negative cells by enabling indirect activation of PDGFR␣, thereby reducing the level of p53. We conclude that the breadth of VEGF's influence extends beyond VEGFR-positive cells and propose a plausible mechanistic explanation of this phenomenon. Receptor tyrosine kinases (RTKs) govern many biological processes. They can be activated in multiple ways, including by their cognate ligands (direct activation), and indirectly, which has also been called transactivation. For instance, circulating autoantibodies and ligands of G protein coupled receptor induce tyrosine phosphorylation of platelet-derived growth factor receptors (PDGFRs) (1-10).In the context of a blinding eye disease called proliferative vitreoretinopathy, indirect activation of PDGFR␣ drives pathogenesis in experimental animals and is associated with this disease in patients (11). Disease initiation involves mislocalization of cells into the vitreous of the eye, whereupon such cells are exposed to a plethora of growth factors that selectively and enduringly activate PDGFR␣ and thereby promotes the viability of the mislocalized cells by reducing the level of p53. The vitreal growth factors that are responsible for indirectly activating PDGFR␣ are outside the PDGF family and hence called non-PDGFs.Attempts to identify which non-PDGFs are responsible for indirectly activating PDGFR␣ led to the discovery of a hierarchy among the three classes of growth factors that engage PDGFR␣ (12, 13). These three classes of growth factors include PDGFs (direct activators), non-PDGFs (indirect activators), and vascular endothelial cell growth factor A (VEGF), which competitively antagonizes PDGF-dependent activation of PDGFR␣ (14). The hierarchy between these three classes of growth factors is shown in Fig. 1A and termed the VEGF/PDGF/non-PDGF paradigm. This diagram illustrates how VEGF promotes the survival of cells via PDGFR␣.As mentioned above, the VEGF/PDGF/non-PDGF paradigm was discovered in a pathological context. In the course of testing its relevance in a physiological setting, which is the focus of this report, the following novel discoveries were made. VEGF promoted survival of VEGF receptor 2 (VEGFR2)-negative cells (such as fibroblasts) during hypoxia in vitro, ex vivo, and in vivo. Furthermore, the VEGF/PDGF/non-PDGF paradigm was a plausible explanation for this phenomenon. MATERIALS AND METHODSCell culture. Primary mouse embryonic fibroblasts (MEFs) were obtained from American Type Culture Collection (Manassas, VA) at passage 2, used between passages 3 to 7, and maintained in high-glucose-containing ...

The microvascular niche instructs T cells in large vessel vasculitis via the VEGF-Jagged1-Notch pathway

“…Notably, VEGF production and neovascularization were strongest in inflamed arteries rich in tissue IFN- γ , suggesting that the strength of aberrant T cell responses regulates VEGF production (17). Thus, besides hypoxia and glucose deficiency, systemic VEGF concentrations may reflect the uncontrolled T cell stimulation occurring in a VEGF-rich host (34, 54, 55). Previous reports have raised the possibility that VEGF can directly inhibit T cell activation (56).…”

Characterizing Glioblastoma Heterogeneity via Single-Cell Receptor Quantification

“…For instance, we have shown VEGF-mediated downregulation of PDGFRs (Chen et al, 2015 ), and discovered that both VEGF–PDGFR binding and PDGF–VEGFR binding is high affinity (Mamer et al, 2017 ). Other cross-family studies have identified VEGF–PDGFR binding and signaling (Ball et al, 2007 ; Pennock et al, 2016 ) and VEGFR–PDGFR dimerization in tumor associated pericytes (Greenberg et al, 2008 ). Altogether, these canonical and cross-family RTK mechanisms suggest several possible receptor activation landscapes that can contribute to tumor growth and drug resistance.…”

“…RTKs are widely expressed transmembrane proteins (Cadena and Gill, 1992 ; Ferrara et al, 2003 ). Upon ligand binding, they are activated via canonical (Mac Gabhann and Popel, 2007 ; Sarabipour and Hristova, 2016 ) and non-canonical (Steinkamp et al, 2014 ; Chen et al, 2015 ; Pennock et al, 2016 ; Mamer et al, 2017 ) ligand-induced dimerization and tyrosine phosphorylation mechanisms. Importantly, unligated receptors can dimerize (Ruch et al, 2007 ; Chung et al, 2010 ; Low-Nam et al, 2011 ; Lin et al, 2012 ; Comps-Agrar et al, 2015 ; King et al, 2016 ; Sarabipour and Hristova, 2016 ; Sarabipour et al, 2016 ) and signal (Wu et al, 2010 ; Sarabipour et al, 2016 ; Kazlauskas, 2017 ), although ligand binding stabilizes the dimeric receptor structure.…”

PDGFs and their receptors

“…Surprisingly, VEGF also provides immediate benefit to some of the VEGFR-negative cell types. It does so by enabling indirect activation of PDGFRα, which, as mentioned above, promotes survival by lowering the level of p53 [72]. The way that VEGF promotes indirect activation of PDGFRα is by competing with PDGF for binding to PDGFRα [5].…”