Vascular endothelial growth factor signalling in endothelial cell survival: A role for NFκB

Angiogenesis is the development of blood capillaries from pre-existing vessels. Vascular endothelial growth factor (VEGF) is a key regulator of vessel growth and regression, and acts as an endothelial survival factor by protecting endothelial cells from apoptosis. Many genes involved in cell proliferation and apoptosis are regulated by the nuclear factor kappa B (NFκB) transcription factor family. This study aimed to address the hypothesis that VEGF-mediated survival effects on endothelium involve NFκB. Using an NFκB-luciferase reporter adenovirus, we observed activation of NFκB following VEGF treatment of human umbilical vein endothelial cells. This was confirmed using electrophoretic mobility shift assay and found to involve nuclear translocation of NFκB sub-unit p65. However, NFκB activation occurred without degradation of inhibitory IκB proteins (IκBα, IκBβ, and IκBε). Instead, tyrosine phosphorylation of IκBα was observed following VEGF treatment, suggesting NFκB activation was mediated by degradation-independent dissociation of IκBα from NFκB. Adenovirus-mediated over-expression of either native IκBα, or of IκBα in which tyrosine residue 42 was mutated to phenylalanine, inhibited induction of NFκB-dependent luciferase activity in response to VEGF. Furthermore, VEGF-induced upregulation of mRNA for the anti-apoptotic protein Bcl-2 and cell survival following serum withdrawal was reduced following IκBα over-expression. This study highlights that different molecular mechanisms of NFκB activation may be involved downstream of stimuli which activate the endothelial lining of blood vessels.