Critical role of protein kinase D in VEGF‐induced vascular permeability and angiogenesis

Abstract

Vascular endothelial growth factor (VEGF) is not only a powerful angiogenic factor but also a potent vascular permeability factor, which disrupts vascular barrier function in diseased tissues. In inflammatory and ischemia tissues, through impairing endothelial cell‐cell junctions VEGF causes vascular permeability and edema, resulting in extensive injury to ischemic tissues after stroke or myocardial infarction. In cancer, VEGF‐mediated disruption of the vascular barrier may potentiate tumour cell extravasation, resulting in widespread metastatic disease. All of these pathological conditions are also associated with increased angiogenesis. The OBJECTIVE of this study is to elucidate the signaling pathways whereby VEGF induces vascular permeability and angiogenesis. Emerging evidence from my group and others supports a crucial role of protein kinase D (PKD) in VEGF signaling and angiogenesis. PKD1 is a member of a novel family of serine/threonine protein kinases,which are potential druggable targets for therapeutics. My laboratory was the first to report that VEGF via its receptor 2 (VEGFR2) stimulated PKD1 activation in vascular ECs, which modulates EC proliferation. Subsequently, we found that PKD1, via phosphorylation of histone deacetylases, regulates EC migration and tube formation. Nascent observations from my group now reveal that PKD1, through its effects on cytoskeleton and adherens junction, regulates vascular permeability. Using Transwell EC permeability assay, we found that the inhibition of PKD1 by pharmacological inhibitors, PKD1 siRNA or adenoviral PKD1 dominant‐negative mutant significantly attenuated VEGF‐stimulated endothelial monolayer permeability. Using in vivo vascular permeability assays in mouse lung and ear microvascular beds, we found that EC‐specific knockout of PKD1 in mice greatly decreased VEGF‐induced vascular permeability. The inhibition of PKD1 by the pharmacological inhibitors also markedly diminished vascular permeability in mice. Mechanistically, we found that PKD1 mediated VEGF‐induced F‐actin stress fiber formation and the dismantlement of endothelial adherens junctions in ECs. In CONCLUSION, our results demonstrate a critical role of PKD1 in VEGF regulation of vascular permeability and angiogenesis. These findings would facilitate development of new therapeutic approaches to prevent or treat inflammation‐ and angiogenesis‐associated diseases.