VEGF-A stimulates podosome-mediated collagen-IV proteolysis in microvascular endothelial cells

Abstract

Podosomes are dynamic cell-matrix contact structures that combine several key abilities, including adhesion, matrix degradation and mechanosensing. These actin-based cytoskeletal structures are well known in monocytic cells, but much less is known about those formed in other lineages. In this study, we characterize podosomes in capillary-derived microvascular endothelial cells. We identify two types of podosomes: constitutive podosomes that form in the absence of specific stimulation and induced podosomes that arise in response to the angiogenic factor VEGF-A. Constitutive and VEGF-A-induced podosomes share similar components but exhibit marked differences in terms of gelatinolytic activity. We also show that extracellular matrix proteins are key determinants of the VEGF-A response: laminin and collagen-IV, but neither collagen-I nor fibronectin are conducive for podosome induction. Moreover, only collagen-IV elicits the formation of proteolytically active podosomes through a mechanism involving increased Src phosphorylation, p190RhoGAP-B relocalisation and MT1-MMP cell surface exposure at podosome sites. We hypothesise that by promoting podosome formation, VEGF-A enables endothelial cells to overcome the basement membrane barrier for sprouting away from the existing vasculature.