Plasmalemmal vesicle-associated protein (PLVAP) is expressed by tumour endothelium and is upregulated by vascular endothelial growth factor-A (VEGF)

Abstract

Vascular endothelial growth factor-A (VEGF) is an important regulator of vascular permeability. In preclinical studies, VEGF induces endothelial fenestrations in pre-existing and neo-vasculature, while inhibition of VEGF leads to a reduction in endothelial fenestrations. Recently, vascular regression in response to VEGF inhibition has been shown to correlate with the presence of endothelial fenestrations. Plasmalemmal vesicle-associated protein (PLVAP) is believed to be a component of diaphragmed endothelial fenestrations, but a direct relationship with VEGF signalling has not been established. The aim of this study was to characterize the expression pattern of PLVAP and investigate whether PLVAP is a transcriptional target of VEGF signal transduction. The expression pattern of PLVAP was characterized in normal and neoplastic human tissues by in situ hybridization and/or immunohistochemistry. The role of VEGF signal transduction in the regulation of PLVAP expression was investigated in vitro using receptor-selective engineered forms of VEGF, a neutralizing monoclonal antibody against VEGF, and inhibitors of downstream signalling pathways. PLVAP mRNA and protein were widely expressed in the endothelium of normal and neoplastic tissues. In cultured endothelial cells, VEGF signalling through receptor 2 stimulated expression of PLVAP total RNA and protein. This induction could be blocked with an anti-VEGF monoclonal antibody and by inhibitors of phosphatidylinositol 3-kinase (LY294002) or p38 mitogen-activated protein kinase (SB203580), but not by PD98059, a mitogen-activated protein/extracellular signal-regulated kinase 1 inhibitor. These data show that PLVAP is more widely expressed in the vasculature of normal tissues than previously thought and that it is expressed in the vasculature of most human tumours. We suggest that PLVAP is a downstream target of VEGF signalling. This work solidifies the association between VEGF and the appearance and maintenance of fenestrations by providing a potential mechanistic link.

Glomerular Endothelial Cells Form Diaphragms during Development and Pathologic Conditions

“…36 Vascular endothelial growth factor (VEGF), which is secreted from podocytes in mature glomeruli, plays a crucial role in the formation and maintenance of fenestrae in GEnC, as well as in various endothelial cell types. [37][38][39][40] VEGF has also been reported to upregulate the expression of PV-1 mRNA and protein in human endothelial cell 41,42 ; however, most GEnC in mature glomeruli do not express PV-1, as reconfirmed in this study. This inconsistence presumably indicates that the intracellular signaling pathways for the formation of fenestrae and the upregulation of PV-1 are not completely identical.…”

“…Upregulation of PV-1 requires the activation of phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase. 41,42 VEGF-phosphatidylinositol 3-kinase-p38 mitogen-activated protein kinase pathway is a candidate for the mechanisms involved in the upregulation of PV-1 in the GEnC of immature and Thy-1.1 nephritic glomeruli. In most GEnC without diaphragms, however, this pathway may be inactivated in adult mature glomeruli by some yet unknown mechanisms.…”

Angiotensin II increases the permeability and PV-1 expression of endothelial cells

“…Strickland et al (40) reported that PV-1 expression induced by VEGF is p38 MAP kinase dependent (40), whereas there was no data about the effect of ANG II on PV-1 expression. Here, we demonstrated that ANG II induced PV-1 expression, similarly to VEGF, also in a p38-dependent manner.…”

“…Cells were then treated with various doses of ANG II or 100 ng/ml VEGF for 24 and 48 h. RNAs were isolated using GenElute Mammalian Total RNA Kit (Sigma) and later transcribed to cDNAs with TaqMan Reverse Transcription kit (Applied Biosystems) on a Bio-Rad iCycler thermal cycler. PV-1 real-time PCR was performed using a TaqMan assay published previously (40) in a Bio-Rad CFX96 thermal cycler. Data were normalized to ribosomal RNA content (TaqMan Ribosomal RNA control reagents, Applied Biosystems, Forster City, CA), relative quantitation being performed using the Bio-Rad CFX Manager Software v. 1.7.…”

“…Activation of p38 is involved in endothelial cell responses as migration, permeability, and cell survival (21,34) and regulates the stability of different mRNAs by activation of MAPKAP2 (MK2) (22). VEGF, as a potent permeability enhancing agent, induces fenestrae formation in vivo and in vitro (10,30) and also increases PV-1 expression (40).…”