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1.  The diaphragms of fenestrated endothelia – gatekeepers of vascular permeability and blood composition 
Developmental cell  2012;23(6):1203-1218.
SUMMARY
Fenestral and stomatal diaphragms are endothelial subcellular structures of unknown function that form on organelles implicated in vascular permeability: fenestrae, transendothelial channels and caveolae. PV1 protein is required for diaphragm formation in vitro. Here, we report that deletion of the PV1-encoding Plvap gene in mice results in the absence of diaphragms and decreased survival. Loss of diaphragms did not affect the fenestrae and transendothelial channels formation but disrupted the barrier function of fenestrated capillaries causing a major leak of plasma proteins. This disruption results in early death of animals due to severe non-inflammatory protein loosing enteropathy. Deletion of PV1 in endothelium, but not the hematopoietic compartment, recapitulates the phenotype of global PV1 deletion, whereas endothelial reconstitution of PV1 rescues the phenotype. Taken together, these data provide genetic evidence for the critical role of the diaphragms in fenestrated capillaries in the maintenance of blood composition.
doi:10.1016/j.devcel.2012.11.003
PMCID: PMC3525343  PMID: 23237953
2.  PV1 downregulation via shRNA inhibits the growth of pancreatic adenocarcinoma xenografts 
PV1 is an endothelial specific protein with structural roles in the formation of diaphragms in endothelial cells of normal vessels. PV1 is also highly expressed on endothelial cells of many solid tumors. Based on in vitro data, PV1 is thought to actively participate in angiogenesis. In order to test whether PV1 has a function in tumor angiogenesis and in tumor growth in vivo, we have treated pancreatic tumor bearing mice by single dose intratumoral delivery of lentiviruses encoding for two different shRNAs targeting murine PV1. We find that PV1 downregulation by shRNAs inhibits the growth of established tumors derived from two different human pancreatic adenocarcinoma cell lines (AsPC-1 and BxPC-3). The effect observed is due to downregulation of PV1 in the tumor endothelial cells of host origin, PV1 being specifically expressed in tumor vascular endothelial cells and not in cancer or other stromal cells. There are no differences in vascular density of tumors treated or not with PV1 shRNA and gain and loss of function of PV1 in endothelial cells does not modify either their proliferation or migration, suggesting that tumor angiogenesis is not impaired. Together, our data argue that down regulation of PV1 in tumor endothelial cells results in the inhibition of tumor growth via a mechanism different from inhibiting angiogenesis.
doi:10.1111/j.1582-4934.2012.01587.x
PMCID: PMC3435473  PMID: 22568538
angiogenesis; fenestrae; vesiculo-vacuolar organelles; caveolae; pancreatic cancer; transendothelial channels; tumor microenvironment
3.  Plasmalemmal vesicle associated protein (PV1) modulates SV40 virus infectivity in CV-1 cells 
Plasmalemmal vesicle associated protein (Plvap/PV1) is a structural protein required for the formation of the stomatal diaphragms of caveolae. Caveolae are plasma membrane invaginations that were implicated in SV40 virus entry in primate cells. Here we show that de novo Plvap/PV1 expression in CV-1 green monkey epithelial cells significantly reduces the ability of SV40 virus to establish productive infection, when cells are incubated with low concentrations of the virus. However, in presence of high viral titers PV1 has no effect on SV40 virus infectivity. Mechanistically, PV1 expression does not reduce the cell surface expression of known SV40 receptors such as GM1 ganglioside and MHC class I proteins. Furthermore, PV1 does not reduce the binding of virus-like particles made by SV40 VP1 protein to the CV-1 cell surface and does not impact their internalization when cells are incubated with either high or low VLP concentrations. These results suggest that PV1 protein is able to block SV40 infectivity at low but not at high viral concentration either by interfering with the infective internalization pathway at the cell surface or at a post internalization step.
doi:10.1016/j.bbrc.2011.07.063
PMCID: PMC3171970  PMID: 21827737
4.  Caveolae, Fenestrae and Transendothelial Channels Retain PV1 on the Surface of Endothelial Cells 
PLoS ONE  2012;7(3):e32655.
PV1 protein is an essential component of stomatal and fenestral diaphragms, which are formed at the plasma membrane of endothelial cells (ECs), on structures such as caveolae, fenestrae and transendothelial channels. Knockout of PV1 in mice results in in utero and perinatal mortality. To be able to interpret the complex PV1 knockout phenotype, it is critical to determine whether the formation of diaphragms is the only cellular role of PV1. We addressed this question by measuring the effect of complete and partial removal of structures capable of forming diaphragms on PV1 protein level. Removal of caveolae in mice by knocking out caveolin-1 or cavin-1 resulted in a dramatic reduction of PV1 protein level in lungs but not kidneys. The magnitude of PV1 reduction correlated with the abundance of structures capable of forming diaphragms in the microvasculature of these organs. The absence of caveolae in the lung ECs did not affect the transcription or translation of PV1, but it caused a sharp increase in PV1 protein internalization rate via a clathrin- and dynamin-independent pathway followed by degradation in lysosomes. Thus, PV1 is retained on the cell surface of ECs by structures capable of forming diaphragms, but undergoes rapid internalization and degradation in the absence of these structures, suggesting that formation of diaphragms is the only role of PV1.
doi:10.1371/journal.pone.0032655
PMCID: PMC3293851  PMID: 22403691

Results 1-4 (4)