Endothelial Cell Shape Research Articles

Nesprin-3 regulates endothelial cell morphology, perinuclear cytoskeletal architecture, and flow-induced polarization

Changes in blood flow regulate gene expression and protein synthesis in vascular endothelial cells, and this regulation is involved in the development of atherosclerosis. How mechanical stimuli are transmitted from the endothelial luminal surface to the nucleus is incompletely understood. The linker of nucleus and cytoskeleton (LINC) complexes have been proposed as part of a continuous physical link between the plasma membrane and subnuclear structures. LINC proteins nesprin-1, -2, and -4 have been shown to mediate nuclear positioning via microtubule motors and actin. Although nesprin-3 connects intermediate filaments to the nucleus, no functional consequences of nesprin-3 mutations on cellular processes have been described. Here we show that nesprin-3 is robustly expressed in human aortic endothelial cells (HAECs) and localizes to the nuclear envelope. Nesprin-3 regulates HAEC morpho-logy, with nesprin-3 knockdown inducing prominent cellular elongation. Nesprin-3 also organizes perinuclear cytoskeletal organization and is required to attach the centrosome to the nuclear envelope. Finally, nesprin-3 is required for flow-induced polarization of the centrosome and flow-induced migration in HAECs. These results represent the most complete description to date of nesprin-3 function and suggest that nesprin-3 regulates vascular endothelial cell shape, perinuclear cytoskeletal architecture, and important aspects of flow-mediated mechanotransduction.

Vascular Cell Adhesion Molecule-1 Expression and Signaling During Disease: Regulation by Reactive Oxygen Species and Antioxidants

The endothelium is immunoregulatory in that inhibiting the function of vascular adhesion molecules blocks leukocyte recruitment and thus tissue inflammation. The function of endothelial cells during leukocyte recruitment is regulated by reactive oxygen species (ROS) and antioxidants. In inflammatory sites and lymph nodes, the endothelium is stimulated to express adhesion molecules that mediate leukocyte binding. Upon leukocyte binding, these adhesion molecules activate endothelial cell signal transduction that then alters endothelial cell shape for the opening of passageways through which leukocytes can migrate. If the stimulation of this opening is blocked, inflammation is blocked. In this review, we focus on the endothelial cell adhesion molecule, vascular cell adhesion molecule-1 (VCAM-1). Expression of VCAM-1 is induced on endothelial cells during inflammatory diseases by several mediators, including ROS. Then, VCAM-1 on the endothelium functions as both a scaffold for leukocyte migration and a trigger of endothelial signaling through NADPH oxidase-generated ROS. These ROS induce signals for the opening of intercellular passageways through which leukocytes migrate. In several inflammatory diseases, inflammation is blocked by inhibition of leukocyte binding to VCAM-1 or by inhibition of VCAM-1 signal transduction. VCAM-1 signal transduction and VCAM-1-dependent inflammation are blocked by antioxidants. Thus, VCAM-1 signaling is a target for intervention by pharmacological agents and by antioxidants during inflammatory diseases. This review discusses ROS and antioxidant functions during activation of VCAM-1 expression and VCAM-1 signaling in inflammatory diseases.

Microtubule‐associated protein EB3 regulates calcium signaling and facilitates increase in endothelial permeability

End binding proteins (EBs) are highly conserved microtubule plus‐end tracking accessory factors that bind to growing microtubule ends and suppress microtubule catastrophe events. We investigated the roles of EB1 and EB3 in regulating endothelial cytoskeletal dynamics and cell shape change, the primary determinants of the permeability of endothelial barrier. Protein depletion experiments showed that EB3, but not EB1, facilitates thrombin‐induced release of calcium from endoplasmic reticulum (ER), and thereby activates calcium entry from extracellular stores. We observed that EB3 interacts with inositol 1,4,5‐thriphosphate receptor type 3 (IP3R3) in lung microvasculature. Cell permeant variant of IP3R3 derivative peptide containing EB3 consensus motif reduced the interaction between EB3 and IP3R3 and mitigated increased endothelial permeability response associated with the cell shape changes. Furthermore, infusion of IP3R3 derivative peptide in ex vivo murine lung preparation attenuates the increase in lung vascular liquid permeability (Kf,c) in response to activation of the Protease‐Activated Receptor ‐1. Intravenous injection of this peptide prevents lung injury and reduces the lethality of polymicrobial sepsis in mice. These data indicate that EB3 regulates calcium signaling in endothelium and facilitates pulmonary vascular leak in disease states.

Minimum drag shape of a semi-ellipsoid exposed to shear flow and its possible relation to the shape of endothelial cell

A semi-ellipsoid attached on a wall is considered as a model problem for the study of blood flow effect on the shape of an endothelial cell. Under the condition that the volume is fixed and one axis of the semi-ellipsoid is aligned to the flow direction, the shape for the minimum drag under the applied shear flow is determined. Both the analytical and numerical approaches are adopted for computation of the minimum drag shape. Since analytical solution is not available for the original model problem, analytical solution to a closely related problem is used to compute the approximate value of the drag force. Adopted is the classical result on the motion of an ellipsoidal particle in a viscous fluid [Jeffery, Proc. Roy. Soc. A (1922)]. To corroborate the analytically obtained results, the model problem has also been studied numerically by using the finite element method (FEM). The minimum drag shape predicted analytically by using Jeffery’s solution is ( a, b, c) = (1.71, 0.67, 0.88), where a is the dimensionless semi-axis in the flow direction, b the height, and c the half width of the semi-ellipsoid. The numerical approach predicts the minimal drag shape as ( a, b, c) = (1.96,0.64,0.80). This result obtained by the FEM method shows good agreement with the result obtained by the boundary integral method [Hazel and Pedley, Biophys. J. (2000)].

Segmentation of Endothelial Cell Boundaries of Rabbit Aortic Images Using a Machine Learning Approach

This paper presents an automatic detection method for thin boundaries of silver-stained endothelial cells (ECs) imaged using light microscopy of endothelium mono-layers from rabbit aortas. To achieve this, a segmentation technique was developed, which relies on a rich feature space to describe the spatial neighbourhood of each pixel and employs a Support Vector Machine (SVM) as a classifier. This segmentation approach is compared, using hand-labelled data, to a number of standard segmentation/thresholding methods commonly applied in microscopy. The importance of different features is also assessed using the method of minimum Redundancy, Maximum Relevance (mRMR), and the effect of different SVM kernels is also considered. The results show that the approach suggested in this paper attains much greater accuracy than standard techniques; in our comparisons with manually labelled data, our proposed technique is able to identify boundary pixels to an accuracy of 93%. More significantly, out of a set of 56 regions of image data, 43 regions were binarised to a useful level of accuracy. The results obtained from the image segmentation technique developed here may be used for the study of shape and alignment of ECs, and hence patterns of blood flow, around arterial branches.

ELR510444, A Novel Microtubule Disruptor with Multiple Mechanisms of Action

Although several microtubule-targeting drugs are in clinical use, there remains a need to identify novel agents that can overcome the limitations of current therapies, including acquired and innate drug resistance and undesired side effects. In this study, we show that ELR510444 has potent microtubule-disrupting activity, causing a loss of cellular microtubules and the formation of aberrant mitotic spindles and leading to mitotic arrest and apoptosis of cancer cells. ELR510444 potently inhibited cell proliferation with an IC(50) value of 30.9 nM in MDA-MB-231 cells, inhibited the rate and extent of purified tubulin assembly, and displaced colchicine from tubulin, indicating that the drug directly interacts with tubulin at the colchicine-binding site. ELR510444 is not a substrate for the P-glycoprotein drug transporter and retains activity in βIII-tubulin-overexpressing cell lines, suggesting that it circumvents both clinically relevant mechanisms of drug resistance to this class of agents. Our data show a close correlation between the concentration of ELR510444 required for inhibition of cellular proliferation and that required to cause significant loss of cellular microtubule density, consistent with its activity as a microtubule depolymerizer. ELR510444 also shows potent antitumor activity in the MDA-MB-231 xenograft model with at least a 2-fold therapeutic window. Studies in tumor endothelial cells show that a low concentration of ELR510444 (30 nM) rapidly alters endothelial cell shape, similar to the effect of the vascular disrupting agent combretastatin A4. These results suggest that ELR510444 is a novel microtubule-disrupting agent with potential antivascular effects and in vivo antitumor efficacy.

Synthesis and Antitumor Activity of 1,5-Disubstituted 1,2,4-Triazoles as Cis-Restricted Combretastatin Analogues

A series of 1-aryl-5-(3',4',5'-trimethoxyphenyl) derivatives and their related 1-(3',4',5'-trimethoxyphenyl)-5-aryl-1,2,4-triazoles, designed as cis-restricted combretastatin analogues, were synthesized and evaluated for antiproliferative activity, inhibitory effects on tubulin polymerization, cell cycle effects, and apoptosis induction. Their activity was greater than, or comparable with, that of the reference compound CA-4. Flow cytometry studies showed that HeLa and Jurkat cells treated with the most active compounds 4l and 4o were arrested in the G2/M phase of the cell cycle in a concentration dependent manner. This effect was accompanied by apoptosis of the cells, mitochondrial depolarization, generation of reactive oxygen species, activation of caspase-3, and PARP cleavage. Compound 4l was also shown to have potential antivascular activity, since it induced endothelial cell shape change in vitro and disrupted the sprouting of endothelial cells in the chick aortic ring assay.

Evaluation of the microstructure of cornea by in vivo confocal microscopy in contact lens wearing and non-contact lens wearing keratoconus patients

To compare the microstructure of the central keratoconic cornea in contact lens wearing and non-contact lens wearing keratoconus subjects. One hundred and one eyes of 56 keratoconic subjects were compared with control patients who wear contact lenses (22 subjects) and controls who do not wear contact lenses (40 subjects). The keratoconic subjects were assessed in 2 groups: the contact lens wearing keratoconus group (37 patients, 64 eyes, 20 female and 17 male; Group 1) and the keratoconus group comprising subjects who do not wear contact lenses (19 patients, 37 eyes, 9 female, 10 male; Group 2). The mean age was 33 +/- 12 years in the contact lens wearer keratoconus group, 31 +/- 12 years in the non-contact lens wearer keratoconus group, 34 +/- 12 years in the non-contact lens wearing control group and 29 +/- 10 years in the contact lens wearing control group. Mean basal epithelial cell density was significantly lower in the contact lens wearer keratoconus group (p < 0.001) and in the non-contact lens wearer keratoconus group (p < 0.001) in comparison with controls. The anterior, intermediate and posterior keratocyte densities were significantly lower in both contact lens wearer keratoconic subjects (p < 0.001, p < 0.001, p < 0.001) and non-contact lens wearer keratoconic subjects (p < 0.001, p < 0.001, p=0.004) as compared to controls. Endothelial cell density was not altered in keratoconic patients. The decrease in basal epithelial cell density and in keratocyte density may highlight the role of apoptosis in keratoconus. Endothelial cell density does not change in keratoconus, but extensive variability in endothelial cell size and shape may be encountered.

Novel aspects of the roles of Rac1 GTPase in the cardiovascular system

Rac1 GTPase is an established master regulator of cell motility through cortical actin re-organization and of reactive oxygen species generation through regulation of NADPH oxidase activity. Numerous molecular and cellular studies have implicated Rac1 in various cardiovascular pathologies: vascular smooth muscle proliferation, cardiomyocyte hypertrophy, and endothelial cell shape change. The physiological relevance of these in vitro findings, however, is just beginning to be reassessed with the newly developed, conditional mouse mutagenesis technology. Conditional gene targeting has also revealed unexpected, cell type-specific roles of Rac1. The aim of this review is to summarize the recent advance made in Rac1 research in the cardiovascular system, with special focus on its novel roles in the regulation of endothelial function, angiogenesis, and endothelium-mediated neuroprotection.

0203 疑似血管マイクロデバイスを用いた内皮細胞表面にかかるせん断応力の分布と形状の関係(GS2:血球と微小循環)

0203 疑似血管マイクロデバイスを用いた内皮細胞表面にかかるせん断応力の分布と形状の関係(GS2:血球と微小循環)

β1 Integrin Establishes Endothelial Cell Polarity and Arteriolar Lumen Formation via a Par3-Dependent Mechanism

Maintenance of single-layered endothelium, squamous endothelial cell shape, and formation of a patent vascular lumen all require defined endothelial cell polarity. Loss of beta1 integrin (Itgb1) in nascent endothelium leads to disruption of arterial endothelial cell polarity and lumen formation. The loss of polarity is manifested as cuboidal-shaped endothelial cells with dysregulated levels and mislocalization of normally polarized cell-cell adhesion molecules, as well as decreased expression of the polarity gene Par3 (pard3). beta1 integrin and Par3 are both localized to the endothelial layer, with preferential expression of Par3 in arterial endothelium. Luminal occlusion is also exclusively noted in arteries, and is partially rescued by replacement of Par3 protein in beta1-deficient vessels. Combined, our findings demonstrate that beta1 integrin functions upstream of Par3 as part of a molecular cascade required for endothelial cell polarity and lumen formation.

Endothelial IQGAP1 regulates efficient lymphocyte transendothelial migration

Leukocyte movement from the blood to the tissues is a fundamental process in acute and chronic inflammatory diseases. While the role of endothelial cells (EC) to recruit leukocytes to sites of inflammation is well known, the mechanisms that control remodeling of EC shape and adhesive contacts during leukocyte transendothelial migration (TEM) are not completely understood. We studied the role of IQGAP1, an adaptor protein that binds to filamentous-actin and microtubules (MT) at interendothelial junctions, during lymphocyte TEM. EC IQGAP1 knockdown decreases MT tethered to the adherens junction, and decreases lymphocyte TEM to approximately 70% (p<0.05) versus control. Similarly, loss of adherens junction-associated MT induced by brief nocodazole (ND) treatment decreases lymphocyte TEM to approximately 65% of control (p<0.01). Confocal microscopy imaging indicates that EC IQGAP1 knockdown and MT depolymerization both result in lymphocyte accumulation above the vascular endothelial cadherin (VE-cadherin) junctions and reduces the fraction of adherent lymphocytes that complete diapedesis across interendothelial cell junctions. However, we observe no change in VE-cadherin gap formation underlying adherent lymphocytes among control, IQGAP1 knockdown, or MT depolymerised EC monolayers. These data indicate that IQGAP1 contributes to MT stability at endothelial junctions. Further, IQGAP1 is involved in junction remodeling required for efficient lymphocyte diapedesis, independent of VE-cadherin gap formation.

Corneal Thickness and Endothelial Cell Characteristics in Patients with Myotonic Dystrophy

To compare the characteristics of the endothelial cells of patients with myotonic dystrophy and those of normal subjects to determine if thicker corneas in patients with myotonic dystrophy are the result of their having abnormal endothelial cells leading to corneal edema. Prospective, comparative case series. Fifty-two eyes of patients with myotonic dystrophy and 52 eyes of normal age- and gender-matched subjects. Central corneal thickness (CCT) and endothelial cell counts and shape were measured with an SP 3000P specular microscope (Topcon, Tokyo, Japan) in patients with myotonic dystrophy and were compared with those of age- and gender-matched healthy subjects. Central corneal thickness, endothelial cell counts, pleomorphism, and coefficient of variation (CoV). In patients with myotonic dystrophy, the mean+/-standard deviation CCT measurement was 533+/-38 microm; the mean+/-standard deviation cell count was 2601+/-365 cell/mm(2); and the mean+/-standard deviation CoV was 23.3+/-4.4 (P<0.001). The mean+/-standard deviation pleomorphism was 64.4+/-8.4%. In healthy subjects, the mean+/-standard deviation CCT measurement was 514+/-27 microm (P = 0.002); the mean+/-standard deviation cell count was 2649+/-363 cell/mm(2) (P = 0.48); the mean+/-standard deviation CoV was 27.6+/-5.5 (P<0.001); and the mean+/-standard deviation pleomorphism was 61.1+/-8.6% (P = 0.04). Thicker corneas found in patients with myotonic dystrophy are not related to endothelial number or appearance as assessed in this study.

Cytoskeletal structure regulates endothelial cell immunogenicity independent of fluid shear stress

The cardiovascular disease atherosclerosis is directly linked to the functions of endothelial cells (ECs), which are affected by fluid shear stress (FSS). High, unidirectional FSS causes EC elongation with aligned cytoskeletal components and nonimmunogenic EC functions that protect against atherosclerosis. In contrast, low, oscillatory FSS is associated with cobblestone-shaped ECs with randomly oriented cytoskeletons and proinflammatory EC functions that promote atherosclerosis. Whether EC shape plays a role in EC immunogenic functions, independent of FSS, has not been previously determined. The goal of this study was to determine the effect of EC elongation and cytoskeletal alignment on the expression of inflammatory genes and functions. With the use of micropatterned lanes, EC elongation and cytoskeletal alignment were achieved in the absence of FSS. EC gene expression of key inflammation markers determined that the elongation and cytoskeletal alignment of micropattern-elongated ECs (MPECs) alone significantly downregulated VCAM-1 while having no effect on E-selectin and ICAM-1. The positive control of FSS-elongated ECs promoted E-selectin and VCAM-1 downregulation and upregulation of ICAM-1. Functionally, monocytic U937 cells formed weaker interactions on the surface of MPECs compared with cobblestone ECs. Interestingly, MPEC expression of the known FSS-dependent transcription factor krüppel-like factor 2 (KLF2), which promotes a nonimmunogenic EC phenotype, was significantly upregulated in MPECs compared with cobblestone ECs. Cytoskeletal regulation of KLF2 expression was shown to be dependent on microtubules. Therefore, the cellular elongation and cytoskeletal alignment of MPECs regulated immunogenic gene expression and functions and may act synergistically with FSS to create an EC surface with reduced inflammatory capability.

Correlating Global Gene Regulation to Angiogenesis in the Developing Chick Extra-Embryonic Vascular System

BackgroundFormation of blood vessels requires the concerted regulation of an unknown number of genes in a spatial-, time- and dosage-dependent manner. Determining genes, which drive vascular maturation is crucial for the identification of new therapeutic targets against pathological angiogenesis.Methology/Principal FindingsWe accessed global gene regulation throughout maturation of the chick chorio-allantoic membrane (CAM), a highly vascularized tissue, using pan genomic microarrays. Seven percent of analyzed genes showed a significant change in expression (>2-fold, FDR<5%) with a peak occurring from E7 to E10, when key morphogenetic and angiogenic genes such as BMP4, SMO, HOXA3, EPAS1 and FGFR2 were upregulated, reflecting the state of an activated endothelium. At later stages, a general decrease in gene expression occurs, including genes encoding mitotic factors or angiogenic mediators such as CYR61, EPAS1, MDK and MYC. We identified putative human orthologs for 77% of significantly regulated genes and determined endothelial cell enrichment for 20% of the orthologs in silico. Vascular expression of several genes including ENC1, FSTL1, JAM2, LDB2, LIMS1, PARVB, PDE3A, PRCP, PTRF and ST6GAL1 was demonstrated by in situ hybridization. Up to 9% of the CAM genes were also overexpressed in human organs with related functions, such as placenta and lung or the thyroid. 21–66% of CAM genes enriched in endothelial cells were deregulated in several human cancer types (P<.0001). Interfering with PARVB (encoding parvin, beta) function profoundly changed human endothelial cell shape, motility and tubulogenesis, suggesting an important role of this gene in the angiogenic process.Conclusions/SignificanceOur study underlines the complexity of gene regulation in a highly vascularized organ during development. We identified a restricted number of novel genes enriched in the endothelium of different species and tissues, which may play crucial roles in normal and pathological angiogenesis.

Protective Effects of Lycopene against H2O2-Induced Oxidative Injury and Apoptosis in Human Endothelial Cells

Oxidative stress is considered to be a major factor contributing to damage of endothelial cells, and is an important component of the etiology of atherosclerosis. In this study, we investigated the effects of lycopene on the oxidative injury and apoptosis of endothelial cells induced by H(2)O(2), and the effects of lycopene on the expression of p53, caspase-3 mRNA in injured cells. In the H(2)O(2) group, endothelial cells were incubated with 400 microM H(2)O(2). In lycopene groups, endothelial cells were pretreated with different concentrations of lycopene then exposed to 400 microM H(2)O(2). In the drug control group, cells were pretreated with probucol then incubated with H(2)O(2). The effects of different concentrations of lycopen on the extent of oxidative injury to the cells were evaluated. The growth conditions and morphological changes of the cells were observed with an inverted microscope. The level of oxidative injury to cells was determined by measuring malondialdehyde (MDA) levels; the viability of cells was detected by MTT assays; the nuclear morphology of cells was observed by Hoechst staining; the apoptotic ratio of cells was measured by flow cytometry; and the expressions of p53 and caspase-3 mRNA were investigated by RT-PCR. Lycopene improved the shape of contracted endothelial cells induced by H(2)O(2) injury, and diminished the level of MDA produced following oxidative injury of cells. The viability of cells increased, and the number of cells characterized by apoptotic nuclear morphology decreased in groups treated with lycopene. Similarly, lycopene significantly diminished the apoptosis ratio of oxidative injured cells, and also downregulated the expressions of p53 and caspase-3 mRNA induced by H(2)O(2). Lycopene and probucol displayed similar protective effects on endothelial cells. Lycopene can decrease the oxidative injury of endothelial cells induced by H(2)O(2), can attenuate the expression of p53 and caspase-3 mRNA in injured cells, and can diminish the apoptosis of injured cells. These findings possibly explain in part why lycopene can prevent atherosclerotic cardiovascular diseases.

The Molecular Basis of Vascular Lumen Formation in the Developing Mouse Aorta

In vertebrates, endothelial cells (ECs) form blood vessels in every tissue. Here, we investigated vascular lumen formation in the developing aorta, the first and largest arterial blood vessel in all vertebrates. Comprehensive imaging, pharmacological manipulation, and genetic approaches reveal that, in mouse embryos, the aortic lumen develops extracellularly between adjacent ECs. We show that ECs adhere to each other, and that CD34-sialomucins, Moesin, F-actin, and non-muscle Myosin II localize at the endothelial cell-cell contact to define the luminal cell surface. Resultant changes in EC shape lead to lumen formation. Importantly, VE-Cadherin and VEGF-A act at different steps. VE-Cadherin is required for localizing CD34-sialomucins to the endothelial cell-cell contact, a prerequisite to Moesin and F-actin recruitment. In contrast, VEGF-A is required for F-actin-nm-Myosin II interactions and EC shape change. Based on these data, we propose a molecular mechanism of in vivo vascular lumen formation in developing blood vessels.

Endothelial cell morphology creates preferred regions for leukocyte transmigration at venular convergences

Leukocyte transmigration (TEM) occurs mainly via endothelial cell (EC) junctions, but whether there is a preference for two‐ or tri‐cellular junctions is not clear. Using intravital confocal microscopy of anesthetized mouse cremaster muscle in combination with immunofluorescence labeling we showed that leukocyte TEM in venular convergences was 8‐fold higher than in straight venular regions. Interestingly, due to the difference in EC size, shape and orientation, the number of tri‐cellular junctions in converging venules is significantly higher than in straight regions (20.7±1.2 vs 12.43±1.1/6000μm2 respectively). The majority (55±1.8%) of adhered leukocytes in venular convergences were found at the tri‐cellular junctions, compared to only 21±2.8% in straight regions. Importantly, 45.1±4% of leukocytes in these straight regions and 59.3±2% in venular convergences used the tri‐cellular junctions for TEM, suggesting tri‐cellular junctions as the preferred route. Leukocyte crawling distances were shorter (17.8±2.4μm vs 26.2±2.6μm) and the TEM efficiency was higher in venular convergences (32.8±6.1 %/total adhered) compared to straight venular regions (14.6±6.1, %/total adhered). We also found that 42.2±4% of the tri‐cellular junctions in both regions were surrounded by ICAM‐1 enriched areas, supporting their role as portals for leukocyte TEM. Supported by NIH HL 18208, HL 75186 and AHA 0615677T

VE‐cadherin‐mediated signaling regulates microtubule dynamics

Disruption of adherens junctions (AJs) in endothelial cells by pro‐inflammatory stimuli such as thrombin induces microtubule (MT) destabilization (Gorovoy et al., J Biol Chem. 2005 280: 26533‐42). Here we determined the signaling mechanism regulating MT dynamics by VE‐cadherin homophilic adhesion. We assessed MT dynamics in human microvascular endothelial monolayers by expressing YFP‐tagged End Binding (EB)‐1 protein, which binds preferentially to the growing ends of MTs. Formation of AJs inhibited MT growth by increasing MT catastrophe frequency whereas disruption of AJs by calcium switch or using VE‐cadherin blocking antibody induced MT persistent growth. We used calcium switch model to address the signaling mechanism downstream of VE‐cadherin adhesion in regulating MT dynamics. We observed that disruption of AJs induced the release of calcium from endoplasmic reticulum and activation of protein phosphatase 2B (PP2B). Using PP2B autoinhibitory peptide we demonstrated that PP2B induced de‐phosphorylation of EB3 (but not EB1 or EB2), the accumulation of EB3 at the MT growing ends, and MT growth. We conclude that signaling activated by VE‐cadherin adhesion regulates MT dynamics through the PP2B‐EB3 axis, and may thereby regulate endothelial cells shape and motility.

Endothelial Cells Form a Phalanx to Block Tumor Metastasis

Tumor blood vessels deliver oxygen poorly, thereby contributing to tumor hypoxia and upregulation of proangiogenic cytokines in an escalating feedback loop. Mazzone et al. (2009) now show that reducing the amount of a protein involved in endothelial oxygen sensing leads to changes in endothelial cell shape that interrupt this feedback loop and reduce tumor metastasis.