Loss of responsiveness to chemotactic factors by deletion of the C-terminal protein interaction site of angiomotin

Mesenchymal Osr1+ cells regulate embryonic lymphatic vessel formation

The lymphatic system is formed during embryonic development by the commitment of specialized lymphatic endothelial cells (LECs) and their subsequent assembly in primary lymphatic vessels. Although lymphatic cells are in continuous contact with mesenchymal cells during development and in adult tissues, the role of mesenchymal cells in lymphatic vasculature development remains poorly characterized. Here, we show that a subpopulation of mesenchymal cells expressing the transcription factor Osr1 are in close association with migrating LECs and established lymphatic vessels in mice. Lineage tracing experiments revealed that Osr1+ cells precede LEC arrival during lymphatic vasculature assembly in the back of the embryo. Using Osr1-deficient embryos and functional in vitro assays, we show that Osr1 acts in a non-cell-autonomous manner controlling proliferation and early migration of LECs to peripheral tissues. Thereby, mesenchymal Osr1+ cells control, in a bimodal manner, the production of extracellular matrix scaffold components and signal ligands crucial for lymphatic vessel formation.

Angiomotin family proteins in the Hippo signaling pathway

The Motin family proteins (Motins) are a class of scaffolding proteins consisting of Angiomotin (AMOT), AMOT-like protein 1 (AMOTL1), and AMOT-like protein 2 (AMOTL2). Motins play a pivotal role in angiogenesis, tumorigenesis, and neurogenesis by modulating multiple cellular signaling pathways. Recent findings indicate that Motins are components of the Hippo pathway, a signaling cascade involved in development and cancer. This review discusses how Motins are integrated into the Hippo signaling network, as either upstream regulators or downstream effectors, to modulate cell proliferation and migration. The repression of YAP/TAZ by Motins contributes to growth inhibition, whereas subcellular localization of Motins and their interactions with actin fibers are critical in regulating cell migration. The net effect of Motins on cell proliferation and migration may contribute to their diverse biological functions.

Role of angiomotin family members in human diseases (Review)

Angiomotin (Amot) family members, including Amot, Amot-like protein 1 (Amotl1) and Amot-like protein 2 (Amotl2), have been found to interact with angiostatins. In addition, Amot family members are involved in various physiological and pathological functions such as embryonic development, angiogenesis and tumorigenesis. Some studies have also demonstrated its regulation in signaling pathways such as the Hippo signaling pathway, AMPK signaling pathway and mTOR signaling pathways. Amot family members play an important role in neural stem cell differentiation, dendritic formation and synaptic maturation. In addition, an increasing number of studies have focused on their function in promoting and/or suppressing cancer, but the underlying mechanisms remain to be elucidated. The present review integrated relevant studies on upstream regulation and downstream signals of Amot family members, as well as the latest progress in physiological and pathological functions and clinical applications, hoping to offer important ideas for further research.

Vasculature is getting Hip(po): Hippo signaling in vascular development and disease

The Hippo signaling pathway regulates developmental organ growth, regeneration, and cell fate decisions. Although the role of the Hippo pathway, and its transcriptional effectors YAP and TAZ, has been well documented in many cell types and species, only recently have the roles for this pathway come to light in vascular development and disease. Experiments in mice, zebrafish, and in vitro have uncovered roles for the Hippo pathway, YAP, and TAZ in vasculogenesis, angiogenesis, and lymphangiogenesis. In addition, the Hippo pathway has been implicated in vascular cancers and cardiovascular diseases, thus identifying it as a potential therapeutic target for the treatment of these conditions. However, despite recent advances, Hippo's role in the vasculature is still underappreciated compared with its role in epithelial tissues. In this review, we appraise our current understanding of the Hippo pathway in blood and lymphatic vessel development and highlight the current knowledge gaps and opportunities for further research.

Comparison of a New 68Ga-Radiolabelled PET Imaging Agent sCD146 and RGD Peptide for In Vivo Evaluation of Angiogenesis in Mouse Model of Myocardial Infarction

Ischemic vascular diseases are associated with elevated tissue expression of angiomotin (AMOT), a promising molecular target for PET imaging. On that basis, we developed an AMOT-targeting radiotracer, ⁶⁸Ga-sCD146 and performed the first in vivo evaluation on a myocardial infarction mice model and then, compared AMOT expression and α_vβ₃-integrin expression with ⁶⁸Ga-sCD146 and ⁶⁸Ga-RGD₂ imaging. After myocardial infarction (MI) induced by permanent ligation of the left anterior descending coronary artery, myocardial perfusion was evaluated by Doppler ultrasound and by ¹⁸F-FDG PET imaging. ⁶⁸Ga-sCD146 and ⁶⁸Ga-RGD₂ PET imaging were performed. In myocardial infarction model, heart-to-muscle ratio of ⁶⁸Ga-sCD146 imaging showed a significantly higher radiotracer uptake in the infarcted area of MI animals than in sham (* p = 0.04). Interestingly, we also observed significant correlations between ⁶⁸Ga-sCD146 imaging and delayed residual perfusion assessed by ¹⁸F-FDG (* p = 0.04), with lowest tissue fibrosis assessed by histological staining (* p = 0.04) and with functional recovery assessed by ultrasound imaging (** p = 0.01). ⁶⁸Ga-sCD146 demonstrated an increase in AMOT expression after MI. Altogether, significant correlations of early post-ischemic ⁶⁸Ga-sCD146 uptake with late heart perfusion, lower tissue fibrosis and better functional recovery, make ⁶⁸Ga-sCD146 a promising radiotracer for tissue angiogenesis assessment after MI.

The Amot/integrin protein complex transmits mechanical forces required for vascular expansion

Vascular development is a complex multistep process involving the coordination of cellular functions such as migration, proliferation, and differentiation. How mechanical forces generated by cells and transmission of these physical forces control vascular development is poorly understood. Using an endothelial-specific genetic model in mice, we show that deletion of the scaffold protein Angiomotin (Amot) inhibits migration and expansion of the physiological and pathological vascular network. We further show that Amot is required for tip cell migration and the extension of cellular filopodia. Exploiting in vivo and in vitro molecular approaches, we show that Amot binds Talin and is essential for relaying forces between fibronectin and the cytoskeleton. Finally, we provide evidence that Amot is an important component of the endothelial integrin adhesome and propose that Amot integrates spatial cues from the extracellular matrix to form a functional vascular network.

Faulty oxygen sensing disrupts angiomotin function in trophoblast cell migration and predisposes to preeclampsia

Human placenta development and a successful pregnancy is incumbent upon precise oxygen-dependent control of trophoblast migration/invasion. Persistent low oxygen leading to failed trophoblast invasion promotes inadequate spiral artery remodeling, a characteristic of preeclampsia. Angiomotin (AMOT) is a multifaceted scaffolding protein involved in cell polarity and migration, yet its upstream regulation and significance in the human placenta remain unknown. Herein, we show that AMOT is primarily expressed in migratory extravillous trophoblast cells (EVTs) of the intermediate and distal anchoring column. Its expression increases after 10 weeks of gestation when oxygen tension rises and EVT migration/invasion peaks. Time-lapse imaging confirmed that the AMOT 80-kDa isoform promotes migration of trophoblastic JEG3 and HTR-8/SVneo cells. In preeclampsia, however, AMOT expression is decreased and its localization to migratory fetomaternal interface EVTs is disrupted. We demonstrate that Jumonji C domain-containing protein 6 (JMJD6), an oxygen sensor, positively regulates AMOT via oxygen-dependent lysyl hydroxylation. Furthermore, in vitro and ex vivo studies show that transforming growth factor-β (TGF-β) regulates AMOT expression, its interaction with polarity protein PAR6, and its subcellular redistribution from tight junctions to cytoskeleton. Our data reveal an oxygen- and TGF-β-driven migratory function for AMOT in the human placenta, and implicate its deficiency in impaired trophoblast migration that plagues preeclampsia.

The physiological role of Motin family and its dysregulation in tumorigenesis

Members in Motin family, or Angiomotins (AMOTs), are adaptor proteins that localize in the membranous, cytoplasmic or nuclear fraction in a cell context-dependent manner. They control the bioprocesses such as migration, tight junction formation, cell polarity, and angiogenesis. Emerging evidences have demonstrated that AMOTs participate in cancer initiation and progression. Many of the previous studies have focused on the involvement of AMOTs in Hippo-YAP1 pathway. However, it has been controversial for years that AMOTs serve as either positive or negative growth regulators in different cancer types because of the various cellular origins. The molecular mechanisms of these opposite roles of AMOTs remain elusive. This review comprehensively summarized how AMOTs function physiologically and how their dysregulation promotes or inhibits tumorigenesis. Better understanding the functional roles of AMOTs in cancers may lead to an improvement of clinical interventions as well as development of novel therapeutic strategies for cancer patients.

Gestational age-related patterns of AMOT methylation are revealed in preterm infant endothelial progenitors

Objective

Preterm birth is associated with altered angiogenesis and with increased risk of cardiovascular dysfunction and hypertension at adulthood. We previously demonstrated that in preterm newborns circulating cord blood endothelial progenitor cells (ECFC), responsible for angio/vasculogenesis, are reduced in number and display altered angiogenic properties. Altered angiogenic function was associated with a decreased expression of pro-angiogenic genes, among which the AMOT gene which is a strong positive regulator of angiogenesis. Such dysregulation may be related to epigenetic factors. In this study we analyse the methylation profiling of the AMOT gene during development, through a comparative analysis of the cord blood ECFC of preterm newborns and their term counterpart.

Methods

We used both cloning-sequencing and pyrosequencing experiments to perform a comparative analysis of the DNA methylation profile of the promoter CpG island of AMOT gene in the cord blood ECFC of 16 preterm newborns (28–35 weeks gestational age-GA) and 15 term newborns (>37 weeks GA).

Results

Twenty nine clones (obtained from 2 term newborns) and forty clones (obtained from 3 preterm newborns) were sequenced. The AMOT gene methylation rate was significantly higher in preterm compared to term newborns (4.5% versus 2.5% respectively: χ2 = 3.84; P = 1.8 10⁻⁰²). Bisulfite pyrosequencing identified four CpG dinucleotides with significantly higher methylation levels in preterm newborns. This CpG-targeted methylation significantly decreased with increasing gestational age.

Conclusions

These findings highlight importance of pro-angiogenic AMOT gene methylation in ECFC, suggesting that epigenetic mechanisms may control the regulation of angiogenesis during development. Therefore they pave the way to specific short term and long term complications of preterm birth by altered angiogenesis.

Regulation of localization and function of the transcriptional co-activator YAP by angiomotin

The Hippo-YAP pathway is a central regulator of cell contact inhibition, proliferation and death. There are conflicting reports regarding the role of Angiomotin (Amot) in regulating this pathway. While some studies suggest a YAP-inhibitory function other studies indicate Amot is required for YAP activity. Here, we describe an Amot-dependent complex comprised of Amot, YAP and Merlin. The phosphorylation of Amot at Serine 176 shifts localization of this complex to the plasma membrane, where it associates with the tight-junction proteins Pals1/PATJ and E-cadherin. Conversely, hypophosphorylated Amot shifts localization of the complex to the nucleus, where it facilitates the association of YAP and TEAD, induces transcriptional activation of YAP target genes and promotes YAP-dependent cell proliferation. We propose that phosphorylation of Amot^S176 is a critical post-translational modification that suppresses YAP’s ability to promote cell proliferation and tumorigenesis by altering the subcellular localization of an essential YAP co-factor.

DOI:http://dx.doi.org/10.7554/eLife.23966.001

Cells in animals and other multi-cellular organisms need to know when and where they should grow and divide. Individual cells communicate with their surrounding environment and each other via signaling pathways such as the Hippo-YAP pathway, which stimulates cells to grow and therefore influences the size of organs. When the Hippo part of the pathway is active it causes a protein known as YAP to move out of a compartment in the cell called the nucleus. Inside the nucleus, YAP helps to activate genes that promote cell growth. If the Hippo pathway can no longer respond to cues from the environment, YAP becomes over-active and can contribute to the development of various cancers. Therefore researchers are trying to better understand how it is regulated.

Many signals both from inside and outside the cell influence YAP activity. For example, some signals block YAP from entering the nucleus, whereas others cause YAP to be broken down entirely. Several studies have recently identified a signal protein called angiomotin as a regulator of YAP. However, the studies provide conflicting reports as to whether angiomotin promotes or inhibits cell growth.

Like many other proteins, angiomotin can be tagged with a small molecule called a phosphate group that can alter its activity. Moleirinho, Hoxha et al. studied human cells containing versions of angiomotin that mimic different forms of the protein with or without the phosphate. The experiments indicate that when a phosphate is attached at a particular position (known as serine 176), angiomotin predominantly interacts with YAP and another protein called Merlin at the cell surface. On the other hand, when angiomotin does not have a phosphate attached to it, all three proteins can move into the nucleus, where YAP is able to activate genes and promote cell growth.

Overall, these findings indicate that adding a phosphate group to angiomotin can act as a switch to regulate where in the cell it and YAP are found and thus, whether YAP is active. Future experiments will investigate which enzymes add the phosphate group to serine 176, and when they are able to do so.

DOI:http://dx.doi.org/10.7554/eLife.23966.002

MicroRNA-497 inhibits cell proliferation, migration, and invasion by targeting AMOT in human osteosarcoma cells

MicroRNAs (miRNAs) have a role in the development and progression of human malignancy. The expression of miR-497 is decreased in malignant tumors, which suggests a role for miR-497 as a tumor suppressor. Angiomotin is encoded by the AMOT gene, which is a target for miR-497. Angiomotin has a role in angiogenesis, cell proliferation, and invasion in human malignancies, including osteosarcoma. However, the role of miR-497 in human osteosarcoma is unknown. This preliminary study included human osteosarcoma tissues and normal tissues from 20 patients, the osteosarcoma cell lines, MG-63, SAOS-2, U-2 OS, and the human osteoblast cell line hFOB (OB3). Western blots for angiomotin and quantitative real-time polymerase chain reaction for the expression of miR-497 and AMOT were performed. Knockdown studies were performed using RNA interference and transfection studies used miR-497 mimics. Quantitative cell migration assays were performed, and cell apoptosis was studied by flow cytometry. Osteosarcoma cells and cell lines showed reduced expression of miR-497 and increased expression of angiomotin. Transfection of osteosarcoma cells with miR-497 mimics suppressed the expression of angiomotin. Results from a dual-luciferase reporter system supported AMOT as a direct target gene of miR-497. Knockdown of AMOT using RNA interference resulted in inhibition of osteosarcoma cell proliferation, migration, and invasion. These preliminary studies support a role for miR-497 as a suppressor of AMOT gene expression in human osteosarcoma cells, resulting in suppression of tumor cell proliferation and invasion. Further studies are recommended to investigate the role of miR-497 in osteosarcoma and other malignant mesenchymal tumors.

MicroRNA-205 inhibits the proliferation and invasion of breast cancer by regulating AMOT expression

It has been reported that the expression of angiomotin (AMOT) is upregulated in breast cancer. However, the regulatory mechanism remains unknown. In the present study, we aimed to ascertain whether the expression of AMOT is regulated by microRNAs (miRNAs) in breast cancer. In the present study, miR-205 was significantly downregulated in breast cancer samples and it was identified to directly target the 3'-untranslated region (3'-UTR) of AMOT in breast cancer MCF-7 cells by luciferase assay. miR-205 and small interfering RNA (siRNA)-mediated AMOT-knockdown experiments revealed that miR-205 significantly inhibited the proliferation and the invasion of MCF-7 cells through a decrease in the expression of AMOT, yet had no effect on apoptosis. Furthermore, we observed that the overexpression of AMOT partially reversed the inhibitory effect of miR-205 on the growth and the invasion of MCF-7 cells. The data indicated that miR-205 regulated the proliferation and the invasion of breast cancer cells through suppression of AMOT expression, at least partly. Therefore, the disordered decreased expression of miR-205 and the resulting AMOT upregulation contributes to breast carcinogenesis, and miR-205-AMOT represents a new potential therapeutic target for the treatment of breast carcinoma.

On the necessity of dissecting sequence similarity scores into segment-specific contributions for inferring protein homology, function prediction and annotation

Background

Protein sequence similarities to any types of non-globular segments (coiled coils, low complexity regions, transmembrane regions, long loops, etc. where either positional sequence conservation is the result of a very simple, physically induced pattern or rather integral sequence properties are critical) are pertinent sources for mistaken homologies. Regretfully, these considerations regularly escape attention in large-scale annotation studies since, often, there is no substitute to manual handling of these cases. Quantitative criteria are required to suppress events of function annotation transfer as a result of false homology assignments.

Results

The sequence homology concept is based on the similarity comparison between the structural elements, the basic building blocks for conferring the overall fold of a protein. We propose to dissect the total similarity score into fold-critical and other, remaining contributions and suggest that, for a valid homology statement, the fold-relevant score contribution should at least be significant on its own. As part of the article, we provide the DissectHMMER software program for dissecting HMMER2/3 scores into segment-specific contributions. We show that DissectHMMER reproduces HMMER2/3 scores with sufficient accuracy and that it is useful in automated decisions about homology for instructive sequence examples. To generalize the dissection concept for cases without 3D structural information, we find that a dissection based on alignment quality is an appropriate surrogate. The approach was applied to a large-scale study of SMART and PFAM domains in the space of seed sequences and in the space of UniProt/SwissProt.

Conclusions

Sequence similarity core dissection with regard to fold-critical and other contributions systematically suppresses false hits and, additionally, recovers previously obscured homology relationships such as the one between aquaporins and formate/nitrite transporters that, so far, was only supported by structure comparison.

The Angiomotins--from discovery to function

Angiomotins were originally identified as angiostatin binding proteins and implicated in the regulation of endothelial cell migration. Recent studies have shed light on the role of Angiomotins and other members of the Motin protein family in epithelial cells and in pathways directly linked to the pathogenesis of cancer. In particular, Motins have been shown to play a role in signaling pathways regulated by small G-proteins and the Hippo-YAP pathway. In this review the role of the Motin protein family in these signaling pathways will be described and open questions will be discussed.

Transient repetitive exposure to low level light therapy enhances collateral blood vessel growth in the ischemic hindlimb of the tight skin mouse

The tight skin mouse (Tsk(-/+)) is a model of scleroderma characterized by impaired vasoreactivity, increased oxidative stress, attenuated angiogenic response to VEGF and production of the angiogenesis inhibitor angiostatin. Low-level light therapy (LLLT) stimulates angiogenesis in myocardial infarction and chemotherapy-induced mucositis. We hypothesize that repetitive LLLT restores vessel growth in the ischemic hindlimb of Tsk(-/+) mice by attenuating angiostatin and enhancing angiomotin effects in vivo. C57Bl/6J and Tsk(-/+) mice underwent ligation of the femoral artery. Relative blood flow to the foot was measured using a laser Doppler imager. Tsk(-/+) mice received LLLT (670 nm, 50 mW cm(-2), 30 J cm(-2)) for 10 min per day for 14 days. Vascular density was determined using lycopersicom lectin staining. Immunofluorescent labeling, Western blot analysis and immunoprecipitation were used to determine angiostatin and angiomotin expression. Recovery of blood flow to the ischemic limb was reduced in Tsk(-/+) compared with C57Bl/6 mice 2 weeks after surgery. LLLT treatment of Tsk(-/+) mice restored blood flow to levels observed in C57Bl/6 mice. Vascular density was decreased, angiostatin expression was enhanced and angiomotin depressed in the ischemic hindlimb of Tsk(-/+) mice. LLLT treatment reversed these abnormalities. LLLT stimulates angiogenesis by increasing angiomotin and decreasing angiostatin expression in the ischemic hindlimb of Tsk(-/+) mice.

The Amotl2 gene inhibits Wnt/β-catenin signaling and regulates embryonic development in zebrafish

The Motin family proteins can regulate cell polarity, cell mobility, and proliferation during embryonic development by controlling distinct signaling pathways. In this study, we demonstrate that amotl2 knockdown in zebrafish wild-type embryos results in embryonic dorsalization, and this effect can be antagonized by co-knockdown of the dorsal inducer β-catenin2. Overexpression of amotl2 in masterblind (mbl) homozygous embryos, in which canonical Wnt signaling is up-regulated due to an axin1 mutation, transforms eyeless phenotype into smaller eyes, whereas co-knockdown of amot, amotl1, and amotl2 leads to development of smaller eyes in mbl heterozygotes. In cultured mammalian cells, Motin family members all possess the ability to attenuate Wnt/β-catenin signaling. Focusing on Amotl2, we show that Amotl2 can associate with and trap β-catenin in the Rab11-positive recycling endosomes, and as a result, the amount of β-catenin in the cytosol and nucleus is reduced. Thus, our findings provide novel insights into functions of Motin family members and regulation of Wnt/β-catenin signaling.

Angiomotin-like2 gene (amotl2) is required for migration and proliferation of endothelial cells during angiogenesis

Angiogenesis involves sprouting, migration, and proliferation of endothelial cells. The angiomotin-like2 gene (amotl2) has been found in blood vessels in zebrafish embryos, but its function in angiogenesis and underlying mechanisms remain unknown. In this study, we demonstrate that knockdown of amotl2 in zebrafish Tg(fli1:EGFP)(y1) and Tg(fli1:nEGFP)(y7) transgenic embryos impairs the intersegmental vessel growth and suppresses proliferation of endothelial cells. Transplantation experiments indicate that function of amotl2 in intersegmental vessel growth is cell-autonomous. AMOTL2 knockdown in cultured human umbilical vein endothelial cells also inhibits cell proliferation and migration and disrupts cell polarity, ultimately interrupting the formation of vascular tube-like structures. Amotl2 promotes MAPK/ERK activation via c-Src, which is dependent on phosphorylation of tyrosine residue at position 103 but independent of the C-terminal PDZ-binding domain. Taking together, our data indicate that Amotl2 plays a pivotal role in polarity, migration and proliferation of angiogenic endothelial cells.

The adaptor protein AMOT promotes the proliferation of mammary epithelial cells via the prolonged activation of the extracellular signal-regulated kinases

The asymmetric organization of epithelial cells is a basic counter to cellular proliferation. However, the mechanisms whereby pro-growth pathways are modulated by intracellular factors that control cell shape are not well understood. This study demonstrates that the adaptor protein Amot, in addition to its established role in regulating cellular asymmetry, also promotes extracellular signal-regulated kinase 1 and 2 (ERK1/2)-dependent proliferation of mammary cells. Specifically, expression of Amot80, but not a mutant lacking its polarity protein interaction domain, enhances ERK1/2-dependent proliferation of MCF7 cells. Further, expression of Amot80 induces nontransformed MCF10A cells to overgrow as disorganized cellular aggregates in Matrigel. Conversely, Amot expression is required for proliferation of breast cancer cells in specific microenvironmental contexts that require ERK1/2 signaling. Thus, Amot is proposed to coordinate the dysregulation of cell polarity with the induction of neoplastic growth in mammary cells.

PIV5 M protein interaction with host protein angiomotin-like 1

Paramyxovirus matrix (M) proteins organize virus assembly, functioning as adapters that link together viral ribonucleoprotein complexes and viral glycoproteins at infected cell plasma membranes. M proteins may also function to recruit and manipulate host factors to assist virus budding, similar to retroviral Gag proteins. By yeast two-hybrid screening, angiomotin-like 1 (AmotL1) was identified as a host factor that interacts with the M protein of parainfluenza virus 5 (PIV5). AmotL1-M protein interaction was observed in yeast, in transfected mammalian cells, and in virus-infected cells. Binding was mapped to a 83-amino acid region derived from the C-terminal portion of AmotL1. Overexpression of M-binding AmotL1-derived polypeptides potently inhibited production of PIV5 VLPs and impaired virus budding. Expression of these polypeptides moderately inhibited production of mumps VLPs, but had no effect on production of Nipah VLPs. siRNA-mediated depletion of AmotL1 protein reduced PIV5 budding, suggesting that this interaction is beneficial to paramyxovirus infection.

Angiomotin p80/p130 ratio: a new indicator of exercise-induced angiogenic activity in skeletal muscles from obese and non-obese rats?

Skeletal muscle capillarisation responds to physiological and pathological conditions with a remarkable plasticity. Angiomotin was recently identified as a new pro-angiogenic molecule. Angiomotin is expressed as two protein isoforms, p80 and p130. Whereas p80 stimulates endothelial cell migration and angiogenesis, p130 is rather characteristic of stabilized and matured vessels. To date, how angiomotin expression is physiologically regulated in vivo remains largely unknown. We thus investigated (1) whether angiomotin was physiologically expressed in skeletal muscle; (2) whether exercise training, known to stimulate muscle angiogenesis, affected angiomotin expression; and (3) whether such regulation was altered in obesity, a pathological situation often associated with an impaired angiogenic activity and some capillary rarefaction in skeletal muscle. Two models of obesity were used: a high fat diet regime and Zucker Diabetic Fatty rats (ZDF). Our results provide evidence that angiomotin was expressed both in capillaries and myofibres. In non-obese rats, the p80 isoform was increased in plantaris muscle in response to endurance training whereas p130 was unaffected. In obese animals, no change was observed for p80 whereas training significantly decreased p130 expression. Exercise training induced angiogenesis in plantaris from both obese and non-obese rats, possibly through the modulation of angiomotin level and its consequences on RhoA-ROCK signalling. In conclusion, any increase in p80 or decrease in p130, as respectively observed in non-obese and obese animals, led to an increased ratio between p80 and p130 isoforms. This increased angiomotin p80/p130 ratio might then directly reflect the enhanced angiogenic ability of skeletal muscle in response to exercise training.

Identification of differential gene expression during porcine conceptus rapid trophoblastic elongation and attachment to uterine luminal epithelium

Early embryonic development in the pig is characterized by a rapid elongation of the conceptus trophectoderm on days 11-12 of gestation. Initially, the conceptus trophoblast is morphologically rearranged from a 10-mm sphere into a tubular shape, transitioning into a thin filamentous form >150 mm in length in 2-3 h, followed by continued expansion within the uterine lumen for several days. Conceptus elongation is critical for establishing adequate placental surface area needed for embryo and fetal survival throughout gestation. The objective of this study was to characterize conceptus gene expression during trophoblastic elongation and the early attachment to the uterine endometrium on days 11-14 of gestation with the GeneChip Porcine Genome Array. In all, 3,759 different probe sets were statistically different in at least one comparison [spherical vs. tubular, spherical vs. day 12 filamentous (D12F), spherical vs. day 14 filamentous (D14F), tubular vs. D12F, tubular vs. D14F, and D12F vs. D14F]. When restricted to the spherical vs. D12F and D12F vs. D14F comparisons, 482 and 232 genes, respectively, were statistically different with greater than twofold change in expression. Utilization of k-means clustering, in addition to the Database for Annotation, Visualization, and Integrated Discovery (DAVID), identified genes of interest. Quantitative RT-PCR expression profiles for interferon-gamma (IFNG), heat shock protein 27 kDa (HSPB1), angiomotin, B-cell linker (BLNK), chemokine ligand 14 (CXCL14), parathyroid hormone-like hormone (PTHLH), and maspin were supportive of the GeneChip Porcine Genome Array data.

The Amot/Patj/Syx signaling complex spatially controls RhoA GTPase activity in migrating endothelial cells

Controlled regulation of Rho GTPase activity is an essential component mediating growth factor-stimulated migration. We have previously shown that angiomotin (Amot), a membrane-associated scaffold protein, plays a critical role during vascular patterning and endothelial migration during embryogenesis. However, the signaling pathways by which Amot controls directional migration are not known. Here we have used peptide pull-down and yeast 2-hybrid (Y2H) screening to identify proteins that interact with the C-terminal PDZ-binding motifs of Amot and its related proteins AmotL1 and 2. We report that Amot and its related proteins bind to the RhoA GTPase exchange factor (RhoGEF) protein Syx. We show that Amot forms a ternary complex together with Patj (or its paralogue Mupp1) and Syx. Using FRET analysis, we provide evidence that Amot controls targeting of RhoA activity to lamellipodia in vitro. We also report that, similar to Amot, morpholino knockdown of Syx in zebrafish results in inhibition of migration of intersegmental arteries. Taken together, our results indicate that the directional migration of capillaries in the embryo is governed by the Amot:Patj/Mupp1:Syx signaling that controls local GTPase activity.

Angiomotin regulates endothelial cell migration during embryonic angiogenesis

The development of the embryonic vascular system into a highly ordered network requires precise control over the migration and branching of endothelial cells (ECs). We have previously identified angiomotin (Amot) as a receptor for the angiogenesis inhibitor angiostatin. Furthermore, DNA vaccination targeting Amot inhibits angiogenesis and tumor growth. However, little is known regarding the role of Amot in physiological angiogenesis. We therefore investigated the role of Amot in embryonic neovascularization during zebrafish and mouse embryogenesis. Here we report that knockdown of Amot in zebrafish reduced the number of filopodia of endothelial tip cells and severely impaired the migration of intersegmental vessels. We further show that 75% of Amot knockout mice die between embryonic day 11 (E11) and E11.5 and exhibit severe vascular insufficiency in the intersomitic region as well as dilated vessels in the brain. Furthermore, using ECs differentiated from embryonic stem (ES) cells, we demonstrate that Amot-deficient cells have intact response to vascular endothelial growth factor (VEGF) in regard to differentiation and proliferation. However, the chemotactic response to VEGF was abolished in Amot-deficient cells. We provide evidence that Amot is important for endothelial polarization during migration and that Amot controls Rac1 activity in endothelial and epithelial cells. Our data demonstrate a critical role for Amot during vascular patterning and endothelial polarization.

Molecular characterization of angiomotin/JEAP family proteins: interaction with MUPP1/Patj and their endogenous properties

We have previously shown that MUPP1, which has an MRE domain and 13 PDZ domains, is expressed in epithelial cells and localize at tight junctions (TJs) and apical membranes. Using yeast two-hybrid screening, we found here that MUPP1 interacts with angiomotin (Amot), JEAP/Amot-like 1 and MASCOT/Amot-like 2, which we refer to as Amot/JEAP family proteins. PDZ2 and -3 were responsible for MUPP1's interaction with Amot and MASCOT, whereas only PDZ3 was responsible for its interaction with JEAP. All the Amot/JEAP family proteins also interacted with Patj, a close relative of MUPP1. The C-terminal PDZ-binding motives of the Amot/JEAP family were required for these interactions. We successfully generated specific antibodies for these proteins and analyzed the endogenous molecular properties of the family in parallel. Immunofluorescence microscopy of cultured epithelial cells showed that in subcellular distribution, the Amot/JEAP family proteins were indistinguishable; they were apparent at TJs as well as apical membranes, and mostly co-localized with MUPP1. They were also located at TJs in several mouse tissues, but each protein showed a distinct tissue distribution. In biochemical fractionation assays, the Amot/JEAP family behaved not as transmembrane but as peripheral membrane proteins. Unexpectedly, the PDZ-binding motives were not necessarily required for their localization to TJs, and dominant negative MUPP1 or Patj did not affect the localization of Amot/JEAP family proteins, suggesting that the interaction with MUPP1/Patj is not necessarily responsible for their proper subcellular distribution.

Amotl2 is essential for cell movements in zebrafish embryo and regulates c-Src translocation

Angiomotin (Amot), the founding member of the Motin family, is involved in angiogenesis by regulating endothelial cell motility, and is required for visceral endoderm movement in mice. However, little is known about biological functions of the other two members of the Motin family, Angiomotin-like1(Amotl1) and Angiomotin-like2 (Amotl2). Here, we have identified zebrafish amotl2 as an Fgf-responsive gene. Zebrafish amotl2 is expressed maternally and in restricted cell types zygotically. Knockdown of amotl2 expression delays epiboly and impairs convergence and extension movement, and amotl2-deficient cells in mosaic embryos fail to migrate properly. This coincides with loss of membrane protrusions and disorder of F-actin. Amotl2 partially co-localizes with RhoB-or EEA1-positive endosomes and the non-receptor tyrosine kinase c-Src. We further demonstrate that Amotl2 interacts preferentially with and facilitates outward translocation of the phosphorylated c-Src, which may in turn regulate the membrane architecture. These data provide the first evidence that amotl2 is essential for cell movements in vertebrate embryos.

A DNA vaccine targeting angiomotin inhibits angiogenesis and suppresses tumor growth

Endogenous angiogenesis inhibitors have shown promise in preclinical trials, but clinical use has been hindered by low half-life in circulation and high production costs. Here, we describe a strategy that targets the angiostatin receptor angiomotin (Amot) by DNA vaccination. The vaccination procedure generated antibodies that detected Amot on the endothelial cell surface. Purified Ig bound to the endothelial cell membrane and inhibited endothelial cell migration. In vivo, DNA vaccination blocked angiogenesis in the matrigel plug assay and prevented growth of transplanted tumors for up to 150 days. We further demonstrate that a combination of DNA vaccines encoding Amot and the extracellular and transmembrane domains of the human EGF receptor 2 (Her-2)/neu oncogene inhibited breast cancer progression and impaired tumor vascularization in Her-2/neu transgenic mice. No toxicity or impairment of normal blood vessels could be detected. This work shows that DNA vaccination targeting Amot may be used to mimic the effect of angiostatin.

Upregulated genes in sporadic, idiopathic pulmonary arterial hypertension

Background

To elucidate further the pathogenesis of sporadic, idiopathic pulmonary arterial hypertension (IPAH) and identify potential therapeutic avenues, differential gene expression in IPAH was examined by suppression subtractive hybridisation (SSH).

Methods

Peripheral lung samples were obtained immediately after removal from patients undergoing lung transplant for IPAH without familial disease, and control tissues consisted of similarly sampled pieces of donor lungs not utilised during transplantation. Pools of lung mRNA from IPAH cases containing plexiform lesions and normal donor lungs were used to generate the tester and driver cDNA libraries, respectively. A subtracted IPAH cDNA library was made by SSH. Clones isolated from this subtracted library were examined for up regulated expression in IPAH using dot blot arrays of positive colony PCR products using both pooled cDNA libraries as probes. Clones verified as being upregulated were sequenced. For two genes the increase in expression was verified by northern blotting and data analysed using Student's unpaired two-tailed t-test.

Results

We present preliminary findings concerning candidate genes upregulated in IPAH. Twenty-seven upregulated genes were identified out of 192 clones examined. Upregulation in individual cases of IPAH was shown by northern blot for tissue inhibitor of metalloproteinase-3 and decorin (P < 0.01) compared with the housekeeping gene glyceraldehydes-3-phosphate dehydrogenase.

Conclusion

Four of the up regulated genes, magic roundabout, hevin, thrombomodulin and sucrose non-fermenting protein-related kinase-1 are expressed specifically by endothelial cells and one, muscleblind-1, by muscle cells, suggesting that they may be associated with plexiform lesions and hypertrophic arterial wall remodelling, respectively.

Angiostatin's molecular mechanism: aspects of specificity and regulation elucidated

Tumor growth requires the development of new vessels that sprout from pre-existing normal vessels in a process known as "angiogenesis" [Folkman (1971) N Engl J Med 285:1182-1186]. These new vessels arise from local capillaries, arteries, and veins in response to the release of soluble growth factors from the tumor mass, enabling these tumors to grow beyond the diffusion-limited size of approximately 2 mm diameter. Angiostatin, a naturally occurring inhibitor of angiogenesis, was discovered based on its ability to block tumor growth in vivo by inhibiting the formation of new tumor blood vessels [O'Reilly et al. (1994a) Cold Spring Harb Symp Quant Biol 59:471-482]. Angiostatin is a proteolytically derived internal fragment of plasminogen and may contain various members of the five plasminogen "kringle" domains, depending on the exact sites of proteolysis. Different forms of angiostatin have measurably different activities, suggesting that much remains to be elucidated about angiostatin biology. A number of groups have sought to identify the native cell surface binding site(s) for angiostatin, resulting in at least five different binding sites proposed for angiostatin on the surface of endothelial cells (EC). This review will consider the data supporting all of the various reported angiostatin binding sites and will focus particular attention on the angiostatin binding protein identified by our group: F(1)F(O) ATP synthase. There have been several developments in the quest to elucidate the mechanism of action of angiostatin and the regulation of its receptor. The purpose of this review is to describe the highlights of research on the mechanism of action of angiostatin, its' interaction with ATP synthase on the EC surface, modulators of its activity, and issues that should be explored in future research related to angiostatin and other anti-angiogenic agents.

Angiomotin Regulates Endothelial Cell-Cell Junctions and Cell Motility

We have previously identified angiomotin by its ability to bind to and mediate the anti-angiogenic properties of angiostatin. In vivo and in vitro data indicate an essential role of angiomotin in endothelial cell motility. Here we show that angiostatin binds angiomotin on the cell surface and provide evidence for a transmembrane model for the topology of both p80 and p130 angiomotin isoforms. Immunofluorescence analysis shows that angiomotin co-localized with ZO-1 in cell-cell contacts in endothelial cells in vitro and in angiogenic blood vessels of the postnatal mouse retina in vivo. Transfection of p80 as well as p130 angiomotin in Chinese hamster ovary cells resulted in junctional localization of both isoforms. Furthermore, p130 angiomotin could recruit ZO-1 to actin stress fibers. The p130 but not p80 isoform could be coprecipitated with MAGI-1b, a component of endothelial tight junctions. Paracellular permeability, as measured by diffusion of fluorescein isothiocyanate-dextran, was reduced by p80 and p130 angiomotin expression with 70 and 88%, respectively, compared with control. Angiostatin did not have any effect on cell permeability but inhibited the migration of angiomotin-expressing cells in the Boyden chamber assay. We conclude that angiomotin, in addition to controlling cell motility, may play a role in the assembly of endothelial cell-cell junctions.

Protein diversity is generated within the motin family of proteins by alternative pre-mRNA splicing

The motin family of proteins is comprised of three polypeptides, angiomotin, angiomotin-like 1, and angiomotin-like 2. Angiomotin is an angiostatin-binding protein that promotes endothelial cell motility and is involved in angiogenesis. The function of human angiomotin-like-1 and angiomotin-like-2, however, remains unknown. In this report, we investigated the potential for molecular diversity within the motin family of proteins through the identification and characterization of alternatively spliced transcripts in endothelial cells, human tissues and a variety of cell lines. We report that the motins display variability at the mRNA level suggesting an intricate regulatory system at the transcriptional and potentially protein level. Some alternative transcripts are expressed in a tissue-specific manner and others give rise to novel protein isoforms. The alternative splicing that occurs within this protein family may have important implications in the regulation of the expression and function of the motins.

Angiomotin expression promotes hemangioendothelioma invasion

Angiomotin was identified by its ability to bind angiostatin and has been shown to mediate its activity in vitro. The family of angiomotin-like protein consists of three members that have coiled-coil domains and conserved c-terminal PDZ-binding motifs. We show here that expression of angiomotin in mouse aortic endothelial (MAE) cells results in stabilization of tubes in the Matrigel assay. Control tubes start to regress after 72 h, whereas MAE-angiomotin (MAE Amot) tubes were stable for over 30 days. In contrast, cells expressing a functional mutant lacking the PDZ protein interaction motif did not migrate and form tubes. Cells from the established tubes invaded into the solidified matrigel. We therefore tested whether angiomotin promotes endothelial invasion. In microcarrier-based invasion in vitro assay, angiomotin-expressing cells invaded collagen matrix and formed tube-like branches. This was confirmed in vivo as injection of MAE-Amot cells promoted tumor growth and invasion into surrounding muscle tissue. Injection of cells transfected with the functional mutant resulted in establishment of noninvasive tumors surrounded by a capsule of fibrous tissue. These tumors remained in constant size or dormant over 3 weeks. Zymogel analysis of the transfected cells did not reveal any differences in proteolytic activity. However, time-lapse photography showed a significant increase in random motility in MAE-Amot cells. We conclude that angiomotin may promote angiogenesis by both stimulating invasion as well as stabilizing established tubes.