Oligomerization-dependent regulation of motility and morphogenesis by the collagen XVIII NC1/endostatin domain

Tumour vasculature at single-cell resolution

Tumours can obtain nutrients and oxygen required to progress and metastasize through the blood supply1. Inducing angiogenesis involves the sprouting of established vessel beds and their maturation into an organized network2,3. Here we generate a comprehensive atlas of tumour vasculature at single-cell resolution, encompassing approximately 200,000 cells from 372 donors representing 31 cancer types. Trajectory inference suggested that tumour angiogenesis was initiated from venous endothelial cells and extended towards arterial endothelial cells. As neovascularization elongates (through angiogenic stages SI, SII and SIII), APLN+ tip cells at the SI stage (APLN+ TipSI) advanced to TipSIII cells with increased Notch signalling. Meanwhile, stalk cells, following tip cells, transitioned from high chemokine expression to elevated TEK (also known as Tie2) expression. Moreover, APLN+ TipSI cells not only were associated with disease progression and poor prognosis but also hold promise for predicting response to anti-VEGF therapy. Lymphatic endothelial cells demonstrated two distinct differentiation lineages: one responsible for lymphangiogenesis and the other involved in antigen presentation. In pericytes, endoplasmic reticulum stress was associated with the proangiogenic BASP1+ matrix-producing pericytes. Furthermore, intercellular communication analysis showed that neovascular endothelial cells could shape an immunosuppressive microenvironment conducive to angiogenesis. This study depicts the complexity of tumour vasculature and has potential clinical significance for anti-angiogenic therapy.

Antibody-Drug Conjugate αEGFR-E-P125A Reduces Triple-negative Breast Cancer Vasculogenic Mimicry, Motility, and Metastasis through Inhibition of EGFR, Integrin, and FAK/STAT3 Signaling

Primary tumor growth and metastasis in triple-negative breast cancer (TNBC) require supporting vasculature, which develop through a combination of endothelial angiogenesis and vasculogenic mimicry (VM), a process associated with aggressive metastatic behavior in which vascular-like structures are lined by tumor cells. We developed αEGFR-E-P125A, an antibody-endostatin fusion protein that delivers a dimeric, mutant endostatin (E-P125A) payload that inhibits TNBC angiogenesis and VM in vitro and in vivo. To characterize the mechanisms associated with induction and inhibition of VM, RNA sequencing (RNA-seq) of MDA-MB-231-4175 TNBC cells grown in a monolayer (two-dimensional) was compared with cells plated on Matrigel undergoing VM [three-dimensional (3D)]. We then compared RNA-seq between TNBC cells in 3D and cells in 3D with VM inhibited by αEGFR-E-P125A (EGFR-E-P125A). Gene set enrichment analysis demonstrated that VM induction activated the IL6-JAK-STAT3 and angiogenesis pathways, which were downregulated by αEGFR-E-P125A treatment.Correlative analysis of the phosphoproteome demonstrated decreased EGFR phosphorylation at Y1069, along with decreased phosphorylation of focal adhesion kinase Y397 and STAT3 Y705 sites downstream of α5β1 integrin. Suppression of phosphorylation events downstream of EGFR and α5β1 integrin demonstrated that αEGFR-E-P125A interferes with ligand-receptor activation, inhibits VM, and overcomes oncogenic signaling associated with EGFR and α5β1 integrin cross-talk. In vivo, αEGFR-E-P125A treatment decreased primary tumor growth and VM, reduced lung metastasis, and confirmed the inhibition of signaling events observed in vitro. Simultaneous inhibition of EGFR and α5β1 integrin signaling by αEGFR-E-P125A is a promising strategy for the inhibition of VM, tumor growth, motility, and metastasis in TNBC and other EGFR-overexpressing tumors.

SIGNIFICANCE

αEGFR-E-P125A reduces VM, angiogenesis, tumor growth, and metastasis by inhibiting EGFR and α5β1 integrin signaling, and is a promising therapeutic agent for TNBC treatment, used alone or in combination with chemotherapy.

Spatially Resolved Transcriptomes of Mammalian Kidneys Illustrate the Molecular Complexity and Interactions of Functional Nephron Segments

Available transcriptomes of the mammalian kidney provide limited information on the spatial interplay between different functional nephron structures due to the required dissociation of tissue with traditional transcriptome-based methodologies. A deeper understanding of the complexity of functional nephron structures requires a non-dissociative transcriptomics approach, such as spatial transcriptomics sequencing (ST-seq). We hypothesize that the application of ST-seq in normal mammalian kidneys will give transcriptomic insights within and across species of physiology at the functional structure level and cellular communication at the cell level. Here, we applied ST-seq in six mice and four human kidneys that were histologically absent of any overt pathology. We defined the location of specific nephron structures in the captured ST-seq datasets using three lines of evidence: pathologist's annotation, marker gene expression, and integration with public single-cell and/or single-nucleus RNA-sequencing datasets. We compared the mouse and human cortical kidney regions. In the human ST-seq datasets, we further investigated the cellular communication within glomeruli and regions of proximal tubules-peritubular capillaries by screening for co-expression of ligand-receptor gene pairs. Gene expression signatures of distinct nephron structures and microvascular regions were spatially resolved within the mouse and human ST-seq datasets. We identified 7,370 differentially expressed genes (p adj < 0.05) distinguishing species, suggesting changes in energy production and metabolism in mouse cortical regions relative to human kidneys. Hundreds of potential ligand-receptor interactions were identified within glomeruli and regions of proximal tubules-peritubular capillaries, including known and novel interactions relevant to kidney physiology. Our application of ST-seq to normal human and murine kidneys confirms current knowledge and localization of transcripts within the kidney. Furthermore, the generated ST-seq datasets provide a valuable resource for the kidney community that can be used to inform future research into this complex organ.

Alpha-single chains of collagen type VI inhibit the fibrogenic effects of triple helical collagen VI in hepatic stellate cells

The interaction of extracellular matrix (ECM) components with hepatic stellate cells (HSCs) is thought to perpetuate fibrosis by stimulating signaling pathways that drive HSC activation, survival and proliferation. Consequently, disrupting the interaction between ECM and HSCs is considered a therapeutical avenue although respective targets and underlying mechanisms remain to be established. Here we have interrogated the interaction between type VI collagen (CVI) and HSCs based on the observation that CVI is 10-fold upregulated during fibrosis, closely associates with HSCs in vivo and promotes cell proliferation and cell survival in cancer cell lines. We exposed primary rat HSCs and a rat hepatic stellate cell line (CFSC) to soluble CVI and determined the rate of proliferation, apoptosis and fibrogenesis in the absence of any additional growth factors. We find that CVI in nanomolar concentrations prevents serum starvation-induced apoptosis. This potent anti-apoptotic effect is accompanied by induction of proliferation and acquisition of a pronounced pro-fibrogenic phenotype characterized by increased α-smooth muscle actin, TGF-β, collagen type I and TIMP-1 expression and diminished proteolytic MMP-13 expression. The CVI-HSC interaction can be disrupted with the monomeric α2(VI) and α3(VI) chains and abrogates the activating CVI effects. Further, functional relevant α3(VI)—derived 30 amino acid peptides lead to near-complete inhibition of the CVI effect. In conclusion, CVI serves as a potent mitogen and activating factor for HSCs. The antagonistic effects of the CVI monomeric chains and peptides point to linear peptide sequences that prevent activation of CVI receptors which may allow a targeted antifibrotic therapy.

Extracellular Matrix and Oxidative Phosphorylation: Important Role in the Regulation of Hypothalamic Function by Gut Microbiota

Background

In previous studies, our team examined the gut microbiota of healthy individuals and depressed patients using fecal microbiota transplantation of germ-free (GF) mice. Our results showed that depression-like and anxiety-like behavioral phenotypes of host mice were increased, but the molecular mechanism by which gut microbiota regulate host behavioral phenotypes is still unclear.

Methods

To investigate the molecular mechanism by which gut microbiota regulate host brain function, adult GF mice were colonized with fecal samples derived from healthy control (HC) individuals or patients with major depressive disorder (MDD). Transcriptomic profiling of hypothalamus samples was performed to detect differentially expressed genes (DEGs). qRT-PCR was used for validation experiments.

Results

Colonization germ-free (CGF) mice had 243 DEGs compared with GF mice. The most enriched KEGG pathways associated with upregulated genes were "protein digestion and absorption," "extracellular matrix (ECM)-receptor interaction," and "focal adhesion." MDD mice had 642 DEGs compared with HC mice. The most enriched KEGG pathways associated with upregulated genes in MDD mice were also "protein digestion and absorption," "ECM-receptor interaction," and "focal adhesion." Meanwhile, the most enriched KEGG pathway associated with downregulated genes in these mice was "oxidative phosphorylation," and genes related to this pathway were found to be highly correlated in PPI network analysis.

Conclusion

In summary, our findings suggested that regulation of ECM is a key mechanism shared by different gut microbiota and that inhibition of energy metabolism in the hypothalamus by gut microbiota derived from MDD patients is a potential mechanism of behavioral regulation and depression.

SorCS2 facilitates release of endostatin from astrocytes and controls post-stroke angiogenesis

SorCS2 is an intracellular sorting receptor of the VPS10P domain receptor gene family recently implicated in oxidative stress response. Here, we interrogated the relevance of stress-related activities of SorCS2 in the brain by exploring its role in ischemic stroke in mouse models and in patients. Although primarily seen in neurons in the healthy brain, expression of SorCS2 was massively induced in astrocytes surrounding the ischemic core in mice following stroke. Post-stroke induction was likely a result of increased levels of transforming growth factor β1 in damaged brain tissue, inducing Sorcs2 gene transcription in astrocytes but not neurons. Induced astrocytic expression of SorCS2 was also seen in stroke patients, substantiating the clinical relevance of this observation. In astrocytes in vitro and in the mouse brain in vivo, SorCS2 specifically controlled release of endostatin, a factor linked to post-stroke angiogenesis. The ability of astrocytes to release endostatin acutely after stroke was lost in mice deficient for SorCS2, resulting in a blunted endostatin response which coincided with impaired vascularization of the ischemic brain. Our findings identified activated astrocytes as a source for endostatin in modulation of post-stroke angiogenesis, and the importance of the sorting receptor SorCS2 in this brain stress response.

DNA methylation exploration for ARDS: a multi-omics and multi-microarray interrelated analysis

Background

Despite advances in clinical management, there are currently no novel therapeutic targets for acute respiratory distress syndrome (ARDS). DNA methylation, as a reversible process involved in the development and progression of many diseases, would be used as potential therapeutic targets to improve the treatment strategies of ARDS. However, the meaningful DNA methylation sites associated with ARDS still remain largely unknown. We sought to determine the difference in DNA methylation between ARDS patients and healthy participants, and simultaneously, the feasible DNA methylation markers for potential therapeutic targets were also explored.

Methods

Microarray data of human blood samples for ARDS and healthy participants up to June 2019 was searched in GEO database. The difference analyses between ARDS and healthy population were performed through limma R package, and furthermore, interrelated analyses of DNA methylation and transcript were accomplished by VennDiagram R package. Perl and sva R package were used to merge microarray data and decrease heterogeneities among different studies. The biological function of screened methylation sites and their regulating genes were annotated according to UniProt database and Pubmed database. GO term and KEGG pathway enrichment analyses were conducted using DAVID 6.8 and KOBAS 3.0. The meaningful DNA methylation markers to distinguish ARDS from healthy controls were explored through ROC (receiver operating characteristic curves) analyses.

Results

Five datasets in GEO databases (one DNA methylation dataset, three mRNA datasets, and one mRNA dataset of healthy people) were enrolled in present analyses finally, and the series were GSE32707, GSE66890, GSE10474, GSE61672, and GSE67530. These databases included 99 patients with ARDS (within 48 h of onset) and 136 healthy participants. Difference analyses indicated 44,439 DNA methylation alterations and 29 difference mRNAs between ARDS and healthy controls. 40 methylation variations regulated transcription of 16 genes was explored via interrelated analysis. According to the functional annotations, 30 DNA methylation sites were related to the imbalance of inflammation or immunity, endothelial function, epithelial function and/or coagulation function. cg03341377, cg24310395, cg07830557 and cg08418670, with AUC up to 0.99, might be the meaningful characteristics with the highest performance to distinguish ARDS from healthy controls.

Conclusions

44,439 DNA methylation alterations and 29 difference mRNAs exist between ARDS and healthy controls. 30 DNA methylation sites may regulate transcription of 10 genes, which take part in pathogenesis of ARDS. These findings could be intervention targets, with validation experiments to be warranted to assess these further.

Collagen 18 and agrin are secreted by neural crest cells to remodel their microenvironment and regulate their migration during enteric nervous system development

The enteric nervous system (ENS) arises from neural crest cells that migrate, proliferate, and differentiate into enteric neurons and glia within the intestinal wall. Many extracellular matrix (ECM) components are present in the embryonic gut, but their role in regulating ENS development is largely unknown. Here, we identify heparan sulfate proteoglycan proteins, including collagen XVIII (Col18) and agrin, as important regulators of enteric neural crest-derived cell (ENCDC) development. In developing avian hindgut, Col18 is expressed at the ENCDC wavefront, while agrin expression occurs later. Both proteins are normally present around enteric ganglia, but are absent in aganglionic gut. Using chick-mouse intestinal chimeras and enteric neurospheres, we show that vagal- and sacral-derived ENCDCs from both species secrete Col18 and agrin. Whereas glia express Col18 and agrin, enteric neurons only express the latter. Functional studies demonstrate that Col18 is permissive whereas agrin is strongly inhibitory to ENCDC migration, consistent with the timing of their expression during ENS development. We conclude that ENCDCs govern their own migration by actively remodeling their microenvironment through secretion of ECM proteins.

Collagen XVIII in tissue homeostasis and dysregulation - Lessons learned from model organisms and human patients

Collagen XVIII is a ubiquitous basement membrane (BM) proteoglycan produced in three tissue-specific isoforms that differ in their N-terminal non-collagenous sequences, but share collagenous and C-terminal non-collagenous domains. The collagenous domain provides flexibility to the large collagen XVIII molecules on account of multiple interruptions in collagenous sequences. Each isoform has a complex multi-domain structure that endows it with an ability to perform various biological functions. The long isoform contains a frizzled-like (Fz) domain with Wnt-inhibiting activity and a unique domain of unknown function (DUF959), which is also present in the medium isoform. All three isoforms share an N-terminal laminin-G-like/thrombospondin-1 sequence whose specific functions still remain unconfirmed. The proteoglycan nature of the isoforms further increases the functional diversity of collagen XVIII. An anti-angiogenic domain termed endostatin resides in the C-terminus of collagen XVIII and is proteolytically cleaved from the parental molecule during the BM breakdown for example in the process of tumour progression. Recombinant endostatin can efficiently reduce tumour angiogenesis and growth in experimental models by inhibiting endothelial cell migration and proliferation or by inducing their death, but its efficacy against human cancers is still a subject of debate. Mutations in the COL18A1 gene result in Knobloch syndrome, a genetic disorder characterised mainly by severe eye defects and encephalocele and, occasionally, other symptoms. Studies with gene-modified mice have elucidated some aspects of this rare disease, highlighting in particular the importance of collagen XVIII in the development of the eye. Research with model organisms have also helped in determining other structural and biological functions of collagen XVIII, such as its requirement in the maintenance of BM integrity and its emerging roles in regulating cell survival, stem or progenitor cell maintenance and differentiation and inflammation. In this review, we summarise current knowledge on the properties and endogenous functions of collagen XVIII in normal situations and tissue dysregulation. When data is available, we discuss the functions of the distinct isoforms and their specific domains.

Extension of the in vivo half-life of endostatin and its improved anti-tumor activities upon fusion to a humanized antibody against tumor-associated glycoprotein 72 in a mouse model of human colorectal carcinoma

Endostatin is an endogenous angiogenesis inhibitor that exhibits potential anti-tumor efficacy in various preclinical animal models. However, its relatively short in vivo half-life and the long-term, frequent administration of high doses limit its widespread clinical use. In this study, we evaluated whether a fusion protein of murine endostatin (mEndo) to a humanized antibody against tumor-associated glycoprotein 72 (TAG-72), which is highly expressed in several human tumor tissues including colon cancer, can extend the serum half-life and improve the anti-tumor efficacy of endostatin by targeted delivery to the tumor mass. The fusion protein (3E8-mEndo) and mEndo showed improved anti-angiogenic activity in vitro and in vivo, predominantly by interfering with pro-angiogenic signaling triggered by vascular endothelial growth factor (VEGF). Moreover, in mice treated with 3E8-mEndo, we observed a markedly prolonged serum half-life and significantly inhibited tumor growth. The improved anti-tumor activity of 3E8-mEndo can be partially explained by increased local concentration in the tumor mass due to targeted delivery of 3E8-mEndo to implanted colon tumors. Collectively, our data clearly indicate that tumor-targeting antibody fusions to endostatin are a powerful strategy that improves the poor pharmacokinetic profile and anti-tumor efficacy of endostatin.

Decoding the Matrix: Instructive Roles of Proteoglycan Receptors

The extracellular matrix is a dynamic repository harboring instructive cues that embody substantial regulatory dominance over many evolutionarily conserved intracellular activities, including proliferation, apoptosis, migration, motility, and autophagy. The matrix also coordinates and parses hierarchical information, such as angiogenesis, tumorigenesis, and immunological responses, typically providing the critical determinants driving each outcome. We provide the first comprehensive review focused on proteoglycan receptors, that is, signaling transmembrane proteins that use secreted proteoglycans as ligands, in addition to their natural ligands. The majority of these receptors belong to an exclusive subset of receptor tyrosine kinases and assorted cell surface receptors that specifically bind, transduce, and modulate fundamental cellular processes following interactions with proteoglycans. The class of small leucine-rich proteoglycans is the most studied so far and constitutes the best understood example of proteoglycan-receptor interactions. Decorin and biglycan evoke autophagy and immunological responses that deter, suppress, or exacerbate pathological conditions such as tumorigenesis, angiogenesis, and chronic inflammatory disease. Basement membrane-associated heparan sulfate proteoglycans (perlecan, agrin, and collagen XVIII) represent a unique cohort and provide proteolytically cleaved bioactive fragments for modulating cellular behavior. The receptors that bind the genuinely multifactorial and multivalent proteoglycans represent a nexus in understanding basic biological pathways and open new avenues for therapeutic and pharmacological intervention.

Attenuation of ultraviolet A-induced alterations in NIH3T3 dermal fibroblasts by melatonin

BACKGROUND

Sun exposure is responsible for long-term clinical skin changes such as photoageing, photodamage and photocancers. Ultraviolet (UV)A wavelengths stimulate the production of reactive oxygen species (ROS) that may contribute to photoageing. To protect against oxidative stress, skin cells have developed several defence systems, including ROS and metal ion scavengers and a battery of detoxifying, haem-degrading and repair enzymes. Melatonin's antioxidant activity is the result of three different but complementary actions: (i) a direct action due to its ability to act as a free radical scavenger; (ii) an indirect action that is a consequence of melatonin's ability to reduce free radical generation (radical avoidance); and (iii) its ability to upregulate antioxidant enzymes.

OBJECTIVES

In this study, we focused our attention on the prevention of photodamage, choosing melatonin as an antioxidant agent.

METHODS

In the present study we analysed the effects of pretreatment of murine fibroblasts cells (NIH3T3) with melatonin (1 mmol L(-1) ) followed by UVA irradiation (15 J cm(-2) ). Thereafter, changes in components of the extracellular matrix and in some antioxidant enzymes (inducible and constitutive haem oxygenase) were evaluated.

RESULTS

We observed that UVA radiation caused altered expression of extracellular matrix proteins and induced the expression of inducible haem oxygenase. This increase was not sufficient to protect the cells from damage. Instead, melatonin pretreatment led to increased expression of haem-degrading enzymes and suppression of UVA-induced photodamage.

CONCLUSIONS

These results suggest that melatonin, as a modifier of the dermatoendocrine system, may have utility in reducing the effects of skin ageing.

The effect of intracellular protein delivery on the anti-tumor activity of recombinant human endostatin

Endostatin (ES), a 20 kDa protein derived from the carboxy-terminus of collagen XVIII is a potent angiogenesis inhibitor, but clinical development has been hindered by poor clinical efficacy and insufficient functional information from which to design agents with improved activity. The present study investigated protein uptake by cells as a determinant of ES activity. We developed a cell-permeable ES protein (HM73ES) with enhanced capacity to enter cells by adding a macromolecule transduction domain (MTD). HM73ES inhibited angiogenesis-associated phenotypes in cultured endothelial cells [as assessed by tube formation, wound-healing, cell proliferation and survival assays]. These effects were accompanied by reductions in MAPK signaling (ERK phosphorylation), and in β-Catenin, c-Myc, STAT3, and VEGF protein expression. The cell-permeable ES displayed greater tissue penetration in mice and suppressed the growth of human tumor xenografts to a significantly greater extent than ES protein without the MTD sequence. Our results suggest that anti-angiogenic activities of native ES are limited at the level of protein uptake and/or subcellular localization, and that much of the activity of ES against tumors depends on one or more intracellular functions. This study will inform future efforts to understand ES function(s) and suggest strategies for improving ES-based cancer therapeutics.

Cell proliferation and migration are modulated by Cdk-1-phosphorylated endothelial-monocyte activating polypeptide II

Background

Endothelial-Monocyte Activating Polypeptide (EMAP II) is a secreted protein with well-established anti-angiogenic activities. Intracellular EMAP II expression is increased during fetal development at epithelial/mesenchymal boundaries and in pathophysiologic fibroproliferative cells of bronchopulmonary dysplasia, emphysema, and scar fibroblast tissue following myocardial ischemia. Precise function and regulation of intracellular EMAP II, however, has not been explored to date.

Methodology/Principal Findings

Here we show that high intracellular EMAP II suppresses cellular proliferation by slowing progression through the G2M cell cycle transition in epithelium and fibroblast. Furthermore, EMAP II binds to and is phosphorylated by Cdk1, and exhibits nuclear/cytoplasmic partitioning, with only nuclear EMAP II being phosphorylated. We observed that extracellular secreted EMAP II induces endothelial cell apoptosis, where as excess intracellular EMAP II facilitates epithelial and fibroblast cells migration.

Conclusions/Significance

Our findings suggest that EMAP II has specific intracellular effects, and that this intracellular function appears to antagonize its extracellular anti-angiogenic effects during fetal development and pulmonary disease progression.

IBC's 22nd Annual Antibody Engineering and 9th Annual Antibody Therapeutics International Conferences and the 2011 Annual Meeting of The Antibody Society, December 5-8, 2011, San Diego, CA

The 22nd Annual Antibody Engineering and 9th Annual Antibody Therapeutics international conferences, and the 2011 Annual Meeting of The Antibody Society, organized by IBC Life Sciences with contributions from The Antibody Society and two Scientific Advisory Boards, were held December 5-8, 2011 in San Diego, CA. The meeting drew ~800 participants who attended sessions on a wide variety of topics relevant to antibody research and development. As a preview to the main events, a pre-conference workshop held on December 4, 2011 focused on antibodies as probes of structure. The Antibody Engineering Conference comprised eight sessions: (1) structure and dynamics of antibodies and their membrane receptor targets; (2) model-guided generation of binding sites; (3) novel selection strategies; (4) antibodies in a complex environment: targeting intracellular and misfolded proteins; (5) rational vaccine design; (6) viral retargeting with engineered binding molecules; (7) the biology behind potential blockbuster antibodies and (8) antibodies as signaling modifiers: where did we go right, and can we learn from success? The Antibody Therapeutics session comprised five sessions: (1)Twenty-five years of therapeutic antibodies: lessons learned and future challenges; (2) preclinical and early stage development of antibody therapeutics; (3) next generation anti-angiogenics; (4) updates of clinical stage antibody therapeutics and (5) antibody drug conjugates and bispecific antibodies.

Targeted delivery of an antibody-mutant human endostatin fusion protein results in enhanced antitumor efficacy

The antiangiogenic protein endostatin showed considerable preclinical antitumor activity, but limited efficacy in phase I/II trials. Prior studies using an anti-HER2 antibody-murine endostatin fusion showed enhanced antitumor activity compared to anti-HER2 antibody or endostatin given alone, or in combination. We have generated two anti-HER2 human endostatin fusion proteins by fusing either wild-type or a mutant human endostatin (huEndo-P125A) to the 3' end of a humanized anti-HER2 IgG3 antibody. Antitumor efficacy was examined in murine and human breast tumor models. HuEndo-P125A antibody fusion protein (αHER2-huEndo-P125A) inhibited VEGF and bFGF induced endothelial cell proliferation, and tube formation in vitro, more efficiently than endostatin alone, wild-type endostatin fusion protein (αHER2-huEndo), or parental anti-HER2 antibody (αHER2 IgG3). Wild-type and mutant human endostatin was rapidly cleared from serum in mice (T½(2) = 2.0-2.1 hours), whereas αHER2-huEndo fusion proteins had a significantly prolonged half-life (T½(2) = 40.7-57.5 hours). Treatment of SK-BR-3 breast cancer xenografts with anti-HER2 IgG3-huEndo-P125A fusion resulted in greater inhibition of tumor growth and improved survival, compared to treatment with either αHER2 IgG3 (P = 0.025), human endostatin (P = 0.034), or anti-HER2 IgG3-huEndo (P = 0.016). αHER2-huEndo-P125A specifically inhibited tumors expressing HER2 in mice simultaneously implanted with murine mammary tumor EMT6 cells and with EMT6 engineered to express HER2 antigen (EMT6-HER2). Targeting of endostatin using antibody fusion proteins could improve antitumor activity of either anti-HER2 antibody and/or endostatin and provides a versatile approach that could be applied to other tumor targets with alternative antibody specificities.

Endostatin binds nerve growth factor and thereby inhibits neurite outgrowth and neuronal migration in-vitro

Endostatin (ES), the C-terminal fragment of collagen XVIII known for its anti-angiogenic properties, is associated with neurological diseases in mammals. In this study, we investigated the effect of ES on nerve growth factor (NGF)-induced neuronal differentiation, migration, neuritogenesis, and neurite extension. ES partially inhibited PC12 cell differentiation and cerebellar granule cell migration. In addition, neurite outgrowth was inhibited in a concentration-dependent manner. This effect was also matrix-dependent, as we observed better inhibition on PC12 cells grown on collagen compared to laminin matrices. Furthermore, we observed partial NGF depletion by collagen and ES, but not by laminin suggesting that NGF-matrix interactions may be important for promoting neuritogenesis, competitive inhibition by ES or low affinity matrix impairs PC12 differentiation and neurite outgrowth. Finally, using a biosensor technique, we demonstrated a direct interaction between NGF and ES suggesting the mechanism of action of ES may involve NGF sequestration. In conclusion, our study demonstrates the inhibitory effect of ES on different steps of neurogenesis including cell differentiation and migration and neuritogenesis by NGF sequestration. Such sequestration may compromise brain repair following injury, but also may play important role in axon finding as well as a potent therapeutical target in diseases involving abnormal elevated neurotrophic growth factor levels. Taken together, this study raises the consideration of ES as a double-edge sword that carries both deleterious and putative therapeutical effects.

Proteoglycans in health and disease: novel roles for proteoglycans in malignancy and their pharmacological targeting

The expression of proteoglycans (PGs), essential macromolecules of the tumor microenvironment, is markedly altered during malignant transformation and tumor progression. Synthesis of stromal PGs is affected by factors secreted by cancer cells and the unique tumor-modified extracellular matrix may either facilitate or counteract the growth of solid tumors. The emerging theme is that this dual activity has intrinsic tissue specificity. Matrix-accumulated PGs, such as versican, perlecan and small leucine-rich PGs, affect cancer cell signaling, growth and survival, cell adhesion, migration and angiogenesis. Furthermore, expression of cell-surface-associated PGs, such as syndecans and glypicans, is also modulated in both tumor and stromal cells. Cell-surface-associated PGs bind various factors that are involved in cell signaling, thereby affecting cell proliferation, adhesion and motility. An important mechanism of action is offered by a proteolytic processing of cell-surface PGs known as ectodomain shedding of syndecans; this facilitates cancer and endothelial cell motility, protects matrix proteases and provides a chemotactic gradient of mitogens. However, syndecans on stromal cells may be important for stromal cell/cancer cell interplay and may promote stromal cell proliferation, migration and angiogenesis. Finally, abnormal PG expression in cancer and stromal cells may serve as a biomarker for tumor progression and patient survival. Enhanced understanding of the regulation of PG metabolism and the involvement of PGs in cancer may offer a novel approach to cancer therapy by targeting the tumor microenvironment. In this minireview, the implication of PGs in cancer development and progression, as well as their pharmacological targeting in malignancy, are presented and discussed.

Antiangiogenic and antitumor effects of Trypanosoma cruzi Calreticulin

Background

In Latin America, 18 million people are infected with Trypanosoma cruzi, the agent of Chagas' disease, with the greatest economic burden. Vertebrate calreticulins (CRT) are multifunctional, intra- and extracellular proteins. In the endoplasmic reticulum (ER) they bind calcium and act as chaperones. Since human CRT (HuCRT) is antiangiogenic and suppresses tumor growth, the presence of these functions in the parasite orthologue may have consequences in the host/parasite interaction. Previously, we have cloned and expressed T. cruzi calreticulin (TcCRT) and shown that TcCRT, translocated from the ER to the area of trypomastigote flagellum emergence, promotes infectivity, inactivates the complement system and inhibits angiogenesis in the chorioallantoid chicken egg membrane. Most likely, derived from these properties, TcCRT displays in vivo inhibitory effects against an experimental mammary tumor.

Methodology and Principal Findings

TcCRT (or its N-terminal vasostatin-like domain, N-TcCRT) a) Abrogates capillary growth in the ex vivo rat aortic ring assay, b) Inhibits capillary morphogenesis in a human umbilical vein endothelial cell (HUVEC) assay, c) Inhibits migration and proliferation of HUVECs and the human endothelial cell line Eahy926. In these assays TcCRT was more effective, in molar terms, than HuCRT: d) In confocal microscopy, live HUVECs and EAhy926 cells, are recognized by FITC-TcCRT, followed by its internalization and accumulation around the host cell nuclei, a phenomenon that is abrogated by Fucoidin, a specific scavenger receptor ligand and, e) Inhibits in vivo the growth of the murine mammary TA3 MTXR tumor cell line.

Conclusions/Significance

We describe herein antiangiogenic and antitumor properties of a parasite chaperone molecule, specifically TcCRT. Perhaps, by virtue of its capacity to inhibit angiogenesis (and the complement system), TcCRT is anti-inflammatory, thus impairing the antiparasite immune response. The TcCRT antiangiogenic effect could also explain, at least partially, the in vivo antitumor effects reported herein and the reports proposing antitumor properties for T. cruzi infection.

In Latin America, 18 million people are infected with Trypanosoma cruzi, a protozoan that causes Chagas' disease. Vertebrate calreticulins (CRTs) are multifunctional, intra- and extracellular calcium binding, chaperone proteins. Since human CRT (HuCRT) inhibits capillary growth (angiogenesis) and suppresses tumor growth, the presence of these functions in T. cruzi CRT (TcCRT) may have interesting consequences in the host/parasite interactions. Previously, we have cloned and expressed TcCRT and shown that, when translocated from the endoplasmic reticulum to the area of trypomastigote flagellum emergence, it promotes infectivity, inactivates the complement system, an innate defense arm and inhibits angiogenesis in the chorioallantoid chicken egg membrane. TcCRT inhibits angiogenesis, since it interferes with endothelial cell multiplication, migration and capillary morphogenesis in vitro, as well as angiogenesis in rat aortic rings. The parasite molecule also displays important antitumor effects. In these activities, TcCRT is more effective than the human counterpart. Perhaps, by virtue of its capacity to inhibit angiogenesis, TcCRT is anti-inflammatory, thus impairing the antiparasite immune response. The TcCRT antiangiogenic effect could also explain, at least partially, the in vivo antitumor effects reported herein and the reports proposing antitumor properties for T. cruzi infection.

LW6, a novel HIF-1 inhibitor, promotes proteasomal degradation of HIF-1alpha via upregulation of VHL in a colon cancer cell line

Hypoxia-inducible factor HIF-1 is responsible for radiation resistance and poor prognosis in cancer therapy. As part of our drug discovery program, a novel HIF inhibitor, LW6, was identified as a small compound that inhibits the accumulation of HIF-1alpha. We found that LW6 decreased HIF-1alpha protein expression without affecting HIF-1beta expression. MG132, a proteasome inhibitor, protected HIF-1alpha from LW6-induced proteasomal degradation, indicating that LW6 affects the stability of the HIF-1alpha protein. We found that LW6 promoted the degradation of wild type HIF-1alpha, but not of a DM-HIF-1alpha with modifications of P402A and P564A, at hydroxylation sites in the oxygen-dependent degradation domain (ODDD). LW6 did not affect the activity of prolyl hydroxylase (PHD), but induced the expression of von Hippel-Lindau (VHL), which interacts with prolyl-hydroxylated HIF-1alpha for proteasomal degradation. In the presence of LW6, knockdown of VHL did not abolish HIF-1alpha protein accumulation, indicating that LW6 degraded HIF-1alpha via regulation of VHL expression. In mice carrying xenografts of human colon cancer HCT116 cells, LW6 demonstrated strong anti-tumor efficacy in vivo and caused a decrease in HIF-1alpha expression in frozen-tissue immunohistochemical staining. These data suggest that LW6 may be valuable in the development of a HIF-1alpha inhibitor for cancer treatment.

Mutations in Lama1 disrupt retinal vascular development and inner limiting membrane formation

The Neuromutagenesis Facility at the Jackson Laboratory generated a mouse model of retinal vasculopathy, nmf223, which is characterized clinically by vitreal fibroplasia and vessel tortuosity. nmf223 homozygotes also have reduced electroretinogram responses, which are coupled histologically with a thinning of the inner nuclear layer. The nmf223 locus was mapped to chromosome 17, and a missense mutation was identified in Lama1 that leads to the substitution of cysteine for a tyrosine at amino acid 265 of laminin alpha1, a basement membrane protein. Despite normal localization of laminin alpha1 and other components of the inner limiting membrane, a reduced integrity of this structure was suggested by ectopic cells and blood vessels within the vitreous. Immunohistochemical characterization of nmf223 homozygous retinas demonstrated the abnormal migration of retinal astrocytes into the vitreous along with the persistence of hyaloid vasculature. The Y265C mutation significantly reduced laminin N-terminal domain (LN) interactions in a bacterial two-hybrid system. Therefore, this mutation could affect interactions between laminin alpha1 and other laminin chains. To expand upon these findings, a Lama1 null mutant, Lama1(tm1.1Olf), was generated that exhibits a similar but more severe retinal phenotype than that seen in nmf223 homozygotes. The increased severity of the Lama1 null mutant phenotype is probably due to the complete loss of the inner limiting membrane in these mice. This first report of viable Lama1 mouse mutants emphasizes the importance of this gene in retinal development. The data presented herein suggest that hypomorphic mutations in human LAMA1 could lead to retinal disease.

Endostatin affects osteoblast behavior in vitro, but collagen XVIII/endostatin is not essential for skeletal development in vivo

Endostatin, a fragment of collagen XVIII, can inhibit vascular endothelial growth factor (VEGF) signaling. VEGF is known to be crucial for bone development. The aims of this study were to investigate the influences of endostatin on osteoblast behavior in vitro and the roles of collagen XVIII/endostatin on bone development in vivo. For the in vitro experiments, MC3T3-E1 osteoblasts were treated with VEGF-A, 2 microg/ml endostatin, 20 microg/ml endostatin, VEGF-A + 2 microg/ml endostatin, or VEGF-A + 20 microg/ml endostatin. Osteoblast proliferation and matrix mineralization were analyzed. Faxitron, pQCT, and histological analyses were performed on hindleg bones of transgenic mice overexpressing endostatin (ES-tg) and mice lacking collagen XVIII (Col18a1 (-/-)) to study bone development in vivo. Treatment of cells with endostatin decreased osteoblast proliferation. Moreover, VEGF-A together with endostatin (2 microg/ml) decreased osteoblast proliferation and matrix mineralization. In vivo, Col18a1 (-/-) and ES-tg mice displayed no differences in bone density or mineral content during bone development, but ES-tg bones grew in length more slowly compared to the controls. The formation of secondary ossification centers was delayed in Col18a1 (-/-) mice. Immunohistochemistry revealed collagen XVIII in basement membranes of periosteal and bone marrow vessels and at muscle attachment sites. In conclusion, endostatin affects osteoblast behavior in vitro, the effects being boosted by simultaneous treatment with VEGF. In vivo, Col18a1 (-/-) and ES-tg mice show mild delays in bone development. These changes are transitory and suggest that collagen XVIII/endostatin does not play an indispensable role in skeletal development.

Flexible heteroarotinoid (Flex-Het) SHetA2 inhibits angiogenesis in vitro and in vivo

Flexible heteroarotinoids (Flex-Hets) compounds regulate growth, differentiation and apoptosis in cancer cells. The hypothesis of this study was that the lead Flex-Het, SHetA2, inhibits angiogenesis by blocking cytokine release from cancer cells. SHetA2 altered secretion of thrombospondin-4 (TSP-4), vascular endothelial growth factor A (VEGF) and fibroblast growth factor (bFGF) proteins from normal and cancerous ovarian and renal cultures. Thymidine phosphorylase (TP) expression was inhibited in cancer, but not normal cultures. Endothelial tube formation was stimulated by conditioned media from cancer but not normal cultures, and SHetA2 reduced secretion of this angiogenic activity. SHetA2 directly inhibited endothelial cell tube formation and proliferation through G1 cell cycle arrest, but not apoptosis. Recombinant TP reversed SHetA2 anti-angiogenic activity. SHetA2 inhibition of in vivo angiogenesis was observed in Caki-1 renal cancer xenografts. In conclusion, SHetA2 inhibits angiogenesis through alteration of angiogenic factor secretion by cancer cells and through direct effects on endothelial cells.

Crystal structure of human collagen XVIII trimerization domain: A novel collagen trimerization Fold

Collagens contain a unique triple-helical structure with a repeating sequence -G-X-Y-, where proline and hydroxyproline are major constituents in X and Y positions, respectively. Folding of the collagen triple helix requires trimerization domains. Once trimerized, collagen chains are correctly aligned and the folding of the triple helix proceeds in a zipper-like fashion. Here we report the isolation, characterization, and crystal structure of the trimerization domain of human type XVIII collagen, a member of the multiplexin family. This domain differs from all other known trimerization domains in other collagens and exhibits a high trimerization potential at picomolar concentrations. Strong chain association and high specificity of binding are needed for multiplexins, which are present at very low levels.

Basement membrane proteoglycans: modulators Par Excellence of cancer growth and angiogenesis

Proteoglycans located in basement membranes, the nanostructures underling epithelial and endothelial layers, are unique in several respects. They are usually large, elongated molecules with a collage of domains that share structural and functional homology with numerous extracellular matrix proteins, growth factors and surface receptors. They mainly carry heparan sulfate side chains and these contribute not only to storing and preserving the biological activity of various heparan sulfate-binding cytokines and growth factors, but also in presenting them in a more "active configuration" to their cognate receptors. Abnormal expression or deregulated function of these proteoglycans affect cancer and angiogenesis, and are critical for the evolution of the tumor microenvironment. This review will focus on the functional roles of the major heparan sulfate proteoglycans from basement membrane zones: perlecan, agrin and collagen XVIII, and on their roles in modulating cancer growth and angiogenesis.

FAK and p38-MAP kinase-dependent activation of apoptosis and caspase-3 in retinal endothelial cells by alpha1(IV)NC1

PURPOSE

To determine the impact of the antiangiogenic factor alpha1(IV)NC1 on vascular endothelial growth factor-mediated proangiogenic activity in mouse retinal endothelial cells (MRECs).

METHODS

Primary culture of MRECs was established as previously described and was used to determine the effects of alpha1(IV)NC1 on the proangiogenic activity of VEGF. Cell proliferation was evaluated using [(3)H]-thymidine incorporation and 3,(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide colorimetric assays. Cell migration was determined using modified Boyden chamber and scratch wound assays and tube formation was assessed on basement membrane matrix (BMM). Intracellular signaling events Bcl-2/Bcl-x(L) and caspase-3/poly (ADP-ribose) polymerase (PARP) activities were evaluated in cells stimulated with VEGF and plated on type IV collagen-coated dishes. Apoptosis was assessed by measuring caspase activity and by performing quantitative fluorescence analysis using fluorescence-activated cell sorting assay. Subcutaneously injected VEGF induced in vivo neovascularization was studied with the BMM plug assay.

RESULTS

VEGF-induced subconfluent MREC proliferation, migration, and tube formation were significantly inhibited by alpha1(IV)NC1 at 1 muM (P < 0.001). alpha1(IV)NC1 induced MREC apoptosis is mediated by inhibition of Bcl-2 and Bcl-x(L) expression and activation of caspase-3/PARP through FAK/p38-MAPK signaling. In addition, alpha1(IV)NC1 dose dependently inhibited VEGF-mediated neovascularization in vivo.

CONCLUSIONS

alpha1(IV)NC1 inhibited VEGF-mediated angiogenesis by promoting apoptosis and caspase-3/PARP activation and by negatively impacting FAK/p38-MAPK phosphorylation, Bcl-2, and Bcl-x(L) expression leading to MREC death. The endothelial-specific inhibitory actions of recombinant alpha1(IV)NC1 may be of benefit in the treatment of a variety of eye diseases with a neovascular component.

Drosophila multiplexin (Dmp) modulates motor axon pathfinding accuracy

Multiplexins are multidomain collagens typically composed of an N-terminal thrombospondin-related domain, an interrupted triple helix and a C-terminal endostatin domain. They feature a clear regulatory function in the development of different tissues, which is chiefly conveyed by the endostatin domain. This domain can be found in proteolytically released monomeric and trimeric versions, and their diverse and opposed effects on the migratory behavior of epithelial and endothelial cell types have been demonstrated in cell culture experiments. The only Drosophila multiplexin displays specific features of both vertebrate multiplexins, collagens XV and XVIII. We characterized the Drosophila multiplexin (dmp) gene and found that three main isoforms are expressed from it, one of which is the monomeric endostatin version. Generation of dmp deletion alleles revealed that Dmp plays a role in motor axon pathfinding, as the mutants exhibit ventral bypass defects of the intersegmental nerve b (ISNb) similar to other motor axon guidance mutants. Transgenic overexpression of monomeric endostatin as well as of full-length Dmp, but not trimeric endostatin, were able to rescue these defects. In contrast, trimeric endostatin increased axon pathfinding accuracy in wild type background. We conclude that Dmp plays a modulating role in motor axon pathfinding and may be part of a buffering system that functions to avoid innervation errors.

A novel peptide from human apolipoprotein(a) inhibits angiogenesis and tumor growth by targeting c-Src phosphorylation in VEGF-induced human umbilical endothelial cells

Many angiogenesis inhibitors are derived from large plasma proteins. Previous studies showed that the Kringle5-like domain (termed KV) in human apolipoprotein (a) is a potential antiangiogenic factor. However, its active region and the underling molecular mechanism remain elusive. Here, we identified an 11-amino acid peptide (named KV11) as the key region for the antiangiogenic function of the KV domain of apolipoprotein (a). We demonstrate that KV11 inhibits angiogenesis in vitro by suppressing human umbilical vein endothelial cell migration and microtubule formation. KV11 inhibits angiogenesis in chicken chorioallantoic membrane assays and mouse corneal micropocket angiogenesis assays in vivo. KV11 peptide shows no effect on tumor cell growth or proliferation, but significantly inhibits tumor growth in SCID mouse xenograft tumor model (p < 0.01) by preventing tumor angiogenesis. We elucidate that KV11 peptide suppresses angiogenesis and tumor progression by targeting the c-Src/ERK signaling pathways. Together, these studies provide the first evidence that KV11 from apolipoprotein KV domain has anti-angiogenesis functions and may be an anti-tumor drug candidate.

Lack of collagen XVIII accelerates cutaneous wound healing, while overexpression of its endostatin domain leads to delayed healing

Endostatin, the C-terminal fragment of collagen XVIII, is known to suppress tumour growth and angiogenesis by inhibiting endothelial cell proliferation and migration. We have previously shown that endostatin and its precursor are important for the structural organization of basement membranes (BM). The aim of this study was to investigate cutaneous wound healing in mice overexpressing endostatin in keratinocytes (ES-tg) and in mice lacking collagen XVIII (Col18a1(-/-)). Excisional wounds were made on the dorsal skin of mice, the wound areas were measured and the wounds were collected for further analyses after 3, 6 or 14 days. The healing of the wounds was delayed in the ES-tg mice and accelerated in the Col18a1(-/-) mice, and the vascularisation rate was accelerated in the Col18a1(-/-) mice, but not affected in the ES-tg mice. Abnormal capillaries with swollen endothelial cells and narrowed lumens were observed in the wounds of the ES-tg mice. In these mice also the formation of the epidermal BM was delayed, and the structure of the epidermal and capillary BMs was more disorganised. Moreover, detachment of the epidermis from the granulation tissue was observed in half (n=10) of the 6-day-old ES-tg wounds, but in none of the controls, suggesting an increased fragility of the epidermal-dermal junction in the presence of an excess of endostatin.

Risk of vascular anomalies with Down syndrome

OBJECTIVE

Patients with Down syndrome have a reduced risk of developing solid tumors. This protective effect has been attributed to increased gene dosage from an additional copy of chromosome 21, and elevated expression of endostatin has been implicated. We hypothesized that vascular anomalies, including infantile hemangioma, an angiogenesis-dependent vascular tumor, and vascular malformations might be similarly inhibited in patients with Down syndrome.

PATIENTS AND METHODS

The Children's Hospital Boston Vascular Anomalies Center database was searched for patients with Down syndrome between 1999 and 2007. In addition, the records of patients with Down syndrome treated at Children's Hospital Boston and the National Birth Defects Center between 1985 and 2007 were reviewed to find concurrent vascular anomalies. Two-sided exact binomial tests were used to evaluate whether patients with vascular anomalies are at reduced risk for Down syndrome or if patients with Down syndrome are at less risk for vascular anomalies compared with the general population. Ninety-five-percent confidence intervals were calculated on the basis of the risk of Down syndrome (1 in 800) and vascular anomalies (1 in 22) in the general population.

RESULTS

Two of the 7354 patients evaluated in our vascular anomalies unit had Down syndrome. Both patients had a lymphatic malformation: one in the orbit and the other in the lower extremity. Six of the 633 patients with Down syndrome had a vascular anomaly (infantile hemangioma [n = 4] or lymphatic malformation [n = 2]). The risk of concurrent Down syndrome and vascular anomalies was different from the corresponding risk in the general population.

CONCLUSIONS

Patients with Down syndrome have a reduced risk of vascular anomalies compared with the general population. Elevated expression of antiangiogenic proteins may protect these patients from developing vascular anomalies, as well as solid tumors.

Endostatin expression in the murine model of ischaemia/reperfusion-induced acute renal failure

BACKGROUND

Renal ischaemia-hypoxia is a leading cause of acute renal failure, a clinical condition associated with rapid loss of renal function and high rates of mortality. Renal proximal tubular cells are the most severely injured during renal ischaemia, caused by the breakdown of the extracellular matrix of the tubular basement membrane. Endostatin is the C-terminal fragment of collagen XVIII generated by proteolytic cleavage and it is well-known as being an inhibitor of angiogenesis. In vitro, endostatin inhibits endothelial cell proliferation and migration, as well as tubule formation. In vivo, it has a potent inhibitory effect on tumour growth. In this study, we analysed endostatin gene expression in C57BL/6 mouse kidneys subjected to ischaemia/reperfusion.

METHODS

Ischaemic renal failure was induced via 45 min of bilateral occlusion of the renal artery and vein, followed by 12 h or 24 h of reperfusion. Whole-kidney homogenate and total RNA were extracted for examination by western blot analysis and quantitative polymerase chain reaction. The immunohistological examination revealed increased endostatin expression in injured kidney, mainly in the proximal tubule and collecting ducts.

RESULTS

Endostatin/collagen XVIII mRNA and protein expression increased during ischaemia and within 12 h of reperfusion. In the western blot assay, we identified increased expression of the 30 kDa endostatin-related fragment and of matrix metalloproteinase-9. CD31 was significantly expressed during reperfusion (P < 0.05). Immunohistological examination revealed glomerular and tubulointerstitial expression of endostatin.

CONCLUSION

These data suggest the local synthesis of a 30 kDa endostatin-related fragment following acute renal failure and suggest its role in the modulation of renal capillary density.

Endostatin: Current concepts about its biological role and mechanisms of action

Endogenous inhibitors of angiogenesis are proved to be a major factor preventing the emergence of clinically manifested stages of human cancer. The protein endostatin, a 20-kD proteolytic fragment of type XVIII collagen, is one of the most active natural inhibitors of angiogenesis. Endostatin specifically inhibits the in vitro and in vivo proliferation of endothelial cells, inducing their apoptosis through inhibition of cyclin D1. On the surface of endothelial cells, endostatin binds with the integrin alpha(5)beta(1) that activates the Src-kinase pathway. The binding of endostatin with integrins also down-regulates the activity of RhoA GTPase and inhibits signaling pathways mediated by small kinases of the Ras and Raf families. All these events promote disassembly of the actin cytoskeleton, disorders in cell-matrix interactions, and decrease in endotheliocyte mobility, i.e., promote the suppression of angiogenesis. Endostatin displays a high antitumor activity in vivo: it inhibits the progression of more than 60 types of tumors. This review summarizes results of numerous studies concerning the biological activity and action mechanism of endostatin.

The NC1 domain of type XIX collagen inhibitsin vivomelanoma growth

Type XIX collagen is a minor collagen that localizes to basement membrane zones, together with types IV, XV, and XVIII collagens. Because several NC1 COOH-terminal domains of other chains from basement membrane collagens were reported to exhibit antitumor activity, we decided to study the effects of the NC1(XIX) collagen domain on tumor progression using an experimental in vivo model of mouse melanoma. We observed a 70% reduction in tumor volume in NC1(XIX)-treated mice compared with the corresponding controls. Histologic examination of the tumors showed a strong decrease in tumor vascularization in treated mice. In vitro, NC1(XIX) inhibited the migrating capacity of tumor cells and their capacity to invade Matrigel. It also inhibited the capacity of human microvascular endothelial cells to form pseudotubes in Matrigel. This effect was accompanied by a strong inhibition of membrane type-1 matrix metalloproteinase (matrix metalloproteinase-14) and vascular endothelial growth factor expression. Collectively, our data indicate that the NC1 domain of type XIX collagen exerts antitumor activity. This effect is mediated by a strong inhibition of the invasive capacities of tumor cells and antiangiogenic effects. NC1(XIX) should now be considered as a new member of the basement membrane collagen-derived matrikine family with antitumor and antiangiogenic activity.

VEGF receptors on PC12 cells mediate transient activation of ERK1/2 and Akt: comparison of nerve growth factor and vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) and endostatin are angiogenic and anti-angiogenic molecules, respectively, that have been implicated in neurogenesis and neuronal survival. Using alkaline phosphatase fusion proteins, we show that the PC12 neuronal cell line contains cell membrane receptors for VEGF but not for endostatin and the collagen XV endostatin homologue. Immunocytochemistry confirmed that proliferating and differentiated PC12 cells express VEGF receptors 1, 2 and neuropilin-1. While no functional effects of VEGF on PC12 cell proliferation and differentiation could be observed, a slight VEGF-induced reduction of caspase-3 activity in differentiated apoptotic PC12 cells was paralleled by transient activation of ERK1/2 and Akt. In direct comparison, nerve growth factor proved to be a strikingly more potent neuroprotective agent than VEGF.

The Morphogenic Properties of Oligomeric Endostatin Are Dependent on Cell Surface Heparan Sulfate

Endostatin has attracted considerable attention because of its ability to inhibit angiogenesis. This property of monomeric endostatin contrasts with that of the trimeric endostatin moiety generated from the intact C-terminal domain of collagen XVIII that induces a promigratory phenotype in endothelial cells. This activity is inhibited by monomeric endostatin. In this study we demonstrate that the effect of oligomeric endostatin can also be inhibited by exogenous glycosaminoglycans in a size-dependent manner, with heparin oligosaccharides containing more than 20 monosaccharide residues having optimal inhibitory activity. Oligomeric endostatin was also found to induce morphological changes in Chinese hamster ovary cells, an epithelial cell line. This novel observation allowed the utilization of a panel of Chinese hamster ovary cell mutants with defined glycosaminoglycan biosynthetic defects. The action of oligomeric endostatin on these cells was shown to be dependent on cell surface glycosaminoglycans, principally heparan sulfate with N- and 6-O-sulfation of glucosamine residues rather than iduronate 2-O-sulfation being important for bioactivity. The responsiveness of a cell line (pgsE-606) with globally reduced heparan sulfate sulfation and shortened S domains, however, indicates that overall heparan sulfate domain patterning is the key determinant of the bioactivity of oligomeric endostatin. Purified heparin-monomeric endostatin constructs generated by zero-length cross-linking techniques were found to be unable to inhibit the action of oligomeric endostatin. This indicates a mechanism for the perturbation of oligomeric endostatin action by its monomeric counterpart via competition for glycosaminoglycan attachment sites at the cell surface.

Differential Expression of Collagen Types XVIII/Endostatin and XV in Normal, Keratoconus, and Scarred Human Corneas

PURPOSE

This study was designed to clarify the expression of 2 closely related collagen (Col) types XVIII and XV, and the proteolytically derived endostatin fragment of ColXVIII in normal, keratoconus, and scarred human corneas.

METHODS

Immunohistochemistry, in situ hybridization, immunoelectron microscopy, and Western immunoblotting were used for human corneal samples obtained from penetrating keratoplasty.

RESULTS

In the normal cornea, ColXVIII was immunolocalized to the corneal and conjunctival epithelial basement membrane (EBM), Descemet s membrane, and the limbal and conjunctival capillaries. Immunoreaction for endostatin was otherwise similar, but it also was present in corneal epithelial cells. Western immunoblotting showed that normal cornea contains several endostatin fragments ranging from 20 to 100 kDa. ColXV was present in the EBM of the limbus and conjunctiva, but not in EBM of the clear cornea. In situ hybridization revealed that corneal basal epithelial cells were responsible for the synthesis of ColXVIII mRNA. Keratoconus cases were characterized by an irregular EBM immunoreactivity for ColXVIII and endostatin and patchy immunoreactivity beneath EBM. In scarred corneas, highly increased immunoreactivity for ColXVIII, endostatin, and ColXV was present within stroma.

CONCLUSIONS

The results indicate that ColXVIII and ColXV are differentially expressed in normal human corneas. Constant expression of ColXVIII by corneal EBM suggests that it is an important structural molecule. Aberrant expression of ColXVIII, endostatin, and ColXV in keratoconus and scarred corneas emphasizes the active role these molecules in the wound healing process.

Collagen XVIII/endostatin is associated with the epithelial-mesenchymal transformation in the atrioventricular valves during cardiac development

Type XVIII collagen is a multidomain protein that contains cleavable C-terminal NC1 and endostatin fragments, which have been shown to either induce or inhibit cell migration. Endostatin is being intensely studied because of its anti-angiogenic activity. Three variants of type XVIII collagen have been reported to be distributed in epithelial and endothelial basement membranes in a tissue-specific manner. The single gene encoding collagen XVIII is on chromosome 21 within the region associated with the congenital heart disease phenotype observed in Down's syndrome. In this study, we investigated the expression pattern of collagen XVIII in embryonic mouse hearts during formation of the atrioventricular (AV) valves. We found that collagen XVIII is localized not only in various basement membranes but is also highly expressed throughout the connective tissue core of the endocardial cushions and forming AV valve leaflets. It was closely associated with the epithelial-mesenchymal transformation of endothelial cells into mesenchymal cushion tissue cells and was localized around these cells as they migrated into the cardiac jelly to form the initial connective tissue elements of the valve leaflets. However, after embryonic day 17.5 collagen XVIII expression decreased rapidly in the connective tissue and thereafter remained detectable only in the basement membranes of the endothelial layer covering the leaflets. The staining pattern observed within the AV endocardial cushions suggests that collagen XVIII may have a role in cardiac valve morphogenesis. These results may help us to better understand normal heart development and the aberrant mechanisms that cause cardiac malformations in Down's syndrome.

Angiogenic inhibitors: a new therapeutic strategy in oncology

Angiogenesis is a multistep, complex and tightly regulated process that is necessary for tumor growth and metastasis. Based on data of preclinical models, several antiangiogenic compounds has been shown to modify activated tumor endothelium, which suggests that these compounds can improve cytotoxic drug delivery. Such agents have entered clinical trials as single agents or in combination with cytotoxic drugs, and have shown promising antitumor activity. The pharmacodynamic and pharmacokinetic characteristics of antiangiogenic drugs are reviewed here. Most of the early clinical testing of these agents was conducted in patients with advanced disease resistant to standard therapies. Phase III trials compared the efficacy of standard chemotherapy alone with standard chemotherapy in combination with an experimental angiogenesis inhibitor. Although some of these studies were negative or controversial, recent studies validated in large clinical trials with an anti-vascular endothelial growth factor antibody demonstrated significant clinical benefit and renewed enthusiasm for this therapeutic strategy. This review describes the clinical studies of antiangiogenic agents and highlights the challenges related to choosing appropriate strategies for the selection of patients, study design and choice of appropriate endpoints for the studies' development.

Diverse biological functions of extracellular collagen processing enzymes

Collagens are abundant proteins in higher organisms, and are formed by a complex biosynthetic pathway involving intracellular and extracellular post-translational modifications. Starting from simple soluble precursors, this interesting pathway produces insoluble functional fibrillar and non-fibrillar elements of the extracellular matrix. The present review highlights recent progress and new insights into biological regulation of extracellular procollagen processing, and some novel functions of byproducts of these extracellular enzymatic transformations. These findings underscore the notion that released propeptides and other proteolytic products of extracellular matrix proteins have important biological functions, and that structural proteins are multifunctional. An emerging concept is that a dynamic interplay exists between extracellular products and byproducts with cells that helps to maintain normal cellular phenotypes and tissue integrity.

Human alpha1 type IV collagen NC1 domain exhibits distinct antiangiogenic activity mediated by alpha1beta1 integrin

Human noncollagenous domain 1 of the alpha1 chain of type IV collagen [alpha1(IV)NC1], or arresten, is derived from the carboxy terminal of type IV collagen. It was shown to inhibit angiogenesis and tumor growth in vivo; however, the mechanisms involved are not known. In the present study we demonstrate that human alpha1(IV)NC1 binds to alpha1beta1 integrin, competes with type IV collagen binding to alpha1beta1 integrin, and inhibits migration, proliferation, and tube formation by ECs. Also, alpha1(IV)NC1 pretreatment inhibited FAK/c-Raf/MEK/ERK1/2/p38 MAPK activation in ECs but had no effect on the PI3K/Akt pathway. In contrast, alpha1(IV)NC1 did not affect proliferation, migration, or the activation of FAK/c-Raf/MEK1/2/p38/ERK1 MAPK pathway in alpha1 integrin receptor knockout ECs. Consistent with this, alpha1(IV)NC1 elicited significant antiangiogenic effects and tumor growth inhibition in vivo but failed to do the same in alpha1 integrin receptor knockout mice. This suggests a highly specific, alpha1beta1 integrin-dependent antiangiogenic activity of alpha1(IV)NC1. In addition, alpha1(IV)NC1 inhibited hypoxia-induced expression of hypoxia-inducible factor 1alpha and VEGF in ECs cultured on type IV collagen by inhibiting ERK1/2 and p38 activation. This unravels a hitherto unknown function of human alpha1(IV)NC1 and suggests a critical role for integrins in hypoxia and hypoxia-induced angiogenesis. Collectively, the above data indicate that alpha1(IV)NC1 is a potential therapeutic candidate for targeting tumor angiogenesis.

Tumstatin, the NC1 domain of alpha3 chain of type IV collagen, is an endogenous inhibitor of pathological angiogenesis and suppresses tumor growth

Angiogenesis, the formation of new blood vessels, is required for physiological development of vertebrates and repair of damaged tissue, but in the pathological setting contributes to progression of cancer. During tumor growth, angiogenesis is supported by up-regulation of angiogenic stimulators (pro-angiogenic) and down-regulation of angiogenic inhibitors (anti-angiogenic). The switch to the angiogenic phenotype (angiogenic switch) allows the tumors to grow and facilitate metastasis. The bioactive NC1 domain of type IV collagen alpha3 chain, called tumstatin, imparts anti-tumor activity by inducing apoptosis of proliferating endothelial cells. Tumstatin binds to alphaVbeta3 integrin via a mechanism independent of the RGD-sequence recognition and inhibits cap-dependent protein synthesis in the proliferating endothelial cells. The physiological level of tumstatin is controlled by matrix metalloproteinase-9, which most effectively cleaves it from the basement membrane and its physiological concentration in the circulation keeps pathological angiogenesis and tumor growth in check. These findings suggest that tumstatin functions as an endogenous inhibitor of pathological angiogenesis and functions as a novel suppressor of proliferating endothelial cells and growth of tumors.

Endostatin signaling and regulation of endothelial cell-matrix interactions

The growth and survival of a malignant tumor are dependent on the formation and maintenance of its own microvasculature, a process termed angiogenesis. Inhibition of this phenomenon is an emerging strategy in cancer therapy. The extracellular matrix surrounding the vascular endothelial cells contains cryptic protein domains, which are exposed by changes in the proteolytic homeostasis of the tumor microenvironment. These fragments transmit local signals, which regulate vascular endothelial cell proliferation and migration. Endostatin, the proteolytic fragment of collagen type XVIII, is a potent inhibitor of tumor angiogenesis in various mouse models and is currently in clinical trials for therapeutic use in human cancer. Multiple cell surface receptors have been described for endostatin, but the signals transmitted by these receptors resulting in the inhibition of angiogenesis have so far been poorly characterized. Studies on the effects of endostatin on cultured endothelial cells suggest that the antimigratory and antiproliferative properties of this molecule are the major mechanisms underlying its antiangiogenic potential. These effects may be a consequence of endostatin modulation of endothelial cell-matrix interactions and pericellular proteolysis.

Invasive trophoblasts generate regulatory collagen XVIII cleavage products

Endostatin, the C-terminal proteolytic fragment of the noncollagenous domain 1 (NC1) of the basement membrane protein collagen XVIII, inhibits cell proliferation and migration. Placental and decidual expression of the peptide suggested a role in angiogenesis and/or extravillous trophoblast differentiation. Here, we demonstrate that supernatants of trophoblastic SGHPL-5 cells, purified first trimester villous trophoblasts and villous explant cultures contain proteases which in vitro cleave 20kDa endostatin from purified, recombinant NC1 domains. However, supernatants of decidual and villous fibroblasts failed to generate the 20kDa endostatin fragment. Moreover, we show that recombinant endostatin inhibits invasion of SGHPL-5 cells through Matrigel invasion chambers. Since mesenchymal cells but not trophoblasts produce collagen XVIII we suspect that invasive trophoblasts may produce endostatin upon contacting the extracellular matrix deposited by decidual stromal cells. Generation of endostatin through trophoblast-derived proteases could play a role in the regulation of trophoblast invasiveness.

Endostatin competes with bFGF for binding to heparin-like glycosaminoglycans

Endostatin is a potent inhibitor of angiogenesis and tumor growth. Here, we used human endothelial cells from lung capillaries to investigate if endostatin competes with the proangiogenic growth factors, bFGF and VEGF, for binding to costimulatory heparan sulfate molecules. Endostatin inhibited 79% and 95% of the increase in proliferation induced by bFGF and VEGF165, respectively. The stimulatory effect of VEGF165 was not affected by the presence of exogenous heparin, while that of bFGF was further enhanced in the presence of up to 0.1 microg/ml heparin. The heparin-binding protein protamine completely blocked bFGF-stimulated proliferation, while it did not affect the response to VEGF165. Simultaneous addition of endostatin and protamine led to additive effects both in inhibition of proliferation and induction of apoptosis. Although bFGF was found to bind more strongly to heparin-Sepharose than endostatin, the latter, but not the former, displaced protamine from heparin in solution, which supports the notion that endostatin can compete with bFGF for binding to heparan sulfate in vivo. Taken as a whole, our results demonstrate that there is a direct connection between the dependence of endostatin activity on heparin-like glycosaminoglycans and its ability to antagonize bFGF.

Endogenous inhibitors of angiogenesis

Angiogenesis, the formation of new blood vessels, is required for many pathologic processes, including invasive tumor growth as well as physiologic organ/tissue maintenance. Angiogenesis during development and adulthood is likely regulated by a balance between endogenous proangiogenic and antiangiogenic factors. It is speculated that tumor growth requires disruption of such balance; thus, the angiogenic switch must be turned "on" for cancer progression. If the angiogenic switch needs to be turned on to facilitate the tumor growth, the question remains as to what the physiologic status of this switch is in the adult human body; is it "off," with inhibitors outweighing the stimulators, or maintained at a fine "balance," keeping the proangiogenic properties of many factors at a delicate "activity" balance with endogenous inhibitors of angiogenesis. The physiologic status of this balance is important to understand as it might determine an individual's predisposition to turn the switch on during pathologic events dependent on angiogenesis. Conceivably, if the physiologic angiogenesis balance in human population exists somewhere between off and even balance, an individual's capacity and rate to turn the switch on might reflect their normal physiologic angiogenic status. In this regard, although extensive knowledge has been gained in our understanding of endogenous growth factors that stimulate angiogenesis, the activities associated with endogenous inhibitors are poorly understood. In this review, we will present an overview of the knowledge gained in studies related to the identification and characterization of 27 different endogenous inhibitors of angiogenesis.

Cathepsin B regulates the intrinsic angiogenic threshold of endothelial cells

The lysosomal protease cathepsin B has been implicated in a variety of pathologies including pancreatitis, tumor angiogenesis, and neuronal diseases. We used a tube formation assay to investigate the role of cathepsin B in angiogenesis. When cultured between two layers of collagen I, primary endothelial cells formed tubes in response to exogenously added VEGF. Overexpressing cathepsin B reduced the VEGF-dependent tube response, whereas pharmacologically or molecularly suppressing cathepsin B eliminated the dependence on exogenous VEGF. However, tube formation still required VEGF receptor activity, which suggested that endothelial cells generated VEGF. Indeed, VEGF mRNA and protein was detectable in cells treated with cathepsin B inhibitor, which correlated with a rise in the level of HIF-1alpha. In addition to boosting the level of proangiogenic factors, blocking cathepsin B activity reduced the amount of the antiangiogenic protein endostatin. Thus endothelial cells have the intrinsic capacity to generate pro- and antiangiogenic agents. These observations complement and expand our appreciation of how endothelial cell-derived proteases regulate angiogenesis.