Isolation and characterization of EMILIN-2, a new component of the growing EMILINs family and a member of the EMI domain-containing superfamily

Emilin2 marks the target region for mesenchymal cell accumulation in bone regeneration

BACKGROUND

Regeneration of injured tissue is dependent on stem/progenitor cells, which can undergo proliferation and maturation processes to replace the lost cells and extracellular matrix (ECM). Bone has a higher regenerative capacity than other tissues, with abundant mesenchymal progenitor cells in the bone marrow, periosteum, and surrounding muscle. However, the treatment of bone fractures is not always successful; a marked number of clinical case reports have described nonunion or delayed healing for various reasons. Supplementation of exogenous stem cells by stem cell therapy is anticipated to improve treatment outcomes; however, there are several drawbacks including the need for special devices for the expansion of stem cells outside the body, low rate of cell viability in the body after transplantation, and oncological complications. The use of endogenous stem/progenitor cells, instead of exogenous cells, would be a possible solution, but it is unclear how these cells migrate towards the injury site.

METHODS

The chemoattractant capacity of the elastin microfibril interface located protein 2 (Emilin2), generated by macrophages, was identified by the migration assay and LC-MS/MS. The functions of Emilin2 in bone regeneration were further studied using Emilin2-/- mice.

RESULTS

The results show that in response to bone injury, there was an increase in Emilin2, an ECM protein. Produced by macrophages, Emilin2 exhibited chemoattractant properties towards mesenchymal cells. Emilin2-/- mice underwent delayed bone regeneration, with a decrease in mesenchymal cells after injury. Local administration of recombinant Emilin2 protein enhanced bone regeneration.

CONCLUSION

Emilin2 plays a crucial role in bone regeneration by increasing mesenchymal cells. Therefore, Emilin2 can be used for the treatment of bone fracture by recruiting endogenous progenitor cells.

Prediction of transcript structure and concentration using RNA-Seq data

Alternative splicing (AS) is a key post-transcriptional modification that helps in increasing protein diversity. Almost 90% of the protein-coding genes in humans are known to undergo AS and code for different transcripts. Some transcripts are associated with diseases such as breast cancer, lung cancer and glioblastoma. Hence, these transcripts can serve as novel therapeutic and prognostic targets for drug discovery. Herein, we have developed a pipeline, Finding Alternative Splicing Events (FASE), as the R package that includes modules to determine the structure and concentration of transcripts using differential AS. To predict the correct structure of expressed transcripts in given conditions, FASE combines the AS events with the information of exons, introns and junctions using graph theory. The estimated concentration of predicted transcripts is reported as the relative expression in terms of log2CPM. Using FASE, we were able to identify several unique transcripts of EMILIN1 and SLK genes in the TCGA-BRCA data, which were validated using RT-PCR. The experimental study demonstrated consistent results, which signify the high accuracy and precision of the developed methods. In conclusion, the developed pipeline, FASE, can efficiently predict novel transcripts that are missed in general transcript-level differential expression analysis. It can be applied selectively from a single gene to simple or complex genome even in multiple experimental conditions for the identification of differential AS-based biomarkers, prognostic targets and novel therapeutics.

Upregulation of EMID1 Accelerates to a Favorable Prognosis and Immune Infiltration in Lung Adenocarcinoma

Lung cancer is a difficult-to-treat cancer. Lung adenocarcinoma (LUAD) is the main subtype of lung cancer. Although there are many ways to treat lung cancer, the survival rate of patients is low. Therefore, novel molecules need to be identified to diagnose and treat LUAD. This study utilized The Cancer Genome Atlas (TCGA) LUAD data to analyze and validate the value of EMID1 as a LUAD diagnostic surface marker and overall survival prognostic marker. Differential expression analysis formally confirmed that decreased EMID1 expression was significantly associated with advanced stage and metastasis of lung cancer. Kaplan–Meier survival analysis showed that the patients with low EMID expression are dismal. The relationship between clinicopathological features and EMID1 was scored using Wilcoxon signed-rank test and R (v.3.5.1) logistic regression and suggested that patients with low EMID1 expression had a worse prognosis than patients with high EMID1 expression. (Gene Ontology) GO, Kyoto Encyclopedia of Genes and Genomes(KEGG), and gene set enrichment analysis (GSEA) were performed to investigate the potential mechanism of EMID1 expression on the prognosis of LUAD and suggested that Notch signaling pathway may be an important biological pathway for EMID1 to play a role in LUAD. Further, combined with univariate and multivariate Cox regression analysis, it was speculated that high and low levels of EMID1 expression and the logistic regression analysis of related clinical variables had significant clinical significance to verify the underlying mechanism of LUAD focus and prognosis. EMID1 plays an important role in the immune milieu of LUAD. Meanwhile, the correlation between tumor-infiltrating immune cells and genes was assessed using CIBERSORT, and it was found that the level of B cell infiltration was positively correlated with the expression of EMID1, all of which were validated in the GEO and GEPIA databases. In all, this study helps to understand the immune microenvironment of LUAD and improve the survival of patients with LUAD. Thus, EMID1 may be a novel immune-related prognostic marker of LUAD.

Cell surface markers for immunophenotyping human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cells (hPSC) self-renew and represent a potentially unlimited source for the production of cardiomyocytes (CMs) suitable for studies of human cardiac development, drug discovery, cardiotoxicity testing, and disease modelling and for cell-based therapies. However, most cardiac differentiation protocols yield mixed cultures of atrial-, ventricular-, and pacemaker-like cells at various stages of development, as well as non-CMs. The proportions and maturation states of these cell types result from disparities among differentiation protocols and time of cultivation, as well as hPSC reprogramming inconsistencies and genetic background variations. The reproducible use of hPSC-CMs for research and therapy is therefore limited by issues of cell population heterogeneity and functional states of maturation. A validated method that overcomes issues of cell heterogeneity is immunophenotyping coupled with live cell sorting, an approach that relies on accessible surface markers restricted to the desired cell type(s). Here we review current progress in unravelling heterogeneity in hPSC-cardiac cultures and in the identification of surface markers suitable for defining cardiac identity, subtype specificity, and maturation states.

Recent Insights Into SREBP as a Direct Mediator of Kidney Fibrosis via Lipid-Independent Pathways

Sterol regulatory-element binding proteins (SREBPs) are classical regulators of cellular lipid metabolism in the kidney and other tissues. SREBPs are currently recognized as versatile transcription factors involved in a myriad of cellular processes. Meanwhile, SREBPs have been recognized to mediate lipotoxicity, contributing to the progression of kidney diseases. SREBP1 has been shown to bind to the promoter region of TGFβ, a major pro-fibrotic signaling mechanism in the kidney. Conversely, TGFβ activates SREBP1 transcriptional activity suggesting a positive feedback loop of SREBP1 in TGFβ signaling. Public ChIP-seq data revealed numerous non-lipid transcriptional targets of SREBPs that plausibly play roles in progressive kidney disease and fibrosis. This review provides new insights into SREBP as a mediator of kidney fibrosis via lipid-independent pathways.

Extracellular matrix: the gatekeeper of tumor angiogenesis

The extracellular matrix is a network of secreted macromolecules that provides a harmonious meshwork for the growth and homeostatic development of organisms. It conveys multiple signaling cascades affecting specific surface receptors that impact cell behavior. During cancer growth, this bioactive meshwork is remodeled and enriched in newly formed blood vessels, which provide nutrients and oxygen to the growing tumor cells. Remodeling of the tumor microenvironment leads to the formation of bioactive fragments that may have a distinct function from their parent molecules, and the balance among these factors directly influence cell viability and metastatic progression. Indeed, the matrix acts as a gatekeeper by regulating the access of cancer cells to nutrients. Here, we will critically evaluate the role of selected matrix constituents in regulating tumor angiogenesis and provide up-to-date information concerning their primary mechanisms of action.

Fibulin-4 deposition requires EMILIN-1 in the extracellular matrix of osteoblasts

Tissue microenvironments formed by extracellular matrix networks play an important role in regulating tissue structure and function. Extracellular microfibrillar networks composed of fibrillins and their associated ligands such as LTBPs, fibulins, and EMILINs are of particular interest in this regard since they provide a specialized cellular microenvironment guiding proper morphology and functional behavior of specialized cell types. To understand how cellular microenvironments composed of intricate microfibrillar networks influence cell fate decisions in a contextual manner, more information about the spatiotemporal localization, deposition, and function of their components is required. By employing confocal immunofluorescence and electron microscopy we investigated the localization and extracellular matrix deposition of EMILIN-1 and -2 in tissues of the skeletal system such as cartilage and bone as well as in in vitro cultures of osteoblasts. We found that upon RNAi mediated depletion of EMILIN-1 in primary calvarial osteoblasts and MC3T3-E1 cells only fibulin-4 matrix deposition was lost while other fibulin family members or LTBPs remained unaffected. Immunoprecipitation and ELISA-style binding assays confirmed a direct interaction between EMILIN-1 and fibulin-4. Our data suggest a new function for EMILIN-1 which implies the guidance of linear fibulin-4 matrix deposition and thereby fibulin-4 fiber formation.

Extracellular Matrix, a Hard Player in Angiogenesis

The extracellular matrix (ECM) is a complex network of proteins, glycoproteins, proteoglycans, and polysaccharides. Through multiple interactions with each other and the cell surface receptors, not only the ECM determines the physical and mechanical properties of the tissues, but also profoundly influences cell behavior and many physiological and pathological processes. One of the functions that have been extensively explored is its impingement on angiogenesis. The strong impact of the ECM in this context is both direct and indirect by virtue of its ability to interact and/or store several growth factors and cytokines. The aim of this review is to provide some examples of the complex molecular mechanisms that are elicited by these molecules in promoting or weakening the angiogenic processes. The scenario is intricate, since matrix remodeling often generates fragments displaying opposite effects compared to those exerted by the whole molecules. Thus, the balance will tilt towards angiogenesis or angiostasis depending on the relative expression of pro- or anti-angiogenetic molecules/fragments composing the matrix of a given tissue. One of the vital aspects of this field of research is that, for its endogenous nature, the ECM can be viewed as a reservoir to draw from for the development of new more efficacious therapies to treat angiogenesis-dependent pathologies.

Targeting of EMILIN-1 and EMILIN-2 to Fibrillin Microfibrils Facilitates their Incorporation into the Extracellular Matrix

Elastin microfibril interface-located proteins (EMILINs) 1 and 2 belong to a family of structurally related extracellular glycoproteins with unique functions in the extracellular space, such as modulation of pro-transforming growth factor-β processing, activation of the extrinsic apoptotic pathway, and regulation of Hedgehog and Wnt ligand bioavailability. However, little is known about how EMILINs may exert their extracellular functions. We therefore investigated the spatiotemporal localization and deposition of EMILIN-1 and -2 within the extracellular space. By using immunoelectron and immunofluorescence microscopy together with biochemical extraction, we showed that EMILIN-1 and -2 are targeted to fibrillin microfibrils in the skin. In addition, during skin wound healing and in vitro matrix fiber assembly by primary dermal fibroblasts, EMILIN-1 and -2 are deposited on and coregulated with fibrillin. Analysis of wounds and mouse embryonic fibroblast cultures showed that EMILIN-1 and -2 network formation also requires the presence of fibronectin. Disruption of microfibrils in fibrillin-1-deficient mice leads to fragmentation of the EMILIN-1 and -2 networks, suggesting an involvement of EMILINs in fibrillin-related skin disorders. The addition of EMILINs to the ligand repertoire of fibrillin strengthens the concept of fibrillin microfibrils as extracellular scaffolds integrating cellular force transmission and growth factor bioactivity.

Diagnosis of Coronary Heart Diseases Using Gene Expression Profiling; Stable Coronary Artery Disease, Cardiac Ischemia with and without Myocardial Necrosis

Cardiovascular disease (including coronary artery disease and myocardial infarction) is one of the leading causes of death in Europe, and is influenced by both environmental and genetic factors. With the recent advances in genomic tools and technologies there is potential to predict and diagnose heart disease using molecular data from analysis of blood cells. We analyzed gene expression data from blood samples taken from normal people (n = 21), non-significant coronary artery disease (n = 93), patients with unstable angina (n = 16), stable coronary artery disease (n = 14) and myocardial infarction (MI; n = 207). We used a feature selection approach to identify a set of gene expression variables which successfully differentiate different cardiovascular diseases. The initial features were discovered by fitting a linear model for each probe set across all arrays of normal individuals and patients with myocardial infarction. Three different feature optimisation algorithms were devised which identified two discriminating sets of genes, one using MI and normal controls (total genes = 6) and another one using MI and unstable angina patients (total genes = 7). In all our classification approaches we used a non-parametric k-nearest neighbour (KNN) classification method (k = 3). The results proved the diagnostic robustness of the final feature sets in discriminating patients with myocardial infarction from healthy controls. Interestingly it also showed efficacy in discriminating myocardial infarction patients from patients with clinical symptoms of cardiac ischemia but no myocardial necrosis or stable coronary artery disease, despite the influence of batch effects and different microarray gene chips and platforms.

Time- and compartment-resolved proteome profiling of the extracellular niche in lung injury and repair

The extracellular matrix (ECM) is a key regulator of tissue morphogenesis and repair. However, its composition and architecture are not well characterized. Here, we monitor remodeling of the extracellular niche in tissue repair in the bleomycin-induced lung injury mouse model. Mass spectrometry quantified 8,366 proteins from total tissue and bronchoalveolar lavage fluid (BALF) over the course of 8 weeks, surveying tissue composition from the onset of inflammation and fibrosis to its full recovery. Combined analysis of proteome, secretome, and transcriptome highlighted post-transcriptional events during tissue fibrogenesis and defined the composition of airway epithelial lining fluid. To comprehensively characterize the ECM, we developed a quantitative detergent solubility profiling (QDSP) method, which identified Emilin-2 and collagen-XXVIII as novel constituents of the provisional repair matrix. QDSP revealed which secreted proteins interact with the ECM, and showed drastically altered association of morphogens to the insoluble matrix upon injury. Thus, our proteomic systems biology study assigns proteins to tissue compartments and uncovers their dynamic regulation upon lung injury and repair, potentially contributing to the development of anti-fibrotic strategies.

Mutations in the intellectual disability gene KDM5C reduce protein stability and demethylase activity

Mutations in KDM5C are an important cause of X-linked intellectual disability in males. KDM5C encodes a histone demethylase, suggesting that alterations in chromatin landscape may contribute to disease. We used primary patient cells and biochemical approaches to investigate the effects of patient mutations on KDM5C expression, stability and catalytic activity. We report and characterize a novel nonsense mutation, c.3223delG (p.V1075Yfs*2), which leads to loss of KDM5C protein. We also characterize two KDM5C missense mutations, c.1439C>T (p.P480L) and c.1204G>T (p.D402Y) that are compatible with protein production, but compromise stability and enzymatic activity. Finally, we demonstrate that a c.2T>C mutation in the translation initiation codon of KDM5C results in translation re-start and production of a N-terminally truncated protein (p.M1_E165del) that is unstable and lacks detectable demethylase activity. Patient fibroblasts do not show global changes in histone methylation but we identify several up-regulated genes, suggesting local changes in chromatin conformation and gene expression. This thorough examination of KDM5C patient mutations demonstrates the utility of examining the molecular consequences of patient mutations on several levels, ranging from enzyme production to catalytic activity, when assessing the functional outcomes of intellectual disability mutations.

EMILIN2 regulates platelet activation, thrombus formation, and clot retraction

Thrombosis, like other cardiovascular diseases, has a strong genetic component, with largely unknown determinants. EMILIN2, Elastin Microfibril Interface Located Protein2, was identified as a candidate gene for thrombosis in mouse and human quantitative trait loci studies. EMILIN2 is expressed during cardiovascular development, on cardiac stem cells, and in heart tissue in animal models of heart disease. In humans, the EMILIN2 gene is located on the short arm of Chromosome 18, and patients with partial and complete deletion of this chromosome region have cardiac malformations. To understand the basis for the thrombotic risk associated with EMILIN2, EMILIN2 deficient mice were generated. The findings of this study indicate that EMILIN2 influences platelet aggregation induced by adenosine diphosphate, collagen, and thrombin with both EMILIN2-deficient platelets and EMILIN2-deficient plasma contributing to the impaired aggregation response. Purified EMILIN2 added to platelets accelerated platelet aggregation and reduced clotting time when added to EMILIN2-deficient mouse and human plasma. Carotid occlusion time was 2-fold longer in mice with platelet-specific EMILIN2 deficiency, but stability of the clot was reduced in mice with both global EMILIN2 deficiency and with platelet-specific EMILIN2 deficiency. In vitro clot retraction was markedly decreased in EMILIN2 deficient mice, indicating that platelet outside-in signaling was dependent on EMILIN2. EMILIN1 deficient mice and EMILIN2:EMILIN1 double deficient mice had suppressed platelet aggregation and delayed clot retraction similar to EMILIN2 mice, but EMILIN2 and EMILIN1 had opposing affects on clot retraction, suggesting that EMILIN1 may attenuate the effects of EMILIN2 on platelet aggregation and thrombosis. In conclusion, these studies identify multiple influences of EMILIN2 in pathophysiology and suggest that its role as a prothrombotic risk factor may arise from its effects on platelet aggregation and platelet mediated clot retraction.

Neutrophil elastase-dependent cleavage compromises the tumor suppressor role of EMILIN1

Proteolysis of the extracellular matrix (ECM) is a key event in tumor growth and progression. The breakdown of ECM can lead to the generation of bioactive fragments that promote cell growth and spread. EMILIN1, a multidomain glycoprotein expressed in several tissues, exerts a crucial regulatory function through the engagement of α4/α9 integrins. Unlike the majority of ECM molecules that elicit a proliferative program, the signals emitting from EMILIN1 engaged by α4/α9β1 integrins are antiproliferative. In this study, aimed to demonstrate if the suppressor role of EMILIN1 was related to its structural integrity, we tested the possibility that EMILIN1 could be specifically cleaved. Among the proteolytic enzymes released in the tumor microenvironment we showed that neutrophil elastase cleaved EMILIN1 in three/four major fragments. The consequence of this proteolytic process was the impairment of its anti-proliferative role. Accordingly, EMILIN1 was digested in sarcomas and ovarian cancers. Sarcoma specimens were infiltrated by neutrophils (PMNs) and stained positively for elastase. The present findings highlight the peculiar activity of PMN elastase in disabling EMILIN1 suppressor function.

Molecular mechanisms of thoracic aortic dissection

Thoracic aortic dissection (TAD) is a highly lethal vascular disease. In many patients with TAD, the aorta progressively dilates and ultimately ruptures. Dissection formation, progression, and rupture cannot be reliably prevented pharmacologically because the molecular mechanisms of aortic wall degeneration are poorly understood. The key histopathologic feature of TAD is medial degeneration, a process characterized by smooth muscle cell depletion and extracellular matrix degradation. These structural changes have a profound impact on the functional properties of the aortic wall and can result from excessive protease-mediated destruction of the extracellular matrix, altered signaling pathways, and altered gene expression. Review of the literature reveals differences in the processes that lead to ascending versus descending and sporadic versus hereditary TAD. These differences add to the complexity of this disease. Although tremendous progress has been made in diagnosing and treating TAD, a better understanding of the molecular, cellular, and genetic mechanisms that cause this disease is necessary to developing more effective preventative and therapeutic treatment strategies.

Copy number variation analysis in 98 individuals with PHACE syndrome

PHACE syndrome is the association of large segmental facial hemangiomas and congenital anomalies, such as posterior fossa malformations, cerebral arterial anomalies, coarctation of the aorta, eye anomalies, and sternal defects. To date, the reported cases of PHACE syndrome have been sporadic, suggesting that PHACE may have a complex pathogenesis. We report here genomic copy number variation (CNV) analysis of 98 individuals with PHACE syndrome as a first step in deciphering a potential genetic basis of PHACE syndrome. A total of 3,772 CNVs (2,507 duplications and 1,265 deletions) were detected in 98 individuals with PHACE syndrome. CNVs were then eliminated if they failed to meet established criteria for quality, spanned centromeres, or did not contain genes. CNVs were defined as "rare" if not documented in the database of genomic variants. Ten rare CNVs were discovered (size range: 134-406  kb), located at 1q32.1, 1q43, 3q26.32-3q26.33, 3p11.1, 7q33, 10q24.32, 12q24.13, 17q11.2, 18p11.31, and Xq28. There were no rare CNV events that occurred in more than one subject. Therefore, further study is needed to determine the significance of these CNVs in the pathogenesis of PHACE syndrome.

EMILIN-3, peculiar member of elastin microfibril interface-located protein (EMILIN) family, has distinct expression pattern, forms oligomeric assemblies, and serves as transforming growth factor β (TGF-β) antagonist

EMILIN-3 is a glycoprotein of the extracellular matrix belonging to a family that contains a characteristic N-terminal cysteine-rich EMI domain. Currently, EMILIN-3 is the least characterized member of the elastin microfibril interface-located protein (EMILIN)/Multimerin family. Using RNA, immunohistochemical, and protein chemistry approaches, we carried out a detailed characterization of the expression and biochemical properties of EMILIN-3 in mouse. During embryonic and postnatal development, EMILIN-3 showed a peculiar and dynamic pattern of gene expression and protein distribution. EMILIN-3 mRNA was first detected at E8.5-E9.5 in the tail bud and in the primitive gut, and at later stages it became abundant in the developing gonads and osteogenic mesenchyme. Interestingly and in contrast to other EMILIN/Multimerin genes, EMILIN-3 was not found in the cardiovascular system. Despite the absence of the globular C1q domain, immunoprecipitation and Western blot analyses demonstrated that EMILIN-3 forms disulfide-bonded homotrimers and higher order oligomers. Circular dichroism spectroscopy indicated that the most C-terminal part of EMILIN-3 has a substantial α-helical content and forms coiled coil structures involved in EMILIN-3 homo-oligomerization. Transfection experiments with recombinant constructs showed that the EMI domain contributes to the higher order self-assembly but was dispensable for homotrimer formation. EMILIN-3 was found to bind heparin with high affinity, a property mediated by the EMI domain, thus revealing a new function for this domain that may contribute to the interaction of EMILIN-3 with other extracellular matrix and/or cell surface molecules. Finally, in vitro experiments showed that EMILIN-3 is able to function as an extracellular regulator of the activity of TGF-β ligands.

The EMILIN/Multimerin family

Elastin microfibrillar interface proteins (EMILINs) and Multimerins (EMILIN1, EMILIN2, Multimerin1, and Multimerin2) constitute a four member family that in addition to the shared C-terminus gC1q domain typical of the gC1q/TNF superfamily members contain a N-terminus unique cysteine-rich EMI domain. These glycoproteins are homotrimeric and assemble into high molecular weight multimers. They are predominantly expressed in the extracellular matrix and contribute to several cellular functions in part associated with the gC1q domain and in part not yet assigned nor linked to other specific regions of the sequence. Among the latter is the control of arterial blood pressure, the inhibition of Bacillus anthracis cell cytotoxicity, the promotion of cell death, the proangiogenic function, and a role in platelet hemostasis. The focus of this review is to highlight the multiplicity of functions and domains of the EMILIN/Multimerin family with a particular emphasis on the regulatory role played by the ligand-receptor interactions of the gC1q domain. EMILIN1 is the most extensively studied member both from the structural and functional point of view. The structure of the gC1q of EMILIN1 solved by NMR highlights unique characteristics compared to other gC1q domains: it shows a marked decrease of the contact surface of the trimeric assembly and while conserving the jelly-roll topology with two β-sheets of antiparallel strands it presents a nine-stranded β-sandwich fold instead of the usual 10-stranded fold. This is likely due to the insertion of nine residues that disrupt the ordered strand organization and forma a highly dynamic protruding loop. In this loop the residue E933 is the site of interaction between gC1q and the α4β1 and α9β1 integrins, and contrary to integrin occupancy that usually upregulates cell growth, when gC1q is ligated by the integrin the cells reduce their proliferative activity.

EMILIN2 (Elastin microfibril interface located protein), potential modifier of thrombosis

BACKGROUND

Elastin microfibril interface located protein 2 (EMILIN2) is an extracellular glycoprotein associated with cardiovascular development. While other EMILIN proteins are reported to play a role in elastogenesis and coagulation, little is known about EMILIN2 function in the cardiovascular system. The objective of this study was to determine whether EMILIN2 could play a role in thrombosis.

RESULTS

EMILIN2 mRNA was expressed in 8 wk old C57BL/6J mice in lung, heart, aorta and bone marrow, with the highest expression in bone marrow. In mouse cells, EMILIN2 mRNA expression in macrophages was higher than expression in endothelial cells and fibroblasts. EMILIN2 was identified with cells and extracellular matrix by immunohistochemistry in the carotid and aorta. After carotid ferric chloride injury, EMILIN2 was abundantly expressed in the thrombus and inhibition of EMILIN2 increased platelet de-aggregation after ADP-stimulated platelet aggregation.

CONCLUSIONS

These results suggest EMILIN2 could play a role in thrombosis as a constituent of the vessel wall and/or a component of the thrombus.

Complement and non-complement activating functions of C1q: A prototypical innate immune molecule

C1q is a versatile innate immune molecule that serves as the initiation subcomponent of the classical complement pathway. In addition, it is also a potent pattern recognition molecule, the versatility of which has fuelled its functional flexibility. C1q recognises an array of self, non-self and altered-self ligands. The broad-spectrum ligand-binding potential of C1q is facilitated by the modular organisation of the heterotrimeric globular head region, its ability to change its conformation in a very subtle way, and the manner in which this ancient molecule appears to have evolved to deal with the different types of ligands. Over recent years, molecules that resemble C1q have been put together to form the C1q family. In this review, we briefly summarise complement-dependent and complement-independent functions of C1q, its cognate receptors and key members of the rapidly growing C1q family.

Mouse chromosome 17 candidate modifier genes for thrombosis

Two overlapping quantitative trait loci (QTLs) for clot stability, Hmtb8 and Hmtb9, were identified on mouse chromosome 17 in an F2 intercross derived from C57BL/6J (B6) and B6-Chr17(A/J) (B6-Chr17) mouse strains. The intervals were in synteny with a QTL for thrombotic susceptibility on chromosome 18 in a human study, and there were 23 homologs between mouse and human. The objective of this study was to determine whether any of these genes in the syntenic region are likely candidates as modifiers for clot stability. Seven genes, Twsg1, Zfp161, Dlgap1, Ralbp1, Myom1, Rab31, and Emilin2, of the 23 genes with single nucleotide polymorphisms (SNPs) in the mRNA-UTR had differential expression in B6 and A/J mice. Dlgap1, Ralbp1, Myom1, and Emilin2 also had nonsynonymous SNPs. In addition, two other genes had nonsynonymous SNPs, Lama1 and Ndc80. Of these nine candidate genes, Emilin2 was selected for further analysis since other EMILIN (Elastin Microfibril Interface Located Protein) proteins have known functions in vascular structure and coagulation. Differences were found between B6 and A/J mice in vessel wall architecture and EMILIN2 protein in plasma, carotid vessel wall, and thrombi formed after ferric chloride injury. In B6-Chr17(A/J) mice both clot stability and Emilin2 mRNA expression were higher compared to those in B6 and A/J mice, suggesting the exposure of epistatic interactions. Although other homologous genes in the QTL region cannot be ruled out as causative genes, further investigation of Emilin2 as a candidate gene for thrombosis susceptibility is warranted.

The extracellular matrix glycoprotein elastin microfibril interface located protein 2: a dual role in the tumor microenvironment

We have recently reported that elastin microfibril interface located protein 2 (EMILIN2), an extracellular matrix (ECM) glycoprotein, triggers cell death through a direct binding to death receptors. EMILIN2 thus influences cell viability through a mechanism that is unique for an ECM molecule. In the present work, we report an additional function for this molecule. First, we identify the region responsible for the proapoptotic effects, a 90-amino acid residue-long coiled-coil fragment toward the N-terminus of the molecule. The fragment recapitulates EMILIN2 proapoptotic mechanisms. In addition, using either the full molecule or the active fragment, for the first time, we demonstrate a significant antitumoral effect in vivo, likely due to a decrease in tumor cell viability. Unexpectedly, tumors treated with EMILIN2 or the deletion mutant display a significant increase of tumor angiogenesis. In view of this novel finding, the cotreatment of the growing tumors with an antiangiogenic drug led, in most cases, to a complete regression of tumor growth. These results grant further support to recent findings that pinpoint the microenvironment as an important regulator of cell fate under both physiological and pathological conditions and disclose the possibility of using EMILIN2 fragments as potent antineoplastic tools for cancer treatment.

NMR-based homology model for the solution structure of the C-terminal globular domain of EMILIN1

EMILIN1 is a glycoprotein of elastic tissues that has been recently linked to the pathogenesis of hypertension. The protein is formed by different independently folded structural domains whose role has been partially elucidated. In this paper the solution structure, inferred from NMR-based homology modelling of the C-terminal trimeric globular C1q domain (gC1q) of EMILIN1, is reported. The high molecular weight and the homotrimeric structure of the protein required the combined use of highly deuterated (15)N, (13)C-labelled samples and TROSY experiments. Starting from a homology model, the protein structure was refined using heteronuclear residual dipolar couplings, chemical shift patterns, NOEs and H-exchange data. Analysis of the gC1q domain structure of EMILIN1 shows that each protomer of the trimer adopts a nine-stranded beta sandwich folding topology which is related to the conformation observed for other proteins of the family. Distinguishing features, however, include a missing edge-strand and an unstructured 19-residue loop. Although the current data do not allow this loop to be precisely defined, the available evidence is consistent with a flexible segment that protrudes from each subunit of the globular trimeric assembly and plays a key role in inter-molecular interactions between the EMILIN1 gC1q homotrimer and its integrin receptor alpha4beta1.

The solution structure of EMILIN1 globular C1q domain reveals a disordered insertion necessary for interaction with the alpha4beta1 integrin

The extracellular matrix protein EMILIN1 (elastin microfibril interface located protein 1) is implicated in maintaining blood pressure homeostasis via the N-terminal elastin microfibril interface domain and in trophoblast invasion of the uterine wall via the globular C1q (gC1q) domain. Here, we describe the first NMR-based homology model structure of the human 52-kDa homotrimer of the EMILIN1 gC1q domain. In contrast to all of the gC1q (crystal) structures solved to date, the 10-stranded beta-sandwich fold of the gC1q domain is reduced to nine beta strands with a consequent increase in the size of the central cavity lumen. An unstructured loop, resulting from an insertion unique to EMILIN1 and EMILIN2 family members and located at the trimer apex upstream of the missing strand, specifically engages the alpha4beta1 integrin. Using both Jurkat T and EA.hy926 endothelial cells as well as site-directed mutagenesis, we demonstrate that the ability of alpha4beta1 integrins to recognize the trimeric EMILIN1 gC1q domain mainly depends on a single glutamic acid residue (Glu(933)). Static and flow adhesion of T cells and haptotactic migration of endothelial cells on gC1q is fully dependent on this residue. Thus, EMILIN1 gC1q-alpha4beta1 represents a unique ligand/receptor system, with a requirement for a 3-fold arrangement of the interaction site.

EMILINs interact with anthrax protective antigen and inhibit toxin action in vitro

The informational spectrum method (ISM) is a virtual spectroscopy method for the fast analysis of potential protein-protein relationships. By applying the ISM approach to the GeneBank protein database the vascular proteins EMILIN1 (Elastin Microfibril Interface Located ProteIN), EMILIN2, MMN1, and MMN2 were identified as additional anthrax PA antigen interacting molecules. This virtual molecular interaction was formally proven by solid phase assays using recombinant proteins. The interaction is independent of the presence of divalent cations and does not involve PA aspartic residue at 683, a critical residue in receptor binding. In fact, the D683A point mutation fully prevented the cell intoxication ability of PA in the presence of Lethal Factor, but it was fully ineffective on the binding of mutated PA to EMILIN1 and EMILIN2. The ISM approach also led to the identification of the potential interaction sites between PA and EMILINs. A PA mutant with a deletion at residue D425 and solid phase protein-protein interaction studies as well as deletion mutant of EMILIN2 confirmed the hypothesized interaction site. Our findings imply that the PA-cell surface receptor interaction is not likely to provide the full explanation for the vascular lesions and prominent hemorrhages that follow Bacillus anthracis infection and spreading and call into play vascular associated proteins such as EMILINs as potential inhibitory proteins.

Regulation of the extrinsic apoptotic pathway by the extracellular matrix glycoprotein EMILIN2

Elastin microfibril interface-located proteins (EMILINs) constitute a family of extracellular matrix (ECM) glycoproteins characterized by the presence of an EMI domain at the N terminus and a gC1q domain at the C terminus. EMILIN1, the archetype molecule of the family, is involved in elastogenesis and hypertension etiology, whereas the function of EMILIN2 has not been resolved. Here, we provide evidence that the expression of EMILIN2 triggers the apoptosis of different cell lines. Cell death depends on the activation of the extrinsic apoptotic pathway following EMILIN2 binding to the TRAIL receptors DR4 and, to a lesser extent, DR5. Binding is followed by receptor clustering, colocalization with lipid rafts, death-inducing signaling complex assembly, and caspase activation. The direct activation of death receptors by an ECM molecule that mimics the activity of the known death receptor ligands is novel. The knockdown of EMILIN2 increases transformed cell survival, and overexpression impairs clonogenicity in soft agar and three-dimensional growth in natural matrices due to massive apoptosis. These data demonstrate an unexpected direct and functional interaction of an ECM constituent with death receptors and discloses an additional mechanism by which ECM cues can negatively affect cell survival.

C1q and its growing family

C1q is the target recognition protein of the classical complement pathway and a major connecting link between innate and acquired immunity. As a charge pattern recognition molecule of innate immunity, C1q can engage a broad range of self and non-self ligands via its heterotrimeric globular (gC1q) domain and thus trigger the classical pathway. The trimeric gC1q signature domain has been identified in a variety of non-complement proteins that can be grouped together as a C1q family. The X-ray crystal structures of the gC1q domain of a few members of the C1q family reveal a compact jelly-roll beta-sandwich fold similar to that of the multifunctional tumor necrosis factor (TNF) ligand family, hence the C1q and TNF superfamily. This review is an update on the structural and functional aspects of the gC1q domain of human C1q. We also mention the diverse range of proteins that utilize a gC1q domain in order to reflect on its importance as a versatile scaffold to support a variety of functions.

Structural and functional anatomy of the globular domain of complement protein C1q

C1q is the first subcomponent of the classical pathway of the complement system and a major connecting link between innate and acquired immunity. As a versatile charge pattern recognition molecule, C1q is capable of engaging a broad range of ligands via its heterotrimeric globular domain (gC1q) which is composed of the C-terminal regions of its A (ghA), B (ghB) and C (ghC) chains. Recent studies using recombinant forms of ghA, ghB and ghC have suggested that the gC1q domain has a modular organization and each chain can have differential ligand specificity. The crystal structure of the gC1q, molecular modeling and protein engineering studies have combined to illustrate how modular organization, charge distribution and the spatial orientation of the heterotrimeric assembly offer versatility of ligand recognition to C1q. Although the biochemical and structural studies have provided novel insights into the structure-function relationships within the gC1q domain, they have also raised many unexpected issues for debate.

Identification of a major microfibril-associated glycoprotein-1-binding domain in fibrillin-2

Using yeast two-hybrid, ligand blotting, and solid phase binding assays, we have shown that microfibril-associated glycoprotein-1 (MAGP-1) interacts with the 8-cysteine motif of fibrillin-2 encoded by exon 24. Binding to this sequence was demonstrated for full-length MAGP-1 as well as for the MAGP-1 matrix-binding domain encoded by exons 7 and 8. The matrix-binding domain, but not the full-length protein, also bound to regions of fibrillin-2 defined by exons 16 and 17, exon 20, and exons 23 and 24. Interestingly, no binding was detected to sequences near the N or C terminus where MAGP-1 and MAGP-2, respectively, were shown to interact with fibrillin-1. The localization of MAGP-1 binding to the 8-Cys domain encoded by exon 24 suggests that the bead structure of microfibrils consists of exon 24 and portions of the central region of fibrillin-2. Exon 24 in fibrillin lies in the region of the molecule where mutations produce the most severe phenotypes associated with Marfan syndrome (fibrillin-1) and congenital contractural arachnodactyly (fibrillin-2). It is possible that these mutations alter the ability of fibrillin to bind MAGP-1, which may contribute to the severity of the disease.

Molecular cloning and characterization of a novel gene, EMILIN-5, and its possible involvement in skeletal development

By analyzing expression profiles of human mesenchymal stem cells incubated in osteogenic supplements, we identified and characterized a novel human cDNA, elastin microfibril interface located protein-5 (EMILIN-5), that is likely to play a significant role in the process of osteogenesis. The deduced EMILIN-5 product consists of 766 amino acids with a cysteine-rich EMI domain at the NH(2) terminus. Western blotting detected EMILIN-5 expression in a variety of osteoblastic cell lines. Immunohistochemistry of mouse embryos 13.5 days post-coitus revealed relatively high levels of EMILIN-5 protein in perichondrium cells of developing limbs. Our findings suggest that the EMILIN-5 gene plays an important role in skeletal development.

EMILIN-1 deficiency induces elastogenesis and vascular cell defects

EMILINs constitute a family of genes of the extracellular matrix with high structural similarity. Four genes have been identified so far in human and mouse. To gain insight into the function of this gene family, EMILIN-1 has been inactivated in the mouse by gene targeting. The homozygous animals were fertile and did not show obvious abnormalities. However, histological and ultrastructural examination revealed alterations of elastic fibers in aorta and skin. Formation of elastic fibers by mutant embryonic fibroblasts in culture was also abnormal. Additional alterations were observed in cell morphology and anchorage of endothelial and smooth muscle cells to elastic lamellae. Considering that EMILIN-1 is adhesive for cells and that the protein binds to elastin and fibulin-5, EMILIN-1 may regulate elastogenesis and vascular cell maintenance by stabilizing molecular interactions between elastic fiber components and by endowing elastic fibers with specific cell adhesion properties.

An emilin family extracellular matrix protein identified in the cochlear basilar membrane

The precise movement of the cochlear basilar membrane (BM) stimulates the sensory hair cells during auditory transduction. However, the molecular composition of the BM that confers its specialized properties of support and elasticity is poorly understood. A differential screen of cochlear RNA from deaf mice lacking thyroid hormone receptor beta was used to identify a sequence encoding a secreted protein, which is abundant in the BM and is expressed at low levels in the heart, lung, and brain. The protein possesses several domains for protein interactions and is related to emilin (elastin microfibril interface-located protein) previously isolated from aorta. This cochlear emilin-2 mRNA is expressed in the tympanic border cells underlying the BM and an antibody detected protein in the extracellular matrix surrounding the collagenous fibers in the BM. These results identify emilin-2 as a major BM component and suggest that it contributes to the developmental assembly or function of the BM.

beta 1 Integrin-dependent cell adhesion to EMILIN-1 is mediated by the gC1q domain

EMILIN-1 (Elastin Microfibril Interface Located ProteIN), the prototype of the EMILIN family, consists of a cysteine-rich domain (EMI domain) at the N terminus, an extended region with a high potential coiled-coil structure, a short collagenous stalk, and a self-interacting globular gC1q-l domain. EMILIN-1 is an adhesive extracellular matrix constituent associated with elastic fibers, detected also in the proximity of cell surfaces. To localize the cell attachment site(s), monoclonal antibodies (mAbs) against EMILIN-1 or the gC1q-1 domain were used to inhibit cell attachment to EMILIN-1. Thus, one mAb mapping to the gC1q-1 domain caused complete inhibition of cell attachment. EMILIN-1 and gC1q-1 displayed a comparable dose-dependent ability to promote cell adhesion. Adhesion kinetics was similar to that of fibronectin (FN), reaching the maximum level of attachment at 20 min, but in the absence of cations adhesion was negligible. The relative adhesion strength to detach 50% of the cells was similar for EMILIN-1 and gC1q-1 (250-270 x g) but lower than that for FN (>>500). Cell adhesion to EMILIN-1 or gC1q-1 was completely blocked by a function-blocking beta(1) integrin subunit mAb. In contrast, adhesion to the complement C1q component was totally unaffected. Among the various function-blocking mAbs against the alpha integrin subunits only the anti-alpha(4) fully abrogated cell adhesion to gC1q-1 and up to 70% to EMILIN-1. Furthermore, only K562 cells transfected with the alpha(4) integrin chain, but not wild type K562, were able to adhere to EMILIN-1 and were specifically inhibited by anti-alpha(4) function-blocking mAb. Finally, cells attached to EMILIN-1 or gC1q-1, compared with cells plated on FN or vitronectin, which appeared well spread out on the substrate with prominent stress fibers and focal contacts, were much smaller with wide ruffles and a different organization status of the actin cytoskeleton along the cell periphery. This pattern was in accord with the ability of EMILIN-1 to promote cell movement.

Expression of the EMILIN-1 gene during mouse development

Expression of EMILIN-1, the first member of a newly discovered family of extracellular matrix genes, has been investigated during mouse development. EMILIN-1 mRNA is detectable in morula and blastocyst by RT-PCR. First expression of the gene is found by in situ hybridization in ectoplacental cone in embryos of 6.5 days and in extraembryonic visceral endoderm at 7.5 days. The allantois is also labeled. Staining of ectoplacental cone-derived secondary trophoblast giant cells and spongiotrophoblast is strong up to 11.5 days and then declines. In the embryo, high levels of mRNA are initially expressed in blood vessels, perineural mesenchyme and somites at 8.5 days. Later on, intense labeling is identified in the mesenchymal component of organs anlage (i.e. lung and liver) and different mesenchymal condensations (i.e. limb bud and branchial arches). At late gestation staining is widely distributed in interstitial connective tissue and smooth muscle cell-rich tissues. The data suggest that EMILIN-1 may have a function in placenta formation and initial organogenesis and a later role in interstitial connective tissue.

Microfibril-associated glycoprotein-2 interacts with fibrillin-1 and fibrillin-2 suggesting a role for MAGP-2 in elastic fiber assembly

Elastic fibers are composed of the protein elastin and a network of 10-12 nm microfibrils. The microfibrillar proteins include, among others, the fibrillins and microfibril-associated glycoproteins-1 and -2 (MAGP-1 and MAGP-2). Little is known about how microfibrillar proteins interact to support fiber assembly. We used the C-terminal half of MAGP-2 in a yeast two-hybrid library screen to identify relevant ligands. Six of 13 positive clones encoded known microfibrillar proteins, including fibrillin-1 and -2. Deletion analysis of partial fibrillin-1 and -2 clones revealed a calcium-binding epidermal growth factor repeat-containing region near the C terminus responsible for binding. This region is distinct from the region of fibrillin-1 reported by others to bind MAGP-1. The MAGP-2 bait was unable to interact productively with other epidermal growth factor repeats in fibrillin-1, demonstrating specificity of the interaction. Deletion analysis of the MAGP-2 bait demonstrated that binding occurred in a core region containing 48% identity and 7 conserved cysteine residues with MAGP-1. Immunoprecipitation of MAGP-2 from transfected COS-7 cells resulted in the coprecipitation of fibrillin. These results demonstrate that MAGP-2 specifically interacts with fibrillin-1 and -2 and suggest that MAGP-2 may help regulate microfibrillar assembly. The results also demonstrate the utility of the yeast two-hybrid system to study protein-protein interactions of the extracellular matrix.

Elastic fibres

Elastic fibres are essential extracellular matrix macromolecules comprising an elastin core surrounded by a mantle of fibrillin-rich microfibrils. They endow connective tissues such as blood vessels, lungs and skin with the critical properties of elasticity and resilience. The biology of elastic fibres is complex because they have multiple components, a tightly regulated developmental deposition, a multi-step hierarchical assembly and unique biomechanical functions. However, their molecular complexity is at last being unravelled by progress in identifying interactions between component molecules, ultrastructural analyses and studies of informative mouse models.