The association of human fibulin-1 with elastic fibers: an immunohistological, ultrastructural, and RNA study

The dual role of fibulins in tumorigenesis

The human fibulin family consists of seven complex extracellular glycoproteins originally characterized as components of elastic fibers in connective tissue. However, beyond its structural role, fibulins are involved in complex biological processes such as cell adhesion, migration or proliferation. Indeed, they have proved to be essential elements in normal physiology, as shown by mouse models lacking these proteins, that evidence several developmental abnormalities and pathological features. Their relevance is also apparent in tumorigenesis, an aspect that has started to be intensely studied. Distinct fibulins are expressed in both tumor and stromal cells and are subjected to multiple expression regulations with either anti or pro-tumor effects. The mechanistic insights that underlie these observations are now commencing to emerge, portraying these proteins as very versatile and active constituents of connective tissue. The aim of this review is to highlight the most relevant connections between fibulins and cancer.

Structure and biology of the intervertebral disk in health and disease

The intervertebral disks along the spine provide motion and protection against mechanical loading. The 3 structural components, nucleus pulposus, annulus fibrosus, and cartilage endplate, function as a synergistic unit, though each has its own role. The cells within each of these components have distinct origins in development and morphology, producing specific extracellular matrix proteins that are organized into unique architectures fit for intervertebral disk function. This article focuses on various aspects of intervertebral disk biology and disruptions that could lead to diseases such as intervertebral disk degeneration.

Fibulin-1 is a marker for arterial extracellular matrix alterations in type 2 diabetes

BACKGROUND

Extracellular matrix alterations are important elements in the arterial changes seen in diabetes, being associated with increased vascular stiffness and the development of cardiovascular diseases. However, no biomarkers for diabetes-related arterial changes have been defined.

METHODS

Mammary artery specimens from 17 men with type 2 diabetes and 18 nondiabetic individuals were used for microarray expression profiling, quantitative real-time PCR, immunoassay, and immunohistochemical analyses. A derived candidate marker, fibulin-1, which is an elastin-associated matrix molecule, was measured immunochemically in plasma from (a) 70 patients scheduled for vascular surgery, (b) 305 patients with type 2 diabetes examined with carotid ultrasonography and echocardiography, and (c) 308 patients with type 2 diabetes, followed for 15 years.

RESULTS

The most upregulated transcript in nonatherosclerotic arterial tissue from patients with type 2 diabetes encoded the extracellular matrix protein, fibulin-1. Higher concentrations of fibulin-1-protein were present in artery extracts from patients with diabetes than extracts from individuals without diabetes, and increased fibulin-1 immunostaining was apparent around the external elastic lamina of diabetic arteries. Patients with diabetes displayed increased plasma concentrations of fibulin-1 (P = 0.006). Plasma fibulin-1 concentrations correlated with hemoglobin A(1c) (P < 0.001), arterial stiffness indices including pulse pressure (P < 0.001), and carotid compliance (P = 0.004), as well as plasma N-terminal pro-B-type natriuretic peptide concentrations (P < 0.001) and were predictive of 15-year mortality (P = 0.013).

CONCLUSIONS

Fibulin-1 accumulates in the arterial wall and in plasma of patients with type 2 diabetes, and appears to be a factor associated with arterial extracellular matrix changes in type 2 diabetes.

Differential expression of elastin assembly genes in patients with Stanford Type A aortic dissection using microarray analysis

OBJECTIVE

Pathologic studies have demonstrated that aortic dissection is initiated by an intimal tear, followed by the rapid growth of an intramural hematoma that dissects the media and is characterized by elastin degradation. Genetic extracellular matrix abnormalities and proteinases may be the predisposing factors in aortic dissection, but little is known about the role of elastic fiber assembly. Fibulin-1 is an extracellular protein that is expressed in the vascular basement membrane. It regulates elastic fiber assembly and hence provides integrity in aortic structure. This study investigates the expression profiles of genes responsible for the elastolysis in the dissected human aorta, especially those coding fibulin-1, matrix metalloproteinase-9 (MMP-9), and elastin.

METHODS

Intraoperative aortic samples were obtained from Chinese patients with Stanford Type A aortic dissection. Both the ascending dissected aortas (primary tear) and the adjacent intact aortas were collected for comparison. Control aortic tissues were obtained from healthy organ donors. The gene profile study was determined by the Affymetrix HG-U133A GeneChip (Affymetrix, Santa Clara, Calif) and analyzed by GeneSpring GX11.0 (Agilent Technologies Inc, Palo Alto, Calif). Only the genes displaying a net signal intensity two-fold higher than the mean background were used for analysis. To evaluate elastin expression, aortic sections were stained with Movat pentachrome stain. Fibulin-1, MMP-9, and elastin mRNA and protein expression were further confirmed by reverse transcriptase polymerase chain reaction (RT-PCR) and immunoblotting, respectively.

RESULTS

Eight male Chinese aortic dissection patients (mean age, 45.8 years) and eight gender- and age-matched organ donors were recruited for the study. On the Affymetrix platform, 2,250 of 22,283 genes (10.1%) were detectable. The dissected and adjacent macroscopically intact aorta displayed similar gene expression patterns. In contrast, 11.2% (252) of the detectable genes were differentially expressed in the dissected and control aortas. Of these, 102 genes were upregulated, and 150 genes were downregulated. Based on the gene ontology, genes that code for extracellular matrix protein components and regulating elastic fiber assembly, like fibulin-1 and elastin, were downregulated, while enzymes like MMP-9 and MMP-11 that degrade matrix proteins were upregulated in dissected aortas. RT-PCR and Western blot results further validated the results.

CONCLUSIONS

Our gender- and age-matched study demonstrated that the alternated genes in the elastin assembly of dissected aortas may predispose structural failure in the aorta leading to dissection. However, no significant gene alterations in the adjacent intact and dissected aortas of the same patient can be found. Therefore, the genetic changes found in the dissected aortas most likely developed before the dissection starts. The inhibition of the aberrant expression of the fibulin-1 gene and that of the related matrix proteinase may open a new avenue for preventing aortic dissection.

Proteomic analysis of human serum for finding pathogenic factors and potential biomarkers in preeclampsia

OBJECTIVE(S)

To apply a novel proteomic method to discover potential pathogenic factors and biomarkers of preeclampsia.

STUDY DESIGN

Sera from five patients complicated with preeclampsia and five healthy pregnant controls were separately pooled. Each pool was treated with peptide ligand library beads (PLLBs) to remove high abundance proteins by affinity and thus enrich low abundance proteins. The proteins from the eluate were analyzed by a combination of 1D Gel-LC-MS/MS. Protein expression levels were quantified using spectral counts and the extracted ion current.

RESULTS

1172 unique proteins in preeclampsia and 1149 in healthy controls were identified in the present study. 51 proteins were differentially expressed between preeclampsia and healthy pregnant women including chorionic somatommammptropin hormone (CSH) and fibulin-1. 31 proteins identified were up-regulated and 20 were down-regulated.

CONCLUSIONS

The results demonstrate that peptide ligand library combining with 1D gel-LC-MS/MS analysis is an efficient method to identify differentially expressed proteins in sera and two biological processes of complement and coagulation activations and lipid metabolism were involved in the pathogenesis of preeclampsia.

Fibulin-1 is increased in asthma--a novel mediator of airway remodeling?

Background

The extracellular matrix is a dynamic and complex network of macromolecules responsible for maintaining and influencing cellular functions of the airway. The role of fibronectin, an extracellular matrix protein, is well documented in asthma. However, the expression and function of fibulin-1, a secreted glycoprotein which interacts with fibronectin, has not been reported. Fibulin-1 is widely expressed in basement membranes in many organs including the lung. There are four isoforms in humans (A–D) of which fibulin-1C and 1D predominate. The objective of this study was to study the expression of fibulin-1 in volunteers with and without asthma, and to examine its function in vitro.

Methodology/Principal Findings

We used immunohistochemistry and dot-blots to examine fibulin-1 levels in bronchial biopsies, bronchoalveolar lavage fluid and serum. Real-time PCR for fibulin-1C and 1D, and ELISA and western blotting for fibulin-1 were used to study the levels in airway smooth muscle cells. The function of fibulin-1C was determined by assessing its role, using an antisense oligonucleotide, in cell proliferation, migration and wound healing. A murine model of airway hyperresponsiveness (AHR) was used to explore the biological significance of fibulin-1. Levels of fibulin-1 were significantly increased in the serum and bronchoalveolar lavage fluid of 21 asthmatics compared with 11 healthy volunteers. In addition fibulin-1 was increased in asthma derived airway smooth muscle cells and fibulin-1C contributed to the enhanced proliferation and wound repair in these cells. These features were reversed when fibulin-1C was suppressed using an antisense oligomer. In a mouse model of AHR, treatment with an AO inhibited the development of AHR to methacholine.

Conclusions

Our data collectively suggest fibulin-1C may be worthy of further investigation as a target for airway remodeling in asthma.

High-resolution two-dimensional gel electrophoresis analysis of atrial tissue proteome reveals down-regulation of fibulin-1 in atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is the most common cardiac arrhythmia found in clinical practice. We combined high-resolution two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS) to compare the atrial proteome of subjects with AF versus controls with sinus rhythm (SR). Our aim was to identify novel differentially regulated proteins that could be related to the development of the arrhythmia.

METHODS

Human atrial appendage tissue samples from patients undergoing heart surgery with AF or SR were analyzed by high-resolution 2-DE. Proteins of interest were identified by MS and validated by western blotting and inmunohistochemistry.

RESULTS

Our analysis allowed the detection of over 2300 protein spots per gel. Following differential image analysis, we found 22 spot differences between the AF and SR groups in the 4-7 isoelectric point range, leading to the identification of 15 differentially regulated proteins. The main group of proteins identified was that of heat shock proteins (HSPs), including TRAP-1, HspB3, HspΒ6 and AHA1. Some of the differences detected between AF and SR for the above proteins were due to post-translational modifications. In addition, we identified the structural protein fibulin-1 as down-regulated in atrial tissue from AF patients.

CONCLUSIONS

High-resolution 2-DE analysis of human atrial tissue revealed that AF is associated with changes in structural proteins and an important number of HSPs. The lower expression of the structural protein fibulin-1 in atrial tissue from AF patients might reflect the myocardial structural changes that take place in the arrhythmia.

Elastic fiber assembly is disrupted by excessive accumulation of chondroitin sulfate in the human dermal fibrotic disease, keloid

Keloid is a fibrotic disease characterized by abnormal accumulation of extracellular matrix in the dermis. The keloid matrix contains excess collagen and glycosaminoglycans (GAGs), but lacks elastic fiber. However, the roles of these matrix components in the pathogenesis of keloid are largely unknown. Here, we show that elastin and DANCE (also known as fibulin-5), a protein required for elastic fiber formation, are not deposited in the extracellular matrix of keloids, due to excess accumulation of chondoitin sulfate (CS), although the expression of elastin and DANCE is not affected. Amount of CS accumulated in the keloid legion was 6.9-fold higher than in normal skin. Fibrillin-1, a scaffold protein for elastic fiber assembly, was abnormally distributed in the keloid matrix. Addition of purified CS to keloid fibroblast culture resulted in abnormal deposition of fibrillin-1, concomitant with significantly decreased accumulation of elastin and DANCE in the extracellular matrix. We propose that CS plays a crucial role in the development of keloid lesions through inhibition of elastic fiber assembly.

Accumulation of TDP-43 and alpha-actin in an amyotrophic lateral sclerosis patient with the K17I ANG mutation

A K17I mutation in the ANG gene encoding angiogenin has been identified in a case that we previously published as ALS with neuronal intranuclear protein inclusions (Seilhean et al. in Acta Neuropathol 108:81-87, 2004). These inclusions were immunoreactive for smooth muscle alpha-actin but not for angiogenin. Moreover, they were not labeled by anti-TDP-43 antibodies, while numerous cytoplasmic inclusions immunoreactive for ubiquitin, p62 and TDP-43 were detected in both oligodendrocytes and neurons in various regions of the central nervous system. In addition, expression of smooth muscle alpha-actin was increased in the liver where severe steatosis was observed. This is the first neuropathological description of a case with an ANG mutation. Angiogenin is known to interact with actin. Like other proteins involved in ALS pathogenesis, such as senataxin, TDP-43 and FUS/TLS, it plays a role in RNA maturation.

Fibulin-4 regulates expression of the tropoelastin gene and consequent elastic-fibre formation by human fibroblasts

Elastic fibres are essential for normal physiology in numerous tissues, including arteries, lungs and skin. Fibulin-4 is an elastic-fibre-associated glycoprotein that is indispensable for elastic-fibre formation in mice. However, the mechanism by which fibulin-4 executes this function remains to be determined. Here, we established an in vitro functional assay system in which fibulin-4 was knocked down in human foreskin fibroblasts using siRNA (small interfering RNA) technology. With two different siRNAs, substantial knockdown of fibulin-4 was achieved, and this suppression was associated with impaired elastic-fibre formation by the fibroblasts. Real-time reverse transcription-PCR analysis showed that knockdown of fibulin-4 expression was accompanied by reduced expression of tropoelastin mRNA. Further analysis showed that this decrease was caused by transcriptional down-regulation of tropoelastin. This effect was selective, since the mRNA level of other elastic-fibre-associated proteins, including fibrillin-1, lysyl oxidase and lysyl oxidase-like-1, was not affected. Moreover, addition of conditioned medium from cultures of CHO (Chinese-hamster ovary) cells overexpressing fibulin-4 stimulated tropoelastin expression and elastic-fibre formation in cultures of Williams-Beuren-syndrome fibroblasts. Knocking down or knocking out fibulin-4 in mice led to a decrease in tropoelastin expression in the aorta. These results indicate that fibulin-4, considered as a structural protein, may also participate in regulating elastic-fibre formation in human cells through an unanticipated mechanism, namely the regulation of tropoelastin expression.

Fibulin-1 and fibrinogen in human atherosclerotic lesions

Fibulin-1 is a fibrinogen-binding blood protein and a component of many extracellular matrices (ECM) including those of blood vessels. In this study, the deposition patterns of fibulin-1 and fibrinogen were examined in human coronary artery atherosclerotic lesions excised by atherectomy from 20 patients. Fibulin-1 deposition was found to be closely overlapping with fibrinogen located within the atherosclerotic lesions and in regions containing fresh thrombi. Pronounced intracellular fibulin-1 immunostaining was apparent in lesion areas rich in macrophages and foam cells, although THP-1 macrophages and foam cells were found not to express fibulin-1. Strong ECM deposition of fibulin-1 was observed in acellular atheromatous and myxomatous regions. By contrast, fibulin-1 was present at relatively low levels in the ECM associated with smooth muscle cells within and outside of lesions and was not detected in sclerotic regions. These results reveal the pattern of fibulin-1 within human atherosclerotic lesions and highlight the potential for fibulin-1, perhaps derived from the blood and acting in conjunction with fibrinogen, to play a role in the etiology and cardiovascular disease progression, particularly with respect to thrombotic aspects of atherosclerosis.

Expression of ECM proteins fibulin-1 and -2 in acute and chronic liver disease and in cultured rat liver cells

Fibulin-2 has previously been considered as a marker to distinguish rat liver myofibroblasts from hepatic stellate cells. The function of other fibulins in acute or chronic liver damage has not yet been investigated. The aim of this study has been to evaluate the expression of fibulin-1 and -2 in models of rat liver injury and in human liver cirrhosis. Their cellular sources have also been investigated. In normal rat liver, fibulin-1 and -2 were both mainly present in the portal field. Fibulin-1-coding transcripts were detected in total RNA of normal rat liver, whereas fibulin-2 mRNA was only detected by sensitive, real-time quantitative polymerase chain reaction. In acute liver injury, the expression of fibulin-1 was significantly increased (17.23-fold after 48 h), whereas that of fibulin-2 was not modified. The expression of both fibulin-1 and -2 was increased in experimental rat liver cirrhosis (19.16- and 26.47-fold, respectively). At the cellular level, fibulin-1 was detectable in hepatocytes, "activated" hepatic stellate cells, and liver myofibroblasts (2.71-, 122.65-, and 469.48-fold over the expression in normal rat liver), whereas fibulin-2 was restricted to liver myofibroblasts and was regulated by transforming growth factor beta-1 (TGF-beta1) in 2-day-old hepatocyte cultures and in liver myofibroblasts. Thus, fibulin-1 and -2 respond differentially to single and repeated damaging noxae, and their expression is differently present in liver cells. Expression of the fibulin-2 gene is regulated by TGF-beta1 in liver myofibroblasts.

Pathway analysis of differentially expressed genes in patients with acute aortic dissection

Background

Acute aortic dissection (AAD) is a life-threatening condition with high mortality and a relatively unclarified pathophysiological mechanism. Although differentially expressed genes in AAD have been recognized, interactions between these genes remain poorly defined. This study was conducted to gain a better understanding of the molecular mechanisms underlying AAD and to support the future development of a clinical test for monitoring patients at high risk.

Materials and Methods

Aortic tissue was collected from 19 patients with AAD (mean age 61.7 ± 13.1 years), and from eight other patients (mean age 32.9 ± 12.2 years) who carried the mutated gene for Marfan syndrome (MS). Six patients (mean age 56.7 ± 12.3 years) served as the control group. The PIQOR^TM Immunology microarray with 1076 probes in quadruplicates was utilized; the differentially expressed genes were analysed in a MedScan search using Pathway Assist software. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and protein analysis were performed.

Results

Interactions of MS fibrillin-1 (FBN1) in the MedScan pathway analysis showed four genes, fibulin-1 (FBLN1), fibulin-2 (FBLN2), decorin (DCN) and microfibrillar associated protein 5 (MFAP5), which were differentially expressed in all tissue from AAD. The validation of these genes by qRT-PCR revealed a minimum of three-fold downregulation of FBLN1 (0.5 ± 0.4 vs. 6.1 ± 2.3 fold, p = 0.003) and of DCN (2.5 ± 1.0 vs. 8.5 ± 4.7 fold, p = 0.04) in AAD compared to MS and control samples.

Conclusions

Downregulation of fibrillin-1 (FBN1) may weaken extracellular components in the aorta and/or interfer with the transmission of cellular signals and eventually cause AAD. Additional research on these four identified genes can be a starting point to develop a diagnostic tool.

New insights into elastic fiber assembly

Elastic fibers provide recoil to tissues that undergo repeated stretch, such as the large arteries and lung. These large extracellular matrix (ECM) structures contain numerous components, and our understanding of elastic fiber assembly is changing as we learn more about the various molecules associated with the assembly process. The main components of elastic fibers are elastin and microfibrils. Elastin makes up the bulk of the mature fiber and is encoded by a single gene. Microfibrils consist mainly of fibrillin, but also contain or associate with proteins such as microfibril associated glycoproteins (MAGPs), fibulins, and EMILIN-1. Microfibrils were thought to facilitate alignment of elastin monomers prior to cross-linking by lysyl oxidase (LOX). We now know that their role, as well as the overall assembly process, is more complex. Elastic fiber formation involves elaborate spatial and temporal regulation of all of the involved proteins and is difficult to recapitulate in adult tissues. This report summarizes the known interactions between elastin and the microfibrillar proteins and their role in elastic fiber assembly based on in vitro studies and evidence from knockout mice. We also propose a model of elastic fiber assembly based on the current data that incorporates interactions between elastin, LOXs, fibulins and the microfibril, as well as the pivotal role played by cells in structuring the final functional fiber.

Aberrant fibrillin-1 expression in early emphysematous human lung: a proposed predisposition for emphysema

Parenchymal destruction, airspace enlargement, and loss of elasticity are hallmarks of pulmonary emphysema. Although the basic mechanism is unknown, there is a consensus that malfunctioning of the extracellular matrix is a major contributor to the pathogenesis of emphysema. In this study, we analyzed the expression of the elastic fiber protein fibrillin-1 in a large number (n=69) of human lung specimens with early-onset emphysema. Specimens were morphologically characterized by the Destructive Index, the Mean Linear Intercept, and the Panel Grading. We observed a strong correlation (P<0.001) of aberrant fibrillin-1 staining with the degree of destruction of lung parenchyma (r=0.71), airspace enlargement (r=0.47), and emphysema-related morphological abnormalities (r=0.69). There were no obvious correlations with age and smoking behavior. Staining for three other extracellular matrix components (type I collagen, type IV collagen, and laminin) was not affected. The aberrant fibrillin-1 staining observed in this study is similar to that observed in Marfan syndrome, a syndrome caused by mutations in the gene encoding fibrillin-1. Strikingly, emphysema is noticed in a number of Marfan patients. This, together with the notion that disruption of the fibrillin-1 gene in mice results in emphysematous lesions, makes fibrillin-1 a strong candidate to be involved in the etiology and pathogenesis of emphysema.

Fibulin-2 is dispensable for mouse development and elastic fiber formation

Fibulin-2 is an extracellular matrix protein belonging to the five-member fibulin family, of which two members have been shown to play essential roles in elastic fiber formation during development. Fibulin-2 interacts with two major constituents of elastic fibers, tropoelastin and fibrillin-1, in vitro and localizes to elastic fibers in many tissues in vivo. The protein is prominently expressed during morphogenesis of the heart and aortic arch vessels and at early stages of cartilage development. To examine its role in vivo, we generated mice that do not express the fibulin-2 gene (Fbln2) through homologous recombination of embryonic stem cells. Unexpectedly, the fibulin-2-null mice were viable and fertile and did not display gross and anatomical abnormalities. Histological and ultrastructural analyses revealed that elastic fibers assembled normally in the absence of fibulin-2. No compensatory up-regulation of mRNAs for other fibulin members was detected in the aorta and skin tissue. However, in the fibulin-2 null aortae, fibulin-1 immunostaining was increased in the inner elastic lamina, where fibulin-2 preferentially localizes. The results demonstrate that fibulin-2 is not required for mouse development and elastic fiber formation and suggest possible functional redundancy between fibulin-1 and fibulin-2.

Loss of fibulin-2 expression is associated with breast cancer progression

Fibulin-2, an extracellular matrix protein expressed by normal epithelia, was found to be down-regulated in several breast cancer cell lines. Fibulin-2 protein expression was also decreased in breast cancer tissue samples as evaluated by immunohistochemistry. Reintroduction of Fibulin-2 into breast cancer cell lines that do not express Fibulin-2 reduced cancer cell motility and invasion in vitro but had no effect on cell growth and adhesion properties. Together with evidence that Fibulin-2 contributes to wound healing and inhibits smooth muscle cell migration, our findings suggest that loss of Fibulin-2 expression may facilitate migration and invasion in breast cancer.

Regulation of breast cancer response to chemotherapy by fibulin-1

Doxorubicin treatment was found to augment the expression of the extracellular matrix (ECM) protein fibulin-1 in cultured human breast cancer cell lines and in MDA-MB-361 tumors grown in athymic mice. Doxorubicin was also found to augment tumor expression of the fibulin-1-binding proteins fibronectin and laminin-1. Growth of breast cancer cell lines on Matrigel, an ECM extract containing fibulin-1 and laminin-1, resulted in lower levels of doxorubicin-induced apoptosis as compared with controls. Moreover, tumors formed by injection of athymic mice with MDA-MB-361 cells mixed with Matrigel were significantly more doxorubicin resistant and displayed lower levels of apoptosis compared with those that formed in the absence of Matrigel. Monoclonal antibodies against fibulin-1 reversed Matrigel-dependent doxorubicin resistance. Furthermore, small interfering RNA-mediated suppression of fibulin-1 expression in breast cancer cells resulted in a 10-fold increase in doxorubicin sensitivity as compared with control cells. Together, these findings point to a role for fibulin-1 in breast cancer chemoresistance.

Domains 16 and 17 of tropoelastin in elastic fibre formation

Naturally occurring mutations are useful in identifying domains that are important for protein function. We studied a mutation in the elastin gene, 800-3G>C, a common disease allele for SVAS (supravalvular aortic stenosis). We showed in primary skin fibroblasts from two different SVAS families that this mutation causes skipping of exons 16-17 and results in a stable mRNA. Tropoelastin lacking domains 16-17 (Delta16-17) was synthesized efficiently and secreted by transfected retinal pigment epithelium cells, but showed the deficient deposition into the extracellular matrix compared with normal as demonstrated by immunofluorescent staining and desmosine assays. Solid-phase binding assays indicated normal molecular interaction of Delta16-17 with fibrillin-1 and fibulin-5. However, self-association of Delta16-17 was diminished as shown by an elevated coacervation temperature. Moreover, negative staining electron microscopy confirmed that Delta16-17 was deficient in forming fibrillar polymers. Domain 16 has high homology with domain 30, which can form a beta-sheet structure facilitating fibre formation. Taken together, we conclude that domains 16-17 are important for self-association of tropoelastin and elastic fibre formation. This study is the first to discover that domains of elastin play an essential role in elastic fibre formation by facilitating homotypic interactions.

A comparative analysis of the fibulin protein family. Biochemical characterization, binding interactions, and tissue localization

Fibulins are a family of five extracellular matrix proteins characterized by tandem arrays of epidermal growth factor-like domains and a C-terminal fibulin-type module. They are widely distributed and often associated with vasculature and elastic tissues. In this study, we expressed the three more recently identified family members, fibulin-3, fibulin-4, and fibulin-5, as recombinant proteins in mammalian cells. The purified proteins showed short rod structures of approximately 20 nm with a globule at one end, after rotary shadowing and electron microscopy. Two forms of mouse fibulin-3 were purified, and the O-glycan profiles of the larger form were characterized. Polyclonal antibodies raised against the purified proteins did not show any cross-reactivity with other family members and were used to assess the levels and localization of the fibulins in mouse tissues. Their binding interactions, cell adhesive properties, and tissue localization were analyzed in parallel with the previously characterized fibulin-1 and -2. Binding to tropoelastin was strong for fibulin-2 and -5, moderate for fibulin-4 and -1, and relatively weak for fibulin-3. Fibulin-4, but not fibulin-3 and -5, exhibited distinct interactions with collagen IV and nidogen-2 and moderate binding to the endostatin domain from collagen XV. Cell adhesive activities were not observed for all fibulins, except mouse fibulin-2, with various cell lines tested. All five fibulins were found in perichondrium and various regions of the lungs. Immunoelectron microscopy localized fibulin-4 and -5 to fibrillin microfibrils at distinct locations. Our studies suggest there are unique and redundant functions shared by these structurally related proteins.

Knockout mice: is it just genetics? Effect of enriched housing on fibulin-4(+/-) mice

BACKGROUND

Fibulin-4 is an extracellular matrix protein expressed by vascular smooth muscle cells that is essential for maintaining arterial integrity. Fibulin-4(-/-) mice die just before birth due to arterial hemorrhage, but fibulin-4(+/-) mice appear to be outwardly normal. Experiments were therefore performed to determine whether fibulin-4(+/-) mice display arterial pathologies on a microscopic scale. After preliminary experiments were performed, a second purpose developed, which was to test the hypothesis that any observed pathologies would be ameliorated by housing the animals in enriched cages.

METHODOLOGY

Fibulin-4(+/-) and wild-type mice were housed either four/cage in standard cages or two per cage in larger cages, each cage containing a tunnel and a wheel. After three weeks the mice were sacrificed, and the aortas perfusion-fixed and excised for light and electron microscopy.

PRINCIPLE FINDINGS

When the mice were in standard cages, localized regions of disorganized extracellular matrix and collagen fibers consistently appeared between some of the medial smooth muscle cells in the fibulin-4(+/-) mice. In the wild-type mice, the smooth muscle cells were closely connected to each other and the media was more compact. The number of disorganized regions per square mm was significantly greater for fibulin-4(+/-) mice (172+/-43 (SEM)) than for wild-type mice (15+/-8) (p<0.01, n = 8). When the mice were in enriched cages, the fibulin-4(+/-) mice showed significantly fewer disorganized regions than those in standard cages (35+/-12) (p<0.05, n = 8). The wild type mice also showed fewer disorganized regions (3+/-2), but this difference was not significant.

CONCLUSIONS

These results indicate that arterial pathologies manifested in fibulin-4(+/-) mice can be reduced by enriching the housing conditions, and imply that appropriate environments may counteract the effects of some genetic deficiencies.

Fibrillin-1 interactions with fibulins depend on the first hybrid domain and provide an adaptor function to tropoelastin

Fibrillin-containing microfibrils in elastic and nonelastic extracellular matrices play important structural and functional roles in various tissues, including blood vessels, lung, skin, and bone. Microfibrils are supramolecular aggregates of several protein and nonprotein components. Recently, a large region in the N-terminal portion of fibrillin-1 was characterized as a multifunctional protein interaction site, including binding sites for fibulin-2 and -5 among others. Using a panel of recombinant fibrillin-1 swapped domain and deletion fragments, we demonstrate here that the conserved first hybrid domain in fibrillin-1 is essential for binding to fibulin-2, -4, and -5. Fibulin-3 and various isoforms of fibulin-1 did not interact with fibrillin-1. Although the first hybrid domain in fibrillin-1 is located in close vicinity to the self-assembly epitope, binding of fibulin-2, -4, and -5 did not interfere with self-assembly. However, these fibulins can associate with microfibrils at various levels of maturity. Formation of ternary complexes between fibrillin-1, fibulins, and tropoelastin demonstrated that fibulin-2 and -5 but much less fibulin-4, are able to act as molecular adaptors between fibrillin-1 and tropoelastin.

GROalpha is highly expressed in adenocarcinoma of the colon and down-regulates fibulin-1

PURPOSE

The growth-related oncogene alpha (GROalpha) is a secreted interleukin-like molecule that interacts with the CXCR2 G-protein-coupled receptor. We found that the mRNA and protein products of GROalpha are more highly expressed in neoplastic than normal colon epithelium, and we studied potential mechanisms by which GROalpha may contribute to tumor initiation or growth.

EXPERIMENTAL DESIGN

Cell lines that constitutively overexpress GROalpha were tested for growth rate, focus formation, and tumor formation in a xenograft model. GROalpha expression was determined by Affymetrix GeneChip (241 microdissected colon samples), real-time PCR (n = 32), and immunohistochemistry. Primary colon cancer samples were also employed to determine copy number changes and loss of heterozygosity related to the GROalpha and fibulin-1 genes.

RESULTS

In cell cultures, GROalpha transfection transformed NIH 3T3 cells, whereas inhibition of GROalpha by inhibitory RNA was associated with apoptosis, decreased growth rate, and marked up-regulation of the matrix protein fibulin-1. Forced expression of GROalpha was associated with decreased expression of fibulin-1. Expression of GROalpha mRNA was higher in primary adenocarcinomas (n = 132), adenomas (n = 32), and metastases (n = 52) than in normal colon epithelium (P < 0.001). These results were confirmed by real-time PCR and by immunohistochemistry. Samples of primary and metastatic colon cancer showed underexpression of fibulin-1 when compared with normal samples. There were no consistent changes in gene copy number of GROalpha or fibulin-1, implying a transcriptional basis for these findings.

CONCLUSION

Elevated expression of GROalpha is frequent in adenocarcinoma of the colon and is associated with down-regulation of the matrix protein fibulin-1 in experimental models and in clinical samples. GROalpha overexpression abrogates contact inhibition in cell culture models, whereas inhibition of GROalpha expression is associated with apoptosis. Importantly, coexpression of fibulin-1 with GROalpha abrogates key aspects of the transformed phenotype, including tumor formation in a murine xenograft model. Targeting GRO proteins may provide new opportunities for treatment of colon cancer.

Expression and Functional Analysis of Fibulin-1 (Fbln1) During Normal and Abnormal Placental Development of the Mouse

The extracellular matrix protein fibulin-1 (FBLN1) is an important component of blood vessel walls, as shown by the lethality of mice with homozygous targeted deletion of the Fbln1 gene. Here, we show that a murine placental overgrowth phenotype is associated with elevated Fbln1 transcript levels, suggesting that the gene and its product have a functional role in placentation. Fbln1 exhibits a specific expression pattern in the mouse placenta. Transcripts could not be detected prior to day 12. In subsequent stages, Fbln1 was expressed strongly in the spongiotrophoblast. Other sites of expression were endothelia of large fetal blood vessels, a tissue type reported to not express this gene. In addition, a subset of giant cells expressed the gene. This giant cell specific expression was strongly increased in hyperplastic placentas. Analysis of the placentation in fibulin null mice did not show any abnormality. Attempts to rescue the placental phenotypes of a congenic model of interspecies hybrid placental dysplasia (IHPD) by normalizing expression of Fbln1 proved that Fbln1 alone is not the key cause of phenotypes in these models of placental hyperplasia.

Fibulin-4 is a target of autoimmunity predominantly in patients with osteoarthritis

Autoimmunity to chondrocyte-producing proteins has been reported in patients with osteoarthritis (OA) as well as in those with rheumatoid arthritis (RA). To answer whether or not OA-specific autoimmunity exist, we performed screening of chondrocyte-producing autoantigens by two-dimensional electrophoresis and Western blotting with each of 20 OA and 20 RA serum samples. We identified an apparently OA-specific autoantigen spot with a molecular mass of 52 kDa and a Isoelectric point of 4.1 as fibulin-4 by mass fingerprinting. By preparing recombinant proteins of fibulin-4, we determined prevalence of the autoantibodies to fibulin-4 in 92 patients with OA, 67 patients with RA, 40 patients with systemic lupus erythematosus, and 43 patients with systemic scleroderma. As a result, the IgG type anti-fibulin-4 autoantibodies were detected in 23.9% of sera from patients with OA, in 8.9% of sera from patients with RA, in 2.5% of sera from patients with systemic lupus erythematosus, and in 9.3% of sera from patients with systemic scleroderma. Furthermore, we immunized DBA/1J, ICR, BALB/c, and C57BL/6 mice with the recombinant fibulin-4 proteins to investigate arthritogenecity of fibulin-4. As a result, mild synovitis was detected in all of the four strains. In addition, we demonstrated expression of fibulin-4 in chondrocytes at both mRNA and protein levels in vivo and in vitro by RT-PCR, Western blotting, and immunohistochemistry. Taken together, fibulin-4, expressed in chondrocytes and recognized as an autoantigen mainly in OA rather than in RA, may play pathogenic roles in OA.

Elastic fibres and vascular structure in hypertension

Blood vessels are dynamic structures composed of cells and extracellular matrix (ECM), which are in continuous cross-talk with each other. Thus, cellular changes in phenotype or in proliferation/death rate affect ECM synthesis. In turn, ECM elements not only provide the structural framework for vascular cells, but they also modulate cellular function through specific receptors. These ECM-cell interactions, together with neurotransmitters, hormones and the mechanical forces imposed by the heart, modulate the structural organization of the vascular wall. It is not surprising that pathological states related to alterations in the nervous, humoral or haemodynamic environment-such as hypertension-are associated with vascular wall remodeling, which, in the end, is deleterious for cardiovascular function. However, the question remains whether these structural alterations are simply a consequence of the disease or if there are early cellular or ECM alterations-determined either genetically or by environmental factors-that can predispose to vascular remodeling independent of hypertension. Elastic fibres might be key elements in the pathophysiology of hypertensive vascular remodeling. In addition to the well known effects of hypertension on elastic fibre fatigue and accelerated degradation, leading to loss of arterial wall resilience, recent investigations have highlighted new roles for individual components of elastic fibres and their degradation products. These elements can act as signal transducers and regulate cellular proliferation, migration, phenotype, and ECM degradation. In this paper, we review current knowledge regarding components of elastic fibres and discuss their possible pathomechanistic associations with vascular structural abnormalities and with hypertension development or progression.

Lysosomal Sialidase (Neuraminidase-1) Is Targeted to the Cell Surface in a Multiprotein Complex That Facilitates Elastic Fiber Assembly

We have established previously that the 67-kDa elastin-binding protein (EBP), identical to the spliced variant of beta-galactosidase, acts as a recyclable chaperone that facilitates secretion of tropoelastin. (Hinek, A., Keeley, F. W., and Callahan, J. W. (1995) Exp. Cell Res. 220, 312-324). We now demonstrate that EBP also forms a cell surface-targeted molecular complex with protective protein/cathepsin A and sialidase (neuraminidase-1), and provide evidence that this sialidase activity is a prerequisite for the subsequent release of tropoelastin. We found that treatment with sialidase inhibitors repressed assembly of elastic fibers in cultures of human skin fibroblasts, aortic smooth muscle cells, and ear cartilage chondrocytes and caused impaired elastogenesis in developing chick embryos. Fibroblasts derived from patients with congenital sialidosis (primary deficiency of neuraminidase-1) and galactosialidosis (secondary deficiency of neuraminidase-1) demonstrated impaired elastogenesis, which could be reversed after their transduction with neuraminidase-1 cDNA or after treatment with bacterial sialidase, which has a similar substrate specificity to human neuraminidase-1. We postulate that neuraminidase-1 catalyzes removal of the terminal sialic acids from carbohydrate chains of microfibrillar glycoproteins and other adjacent matrix glycoconjugates, unmasking their penultimate galactosugars. In turn, the exposed galactosugars interact with the galectin domain of EBP, thereby inducing the release of transported tropoelastin molecules and facilitating their subsequent assembly into elastic fibers.

Development of a new in vitro model of elastic fiber assembly in human pigmented epithelial cells

OBJECTIVES

We developed an in vitro model of elastic fiber assembly that provides a comparison of the efficiency of different tropoelastin molecules to organize into fibers.

DESIGN AND METHODS

Recombinant tropoelastin was added to ARPE-19 cell culture medium. The elastic fiber assembly was evaluated by immunofluorescence staining, the quantitative analysis of cross-linking amino acids, and semi-quantitative analysis of matrix-associated tropoelastin.

RESULTS

We confirmed that ARPE-19 cells express fibrillin-containing microfibrils and lysyl oxidase, but they do not express tropoelastin. Immunofluorescence staining showed a dose- and time-dependent increase in the extracellular matrix. The quantity of cross-linking amino acids and matrix-associated tropoelastin also increased together with the matrix-associated elastin. Moreover, the analysis of a radioimmunoprecipitation assay (RIPA) buffer-soluble fraction indicated that tropoelastin interacted with microfibrils and cross-linked elastin was detected as a super molecular complex.

CONCLUSION

These observations indicate that this in vitro model is especially useful for the analysis of mechanisms of elastic fiber formation.

Fibulins and cancer: friend or foe?

The fibulins are a family of secreted glycoproteins, which are characterised by repeated epidermal-growth-factor-like domains and a unique C-terminal structure. Six distinct fibulin genes, encoding at least nine protein products generated by alternative splicing, have been identified. Considerable evidence is available pointing towards a structural role for fibulins within the extracellular matrix. Fibulins have been shown to modulate cell morphology, growth, adhesion and motility. The dysregulation of certain fibulins occurs in a range of human disorders, including cancer. Indeed, both tumour suppressive and oncogenic activities have been proposed for members of the fibulin family. Herein, we discuss the possible roles of fibulins in cancer, in addition to their diagnostic and therapeutic potential.

Fibulin-5 deposition in human skin: decrease with ageing and ultraviolet B exposure and increase in solar elastosis

BACKGROUND

Fibulin-5 was recently found as a secreted extracellular matrix protein that functions as a scaffold for elastic fibres. However, the distribution of fibulin-5 in human skin and its changes during the ageing process are not known.

OBJECTIVES

To explore the involvement of fibulin-5 in skin ageing, the age-dependent changes in fibulin-5 localization in human skin were examined compared with those of other elastic fibre components including elastin, fibrillin-1 and fibulin-2. Methods The distribution of elastin, fibrillin-1, fibrillin-2, fibulin-2 and fibulin-5 was investigated by means of immunohistochemistry using their specific antibodies. Skin samples were recovered from 12 healthy subjects undergoing plastic surgery. Ultraviolet (UV) B-irradiated or control nonirradiated buttock skin samples were obtained from two healthy volunteers at 2 days after the irradiation at 2 minimal erythemal doses.

RESULTS

In the reticular dermis of young sun-protected skin from the upper arm, fibulin-5 colocalized with the other elastic fibre components, while in the papillary dermis fibulin-5 showed candelabra-like structures perpendicular to the epidermis with an unstained area just beneath the epidermis, which was similar to that of elastin but not fibrillin-1. Fibulin-5 in the reticular dermis decreased and disappeared with age even in sun-protected skin from the thigh, abdomen and upper arm. In sun-exposed skin, fibulin-5 was extremely reduced in the dermis of cheek skin even from a 20-year-old man. UVB irradiation reduced fibulin-5, fibulin-2 and elastin markedly, moderately and weakly, respectively, compared with levels in control nontreated skin. Interestingly, the deposition of fibulin-5 was increased in solar elastosis, like that of other elastic fibre components.

CONCLUSIONS

These results suggest that fibulin-5 is a good marker of skin ageing and that the earlier loss of fibulin-5 may involve age-dependent changes in other elastic fibre components.

Progesterone induces the fibulin-1 expression in human endometrial stromal cells

BACKGROUND

By using microarray analysis with human endometrial stromal cells (ESCs), we previously reported that the mRNA for fibulin-1, an extracellular matrix as well as a plasma glycoprotein, is up-regulated by progesterone. In the present study, we tried to clarify the spatial and temporal regulation mechanism of fibulin-1 in the human endometrium.

METHODS AND RESULTS

Quantitative analysis with real-time PCR experiments on human endometrial tissues showed significantly higher fibulin-1 mRNA expressions in secretory phase endometria than in proliferative phase. Immunohistochemical studies revealed that the fibulin-1 protein is expressed in the glandular epithelium in proliferative phase endometria, and that expression switched to the stroma in secretory phase endometria. In culture experiments with ESCs, a significant increase of fibulin-1 mRNA expression was observed in cells treated with 6 alpha-methyl-17 alpha-hydroxy-progesterone acetate (MPA) or 8 bromoadenosine 3':5'-cyclic monophosphate (8-Br-cAMP). MPA stimulated the fibulin-1 mRNA expression in a dose-dependent manner, and a progesterone antagonist, RU-486, inhibited the stimulatory effect almost completely. By contrast, beta-estradiol alone did not increase the fibulin-1 mRNA expression.

CONCLUSIONS

These results suggest that fiblin-1 is an important molecule that mediates progesterone action in human ESC differentiation towards implantation.

Extracellular matrix alterations in brains lacking four of its components

The organization of the brain extracellular matrix appears to be based on aggregates of hyaluronan and proteoglycans, connected by oligomeric glycoproteins. Mild phenotypical consequences were reported from several mouse strains lacking components of this matrix such as neurocan, brevican, tenascin-R, and tenascin-C. To further challenge the flexibility of the extracellular matrix network of the brain, mice lacking all four brain extracellular matrix molecules were generated, which were found to be viable and fertile. Analysis of the brains of 1-month-old quadruple KO mice revealed increased protein levels of fibulin-1 and fibulin-2. Histochemical analysis showed an unusual parenchymal deposition of these fibulins. The quadruple KO mice also displayed obvious changes in the pattern of deposition of hyaluronan. Further, an almost quadruple knockout like extracellular environment was noticed in the brains of triple knockout mice lacking both tenascins and brevican, since these brains had strongly reduced levels of neurocan.

FGF-18 is upregulated in the postnatal rat lung and enhances elastogenesis in myofibroblasts

The fibroblast growth factors (FGFs) are key players in fetal lung development, but little is known about their status in postnatal lung. Here, we investigated the expression pattern of FGF-18 transcripts through the perinatal period and evidenced a sevenfold increase after birth that paralleled changes in elastin expression. In vitro, recombinant human (rh)FGF-18 had a mitogenic activity on day 21 fetal rat lung fibroblasts and stimulated its own expression in the latter, whereas FGF-2 inhibited it. At 50 or 100 ng/ml, rhFGF-18 increased the expression of α-smooth muscle actin (α-SMA; 2.5-fold), a characteristic marker of myofibroblasts, of tropoelastin (6.5-fold), of lysyl oxidase (2-fold), and of fibulins 1 and 5 (8- and 2.2-fold) in confluent fibroblasts isolated from fetal day 21 lung; similar results were obtained with fibroblasts from day 3 postnatal lungs. Elastin protein expression was also slightly increased in fetal fibroblasts. Lung analysis on day 4 in rat pups that had received rhFGF-18 (3 μg) on days 0 and 1 showed a 1.7-fold increase of tropoelastin transcripts, whereas α-SMA transcripts were unchanged. In contrast, rhFGF-2 markedly decreased expression of elastin in vitro and in vivo and of fibulin 5 in vitro. In addition, vitamin A, which is known to enhance alveolar development, elevated FGF-18 and elastin expressions in day 2 lungs, thus advancing the biological increase. We postulate that FGF-18 is involved in postnatal lung development through stimulating myofibroblast proliferation and differentiation.

Elastin

Elastin is a key extracellular matrix protein that is critical to the elasticity and resilience of many vertebrate tissues including large arteries, lung, ligament, tendon, skin, and elastic cartilage. Tropoelastin associates with multiple tropoelastin molecules during the major phase of elastogenesis through coacervation, where this process is directed by the precise patterning of mostly alternating hydrophobic and hydrophilic sequences that dictate intermolecular alignment. Massively crosslinked arrays of tropoelastin (typically in association with microfibrils) contribute to tissue structural integrity and biomechanics through persistent flexibility, allowing for repeated stretch and relaxation cycles that critically depend on hydrated environments. Elastin sequences interact with multiple proteins found in or colocalized with microfibrils, and bind to elastogenic cell surface receptors. Knowledge of the major stages in elastin assembly has facilitated the construction of in vitro models of elastogenesis, leading to the identification of precise molecular regions that are critical to elastin-based protein interactions.

Fluctuations of intracellular iron modulate elastin production

Production of insoluble elastin, the major component of elastic fibers, can be modulated by numerous intrinsic and exogenous factors. Because patients with hemolytic disorders characterized with fluctuations in iron concentration demonstrate defective elastic fibers, we speculated that iron might also modulate elastogenesis. In the present report we demonstrate that treatment of cultured human skin fibroblasts with low concentration of iron 2-20 microm (ferric ammonium citrate) induced a significant increase in the synthesis of tropoelastin and deposition of insoluble elastin. Northern blot and real-time reverse transcription-PCR analysis revealed that treatment with 20 microm iron led to an increase of approximately 3-fold in elastin mRNA levels. Because treatment with an intracellular iron chelator, desferrioxamine, caused a significant decrease in elastin mRNA level and consequent inhibition of elastin deposition, we conclude that iron facilitates elastin gene expression. Our experimental evidence also demonstrates the existence of an opposite effect, in which higher, but not cytotoxic concentrations of iron (100-400 microm) induced the production of intracellular reactive oxygen species that coincided with a significant decrease in elastin message stability and the disappearance of iron-dependent stimulatory effect on elastogenesis. This stimulatory elastogenic effect was reversed, however, in cultures simultaneously treated with high iron concentration (200 microm) and the intracellular hydroxyl radical scavenger, dimethylthiourea. Thus, presented data, for the first time, demonstrate the existence of two opposite iron-dependent mechanisms that may affect the steady state of elastin message. We speculate that extreme fluctuations in intracellular iron levels result in impaired elastic fiber production as observed in hemolytic diseases.

Fibulins: physiological and disease perspectives

The fibulins are a family of proteins that are associated with basement membranes and elastic extracellular matrix fibres. This review summarizes findings from studies of animal models of fibulin deficiency, human fibulin gene mutations, human tumours and injury models that have advanced our understanding of the normal and pathological roles of members of this formerly obscure family.

MAGP-2 has multiple binding regions on fibrillins and has covalent periodic association with fibrillin-containing microfibrils

The interactions of microfibril-associated glycoprotein (MAGP)-2 have been investigated with fibrillins and fibrillin-containing microfibrils. Solid phase binding assays were conducted with recombinant fragments covering fibrillin-1 and most of fibrillin-2. MAGP-2, and its structure relative MAGP-1, were found to bind two fragments spanning the N-terminal half of fibrillin-1 and an N-terminal fragment of fibrillin-2. Blocking experiments indicated that MAGP-2 had a binding site(s) close to the N terminus of the fibrillin-1 molecule that was distinct from that for MAGP-1 and an additional, more central binding site(s) that may be shared by the two MAGPs. Immunogold labeling of developing nuchal ligament tissue showed that MAGP-2 had regular covalent and periodic (about 56 nm) association with fibrillin-containing microfibrils of elastic fibers in this tissue. Further analysis of isolated microfibrils indicated that MAGP-2 was attached at two points along the microfibril substructure, "site 1" on the "beads" and "site 2" at the "shoulder" of the interbead region close to where the two "arms" fuse. In contrast, MAGP-1 was located only on the beads. Comparison of the MAGP-2 binding data with known fibrillin epitope maps of the microfibrils showed that site 1 correlated with the N-terminal MAGP-2 binding region, and site 2 correlated with the second, more central, MAGP-2 binding region on the fibrillin-1 molecule. Of particular note, immunolabeling at site 2 was markedly decreased, relative to that at site 1, on extended microfibrils with bead-to-bead periods over 90 nm, suggesting that site 2 may move toward the beads when the microfibril is stretched. The study points to MAGP-2 being an integral component of some populations of fibrillin-containing microfibrils. Moreover, the identification of multiple MAGP-binding sequences on fibrillins supports the concept that MAGPs may function as molecular cross-linkers, stabilizing fibrillin monomers in folded conformation within or between the microfibrils, and thus MAGPs may be implicated in the modulation of the elasticity of these structures.

Immunological and pathobiological roles of fibulin-1 in breast cancer

Fibulin-1 (Fbln-1) is an immunogenic breast cancer-related glycoprotein identified by serological analysis of cDNA expression library (SEREX) strategy. Here, we show that dendritic cells from two breast cancer patients elicited a CD4(+)-mediated T-cell response to Fbln-1 presentation. In both patients, an antibody response to Fbln-1 was also found. By contrast, a Fbln-1-seronegative patient and a weakly seropositive patient demonstrated no such T-cell response. Analysis of human breast cancers for Fbln-1 RNA and protein expression revealed the presence of Fbln-1C and -1D variants. Fbln-1 was detected in the cytoplasm and at the cell surface of different human breast carcinoma cell lines. Immunohistochemical analysis of 528 archival primary breast carcinomas showed the expression of Fbln-1 in 35% of the cases. When the immunohistochemical findings were compared against pathobiological information associated with each specimen, an inverse relationship between Fbln-1 and cathepsin D expression was observed (P=0.04). Furthermore, even though long-term survival was similar between Fbln-1-positive and -negative cases, the survival of Fbln-1-positive cases improved when a lymphoid infiltrate was present at the tumour site. Taken together, our findings of an Fbln-1-specific immunity and the improved survival associated with Fbln-1 expression in the presence of lymphoid infiltration point to a role of Fbln-1 in tumour immunosurveillance.

Fibulins in development and heritable disease

Fibulins are a family of five extracellular glycoproteins found in a variety of tissues in association with diverse supramolecular structures, including elastic fibers, basement membrane networks, fibronectin microfibrils, and proteoglycan aggregates. Studies of the developmental expression patterns have indicated that several fibulins are prominently expressed at sites of epithelial-mesenchymal transformations during embryogenesis; among these sites, the cardiovascular system has been analyzed in more detail. Gene targeting of fibulins in mice has provided important insights into their biological roles, and has led to the identification of gene mutations in a congenital disorder of humans, cutis laxa. Genetic linkage and molecular studies have also associated several fibulin genes with various human heritable disorders that affect a wide range of organs, including limb, eye, blood, and arteries. In this review, we discuss the role of fibulins in development, with an emphasis on the cardiovascular system, and their involvement in human genetic disease.

MYH9 spectrum of autosomal-dominant giant platelet syndromes: unexpected association with fibulin-1 variant-D inactivation

The autosomal-dominant giant platelet syndromes (Fechtner, Epstein, and Sebastian platelet syndromes and May-Hegglin anomaly) represent a group of disorders characterized by variable degrees of macrothrombocytopenia with further combinations of neutrophil inclusion bodies and Alport-like syndrome manifestations, namely, deafness, renal disease, and eye abnormalities. The disease-causing gene of these giant platelet syndromes was previously mapped by us to chromosome 22. Following their successful mapping, these syndromes were shown to represent a broad phenotypic spectrum of disorders caused by different mutations in the nonmuscle myosin heavy chain 9 gene (MYH9). In this study, we examined the potential role of another gene, fibulin-1, encoding an extracellular matrix protein as a disease modifier. Eight unrelated families with autosomal-dominant giant platelet syndromes were studied for DNA sequence mutations and expression of the four fibulin-1 splice variants (A-D). A mutation in the splice acceptor site of fibulin-1 exon 19 was found in affected individuals of the Israeli Fechtner family, whereas no MYH9 mutations were identified. Unexpectedly, fibulin-1 variant D expression was absent in affected individuals from all eight families and coupled with expression of a putative antisense RNA. Transfection of the putative antisense RNA into H1299 cells abolished variant D expression. Based on the observation that only affected individuals lack variant D expression and demonstrate antisense RNA overexpression, we suggest that these autosomal-dominant giant platelet syndromes are associated, and may be modified, by aberrant antisense gene regulation of the fibulin-1 gene.

Monoclonal antibody to fibulin-1 generated by genetic immunization

Fibulin-1 (Fbln-1) is an extracellular matrix (ECM) and plasma glycoprotein. Considering the growing evidence indicating that Fbln-1 plays a role in cancer we sought to develop monospecific antibodies to better facilitate further studies of the function of Fbln-1 in breast cancer. Using a plasmid expression vector encoding full-length human Fbln-1D as an immunogen and CpG oligodeoxyribonucleotides as adjuvant a monoclonal antibody (MAb) against Fbln-1 was produced. This MAb, designated MEM-2 was of IgM isotype and reacted with bacterially expressed Fbln-1. Furthermore, MEM-2 reacted with Fbln-1 expressed in the ECM released by cultured human breast carcinoma SKBR-3 cells in ELISA, and also with Fbln-1 present in SKBR-3 cell extract in immunoprecipitation and Western blotting. MEM-2 also reacted with Fbln-1 in human breast carcinoma specimens. These findings illustrate the utility of genetic immunization as a means of generating monoclonal antibodies to tumor-related ECM proteins. MEM-2 represents a useful new tool for the study of Fbln-1 in breast cancer.

Pseudoxanthoma elasticum: a clinical, histopathological, and molecular update

Pseudoxanthoma elasticum is an autosomally inherited disorder that is associated with the accumulation of mineralized and fragmented elastic fibers in the skin, Bruch's membrane in the retina, and vessel walls. The ophthalmic and dermatologic expression of pseudoxanthoma elasticum and its vascular complications are heterogeneous, with considerable variation in phenotype, progression, and mode of inheritance. Using linkage analysis and mutation detection techniques, mutations in the ABCC6 gene were recently implicated in the etiology of pseudoxanthoma elasticum. ABCC6 encodes the sixth member of the ATP-binding cassette transporter and multidrug resistance protein family (MRP6). In humans, this transmembrane protein is highly expressed in the liver and kidney. Lower expression was found in tissues affected by pseudoxanthoma elasticum, including skin, retina, and vessel walls. So far, the substrates transported by the ABCC6 protein and its physiological role in the etiology of pseudoxanthoma elasticum are not known. A functional transport study of rat MRP6 suggests that small peptides such as the endothelin receptor antagonist BQ123 are transported by MRP6. Similar molecules transported by ABCC6 in humans may be essential for extracellular matrix deposition or turnover of connective tissue at specific sites in the body. One of these sites is Bruch's membrane. This review is an update on etiology of pseudoxanthoma elasticum, including its clinical and genetic features, pathogenesis, and biomolecular basis.

Fibulins: a versatile family of extracellular matrix proteins

Fibulins are a newly recognized family of extracellular matrix proteins. The five known members of the family share an elongated structure and many calcium-binding sites, owing to the presence of tandem arrays of epidermal growth factor-like domains. They have overlapping binding sites for several basement-membrane proteins, tropoelastin, fibrillin, fibronectin and proteoglycans, and they participate in diverse supramolecular structures. New insights into their biological roles are now emerging from studies of transgenic mice and of some inherited human diseases.

Codistribution analysis of elastin and related fibrillar proteins in early vertebrate development

Elastin is an extracellular matrix protein found in adult and neonatal vasculature, lung, skin and connective tissue. It is secreted as tropoelastin, a soluble protein that is cross-linked in the tissue space to form an insoluble elastin matrix. Cross-linked elastin can be found in association with several microfibril-associated proteins including fibrillin-1, fibrillin-2 and fibulin-1 suggesting that these proteins contribute to elastic fiber assembly, structure or function. To date, the earliest reported elastin expression was in the conotruncal region of the developing avian heart at 3.5 days of gestation. Here we report that elastin expression begins at significantly earlier developmental stages. Using a novel immunolabeling method, the deposition of elastin, fibrillin-1 and -2 and fibulin-1 was analyzed in avian embryos at several time points during the first 2 days of development. Elastin was found at the midline associated with axial structures such as the notochord and somites at 23 h of development. Fibrillin-1 and -2 and fibulin-1 were also expressed at the embryonic midline at this stage with fibrillin-1 and fibulin-1 showing a high degree of colocalization with elastin in fibers surrounding midline structures. The expression of these genes was confirmed by conventional immunoblotting and mRNA detection methods. Our results demonstrate that elastin polypeptide deposition occurs much earlier than was previously appreciated. Furthermore, the results suggest that elastin deposition at the early embryonic midline is accompanied by the deposition and organization of a number of extracellular matrix polypeptides. These filamentous extracellular matrix structures may act to transduce or otherwise stabilize dynamic forces generated during embryogenesis.

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.

New insights into the role of extracellular matrix during tumor onset and progression

Recently, a view of the tumor as a functional tissue interconnected with the microenvironment has recently been described. For many years, the stroma has been studied in the context of the malignant lesion, and only rarely has its role been considered before carcinogenic lesions appear. Recent studies have provided evidence that stromal cells and their products can cause the transformation of adjacent cells through transient signaling that leads to the disruption of homeostatic regulation, including control of tissue architecture, adhesion, cell death, and proliferation. It is now well established that tumor progression requires a continually evolving network of interactions between neoplastic cells and extracellular matrix. A relevant step of this process is the remodeling of microenvironment which surrounds tumors leading to the release of ECM-associated growth factors which can then stimulate tumor and/or endothelial cells. Finally, tumor cells reorganizing the extracellular matrix to facilitate communications and escape the homeostatic control exerted by the microenvironment modify response to cytotoxic treatments.

Context-specific effects of fibulin-5 (DANCE/EVEC) on cell proliferation, motility, and invasion. Fibulin-5 is induced by transforming growth factor-beta and affects protein kinase cascades

Fibulin-5 (FBLN-5; also known as DANCE or EVEC) is an integrin-binding extracellular matrix protein that mediates endothelial cell adhesion; it is also a calcium-dependent elastin-binding protein that scaffolds cells to elastic fibers, thereby preventing elastinopathy in the skin, lung, and vasculature. Transforming growth factor-beta (TGF-beta) regulates the production of cytokines, growth factors, and extracellular matrix proteins by a variety of cell types and tissues. We show here that TGF-beta stimulates murine 3T3-L1 fibroblasts to synthesize FBLN-5 transcript and protein through a Smad3-independent pathway. Overexpression of FBLN-5 in 3T3-L1 cells increased DNA synthesis and enhanced basal and TGF-beta-stimulated activation of ERK1/ERK2 and p38 mitogen-activated protein kinase (MAPK). FBLN-5 overexpression also augmented the tumorigenicity of human HT1080 fibrosarcoma cells by increasing their DNA synthesis, migration toward fibronectin, and invasion through synthetic basement membranes. In stark contrast, FBLN-5 expression was down-regulated in the majority of metastatic human malignancies, particularly in cancers of the kidney, breast, ovary, and colon. Unlike its proliferative response in fibroblasts, FBLN-5 overexpression in mink lung Mv1Lu epithelial cells resulted in an antiproliferative response, reducing their DNA synthesis and cyclin A expression. Moreover, FBLN-5 synergizes with TGF-beta in stimulating AP-1 activity in Mv1Lu cells, an effect that was abrogated by overexpression of dominant-negative versions of either MKK1 or p38 MAPKalpha. Accordingly, both the stimulation and duration of ERK1/ERK2 and p38 MAPK by TGF-beta was enhanced in Mv1Lu cells expressing FBLN-5. Our findings identify FBLN-5 as a novel TGF-beta-inducible target gene that regulates cell growth and motility in a context-specific manner and affects protein kinase activation by TGF-beta. Our findings also indicate that aberrant FBLN-5 expression likely contributes to tumor development in humans.