Localization of heparin-binding epidermal growth factor-like growth factor in human coronary arteries. Possible roles of HB-EGF in the formation of coronary atherosclerosis

Identification of Critical Genes Differentiating Stable and Unstable Atherosclerotic Plaques: A Bioinformatic and Computational Analysis

BACKGROUND

Identification of biomarkers to distinguish between stable and unstable plaque formation would be very useful to predict plaque vulnerability.

METHODS

We downloaded microarray profiles of gene set enrichment (GSE) accession numbers including GSE71226 and GSE20680 (group A: containing healthy vs stable plaque samples) and GSE62646 and GSE34822 (group B: containing stable vs unstable plaque samples) from Gene expression omnibus (GEO) database. Differentially expressed genes were compared in both data sets of each group.

RESULTS

Ten and 12 key genes were screened in groups A and B, respectively. Gene Ontology (GO) enrichment was applied by the plugin "BiNGO" (Biological networks gene ontology tool) of the Cytoscape. The key genes were mostly enriched in the biological process of positive regulation of the cellular process. The protein-protein interaction and co-expression network were analyzed by the STRING (search tool for the retrieval of interacting genes/proteins) and GeneMANIA (gene multiple association network integration algorithm) plugin of Cytoscape, respectively, which showed that Epidermal growth factor (EGF), Heparin-binding EGF like growth factor (HBEGF), and Matrix metalloproteinase 9 (MMP9) were at the core of the network. Further validation of key genes using two datasets showed that Phosphodiesterase 5A (PDE5A) and Protein S (PROS1) were decreased in unstable plaques, while Suppressor of cytokine signaling (SOCS3), HBEGF, and Leukocyte immunoglobulin-like receptor B4 (LILRB4) were increased.

CONCLUSION

The present study used several datasets to identify key genes associated with stable and unstable atherosclerotic plaque.

Expanding the Disorder-Function Paradigm in the C-Terminal Tails of Erbbs

ErbBs are receptor tyrosine kinases involved not only in development, but also in a wide variety of diseases, particularly cancer. Their extracellular, transmembrane, juxtamembrane, and kinase folded domains were described extensively over the past 20 years, structurally and functionally. However, their whole C-terminal tails (CTs) following the kinase domain were only described at atomic resolution in the last 4 years. They were shown to be intrinsically disordered. The CTs are known to be tyrosine-phosphorylated when the activated homo- or hetero-dimers of ErbBs are formed. Their phosphorylation triggers interaction with phosphotyrosine binding (PTB) or Src Homology 2 (SH2) domains and activates several signaling pathways controling cellular motility, proliferation, adhesion, and apoptosis. Beyond this passive role of phosphorylated domain and site display for partners, recent structural and function studies unveiled active roles in regulation of phosphorylation and interaction: the CT regulates activity of the kinase domain; different phosphorylation states have different compaction levels, potentially modulating the succession of phosphorylation events; and prolines have an important role in structure, dynamics, and possibly regulatory interactions. Here, we review both the canonical role of the disordered CT domains of ErbBs as phosphotyrosine display domains and the recent findings that expand the known range of their regulation functions linked to specific structural and dynamic features.

Progression from normal vessel wall to atherosclerotic plaque: lessons from an optical coherence tomography study with follow-up of over 5 years

The initial process of atherosclerotic development has not been systematically evaluated. This study aimed to observe atherosclerotic progression from normal vessel wall (NVW) to atherosclerotic plaque and examine local factors associated with such progression using > 5-year long-term follow-up data obtained by serial optical coherence tomography (OCT). A total of 49 patients who underwent serial OCT for lesions with NVW over 5 years (average: 6.9 years) were enrolled. NVW was defined as a vessel wall with an OCT-detectable three-layer structure and intimal thickness ≤ 300 μm. Baseline and follow-up OCT images were matched, and OCT cross sections with NVW > 30° were enrolled. Cross sections were diagnosed as "progression" when the NVW in these cross sections was reduced by > 30° at > 5-year follow-up. Atherogenic progression from NVW to atherosclerotic plaque was observed in 40.8% of enrolled cross sections. The incidence of microchannels in an adjacent atherosclerotic plaque within the same cross section (6.7 vs. 3.3%; p = 0.046) and eccentric distribution of atherosclerotic plaque (25.0 vs. 12.6%; p < 0.001) at baseline was significantly higher in cross sections with progression than in those without. Cross sections with progression exhibited significantly higher NVW intimal thickness at baseline than cross sections without progression (200.1 ± 53.7 vs. 180.2 ± 59.6 μm; p < 0.001). Multivariate analysis revealed that the presence of microchannels in an adjacent atherosclerotic plaque, eccentric distribution of atherosclerotic plaque, and greater NVW intimal thickness at baseline were independently associated with progression at follow-up. The presence of microchannels in an adjacent atherosclerotic plaque, eccentric distribution of atherosclerotic plaque, and greater NVW intimal thickness were potentially associated with initial atherosclerotic development from NVW to atherosclerotic plaque.

Role of Heparin-Binding Epidermal Growth Factor-Like Growth Factor in Oxidative Stress-Associated Metabolic Diseases

Heparin-binding EGF-like growth factor (HB-EGF) is an EGF family member that interacts with epidermal growth factor receptor (EGFR) and ERBB4. Since HB-EGF was first identified as a novel growth factor secreted from a human macrophage cell line, numerous pathological and physiological functions related to cell proliferation, migration, and inflammation have been reported. Notably, the expression of HB-EGF is sensitively upregulated by oxidative stress in the endothelial cells and functions for auto- and paracrine-EGFR signaling. Overnutrition and obesity cause elevation of HB-EGF expression and EGFR signaling in the hepatic and vascular systems. Modulations of HB-EGF signaling showed a series of protections against phenotypes related to metabolic syndrome and advanced metabolic diseases, suggesting HB-EGF as a potential target against metabolic diseases.

Atherosclerosis and the Capillary Network; Pathophysiology and Potential Therapeutic Strategies

Atherosclerosis and associated ischemic organ dysfunction represent the number one cause of mortality worldwide. While the key drivers of atherosclerosis, arterial hypertension, hypercholesterolemia and diabetes mellitus, are well known disease entities and their contribution to the formation of atherosclerotic plaques are intensively studied and well understood, less effort is put on the effect of these disease states on microvascular structure an integrity. In this review we summarize the pathological changes occurring in the vascular system in response to prolonged exposure to these major risk factors, with a particular focus on the differences between these pathological alterations of the vessel wall in larger arteries as compared to the microcirculation. Furthermore, we intend to highlight potential therapeutic strategies to improve microvascular function during atherosclerotic vessel disease.

Circulating levels of inflammatory parameters pentraxin-3, cyclophilin and heparin-binding epidermal growth factor-like growth factor in patients with ST-elevation myocardial infarction

Inflammatory biomarkers - pentraxin-3 (PTX3), cyclophilin A (CypA) and heparin-binding epidermal growth factor-like growth factor (HB-EGF) were examined in patients with ST-segment elevation myocardial infarction (STEMI) undergoing revascularization with primary percutaneous coronary intervention (pPCI) and stent implanting. Investigated parameters were compared between patients with and without obstructive coronary artery disease (CAD). In addition, their changes were tested in circulation before and immediately after pPCI. The study group consisted of 81 STEMI patients. Patients were classified in the STEMI-CAD group if they had significant obstructive CAD or in MINOCA group if they had no significant stenosis. In STEMI-CAD patients inflammatory parameters were determined prior to and after pPCI intervention. Immediately after pPCI, in STEMI-CAD patients levels of PTX3 were significantly lower (1.52 vs. 2.17 μg/L, p < .001), while the levels of HB-EGF (14.61 vs. 12.03 pg/L, p < .001) and CyPA (15.95 vs. 8.62 μg/L, p < .001) were significantly higher compared to levels before pPCI. STEMI-CAD patients had lower PTX3 values 2.17 μg/L (1.55-5.10 μg/L) than MINOCA patients 5.06 μg/L (2.77-6.7 μg/L), p = .046. Diagnostic accuracy of PTX3 for discrimination MINOCA from STEMI-CAD patients was low (area under receiver operating characteristic curve = 0.770). Evaluation of PTX3 values may be helpful in the understanding of MINOCA aetiology but they couldn't distinguish stenosis severity in STEMI patients. Inflammatory biomarkers significantly changed after pPCI but the possibility of clinical use of these biomarkers needs to be evaluated in a larger prospective study.

Smooth muscle cell fate and plasticity in atherosclerosis

Current knowledge suggests that intimal smooth muscle cells (SMCs) in native atherosclerotic plaque derive mainly from the medial arterial layer. During this process, SMCs undergo complex structural and functional changes giving rise to a broad spectrum of phenotypes. Classically, intimal SMCs are described as dedifferentiated/synthetic SMCs, a phenotype characterized by reduced expression of contractile proteins. Intimal SMCs are considered to have a beneficial role by contributing to the fibrous cap and thereby stabilizing atherosclerotic plaque. However, intimal SMCs can lose their properties to such an extent that they become hard to identify, contribute significantly to the foam cell population, and acquire inflammatory-like cell features. This review highlights mechanisms of SMC plasticity in different stages of native atherosclerotic plaque formation, their potential for monoclonal or oligoclonal expansion, as well as recent findings demonstrating the underestimated deleterious role of SMCs in this disease.

Heparin-binding EGF-like growth factor (HB-EGF) antisense oligonucleotide protected against hyperlipidemia-associated atherosclerosis

BACKGROUND AND AIMS

Heparin-binding EGF-like growth factor (HB-EGF) is a representative EGF family member that interacts with EGFR under diverse stress environment. Previously, we reported that the HB-EGF-targeting using antisense oligonucleotide (ASO) effectively suppressed an aortic aneurysm in the vessel wall and circulatory lipid levels. In this study, we further examined the effects of the HB-EGF ASO administration on the development of hyperlipidemia-associated atherosclerosis using an atherogenic mouse model.

METHODS AND RESULTS

The male and female LDLR deficient mice under Western diet containing 21% fat and 0.2% cholesterol content were cotreated with control and HB-EGF ASOs for 12 weeks. We observed that the HB-EGF ASO administration effectively downregulated circulatory VLDL- and LDL-associated lipid levels in circulation; concordantly, the HB-EGF targeting effectively suppressed the development of atherosclerosis in the aorta. An EGFR blocker BIBX1382 administration suppressed the hepatic TG secretion rate, suggesting a positive role of the HB-EGF signaling for the hepatic VLDL production. We newly observed that there was a significant improvement of the insulin sensitivity by the HB-EGF ASO administration in a mouse model under the Western diet as demonstrated by the improvement of the glucose and insulin tolerances.

CONCLUSION

The HB-EGF ASO administration effectively downregulated circulatory lipid levels by suppressing hepatic VLDL production rate, which leads to effective protection against atherosclerosis in the vascular wall.

Targeting hepatic heparin-binding EGF-like growth factor (HB-EGF) induces anti-hyperlipidemia leading to reduction of angiotensin II-induced aneurysm development

Objective

The upregulated expression of heparin binding EGF-like growth factor (HB-EGF) in the vessel and circulation is associated with risk of cardiovascular disease. In this study, we tested the effects of HB-EGF targeting using HB-EGF-specific antisense oligonucleotide (ASO) on the development of aortic aneurysm in a mouse aneurysm model.

Approach and results

Low-density lipoprotein receptor (LDLR) deficient mice (male, 16 weeks of age) were injected with control and HB-EGF ASOs for 10 weeks. To induce aneurysm, the mice were fed a high fat diet (22% fat, 0.2% cholesterol; w/w) at 5 week point of ASO administration and infused with angiotensin II (AngII, 1,000ng/kg/min) for the last 4 weeks of ASO administration. We confirmed that the HB-EGF ASO administration significantly downregulated HB-EGF expression in multiple tissues including the liver. Importantly, the HB-EGF ASO administration significantly suppressed development of aortic aneurysms including thoracic and abdominal types. Interestingly, the HB-EGF ASO administration induced a remarkable anti-hyperlipidemic effect by suppressing very low density lipoprotein (VLDL) level in the blood. Mechanistically, the HB-EGF targeting suppressed hepatic VLDL secretion rate without changing heparin-releasable plasma triglyceride (TG) hydrolytic activity or fecal neutral cholesterol excretion rate.

Conclusion

This result suggested that the HB-EGF targeting induced protection against aneurysm development through anti-hyperlipidemic effects. Suppression of hepatic VLDL production process appears to be a key mechanism for the anti-hyperlipidemic effects by the HB-EGF targeting.

Inhibition of epidermal growth factor receptor attenuates atherosclerosis via decreasing inflammation and oxidative stress

Atherosclerosis is a progressive disease leading to loss of vascular homeostasis and entails fibrosis, macrophage foam cell formation, and smooth muscle cell proliferation. Recent studies have reported that epidermal growth factor receptor (EGFR) is involved vascular pathophysiology and in the regulation of oxidative stress in macrophages. Although, oxidative stress and inflammation play a critical role in the development of atherosclerosis, the underlying mechanisms are complex and not completely understood. In the present study, we have elucidated the role of EGFR in high-fat diet-induced atherosclerosis in apolipoprotein E null mice. We show increased EGFR phosphorylation and activity in atherosclerotic lesion development. EGFR inhibition prevented oxidative stress, macrophage infiltration, induction of pro-inflammatory cytokines, and SMC proliferation within the lesions. We further show that EGFR is activated through toll-like receptor 4. Disruption of toll-like receptor 4 or the EGFR pathway led to reduced inflammatory activity and foam cell formation. These studies provide evidence that EGFR plays a key role on the pathogenesis of atherosclerosis, and suggests that EGFR may be a potential therapeutic target in the prevention of atherosclerosis development.

Mutually Supportive Mechanisms of Inflammation and Vascular Remodeling

Chronic inflammation is often accompanied by angiogenesis, the development of new blood vessels from existing ones. This vascular response is a response to chronic hypoxia and/or ischemia, but is also contributory to the progression of disorders including atherosclerosis, arthritis, and tumor growth. Proinflammatory and proangiogenic mediators and signaling pathways form a complex and interrelated network in these conditions, and many factors exert multiple effects. Inflammation drives angiogenesis by direct and indirect mechanisms, promoting endothelial proliferation, migration, and vessel sprouting, but also by mediating extracellular matrix remodeling and release of sequestered growth factors, and recruitment of proangiogenic leukocyte subsets. The role of inflammation in promoting angiogenesis is well documented, but by facilitating greater infiltration of leukocytes and plasma proteins into inflamed tissues, angiogenesis can also propagate chronic inflammation. This review examines the mutually supportive relationship between angiogenesis and inflammation, and considers how these interactions might be exploited to promote resolution of chronic inflammatory or angiogenic disorders.

So Much Cholesterol: the unrecognized importance of smooth muscle cells in atherosclerotic foam cell formation

PURPOSE OF REVIEW

Smooth muscle cells (SMCs) form the thickened intimal layer in atherosclerosis-prone arteries in early life, and provide the initial site for retention and uptake of atherogenic lipoproteins. Here we review current knowledge regarding the importance of SMCs in the deposition of cholesterol in atherosclerotic plaque.

RECENT FINDINGS

SMCs were found to comprise at least 50% of total foam cells in human coronary artery atherosclerosis, and exhibit a selective loss of expression of the cholesterol efflux promoter ATP-binding cassette transporter A1. Cholesterol loading induced a loss of SMC gene expression and an increase in macrophage and proinflammatory marker expression by cultured mouse and human arterial SMCs, with reversal of these effects upon removal of the excess cholesterol. Mice engineered to track all cells of SMC lineage indicated that, at most, SMCs make up about one-third of total cells in atherosclerotic plaque in these animals.

SUMMARY

SMCs appear to be the origin of the majority of foam cells in human atherosclerotic plaque. Recent studies suggest a renaissance of research on the role of SMCs in atherosclerosis is needed to make the next leap forward in the prevention and treatment of this disease.

Analysis of stromal cell secretomes reveals a critical role for stromal cell-derived hepatocyte growth factor and fibronectin in angiogenesis

OBJECTIVE

Angiogenesis requires tightly coordinated crosstalk between endothelial cells (ECs) and stromal cells, such as fibroblasts and smooth muscle cells. The specific molecular mechanisms moderating this process are still poorly understood.

METHODS AND RESULTS

Stromal cell-derived factors are essential for EC sprouting and lumen formation. We therefore compared the abilities of 2 primary fibroblast isolates and a primary smooth muscle cell isolate to promote in vitro angiogenesis, and analyzed their secretomes using a combination of nano liquid chromatography-mass spectrometry/mass spectrometry, quantitative PCR, and ELISA. Each isolate exhibited a different level of angiogenic ability. Using quantitative MS, we then compared the secretomes of a fibroblast isolate exhibiting low angiogenic activity, a fibroblast isolate exhibiting high angiogenic activity, and human umbilical vein ECs. High angiogenic fibroblast supernatants exhibited an overabundance of proteins associated with extracellular matrix constituents compared with low angiogenic fibroblasts or ECs. Finally, small interfering RNA technology and purified protein were used to confirm a role for stromal cell-derived hepatocyte growth factor and fibronectin in inducing EC sprouting.

CONCLUSIONS

Differences in stromal cell ability to induce angiogenesis are a result of differences in the secreted proteomes of both extracellular matrix proteins and proangiogenic growth factors.

Heparin-binding EGF-like growth factor promotes epithelial-mesenchymal transition in human keratinocytes

We have shown that autocrine proliferation of human keratinocytes (KC) is strongly dependent upon amphiregulin (AREG), whereas blockade of heparin-binding EGF-like growth factor (HB-EGF) inhibits KC migration in scratch wound assays. Here we demonstrate that expression of soluble HB-EGF (sHB-EGF) or full-length transmembrane HB-EGF (proHB-EGF), but not proAREG, results in profound increases in KC migration and invasiveness in monolayer culture. Coincident with these changes, HB-EGF significantly decreases mRNA expression of several epithelial markers including keratins 1, 5, 10, and 14, while increasing expression of markers of cellular motility including SNAI1, ZEB1, COX-2 and MMP1. Immunostaining revealed HB-EGF-induced expression of the mesenchymal protein vimentin and decreased expression of E-cadherin as well as nuclear translocation of β-catenin. Suggestive of a trade-off between KC motility and proliferation, overexpression of HB-EGF also reduced KC growth by more than 90%. We also show that HB-EGF is strongly induced in regenerating epidermis after partial thickness wounding of human skin. Taken together, our data suggest that expression of HB-EGF in human KC triggers a migratory and invasive phenotype with many features of epithelial-mesenchymal transition (EMT), which may be beneficial in the context of cutaneous wound healing.

Metalloproteinase processing of HBEGF is a proximal event in the response of human aortic endothelial cells to oxidized phospholipids

OBJECTIVE

Atherosclerosis is a chronic inflammatory disease initiated by monocyte recruitment and retention in the vessel wall. An important mediator of monocyte endothelial interaction is the chemokine interleukin (IL)-8. The oxidation products of phospholipids, including oxidized 1-palmitoyl-2-arachidonyl-sn-glycerol-3-phosphocholine (Ox-PAPC), accumulate in atherosclerotic lesions and strongly induce IL-8 in human aortic endothelial cells (HAECs). The goal of this study was to identify the proximal events leading to induction of IL-8 by Ox-PAPC in vascular endothelial cells.

METHODS AND RESULTS

In a systems genetics analysis of HAECs isolated from 96 different human donors, we showed that heparin-binding EGF-like growth factor (HBEGF) transcript levels are strongly correlated to IL-8 induction by Ox-PAPC. The silencing and overexpression of HBEGF in HAECs confirmed the role of HBEGF in regulating IL-8 expression. HBEGF has been shown to be stored in an inactive form and activation is dependent on processing by a dysintegrin and metalloproteinases (ADAM) to a form that can activate the epidermal growth factor (EGF) receptor. Ox-PAPC was shown to rapidly induce HBEGF processing and EGF receptor activation in HAECs. Using siRNA we identified 3 ADAMs that regulate IL-8 induction and directly demonstrated that Ox-PAPC increases ADAM activity in the cells using a substrate cleavage assay. We provide evidence for one mechanism of Ox-PAPC activation of ADAM involving covalent binding of Ox-PAPC to cysteine on ADAM. Free thiol cysteine analogs showed inhibition of IL-8 induction by Ox-PAPC, and both a cysteine analog and a cell surface thiol blocker strongly inhibited ADAM activity induction by Ox-PAPC. Using microarray analyses, we determined that this ADAM pathway may regulate at least 30% of genes induced by Ox-PAPC in HAECs.

CONCLUSIONS

This study is the first report demonstrating a role for the ADAM-HBEGF-EGF receptor axis in Ox-PAPC induction of IL-8 in HAECs. These studies highlight a role for specific ADAMs as initiators of Ox-PAPC action and provide evidence for a role of covalent interaction of Ox-PAPC in activation of ADAMs.

MicroRNA-132 targets HB-EGF upon IgE-mediated activation in murine and human mast cells

MicroRNAs provide an additional layer in the regulation of gene expression acting as repressors with several targets at the posttranscriptional level. This study describes microRNA expression patterns during differentiation and activation of mast cells. The expression levels of 567 different mouse miRNAs were compared by microarray between c-Kit+ committed progenitors, mucosal mast cells, resting and IgE-crosslinked BMMCs in vitro. The strongest upregulation of miR-132 upon IgE-mediated activation was validated in human cord blood-derived mast cells as well. HB-EGF growth factor also upregulated upon activation and was ranked high by more prediction algorithms. Co-transfection of miR-132 mimicking precursor and the 3'UTR of human Hbegf-containing luciferase vector proves that the predicted binding site is functional. In line with this, neutralization of miR-132 by anti-miR inhibitor leads to sustained production of HB-EGF protein in activated mast cells. Our data provide a novel example for negative regulation of a growth factor by an upregulated miRNA.

IL-8-mediated angiogenic responses of endothelial cells to lipid antigen activation of iNKT cells depend on EGFR transactivation

iNKT cells are a unique T cell subset, which is CD1d-restricted and specific for glycolipid antigens. In advanced atherosclerotic plaques, focal collections of inflammatory cells correlate with areas of intraplaque neovascularization. We reported recently that iNKT cells might facilitate intraplaque neovascularization by enhancing EC migration and sprouting in an IL-8-dependent manner. This study investigated the participating effector mechanisms. In ECs, CM, derived from antigen-stimulated human iNKT cells (CM+), induced up-regulation of IL-8R CXCR2 and the phosphorylation of EGFR and of multiple intracellular signaling effectors, including FAK, Src, Erk, Jnk, p38-MAPK, and STAT1 and -3. We found that a cascade of events, which were IL-8-dependent and involved EGFR activation, was responsible for signaling through FAK and Src kinases and necessary for acquisition of angiogenic morphology, migration in a two-dimensional wound assay, and sprout outgrowth in a three-dimensional model of angiogenesis in vitro. The data support that IL-8-dependent activation of angiogenic behavior in ECs, in response to activated iNKT, involves CXCR2, transactivation of EGFR, and subsequent FAK/Src signaling. We found too that activated iNKT increased VEGFR2 expression in ECs. Functional studies confirmed that EGF is the motogenic-enhancing factor in CM+ and is necessary, together with an exogenous source of VEGF, for iNKT-promoted sprout formation. EGFR inhibition may represent a novel therapeutic modality aimed at plaque stabilization through control of neovascularization within developing atherosclerotic plaques.

Plasma kallikrein promotes epidermal growth factor receptor transactivation and signaling in vascular smooth muscle through direct activation of protease-activated receptors

The kallikrein-kinin system, along with the interlocking renin-angiotensin system, is a key regulator of vascular contractility and injury response. The principal effectors of the kallikrein-kinin system are plasma and tissue kallikreins, proteases that cleave high molecular weight kininogen to produce bradykinin. Most of the cellular actions of kallikrein (KK) are thought to be mediated by bradykinin, which acts via G protein-coupled B1 and B2 bradykinin receptors on VSMCs and endothelial cells. Here, we find that primary aortic vascular smooth muscle but not endothelial cells possess the ability to activate plasma prekallikrein. Surprisingly, exposing VSMCs to prekallikrein leads to activation of the ERK1/2 mitogen-activated protein kinase cascade via a mechanism that requires kallikrein activity but does not involve bradykinin receptors. In transfected HEK293 cells, we find that plasma kallikrein directly activates G protein-coupled protease-activated receptors (PARs) 1 and 2, which possess consensus kallikrein cleavage sites, but not PAR4. In vascular smooth muscles, KK stimulates ADAM (a disintegrin and metalloprotease) 17 activity via a PAR1/2 receptor-dependent mechanism, leading sequentially to release of the endogenous ADAM17 substrates, amphiregulin and tumor necrosis factor-α, metalloprotease-dependent transactivation of epidermal growth factor receptors, and metalloprotease and epidermal growth factor receptor-dependent ERK1/2 activation. These results suggest a novel mechanism of bradykinin-independent kallikrein action that may contribute to the regulation of vascular responses in pathophysiologic states, such as diabetes mellitus.

The heparin-binding domain of HB-EGF mediates localization to sites of cell-cell contact and prevents HB-EGF proteolytic release

Heparin-binding EGF-like growth factor (HB-EGF) is a ligand for EGF receptor (EGFR) and possesses the ability to signal in juxtacrine, autocrine and/or paracrine mode, with these alternatives being governed by the degree of proteolytic release of the ligand. Although the spatial range of diffusion of released HB-EGF is restricted by binding heparan-sulfate proteoglycans (HSPGs) in the extracellular matrix and/or cellular glycocalyx, ascertaining mechanisms governing non-released HB-EGF localization is also important for understanding its effects. We have employed a new method for independently tracking the localization of the extracellular EGF-like domain of HB-EGF and the cytoplasmic C-terminus. A striking observation was the absence of the HB-EGF transmembrane pro-form from the leading edge of COS-7 cells in a wound-closure assay; instead, this protein localized in regions of cell-cell contact. A battery of detailed experiments found that this localization derives from a trans interaction between extracellular HSPGs and the HB-EGF heparin-binding domain, and that disruption of this interaction leads to increased release of soluble ligand and a switch in cell phenotype from juxtacrine-induced growth inhibition to autocrine-induced proliferation. Our results indicate that extracellular HSPGs serve to sequester the transmembrane pro-form of HB-EGF at the point of cell-cell contact, and that this plays a role in governing the balance between juxtacrine versus autocrine and paracrine signaling.

Heparin-binding EGF-like growth factor in human serum. Association with high blood cholesterol and heart hypertrophy

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) belongs to the EGF family of growth factors which are ligands of the ErbB receptors. Studies in animals suggest the role of HB-EGF in several pathogenic processes such as atherosclerosis and heart hypertrophy. Here, we set up an assay to measure HB-EGF in human serum. Our ELISA determined serum HB-EGF in the range of 0.03-3 nM. It did not cross-react with EGF or with transforming growth factor-alpha. The mean serum HB-EGF was 0.26 nM (confidence interval: 0.13-0.39) in women and 0.28 nM (confidence interval: 0.09-0.47) in men. In a cohort of 121 healthy volunteers, we identified nine individuals with high serum HB-EGF (above 0.47 nM). These individuals had higher left ventricle mass (determined by Colour Doppler echocardiography) and greater total and low density lipoprotein cholesterol than control. On the basis of our results, we propose that increased serum HB-EGF is associated with heart hypertrophy and elevated blood cholesterol.

Metalloproteinase-mediated, context-dependent function of amphiregulin and HB-EGF in human keratinocytes and skin

Human keratinocytes (KCs) express multiple EGF receptor (EGFR) ligands; however, their functions in specific cellular contexts remain largely undefined. To address this issue, first we measured mRNA and protein levels for multiple EGFR ligands in KCs and skin. Amphiregulin (AREG) was by far the most abundant EGFR ligand in cultured KCs, with >19 times more mRNA and >7.5 times more shed protein than any other family member. EGFR ligand expression in normal skin was low (<8 per thousand of RPLP0/36B4); however, HB-EGF and AREG mRNAs were strongly induced in human skin organ culture. KC migration in scratch wound assays was highly metalloproteinase (MP)- and EGFR dependent, and was markedly inhibited by EGFR ligand antibodies. However, lentivirus-mediated expression of soluble HB-EGF, but not soluble AREG, strongly enhanced KC migration, even in the presence of MP inhibitors. Lysophosphatidic acid (LPA)-induced ERK phosphorylation was also strongly EGFR and MP dependent and markedly inhibited by neutralization of HB-EGF. In contrast, autocrine KC proliferation and ERK phosphorylation were selectively blocked by neutralization of AREG. These data show that distinct EGFR ligands stimulate KC behavior in different cellular contexts, and in an MP-dependent fashion.

Cell migration in response to the amino-terminal fragment of urokinase requires epidermal growth factor receptor activation through an ADAM-mediated mechanism

BACKGROUND

Cell migration is an integral component of intimal hyperplasia development and proteases are pivotal in the process. Understanding the role of urokinase signaling within the cells of vasculature remains poorly defined. The study examines the role of amino-terminal fragment (ATF) of urokinase on a pivotal cross-talk receptor, epidermal growth factor receptor (EGFR). EGFR is transactivated by both G-protein-coupled receptors and receptor tyrosine kinases and is key to many of their responses. We hypothesize that A Disintegrin and Metalloproteinase Domains (ADAM) allows the transactivation of EGFR by ATF.

OBJECTIVE

To determine the role of ADAM in EGFR transactivation by ATF in human vascular smooth muscle cells (VSMC) during cell migration.

METHODS

Human coronary VSMC were cultured in vitro. Assays of EGFR phosphorylation were examined in response to ATF (10 nM) in the presence and absence of the matrix metalloprotease (MMP) inhibitor GM6001, the ADAM inhibitors TAPI-0 and TAPI-1, heparin binding epidermal growth factor (HB-EGF) inhibitor, CRM197, HB-EGF inhibitory antibodies, epidermal growth factor (EGF) inhibitory antibodies, and the EGFR inhibitor AG1478. The small interference ribonucleic acid (siRNA) against EGFR and ADAM-9, ADAM-10, ADAM-12, and adenoviral delivered Gbg inhibitor, betaARK(CT) were also used.

RESULTS

ATF produced concentration-dependent VSMC migration (by wound assay and Boyden chamber), which was inhibited by increasing concentrations of AG1478. ATF was shown to induce time-dependent EGFR phosphorylation, which peaked at fourfold greater than control. Pre-incubation with the Gbetagamma inhibitor betaARK(CT) inhibited EGFR activation by ATF. This migratory and EGFR response was inhibited by AG1478 in a concentration-dependent manner. Incubation with siRNA against EGFR blocked the ATF-mediated migratory and EGFR responses. EGFR phosphorylation by ATF was blocked by inhibition of MMP activity and the ligand HB-EGF. The presence of the ADAM inhibitors, TAPI-0 and TAPI-1 significantly decreased EGFR activation. EGFR phosphorylation by EGF was not interrupted by inhibition of MMP, ADAMs, or HB-EGF. Direct blockade of the EGFR prevented activation by both ATF and EGF. Incubation with siRNA to ADAM-9 and -10 significantly reduced HB-EGF release from VSMC and EGFR activation in response to ATF. The siRNA against ADAM-12 had no effect.

CONCLUSION

ATF can induce transactivation of EGFR by an ADAM-mediated, HB-EGF-dependent process. Targeting a pivotal cross-talk receptor such as EGFR is an attractive molecular target to inhibit cell migration.

Autoimmune-mediated atherothrombosis

Autoimmune vascular inflammation and oxidative stress (lipid peroxidation) are common in systemic autoimmune diseases and contribute to the oxidative modification of low-density lipoprotein (oxLDL) and oxLDL/beta2GPI complex formation. Circulating oxLDL/beta2GPI complexes have been detected in patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS). The presence of antibodies to oxLDL/beta2GPI complexes indicates that these complexes are immunogenic, and the coexistence of complexes and antibodies has pointed to an active proatherogenic role in the development of autoimmune vascular complications. Immunohistochemical staining of atherosclerotic lesions suggest that these complexes are formed in the arterial wall and released into circulation. The in vitro macrophage uptake of oxLDL/beta2GPI complexes was significantly increased in the presence of antiphospholipid antibodies, either beta2GPI-dependent anticardiolipin or anti-beta2GPI antibodies, suggesting that macrophage Fcgamma receptors are involved in lipid intracellular influx and foam cell formation. These findings provide an explanation for the accelerated development of atherosclerosis seen in SLE and APS. The presence of circulating oxLDL/beta2GPI complexes and IgG antibodies to these complexes indicate significant vascular injury and oxidative stress as well as an active role in autoimmune-mediated atherothrombosis.

Insulin-induced epidermal growth factor activation in vascular smooth muscle cells is ADAM-dependent

BACKGROUND

With the rise in metabolic syndrome, understanding the role of insulin signaling within the cells of vasculature has become more important but yet remains poorly defined. This study examines the role of insulin actions on a pivotal cross-talk receptor, epidermal growth factor receptor (EGFR). EGFR is transactivated by both G-protein-coupled receptors and receptor-linked tyrosine kinases and is key to many of their responses.

OBJECTIVE

To determine the pathway of EGFR transactivation by insulin in human vascular smooth muscle cells (VSMC).

METHODS

VSMC were cultured in vitro. Assays of EGFR phosphorylation were examined in response to insulin in the presence and absence of the plasmin inhibitors (e-aminocaproic acid and aprotinin) matrix metalloprotease (MMP) inhibitor GM6001, the A disintegrin and metalloproteinase domain (ADAM) inhibitors tumor necrosis factor-alpha protease inhibitor (TAPI)-0 and TAPI-1, heparin-binding epidermal growth factor (HB-EGF) inhibitor, CRM197, HB-EGF inhibitory antibodies, EGF inhibitory antibodies, and the EGFR inhibitor AG1478.

RESULTS

Insulin induced time-dependent EGFR phosphorylation, which was inhibited by AG1478 in a concentration-dependent manner. Application of the plasmin inhibitors did not block the response. EGFR phosphorylation by insulin was blocked by inhibition of MMP activity and the ligand HB-EGF. The presence of the ADAM inhibitors, TAPI-0 and TAPI-1 significantly decreased EGFR activation. EGFR phosphorylation by EGF was not interrupted by inhibition of plasmin, MMPs TAPIs, or HB-EGF. Direct blockade of the EGFR prevented activation by both insulin and EGF.

CONCLUSION

Insulin can induce transactivation of EGFR by an ADAM-mediated, HB-EGF-dependent process. This is the first description of cross-talk via ADAM between insulin and EGFR in VSMC. Targeting a pivotal cross-talk receptor such as EGFR, which can be transactivated by both G-protein-coupled receptors and receptor tyrosine kinases is an attractive molecular target.

Heparin-binding epidermal growth factor-like growth factor signaling in flow-induced arterial remodeling

Heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) is activated by reduced endothelial shear stress and stimulates smooth muscle cell proliferation in vitro. Moreover, HB-EGF is augmented at sites of intimal hyperplasia and atherosclerosis, conditions favored by low/disturbed shear stress. We thus tested whether HB-EGF contributes to low flow-induced negative hypertrophic remodeling (FINR) of a mouse carotid artery. Blood flow was surgically decreased in the left and increased in the right common carotid arteries. After 21 days, the left carotid artery exhibited lumen narrowing, thickening of intima-media and adventitia, and increased circumference that were inhibited by approximately 50% in HB-EGF(+/-) and approximately 90% in HB-EGF(-/-) mice. FINR was also inhibited by the EGF receptor inhibitor AG1478. In contrast, eutrophic outward remodeling of the right carotid artery was unaffected in HB-EGF(+/-) and HB-EGF(-/-) mice, nor by AG1478. FINR-induced proliferation and leukocyte accumulation were reduced in HB-EGF(-/-). FINR was associated with increased reactive oxygen species, increased expression of pro-HB-EGF and tumor necrosis factor alpha-converting enzyme (pro-HB-EGF sheddase), increased phosphorylation of EGF receptor and extracellular signal-regulated kinase 1/2, and increased nuclear factor kappaB activity. Apocynin and deletion of p47(phox) inhibited FINR, whereas deletion of HB-EGF abolished nuclear factor kappaB activation in smooth muscle cells. These findings suggest that HB-EGF signaling is required for low flow-induced hypertrophic remodeling and may participate in vascular wall disease and remodeling.

Adrenomedullin antagonizes angiotensin II-stimulated proliferation of human aortic smooth muscle cells

The vasodilating peptide adrenomedullin has been reported to regulate vascular tone as well as proliferation and differentiation of various cell types in an autocrine/paracrine manner. Conflicting data have been reported on the adrenomedullin (AM) effect on vascular smooth muscle cell proliferation, a process involved in the progression of vascular remodeling and atherosclerotic lesion. In this paper we investigate the effect of AM on proliferation of human aorta smooth muscle cell (HASMC). AM showed a potent dose-dependent inhibiting effect on angiotensin II (AngII) induced-proliferation and a stimulatory effect on proliferation of quiescent cells. The cAMP/PKA pathway was involved in the AM inhibitory effect of AngII-induced proliferation in HASMC. PI3K/Akt and ERK pathways were involved in the proliferative effect exerted by AM per se. Our results suggest that AM plays a role in the regulation of HASMC growth antagonizing the AngII effect and may be involved in conditions of altered regulation of the blood vessels.

Accelerated atheroma in the antiphospholipid syndrome

Increased cardiovascular morbidity and mortality due to the pre-mature or accelerated development of atherosclerosis has been reported in patients with systemic autoimmune diseases such as systemic lupus erythematosus. These findings motivated a great deal of research into the role of autoimmunity in atherogenesis. The relationship between atherosclerosis and cholesterol metabolism to atherosclerosis has been well established. However, the participation of newer inflammatory and immunologic mechanisms are emerging as relevant factors for the initiation and progression of atherosclerotic lesions.

Intravenous immunoglobulin and atherosclerosis

Several inflammatory and immunological factors have been established as important contributors to atherogenesis. Among these, oxidized low-density lipoprotein (oxLDL) play a central role in the initiation and progression of atherosclerotic lesions. In atherosclerotic lesions, oxLDL was also found to co-localize with beta2-glycoprotein I (beta2-GPI). Immunoglobulin (Ig)G autoantibodies against beta2-GPI complexed with oxLDL are pro-atherogenic because they increase uptake of the complexes by macrophages. In contrast, IgM natural anti-oxLDL antibodies derived from atherosclerosis-prone apolipoprotein E (ApoE) deficient mice reduced incidence of atherosclerosis. Such anti-oxLDL antibodies have been found in humans, and the accumulating evidences seem to support the idea that anti-oxLDL antibodies have a protective role for atherogenesis. Intravenous immunoglobulins (IVIgs) contain natural anti-oxLDL antibodies and infusion of IVIg into ApoE-deficient mice has been reported to decrease atherosclerosis. The anti-atherogenic property of IVIg may be derived from non-antigen-specific antibody binding to FCgamma receptors, which blocks foam cell formation of macrophages. Several other possible mechanisms are also discussed.

Plasmin-induced smooth muscle cell proliferation requires epidermal growth factor activation through an extracellular pathway

BACKGROUND

Plasminogen activators are used routinely for thrombolysis. They lead to the generation of the protease, plasmin, which can induce smooth muscle cell proliferation and may thus promote further intimal hyperplasia in the thrombolysed vessel. We have shown recently that plasmin induces extracellular signal-regulated kinase 1/2 (ERK1/2)-mediated cell proliferation. Plasmin can also activate metalloproteinases on the cell surface, which can release the tethered ligand heparin-binding epidermal growth factor (HB-EGF), which can in turn activate the epidermal growth factor receptor (EGFR).

METHODS

Murine aortic smooth muscle cells were cultured in vitro. Assays of DNA synthesis and cell proliferation, EGFR phosphorylation, and ERK1/2 activation were examined in response to plasmin in the presence and absence of the plasmin inhibitors (epsilon-aminocaproic acid and aprotinin), matrix metalloproteinase (MMP) inhibitor GM6001, HB-EGF inhibitor CRM197, HB-EGF inhibitory antibodies, EGF inhibitory antibodies, and the EGFR inhibitor AG1478.

RESULTS

Plasmin-induced smooth muscle cell DNA synthesis, which was blocked by EGFR and HB-EGF inhibition. Plasmin-induced time-dependent EGFR phosphorylation and ERK1/2 activation, which were inhibited by AG1478. This response was dependent on the proteolytic activity of plasmin since both plasmin inhibitors blocked the response. EGFR phosphorylation by plasmin was blocked by inhibition of MMP activity and the ligand HB-EGF. EGFR phosphorylation by EGF was not interrupted by inhibition of plasmin, MMPs, or HB-EGF. Direct blockade of the EGFR prevented activation by both plasmin and EGF.

CONCLUSIONS

Plasmin can induce smooth muscle cell proliferation through activation of EGFR by an extracellular MMP-mediated, HB-EGF-dependent process.

The epidermal growth factor receptors and their family of ligands: their putative role in atherogenesis

The epidermal growth factor receptor is a member of type-I growth factor receptor family with tyrosine kinase activity that is activated following the binding of multiple cognate ligands. Several members of the EGF family of ligands are expressed by cells involved in atherogenesis. EGF receptor mediated processes have been well characterised within epithelial, smooth muscle and tumour cell lines in vitro, and the EGF receptor has been identified immunocytochemically on intimal smooth muscle cells within atherosclerotic plaques. There is also limited evidence for the expression of the EGF receptor family on leukocytes, although their function has yet to be clarified. In this review, we will discuss the biological functions of this receptor and its ligands and their potential to modulate the function of cells involved in the atherosclerotic process.

Heparin-binding EGF-like growth factor induces expression of lectin-like oxidized LDL receptor-1 in vascular smooth muscle cells

Receptor-mediated endocytosis of oxidized LDL (Ox-LDL) has been implicated in lipid accumulation and vascular cell dysfunction. Lectin-like Ox-LDL receptor-1 (LOX-1) is highly inducible by proinflammatory cytokines, as well as angiotensin II and Ox-LDL in vitro. LOX-1 is expressed in macrophages and smooth muscle cells accumulated in the intima of advanced atherosclerotic plaques in vivo. Here we show that heparin-binding epidermal growth factor-like growth factor (HB-EGF), a potent mitogen for vascular smooth muscle cells, induces LOX-1 expression in cultured bovine aortic smooth muscle cells. HB-EGF (1-100 ng/ml) induced LOX-1 expression, which was peaked between 8 and 16 h after HB-EGF stimulation. HB-EGF-induced expression of LOX-1 was suppressed by ZD1839, an inhibitor of EGF receptor phosphorylation. Both MEK and p38 mitogen-activated protein kinase (MAPK) inhibitors significantly blocked LOX-1 upregulation induced by HB-EGF. Phosphatidylinositol 3-kinase (PI3K) inhibitors also blocked HB-EGF-induced LOX-1 expression. HB-EGF induced phosphorylation of ERK, p38 MAPK and Akt, which were suppressed by ZD1839. Upregulated expression of LOX-1 was associated with enhanced uptake of DiI-labeled Ox-LDL in smooth muscle cells. Taken together, HB-EGF can also act as an inducer of LOX-1 expression and play an integral role in foam cell transformation, cellular dysfunction, and proliferation of smooth muscle cells in atherogenesis.

Suppression of 3-deoxyglucosone and heparin-binding epidermal growth factor-like growth factor mRNA expression by an aldose reductase inhibitor in rat vascular smooth muscle cells

Reactive carbonyl compounds and oxidative stress have been recently shown to up-regulate the expression of heparin-binding epidermal growth factor-like growth factor (HB-EGF), a potent mitogen for vascular smooth muscle cells (SMCs) produced by SMC themselves. Because the polyol pathway has been reported to influence the formation of carbonyl compounds and the oxidative stress in various cells, we conducted this study to investigate whether the polyol pathway affects HB-EGF expression along with the generation of carbonyl compounds and the oxidative stress in SMCs. We found that, compared with those cultured with 5.5mM glucose, SMCs cultured with 40 mM glucose showed the accelerated thymidine incorporation, elevated levels of intracellular sorbitol, 3-deoxyglucosone (3-DG), advanced glycation end products (AGEs), and thiobarbituric acid-reactive substances (TBARS) along with the enhanced expression of HB-EGF mRNA. An aldose reductase inhibitor (ARI), SNK-860, significantly inhibited all of these abnormalities, while aminoguanidine suppressed 3-DG levels and HB-EGF mRNA expression independent of sorbitol levels. The results suggest that the polyol pathway may play a substantial role in SMC hyperplasia under hyperglycemic condition in part by affecting HB-EGF mRNA expression via the production of carbonyl compounds and oxidative stress.

A role of heparin-binding epidermal growth factor-like growth factor in cardiac remodeling after myocardial infarction

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is known to induce cell growth in various cell types via transactivation of epidermal growth factor receptor (EGFR). To investigate the involvement of HB-EGF and EGFR in cardiac remodeling after myocardial infarction (MI), we examined the expressions of mRNA and protein in rat hearts 6 weeks after MI-induction. Where increased expressions of HB-EGF mRNA and protein were observed, infarcted myocardium was replaced by extracellular matrix and interstitial fibroblasts. EGFR mRNA and protein expression did not show significant changes in sham-operated heart tissues, non-infarcted region, and infarcted region. In vitro study demonstrated that HB-EGF mRNA was expressed mainly in cultured fibroblasts rather than in myocytes. We suggest that the interaction between HB-EGF and EGFR transactivation is closely related to the proliferation of cardiac fibroblasts and cardiac remodeling after MI in an autocrine, paracrine, and juxtacrine manner.

Increased plasma HB-EGF associated with obesity and coronary artery disease

The mechanism by which the obese subjects are more associated with vascular disease remains unclear. We reported that the adipose tissues produce and secrete many bioactive molecules, conceptualized as adipocytokines. Heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF), produced locally by vascular macrophages and smooth muscle cells, has been suggested to induce the migration and proliferation of vascular smooth muscle cells. The current study reveals that (1) HB-EGF mRNA is abundantly expressed in human adipose tissue, (2) HB-EGF mRNA increases in the fat tissues of obese mice, (3) plasma HB-EGF levels increase in parallel with fat accumulation in human, and (4) the subjects with coronary artery disease have higher plasma HB-EGF levels, associated with fat accumulation. These results suggest that increased plasma HB-EGF derived from the accumulated fat contributes to the higher incidence of vascular disease in obesity, proposing HB-EGF as an adipocytokine directly linking adipovascular axis.

Anti-beta 2-glycoprotein I autoantibodies and atherosclerosis

beta 2-Glycoprotein I (beta 2-GPI) is a major antigen for antiphospholipid antibodies (aPL) present in patients with antiphospholipid syndrome (APS). We previously reported that beta 2-GPI specifically binds to oxidized low-density lipoprotein (oxLDL). Further, a ligand specific for beta 2-GPI, oxLig-1, purified from the extracted lipids of oxLDL was identified as 7-ketocholesterol-9-carboxynonanoate (i.e., 9-oxo-9-(7-ketocholest-5-en-3 beta-yloxy) nonanoic acid) OxLig-1 was recognized by beta 2-GPI and subsequently by anti-beta 2-GPI autoantibodies. Binding of liposomes containing oxLig-1 to macrophages were significantly enhanced in the presence of both beta 2-GPI and an anti-beta 2-GPI autoantibody derived from (NZW x BXSB) F1 mouse, an animal APS model, or from APS patients. Anti-beta 2-GPI autoantibodies derived from APS patients with episodes of arterial thrombosis were detected in ELISA, using a solid phase beta 2-GPI complex with oxLig-1. It was also reported that LDL-receptor-deficient mice that were fed a chow diet and immunized with beta 2-GPI had an accelerated atherosclerosis and that beta 2-GPI was abundantly expressed within subendothelial regions and intimal-medial borders of human atherosclerotic plaques. All of these observations strongly suggest that autoimmune atherogenesis linked to beta 2-GPI interaction with oxLDL and autoantibodies may be present in APS.

Vascular smooth muscle growth: autocrine growth mechanisms

Vascular smooth muscle cells (VSMC) exhibit several growth responses to agonists that regulate their function including proliferation (hyperplasia with an increase in cell number), hypertrophy (an increase in cell size without change in DNA content), endoreduplication (an increase in DNA content and usually size), and apoptosis. Both autocrine growth mechanisms (in which the individual cell synthesizes and/or secretes a substance that stimulates that same cell type to undergo a growth response) and paracrine growth mechanisms (in which the individual cells responding to the growth factor synthesize and/or secrete a substance that stimulates neighboring cells of another cell type) are important in VSMC growth. In this review I discuss the autocrine and paracrine growth factors important for VSMC growth in culture and in vessels. Four mechanisms by which individual agonists signal are described: direct effects of agonists on their receptors, transactivation of tyrosine kinase-coupled receptors, generation of reactive oxygen species, and induction/secretion of other growth and survival factors. Additional growth effects mediated by changes in cell matrix are discussed. The temporal and spatial coordination of these events are shown to modulate the environment in which other growth factors initiate cell cycle events. Finally, the heterogeneous nature of VSMC developmental origin provides another level of complexity in VSMC growth mechanisms.

EGF family ligand-dependent phenotypic modulation of smooth muscle cells through EGF receptor

The phenotypic modulation of smooth muscle cells (SMCs) is closely associated with the development and progression of various SMC diseases. We investigated the molecular mechanism of phenotypic modulation triggered by EGF family ligands using a primary culture system of differentiated SMCs. Among four EGF-receptor (EGFR) family members, the EGFR was solely activated by EGF, heparin-binding EGF (HB-EGF), transforming growth factor alpha (TGF alpha), epiregulin (ER), and betacellulin (BTC), resulting in induction of phenotypic modulation of SMCs. This effect was mediated through the coordinated activation of the extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38MAPK) pathways. These results suggest that EGF family ligand- and EGFR-triggered signaling pathways are critically involved in the phenotypic modulation of SMCs.

Untangling the ErbB signalling network

When epidermal growth factor and its relatives bind the ErbB family of receptors, they trigger a rich network of signalling pathways, culminating in responses ranging from cell division to death, motility to adhesion. The network is often dysregulated in cancer and lends credence to the mantra that molecular understanding yields clinical benefit: over 25,000 women with breast cancer have now been treated with trastuzumab (Herceptin), a recombinant antibody designed to block the receptor ErbB2. Likewise, small-molecule enzyme inhibitors and monoclonal antibodies to ErbB1 are in advanced phases of clinical testing. What can this pathway teach us about translating basic science into clinical use?

Heparin-binding EGF-like growth factor

HB-EGF is a heparin-binding member of the EGF family that was initially identified in the conditioned medium of human macrophages. Soluble mature HB-EGF is proteolytically processed from a larger membrane-anchored precursor and is a potent mitogen and chemotactic factor for fibroblasts, smooth muscle cells but not endothelial cells. HB-EGF activates two EGF receptor subtypes, HER1 and HER4 and binds to cell surface HSPG. The transmembrane form of HB-EGF is a juxtacrine growth and adhesion factor and is uniquely the receptor for diphtheria toxin. HB-EGF gene expression is highly regulated, for example by cytokines, growth factors, and transcription factors such as MyoD. HB-EGF has been implicated as a participant in a variety of normal physiological processes such as blastocyst implantation and wound healing, and in pathological processes such as tumor growth, SMC hyperplasia and atherosclerosis.