Heparin-binding EGF-like growth factor synthesis by smooth muscle cells

HB-EGF stimulates eNOS expression and nitric oxide production and promotes eNOS dependent angiogenesis

Heparin-binding EGF-like growth factor (HB-EGF) is a member of the epidermal growth factor (EGF) family of ligands that is expressed by many cell types including endothelial cells. We have previously shown that HB-EGF stimulates angiogenesis in vitro in human umbilical vein endothelial cells (HUVEC). Nitric oxide (NO) derived from endothelial nitric oxide synthase (eNOS) is an important regulator of angiogenesis. However, the role of HB-EGF in regulation of eNOS has not yet been investigated. Whether HB-EGF-induced endothelial cell migration and vascular network formation are mediated via production of NO from eNOS is also unknown. To address these questions, we stimulated HUVEC with HB-EGF and evaluated the expression of eNOS at the mRNA and protein levels. HB-EGF significantly upregulated expression of eNOS mRNA, stimulated eNOS protein production, and increased NO release from HUVEC. HB-EGF phosphorylated eNOS in a phosphatidylinositol 3-kinase (PI3K) dependent fashion, and stimulated in vitro angiogenesis. eNOS siRNA inhibited HB-EGF-stimulated HUVEC migration in a scratch assay. NG-nitro-L-arginine-methyl-ester (L-NAME) and L-N5-(1-lminoethyl)ornithine,dihydochloride (L-NIO) (specific inhibitors of eNOS) also abolished HB-EGF-induced HUVEC migration and angiogenesis. More importantly, we found that HB-EGF also promotes angiogenesis in vivo in the Marigel plug assay. Lastly, inhibition of the p38 MAPK pathway enhanced HB-EGF-induced EC migration and angiogenesis. We conclude that HB-EGF, through its interaction with EGF receptors (EGFR), stimulates eNOS activation and NO production via a PI3K-dependent pathway. Thus, activation of eNOS appears to be one of the key signaling pathways necessary for HB-EGF mediated angiogenesis. These novel findings highlight an important role for HB-EGF as a regulator of endothelial cell function.

Proteolytic processing of TGFα redirects its mitogenic activity: the membrane-anchored form is autocrine, the secreted form is paracrine

Wild-type transforming growth factor alpha (TGFalpha) expression in lactotrope cells in the pituitary gland led to lactotrope-specific pituitary hyperplasia and adenomata. To indicate whether the EGF receptor is involved in this TGFalpha-mediated phenotype, we bred TGFalpha mice with mice expressing the cytoplasmic truncated-EGF receptor (EGFR-tr), which is dominant-negative in other models. These bitransgenic mice developed pituitary pathology despite expression of the dominant-negative receptor. To further characterize this observation, we generated two lineages of transgenic mice that overexpress mutant forms of TGFalpha: a processed soluble form (s TGFalpha) and a cytoplasmic-deleted form (TGFalphaDeltaC). While sTGFalpha expression in lactotrope cells failed to induce autocrine lactotrope hyperplasia, the pituitary became very enlarged due to proliferation of neighboring interstitial cells. In contrast, the TGFalphaDeltaC mice did not develop a phenotype, although the mRNA and protein were present in the pituitary and this form of TGFalpha was confirmed to be biologically active and targeted properly to the plasma membrane of cultured CHO cells. The results suggest that the cytoplasmic domain of TGFalpha is required for autocrine parenchymal tumor formation in the pituitary gland. This signal cannot be inhibited by the EGFR-tr. Conversely, the released form of TGFalpha appears to have primarily paracrine activity.

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.

Angiopoietin-regulated recruitment of vascular smooth muscle cells by endothelial-derived heparin binding EGF-like growth factor

Recruitment of vascular smooth muscle cells (SMC) by endothelial cells (EC) is essential for angiogenesis. Endothelial-derived heparin binding EGF-like growth factor (HB-EGF) was shown to mediate this process by signaling via ErbB1 and ErbB2 receptors in SMCs. 1) Analysis of ErbB-ligands demonstrated that primary ECs expressed only HB-EGF and neuregulin-1. 2) Primary SMCs expressed ErbB1 and ErbB2, but not ErbB3 or ErbB4. 3) Consistent with their known receptor specificities, recombinant HB-EGF, but not neuregulin-1, stimulated tyrosine phosphorylation of ErbB1 and ErbB2 and migration in SMCs. 4) Neutralization of HB-EGF or inhibition of ErbB1 or ErbB2 blocked 70-90% of the potential of ECs to stimulate SMC migration. Moreover, 5) angiopoietin-1, an EC effector with a role in recruitment of SMC-like cells to vascular structures in vivo, enhanced EC-stimulated SMC migration by a mechanism involving up-regulation of endothelial HB-EGF. Finally, 6) immunohistochemical analysis of developing human tissues demonstrated that HB-EGF was expressed in vivo in ECs associated with SMCs or pericytes but not in ECs of the hyaloid vessels not associated with SMCs. These results suggest an important role for HB-EGF and ErbB receptors in the recruitment of SMCs by ECs and elaborate on the mechanism by which angiopoietins exert their vascular effects.

The role of ultraviolet irradiation and heparin-binding epidermal growth factor-like growth factor in the pathogenesis of pterygium

Ultraviolet (UV) light is one of the major factors implicated in the pathogenesis of pterygium. The mechanism by which UV light induces this disease remains elusive. The aim of this study was to evaluate the effects of UVB irradiation on the expression of growth factors in cultured pterygium epithelial cells and to demonstrate their distribution within pterygium. We cultured pterygial epithelial cells from pterygium explants and these cells were exposed to 20 mJ/cm(2) of UVB. Total RNA was extracted at 0, 6, and 12 hours after irradiation. (32)P-labeled cDNA was synthesized and analyzed using microarray technology to determine the differential expression of 268 growth factor and cytokine related genes. Semiquantitative reverse transcriptase-polymerase chain reaction was used to corroborate this data. Conditioned media derived from cells exposed to UVB irradiation was analyzed for protein expression by enzyme-linked immunosorbent assay. Immunohistochemistry was used to evaluate the distribution of heparin-binding epidermal growth factor-like growth factor (HB-EGF) in pterygium tissue. Analysis of the hybridization signals revealed that the genes encoding HB-EGF, fibroblast growth factor 3, and cytotoxic trail ligand receptor were consistently elevated at 6 and 12 hours after UVB treatment. HB-EGF mRNA was elevated 6.8-fold at 6 hours after irradiation and was augmented in culture supernatants after the same treatment. Furthermore, HB-EGF reactivity was identified in the epithelium and vasculature of pterygium by immunohistochemistry. HB-EGF was present in normal limbal epithelium, although it was not induced in cultured limbal epithelial cells by UV irradiation. HB-EGF is a potent mitogen, localized in pterygium tissue, and significantly induced by UVB in pterygium-derived epithelial cells. We postulate that this growth factor is a major driving force in the development of pterygia and a means by which UV irradiation causes the pathogenesis of pterygium.

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.

Quantitation of the mRNA expression of the epidermal growth factor system: selective induction of heparin-binding epidermal growth factor-like growth factor and amphiregulin expression by growth factor stimulation of prostate stromal cells

The epidermal growth factor (EGF) system is a rapidly expanding system of growth factors involved in many aspects of normal and cancerous growth. We have developed a method for the quantitation of mRNA coding for all six growth factors activating the human EGF receptor (HER-1) and for the quantitation of mRNA for the receptors HER-1 and its preferred dimerization partner, HER-2. The method is based on the generation of specific RNA standards, which are amplified by reverse transcriptase-polymerase chain reaction (RT-PCR) with the sample RNA and a set of calibrators. The resulting calibration curve is used to quantitate the unknown samples, which require only a single RT-PCR reaction. Our method has the advantage that quantitation is based on coamplification of an internal RNA standard, thereby controlling both the PCR and RT reactions. In addition, the RNA standards for all growth factors and receptors are combined in a single RT reaction, which minimizes variation and allows the quantitation of all eight mRNA species with only 0.1 microg RNA. This makes the method suitable for studies in which the supply of material is limited. The developed method has enabled us to demonstrate that prostate stromal cells in primary culture express EGF, heparin-binding EGF (HB-EGF), amphiregulin, betacellulin, and epiregulin as well as the HER-1 and HER-2 receptors, whereas no transforming growth factor-alpha mRNA is found. Furthermore, activation of the EGF system in these cells by stimulation with HB-EGF or EGF in mitogenic doses causes a selective increase in the expression of amphiregulin and HB-EGF mRNA (more than 15-fold and 25-fold, respectively), whereas there is no increase in the expression of mRNA for the other growth factors or receptors. In accord with the increase in amphiregulin mRNA, the amount of amphiregulin peptide released from the cells is also increased. The selective induction of amphiregulin and HB-EGF by growth factor stimulation may represent a mechanism to amplify the initial growth factor signal in prostate stromal cells.

Heparin-binding molecules with growth factor activities in regenerating-tissues of the starfish Asterias rubens

Regenerating-tissues of the starfish Asterias rubens were studied for the presence of growth factors liable to stimulate the proliferation of fibroblast and epithelial cells (3T3, BHK21 and Hela cells). As a first attempt to isolate growth factors, the extracts were fixed on heparin-affinity column and were eluted by 1-1.2 M NaCl. After separation on a Vydac C18 HPLC column. a fraction that stimulates the proliferation of fibroblast cells was isolated. It contained four different peptides, separated by electrophoresis, and for which the amino acid composition and molecular mass were determined. All the peptides were lysine rich and one presented an amino-acid composition comparable to basic-fibroblast growth factor (b-FGF) while its molecular weight was higher.

Intercellular communication between vascular smooth muscle and endothelial cells mediated by heparin-binding epidermal growth factor-like growth factor and vascular endothelial growth factor

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a potent mitogen and migration factor for vascular smooth muscle cells (SMC), promoted neovascularization in vivo in the rabbit cornea. MRI demonstrated quantitatively the angiogenic effect of HB-EGF when introduced subcutaneously into nude mice. HB-EGF is not directly mitogenic to endothelial cells but it induced the migration of bovine endothelial cells and release of endothelial cell mitogenic activity from bovine vascular SMC. This mitogenic activity was specifically blocked by neutralizing anti-vascular endothelial growth factor (VEGF) antibodies. In contrast, EGF or transforming growth factor-alpha (TGF-alpha) had almost no effect on release of endothelial mitogenicity from SMC. In addition, RT-PCR analysis demonstrated that VEGF165 mRNA levels were increased in vascular SMC 4-10-fold by 0.35-2 nM of HB-EGF, respectively. Our data suggest that HB-EGF, as a mediator of intercellular communication, may play a new important role in supporting wound healing, tumor progression and atherosclerosis by stimulating angiogenesis.

Cytotoxic effects of basic FGF and heparin binding EGF conjugated with cytotoxin saporin on vascular cell cultures

Vascular smooth muscle cell (SMC) proliferation is an integral component of intimal lesion formation. In this study we compared the mitogenic effects of basic fibroblast growth factor (bFGF) and heparin binding epidermal growth factor (HBEGF) and the cytotoxic effects of bFGF and HBEGF conjugated with plant cytotoxin saporin (SAP) on vascular cell cultures. Human vascular SMCs and endothelial cells were cultured and FGF receptor-1 (FGFR-1) and EGF receptor (EGFR) expression were detected by immunohistochemical staining. Cells were grown in 24-well plates. Variable amounts of testing drugs (bFGF, HBEGF, SAP, bFGF-SAP, or HBEGF-SAP) were added to quadruplicate wells after 24 h. Cells without drugs were used as control. The total number of cells was counted at 72 h using a hemocytometer. The cultured human vascular SMCs and endothelial cells expressed both FGFR-1 and EGFR with predominant perinuclear localization. bFGF and HBEGF demonstrated equally potent mitogenic effects on SMC proliferation. SAP alone showed a limited cytotoxic effect on both SMCs and endothelial cells. bFGF had a more potent effect on endothelial cell proliferation than HBEGF. bFGF-SAP was equally cytotoxic for both SMCs and endothelial cells, while HBEGF-SAP had a more selectively cytotoxic effect on SMCs than on endothelial cells. These data suggest that the mitogenic effects of bFGF and HBEGF and the cytotoxic effects of bFGF-SAP and HBEGF-SAP may both be mediated by their corresponding growth factor receptors. Because of its selective cytotoxic effect on SMCs, HBEGF-SAP may become a more attractive agent for controlling intimal lesion formation.

The effect of cilostazol, a cyclic nucleotide phosphodiesterase III inhibitor, on heparin-binding EGF-like growth factor expression in macrophages and vascular smooth muscle cells

Heparin-binding EGF-like growth factor (HB-EGF) is a mitogen for smooth muscle cells (SMC) and is detected in SMC and macrophages in atherosclerotic plaques, suggesting that HB-EGF may be associated with the pathogenesis of atherosclerosis. The present study indicates that cilostazol, a phosphodiesterase III inhibitor, suppresses the expression of HB-EGF in rat aortic SMC and in U-937 cells, a macrophage-like cell line, stimulated by lipopolysaccharide. Further, cilostazol diminished the induction of HB-EGF mRNA by methylglyoxsal, which is a reactive dicarbonyl metabolite produced as the result of a glycation reaction and which might be associated with macroangiopathy caused by hyperglycemia. Cilostazol suppressed the production of HB-EGF protein in the conditioned medium of SMC. These data suggest that cilostazol might act by suppressing the progression of atherogenesis by means of suppressing the expression of HB-EGF in SMC and macrophages.

Expression of heparin-binding epidermal growth factor-like growth factor in neointimal cells induced by balloon injury in rat carotid arteries

Balloon catheter injury of rat carotid arteries induces migration and proliferation of smooth muscle cells (SMCs), with subsequent neointimal formation. Several growth factors, such as platelet-derived growth factor and basic fibroblast growth factor, have been shown to be involved in this process, but the mechanisms that modulate the growth and/or migratory properties of SMCs remain unclear. In this study, we investigated whether heparin-binding epidermal growth factor-like growth factor (HB-EGF), which is known to be a potent SMC stimulator from in vitro study, is associated with the proliferative response of SMCs to arterial injury. Northern blot analysis showed that the transcript levels of HB-EGF increased rapidly approximately 12-fold within 2 hours after injury and declined by 2 days but remained 3-fold at 14 days. In situ hybridization analysis demonstrated that the transcript of HB-EGF remained strongly expressed in the neointima, especially near the luminal surface, at 14 days after injury. Immunohistochemical staining showed that HB-EGF protein was positive in the endothelium and only faintly visible in medial SMCs in uninjured vessels. In contrast, 2 days after injury, positive HB-EGF immunostaining was detected in the medial SMCs along the luminal surface. At 7 days, the neointimal SMCs exhibited strong immunostaining for HB-EGF, and at 14 days, they exhibited a gradient of HB-EGF expression with strong immunoreactivity in the most luminal cells. SMCs labeled with 5-bromo-2'-deoxyuridine in their nuclei showed strong immunostaining for HB-EGF protein. Furthermore, the epidermal growth factor receptor to which HB-EGF can bind was also immunostained positively in neointimal SMCs. These data suggest that HB-EGF may play an important role of the proliferation and migration of SMCs in the process of neointimal accumulation induced by arterial injury, probably in an autocrine, paracrine, and/or juxtacrine manner.

Heparin-binding epidermal growth factor-like growth factor regulates fibroblast growth factor-2 expression in aortic smooth muscle cells

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a vascular smooth muscle cell (SMC) mitogen and chemotactic factor that is expressed by endothelial cells, SMCs, monocytes/macrophages, and T lymphocytes. Both the membrane-anchored HB-EGF precursor and the secreted mature HB-EGF protein are biologically active; thus, HB-EGF may stimulate SMC growth via autocrine, paracrine, and juxtacrine mechanisms. In the present study, we report that HB-EGF treatment of serum-starved at aortic SMCs can induce fibroblast growth factor (FGF)-2 (basic FGF) gene expression but not FGF-1 (acidic FGF) gene expression. Increased FGF-2 mRNA expression is first detectable at 1 hour after HB-EGF addition, and maximal FGF-2 mRNA levels, corresponding to an approximately 46-fold level of induction, are present at 4 hours. The effect of HB-EGF on FGF-2 mRNA levels appears to be mediated primarily by a transcriptional mechanism and requires de novo synthesized proteins. HB-EGF induction of FGF-2 mRNA levels can be inhibited by treating cells with the anti-inflammatory glucocorticoid dexamethasone or the glycosaminoglycan heparin. Finally, Western blot analyses indicate that HB-EGF-treated SMCs also produce an increased amount of FGF-2 protein. These results indicate that HB-EGF expressed at sites of vascular injury or inflammation in vivo may upregulate FGF-2 production by SMCs.

The role of growth factors in vascular cell development and differentiation

The control of vascular growth and differentiation is a complex system of activity and interaction between positive and negative modulators of these processes. A number of important stimulators and inhibitors of both smooth muscle cells and endothelial cells have now been purified and biochemically characterized. Imbalances in the activity of these factors can result in serious pathologies. In this chapter, we briefly discuss the biology of blood vessel development and growth, review the current literature which describes these stimulators and inhibitors, and discuss current therapeutic strategies designed around these growth modulators.

Localization of heparin-binding EGF-like growth factor in the smooth muscle cells and macrophages of human atherosclerotic plaques

Heparin-binding EGF-like growth factor (HB-EGF) is a potent chemoattractant and mitogen for smooth muscle cells (SMC) in culture. To elucidate whether HB-EGF is implicated in the pathogenesis of human atherosclerosis, we examined immunohistochemical localization of HB-EGF in human aortic walls and atherosclerotic plaques. The medial SMC of the aorta in babies and children synthesized HB-EGF protein, while the number of SMC producing HB-EGF was dramatically decreased in young and middle-aged adults. In atherosclerotic plaques, however, marked production of HB-EGF protein was detected in SMC and macrophages of the plaques. Furthermore, EGF receptors, to which HB-EGF is known to bind, were detected in plaque SMC. These data suggest that HB-EGF may be implicated in the migration and proliferation of SMC that occurs in the normal development of arterial walls, and in the formation of atherosclerotic plaques.