Interaction of heparin-binding EGF-like growth factor (HB-EGF) with the epidermal growth factor receptor: modulation by heparin, heparinase, or synthetic heparin-binding HB-EGF fragments

Cannabinoid Drugs-Related Neuroprotection as a Potential Therapeutic Tool Against Chemotherapy-Induced Cognitive Impairment

In recent years, and particularly associated with the increase of cancer patients’ life expectancy, the occurrence of cancer treatment sequelae, including cognitive impairments, has received considerable attention. Chemotherapy-induced cognitive impairments (CICI) can be observed not only during pharmacological treatment of the disease but also long after cessation of this therapy. The lack of effective tools for its diagnosis together with the limited treatments currently available for alleviation of the side-effects induced by chemotherapeutic agents, demonstrates the need of a better understanding of the mechanisms underlying the pathology. This review focuses on the comprehensive appraisal of two main processes associated with the development of CICI: neuroinflammation and oxidative stress, and proposes the endogenous cannabinoid system (ECS) as a new therapeutic target against CICI. The neuroprotective role of the ECS, well described in other cognitive-related neuropathologies, seems to be able to reduce the activation of pro-inflammatory cytokines involved in the neuroinflammatory supraspinal processes underlying CICI. This review also provides evidence supporting the role of cannabinoid-based drugs in the modulation of oxidative stress processes that underpin cognitive impairments, and warrant the investigation of endocannabinoid components, still unknown, that may mediate the molecular mechanism behind this neuroprotective activity. Finally, this review points forward the urgent need of research focused on the understanding of CICI and the investigation of new therapeutic targets.

Protease-mediated human smooth muscle cell proliferation by urokinase requires epidermal growth factor receptor transactivation by triple membrane signaling

BACKGROUND

Urokinase (uPA) modulates cellular and extracellular matrix responses within the microenvironment of the vessel wall and has been shown to activate the epidermal growth factor receptor (EGFR). This study examines the role of the protease domain of uPA during EGFR activation in human vascular smooth muscle cells (VSMC).

METHODS

Human coronary VSMC were cultured in vitro. Assays of cell proliferation and EGFR phosphorylation were examined in response to the carboxyterminal fragment of uPA (CTF) in the presence and absence of the plasmin, metalloprotease and a disintegrin and metalloproteinase (ADAM) inhibitors, heparin-bound epidermal growth factor (HB-EGF), and EGFR inhibitors, and small interfering RNA to EGFR and ADAMs.

RESULTS

CTF produced a dose-dependent increase in DNA synthesis and cell proliferation in human VSMC, which was blocked in a dose-dependent manner by both plasmin inhibitors and the EGFR inhibitor, AG1478. CTF induced time-dependent EGFR phosphorylation, which was blocked by inhibitors of plasmin and metalloproteinases activity. The presence of urokinase plasminogen activator receptor was not required. Inhibition of ADAM-10 and -12, and of HB-EGF blocked EGFR activation in response to CTF. CTF-mediated activation of EGFR was mediated through Gβγ, src, and NAD(P)H oxidase.

CONCLUSIONS

In human coronary VSMC, uPA induces uPAR-independent, domain-dependent smooth muscle cell proliferation through transactivation of EGFR by a plasmin-mediated, ADAM-induced, and HB-EGF-dependent process, which is mediated by the intracellular pathways involving Gαi, Gβγ, src, and NAD(P)H oxidase.

Non-anticoagulant derivatives of heparin for the management of asthma: distant dream or close reality?

INTRODUCTION

Approximately 300 million people worldwide are currently affected by asthma. Improvements in the understanding of the mechanisms involved in such inflammatory airway disorders has led to the recognition of new therapeutic approaches. Heparin, a widely used anticoagulant, has been shown to be beneficial in the management of asthma. It belongs to the family of highly sulphated polysaccharides referred to as glycosaminoglycans, containing a heterogeneous mixture of both anticoagulant and non-anticoagulant polysaccharides. Experimental findings have suggested that heparin has potential anti-asthmatic properties owing to the ability of its non-anticoagulant oligosaccharides to bind and modulate the activity of a wide range of biological molecules involved in the inflammatory process.

AREAS COVERED

This review focuses on the potential mechanisms of action and clinical application of heparin as an anti-inflammatory agent for the management of asthma.

EXPERT OPINION

Heparin may play a significant role in the management of asthma. However, these properties are often hindered by the presence of anticoagulant oligosaccharides, which possess a significant risk of bleeding. Therefore, its therapeutic potential must be explored using well-designed clinical studies that focus on identifying and isolating the anti-inflammatory oligosaccharides of heparin and further elucidating the structure and mechanisms of actions of these non-anticoagulant oligosaccharides.

Low-concentration heparin suppresses ionomycin-activated CAMK-II/EGF receptor- and ERK-mediated signaling in mesangial cells

Heparin and endogenous heparinoids inhibit the proliferation of smooth muscle cells, including renal mesangial cells; multiple effects on signaling pathways are well established, including effects on PKC, Erk, and CaMK-II. Many studies have used heparin at concentrations of 100 microg/ml or higher, whereas endogenous concentrations of heparinoids are much lower. Here we report the effects of low-concentration (1 microg/ml) heparin on activation of several kinases and subsequent induction of the c-fos gene in mesangial cells in response to the calcium ionophore, ionomycin, in the absence of serum factors. Ionomycin rapidly increases the phosphorylation of CaMK-II (by 30 s), and subsequently of the EGF receptor (EGFR), c-Src, and Erk 1/2. Low-dose heparin suppresses the ionomycin-dependent phosphorylation of EGFR, c-Src, and Erk 1/2, but not of CaMK-II, whereas inhibition of activated CaMK-II reduces phosphorylation of EGFR, c-Src, and Erk. Our data support a mechanism whereby heparin acts at the cell surface to suppress downstream targets of CaMK-II, including EGFR, leading in turn to a decrease in Erk- (but not c-Src-) dependent induction of c-fos.

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.

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 EGF-like Growth Factor Decreases Neutrophil–Endothelial Cell Interactions

BACKGROUND

Hyperadhesiveness of neutrophils (PMN) to vascular endothelial cells (EC) followed by neutrophil transendothelial migration play important roles in the initiation of ischemia/reperfusion (I/R)-mediated injury. We investigated whether the ability of heparin-binding EGF-like growth factor (HB-EGF) to decrease intestinal injury after intestinal I/R is mediated, in part, by its ability to affect PMN-EC interactions and EC junctional integrity.

MATERIALS AND METHODS

Human umbilical vein EC monolayers were treated with HB-EGF (100 ng/mL) or phosphate-buffered saline followed by anoxia/reoxygenation (A/R). Simultaneously, labeled human PMN were treated with HB-EGF or phosphate-buffered saline and then co-incubated with EC for determination of PMN-EC adherence and PMN transendothelial migration. EC junctional integrity was also determined.

RESULTS

PMN-EC adhesion increased after exposure of EC to A/R compared to EC exposed to normoxia (87% versus 64% binding, P < 0.05, Wilcoxon rank sum test). A/R-induced PMN-EC hyperadherence was significantly decreased by treatment of PMN with HB-EGF compared to nontreated cells (51% versus 87% binding, P < 0.05). HB-EGF significantly decreased PMN transendothelial migration and also augmented EC tight junctional integrity after A/R.

CONCLUSIONS

HB-EGF significantly reduces A/R-induced PMN-EC adhesion and PMN transendothelial migration and augments junctional integrity in vitro. Thus, HB-EGF acts not only as a potent cytoprotective agent for the intestine, but as an anti-inflammatory agent as well.

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.

Cannabinoids induce cancer cell proliferation via tumor necrosis factor alpha-converting enzyme (TACE/ADAM17)-mediated transactivation of the epidermal growth factor receptor

Cannabinoids, the active components of marijuana and their endogenous counterparts were reported as useful analgetic agents to accompany primary cancer treatment by preventing nausea, vomiting, and pain and by stimulating appetite. Moreover, they have been shown to inhibit cell growth and to induce apoptosis in tumor cells. Here, we demonstrate that anandamide, Delta(9)-tetrahydrocannabinol (THC), HU-210, and Win55,212-2 promote mitogenic kinase signaling in cancer cells. Treatment of the glioblastoma cell line U373-MG and the lung carcinoma cell line NCI-H292 with nanomolar concentrations of THC led to accelerated cell proliferation that was completely dependent on metalloprotease and epidermal growth factor receptor (EGFR) activity. EGFR signal transactivation was identified as the mechanistic link between cannabinoid receptors and the activation of the mitogen-activated protein kinases extracellular signal-regulated kinase 1/2 as well as prosurvival protein kinase B (Akt/PKB) signaling. Depending on the cellular context, signal cross-communication was mediated by shedding of proAmphiregulin (proAR) and/or proHeparin-binding epidermal growth factor-like growth factor (proHB-EGF) by tumor necrosis factor alpha converting enzyme (TACE/ADAM17). Taken together, our data show that concentrations of THC comparable with those detected in the serum of patients after THC administration accelerate proliferation of cancer cells instead of apoptosis and thereby contribute to cancer progression in patients.

Heparin binding-epidermal growth factor improves blastocyst hatching and trophoblast outgrowth in the golden hamster

The effect of heparin binding-epidermal growth factor (HB-EGF) on the in-vitro development of hamster 8-cell embryos was investigated. Supplementation of HB-EGF to culture medium accelerated zona escape of blastocysts (63 +/- 9% compared with 33 +/- 9% after 36 h; P < 0.05). Complete zona escape of blastocysts persisted even after 48 h (61 +/- 11% versus 30 +/- 4%) and 60 h (75 +/- 6% versus 42 +/- 8%). Addition of anti-HB-EGF antibody drastically reduced the percentage of zona escaped-blastocysts (30.0 +/- 5.0% versus 92.3 +/- 2.8%; P < 0.05). Interestingly, a significant increase in the area of trophoblast outgrowth occurred in the presence of HB-EGF (116 x 10(3) +/- 8 x 10(3) microm(2) versus 74 x 10(3) +/- 8 x 10(3) microm(2) at 48 h; P < 0.05). This, however, was not due to an increased number of trophectodermal cells in HB-EGF-treated blastocysts. Immunoreactive HB-EGF was localized in blastocysts and uterine sections, visible by intense immunostaining in the luminal epithelium, particularly on the apical surface. Moreover, the expression of HB-EGF in the uterus was maximum on day 4 of pregnancy, coinciding with the timing of zona escape and implantation. The receptor of HB-EGF, viz. EGF receptor was also detected in blastocysts and the luminal epithelium of day 4 pregnant uterus. These results show that HB-EGF improves blastocyst hatching and trophoblast outgrowth in hamsters.

The metalloendopeptidase nardilysin (NRDc) is potently inhibited by heparin-binding epidermal growth factor-like growth factor (HB-EGF)

Nardilysin (N-arginine dibasic convertase, or NRDc) is a cytosolic and cell-surface metalloendopeptidase that, in vitro, cleaves substrates upstream of Arg or Lys in basic pairs. NRDc differs from most of the other members of the M16 family of metalloendopeptidases by a 90 amino acid acidic domain (DAC) inserted close to its active site. At the cell surface, NRDc binds heparin-binding epidermal growth factor-like growth factor (HB-EGF) and enhances HB-EGF-induced cell migration. An active-site mutant of NRDc fulfills this function as well as wild-type NRDc, indicating that the enzyme activity is not required for this process. We now demonstrate that NRDc starts at Met(49). Furthermore, we show that HB-EGF not only binds to NRDc but also potently inhibits its enzymic activity. NRDc-HB-EGF interaction involves the 21 amino acid heparin-binding domain (P21) of the growth factor, the DAC of NRDc and most probably its active site. Only disulphide-bonded P21 dimers are inhibitory. We also show that Ca(2+), via the DAC, regulates both NRDc activity and HB-EGF binding. We conclude that the DAC is thus a key regulatory element for the two distinct functions that NRDc fulfills, i.e. as an HB-EGF modulator and a peptidase.

Heparin-binding EGF-like growth factor (HB-EGF) decreases oxygen free radical production in vitro and in vivo

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) has been shown to protect intestinal epithelial cells from anoxia/reoxygenation in vitro, and to protect the intestines from ischemia/reperfusion (I/R) injury in vivo. The goal of the present study was to determine whether the cytoprotective effects of HB-EGF were due, in part, to its ability to decrease reactive oxygen species (ROS) production. Human whole blood, polymorphonuclear leukocytes, and monocytes, as well as rat intestinal epithelial cells, were exposed to stimuli designed to produce an oxidative burst in these cells. Treatment of the cells with HB-EGF led to a significant decrease in oxidative burst production. In vivo, total midgut I/R injury in rats led to increased ROS production, which was markedly decreased by HB-EGF treatment. Histochemically, I/R injury led to increased ROS production, which was significantly decreased with HB-EGF treatment. HB-EGF cytoprotection is due, in part, to its ability to decrease ROS production. Future studies will determine the mechanisms by which HB-EGF exerts these effects.

Receptor-based antidote for diphtheria

Although equine diphtheria antitoxin may be an effective therapy for human diphtheria, its use often induces serum sickness. We describe here a strategy for developing an alternative treatment based on the human diphtheria toxin (DT) receptor/heparin-binding epidermal growth factor-like growth factor (HB-EGF) precursor. Recombinant mature human HB-EGF acts as a soluble receptor analog, binding radioiodinated DT and preventing its binding to the cellular DT receptor/HB-EGF precursor. However, the possibility existed that radioiodinated DT-HB-EGF complexes associate with cells due to the binding of the heparin-binding domain of recombinant HB-EGF to cell surface heparan sulfate proteoglycans. This possibility was confirmed by performing DT binding studies in the presence of heparin. A recombinant truncated HB-EGF (residues 106 to 149), which lacks most of the heparin-binding domain, showed an essentially heparin-independent binding of radioiodinated DT to cells. Furthermore, it was a more effective inhibitor of DT binding than was recombinant mature HB-EGF. Since mature HB-EGF is a known ligand for the EGF receptor and is thus highly mitogenic (tumorigenic), we then changed amino acid residues in the EGF-like domain of the recombinant truncated HB-EGF and demonstrated that this DT receptor analog (I117A/L148A) displayed a low mitogenic effect. The truncated (I117A/L148A) HB-EGF protein retained high DT binding affinity, as confirmed by using surface plasmon resonance. Our results suggest that the truncated (I117A/L148A) HB-EGF protein could be an effective, safe antidote for human diphtheria.

Heparin-binding EGF-like growth factor down regulates proinflammatory cytokine-induced nitric oxide and inducible nitric oxide synthase production in intestinal epithelial cells

We have previously shown that heparin-binding EGF-like growth factor (HB-EGF) protects intestinal epithelial cells (IEC) from necrosis and apoptosis in vitro and from intestinal ischemia/reperfusion injury in vivo; however, the mechanisms of HB-EGF cytoprotection are unclear. Overproduction of iNOS and NO have been implicated in the pathogenesis of several forms of ischemia/reperfusion injury. We therefore studied whether HB-EGF could down-regulate proinflammatory cytokine-induced iNOS and NO production in intestinal epithelial cells in vitro. DLD-1 human intestinal epithelial cells were exposed to the proinflammatory cytokines interleukin-1beta (IL-1beta) (20 ng/ml) and interferon-gamma (IFN-gamma) (10 ng/ml) to stimulate iNOS induction and NO production. Cells were treated with HB-EGF (0-100 ng/ml) either before or with cytokine exposure, and cells and supernatants were harvested 24 and 48 h later. Accumulated NO was measured in supernatants by chemiluminescence. Total RNA was extracted from cell lysates for iNOS mRNA quantification using real-time reverse transcription-polymerase chain reaction (RT-PCR), and total protein was extracted from cell lysates for detection of iNOS protein. HB-EGF significantly decreased cytokine-induced NO production in a dose dependent manner, and NO reduction was associated with iNOS suppression at both the mRNA and protein levels. While cytokine exposure resulted in a significant increase in iNOS mRNA expression in these cells (109 plus minus 9 fold), HB-EGF reduced iNOS expression by 5.7-fold (P < 0.05). These results suggest that HB-EGF may exert its cytoprotective effects, in part, by down-regulating iNOS and NO production, and provides further rationale for additional testing of the effects of HB-EGF in the treatment of intestinal ischemia/reperfusion injury in vivo.

Heparin-binding EGF-like growth factor is present in human amniotic fluid and breast milk

BACKGROUND/PURPOSE

Heparin-binding EGF-like growth factor (HB-EGF) is a member of the epidermal growth factor (EGF) family that has been implicated in the healing of various organ injuries. Endogenous HB-EGF production is upregulated in response to injury to the kidney, liver, brain, skin, and intestine. Exogenous administration of HB-EGF protects against intestinal epithelial cell apoptosis and necrosis and intestinal ischemia/reperfusion (I/R) injury. This study examines the presence of endogenous HB-EGF in human amniotic fluid and breast milk, fluids that are in intimate contact with the developing and neonatal gastrointestinal tract.

METHODS

Breast milk samples were collected from lactating women and amniotic fluid was gathered from full-term uteri (cesarian sections) or preterm uteri (amniocentesis). Crude and partially purified breast milk and amniotic fluid samples were analyzed for HB-EGF levels using an HB-EGF-specific enzyme-linked immunosorbent assay (ELISA).

RESULTS

Analysis results showed detectable HB-EGF levels in human amniotic fluid and breast milk, ranging from 0.2 to 230 pg/mL. Breast milk and amniotic fluid subjected to heparin affinity or HB-EGF-affinity column chromatography showed bioactivity eluting at positions consistent with those known for native HB-EGF.

CONCLUSIONS

This study represents the first report of detectable HB-EGF in human amniotic fluid and breast milk. The presence of HB-EGF in these fluids may serve a role in the development of the gastrointestinal tract in utero, and in protection against gut mucosal injury after birth.

Heparin-binding EGF-like growth factor decreases inducible nitric oxide synthase and nitric oxide production after intestinal ischemia/reperfusion injury

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) has been shown to protect intestine from ischemia/reperfusion (I/R) injury in vivo and to down-regulate inducible nitric oxide synthase (iNOS) and nitric oxide (NO) production in intestinal epithelial cells in vitro. The present study was undertaken to investigate whether HB-EGF could modulate the iNOS/NO axis after total midgut I/R injury in rats. I/R injury induced a significant increase in iNOS gene expression (quantified by real-time RT-PCR) and protein production (detected by western blots), as well as elevation of serum NO levels (measured by chemiluminescence assay). Nitrotyrosine (NT) and iNOS production colocalized immunohistochemically, with positive staining found mainly in villous and crypt epithelial cells, as well as ganglion cells. Intraluminal administration of HB-EGF 45 min after the start of a 90-min ischemic interval significantly decreased I/R-induced iNOS gene expression and protein production, as well as serum NO levels. Immunohistochemically, HB-EGF administration led to elimination of iNOS and NT staining in crypt epithelial cells and ganglion cells, with only weak staining that remained in villous epithelial cells. Thus, HB-EGF protects the intestine from I/R injury, at least partially, through down-regulation of the iNOS/NO/NT pathway, a mechanism that is central to I/R injury in multiple organ systems.

Heparin-binding EGF-like growth factor decreases apoptosis in intestinal epithelial cells in vitro

BACKGROUND/PURPOSE

The production of heparin-binding EGF-like growth factor (HB-EGF) is upregulated during organ injury and has a cytoprotective effect during hypoxic stress in intestinal epithelial cells in vitro and intestinal ischemia-reperfusion injuries in vivo. The purpose of this study was to determine if HB-EGF-related cytoprotection is manifested through alterations in apoptosis.

METHODS

Human intestinal epithelial cell monolayers (DLD-1 and Caco-2) were stimulated with interleukin (IL)-1 (20 ng/mL), tumor necrosis factor (TNF)-alpha (40 ng/mL), and interferon (IFN)-gamma (10 ng/mL) with or without HB-EGF (1, 10 or 100 ng/mL) and analyzed for rates of apoptosis utilizing a Cell Death Detection ELISA and flow cytometry.

RESULTS

ELISA results showed a 3-fold increase in the level of apoptosis during stimulation with cytokines compared with nonstimulated cells (P <.05). Relative levels of cytokine induced apoptosis were reduced after 12 hours of HB-EGF exposure (P <.05) in a dose-dependent fashion. Results of flow cytometric analysis also showed a reduction in apoptosis at 6 hours when cell monolayers were stimulated with cytokines in conjunction with HB-EGF compared with cytokines alone (P <.05).

CONCLUSIONS

HB-EGF downregulated apoptosis in intestinal epithelial cells exposed to proinflammatory cytokines in vitro. The results of this study suggest that alterations in apoptosis may represent a possible mechanism by which this growth factor exerts its cytoprotective effect at the mucosal level during the proinflammatory state.

Site-directed mutagenesis of heparin-binding EGF-like growth factor (HB-EGF): analysis of O-glycosylation sites and properties

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a 22 kDa, O-glycosylated protein. HeLa cells infected with a recombinant vaccinia virus expressing human HB-EGF produced a secreted, bioactive protein, with Mr 22,000 that was decreased to 14,000 by treatment with O-glycanase. Site-directed mutagenesis of HB-EGF cDNA using oligonucleotide- and PCR-directed techniques was performed to change the potential glycosylation sites, Thr75 and Thr85, to alanine residues to prevent O-glycosylation. Purification and characterization of the mutant proteins demonstrated that: (i) both O-glycosylation sites of HB-EGF are utilized, (ii) HB-EGF secretion does not require O-glycosylation, (iii) removal of O-glycans does not affect proteolytic cleavage of the HB-EGF precursor, nor does it influence HB-EGF intracellular trafficking or subcellular localization, and (iv) HB-EGF produced by HeLa cells is heavily sialylated. Comparisons between glycosylation mutants and wild-type HB-EGF revealed no significant apparent differences in receptor binding activity.

Heparin blockade of thrombin-induced smooth muscle cell migration involves inhibition of epidermal growth factor (EGF) receptor transactivation by heparin-binding EGF-like growth factor

Agonists of G protein-coupled receptors, such as thrombin, act in part by transactivating the epidermal growth factor (EGF) receptor (EGFR). Although at first a ligand-independent mechanism for EGFR transactivation was postulated, it has recently been shown that this transactivation by various G protein-coupled receptor agonists can involve heparin-binding EGF-like growth factor (HB-EGF). Because thrombin stimulation of vascular smooth muscle cell migration is blocked by heparin and because heparin can displace HB-EGF, we investigated the possibility that thrombin stimulation of smooth muscle cells (SMCs) depends on EGFR activation by HB-EGF. In rat SMCs, EGFR phosphorylation and extracellular signal-regulated kinase (ERK) activation in response to thrombin are inhibited not only by the EGFR inhibitor AG1478 and by EGFR blocking antibody but also by heparin and by neutralizing HB-EGF antibody. HB-EGF-dependent signaling induced by thrombin is inhibited by batimastat, which suggests a requirement for pro-HB-EGF shedding by a metalloproteinase. We further demonstrate that this novel pathway is required for the migration of rat and baboon SMCs in response to thrombin. We conclude from these data that the inhibitory effect of heparin on SMC migration induced by thrombin relies, at least in part, on a blockade of HB-EGF-mediated EGFR transactivation.

Heparin-binding epidermal growth factor-like growth factor protects rat intestine from ischemia/reperfusion injury

BACKGROUND

We have shown previously that heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) is cytoprotective for intestinal epithelial cells exposed to hypoxia in vitro. We now examine the effects of HB-EGF on the recovery of small intestine from ischemic injury in vivo.

METHODS

Segmental intestinal ischemia of 60-min duration was produced in adult rats by occlusion of a first-order branch of the superior mesenteric artery. Recombinant HB-EGF (100 microg) was injected intraluminally into the proximal small bowel after 45 min of ischemia in experimental animals, and buffered saline was injected in control animals. Animals were sacrificed after 48 h, and the affected bowel was resected, processed, and examined microscopically, with histologic grading of the ischemic injury. Additional animals were allowed to recover for up to 1 month to evaluate mortality differences.

RESULTS

Intraluminal administration of HB-EGF resulted in significantly decreased extent and severity of ischemia/reperfusion injury, with significantly decreased grade of injury in the HB-EGF-treated compared with nontreated animals (average injury grade 0.66 compared with 2.44, respectively). Moreover, the mortality rate was significantly lower in the HB-EGF-treated animals compared with nontreated animals (0% vs 25%, respectively). HB-EGF-treated animals had increased weight gain in the postischemia recovery period.

CONCLUSIONS

We conclude that HB-EGF, given intraluminally, reduces both the amount and the severity of ischemia/reperfusion injury in the small bowel, reduces the mortality associated with intestinal ischemia, and may enhance intestinal recovery. The in vitro and in vivo cytoprotective effects of this growth factor suggest that it may, in the future, be clinically useful in treating patients with intestinal ischemia.

Glycosaminoglycans differentially bind HARP and modulate its biological activity

Heparin affin regulatory peptide (HARP) is a polypeptide belonging to a family of heparin binding growth/differentiation factors. The high affinity of HARP for heparin suggests that this secreted polypeptide should also bind to heparan sulfate proteoglycans derived from cell surface and extracellular matrix defined as extracellular compartments. Using Western blot analysis, we detected HARP bound to heparan sulfate proteoglycans in the extracellular compartments of MDA-MB 231 and MC 3T3-E1 as well as NIH3T3 cells overexpressing HARP protein. Heparitinase treatment of BEL cells inhibited HARP-induced cell proliferation, and the biological activity of HARP in this system was restored by the addition of heparin. We report that heparan sulfate, dermatan sulfate, and to a lesser extent, chondroitin sulfate A, displaced HARP bound to the extracellular compartment. Binding analyses with a biosensor showed that HARP bound heparin with fast association and dissociation kinetics (kass = 1.6 x 10(6) M-1 s-1; kdiss = 0.02 s-1), yielding a Kd value of 13 nM; the interaction between HARP and dermatan sulfate was characterized by slower association kinetics (kass = 0.68 x 10(6) M-1 s-1) and a lower affinity (Kd = 51 nM). Exogenous heparin, heparan sulfate, and dermatan sulfate potentiated the growth-stimulatory activity of HARP, suggesting that corresponding proteoglycans could be involved in the regulation of the mitogenic activity of HARP.

Heparin-binding epidermal growth factor-like growth factor in hippocampus: modulation of expression by seizures and anti-excitotoxic action

The expression of heparin-binding epidermal growth factor-like growth factor (HB-EGF), an EGF receptor ligand, was investigated in rat forebrain under basal conditions and after kainate-induced excitotoxic seizures. In addition, a potential neuroprotective role for HB-EGF was assessed in hippocampal cultures. In situ hybridization analysis of HB-EGF mRNA in developing rat hippocampus revealed its expression in all principle cell layers of hippocampus from birth to postnatal day (P) 7, whereas from P14 through adulthood, expression decreased in the pyramidal cell layer versus the dentate gyrus granule cells. After kainate-induced excitotoxic seizures, levels of HB-EGF mRNA increased markedly in the hippocampus, as well as in several other cortical and limbic forebrain regions. In the hippocampus, HB-EGF mRNA expression increased within 3 hr after kainate treatment, continued to increase until 24 hr, and then decreased; increases occurred in the dentate gyrus granule cells, in the molecular layer of the dentate gyrus, and in and around hippocampal pyramidal CA3 and CA1 neurons. At 48 hr after kainate treatment, HB-EGF mRNA remained elevated in vulnerable brain regions of the hippocampus and amygdaloid complex. Western blot analysis revealed increased levels of HB-EGF protein in the hippocampus after kainate administration, with a peak at 24 hr. Pretreatment of embryonic hippocampal cell cultures with HB-EGF protected neurons against kainate toxicity. The kainate-induced elevation of [Ca2+]i in hippocampal neurons was not altered in cultures pretreated with HB-EGF, suggesting an excitoprotective mechanism different from that of previously characterized excitoprotective growth factors. Taken together, these results suggest that HB-EGF may function as an endogenous neuroprotective agent after seizure-induced neural activity/injury.

Induction of anchorage independent growth by heparin-binding EGF-like growth factor (HB-EGF)

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is initially synthesized as a membrane bound protein that is subsequently processed to yield an approximately 74 amino acid secreted product. To investigate the biological activities of HB-EGF and its role(s) in tumor formation, the full-length HB-EGF cDNA was cloned under the regulation of the mouse metallothionein promoter and stably expressed in HB-EGF deficient mouse L cells. HB-EGF immunoreactive proteins of 21 and 24 kDa were observed from transfected MLC lysates, and these lysates exhibited the ability to bind to the EGF receptor, stimulate 3H-thymidine uptake in BALB/c-3T3 cells, and induce anchorage independent growth (AIG) of normal rat kidney (NRK) cells. Furthermore, NRK cells treated with either E. coli-derived or vaccinia virus-derived HB-EGF, as well as NRK cells directly transfected with the HB-EGF construct, demonstrated AIG. We conclude that HB-EGF is a potent growth factor capable of stimulating altered cell growth and anchorage independence.

Removal of the membrane-anchoring domain of epidermal growth factor leads to intracrine signaling and disruption of mammary epithelial cell organization

Autocrine EGF-receptor (EGFR) ligands are normally made as membrane-anchored precursors that are proteolytically processed to yield mature, soluble peptides. To explore the function of the membrane-anchoring domain of EGF, we expressed artificial EGF genes either with or without this structure in human mammary epithelial cells (HMEC). These cells require activation of the EGFR for cell proliferation. We found that HMEC expressing high levels of membrane- anchored EGF grew at a maximal rate that was not increased by exogenous EGF, but could be inhibited by anti-EGFR antibodies. In contrast, when cells expressed EGF lacking the membrane-anchoring domain (sEGF), their proliferation rate, growth at clonal densities, and receptor substrate phosphorylation were not affected by anti-EGFR antibodies. The sEGF was found to be colocalized with the EGFR within small cytoplasmic vesicles. It thus appears that removal of the membrane-anchoring domain converts autocrine to intracrine signaling. Significantly, sEGF inhibited the organization of HMEC on Matrigel, suggesting that spatial restriction of EGF access to its receptor is necessary for organization. Our results indicate that an important role of the membrane-anchoring domain of EGFR ligands is to restrict the cellular compartments in which the receptor is activated.

Heparin-binding EGF-like growth factor is cytoprotective for intestinal epithelial cells exposed to hypoxia

BACKGROUND

During recovery from intestinal ischemic injury, there is rapid growth of intestinal epithelia with regeneration of damaged villi. This study examines the effects of heparin-binding EGF-like growth factor (HB-EGF) on the recovery of intestinal epithelial cells exposed to hypoxia.

METHODS

The cytoprotective effects of HB-EGF were analyzed by placing IEC-18 cells in an anaerobic chamber with various timed HB-EGF treatments (prehypoxia, posthypoxia, pre- and posthypoxia, and no treatment). After 10 hours of hypoxia, lactate dehydrogenase (LDH) release, actin-filament (structural) integrity, adenosine triphosphate (ATP) levels, and posthypoxia proliferative activity were evaluated.

RESULTS

LDH analysis showed that HB-EGF exerted a cytoprotective effect during hypoxia. Pretreated cells had a significantly lower death rate during recovery (7.48%) compared with cells with no HB-EGF treatment (22.19%, P < .009). Confocal microscopic structural analysis of posthypoxia cells showed that F-actin structure was maintained in treated cells, whereas nontreated cells showed increased structural deterioration. ATP levels were significantly higher in the HB-EGF-treated cells compared with nontreated cells at 48 hours (P < .05). Finally, HB-EGF-treated cells had a significantly improved proliferative ability compared with nontreated cells during recovery from hypoxia (P < .05).

CONCLUSIONS

HB-EGF is a mitogenic growth factor for intestinal epithelial cells. Moreover, HB-EGF appears to protect intestinal epithelial cells from hypoxia, in part via maintenance of cytoskeletal structure and ATP stores. Finally, HB-EGF-treated cells also appear to have better proliferative abilities during recovery from hypoxia.

Expression of heparin-binding epidermal growth factor-like growth factor in rat brain

According to a recent report, messenger RNA coding for a member of the epidermal growth factor (EGF) family, heparin-binding EGF-like growth factor (HB-EGF), is expressed in the central nervous system (CNS). To obtain information about the role of HB-EGF in the brain, we carried out Northern analysis, in situ hybridization, and immunohistochemical studies evaluating the distribution and amounts of the growth factor using cDNA HB-EGF probes and an antibody raised against synthetic HB-EGF propeptide. Northern analysis revealed transcripts for HB-EGF in all regions of normal rat brain. Immunohistochemically, HB-EGF was demonstrated extensively in neurons at levels varying according to location. HB-EGF mRNA also was detected in neurons, suggesting that the growth factor is produced in these cells. HB-EGF mRNA and immunoreactivity were also demonstrated in interfascicular oligodendrocytes. These findings suggest that HB-EGF is a physiologic ligand for brain EGF receptors, and is likely to be important in neural function.

Characterization of cell-associated and soluble forms of connective tissue growth factor (CTGF) produced by fibroblast cells in vitro

Connective tissue growth factor (CTGF) is a mitogenic and chemotactic factor for cultured fibroblasts that has been implicated in wound healing, fibrotic disorders and uterine function. Although the primary translational products of the mouse, human and pig CTGF (mCTGF, hCTGF, pCTGF) genes are predicted to be secreted and of approximate M(r) 38,000, 10 kDa biologically active forms of pCTGF have recently been described. In this report, we show that human foreskin fibroblasts (HFFs) and mouse connective tissue fibroblasts contained 2.4 kb CTGF transcripts, stained positively with an anti-CTGF[81-94] peptide antiserum, and produced a 38 kDa protein that was immunoprecipitated by an anti-CTGF[247-260] peptide antiserum. While 38 kDa CTGF was readily detected in cell lysates, it was non- or barely detectable in conditioned medium. 38 kDa CTGF remained cell-associated for at least 5 days after synthesis and was not releasable by treatment of the cells with trypsin, heparin, 1 M NaCl or low pH. Purification of CTGF from human or mouse fibroblast conditioned medium resulted in the isolation of 10-12 kDa CTGF proteins that were heparin-binding, bioactive, and reactive with anti-CTGF[247-260] on Western blots. Whereas 10 kDa CTGF stimulated DNA synthesis in 3T3 cells to the same extent as platelet-derived growth factor (PDGF)-AA, -AB, or -BB, it did not compete with 125I-PDGF-BB for binding to alpha alpha, alpha beta or beta beta PDGF receptors (PDGF-R), did not stimulate tyrosine phosphorylation of PDGF-alpha-R or -beta-R, and was not antagonized by a neutralizing PDGF-R-alpha antiserum. These data show that, in cultured fibroblasts, 38 kDa CTGF is principally cell-associated whereas low mass forms of CTGF are soluble and biologically active. They further demonstrate that, contrary to the previously proposed properties of 38 kDa CTGF, 10 kDa CTGF does not bind to PDGF-R and stimulates Balb/c 3T3 cell mitosis via a PDGF-R-independent mechanism.

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.

Epidermal growth factor receptor (EGFR) and EGFR mutations, function and possible role in clinical trials

The epidermal growth factor receptor (EGFR) is a growth factor receptor that induces cell differentiation and proliferation upon activation through the binding of one of its ligands. The receptor is located at the cell surface, where the binding of a ligand activates a tyrosine kinase in the intracellular region of the receptor. This tyrosine kinase phosphorylates a number of intracellular substrates that activates pathways leading to cell growth, DNA synthesis and the expression of oncogenes such as fos and jun. EGFR is thought to be involved the development of cancer, as the EGFR gene is often amplified, and/or mutated in cancer cells. In this review we will focus on: (I) the structure and function of EGFR, (II) implications of receptor/ligand coexpression and EGFR mutations or overexpression, (III) its effect on cancer cells, (IV) the development of the malignant phenotype and (V) the clinical aspects of therapeutic targeting of EGFR.

Immunohistochemical localization of heparin-binding epidermal growth factor-like growth factor in normal skin and skin cancers

Heparin-binding epidermal growth factor (EGF)-like growth factor is a 22-kDa glycoprotein that was originally identified as a secreted product of cultured human macrophages. Although the growth factor mRNA has been identified in various cells and tissues, the tissue distribution of the protein itself has rarely been demonstrated. In this study, the EGF-like growth factor was detected immunohistochemically in a variety of human skin samples by indirect immunofluorescence using a polyclonal rabbit antiserum raised against residues 26-41 of mature heparin-binding EGF. The keratinocytes of a variety of epithelium-derived structures demonstrated reproducible, specific staining for the EGF. In normal tissues, this staining was prominent in the basal cells of the epidermis and in the epithelial cells lining epidermal appendages such as hair follicles, sebaceous sweat glands and eccrine sweat glands. In addition, specific staining was detected in skin cancers derived from the basal epithelial cell layer, including basal and squamous cell carcinomas of the skin, with no staining detected in melanoma specimens. Immunoreactive heparin-binding EGF was characteristically associated with the surface of cells. With minor exceptions, the immunoreactive sites are identical to the known EGF receptor distribution in the skin, and suggest that keratinocyte-derived heparin-binding EGF may act in concert with other EGF family members in processes such as skin morphogenesis and wound repair, as well as in the development of skin cancers.

Connective tissue growth factor: a mediator of TGF-beta action on fibroblasts

Connective tissue growth factor (CTGF) is a cysteine-rich mitogenic peptide that binds heparin and is secreted by fibroblasts after activation with transforming growth factor beta (TGF-beta). CTGF is a member of a highly conserved family of peptides that include immediate early gene products cef10, cyr61, fisp12; a putative avian proto-oncogene, nov; and a drosophila gene, twisted gastrulation, tsg, that controls medial mesoderm induction during dorsal-ventral axis pattern formation, a process also controlled by TGF-beta related peptides (dpp, scw). In the adult mammal, CTGF functions as a downstream mediator of TGF-beta action on connective tissue cells, where it stimulates cell proliferation and extracellular matrix synthesis. CTGF does not appear to act on epithelial cells or immune cells. Because the biological actions of TGF-beta are complex and affect many different cell types, CTGF may serve as a more specific target for selective intervention in processes involving connective tissue formation during wound repair or fibrotic disorders. Northern blot and in situ hybridization studies have demonstrated that CTGF is coordinately expressed with TGF-beta in every fibrotic disorder examined to date. Agents that inhibit CTGF production or action could lead to the development of new therapeutic approaches for the control of fibrotic disorders in humans.

Purification and characterization of novel heparin-binding growth factors in uterine secretory fluids. Identification as heparin-regulated Mr 10,000 forms of connective tissue growth factor

Uterine growth factors are potential effector molecules in embryo growth signaling pathways. Pig uterine luminal flushings contained a heparin-binding growth factor (HBGF) that required 0.8 M NaCl for elution from heparin columns and was termed HBGF-0.8. This factor, which was heat- and acid-labile and of Mr 10,000 as assessed by gel filtration, stimulated DNA synthesis in fibroblasts and smooth muscle cells but not endothelial cells. Two forms of HBGF-0.8, termed HBGF-0.8-P1 and HBGF-0.8-P2, exhibited differential heparin-binding properties. SDS-polyacrylamide gel electrophoresis showed that each form of HBGF-0.8 migrated with an apparent Mr of 10, 000 under reducing conditions. Amino acid sequencing revealed the N-terminal sequence EENIKKGKKXIRTPKI for HBGF-0.8-P1 and ENIKKGKKXIRT for HBGF-0.8-P2. These sequences corresponded, respectively, to residues 247-262 and 248-259 of the 349-residue predicted primary translation product of porcine connective tissue growth factor (pCTGF). 10-kDa CTGF-mediated fibroblast DNA synthesis was modulated by exogenous heparin, and CTGF-immunoreactive proteins of 10, 16, and 20 kDa were present in unfractionated uterine luminal flushings. These data reveal the identity of a novel growth factor in uterine fluids as a highly truncated form of CTGF and show that the N-terminal two-thirds of the CTGF primary translation product is not required for mitogenic activity or heparin binding.

Characterization of a novel amphiregulin-related molecule in 12-O-tetradecanoylphorbol-13-acetate-treated breast cancer cells

Amphiregulin (AR) can be induced at the mRNA level by 17-beta-estradiol (E2) or the phorbol ester tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). This study compares the effects of TPA and E2 on the regulation of processing of AR isoforms and on subcellular localization in human MCF-7 breast cancer cells. AR was localized in the nucleus of MCF-7 cells after E2 treatment, whereas it was predominantly secreted after TPA treatment. AR isoforms of 28, 18, and 10 kDa and an additional species of approximately 55-60 kDa were detected in the cellular conditioned media after TPA stimulation. Expression of this unusual AR isoform was inhibited by protein kinase C (PKC) inhibitors such as bryostatin or H-7. The biochemical properties of this isoform are consistent with it being an N-linked glycosylated form of the AR precursor that contains unprocessed mannose residues. The size of this large isoform is reduced to approximately 40 kDa after treating the TPA-induced MCF-7 cells with tunicamycin or treating the conditioned media of such cells with N-glycosidase F or with endoglycosidase H. Moreover, this isoform is able to blind several lectins with specificity for mannose residues. The 55-60 kDa glycosylated AR isoform, like lower Mr AR isoforms, is able to bind to heparin and to stimulate the growth of MCF-10A cells by interacting with the EGF receptor. These data suggest that TPA activation of PKC may be involved in post-translational modifications of AR, such as glycosylation, and in alteration of its subcellular routing to predominantly a secretory pathway.

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.

Targeting the epidermal growth factor receptor for therapy of carcinomas

As a group, the carcinomas represent a substantial proportion of all human malignancies, but, with relatively few exceptions, current treatments are ineffective. Modification of existing chemotherapeutic agents has not led to significant improvements in the survival of carcinoma patients, and development of new therapeutic strategies is imperative. It is now becoming apparent that activation of the epidermal growth factor receptor (EGF-R) has much wider implications than a straightforward stimulation of cell division. The pleiotropic effects of EGF-R signalling may influence tumour behaviour and the response of carcinomas to treatment; these are important considerations for the development of new therapies that aim to exploit the expression or modulate the function of the EGF-R in these tumours.

Cardiac allograft vasculopathy. Preferential regulation of endothelial cell-derived mesenchymal growth factors in response to a donor-specific cell-mediated allogeneic response

We have previously reported that cell-mediated immunity to vascular endothelium is associated with the development of cardiac allograft vasculopathy (CAV). The mechanism by which a cell-mediated immune response to the coronary vascular is translated into the development of CAV is, however unknown. Peripheral blood mononuclear cells (PBMCs) obtained serially following cardiac transplantation were cocultured with donor-specific human aortic endothelial cells (HAECs) in 47 allograft recipients, 9 of whom had CAV (CAV+) at 1 year by angiography. At 20 hr following coculture, HAEC poly (A+) RNA was isolated, reverse-transcribed, and the cDNA-amplified (PCR) for a panel of growth factors (GFs) known to alter smooth muscle cell proliferation or migration. Relative quantitation of PCR product was performed using high-pressure liquid chromatography (HPLC). Three patterns of GF regulation were observed depending on the GF, the time posttransplant, and whether the patient had CAV: (1) no regulation (TGF-beta, PDGF-A early post-tx); (2) upregulation irrespective of CAV (bFGF, PDGF-B, TGF-alpha early post-tx); and (3) preferential or exclusive upregulation by CAV+ patients (PDGF-A and TGF-alpha late post-tx, HB-EGF early and late post-tx). For example, using PBMCs as stimulators, obtained 6 months posttransplant from CAV+ patients, increases in HAEC-derived PDGF-A chain (31 +/- 7 to 69 +/- 11), TGF-alpha (97 +/- 27 to 201 +/- 23), and HB-EGF (78 +/- 16 to 173 +/- 27) mRNA were demonstrated (all P<0.05 or greater using HPLC peak area as units). These data demonstrate that cell-mediated activation of vascular endothelial cells in patients with CAV results in preferential upregulation of certain endothelial-derived mesenchymal growth factors capable of stimulating smooth muscle cell proliferation and migration.

Characterization of the gene encoding murine heparin-binding epidermal growth factor-like growth factor

The mouse gene (mHB-EGF) encoding heparin-binding epidermal growth factor-like growth factor was isolated from a mouse 129SVJ genomic library. DNA sequence analysis confirmed that the clone contained six exons (I-VI) and five introns (A-E), and spanned approx. 14 kb of DNA. PCR analysis showed that introns A-E of mHB-EGF are 203 bp, 2.5 kb, 5.5 kb, 825 bp and 272 bp in length, respectively. These results establish that mHB-EGF is similar in organization to human HB-EGF (hHB-EGF). However, DNA sequence analysis of introns A-E of mHB-EGF failed to show significant overall homology with those of hHB-EGF.

Production of heparin-binding epidermal growth factor-like growth factor (HB-EGF) at sites of thermal injury in pediatric patients

Fluids that accumulate at wound sites may be an important reservoir of growth factors that promote the normal wound healing response. The presence of heparin-binding growth factors was studied in burn wound fluid (BWF) from 45 pediatric patients who had sustained partial thickness burns. One of the growth factors present was similar to platelet-derived growth factor (PDGF) based on its heparin affinity, inhibition of bioactivity by a PDGF antiserum, and detection in a PDGF-AB enzyme-linked immunosorbent assay. A second growth factor was identified as heparin-binding epidermal growth factor-like growth factor (HB-EGF) based on its heparin affinity, competition with 125I-labeled epidermal growth factor (EGF) for EGF receptor binding, and recognition in biological assays and Western blots by two HB-EGF antisera. Amino acid sequence analysis of one form of this second growth factor verified its identity as an N-terminally truncated form of HB-EGF. Immunohistochemical analysis of partial thickness burns demonstrated the presence of HB-EGF in the advancing epithelial margin, islands of regenerating epithelium within the burn wound, and in the duct and proximal tubules of eccrine sweat glands. HB-EGF in the surface epithelium of burn wounds was uniformally distributed, whereas it was restricted to the basal epithelium in nonburned skin. These data support a role for PDGF and HB-EGF in burn wound healing and suggest that the response to injury includes deposition of HB-EGF and PDGF into blister fluid and a redistribution of HB-EGF in the surface epithelium near the wound site.

Carboxyl-terminal truncation of leucine76 converts heparin-binding EGF-like growth factor from a heparin-enhancible to a heparin-suppressible growth factor

Previous studies have indicated that heparin differentially regulates heparin-binding EGF-like growth factor (HB-EGF) and amphiregulin (AR) mitogenic activity. To further explore this phenomenon, these mitogens were compared under identical cell culture conditions in two different assays. The results of our present investigation demonstrated that AR-mediated mitogenic activity in the murine AKR-2B fibroblast-like cell line was inhibited by heparin, while HB-EGF activity was enhanced. However, the absolute effect of heparin appeared to be cell type specific since HB-EGF mitogenic activity was not dramatically affected by coincubation with heparin when tested on human dermal fibroblasts. Several studies have indicated that mutation of a conserved leucine in the carboxyl-terminal region of both EGF and transforming growth factor-alpha results in decreased affinity for EGF receptors. Since this leucine is present in the analogous position of HB-EGF, but absent in AR, we examined the effect of deleting this residue by carboxyl-terminal truncation of HB-EGF. Analysis of recombinant forms of HB-EGF demonstrated that HB-EGF can be converted to a heparin-inhibited growth factor if the putative mature form of the protein is truncated by two residues (leucine76 and proline77) at the carboxyl terminus. Further analysis demonstrated that only leucine76 appears to be required for heparin-dependent enhancement of HB-EGF-mediated mitogenic activity, indicating that this amino acid may play a pivotal role in controlling the response of HB-EGF to heparin or related glycosaminoglycan sulfates. Our results also suggest that expression of different HB-EGF forms in vivo could result in the production of HB-EGFs with divergent responses to sulfated glycosaminoglycans and proteoglycans.

Differential effects of a heparin antagonist (hexadimethrine) or chlorate on amphiregulin, basic fibroblast growth factor, and heparin-binding EGF-like growth factor activity

Amphiregulin (AR) and heparin-binding EGF-like growth factor (HB-EGF) are two recently identified members of the EGF family. Both AR and HB-EGF share with EGF the ability to interact with the type-1 EGF receptor; however, AR and HB-EGF differ from EGF in that both of these mitogens bind to heparin while EGF does not. To determine whether interactions with heparin-like molecules on the cell surface influence binding of AR and HB-EGF with EGF receptors and the subsequent mitogenic activity exerted by these growth factors, murine AKR-2B and Balb/MK-2 cells were treated with either an inhibitor of proteoglycan sulfation (chlorate) or a heparin antagonist (hexadimethrine). As expected, neither treatment significantly altered the specific binding of 125I-EGF on AKR-2B cells. Interestingly, treatment with either chlorate or hexadimethrine inhibited the ability of AR to compete with 125I-EGF for cell surface binding and also attenuated AR-mediated DNA synthesis. Thus, as has been suggested for other heparin-binding growth factors such as basic fibroblast growth factor (bFGF), the interaction of AR with an EGF-binding receptor appears to be facilitated by interaction with cell-associated sulfated glycosaminoglycans or proteoglycans. Unexpectedly, however, neither chlorate nor hexadimethrine treatment caused an inhibition of HB-EGF-induced mitogenic activity. Chlorate treatment did not significantly alter the ability of HB-EGF to compete with 125I-EGF for cell surface binding sites, however, heparin and hexadimethrine reduced the ability of HB-EGF to compete for 125I-EGF binding. These results suggest that, in AKR-2B cells, HB-EGF may mediate its mitogenic response at least in part through a receptor which appears to be selective for HB-EGF and permits HB-EGF-mediated mitogenic responses in the presence of hexadimethrine or heparin. Finally, hexadimethrine inhibited the specific binding and mitogenic activity of bFGF, suggesting that this cationic polymer can function as an antagonist of heparin-binding mitogens other than AR.

Biochemical and mitogenic properties of the heparin-binding growth factor HARP

Heparin affin regulatory peptide (HARP), also called Pleiotrophin (PTN), is a polypeptide that displays a high affinity for heparin and that shares approximately 50% sequence homology with Midkine (MK). According to this structural homology, these two molecules constitute a new family of heparin-binding proteins. The biological properties of HARP and MK remain largely a subject of debate. Both proteins have been described as neurite outgrowth promoting agents whereas until recently the mitogenic activity has been controversial. The aim of this review is to summarize the information on HARP with special focus on the recent data relating to its mitogenic properties.

Heparin-dependent binding and autophosphorylation of epidermal growth factor (EGF) receptor by heparin-binding EGF-like growth factor but not by EGF

Heparin-binding EGF-like growth factor (HB-EGF) is a recently identified member of the EGF family of growth factors and a potent mitogen for smooth muscle cells and fibroblasts. Chinese hamster ovary (CHO) cells genetically engineered to express the human EGF receptor bind with high affinity both EGF and HB-EGF. CHO mutant cells lacking heparan sulfate proteoglycans (HSPG) bind EGF equally well to wild-type cells and EGF binding is not affected by exogenous heparin. However, HSPG-deficient EGF receptor-expressing cells do not bind significant levels of HB-EGF unless heparin is present in the binding medium. Moreover, binding of radiolabeled EGF to HSPG-deficient EGF receptor-expressing cells is efficiently displaced by nonlabeled HB-EGF only in the presence of heparin. Signal transduction by the EGF receptor tyrosine kinase as evidenced by receptor autophosphorylation is induced by HB-EGF only in the presence of heparin, in contrast to EGF-induced receptor autophosphorylation, which is independent of heparin. These results directly demonstrate that HB-EGF but not EGF requires heparin or cell surface HSPG for binding and activation of the EGF receptor and that HB-EGF receptor interactions can be tightly regulated by the available local concentration of heparin-like molecules.

The heparin-binding domain of heparin-binding EGF-like growth factor can target Pseudomonas exotoxin to kill cells exclusively through heparan sulfate proteoglycans

Heparin-binding EGF-like growth factor (HB-EGF) is a smooth muscle cell mitogen composed of both EGF receptor and heparin-binding domains. To better understand the function of its domains, intact HB-EGF or its heparin-binding (HB) domain (amino acids 1-45) were fused to a mutant Pseudomonas exotoxin with an inactivated cell-binding domain. The resulting chimeric toxins, HB-EGF-PE* and HB-PE*, were tested on tumor cells, proliferating smooth muscle cells and a mutant Chinese hamster ovary cell line deficient in heparan sulfate proteoglycans (HSPGs). Two targets were found for HB-EGF-PE*. Cells were killed mainly through EGF receptors, but the HB domain was responsible for killing via HSPGs. HB-PE* did not bind to the EGF receptor and thus was cytotoxic by interacting exclusively with HSPGs. We conclude that the HB domain of HB-EGF is able to mediate internalization through HSPGs, without requiring the EGF receptor.