Diphtheria toxin binds to the epidermal growth factor (EGF)-like domain of human heparin-binding EGF-like growth factor/diphtheria toxin receptor and inhibits specifically its mitogenic activity

Duct cells contribute to regeneration of endocrine and acinar cells following pancreatic damage in adult mice

BACKGROUND & AIMS

There have been conflicting results on a cell of origin in pancreatic regeneration. These discrepancies predominantly stem from lack of specific markers for the pancreatic precursors/stem cells, as well as differences in the targeted cells and severity of tissue injury in the experimental models so far proposed. We attempted to create a model that used diphtheria toxin receptor (DTR) to ablate specific cell populations, control the extent of injury, and avoid induction of the inflammatory response.

METHODS

To target specific types of pancreatic cells, we crossed R26DTR or R26DTR/lacZ mice with transgenic mice that express the Cre recombinase in the pancreas, under control of the Pdx1 (global pancreatic) or elastase (acinar-specific) promoters.

RESULTS

Exposure of PdxCre;R26DTR mice to diphtheria toxin resulted in extensive ablation of acinar and endocrine tissues but not ductal cells. Surviving cells within the ductal compartment contributed to regeneration of endocrine and acinar cells via recapitulation of the embryonic pancreatic developmental program. However, following selective ablation of acinar tissue in ElaCreERT2;R26DTR mice, regeneration likely occurred by reprogramming of ductal cells to acinar lineage.

CONCLUSIONS

In the pancreas of adult mice, epithelial cells within the ductal compartment contribute to regeneration of endocrine and acinar cells. The severity of injury determines the regenerative mechanisms and cell types that contribute to this process.

HB-EGF synthesis and release induced by cholesterol depletion of human epidermal keratinocytes is controlled by extracellular ATP and involves both p38 and ERK1/2 signaling pathways

The heparin-binding EGF-like growth factor (HB-EGF) is an autocrine/paracrine keratinocyte growth factor, which binds to the epidermal growth factor (EGF) receptor family and plays a critical role during the re-epithelialization of cutaneous wound by stimulating the keratinocytes proliferation and migration. In this study, cellular stressing condition in autocrine cultures of human keratinocytes was induced by cholesterol depletion using methyl-beta-cyclodextrin (MβCD). MβCD treatment induces the expression and the release of HB-EGF. By analysis of the culture media, large amounts of cellular ATP were measured particularly after 1 h of MβCD treatment. To investigate whether ATP contributes to the expression of HB-EGF, the nonhydrolyzable ATP analogue, ATP-γ-S, was used to mimic the extracellular ATP released. We report that keratinocytes stimulated with ATP-γ-S induce HB-EGF expression and activate EGFR and ERK1/2. Using an antagonist of P2 purinergic receptors, we demonstrate that HB-EGF synthesis induced by lipid rafts disruption is dependent on ATP interaction with P2 purinergic receptors. Moreover, our data suggest that both MAPKs p38 and ERK1/2 are involved together or independently in the regulation of HB-EGF gene expression. These findings provide new insight into the signaling pathway by which HB-EGF is expressed after lipid rafts disruption. In summary, after lipid raft disruption, keratinocytes release large amount of extracellular ATP. ATP induces HB-EGF synthesis and release by interacting with the P2 purinergic receptor and through p38 and ERK1/2 signaling in response to a challenging environment. A release of ATP acts as an early stress response in keratinocytes.

Targeting the heparin-binding epidermal growth factor-like growth factor in ovarian cancer therapy

PURPOSE OF REVIEW

Therapeutics targeting the ErbB protein family receptors have not always yielded favorable or successful results in present cancer therapy. This review discusses the possibility of the clinical adaptation of targeting against heparin-binding epidermal growth factor-like growth factor (HB-EGF), one of the ligands of the ErbB system, in ovarian cancer therapy.

RECENT FINDINGS

We have previously described the results of studies concerning roles of HB-EGF in tumor formation in ovarian cancer. In brief, lisophosphatidic acid (LPA) and HB-EGF are predominantly expressed in advanced ovarian cancer, and LPA-induced, a disintegrin and metalloprotease-mediated ectodomain shedding of HB-EGF was found to be critical to tumor formation. We also noted that exogenous expression of HB-EGF enhanced tumor formation but inhibition blocked both extracellular signal-related kinase and serine/threonine protein kinase activation. Finally we investigated the antitumor effects of CRM197 - a specific HB-EGF inhibitor - on ovarian cancer cells by evaluating human ovarian cancer cell proliferation.

SUMMARY

We discuss alternative strategies to develop the chemotherapeutic agent based on targeting ErbB family ligands rather than their receptors. A phase I study of CRM197 for advanced ovarian cancer has already begun, which is the first approved trial of ErbB-ligand-targeted therapy. We also discuss clinical adaptations based on combination of CRM197 with other conventional chemotherapeutic agents.

Selective depletion of mouse kidney proximal straight tubule cells causes acute kidney injury

The proximal straight tubule (S3 segment) of the kidney is highly susceptible to ischemia and toxic insults but has a remarkable capacity to repair its structure and function. In response to such injuries, complex processes take place to regenerate the epithelial cells of the S3 segment; however, the precise molecular mechanisms of this regeneration are still being investigated. By applying the “toxin receptor mediated cell knockout” method under the control of the S3 segment-specific promoter/enhancer, Gsl5, which drives core 2 β-1,6-N-acetylglucosaminyltransferase gene expression, we established a transgenic mouse line expressing the human diphtheria toxin (DT) receptor only in the S3 segment. The administration of DT to these transgenic mice caused the selective ablation of S3 segment cells in a dose-dependent manner, and transgenic mice exhibited polyuria containing serum albumin and subsequently developed oliguria. An increase in the concentration of blood urea nitrogen was also observed, and the peak BUN levels occurred 3–7 days after DT administration. Histological analysis revealed that the most severe injury occurred in the S3 segments of the proximal tubule, in which tubular cells were exfoliated into the tubular lumen. In addition, aquaporin 7, which is localized exclusively to the S3 segment, was diminished. These results indicate that this transgenic mouse can suffer acute kidney injury (AKI) caused by S3 segment-specific damage after DT administration. This transgenic line offers an excellent model to uncover the mechanisms of AKI and its rapid recovery.

Mice overexpressing the gene for heparin-binding epidermal growth factor-like growth factor (HB-EGF) have increased resistance to hemorrhagic shock and resuscitation

BACKGROUND

The aim of the current study was to determine whether overexpression of heparin-binding epidermal growth factor-like growth factor (HB-EGF) could protect the intestines from injury after hemorrhagic shock and resuscitation in mice.

METHODS

Hemorrhagic shock and resuscitation was induced in HB-EGF transgenic and wild type mice. Cross-reacting material 197 (5 mg/kg) was administered to a subset of HB-EGF transgenic mice to block the overexpressed HB-EGF. Intestinal histologic injury scores, intestinal epithelial cell apoptosis indices, and gut barrier function were determined. The Student t test and 1-way analysis of variance were employed to compare the differences between groups.

RESULTS

All mice subjected to hemorrhagic shock and resuscitation had significantly increased intestinal histologic injury scores, apoptosis indices, and intestinal permeability compared with sham-operated mice. Compared with wild type mice, HB-EGF transgenic mice had significantly decreased histologic injury (mean injury grade 2.79 ± 0.84 vs 3.88 ± 1.43, P = .02), apoptosis indices (mean apoptosis index 8.77 ± 5.23 vs 17.91 ± 13.23, P = .03), and mucosal permeability (FITC-dextran 4 clearance 13.06 ± 5.67 vs 20.03 ± 7.81 nL/min/ m(2), P = .02) at 3 hours of reperfusion. HB-EGF transgenic mice subjected to hemorrhagic shock and resuscitation and treated with cross-reacting material 197 had a significantly increased histologic injury (mean injury grade 3.63 ± 1.00 vs 2.79 ± 0.84, P = .04) and mucosal permeability (FITC-dextran 4 clearance 22.87 ± 9.69 vs 13.06 ± 5.67 nL/min/cm2, P = .01) at 3 hours of reperfusion compared with non-cross-reacting material 197 treated transgenic mice, with no significant changes in apoptosis indices. Cross-reacting material 197 did not reverse the decreased apoptosis observed in HB-EGF transgenic mice subjected to hemorrhagic shock and resuscitation, which suggests that mechanisms in addition to decreased apoptosis may be responsible for the intestinal cytoprotective effects of endogenous HB-EGF overexpression.

CONCLUSION

Overexpression of HB-EGF increases resistance to hemorrhagic shock and resuscitation in mice.

Migration of growth factor-stimulated epithelial and endothelial cells depends on EGFR transactivation by ADAM17

The fibroblast growth factor receptor 2-IIIb (FGFR2b) and the vascular endothelial growth factor receptor 2 (VEGFR2) are tyrosine kinases that can promote cell migration and proliferation and have important roles in embryonic development and cancer. Here we show that FGF7/FGFR2b-dependent activation of epidermal growth factor receptor (EGFR)/ERK1/2 signalling and cell migration in epithelial cells require stimulation of the membrane-anchored metalloproteinase ADAM17 and release of heparin-binding epidermal growth factor (HB-EGF). Moreover, VEGF-A/VEGFR2-induced migration of human umbilical vein endothelial cells also depends on EGFR/ERK1/2 signalling and shedding of the ADAM17 substrate HB-EGF. The pathway used by the FGF7/FGFR2b signalling axis to stimulate shedding of substrates of ADAM17, including ligands of the EGFR, involves Src, p38 mitogen-activated protein-kinase and PI3K, but does not require the cytoplasmic domain of ADAM17. Based on these findings, ADAM17 emerges as a central component in a triple membrane-spanning pathway between FGFR2b or VEGFR2 and EGFR/ERK1/2 that is required for cell migration in keratinocytes and presumably also in endothelial cells.

CRM197-induced blood-brain barrier permeability increase is mediated by upregulation of caveolin-1 protein

Cross-reacting material 197 (CRM197), a non-toxin mutant of diphtheria toxin, could act as a diphtheria toxin receptor-specific carrier protein for the targeted delivery of macromolecular substances across the blood-brain barrier (BBB) in vitro. This study was performed to investigate the effects and mechanisms of CRM197 on the permeability of BBB in guinea pigs. Data from the Evans blue extravasation showed that the BBB permeability significantly increased after CRM197 injection in a dose-dependent manner. Transmission electron microscopy indicated CRM197 could induce increased pinocytotic vesicles and vacuoles in brain microvascular endothelial cells. Immunohistochemistry and western blot assay revealed that CRM197 enhanced caveolin-1 protein expression in brain microvessels. The caveolin-1 protein in the membrane fraction of microvessels began to upregulate at 5 min and reached the peak at 10 min after CRM197 treatment, associated by diminished expression of several tight junction-associated proteins ZO-1, occludin, and claudin-5. Thus, our results indicate that the in vivo targeting CRM197 leads to increased BBB permeability via upregulation of caveolin-1 protein, increased pinocytotic vesicles, and redistribution of tight junction-associated proteins in brain microvessels. CRM197 may have a potential application for targeted drug delivery across the BBB.

HB-EGF orchestrates the complex signals involved in triple-negative and trastuzumab-resistant breast cancer

A number of therapeutic strategies targeting epidermal growth factor receptor (EGFR) have not always led to success in the present state of breast cancer therapy. Notably, there is currently no way to treat trastuzumab-resistant and triple-negative breast cancer (TNBC). Here, we found that heparin-binding epidermal growth factor-like growth factor (HB-EGF), a member of the EGFR ligands, was predominantly expressed in breast cancer and that treatment with crossreacting material 197 (CRM197), a specific inhibitor of HB-EGF, blocked ERK as well as AKT activation via complexes of EGFR and unknown growth factor receptors in TNBC or through complexes of EGFR and human epidermal growth factor receptor-2 in trastuzumab-resistant breast cancer, caused significant cell apoptosis and inhibited tumor growth. Accordingly, we can provide a novel concept that a certain EGFR ligand is recognized as a rational target against breast cancer. In addition, it is plausible that CRM197 could be an effective anticancer agent for molecularly targeted therapies.

Bioactivity of immobilized EGF on self-assembled monolayers: optimization of the immobilization process

Last trends in Biomaterials focus the mimic of cellular environments capable to control cellular responses. Epidermal growth factor (EGF) is a pleiotropic cytokine known to regulate cell proliferation, differentiation, and death. This study aims to optimize the immobilization of EGF on 11-mercapto-1-undecyl-tetra(ethylene)glycol (EG4)-self-assembled monolayers (SAMs) and to establish a new model surface to study EGF-mediated signaling. Gold substrates were modified with a monolayer of EG4 and N,N'-carbonyldiimidazole (CDI) was used to activate hydroxyl terminated groups of EG4-SAMs. EGF was then immobilized on activated EG4-SAMs at pH 7.4, 4 degrees C, and 100 rpm. Different immobilization reaction times were tested as well as different CDI concentrations to optimize the reaction conditions and obtain a range of immobilized EGF concentrations on the surfaces. Surface characterization of EGF-SAMs was performed using radiolabeling, water contact angle measurements, X-ray photoelectron spectroscopy, and ELISA. Phosphorylation of EGFR on BT-20 breast cancer cell line by EGF-SAMs was tested by immunostaining. EGF was successfully immobilized on EG4-SAMs, at 4 degrees C and pH 7.4 in a range of concentrations from 3.6 +/- 0.8 to 17.6 +/- 1.5 ng/cm(2). The concentration of EGF increases with immobilization time and with the CDI concentration reaching the maximum for surfaces activated with 30 mg/mL of CDI after 48 h. The bioactivity of EGF-SAMs was confirmed by immunostaining of phospho-EGFR of BT-20 cells. This study described EGF immobilization on EG4-SAMs at different concentrations, which could be important surface models to study specific protein interactions at the molecular level evolving EGF-family of proteins.

Heparin-binding epidermal growth factor-like growth factor overexpression in transgenic mice increases resistance to necrotizing enterocolitis

BACKGROUND

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency and the leading surgical cause of death in premature infants. We have shown that administration of exogenous heparin-binding epidermal growth factor-like growth factor (HB-EGF) in mice protects the intestines from experimental NEC. The aim of the current study was to evaluate the effect of gain-of-function of endogenous HB-EGF on susceptibility to NEC.

METHODS

Neonatal HB-EGF transgenic (TG) mice and their wild-type (WT) counterparts were exposed to experimental NEC. An additional group of HB-EGF TG pups were also exposed to NEC, but received the HB-EGF antagonist cross-reacting material 197 (CRM197) injected subcutaneously immediately after birth. To examine gut barrier function, HB-EGF TG and WT pups received intragastric fluorescein isothiocyanate-labeled dextran under basal and stressed conditions, and serum fluorescein isothiocyanate-labeled dextran levels were measured.

RESULTS

Wild-type mice had an incidence of NEC of 54.2%, whereas HB-EGF TG mice had a significantly decreased incidence of NEC of 22.7% (P = .03). Importantly, administration of CRM197 to HB-EGF TG pups significantly increased the incidence of NEC to 65% (P = .004). HB-EGF TG mice had significantly decreased intestinal permeability compared to WT mice both under basal and stressed conditions.

CONCLUSIONS

Our results provide evidence that overexpression of the HB-EGF gene decreases susceptibility to NEC and that administration of the HB-EGF antagonist CRM197 reverses this protective effect.

Membrane type 1-matrix metalloproteinase cleaves off the NH2-terminal portion of heparin-binding epidermal growth factor and converts it into a heparin-independent growth factor

Epidermal growth factor (EGF) receptors (ErbB) and EGF family members represent promising targets for cancer therapy. Heparin-binding EGF (HB-EGF) is a member of the EGF family and is an important target for therapy in some types of human cancers. Processing of HB-EGF by proprotein convertases, and successively, by ADAM family proteases, generates a soluble growth factor that requires heparin as a cofactor. Although heparin potentiates HB-EGF activity in vitro, it is not clear how the heparin-binding activity of HB-EGF is regulated. Here, we show that membrane type 1-matrix metalloproteinase (MT1-MMP; MMP14), a potent invasion-promoting protease, markedly enhances HB-EGF-dependent tumor formation in mice. MT1-MMP additionally cleaves HB-EGF and removes the NH(2)-terminal 20 amino acids that are important for binding heparin. Consequently, the processing of HB-EGF by MT1-MMP converts HB-EGF into a heparin-independent growth factor with enhanced mitogenic activity, and thereby, expression of both proteins costimulates tumor cell growth in vitro and in vivo. The ErbB family of receptors expressed in human gastric carcinoma cells play a role in mediating enhanced HB-EGF activity by MT1-MMP during invasive cell growth in collagen. Thus, we shed light on a new mechanism whereby HB-EGF activity is regulated that should be considered when designing HB-EGF-targeted cancer therapy.

Anti-human HB-EGF monoclonal antibodies inhibiting ectodomain shedding of HB-EGF and diphtheria toxin binding

HB-EGF is a member of the EGF family of growth factors that bind and activate the EGF receptor. HB-EGF is synthesized as a membrane-anchored protein (proHB-EGF), and then proteolytically cleaved, resulting in the mitogenically active soluble form. ProHB-EGF functions as the receptor for the diphtheria toxin (DT). HB-EGF plays pivotal roles in pathophysiological processes, including cancer. Monoclonal antibodies (mAbs) specific for HB-EGF could be an important tool in HB-EGF research. However, few such mAbs have been established to date. In this study, we newly generated seven clones of hybridoma-derived mAbs by immunizing HB-EGF null mice with recombinant human HB-EGF protein. All mAbs specifically bound to human HB-EGF but not to mouse HB-EGF. Epitope mapping analysis showed that most of the mAbs recognized the EGF-like domain. Although none of the newly isolated mAbs directly inhibited the mitogenic activity of HB-EGF for EGFR-expressing cells, some strongly inhibited DT-binding. Interestingly, some of the mAbs efficiently inhibited ectodomain shedding of proHB-EGF, and consequently prevented the cell growth of the EGFR-expressing cells in a co-culture system with proHB-EGF-expressing cells. Hence, these new anti-HB-EGF mAbs may advance clinical as well as basic research on HB-EGF.

Cytosolic phospholipase A2 activation correlates with HER2 overexpression and mediates estrogen-dependent breast cancer cell growth

Cytosolic phospholipase A(2)alpha (cPLA(2)alpha) catalyzes the hydrolysis of membrane glycerol-phospholipids to release arachidonic acid as the first step of the eicosanoid signaling pathway. This pathway contributes to proliferation in breast cancer, and numerous studies have demonstrated a crucial role of cyclooxygenase 2 and prostaglandin E(2) release in breast cancer progression. The role of cPLA(2)alpha activation is less clear, and we recently showed that 17beta-estradiol (E2) can rapidly activate cPLA(2)alpha in MCF-7 breast cancer cells. Overexpression or gene amplification of HER2 is found in approximately 30% of breast cancer patients and correlates with a poor clinical outcome and resistance to endocrine therapy. This study reports the first evidence for a correlation between cPLA(2)alpha enzymatic activity and overexpression of the HER2 receptor. The activation of cPLA(2)alpha in response to E2 treatment was biphasic with the first phase dependent on trans-activation through the matrix metalloproteinase-dependent release of heparin-bound epidermal growth factor. EGFR/HER2 heterodimerization resulted in downstream signaling through the ERK1/2 cascade to promote cPLA(2)alpha phosphorylation at Ser505. There was a correlation between HER2 and cPLA(2)alpha expression in six breast cancer cell lines examined, and inhibition of HER2 activation or expression in the SKBR3 cell line using herceptin or HER2-specific small interfering RNA, respectively, resulted in decreased activation and expression of cPLA(2)alpha. Pharmacological blockade of cPLA(2)alpha using a specific antagonist suppressed the growth of both MCF-7 and SKBR3 cells by reducing E2-induced proliferation and by stimulating cellular apoptosis and necrosis. This study highlights cPLAalpha(2) as a potential target for therapeutic intervention in endocrine-dependent and endocrine-independent breast cancer.

Function-specific intracellular signaling pathways downstream of heparin-binding EGF-like growth factor utilized by human trophoblasts

Heparin-binding EGF-like growth factor (HBEGF) is expressed by trophoblast cells throughout gestation. First-trimester cytotrophoblast cells are protected from hypoxia-induced apoptosis because of the accumulation of HBEGF through a posttranscriptional autocrine mechanism. Exogenous application of HBEGF is cytoprotective in a hypoxia/reoxygenation (H/R) injury model and initiates trophoblast extravillous differentiation to an invasive phenotype. The downstream signaling pathways induced by HBEGF that mediate these various cellular activities were identified using two human first-trimester cytotrophoblast cell lines, HTR-8/SVneo and SW.71, with similar results. Recombinant HBEGF (1 nM) induced transient phosphorylation of MAPK3/1 (ERK), MAPK14 (p38), and AKT within 15 min and JNK after 1-2 h. To determine which downstream pathways regulate the various functions of HBEGF, cells were treated with specific inhibitors of the ERK upstream regulator MEK (U0126), the AKT upstream regulator phosphoinositide-3 (PI3)-kinase (LY294002), MAPK14 (SB203580), and JNK (SP600125), as well as with inactive structural analogues. Only SB203580 specifically prevented HBEGF-mediated rescue during H/R, while each inhibitor attenuated HBEGF-stimulated cell migration. Accumulation of HBEGF at reduced oxygen was blocked only by a combination of U0126, SB203580, and SP600125. We conclude that HBEGF advances trophoblast extravillous differentiation through coordinate activation of PI3 kinase, ERK, MAPK14, and JNK, while only MAPK14 is required for its antiapoptotic activity. Additionally, hypoxia induces an autocrine increase in HBEGF protein levels through MAPK14, JNK or ERK. These experiments reveal a complexity of the intracellular signaling circuitry that regulates trophoblast functions critical for implantation and placentation.

The epoxyeicosatrienoic acid-stimulated phosphorylation of EGF-R involves the activation of metalloproteinases and the release of HB-EGF in cancer cells

AIM

To test the hypothesis that the epoxyeicosatrienoic acid (EET)-induced transactivation of EGF-R depends on the activation of metalloproteinases and the subsequent release of HB-EGF in cancer cells.

METHODS

Exogenous 14,15-EET were added to four human-derived cancer cell lines Tca-8113, A549, HepG2, and MDA-MB-231, or these same cell lines were transfected with a mutant CYP epoxygenase (CYP102 F87V, an active 14,15-epoxygenase). The effects of elevated EET levels on the phosphorylation of tyrosine residues in the EGF receptor and on ERK1/2 activation were then assessed.

RESULTS

Both the addition of 14,15-EET and the transfection of cells with CYP102 F87V markedly increased the phosphorylation of the tyrosine residues of EGF-R and ERK1/2, an effect that was blocked by a selective EGF-R tyrosine kinase inhibitor (tyrphostin AG1478), a broad-spectrum metalloproteinase inhibitor (1,10-phenanthroline), and an inhibitor of HB-EGF release (CRM197) in Tca-8113 cells. In addition, AG1478, 1,10-phenanthroline, and CRM197 also inhibited the tyrosine phosphorylation of EGF-R and ERK1/2 that was induced by 14,15-EET in the A549, HepG2, and MDA-MB-231 cell lines.

CONCLUSION

These results suggest that the EET-induced transactivation of EGF-R depends on activation of metalloproteinases and the subsequent release of HB-EGF in cancer cell lines.

A review of the international issues surrounding the availability and demand for diphtheria antitoxin for therapeutic use

Diphtheria treatment requires early administration of diphtheria antitoxin (DAT), an immunoglobulin preparation that neutralises circulating diphtheria toxin. Here, we review issues relating to the supply and use of DAT and assess its availability by means of an international survey. Results showed that several countries do not currently hold DAT stockpiles due to low prevalence, and hence perceived risk of diphtheria, and/or difficulties in obtaining DAT supplies. The potential for importation of cases into any country exists globally, since diphtheria remains endemic in many regions. It is therefore important that DAT be readily available - particularly since waning diphtheria immunity has been observed among adult populations in countries with good vaccination coverage. Options for diphtheria therapy are discussed.

Epidermal growth factor receptor regulates pancreatic fibrosis

The development of pancreatic fibrosis has been shown to be a major component in several diseases of the pancreas including pancreatic cancer, chronic pancreatitis, and type 2 diabetes mellitus, but its actual role in the progression of these disorders is still unknown. This fibrosis is characterized by stromal expansion and the excessive deposition of extracellular matrix (ECM) that replaces pancreatic tissue. This eventually leads to dysregulation of ECM turnover, production of cytokines, restriction of blood flow, and often exocrine and endocrine insufficiencies. Activated pancreatic stellate cells (PSCs) have been identified as key mediators in the progression of pancreatic fibrosis, serving as the predominant source of excess ECM proteins. Previously, we found that overexpression of the growth factor heparin-binding epidermal growth factor-like growth factor (HB-EGF) in pancreatic islets led to intraislet fibrosis. HB-EGF binds to and activates two receptors, epidermal growth factor receptor (EGFR) and ErbB4, as well as heparin moieties and CD9/DRAP27. To understand the mechanism underlying the induction of fibrogenesis by HB-EGF, we utilized a hypomorphic allele of Egfr, the Waved-2 allele, to demonstrate that EGFR signaling regulates fibrogenesis in vivo. Using an in vitro cell migration assay, we show that HB-EGF regulates both chemoattraction and stimulation of proliferation of PSCs via EGFR activation.

Synergistic anti-tumor effect of paclitaxel with CRM197, an inhibitor of HB-EGF, in ovarian cancer

Heparin-binding EGF-like growth factor (HB-EGF) plays a pivotal role in tumor growth and clinical outcomes in patients with ovarian cancer, leading to the validation of HB-EGF as a target for ovarian cancer therapy. In this study, we investigated the anti-tumor effects of paclitaxel, as an anti-cancer agent, and CRM197, as a specific inhibitor off HB-EGF, in ovarian cancer. Paclitaxel induced transient ERK activation and sustained activation of JNK and p38 MAPK through the ectodomain shedding of HB-EGF in SKOV3 cells. In addition, the overexpression of HB-EGF in paclitaxel-treated SKOV3 cells resulted in modulation of paclitaxel-evoked MAPK signaling, including marked activation of ERK and Akt, and minimized activation of JNK and p38 MAPK, indicating that HB-EGF is involved in drug sensitivity through the balance of anti-apoptotic and pro-apoptotic signals induced by paclitaxel. The combination of paclitaxel with CRM197 had an inhibitory effect on cell proliferation and enhanced apoptosis via the inhibition of ERK and Akt activation and the stimulation of p38 and JNK activation. More prominently, the administration of paclitaxel with CRM197 resulted in synergistic anti-tumor effects in SKOV3 cells and in SKOV3 cells overexpressing HB-EGF in xenografted mice. Accordingly, inhibitory agents against HB-EGF, such as CRM197, represent possible chemotherapeutic and chemosensitizing agents for ovarian cancer.

ERBBs in the gastrointestinal tract: recent progress and new perspectives

The gastrointestinal epithelium does much more than provide a physical barrier between the intestinal lumen and our internal milieu. It is actively engaged in absorption and secretion of salt and water via ion transporters, exchangers and selective ion channels. It is also a continuously self-renewing epithelium that undergoes ordered growth and differentiation along its vertical axis. From this dual perspective, we will consider the actions of the ERBB family of ligands and receptors in the maintenance of gastrointestinal homeostasis and discuss instances when the actions of this family go awry such as in cancer and Ménétrier's disease.

The anti-EGFR monoclonal antibody blocks cisplatin-induced activation of EGFR signaling mediated by HB-EGF

Cisplatin is a key agent in combination chemotherapy for various types of solid tumor. We now show that cisplatin activates signaling by the epidermal growth factor receptor (EGFR) by inducing cleavage of heparin-binding epidermal growth factor-like growth factor (HB-EGF). Matuzumab, a monoclonal antibody to EGFR, inhibited cisplatin-induced EGFR signaling, likely through competition with the soluble form of HB-EGF for binding to EGFR. Matuzumab enhanced the antitumor effect of cisplatin in nude mice harboring human non-small cell lung cancer xenografts. Our findings shed light on the mechanism by which monoclonal antibodies to EGFR might augment the efficacy of cisplatin.

Multiple mechanisms are responsible for transactivation of the epidermal growth factor receptor in mammary epithelial cells

The number of distinct signaling pathways that can transactivate the epidermal growth factor receptor (EGFR) in a single cell type is unclear. Using a single strain of human mammary epithelial cells, we found that a wide variety of agonists, such as lysophosphatidic acid (LPA), uridine triphosphate, growth hormone, vascular endothelial growth factor, insulin-like growth factor-1 (IGF-1), and tumor necrosis factor-alpha, require EGFR activity to induce ERK phosphorylation. In contrast, hepatocyte growth factor can stimulate ERK phosphorylation independent of the EGFR. EGFR transactivation also correlated with an increase in cell proliferation and could be inhibited with metalloprotease inhibitors. However, there were significant differences with respect to transactivation kinetics and sensitivity to different inhibitors. In particular, IGF-1 displayed relatively slow transactivation kinetics and was resistant to inhibition by the selective ADAM-17 inhibitor WAY-022 compared with LPA-induced transactivation. Studies using anti-ligand antibodies showed that IGF-1 transactivation required amphiregulin production, whereas LPA was dependent on multiple ligands. Direct measurement of ligand shedding confirmed that LPA treatment stimulated shedding of multiple EGFR ligands, but paradoxically, IGF-1 had little effect on the shedding rate of any ligand, including amphiregulin. Instead, IGF-1 appeared to work by enhancing EGFR activation of Ras in response to constitutively produced amphiregulin. This enhancement of EGFR signaling was independent of both receptor phosphorylation and PI-3-kinase activity, suggestive of a novel mechanism. Our studies demonstrate that within a single cell type, the EGFR autocrine system can couple multiple signaling pathways to ERK activation and that this modulation of EGFR autocrine signaling can be accomplished at multiple regulatory steps.

The significance of disulfide bonding in biological activity of HB-EGF, a mutagenesis approach

A site-directed mutagenesis approach was taken to disrupt each of 3 disulfide bonds within human HB-EGF by substituting serine for both cysteine residues that contribute to disulfide bonding. Each HB-EGF disulfide analogue (HB-EGF-Cys/Ser(108/121), HB-EGF-Cys/Ser(116/132), and HB-EGF-Cys/Ser(134/143)) was cloned under the regulation of the mouse metallothionein (MT) promoter and stably expressed in mouse fibroblasts. HB-EGF immunoreactive proteins with M(r) of 6.5, 21 and 24 kDa were observed from lysates of HB-EGF and each HB-EGF disulfide analogue. HB-EGF immunohistochemical analyses of each HB-EGF stable cell line demonstrated ubiquitous protein expression except HB-EGF-Cys/Ser(108/121) and HB-EGF-Cys/Ser(116/132) stable cell lines which exhibited accumulated expression immediately outside the nucleus. rHB-EGF, HB-EGF, and HB-EGF(134/143) proteins competed with 125I-EGF in an A431 competitive binding assay, whereas HB-EGF-Cys/Ser(108/121) and HB-EGF-Cys/Ser(116/132) failed to compete. Each HB-EGF disulfide analogue lacked the ability to stimulate tyrosine phosphorylation of the 170 kDa EGFR. These results suggest that HB-EGF-Cys/Ser(134/143) antagonizes EGFRs.

Expression of heparin-binding EGF-like growth factor in term chorionic villous explants and its role in trophoblast survival

Heparin-binding EGF-like growth factor (HBEGF) induces trophoblast extravillous differentiation and prevents apoptosis. These functions are compromised in preeclampsia. Because HBEGF is downregulated in placentas delivered by women with preeclampsia, we have examined its expression and cytoprotective activity in term villous explants. Chorionic villous explants prepared from non-pathological placentas collected by cesarean section at term were cultured at either 20% or 2% O2 and treated with the HBEGF antagonist CRM197 or recombinant HBEGF. Paraffin sections were assayed for trophoblast death, proliferation and HBEGF expression using the TUNEL method, immunohistochemistry for nuclear Ki67 expression and semi-quantitative immunohistochemistry with image analysis, respectively. Trophoblast cell death was increased significantly after 8h of culture with CRM197 or by culture for 2h at 2% O2. Exogenous HBEGF prevented cell death due to hypoxia. Proliferative capacity was not affected by culture at either 20% or 2% O2. Contrary to first trimester placenta, term trophoblasts do not elevate HBEGF expression in response to hypoxia. However, low endogenous levels of HBEGF are required to maintain survival. Therefore, HBEGF-mediated signaling significantly reduces trophoblast cell death at term and its deficiency in preeclampsia could negatively impact trophoblast survival.

Transcutaneous immunization with cross-reacting material CRM(197) of diphtheria toxin boosts functional antibody levels in mice primed parenterally with adsorbed diphtheria toxoid vaccine

Transcutaneous immunization (TCI) capitalizes on the accessibility and immunocompetence of the skin, elicits protective immunity, simplifies vaccine delivery, and may be particularly advantageous when frequent boosting is required. In this study we examined the potential of TCI to boost preexisting immune responses to diphtheria in mice. The cross-reacting material (CRM(197)) of diphtheria toxin was used as the boosting antigen and was administered alone or together with either one of two commonly used mucosal adjuvants, cholera toxin (CT) and a partially detoxified mutant of heat-labile enterotoxin of Escherichia coli (LTR72). We report that TCI with CRM(197) significantly boosted preexisting immune responses elicited after parenteral priming with aluminum hydroxide-adsorbed diphtheria toxoid (DTxd) vaccine. In the presence of LTR72 as an adjuvant, toxin-neutralizing antibody titers were significantly higher than those elicited by CRM(197) alone and were comparable to the functional antibody levels induced after parenteral booster immunization with the adsorbed DTxd vaccine. Time course study showed that high levels of toxin-neutralizing antibodies persisted for at least 14 weeks after the transcutaneous boost. In addition, TCI resulted in a vigorous antigen-specific proliferative response in all groups of mice boosted with the CRM(197) protein. These findings highlight the promising prospect of using booster administrations of CRM(197) via the transcutaneous route to establish good herd immunity against diphtheria.

Heparin-binding epidermal growth factor and Src family kinases in proliferation of renal epithelial cells

Our recent studies have shown that proliferation of renal proximal tubular cells (RPTC) in the absence of growth factors requires activation of the epidermal growth factor (EGF) receptor. We sought to identify the endogenous EGF receptor ligand and investigate the mechanism(s) by which RPTC proliferate in different models. RPTC expressed both pro- and cleaved forms of heparin-binding epidermal growth factor (HB-EGF) and several metalloproteinases (MMP-2, -3, -9, and ADAM10, ADAM17) that have been reported to cleave HB-EGF. Treatment of RPTC with CRM 197, an inhibitor of HB-EGF binding to the EGF receptor, or downregulation of HB-EGF with small interfering RNA inhibited RPTC proliferation following plating. Furthermore, GM6001 (pan-MMP inhibitor), tumor-necrosis factor protease inhibitor-1 (TAPI-1; MMP and ADAM17 inhibitor), and GW280264X (ADAM10 and -17 inhibitor), but not GI254023X (ADAM10 inhibitor), attenuated the proliferation after plating. Although EGF receptor activation is required for RPTC proliferation after oxidant injury, CRM197, GM6001, and TAPI-1 did not block this response. In contrast, inhibition of Src with PP1 blocked EGF receptor activation and RPTC proliferation after oxidant injury. In addition, PP1 treatment attenuated HB-EGF-enhanced RPTC proliferation. We suggest that RPTC proliferation after plating is mediated by HB-EGF produced through an autocrine/paracrine mechanism and RPTC proliferation following oxidant injury is mediated by Src without involvement of HB-EGF.

Oligomerization of membrane-bound diphtheria toxin (CRM197) facilitates a transition to the open form and deep insertion

Diphtheria toxin (DT) contains separate domains for receptor-specific binding, translocation, and enzymatic activity. After binding to cells, DT is taken up into endosome-like acidic compartments where the translocation domain inserts into the endosomal membrane and releases the catalytic domain into the cytosol. The process by which the catalytic domain is translocated across the endosomal membrane is known to involve pH-induced conformational changes; however, the molecular mechanisms are not yet understood, in large part due to the challenge of probing the conformation of the membrane-bound protein. In this work neutron reflection provided detailed conformational information for membrane-bound DT (CRM197) in situ. The data revealed that the bound toxin oligomerizes with increasing DT concentration and that the oligomeric form (and only the oligomeric form) undergoes a large extension into solution with decreasing pH that coincides with deep insertion of residues into the membrane. We interpret the large extension as a transition to the open form. These results thus indicate that as a function of bulk DT concentration, adsorbed DT passes from an inactive state with a monomeric dimension normal to the plane of the membrane to an active state with a dimeric dimension normal to the plane of the membrane.

Diphtheria toxin mutant CRM197 is an inhibitor of protein synthesis that induces cellular toxicity

Diphtheria toxin (DT) ADP-rybosylates elongation factor-2 on a modified histidine residue called diphthamide, leading to a block in protein synthesis. CRM197 is a nontoxic DT mutant commonly used as a carrier for conjugate vaccines, and may have a potential as an anti-tumor agent. We now report that CRM197 expression is indeed toxic to cells, and inhibits protein synthesis. These results should be considered for future vaccine studies, and to investigate the mechanism of CRM197-mediated anti-tumor effect.

Secretion of IL-13 by airway epithelial cells enhances epithelial repair via HB-EGF

Inappropriate repair after injury to the epithelium generates persistent activation, which may contribute to airway remodeling. In the present study we hypothesized that IL-13 is a normal mediator of airway epithelial repair. Mechanical injury of confluent airway epithelial cell (AEC) monolayers induced expression and release of IL-13 in a time-dependent manner coordinate with repair. Neutralizing of IL-13 secreted from injured epithelial cells by shIL-13Ralpha2.FC significantly reduced epithelial repair. Moreover, exogenous IL-13 enhanced epithelial repair and induced epidermal growth factor receptor (EGFR) phosphorylation. We examined secretion of two EGFR ligands, epidermal growth factor (EGF) and heparin-binding EGF (HB-EGF), after mechanical injury. Our data showed a sequential release of the EGF and HB-EGF by AEC after injury. Interestingly, we found that IL-13 induces HB-EGF, but not EGF, synthesis and release from AEC. IL-13-induced EGFR phosphorylation and the IL-13-reparative effect on AEC are mediated via HB-EGF. Finally, we demonstrated that inhibition of EGFR tyrosine kinase activity by tyrphostin AG1478 increases IL-13 release after injury, suggesting negative feedback between EGFR and IL-13 during repair. Our data, for the first time, showed that IL-13 plays an important role in epithelial repair, and that its effect is mediated through the autocrine release of HB-EGF and activation of EGFR. Dysregulation of EGFR phosphorylation may contribute to a persistent repair phenotype and chronically increased IL-13 release, and in turn result in airway remodeling.

Epidermal growth factor-like growth factors prevent apoptosis of alcohol-exposed human placental cytotrophoblast cells

Maternal alcohol abuse during pregnancy can produce an array of birth defects comprising fetal alcohol syndrome. A hallmark of fetal alcohol syndrome is intrauterine growth retardation, which is associated with elevated apoptosis of placental cytotrophoblast cells. Using a human first trimester cytotrophoblast cell line, we examined the relationship between exposure to ethanol and cytotrophoblast survival, as well as the ameliorating effects of epidermal growth factor (EGF)-like growth factors produced by human cytotrophoblast cells. After exposure to 0-100 mM ethanol, cell death was quantified by the TUNEL method, and expression of the nuclear proliferation marker, Ki67, was measured by immunohistochemistry. The mode of cell death was determined by assessing annexin V binding, caspase 3 activation, pyknotic nuclear morphology, reduction of TUNEL by caspase inhibition, and cellular release of lactate dehydrogenase. Ethanol significantly reduced proliferation and increased cell death approximately 2.5-fold through the apoptotic pathway within 1-2 h of exposure to 50 mM alcohol. Exposure to 25-50 mM ethanol significantly increased transforming growth factor alpha (TGFA) and heparin-binding EGF-like growth factor (HBEGF), but not EGF or amphiregulin (AREG). When cytotrophoblasts were exposed concurrently to 100 mM ethanol and 1 nM HBEGF or TGFA, the increase in apoptosis was prevented, while EGF ameliorated at 10 nM and AREG was weakly effective. HBEGF survival-promoting activity required ligation of either of its cognate receptors, HER1 or HER4. These findings reveal the potential for ethanol to rapidly induce cytotrophoblast apoptosis. However, survival factor induction could provide cytotrophoblasts with an endogenous cytoprotective mechanism.

Heparin-binding EGF-like growth factor mediates oxyhemoglobin-induced suppression of voltage-dependent potassium channels in rabbit cerebral artery myocytes

Oxyhemoglobin (OxyHb) can suppress voltage-dependent K(+) channel (K(V)) currents through protein tyrosine kinase activation, which may contribute to cerebral vasospasm following subarachnoid hemorrhage. Here we have tested the hypothesis that shedding of heparin-binding EGF-like growth factor (HB-EGF) and the resulting activation of the tyrosine kinase EGF receptor (EGFR) underlie OxyHb-induced K(V) channel suppression in the cerebral vasculature. With the use of the conventional whole cell patch-clamp technique, two EGFR ligands, EGF and HB-EGF, were found to mimic OxyHb-induced K(V) suppression in rabbit cerebral artery myocytes. K(V) current suppression by OxyHb or EGF ligands was eliminated by a specific EGFR inhibitor, AG-1478, but was unaffected by PKC inhibition. Compounds (heparin and CRM-197) that specifically interfere with HB-EGF signaling eliminated OxyHb-induced K(V) suppression, suggesting that HB-EGF is the EGFR ligand involved in this pathway. HB-EGF exists as a precursor protein that, when cleaved by matrix metalloproteases (MMPs), causes EGFR activation. MMP activation was detected in OxyHb-treated arteries by gelatin zymography. Furthermore, the MMP inhibitor (GM-6001) abolished OxyHb-induced K(V) current suppression. We also observed K(V) current suppression due to EGFR activation in human cerebral artery myocytes. In conclusion, these data demonstrate that OxyHb induces MMP activation, causing HB-EGF shedding and enhanced EGFR activity, ultimately leading to K(V) channel suppression. We propose that EGFR-mediated K(V) suppression contributes to vascular pathologies, such as cerebral vasospasm, and may play a more widespread role in the regulation of regional blood flow and peripheral resistance.

Protective role of macrophages in noninflammatory lung injury caused by selective ablation of alveolar epithelial type II Cells

Macrophages have a wide variety of activities and it is largely unknown how the diverse phenotypes of macrophages contribute to pathological conditions in the different types of tissue injury in vivo. In this study we established a novel animal model of acute respiratory distress syndrome caused by the dysfunction of alveolar epithelial type II (AE2) cells and examined the roles of alveolar macrophages in the acute lung injury. The human diphtheria toxin (DT) receptor (DTR), heparin-binding epidermal growth factor-like growth factor (HB-EGF), was expressed under the control of the lysozyme M (LysM) gene promoter in the mice. When DT was administrated to the mice they suffered from acute lung injury and died within 4 days. Immunohistochemical examination revealed that AE2 cells as well as alveolar macrophages were deleted via apoptosis in the mice treated with DT. Consistent with the deletion of AE2 cells, the amount of surfactant proteins in bronchoalveolar lavage fluid was greatly reduced in the DT-treated transgenic mice. When bone marrow from wild-type mice was transplanted into irradiated LysM-DTR mice, the alveolar macrophages became resistant to DT but the mice still suffered from acute lung injury by DT administration. Compared with the mice in which both AE2 cells and macrophages were deleted by DT administration, the DT-treated LysM-DTR mice with DT-resistant macrophages showed less severe lung injury with a reduced amount of hepatocyte growth factor in bronchoalveolar lavage fluid. These results indicate that macrophages play a protective role in noninflammatory lung injury caused by the selective ablation of AE2 cells.

Preconditioning-mimetics bradykinin and DADLE activate PI3-kinase through divergent pathways

We previously reported that pharmacological preconditioning of rabbit hearts with acetylcholine involves activation of phosphatidylinositol 3-kinase (PI3-K) through transactivation of the epidermal growth factor receptor (EGFR). Transactivation is thought to be initiated by cleavage of membrane-bound pro-heparin-binding EGF-like growth factor (HB-EGF) by a membrane metalloproteinase thus releasing HB-EGF which binds to the EGFR. This pathway leads to redox signaling with the generation of reactive oxygen species (ROS) by mitochondria. We tested whether preconditioning's physiological triggers, bradykinin and opioid, also signal through the EGFR. Both bradykinin and the synthetic delta-opioid agonist DADLE increased ROS production in isolated cardiomyocytes by approximately 50%. DADLE's effect was abrogated by either metalloproteinase inhibitor III (MPI) or the diphtheria toxin mutant CRM-197 which blocks heparin-binding EGF shedding indicating that DADLE signals through EGFR transactivation. MPI also blocked DADLE's infarct-sparing effect in whole hearts. Additionally, blocking Src kinase (a component of the EGFR's signaling complex) with PP2 or PI3-K with wortmannin blocked DADLE's effect on cardiomyocyte ROS production and PP2 blocked DADLE's salvage of ischemic myocardium. Finally, DADLE increased phosphorylation of Akt and extracellular signal-regulated protein kinases (ERK) 1/2 in left ventricular myocardium, and this increase was blocked by the EGFR antagonist AG1478. On the other hand, neither MPI nor CRM-197 prevented bradykinin from increasing ROS production, and MPI did not affect bradykinin's infarct-sparing effect in intact hearts. Conversely, both PP2 and wortmannin blocked bradykinin's effect on ROS generation and also aborted bradykinin's cardioprotective effect in intact hearts. While bradykinin also increased phosphorylation of Akt and ERK in myocardium, that increase was not affected by AG1478. Hence bradykinin, unlike acetylcholine or opioid, does not transactivate EGFR, although all 3 agonists do signal through Src and PI3-K.

Apical epidermal growth factor receptor signaling: regulation of stretch-dependent exocytosis in bladder umbrella cells

The apical surface of polarized epithelial cells receives input from mediators, growth factors, and mechanical stimuli. How these stimuli are coordinated to regulate complex cellular functions such as polarized membrane traffic is not understood. We analyzed the requirement for growth factor signaling and mechanical stimuli in umbrella cells, which line the mucosal surface of the bladder and dynamically insert and remove apical membrane in response to stretch. We observed that stretch-stimulated exocytosis required apical epidermal growth factor (EGF) receptor activation and that activation occurred in an autocrine manner downstream of heparin-binding EGF-like growth factor precursor cleavage. Long-term changes in apical exocytosis depended on protein synthesis, which occurred upon EGF receptor-dependent activation of mitogen-activated protein kinase signaling. Our results indicate a novel physiological role for the EGF receptor that couples upstream mechanical stimuli to downstream apical EGF receptor activation that may regulate apical surface area changes during bladder filling.

Lysophosphatidic acid promoting corneal epithelial wound healing by transactivation of epidermal growth factor receptor

PURPOSE

To identify the underlying mechanisms by which lipid mediator lysophosphatidic acid (LPA) acts as a growth factor in stimulating extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3'-kinase (PI3K) during corneal epithelial wound healing.

METHODS

Epithelial debridement wounds in cultured porcine corneas and scratch wounds in an epithelial monolayer of SV40-immortalized human corneal epithelial (THCE) cells were allowed to heal in the presence or absence of an epidermal growth factor receptor (EGFR) inhibitor (tyrphostin AG1478), a matrix metalloproteinase inhibitor (GM6001), or a heparin-binding EGF-like growth factor (HB-EGF) antagonist (CRM197) with or without LPA. EGFR activation was analyzed by immunoprecipitation using EGFR antibodies and Western blotting with phosphotyrosine antibodies. Phosphorylation of ERK and AKT (a major substrate of PI3K) was analyzed by Western blotting with antibodies specific to the phosphorylated proteins. Wound- and LPA-induced shedding of HB-EGF was assessed by measuring the release of alkaline phosphatase (AP) in a stable THCE cell line that expressed HB-EGF with AP inserted in the heparin-binding site.

RESULTS

In organ and cell culture models, LPA enhanced corneal epithelial wound healing. LPA-stimulated and spontaneous wound closure was attenuated by AG1478, GM6001, or CRM197. Consistent with the effects on epithelial migration, these inhibitors, as well as the Src kinase inhibitor (PP2), retarded LPA-induced activation of EGFR and its downstream effectors ERK and AKT in THCE cells. Unlike exogenously added HB-EGF, LPA stimulated moderate EGFR phosphorylation; the level of phosphorylated EGFR was similar to that induced by wounding. However, LPA appeared to prolong wound-induced EGFR signaling. The release of HB-EGF assessed by AP activity increased significantly in response to wounding, LPA, or both, and the release of HB-EGF-AP induced by LPA was inhibited by PP2 and GM6001.

CONCLUSIONS

LPA accelerates corneal epithelial wound healing through its ability to induce autocrine HB-EGF signaling. Transactivation of EGFR by LPA represents a convergent signaling pathway accessible to stimuli such as growth factors and ligands of G-protein-coupled receptors in response to pathophysiological challenge in human corneal epithelial cells.

Pore-forming Staphylococcus aureus alpha-toxin triggers epidermal growth factor receptor-dependent proliferation

Staphylococcal alpha-toxin is an archetypal killer protein that homo-oligomerizes in target cells to create small transmembrane pores. The membrane-perforating beta-barrel motif is a conserved attack element of cytolysins of Gram-positive and Gram-negative bacteria. Following the recognition that nucleated cells can survive membrane permeabilization, a profile of abundant transcripts was obtained in transiently perforated keratinocytes. Several immediate early genes were found to be upregulated, reminiscent of the cellular response to growth factors. Cell cycle analyses revealed doubling of S + G2/M phase cells 26 h post toxin treatment. Determination of cell counts uncovered that after an initial drop, numbers increased to exceed the controls after 2 days. A non-lytic alpha-toxin mutant remained without effect. The alpha-toxin pore is too small to allow egress of cytosolic growth factors, and evidence was instead obtained for growth signalling via the epidermal growth factor receptor (EGFR). Inhibition of the EGFR or of EGFR-proligand-processing blocked the mitogenic effect of alpha-toxin. Western blots with phospho-specific antibodies revealed activation of the EGFR, and of the adapter protein Shc. Immediate early response and proliferation upon transient plasma membrane pore formation by bacterial toxins may represent a novel facet of the complex interaction between pathogen and host.

A Diphtheria Toxin Receptor Deficient in Epidermal Growth Factor–Like Biological Activity

Targeted cell ablation in animals is a powerful method for analyzing the physiological function of cell populations and generating various animal models of organ dysfunction. To achieve more specific and conditional ablation of target cells, we have developed a method termed Toxin Receptor mediated Cell Knockout (TRECK). A potential shortcoming of this method, however, is that overexpression of human heparin-binding epidermal growth factor-like growth factor (hHB-EGF) as a diphtheria toxin (DT) receptor in target cells or tissues may cause abnormalities in transgenic mice, since hHB-EGF is a member of the EGF growth factor family. To create novel DT receptors that are defective in growth factor activity and resistant to metalloprotease-cleavage, we mutated five amino acids in the extracellular EGF-like domain of hHB-EGF, which contains both DT-binding and protease-cleavage sites. Two of the resultant hHB-EGF mutants, I117A/L148V and I117V/L148V, possessed little growth factor activity but retained DT receptor activity. Furthermore, these mutants were resistant to metalloprotease-cleavage by 12-O-tetradecanoylphorbol-13-acetate stimulation, which is expected to enhance DT receptor activity. These novel DT receptors should be useful for the generation of transgenic mice by TRECK.

Mechanisms for prostaglandin E2 formation caused by proteinase-activated receptor-1 activation in rat gastric mucosal epithelial cells

Proteinase-activated receptor-1 (PAR1), a thrombin receptor, plays a protective role in gastric mucosa via prostanoid formation. Thus, we studied effects of PAR1 stimulation on prostaglandin E(2) (PGE(2)) formation in rat normal gastric mucosal epithelial RGM1 cells and analyzed the underlying signal transduction mechanisms. The PAR1-activating peptide (PAR1-AP) and thrombin increased PGE(2) release from RGM1 cells for 18h, an effect being suppressed by inhibitors of COX-1, COX-2, MEK, p38 MAP kinase (p38 MAPK), protein kinase C (PKC), Src and EGF receptor-tyrosine kinase (EGFR-TK), but not JNK and matrix metalloproteinase (MMP)/a disintegrin and metalloproteinases (ADAMs). PAR1-AP caused persistent (6h or more) and transient (5min) phosphorylation of ERK and p38 MAPK, respectively, followed by delayed reinforcement at 18h. PAR1-AP up-regulated COX-2 in a manner dependent on MEK and EGFR-TK, but not p38 MAPK. The PAR1-mediated persistent ERK phosphorylation was reduced by inhibitors of Src and EGFR-TK. PAR1-AP actually phosphorylated EGF receptors and up-regulated mRNA for heparin-binding-EGF (HB-EGF), the latter effect being blocked by inhibitors of Src, EGFR-TK and MEK. Heparin, an inhibitor for HB-EGF, suppressed PAR1-mediated PGE(2) formation and persistent ERK phosphorylation. These results suggest that PAR1 up-regulates COX-2 via persistent activation of MEK/ERK that is dependent on EGFR-TK activation following induction of HB-EGF, leading to PGE(2) formation. In addition, our data also indicate involvement of COX-1, PKC and p38 MAPK in PAR1-triggered PGE(2) formation. PAR1, thus stimulates complex multiple signaling pathways responsible for PGE(2) formation in RGM1 cells.

Duration of the initial TCR stimulus controls the magnitude but not functionality of the CD8+ T cell response

CD8⁺ T cells only require a brief stimulation with antigen in vitro to divide and differentiate into effector and memory cells upon transfer in vivo. The efficiency of clonal expansion and the functional characteristics of memory cells derived from briefly stimulated cells are poorly defined. We developed a system that allowed us to examine programming entirely in vivo. This was achieved by rapidly killing peptide-pulsed DCs carrying a diphtheria toxin receptor transgene with timed injections of diphtheria toxin without altering the course of an accompanying infection. The magnitude of clonal expansion, but not the functionality of the effector cells, correlated directly with the duration of antigen exposure. Furthermore, memory T cells were capable of mounting a secondary response, regardless of the length of antigen encounter during the primary response. These results indicate that the duration of initial antigen encounter influences the magnitude of the primary response, but does not program responsiveness during the secondary challenge.

Heparin binding EGF is necessary for vasospastic response to endothelin

Endothelin-1 (ET-1), a powerful vasoconstrictor, is involved in vasospastic diseases such as coronary artery disease and subarachnoidal hemorrhage, as well as in renal and cardiovascular fibrotic remodeling. Transactivation of the epidermal growth factor receptor (EGFR) mediates ET-1 signaling in vascular smooth muscle cells (VSMCs) and isolated arteries. Moreover, EGFR is required for a full constrictive response to ET-1. However, the relevant mechanisms mediating EGFR transactivation in response to ET-1 have not been identified. The present study used isolated arteries and VSMCs to investigate the role of the EGFR ligand heparin binding-epidermal growth factor (HB-EGF) in ET-1-induced transactivation of EGFR, intracellular calcium mobilization, and VSMCs contraction. While baseline blood pressures were similar in HB-EGF-deficient and in wild-type littermate mice, the vasoconstrictor actions of ET-1 were attenuated in HB-EGF-/- animals. In isolated mouse carotid artery segments mounted in an arteriograph, ET-1 caused only a weak increase in isovolumetric tone in HB-EGF-deficient vessels, and this effect was mimicked by inhibition of EGFR tyrosine kinase or phosphoinositide 3-kinase (PI3K) in wild-type arteries with or without endothelium, indicating a specific role in VSMCs. EGFR or PI3K inhibitors had no effect on KCl-induced contraction, which was normal in HB-EGF-deficient mice. To confirm that the abnormal responses in HB-EGF-deficient mice were due to impaired EGFR signaling, we studied VSMCs from waved-2 (wa2) mice; these animals have a mutation causing a partial loss of function of EGFR tyrosine kinase activity. The ET-1-induced calcium peak was reduced by 30% in VSMCs from wa2 mice and from HB-EGF-/- mice. This effect was reproduced by preincubation of wild-type VSMCs with EGFR inhibitor AG1478 and PI3K inhibitors LY294002 and wortmannin. ProHB-EGF is bound to the cell membrane and released after cleavage by metalloproteinases; its action may contribute to effects of GPCR agonists on cell growth. Pretreatment of mouse VSMCs with batimastat, a metalloproteinase inhibitor, significantly attenuated ET-1-induced [Ca(2+)](i) response in wild-type cells. Human proHB-EGF has been shown to be the endogenous receptor for Corynebacterium diphteriae toxin (DT). Mutated DT toxin (CRM197) is devoid of toxicity but it neutralizes HB-EGF binding to EGFR. Pretreatment of human VSMCs from internal mammary arteries with CRM197 significantly blunted ET-1-stimulated calcium transients. In conclusion, these findings suggest that the mechanism of ET-1-induced vasoconstriction involves HB-EGF-mediated transactivation of the EGFR. This functional cascade requires modulation of agonist-induced calcium transient by EGFR and PI3K with extremely fast kinetics, suggesting a novel paradigm for GPCR-mediated calcium signaling, which may offer future therapeutic targets.

Injury-induced innate immune response in human skin mediated by transactivation of the epidermal growth factor receptor

We found that sterile wounding of human skin induced epidermal expression of the antimicrobial (poly)peptides human beta-defensin-3, neutrophil gelatinase-associated lipocalin, and secretory leukocyte protease inhibitor through activation of the epidermal growth factor receptor. After skin wounding, the receptor was activated by heparin-binding epidermal growth factor that was released by a metalloprotease-dependent mechanism. Activation of the epidermal growth factor receptor generated antimicrobial concentrations of human beta-defensin-3 and increased the activity of organotypic epidermal cultures against Staphylococcus aureus. These data demonstrate that sterile wounding initiates an innate immune response that increases resistance to overt infection and microbial colonization.

N-Terminal Proteolysis of the Endothelin B Receptor Abolishes Its Ability to Induce EGF Receptor Transactivation and Contractile Protein Expression in Vascular Smooth Muscle Cells

OBJECTIVE

The extracellular N terminus of the endothelin B (ETB) receptor is cleaved by a metalloprotease in an agonist-dependent manner, but the physiological role of this N-terminal proteolysis is not known. In this study, we aimed to determine the functional role of the ETB receptor and of its N-terminal cleavage in vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

VSMCs expressing either the full-length ETB receptor or an N-terminally truncated ETB receptor (corresponding to the N-terminally cleaved receptor) were analyzed for ligand-induced mitogen-activated protein kinase activation and expression of contractile proteins. In VSMCs expressing the full-length ETB receptor, IRL1620 (an ETB-selective agonist) induced a biphasic extracellular signal-regulated kinase 1/2 (ERK1/2) activation and increased expression of contractile proteins (smooth muscle myosin-1 [SM-1]/SM-2, SM22alpha, and alpha-actin). Interestingly, the second phase of ERK1/2 activation required metalloprotease activity, epidermal growth factor (EGF) receptor transactivation, and predominantly activation of Gi proteins. In contrast, in VSMCs expressing N-terminally truncated ETB receptors, IRL1620 did not elicit EGF transactivation and failed to increase contractile protein expression.

CONCLUSIONS

This study is the first to show that stimulation of full-length ETB receptors promotes expression of contractile proteins and may thus participate in the differentiation of VSMCs.

alpha(2)-Adrenergic receptors activate MAPK and Akt through a pathway involving arachidonic acid metabolism by cytochrome P450-dependent epoxygenase, matrix metalloproteinase activation and subtype-specific transactivation of EGFR

Previous study carried out on PC12 cells expressing each alpha(2)-adrenergic receptor subtype individually (PC12/alpha(2A), /alpha(2B) or /alpha(2C)) have shown that epinephrine causes activation of PI3K and phosphorylation of Erk 1/2. The signal transduction mechanisms whereby each alpha(2)-AR subtype triggers these actions were investigated in the present study. In all three clones, epinephrine-induced phosphorylation of MAPK or Akt was abolished by prior treatment with ketoconazole, but not with indomethacin or nordihydroguaiaretic acid. On the other hand, treatment of the clones with epinephrine caused a rapid increase of AA release, which was fully abolished by the PLC inhibitor U73122, but was unaffected by the PLA(2) inhibitor quinacrine. The effects of epinephrine on MAPK and Akt were mimicked by cell exposure to exogenous AA. Furthermore, whereas U73122 abolished the effects of epinephrine, quinacrine only prevented the effects of epinephrine, suggesting that AA release through PLC and its metabolites are responsible for MAPK and Akt activation by alpha(2)-ARs. Treatment with 1,10-phenanthroline, CRM197, or tyrphostin AG1478 suppressed MAPK and Akt phosphorylation by epinephrine or AA, in a subtype-specific manner. Furthermore, conditioned culture medium from epinephrine-treated PC12/alpha(2) induced MAPK and Akt phosphorylation in wild-type PC12. Inhibition of NGFR tyrosine phosphorylation had no effect but the src inhibitor PP1 abolished MAPK and Akt phosphorylation in all three clones. Our results provide evidence for a putative pathway by which alpha(2)-ARs activate MAPK and Akt in PC12 cells, involving stimulation of PLC, AA release, AA metabolism by cytochrome P450-dependent epoxygenase, stimulation of matrix metalloproteinases and subtype-specific transactivation of EGFR through src activation and heparin-binding EGF-like growth factor release.

Heparin-binding epidermal growth factor-like growth factor as a novel targeting molecule for cancer therapy

HB-EGF, a member of the EGF family of growth factors, exerts its biological activity through activation of the EGFR and other ErbB receptors. HB-EGF participates in diverse biological processes, including heart development and maintenance, skin wound healing, eyelid formation, blastocyst implantation, progression of atherosclerosis and tumor formation, through the activation of signaling molecules downstream of ErbB receptors and interactions with molecules associated with HB-EGF. Recent studies have indicated that HB-EGF gene expression is significantly elevated in many human cancers and its expression level in a number of cancer-derived cell lines is much higher than those of other EGFR ligands. Several lines of evidence have indicated that HB-EGF plays a key role in the acquisition of malignant phenotypes, such as tumorigenicity, invasion, metastasis and resistance to chemotherapy. Studies in vitro and in vivo have indicated that HB-EGF expression is essential for tumor formation of cancer-derived cell lines. CRM197, a specific inhibitor of HB-EGF, and an antibody against HB-EGF are both able to inhibit tumor growth in nude mice. These results indicate that HB-EGF is a promising target for cancer therapy, and that the development of targeting tools against HB-EGF could represent a novel type of therapeutic strategy, as an alternative to targeting ErbB receptors.

Role of EGF Receptor Activation in Angiotensin II–Induced Renal Epithelial Cell Hypertrophy

For determination of the molecular mechanisms underlying the induction of epithelial cell hypertrophy by angiotensin II (Ang II), a well-characterized porcine renal proximal tubular cell line LLCPKcl4, which does not express endogenous Ang II receptor subtypes, was transfected with cDNA encoding Ang II subtype 1 receptor (AT1R/Cl4). Ang II transactivated the EGF receptor (EGFR) in these AT1R/Cl4 cells, which was blocked by the selective AT1R antagonist losartan but not by the selective AT2R antagonist PD123319. Ang II did not transactivate EGFR in empty vector-transfected LLCPKcl4 cells (Vector/Cl4). Ang II elicited release of soluble heparin-binding EGF-like growth factor (HB-EGF) from AT1R/Cl4 cells, and Ang II-induced EGFR activation was prevented by pretreatment with the specific HB-EGF inhibitor CRM197 or the metalloproteinase inhibitors batimastat or phenanthroline, none of which had any effect on EGFR activation by exogenously administered EGF. Ang II stimulated protein synthesis and cell hypertrophy in AT1R/Cl4 cells without increasing cell number, and signaling studies revealed that Ang II stimulated phosphorylation of the 40S ribosomal protein S6 and the eukaryotic translation initiation factor 4E-binding protein 1, the two downstream target proteins of the mammalian target of rapamycin, which is a central regulator of protein synthesis and cell size. Ang II-induced mammalian target of rapamycin activation, [3H]leucine incorporation, and cellular hypertrophy were inhibited by pretreatment with either batimastat or CRM197 or by pretreatment with rapamycin or the EGFR tyrosine kinase inhibitor AG1478. Ang II also stimulated Smad 2/3 phosphorylation, which was blocked by a selective TGF-beta receptor I kinase inhibitor but not by CRM197. With blockade of TGF-beta receptor, Ang II-mediated hypertrophy was converted into cell proliferation, which was blocked by CRM197. In summary, this is the first demonstration that HB-EGF shedding-dependent EGFR transactivation, along with activation of TGF-beta signaling pathways, mediates Ang II-induced renal tubular epithelial cell hypertrophy.

Epithelial cell motility is triggered by activation of the EGF receptor through phosphatidic acid signaling

Phospholipase D catalyzes the hydrolysis of phosphatidylcholine to generate phosphatidic acid, and there is currently much interest in elucidating messenger functions for this molecule. We report here that wounding sheets of corneal epithelial and Madin Darby canine kidney cells induces strong activation of phospholipase D, and we provide evidence that activation is amplified through a positive feed-back loop. Short-chain analogues of phosphatidic acid induce motility robustly in corneal and other epithelial cell types. The effects of these analogues were not the result of their conversion to the corresponding diacylglycerol or lysophosphatidic acid, implying that phosphatidic acid acts directly on one or more cellular targets. Strikingly, phosphatidic acid signaling was found to stimulate the epidermal growth factor receptor (EGFR) through a transactivation process. Healing of wounds in sheets of corneal epithelial cells is absolutely dependent on epidermal growth factor receptor signaling, and the present data suggest that its activation is a result of wound-induced phospholipase D activation.

Human trophoblast survival at low oxygen concentrations requires metalloproteinase-mediated shedding of heparin-binding EGF-like growth factor

Heparin-binding EGF-like growth factor (HBEGF), which is expressed in the placenta during normal pregnancy, is down regulated in pre-eclampsia, a human pregnancy disorder associated with poor trophoblast differentiation and survival. This growth factor protects against apoptosis during stress, suggesting a role in trophoblast survival in the relatively low O(2) ( approximately 2%) environment of the first trimester conceptus. Using a well-characterized human first trimester cytotrophoblast cell line, we found that a 4-hour exposure to 2% O(2) upregulates HBEGF synthesis and secretion independently of an increase in its mRNA. Five other expressed members of the EGF family are largely unaffected. At 2% O(2), signaling via HER1 or HER4, known HBEGF receptors, is required for both HBEGF upregulation and protection against apoptosis. This positive-feedback loop is dependent on metalloproteinase-mediated cleavage and shedding of the HBEGF ectodomain. The restoration of trophoblast survival by the addition of soluble HBEGF in cultures exposed to low O(2) and metalloproteinase inhibitor suggests that the effects of HBEGF are mediated by autocrine/paracrine, rather than juxtacrine, signaling. Our results provide evidence that a post-transcriptional mechanism induced in trophoblasts by low O(2) rapidly amplifies HBEGF signaling to inhibit apoptosis. These findings have a high clinical significance, as the downregulation of HBEGF in pre-eclampsia is likely to be a contributing factor leading to the demise of trophoblasts.