Recombinant human betacellulin. Molecular structure, biological activities, and receptor interaction

Multiple post-translational modifications ensure EGFR functionality: Potential therapeutic targets to overcome its drug-resistance mutations

Epidermal growth factor receptor (EGFR) mutation is the most common driver mutation in non-small cell lung cancer (NSCLC). The first-line therapy for advanced NSCLC patients with EGFR-sensitive mutation is the EGFR tyrosine kinase inhibitor (EGFR-TKI). However, most NSCLC patients with EGFR mutation will develop resistant mutations in EGFR-TKI therapy. With further studies, resistance mechanisms represented by EGFR-T790M mutations have revealed the impact of EGFR mutations in situ on EGFR-TKIs sensitivity. The third-generation EGFR-TKIs inhibit both EGFR-sensitive mutations and T790M mutations. The emergence of novel mutations such as EGFR-C797S and EGFR-L718Q may decrease efficacy. Searching for new targets to overcome EGFR-TKI resistance becomes a key challenge. Therefore, an in-depth understanding of the regulatory mechanisms of EGFR is essential to find novel targets to overcome drug-resistant mutations in EGFR-TKIs. EGFR, as a receptor-type tyrosine kinase, undergoes homo/heterodimerization and autophosphorylation upon binding to ligands, which activates multiple downstream signaling pathways. Interestingly, there is growing evidence that the kinase activity of EGFR is affected not only by phosphorylation but also by various post-translational modifications (PTMs, such as S-palmitoylation, S-nitrosylation, Methylation, etc.). In this review, we systematically review the effects of different protein PTMs on EGFR kinase activity and its functionality and suggest that influencing EGFR kinase activity by modulating multiple EGFR sites are potential targets to overcome EGFR-TKIs resistance mutations.

Betacellulin promotes tumor development and EGFR mutant lung cancer growth by stimulating the EGFR pathway and suppressing apoptosis

Oncogenic mutations in the EGFR gene account for 15-20% of lung adenocarcinoma (LUAD) cases. However, the mechanism for EGFR driven tumor development and growth is not fully understood. Here, using an mRNA expression profiling-based approach we identified betacellulin (BTC) as one the gene upregulated by oncogenic EGFR in an MAP kinase-dependent manner. BTC protein expression was markedly increased in LUAD patient samples compared to normal lung tissue, with higher expression in EGFR-mutant LUAD. BTC was sufficient to transform immortalized mouse cells, initiate tumor development in mice, and promote the survival of immortalized human lung epithelial cells. Conversely, knockdown of BTC inhibited the growth of EGFR-mutant human LUAD cells in culture and their tumor-forming ability in mice. Mechanistically, BTC knockdown resulted in attenuated EGFR signaling and apoptosis induction. Collectively, these results demonstrate a key role of BTC in EGFR-mutant LUAD, with potential therapeutic implications in LUAD and other EGFR-mutant cancers.

Epidermal Growth Factor Receptor Expression in the Corneal Epithelium

A properly functioning cornea is critical to clear vision and healthy eyes. As the most anterior portion of the eye, it plays an essential role in refracting light onto the retina and as an anatomical barrier to the environment. Proper vision requires that all layers be properly formed and fully intact. In this article, we discuss the role of the epidermal growth factor receptor (EGFR) in maintaining and restoring the outermost layer of the cornea, the epithelium. It has been known for some time that the addition of epidermal growth factor (EGF) promotes the restoration of the corneal epithelium and patients using EGFR inhibitors as anti-cancer therapies are at increased risk of corneal erosions. However, the use of EGF in the clinic has been limited by downregulation of the receptor. More recent advances in EGFR signaling and trafficking in corneal epithelial cells have provided new insights in how to overcome receptor desensitization. We examine new strategies for overcoming the limitations of high ligand and receptor expression that alter trafficking of the ligand:receptor complex to sustain receptor signaling.

Novel Approaches and Challenges of Discovery of Exosite Modulators of a Disintegrin and Metalloprotease 10

A disintegrin and metaproteinase 10 is an important target for multiple therapeutic areas, however, despite drug discovery efforts by both industry and academia no compounds have reached the clinic so far. The lack of enzyme and substrate selectivity of developmental drugs is believed to be a main obstacle to the success. In this review, we will focus on novel approaches and associated challenges in discovery of ADAM10 selective modulators that can overcome shortcomings of previous generations of compounds and be translated into the clinic.

Betacellulin (BTC) Biases the EGFR To Dimerize with ErbB3

There are 13 known endogenous ligands for the epidermal growth factor receptor (EGFR) and its closely related ErbB receptor family members. We previously reported that betacellulin (BTC) is more efficacious than epidermal growth factor (EGF) in mediating corneal wound healing, although the molecular basis for this difference was unknown. For the most part, differences between ligands can be attributed to variability in binding properties, such as the unique rate of association and dissociation, pH sensitivity, and selective binding to individual ErbB family members of each ligand. However, this was not the case for BTC. Despite being better at promoting wound healing via enhanced cell migration, BTC has reduced receptor affinity and weaker induction of EGFR phosphorylation. These data indicate that the response of BTC is not due to enhanced affinity or kinase activity. Receptor phosphorylation and proximity ligation assays indicate that BTC treatment significantly increases ErbB3 phosphorylation and EGFR-ErbB3 heterodimers when compared with EGF treatment. We observed that EGFR-ErbB3 heterodimers contribute to cell migration, because the addition of an ErbB3 antagonist (MM-121) or RNA interference-mediated knockdown of ErbB3 attenuates BTC-stimulated cell migration compared with EGF. Thus, we demonstrate that, despite both ligands binding to the EGFR, BTC biases the EGFR to dimerize with ErbB3 to regulate the biologic response.

Molecular mechanism of cell death induced by king cobra (Ophiophagus hannah) venom l-amino acid oxidase

Snake venom LAAOs have been reported to exhibit a wide range of pharmacological activities, including cytotoxic, edema-inducing, platelet aggregation-inducing/platelet aggregation-inhibiting, bactericidal and antiviral activities. A heat-stable form of l-amino acid oxidase isolated from king cobra (Ophiophagus hannah) venom (OH-LAAO) has been shown to exhibit very potent cytotoxicity against human tumorigenic cells but not in their non-tumorigenic counterparts, and the cytotoxicity was due to the apoptosis-inducing effect of the enzyme. In this work, the molecular mechanism of cell death induced by OH-LAAO was investigated. The enzyme exerts its apoptosis-inducing effect presumably via both intrinsic and extrinsic pathways as suggested by the increase in caspase-8 and -9 activities. Oligonucleotide microarray analysis showed that the expression of a total of 178 genes was significantly altered as a result of oxidative stress induced by the hydrogen peroxide generated by the enzyme. Of the 178 genes, at least 27 genes are involved in apoptosis and cell death. These alterations of gene expression was presumably caused by the direct cytotoxic effect of H2O2 generated during the enzymatic reaction, as well as the non-specific oxidative modifications of signaling molecules that eventually lead to apoptosis and cell death. The very substantial up-regulation of cytochrome P450 genes may also contribute to the potent cytotoxic action of OH-LAAO by producing excessive reactive oxygen species (ROS). In conclusion, the potent apoptosis inducing activity of OH-LAAO was likely due to the direct cytotoxic effect of H2O2 generated during the enzymatic reaction, as well as the non-specific oxidation of signalling molecules.

EGFR signaling patterns are regulated by its different ligands

EGF receptor (EGFR) and its signaling have been investigated for many years, but how its different ligands regulate signaling has not been thoroughly explored. When investigating EGFR activation and downstream signaling in HeLa cells using a panel of ligands, we found a ligand-dependent differential activation of EGFR and the signaling pathways Akt, PLCγ and STAT with HB-EGF and BTC being the most potent ligands. All the tested ligands induced full activation of Erk signaling at 1 nM, whereas only HB-EGF and partly BTC and EGF induced strong activation of Akt, STAT3 and PLCγ at this concentration. Interestingly, we also found that the high activation potencies of HB-EGF and BTC could only partially be explained by their binding affinities, and are therefore likely to be regulated by other mechanisms. We thus suggest that the signaling pathways initiated from the EGFR vary depending on the ligands bound in a cell specific manner.

The ABC of BTC: structural properties and biological roles of betacellulin

Betacellulin was initially detected as a growth-promoting factor in the conditioned medium of a mouse pancreatic β-cell tumor cell line. Sequencing of the purified protein and of the cloned cDNA supported the assumption that betacellulin is a new ligand of the epidermal growth factor receptor (EGFR), which was later confirmed experimentally. As a typical EGFR ligand, betacellulin is expressed by a variety of cell types and tissues, and the soluble growth factor is proteolytically cleaved from a larger membrane-anchored precursor. Importantly, BTC can - in addition to the EGFR - bind and activate all possible heterodimeric combinations of the related ERBB receptors including the highly oncogenic ERBB2/3 dimer, as well as homodimers of ERBB4. While a large number of studies attest a role for betacellulin in the differentiation of pancreatic β-cells, the last decade witnessed the association of betacellulin with a large number of additional biological processes, ranging from reproduction to the control of neural stem cells.

Cell and molecular biology of epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) has been one of the most intensely studied cell surface receptors due to its well-established roles in developmental biology, tissue homeostasis, and cancer biology. The EGFR has been critical for creating paradigms for numerous aspects of cell biology, such as ligand binding, signal transduction, and membrane trafficking. Despite this history of discovery, there is a continual stream of evidence that only the surface has been scratched. New ways of receptor regulation continue to be identified, each of which is a potential molecular target for manipulating EGFR signaling and the resultant changes in cell and tissue biology. This chapter is an update on EGFR-mediated signaling, and describes some recent developments in the regulation of receptor biology.

A systems biology approach using metabolomic data reveals genes and pathways interacting to modulate divergent growth in cattle

BACKGROUND

Systems biology enables the identification of gene networks that modulate complex traits. Comprehensive metabolomic analyses provide innovative phenotypes that are intermediate between the initiator of genetic variability, the genome, and raw phenotypes that are influenced by a large number of environmental effects. The present study combines two concepts, systems biology and metabolic analyses, in an approach without prior functional hypothesis in order to dissect genes and molecular pathways that modulate differential growth at the onset of puberty in male cattle. Furthermore, this integrative strategy was applied to specifically explore distinctive gene interactions of non-SMC condensin I complex, subunit G (NCAPG) and myostatin (GDF8), known modulators of pre- and postnatal growth that are only partially understood for their molecular pathways affecting differential body weight.

RESULTS

Our study successfully established gene networks and interacting partners affecting growth at the onset of puberty in cattle. We demonstrated the biological relevance of the created networks by comparison to randomly created networks. Our data showed that GnRH (Gonadotropin-releasing hormone) signaling is associated with divergent growth at the onset of puberty and revealed two highly connected hubs, BTC and DGKH, within the network. Both genes are known to directly interact with the GnRH signaling pathway. Furthermore, a gene interaction network for NCAPG containing 14 densely connected genes revealed novel information concerning the functional role of NCAPG in divergent growth.

CONCLUSIONS

Merging both concepts, systems biology and metabolomic analyses, successfully yielded new insights into gene networks and interacting partners affecting growth at the onset of puberty in cattle. Genetic modulation in GnRH signaling was identified as key modifier of differential cattle growth at the onset of puberty. In addition, the benefit of our innovative concept without prior functional hypothesis was demonstrated by data suggesting that NCAPG might contribute to vascular smooth muscle contraction by indirect effects on the NO pathway via modulation of arginine metabolism. Our study shows for the first time in cattle that integration of genetic, physiological and metabolomics data in a systems biology approach will enable (or contribute to) an improved understanding of metabolic and gene networks and genotype-phenotype relationships.

Thyroid cancer cell resistance to gefitinib depends on the constitutive oncogenic activation of the ERK pathway

CONTEXT

Poorly differentiated thyroid carcinomas are refractory to common anticancer therapies, and novel inhibitors are being tested in these deadly malignancies. The epidermal growth factor receptor (EGFR) tyrosine kinase represents an attractive target for treatment because it is up-regulated in thyroid cancer and plays a role in cancer progression. However, EGFR inhibitors have provided poor results in thyroid carcinomas.

OBJECTIVE

We evaluated the possible mechanism underlying the resistance of thyroid cancer cells to EGFR inhibitors.

DESIGN

We tested the effect of the EGFR tyrosine kinase inhibitor gefitinib in a panel of thyroid cancer cell lines.

RESULTS

We found that in most of the cell lines, although gefitinib inhibited EGFR phosphorylation, it was poorly effective in reducing cell viability. gefitinib, however, was able to inhibit epidermal growth factor-induced cell migration and matrix invasion. In most thyroid cancer cell lines, gefitinib significantly inhibited Akt phosphorylation by inhibiting EGFR activation, but it had limited or no effect on ERK phosphorylation. The poor cell response to gefitinib was associated with genetic alterations, leading to constitutive activation of the ERK pathway, including BRAF(V600E) and HRAS(G12A/Q61R) mutations and RET/PTC1 rearrangement. When BRAF(V600E)-positive thyroid cancer cells were incubated with the specific BRAF inhibitor PLX4032, sensitivity to gefitinib was restored. Similar results were obtained with rat sarcoma and RET/papillary thyroid cancer inhibitors.

CONCLUSIONS

These results indicate that thyroid cancer resistance to gefitinib is due to the constitutive activation of the mitogenic pathway by either signals downstream of EGFR or other tyrosine kinase receptors. This resistance can be overcome by the combined use of selective inhibitors.

Targeting the epidermal growth factor receptor in solid tumor malignancies

The epidermal growth factor receptor (EGFR) is over-expressed, as well as mutated, in many types of cancers. In particular, the EGFR variant type III mutant (EGFRvIII) has attracted much attention as it is frequently and exclusively found on many tumor cells, and hence both EGFR and EGFRvIII have been proposed as valid targets in many cancer therapy settings. Different strategies have been developed in order to either inhibit EGFR/EGFRvIII activity or to ablate EGFR/EGFRvIII-positive tumor cells. Drugs that inhibit these receptors include monoclonal antibodies (mAbs) that bind to the extracellular part of EGFR, blocking the binding sites for the EGFR ligands, and intracellular tyrosine kinase inhibitors (TKIs) that block the ATP binding site of the tyrosine kinase domain. Besides an EGFRvIII-targeted vaccine, conjugated anti-EGFR mAbs have been used in different settings to deliver lethal agents to the EGFR/EGFRvIII-positive cells; among these are radio-labelled mAbs and immunotoxins. This article reviews the current status and efficacy of EGFR/EGFRvIII-targeted therapies.

Association of amphiregulin with the cetuximab sensitivity of gastric cancer cell lines

The therapeutic activity of the epidermal growth factor receptor (EGFR)-directed monoclonal antibody cetuximab in gastric cancer is currently being investigated in clinical studies. Reliable biomarkers for the identification of patients who are likely to benefit from this treatment are not available. In this study, we assessed the activity of cetuximab in five gastric cancer cell lines (AGS, AZ521, Hs746T, LMSU and MKN1). The viability of two of these cell lines, AZ521 and MKN1, was significantly reduced by cetuximab treatment. High expression and secretion levels of the EGFR-binding ligand, amphiregulin (AREG), were associated with cetuximab responsiveness. MET activation and mutations in Kirsten-Ras gene (KRAS) were associated with cetuximab resistance. By introducing a hierarchy between these markers, we established a model that facilitated the correct classification of all five gastric cancer cell lines as cetuximab responsive or non-responsive. The highest priority was allocated to activating KRAS mutations, followed by MET activation and finally by the levels of secreted AREG. In order to validate these results, we used three additional human gastric cancer cell lines (KATOIII, MKN28 and MKN45). In conclusion, we propose that our model allows the response of gastric cancer cell lines to cetuximab treatment to be predicted.

Forebrain specific heparin-binding epidermal growth factor-like growth factor knockout mice show exacerbated ischemia and reperfusion injury

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a hypoxia-inducible neuroprotective protein that also stimulates proliferation of neuronal precursor cells. In this study, we investigated the possible role of HB-EGF in ischemia and reperfusion injury by measuring the changes in its mRNA expression following focal cerebral ischemia. We also examined neural damage after a middle cerebral artery occlusion (MCAO) and reperfusion in ventral forebrain specific HB-EGF knockout (KO) mice. The levels of HB-EGF mRNA in the cerebral cortex of wild-type (WT) mice were significantly increased 3-24 h after MCAO and reperfusion. Cerebral infraction in HB-EGF KO mice was aggravated at 1 day and 6 days after MCAO and reperfusion compared with WT mice. The number of terminal deoxynucleotidyl transferase (TdT)-mediated dNTP nick end labeling (TUNEL) and an oxidative stress marker, 8-hydroxy-2'-deoxyguanosine (8-OHdG) positive cells, were higher in HB-EGF KO mice than in WT mice. On the other hand, fewer bromodeoxyuridine (BrdU) positive cells were found in the subventricular zone in HB-EGF KO mice compared with WT mice. These results indicate that HB-EGF may play a pivotal role in ischemia and reperfusion injury and that endogenously synthesized HB-EGF is necessary for both the neuroprotective effect and for regulation of cell proliferation in the subventricular zone.

Betacellulin induces increased retinal vascular permeability in mice

Background

Diabetic maculopathy, the leading cause of vision loss in patients with type 2 diabetes, is characterized by hyper-permeability of retinal blood vessels with subsequent formation of macular edema and hard exudates. The degree of hyperglycemia and duration of diabetes have been suggested to be good predictors of retinal complications. Intervention studies have determined that while intensive treatment of diabetes reduced the development of proliferative diabetic retinopathy it was associated with a two to three-fold increased risk of severe hypoglycemia. Thus we hypothesized the need to identify downstream glycemic targets, which induce retinal vascular permeability that could be targeted therapeutically without the additional risks associated with intensive treatment of the hyperglycemia. Betacellulin is a 32 kD member of the epidermal growth factor family with mitogenic properties for the retinal pigment epithelial cells. This led us to hypothesize a role for betacellulin in the retinal vascular complications associated with diabetes.

Methods and Findings

In this study, using a mouse model of diabetes, we demonstrate that diabetic mice have accentuated retinal vascular permeability with a concomitant increased expression of a cleaved soluble form of betacellulin (s-Btc) in the retina. Intravitreal injection of soluble betacellulin induced retinal vascular permeability in normoglycemic and hyperglycemic mice. Western blot analysis of retinas from patients with diabetic retinopathy showed an increase in the active soluble form of betacellulin. In addition, an increase in the levels of A disintegrin and metalloproteinase (ADAM)-10 which plays a role in the cleavage of betacellulin was seen in the retinas of diabetic mice and humans.

Conclusions

These results suggest that excessive amounts of betacellulin in the retina may contribute to the pathogenesis of diabetic macular edema.

Betacellulin inhibits osteogenic differentiation and stimulates proliferation through HIF-1alpha

Cellular signaling via epidermal growth factor (EGF) and EGF-like ligands can determine cell fate and behavior. Osteoblasts, which are responsible for forming and mineralizing osteoid, express EGF receptors and alter rates of proliferation and differentiation in response to EGF receptor activation. Transgenic mice over-expressing the EGF-like ligand betacellulin (BTC) exhibit increased cortical bone deposition; however, because the transgene is ubiquitously expressed in these mice, the identity of cells affected by BTC and responsible for increased cortical bone thickness remains unknown. We have therefore examined the influence of BTC upon mesenchymal stem cell (MSC) and pre-osteoblast differentiation and proliferation. BTC decreases the expression of osteogenic markers in both MSCs and pre-osteoblasts; interestingly, increases in proliferation require hypoxia-inducible factor-alpha (HIF-α), as an HIF antagonist prevents BTC-driven proliferation. Both MSCs and pre-osteoblasts express EGF receptors ErbB1, ErbB2, and ErbB3, with no change in expression under osteogenic differentiation. These are the first data that demonstrate an influence of BTC upon MSCs and the first to implicate HIF-α in BTC-mediated proliferation.

Generation and characterization of conditional heparin-binding EGF-like growth factor knockout mice

Recently, neurotrophic factors and cytokines have been shown to be associated in psychiatric disorders, such as schizophrenia, bipolar disorder, and depression. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a member of the EGF family, serves as a neurotrophic molecular and plays a significant role in the brain. We generated mice in which HB-EGF activity is disrupted specifically in the ventral forebrain. These knockout mice showed (a) behavioral abnormalities similar to those described in psychiatric disorders, which were ameliorated by typical or atypical antipsychotics, (b) altered dopamine and serotonin levels in the brain, (c) decreases in spine density in neurons of the prefrontal cortex, (d) reductions in the protein levels of the NR1 subunit of the N-methyl-D-aspartate (NMDA) receptor and post-synaptic protein-95 (PSD-95), (e) decreases in the EGF receptor, and in the calcium/calmodulin-dependent protein kinase II (CaMK II) signal cascade. These results suggest the alterations affecting HB-EGF signaling could comprise a contributing factor in psychiatric disorder.

Nonlinear pharmacokinetics of therapeutic proteins resulting from receptor mediated endocytosis

Receptor mediated endocytosis (RME) plays a major role in the disposition of therapeutic protein drugs in the body. It is suspected to be a major source of nonlinear pharmacokinetic behavior observed in clinical pharmacokinetic data. So far, mostly empirical or semi-mechanistic approaches have been used to represent RME. A thorough understanding of the impact of the properties of the drug and of the receptor system on the resulting nonlinear disposition is still missing, as is how to best represent RME in pharmacokinetic models. In this article, we present a detailed mechanistic model of RME that explicitly takes into account receptor binding and trafficking inside the cell and that is used to derive reduced models of RME which retain a mechanistic interpretation. We find that RME can be described by an extended Michaelis–Menten model that accounts for both the distribution and the elimination aspect of RME. If the amount of drug in the receptor system is negligible a standard Michaelis–Menten model is capable of describing the elimination by RME. Notably, a receptor system can efficiently eliminate drug from the extracellular space even if the total number of receptors is small. We find that drug elimination by RME can result in substantial nonlinear pharmacokinetics. The extent of nonlinearity is higher for drug/receptor systems with higher receptor availability at the membrane, or faster internalization and degradation of extracellular drug. Our approach is exemplified for the epidermal growth factor receptor system.

A betacellulin mutant promotes differentiation of pancreatic acinar AR42J cells into insulin-producing cells with low affinity of binding to ErbB1

Betacellulin (BTC) is one of the members of the epidermal growth factor (EGF) ligand family of ErbB receptor tyrosine kinases. It is a differentiation factor as well as a potent mitogen. BTC promotes the differentiation of pancreatic acinar-derived AR42J cells into insulin-producing cells. It independently and preferentially binds to two type I tyrosine kinase receptors, the EGF receptor (ErbB1) and ErbB4. However, the physiochemical characteristics of BTC that are responsible for its preferential binding to these two receptors have not been fully defined. In this study, to investigate the essential amino acid residues of BTC for binding to the two receptors, we introduced point mutations into the EGF domain of BTC employing error-prone PCR. The receptor binding abilities of 190 mutants expressed in Escherichia coli were assessed by enzyme immunoassay. Replacement of the glutamic acid residue at position 88 with a lysine residue in BTC was found to produce a significant loss of affinity for binding to ErbB1, while the affinity of binding to ErbB4 was unchanged. In addition, the mutant of BTC-E/88/K showed less growth-promoting activity on BALB/c 3T3 cells compared with that of the wild-type BTC protein. Interestingly, the BTC mutant protein promoted differentiation of pancreatic acinar AR42J cells at a high frequency into insulin-producing cells compared with AR42J cells that were treated with wild-type BTC protein. These results indicate the possibility of designing BTC mutants, which have an activity of inducing differentiation only, without facilitating growth promotion.

Population pharmacokinetic data analysis of three phase I studies of matuzumab, a humanised anti-EGFR monoclonal antibody in clinical cancer development

A population pharmacokinetic model based on data from three phase I studies was to be developed including a covariate analysis to describe the concentration–time profiles of matuzumab, a novel humanised monoclonal antibody. Matuzumab was administered as multiple 1 h i.v. infusions with 11 different dosing regimens ranging from 400 to 2000 mg, q1w–q3w. For analysis, 90 patients with 1256 serum concentration–time data were simultaneously fitted using the software NONMEM™. Data were best described using a two-compartment model with the parameters central (V₁) and peripheral distribution volume (V₂), intercompartmental (Q) and linear (CLL) clearance and an additional nonlinear elimination pathway (K_m, V_max). Structural parameters were in agreement with immunoglobulin characteristics. In total, interindividual variability on V_max, CLL, V₁ and V₂ and interoccasion variability on CLL was 22–62% CV. A covariate analysis identified weight having an influence on V₁ (+0.44% per kg) and CLL (+0.87% per kg). All parameters were estimated with good precision (RSE<39%). A robust population pharmacokinetic model for matuzumab was developed, including a nonlinear pharmacokinetic process. In addition, relevant and plausible covariates were identified and incorporated into the model. When correlated to efficacy, this model could serve as a tool to guide dose selection for this ‘targeted’ cancer therapy.

The binding of human betacellulin to heparin, heparan sulfate and related polysaccharides

Recombinant human betacellulin binds strongly to heparin, requiring of the order of 0.8 M NaCl for its elution from a heparin affinity matrix. This is in complete contrast to the prototypic member of its cytokine superfamily, epidermal growth factor, which fails to bind to the column at physiological pH and strength. We used a well-established heparin binding ELISA to demonstrate that fucoidan and a highly sulfated variant of heparan sulfate compete strongly for heparin binding. Low sulfated heparan sulfates and also chondroitin sulfates are weaker competitors. Moreover, although competitive activity is reduced by selective desulfation, residual binding to extensively desulfated heparin remains. Even carboxyl reduction followed by extensive desulfation does not completely remove activity. We further demonstrate that both hyaluronic acid and the E. coli capsular polysaccharide K5, both of which are unsulfated polysaccharides with unbranched chains of alternating N-acetylglucosamine linked beta(1-4) to glucuronic acid, are also capable of a limited degree of competition with heparin. Heparin protects betacellulin from proteolysis by LysC, but K5 polysaccharide does not. Betacellulin possesses a prominent cluster of basic residues, which is likely to constitute a binding site for sulfated polysaccharides, but the binding of nonsulfated polysaccharides may take place at a different site.

Hydrogen peroxide and endothelin-1 are novel activators of betacellulin ectodomain shedding

The betacellulin precursor (pro-BTC) is a novel substrate for ADAM10-mediated ectodomain shedding. In this report, we investigated the ability of novel physiologically relevant stimuli, including G-protein coupled receptor (GPCR) agonists and reactive oxygen species (ROS), to stimulate pro-BTC shedding. We found that in breast adenocarcinoma MCF7 cells overexpressing pro-BTC, hydrogen peroxide (H2O2) was a powerful stimulator of ectodomain shedding. The stimulation of pro-BTC shedding by H2O2 was blocked by the broad-spectrum metalloprotease inhibitor TAPI-0 but was still functional in ADAM17 (TACE)-deficient stomach epithelial cells indicating the involvement of a distinct metalloprotease. H2O2-induced pro-BTC shedding was blocked by co-culturing cells in the anti-oxidant N-acetyl-L-cysteine but was unaffected by culture in calcium-deficient media. By contrast, calcium ionophore, which is a previously characterized activator of pro-BTC shedding, was sensitive to calcium depletion but was unaffected by co-culture with the anti-oxidant, identifying a clear distinction between these stimuli. We found that in vascular smooth muscle cells overexpressing pro-BTC, the GPCR agonist endothelin-1 (ET-1) was a strong inducer of ectodomain shedding. This was blocked by a metalloprotease inhibitor and by overexpression of catalytically inactive E385A ADAM10. However, overexpression of wild-type ADAM10 or ADAM17 led to an increase in ET-1-induced pro-BTC shedding providing evidence for an involvement of both enzymes in this process. This study identifies ROS and ET-1 as two novel inducers of pro-BTC shedding and lends support to the notion of activated shedding occurring under the control of physiologically relevant stimuli.

Mechanism of action of potato carboxypeptidase inhibitor (PCI) as an EGF blocker

The epidermal growth factor receptor (EGFR) signal transduction pathway plays a prominent role in the development of carcinomas, and is an interesting target for antitumoral therapy. We have previously described how potato carboxypeptidase inhibitor (PCI), a 39-amino acid protease inhibitor with a T-Knot motif, binds to EGFR receptor and inhibits the activation of receptor protein tyrosine kinase. In this paper it is shown that PCI interferes with EGFR activation through inhibition of receptor dimerization and receptor transphosphorylation induced by epidermal growth factor (EGF) and by transforming growth factor alpha (TGF-alpha). Moreover, PCI blocks the formation and activation of ErbB1/ErbB-2 heterodimers that have a prominent role in carcinoma development. As a result of these effects, PCI interferes in the EGFR signal transduction pathway by reversing the effects of EGF on the growth of two tumoral cell lines, A431 and MDA-MB-453, and promotes EGFR down-regulation. These results show that PCI acts as an EGF/TGF-alpha antagonist, which suggests its therapeutic potential in the treatment of carcinomas.

Molecular scanning of the betacellulin gene for mutations in type 2 diabetic patients

Betacellulin (BTC), a member of the epidermal growth factor (EGF) family, is an important factor in the growth and/or differentiation of pancreatic beta cells. In this point of view, we determined the transcriptional start site of the human BTC gene and screened the protein-coding region for mutations. The transcriptional start site was located 347 bp upstream from the translational initiation codon. After screening the protein coding exons (exons 1-5), we identified two novel missense mutations, Cys (TGC) to Gly (GGC) at codon 7 (C7G) and Leu (TTG) to Met (ATG) at codon 124 (L124M), and a single nucleotide substitution (-31c/t) in the intron 2. The C7G was located in the signal peptide and the L124M in the transmembrane domain and this Leu at codon 124 was conserved among human, bovine, rat, and mouse. The frequencies of these variants, however, were similar between type 2 diabetic patients (n = 228) and non-diabetic control subjects (n = 170). These data suggest that genetic variations in the protein-coding region of the human BTC gene are unlikely to be a major contributor to development of type 2 diabetes.

ADAM10 Mediates Ectodomain Shedding of the Betacellulin Precursor Activated by p-Aminophenylmercuric Acetate and Extracellular Calcium Influx

Betacellulin belongs to the family of epidermal growth factor-like growth factors that are expressed as transmembrane precursors and undergo proteolytic ectodomain shedding to release a soluble mature growth factor. In this study, we investigated the ectodomain shedding of the betacellulin precursor (pro-BTC) in conditionally immortalized wild-type (WT) and ADAM-deficient cell lines. Sequential ectodomain cleavage of the predominant cell-surface 40-kDa form of pro-BTC generated a major (26-28 kDa) and two minor (20 and 15 kDa) soluble forms and a cellular remnant lacking the ectodomain (12 kDa). Pro-BTC shedding was activated by calcium ionophore (A23187) and by the metalloprotease activator p-aminophenylmercuric acetate (APMA), but not by phorbol esters. Culturing cells in calcium-free medium or with the protein kinase Cdelta inhibitor rottlerin, but not with broad-based protein kinase C inhibitors, blocked A23187-activated pro-BTC shedding. These same treatments were without effect for constitutive and APMA-induced cleavage events. All pro-BTC shedding was blocked by treatment with a broad-spectrum metalloprotease inhibitor (GM6001). In addition, constitutive and activated pro-BTC shedding was differentially blocked by TIMP-1 or TIMP-3, but was insensitive to treatment with TIMP-2. Pro-BTC shedding was functional in cells from ADAM17- and ADAM9-deficient mice and in cells overexpressing WT or catalytically inactive ADAM17. In contrast, overexpression of WT ADAM10 enhanced constitutive and activated shedding of pro-BTC, whereas overexpression of catalytically inactive ADAM10 reduced shedding. These results demonstrate, for the first time, activated pro-BTC shedding in response to extracellular calcium influx and APMA and provide evidence that ADAM10 mediates constitutive and activated pro-BTC shedding.

Betacellulin improves glucose metabolism by promoting conversion of intraislet precursor cells to beta-cells in streptozotocin-treated mice

Betacellulin (BTC) induces differentiation of pancreatic beta-cells and promotes regeneration of beta-cells in experimental diabetes. The present study was conducted to determine if BTC improved glucose metabolism in severe diabetes induced by a high dose of streptozotocin (STZ) in mice. Male ICR mice were injected with 200 microg/g ip STZ, and various doses of BTC were administered daily for 14 days. The plasma glucose concentration increased to a level of >500 mg/dl in STZ-injected mice. BTC (0.2 microg/g) significantly reduced the plasma glucose concentration, but a higher concentration was ineffective. The effect of BTC was marked by day 4 but became smaller on day 6 or later. The plasma insulin concentration and the insulin content were significantly higher in mice treated with 0.1 and 0.2 microg/g BTC. BTC treatment significantly increased the number of beta-cells in each islet as well as the number of insulin-positive islets. Within islets, the numbers of 5-bromo-2-deoxyuridine/somatostatin-positive cells and pancreatic duodenal homeobox-1/somatostatin-positive cells were significantly increased by BTC. These results indicate that BTC improved hyperglycemia induced by a high dose of STZ by promoting neoformation of beta-cells, mainly from somatostatin-positive islet cells.

Betacellulin induces angiogenesis through activation of mitogen-activated protein kinase and phosphatidylinositol 3'-kinase in endothelial cell

Betacellulin (BTC) is a member of the epidermal growth factor (EGF) family, and it acts through EGF receptors. We asked whether BTC could be an angiogenic factor. Using human umbilical vein endothelial cells (HUVECs), we examined the effect of BTC on kinases and angiogenic processes. BTC induced ERK1/2 and Akt phosphorylation in a dose- and time-dependent manner. BTC induced phosphorylation of all three EGF receptors present on HUVECs: ErbB2, ErbB3, and ErbB4. Pretreatment with effective concentrations of ErbB1 inhibitor did not suppress BTC-induced kinase phosphorylation. BTC, EGF, VEGF (all at 10 ng/ml) produced similar increases in DNA synthesis. BTC, EGF, and VEGF all significantly increased endothelial cell migration. In addition, BTC promoted survival in a dose-dependent manner, and its effect was inhibited by pretreatment with PtdIns 3'-kinase inhibitor wortmannin or MEK1/2 inhibitor PD98059. Both BTC and EGF produced similar increases in tube formation in collagen gels. BTC-induced tube formation was suppressed by PD98059, wortmannin, and LY294002. In the mouse Matrigel plug assay, BTC (100 ng/ml) promoted neovessel formation, and its effect was suppressed by a combination of wortmannin and PD98059. Taken together, these data show that BTC exerts potent angiogenic activity through activation of EGF receptors, mitogen-activated protein kinase, and PtdIns 3'-kinase/Akt in endothelial cells.

Solution structure of betacellulin, a new member of EGF-family ligands

The solution structure of the EGF-like domain of betacellulin (BTCe), a newly discovered member of the epidermal growth factor (EGF) family, has been determined using two-dimensional nuclear magnetic resonance spectroscopy. This is the first report to identify the solution structure of the EGF-family ligand monomers that interact with both ErbB-1 and ErbB-4. The solution structure of BTCe was calculated using 538 NMR-derived restraints. The overall structure of BTCe was stabilized by three disulfide bonds, a hydrophobic core, and 23 hydrogen bonds. It appears that BTCe is comprised of five beta-strands and one short 3(10) helical turn. The secondary structural elements of BTCe are basically similar to those of the other EGF-family proteins, except that several significant variations of the structural properties were found. It is suggested that the structural variations between BTCe and the other EGF-family ligands may affect the specific receptor-recognition properties of EGF-family ligands.

Genomic structure and promoter characterization of the gene encoding the ErbB ligand betacellulin

Betacellulin (BTC) belongs to the epidermal growth factor (EGF) family of peptide ligands that are characterized by a six-cysteine consensus motif (EGF-motif) that forms three intra-molecular disulfide bonds, crucial for binding the ErbB receptor family. A variety of in vitro studies have identified BTC as an important factor in the growth and/or differentiation of pancreatic islet cells. The molecular mechanisms that regulate the transcription of the BTC gene however have not been delineated. As an initial step, we have characterized the genomic structure of the mouse BTC (mBTC) gene. mBTC cDNA was used as a probe to screen a mouse 129/SVJ genomic bacterial artificial chromosome (BAC) library. Three positive clones containing the entire gene were isolated. DNA sequence analysis identified six exons (1-6) and five introns (A-E); a structure conserved among the EGF family. PCR analysis showed that introns A-E are approximately 7.8, 8.9, 3.8, 1.4 and 1.4 kb in length, respectively. The EGF-motif is encoded by exons 3 and 4 with an intron (intron C) disrupting the coding sequence between the second and third disulfide loops. All exon-intron boundaries are consistent with the "gt-ag" rule. Multiple transcription start sites and one poly(A) site, located 18 bp downstream of a polyadenylation signal sequence, were identified by 5'- and 3'-RACE, respectively. Approximately 2.6 kb of 5'-flanking region was sequenced and was shown to lack consensus TATA and CCAAT boxes, but was found to contain several putative cis-acting regulatory elements. These included consensus binding sites for transcription factors HNF3 beta, USF, Nkx2-5, AP-4, and Sp1. Functional promoter analysis of the 5'-flanking region in COS-7 cells, using 5'-deletion fragments (-168/+335; -635/+335; -732/+335; -1175/+335; -1698/+335) cloned into a promoterless firefly luciferase reporter vector, identified basal promoter activity and both positive and negative cis-acting elements.

Adhesion molecules and implantation

Endometrial receptivity towards embryo implantation is a complex process that involves the ovary, endometrium and embryo. The dialog between the ovary and the endometrium provides the hormonal stimulus for establishment of a successful pregnancy. The hormones estrogen and progesterone act in concert to stimulate the expression of key molecules necessary for embryos to attach and invade. It is thought that initial attachment of the embryo involves cell adhesion events. The best characterized cell adhesion molecule on the luminal surface of the endometrium is the alphavbeta3 integrin. Its ligand osteopontin (OPN) is co-localized with alphavbeta3 and may play a role in endometrial or embryo signaling or facilitate embryo attachment to the apical surface prior to invasion. Surprising new evidence suggests that these two proteins are differentially regulated. Acting directly on endometrial epithelium, progesterone stimulates OPN expression. Using a stromal-mediated paracrine mechanism, HB-EGF or other EGF molecules appear to stimulate epithelial alphavbeta3 expression. In this article, we review what is known about these two pathways.

Tumor necrosis factor-alpha converting enzyme (TACE) regulates epidermal growth factor receptor ligand availability

We previously implicated tumor necrosis factor-alpha converting enzyme (TACE/ADAM17) in the processing of the integral membrane precursor to soluble transforming growth factor-alpha (TGF-alpha), pro-TGF-alpha. Here we examined TGF-alpha processing in a physiologically relevant cell model, primary keratinocytes, showing that cells lacking TACE activity shed dramatically less TGF-alpha as compared with wild-type cultures and that TGF-alpha cleavage was partially restored by infection of TACE-deficient cells with TACE-encoding adenovirus. Moreover, cotransfection of TACE-deficient fibroblasts with pro-TGF-alpha and TACE cDNAs increased shedding of mature TGF-alpha with concomitant conversion of cell-associated pro-TGF-alpha to a processed form. Purified TACE accurately cleaved pro-TGF-alpha in vitro at the N-terminal site and also cleaved a soluble form of pro-TGF-alpha containing only the ectodomain at the C-terminal site. In vitro, TACE accurately cleaved peptides corresponding to cleavage sites of several epidermal growth factor (EGF) family members, and transfection of TACE into TACE-deficient cells increased the shedding of amphiregulin and heparin-binding EGF (HB-EGF) proteins. Consistent with the hypothesis that TACE regulates EGF receptor (EGFR) ligand availability in vivo, mice heterozygous for Tace and homozygous for an impaired EGFR allele (wa-2) were born with open eyes significantly more often than Tace(+/+)Egfr(wa-2)(/)(wa-2) counterparts. Collectively, these data support a broad role for TACE in the regulated shedding of EGFR ligands.

Novel betacellulin derivatives. Separation of the differentiation activity from the mitogenic activity

Betacellulin (BTC) is a member of the epidermal growth factor family. It has two biological activities: mitogenic activity in fibroblasts and vascular smooth muscle cells, and differentiation activity for the differentiation of pancreatic acinar AR42J cells into insulin-secreting cells. The previous finding that recombinant BTC promotes the neogenesis of beta-cells in a mouse model supports the possibility that BTC is a therapeutic protein. However, the mitogenic activity of BTC may not be needed for differentiation into beta-cells and may cause a side effect in clinical use. We prepared several derivatives of BTC to segregate the two activities, to decrease the mitogenic activity, and to maintain the differentiation activity. We succeeded in obtaining BTC derivatives segregated by the two biological activities by preparing truncated-type derivatives. A derivative of BTC, BTC24-76, with a truncated N-terminal 23 amino acids and C-terminal 4 amino acids, was 2.5-fold more active in differentiation and had one-tenth of the mitogenic activity. The derivatives described in the present study should be helpful in future applications as therapeutic proteins and in basic research for discovery of a BTC-specific receptor.

Cloning and biological activity of epigen, a novel member of the epidermal growth factor superfamily

High throughput sequencing of a mouse keratinocyte library was used to identify an expressed sequence tag with homology to the epidermal growth factor (EGF) family of growth factors. We have named the protein encoded by this expressed sequence tag Epigen, for epithelial mitogen. Epigen encodes a protein of 152 amino acids that contains features characteristic of the EGF superfamily. Two hydrophobic regions, corresponding to a putative signal sequence and transmembrane domain, flank a core of amino acids encompassing six cysteine residues and two putative N-linked glycosylation sites. Epigen shows 24-37% identity to members of the EGF superfamily including EGF, transforming growth factor alpha, and Epiregulin. Northern blotting of several adult mouse tissues indicated that Epigen was present in testis, heart, and liver. Recombinant Epigen was synthesized in Escherichia coli and refolded, and its biological activity was compared with that of EGF and transforming growth factor alpha in several assays. In epithelial cells, Epigen stimulated the phosphorylation of c-erbB-1 and mitogen-activated protein kinases and also activated a reporter gene containing enhancer sequences present in the c-fos promoter. Epigen also stimulated the proliferation of HaCaT cells, and this proliferation was blocked by an antibody to the extracellular domain of the receptor tyrosine kinase c-erbB-1. Thus, Epigen is the newest member of the EGF superfamily and, with its ability to promote the growth of epithelial cells, may constitute a novel molecular target for wound-healing therapy.

Immunohistochemical localization of Betacellulin, a member of epidermal growth factor family, in atherosclerotic plaques of human aorta

Betacellulin (BTC), a new member of the EGF family, has been reported to be a potent mitogen for rat vascular smooth muscle cells (SMCs). BTC mRNA is known to be expressed in several human organs. However, the localization of BTC in human vascular tissues has not yet been clarified. We investigated whether or not BTC protein is involved in the pathogenesis of human atherosclerosis. Recombinant human BTC showed a mitogenic activity on cultured human aortic SMCs by measuring [3H]thymidine incorporation. The immunohistochemical localization of BTC, SMCs, macrophages, EGF receptors and ErbB4 was examined in autopsied human aortas. BTC was detected in both intimal and medial SMCs of the aortic wall. The percentage of BTC-positive medial SMCs in early types of atherosclerotic lesions decreased with age, but in adult, it was significantly higher in advanced types than in early types of atherosclerotic lesions. BTC-positive SMCs were predominantly localized in the medial side of the intima. Furthermore, numerous BTC-positive SMCs and macrophages were observed around the core lesion of atherosclerotic plaques. Receptors for BTC, EGF receptor and ErbB4, were expressed on SMCs, suggesting that BTC is associated with EGF receptor family-mediated signaling. BTC is produced in human aortic tissue and might play important roles in atherogenesis.

Receptor-ligand interactions studied with homogeneous fluorescence-based assays suitable for miniaturized screening

Cell membrane receptors play a central role in controlling cellular functions, making them the target of drugs for a wide variety of diseases. This report describes how a recently developed method, fluorescence intensity distribution analysis (FIDA), can be used to develop homogeneous, nonradioactive high throughput screening assays for membrane receptors. With FIDA, free ligand and ligand accumulated on receptor-bearing membrane vesicles can be distinguished on the basis of their particle brightness. This allows the concentration of both bound and free ligand to be determined reliably from a single measurement, without any separation. We demonstrate that ligand affinity, receptor expression level, and potency of inhibitors can be determined using the epidermal growth factor and beta(2)-adrenergic receptors as model systems. Highly focused confocal optics enable single-molecule sensitivity, and sample volumes can thus be reduced to 1 microl without affecting the quality of the fluorescence signal. Our results demonstrate that FIDA is an ideal method for membrane receptor assays offering substantial benefits for assay development and high throughput pharmaceutical screening.

Structure-function and biological role of betacellulin

Betacellulin (BTC) belongs to the epidermal growth factor (EGF) family of peptide ligands that are characterised by a six-cysteine consensus motif that forms three intra-molecular disulfide bonds crucial for binding the ErbB receptor family. BTC was initially described, purified and cloned from a mouse insulinoma cell line. BTC is proteolytically processed from a larger membrane-anchored precursor and is a potent mitogen for a wide variety of cell types. BTC binds and activates ErbB-1 and ErbB-4 homodimers and is further characterised by its unique ability to activate all possible heterodimeric ErbB receptors. BTC is widely expressed in most tissues and various body fluids, including milk. Expression is particularly high in the pancreas where it is thought to play a role in the differentiation of pancreatic beta cells. While much is known about the ErbB receptor binding characteristics of BTC and its effect on a variety of cultured cells under different conditions, the challenge that lies ahead is to determine the role of BTC in vivo. This review will focus on the structure of BTC and the various biological effects ascribed to this member of the EGF family.

Molecular cloning and expression of rat betacellulin cDNA

The cDNA encoding an entire open reading frame of rat betacellulin has been cloned from rat kidney. Expression of this cDNA in COS7 cells showed a significant amount of mitogenic activity in the culture media. Western blotting of the cell lysates suggested that the membrane-anchored precursor was cleaved to release its ectodomain very efficiently.

Identification of an alternatively spliced mRNA transcript of human betacellulin lacking the C-loop of the EGF motif and the transmembrane domain

This paper describes the cloning and characterization of a novel cDNA encoding a short form of betacellulin (BTC-beta), and reports the expression of this mRNA in a variety of human tissues and cell types. BTC-beta is likely the result of alternative splicing. This splicing event leads to the generation of an mRNA encoding an unusual BTC precursor in which the C-loop of the EGF domain and the transmembrane domain are deleted while the remainder of the mature molecule is fused in-frame to the C-terminal cytoplasmic tail.

Binding specificities and affinities of egf domains for ErbB receptors

ErbB receptor activation is a complex process and is dependent upon the type and number of receptors expressed on a given cell. Previous studies with defined combinations of ErbB receptors expressed in mammalian cells have helped elucidate specific biological responses for many of the recognized gene products that serve as ligands for these receptors. However, no study has examined the binding of these ligands in a defined experimental system. To address this issue, the relative binding affinities of the egf domains of eleven ErbB ligands were measured on six ErbB receptor combinations using a soluble receptor-ligand binding format. The ErbB2/4 heterodimer was shown to bind all ligands tested with moderate to very high affinity. In contrast, ErbB3 showed much more restrictive ligand binding specificity and measurable binding was observed only with heregulin, neuregulin2beta, epiregulin and the synthetic heregulin/egf chimera, biregulin. These studies also revealed that ErbB2 preferentially enhances ligand binding to ErbB3 or ErbB4 and to a lesser degree to ErbB1.

Biological actions of the epidermal growth factors-like domain peptides of mouse schwannoma-derived growth factor and human amphiregulin

Several members of the epidermal growth factor (EGF) family of growth factors that contain EGF-like units at their carboxy portion have been isolated and characterized. Schwannoma-derived growth factor (SDGF) and amphiregulin (AR) are members of this family. SDGF has high sequence homology to AR, and is known to be not only a potent mitogen for astrocytes and fibroblasts but also a neurotrophic factor. We previously confirmed that the synthetic EGF-like peptides SDGF(38-80) and AR(44-84), corresponding to the EGF-like domain of mouse SDGF and human AR, respectively, formed similar disulfide bond patterns to that of EGF. In the present study, we further investigated the biological actions of these two EGF-like peptides on several cultured cell lines. We found that SDGF(38-80) and AR(44-84) have weak mitogenic activity in NIH/3T3 cells and weak binding affinity to the EGF receptor on the surface of A431 cells compared with EGF. However, SDGF(38-80) and EGF induced short neurite outgrowth in PC12 h cells, a subclone of PC12 cells, at 100 nM. In addition, a significant increase in acetylcholinesterase (AChE) activity induced by SDGF(38-80) was observed at a concentration similar range to that of EGF, which is known as a differentiation marker of these cells. The effect of AR(44-84) in PC12 h cells was weaker than those of SDGF(38-80) and EGF, but the AChE activity was significantly increased by the addition of 100 nM AR(44-84), which did not stimulate NIH/3T3 cell growth. These results also suggest that SDGF(38-80) and AR(44-84) may be effective for neuronal differentiation rather than proliferation.

Complexity of EGF receptor signalling revealed in Drosophila

The multiple roles of the Drosophila epidermal growth factor receptor (EGFR) require that its activation is regulated precisely. Recent work has highlighted two important control mechanisms: the existence of multiple ligands with distinct properties and the interaction between EGFR pathway and other signalling pathways. The integration of signalling pathways into networks is beginning to be understood.

TGF alpha is dispensable for skin tumorigenesis in Tg.AC mice

Alterations in growth factor signaling pathways frequently accompany the development and maintenance of epithelial neoplasia. Transforming growth factor alpha (TGF alpha) and its epidermal growth factor receptor have been thought to play an especially important role in epithelial neoplasia. In this study, mice were derived genetically deficient (null) in functional TGF alpha expression and carrying the Tg.AC/v-Ha-ras transgene. The goals were to determine if (a) papillomagenesis was dependent on TGF alpha and (b) progression to malignancy was dependent on TGF alpha expression. Groups of male and female mice heterozygous or homozygous for the TGF alpha null allele and hemizygous for the Tg.AC transgene were treated twice weekly for 10 or 15 wk with doses of 12-O-tetradecanoylphorbol-13-acetate (TPA) known to produce papillomas in Tg.AC mice. Papillomas were readily induced in both male and female TGF alpha null mice. Malignant progression of papillomas was observed in all TGF alpha null treatment groups. Additionally, we examined the response of TGF alpha null mice to full thickness dorsal wounds, a stimulus known to promote papillomagenesis in Tg.AC mice. As in the TPA study, papillomas were induced in both male and female TGF alpha null mice. These studies indicate that TGF alpha is not required for the induction and maintenance of papillomas nor is it essential for the malignant conversion of papillomas in Tg.AC mice.

Constitutively tyrosine phosphorylated p52 Shc in breast cancer cells: correlation with ErbB2 and p66 Shc expression

Breast cancer cell lines display a wide variety of growth factor receptors, and considerable evidence implicates signaling from these receptors, especially ErbB2, in the important early stages of this disease, contributing to malignant progression. If this is true, then we would hypothesize that a useful prognostic indicator would be the level of activity of a second messenger protein used in common by these receptors. One such second messenger is the Shc adapter protein, which is activated when tyrosine phosphorylated by receptors. Therefore, one prediction from the hypothesis is that the level of tyrosine-phosphorylated Shc (PY-Shc) in breast cancer cell lines would correlate with total receptor tyrosine kinase activity. To begin to test this prediction, we examined Shc tyrosine phosphorylation in a diverse group of breast cancer cell lines that display varied levels of ErbB2. Using Shc immunoprecipitation and anti-phosphotyrosine immunoblotting analysis, we found a strong correlation between the level of ErbB2 overexpression (r = 0.91, p < 0.0002) and PY-ErbB2 levels (r = 0.89, p = 0.0005) compared with the level of tyrosine phosphorylation of the p52 and p46 Shc isoforms. Consistent with Shc tyrosine phosphorylation being driven by ErbB2, an ErbB2-specific tyrosine kinase inhibitor markedly reduced Shc tyrosine phosphorylation. Unexpectedly, although all cell lines had comparable total amounts of p52 and p46 Shc, the amount of an inhibitory Shc isoform, p66, was inversely related to the level of ErbB2 expression (r = -0.86, p = 0.0013). This suggests that reduced p66 Shc expression may play a role in ErbB2-positive breast cancer. In summary, these data are consistent with our prediction that the cellular level of PY-Shc would correlate with the levels of activated ErbB2 displayed by cell lines derived from breast cancers.

Changes in heregulin beta1 (HRGbeta1) signaling after inhibition of ErbB-2 expression in a human breast cancer cell line

Specific biological responses to the erbB3-erbB4 ligand heregulin (HRG) have been postulated to be due to the formation of heterodimers of those receptors with erbB2. To test the role that erbB2 plays in the response to HRG in a human breast carcinoma cell line, antisense oriented erbB2 was stably transfected into AU565 cells. In the absence of HRG, inhibition of erbB2 expression slowed cell growth, leading to accumulation of cells in the G2/M phase, and suppressed colony growth in soft agar. Low concentrations of HRG induced cell proliferation in both the erbB2-nonexpressing cells and the parental AU565 cells. In contrast, high concentrations of HRG failed to induce differentiation of the erbB2-nonexpressing cells as compared with the parental cells. ErbB3 expression was significantly decreased in the erbB2 nonexpressing cells. ErbB3 was constitutively tyrosine phosphorylated in both the parental AU565 cells and in the erbB2 nonexpressing cells. HRG further increased tyrosine phosphorylation of erbB3 with a maximum response at 1 ng/ml of HRG in erbB2 nonexpressing cells, as compared with 10 ng/ml of HRG in AU565 cells. This finding suggested that the biochemical responsiveness of erbB3 to HRG was changed, but not abrogated, by inhibition of erbB2 expression. These results suggest that inhibition of erbB2 expression modulates, but does not abolish, HRG mediated signal transduction pathways in a human breast cancer cell line.

Analysis of the ability of 12-O-tetradecanoylphorbol-13-acetate to induce epidermal hyperplasia, transforming growth factor-alpha, and skin tumor promotion in wa-1 mice

Wa-1 mutant mice possess a defect in the production of transforming growth factor-alpha (TGF-alpha) that leads to a phenotype characterized by wavy hair and curly whiskers. In light of recent evidence indicating the importance of TGF-alpha in epithelial tumorigenesis, this study characterizes the responsiveness of wa-1 mice to skin tumor promotion by the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA). The responsiveness of wa-1 mice to TPA was compared with that of SENCAR and C57BL/6 mice, representing mouse lines highly sensitive and resistant to skin tumor promotion, respectively. Wa-1 mice were found to be very resistant to skin tumor promotion by TPA after initiation with 10 nmol DMBA, similar to C57BL/6 mice. TPA failed to induce a dramatic increase in TGF-alpha mRNA and protein in the skin of wa-1 mice, whereas TGF-alpha mRNA and protein were dramatically induced in the skin (both epidermis and dermis) of SENCAR and C57BL/6 mice. TPA treatment dramatically increased mRNA levels of two other EGF receptor ligands, amphiregulin and heparin binding-EGF, however, in the skin of all three mouse lines. Comparison of histologic changes in skin revealed that wa-1 mice exhibited only modest sustained epidermal hyperplasia after multiple treatments with TPA, similar in magnitude to that of C57BL/6 mice and significantly lower than that of SENCAR mice. The current data indicate that wa-1 mice are relatively resistant to TPA promotion. Possible mechanisms for this resistance are discussed.

Cripto enhances the tyrosine phosphorylation of Shc and activates mitogen-activated protein kinase (MAPK) in mammary epithelial cells

Cripto-1 (CR-1), a recently discovered protein of the epidermal growth factor (EGF) family, was found to interact with a high affinity, saturable binding site(s) on HC-11 mouse mammary epithelial cells and on several different human breast cancer cell lines. This receptor exhibits specificity for CR-1, since other EGF-related peptides including EGF, transforming growth factor alpha, heparin-binding EGF-like growth factor, amphiregulin, epiregulin, betacellulin, or heregulin beta1 that bind to either the EGF receptor or to other type 1 receptor tyrosine kinases such as erb B-3 or erb B-4 fail to compete for binding. Conversely, CR-1 was found not to directly bind to or to activate the tyrosine kinases associated with the EGFR, erb B-2, erb B-3, or erb B-4 either alone or in various pairwise combinations which have been ectopically expressed in Ba/F3 mouse pro-B lymphocyte cells. However, exogenous CR-1 could induce an increase in the tyrosine phosphorylation of 185- and 120-kDa proteins and a rapid (within 3-5 min) increase in the tyrosine phosphorylation of the SH2-containing adaptor proteins p66, p52, and p46 Shc in mouse mammary HC-11 epithelial cells and in human MDA-MB-453 and SKBr-3 breast cancer cells. CR-1 was also found to promote an increase in the association of the adaptor Grb2-guanine nucleotide exchange factor-mouse son of sevenless (mSOS) signaling complex with tyrosine-phosphorylated Shc in HC-11 cells. Finally, CR-1 was able to increase p42(erk-2) mitogen-activated protein kinase (MAPK) activity in HC-11 cells within 5-10 min of treatment. These data demonstrate that CR-1 can function through a receptor which activates intracellular components in the ras/raf/MEK/MAPK pathway.

Post-transcriptional control regulates transforming growth factor alpha in the human carcinoma KB cell line

Expression of epidermal growth factor receptor (EGF-R) antisense RNA results in a drastic reduction of EGF-R levels in the human carcinoma KB cell line and induces a reversion of their transformed phenotype (Moroni, M. C., Willingham, M. C., and Beguinot, L. (1992) J. Biol. Chem. 267, 2714-2722). We used parental and EGF-R antisense KB clones as a genetic system to study, in the same cell line, the role of transforming growth factor alpha (TGF-alpha) in the establishment and maintenance of the transformed phenotype. KB cells produce TGF-alpha mRNA, and their conditioned medium is able to sustain growth of antisense cells, mimicking the effect of exogenous EGF or TGF-alpha. In antisense cells there is a marked reduction of TGF-alpha mRNA steady-state levels. In addition, the decrease in TGF-alpha parallels the levels of residual EGF-R in the various antisense clones, indicating a direct correlation between receptors and growth factor levels. The addition of exogenous TGF-alpha (10 ng/ml) to antisense clones induces TGF-alpha levels. The half-life of TGF-alpha mRNA is 40-60 min in antisense cells and more than 8 h in parental KB cells, as determined by actinomycin D decay curves. This result indicates a predominant regulation of TGF-alpha mRNA at the post-transcriptional level. Nuclear run-on experiments show that there is only a marginal effect at the transcriptional level. We conclude that the autocrine loop responsible for the transformed phenotype of the human carcinoma KB cell line is dependent on both elevated levels of EGF-R and the presence of TGF-alpha. In addition, TGF-alpha is able to induce its own mRNA via a signal due to activation of the EGF-R acting predominantly at the post-transcriptional level.

Epidermal growth factor-related peptides activate distinct subsets of ErbB receptors and differ in their biological activities

Numerous epidermal growth factor (EGF)-related peptide binding members of the ErbB family of receptor tyrosine kinases have been described. While several EGF agonists bind and activate ErbB-1/EGF receptor, neu differentiation factor (NDF) functions as a ligand for ErbB-3 and ErbB-4. However, it is currently unknown which specific subsets of ErbB receptors become activated in response to each of these ligands. The present study addresses this issue using the T47D breast tumor cell line, which expresses moderate levels of all the presently known ErbB receptors. We show that all the EGF agonists, but not NDF, stimulated tyrosine phosphorylation of ErbB-1. In contrast, all the EGF-related factors except amphiregulin were able to induce tyrosine phosphorylation of ErbB-2. The ability to induce tyrosine phosphorylation of ErbB-3 varied dramatically among the different EGF-related peptides. While EGF, transforming growth factor (TGF)-alpha, and amphiregulin only had a moderate effect, NDF dramatically increased the ErbB-3 phosphotyrosine content. Most notably, heparin binding EGF-related growth factor (HB-EGF) and betacellulin (BTC) were more effective than other EGF agonists. Consequently, only NDF, HB-EGF, and BTC significantly stimulated association of phosphatidylinositol kinase activity with ErbB-3. Among the EGF agonists, HB-EGF induced a low level of ErbB-4 tyrosine phosphorylation, while BTC was as efficient as NDF in activating ErbB-4. The BTC activation of ErbB-4 appears to be independent of ErbB-1, as shown by pretreatment of cells with an antibody that inhibits binding of EGF agonists to ErbB-1. As a result of the differential activation of ErbB receptors, most of the EGF-related growth factors had distinguishable biological activities on cultured mammary epithelial cell lines.