Group 3 innate lymphoid cells produce the growth factor HB-EGF to protect the intestine from TNF-mediated inflammation

Tumor necrosis factor (TNF) drives chronic inflammation and cell death in the intestine, and blocking TNF is a therapeutic approach in inflammatory bowel disease (IBD). Despite this knowledge, the pathways that protect the intestine from TNF are incompletely understood. Here we demonstrate that group 3 innate lymphoid cells (ILC3s) protect the intestinal epithelium from TNF-induced cell death. This occurs independent of interleukin-22 (IL-22), and we identify that ILC3s are a dominant source of heparin-binding epidermal growth factor-like growth factor (HB-EGF). ILC3s produce HB-EGF in response to prostaglandin E2 (PGE2) and engagement of the EP2 receptor. Mice lacking ILC3-derived HB-EGF exhibit increased susceptibility to TNF-mediated epithelial cell death and experimental intestinal inflammation. Finally, human ILC3s produce HB-EGF and are reduced from the inflamed intestine. These results define an essential role for ILC3-derived HB-EGF in protecting the intestine from TNF and indicate that disruption of this pathway contributes to IBD.

Spread of genetically similar noroviruses in Bangkok, Thailand, through symptomatic and asymptomatic individuals

Norovirus infection is a major cause of acute gastroenteritis, although some infected individuals are asymptomatic. GII.4 is the predominant genotype worldwide and, since 2000, has been the most prevalent in patients in Thailand with acute gastroenteritis. We screened stool samples for norovirus in 786 patients with acute gastroenteritis who were admitted to a hospital in Bangkok from 2017 to early 2019 and detected it in 136 specimens (17.3%). Eight and 124 specimens were positive for the GI and GII genogroups, respectively, and the remaining 4 specimens were double-positive. Nine genotypes (GI.3, GI.5, GII.2, GII.3, GII.4, GII.6, GII.8, GII.13, and GII.17) were identified from 140 strains, and 72 strains (51.4%) were GII.4. We had previously conducted a one-year survey of norovirus infection in residents of a community in Bangkok from May 2018 to April 2019 and found that a substantial portion of the residents were infected asymptomatically. The 9 genotypes identified in the patients were also commonly identified in the community residents. To investigate the relationship between noroviruses identified in the acute gastroenteritis patients and those identified in the community residents, phylogenetic tree analysis was conducted. Of the 9 genotypes, 8 showed similarities in both their genomic sequences and their deduced amino acid sequences. In addition, strain replacement of GI.3 was observed in both the patients and the community residents within the overlapping period. These results suggested that norovirus spreads efficiently to the community by simultaneously causing symptomatic and asymptomatic infections.

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GII.4 Sydney predominated in gastroenteritis patients of Bangkok during 2017–2019.

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Common norovirus genotypes spread in symptomatic and asymptomatic individuals.

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Noroviruses in symptomatic and asymptomatic individuals share genetical similarity.

Identification of GII.14[P7] norovirus and its genomic mutations from a case of long-term infection in a post-symptomatic individual

Norovirus is a leading cause of acute gastroenteritis worldwide. Norovirus shedding typically lasts one week to one month after the onset of diarrhea in immunocompetent hosts. The occurrence of mutations in the genome during infection has contributed to the evolution of norovirus. It has been suggested that genomic mutations in the P2-domain of capsid protein VP1, the major antigenic site for virus clearance, are involved in the evasion of host immunity and prolonged shedding of norovirus. In our previous study, we found a case of long-term shedding of GII.14 norovirus in a post-symptomatic immunocompetent individual that lasted about three months. In this study, we characterized the genomic sequence of the GII.14 strain to gain insight into the context of long-term shedding. By sequencing a 4.8 kb region of the genome corresponding to half of ORF1 and the entire ORF2 and ORF3, which encode several non-structural proteins and the structural proteins VP1 and VP2, the GII.14 strain was found to be classified as recombinant GII.14[P7]. Six point-mutations occurred during the three-month period of infection in a time-dependent manner in the genomic regions encoding RNA-dependent RNA polymerase, VP1, and VP2. Three of the six mutations were sense mutations, but no amino acid substitution was identified in the P2-domain of VP1. These results suggest that there is a mechanism by which long-term shedding of norovirus occurs in immunocompetent individuals independent of P2-domain mutations.

Norovirus transmission mediated by asymptomatic family members in households

The transmission of human norovirus excreted from infected persons occasionally causes sporadic infections and outbreaks. Both symptomatic patients and asymptomatic carriers have been reported to contribute to norovirus transmission, but little is known about the magnitude of the contribution of asymptomatic carriers. We carried out a 1-year survey of residents of a district of Bangkok, Thailand to determine the percentage of norovirus transmissions originating from asymptomatic individuals. We screened 38 individuals recruited from 16 families from May 2018 to April 2019 for GI and GII genotypes. Norovirus was detected every month, and 101 of 716 stool samples (14.1%) from individuals with no symptoms of acute gastroenteritis were norovirus-positive. The average infection frequency was 2.4 times per person per year. Fourteen genotypes were identified from the positive samples, with GII.4 being detected most frequently. Notably, 89.1% of the norovirus-positive samples were provided by individuals with no diarrhea episode. Similar to cases of symptomatic infections in Thailand, asymptomatic infections were observed most frequently in December. We detected 4 cases of NV infection caused by household transmission, and 3 of the 4 transmissions originated from asymptomatic individuals. We also identified a case in which norovirus derived from an asymptomatic individual caused diarrhea in a family member. These results suggest that asymptomatic individuals play a substantial role in both the maintenance and spreading of norovirus in a community through household transmission.

Abstract 4424: Micro-RNA mediated deregulation of hHB-EGF in ovarian cancer

Background: Aberrant expression of microRNAs (miRNAs) has been implicated in human carcinogenesis where they function as oncogenes or tumor suppressor genes. Overexpression of HB-EGF, member of the epidermal growth factor (EGF) family, plays pivotal role in ovarian carcinogenesis. However the molecular mechanisms underlying miRNA(s) mediated aberrant function of HB-EGF in ovarian carcinoma remain unresolved. Here, we investigated the miRNA(s) mediated deregulation of HB-EGF in human ovarian carcinogenesis.

Methods: Web-based bioinformatics algorithms were used to identify candidate miRNAs with putative binding sites on target hHB-EGF mRNA. Expression of miRNAs and mRNA were checked by real-time PCR whereas protein expression was investigated by western blotting assay. Luciferase reporter assay was carried out to examine miR-27a target on 3´UTR of hHB-EGF mRNA. Changes in the oncogenic effects of HB-EGF were studied after gain/loss -of-function of the miR-27a using soft agar colony formation assay and 3D collagen culture. In vivo tumor growth potential of miR-27a was measured in BALB/c nude mice.

Results: By using web-based bioinformatics algorithms 11 miRNAs ((miR-27a/b, -29a/b/c, -96, -128, -132, -182,-194, -212) having putative binding sites on the 3′UTR of hHB-EGF mRNA have been selected for further analysis. Among the putative candidates miR-27a showed maximum reciprocal expression with hHB-EGF and thus we selected miR-27a as promising candidate for hHB-EGF regulation. Overexpression of miR-27a significantly inhibited the hHB-EGF expression in SKOV3 cells by almost 50% and miR-27a inhibitors (anti-miR-27a) upregulated the expression of endogenous hHB-EGF mRNA whereas miR-27a overexpression decreased hHB-EGF protein level in MCAS cells suggesting that miR-27a modulate endogenous hHB-EGF expression both at mRNA and protein level. Luciferase reporter assay revealed that miR-27a directly targets 3´UTR of hHB-EGF mRNA at the predicted site. Ectopic expression of miR-27a suppresses in-vitro growth of SKOV3 ovarian cancer cells. In addition, in-vivo tumorigenecity of SKOV3 cells was also inhibited by miR-27a treatment.

Conclusion: The current study has identified novel miR-27a that negatively regulates hHB-EGF expression by directly targeting 3`UTR of its mRNA. This miR-27a might act as oncosupressor in human epithelial ovarian cancer.

Citation Format: Md. Mustafizur Rahman, Razia Sultana, Ryo Iwamoto, Eisuke Mekada. Micro-RNA mediated deregulation of hHB-EGF in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4424.

Double deletion of tetraspanins CD9 and CD81 in mice leads to a syndrome resembling accelerated aging

Chronic obstructive pulmonary disease (COPD) has been recently characterized as a disease of accelerated lung aging, but the mechanism remains unclear. Tetraspanins have emerged as key players in malignancy and inflammatory diseases. Here, we found that CD9/CD81 double knockout (DKO) mice with a COPD-like phenotype progressively developed a syndrome resembling human aging, including cataracts, hair loss, and atrophy of various organs, including thymus, muscle, and testis, resulting in shorter survival than wild-type (WT) mice. Consistent with this, DNA microarray analysis of DKO mouse lungs revealed differential expression of genes involved in cell death, inflammation, and the sirtuin-1 (SIRT1) pathway. Accordingly, expression of SIRT1 was reduced in DKO mouse lungs. Importantly, siRNA knockdown of CD9 and CD81 in lung epithelial cells additively decreased SIRT1 and Foxo3a expression, but reciprocally upregulated the expression of p21 and p53, leading to reduced cell proliferation and elevated apoptosis. Furthermore, deletion of these tetraspanins increased the expression of pro-inflammatory genes and IL-8. Hence, CD9 and CD81 might coordinately prevent senescence and inflammation, partly by maintaining SIRT1 expression. Altogether, CD9/CD81 DKO mice represent a novel model for both COPD and accelerated senescence.

BK-UM in patients with recurrent ovarian cancer or peritoneal cancer: a first-in-human phase-I study

Background

BK-UM (CRM197) is a mutant form of diphtheria toxin and a specific inhibitor of heparin-binding epidermal growth factor-like growth factor (HB-EGF). We assessed the safety, pharmacokinetics, recommended dose, and efficacy of BK-UM in patients with recurrent ovarian cancer (OC) or peritoneal cancer (PC), and measured HB-EGF levels in serum and abdominal fluid after BK-UM administration.

Methods

Eleven patients with advanced or recurrent OC or PC were enrolled and treated with BK-UM via the intraperitoneal route. The dose was escalated (1.0, 2.0, 3.3, and 5.0 mg/m²) using a 3 + 3 design.

Results

Eight of 11 patients completed treatment. No dose-limiting toxicity (DLT) was experienced at dose levels 1 (1.0 mg/m²) and 2 (2.0 mg/m²). Grade 3 transient hypotension as an adverse event (defined as a DLT in the present study) was observed in two of four patients at dose level 3 (3.3 mg/m²). Treatment with BK-UM was associated with decreases in HB-EGF levels in serum and abdominal fluid in seven of 11 patients and five of eight patients, respectively. Clinical outcomes included a partial response in one patient, stable disease in five patients, and progressive disease in five patients.

Conclusions

BK-UM was well tolerated at doses of 1.0 and 2.0 mg/m², with evidence for clinical efficacy in patients with recurrent OC or PC. A dose of 2.0 mg/m² BK-UM is recommended for subsequent clinical trials.

Trial registration

This trial was prospectively performed as an investigator-initiated clinical trial. The trial numbers are UMIN000001002 and UMIN000001001, with registration dates of 1/30/2008 and 2/4/2008, respectively. UMIN000001001 was registered as a trial for the continuous administration of BK-UM after UMIN000001002.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3071-5) contains supplementary material, which is available to authorized users.

Reconstitution of a metastatic-resistant tumor microenvironment with cancer-associated fibroblasts enables metastasis

The tumor microenvironment is critical for metastasis to occur. Subcutaneous xenografts of tumors in immunodeficient mice are usually encapsulated and rarely metastasize as opposed to orthotopic tumors which metastasize if the original tumor was metastatic. In the present report, we were able to reconstitute a metastatic tumor microenvironment by subcutaneously co-transplanting a human cervical cancer cell line and human cervical cancer-associated fibroblasts (CAFs), in athymic mice, which resulted in lymph node metastasis in 40% of the animals. In contrast, no metastasis occurred from the cervical cancer without CAFs. These results suggest that CAFs can overcome an anti-metastatic tumor environment and are a potential target to prevent metastasis.

ErbB1 and ErbB4 generate opposing signals regulating mesenchymal cell proliferation during valvulogenesis

HB-EGF plays an indispensable role in suppression of cell proliferation during mouse valvulogenesis. However, ligands of the EGF receptor (EGFR/ErbB1), including HB-EGF, are generally considered as growth-promoting factors as shown in cancers. HB-EGF binds to and activates ErbB1 and ErbB4. We investigated the role of ErbB receptors in valvulogenesis in vivo using ErbB1- and ErbB4-deficient mice, and an ex vivo model of endocardial cushion explants. We show that HB-EGF suppresses valve mesenchymal cell proliferation through a heterodimer of ErbB1 and ErbB4, and an ErbB1 ligand(s) promotes cell proliferation through a homodimer of ErbB1. Moreover, a rescue experiment with cleavable or uncleavable isoforms of ErbB4 in ERBB4 null cells indicates that the cleavable JM-a-type, but not the uncleavable JM-b-type, of ErbB4 rescues the defect of the null cells. These data suggest that the cytoplasmic intracellular domain of ErbB4, rather than the membrane-anchored tyrosine kinase, achieves this suppression. Our study demonstrates that opposing signals generated by different ErbB dimer combinations function in the same cardiac cushion mesenchymal cells for proper cardiac valve formation.

Characterization of a Novel Anti-Human HB-EGF Monoclonal Antibody Applicable for Paraffin-Embedded Tissues and Diagnosis of HB-EGF-Related Cancers

Heparin-binding EGF-like growth factor (HB-EGF) is a member of the EGF family of growth factors that bind to and activate the EGF receptor (EGFR/ErbB1) and ErbB4. HB-EGF plays pivotal roles in pathophysiological processes, including cancer. Thus, monoclonal antibodies (mAbs) for HB-EGF detection could be an important tool in the therapeutic diagnosis of HB-EGF-related cancers and other diseases. However, few mAbs, especially those applicable for immunohistochemistry (IHC), have been established to date. In this study, we generated a clone of hybridoma-derived mAb 2-108 by immunizing mice with recombinant human HB-EGF protein expressed by human cells. The mAb 2-108 specifically bound to human HB-EGF but not to mouse HB-EGF and was successful in immunoblotting, even under reducing conditions, immunoprecipitation, and immunofluorescence for unfixed as well as paraformaldehyde-fixed cells. Notably, this mAb was effective in IHC of paraffin-embedded tumor specimens. Epitope mapping analysis showed that mAb 2-108 recognized the N-terminal prodomain in HB-EGF. These results indicate that this new anti-HB-EGF mAb 2-108 would be useful in the diagnosis of HB-EGF-related cancers and would be a strong tool in both basic and clinical research on HB-EGF.

Identification of diphtheria toxin R domain mutants with enhanced inhibitory activity against HB-EGF

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a ligand of EGF receptor, is involved in the growth and malignant progression of cancers. Cross-reacting material 197, CRM197, a non-toxic mutant of diphtheria toxin (DT), specifically binds to the EGF-like domain of HB-EGF and inhibits its mitogenic activity, thus CRM197 is currently under evaluation in clinical trials for cancer therapy. To develop more potent DT mutants than CRM197, we screened various mutant proteins of R domain of DT, the binding site for HB-EGF. A variety of R-domain mutant proteins fused with maltose-binding protein were produced and their inhibitory activity was evaluated in vitro. We found four R domain mutants that showed much higher inhibitory activity against HB-EGF than wild-type (WT) R domain. These R domain mutants suppressed HB-EGF-dependent cell proliferation more effectively than WT R domain. Surface plasmon resonance revealed their higher affinity to HB-EGF than WT R domain. CRM197(R460H) carrying the newly identified mutation showed increased cell proliferation inhibitory activity and affinity to HB-EGF. These results suggest that CRM197(R460H) or other recombinant proteins carrying newly identified mutation(s) in the R domain are potential therapeutics targeting HB-EGF.

Pre-clinical study of BK-UM, a novel inhibitor of HB-EGF, for ovarian cancer therapy

BACKGROUND/AIM

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a member of the epidermal growth factor family, is a target for ovarian cancer therapy. The present study investigated the administration schedule of BK-UM, an anticancer agent targeting HB-EGF.

MATERIALS AND METHODS

The ovarian cancer cell line, RMG-I, was injected subcutaneously into five-week-old female nude mice. The BK-UM was administered intraperitoneally, using three administration schedules with different doses. The tumor volume was calculated every week. Statistical significance was assessed using the Mann-Whitney U-test.

RESULTS

At doses >0.1 mg/kg, BK-UM displayed significant antitumor effects, although the antitumor effects and body weights of mice did not significantly differ by dose or by three different administration schedules. At a dose <0.1 mg/kg, however, BK-UM had little inhibitory effect on tumor growth.

CONCLUSION

Daily administration of BK-UM, which has a potentially dose-dependent antitumor effect, may be the optimal schedule for clinical application.

Co-occurrence of tetraspanin and ROS generators: Conservation in protein cross-linking and other developmental processes

The nematode exoskeleton, commonly called the cuticle, is a highly structured extracellular matrix mainly composed of collagen. Secreted collagen molecules from the underlying epidermal cells are cross-linked via their tyrosyl residues. Reactive oxygen species (ROS) are required for the cross-linking reaction to produce tyrosyl radicals. The conserved ROS generator enzyme in C. elegans, BLI-3/CeDUOX1, a homolog of dual oxidases (DUOXs), is responsible for production of hydrogen peroxide. The ROS generation system must be properly controlled since ROS are highly reactive molecules that irreversibly inhibit the functions of cellular components such as nucleic acids and proteins. We recently reported that the ROS generation system directed by BLI-3 requires the tetraspanin protein, TSP-15. Herein we outline the process of cuticle development with a focus on the molecular roles of TSP-15 in the BLI-3 system. We also propose the co-occurrence of tetraspanin and ROS generators by convergent evolution.

Metastasis suppressor tetraspanin CD82/KAI1 regulates ubiquitylation of epidermal growth factor receptor

Ligand-induced ubiquitylation of EGF receptor (EGFR) is an important regulatory mechanism that controls endocytic trafficking of the receptor and its signaling potential. Here we report that tetraspanin CD82/KAI1 specifically suppresses ubiquitylation of EGFR after stimulation with heparin-binding EGF or amphiregulin and alters the rate of recruitment of the activated receptor to EEA1-positive endosomes. The suppressive effect of CD82 is dependent on the heparin-binding domain of the ligand. Deletion of the C-terminal cytoplasmic domain of CD82 (CD82ΔC mutant) inhibits endocytic trafficking of the tetraspanin and compromises its activity toward heparin-binding EGF-activated EGFR. Reduced ubiquitylation of EGFR is accompanied by PKC-dependent increase in serine phosphorylation of c-Cbl in cells expressing elevated levels of CD82. Furthermore, phosphorylation of threonine 654 (PKC phosphorylation site) in the juxtamembrane domain of the receptor is considerably increased in CD82-expressing cells. These results describe previously unsuspected links between tetraspanin proteins and ubiquitylation of their molecular partners (e.g., EGFR). Our data identify CD82 as a new regulator of c-Cbl, which discriminatively controls the activity of this E3 ubiquitin ligase toward heparin-binding ligand-EGFR pairs. Taken together, these observations provide an important new insight into the modulatory role of CD82 in endocytic trafficking of EGF receptor.

Conditional loss of heparin-binding EGF-like growth factor results in enhanced liver fibrosis after bile duct ligation in mice

Our aims were to evaluate the involvement of heparin-binding EGF-like growth factor (HB-EGF) in liver fibrogenesis of humans and mice and to elucidate the effect of HB-EGF deficiency on cholestatic liver fibrosis using conditional HB-EGF knockout (KO) mice. We first demonstrated that gene expression of HB-EGF had a positive significant correlation with that of collagen in human fibrotic livers, and was increased in bile duct ligation (BDL)-induced fibrotic livers in mouse. We then generated conditional HB-EGF knockout (KO) mice using the interferon inducible Mx-1 promoter driven Cre recombinase transgene and wild type (WT) and KO mice were subjected to BDL. After BDL, KO mice exhibited enhanced liver fibrosis with increased expression of collagen, compared with WT mice. Finally, we used mouse hepatic stellate cells (HSCs) to examine the role of HB-EGF in the activation of these cells and showed that HB-EGF antagonized TGF-β-induced gene expression of collagen in mouse primary HSCs. Interestingly, HB-EGF did not prevent the TGF-β-induced nuclear accumulation of Smad3, but did lead to stabilization of the Smad transcriptional co-repressor TG-interacting factor. In conclusion, our data suggest a possible protective role of HB-EGF in cholestatic liver fibrosis.

Conditional knockout of heparin-binding epidermal growth factor-like growth factor in the liver accelerates carbon tetrachloride-induced liver injury in mice

AIM

  We previously demonstrated that heparin-binding epidermal growth factor-like growth factor (HB-EGF) is induced in response to several liver injuries. Because the HB-EGF knockout (KO) mice die in utero or immediately after birth due to cardiac defects, the loss of function study in vivo is limited. Here, we generated liver-specific HB-EGF conditional knockout mice using the interferon-inducible Mx-1 promoter driven cre recombinase transgene and investigated its role during acute liver injury.

METHODS

  We induced acute liver injury by a single i.p. injection of carbon tetrachloride (CCl4 ) in HB-EGF KO mice and wild-type mice and liver damage was assessed by biochemical and immunohistochemical analysis. We also used AML12 mouse hepatocyte cell lines to examine the molecular mechanism of HB-EGF-dependent anti-apoptosis and wound-healing process of the liver in vitro.

RESULTS

  HB-EGF KO mice exhibited a significant increase of alanine aminotransferase level and also showed a significant increase in the number of apoptotic hepatocytes assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling staining at 24 h after CCl4 injection. We also demonstrated that HB-EGF treatment inhibited tumor necrosis factor-α-induced apoptosis of AML12 mouse hepatocytes and promoted the wound-healing response of these cells.

CONCLUSION

  This study showed that HB-EGF plays a protective role during acute liver injury.

Soluble heparin-binding EGF-like growth factor (HB-EGF) detected by newly developed immuno-PCR method is a clear-cut serological biomarker for ovarian cancer

Heparin-binding EGF-like growth factor (HB-EGF) is a member of the EGF family of growth factors that bind to 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. HB-EGF plays pivotal roles in pathophysiological processes such as development and cell proliferation. In this study, we developed an immuno-PCR system for the determination of soluble HB-EGF concentrations in human serum. Utilizing a monoclonal antibody with neutralizing activity against HB-EGF as a capture antibody resulted in increasing selectivity for an active form of HB-EGF in serum, and immuno-PCR system improved its sensitivity compared to the currently available methods. As a result of measurement of HB-EGF in 20 ovarian cancer patients and 20 healthy volunteers, ovarian cancer patients showed significantly higher concentrations than healthy volunteers (P< 0.05), which indicates that soluble HB-EGF detected by newly developed immuno-PCR system can be useful serological biomarkers such as a diagnostic biomarker for ovarian cancer, and a predictive and pharmacodynamic biomarker for anti-HB-EGF targeted therapies under development.

Tetraspanin is required for generation of reactive oxygen species by the dual oxidase system in Caenorhabditis elegans

Reactive oxygen species (ROS) are toxic but essential molecules responsible for host defense and cellular signaling. Conserved NADPH oxidase (NOX) family enzymes direct the regulated production of ROS. Hydrogen peroxide (H₂O₂) generated by dual oxidases (DUOXs), a member of the NOX family, is crucial for innate mucosal immunity. In addition, H₂O₂ is required for cellular signaling mediated by protein modifications, such as the thyroid hormone biosynthetic pathway in mammals. In contrast to other NOX isozymes, the regulatory mechanisms of DUOX activity are less understood. Using Caenorhabditis elegans as a model, we demonstrate that the tetraspanin protein is required for induction of the DUOX signaling pathway in conjunction with the dual oxidase maturation factor (DUOXA). In the current study, we show that genetic mutation of DUOX (bli-3), DUOXA (doxa-1), and peroxidase (mlt-7) in C. elegans causes the same defects as a tetraspanin tsp-15 mutant, represented by exoskeletal deficiencies due to the failure of tyrosine cross-linking of collagen. The deficiency in the tsp-15 mutant was restored by co-expression of bli-3 and doxa-1, indicating the involvement of tsp-15 in the generation of ROS. H₂O₂ generation by BLI-3 was completely dependent on TSP-15 when reconstituted in mammalian cells. We also demonstrated that TSP-15, BLI-3, and DOXA-1 form complexes in vitro and in vivo. Cell-fusion-based analysis suggested that association with TSP-15 at the cell surface is crucial for BLI-3 activation to release H₂O₂. This study provides the first evidence for an essential role of tetraspanin in ROS generation.

ROS are highly reactive molecules, which can be inappropriately produced during aerobic metabolism or by exogenous stresses such as exposure to UV light and radiation. ROS interact with cellular components including nucleic acids, lipids, and proteins and irreversibly inhibit their functions. However, ROS are essential for innate host defense and multiple physiological processes and are generated by conserved NADPH oxidase (NOX) family enzymes. The release of ROS by ROS generator enzymes must be properly controlled, as chronic oxidative stress can cause an imbalance of the redox state and is often associated with disease and aging. Using C. elegans as a model, we identified a tetraspanin (TSP-15) protein as a new key component of the ROS generation system controlled by dual oxidase (BLI-3), a unique NOX isozyme in C. elegans. Mutants of both bli-3 and tsp-15 developed the same defects in extracellular matrix cross-linking. Using a combination of genetics and reconstitution experiments in mammalian cells, we have demonstrated a novel requirement of tetraspanin for dual oxidase-dependent ROS generation via complex formation at the cell surface.

Abstract 1516: HB-EGF and PDGF mediate reciprocal interactions of carcinoma cells with cancer-associated fibroblasts to support progression of uterine cervical cancers

Tumor stroma drives the growth and progression of cancers. A heparin-binding epidermal growth factor-like growth factor, HB-EGF, is an EGF receptor ligand that stimulates cell growth in an autocrine or paracrine fashion. While elevated expression of HB-EGF in cancer cells and its contribution to tumor progression are well documented, the effects of HB-EGF expression in the tumor stroma have not been clarified. Here, we show that HB-EGF is expressed in stromal fibroblasts where it promotes tumor cell proliferation. In uterine cervical cancers, HB-EGF was detected immunohistochemically in the stroma proximal to the cancer epithelium. Proliferation of cervical cancer cells in vitro was enhanced by coculture with fibroblasts isolated from tumor tissues of patients with cervical cancer. Inhibition of HB-EGF function or treatment with platelet-derived growth factor (PDGF) inhibitors abrogated cancer cell growth enhanced by cervical cancer-associated fibroblast (CCF) coculture. Furthermore, tumor formation in a mouse xenograft model was enhanced by cotransplantation of CCF or mouse embryonic fibroblasts but not with embryonic fibroblasts from HB-EGF-deficient mice. Conversely, conditioned medium from cancer cells induced HB-EGF expression in CCF and mechanistic investigations established that PDGF was the primary factor responsible. Together, our findings indicate that HB-EGF and PDGF reciprocally mediate the interaction of cancer cells with cancer-associated fibroblasts, promoting cancer cell proliferation in a paracrine manner that has implications for novel combinatorial cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1516. doi:1538-7445.AM2012-1516

Assessment of HB-EGF levels in peritoneal fluid and serum of ovarian cancer patients using ELISA

BACKGROUND

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a rational target for ovarian cancer therapy. The aim of this study was to examine HB-EGF levels in the peritoneal fluid and serum of ovarian cancer (OVCA) patients.

PATIENTS AND METHODS

Samples were collected from six healthy women, 21 OVCA patients, and 21 ovarian cyst patients. HB-EGF levels were measured using a sandwich ELISA kit and calculated using a parallel line assay.

RESULTS

No significant difference between the slopes of the standard and sample curves was observed at an anti-HB-EGF antibody concentration of 1.6 μg/ml. HB-EGF levels in the peritoneal fluid and serum of OVCA patients were significantly higher than those in patients with ovarian cysts or controls. Serum HB-EGF levels were also significantly correlated with levels in peritoneal fluid in OVCA patients.

CONCLUSION

We developed an assay for the exact measurement of HB-EGF levels in peritoneal fluid and serum.

HB-EGF function in cardiac valve development requires interaction with heparan sulfate proteoglycans

HB-EGF, a member of the EGF family of growth factors, plays an important role in cardiac valve development by suppressing mesenchymal cell proliferation. Here, we show that HB-EGF must interact with heparan sulfate proteoglycans (HSPGs) to properly function in this process. In developing valves, HB-EGF is synthesized in endocardial cells but accumulates in the mesenchyme by interacting with HSPGs. Disrupting the interaction between HB-EGF and HSPGs in an ex vivo model of endocardial cushion explants resulted in increased mesenchymal cell proliferation. Moreover, homozygous knock-in mice (HBΔhb/Δhb) expressing a mutant HB-EGF that cannot bind to HSPGs developed enlarged cardiac valves with hyperproliferation of mesenchymal cells; this resulted in a phenotype that resembled that of Hbegf-null mice. Interestingly, although Hbegf-null mice had abnormal heart chambers and lung alveoli, HBΔhb/Δhb mice did not exhibit these defects. These results indicate that interactions with HSPGs are essential for the function of HB-EGF, especially in cardiac valve development, in which HB-EGF suppresses mesenchymal cell proliferation.

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.

Integrin signal masks growth-promotion activity of HB-EGF in monolayer cell cultures

The extracellular environment and tissue architecture contribute to proper cell function and growth control. Cells growing in monolayers on standard polystyrene tissue culture plates differ in their shape, growth rate and response to external stimuli, compared with cells growing in vivo. Here, we showed that the EGFR (epidermal growth factor receptor) ligand heparin-binding EGF-like growth factor (HB-EGF) strongly stimulated cell growth in nude mice, but not in cells cultured in vitro. We explored the effects of HB-EGF on cell growth under various cell culture conditions and found that growth promotion by HB-EGF was needed in three-dimensional (3D) or two-dimensional (2D) culture systems in which cell-matrix adhesion was reduced. Under such conditions, cell growth was extremely suppressed in the absence of HB-EGF, but markedly potentiated in the presence of HB-EGF. When the integrin signal was reduced using antibodies or knockout of either integrin β1 or focal adhesion kinase (FAK), cells showed HB-EGF-dependent growth. We also showed that EGF, transforming growth factor-α (TGFα) or ligands of other receptor tyrosine kinases (RTKs) stimulated cell growth in 3D culture, but not in tissue culture plates. These results indicate that the integrin signal was sufficient to support cell growth in 2D tissue culture plates without addition of the growth factor, whereas stimulation by growth factors was clearly demonstrated in culture systems in which integrin signals were attenuated.

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.

Double deficiency of tetraspanins CD9 and CD81 alters cell motility and protease production of macrophages and causes chronic obstructive pulmonary disease-like phenotype in mice

CD9 and CD81 are closely related tetraspanins that regulate cell motility and signaling by facilitating the organization of multimolecular membrane complexes, including integrins. We show that CD9 and CD81 are down-regulated in smoking-related inflammatory response of a macrophage line, RAW264.7. When functions of CD9 and CD81 were ablated with monoclonal antibody treatment, small interfering RNA transfection, or gene knock-out, macrophages were less motile and produced larger amounts of matrix metalloproteinase (MMP)-2 and MMP-9 than control cells in vitro. In line with this, CD9/CD81 double-knock-out mice spontaneously developed pulmonary emphysema, a major pathological component of chronic obstructive pulmonary disease (COPD). The mutant lung contained an increased number of alveolar macrophages with elevated activities of MMP-2 and MMP-9 and progressively displayed enlarged airspace and disruption of elastic fibers in the alveoli. Secretory cell metaplasia, a finding similar to goblet cell metaplasia in cigarette smokers, was also observed in the epithelium of terminal bronchioles. With aging, the double-knockout mice showed extrapulmonary phenotypes, including weight loss, kyphosis, and osteopenia. These results suggest that the tetraspanins CD9 and CD81 regulate cell motility and protease production of macrophages and that their dysfunction may underlie the progression of COPD.

HB-EGF decelerates cell proliferation synergistically with TGFalpha in perinatal distal lung development

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a member of the EGF family of growth factors that is suggested to be involved in distal lung development. In HB-EGF null (HB(del/del)) newborns, a histopathologic analysis revealed abnormally thick saccular walls occurring from embryonic day 18.5 that reduced the terminal saccular space area. HB-EGF gene deletion resulted in a significant increase in cell proliferation, indicating that HB-EGF suppresses distal lung cell proliferation. Furthermore, an analysis of saccular morphology and proliferation in HB-EGF and transforming growth factor-alpha (TGFalpha) double-mutant newborns revealed that HB-EGF and TGFalpha function synergistically in this suppression. Finally, crosses between HB(del/del) mice and waved 2 mice, a hypomorphic EGF receptor (EGFR) mutant strain, suggest that HB-EGF and EGFR cooperate in this process. Thus, HB-EGF has a novel suppressive function that contributes to decelerating distal lung cell proliferation synergistically with TGFalpha through EGFR in perinatal distal lung development.

Biologic significance of receptor-binding cancer antigen expressed on SiSo cells (RCAS1) as a pivotal regulator of tumor growth through angiogenesis in human uterine cancer

BACKGROUND

The expression of receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is related significantly to the overall survival of patients with various cancers. RCAS1 reportedly induces apoptotic cell death in peripheral lymphocytes, which may contribute to the escape of tumor cells from immune surveillance. RCAS1 expression also has been related to tumor invasiveness and size in uterine cervical cancer. To clarify whether RCAS1 exacerbates tumor progression, the authors investigated the association between RCAS1 expression and tumor growth potential.

METHODS

The authors constructed small interfering ribonucleic acid (RNA) (siRNA) to target RCAS1. After transfection of siRNA and the RCAS1-encoding gene, growth of tumor cells was assessed in vitro and in vivo. The correlation between RCAS1 expression and angiogenesis was investigated in the transfected cells and in inoculated tumors from nude mice. In addition, the same association was investigated immunohistochemically with tissue samples from patients with uterine cervical cancer.

RESULTS

Knockdown of RCAS1 expression by siRNA significantly suppressed the in vivo growth of SiSo and HOUA tumor cells (P < .005); however, in vitro cell growth was not affected significantly. Enhanced RCAS1 expression significantly promoted in vivo growth, but not in vitro growth, of tumors derived from COS-7 cells (P = .0039). Introduction of the RCAS1-encoding gene increased expression of vascular endothelial growth factor (VEGF). In uterine cervical cancer, RCAS1 expression was associated significantly with VEGF expression (P = .0407) and with microvessel density (P = .0108).

CONCLUSIONS

RCAS1 may be a pivotal regulator of tumor growth through angiogenesis. Continued exploration of the biologic function of RCAS1 may allow the development of novel therapeutic strategies for uterine cancer.

Validation of HB-EGF and amphiregulin as targets for human cancer therapy

Aberrant expression levels of epidermal growth factor receptor (EGFR) and its cognate ligands have been recognized as one of the causes of cancer progression. To investigate the validity of EGFR ligands as targets for cancer therapy, we examined the expression of EGFR ligands and in vitro anti-tumor effects of small interference RNA (siRNA) for EGFR ligands in various cancer cells. HB-EGF expression was dominantly elevated in ovarian, gastric, and breast cancer, melanoma and glioblastoma cells, whereas amphiregulin was primarily expressed in pancreatic, colon, and prostate cancer, renal cell carcinoma and cholangiocarcinoma cells. Transfection of siRNAs for HB-EGF or amphiregulin into these cells significantly increased the numbers of apoptotic cells with attenuation of EGFR and ERK activation. In lung cancer cells, any EGFR ligand was not recognized as a validated target for cancer therapy. These results suggest that HB-EGF and amphiregulin are promising targets for cancer therapy.

New approach to cancer therapy: heparin binding-epidermal growth factor-like growth factor as a novel targeting molecule

Heparin binding-epidermal growth factor-like growth factor (HB-EGF) is one of the EGF receptor ligands and possesses several functional domains. It is involved in diverse biological processes, including wound healing, blast implantation, atherosclerosis and tumor formation, through its interactions with various molecules. We have reported that HB-EGF gene expression is significantly elevated in human ovarian cancer, and further demonstrated that HB-EGF plays key roles in the acquisition of malignant phenotypes, such as cell survival in peritoneal fluid, cell adhesion on extracellular matrices, invasion, angiogenesis, tumorigenicity, and chemoresistance in ovarian cancer. Thus, HB-EGF was considered as a promising target for cancer therapy. In vitro as well as in vivo experiments have revealed that cross-reacting material 197 (CRMI97), a specific inhibitor of HB-EGF, or a small interfering RNA for HB-EGF can block each step involved in peritoneal dissemination. According to these pieces of evidence, the development of targeting tools against HB-EGF, such as CRM197, could allow us to improve the prognosis of cancer patients.

Sulfated glycosaminoglycans are necessary for Nodal signal transmission from the node to the left lateral plate in the mouse embryo

Situs-specific organogenesis in the mouse results from leftward fluid flow in the node cavity and subsequent left-sided expression of Nodal in the lateral plate mesoderm (LPM). Nodal expression at the node is essential for the subsequent asymmetric Nodal expression in the left LPM, but the precise role of Nodal produced at the node has remained unknown. We have now investigated how the Nodal signal is transferred from the node to the LPM. Externally supplied Nodal protein failed to signal to the LPM,suggesting that the Nodal signal is transferred to the LPM via an internal route rather than an external one. Transgenic rescue experiments showed that the Nodal co-receptor Cryptic (Cfc1) is required only in the LPM, not at the node, for asymmetric Nodal expression in the LPM, indicating that the Nodal signal is not relayed indirectly between the node and LPM. Nodal interacts in vitro with sulfated glycosaminoglycans (GAGs), which are specifically localized to the basement membrane-like structure between the node and LPM in the mouse embryo. Inhibition of sulfated GAG biosynthesis prevents Nodal expression in the LPM. These data suggest that Nodal produced at the node might travel directly to the LPM via interaction with sulfated GAGs.

Diphtheria toxin mutant CRM197 possesses weak EF2-ADP-ribosyl activity that potentiates its anti-tumorigenic activity

CRM197, a mutated diphtheria toxin (DT), has long been recognized to be a non-toxic protein. Based on its non-toxic feature, this protein has been utilized for various purposes, including as an inhibitor of heparin-binding EGF-like growth factor (HB-EGF) and as an immunological adjuvant for vaccination. Here we show evidence that CRM197 has a weak toxicity. This toxicity was observed in cells over-expressing the DT receptor/proHB-EGF, but not in parental cells, indicating that the toxicity was mediated through DT receptor. CRM197 did not show any toxicity toward DT-resistant cells, which have a mutation in elongation factor 2, and a cell-free assay revealed the existence of weak EF-2-ADP ribosylation activity in fragment A of CRM197. Thus, the present study indicates a requirement for specific care in the use of CRM197 at a high dosage, although the toxicity of CRM197 is about 10(6) times less than that of wild-type DT. We found that a monoclonal antibody to DT inhibited CRM197 toxicity, but did not affect the inhibitory activity of CRM197 toward HB-EGF-induced mitogenic activity. CRM197 strongly inhibits tumour growth in nude mice. The anti-DT monoclonal antibody administered with CRM197 reduced the anti- tumourigenic effect of CRM197, indicating that the toxicity of CRM197 potentiates its anti- tumourigenic effect.

Parasporin-1, a Novel Cytotoxic Protein from Bacillus thuringiensis, Induces Ca2+ Influx and a Sustained Elevation of the Cytoplasmic Ca2+ Concentration in Toxin-sensitive Cells

Parasporin-1 is a novel non-insecticidal inclusion protein from Bacillus thuringiensis that is cytotoxic to specific mammalian cells. In this study, we investigated the effects of parasporin-1 on toxin-sensitive cell lines to elucidate the cytotoxic mechanism of parasporin-1. Parasporin-1 is not a membrane pore-forming toxin as evidenced by measurements of lactate dehydrogenase release, propidium iodide penetration, and membrane potential in parasporin-1-treated cells. Parasporin-1 decreased the level of cellular protein and DNA synthesis in parasporin-1-sensitive HeLa cells. The earliest change observed in cells treated with this toxin was a rapid elevation of the intracellular free-Ca(2+) concentration; increases in the intracellular Ca(2+) levels were observed 1-3 min following parasporin-1 treatment. Using four different cell lines, we found that the degree of cellular sensitivity to parasporin-1 was positively correlated with the size of the increase in the intracellular Ca(2+) concentration. The toxin-induced elevation of the intracellular Ca(2+) concentration was markedly decreased in low-Ca(2+) buffer and was not observed in Ca(2+)-free buffer. Accordingly, the cytotoxicity of parasporin-1 decreased in the low-Ca(2+) buffer and was restored by the addition of Ca(2+) to the extracellular medium. Suramin, which inhibits trimeric G-protein signaling, suppressed both the Ca(2+) influx and the cytotoxicity of parasporin-1. In parasporin-1-treated HeLa cells, degradation of pro-caspase-3 and poly(ADP-ribose) polymerase was observed. Furthermore, synthetic caspase inhibitors blocked the cytotoxic activity of parasporin-1. These results indicate that parasporin-1 activates apoptotic signaling in these cells as a result of the increased Ca(2+) level and that the Ca(2+) influx is the first step in the pathway that underlies parasporin-1 toxicity.

Possible involvement of CD81 in acrosome reaction of sperm in mice

Tetraspanin CD81 is closely homologous in amino acid sequence with CD9. CD9 is well known to be involved in sperm-egg fusion, and CD81 has also been reported to be involved in membrane fusion events. However, the function of CD81 as well as that of CD9 in membrane fusion remains unclear. Here, we report that disruption of the mouse CD81 gene led to a reduction in the fecundity of female mice, and CD81-/- eggs had impaired ability to fuse with sperm. Furthermore, we demonstrated that when CD81-/- eggs were incubated with sperm, some of the sperm that penetrated into the perivitelline space of CD81-/- eggs had not yet undergone the acrosome reaction, indicating that the impaired fusibility of CD81-/- eggs may be in part caused by failure of the acrosome reaction of sperm. In addition, we showed that CD81 was highly expressed in granulosa cells, somatic cells that surround oocytes. Our observations suggest that there is an interaction between sperm and CD81 on somatic cells surrounding eggs before the direct interaction of sperm and eggs. Our results may provide new clues for clarifying the cellular mechanism of the acrosome reaction, which is required for sperm-egg fusion.

Loss of HB-EGF in smooth muscle or endothelial cell lineages causes heart malformation

Epidermal growth factor (EGF) and ErbB family molecules play a role in heart development and function. To investigate the role of EGF family member, heparin-binding EGF-like growth factor (HB-EGF) in heart development, smooth muscle and endothelial cell lineage-specific HB-EGF knockout mice were generated using the Cre/loxP system in combination with the SM22alpha or TIE2 promoter. HB-EGF knockout mice displayed enlarged heart valves, and over half of these mice died during the first postnatal week, while survivors showed cardiac hypertrophy. These results suggest that expression of HB-EGF in smooth muscle and/or endothelial cell lineages is essential for proper heart development and function in mice.

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.

Cytoplasmic domain phosphorylation of heparin-binding EGF-like growth factor

Heparin-binding EGF-like growth factor (HB-EGF) is synthesized as a transmembrane precursor protein that is anchored to the plasma membrane. The extracellular EGF-like domain acts as a mitogen and motogen upon ectodomain shedding, but the functional roles of the transmembrane and cytoplasmic domains are largely unknown. We demonstrate here that cytoplasmic domain of HB-EGF is phosphorylated by external stimuli, and that the phosphorylation site is involved in HB-EGF-dependent tumorigenesis. Treatment of Vero cells overexpressing human HB-EGF with 12-O-tetradecanoylphorbol-13-acetate (TPA) caused ectodomain shedding of HB-EGF and generated two carboxyl (C)-terminal fragments with distinct electrophoretic mobilities. Mutation analysis showed that Ser207 in the cytoplasmic domain of HB-EGF is phosphorylated upon TPA stimulation, generating two C-terminal fragments with distinct phosphorylation states. Treatment of cells with lysophosphatidic acid, anisomycin, and calcium ionophore, all of which are known to induce ectodomain shedding, also caused phosphorylation of HB-EGF. Although ectodomain shedding and phosphorylation of HB-EGF occurred coordinately, Ala substitution of Ser207 had no effect on TPA-induced or constitutive ectodomain shedding. Injection of cells overexpressing HB-EGF into nude mice showed that Ala substitution of Ser207 reduced the tumorigenic activity of HB-EGF, even though the cell surface level and ectodomain shedding of HB-EGF were not affected by the mutation. Moreover, we found that the cytoplasmic domain of another EGFR ligand, transforming growth factor-alpha, is phosphorylated upon TPA stimulation. Thus, the present results suggest a novel role for the cytoplasmic domain of HB-EGF and other EGF family growth factors that is regulated by phosphorylation.

FRA1 is a determinant for the difference in RAS-induced transformation between human and rat fibroblasts

Human diploid fibroblasts (HDF) immortalized by hTERT and simian virus 40 (SV40) early region (ER) exhibit a limited degree of transformation upon the expression of activated H-RAS (H-RAS V12) compared with rat embryonic fibroblasts (REF) immortalized by SV40 ER. Here, we identified FRA1 as a determinant for this difference in RAS-induced transformation. FRA1 was not induced by H-RAS V12 in the immortalized HDF, in contrast to its marked accumulation in the immortalized REF. Ectopic expression of FRA1 significantly enhanced anchorage-independent growth of various HDF expressing hTERT, SV40 ER, and H-RAS V12. More importantly, FRA1 could induce anchorage-independent growth as well as nude mice tumor formation of the immortalized HDF in the absence of H-RAS V12. The results of an in vitro kinase assay clearly showed that the RAS-induced extracellular signal-regulated kinase (ERK) activation, which is responsible for FRA1 induction, was markedly attenuated in the HDF compared with that in the REF, despite no obvious differences in the phosphorylation status of ERK between the species. Our results strongly suggest that HDF negatively regulate the mitogen-activated protein kinase kinase (MEK)/ERK pathway more efficiently than REF, and consequently express less malignant phenotypes in response to H-RAS V12.

ErbB and HB-EGF Signaling in Heart Development and Function

The epidermal growth factor (EGF)-ErbB signaling network is composed of multiple ligands of the EGF family and four tyrosine kinase receptors of the ErbB family. In higher vertebrates, these four receptors bind a multitude of ligands. Ligand binding induces the formation of various homo- and heterodimers of ErbB, potentially providing for a high degree of signal diversity. ErbB receptors and their ligands are expressed in a variety of tissues throughout development. Recent advances in gene targeting strategies in mice have revealed that the EGF-ErbB signaling network has fundamental roles in development, proliferation, differentiation, and homeostasis in mammals. The heparin-binding EGF-like growth factor (HB-EGF) is a member of the EGF family of growth factors that binds to and activates the EGF receptor (EGFR/ErbB1) and ErbB4. Recent studies using several mutant mice lacking HB-EGF expression have revealed that HB-EGF has a critical role in normal heart function and in normal cardiac valve formation in conjunction with ErbB receptors. HB-EGF signaling through ErbB2 is essential for the maintenance of homeostasis in the adult heart, whereas HB-EGF signaling through EGFR is required during cardiac valve development. In this review, we introduce and discuss the role of ErbB receptors in heart function and development, focusing on the physiological function of HB-EGF in these processes.