Amplification of HER-2 in gastric carcinoma: association with Topoisomerase IIα gene amplification, intestinal type, poor prognosis and sensitivity to trastuzumab

BACKGROUND

HER-2/neu gene amplification has predictive value in breast cancer patients responding to trastuzumab. We wanted to investigate the frequency and clinical significance of HER-2/neu amplification in gastric carcinoma.

PATIENTS AND METHODS

The frequency of HER-2/neu and Topoisomerase IIalpha gene amplification was studied in adenocarcinomas of the stomach (n=131) and the gastroesophageal junction (n=100) by chromogenic in situ hybridization (CISH). Sensitivity of a gastric cancer cell line N87 with HER-2/neu amplification to trastuzumab was studied by a cell viability assay and compared with that of a HER-2 amplified breast cancer cell line SKBR-3. Growth inhibition of N87 cells was also verified in vivo in N87 xenograft tumors.

RESULTS

HER-2/neu amplification was present in 16 (12.2%) of the 131 gastric and in 24 (24.0%) of the 100 gastroesophageal adenocarcinomas. Co-amplification of Topoisomerase IIalpha was present in the majority of gastric (63%) and esophagogastric junction cancers (68%) with HER-2/neu amplification. HER-2/neu amplification was more common in the intestinal histologic type of gastric cancer (21.5%) than in the diffuse (2%) or the mixed/anaplastic type (5%, P=0.0051), but it was not associated with gender, age at diagnosis or clinical stage. Presence of HER-2/neu amplification was associated with poor carcinoma-specific survival (P=0.0089). HER-2/neu targeting antibody trastuzumab inhibited the growth of a p185(HER-2/neu) overexpressing gastric and breast carcinoma cell lines (N87 and SKBR-3) with equal efficacy.

CONCLUSIONS

HER-2/neu amplification is common in the intestinal type of gastric carcinoma, and it is associated with a poor outcome. HER-2 might be a useful target in this disease, and this hypothesis deserves to be investigated in clinical trials.

Activation of HER4 by heparin-binding EGF-like growth factor stimulates chemotaxis but not proliferation

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a potent mitogen and chemotactic factor for fibroblasts, smooth muscle cells and keratinocytes. It is demonstrated that HB-EGF is not only a ligand for HER1, as previously reported, but for HER4 as well. HB-EGF binds to NIH 3T3 cells overexpressing either HER1 or HER4 alone, but not HER2 or HER3 alone. Binding to HER4 is independent of HER1. The ability of HB-EGF to bind to two different receptors is in contrast to EGF which binds to HER1, but not to HER4, and heregulin-beta1 which binds to HER4, but not to HER1. Besides binding, HB-EGF activates HER4. For example (i) it induces tyrosine phosphorylation of HER4 in cells overexpressing this receptor and of endogenous HER4 in MDA-MB-453 cells and astrocytes; (ii) it induces association of phosphatidylinositol 3-kinase (PI3-K) activity with HER4; and (iii) it is a potent chemotactic factor for cells overexpressing HER4. Chemotaxis is inhibited by wortmannin, a PI3-K inhibitor, suggesting a possible role for PI3-K in mediating HB-EGF-stimulated chemotaxis. On the other hand, HB-EGF is not a mitogen for cells expressing HER4, in contrast to its ability to stimulate both chemotaxis and proliferation in cells expressing HER1. It was concluded that HER4 is a newly described receptor for HB-EGF and that HB-EGF can activate two EGF receptor subtypes, HER1 and HER4, but with different biological responses.

High frequency of BRAF V600E mutations in ameloblastoma

Ameloblastoma is a benign but locally infiltrative odontogenic neoplasm. Although ameloblastomas rarely metastasise, recurrences together with radical surgery often result in facial deformity and significant morbidity. Development of non-invasive therapies has been precluded by a lack of understanding of the molecular background of ameloblastoma pathogenesis. When addressing the role of ERBB receptors as potential new targets for ameloblastoma, we discovered significant EGFR over-expression in clinical samples using real-time RT-PCR, but observed variable sensitivity of novel primary ameloblastoma cells to EGFR-targeted drugs in vitro. In the quest for mutations downstream of EGFR that could explain this apparent discrepancy, Sanger sequencing revealed an oncogenic BRAF V600E mutation in the cell line resistant to EGFR inhibition. Further analysis of the clinical samples by Sanger sequencing and BRAF V600E-specific immunohistochemistry demonstrated a high frequency of BRAF V600E mutations (15 of 24 samples, 63%). These data provide novel insight into the poorly understood molecular pathogenesis of ameloblastoma and offer a rationale to test drugs targeting EGFR or mutant BRAF as novel therapies for ameloblastoma.

Signaling via ErbB2 and ErbB3 associates with resistance and epidermal growth factor receptor (EGFR) amplification with sensitivity to EGFR inhibitor gefitinib in head and neck squamous cell carcinoma cells

PURPOSE

The epidermal growth factor receptor (EGFR) inhibitor gefitinib (Iressa) has shown antitumor activity in clinical trials against cancers, such as non-small cell lung cancer and head and neck squamous cell carcinoma (HNSCC). Research on non-small cell lung cancer has elucidated factors that may predict response to gefitinib. Less is known about molecular markers that may predict response to gefitinib in HNSCC patients.

EXPERIMENTAL DESIGN

We analyzed possible associations of responsiveness to gefitinib with molecular markers of the EGFR/ErbB receptor family signaling pathway using 10 established HNSCC lines in vitro. IC50 of gefitinib sensitivity was determined using clonogenic survival assays. ErbB signaling was assessed by Western and real-time reverse transcription-PCR analyses of EGFR, ErbB2, ErbB3, and ErbB4 expression levels as well as by phosphorylation analysis of pEGFR, pErbB2, pErbB3, pAkt, and pErk. EGFR sequences encoding kinase domain and EGFR gene copy numbers were determined by cDNA sequencing and real-time PCR, respectively. Finally, responsiveness to gefitinib was compared with responsiveness to the anti-EGFR antibody cetuximab (Erbitux).

RESULTS

Expression levels of pErbB2 (P = 0.02) and total ErbB3 protein (P = 0.02) associated with resistance to gefitinib. Combining gefitinib with pertuzumab (Omnitarg), an antibody targeting ErbB2 heterodimerization, provided additional growth-inhibitory effect over gefitinib alone on relatively gefitinib-resistant HNSCC cell lines. The same markers did not predict resistance to cetuximab. In contrast, a similar trend suggesting association between EGFR gene copy number and drug sensitivity was observed for both gefitinib (P = 0.0498) and cetuximab (P = 0.053). No activating EGFR mutations were identified.

CONCLUSIONS

EGFR amplification may predict sensitivity to gefitinib in HNSCC. However, other EGFR/ErbB receptor family members than EGFR may contribute to resistance to gefitinib. ErbB2 and ErbB3 may have potential as predictive markers and as therapeutic targets for combination therapy in treatment of HNSCC with gefitinib.

Induced expression of syndecan in healing wounds

We have studied the expression of an integral cell surface proteoglycan, syndecan, during the healing of cutaneous wounds, using immunohistochemical and in situ hybridization methods. In normal mouse skin, both syndecan antigen and mRNA were found to be expressed exclusively by epidermal and hair follicle cells. After incision and subsequent suturing, remarkably increased amounts of syndecan on the cell surfaces of migrating and proliferating epidermal cells and on hair follicle cells adjacent to wound margins were noted. This increased syndecan expression was shown to be a consequence of greater amounts of syndecan mRNA. Induction was observed already 1 d after wounding, was most significant at the time of intense cell proliferation, and was still observable 14 d after incision. The migrating cells of the leading edge of the epithelium also showed enhanced syndecan expression, although clearly less than that seen in the proliferating epithelium. The merging epithelial cells at the site of incision showed little or no syndecan expression; increased syndecan expression, however, was detected during later epithelial stratification. When wounds were left unsutured, in situ hybridization experiments also revealed scattered syndecan-positive signals in the granulation tissue near the migrating epidermal sheet. By immunohistochemical analysis, positive staining in granulation tissue was observed around vascular endothelial cells in a subpopulation of growing capillaries. Induction of syndecan in granulation tissue both at the protein and mRNA levels was temporally and spatially highly restricted. Granulation tissue, which formed in viscose cellulose sponge cylinders placed under the skin of rats, was also found to produce 3.4 and 2.6 kb mRNA species of syndecan similar to that observed in the normal murine mammary epithelial cell line, NMuMG. These results suggest that syndecan may have a unique and important role as a cell adhesion and a growth factor-binding molecule not only during embryogenesis but also during tissue regeneration in mature tissues.

A novel juxtamembrane domain isoform of HER4/ErbB4. Isoform-specific tissue distribution and differential processing in response to phorbol ester

Human epidermal growth factor receptor 4 (HER4) is a member of the epidermal growth factor (EGF) receptor subfamily of receptor tyrosine kinases that is activated by neuregulins (NRG), betacellulin (BTC), and heparin-binding EGF-like growth factor. Sequencing of full-length human HER4 cDNAs revealed the existence of two HER4 isoforms that differed by insertion of either 23 or 13 alternative amino acids in the extracellular juxtamembrane (JM) region. The 23-amino acid form (HER4 JM-a) and the 13-amino acid form (HER4 JM-b) were expressed in a tissue-specific manner, as demonstrated by reverse transcriptase-polymerase chain reaction analysis of mouse and human tissues. Both isoforms were expressed in neural tissues such as cerebellum, whereas kidney expressed HER4 JM-a only and heart HER4 JM-b only. In situ hybridization using specific oligonucleotides demonstrated transcription of both JM-a and JM-b isoforms in the mouse cerebellum. Tyrosine phosphorylation analysis indicated that both receptor isoforms were activated to the same extent by NRG-beta1 and BTC, and to a lesser extent by NRG-alpha1 and heparin-binding EGF-like growth factor. A functional difference was found, however, in response to phorbol ester treatment. Stimulation of cells with phorbol ester resulted in a loss of 125I-NRG-beta1 binding and in a reduction of total cell-associated HER4 protein in HER4 JM-a transfectants but not in HER4 JM-b transfectants. It was concluded that novel alternatively spliced isoforms of HER4 exist, that they are distributed differentially in vivo in mouse and human tissues, that they are both activated by HER4 ligands, and that they may represent cleavable and noncleavable forms of HER4.

Cleavable ErbB4 isoform in estrogen receptor-regulated growth of breast cancer cells

ErbB1 and ErbB2 receptors are well-characterized targets for anticancer drugs, but the clinical relevance of the related ErbB4 receptor is unknown. Here, we have assessed the clinical significance of the proteolytically cleavable ErbB4 isoforms in breast cancer patients and investigated their functions in vitro. The expression of transcripts encoding the cleavable ErbB4 isoforms associated with estrogen receptor-alpha (ER) expression (P < 0.001) and a high histologic grade of differentiation (P </= 0.002) in real-time reverse transcription-PCR analysis of 62 breast cancer samples. Despite high ErbB4 mRNA expression levels in a subset of samples, ErbB4 gene amplification was not observed. High ErbB4 protein expression levels, as assessed by immunohistochemistry, associated with a favorable outcome in ER-positive cases from a series of 458 breast cancer patients (P = 0.01), whereas no association between ErbB4 expression and survival was found among women with ER-negative cancer (P = 0.86). However, nuclear ErbB4 immunoreactivity was associated with poor survival as compared with women whose cancer had membranous ErbB4 staining (P = 0.04). In vitro, overexpression of a cleavable ErbB4 isoform in ER-positive breast cancer cells resulted in translocation of a proteolytically released intracellular ErbB4 receptor fragment into the nucleus, as well as, enhanced proliferation, anchorage-independent growth, and estrogen response element-mediated transcriptional activity. These results suggest that the association of ErbB4 expression with clinical outcome is dependent on the subcellular localization of ErbB4 and that a proteinase-cleavable ErbB4 isoform promotes growth of ER-positive breast cancer and enhances ER-mediated gene transcription.

A natural ErbB4 isoform that does not activate phosphoinositide 3-kinase mediates proliferation but not survival or chemotaxis

ErbB4 is a member of the epidermal growth factor receptor (ErbB) family that mediates cellular responses activated by neuregulins (NRG) and other epidermal growth factor-like growth factors. Two naturally occurring ErbB4 isoforms, ErbB4 CYT-1 and ErbB4 CYT-2, have previously been identified. Unlike ErbB4 CYT-1, ErbB4 CYT-2 lacks a phosphoinositide 3-kinase (PI3-K)-binding site and is incapable of activating PI3-K. We have now examined the consequences of the inability of this isoform to activate PI3-K on cell proliferation, survival, and chemotaxis in response to NRG-1beta: (i) NRG-1beta stimulated proliferation of cells expressing either ErbB4 CYT-1 or ErbB4 CYT-2. Consistent with the mitogenic responsiveness, analysis of downstream signaling showed that Shc and MAPK were phosphorylated after stimulating either isoform with NRG-1beta. (ii) NRG-1beta protected cells expressing ErbB4 CYT-1 but not cells expressing ErbB4 CYT-2 from starvation-induced apoptosis as measured by effects on cell number and 4', 6-diamidino-2-phenylindole staining. Furthermore, in cells expressing ErbB4 CYT-2, Akt, a protein kinase that mediates cell survival, was not phosphorylated. (iii) NRG-1beta stimulated chemotaxis and membrane ruffling in cells expressing ErbB4 CYT-1 but not in cells expressing ErbB4 CYT-2. In summary, ErbB4 CYT-2 can mediate proliferation but not chemotaxis or survival. These results suggest a novel mechanism by which cellular responses such as chemotaxis and survival may be regulated by the expression of alternative receptor-tyrosine kinase isoforms that differ in their coupling to PI3-K signaling.

The epidermal growth factor receptor couples transforming growth factor-alpha, heparin-binding epidermal growth factor-like factor, and amphiregulin to Neu, ErbB-3, and ErbB-4

The epidermal growth factor (EGF) family hormones amphiregulin (AR), transforming growth factor-alpha (TGF-alpha), and heparin-binding EGF-like growth factor (HB-EGF) are thought to play significant roles in the genesis or progression of a number of human malignancies. However, the ability of these ligands to activate all four erbB family receptors has not been evaluated. Therefore, we have assessed the stimulation of erbB family receptor tyrosine phosphorylation by these hormones in a panel of mouse Ba/F3 cell lines expressing the four erbB family receptors, singly and in pairwise combinations. We also measured the stimulation of interleukin-3-independent survival or proliferation in this panel of Ba/F3 cell lines to compare the patterns of erbB family receptor coupling to physiologic responses induced by these peptides. EGF, TGF-alpha, AR, and HB-EGF all stimulated qualitatively similar patterns of erbB family receptor tyrosine phosphorylation and coupling to physiologic responses. Therefore, EGF, TGF-alpha, AR, and HB-EGF are functionally identical in this model system and behave differently from the EGF family hormones betacellulin and neuregulins.

Characterization of a naturally occurring ErbB4 isoform that does not bind or activate phosphatidyl inositol 3-kinase

Receptor tyrosine kinases regulate cell behavior by activating specific signal transduction cascades. Epidermal growth factor (EGF) receptor tyrosine kinases include ErbB1, ErbB2, ErbB3 and ErbB4. ErbB4 is a tyrosine kinase receptor that binds neuregulins (NRG) and several other EGF family members. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis identified two isoforms of ErbB4 that differed in their cytoplasmic domain sequences. Specifically, RT-PCR using primers flanking the putative phosphatidyl inositol 3-kinase (PI3-K) binding site of ErbB4 generated two specific bands when human and mouse heart and kidney tissues were analysed. Cloning and sequencing of these RT-PCR products revealed that one of the ErbB4 isoforms (ErbB4 CYT-2) lacked a 16 amino acid sequence including a putative PI3-K binding site, that was present in the other isoform (ErbB4 CYT-1). RT-PCR analysis of mouse tissues suggested that the expression of ErbB4 CYT-1 and ErbB4 CYT-2 was tissue-specific. Heart, breast and abdominal aorta expressed predominantly ErbB4 CYT-1 whereas neural tissues and kidney expressed predominantly ErbB4 CYT-2. To ascertain whether the absence of the putative PI3-K binding site in ErbB4 CYT-2 also resulted in the loss of PI3-K activity, NIH3T3 cell lines overexpressing ErbB4 CYT-1 or ErbB4 CYT-2 were produced. NRG-1 bound to and stimulated equivalent tyrosine phosphorylation of both isoforms. However, unlike ErbB4 CYT-1, the ErbB4 CYT-2 isoform was unable to bind the p85 subunit of PI3-K and to stimulate PI3-K activity in these cells. Furthermore, tyrosine phosphorylation of p85 or association of PI3-K activity with phosphotyrosine was not induced in NRG-1 treated cells expressing ErbB4 CYT-2, indicating that this isoform was incapable of activating PI3-K even indirectly. It was concluded that a novel naturally occurring ErbB4 isoform exists with a deletion of the cytoplasmic domain sequence required for the activation of the PI3-K intracellular signal transduction pathway and that this is the only PI3-K binding site in ErbB4.

Proteolytic cleavage and phosphorylation of a tumor-associated ErbB4 isoform promote ligand-independent survival and cancer cell growth

The ErbB1 and ErbB2 receptors are oncogenes with therapeutic significance in human cancer, whereas the transforming potential of the related ErbB4 receptor has remained controversial. Here, we have addressed whether four alternatively spliced ErbB4 isoforms differ in regulating cellular responses relevant for tumor growth. We show that the two tumor necrosis factor-alpha converting enzyme (TACE)-cleavable ErbB4 isoforms (the juxtamembrane [JM]-a isoforms) were overexpressed in a subset of primary human breast cancers together with TACE. The overexpression of the JM-a cytoplasmic (CYT)-2 ErbB4 isoform promoted ErbB4 phosphorylation, survival of interleukin-3-dependent cells, and proliferation of breast cancer cells even in the absence of ligand stimulation, whereas activation of the other three ErbB4 isoforms required ligand stimulation. Ligand-independent cellular responses to ErbB4 JM-a CYT-2 overexpression were regulated by both tyrosine kinase activity and a two-step proteolytic generation of an intracellular receptor fragment involving first a TACE-like proteinase, followed by gamma-secretase activity. These data suggest a novel transforming mechanism for the ErbB4 receptor in human breast cancer that is 1) specific for a single receptor isoform and 2) depends on proteinase cleavage and kinase activity but not ligand activation of the receptor.

ERBB4 mutations that disrupt the neuregulin-ErbB4 pathway cause amyotrophic lateral sclerosis type 19

Amyotrophic lateral sclerosis (ALS) is a devastating neurological disorder characterized by the degeneration of motor neurons and typically results in death within 3-5 years from onset. Familial ALS (FALS) comprises 5%-10% of ALS cases, and the identification of genes associated with FALS is indispensable to elucidating the molecular pathogenesis. We identified a Japanese family affected by late-onset, autosomal-dominant ALS in which mutations in genes known to be associated with FALS were excluded. A whole- genome sequencing and parametric linkage analysis under the assumption of an autosomal-dominant mode of inheritance with incomplete penetrance revealed the mutation c.2780G>A (p. Arg927Gln) in ERBB4. An extensive mutational analysis revealed the same mutation in a Canadian individual with familial ALS and a de novo mutation, c.3823C>T (p. Arg1275Trp), in a Japanese simplex case. These amino acid substitutions involve amino acids highly conserved among species, are predicted as probably damaging, and are located within a tyrosine kinase domain (p. Arg927Gln) or a C-terminal domain (p. Arg1275Trp), both of which mediate essential functions of ErbB4 as a receptor tyrosine kinase. Functional analysis revealed that these mutations led to a reduced autophosphorylation of ErbB4 upon neuregulin-1 (NRG-1) stimulation. Clinical presentations of the individuals with mutations were characterized by the involvement of both upper and lower motor neurons, a lack of obvious cognitive dysfunction, and relatively slow progression. This study indicates that disruption of the neuregulin-ErbB4 pathway is involved in the pathogenesis of ALS and potentially paves the way for the development of innovative therapeutic strategies such using NRGs or their agonists to upregulate ErbB4 functions.

Role of ErbB4 in breast cancer

Members of the ErbB subfamily of receptor tyrosine kinases are important regulators of normal mammary gland physiology, and aberrations in their signaling have been associated with breast tumorigenesis. Therapeutics targeting epidermal growth factor receptor (EGFR = ErbB1) or ErbB2 in breast cancer have been approved for clinical use. In contrast, relatively little is known about the biological significance of ErbB4 signaling in breast cancer. This review focuses on recent advances in our understanding about the role of ErbB4 in breast carcinogenesis, as well as in the potential clinical relevance of ErbB4 in breast cancer prognostics and therapy.

Endothelial Cells Regulate Physiological Cardiomyocyte Growth via VEGFR2-Mediated Paracrine Signaling

Supplemental Digital Content is available in the text.

Background:

Heart failure, which is a major global health problem, is often preceded by pathological cardiac hypertrophy. The expansion of the cardiac vasculature, to maintain adequate supply of oxygen and nutrients, is a key determinant of whether the heart grows in a physiological compensated manner or a pathological decompensated manner. Bidirectional endothelial cell (EC)–cardiomyocyte (CMC) cross talk via cardiokine and angiocrine signaling plays an essential role in the regulation of cardiac growth and homeostasis. Currently, the mechanisms involved in the EC-CMC interaction are not fully understood, and very little is known about the EC-derived signals involved. Understanding how an excess of angiogenesis induces cardiac hypertrophy and how ECs regulate CMC homeostasis could provide novel therapeutic targets for heart failure.

Methods:

Genetic mouse models were used to delete vascular endothelial growth factor (VEGF) receptors, adeno-associated viral vectors to transduce the myocardium, and pharmacological inhibitors to block VEGF and ErbB signaling in vivo. Cell culture experiments were used for mechanistic studies, and quantitative polymerase chain reaction, microarrays, ELISA, and immunohistochemistry were used to analyze the cardiac phenotypes.

Results:

Both EC deletion of VEGF receptor (VEGFR)-1 and adeno-associated viral vector–mediated delivery of the VEGFR1-specific ligands VEGF-B or placental growth factor into the myocardium increased the coronary vasculature and induced CMC hypertrophy in adult mice. The resulting cardiac hypertrophy was physiological, as indicated by preserved cardiac function and exercise capacity and lack of pathological gene activation. These changes were mediated by increased VEGF signaling via endothelial VEGFR2, because the effects of VEGF-B and placental growth factor on both angiogenesis and CMC growth were fully inhibited by treatment with antibodies blocking VEGFR2 or by endothelial deletion of VEGFR2. To identify activated pathways downstream of VEGFR2, whole-genome transcriptomics and secretome analyses were performed, and the Notch and ErbB pathways were shown to be involved in transducing signals for EC-CMC cross talk in response to angiogenesis. Pharmacological or genetic blocking of ErbB signaling also inhibited part of the VEGF-B–induced effects in the heart.

Conclusions:

This study reveals that cross talk between the EC VEGFR2 and CMC ErbB signaling pathways coordinates CMC hypertrophy with angiogenesis, contributing to physiological cardiac growth.

N-arginine dibasic convertase is a specific receptor for heparin-binding EGF-like growth factor that mediates cell migration

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a mitogen and chemotactic factor, binds to two receptor tyrosine kinases, erbB1 and erbB4. Now we demonstrate that HB-EGF also binds to a novel 140 kDa receptor on MDA-MB 453 cells. Purification of this receptor showed it to be identical to N-arginine dibasic convertase (NRDc), a metalloendopeptidase of the M16 family. Binding to cell surface NRDc and NRDc in solution was highly specific for HB-EGF among EGF family members. When overexpressed in cells, NRDc enhanced their migration in response to HB-EGF but not to EGF. Conversely, inhibition of endogenous NRDc expression in cells by antisense morpholino oligonucleotides inhibited HB-EGF-induced cell migration. Anti-erbB1 neutralizing antibodies completely abrogated the ability of NRDc to enhance HB-EGF-dependent migration, demonstrating that this NRDc activity was dependent on erbB1 signaling. Although NRDc is a metalloproteinase, enzymatic activity was not required for HB-EGF binding or enhancement of cell migration; neither did NRDc cleave HB-EGF. Together, these results suggest that NRDc is a novel specific receptor for HB-EGF that modulates HB-EGF-induced cell migration via erbB1.

Erbb4 and its isoforms: selective regulation of growth factor responses by naturally occurring receptor variants

ErbB4 is a member of the epidermal growth factor receptor (EGFR, ErbB) family that mediates responses to neuregulins and other EGF-like growth factors. ErbB4 is a central regulator of cardiovascular and neural development as well as differentiation of the mammary gland. A role for ErbB4 has also been implicated in malignancies and heart diseases. Four structurally and functionally distinct ErbB4 isoforms have recently been identified. One pair of isoforms differs within their extracellular juxtamembrane domains. These juxtamembrane ErbB4 isoforms are either susceptible or resistant to proteolytic processing that release a soluble receptor ectodomain. Another pair of ErbB4 isoforms differs within their cytoplasmic tails. Analysis of the intracellular signal transduction pathways indicates that both cytoplasmic ErbB4 isoforms can couple to the Shc-MAPK signaling pathway, while the other one is incapable of coupling to the phosphoinositide 3-kinase (PI3-K)-Akt pathway. The differences in the activation of signaling cascades are reflected in the cellular responses stimulated via the cytoplasmic isoforms. Both cytoplasmic ErbB4 isoforms can stimulate proliferation, but the isoform that cannot activate PI3-K is defective in stimulating cellular survival and chemotaxis. Together these four naturally occurring receptor variants provide a new level of diversity to the control of growth factor-stimulated cellular responses. Thus, the ErbB4 isoforms may have distinct and specific roles in the regulation of various developmental and pathological processes.

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

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

Association of Wwox with ErbB4 in breast cancer

WWOX, WW domain-containing oxidoreductase, is a tumor suppressor that is altered in many human cancers, including breast cancer. Wwox interacts with the ErbB4 receptor, reduces nuclear translocation of the cleaved intracellular domain of ErbB4, and inhibits its transactivation function mediated through Yes-associated protein. Here, we assessed the clinical significance of the Wwox-ErbB4 association. We determined Wwox protein expression by immunohistochemistry in a series of 556 breast cancers. Wwox expression was absent in 36% of the cancers, and loss of Wwox expression was associated with unfavorable outcome (P = 0.02). Membranous location of ErbB4 was associated with favorable survival compared with women whose cancer lacked such ErbB4 expression (P = 0.02). Wwox expression was strongly associated with membranous ErbB4 localization (P = 0.0003) and with overall ErbB4 expression (P = 0.0002). Coexpression of membranous ErbB4 and Wwox was associated with favorable outcome compared with cases with membranous ErbB4 and no Wwox immunoreactivity (P = 0.002). In vitro, Wwox associated with the two ErbB4 isoforms, JM-a CYT-1 and JM-a CYT-2, expressed in breast cancer. Moreover, expression of Wwox both in vitro and in vivo led to accumulation of total full-length membrane-associated ErbB4. These results suggest that expression of Wwox is associated with ErbB4 expression and that their coexpression has prognostic significance in breast cancer.

Heparin-binding EGF-like growth factor interacts with mouse blastocysts independently of ErbB1: a possible role for heparan sulfate proteoglycans and ErbB4 in blastocyst implantation

Blastocyst implantation requires molecular and cellular interactions between the uterine luminal epithelium and blastocyst trophectoderm. We have previously shown that heparin-binding EGF-like growth factor (HB-EGF) is induced in the mouse luminal epithelium solely at the site of blastocyst apposition at 16:00 hours on day 4 of pregnancy prior to the attachment reaction (22:00-23:00 hours), and that HB-EGF promotes blastocyst growth, zona-hatching and trophoblast outgrowth. To delineate which EGF receptors participate in blastocyst activation, the toxicity of chimeric toxins composed of HB-EGF or TGF-(&agr;) coupled to Pseudomonas exotoxin (PE) were used as measures of receptor expression. TGF-(&agr;) or HB-EGF binds to EGF-receptor (ErbB1), while HB-EGF, in addition, binds to ErbB4. The results indicate that ErbB1 is inefficient in mediating TGF-(&agr;)-PE or HB-EGF-PE toxicity as follows: (i) TGF-(&agr;)-PE was relatively inferior in killing blastocysts, 100-fold less than HB-EGF-PE, (ii) analysis of blastocysts isolated from cross-bred egfr+/- mice demonstrated that HB-EGF-PE, but not TGF-(&agr;)-PE, killed egfr-/- blastocysts, and (iii) blastocysts that survived TGF-(&agr;)-PE were nevertheless killed by HB-EGF-PE. HB-EGF-PE toxicity was partially mediated by cell surface heparan sulfate proteoglycans (HSPG), since a peptide corresponding to the heparin-binding domain of HB-EGF as well as heparitinase treatment protected the blastocysts from the toxic effects of HB-EGF-PE by about 40%. ErbB4 is a candidate for being an HB-EGF-responsive receptor since RT-PCR analysis demonstrated that day 4 mouse blastocysts express two different erbB4 isoforms and immunostaining with anti-ErbB4 antibodies confirmed that ErbB4 protein is expressed at the apical surface of the trophectoderm cells. It is concluded that (i) HB-EGF interacts with the blastocyst cell surface via high-affinity receptors other than ErbB1, (ii) the HB-EGF interaction with high-affinity blastocysts receptors is regulated by heparan sulfate, and (iii) ErbB4 is a candidate for being a high-affinity receptor for HB-EGF on the surface of implantation-competent blastocysts.

Inhibition by the soluble syndecan-1 ectodomains delays wound repair in mice overexpressing syndecan-1

Wound repair is a tightly regulated process stimulated by proteases, growth factors, and chemokines, which are modulated by heparan sulfate. To characterize further the role of the heparan sulfate proteoglycan syndecan-1 in wound repair, we generated mice overexpressing syndecan-1 (Snd/Snd) and studied dermal wound repair. Wound closure, reepithelialization, granulation tissue formation, and remodeling were delayed in Snd/Snd mice. Soluble syndecan-1 was increased, and shedding was prolonged in wounds from Snd/Snd mice. Excess syndecan-1 increased the elastolytic activity of wound fluids. Additionally, cells in the granulation tissue and keratinocytes at wound edges showed markedly reduced proliferation rates in Snd/Snd mice. Skin grafting experiments between Snd/Snd and control mice indicated that the slower growth rate was mainly due to a soluble factor in the Snd/Snd mouse skin. Syndecan-1 immunodepletion and further degradation experiments identified syndecan-1 ectodomain as a dominant negative inhibitor of cell proliferation. These studies indicate that shed syndecan-1 ectodomain may enhance proteolytic activity and inhibit cell proliferation during wound repair.

Endothelial cell-matrix interactions

Dynamic interactions between endothelial cells and components of their surrounding extracellular matrix are necessary for the invasion, migration, and survival of endothelial cells during angiogenesis. These interactions are mediated by matrix receptors that initiate intracellular signaling cascades in response to binding to specific extracellular matrix molecules. The interactions between endothelial cells and their environment are also modulated by enzymes that degrade different matrix components and thus enable endothelial invasion. Recent reports on gene targeting in mice have confirmed the role of two classes of matrix receptors, integrins and cell surface heparan sulfate proteoglycans, and a group of matrix degrading proteolytic enzymes, matrix metalloproteinases, in angiogenesis. The significance of endothelial cell-matrix interactions is further supported by several ongoing clinical trials that analyze the effects of drugs blocking this interaction on angiogenesis-dependent growth of human tumors.

Neurite growth-promoting protein (amphoterin, p30) binds syndecan

A new ligand for syndecan (a cell surface heparan sulfate-rich proteoglycan) has been discovered. In the solid-phase binding assay utilizing small nitrocellulose discs to immobilize matrix molecules, binding of syndecan to neurite growth-promoting protein, p30/amphoterin, was observed. This binding was strongly dependent on the concentration of amphoterin used to coat the discs, but was saturable with an excess amount of syndecan. The interaction was inhibitable with heparan sulfate and heparin but less effectively with chondroitin sulfate, indicating that heparan sulfate chains of syndecan were involved in the binding. Anti-amphoterin antibodies inhibited the binding partially. Mouse mammary epithelial cells were shown to bind amphoterin directly but not after trypsin treatment or in the presence of heparin and to produce amphoterin in the extracellular space. Both syndecan and amphoterin were found to localize on lateral surfaces of newly adhered mammary epithelial cells. Toward confluency amphoterin amounts decreased. Because amphoterin can be localized to the same sites with syndecan and because of their interaction, amphoterin is a new putative pericellular ligand for syndecan. These interactions may be involved in the regulation of cell behavior.