Neuregulin-1 and human epidermal growth factor receptors 2 and 3 play a role in human lung development in vitro

Development of a reliable cell-based reporter gene assay to measure the bioactivity of anti-HER2 therapeutic antibodies

Human epidermal growth factor receptor 2 (HER2) is a key player in the pathogenesis and progression of breast cancer and is currently a primary target for breast cancer immunotherapy. Bioactivity determination is necessary to guarantee the safety and efficacy of therapeutic antibodies targeting HER2. Nevertheless, currently available bioassays for measuring the bioactivity of anti-HER2 mAbs are either not representative or have high variability. Here, we established a reliable reporter gene assay (RGA) based on T47D-SRE-Luc cell line that expresses endogenous HER2 and luciferase controlled by serum response element (SRE) to measure the bioactivity of anti-HER2 antibodies. Neuregulin-1 (NRG-1) can lead to the heterodimerization of HER2 on the cell membrane and induce the expression of downstream SRE-controlled luciferase, while pertuzumab can dose-dependently reverse the reaction, resulting in a good dose-response curve reflecting the activity of the antibody. After optimizing the relevant assay parameters, the established RGA was fully validated based on ICH-Q2 (R1), which demonstrated that the method had excellent specificity, accuracy, precision, linearity, and stability. In summary, this robust and innovative bioactivity determination assay can be applied in the development and screening, release control, biosimilar assessment and stability studies of anti-HER2 mAbs.

Airway Epithelial Dysfunction in Asthma: Relevant to Epidermal Growth Factor Receptors and Airway Epithelial Cells

Airway epithelium plays an important role as the first barrier from external pathogens, including bacteria, viruses, chemical substances, and allergic components. Airway epithelial cells also have pivotal roles as immunological coordinators of defense mechanisms to transfer signals to immunologic cells to eliminate external pathogens from airways. Impaired airway epithelium allows the pathogens to remain in the airway epithelium, which induces aberrant immunological reactions. Dysregulated functions of asthmatic airway epithelium have been reported in terms of impaired wound repair, fragile tight junctions, and excessive proliferation, leading to airway remodeling, which contributes to aberrant airway responses caused by external pathogens. To maintain airway epithelium integrity, a family of epidermal growth factor receptors (EGFR) have pivotal roles in mechanisms of cell growth, proliferation, and differentiation. There are extensive studies focusing on the relation between EGFR and asthma pathophysiology, which describe airway remodeling, airway hypermucus secretion, as well as immunological responses of airway inflammation. Furthermore, the second EGFR family member, erythroblastosis oncogene B2 (ErbB2), has been recognized to be involved with impaired wound recovery and epithelial differentiation in asthmatic airway epithelium. In this review, the roles of the EGFR family in asthmatic airway epithelium are focused on to elucidate the pathogenesis of airway epithelial dysfunction in asthma.

Mechanical stretch regulates the expression of specific miRNA in extracellular vesicles released from lung epithelial cells

The underlying mechanism of normal lung organogenesis is not well understood. An increasing number of studies are demonstrating that extracellular vesicles (EVs) play critical roles in organ development by delivering microRNAs (miRNA) to neighboring and distant cells. miRNAs are important for fetal lung growth; however, the role of miRNA-EVs (miRNAs packaged inside the EVs) during fetal lung development is unexplored. The aim of this study was to examine the expression of miRNA-EVs in MLE-12, a murine lung epithelial cell line subjected to mechanical stretch in vitro with the long-term goal to investigate their potential role in the fetal lung development. Both cyclic and continuous mechanical stretch regulate miRNA differentially in EVs released from MLE-12 and intracellularly, demonstrating that mechanical signals regulate the expression of miRNA-EVs in lung epithelial cells. These results provide a proof-of-concept for the potential role that miRNA-EVs could play in the development of fetal lung.

Genome-Wide Association Analysis of Single-Breath DlCO

Dl_CO is a widely used pulmonary function test in clinical practice and a particularly useful measure for assessing patients with chronic obstructive pulmonary disease (COPD). We hypothesized that elucidating genetic determinants of Dl_CO could lead to better understanding of the genetic architecture of COPD. We estimated the heritability of Dl_CO using common genetic variants and performed genome-wide association analyses in four cohorts enriched for subjects with COPD (COPDGene [Genetic Epidemiology of COPD], NETT [National Emphysema Treatment Trial], GenKOLS [Genetics of Chronic Obstructive Lung Disease study], and TESRA [Treatment of Emphysema With a Gamma-Selective Retinoid Agonist study]) using a combined European ancestry white dataset and a COPDGene African American dataset. We assessed our genome-wide significant and suggestive associations for Dl_CO in previously reported genome-wide association studies of COPD and related traits. We also characterized associations of known COPD-associated variants and Dl_CO. We estimated the SNP-based heritability of Dl_CO in the European ancestry white population to be 22% (P = 0.0004). We identified three genome-wide significant associations with Dl_CO: variants near TGFB2, CHRNA3, and PDE11A loci (P < 5 × 10^-8). In addition, 12 loci were suggestively associated with Dl_CO in European ancestry white (P < 1 × 10^-5 in the combined analysis and P < 0.05 in both COPDGene and GenKOLS), including variants near NEGR1, CADM2, PCDH7, RETREG1, DACT2, NRG1, ANKRD18A, KRT86, NTN4, ARHGAP28, INSR, and PCBP3. Some Dl_CO-associated variants were also associated with COPD, emphysema, and/or spirometric values. Among 25 previously reported COPD loci, TGFB2, CHRNA3/CHRNA5, FAM13A, DSP, and CYP2A6 were associated with Dl_CO (P < 0.001). We identified several genetic loci that were significantly associated with Dl_CO and characterized effects of known COPD-associated loci on Dl_CO. These results could lead to better understanding of the heterogeneous nature of COPD.

Impact of the Neuregulin rs35753505 C/T Polymorphisms on Neuregulin 1 Levels in Preterm Infants

BACKGROUND:

Neuregulin (NRG) 1 plays an important role in the development of various organ systems in human. Single nucleotide polymorphisms rs35753505 C/Tof the gene encoding NRG1 evident as allele C and T with genotypes of CT, CC, and TT are believed to have an impact on NRG1 levels.

AIM:

To determine the impact of the NRGrs35753505 C/T polymorphisms on NRG1 levels in preterm infants.

METHODS:

A cross-sectional study was conducted from February to December 2018, whereas 48 eligible preterm infants with a gestational age of 32- < 37 weeks were enrolled. An umbilical cord blood specimen was collected for determination of NRG1 levels with enzyme-linked immunosorbent assay (ELISA) and NRG1 polymorphisms with polymerase chain reaction (PCR). Statistical analysis was performed with 95%CI and P value of < 0.05 was considered statistically significant.

RESULTS:

Median value of NRG1 levels (174.4 pg/ml) served as a cut off value. NRG 1 polymorphisms composed distribution of CC (31%), CT (42%), TT (27%) genotypes and distribution of C and T alleles were 52% and 48%. The median NRG1 levels in CC and CT genotypes were significantly lower compared to TT genotype (151.1 pg/ml vs 407.2 pg/ml, P = 0.005 and 159.1 pg/ml vs 407.2 pg/ml, P = 0.009). Subjects with C allele had significantly lower median NRG1 levels than T allele (151.1 pg/ml vs 407.2 pg/ml, P = 0.002). Subjects with CC and CT genotypes had higher risk to develop lower NRG1 levels compared to TT genotype (OR = 8.25, P = 0.016 and OR = 10.74, P = 0.005, respectively).

CONCLUSION:

Allele C is associated with lower NRG1 levels. Preterm infants with CC and CT genotypes pose a higher risk to have lower NRG1 levels.

Interleukin-6 is required for Neuregulin-1 induced HER2 signaling in lung epithelium

A clear understanding of the mechanisms that regulate the alveolar epithelium's barrier is critical to develop new therapeutic strategies to mitigate lung injury. The HER2/HER3 receptor tyrosine kinase complex plays a central role in maintaining the alveolar-capillary barrier. This receptor complex is activated by its ligand, neuregulin-1 (NRG-1). Interleukin-6 (IL-6) is also known to induce HER2 signaling through HER2 transphosphorylation by the IL-6 receptor (IL-6R) complex (1). Due to this interaction, we hypothesized that NRG-1 and IL-6 cooperatively interacted to activate the HER2/HER3 complex. Studies were performed in cultured pulmonary epithelial cells measuring the HER2/IL-6/IL-6R/GP130 interaction and receptor activation by western blotting and confocal microscopy, IL-6 production by ELISA, and IL-6 inhibition using specific antibodies, small molecule inhibitors and shRNA. We found that IL-6 was required for NRG-1 induced activation of HER2 in pulmonary epithelial cells. IL-6 inhibition led to a decrease in NRG-1 induced HER2 activation. The IL-6R and GP130, a subunit of the IL-6R complex, were physically associated with HER2 and were required for NRG-1 induced HER2 activation. Inhibition of GP130, the β-subunit of the IL-6 receptor decreased NRG-1 induced HER2 activation lower than control by 38% Finally, HER2 activation increased IL-6 secretion more than two-fold over resting cells (526 ± 131 vs 231 ± 39.7 pg/ml), and inhibition of HER2 gene expression decreased basal IL-6 secretion over 80% (89 + 4.6 vs 1.3 + 0.8 pg/ml). These findings identify a requirement for IL-6 and the IL-6R complex to allow NRG-1 mediated HER2 activation, and a HER2 driven IL-6 production feedback loop.

HER2 Signaling Implicated in Regulating Alveolar Epithelial Permeability with Cyclic Stretch

Mechanical ventilation can be damaging, and can cause or exacerbate ventilator-induced lung injury (VILI). The human epidermal growth factor receptor (HER) ligand neuregulin-1 (NRG1) activates HER2 heterodimerization with HER3, and has been implicated in inflammatory injuries. We hypothesized that HER2 activation contributes to VILI. We analyzed a database of differentially expressed genes between cyclically stretched and unstretched rat alveolar epithelial cells (RAEC) for HER ligands and validated the differential expression. The effect of the ligand and HER2 inhibition on RAEC permeability was tested, and in vivo relevance was assessed in a rat model of VILI. Analysis of our expression array revealed the upregulation of NRG1 and amphiregulin (AREG) with stretch. NRG1 protein, but not AREG, increased after stretch in culture media. Treatment with an NRG1-cleavage inhibitor (TAPI2) or an inhibitor of NRG1-binding (anti-HER3 antibody) reduced HER2 phosphorylation and partially mitigated stretch-induced permeability, with the upregulation of claudin-7. The results were reproduced by treatment with a direct inhibitor of HER2 phosphorylation (AG825). The transfection of microRNA miR-15b, predicted to negatively regulate NRG1, also attenuated stretch-induced permeability, and was associated with lower NRG1 mRNA levels. In rats ventilated at damaging tidal volumes, AG825 partly attenuated VILI. We concluded that cyclic stretch activates HER2 via the HER3 ligand NRG1, leading to increased permeability. Outcomes were mitigated by the downregulation of NRG1, prevention of NRG1 binding, and most strongly by the direct inhibition of HER2. In vivo HER2 inhibition also attenuated VILI. Ligand-dependent HER2 activation is a potential target for reducing VILI.

Epidermal growth factor receptor inhibition with Gefitinib does not alter lung responses to mechanical ventilation in fetal, preterm lambs

BACKGROUND

Epidermal growth factor receptor (EGFR) is important for airway branching and lung maturation. Mechanical ventilation of preterm lambs causes increases in EGFR and EGFR ligand mRNA in the lung. Abnormal EGFR signaling may contribute to the development of bronchopulmonary dysplasia.

HYPOTHESIS

Inhibition of EGFR signaling will decrease airway epithelial cell proliferation and lung inflammation caused by mechanical ventilation in preterm, fetal sheep.

METHODS

Following exposure of the fetal head and chest at 123±1 day gestational age and with placental circulation intact, fetal lambs (n = 4-6/group) were randomized to either: 1) Gefitinib 15 mg IV and 1 mg intra-tracheal or 2) saline IV and IT. Lambs were further assigned to 15 minutes of either: a) Injurious mechanical ventilation (MV) or b) Continuous positive airway pressure (CPAP) 5 cmH2O. After the 15 minute intervention, the animals were returned to the uterus and delivered after i) 6 or ii) 24 hours in utero.

RESULTS

MV caused lung injury and inflammation, increased lung mRNA for cytokines and EGFR ligands, caused airway epithelial cell proliferation, and decreased airway epithelial phosphorylated ERK1/2. Responses to MV were unchanged by Gefitinib. Gefitinib altered expression of EGFR mRNA in the lung and liver of both CPAP and MV animals. Gefitinib decreased the liver SAA3 mRNA response to MV at 6 hours. There were no differences in markers of lung injury or inflammation between CPAP animals receiving Gefitinib or saline.

CONCLUSION

Inhibition of the EGFR pathway did not alter acute lung inflammation or injury from mechanical ventilation in preterm sheep.

What is the identity of fibroblast-pneumocyte factor?

Glucocorticoid induction of pulmonary surfactant involves a mesenchyme-derived protein first characterized in 1978 by Smith and termed fibroblast-pneumocyte factor (FPF). Despite a number of agents having been postulated as being FPF, its identity has remained obscure. In the past decade, three strong candidates for FPF have arisen. This review examines the evidence that keratinocyte growth factor (KGF), leptin or neuregulin-1β (NRG-1β) act as FPF or components of it. As with FPF production, glucocorticoids enhance the concentration of each of these agents in fibroblast-conditioned media. Moreover, each stimulates the synthesis of surfactant-associated phospholipids and proteins in type II pneumocytes. Further, some have unique activities, for example, KGF also minimizes lung injury through enhanced epithelial cell proliferation and NRG-1β enhances surfactant phospholipid secretion and β-adrenergic receptor activity in type II cells. However, even though these agents have attributes in common with FPF, it is inappropriate to specify any one of these agents as FPF. Rather, it appears that each contributes to separate mesenchymal-epithelial signaling mechanisms involved in different aspects of lung development. Given that the production of pulmonary surfactant is essential for postnatal survival, it is reasonable to suggest that several mechanisms independently regulate surfactant synthesis.

Immunohistochemical localization of epidermal growth factor system in the lung of the Japanese quail (Coturnix coturnix japonica) during the post-hatching period

The purpose of this study is to determine the possible changes in the localization of the four Epidermal Growth Factor Receptors and three ligands in quail lungs from the first day of hatching until the 125th after hatching using immunohistochemical methods. Immunohistochemical results demonstrated that four EGFRs and their ligands are chiefly located in the cytoplasm of cells. Additionally, ErbB4, AREG, and NRG1 are localized to the nucleus and nucleolus, but EGF is present in the nucleolus. ErbB2 was also found in the cell membrane. In the epithelium of secondary bronchi, the goblet cells only exhibited ErbB1 and ErbB2, whereas the basal and ciliated cells exhibited EGFRs and ligands immunoreactivity. The atrial granular cells displayed moderate levels of ErbB1-ErbB3 and EGF and strong levels of ErbB4, AREG, and NRG1 immunoreactivity. While the squamous atrial cells and squamous respiratory cells of air capillaries and endothelial cells of blood capillaries exhibited moderate to strong ErbB2, ErbB4, AREG, and NRG1 immunoreactivity, they had negative or weak ErbB1, ErbB3, and EGF immunoreactivity. The expression levels of ErbB2-ErbB4, EGF, AREG, and NRG1 were also detected in fibroblasts. Although ErbB2 was highly expressed in the bronchial and vascular smooth muscle cells, weak expression of ErbB1, ErbB3, AREG and EGF and moderate expression of ErbB4 and NRG1 were observed. Macrophages were only negative for ErbB1. In conclusion, these data indicate that the EGFR-system is functionally active at hatching, which supports the hypothesis that the members of EGFR-system play several cell-specific roles in quail lung growth after hatching.

HER2 activation results in β-catenin-dependent changes in pulmonary epithelial permeability

The receptor tyrosine kinase human epidermal growth factor receptor-2 (HER2) is known to regulate pulmonary epithelial barrier function; however, the mechanisms behind this effect remain unidentified. We hypothesized that HER2 signaling alters the epithelial barrier through an interaction with the adherens junction (AJ) protein β-catenin, leading to dissolution of the AJ. In quiescent pulmonary epithelial cells, HER2 and β-catenin colocalized along the lateral intercellular junction. HER2 activation by the ligand neuregulin-1 was associated with tyrosine phosphorylation of β-catenin, dissociation of β-catenin from E-cadherin, and decreased E-cadherin-mediated cell adhesion. All effects were blocked with the HER2 inhibitor lapatinib. β-Catenin knockdown using shRNA significantly attenuated neuregulin-1-induced decreases in pulmonary epithelial resistance in vitro. Our data indicate that HER2 interacts with β-catenin, leading to dissolution of the AJ, decreased cell-cell adhesion, and disruption of the pulmonary epithelial barrier.

Signalling between microvascular endothelium and cardiomyocytes through neuregulin

Heterocellular communication in the heart is an important mechanism for matching circulatory demands with cardiac structure and function, and neuregulins (Nrgs) play an important role in transducing this signal between the hearts' vasculature and musculature. Here, we review the current knowledge regarding Nrgs, explaining their roles in transducing signals between the heart's microvasculature and cardiomyocytes. We highlight intriguing areas being investigated for developing new, Nrg-mediated strategies to heal the heart in acquired and congenital heart diseases, and note avenues for future research.

Role of neuregulin-1β in dexamethasone-enhanced surfactant synthesis in fetal type II cells

It is well established that glucocorticoids elevate the production of fibroblast-pneumocyte factor (FPF), which induces type II cells to synthesize surfactant phospholipids. FPF, however, has not been identified and it is not clear whether it is a single factor or a complex mixture of factors. In this study it has been shown that, when lung fibroblasts are exposed to dexamethasone, the concentration of neuregulin-1β (NRG1β) in conditioned medium is elevated 2-fold (P<0.05), even though NRG1β gene expression is unaffected. This, together with the finding that exposure of type II cells to NRG1β directly stimulates by 3-fold the rate of phospholipid synthesis (P<0.05), suggests that NRG1β is a component of FPF that promotes lung development.

Dissociated presenilin-1 and TACE processing of ErbB4 in lung alveolar type II cell differentiation

Neuregulin (NRG) stimulation of ErbB4 signaling is important for type II cell surfactant synthesis. ErbB4 may mediate gene expression via a non-canonical pathway involving enzymatic cleavage releasing its intracellular domain (4ICD) for nuclear trafficking and gene regulation. The accepted model for release of 4ICD is consecutive cleavage by Tumor necrosis factor alpha Converting Enzyme (TACE) and γ-secretase enzymes. Here, we show that 4ICD mediates surfactant synthesis and its release by γ-secretase is not dependent on previous TACE cleavage. We used siRNA to silence Presenilin-1 (PSEN-1) expression in a mouse lung type II epithelial cell line (MLE12 cells), and both siRNA knockdown and chemical inhibition of TACE. Knockdown of PSEN-1 significantly decreased baseline and NRG-stimulated surfactant phospholipid synthesis, expression of the surfactant proteins SP-B and SP-C, as well as 4ICD levels, with no change in ErbB4 ectodomain shedding. Neither siRNA knockdown nor chemical inhibition of TACE inhibited 4ICD release or surfactant synthesis. PSEN-1 cleavage of ErbB4 for non-canonical signaling through 4ICD release does not require prior cleavage by TACE.

Targeting EGFR signalling in chronic lung disease: therapeutic challenges and opportunities

Chronic respiratory diseases, including pulmonary fibrosis, chronic obstructive pulmonary disease (COPD) and lung cancer, are the second leading cause of death among Europeans. Despite this, there have been only a few therapeutic advances in these conditions over the past 20 years. In this review we provide evidence that targeting the epidermal growth factor receptor (EGFR) signalling pathway may represent a novel therapeutic panacea for treating chronic lung disease. Using evidence from human patient samples, transgenic animal models, and cell and molecular biology studies we highlight the roles of this signalling pathway in lung development, homeostasis, repair, and disease ontogeny. We identify mechanisms underlying lung EGFR pathway regulation and suggest how targeting these mechanisms using new and existing therapies has the potential to improve future lung cancer, COPD and pulmonary fibrosis patient outcomes.

Strain-induced differentiation of fetal type II epithelial cells is mediated via the integrin α6β1-ADAM17/tumor necrosis factor-α-converting enzyme (TACE) signaling pathway

Mechanical forces are critical for normal fetal lung development. However, the mechanisms regulating this process are not well-characterized. We hypothesized that strain-induced release of HB-EGF and TGF-α is mediated via integrin-ADAM17/TACE interactions. Employing an in vitro system to simulate mechanical forces in fetal lung development, we showed that mechanical strain of fetal epithelial cells actives TACE, releases HB-EGF and TGF-α, and promotes differentiation. In contrast, in samples incubated with the TACE inhibitor IC-3 or in cells isolated from TACE knock-out mice, mechanical strain did not release ligands or promote cell differentiation, which were both rescued after transfection of ADAM17. Cell adhesion assay and co-immunoprecipitation experiments in wild-type and TACE knock-out cells using several TACE constructs demonstrated not only that integrins α6 and β1 bind to TACE via the disintegrin domain but also that mechanical strain enhances these interactions. Furthermore, force applied to these integrin receptors by magnetic beads activated TACE and shed HB-EGF and TGF-α. The contribution of integrins α6 and β1 to differentiation of fetal epithelial cells by strain was demonstrated by blocking their binding site with specific antibodies and by culturing the cells on membranes coated with anti-integrin α6 and β1 antibodies. In conclusion, mechanical strain releases HB-EGF and TGF-α and promotes fetal type II cell differentiation via α6β1 integrin-ADAM17/TACE signaling pathway. These investigations provide novel mechanistic information on how mechanical forces promote fetal lung development and specifically differentiation of epithelial cells. This information could be also relevant to other tissues exposed to mechanical forces.

Human epidermal growth factor receptor signaling in acute lung injury

Acute lung injury (ALI) is a syndrome marked by increased permeability across the pulmonary epithelium resulting in pulmonary edema. Recent evidence suggests that members of the human epidermal growth factor receptor (HER) family are activated in alveolar epithelial cells during ALI and regulate alveolar epithelial barrier function. These tyrosine kinase receptors, which also participate in the pathophysiology of pulmonary epithelial malignancies, regulate cell growth, differentiation, and migration as well as cell-cell adhesion, all processes that influence epithelial injury and repair. In this review we outline mechanisms of epithelial injury and repair in ALI, activation patterns of this receptor family in pulmonary epithelial cells as a consequence injury, how receptor activation alters alveolar permeability, and the possible intracellular signaling pathways involved. Finally, we propose a theoretical model for how HER-mediated modulation of alveolar permeability might affect lung injury and repair. Understanding how these receptors signal has direct therapeutic implications in lung injury and other diseases characterized by altered epithelial barrier function.

Human epidermal growth factor receptor signaling in acute lung injury

Acute lung injury (ALI) is a syndrome marked by increased permeability across the pulmonary epithelium resulting in pulmonary edema. Recent evidence suggests that members of the human epidermal growth factor receptor (HER) family are activated in alveolar epithelial cells during ALI and regulate alveolar epithelial barrier function. These tyrosine kinase receptors, which also participate in the pathophysiology of pulmonary epithelial malignancies, regulate cell growth, differentiation, and migration as well as cell-cell adhesion, all processes that influence epithelial injury and repair. In this review we outline mechanisms of epithelial injury and repair in ALI, activation patterns of this receptor family in pulmonary epithelial cells as a consequence injury, how receptor activation alters alveolar permeability, and the possible intracellular signaling pathways involved. Finally, we propose a theoretical model for how HER-mediated modulation of alveolar permeability might affect lung injury and repair. Understanding how these receptors signal has direct therapeutic implications in lung injury and other diseases characterized by altered epithelial barrier function.

Bronchoalveolar lavage neuregulin-1 is elevated in acute lung injury and correlates with inflammation

Shedding of neuregulin (NRG)-1 from the pulmonary epithelium leads to activation of the epithelial human epidermal growth factor receptor (HER)2 receptor, increased pulmonary epithelial permeability and acute lung injury (ALI). We sought to determine whether NRG-1 was detectable and elevated in bronchoalveolar lavage (BAL) and plasma from patients with ALI compared with controls and to determine whether a correlation exists between NRG-1 and inflammation and outcome in ALI. Matched BAL and plasma samples were obtained from 23 ALI patients requiring intubation and mechanical ventilation. Control patients (n=5) included healthy volunteers. NRG-1 and indices of inflammation were measured in BAL and plasma via ELISA. The mean±sd BAL NRG-1 concentration in ALI patients was 187.0±21.35 pg·mL(-1) compared with 85.50±9.2 pg·mL(-1) in controls (p=0.001). Increased BAL NRG-1 was associated with markers of inflammation, and inversely correlated with ventilator-free days (VFDs; r= -0.51, p=0.015). Plasma NRG-1 was elevated in ALI patients compared with controls (611.7±354.2 versus 25.17±19.33 pg·mL(-1), p<0.001) and inversely correlated with VFDs (r= -0.51, p=0.04). These results confirm shedding of NRG-1 in ALI and suggest that the NRG-1-HER2 pathway is active in patients with ALI.

Stretch-induced fetal type II cell differentiation is mediated via ErbB1-ErbB4 interactions

Stretch-induced differentiation of lung fetal type II epithelial cells is mediated through EGFR (ErbB1) via release of HB-EGF and TGF-α ligands. Employing an EGFR knock-out mice model, we further investigated the role of the ErbB family of receptors in mechanotranduction during lung development. Deletion of EGFR prevented endogenous and mechanical stretch-induced type II cell differentiation via the ERK pathway, which was rescued by overexpression of a constitutively active MEK. Interestingly, the expression of ErbB4, the only ErbB receptor that EGFR co-precipitates in wild-type cells, was decreased in EGFR-deficient type II cells. Similar to EGFR, ErbB4 was activated by stretch and participated in ERK phosphorylation and type II cell differentiation. However, neuregulin (NRG) or stretch-induced ErbB4 activation were blunted in EGFR-deficient cells and not rescued after ErbB4 overexpression, suggesting that induction of ErbB4 phosphorylation is EGFR-dependent. Finally, we addressed how shedding of ligands is regulated by EGFR. In knock-out cells, TGF-α, a ligand for EGFR, was not released by stretch, while HB-EGF, a ligand for EGFR and ErbB4, was shed by stretch although to a lower magnitude than in normal cells. Release of these ligands was inhibited by blocking EGFR and ERK pathway. In conclusion, our studies show that EGFR and ErbB4 regulate stretch-induced type II cell differentiation via ERK pathway. Interactions between these two receptors are important for mechanical signals in lung fetal type II cells. These studies provide novel insights into the cell signaling mechanisms regulating ErbB family receptors in lung cell differentiation.

DNA methylation profiling defines clinically relevant biological subsets of non-small cell lung cancer

PURPOSE

Non-small cell lung cancers (NSCLC) comprise multiple distinct biologic groups with different prognoses. For example, patients with epithelial-like tumors have a better prognosis and exhibit greater sensitivity to inhibitors of the epidermal growth factor receptor (EGFR) pathway than patients with mesenchymal-like tumors. Here, we test the hypothesis that epithelial-like NSCLCs can be distinguished from mesenchymal-like NSCLCs on the basis of global DNA methylation patterns.

EXPERIMENTAL DESIGN

To determine whether phenotypic subsets of NSCLCs can be defined on the basis of their DNA methylation patterns, we combined microfluidics-based gene expression analysis and genome-wide methylation profiling. We derived robust classifiers for both gene expression and methylation in cell lines and tested these classifiers in surgically resected NSCLC tumors. We validate our approach using quantitative reverse transcriptase PCR and methylation-specific PCR in formalin-fixed biopsies from patients with NSCLC who went on to fail front-line chemotherapy.

RESULTS

We show that patterns of methylation divide NSCLCs into epithelial-like and mesenchymal-like subsets as defined by gene expression and that these signatures are similarly correlated in NSCLC cell lines and tumors. We identify multiple differentially methylated regions, including one in ERBB2 and one in ZEB2, whose methylation status is strongly associated with an epithelial phenotype in NSCLC cell lines, surgically resected tumors, and formalin-fixed biopsies from patients with NSCLC who went on to fail front-line chemotherapy.

CONCLUSIONS

Our data show that patterns of DNA methylation can divide NSCLCs into two phenotypically distinct subtypes of tumors and provide proof of principle that differences in DNA methylation can be used as a platform for predictive biomarker discovery and development.

Regulation of cigarette smoke-induced mucin expression by neuregulin1β/ErbB3 signalling in human airway epithelial cells

Mucus hypersecretion is an important manifestation in patients with chronic obstructive pulmonary diseases (COPD). Cigarette smoke is importantly implicated in the pathogenesis of COPD. Previous studies have shown that cigarette smoke-induced MUC5AC (a major component of airway mucus) expression involving ErbB1 (EGF receptor) signalling pathway. Recently, it has been reported that cigarette smoke induces ErbB3 activation in airway epithelia to secret mucus, and the ligand of ErbB3, neuregulin (NRG) 1β, induces MU5AC expression in human bronchial epithelial cells. In the present study, we have suggested that NRG1β/ErbB3 signalling is activated by cigarette smoke, resulting in the activation of a variety of signal cascade pathways, leading to mucin production in human bronchial epithelial (16HBE) cells. We show that cigarette smoke increases NRG1β release, ErbB3 phosphorylation and MUC5AC production. These effects are prevented by an ErbB3-neutralizing antibody and by specific knockdown using small interfering RNA (siRNA) for NRG1β, implicating NRG1β-dependent ErbB3 activation in the responses. Cigarette smoke activates ERK1/2, c-Jun N-terminal kinase (JNK) mitogen-activated protein kinases (MAPKs) and phosphatidylinositol 3-kinase (PI3-K) signalling pathways, which are also inhibited by an ErbB3-neutralizing antibody and NRG1β siRNA, indicating the regulation of cigarette smoke-activated pathways by NRG1β/ErbB3 signalling. Furthermore, pre-treatments with metalloprotease inhibitor (TNF-α protease inhibitor-1) and specific knockdown of TNF-α-converting enzyme (TACE) with TACE siRNA prevented cigarette smoke-induced NRG1β release, ErbB3 phosphorylation and mucin production, suggesting the role of TACE in cigarette smoke-mediated NRG1β/ErbB3 signalling activation. These results suggest that NRG1β/ErbB3 signalling regulates cigarette smoke-induced mucin overproduction via the MAPK and PI3K signal pathways in 16HBE cells.

Neuregulin-1-human epidermal receptor-2 signaling is a central regulator of pulmonary epithelial permeability and acute lung injury

The mechanisms behind the loss of epithelial barrier function leading to alveolar flooding in acute lung injury (ALI) are incompletely understood. We hypothesized that the tyrosine kinase receptor human epidermal growth factor receptor-2 (HER2) would be activated in an inflammatory setting and participate in ALI. Interleukin-1β (IL-1β) exposure resulted in HER2 activation in human epithelial cells and markedly increased conductance across a monolayer of airway epithelial cells. Upon HER2 blockade, conductance changes were significantly decreased. Mechanistic studies revealed that HER2 trans-activation by IL-1β required a disintegrin and metalloprotease 17 (ADAM17)-dependent shedding of the ligand neuregulin-1 (NRG-1). In murine models of ALI, NRG-1-HER2 signaling was activated, and ADAM17 blockade resulted in decreased NRG-1 shedding, HER2 activation, and lung injury in vivo. Finally, NRG-1 was detectable and elevated in pulmonary edema fluid from patients with ALI. These results suggest that the ADAM17-NRG-1-HER2 axis modulates the alveolar epithelial barrier and contributes to the pathophysiology of ALI.

Heparan sulfate in lung morphogenesis: The elephant in the room

Heparan sulfate (HS) is a structurally complex polysaccharide located on the cell surface and in the extracellular matrix, where it participates in numerous biological processes through interactions with a vast number of regulatory proteins such as growth factors and morphogens. HS is crucial for lung development; disruption of HS synthesis in flies and mice results in a major aberration of airway branching, and in mice, it results in neonatal death as a consequence of malformed lungs and respiratory distress. Epithelial-mesenchymal interactions governing lung morphogenesis are directed by various diffusible proteins, many of which bind to, and are regulated by HS, including fibroblast growth factors, sonic hedgehog, and bone morphogenetic proteins. The majority of research into the molecular mechanisms underlying defective lung morphogenesis and pulmonary pathologies, such as bronchopulmonary dysplasia and pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH), has focused on abnormal protein expression. The potential contribution of HS to abnormalities of lung development has yet to be explored to any significant extent, which is somewhat surprising given the abnormal lung phenotype exhibited by mutant mice synthesizing abnormal HS. This review summarizes our current understanding of the role of HS and HS-binding proteins in lung morphogenesis and will present in vitro and in vivo evidence for the fundamental importance of HS in airway development. Finally, we will discuss the future possibility of HS-based therapeutics for ameliorating insufficient lung growth associated with lung diseases such as CDH.

Re-epithelialization from human skin explant cultures is promoted by ligand-activated HER3 receptor

BACKGROUND

Ligand-stimulated epidermal growth factor receptor (EGFR/HER1) plays a fundamental role in skin biology as potent transducer of mitotic and anti-apoptotic stimuli in keratinocytes. In human epidermis, at least two additional EGFR family members--HER2 and HER3--are expressed but their biological functions in normal and diseased human skin remain obscure.

OBJECTIVE

Here, we studied the expression and biological impact of HER3 in regenerating human epidermis formed from skin explants adhered to acellular dermis.

METHODS

Neoepidermal HER3 expression was examined by quantitative real-time reverse transcriptase polymerase chain reaction, immunohistochemistry and Western blot analysis. The dynamic effect of HER3 receptor stimulation by recombinant heregulin (HRG)-beta1 was assessed by fluorescence imaging of re-epithelialization.

RESULTS

In the neoepidermis, HER3 mRNA and protein were detected with activated receptors being immunolocalized at basal and low suprabasal levels. Exogenous HRG-beta1 at 10-20 ng/ml increased the outgrowth rate corresponding to approximately 30% the response of exogenous EGF. The growth-promoting effect of HRG-beta1 was associated with enhanced HER3 phosphorylation, keratinocyte proliferation and thickening of viable neoepidermis whereas blockade of ligand-binding to HER3 delayed the outgrowth process and inhibited both constitutive and ligand-induced HER3 phosphorylation. HER2 antagonism using an anti-dimerization antibody, pertuzumab, impeded the re-epithelialization rate. In addition, a selective HER2 kinase inhibitor, CP654577, downregulated phospho-HER3 expression suggesting that transactivation of kinase-deficient HER3 was accomplished through dimerization with HER2.

CONCLUSION

The study emphasizes the central role of EGFR in epidermal renewal and demonstrates that HRG-activated HER3 contributes to the outgrowth process of epidermis in vitro.

Regulation of neuregulin 1beta1-induced MUC5AC and MUC5B expression in human airway epithelium

Excessive mucus production has been linked to many of the pathologic features of respiratory diseases, including obstruction of the airways, decline in lung function, increased rates of mortality, and increased infections. The mucins, MUC5AC and MUC5B, contribute to the viscoelastic properties of mucus, and are found at elevated levels in the airways of individuals with chronic respiratory diseases. The T helper type 2 cell cytokine, IL-13, is known to regulate MUC5AC expression in goblet cells of the airways, although much less is known about the regulation of MUC5B expression. In a study to further understand the mediators of MUC5AC and MUC5B expression, neuregulin (NRG) 1beta1 was identified as novel regulator of goblet cell formation in primary cultures of human bronchial epithelial cells (HBECs). NRG1beta1 increased expression of MUCAC and MUC5B proteins in a time- and dose-dependent fashion in HBEC cultures. NRG1beta1-induced expression of MU5AC and MUC5B was shown to involve v-erb-b2 erythroblastic leukemia viral oncogene homolog (ErbB) and ErbB3 receptors, but not ErbB4 receptors. Treatment of HBECs with inhibitors of p38 mitogen-activated protein kinase, extracellular signal-regulated kinase1/2, and phosphatidylinositol 3-kinase indicated that these kinases were involved in NRG1beta1-induced MUC5AC and MUC5B expression. Additionally, NRG1beta1 was shown to induce the phosphorylation of the ErbB2 receptor, AKT, and extracellular signal-regulated kinase 1/2. NRG1beta1 protein was found increased in the airways of antigen-challenged mice, together with increases in MUC5AC and MUC5B message. Together, these data indicate that NRG1beta1 is a novel mediator of MUC5AC and MUC5B expression in HBECs, and may represent a novel therapeutic target for mucus hypersecretion in respiratory diseases.

Up-regulated expression of ADAM17 in gastrointestinal stromal tumors: coexpression with EGFR and EGFR ligands

Metalloproteinase activities of a disintegrin and metalloproteinases (ADAMs), matrix metalloproteinases (MMPs), and membrane type (MT-)MMPs are involved in many aspects of tumor biology. ADAMs are transmembrane proteins that cleave membrane-anchored proteins to release soluble factors, and thereby mediate important biological phenomena in tumors. The aim of this study was to analyze histopathology, expression and roles of metalloproteinases, especially ADAMs, in gastric gastrointestinal stromal tumor (GIST). Histopathology and immunohistochemical expression of ADAMs were examined in 89 gastric GISTs. In 11 GISTs, ADAM expression was examined at mRNA and protein levels by reverse transcription-polymerase chain reaction (RT-PCR) and immunoblotting, respectively. RT-PCR analysis showed frequent expression of ADAM9 (91%), ADAM10 (64%), ADAM17 (82%), MMP-2 (82%), and MT1-MMP (73%). However, ADAM17 and MMP-2 were the only metalloproteinases that were up-regulated in GISTs at the protein level compared with non-neoplastic gastric tissues. ADAM17 was immunohistochemically expressed in 93% of GIST versus 16% of normal gastric tissues. Furthermore, CD117-positive interstitial cells of Cajal in normal gastric tissues were all negative for ADAM17 with double immunostaining. Expressions of epidermal growth factor receptor (EGFR) and several EGFR ligands such as amphiregulin, heparin-binding epidermal growth factor (HB-EGF), betacellulin, and epiregulin were also demonstrated in GIST by RT-PCR. Protein expression of EGFR, phosphorylated EGFR, amphiregulin, and HB-EGF, both of which can be shed by ADAM17, was confirmed in tumors coexpressing ADAM17 by immunoblotting. Moreover, proteolytically cleaved soluble forms of amphiregulin were identified in tumor extracts. Considered together, the results suggest that ADAM17 may contribute to the progression and growth of GIST through shedding of EGFR ligands and consequent EGFR stimulation. ADAM17, as a major sheddase in GIST, could be potentially a suitable target in anticancer treatment of imatinib-resistant GISTs.

The ERBB3 receptor in cancer and cancer gene therapy

ERBB3, a member of the epidermal growth factor receptor (EGFR) family, is unique in that its tyrosine kinase domain is functionally defective. It is activated by neuregulins, by other ERBB and nonERBB receptors as well as by other kinases, and by novel mechanisms. Downstream it interacts prominently with the phosphoinositol 3-kinase/AKT survival/mitogenic pathway, but also with GRB, SHC, SRC, ABL, rasGAP, SYK and the transcription regulator EBP1. There are likely important but poorly understood roles for nuclear localization and for secreted isoforms. Studies of ERBB3 expression in primary cancers and of its mechanistic contributions in cultured cells have implicated it, with varying degrees of certainty, with causation or sustenance of cancers of the breast, ovary, prostate, certain brain cells, retina, melanocytes, colon, pancreas, stomach, oral cavity and lung. Recent results link high ERBB3 activity with escape from therapy targeting other ERBBs in lung and breast cancers. Thus a wide and centrally important role for ERBB3 in cancer is becoming increasingly apparent. Several approaches for targeting ERBB3 in cancers have been tested or proposed. Small inhibitory RNA (siRNA) to ERBB3 or AKT is showing promise as a therapeutic approach to treatment of lung adenocarcinoma.

Surfactant maturation is not delayed in human fetuses with diaphragmatic hernia

BACKGROUND

Pulmonary hypoplasia and persistent pulmonary hypertension account for significant mortality and morbidity in neonates with congenital diaphragmatic hernia (CDH). Global lung immaturity and studies in animal models suggest the presence of surfactant deficiency that may further complicate the pathophysiology of CDH. However, data about surfactant status in human fetuses with CDH at birth are contradictory. The lack of a chronological study of surfactant content in late pregnancy has been a significant limitation. The appropriateness of administering surfactant supplements to neonates with CDH is therefore a debated question.

METHODS AND FINDINGS

We investigated surfactant content in human fetuses with CDH compared to age-matched fetuses with nonpulmonary diseases used as controls. Concentrations of disaturated phosphatidylcholine and surfactant proteins were found to be similar at a given stage of pregnancy, with both components showing a similar pattern of increase with progressing pregnancy in fetuses with CDH and in control fetuses. Thyroid transcription factor 1, a critical regulator of surfactant protein transcription, similarly displayed no difference in abundance. Finally, we examined the expression of three glucocorticoid-regulated diffusible mediators involved in lung epithelial maturation, namely: keratinocyte growth factor (KGF), leptin, and neuregulin 1 beta 1 (NRG1-beta1). KGF expression decreased slightly with time in control fetuses, but remained unchanged in fetuses with CDH. Leptin and NRG1-beta1 similarly increased in late pregnancy in control and CDH lungs. These maturation factors were also determined in the sheep fetus with surgical diaphragmatic hernia, in which surfactant deficiency has been reported previously. In contrast to the findings in humans, surgical diaphragmatic hernia in the sheep fetus was associated with decreased KGF and neuregulin expression. Fetoscopic endoluminal tracheal occlusion performed in the sheep model to correct lung hypoplasia increased leptin expression, partially restored KGF expression, and fully restored neuregulin expression.

CONCLUSIONS

Our results indicate that CDH does not impair surfactant storage in human fetuses. CDH lungs exhibited no trend toward a decrease in contents, or a delay in developmental changes for any of the studied surfactant components and surfactant maturation factors. Surfactant amounts are likely to be appropriate to lung size. These findings therefore do not support the use of surfactant therapy for infants with CDH. Moreover, they raise the question of the relevance of CDH animal models to explore lung biochemical maturity.

ErbB receptor dimerization, localization, and co-localization in mouse lung type II epithelial cells

ErbB receptors are crucial for embryonic neuronal and cardiac development. ErbB receptor ligands neuregulin (NRG) and epidermal growth factor (EGF) play a major role in the developing lung, specifically in mesenchymal induced fetal surfactant synthesis by type II epithelial cells. Different erbB receptor ligands cause diverse biologic effects by stimulating specific erbB-dimers. It is not known how dimerization, cellular localization, and co-localization of erbB dimers are regulated in type II epithelial cells. We hypothesized that erbB receptors have a distinct dimerization, localization, and co-localization pattern in type II cells. In mouse type II epithelial cells, which express all four erbB receptors, erbB1 and erbB4 were the preferred dimerization partners. These dimerization patterns were ligand independent. Confocal microscopy showed these transmembrane receptors exhibited a strong nuclear localization. In non-stimulated cells, both erbB1 and erbB2 were predominantly localized to the nucleus and less intensely to the cytoplasm. However, erbB1 was mainly found in the nucleoli, whereas erbB2 spared the nucleolar region. ErbB3 was exclusively located in the nucleoli. ErbB4 was diffusely located in nucleus and cytoplasm, and like erbB2 spared the nucleolar region. Short stimulation with either EGF or NRG led to a more pronounced nuclear staining for erbB1, erbB2, and erbB4. All four receptors co-localized with each other after stimulation, but with varying intensity. The two known stimulators of fetal surfactant synthesis, NRG and NRG-containing fibroblast conditioned medium, changed cellular localization of the dimerization partners erbB4 and erbB2 in a distinct fashion. We conclude that erbB receptors have a receptor-specific localization and dimerization pattern in type II epithelial cells.

Inactivation of neuregulin-1 by nitration

Nitration is a posttranslational modification that can compromise protein function. We hypothesized that nitration of growth factors secreted in the lung may alter their interaction with their respective receptors and modulate the normal growth and differentiation program induced by ligand-receptor interaction. We tested this hypothesis in vitro by nitration of neuregulin-1's (NRG-1) EGF-like domain and studying the effect on NRG-1's activity. Nitration of NRG-1's (nNRG-1) EGF-like domain resulted in an inability to activate its receptor, the human epidermal growth factor receptors 2 and 3 (HER2/HER3) heterodimer, as defined by loss of HER2 tyrosine phosphorylation induced by nNRG-1 in MCF-7 cells. Receptor activation was not restored with increasing nNRG-1 concentration or exposure times. nNRG-1 did not compete with NRG-1 for HER2/HER3 binding in competition assays. In addition, nNRG-1 no longer induced proliferation of the MCF-7 cell line, as MCF-7 cells exposed to nNRG-1 and NRG-1 concurrently had the same proliferation rate as that induced by NRG-1 alone. Thus nitration of NRG-1's EGF-like domain caused it to lose its ability to bind and activate its receptor with loss of ligand-induced proliferation. Posttranslational nitration of growth factors in states where reactive nitrogen species are increased may be an important means of regulating growth factor receptor effects in the lung.

A role for surfactant protein D in innate immunity of the human prostate

OBJECTIVES

Surfactant protein D (SP-D) is a member of the collectin family of proteins, which are involved in host defense mechanisms in the lung. In the present study, we found that SP-D is produced in the human prostate where it may play a role in innate immunity.

METHODS AND RESULTS

Using reverse-transcriptase PCR and Western blot analysis, we demonstrate that SP-D mRNA and protein are present in human prostate tissue. In situ hybridization and immunohistochemistry revealed that SP-D mRNA and protein are localized in epithelial cells of prostate glands. Prostate glands that are surrounded by inflammatory cells produce increased amounts of SP-D protein. We also show that SP-D inhibits the infection of LNCaP and P69SV40T prostate epithelial cells by Chlamydia trachomatis in an in vitro infection assay. Furthermore, using truncated human SP-D mutants, we demonstrate that SP-D binds to Chlamydia trachomatis via its carboxy-terminal lectin domains.

CONCLUSIONS

Our in vitro studies suggest that SP-D protects the prostate from infection by pathogens. SP-D protein levels are increased at sites of inflammation in the prostate, suggesting SP-D may also contribute more generally to inflammatory regulation in the prostate.

Basal-like Cells Constitute the Proliferating Cell Population in Cystic Fibrosis Airways

RATIONALE

Cystic fibrosis airways are recurrently exposed to noxious stimuli, leading to epithelial injury. Previous reports suggest that cystic fibrosis airway epithelia may respond to injury by increasing proliferation.

OBJECTIVES

We sought to determine the characteristics of the proliferating cell population in cystic fibrosis airways.

METHODS

Six cystic fibrosis and six normal lung sections from lung transplant recipients or lung surgery were obtained from the Duke Hospital pathology archives. Sections containing bronchi were evaluated for epithelial cell proliferation using immunohistochemistry for a nuclear proliferation antigen, Ki-67, and image analysis; immunohistochemistry for basal cells using a cytokeratin 5/14 antibody; and immunohistochemistry for the epidermal growth factor receptor and ErbB2, two receptor tyrosine kinases implicated in epithelial proliferation and differentiation.

RESULTS

Overall, cystic fibrosis sections had a greater proliferation index than control sections with 25.1 +/- 2.1% positively staining nuclei/total nuclei compared with control sections, 4.6 +/- 0.9% (p = 0.002). In cystic fibrosis sections only, there were areas of hyperplastic cuboidal cells adjacent to normal pseudostratified columnar epithelial sections; in these areas of epithelial hyperplasia, there was uniform Ki-67 staining, indicating a zone of proliferating cells. The proliferating cell population also expressed the basal cell cytokeratins 5/14 and epidermal growth factor receptor. Expression of ErbB2 was diminished in the proliferating cells.

CONCLUSIONS

Our results suggest that basal-like cells, expressing the epidermal growth factor receptor, constitute the proliferating cell population in cystic fibrosis airways.

Roles for neuregulins in human cancer

The human epidermal growth factor (EGF) receptor (HER) family of receptor tyrosine kinases has frequently been implicated in cancer. Apart from overexpression or mutation of these receptors, also the aberrant autocrine or paracrine activation of HERs by EGF-like ligands may be important in cancer progression. Neuregulins constitute a family of EGF-like ligands that bind to HER3 or HER4, preferably forming heterodimers with the orphan receptor HER2. Mesenchymal neuregulin typically serves as a pro-survival and pro-differentiation signal for adjacent epithelia. Disruption of the balance between proliferation and differentiation, because of autocrine production by the epithelial cells, increased sensitivity to paracrine signals or disruption of the spatial organization, may lead to constitutive receptor activation, in the absence of receptor overexpression. Consequently, the analysis of ligand expression and/or activated receptors in tumor samples may broaden the group of patients that can benefit from targeted therapies.

ErbB2 activity is required for airway epithelial repair following neutrophil elastase exposure

In cystic fibrosis and chronic bronchitis, airways are chronically injured by exposure to neutrophil elastase (NE). We sought to identify factors required for epithelial repair following NE exposure. Normal human bronchial epithelial cells were treated with NE (50 nM, 22 h) or control vehicle. Following NE treatment, we found a marked and sustained decrease in epithelial proliferation as detected by Ki67 immunostaining. 3H-thymidine incorporation was also initially depressed but increased over 72 h in NE-treated cells, which suggests that DNA synthesis constitutes an early repair process following NE exposure. We hypothesized that ErbB2 receptor tyrosine kinase, a regulator of cancer cell proliferation, was required for epithelial DNA synthesis following NE exposure. Immediately following NE treatment, by flow cytometry analysis, we found a decrease in ErbB2 surface expression. Protein levels of the full-length 185 kD ErbB2 receptor significantly decreased following NE treatment and smaller ErbB2-positive bands, ranging in size from 23 to 40 kD, appeared, which suggests that NE caused ErbB2 degradation. By real-time RT-PCR analysis, we found no change in ErbB2 mRNA expression following NE treatment, which suggests that changes in ErbB2 protein levels were regulated at the post-translational level. Following NE treatment, full-length 185 kD ErbB2 levels increased to pretreatment levels, correlating with the increase in thymidine incorporation during the same time period. Importantly, inhibition of ErbB2 activity with AG825 (5 microM) or Herceptin (3.1 microM), an ErbB2-neutralizing antibody, blocked thymidine incorporation only in NE-treated cells. These results suggest ErbB2 is a critical factor for epithelial recovery following NE exposure.

Inactivation of ErbB3 by siRNA promotes apoptosis and attenuates growth and invasiveness of human lung adenocarcinoma cell line A549

The ErbB3 receptor and the downstream signaling kinase Akt are implicated in proliferation of lung adenocarcinoma cells. Inhibition by siRNAs to ErbB3 and Akt isoforms 1, 2 and 3 was utilized to investigate the contribution of these molecules to tumor survival, spreading and invasiveness, and the roles of specific Akt isoforms. ErbB3 siRNA stably and dose-dependently suppressed ErbB3 protein for 2 days or more, and reduced cell numbers, by both suppressing cell cycle and causing apoptosis and necrosis. It also inhibited soft agar growth, cell motility and migration, and invasiveness. Akt1, 2 and 3 siRNAs had similar suppressive effects on cell number, apoptosis/necrosis and soft agar growth. However, although Akt1 siRNA had no effect on cell migration or invasion, Akt2 siRNA effectively suppressed both activities, and Akt3 siRNA had moderate effectiveness. In A549 cells, ErbB3 is indicated as having major effects on cell division, survival, motility, migration and invasiveness. All three Akt isoforms are to varying degrees involved in these cell behaviors, with Akt2 especially implicated in migration and invasion. ErbB3 and the Akts are promising targets for therapy, and siRNAs may be useful for this purpose.

Expression of mutant human epidermal receptor 3 attenuates lung fibrosis and improves survival in mice

Neuregulin-1 (NRG-1), binding to the human epidermal growth factor receptor HER2/HER3, plays a role in pulmonary epithelial cell proliferation and recovery from injury in vitro. We hypothesized that activation of HER2/HER3 by NRG-1 would also play a role in recovery from in vivo lung injury. We tested this hypothesis using bleomycin lung injury of transgenic mice incapable of signaling through HER2/HER3 due to lung-specific dominant-negative HER3 (DNHER3) expression. In animals expressing DNHER3, protein leak, cell infiltration, and NRG-1 levels in bronchoalveolar lavage fluid increased after injury, similar to that in nontransgenic littermate control animals. However, HER2/HER3 was not activated, and DNHER3 animals displayed fewer lung morphological changes at 10 and 21 days after injury (P = 0.01). In addition, they contained 51% less collagen in injured lungs (P = 0.04). Transforming growth factor-beta1 did not increase in bronchoalveolar lavage fluid from DNHER3 mice compared with nontransgenic littermate mice (P = 0.001), suggesting that a mechanism for the decreased fibrosis was lack of transforming growth factor-beta1 induction in DNHER3 mice. Severe lung injury (0.08 units bleomycin) resulted in 80% mortality of nontransgenic mice, but only 35% mortality of DNHER3 transgenic mice (P = 0.04). Thus inhibition of HER2/HER3 signaling protects against pulmonary fibrosis and improves survival.

Neuregulin-1 induces branching morphogenesis in the developing lung through a P13K signal pathway

Neuregulin-1 (NRG-1) induces signal transduction through the activation of its receptor, a heterodimer of human epidermal growth factor receptors 2 and 3 (HER2/HER3). Signal transduction through this receptor/ligand system plays a critical role in the developing heart, mammary gland, and nervous systems. Previous studies showed that NRG-1-induced HER2 activation resulted in pulmonary epithelial cell proliferation in the human fetal lung. The authors hypothesized that NRG-1 further contributes to lung development and maturation by inducing branching morphogenesis. In the present study, the authors show that NRG-1, HER2, and HER3, but not HER4, are expressed in the developing mouse lung. Addition of NRG-1 to fetal lung explants increased lung branching morphogenesis by 32% (P < .05). This increase in branching was blocked by 2C4, an antibody directed against HER2 that inhibits its dimerization and subsequent NRG-1-induced signal transduction. To gain an understanding of the intracellular signaling pathways involved in NRG-1-induced branching morphogenesis, the authors specifically blocked the phosphatidylinositol-3 kinase (PI3K) and mitogen activation protein kinase (MAPK) pathways. Inhibition of PI3K signaling significantly decreased NRG-1-induced branching morphogenesis (P < .05). Inhibition of NRG-1-induced MAPK activation had no effect on explant branching morphogenesis. These data suggest that NRG-1, binding to the HER2/HER3 heterodimer receptor complex, induces pulmonary branching morphogenesis through HER2 activation of the PI3K pathway.

Surfactant protein D is present in the human female reproductive tract and inhibits Chlamydia trachomatis infection

Surfactant protein D (SP-D) is a lung collectin involved in innate host defence mechanisms in the lung. SP-D is also expressed at other mucosal sites throughout the human body. In the present study, we show that SP-D mRNA and protein are expressed in the human female reproductive tract. SP-D protein was localized in the apical portion of the reproductive epithelial cells. We also demonstrate that endometrial and endocervical cell lines and primary endocervical cells in culture produce SP-D mRNA and protein. Chlamydia trachomatis is an intracellular pathogen that infects the female reproductive tract, primarily the cervix, and is responsible for the most prevalent infectious disease in the USA. Untreated chlamydial infections of the female reproductive tract often result in sterility of the infected woman. Since SP-D protein is produced in cervical glands, we examined the effect of SP-D on chlamydial infection of cervical epithelial cells in vitro. We found that SP-D protein inhibits the infection of HeLa cells (an endocervical epithelial cell line) by C. trachomatis in a dose-dependent manner. We further demonstrate that the SP-D lectin-binding domain is involved in inhibiting infection of HeLa cells by Chlamydia. In conclusion, we detected SP-D in the female reproductive tract and determined that one of the functions of the SP-D protein may be to protect cervical epithelial cells from infection by C. trachomatis.

Role of proneuregulin 1 cleavage and human epidermal growth factor receptor activation in hypertonic aquaporin induction

Mammalian cells are confronted with changes in extracellular osmolality at various sites, including the aqueous layer above the lung epithelium. Hypertonic shock induces the activation of mitogen-activated protein kinases and the expression of a defined set of genes, including aquaporins. We investigated upstream components of the response to hypertonicity in lung epithelial cells and found that before extracellular signal-regulated kinase activation and aquaporin synthesis, the membrane-bound prohormone neuregulin 1-beta is cleaved and binds to human epidermal growth factor receptor 3 (HER3). The signaling is prevented by matrix metalloproteinase inhibition, inhibition of neuregulin 1-beta binding to HER3, and inhibition of HER tyrosine kinase activity. Inhibition of HER activation interferes with the hypertonic induction of two different aquaporins in three distinct cell lines of mouse and human origin. We propose that ligand-dependent HER activation constitutes a generalized signaling principle in the mammalian hypertonic stress response relevant to aquaporin expression.

Autocrine activation of ErbB2/ErbB3 receptor complex by NRG-1 in non-small cell lung cancer cell lines

Our prior studies identified co-expression of the human epidermal growth factor-like receptors 2 (ErbB2) and 3 (ErbB3), as well as the growth factor neuregulin-1 (NRG-1) in normal lung epithelium and lung cancers. As ErbB2 and ErbB3 dimerize to produce a high affinity receptor for NRG-1, we postulated that an autocrine growth loop was present in transformed and non-transformed pulmonary epithelial cells. To test this hypothesis, we examined four cell lines derived from human non-small cell carcinomas for: (1) ErbB2 and ErbB3 expression and endogenous activation; (2) NRG-1 expression and secretion/shedding; and (3) the effect of receptor blockade on autocrine receptor activation. Our studies found that ErbB2 and ErbB3 were expressed by each of these cell lines. In addition, the NRG-1 gene was also expressed with both major isoforms of NRG-1 (NRG-1alpha and NRG-1beta) found intracellularly. Only the NRG-1alpha isoform, however, was found secreted/shed into the culture medium. The secreted/shed NRG-1alpha was capable of activating the ErbB2/ErbB3 receptor complex expressed on the breast adenocarcinoma cell line MCF-7. Basal ErbB2 phosphorylation was identified in all lung cancer cell lines and was inhibited with an antibody that blocked the NRG-1 binding site on ErbB3. Taken together, these data show that secreted NRG-1alpha can activate the ErbB2/ErbB3 heterodimer in an autocrine fashion. The identification of a NRG-1alpha/ErbB2/ErbB3 autocrine loop raises the possibility that interruption of this loop may have therapeutic potential in lung cancer.

Role of neuregulin-1 beta in the developing lung

Neuregulins play a critical role in the developing heart, nervous, and mammary systems. Neuregulin-1-induced cardiac, neuronal, and mammary differentiation is based on a cell-cell communication model, where the ligand neuregulin-1 is produced and secreted by one cell type, which does not express its receptors erbB3 and erbB4 and acts on neighboring cell types that do express these receptors. We proposed that neuregulin-1 affects fetal lung maturation through a similar mechanism. Immunostaining showed neuregulin-1 in fetal lung that increased in fibroblasts at the onset of surfactant synthesis. Neuregulin-1 beta was found to be secreted by the fetal lung fibroblast and stimulated type II cell surfactant synthesis. Both fetal lung fibroblast-conditioned media and neuregulin-1 stimulated erbB2 receptor phosphorylation in type II cells. The effects of neuregulin-1 and of fibroblast-conditioned media on both surfactant synthesis and type II cell erbB2 phosphorylation were specifically blocked by antibody to neuregulin-1. Thus, neuregulin-1 beta may control fetal lung maturation through mesenchymal-epithelial interactions in a paracrine mechanism similar to that described for the developing heart, brain, and mammary systems.

Lung tumorigenesis associated with erb-B-2 and erb-B-3 overexpression in human erb-B-3 transgenic mice is enhanced by methylnitrosourea

Erb-B-3 overexpression is associated with poor prognosis in non-small cell lung cancer and is often overexpressed in breast cancers. MMTVhuman-erb-B-3 transgenic mice were generated to evaluate the impact of erb-B-3 overexpression on lung and mammary gland tumorigenesis. These transgenic mice developed a high incidence of lung adenocarcinomas but not mammary gland tumors. The tumors overexpressed transgenic human [h]-erb-B-3 but also overexpressed endogenous erb-B-2, indicating that the heterodimer of h-erb-B-3-erb-B-2 was required for proliferative signal transduction to the nucleus. Lung tumor latency was shorter and the incidence higher in erb-B-3 transgenic mice treated with the methylating agent, methylnitrosourea [MNU]. In MNU treated mice, K-ras activating point mutations in codon 12, synergized with h-erb-B-3 in lung tumorogenesis. In bitransgenic MMTVrat-erb-B2/MMTV-human-erb-B-3 mice, lung tumor latency was also significantly shortened. Unlike over-expression of rat-erb-B-2, overexpression of h-erb-B-3 did not alter the incidence or latency of mammary tumors. Coupled erb-B-2 and erb-B-3 overexpression as well as K-ras activation induced signaling through mitogen-activated protein kinase (MAPK). This animal model links erb-B-3 with lung cancer, suggests that erb-B-2 and erb-B-3 heterodimerization is a necessary intermediate, and documents latency shortening by methylating agent-induced mutation of K-ras. This erb-B-3 mouse lung cancer model will help dissect genetic changes in lung tumorigenesis and may be useful for chemoprevention studies.

Neuregulin-1 activates the JAK-STAT pathway and regulates lung epithelial cell proliferation

Neuregulin-1 (NRG-1) is part of a family of proteins whose members are structurally related to epidermal growth factor. NRG-1 induces cell proliferation through a high-affinity receptor complex composed of a heterodimer of human epidermal growth factor-like receptor (HER) 2 and 3. In this study, we show that NRG-1 activates the Janus kinases (JAK) and signal transducer and activator of transcription proteins (STAT). NRG-1 induced a rapid and transient increase in tyrosine phosphorylation of TYK2 and JAK3, but not JAK1 or JAK2, and induced STAT3 and STAT5 tyrosine phosphorylation. Upon phosphorylation, STAT3 translocated to the nucleus within 1 h. Activation of the JAK-STAT pathway was dependent on HER2/HER3 heterodimerization and was necessary for NRG-1-induced proliferation. Inhibition of HER2's ability to dimerize using the HER2-specific antibody 2C4 completely blocked NRG-1-induced JAK3, TYK2, STAT3, and STAT5 tyrosine phosphorylation. Blocking the JAK-STAT pathway with a specific JAK-STAT pathway inhibitor, AG490, inhibited NRG-1-induced JAK and STAT phosphorylation and cell proliferation. These data suggest that NRG-1 activates the JAK-STAT signal transduction pathway through its high-affinity receptor, the HER2/HER3 heterodimer. This pathway plays an important role in NRG-1-stimulated proliferation of pulmonary epithelial cells.

Expression of ErbB3, ErbB4, and neuregulin-1 mRNA during tooth development

The receptor tyrosine kinases ErbB3 and ErbB4, which bind to various variants of neuregulin (NRG), play fundamental roles in neural development and in organs, which form through epithelial-mesenchymal interactions. Here, we demonstrate that NRG-1 and the receptors ErbB3 and ErbB4 are expressed locally during rodent tooth development. However, the mRNA expression patterns of ErbB3 and ErbB4 were distinctly different during odontogenesis. Examinations of teeth in genetically heart-rescued ErbB4-/- mice did not reveal any obvious deviation from the normal phenotype. The results suggest that ErbB3 and ErbB4 may participate in tooth morphogenesis. The specific interactions between NRG isoforms and ErbB receptors during this process remain to be determined.

Asthmatic epithelial cell proliferation and stimulation of collagen production: human asthmatic epithelial cells stimulate collagen type III production by human lung myofibroblasts after segmental allergen challenge

Epithelial injury and subepithelial collagen deposition are characteristic of asthma. We hypothesized that epithelial cell proliferation increases after airway injury in asthmatics, that epithelial cells stimulate lung myofibroblast collagen production, and that both processes are modulated by allergen-recruited inflammatory cells. Epithelial cells obtained at baseline, 1 d, and 1 and 2 wk after endobronchial allergen challenge from asthmatics and nonasthmatics were placed in culture, with and without bronchoalveolar lavage cells obtained from the same segment. Epithelial cell proliferation and collagen synthesis by human lung myofibroblasts stimulated with culture medium from these epithelial cells were determined. Epithelial proliferation increased (108 +/- 50% above baseline, p = 0.01 for d, and p = 0.004 for group x day interaction) 1 wk postchallenge in cells from asthmatics, but not from nonasthmatics, and required bronchoalveolar lavage cell coculture. Culture medium from epithelium harvested from asthmatics, but not from nonasthmatics, at 1 to 2 wk postchallenge stimulated collagen type III production 50% to 70% (p = 0.043 for clinical group, p = 0.012 for day, and p = 0.022 for group x day interaction), but not collagen type I. This effect was independent of an acute eosinophilic response. We conclude that epithelial cells from asthmatics, but not from nonasthmatics, are stimulated to proliferate after allergen challenge, and over 1 to 2 wk postchallenge, stimulate collagen type III synthesis by lung myofibroblasts. Epithelial cell proliferation appears dependent upon infiltrating inflammatory cells, but stimulation of collagen type III does not.

VEGF induces airway epithelial cell proliferation in human fetal lung in vitro

Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen involved in normal and abnormal angiogenesis. VEGF mRNA and protein are abundant in distal epithelium of midtrimester human fetal lung. In the present study, we identified immunoreactivity for KDR, a major VEGF-specific receptor, in distal lung epithelial cells of human fetal lung tissue, suggesting a possible autocrine or paracrine regulatory role for VEGF in pulmonary epithelial cell growth and differentiation. Addition of exogenous VEGF to human fetal lung explants resulted in increased epithelium volume density and lumen volume density in the tissues, both morphometric parameters of tissue differentiation. Cellular proliferation demonstrated by bromodeoxyuridine uptake was prominent in distal airway epithelial cells and increased in the VEGF-treated explants. VEGF-treated explants also demonstrated increased surfactant protein (SP) A mRNA, SP-C mRNA, and SP-A protein levels compared with controls. However, SP-B mRNA levels were unaffected by VEGF treatment. [(3)H]choline incorporation into total phosphatidylcholine was increased by VEGF treatment, but incorporation into disaturated phosphatidylcholine was not affected by exogenous VEGF. Based on these observations, we conclude that VEGF may be an important autocrine growth factor for distal airway epithelial cells in the developing human lung.