Distribution of integrin cell adhesion receptors on normal bronchial epithelial cells and lung cancer cells in vitro and in vivo

Pathobiology of Airway Remodeling in Asthma: The Emerging Role of Integrins

Airway remodeling is a complex clinical feature of asthma that involves long-term disruption and modification of airway architecture, which contributes significantly to airway hyperresponsiveness (AHR) and lung function decline. It is characterized by thickening of the airway smooth muscle layer, deposition of a matrix below the airway epithelium, resulting in subepithelial fibrosis, changes within the airway epithelium, leading to disruption of the barrier, and excessive mucous production and angiogenesis within the airway wall. Airway remodeling contributes to stiffer and less compliant airways in asthma and leads to persistent, irreversible airflow obstruction. Current asthma treatments aim to reduce airway inflammation and exacerbations but none are targeted towards airway remodeling. Inhibiting the development of airway remodeling or reversing established remodeling has the potential to dramatically improve symptoms and disease burden in asthmatic patients. Integrins are a family of transmembrane heterodimeric proteins that serve as the primary receptors for extracellular matrix (ECM) components, mediating cell-cell and cell-ECM interactions to initiate intracellular signaling cascades. Cells present within the lungs, including structural and inflammatory cells, express a wide and varying range of integrin heterodimer combinations and permutations. Integrins are emerging as an important regulator of inflammation, repair, remodeling, and fibrosis in the lung, particularly in chronic lung diseases such as asthma. Here, we provide a comprehensive summary of the current state of knowledge on integrins in the asthmatic airway and how these integrins promote the remodeling process, and emphasize their potential involvement in airway disease.

Cells of the human respiratory tract support the replication of pathogenic Old World orthohantavirus Puumala

BACKGROUND

Transmission of all known pathogenic orthohantaviruses (family Hantaviridae) usually occurs via inhalation of aerosols contaminated with viral particles derived from infected rodents and organ manifestation of infections is characterized by lung and kidney involvement. Orthohantaviruses found in Eurasia cause hemorrhagic fever with renal syndrome (HFRS) and New World orthohantaviruses cause hantavirus cardiopulmonary syndrome (HCPS). However, cases of infection with Old World orthohantaviruses with severe pulmonary manifestations have also been observed. Therefore, human airway cells may represent initial targets for orthohantavirus infection and may also play a role in the pathogenesis of infections with Eurasian orthohantaviruses.

METHODS

We analyzed the permissiveness of primary endothelial cells of the human pulmonary microvasculature and of primary human epithelial cells derived from bronchi, bronchioles and alveoli for Old World orthohantavirus Puumala virus (PUUV) in vitro. In addition, we examined the expression of orthohantaviral receptors in these cell types. To minimize donor-specific effects, cells from two different donors were tested for each cell type.

RESULTS

Productive infection with PUUV was observed for endothelial cells of the microvasculature and for the three tested epithelial cell types derived from different sites of the respiratory tract. Interestingly, infection and particle release were also detected in bronchial and bronchiolar epithelial cells although expression of the orthohantaviral receptor integrin β₃ was not detectable in these cell types. In addition, replication kinetics and viral release demonstrate enormous donor-specific variations.

CONCLUSIONS

The human respiratory epithelium is among the first targets of orthohantaviral infection and may contribute to virus replication, dissemination and pathogenesis of HFRS-causing orthohantaviruses. Differences in initial pulmonary infection due to donor-specific factors may play a role in the observed broad variance of severity and symptoms of orthohantavirus disease in patients. The absence of detectable levels of integrin α_Vβ₃ surface expression on bronchial and small airway epithelial cells indicates an alternate mode of orthohantaviral entry in these cells that is independent from integrin β₃.

Integrins as Therapeutic Targets for Respiratory Diseases

Integrins are a large family of transmembrane heterodimeric proteins that constitute the main receptors for extracellular matrix components. Integrins were initially thought to be primarily involved in the maintenance of cell adhesion and tissue integrity. However, it is now appreciated that integrins play important roles in many other biological processes such as cell survival, proliferation, differentiation, migration, cell shape and polarity. Lung cells express numerous combinations and permutations of integrin heterodimers. The complexity and diversity of different integrin heterodimers being implicated in different lung diseases present a major challenge for drug development. Here we provide a comprehensive overview of the current knowledge of integrins from studies in cell culture to integrin knockout mouse models and provide an update of results from clinical trials for which integrins are therapeutic targets with a focus on respiratory diseases (asthma, emphysema, pneumonia, lung cancer, pulmonary fibrosis and sarcoidosis).

Laminin-332 and α3β1 integrin-supported migration of bronchial epithelial cells is modulated by fibronectin

The repair of the bronchiolar epithelium damaged by cell-mediated, physical, or chemical insult requires epithelial cell migration over a provisional matrix composed of complexes of extracellular matrix molecules, including fibronectin and laminin. These matrix molecules support migration and enhance cell adhesion. When cells adhere too tightly to their matrix they fail to move; but if they adhere too little, they are unable to develop the traction force necessary for motility. Thus, we investigated the relative contributions of laminin and fibronectin to bronchiolar cell adhesion and migration using the immortalized bronchial lung epithelial cell line (BEP2D) and normal human bronchial epithelial (NHBE) cells, both of which assemble a laminin α3β3γ2 (LM332)/fibronectin-rich matrix. Intriguingly, BEP2D and NHBE cells migrate significantly faster on an LM332-rich matrix than on fibronectin. Moreover, addition of fibronectin to LM332 matrix suppresses motility of both cell types. Finally, fibronectin enhances the adhesion of both BEP2D and NHBE cells to LM332-coated surfaces. These results suggest that fibronectin fine tunes LM332-mediated migration by boosting bronchiolar cell adhesion to substrate. We suggest that, during epithelial wound healing of the injured airway, fibronectin plays an important adhesive role for laminin-driven epithelial cell motility by promoting a stable cellular interaction with the provisional matrix.

Human bronchial epithelial cells differentiate to 3D glandular acini on basement membrane matrix

To create a model system that investigates mechanisms resulting in hyperplasia and hypertrophy of respiratory tract submucosal glands, we developed an in vitro three-dimensional (3D) system wherein normal human bronchial epithelial (HBE) cells differentiated into glandular acini when grown on a basement membrane matrix. The differentiation of primary HBE cells into glandular acini was monitored temporally by light microscopy. Apoptosis-induced lumen formation was observed by immunofluorescence analysis. The acinar cells expressed and secreted MUC5B mucin (marker for glandular mucous cells) and lysozyme, lactoferrin, and zinc-α2-glycoprotein (markers for glandular serous cells) at Day 22. β-Tubulin IV, a marker for ciliated cells, was not detected. Expression of mucous and serous cell markers in HBE glandular acini demonstrated that HBE cells grown on a basement membrane matrix differentiated into acini that exhibit molecular characteristics of respiratory tract glandular acinar cells. Inhibition studies with neutralizing antibodies resulted in a marked decrease in size of the spheroids at Day 7, demonstrating that laminin (a major component of the basement membrane matrix), the cell surface receptor integrin α6, and the cell junction marker E-cadherin have functional roles in HBE acinar morphogenesis. No significant variability was detected in the average size of glandular acini formed by HBE cells from two normal individuals. These results demonstrated that this in vitro model system is reproducible, stable, and potentially useful for studies of glandular differentiation and hyperplasia.

Integrin expression profiling identifies integrin alpha5 and beta1 as prognostic factors in early stage non-small cell lung cancer

Background

Selection of early stage non-small cell lung cancer patients with a high risk of recurrence is warranted in order to select patients who will benefit from adjuvant treatment strategies. We evaluated the prognostic value of integrin expression profiles in a retrospective study on frozen primary tumors of 68 patients with early stage non-small cell lung cancer.

Methods

A retrospective study was performed on frozen primary tumors of 68 early stage non-small cell lung cancer patients with a follow up of at least 10 years. From all tumor tissues, RNA was isolated and reverse transcribed into cDNA. qPCR was used to generate mRNA expression profiles including integrins alpha1, 2, 3, 4, 5, 6, 7, 11, and V as well as integrins beta1, 3, 4, 5, 6, and 8.

Results

The expression levels of integrins alpha5, beta1 and beta3 predicted overall survival and disease free survival in early stage NSCLC patients. There was no association between integrin expression and lymph node metastases. Comparison between the histological subtypes revealed a distinct integrin signature for squamous cell carcinoma while the profiles of adenocarcinoma and large cell carcinoma were largely the same.

Conclusion

Integrin expression in NSCLC is important for the development and behavior of the tumor and influences the survival of the patient. Determining the integrin expression profile might serve as a tool in predicting the prognosis of individual patients.

EXPRESSION OF ANGIOSTATIN, INTEGRINαvβ3, AND VITRONECTIN IN HUMAN LUNGS IN SEPSIS

Angiostatin, integrin alphavbeta3, and vitronectin play important roles in inflammation. However, there is very little information on expression of these molecules in the lungs of humans with sepsis. Therefore, as a first step to eventually study the function of these molecules, the authors conducted an immunohistochemical study to evaluate their expression in lungs of normal (N = 8) and sepsis patients (N = 8). In normal lungs, angiostatin expression was minimal in the alveolar septa and alveolar macrophages, and absent in large blood vessels, bronchioles, and interstitium. In sepsis patients, the staining was intense in the septa, neutrophils, alveolar macrophages, and large blood vessels. Integrin alphavbeta3 staining was observed in occasional bronchiolar epithelial cells and a few alveolar macrophages in the normal lungs. The integrin was expressed extensively and intensely in bronchiolar epithelium and alveolar macrophages, and with lesser intensity in large blood vessels in inflamed lungs. Compared to the normal lung, vitronectin expression was increased in alveolar macrophages and in vascular smooth muscles in inflamed lungs. These data show cell-specific increase in the expression of integrin alphavbeta3, angiostatin, and vitronectin in inflamed lungs of sepsis patients. Because all these molecules can have significant influence on inflammation, the data reported in this manuscript create a need for further investigation.

Role of A disintegrin and metalloprotease-12 in neutrophil recruitment induced by airway epithelium

Among proteases, metalloproteases are implicated in tissue remodeling, as shown in numerous diseases including allergy. ADAMs (A Disintegrin And Metalloprotease) metalloproteases are implicated in physiologic processes such as cytokine and growth factor shedding, cell migration, adhesion, or repulsion. Our aim was to measure ADAM-12 expression in airway epithelium and to define its role during the allergic response. To raise this question, we analyzed the ADAM-12 expression ex vivo after allergen exposure in patients with allergic rhinitis and in vitro in cultured primary human airway epithelial cells (AEC). Clones of BEAS-2B cells transfected with the full-length form of ADAM-12 were generated to study the consequences of ADAM-12 up-regulation on AEC function. After allergen challenge, a strong increase of ADAM-12 expression was observed in airway epithelium from patients with allergic rhinitis but not from control subjects. In contrast with the other HB-epidermal growth factor sheddases, ADAM-10 and -17, TNF-alpha in vitro increased the expression of ADAM-12 by AEC, an effect amplified by IL-4 and IL-13. Up-regulation of ADAM-12 in AEC increased the expression of alpha3 and alpha4 integrins and to the modulation of cell migration on fibronectin but not on collagen. Moreover, overexpression of ADAM-12 in BEAS-2B enhanced the secretion of CXCL1 and CXCL8 and their capacity to recruit neutrophils. CD47 was strongly decreased by ADAM-12 overexpression, a process associated with a reduced adhesion of neutrophils. These effects were mainly dependent on epidermal growth factor receptor activation. In summary, ADAM-12 is produced during allergic reaction by AEC and might increase neutrophil recruitment within airway mucosa.

A peptide selected by biopanning identifies the integrin alphavbeta6 as a prognostic biomarker for nonsmall cell lung cancer

The development of new modes of diagnosis and targeted therapy for lung cancer is dependent on the identification of unique cell surface features on cancer cells and isolation of reagents that bind with high affinity and specificity to these biomarkers. We recently isolated a 20-mer peptide which binds to the lung adenocarcinoma cell line, H2009, from a phage-displayed peptide library. We show here that the cellular receptor for this peptide, TP H2009.1, is the uniquely expressed integrin, alphavbeta6, and the peptide binding to lung cancer cell lines correlates to integrin expression. The peptide is able to mediate cell-specific uptake of a fluorescent nanoparticle via this receptor. Expression of alphavbeta6 was assessed on 311 human lung cancer samples. The expression of this integrin is widespread in early-stage nonsmall cell lung carcinoma (NSCLC). Log-rank test and Cox regression analyses show that expression of this integrin is significantly associated with poor patient outcome. Preferential expression is observed in the tumors compared with the surrounding normal lung tissue. Our data indicate that alphavbeta6 is a prognostic biomarker for NSCLC and may serve as a receptor for targeted therapies. Thus, cell-specific peptides isolated from phage biopanning can be used for the discovery of cell surface biomarkers, emphasizing the utility of peptide libraries to probe the surface of a cell.

Deletion of core fucosylation on alpha3beta1 integrin down-regulates its functions

The core fucosylation (alpha1,6-fucosylation) of glycoprotein is widely distributed in mammalian tissues. Recently alpha1,6-fucosylation has been further reported to be very crucial by the study of alpha1,6-fucosyltransferase (Fut8)-knock-out mice, which shows the phenotype of emphysema-like changes in the lung and severe growth retardation. In this study, we extensively investigated the effect of core fucosylation on alpha3beta1 integrin and found for the first time that Fut8 makes an important contribution to the functions of this integrin. The role of core fucosylation in alpha3beta1 integrin-mediated events has been studied by using Fut8(+/+) and Fut8(-/-) embryonic fibroblasts, respectively. We found that the core fucosylation of alpha3beta1 integrin, the major receptor for laminin 5, was abundant in Fut8(+/+) cells but was totally abolished in Fut8(-/-) cells, which was associated with the deficient migration mediated by alpha3beta1 integrin in Fut8(-/-) cells. Moreover integrin-mediated cell signaling was reduced in Fut8(-/-) cells. The reintroduction of Fut8 potentially restored laminin 5-induced migration and intracellular signaling. Collectively, these results suggested that core fucosylation is essential for the functions of alpha3beta1 integrin.

The αvβ6 integrin receptor for Foot-and-mouth disease virus is expressed constitutively on the epithelial cells targeted in cattle

Field strains ofFoot-and-mouth disease virus(FMDV) use a number ofαv-integrins as receptors to initiate infection on cultured cells, and integrins are believed to be the receptors used to target epithelial cells in animals. In this study, immunofluorescence confocal microscopy and real-time RT-PCR were used to investigate expression of two of the integrin receptors of FMDV,αvβ6 andαvβ3, within various epithelia targeted by this virus in cattle. These studies show thatαvβ6 is expressed constitutively on the surfaces of epithelial cells at sites where infectious lesions occur during a natural infection, but not at sites where lesions are not normally formed. Expression ofαvβ6 protein at these sites showed a good correlation with the relative abundance ofβ6 mRNA. In contrast,αvβ3 protein was only detected at low levels on the vasculature and not on the epithelial cells of any of the tissues investigated. Together, these data suggest that in cattle,αvβ6, rather thanαvβ3, serves as the major receptor that determines the tropism of FMDV for the epithelia normally targeted by this virus.

Epithelial cells and fibroblasts: structural repair and remodelling in the airways

Extensive lesions and changes in the architecture of the airway walls are commonly described in patients with respiratory infections, asthma, chronic bronchitis and interstitial lung diseases. Current knowledge identifies in airway epithelial cells and in fibroblasts the two cell types mainly involved in tissue repair after injury. During inflammatory respiratory disorders, extensive injury of airway epithelium may occur, with shedding of a large sheet of damaged cells in the bronchial and alveolar lumen but also with activation of the surviving epithelial cells and of the underlying fibroblasts. Indeed, besides acting as a physical and functional barrier to external agents, the epithelial surface of the bronchi has the capability to modulate the repair processes through the secretion of extracellular matrix proteins and the interaction with interstitial fibroblasts. Besides releasing pro-inflammatory cytokines and chemokines, the surviving epithelial cells and the underlying fibroblasts secrete factors contributing to airway repair, including the formation of the provisional extracellular matrix. This is indeed the substrate to which the epithelial cells at the edge of the lesion can attach to migrate in order to reconstitute the surface layer. In these processes airway epithelial cells receive the support of bronchial wall fibroblasts which actively release cytokines stimulating epithelial cell functions.

Integrin alphavbeta8 functions as a receptor for foot-and-mouth disease virus: role of the beta-chain cytodomain in integrin-mediated infection

Field isolates of foot-and-mouth disease virus (FMDV) have been shown to use three alphav integrins, alphavbeta1, alphavbeta3, and alphavbeta6, as cellular receptors. Binding to the integrin is mediated by a highly conserved RGD motif located on a surface-exposed loop of VP1. The RGD tripeptide is recognized by several other members of the integrin family, which therefore have the potential to act as receptors for FMDV. Here we show that SW480 cells are made susceptible to FMDV following transfection with human beta8 cDNA and expression of alphavbeta8 at the cell surface. The involvement of alphavbeta8 in infection was confirmed by showing that virus binding and infection of the transfected cells are inhibited by RGD-containing peptides and by function-blocking monoclonal antibodies specific for either the alphavbeta8 heterodimer or the alphav chain. Similar results were obtained with a chimeric alphavbeta8 including the beta6 cytodomain (alphavbeta8/6), showing that the beta6 cytodomain can substitute efficiently for the corresponding region of beta8. In contrast, virus binding to alphavbeta6 including the beta8 cytodomain (alphavbeta6/8) was lower than that of the wild-type integrin, and this binding did not lead to infection. Further, the alphavbeta6 chimera was recognized poorly by antibodies specific for the ectodomain of alphavbeta6 and displayed a relaxed sequence-binding specificity relative to that of wild-type integrin. These data suggest that the beta6 cytodomain is important for maintaining alphavbeta6 in a conformation required for productive infection by FMDV.

Isolation of lung tumor specific peptides from a random peptide library: generation of diagnostic and cell-targeting reagents

Discovery of ligands specific to receptor(s) on a surface of a cancer cell could impact clinical issues including functional diagnosis and cell-specific drug delivery. Using a phage display approach, we have isolated 20-mer peptide ligands that bind to 3 different human lung tumor cell lines, NCI-H1299, NCI-H2009, and A549. The panning protocol is unbiased with no selection pressure towards binding a particular cellular receptor. The isolated phage bind to their target cells 24-300 times better than a control phage. Furthermore, the isolated peptides display remarkable cell-specificities and are able to discriminate between normal and cancerous cells as well as different lung tumor cells. The cell-specificities are not coincident with tumor classes indicating that the peptides are able to recognize cell-surface features that are not represented within the classification of tumor type. The isolated peptides are functional outside of the context of the phage and multimerization of the peptide increases its affinity for its given cell type, thus expanding their utility in clinical situations.

Functions of pulmonary epithelial integrins: from development to disease

Signals from integrins are now known to play critical roles in virtually every aspect of the behavior of epithelial cells, including survival, proliferation, maintenance of polarity, secretory differentiation, and malignant transformation. The cells that line the conducting airways and alveoli of the lung, like most surface epithelia, simultaneously express multiple members of the integrin family, including several with broadly overlapping ligand binding specificities. Although multiple integrins on airway epithelial cells may support adhesion to the same ligands, the functional roles of each integrin that has been examined in detail are quite distinct. Findings from mice expressing null mutations of some of these integrins have identified roles for epithelial cells and epithelial integrins in lung development and in the regulation of lung inflammation, macrophage protease expression, pulmonary fibrosis, and the pulmonary edema that follows acute lung injury. Epithelial integrins are thus attractive targets for intervention in a number of common lung disorders.

Foot-and-mouth disease virus receptors: comparison of bovine alpha(V) integrin utilization by type A and O viruses

Three members of the alpha(V) integrin family of cellular receptors, alpha(V)beta(1), alpha(V)beta(3), and alpha(V)beta(6), have been identified as receptors for foot-and-mouth disease virus (FMDV) in vitro. The virus interacts with these receptors via a highly conserved arginine-glycine-aspartic acid (RGD) amino acid sequence motif located within the betaG-betaH (G-H) loop of VP1. Other alpha(V) integrins, as well as several other integrins, recognize and bind to RGD motifs on their natural ligands and also may be candidate receptors for FMDV. To analyze the roles of the alpha(V) integrins from a susceptible species as viral receptors, we molecularly cloned the bovine beta(1), beta(5), and beta(6) integrin subunits. Using these subunits, along with previously cloned bovine alpha(V) and beta(3) subunits, in a transient expression assay system, we compared the efficiencies of infection mediated by alpha(V)beta(1), alpha(V)beta(3), alpha(V)beta(5), and alpha(V)beta(6) among three strains of FMDV serotype A and two strains of serotype O. While all the viruses could infect cells expressing these integrins, they exhibited different efficiencies of integrin utilization. All the type A viruses used alpha(V)beta(3) and alpha(V)beta(6) with relatively high efficiency, while only one virus utilized alpha(V)beta(1) with moderate efficiency. In contrast, both type O viruses utilized alpha(V)beta(6) and alpha(V)beta(1) with higher efficiency than alpha(V)beta(3). Only low levels of viral replication were detected in alpha(V)beta(5)-expressing cells infected with either serotype. Experiments in which the ligand-binding domains among the beta subunits were exchanged indicated that this region of the integrin subunit appears to contribute to the differences in integrin utilizations among strains. In contrast, the G-H loops of the different viruses do not appear to be involved in this phenomenon. Thus, the ability of the virus to utilize multiple integrins in vitro may be a reflection of the use of multiple receptors during the course of infection within the susceptible host.

Negative impact of DEP exposure on human airway epithelial cell adhesion, stiffness, and repair

Epidemiological and experimental studies suggest that diesel exhaust particles (DEPs) may be associated with increased respiratory mortality and morbidity. Several recent studies have also shown that DEPs increase the production of inflammatory cytokines by human bronchial epithelium (HBE) cells in vitro. The present study investigates the effects of DEPs on the interaction of l-HBE cells (16HBE14o-) with the cell and matrix microenvironment based on evaluation of integrin-type cell/matrix ligand expression, cytoskeleton (CSK) stiffness, and matrix remodeling via matrix metalloproteinase (MMP)-1, MMP-2, and MMP-9 expression. The results showed that DEP exposure induced: 1) a net dose-dependent decrease in CSK stiffness through actin fibers, 2) a concomitant specific reduction of both alpha(3)- and beta(1)-integrin subunits extensively expressed on the HBE cell surface, 3) a decrease in the level of CD44, which is a major HBE cell-cell and HBE cell-matrix adhesion molecule; and 4) an isolated decrease in MMP-1 expression without any change in tissue inhibitor of matrix metalloproteinase (TIMP)-1 or TIMP-2 tissue inhibitors. Restrictive modulation of cell-matrix interaction, cell-cell connection, CSK stiffness, and fibrillary collagen remodeling results in a decreased wound closure capacity and an increased deadhesion capacity. In conclusion, on the basis of these results, we can propose that, in addition to their ability to increase the production of inflammatory cytokines, DEPs could also alter the links between actin CSK and the extracellular matrix, suggesting that they might facilitate HBE cell detachment in vivo.

A comparative study of primary and immortalized cell adhesion characteristics to modified polymer surfaces: toward the goal of effective re-epithelialization

Facilitating tissue regeneration or replacement requires development of synthetic surfaces that promote cell adhesion, migration, and proliferation. Two successful approaches have been to incorporate minimal cell adhesion recognition sequences at the biomaterial surface and to integrate the entire adhesion molecule into a compatible synthetic matrix. While adhesion assays using immortalized cell lines are important in evaluating synthetic materials, cell type and source play a significant role in the ability of such models to mimic real tissues. Models that utilize multiple cell types or primary cells are more representative of native tissues than models that use single cell types or primary cells. In this study we investigated primary respiratory epithelial cell (REC) adhesion to modified fluoropolymers incorporating simple functional groups and minimal peptide recognition sequences, and we evaluated the potential of hybrid biopolymer materials to support adhesion and proliferation. X-ray photoelectron spectroscopy (XPS) was used to verify substrate surface composition. Significant differences were found in the adhesion characteristics of primary REC and in the A549 lung carcinoma cell line. Model systems composed of multiple cell types and/or primary cells necessarily represent increased levels of complexity for an investigation of cellular responses to synthetic surfaces. When evaluating biomaterials, adhesion studies using immortalized cell lines cannot necessarily be extrapolated to normal cell behavior.

Integrin alphavbeta1 is a receptor for foot-and-mouth disease virus

Infection by field strains of Foot-and-mouth disease virus (FMDV) is initiated by binding to certain species of arginine-glycine-aspartic acid (RGD)-dependent integrin including alphavbeta3 and the epithelial integrin alphavbeta6. In this report we show that the integrin alphavbeta1, when expressed as a human/hamster heterodimer on transfected CHOB2 cells, is a receptor for FMDV. Virus binding and infection mediated by alphavbeta1 was inefficient in the presence of physiological concentrations of calcium and magnesium but were significantly enhanced by reagents that activate the integrin and promote ligand binding. The ability of chimeric alpha5/alphav integrin subunits, in association with the beta1 chain, to bind FMDV and mediate infection matched the ligand binding specificity of alphavbeta1, not alpha5beta1, thus providing further evidence for the receptor role of alphavbeta1. In addition, data are presented suggesting that amino acid residues near the RGD motif may be important for differentiating between the binding specificities of alphavbeta1 and alphavbeta6.

Role of alpha(3)beta(1) integrin in tubulogenesis of Madin-Darby canine kidney cells

BACKGROUND

We isolated several Madin-Darby canine kidney (MDCK) subclones that exhibit different degrees of branching tubulogenesis in lower concentrations of collagen gel. The M634 clone formed cell aggregates in 0.3% collagen gel, but developed branching tubules vigorously in 0.1% collagen gel. In contrast, the Y224 clone formed cysts in 0.3% collagen gel and displayed fewer branching structures in 0.1% collagen gel. Morphologically, M634 cells exhibited higher levels of cell scattering as well as collagen-induced cell migration than Y224. We conducted this study to delineate the underlying mechanism of branching tubulogenesis in M634 cells.

METHODS

Components of the focal contact machinery were analyzed in both cell lines, including the extracellular matrix glycoproteins fibronectin, laminin, and vitronectin; cytoskeleton-associated elements alpha-actinin, talin, and vinculin; and receptors for extracellular matrix and alpha(2), alpha(3), alpha(5), alpha(v), beta(1), and beta(3) integrins. Furthermore, we established several stable transfectants of alpha(3) integrin antisense RNA in M634 cells to examine the role of alpha(3)beta(1) integrin in branching morphogenesis directly.

RESULTS

There were no obvious differences in levels of the focal adhesion complex proteins between M634 and Y224 cells, except that the content of the alpha(3) and beta1 integrins were 1.2- and 0.6-fold higher in M634 cells, respectively. The expression of alpha(3) integrin antisense RNA significantly lowered the levels of alpha(3) integrin mRNA and protein. The potential of cell scattering, migration, and branching tubulogenesis in M634 cells was inhibited according to the decrease in alpha(3) integrin expression.

CONCLUSION

Our data indicate that expression of alpha(3)beta(1) integrin regulates cell scattering, migration, and branching tubulogenesis of MDCK cells, possibly via adhesion to or serving as a signaling molecule for type I collagen.

Invasion of human respiratory epithelial cells by Bordetella pertussis: Possible role for a filamentous hemagglutinin Arg-Gly-Asp sequence and α5β1 integrin

Bordetella pertussis, the agent of whooping cough, is capable of invading human respiratory epithelial cells. In this study, we investigated the mechanisms by which B. pertussis invades the human lung epithelial cell line A549 and normal human bronchial epithelial (NHBE) cells. In vitro adhesion and invasion assays using both cell types with a virulent B. pertussis strain and its isogenic mutants revealed profound defects in a mutant deficient in filamentous hemagglutinin (FHA) expression. In addition, a mutant in which an FHA Arg-Gly-Asp (RGD) site had been changed to Arg-Ala-Asp had significantly diminished invasiveness, although its adhesiveness was comparable to that of the parental strain. Furthermore, a synthetic RGD-containing hexapeptide inhibited invasion of both cell types by the virulent strain. These results demonstrate that an RGD sequence of FHA is involved in B. pertussis invasion of epithelial cells in vitro. Monoclonal antibodies directed against human alpha5beta1 integrin, but not other integrins, blocked invasion, indicating that this integrin is involved in B. pertussis invasion. Taken together, these findings suggest that B. pertussis FHA may promote invasion of human respiratory epithelial cells through the interaction of its RGD sequence with host cell alpha5beta1 integrin.

Initiation of apoptosis by actin cytoskeletal derangement in human airway epithelial cells

Changes in epithelial cell shape can lead to cell death and detachment. Actin filaments are cleaved during apoptosis, but whether disruption in the actin cytoskeletal network, as one manifestation of cell shape change, can itself induce apoptosis is not known. We tested this hypothesis in the airway epithelial cell line 1HAEo(-) and in primary airway epithelial cells by preventing actin filament elongation with cytochalasin D or by aggregating actin filaments with jasplakinolide. Disruption of actin filament integrity promptly induced apoptosis in adherent epithelial cells within 5 h. Jasplakinolide-induced apoptosis did not disrupt focal adhesions, whereas cytochalasin D-induced apoptosis decreased focal adhesion protein expression and occurred despite ligation of the fibronectin receptor. Death induction was abrogated by the caspase inhibitors z-VAD-fmk and Ac-DEVD-cho but not by blocking the Fas (CD95) receptor. Whereas cytochalasin D--induced apoptosis was associated with cleavage of pro-caspase-8, jasplakinolide-induced apoptosis was not. Both agents induced formation of a death-inducing signaling complex. These data demonstrate that disruption of actin filament integrity with either cytochalasin D or jasplakinolide induces apoptosis in airway epithelial cells but by different mechanisms, and suggest that actin may be an early modulator of apoptotic commitment.

Adenovirus type 7 penton purification of soluble pentamers from Escherichia coli and development of an integrin-dependent gene delivery system

Adenoviral gene therapy vectors suffer from the disadvantages of toxicity and immunogenicity associated with the expression of adenoviral genes from the vector backbone. We report here an alternative strategy for gene delivery that utilizes a single component of the adenoviral type 7 capsid, the penton base (Ad7PB). The Ad7PB gene was sequenced and its amino-acid composition was deduced from its nucleotide sequence. The penton was expressed in Escherichia coli as a soluble C-terminal fusion with glutathione S-transferase (GST-Ad7PB) and was purified by single-step affinity chromatography. Both GST-Ad7PB and cleaved (GST-free) Ad7PB retained the ability to fold into pentamers as observed by electron microscopy. GST-Ad7PB was able to bind a synthetic peptide (FK20) derived from the Ad type 7 fiber and retard DNA through a polylysine chain present at the C-terminus of this linker peptide. GST-Ad7PB was an effective cell transfecting agent when assayed on 293 cells. Transfection was not dependent upon the presence of lysosomotropic agents indicating efficient endosome escape capability. Excess of an RGD-containing peptide derived from Ad7PB was able to inhibit transfection indicating specific integrin-mediated uptake of the GST-Ad7PB-FK20-DNA complexes. We propose that Ad7 pentons can be developed into integrin-specific gene delivery agents.

Integrin alpha(3)-subunit expression modulates alveolar epithelial cell monolayer formation

We investigated expression of the alpha(3)-integrin subunit by rat alveolar epithelial cells (AECs) grown in primary culture as well as the effects of monoclonal antibodies with blocking activity against the alpha(3)-integrin subunit on AEC monolayer formation. alpha(3)-Integrin subunit mRNA and protein were detectable in AECs on day 1 and increased with time in culture. alpha(3)- and beta(1)-integrin subunits coprecipitated in immunoprecipitation experiments with alpha(3)- and beta(1)-subunit-specific antibodies, consistent with their association as the alpha(3)beta(1)-integrin receptor at the cell membrane. Treatment with blocking anti-alpha(3) monoclonal antibody from day 0 delayed development of transepithelial resistance, reduced transepithelial resistance through day 5 compared with that in untreated AECs, and resulted in large subconfluent patches in monolayers viewed by scanning electron microscopy on day 3. These data indicate that alpha(3)- and beta(1)-integrin subunits are expressed in AEC monolayers where they form the heterodimeric alpha(3)beta(1)-integrin receptor at the cell membrane. Blockade of the alpha(3)-integrin subunit inhibits formation of confluent AEC monolayers. We conclude that the alpha(3)-integrin subunit modulates formation of AEC monolayers by virtue of the key role of the alpha(3)beta(1)-integrin receptor in AEC adhesion.

The epithelial integrin alphavbeta6 is a receptor for foot-and-mouth disease virus

Field isolates of foot-and-mouth disease virus (FMDV) have been shown to use the RGD-dependent integrin alphavbeta3 as a cellular receptor on cultured cells. However, several other RGD-dependent integrins may have the potential to act as receptors for FMDV in vivo. Of these, alphavbeta6 is a likely candidate for use as a receptor by FMDV as it is expressed on epithelial cells, which correlates with the tissue tropism of the virus. In this report, we show that human colon carcinoma cells (SW480) that are normally nonpermissive for FMDV become susceptible to infection as a result of transfection with the integrin beta6 subunit and expression of alphavbeta6 at the cell surface. Integrin alphavbeta6 is the major site for virus attachment on the beta6-transfected cells, and binding to alphavbeta6 serves to increase the rate of virus entry into these cells. In addition, we show that virus binding and infection of the beta6-transfected cells is mediated through an RGD-dependent interaction that is specifically inhibited by a monoclonal antibody (10D5) that recognizes alphavbeta6. These studies establish a role for alphavbeta6 as a cellular receptor for FMDV.

Foot-and-mouth disease virus is a ligand for the high-affinity binding conformation of integrin alpha5beta1: influence of the leucine residue within the RGDL motif on selectivity of integrin binding

Field isolates of foot-and-mouth disease virus (FMDV) use RGD-dependent integrins as receptors for internalization, whereas strains that are adapted for growth in cultured cell lines appear to be able to use alternative receptors like heparan sulphate proteoglycans (HSPG). The ligand-binding potential of integrins is regulated by changes in the conformation of their ectodomains and the ligand-binding state would be expected to be an important determinant of tropism for viruses that use integrins as cellular receptors. Currently, alphavbeta3 is the only integrin that has been shown to act as a receptor for FMDV. In this study, a solid-phase receptor-binding assay has been used to characterize the binding of FMDV to purified preparations of the human integrin alpha5beta1, in the absence of HSPG and other RGD-binding integrins. In this assay, binding of FMDV resembled authentic ligand binding to alpha5beta1 in its dependence on divalent cations and specific inhibition by RGD peptides. Most importantly, binding was found to be critically dependent on the conformation of the integrin, as virus bound only after induction of the high-affinity ligand-binding state. In addition, the identity of the amino acid residue immediately following the RGD motif is shown to influence differentially the ability of FMDV to bind integrins alpha5beta1 and alphavbeta3 and evidence is provided that alpha5beta1 might be an important FMDV receptor in vivo.

Histopathologic features of early and progressive asthma

During the last decade, morphologic studies on bronchial biopsy specimens have led to our present understanding of asthma as an inflammatory airways disease. However, little knowledge exists about the sequence of cellular events during the disease or of possible mucosal changes early in asthma. So far the primary cause, the site of damage, and the mechanisms inducing the inflammatory reaction remain to be elucidated. A multifactorial genetic susceptibility may be important for the development of asthma. Suggested factors that may trigger changes in the cells' morphologic and functional phenotype are viral infections, allergen exposure, maternal factors, diet, and smoking. Current evidence has implied that interactions between epithelial cells and the subepithelial connective tissue in the mucosa are important for normal homeostatic balance. Changes in airway epithelial phenotype possibly resulting from altered gene expression in its lining cells may be very important even as a first line change in asthma.

Vascular expression of the alpha(v)beta(3)-integrin in lung and other organs

The expression of the alpha(v)beta(3)-integrin in nonproliferating vascular beds remains unclear. To determine possible organ-specific differences, we compared alpha(v)beta(3)-integrin expression in the lung and other organs. Paraffin-embedded tissue sections of lung, liver, brain, muscle and skin obtained from rats were processed for immunohistochemistry with a monoclonal (LM609) and a polyclonal antibody (AB1903) against the alpha(v)beta(3)-integrin. Immunogold electron microscopy was used to localize alpha(v)beta(3)-integrin in rat lung microvasculature. With the use of custom-designed primers, lung sections were subjected to in situ PCR in a thermal cycler to amplify alpha(v) or beta(3) mRNA. To confirm specific amplification, PCR products were further hybridized in situ with an alpha(v) or beta(3) cDNA probe. In the lung, the alpha(v)beta(3)-integrin protein as well as alpha(v) and beta(3) mRNAs was extensively evident in the endothelium of extra-alveolar and alveolar microvessels, in vascular smooth muscle, and in large bronchial epithelium but not in the epithelium of alveolar ducts or alveoli. Ultrastructural immunogold labeling showed the presence of the integrin on the luminal and abluminal faces of the lung microvascular endothelium but not on the apical surface of the alveolar epithelium. Staining for the integrin was generally negative in blood vessels of several systemic organs, although weak staining was evident in branches of the hepatic portal vein. The constitutive presence of the alpha(v) and beta(3) mRNAs and the alpha(v)beta(3)-integrin in the lung microvascular bed suggests that gene transcription for the integrin is ongoing in lung vessels. Because it binds vitronectin, the lung vascular alpha(v)beta(3)-integrin may play a role in ligation of bloodborne, vitronectin-containing macromolecular complexes formed in inflammation.

Partial rescue of epithelial phenotype in integrin beta4 null mice by a keratin-5 promoter driven human integrin beta4 transgene

Integrin beta4 null mice exhibit extensive epidermal detachment, reminiscent of the human skin blistering disease junctional epidermolysis bullosa associated with pyloric atresia. Hemidesmosomes, the stable adhesion structures of squamous epithelia, are not formed in the absence of alpha6beta4. Null mutant mice die shortly after birth, but apart from their striking epithelial phenotype, no obvious developmental defects have been observed. To elucidate the cause of death in these mice, we generated transgenic mice with a heterologous construct consisting of the squamous epithelial-specific keratin-5 promoter and a human integrin beta4 subunit cDNA. The transgene was not expressed in the presence of endogenous beta4, probably as a result of competition for a limited pool of alpha6 subunits. In a beta4 null background, however, the transgene was expressed, and its expression pattern followed that of squamous epithelial-specific keratins. These rescued pups appeared healthy and ultrastructural analysis revealed that the interspecies heterodimer alpha6(mouse)/beta4(human) was sufficient to trigger the assembly of hemidesmosomes. After a variable period of up to 48 hours after birth these animals began to exhibit haemorrhages at the plantar and palmar areas. We observed the formation of small blisters and found that the transgene was not detectably expressed in this region, which is devoid of hair follicles. The rescued neonates became increasingly cyanotic and died soon after the onset of this phenomenon. We performed a developmental study of the expression of beta4 in the complete respiratory tract, but we found no correlation between the spatiotemporal distribution of beta4 and the onset of the respiratory insufficiency. It became clear, however, that there was a gradual detachment of squamous epithelia in the oral and nasal cavities which led to obstruction of the respiratory tract, suggesting that in beta4 null and rescued mice, neonatal death was a direct consequence of decreased adhesion properties of hairless squamous epithelia, rather than a developmental defect of the lungs.

Intracellular S-glutathionyl adducts in murine lung and human bronchoepithelial cells after exposure to diisocyanatotoluene

Diisocyanatotoluene (toluene diisocyanate, TDI), a 4:1 mixture of 2, 4- and 2,6-isomers used in the preparation of polyurethanes, causes occupational asthma by an as yet unknown mechanism. We previously showed that it forms adducts with the apical surface of the bronchoepithelium in vivo, and with ciliary microtubules in cultured human bronchoepithelial (HBE) cells. These results suggested that TDI may not enter HBE cells. In vitro studies, however, showed that TDI avidly forms bis adducts with glutathione (GSH) and that these adducts transfer monoisocyanato-monoglutathionyl-TDI to a sulfhydryl-containing peptide. This study sought to elucidate intracellular reactions of TDI. Using an electron paramagnetic resonance spectrometric (EPR) method, we established that the level of thiol-dependent quenching of phenoxyl radicals of etoposide was decreased >40% in pulmonary tissue of mice that received TDI intrabronchially. Similarly, HBE cells exposed to 100 ppb TDI vapor experienced a >30% reduction in thiol levels as determined with a thiol-specific fluorescent probe (ThioGlo 1). HPLC/UV analysis of lysates from HBE cells exposed to 200 and 500 ppb TDI vapor suggested a dose-related formation of S-glutathionyl adducts. Data from the 500 ppb TDI-treated HBE cells verified the identity of the 2-monoglutathionyl-4-monoisocyanato adduct. The results provide firm evidence that TDI enters pulmonary cells and reacts with GSH. This rapid reaction leading to formation of S-glutathionyl adducts of TDI suggests the importance of cellular thiols in TDI-induced pulmonary disease.

Selective expression of RT6 superfamily in human bronchial epithelial cells

RT6 proteins are glycosylphosphatidylinositol (GPI)-linked alloantigens that are localized to cytotoxic T lymphocytes and that have nicotinamide adenine dinucleotide glycohydrolase and adenosine diphosphate (ADP)-ribosyltransferase activities. In view of the importance of GPI-linked surface proteins in mediating interactions of cells with their milieu, and the varied functions of airway cells in inflammation, we undertook the present study to determine whether human homologues of the RT6 superfamily of ADP-ribosyltransferases (ART) are expressed in pulmonary epithelial cells. We hypothesized that these surface proteins or related family members may be present in cells that interact with inflammatory cells, and that they may thereby be involved in intercellular signaling. Using in situ analysis and Northern blot analysis, we identified ART1 messenger RNA (mRNA) in airway epithelial cells. As expected for GPI-anchored proteins, the localization of ART1 at the apical surface of ciliated epithelial cells was demonstrated by staining with polyclonal anti-ART1 antibody, and was confirmed by loss of this immunoreactivity after treatment with phosphatidylinositol-specific phospholipase C (PI-PLC), which selectively cleaves GPI anchors and releases proteins from the plasma membrane. Using in situ hybridization with specific ART3 and ART4 oligonucleotides, we also identified two additional members of the RT6 superfamily in epithelial cells. In accord with these findings, we identified ART3 and ART4 mRNAs through reverse transcription- polymerase chain reaction of polyadenine-positive RNA from human trachea. Interestingly, these proteins appeared to be preferentially localized to the airway epithelium. The localized expression of these members of the RT6 superfamily in human pulmonary epithelial cells may reflect a role for them in cell-cell signaling during immune responses within the airway.

Cadherin and catenin expression in normal human bronchial epithelium and non-small cell lung cancer

Cadherins are transmembrane cell adhesion molecules (CAMS) that mediate cell-cell interactions and are important for maintenance of epithelial cell integrity. This function is dependent on an indirect interaction between the cytoplasmic domain of the cadherin molecule with three cytoplasmic proteins known as alpha-, beta-, and gamma-catenin (-cat). Growing evidence suggests that alterations in cadherin or catenin expression or function may be important to the development of an invasive or metastatic phenotype. Immunohistochemical techniques were used to study the expression of the two major epithelial cadherins, E-cadherin (E-cad) and P-cadherin (P-cad) as well as alpha- and gamma-cat in normal bronchial epithelium and in a series of carefully TMN-staged pulmonary adenocarcinomas (n = 21) and squamous cell carcinomas (n = 7). The cadherin profile of normal pseudostratified bronchial epithelium was heterogeneous. Basilar cells strongly expressed P-cad, alpha- and gamma-cat, while columnar cells moderately expressed E-cad, alpha- and gamma-cat. In contrast to other epithelial tumors, E-cad on non-small cell lung carcinomas was actually upregulated, however, a decrease in P-cad expression was noted in 68%. At least one cadherin or catenin was downregulated, compared to normal bronchial epithelium, in 82% of tumors examined. With the exception of an association between loss of P-cad expression and poorly differentiated state, changes in cadherin and catenin expression levels were not significantly correlated to tumor stage, cell type, or nodal status. These findings illustrate that alteration of expression of cadherins and catenins are often found in non-small cell lung carcinoma when compared to the progenitor bronchial epithelium, and may play a role in the development of the malignant phenotype.

Interactions of soluble recombinant integrin alphav beta5 with human adenoviruses

alphav integrins have been identified as coreceptors for adenovirus (Ad) internalization; however, direct interactions of these molecules with Ad have not been demonstrated. We report here the expression of soluble integrin alphav beta5, which retains the ability to recognize the Ad penton base as well as vitronectin, an Arg Gly Asp (RGD)-containing extracellular matrix protein. Soluble integrin alphav beta5 reacted with seven different Ad serotypes (subgroups A to E) in solid-phase binding assays. The soluble integrin exhibited different levels of binding to each Ad serotype; however, binding to multiple Ad types required the presence of divalent metal cations and was inhibited by a synthetic RGD peptide, indicating that RGD and cation-binding sequences regulate Ad interactions with alphav beta5. Incubation of Ad particles with soluble alphav beta5 integrin also inhibited subsequent Ad internalization into epithelial cells as well as virus attachment to monocytic cells. These findings suggest that soluble alphav integrins or antagonists of these coreceptors could be used to limit infection by multiple Ad types. The generation of soluble alphav integrins should also permit further detailed kinetic and structural analysis of Ad interactions with its coreceptors.

Expression of epithelial markers in nocturnal asthma

BACKGROUND

Although the airway epithelium participates in inflammation and repair, the circadian expression of epithelial cell markers involved in these processes has not been investigated.

OBJECTIVE

We sought to determine whether expression of CD51 (vitronectin and fibronectin receptor), CD54 (intercellular adhesion molecule-1), HLA-DR (activation marker), CD29 (beta1 integrin), CD49b (collagen receptor), and CD11b (complement receptor) exhibit a circadian rhythm in asthma.

METHODS

Eleven patients with nocturnal asthma (NA), 9 subjects with nonnocturnal asthma (NNA), and 10 control subjects underwent bronchoscopy at 4 PM and 4 AM in a random order 1 week apart, with brushing of the proximal and distal airways. The percentage of cells staining for a particular marker was determined.

RESULTS

At 4 PM, HLA-DR in the proximal airways and CD54 in the distal airways was significantly greater in control subjects as compared with asthmatic subjects (HLA-DR, control subjects: 10.0% [range, 5.0% to 21.0%]; NNA: 8.0% [range, 4.0% to 14.5%] NA: 3.5% [range, 2.0% to 6.0%], P = .01; CD54, control subjects: 17.0% [range, 8.0% to 25.0%], NNA: 8.0% [range, 5.3% to 11.5%], NA: 7.0% [range, 4.0% to 15.0%], P = .O;). At 4 AM, CD51 in the distal airways was significantly greater in patients with NA as compared with patients with NNA and control subjects (control subjects, 23.0% [range, 13.8% to 30.5%]; NNA, 32.0% [range, 13.0% to 35.0%]; NA, 40.0% [range, 23.0% to 50.0%], P = .05). Expression of CD51 in the distal airways correlated with the degree of airway obstruction (r = -0.57, P = .001). Control subjects exhibited significant circadian variation in the expression of HLA-DR in the proximal airways and CD54 in the distal airways.

CONCLUSION

The increased CD51 at night in patients with NA may be related to increased airway inflammation and repair processes in response to injury. The circadian changes in CD54 and HLA-DR in control subjects require further study to determine their significance. (J Allergy Clin

Ozone alters the distribution of beta1 integrins in cultured primate bronchial epithelial cells

The effects of 0.5 ppm ozone exposure for 6 h on the synthesis and distribution of beta1 integrins were examined in bronchial epithelial cells cultured at an air-cell interface. Ozone exposure damaged cilia and caused significant cell loss. Immunocytochemical localization and quantification of the beta1 subunit in the remaining attached cells using scanning laser cytometry demonstrated time-dependent changes in beta1 distribution in response to ozone. Although no changes were detected immediately after exposure, beta1 immunoreactivity increased 23 +/- 5% and 66 +/- 6% at 6 and 24 h, respectively. The increased immunostaining was localized at the apical surfaces and, to a lesser extent, at cell-cell contacts of cultured cells. Furthermore, integrin redistribution was not due to increased messenger RNA (mRNA) levels and protein synthesis because levels of beta1 mRNA and newly synthesized beta1 protein did not change after ozone exposure. However, immunoprecipitation analysis of beta1 integrins in lysates from equal numbers of cells showed that ozone-exposed cells contained 90 +/- 15% more total beta1 subunit at 24 h after exposure. In addition, our results demonstrated the presence of the alpha5beta1 integrin complex in bronchial epithelial cells and that the detergent-soluble amount of its associated beta1 subunit increased 60 +/- 10% in lysates of ozone-exposed cells. In conclusion, ozone altered cellular distribution of beta1 integrins in the remaining attached cells subsequent to cell injury and loss. The changes in beta1 distribution might be due to increased detergent extractibility of beta1 integrins rather than a real increase in the synthesis of beta1 integrins.

Modulation of laminin integrin receptors in the postnatal and adult rat lung

Recent studies have shown that type II pneumocytes, at birth and day 3 postnatally, have a diffuse distribution and localize at alveolar 'corners' between 3 and 7 days. Since alpha 3 beta 1 and alpha 6 beta 1 are laminin-binding receptors that are well expressed by rat type II alveolar epithelial cells, we postulated that they may play a role in the localization of the cells in the alveolus. To begin the evaluation of this hypothesis, we studied the temporal and spatial expression of the alpha 3, alpha 6, and beta 1 integrin subunit protein and mRNA in whole rat lungs during postnatal development by immunofluorescence, confocal microscopy, and Northern blot analysis. The temporal expression of proteins analyzed by immunochemistry, with integrin subunit specific antibodies, increased during the 3- to 7-day postnatal period and in adult lungs. Densitometric values of the alpha 3, alpha 6, and beta 1 mRNA expression, normalized to 28S rRNA, quadrupled from day 1 to day 3 postnatally. The mRNA expression of different integrin chains was elevated 1.5- to threefold from days 5 to 7 postnatally compared to day 1 levels. The alpha 3 and alpha 6 integrin subunit mRNA decreased to newborn levels in adult lungs, whereas the beta 1 integrin mRNA in adult lungs was expressed at approximately 50% of its level in newborn lungs. We postulate that the increases in alpha 3, alpha 6, and beta 1 integrin mRNA expression during the early neonatal period may be important for the spatial distribution of type II pneumocytes.

Genomic organization of the human alpha 3 integrin subunit gene

The alpha 3 beta 1 integrin is a receptor for various laminin isoforms and plays an important role in the maintenance of tissue integrity. We have characterized the genomic structure of the complete gene for the human alpha 3 integrin subunit. The gene contains 26 exons spanning a region of 36.3 kb of genomic DNA. Its structure closely resembles that of alpha 6, another of the three integrin alpha-subunits that are part of laminin receptors, except that it lacks the corresponding exon 5A, which encodes an X1 region in the extracellular domain of alpha 6. However, the alpha 3 gene contains the equivalent of an exon 5B for an X2-like region, which in alpha 6 and alpha 7 is present only in certain tissue-specific alternative transcripts. The two A and B cytoplasmic variants of alpha 3, which are common to the three laminin receptor integrin alpha-subunits, are encoded by separate exons.

Adhesive characteristics of type II pneumocyte subpopulations from saline- and silica-treated rats

Alveolar epithelial cells isolated from silica-treated rat lungs provide a system for the in vitro study of repair mechanisms. In studies of type II cell interactions with the extracellular matrix, we observed that type IIB pneumocytes from silica-treated rats adhered to tissue culture plastic more readily than do normal type II cells. This paper examines the adhesion characteristics of IIA and IIB cells and their modulation by divalent cations. We describe differences in the adhesive behavior of two subpopulations of freshly isolated type II pneumocytes from saline- and silica-treated rats. The observations have implications for repair and tissue remodeling in the lung.

Foot-and-mouth disease virus virulent for cattle utilizes the integrin alpha(v)beta3 as its receptor

Adsorption and plaque formation of foot-and-mouth disease virus (FMDV) serotype A12 are inhibited by antibodies to the integrin alpha(v)beta3 (A. Berinstein et al., J. Virol. 69:2664-2666, 1995). A human cell line, K562, which does not normally express alpha(v)beta3 cannot replicate this serotype unless cells are transfected with cDNAs encoding this integrin (K562-alpha(v)beta3 cells). In contrast, we found that a tissue culture-propagated FMDV, type O1BFS, was able to replicate in nontransfected K562 cells, and replication was not inhibited by antibodies to the endogenously expressed integrin alpha5beta1. A recent report indicating that cell surface heparan sulfate (HS) was required for efficient infection of type O1 (T. Jackson et al., J. Virol. 70:5282-5287, 1996) led us to examine the role of HS and alpha(v)beta3 in FMDV infection. We transfected normal CHO cells, which express HS but not alpha(v)beta3, and two HS-deficient CHO cell lines with cDNAs encoding human alpha(v)beta3, producing a panel of cells that expressed one or both receptors. In these cells, type A12 replication was dependent on expression of alpha(v)beta3, whereas type O1BFS replicated to high titer in normal CHO cells but could not replicate in HS-deficient cells even when they expressed alpha(v)beta3. We have also analyzed two genetically engineered variants of type O1Campos, vCRM4, which has greatly reduced virulence in cattle and can bind to heparin-Sepharose columns, and vCRM8, which is highly virulent in cattle and cannot bind to heparin-Sepharose. vCRM4 replicated in wild-type K562 cells and normal, nontransfected CHO (HS+ alpha(v)beta3-) cells, whereas vCRM8 replicated only in K562 and CHO cells transfected with alpha(v)beta3 cDNAs. A similar result was also obtained in assays using a vCRM4 virus with an engineered RGD-->KGE mutation. These results indicate that virulent FMDV utilizes the alpha(v)beta3 integrin as a primary receptor for infection and that adaptation of type O1 virus to cell culture results in the ability of the virus to utilize HS as a receptor and a concomitant loss of virulence.

Isolation and characterization of basal cells from human upper respiratory epithelium

Cellular pathways of normal and reparative differentiation of upper airway epithelium are not well understood. Of the three main cell types, basal and secretory cells are known to divide, while ciliated cells are considered terminally differentiated. Several investigations support the role of the basal cell as a progenitor cell type, but others suggest that the secretory cell can regenerate a complete mucocilliary epithelium. Thus, lineage relationships within renewing adult epithelia are still unclear. Understanding the pathways involved in upper airway epithelial cell differentiation is critical for studying injury and repair mechanisms and for developing clinical strategies for tracheal reconstruction. We undertook the current studies to determine the integrin profile of isolated human upper airway basal cells. Respiratory epithelial cells (REC) were isolated by elastase digestion, stained with FITC-labeled Griffonia simplicifolia isolectin B4 (GSI-B4), and sorted by flow cytometry. Approximately 80% of the lectin-positive cells were basal cells, as determined by morphology and cytokeratin staining. These cells expressed integrins alpha 1, alpha 2, alpha 3, alpha 5, alpha v beta 5, beta 1, beta 3, and alpha 6 beta 4, by immunohistochemistry. This is the first report to identify the integrin profile of isolated human upper airway basal cells. These basal cells could be maintained on type I collagen for at least 7 days, where they became partially confluent and retained expression of cytokeratins 5 and 14. Availability of pure populations of basal cells should permit investigations of their role in both normal and maladaptive repair of adult upper airway epithelium.