Cigarette smoke disrupts the integrity of airway adherens junctions through the aberrant interaction of p120-catenin with the cytoplasmic tail of MUC1

Adherens junctions (AJs) containing epithelial cadherin (E-cad) bound to p120-catenin (p120ctn) and β-catenin (β-ctn) play a crucial role in regulating cell-cell adhesion. Cigarette smoke abrogates cell-cell adhesion between epithelial cells by disrupting E-cad, a hallmark of epithelial-mesenchymal transition (EMT), yet the underlying mechanism remains unknown. We used an organotypic culture of primary human bronchial epithelial (HBE) cells treated with smoke-concentrated medium (Smk) to establish an essential role for the interaction between p120ctn and the cytoplasmic tail of MUC1 (MUC1-CT) in regulating E-cad disruption. Within the first 4 h of smoke exposure, apical MUC1-CT repositioned to the basolateral membrane of pseudo-stratified HBE cells, where it interacted with p120ctn. A time-dependent increase in MUC1-CT/p120ctn complexes occurred in conjunction with a time-dependent dissociation of p120ctn/E-cad/β-ctn complexes, as well as the coordinated degradation of p120ctn and E-cad. Interestingly, Smk induced a similar interaction between MUC1-CT and β-ctn, but this occurred 44 h after MUC1-CT's initial interaction with p120ctn, and well after the AJs were destroyed. Blocking MUC1-CT's interaction with p120ctn using a MUC1-CT dominant-negative peptide, PMIP, successfully abolished Smk's disruptive effects on AJs and recovered apical-basolateral polarity of HBE cells. The MUC1-CT/p120ctn interaction was highly dependent on EGFR/Src/Jnk-mediated tyrosine phosphorylation (TyrP) of MUC1-CT. Accordingly, EGFR, Src or Jnk inhibitors (AG1478, PP2, SP600125, respectively) abrogated Smk-induced MUC1-CT-TyrP, MUC1-CT/p120ctn interaction, AJ disruption, and loss of cellular polarity. Our work identified MUC1-CT and p120ctn as important regulators of epithelial polarity and cell-cell adhesion during a smoke-induced EMT-like process. Novel therapeutics designed to inhibit MUC1-CT/p120ctn complex formation may prevent EMT in the smoker's airway.

TACE/ADAM-17 phosphorylation by PKC-epsilon mediates premalignant changes in tobacco smoke-exposed lung cells

BACKGROUND

Tobacco smoke predisposes humans and animals to develop lung tumors, but the molecular events responsible for this are poorly understood. We recently showed that signaling mechanisms triggered by smoke in lung cells could lead to the activation of a growth factor signaling pathway, thereby promoting hyperproliferation of lung epithelial cells. Hyperproliferation is considered a premalignant change in the lung, in that increased rates of DNA synthesis are associated with an increased number of DNA copying errors, events that are exacerbated in the presence of tobacco smoke carcinogens. Despite the existence of DNA repair mechanisms, a small percentage of these errors go unrepaired and can lead to tumorigenic mutations. The results of our previous study showed that an early event following smoke exposure was the generation of oxygen radicals through the activation of NADPH oxidase. Although it was clear that these radicals transduced signals through the epidermal growth factor receptor (EGFR), and that this was mediated by TACE-dependent cleavage of amphiregulin, it remained uncertain how oxygen radicals were able to activate TACE.

PRINCIPAL FINDINGS

In the present study, we demonstrate for the first time that phosphorylation of TACE at serine/threonine residues by tobacco smoke induces amphiregulin release and EGFR activation. TACE phosphorylation is triggered in smoke-exposed lung cells by the ROS-induced activation of PKC through the action of SRC kinase. Furthermore, we identified PKCε as the PKC isoform involved in smoke-induced TACE activation and hyperproliferation of lung cells.

CONCLUSIONS

Our data elucidate new signaling paradigms by which tobacco smoke promotes TACE activation and hyperproliferation of lung cells.

Leukotriene D4 upregulates MUC2 gene transcription in human epithelial cells

BACKGROUND/AIMS

Leukotriene (LT) D(4) has been shown to induce mucus secretion in the airways. Excessive mucus secretion characterizes airway inflammatory disease such as asthma, allergic rhinitis. However, little is known about the effect of LTD(4) on mucin gene expression. The aim of this study was to investigate the effect of LTD(4) on MUC2 gene expression in cultured epithelial cells (HM3-MUC2 cells).

METHODS

HM3-MUC2 cells were treated with LTD(4) for 2 or 6 h. Reporter gene assay was mainly used for analysis.MUC2 protein levels were measured using an enzyme-linked immunosorbent assay.

RESULTS

LTD(4) significantly increased MUC2 gene transcriptional activity in a dose-dependent manner. Pranlukast, which is a selective antagonist of CysLT(1) receptor, inhibited LTD(4)-induced MUC2 gene transcriptional activity in a dose-dependent manner. LTD(4)-induced MUC2 gene transcriptional activity was also suppressed by a G-protein inhibitor (pertussis toxin),a protein kinase C (PKC) inhibitor (bisindolylmaleimide), a mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) inhibitor (PD98059), an extracellular signal regulated kinase-2 (ERK-2) inhibitor (AG126) and a nuclear factor kappaB (NF-kappaB) inhibitor. In addition, pranlukast inhibited LTD(4)-induced NF-kappaB activity.

CONCLUSION

These results suggest that LTD(4 )upregulates MUC2 gene transcription via a signaling pathway involving CysLT(1) receptor, G-protein, PKC, MEK, ERK and NF-kappaB.

Exposure of human corneal epithelial cells to contact lenses in vitro suppresses the upregulation of human β-defensin-2 in response to antigens of Pseudomonas aeruginosa

Bacterial keratitis is a sight-threatening complication of contact lens wear, and Pseudomonas aeruginosa is a commonly isolated pathogen. The mechanisms by which lenses predispose the cornea to P. aeruginosa infection are unknown. Corneal epithelial cells express numerous innate defenses, some of which have bactericidal effects against P. aeruginosa. One of these is human beta-defensin-2 (hBD-2), which is upregulated in response to lipopolysaccharide or flagellin antigens. We hypothesized that prior exposure of corneal epithelia to a contact lens would interfere with upregulation of hBD-2 in response to P. aeruginosa. A novel in vitro model was used in which cultured human corneal epithelial cells were exposed to a hydrophilic contact lens for up to 3.5 days prior to challenge with a culture supernatant of P. aeruginosa antigens for 6h. Without prior lens exposure, the supernatant caused >2-fold upregulation of hBD-2 mRNA message and expression of hBD-2 peptide. Prior contact lens exposure blocked this upregulation without obvious effects on cell health. Western immunoblot and luciferase reporter studies showed that Pseudomonas-induced hBD-2 upregulation involved MyD88, c-Jun N-terminal kinase and both AP-1 and NF-kappaB transcription factors. Contact lenses did not affect surface expression of Toll-like receptor-2, -4 or -5, but did block antigen activation of AP-1, but not NF-kappaB, transcription factors. These data show that contact lenses can interfere with epithelial defense responses to bacterial antigens in vitro, and if translated in vivo, could help predispose the cornea to infection.

Wnt and Hedgehog are critical mediators of cigarette smoke-induced lung cancer

Background

Lung cancer is the leading cause of cancer death in the world, and greater than 90% of lung cancers are cigarette smoke-related. Current treatment options are inadequate, because the molecular basis of cigarette-induced lung cancer is poorly understood.

Methodology/Principal Findings

Here, we show that human primary or immortalized bronchial epithelial cells exposed to cigarette smoke for eight days in culture rapidly proliferate, show anchorage-independent growth, and form tumors in nude mice. Using this model of the early stages of smoke-induced tumorigenesis, we examined the molecular changes leading to lung cancer. We observed that the embryonic signaling pathways mediated by Hedgehog and Wnt are activated by smoke. Pharmacological inhibition of these pathways blocked the transformed phenotype.

Conclusions/Significance

These experiments provide a model in which the early stages of smoke-induced tumorigenesis can be elicited, and should permit us to identify molecular changes driving this process. Results obtained so far indicate that smoke-induced lung tumors are driven by activation of two embryonic regulatory pathways, Hedgehog (Hh) and Wnt. Based on the current and emerging availability of drugs to inhibit Hh and Wnt signaling, it is possible that an understanding of the role of Hh and Wnt in lung cancer pathogenesis will lead to the development of new therapies.

AsialoGM1 and TLR5 cooperate in flagellin-induced nucleotide signaling to activate Erk1/2

Bacterial flagellin can interact with both Toll-like receptor 5 (TLR5) and the cell surface glycolipid, asialoGM1, to activate an innate immune response. The induction of mucin by flagellin in human lung epithelial cells (NCIH292) is dependent on asialoGM1 ligation, ATP receptor signaling, Ca2+ mobilization, and Erk1/2 activation. Conversely, the activation of NF-kappaB by flagellin is dependent on signaling through TLR5. These results prompted us to ask whether the flagellin-induced TLR5 signaling pathway was intersecting with or mutually independent of the nucleotide receptor pathway activated downstream of asialoGM1. Herein, we demonstrate that the release of ATP induced by flagellin is dependent on a Toll signaling cascade. Although Toll was able to activate NF-kappaB in the absence of extracellular ATP, Toll required ATP to activate Erk1/2. These results suggest interdependence between the asialoGM1 and TLR5 pathways and reveal a previously unsuspected role for autocrine extracellular ATP signaling in TLR signaling.

Immune complex-dependent remodeling of the airway vasculature in response to a chronic bacterial infection

Chronic inflammation in the airways is associated with dramatic architectural changes in the walls of the airways and in the vasculature they contain. In this study, we show that the adaptive immune system is essential for airway remodeling that occurs in mice that are chronically infected with the respiratory pathogen Mycoplasma pulmonis. Angiogenesis, lymphangiogenesis, and epithelial remodeling were greatly reduced in mice that lacked B cells. Substantiating a role for Ab and airway immune complexes, we found that the transfer of immune serum to B cell-deficient mice could reconstitute pathogen-induced angiogenesis. Inflammatory cells recruited to the infected airways were activated by the humoral response, and this activation correlated with the induction of genes for remodeling factors such as vascular endothelial growth factor-D. The results reveal a novel pathway whereby T cell-dependent humoral immunity to a persistent airway infection can induce inflammation-dependent angiogenesis, lymphangiogenesis, and chronic airway pathology.

New HIV-Drug Inhibits In Vitro Bladder Cancer Migration and Invasion

OBJECTIVE

The CXCR4/CXCL12 axis appears crucial in the metastasis of bladder cancer. Our aim was to evaluate the potency of the CXCR4 antagonist, 4F-benzoyl-TE14011 (4F-bTE), as an anti-metastatic drug in this disease. In this study, we assessed the ability of 4F-bTE to inhibit tumor cell motility, invasion through extracellular matrix (ECM), matrix metalloproteinase (MMP) secretion and cytoskeletal responses to chemokine.

METHODS

To assess the degree to which cells could migrate and invade ECM under various conditions, we used TCCSUP bladder cancer cells in a Boyden chamber system. To monitor actin polymerization, we stained cells on chamber slides with AlexaFluor 594 phalloidin. To measure matrix-metalloproteinase-2 and -9 (MMP) activity, we used gelatin zymography. To assess the effects of the CXCR4 antagonist 4F-bTE on each of the above parameters, we exposed bladder cancer cells either to chemokine CXCL12, alone, or to both CXCL12 and 4F-bTE. We also monitored cells for apoptotic and necrotic changes during drug treatment.

RESULTS

The CXCR4 antagonist 4F-bTE markedly decreased CXCL12-induced bladder cancer cell migration and ECM invasion in Boyden chamber assays. The antagonist also blocked chemokine-induced actin polymerization as well as the induction of MMP-2 and MMP-9 in these cells.

CONCLUSION

The CXCR4 antagonist 4F-bTE has the potential to inhibit expression of the metastatic phenotype and may provide therapeutic value to patients.

CXCR4 expression reflects tumor progression and regulates motility of bladder cancer cells

Transitional cell carcinoma of the urinary bladder remains life threatening due to the high occurrence of metastases. Emerging evidence suggests that chemokines and their receptors play a critical role in tumor metastases. In our study, we performed a systematic analysis of the mRNA and protein expression levels of all 18 chemokine receptors in normal urothelium and bladder cancer. CXCR4 was the only chemokine receptor whose mRNA expression level was upregulated in bladder cancer cell lines as well as in invasive and locally advanced bladder cancer tissue samples (pT2-pT4). In contrast, superficial bladder tumors (pTa and pT1) displayed low CXCR4 expression levels and normal urothelial cells were negative for CXCR4. Immunohistochemistry of a bladder cancer tissue microarray (TMA) confirmed that a subgroup of invasive bladder cancers revealed a high CXCR4 protein expression, while superficial bladder tumors showed low immunoreactivity. To investigate the functional significance of CXCR4 expression, we performed migration and invasion assays. Exposure of CXCR4-positive bladder cancer cells to CXCL12 in a Boyden chamber type assay provoked a significant increase in migration as well as invasion across a Matrigel barrier. Enhanced migration and invasion were inhibited by a CXCR4-specific blocking antibody. In contrast, normal urothelial cells did not respond to CXCL12 and lacked chemotactic migration. In conclusion, bladder cancer cells express CXCR4 progressively with advanced tumorigenesis and this receptor interacts with CXCL12 to mediate tumor chemotaxis and invasion through connective tissue. These properties identify CXCR4 as a potential target for the attenuation of bladder cancer metastases.

Sp1 is involved in the transcriptional activation of lysozyme in epithelial cells

Lysozyme protects us from the ever-present danger of bacterial infection. The expression of lysozyme is, in part, regulated by the Ets factor, myeloid elf-1-like factor (MEF). MEF binds to the ETS site of the lysozyme promoter at -46 to -40bp. Closer analysis of the promoter using a series of deletion mutants and point mutants indicated that the region around -75bp is also essential in regulating the activity of lysozyme. The sequences in this region correspond to the Sp1 consensus binding site. Sp1 is known to regulate a variety of house-keeping and tissue-specific genes by itself or with other transcription factors like AP-1 or ETS. We indicate here that Sp1 regulates the lysozyme gene by binding to the GT-core sequences of lysozyme promoter. Treatment with mithramycin A down-regulated the promoter activity and the transfection of anti-sense Sp1 induced a decrease in the endogenous expression of lysozyme.

Pranlukast inhibits NF-kappaB activation and MUC2 gene expression in cultured human epithelial cells

Pranlukast is a selective cysteinyl leukotriene(1 )(cysLT(1)) receptor antagonist, and is now widely used in the treatment of asthma. The anti-asthmatic effect of pranlukast may be rendered not only by antileukotriene activity, but also by other pharmacological activity. This study was designed to investigate whether pranlukast had inhibitory effects on nuclear factor-kappaB (NF-kappaB) activation and mucin gene expression in cultured human epithelial cells. Luciferase assay was mainly used for analysis. Cultured epithelial cells were transfected with NF-kappaB luciferase vector, MUC2 or MUC5AC luciferase vectors. Lipopolysaccharide (LPS) significantly increased NF-kappaB activation in NCI-H292 cells, which was inhibited by the pretreatment by pranlukast in a dose-dependent manner. Either LTD(4) or pranlukast alone did not increase NF-kappaB activation in NCI-H292 cells. Pranlukast also inhibited NF-kappaB activation induced by phorbol 12-myristate 13-acetate (PMA). Pranlukast also significantly inhibited LPS-induced MUC2 mRNA expression by reverse transcription-polymerase chain reaction (RT-PCR) analysis in NCI-H292 cells. Pranlukast also inhibited LPS-induced MUC2 gene expression in HM3-MUC2 cells. However, pranlukast did not inhibit MUC5AC gene transcription activity induced by lipoteichoic acid (LTA) in NCI-H292 cells. These results suggest that pranlukast may inhibit NF-kappaB activation and MUC2 gene transcription through pathways distinct from cysLT(1) receptor antagonism in cultured human epithelial cells.

Tobacco smoke control of mucin production in lung cells requires oxygen radicals AP-1 and JNK

In smokers' lungs, excessive mucus clogs small airways, impairing respiration and promoting recurrent infection. A breakthrough in understanding this pathology was the realization that smoke could directly stimulate mucin synthesis in lung epithelial cells and that this phenomenon was dependent on the cell surface receptor for epidermal growth factor, EGFR. Distal steps in the smoke-triggered pathway have not yet been determined. We report here that the predominant airway mucin (MUC5AC) undergoes transcriptional up-regulation in response to tobacco smoke; this is mediated by an AP-1-containing response element, which binds JunD and Fra-2. These transcription factors require phosphorylation by upstream kinases JNK and ERK, respectively. Whereas ERK activation results from the upstream activation of EGFR, JNK activation is chiefly EGFR-independent. Our experiments demonstrated that smoke activates JNK via a Src-dependent, EGFR-independent signaling cascade initiated by smoke-induced reactive oxygen species. Taken together with our earlier results, these data indicate that the induction of mucin by smoke is the combined effect of mutually independent, reactive oxygen species activation of both EGFR and JNK.

Adenosine up-regulation of the mucin gene, MUC2, in asthma

Mucus hypersecretion is a hallmark of asthma that contributes to airway obstruction. While the etiology is not well understood, hypersecretion has been linked to the presence of cytokines such as IL-4, IL-5, IL-9, and IL-13 in the inflamed airway. The presence of adenosine has also been noted in asthmatic airways, and adenosine-mediated signaling in mast cells has been implicated in the severe bronchoconstriction and inflammation prevalent in these patients (1, 2). Here we examine the possibility that adenosine also contributes to mucus hypersecretion by airway epithelial cells. Results in cultured airway epithelial cells showed that MUC2 mucin expression increased in response to adenosine. This appeared to be mediated by a pathway initiated at the adenosine A1 receptor that transduced signals through a Ca2+-activated Cl- channel and EGFR. That this signaling cascade is relevant to asthmatic hypersecretion was indicated by results showing that mucin induction by asthmatic tracheal aspirates was reduced by A1, CLCA1, and EGFR inhibitors. These results suggest that adenosine cooperates with inflammatory cytokines to stimulate mucin production in the asthmatic airway and supports the use of A1, CLCA1, and EGFR inhibitors in the treatment of asthma.

Roxithromycin Suppresses Mucin Gene Expression in Epithelial Cells

Macrolide antibiotics are believed to inhibit mucus secretion but the mechanism of action is unclear. This study was designed to investigate an effect of roxithromycin on MUC2 gene expression in cultured intestinal epithelial cells (HM3-MUC2 cells). A reporter gene assay was used for analysis. Roxithromycin suppressed MUC2 gene transcriptional activity in a dose-dependent manner in HM3-MUC2 cells. Phorbol 12-myristate 13-acetate (PMA), lipoteichoic acid (LTA), lipopolysaccharide (LPS) and leukotriene D4 (LTD4) significantly increased MUC2 luciferase activities in the following order: PMA > LTA > LTD4 > LPS. Roxithromycin also decreased MUC2 gene transcriptional activity induced by PMA in a dose-dependent manner. NF-kappaB activation, but not AP-1 activation, was significantly suppressed by roxithromycin in HM3-MUC2 cells. A suppression of NF-kappaB activation was also observed in NCI-H292 cells. These results suggest that roxithromycin suppresses MUC2 gene expression in epithelial cells and that this suppression is probably via inhibition of NF-kappaB activation.

The microvesicle as a vehicle for EMMPRIN in tumor-stromal interactions

EMMPRIN is a transmembrane glycoprotein expressed at high levels by tumor cells. It has been identified as a tumor-derived factor that can stimulate matrix metalloproteinase expression in fibroblasts and hence facilitate tumor invasion and metastasis. Recent studies have shown that full-length EMMPRIN is released by tumor cells, but the mechanism of release remains unclear. Here, we show that EMMPRIN is released from the surface of NCI-H460 cells via microvesicle shedding. However, these vesicles are unstable and rapidly break down to release bioactive EMMPRIN. Although microvesicle shedding has been considered a constitutive process in tumor cells, our data show that it can be amplified upon cell exposure to PMA, elucidating at least one signalling cascade responsible for EMMPRIN release. This pathway is dependent on protein kinase C, calcium mobilization and mitogen-activated protein kinase kinase (MEK 1/2). Thus, the results outline a novel form of tumor-stromal interaction in which extracellular matrix degradation by fibroblasts is controlled through the microvesicular release of EMMPRIN from tumor cells.

Detection of Occult Tumor Cells in Lymph Nodes from Bladder Cancer Patients by MUC7 Nested RT-PCR

OBJECTIVE

Systemic progression is the prevalent form of bladder tumor recurrence after radical cystectomy. The detection of occult bladder tumor cells in histopathologically normal lymph nodes could be of prognostic value. We examined the possibility that mucin 7 (MUC7) RNA might reflect the presence of occult tumor cells in lymph nodes from bladder cancer patients. We used the polymerase chain reaction (RT-PCR), a highly sensitive assay, to monitor MUC7 RNA.

METHODS

We collected 240 pelvic lymph nodes from 25 bladder cancer patients undergoing radical cystectomy. We also obtained 20 lymph nodes from patients with prostate cancer and interstitial cystitis to use as negative controls. Each lymph node was divided in two parts to provide tissue for both histopathological and PCR analysis.

RESULTS

166/240 lymph nodes from bladder cancer patients were usable for MUC7 RT-PCR. By conventional histopathology, six of these nodes contained metastases. MUC7 RT-PCR analysis was positive for five of the six histologically proven lymph node metastases. Histopathological reevaluation of the sixth node revealed tumor in an adjacent vein, not in the lymph node, itself. In contrast, 46/160 (29%) histologically classified normal lymph nodes (pN0) from 17 bladder cancer patients were positive for MUC7. All 20 lymph nodes from control patients were MUC7-negative.

CONCLUSION

MUC7 RT-PCR is a specific and sensitive method for the detection of occult tumor cells in lymph nodes from bladder cancer patients. Long-term observation will be necessary to evaluate the clinical value of MUC7 as a prognostic indicator of lymph node metastasis and disease progression.

Viral dsRNA activates mucin transcription in airway epithelial cells

Double-stranded (ds) RNA is a biologically active component of many viruses including rhinoviruses infecting the upper respiratory tract. Mucus production is a common symptom of such infections. Here, we show that mucin, the glycoprotein subunit of mucus gels, is transcriptionally upregulated in an NF-kappaB- and p38-dependent manner when homogeneous cultures of epithelial cells are exposed to dsRNA. Furthermore, upstream of p38 in this system, dsRNA stimulates the extracellular release of ATP and activation of cell surface ATP receptors, which are G protein-coupled. This results in the stimulation of phospholipase C and protein kinase C. These findings suggest that ATP receptor antagonists could be used to modulate mucus production induced by virus.

Toxicity of chemical components of fine particles inhaled by aged rats: effects of concentration

This study tested the hypothesis that exposure to mixtures containing fine particles and ozone (O3) would cause pulmonary injury and decrements in functions of immunological cells in exposed rats (22-24 months old) in a dose-dependent manner. Rats were exposed to high and low concentrations of ammonium bisulfate and elemental carbon and to 0.2 ppm O3. Control groups were exposed to purified air or O3 alone. The biological end points measured included histopathological markers of lung injury, bronchoalveolar lung fluid proteins, and measures of the function of the lung's innate immunological defenses (macrophage antigen-directed phagocytosis and respiratory burst activity). Exposure to O3 alone at 0.2 ppm did not result in significant changes in any of the measured end points. Exposures to the particle mixtures plus O3 produced statistically significant changes consistent with adverse effects. The low-concentration mixture produced effects that were statistically significant compared to purified air but, with the exception of macrophage Fc receptor binding, exposure to the high-concentration mixture did not. The effects of the low- and high-concentration mixtures were not significantly different. The study supports previous work that indicated that particle + O3 mixtures were more toxic than O3 alone.

Tobacco smoke-induced lung cell proliferation mediated by tumor necrosis factor alpha-converting enzyme and amphiregulin

Cells dividing at the time of carcinogen exposure are at particular risk for neoplasia. Tobacco smoke contains numerous carcinogens, and we find that smoke, in the absence of exogenous growth factors, is capable of stimulating cell proliferation. The smoke-triggered mechanism includes the generation of oxygen radicals, which in turn stimulate tumor necrosis factor alpha-converting enzyme (a disintegrin and metalloproteinase (ADAM) 17) to cleave transmembrane amphiregulin, a ligand for the epidermal growth factor receptor (EGFR). The binding of amphiregulin to EGFR then stimulates proliferation of lung epithelial cells. These results shed light on the pathogenesis of lung cancer, suggest novel drug targets for the reduction of cancer risk in smokers, and provide insight into how EGFR integrates responses to diverse noxious stimuli.

Mechanisms by which gram-positive bacteria and tobacco smoke stimulate mucin induction through the epidermal growth factor receptor (EGFR)

Mucin, the major macromolecular component of mucus, is generally considered to be a protective substance. When overproduced in a variety of lung diseases, however, mucin gives rise to clinical problems such as airway obstruction and recurrent infection. Our approach to identifying drug targets for the control of mucin overproduction is the analysis of cellular signalling pathways linking stimuli in the diseased lung to mucin transcription. Here we show that mucin transcription in response to both gram-positive bacteria and tobacco smoke is mediated through activation of the epidermal growth factor receptor (EGFR). The mode of activation of EGFR in response to bacterial lipoteichoic acid involves cleavage of the transmembrane ligand HBEGF by ADAM 10, whereas the activation of EGFR in response to smoke involves cleavage of amphiregulin by ADAM 17.

Platelet-activating factor receptor and ADAM10 mediate responses to Staphylococcus aureus in epithelial cells

In the lungs of cystic fibrosis patients, overproduction of mucus leads to morbidity and mortality by obstructing airflow and shielding bacteria from antibiotics. Here we demonstrate that overproduction of mucus is a direct result of the activation of mucin gene expression by Gram-positive bacteria. Bacterial lipoteichoic acid activates the platelet-activating factor receptor, which is G protein-coupled. This results in activation of a disintegrin and metalloproteinase (ADAM10), kuzbanian, cleavage of pro heparin-binding epidermal growth factor and activation of the epidermal growth factor receptor. Unlike responses in macrophages, the epithelial-cell response to lipoteichoic acid does not require Toll-like receptor 2 or 4.

Signaling networks controlling mucin production in response to Gram-positive and Gram-negative bacteria

Human lung cells exposed to pathogenic bacteria upregulate the production of mucin, the major macromolecular component of mucus. Generally this upregulation is beneficial for the host, however, in the lungs of cystic fibrosis patients, overproduction of mucin can lead to the plugging of pulmonary airways. Mucus plugging impedes airflow and creates an environment that is highly compartmentalized: those bacteria within the mucus layer are shielded from high doses of antibiotics whereas those outside the mucus are exposed. These conditions augment mutation rate and the development of drug resistance in bacteria that colonize the lungs of cystic fibrosis patients. While therapeutic inhibition of mucin induction would improve airflow and reduce antibiotic resistance in these patients, the challenge is to develop drugs that block excessive mucin production while leaving beneficial aspects of the response intact. To do this, we must understand the molecular mechanisms underlying mucin production. Here we review the signal transduction pathways that control mucin production in response to Gram-positive and Gram-negative bacteria.

ATP transduces signals from ASGM1, a glycolipid that functions as a bacterial receptor

The flagella of the Gram-negative bacterium Pseudomonas aeruginosa serve not only for motility but also to bind bacteria to the host cell glycolipid asialoGM1 (ASGM1) through the protein flagellin. This interaction triggers defensive responses in host cells. How this response occurs is unclear because ASGM1 lacks transmembrane and cytoplasmic domains and there is little information about the downstream effectors that connect ASGM1 ligation to the initiation of host defense responses. Here, we show that ASGM1 ligation promotes ATP release from the host cell, followed by autocrine activation of a nucleotide receptor. This response links ASGM1 to cytoplasmic signaling molecules and results in activation of phospholipase C, Ca(2+) mobilization, phosphorylation of a mitogen-activated protein kinase (Erk 1/2), and activation of mucin transcription. These results indicate that bacterial interaction with host cells can trigger autocrine nucleotide signaling and suggest that agents affecting nucleotide receptors may modulate host responses to bacteria.

Regulation of mucin gene expression in human tracheobronchial epithelial cells by thyroid hormone

We reported previously that the expression of the gene encoding MUC5AC mucin in human airway epithelial cells is controlled by retinoic acid via the retinoic acid receptor (RAR)-alpha and that 3,3',5-tri-iodothyronine (T(3)) inhibits the expression of MUC5AC. The purpose of the present study was to identify mechanisms mediating the effect of T(3). T(3) has been shown to inhibit gene expression via several mechanisms, either by enhancing or repressing the transcription of target genes or by the regulation of post-transcriptional events. Results showed that T(3) strongly inhibited MUC5AC-driven luciferase activity in normal human tracheobronchial epithelial cells that had been transiently transfected with a MUC5AC-luciferase reporter construct; however, it did not affect MUC5AC mRNA stability. These results indicate that T(3) suppresses MUC5AC expression at the transcriptional level. An analysis of deletion constructs showed that deletion of the region downstream of 3 kb resulted in markedly decreased levels of MUC5AC transcription in the absence of T(3) (i.e. under control conditions) as well as a loss of responsiveness to the inhibitory effects of T(3). This suggests that this region might contain elements important for the activation as well as the repression of MUC5AC transcription. To determine whether T(3) modulates retinoic-acid-dependent MUC5AC transcription via an alteration in the abundance of retinoid receptor proteins, we examined the type and abundance of these receptors in nuclear extracts of airway epithelial cells grown in the presence or absence of T(3). Western blots showed that T(3) markedly decreased several types of retinoid receptor while not affecting T(3) receptor proteins. Consistent with this finding were gel-shift assays revealing a decrease in RAR-retinoic acid response element complexes obtained from T(3)-treated cells. We propose that T(3) might inhibit retinoid-dependent MUC5AC expression by decreasing retinoid receptor levels and thereby decreasing the transcriptional activation of this gene for mucins.

The transcriptional responses of respiratory epithelial cells to Bordetella pertussis reveal host defensive and pathogen counter-defensive strategies

Bordetella pertussis, the causative agent of whooping cough, has many well-studied virulence factors and a characteristic clinical presentation. Despite this information, it is not clear how B. pertussis interaction with host cells leads to disease. In this study, we examined the interaction of B. pertussis with a human bronchial epithelial cell line (BEAS-2B) and measured host transcriptional profiles by using high-density DNA microarrays. The early transcriptional response to this pathogen is dominated by altered expression of cytokines, DNA-binding proteins, and NFkappaB-regulated genes. This previously unrecognized response to B. pertussis was modified in similar but nonidentical fashions by the antiinflammatory agents dexamethasone and sodium salicylate. Cytokine protein expression was confirmed, as was neutrophil chemoattraction. We show that B. pertussis induces mucin gene transcription by BEAS-2B cells then counters this defense by using mucin as a binding substrate. A set of genes is described for which the catalytic activity of pertussis toxin is both necessary and sufficient to regulate transcription. Host genomic transcriptional profiling, in combination with functional assays to evaluate subsequent biological events, provides insight into the complex interaction of host and pathogen.

Allergen-induced IL-9 directly stimulates mucin transcription in respiratory epithelial cells

A hallmark of asthma is mucin overproduction, a condition that contributes to airway obstruction. The events responsible for mucin overproduction are not known but are thought to be associated with mediators of chronic inflammation. Others have shown that T-helper 2 (Th2) lymphocytes are required for mucous cell metaplasia, which then leads to mucin overproduction in animal models of allergy. We hypothesized that Th2 cell mediators are present in asthmatic airway fluid and directly stimulate mucin synthesis in airway epithelial cells. Results in cultured airway epithelial cells showed that samples of asthmatic fluid stimulated mucin (MUC5AC) synthesis severalfold more potently than non-asthmatic fluid. Consistent with this, lavage fluid from the airways of allergen-challenged dogs stimulated mucin synthesis severalfold more potently than that from non-allergen-challenged dogs. Fractionation of dog samples revealed 2 active fractions at <10 kDa and 30-100 kDa. Th2 cytokines in these molecular weight ranges are IL-9 (36 kDa), IL-5 (56 kDa), and IL-13 (10 kDa). Antibody blockade of ligand-receptor interaction for IL-9 (but not IL-5 or IL-13) inhibited mucin stimulation by dog airway fluid. Furthermore, recombinant IL-9, but not IL-5 or IL-13, stimulated mucin synthesis. These results indicate that IL-9 may account for as much as 50-60% of the mucin-stimulating activity of lung fluids in allergic airway disease.

Control of mucin transcription by diverse injury-induced signaling pathways

Mucin production is an evolutionarily ancient defense mechanism that is retained in mammals and operates at all mucosal surfaces to protect the host against pathogens and irritants. As in lower organisms, the mammalian mucosa (epithelium) produces mucin in response to diverse insults. Our studies aim to understand the intracellular signaling and gene regulation mechanisms mediating mucin production in response to clinically important insults. To date, we find that the signaling pathway triggered by each type of insult is distinct. Relatively common, however, is the involvement of the protein tyrosine kinase c-Src, the MAP kinase kinase MEK 1/2, and the transcription factor NF-kappaB. Basbaum C, Lemjabbar H, Longphre M, Li D, Gensch E, McNamara N. Control of mucin transcription by diverse injury-induced signaling pathways.

[Novel transcription factor MEF is associated with the function of lung epithelial cells]

Lysozyme is an important component of innate immunity against common pathogens at mucosal surfaces. We previously cloned and characterized the bovine lysozyme 5A (lys5A) promoter with the purpose of determining cis- and trans-acting elements controlling airway epithelial cell-specific expression. We found that such expression is controlled by protein binding to an ETS consensus sequence located approximately at -46 to -40 bp from the transcription start site. The identity of the ETS-related protein responsible for gene transactivation was unknown. In this study, we screened six ETS-related proteins by transient transfection into epithelial cells and fibroblasts. Results showed that among these factors, the myeloid Elf-I-like factor (MEF) was the most potent. Gel shift analysis of epithelial cell nuclear extracts using a lys5A probe including the ETS-binding site (-50/-31) yielded a single band with retarded mobility. This band was super-shifted by an antibody directed against MEF. Supporting the possibility that MEF is responsible for functional transactivation of lysozyme in epithelial cells, we found that antisense MEF mRNA decreased lys5A promoter activity and that MEF overexpression in stably transfected cells increased lysozyme mRNA and protein expression. We conclude that MEF is required for epithelial cell transactivation of lysozyme.

Myeloid ELF-1-like factor up-regulates lysozyme transcription in epithelial cells

Lysozyme is an important component of innate immunity against common pathogens at mucosal surfaces. We previously cloned and characterized the bovine lysozyme 5A (lys5A) promoter with the purpose of determining cis- and trans-acting elements controlling airway epithelial cell-specific expression. We found that such expression is controlled by protein binding to an ETS consensus sequence located approximately at -46 to -40 bp from the transcription start site. The identity of the ETS-related protein responsible for gene transactivation was unknown. In this study, we screened six ETS-related proteins by transient transfection into epithelial cells and fibroblasts. Results showed that among these factors, the myeloid Elf-1-like factor (MEF) was the most potent. Gel shift analysis of epithelial cell nuclear extracts using a lys5A probe including the ETS-binding site (-50/-31) yielded a single band with retarded mobility. This band was supershifted by an antibody directed against MEF. Supporting the possibility that MEF is responsible for functional transactivation of lysozyme in epithelial cells, we found that antisense MEF mRNA decreased lys5A promoter activity and that MEF overexpression in stably transfected cells increased lysozyme mRNA and protein expression. We conclude that MEF is required for epithelial cell transactivation of lysozyme.

Long-lasting effects of chronic ozone exposure on rat nasal epithelium

Ozone, the principal oxidant pollutant in photochemical smog, causes airway epithelial injury in the upper and lower respiratory tract of laboratory animals. We have recently reported that long-term inhalation exposure to ozone causes mucous-cell metaplasia (MCM) in the surface epithelium lining the nasal airways of F344 rats. The principal objective of the present study was to determine the persistence of ozone-induced MCM in the nasal epithelium after the end of a chronic exposure. Male F344/N rats were exposed to 0, 0.25, or 0.5 ppm ozone, for 8 h/d, 7 d/wk for 13 wk. Animals were killed 8 h, 4 wk, or 13 wk after the end of the chronic exposure. Ozone-related alterations in the nasal epithelium were qualitatively and quantitatively characterized through histochemistry, image analysis, and morphometric techniques. Some rats were exposed for an additional 8 h to 0.5 ppm ozone at 13 wk after the end of the chronic exposure to determine whether previous ozone exposure results in persistent changes in the sensitivity of nasal epithelium to acute injury. At the end of the chronic exposure, hyperplasia was present in the nasal epithelium of rats exposed to 0.25 and 0.5 ppm ozone. By 13 wk postexposure, this proliferative alteration was still evident only in the rats exposed to 0.5 ppm ozone. Ozone-induced MCM with associated intraepithelial mucosubstances was evident only in the nasal tissues of rats exposed to 0.5 ppm ozone. Though attenuated, these alterations in the nasal mucous apparatus were still detectable at 13 wk after the end of the exposure. At this same time after the chronic exposure, an acute (8 h) exposure to 0.5 ppm ozone induced an additional increase of mucosubstances in the nasal epithelium of rats previously exposed to 0.5 ppm ozone, but not in rats chronically exposed to 0 or 2.5 ppm ozone. The persistent nature of the ozone-induced MCM in rats documented in this report suggests that ozone exposure may have the potential to induce similar long-lasting alterations in the airways of humans.

Tumor-derived EMMPRIN (extracellular matrix metalloproteinase inducer) stimulates collagenase transcription through MAPK p38

EMMPRIN (extracellular matrix metalloproteinase inducer) stimulates fibroblast metalloproteinases (MMP) 1, 2 and 3 (Kataoka et al. (1993) Cancer Res. 53, 3154-3158). Here we focus on MMP-1, showing that in lung tumors, MMP-1's cognate mRNA is strongly expressed in stromal fibroblasts adjacent to EMMPRIN-expressing tumor cells. In vitro, EMMPRIN upregulates MMP-1 mRNA expression in a concentration-dependent manner, with a peak accumulation at 24 h. The response is genistein-sensitive, suggesting it is dependent on tyrosine kinase activity. Analysis of tyrosine phosphorylation-dependent MAP kinases ERK 1/2, SAPK/JNK, and p38 showed that the activity of p38 but not that of the other 2 kinases was elevated in response to EMMPRIN. That p38 activity was required for EMMPRIN stimulation of MMP-1 was evident from results showing that the p38 inhibitor SB203580 blocked this response. This is the first available information regarding the mechanism by which tumor-associated molecules upregulate MMP synthesis in stromal fibroblasts.

Activation of NF-kappaB via a Src-dependent Ras-MAPK-pp90rsk pathway is required for Pseudomonas aeruginosa-induced mucin overproduction in epithelial cells

Cystic fibrosis (CF) is an autosomal recessive disorder, the most common lethal genetic disease in Caucasians. Respiratory disease is the major cause of morbidity and mortality. Indeed, 95% of CF patients die of respiratory failure. Pseudomonas aeruginosa, an opportunistic pathogen, chronically infects the lungs of over 85% of CF patients. It is ineradicable by antibiotics and responsible for airway mucus overproduction that contributes to airway obstruction and death. The molecular mechanisms underlying this pathology are unknown. Here we show that P. aeruginosa activates a c-Src-Ras-MEK1/2-MAPK-pp90rsk signaling pathway that leads to activation of nuclear factor NF-kappaB (p65/p50). Activated NF-kappaB binds to a kappaB site in the 5'-flanking region of the MUC2 gene and activates MUC2 mucin transcription. These studies bring new insight into bacterial-epithelial interactions and more specifically into the molecular pathogenesis of cystic fibrosis. Understanding these signaling and gene regulatory mechanisms opens up new therapeutic targets for cystic fibrosis.

Mucin gene (MUC 2 and MUC 5AC) upregulation by Gram-positive and Gram-negative bacteria

Bacterial infection of the lung is associated with mucin overproduction. In partial explanation of this phenomenon, we recently reported that supernatant from the Gram-negative organism Pseudomonas (P.) aeruginosa contained an activity that upregulated transcription of the MUC 2 mucin gene [J.-D. Li, A. Dohrman, M. Gallup, S. Miyata, J. Gum, Y. Kim, J. Nadel, A. Prince, C. Basbaum, Transcriptional activation of mucin by P. aeruginosa lipopolysaccharide in the pathogenesis of cystic fibrosis lung disease, Proc. Natl. Acad. Sci. U.S.A., 94 (1997) 967-972]. The purpose of the present study was to determine whether mucin genes other than MUC 2 are so regulated and whether Gram-positive organisms also contain mucin stimulatory activity. Results from in situ hybridization and RNase protection assays showed that P. aeruginosa upregulates MUC 5AC as well as MUC 2 in both bronchial explants and cultured airway epithelial cells. The upregulation of both genes by P. aeruginosa can be mimicked by lipopolysaccharide (LPS) and can be blocked by the tyrosine kinase inhibitor genistein. In addition, both genes are upregulated by a variety of Gram-positive as well as Gram-negative organisms showing the same rank order of potency. These data indicate the existence of a general mechanism by which epithelial cells respond to the presence of bacteria by increasing mucin synthesis.

Sp1 protein contributes to airway-specific rat MUC 2 mucin gene transcription

We have shown increases in the abundance of airway mucin mRNA during the pathogenesis of chronic obstructive pulmonary disease in rat models (Jany et al., 1991) and now seek to determine the underlying mechanisms. As transcriptional modulation may be involved, we provide here a functional analysis of the 5' flanking region of a rat mucin gene (MUC 2). Using deletion mutants to bp -859, we constructed expression cassettes in CAT vectors and transfected them into two MUC 2-expressing cell lines, SPOC 1, a rat airway epithelial cell line and IEC-6, a rat intestinal epithelial cell line, and into one MUC 2 non-expressing cell line, FR, a rat skin fibroblast cell line. Results indicated that nucleotides -59 to -40 mediated high level expression in SPOC 1, but not in the other cells. Used as a probe in gel shift assays, fragment -59/-40 formed complexes of differing mobilities when incubated with nuclear protein extracts from the three cell types. Mutation of the putative Sp1 binding site in the probe sequence interfered with protein binding in all three cell types, but anti-Sp1 antibody supershifted a band formed only by airway cell extracts. A model of airway cell-specific MUC 2 transcription is proposed.

A novel role for murine IL-4 in vivo: induction of MUC5AC gene expression and mucin hypersecretion

Mucus hypersecretion and plugging of lower respiratory tract airways contributes to the morbidity and mortality associated with asthma. Interleukin (IL)-4 plays a putative role in some forms of asthma. Thus, transgenic mice that overexpress murine IL-4 selectively within the lung were used to study the effect of IL-4 on mucus glycoprotein gene expression and mucin release. Histologic examination of lung sections from IL-4 mice revealed that nonciliated epithelial cells from conducting airways were hypertrophic, due at least in part to the accumulation of mucus glycoprotein. The cytoplasm of these cells stained positively for glycoproteins using mucicarmine, alcian blue (AB), and periodic acid-Schiff (PAS). Ciliated cells were also enlarged but did not show any mucin-specific staining. Inclusion granules typically found in nonciliated (Clara) cells of control mice were absent in the IL-4 transgenic mice. Northern blot analysis of total RNA from lung tissue revealed that the expression of the MUC5AC, but not MUC2, mucin gene was distinctly upgraded in IL-4 transgenic mice compared to transgene-negative controls. In addition, a 5- to 10-fold increase in AB- and PAS-positive material was found in lavage fluid from IL-4 overexpressing mice compared to transgene-negative controls. Thus, the overexpression of IL-4 locally within the lung enhances mucus glycoprotein synthesis by altering gene expression, results in the accumulation of mucus glycoprotein in nonciliated epithelial cells, and induces the release of mucus into the airway lumen. We therefore hypothesize that the overproduction of mucus seen in some patients with asthma may be a direct result of the action of IL-4 within the inflamed lung.

Transcriptional regulation of the lysozyme gene in airway gland serous cells

Lysozyme is expressed in serous, but not mucous, cells of the tracheobronchial glands and thereby constitutes a marker of the serous cell lineage in these glands. To identify DNA regulatory elements and transcription factors mediating the commitment of progenitor cells to the serous cell lineage, we have characterized the regulatory activity and DNA-protein interactions of the 5'-flanking region of the bovine lysozyme gene lys 5a. Results obtained from these studies indicate that although approximately 94 bp of 5'flanking DNA are necessary for high level expression in transient transfection assays, an evolutionarily conserved promoter within 66 bp of the transcription start site is sufficient to confer serous cell-specific expression. Farther upstream, within 6.1 kb of the 5' flanking region, are 4 silencers. Analysis of the serous cell-specific lysozyme promoter by electrophoretic mobility shift assay (EMSA) revealed the presence of binding sites for 3 serous cell nuclear proteins, designated LSF1, LSF2 and LSF3. Binding of LSF2 and LSF3 was localized to a 20-mer subdomain (-50/-30) of the cell-specific promoter using binding competition assays. More accurate identification of the protein binding site(s) was achieved through the use of mutagenesis, which implicated the motif 5' AAGGAAT 3' (-46/-40) in both protein binding and serous cell-specific transcriptional activity. This motif has previously been identified as a binding site for ets protein transcription factors, suggesting that serous cell-specific regulation of lys 5a transcription is partly controlled by the binding of ets-like protein(s) to the motif 5'AGGAAGT3'.

[Mucin gene--regulation of the expression of MUC2 and MUC3 mucin gene in the airway]

Mucus hypersecretion is a characteristic feature of several human airway diseases, including chronic bronchitis, cystic fibrosis and asthma. Analysis of rat disease models has suggested that mucin synthesis is up-regulated as part of the disease process. To understand the primary structure of secretory mucins, several cDNAs encoding airway mucin have been isolated. In most cases, full-length sequences have not been obtained. In this review, we focused on the MUC2 and MUC3 mucin gene. MUC2 mucin has been reported to be expressed in the human lung with airway disease and in the rat lung with infection and exposure to irritant such as SO2. MUC3 is also expressed in the bronchus. Less is known about the structure and the expression pattern of the MUC3 mucin gene. Recent findings show that the expression pattern of the MUC2 and MUC3 mucin genes differ strikingly, suggesting that they play distinct functional roles in the airway and intestine. Functional analysis of mucin gene promoter will provide better understanding of the regulation of its expression in the airway under both normal and pathological conditions.

Upregulation of the 72-kDa type IV collagenase in epithelial and stromal cells during rat tracheal gland morphogenesis

Submucosal glands secrete most of the mucus that lubricates the tracheal surface and protects it from irritants and infection. These glands develop postnatally in the rat, permitting convenient study of the mechanisms controlling this process. One such mechanism involves degradation of the supportive connective tissue matrix at the front of the growing glands. We recently showed that tracheal gland cell invasion of collagen gels in vitro is dependent on secretion of a 72-kDa type IV collagenase. In the present study, we show that the activity of this enzyme (also referred to as matrix metalloproteinase-2 or gelatinase A) is elevated at the time of gland development in vivo. That this increase is at least partly mediated at the level of steady-state mRNA was indicated by semiquantitative PCR analysis of gland-enriched, microdissected tissue samples. Immunohistochemistry revealed that the enzyme was present at the interface between the glands and extracellular matrix. In situ hybridization revealed that the cognate mRNA was present in epithelial cells of glands undergoing morphogenesis (particularly Postnatal Day 7) but not in those of adult glands or the surface epithelium. At all ages, stromal cells below the surface epithelium were labeled; labeling intensity was highest at the time and location of gland morphogenesis. These findings suggest that the 72-kDa type IV collagenase is developmentally regulated in gland and stromal cells at the level of steady-state mRNA and plays a role in the degradation of extracellular matrix during tracheobronchial gland morphogenesis.

Concurrent increases in the storage and release of mucin-like molecules by rat airway epithelial cells in response to bacterial endotoxin

Mucus hypersecretion is a prominent response of the airways to bacterial infections. Recent findings showed that bacterial endotoxin, a lipopolysaccharide complex released from the bacterial cell wall, was able to induce at least one component of the hypersecretory response, i.e., an increase in the amount of stored epithelial mucosubstances (1, 2). The goal of the present study was to determine whether endotoxin also was capable of increasing mucosubstance release from cells. Based on evidence that human mucin antibodies A10G5 and B6E8 cross-reacted with rat mucin-like molecules, we used the antibodies in enzyme-linked immunosorbent assays (ELISA) to compare mucin concentrations in bronchoalveolar lavage (BAL) fluid from endotoxin-treated and control rats. Results showed that endotoxin treatment increased the amount of released mucin over that in controls 1.5-fold at 96 h and 2.5-fold at 168 h after instillation. Thus, these studies have defined the previously detected mucosubstances as mucin-like molecules and showed that endotoxin increases their release from, as well as their storage in, rat airway epithelium. Concurrent increases in storage and release suggest that endotoxin also stimulates mucin synthesis and/or stability.

Expression of gelatinase A, a mediator of extracellular matrix remodeling, by tracheal gland serous cells in culture and in vivo

Tracheal gland morphogenesis and gland hypertrophy in disease involve the penetration of epithelial cells into the submucosa, a process that requires digestion of the basal lamina and the surrounding extracellular matrix. We observed that bovine tracheal gland cells invaded collagen substrates and were inhibited from doing so in the presence of a metalloproteinase inhibitor GM6001. The gland cells, but not bovine tracheal surface epithelial cells, secreted a 72-kDa metalloproteinase. The purified enzyme could be activated with 4-aminophenylmercuric acetate and converted to an active 65-kDa form that was far more effective in degrading denatured collagen (gelatin) than nondenatured type I and IV collagens and was ineffective in degrading intact interstitial collagen fibers. At 25 degrees C, the initial rate of degradation of acid-solubilized type I collagen was approximately 50 mg of type I collagen cleaved per min per mg of enzyme, whereas acid-solubilized type IV collagen was degraded at approximately 250 mg cleaved per min per mg of enzyme. In contrast, at the same temperature, heat-denatured type I collagen was degraded 1000-fold more rapidly, while heat-denatured type IV collagen was cleaved 50-fold more rapidly. The activity of the enzyme was maximal at pH 7-8 and was completely abolished by the metalloproteinase inhibitors EDTA and 1,10-phenanthroline. In immunoblots, the enzyme was recognized by an antibody directed against human gelatinase A, the 72-kDa gelatinase. The purified enzyme disrupted the distribution pattern of type IV collagen in the gland basal lamina, as well as of interstitial collagen in the underlying stromal tissue, as shown in tissue sections by immunocytochemistry. Using an antibody directed against the purified enzyme, we also showed by immunocytochemistry that the gelatinase was present in tracheal tissue and was specifically located at the periphery of some tracheal gland acini. Northern blots showed higher concentrations of gelatinase A mRNA in glands than in epithelium microdissected from adult cow tracheas. These data indicate that gelatinase A is a specialized product of the tracheal gland epithelial cell, a cell type normally invasive as part of its developmental program; the enzyme may play an important role in normal gland development and disease-associated hypertrophy.

Identification of decorin proteoglycan in bovine tracheal serous cells in culture and localization of decorin mRNA in situ

Bovine tracheal submucosal gland serous cells in culture synthesize and secrete proteoglycans and not mucin glycoconjugates. We are interested in the characterization and role of these proteoglycans in airway secretions. The major [35S]methionine-labeled proteoglycan present is identified as the small chondroitin/dermatan sulfate proteoglycan decorin (PG II. PG40). Consistent with its identity as decorin this proteoglycan showed average apparent molecular weights of 75,000 to 130,000 with a core protein of an average, M(r) of about 40,000 and with glycosaminoglycan chains sensitive to chondroitinase ABC lyase of an average M(r) of about 25,000. These data were obtained from gel chromatographic and SDS-PAGE analyses. Northern blot analysis and partial amino acid sequencing of the purified protein further confirmed its identity as decorin. In situ hybridization studies using a decorin riboprobe revealed no expression of decorin in the surface epithelium and only low levels of expression in submucosal gland epithelial cells of bovine tracheal tissue. However, high levels of expression were localized to cells which are peripheral to tracheal submucosal gland epithelial cells and which contact with the extracellular matrix.