An ELISA method for the quantitation of tracheal mucins from human and nonhuman primates

Activation of JNK and p38 in MCF-7 Cells and the In Vitro Anticancer Activity of Alnus hirsuta Extract

JNK and p38 are important mitogen-activated protein kinases (MAPKs) that respond to stress stimuli. The stress-activated MAPKs associated with apoptotic cell death play vital roles in mammalian cells. Alnus hirsuta, which contains abundant diarylheptanoids derivatives, is a valuable medicinal plant. The CHCl3 extract (AHC) containing platyphyllenone (1) and platyphyllone (3) as main compounds showed in vitro anticancer effects. We report the biological activities of A. hirsuta extract associated with the regulation of apoptosis and JNK and p38 in MCF-7 breast cancer cells. Levels of phospho-JNK and phospho-p38 by AHC treatment were evaluated by enzyme-linked immunosorbent assay (ELISA). ROS production, apoptotic effect, and DNA contents of the cells were measured by flow cytometry. The two diarylheptanoids 1 and 3 and the AHC extract exhibited cytotoxic effects on MCF-7 cells in MTT assay, with IC50 values of 18.1, 46.9, 260.0 μg/mL, respectively. AHC induced ROS generation and elevated the endogenous levels of phospho-JNK and phospho-p38. AHC resulted in apoptosis and cell cycle arrest. We suggest that the antitumor effect of A. hirsuta extract is achieved by apoptosis promotion and cell cycle arrest mediated by the activation of JNK and p38 signaling pathway via ROS generation.

Strategies for measuring airway mucus and mucins

Mucus secretion and mucociliary transport are essential defense mechanisms of the airways. Deviations in mucus composition and secretion can impede mucociliary transport and elicit airway obstruction. As such, mucus abnormalities are hallmark features of many respiratory diseases, including asthma, cystic fibrosis and chronic obstructive pulmonary disease (COPD). Studying mucus composition and its physical properties has therefore been of significant interest both clinically and scientifically. Yet, measuring mucus production, output, composition and transport presents several challenges. Here we summarize and discuss the advantages and limitations of several techniques from five broadly characterized strategies used to measure mucus secretion, composition and mucociliary transport, with an emphasis on the gel-forming mucins. Further, we summarize advances in the field, as well as suggest potential areas of improvement moving forward.

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

Pandemic Swine H1N1 Influenza Viruses with Almost Undetectable Neuraminidase Activity Are Not Transmitted via Aerosols in Ferrets and Are Inhibited by Human Mucus but Not Swine Mucus

A balance between the functions of the influenza virus surface proteins hemagglutinin (HA) and neuraminidase (NA) is thought to be important for the transmission of viruses between humans. Here we describe two pandemic H1N1 viruses, A/swine/Virginia/1814-1/2012 and A/swine/Virginia/1814-2/2012 (pH1N1low-1 and -2, respectively), that were isolated from swine symptomatic for influenza. The enzymatic activity of the NA of these viruses was almost undetectable, while the HA binding affinity for α2,6 sialic acids was greater than that of the highly homologous pH1N1 viruses A/swine/Pennsylvania/2436/2012 and A/swine/Minnesota/2499/2012 (pH1N1-1 and -2), which exhibited better-balanced HA and NA activities. The in vitro growth kinetics of pH1N1low and pH1N1 viruses were similar, but aerosol transmission of pH1N1low-1 was abrogated and transmission via direct contact in ferrets was significantly impaired compared to pH1N1-1, which transmitted by direct and aerosol contact. In normal human bronchial epithelial cells, pH1N1low-1 was significantly inhibited by mucus but pH1N1-1 was not. In Madin-Darby canine kidney cell cultures overlaid with human or swine mucus, human mucus inhibited pH1N1low-1 but swine mucus did not. These data show that the interaction between viruses and mucus may be an important factor in viral transmissibility and could be a barrier for interspecies transmission between humans and swine for influenza viruses.

IMPORTANCE

A balance between the functions of the influenza virus surface proteins hemagglutinin (HA) and neuraminidase (NA) is thought to be important for transmission of viruses from swine to humans. Here we show that a swine virus with extremely functionally mismatched HA and NAs (pH1N1low-1) cannot transmit via aerosol in ferrets, while another highly homologous virus with HA and NAs that are better matched functionally (pH1N1-1) can transmit via aerosol. These viruses show similar growth kinetics in Madin-Darby canine kidney (MDCK) cells, but pH1N1low-1 is significantly inhibited by mucus in normal human bronchial epithelial cells whereas pH1N1-1 is not. Further, human mucus could inhibit these viruses, but swine mucus could not. These data show that the interaction between viruses and mucus may be an important factor in viral transmissibility and could be a species barrier between humans and swine for influenza viruses.

Role of MARCKS in regulated secretion from mast cells and airway goblet cells

MARCKS (myristoylated alanine-rich C kinase substrate) is postulated to regulate the passage of secretory granules through cortical actin in the early phase of exocytosis. There are, however, three proposed mechanisms of action, all of which were derived from studies using synthetic peptides representing either the central phosphorylation site domain or the upstream, NH2-terminal domain: it tethers actin to the plasma membrane and/or to secretory granules, and/or it sequesters PIP2. Using MARCKS-null mice, we probed for a loss of function secretory phenotype in mast cells harvested from embryonic livers and maturated in vivo [embryonic hepatic-derived mast cells (eHMCs)]. Both wild-type (WT) and MARCKS-null eHMCs exhibited full exocytic responses upon FcϵRI receptor activation with DNP-BSA (2,4-dinitrophenyl-BSA), whether they were in suspension or adherent. The secretory responses of MARCKS-null eHMCs were consistently higher than those of WT cells, but the differences had sporadic statistical significance. The MARCKS-null cells exhibited faster secretory kinetics, however, achieving the plateau phase of the response with a t½ ∼2.5-fold faster. Hence, MARCKS appears to be a nonessential regulatory protein in mast cell exocytosis but exerts a negative modulation. Surprisingly, the MARCKS NH2-terminal peptide, MANS, which has been reported to inhibit mucin secretion from airway goblet cells (Li Y, Martin LD, Spizz G, Adler KB. J Biol Chem 276: 40982-40990, 2001), inhibited hexosaminidase secretion from WT and MARCKS-null eHMCs, leading us to reexamine its effects on mucin secretion. Results from studies using peptide inhibitors with human bronchial epithelial cells and with binding assays using purified mucins suggested that MANS inhibited the mucin binding assay, rather than the secretory response.

MARCKS and HSP70 interactions regulate mucin secretion by human airway epithelial cells in vitro

Myristoylated alanine-rich C kinase substrate (MARCKS) protein has been recognized as a key regulatory molecule controlling mucin secretion by airway epithelial cells in vitro and in vivo. We recently showed that two intracellular chaperones, heat shock protein 70 (HSP70) and cysteine string protein (CSP), associate with MARCKS in the secretory mechanism. To elucidate more fully MARCKS-HSP70 interactions in this process, studies were performed in well-differentiated normal human bronchial epithelial (NHBE) cells maintained in air-liquid interface culture utilizing specific pharmacological inhibition of HSP70 with pyrimidinone MAL3-101 and siRNA approaches. The results indicate that HSP70 interaction with MARCKS is enhanced after exposure of the cells to the protein kinase C activator/mucin secretagogue, phorbol 12-myristate 13-acetate (PMA). Pretreatment of NHBEs with MAL3-101 attenuated in a concentration-dependent manner PMA-stimulated mucin secretion and interactions among HSP70, MARCKS, and CSP. In additional studies, trafficking of MARCKS in living NHBE cells was investigated after transfecting cells with fluorescently tagged DNA constructs: MARCKS-yellow fluorescent protein, and/or HSP70-cyan fluorescent protein. Cells were treated with PMA 48 h posttransfection, and trafficking of the constructs was examined by confocal microscopy. MARCKS translocated rapidly from plasma membrane to cytoplasm, whereas HSP70 was observed in the cytoplasm and appeared to associate with MARCKS after PMA exposure. Pretreatment of cells with either MAL3-101 or HSP70 siRNA inhibited translocation of MARCKS. These results provide evidence of a role for HSP70 in mediating mucin secretion via interactions with MARCKS and that these interactions are critical for the cytoplasmic translocation of MARCKS upon its phosphorylation.

Calpain and MARCKS protein regulation of airway mucin secretion

Hypersecretion of mucin plays an important role in the pathophysiology of many inflammatory airway diseases, including asthma, chronic bronchitis, and cystic fibrosis. Myristoylated alanine-rich C-kinase substrate (MARCKS) protein has been shown to play an important role in regulation of airway mucin secretion, as peptides analogous to the amino (N)-terminus of MARCKS attenuate mucin secretion by airway epithelium in vitro and in vivo. Here, we investigated a potential role for the protease Calpain, a calcium-dependent cysteine protease that can cleave MARCKS, in the MARCKS-related secretory mechanism. We theorized that Calpain might cleave MARCKS near the N-terminus, thereby attenuating the ability of MARCKS to bind to membranes and/or creating a small N-terminal peptide that could act as a competitive intracellular inhibitor to remaining endogenous full-length MARCKS molecules. Primary normal human bronchial epithelial (NHBE) cells and the virally-transformed human bronchial epithelial HBE1 cell line were exposed to phorbol-12-myristate-13-acetate (PMA) to stimulate the Protein Kinase C (PKC) pathway, leading to enhanced mucin secretion, and Calpain activity within the cells was measured with a fluorescent cleavage assay. Calpain activity was increased by PMA, and pretreatment of the cells with Calpain inhibitors reduced both Calpain activity and mucin secretion in a concentration-dependent manner. Thus, as opposed to the original hypothesis, inactivating Calpain caused a decrease rather than an increase in secretion. HBE1 cells transfected with DNA constructs encoding a MARCKS-YFP fusion protein showed cleavage at a putative site near the N-terminus in response to PMA. Cleavage of MARCKS by Calpain may have an important role in regulation of the PKC/MARCKS pathway regulating airway mucin secretion.

SERCA2 regulates non-CF and CF airway epithelial cell response to ozone

Calcium mobilization can regulate a wide range of essential functions of respiratory epithelium, including ion transport, ciliary beat frequency, and secretion of mucus, all of which are modified in cystic fibrosis (CF). SERCA2, an important controller of calcium signaling, is deficient in CF epithelium. We conducted this study to determine whether SERCA2 deficiency can modulate airway epithelial responses to environmental oxidants such as ozone. This could contribute to the pathogenesis of pulmonary exacerbations, which are important and frequent clinical events in CF. To address this, we used air-liquid interface (ALI) cultures of non-CF and CF cell lines, as well as differentiated cultures of cells derived from non-CF and CF patients. We found that ozone exposure caused enhanced membrane damage, mitochondrial dysfunction and apoptotic cell death in CF airway epithelial cell lines relative to non-CF. Ozone exposure caused increased proinflammatory cytokine production in CF airway epithelial cell lines. Elevated proinflammatory cytokine production also was observed in shRNA-mediated SERCA2 knockdown cells. Overexpression of SERCA2 reversed ozone-induced proinflammatory cytokine production. Ozone-induced proinflammatory cytokine production was NF-κB- dependent. In a stable NF-κB reporter cell line, SERCA2 inhibition and knockdown both upregulated cytomix-induced NF-κB activity, indicating importance of SERCA2 in modulating NF-κB activity. In this system, increased NF-κB activity was also accompanied by increased IL-8 production. Ozone also induced NF-κB activity and IL-8 release, an effect that was greater in SERCA2-silenced NF-κB-reporter cells. SERCA2 overexpression reversed cytomix-induced increased IL-8 release and total nuclear p65 in CFTR-deficient (16HBE-AS) cells. These studies suggest that SERCA2 is an important regulator of the proinflammatory response of airway epithelial cells and could be a potential therapeutic target.

Mucin granule-associated proteins in human bronchial epithelial cells: the airway goblet cell "granulome"

Background

Excess mucus in the airways leads to obstruction in diseases such as chronic bronchitis, asthma, and cystic fibrosis. Mucins, the highly glycosolated protein components of mucus, are stored in membrane-bound granules housed in the cytoplasm of airway epithelial "goblet" cells until they are secreted into the airway lumen via an exocytotic process. Precise mechanism(s) of mucin secretion, including the specific proteins involved in the process, have yet to be elucidated. Previously, we have shown that the Myristoylated Alanine-Rich C Kinase Substrate (MARCKS) protein regulates mucin secretion by orchestrating translocation of mucin granules from the cytosol to the plasma membrane, where the granules dock, fuse and release their contents into the airway lumen. Associated with MARCKS in this process are chaperone (Heat Shock Protein 70 [HSP70], Cysteine string protein [CSP]) and cytoskeletal (actin, myosin) proteins. However, additional granule-associated proteins that may be involved in secretion have not yet been elucidated.

Methods

Here, we isolated mucin granules and granule membranes from primary cultures of well differentiated human bronchial epithelial cells utilizing a novel technique of immuno-isolation, based on the presence of the calcium activated chloride channel hCLCA1 (the human ortholog of murine Gob-5) on the granule membranes, and verified via Western blotting and co-immunoprecipitation that MARCKS, HSP70, CSP and hCLCA1 were present on the granule membranes and associated with each other. We then subjected the isolated granules/membranes to liquid chromatography mass spectrometry (LC-MS/MS) to identify other granule associated proteins.

Results

A number of additional cytoskeletal (e.g. Myosin Vc) and regulatory proteins (e.g. Protein phosphatase 4) associated with the granules and could play a role in secretion were discovered. This is the first description of the airway goblet cell "granulome."

Mucin production during prenatal and postnatal murine lung development

Mucus is a protective gel that lines respiratory tract surfaces. To identify potential roles for secreted gel--forming mucins in lung development, we isolated murine lungs on embryonic days (E) 12.5-18.5, and postnatal days (PN) days 5, 14, and 28. We measured the mucin gene expression by quantitative RT-PCR, and localization by histochemical and immunohistochemical labeling. Alcian blue/periodic acid--Schiff--positive cells are present from E15.5 through PN28. Muc5b transcripts were abundant at all time points from E14.5 to PN28. By contrast, transcript levels of Muc5ac and Muc2 were approximately 300 and 85,000 times lower, respectively. These data are supported by immunohistochemical studies demonstrating the production and localization of Muc5ac and Muc5b protein. This study indicates that mucin production is prominent in developing murine lungs and that Muc5b is an early, abundant, and persistent marker of bronchial airway secretory cells, thereby implicating it as an intrinsic component of homeostatic mucosal defense in the lungs.

Airway eosinophilia in remission and progression of asthma: accumulation with a fast decline of FEV(1)

BACKGROUND

As it is unknown whether complete asthma remission or progression of asthma is associated with airway inflammation and remodeling, we assessed these characteristics in bronchial biopsies of relevant subsets of asthma patients.

METHODS

Sputum and bronchial biopsies were obtained from asthma patients in remission (PC(20) histamine> 32 mg/ml, PC(20) AMP> 320 mg/ml) and from those with either a slow FEV(1) decline (< 30 ml/year) or fast decline (> 30 ml/year). Inflammatory cells and mediators were determined in sputum, inflammatory cells and aspects of airway remodeling in bronchial biopsies.

RESULTS

Asthmatics in remission and asthma patients with a slow FEV(1) decline had a similar extent of airway inflammation and remodeling in sputum and bronchial biopsies. Asthma patients with a fast FEV(1) decline had high sputum eosinophil numbers. Moreover, FEV(1) decline (ml/year) correlated with sputum eosinophil numbers (Rs=0.51, p=0.003) and ECP levels (Rs=0.57, p=0.001). Airway remodeling, i.e. basement membrane thickness, correlated with sputum eosinophils (Rs=0.69, p<0.001), sputum ECP (Rs=0.46, p=0.018) and airway wall eosinophil numbers (Rs=0.49, p=0.002).

CONCLUSIONS

Asthma, even when in remission, is accompanied by airway inflammation and remodeling. Data suggest that eosinophils are important in a subset of asthma patients by association to accelerated FEV(1) decline and change of basement membrane thickness.

NF-κB mediates IL-1β- and IL-17A-induced MUC5B expression in airway epithelial cells

A major pathological feature of chronic airway diseases is the elevated expression of gel-forming mucins. NF-κB activation in airway epithelial cells has been shown to play a proinflammatory role in chronic airway diseases; however, the specific role of NF-κB in mucin gene expression has not been characterized. In this study, we show that the proinflammatory cytokines, IL-1β and IL-17A, both of which use the NF-κB pathway, are potent inducers of MUC5B mRNA expression in both well differentiated primary normal human bronchial epithelial cells and the human bronchial epithelial cell line, HBE1. MUC5B induction by these cytokines was both time- and dose-dependent, and was attenuated by the small molecule inhibitor, NF-κB inhibitor III, as well as p65 small interfering RNA, suggesting that the regulation of MUC5B expression by these cytokines is via an NF-κB-based transcriptional mechanism. Deletion analysis of the MUC5B promoter demonstrated that IL-1β- and IL-17A-induced promoter activity resides within the -4.17-kb to -2.56-kb region relative to the transcriptional start site. This region contains three putative κB-binding sites (NF-κB-1, -3,786/-3,774; NF-κB-2, -3,173/-3,161; and NF-κB-3, -2,921/-2,909). Chromatin immunoprecipitation analysis confirmed enhanced binding of the p50 NF-κB subunit to the NF-κB-3 site after cytokine stimulation. We conclude that an NF-κB-based transcriptional mechanism is involved in MUC5B regulation by IL-1β and IL-17A in airway epithelium. This is the first demonstration of the participation of NF-κB and its specific binding site in cytokine-mediated airway MUC5B expression.

The carbohydrate moiety and high molecular weight carrier of histo-blood group antigens are both required for norovirus-receptor recognition

Histo-blood group antigens (HBGAs) on human intestinal epithelium serve as receptors for noroviruses (NVs). These antigens also are expressed in milk and may act as decoy receptors to protect breast-fed infants and others against NV disease. In this study we demonstrated that human milk is highly variable in synthesis of HBGAs, which differs from that of saliva; a large quantity of small, soluble HBGAs are found in milk, but much less in saliva and are recognized by MAbs, but not by NVs. There is another group of HBGAs, of high MW, found in both milk and saliva, and recognized by both NVs and MAbs. These results suggest that the specificity of NVs and MAbs to HBGAs are different and the backbones in addition to the carbohydrate moiety are required for NV recognition. Further studies to define the structure and genetics of the high MW milk glycans are necessary.

Interleukin-13-induced mucous metaplasia increases susceptibility of human airway epithelium to rhinovirus infection

Infection of airway epithelium by rhinovirus is the most common cause of asthma exacerbations. Even in mild asthma, airway epithelium exhibits mucous metaplasia, which increases with increasing severity of the disease. We previously showed that squamous cultures of human airway epithelium manifest rhinoviral infection at levels many times higher than in well-differentiated cultures of a mucociliary phenotype. Here we tested the hypothesis that mucous metaplasia is also associated with increased levels of rhinoviral infection. Mucous metaplasia was induced with IL-13, which doubled the numbers of goblet cells. In both control (mucociliary) and IL-13- treated (mucous metaplastic) cultures, goblet cells were preferentially infected by rhinovirus. IL-13 doubled the numbers of infected cells by increasing the numbers of infected goblet cells. Furthermore, IL-13 increased both the maturity of goblet cells and the probability that a goblet cell would be infected. The infection of cells other than goblet cells was unaltered by IL-13. Treatment with IL-13 did not alter the levels of rhinovirus receptor ICAM-1, nor did the proliferative effects of IL-13 enhance infection, because rhinovirus did not colocalize with dividing cells. However, the induction of mucous metaplasia caused changes in the apical membrane structure, notably a marked decrease in overall ciliation, and an increase in the overall flatness of the apical surface. We conclude that mucous metaplasia in asthma increases the susceptibility of airway epithelium to infection by rhinovirus because of changes in the overall architecture of the apical surface.

Induced sputum concentrations of mucin in patients with asthma and chronic cough

BACKGROUND

Mucus hypersecretion is an important pathophysiologic index of airway disease. Measurement of secreted mucin in sputum has been reported in asthma, but not in chronic cough with or without increased sputum production.

METHODS

We studied 49 patients with classic asthma (CA), 39 with cough-variant asthma (CVA), nine and five with chronic cough associated with sinobronchial syndrome (SBS) and gastroesophageal reflux disease (GERD), respectively, and 11 healthy controls. Seventeen patients with CA, but none from the other groups, were taking antiinflammatory medications. Mucin levels in induced sputum supernatants were measured by enzyme-linked immunosorbent assay, which detects airway mucin, probably including MUC5AC and MUC5B.

RESULTS

Mucin levels were higher in patients with CA (674.2 +/- 548.8 microg/mL) and SBS (638.4 +/- 650.7 microg/mL) than in controls (212.0 +/- 167.1 microg/mL) (P = .0037 and .044). They were also higher in patients with CA than in those with CVA (350.4 +/- 374.0 microg/mL) and GERD (134.3 +/- 93.1 microg/mL) (P = .0016 and 0.015), but results did not differ between the latter groups and controls. When the four disease groups were combined, patients with frequent sputum production had greater mucin levels than those with occasional (P = .0023) or no sputum production (P < .0001). Patients with CA showed negative correlations of mucin levels with respiratory resistance indices on impulse oscillation and with airway sensitivity to methacholine.

CONCLUSIONS

Sputum mucin levels differ in various respiratory conditions when compared with controls, primarily reflecting the degree of sputum production. Airway mucin might possibly exert protective effects in asthma, at least between exacerbations, but this issue needs to be further clarified by future studies.

Expression of conserved mucin domains by epithelial tissues in various mammalian species

Mucins are related to infectious and non-infectious diseases in Veterinary and Human Medicine. MUC1 mucin is a transmembrane glycoprotein expressed on the apical surface of human epithelia while MUC5AC is the predominant secreted mucin expressed in human gastric epithelium and goblet cells of lung and eyes. MUC5AC C-terminus cysteine rich regions and the cytoplasmic tail of MUC1 domains are conserved among several mammalian species.

OBJECTIVE

to compare the expression of MUC1 and MUC5AC mucins in mammalian epithelia. CT33 anti-MUC1 cytoplasmic tail (MUC1CT) polyclonal antibody and 45M1 anti-MUC5AC monoclonal antibody were employed. By immunohistochemistry, MUC1CT was expressed in most tissues while MUC5AC was restricted to gastric surface epithelium and goblet cells from trachea and lung. By western blot, MUC1CT showed a band at approximately 35 kDa in most tissues; MUC5AC revealed bands at >180 kDa in stomach and lung secretions from rat, cat, pig and cow. When rat MUC5AC was immunoprecipitated, a band at about 180 kDa was obtained.

MARCKS regulation of mucin secretion by airway epithelium in vitro: interaction with chaperones

We have reported previously that myristoylated alanine-rich C kinase substrate (MARCKS) is a key regulatory molecule controlling mucin secretion by airway epithelial cells in vitro and in vivo. The results of those studies supported a mechanism whereby MARCKS, upon phosphorylation by protein kinase C (PKC), translocates from plasma membrane to cytoplasm, where its binding to membranes of intracellular mucin granules is a key component of the secretory pathway. It remains unknown how MARCKS is targeted to and/or preferentially attaches to mucin granule membranes. We hypothesized that the chaperone cysteine string protein (CSP) may play an important role in this process. CSP was shown to associate with membranes of intracellular mucin granules in well-differentiated normal human bronchial epithelial (NHBE) cells in vitro, as determined by ultrastructural immunohistochemistry and Western blotting of isolated granule membranes. CSP in these cells complexed with MARCKS, as shown by co-immunoprecipitation. Given reported associations between CSP and a second chaperone, heat shock protein 70 (HSP70), a role for HSP70 in the MARCKS-dependent secretory mechanism also was investigated. HSP70 appeared to form a trimeric complex with MARCKS and CSP associated with mucin granule membranes within airway epithelial cells. Transfection of the HBE1 human bronchial epithelial cell line with siRNAs targeting sequences of MARCKS, CSP, or HSP70 resulted, in each case, in significant knockdown of expression of these proteins and subsequent attenuation of mucin secretion. The results provide the first evidence that CSP and HSP70, and their interactions with MARCKS, are involved in mucin secretion.

Protein kinase C delta regulates airway mucin secretion via phosphorylation of MARCKS protein

Mucin hypersecretion is a major pathological feature of many respiratory diseases, yet cellular mechanisms regulating secretion of mucin have not been fully elucidated. Previously, we reported that mucin hypersecretion induced by human neutrophil elastase involves activation of protein kinase C (PKC), specifically the delta-isoform (PKC delta). Here, we further investigated the role of PKC delta in mucin hypersecretion using both primary human bronchial epithelial cells and the human bronchial epithelial 1 cell line as in vitro model systems. Phorbol-12-myristate-13-acetate (PMA)-induced mucin hypersecretion was significantly attenuated by rottlerin, a PKC delta-selective inhibitor. Rottlerin also reduced PMA- or human neutrophil elastase-induced phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS) protein in these cells. Both secretion and MARCKS phosphorylation were significantly enhanced by the PKC delta activator bryostatin 1. A dominant-negative PKC delta construct (pEGFP-N1/PKC delta K376R) transfected into human bronchial epithelial 1 cells significantly attenuated both PMA-induced mucin secretion and phosphorylation of MARCKS, whereas transfection of a wild-type construct increased PKC delta and enhanced mucin secretion and MARCKS phosphorylation. Similar transfections of a dominant-negative or wild-type PKC epsilon construct did not affect either mucin secretion or MARCKS phosphorylation. The results suggest that PKC delta plays an important role in mucin secretion by airway epithelium via regulation of MARCKS phosphorylation.

Protease-activated receptor-2 (PAR-2) is a weak enhancer of mucin secretion by human bronchial epithelial cells in vitro

PAR-2, a member of a family of G-protein-coupled receptors, can be activated by serine proteases via proteolytic cleavage. PAR-2 expression is known to be upregulated in respiratory epithelium subsequent to inflammation in asthma and chronic obstructive pulmonary disease (COPD). Since these diseases also are characterized by excessive mucus production and secretion, we investigated whether PAR-2 could be linked to mucin hypersecretion by airway epithelium. Normal human bronchial epithelial (NHBE) cells in primary culture or the human bronchial epithelial cell lines, NCI-H292 and HBE-1, were used. NHBE, NCI-H292, and HBE-1 cells expressed prominent levels of PAR-2 protein. Short-term (30min) exposure of cells to the synthetic PAR-2 agonist peptide (SLIGKV-NH2) elicited a small but statistically significant increase in mucin secretion at high concentrations (100microM and 1000microM), compared to a control peptide with reversed amino acid sequence (VKGILS-NH2). Neither human lung tryptase nor bovine pancreatic trypsin, both PAR-2 agonists, affected NHBE cell mucin secretion when added over a range of concentrations. Knockdown of PAR-2 expression by siRNA blocked the stimulatory effect of the AP. The results suggest that, since PAR-2 activation only weakly increases mucin secretion by human airway epithelial cells in vitro, PAR-2 probably is not a significant contributor to mucin hypersecretion in inflamed airways.

Mechanisms of mucin production by rhinovirus infection in cultured human airway epithelial cells

Mucus hypersecretion relates to exacerbations of bronchial asthma and chronic obstructive pulmonary disease (COPD) caused by rhinovirus (RV) infection. We examined the mechanisms of RV infection-induced mucin production in human tracheal surface epithelial cells and submucosal gland cells. RV14 up-regulated the mRNA expression of MUC2, MUC3, MUC5AC, MUC5B and MUC6, and increased MUC5AC and total mucin concentration in supernatants and lysates of the surface cells. An inhibitor of the nuclear factor kappaB caffeic acid phenylethyl ester, inhibitors of selective p44/42 mitogen-activated protein kinase-kinase PD98059 and U0126, and a selective Src inhibitor PP1 attenuated MUC5AC mRNA expression, and secretion and production of MUC5AC and total mucin glycoprotein in the surface cells. In the gland cells, RV14 also increased mRNA expression of MUC2, MUC5AC, MUC5B and MUC7, and the inhibitors attenuated the secretion of total mucin glycoprotein. Src-related p44/42 mitogen-activated protein kinase pathway may be associated with RV-induced mucin hypersecretion in human airways.

Human neutrophil elastase induces hypersecretion of mucin from well-differentiated human bronchial epithelial cells in vitro via a protein kinase C{delta}-mediated mechanism

The presence of mucus obstruction and neutrophil-predominant inflammation in several lung disorders, such as cystic fibrosis, suggests a relationship between neutrophils and excess mucus production. Mechanisms of human neutrophil elastase (HNE)-induced mucin secretion by well-differentiated normal human bronchial epithelial (NHBE) cells maintained in air/liquid interface culture were investigated. HNE increased mucin secretion in a concentration-dependent manner, with maximal stimulation (more than twofold) occurring within a short (15 minutes) time period. Mucins MUC 5 AC and MUC 5 B, but not MUC 2, were released in response to HNE. Stimulation of mucin secretion required partial elastase enzymatic activity and did not appear to involve a soluble product released by the cells. HNE-stimulated secretion involved activation of protein kinase C (PKC), as HNE exposure rapidly provoked PKC enzymatic activity that was attenuated by the general PKC inhibitors calphostin C and bisindoylmaleimide I. Of the different isoforms, PKCalpha, delta, zeta, lambda, iota, and epsilon were constitutively expressed in NHBE cells while PKCbeta, eta, and mu were PMA-inducible. PKCdelta was the only isoform to translocate from cytoplasm to membrane in response to HNE. Inhibition of PKCdelta attenuated HNE-mediated mucin secretion. The results suggest HNE stimulation of mucin release by human airway epithelial cells involves intracellular activation of PKC, specifically the delta isoform.

Membrane capacitance and conductance changes parallel mucin secretion in the human airway epithelium

Measurement of the magnitude and kinetics of exocytosis from intact epithelia has historically been difficult. Using well-differentiated cultures of human bronchial epithelial cells, we describe the use of transepithelial impedance analysis to enable the real-time quantification of mucin secretagogue-induced changes in membrane capacitance (surface area) and conductance. ATPgammaS, UTP, ionomycin, and PMA induced robust increases in total cellular capacitance that were demonstrated to be dominated by a specific increase in apical membrane surface area. The UTP-induced increase in capacitance occurred in parallel with goblet cell emptying and the secretion of mucin and was associated with decreases in apical and basolateral membrane resistances. The magnitude and kinetics of the capacitance increases were dependent on the agonist and the sidedness of the stimulation. The peak increase in capacitance induced by UTP was approximately 30 mucin granule fusions per goblet cell. Secretagogue-induced decreases in apical membrane resistance were independent of exocytosis, although each of the secretagogues induced profound reductions in basolateral membrane resistance. Transepithelial impedance analysis offers the potential to study morphological and conductance changes in cultured human bronchial epithelial cells.

An enzyme-linked immunosorbent assay (ELISA) for the determination of mucin levels in bronchoalveolar lavage fluid

INTRODUCTION

A method to measure the mucin concentration in bronchoalveolar lavage (BAL) fluid was developed to aid efforts to identify pharmacologically the mechanisms that modulate pathophysiological mucin secretion. Mucins are the major macromolecular components of mucus. In the airways, mucus is the first line of defense against inhaled microorganisms (infection) and particulates (irritation).

METHODS

An enzyme-linked immunosorbent assay (ELISA) was developed, comparing two monoclonal anti-mucin antibodies (A10G5 and 45M1) raised to human mucin, to quantify the mucin in BAL fluid from animal models of pulmonary inflammation. To validate the ELISA method, rats were exposed to ovalbumin (OVA, in sensitized rats), lipopolysaccharide (LPS), vanadium pentoxide (V(2)O(5)), or saline. One hundred microliters of BAL fluid was analyzed for mucin concentration. Pooled BAL fluid from untreated rats was used as an internal "plate standard", as a standard mucin that cross-reacts with A10G5 was unavailable.

RESULTS

We found both antibodies reacted with rat, human, and guinea-pig mucin; where the 45M1 antibody also reacted with the mucin in porcine BAL, while A10G5 did not. We determined the mucin concentration in each BAL fluid sample relative to the standard, defined as a mucin concentration of 100 plate units. BAL fluid from LPS (218+/-25 plate units, n=5), OVA (386+/-31, n=3), V(2)O(5) (1208+/-450, n=6) challenged rats displayed significantly elevated mucin concentration over their saline controls (126+/-22, n=12). Subsequently, the 45M1 antibody displayed immunoreactivity with a commercially available crude preparation of porcine stomach mucin, allowing us to calculate the concentration of mucin directly compared to the known concentration of the porcine stomach mucin standard. Both the 45M1 and A10G5 based ELISA assays detected higher mucin content in the saline challenged rat than the saline challenged guinea pig BAL.

DISCUSSION

The recent availability of the 45M1 antibody and the use of the crude purification of porcine stomach mucin as a reference standard should allow for direct comparison of mucin concentration in BAL (and other fluids).

Secretion of lactoferrin and lysozyme by cultures of human airway epithelium

Lactoferrin and lysozyme are important antimicrobial compounds of airway surface liquid, derived predominantly from serous cells of submucosal glands but also from surface epithelium. Here we compared release of these compounds from the following human cell cultures: primary cultures of tracheal epithelium (HTE), Calu-3 cells (a lung adenocarcinoma cell line frequently used as a model of serous gland cells), 16HBE14o- cells (an SV40 transformed line from airway surface epithelium), T84 cells (a colon carcinoma cell line), and human foreskin fibroblasts (HFF). For lysozyme, baseline secretory rates were in the order Calu-3 > 16HBE14o- > HTE ≈ T84 > HFF = 0; for lactoferrin, the only cell type showing measurable release was HTE; for mucus, HTE > Calu-3 > 16HBE14o- ≈ T84 > HFF = 0. A wide variety of neurohumoral agents and inflammatory stimuli was without effect on lactoferrin and lysozyme release from HTE or Calu-3 cells, although forskolin did stimulate secretion of water and lysozyme from Calu-3 cells. However, the concentration of lysozyme in the forskolin-induced secretions was much less than in airway gland secretions. Thus our data cast doubt on the utility of Calu-3 cells as a model of airway serous gland cells but do suggest that HTE could prove highly suitable for studies of mucin synthesis and release.

Heterogeneity of airways mucus: variations in the amounts and glycoforms of the major oligomeric mucins MUC5AC and MUC5B

Respiratory mucus contains a mixture of gel-forming mucins but the functional significance of these different mucin species is unknown. To help gain a better understanding of mucus in airways we therefore need to ascertain the concentration of each of the gel-forming mucins within respiratory secretions. Thus the aim of this study was to determine the amounts of specific gel-forming mucins directly from solubilized secretions of the airways and purified mucin preparations. We investigated the feasibility of using direct-binding ELISA employing mucin-specific antisera but were unable to obtain reliable data owing to interference with the immobilization of the mucins on the assay surface by 6 M urea and high levels of non-mucin proteins. We therefore developed an alternative approach based on quantitative Western blotting after agarose-gel electrophoresis, which was not subject to these problems. Here we demonstrate that this procedure provides reliable and reproducible data and have employed it to determine the amounts of the MUC2, MUC5AC and MUC5B mucins in saline-induced sputa from healthy airways and spontaneous sputa from asthmatic airways. Additionally we have used this procedure to analyse these glycoproteins in mucin preparations purified from cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) mucus. Our findings indicate that MUC5AC and MUC5B are the major oligomeric mucins and that airways mucus contains variable amounts of these glycoproteins. By contrast, the MUC2 mucin comprised, at most, only 2.5% of the weight of the gel-forming mucins, indicating that MUC2 is a minor component in sputum. Finally, we show that the amounts and glycosylated variants of the MUC5AC and MUC5B mucins can be altered significantly in diseased airways with, for instance, an increase in the low-charge form of the MUC5B mucin in CF and COPD mucus.

MARCKS protein is a key molecule regulating mucin secretion by human airway epithelial cells in vitro

Hypersecretion of airway mucin characterizes numerous respiratory diseases. Although diverse pathological stimuli can provoke exocytotic release of mucin from secretory cells of the airway epithelium, mechanisms involved remain obscure. This report describes a new paradigm for the intracellular signaling mechanism regulating airway mucin secretion. Direct evidence is provided that the myristoylated alanine-rich C kinase substrate (MARCKS) is a central regulatory molecule linking secretagogue stimulation at the cell surface to mucin granule release by differentiated normal human bronchial epithelial cells in vitro. Down-regulation of MARCKS expression or disruption of MARCKS function in these cells inhibits the secretory response to subsequent stimulation. The intracellular mechanism controlling this secretory process involves cooperative action of two separate protein kinases, protein kinase C and cGMP-dependent protein kinase. Upon stimulation, activated protein kinase C phosphorylates MARCKS, causing translocation of MARCKS from the plasma membrane to the cytoplasm, where it is then dephosphorylated by a protein phosphatase 2A that is activated by cGMP-dependent protein kinase, and associates with both actin and myosin. Dephosphorylated cytoplasmic MARCKS would also be free to interact with mucin granule membranes and thus could link granules to the contractile cytoskeleton, mediating their movement to the cell periphery and subsequent exocytosis. These findings suggest several novel intracellular targets for pharmacological intervention in disorders involving aberrant secretion of respiratory mucin and may relate to other lesions involving exocytosis of membrane-bound granules in various cells and tissues.

Differential regulation of airway mucin gene expression and mucin secretion by extracellular nucleotide triphosphates

The effects of extracellular nucleotide triphosphates on the stimulation of mucin production by airway epithelial cells were examined. The order of potency in stimulating mucin secretion in primary cultures of human tracheobronchial epithelial cells is: uridine 5'-triphosphate (UTP) approximately equal to adenosine 5'-triphosphate (ATP) approximately equal to ATP-gamma-S > uridine 5'-diphosphate approximately equal to adenosine 5'-diphosphate > alpha,beta-methylene ATP >> adenosine. However, only UTP can increase mucin gene (MUC5AC, MUC5B) expression; ATP and other analogues have no stimulatory effect. The stimulation of MUC5AC and MUC5B expression by UTP is time- and dose-dependent. A similar effect on the elevation of mucous cell population in mouse airway epithelium can be demonstrated in vivo by an intratracheal instillation of UTP-saline solution. The stimulatory effect of UTP or ATP on mucin secretion was inhibited by pertussis toxin, U73122, and Calphostin C, but not by PD98059, suggesting a G-protein/ phospholipase (PL) C/protein kinase (PK) C-dependent and mitogen-activated protein kinase (MAPK)-independent signaling pathway. However, the stimulatory effect of UTP on mucin gene expression was sensitive to pertussis toxin and PD98059, but not to Calphostin C and U73122, suggesting a G-protein/MAPK-dependent and PLC/PKC-independent signaling pathway. These findings are the first demonstration that UTP, a pyrimidine nucleotide triphosphate, can enhance both mucin secretion and mucin gene expression through different signaling pathways.

Mild and moderate asthma is associated with airway goblet cell hyperplasia and abnormalities in mucin gene expression

Excessive airway mucus is an important cause of morbidity and mortality in asthma, but the relationship between accumulation of mucus and goblet cell size, number, and function is incompletely understood. To address these questions, stored mucin in the epithelium and goblet cell size and number were measured morphometrically, and mucin gene expression was measured by polymerase chain reaction and immunohistochemistry in endobronchial biopsies from 13 subjects with mild and moderate asthma and from 12 healthy control subjects. Secreted mucin was measured in induced sputum. We found that stored mucin in the airway epithelium was three times higher than normal in the subjects with asthma (p < 0.005). Goblet cell size was similar in both groups, but goblet cell number was significantly higher in the subjects with asthma (93,043 +/- 15,824 versus 41,959 +/- 9,230/mm3, p < 0.05). In mild asthma (FEV1 > or = 80% pred, n = 7), the level of stored mucin was as high as in moderate asthma (FEV1 < 80% pred, n = 6), but the level of secreted mucin was significantly lower (28.4 +/- 6.3 versus 73.5 +/- 47.5 microg/ml, p < 0.05). Secreted mucin was inversely correlated with stored mucin for the whole asthma group (rs = -0.78, p = 0.007). MUC5AC was the predominant mucin gene expressed in healthy subjects and subjects with asthma, and MUC5AC protein was increased in the subjects with asthma. We conclude that even mild asthma is associated with goblet cell hyperplasia and increased stored mucin in the airway epithelium, whereas moderate asthma is associated with increased stored mucin and secreted mucin. These findings suggest that acute degranulation of hyperplastic goblet cells may represent a mechanism for asthma exacerbations in mild and moderate asthma and that chronic degranulation of goblet cells may contribute to chronic airway narrowing in moderate asthma.

Cross-species immunoreactivity of airway mucin as revealed by monoclonal antibodies directed against mucins from human, hamster, and rat

Airway mucin plays crucial role in host-defense and has been implicated in pathophysiology of various airway diseases including asthma and cystic fibrosis. The analysis of airway mucin has been hampered mostly by the lack of specific and efficient methods for the detection of mucin. Recent production of antibodies against airway mucin from several species and also the development of immunoassay procedures make it more efficient to study the airway mucin. However, the cross-species immunoreactivity of antibodies against airway mucin has not been clearly demonstrated and this prompted us to investigate the cross-species immunoreactivity of monoclonal antibodies against human (HM02), hamster (HTA), and rat airway mucin (RT03), which is three most widely used species in the study of mucin. All the monoclonal antibodies (MAbs) used in this study is IgM isotype and recognizes N-acetyl-galactosamine-linked carbohydrate core or backbone portion of airway mucin. In enzyme-linked immunoadsorbent assay (ELISA), Western blot, immunoprecipitation, and immunohistochemical staining experiments, it was demonstrated that human and hamster airway mucin showed strong cross-species immunoreactivity. However, rat airway mucin did not show any cross-species immunoreactivity against human and hamster airway mucin. Endotoxin-induced secretory cell metaplasia and hence the increase in mucin release from hamster airway mucin could be detected with antibodies against hamster and human airway mucin in vivo and in vitro. However, the same increase from rat airway could only be detected with antibody against rat airway mucin but not with antibodies against human and hamster airway mucin. In addition, the increase in mucin release from asthmatic patients could be detected with antibodies against human and hamster airway mucin but not with the antibody against rat airway mucin. The data from the present study implicates that the carbohydrate chain of human and hamster airway mucin, but not that of rat airway mucin, share common antigenic structure. In case of the interspecies use of the antibodies against airway mucin, it would be more desirable to clearly identify the cross-species immunoreactivity otherwise might lead to erroneous results.

Secretory cell differentiation and mucus secretion in cultures of human nasal epithelial cells: use of a monoclonal antibody to study human nasal mucin

We have developed an air-liquid interface culture system for human nasal epithelial cells that differentiate into mucociliary phenotypes in a defined serum-free medium. Dissociated cells obtained from nasal polyps were cultured on a collagen gel substrate. At confluence, the cells lost characteristics of differentiated cells, and secretory cell and ciliated cell differentiation appeared after 7 days in an air-liquid interface. After 21 days, about half of the epithelial cells were stained with Alcian blue-periodic acid-Schiff stain or monoclonal antibody HCS18, which was directed against human nasal mucin specific for epithelial secretory (goblet) cells. The quantitative examination using the antibody HCS18 revealed that the antibody-reactive nasal mucin was secreted only on the apical side of the cultures, and interleukin-1beta and tumor necrosis factor alpha stimulated these mucus secretions. The culture system with an antimucin monoclonal antibody developed in this study should be useful for studying polarized mucus secretion from human nasal epithelial cells.

Production and characterization of monoclonal antibodies against human airway mucins

The objective of this study was to generate and characterize monoclonal antibodies (MAbs) against human airway mucins, and therefore, should serve as a useful tool in studying the regulation of airway mucins in various physiological or pathological situations of human airway. As an antigen, we used a high molecular mass mucin preparation purified from the sputum of normal human subjects. Two monoclonal hybridomas, namely MAbs HM02 and HM03 were obtained and they showed strong immunoreactivity against purified or crude mucin in sputum or bronchial washing of normal human subject. With the high immunoreactivity of these MAbs, mucin contents could be analyzed with more than 100-fold dilution of human airway secretion. The antibodies recognized carbohydrate epitopes because their immunoreactivity was completely abolished by treatment of the mucin with 5 mM periodate. Further characterization of MAbs HM02 and HM03 showed that: (1) they belong to the IgM type; (2) they bind to high molecular mass mucins based on Western blot; (3) they could indirectly immunoprecipitate human airway mucin and as we know, this is the first to demonstrate immunoprecipitation of human airway mucin with anti-human mucin antibodies; and (4) they bind to the goblet cell in airway epithelium as well as some submucosal glands based on immunohistochemistry. Therefore, MAbs HM02 and HM03 should be able to serve as an invaluable tool in studying the regulation of airway mucins in various physiological and pathological situations of human airway.

A monoclonal antibody against hamster tracheal mucin, which recognizes N-acetyl-galactosamine containing carbohydrate chains as an epitope

Airway mucin that is present in airway secretion, plays an important role in host-defense by trapping airborne particles and removing them by mucociliary transport system. For the study of mucin, it is crucially important to have antibodies specific against mucin because other commonly used methods such as histologic stain for the detection of mucin usually suffer from varying levels of nonspecificity. In this study, we produced a monoclonal antibody (MAb) against hamster airway mucin, which is one of the most commonly used animal species for the study of mucin in vitro, and characterized its immunological properties along with the determination of the epitope it recognizes. The MAb, which was named MAb HTA, was IgM isotype and specific against mucin from both in vitro cell culture and in vivo airway secretion. In Western blot, MAb HTA specifically recognized high molecular weight airway mucin, which was also confirmed by the appearance of peak profile of immunological signal only on void volume fraction in Sepharose CL-4B gel filtration chromatography. It also immunoprecipitated high molecular weight hamster airway mucin with the aid of antimouse IgM agarose. In immunohistochemical stain of hamster trachea, it showed strong signal on airway epithelium and also on the mucin secreting goblet cell granules. The immunological signal was greatly increased by the treatment of endotoxin, which has been reported to cause airway secretory cell metaplasia. The MAb HTA recognized carbohydrate chains containing N-acetyl-galactosamine, one of the linking sugars of airway mucin, as an epitope. Treatment of mucin with N-acetyl-galactosaminidase caused great reduction of immunological signal. To the best of our knowledge, this is the first to report a MAb that recognizes N-acetylgalactosamine, a linking sugar of airway mucin. The specificity of MAb HTA against airway mucin and the clear demonstration of the epitope it recognizes should greatly aid the pharmacological and biochemical study of mucin in various physiological and pathological situations.

Restoration of the mucous phenotype by retinoic acid in retinoid-deficient human bronchial cell cultures: changes in mucin gene expression

Retinoid-deficient cultures of airway epithelial cells undergo squamous differentiation. Treatment of such cultures with retinoic acid (RA) leads to restoration of the mucous phenotype. The purpose of our study was to characterize the cellular and molecular changes following RA treatment of retinoid-deficient human tracheobronchial epithelial cell cultures. Of particular interest was to determine when during the conversion of the squamous to the mucous phenotype the mucin genes MUC2, MUC5AC, and MUC5B were expressed. We used cornifin alpha and secreted mucin as markers to monitor the squamous and mucous phenotypes, respectively. Our studies showed that the RA responsiveness of the cultures progressively decreased with protracted retinoid deficiency, requiring higher RA concentrations to restore the mucous phenotype. Within 12 h after the start of RA treatment, cornifin alpha expression decreased, signaling the beginning of a change in cellular phenotype. At 24 h after addition of RA to the cultures, a significant number of mucous cells appeared, and at 72 h mucin was secreted in measurable amounts. Induction of mucin gene expression occurred sequentially: MUC2, MUC5AC, and MUC5B mRNAs were upregulated at 24, 48, and 72 h, respectively. When cultures maintained in 10(-8) M RA were treated with 10(-6) M RA, MUC2 but not MUC5AC and MUC5B mRNA levels were upregulated within 6 h. Our study indicates that MUC2 mRNA is an early marker of mucous differentiation, whereas MUC5AC and MUC5B mRNAs are expressed during more advanced stages of mucous differentiation. Our studies further suggest that each of the mucin genes is regulated by distinct mechanisms.

Integration of growth factor, extracellular matrix, and retinoid signals during bronchial epithelial cell differentiation

Epithelial cell differentiation is regulated by specific combinations of growth factors, hormones, and extracellular matrix (ECM). How these divergent signals are integrated is largely unknown. We used primary cultures of normal human bronchial epithelial cells (NHBEs) to investigate mechanisms of signal integration. In defined, serum-free media, NHBEs undergo mucosecretory differentiation only when grown in the presence of retinoids and on the appropriate substratum (collagen gels). We identified the retinoic acid receptor beta (RARbeta) gene as an early marker of NHBE differentiation. In contrast to immortalized cell lines, in NHBEs strong retinoid-induced RARbeta transcription occurs only when cells are grown on collagen gels, and it requires new protein synthesis and a cis-acting element that maps outside the known RARbeta promoter elements. NHBEs grown on collagen gels exhibit reduced epidermal growth factor (EGF)-induced Raf, MEK, and mitogen-activated protein kinase (MAPK) activity. This correlates with a specific inability to achieve high levels of p66(SHC) tyrosyl phosphorylation and association of p66(SHC) with GRB2, despite high levels of EGF receptor (EGFR) autophosphorylation. Notably, inhibition of EGFR or MEK/MAPK activation replaces the ECM requirement for RARbeta induction. Our results strongly suggest that a key mechanism by which specific ECMs facilitate retinoid-induced mucosecretory differentiation of NHBEs is by restricting the level of EGFR-dependent MEK/MAPK activation evoked by autocrine and/or paracrine EGFR ligands.

Production and characterization of monoclonal antibodies against rat tracheal mucins

The objective of this study was to generate and characterize monoclonal antibodies against rat airway mucins. Therefore, it should serve as a useful tool in studying the regulation of airway mucins using various in vivo rat models that are currently available. As an antigen, we used a high molecular mass mucin preparation purified from the spent media of rat tracheal surface epithelial cells in primary culture. Seven monoclonal hybridomas were obtained, among which mAbRT03 showed the highest immunoreactivity against the mucin. All of the antibodies secreted by these hybridomas recognized carbohydrate epitopes but not sialic acid residues, since their immunoreactivity was completely abolished by treatment of the mucin with 20 mM periodate but not with neuraminidase. Further characterization of mAbRT03 showed that (1) it belongs to the IgM type, (2) it binds to high molecular mass mucins based on Western blot, (3) it could indirectly immunoprecipitate rat airway mucin--and, as we know, this is the first demonstration of immunoprecipitation of airway mucin with anti-mucin antibodies--(4) it binds to the luminal side of tracheal epithelium as well as some goblet cells based on immunohistochemistry, and (5) it also recognizes in vivo airway mucins from rats, but not from human nor hamsters, which have been purified from the airway lavage fluids. This is the first monoclonal antibody against rat airway mucin, which has been developed against purified rat airway mucins. Therefore, mAbRT03 should be able to serve as an invaluable tool in studying the regulation of airway mucins using various intact rat models that are currently available.

Comparison between ELISA and gel-filtration assay for the quantitation of airway mucins

In this study, we developed immunoassay methods for the more convenient and effective detection of rat tracheal mucin and the results were compared with those of [3H]glucosamine based gel-filtration method. A monoclonal anti-rat tracheal mucin antibody, mAbRT03, which specifically recognizes rat tracheal mucins, was used throughout in this study. To induce mucin secretion, varying concentrations of ATP (0-2 mM) were applied to the primary rat tracheal surface epithelial (RTSE) cell culture which had been metabolically radiolabeled with [3H]glucosamine and the secretion of mucin was analyzed both by the immunoassay and the gel-filtration chromatography methods. For the immunoassay, the following two procedures were employed. 1) Simple ELISA; the culture spent media were directly coated onto the assay plate and the immunoreactivity with mAbRT03 was assessed from the standard curve generated with the purified rat mucin. 2) Inhibition ELISA; A known amount of the purified rat mucin was coated onto the assay plate and then ATP-stimulated culture spent media were added to inhibit the immunoreactivity with mAbRT03. The contents of mucin in the sample were calculated from the standard inhibition curve which was generated with the purified rat mucin. The assay results obtained from the immunoassays were identical with those from the gel-filtration methods. The present result indicates that ELISA can be substituted for the laborious, time-consuming gel-filtration assay in studying the regulation of airway mucin release from cultured airway epithelial cells.

Elevated serum levels of mucin-associated antigen in patients with acute respiratory distress syndrome

Increased serum levels of mucin-associated antigen have been previously demonstrated in patients with cystic fibrosis (CF) and interstitial pneumonia, and in lung-transplant recipients. The present study assessed the serum airway mucin levels in patients with acute respiratory distress syndrome (ARDS). An enzyme-linked immunosorbent assay (ELISA) method with a human-airway-mucin-specific monoclonal antibody (17Q2) was used to measure serum mucin levels in normal subjects, chronic smokers, patients with chronic bronchitis and other pulmonary diseases, patients with acute cardiogenic lung edema, and patients with ARDS. The serum mucin levels measured 9.9 +/- 0.8 ng/ml (mean +/- SEM, n = 59) in normal subjects, 12.7 +/- 1.6 ng/ml (n = 29) in chronic smokers, 21.8 +/- 1.9 ng/ml (n = 28) in patients with chronic bronchitis and other pulmonary diseases, 9.0 +/- 3.1 ng/ml (n = 5) in patients with acute cardiogenic lung edema. The serum mucin level was 53.8 +/- 6.6 ng/ml (n = 13) in patients with ARDS (p < 0.05, as compared with the four other groups). Serial measurements of serum mucin levels were obtained in patients with ARDS. Statistical analysis showed an inverse correlation of serial measurements of serum mucin with static respiratory-system compliance (p = 0.021), an inverse correlation of sequential serum mucin levels and log(Pa(O2)/Fl(O2)) (p = 0.016), and a positive correlation of sequential serum mucin levels and lung injury score (LIS) (p = 0.019). Gel-filtration analysis showed that mucin-associated antigens in ARDS sera were polydispersed and smaller than the antigens in normal sera. This study indicates that an increasing amount of degraded mucin occurs in patients with ARDS.

Production and characterization of monoclonal antibodies against guinea pig tracheal mucins

Thirty-five hybridomas that secrete mouse monoclonal antibodies (MAb) against guinea pig (G.P.) tracheal mucins were established. The MAbs were characterized immunologically, biochemically, and immunohistochemically at both light and electron microscopic levels. Isotyping of the MAbs revealed 14 to be IgM, 13 IgG1, 3 IgG2, and 5 IgG3. The MAbs demonstrated various patterns of binding in immunoblots against mucins derived from G.P. tracheal explants. This suggested the presence of "subpopulations" of G.P. tracheal mucins with specific MAbs binding to different epitopes on the mucin molecules. Periodate oxidation indicated that 33 of the 35 MAbs recognized carbohydrate epitopes on the mucin molecules. Ten of the MAbs also reacted with both bovine and ferret tracheal mucins, while 7 and 6 MAbs bound only to bovine and ferret tracheal mucins, respectively. The generated MAbs should be useful for immunomeasurement of mucin secretion in vivo (e.g., in bronchoalveolar or airway lavage fluid) and in vitro (e.g., cell and organ cultures) from cells of guinea pig and (with certain MAbs) bovine and ferret origin.

Characterization of a unique mucin-like glycoprotein secreted by a human endometrial adenocarcinoma cell line (Ishikawa)

A human endometrial adenocarcinoma cell line (Ishikawa) has been shown to incorporate [3H]glucosamine and to secrete a radiolabeled high molecular weight compound which is excluded from a Sepharose CL-2B column. The excluded material was resistant to hyaluronidase, chondroitinase ABC, and heparinase. These findings rule out the possibility of this material being a proteoglycan. The susceptibility of this material to digestion with pronase, neuraminidase, and alkaline borohydride treatment strongly suggests that the excluded material is an O-glycosidic glycoprotein. The glycoprotein secreted by Ishikawa cells (ICGP) did not react immunologically with antibodies against either lactoferrin or fibronectin, but did react with an antibody made against tracheal mucin. Conversely, immunoblot analysis revealed that an antibody made against ICGP did not recognize hyaluronic acid, chondroitin, heparin, nasal turbinate mucin, bovine submaxillary gland mucin, lactoferrin, or fibronectin, but did recognize tracheal mucin. Analysis of ICGP amino acid and carbohydrate composition showed that it is rich in serine, threonine, glutamic acid, aspartic acid, and N-acetylneuraminic acid. In this respect, ICGP differs from other mucins, even though it is immunologically similar to respiratory mucin; hence we may consider ICGP to be a mucin-like glycoprotein. Secretion of ICGP can be modulated by Ca(2+)-ionophore and other mucus secretagogues, such as platelet activating factor, carbachol, and monocyte/macrophage mucus secretagogue, all mediators of lung inflammation. Ishikawa cells and anti-ICGP antibody may be used in studies on in vitro regulation of mucin-like glycoprotein synthesis and secretion in the respiratory tract as well as in the endometrium.

Nucleotide regulation of goblet cells in human airway epithelial explants: normal exocytosis in cystic fibrosis

The regulation of mucin secretion by airway goblet cells is poorly understood and the receptor-based regulatory mechanisms have not been described in human airways. In the present study, we report that extracellular triphosphate nucleotides regulate the rate of granule release from goblet cells in both normal and cystic fibrosis (CF) airway epithelial explants. Explants isolated from nasal and tracheobronchial tissues were mounted in perfusion chambers and the secretory activity was assessed by videomicroscopic determination of degranulation in single goblet cells and by ELISA determination of mucins secreted into the mucosal perfusate. Baseline degranulation was measured at 0.05 degranulation events (DE)/min. In normal goblet cells, mucosal ATP (10(-4) M, n = 17) induced a biphasic secretory response comprising 29.1 +/- 4.9 DE during the first 5 min, with an initial rate of 118.2 +/- 10.2 DE/min. Mucosal UTP (10(-4) M, n = 9) induced a similar response to ATP (initial rate: 89.2 +/- 23.9 DE/min, 17.9 +/- 5.1 DE in 5 min), but mucosal 2-MeSATP was not an effective agonist (initial rate: 1.5 +/- 1.4 DE/min, 2.3 +/- 0.5 DE in 5 min). Determination of mucins by ELISA confirmed that both ATP and UTP induced similar secretory responses but that 2-MeSATP was not effective. In CF explants, mucosal UTP (10(-4) M, n = 6) induced similar responses to those observed in normal tissues (initial rate: 82.5 +/- 27.5 DE/min, 18.8 +/- 4.1 DE in 5 min). We conclude that human nasal and tracheobronchial goblet cells are stimulated by mucosal nucleotides, probably via a 5'-nucleotide receptor, and that this response is unaffected by CF.

Markers of mucus secretion and DNA levels in induced sputum from asthmatic and from healthy subjects

To determine whether markers of mucus secretion can be quantified in airway lining fluid from asthmatic and from healthy subjects, we measured levels of a mucin-like glycoprotein (MLG) and lactoferrin in sputum induced by inhalation of hypertonic (3%) saline in 18 asthmatic and in 10 healthy subjects. Because DNA, like mucin, contributes to the viscosity of airway secretions, we also measured DNA levels in the induced sputum samples. To control for the presence of saliva in sputum, we also analyzed saliva samples from all subjects. The entire sputum sample and the saliva sample were reduced using dithiotreitol, and biochemical analysis was performed on supernatants obtained after centrifugation. We found that induced sputum from asthmatic subjects had higher levels of MLG [2,574.4 +/- 907.8 (mean +/- SEM) versus 562.2 +/- 90.5 micrograms/ml, p < 0.007] and DNA (7.1 +/- 1.6 versus 3.6 +/- 0.6 micrograms/ml, p < 0.05), but the difference in lactoferrin levels failed to reach statistical significance. However, in the subgroup of asthmatic subjects who gave a history of sputum production (n = 9), lactoferrin levels were higher than in the healthy control subjects (118.9 +/- 46.3 versus 35.2 +/- 6.5 micrograms/ml, p < 0.05). The very low levels of MLG, DNA, and lactoferrin measured in saliva were not significantly different in asthmatic subjects from those in healthy subjects. We conclude that measurement of markers of mucus secretion in induced sputum is feasible in asthmatic and healthy subjects, and it reveals abnormally high markers of mucus secretion in subjects with stable asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

Secretory differentiation and cell type identification of a human fetal bronchial epithelial cell line (HFBE)

A human fetal bronchial epithelial cell line (HFBE) grew in an undifferentiated pattern under conventional culture conditions. Despite a somewhat fibroblastic shape the cells maintained immunoreactivity to cytokeratin, carcinoembryonic antigen and epithelial membrane antigen. When grown on a collagen gel in a growth-hormone-supplemented medium, their spindle shape became more conspicuous. With an additional supplement of vitamin A (6 micrograms/ml), most of the cells underwent differentiation by producing many bright inclusion bodies which proved to be strongly positive with periodic acid-Schiff and weakly positive with alcian blue staining. Electron microscopy revealed a well-developed rough endoplasmic reticulum, an enlarged Golgi apparatus and many highly electron-dense secretory granules resembling those of Clara cells. Biochemical analysis demonstrated that HFBE cells cultured on collagen gel with vitamin A secreted hyaluronic acid and neutral glycoproteins containing mainly N-linked glycoproteins whose glycans were of a complex type. A monoclonal antibody (SEC-41) generated against the neutral glycoproteins detected a glycoprotein of approximately 52 kDa in the spent culture medium of differentiated HFBE cells. This antibody also reacted with the intracytoplasmic secretory granules in these cells. When tested on frozen sections of lung tissue, the immunohistochemical reactivity of the SEC-41 antibody was confined to Clara cells, some type II pneumocytes in the adult lung, and respiratory epithelial cells in the fetal lung. Moreover, this antibody could detect secretory glycoprotein in broncho-alveolar lavages from two patients. This paper clearly demonstrates that cells derived from human fetal bronchial epithelium can be cultivated in an undifferentiated precursor state and, under appropriate culture conditions, can be stimulated to undergo differentiation into a Clara cell type.

Differentiation of Clara cell (distal type) antigen in human fetal bronchial epithelial cell line (HFBE)

A human fetal bronchial cell line (HFBE) grew in an undifferentiated pattern under conventional culture conditions. Despite a somewhat fibroblastic shape, however, they still maintained an immuno-reactivity to cytokeratin, carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA). When grown on a collagen gel in a growth hormone-supplemented medium, their spindle shape became more conspicuous. With the additional supplement of 6 micrograms/ml vitamin A, most of the cells underwent differentiation by producing many bright inclusion bodies which proved to be strongly positive to periodic acid Schiff (PAS) and barely positive to alcian-blue (AB) staining. Electron microscopy revealed well-developed rough endoplasmic reticulum (rER), enlarged Golgi apparatus and many highly electron-dense secretory granules resembling those of Clara cells. Biochemical analysis demonstrated that HFBE cells cultured on collagen gel with vitamin A secreted products containing glycoconjugates of two different molecular weights. The higher molecular weight-product was identified as hyaluronic acid and the lower molecular weight-product as a mixture of neutral glycoproteins containing mainly N-linked glycoproteins whose glycans were of a complex type. While the secretion of hyaluronic acid was inhibited by vitamin A in a dose-dependent manner, that of the neutral glycoproteins was most enhanced by vitamin A in the range from the physiological concentration of 600 ng/ml to 6 micrograms/ml. A monoclonal antibody (SEC-41) generated against the secretory products with the lower molecular weight detected a glycoprotein of approximately 52 kd in the spent culture medium of differentiated HFBE cells. This antibody also reacted with the intra-cytoplasmic secretory granules in these cells. When tested on freeze-sectioned lung tissue, immunohistochemical reactivity of SEC-41 antibody was confined to Clara cells, some type II pneumocytes in the adult lung and respiratory epithelial cells of the fetal lung tissue. Moreover, this antibody could detect the secretory glycoproteins in the broncho-alveolar lavages (BAL) of two human cases. This paper has clearly demonstrated that cells derived from human fetal bronchial epithelium can be cultivated in an undifferentiated precursor state and under appropriate culture conditions they can be stimulated to undergo differentiation into a Clara cell type.

Characterization of the mucin differentiation in human lung adenocarcinoma cell lines

Four human lung adenocarcinoma cell lines were established in serum-free F12 medium supplemented with insulin, transferrin, hydrocortisone, cholera toxin, selenium, epidermal growth factor, bovine hypothalamic extract, and retinoic acid. Histochemical analyses with periodic acid-Schiff with and without diastase treatment (PAS-D technique) and immunocytochemistry with a mucin-specific monoclonal antibody demonstrated that three of the cell lines (CL2, CL3, and NCL2) were capable of mucin production. Biochemical characterizations of mucin produced by adenocarcinoma cells were focused on one of the cell lines, CL2 cells, which showed the most prominent reactivity with mucin-specific monoclonal antibody. Biochemical analysis using the mucin precursors [3H]glucosamine and [14C]serine indicated that CL2 cells can synthesize high-molecular-weight (M(r) greater than 200 kD) glycoprotein molecules that can be immunoprecipitated by this mucin-specific monoclonal antibody. The high-molecular-weight glycoproteins isolated from CL2 cells specifically reacted with mucin-specific monoclonal antibody by Western blot analysis, and composition analyses showed high levels of serine and threonine and a low level of aromatic amino acids, which are similar to human airway mucin. These observations suggest that lung adenocarcinoma CL2 cells cultured in this serum-free medium can retain function of airway mucin synthesis. Cell kinetic studies of these four cell lines showed that the cell line (CL1) without the mucin differentiation had a higher proliferative index and a shorter population doubling time as compared with the other three cell lines (CL2, CL3, and NCL2) with mucin differentiation. Examination of the retinoblastoma protein expressions in these adenocarcinoma cell lines revealed a phosphorylated pattern that correlated inversely with the mucin synthesis status of these cell lines.(ABSTRACT TRUNCATED AT 250 WORDS)

An unusual expression of a squamous cell marker, small proline-rich protein gene, in tracheobronchial epithelium: differential regulation and gene mapping

An unusual expression of a putative squamous cell marker, small proline-rich protein (spr1), in mucociliary epithelial cells of conducting airways was demonstrated in a serum-free culture system. A cDNA clone was isolated from the cDNA library of monkey tracheobronchial epithelial (TBE) cells by differential hybridization. This cDNA clone, MT5, exhibited 98% homology to a DNA sequence obtained from human keratinocytes treated with either UV light or phorbol esters (T. Kartasova et al., 1988, Mol. Cell. Biol. 8:2195-2230). The predicted peptide of MT5 is unusual for its high content of proline (29%), glutamine (18%), and cysteine (9%) and its repeated PKVPEPC units. The level of spr1 mRNA in cultured cells was inhibited more than 90% by vitamin A. In contrast, phorbol 12-myristate 13-acetate (PMA) stimulated the level of spr1 mRNA by 3- to 8-fold. This differential regulation coincided with the effects of these chemicals on the cornification of cultured TBE cells. Using MT5 as a probe, we have localized the tracheal spr1 gene on the human chromosome 1 by a Southern blot analysis using a panel of human-rodent somatic cell hybrid DNAs. The gene was further sublocalized to bands q22-23 by in situ hybridization.