Dieter C. Gruenert

Bioluminescence detection of ATP release mechanisms in epithelia

Autocrine and paracrine release of and extracellular signaling by ATP is a ubiquitous cell biological and physiological process. Despite this knowledge, the mechanisms and physiological roles of cellular ATP release are unknown. We tested the hypothesis that epithelia release ATP under basal and stimulated conditions by using a newly designed and highly sensitive assay for bioluminescence detection of ATP released from polarized epithelial monolayers. This bioluminescence assay measures ATP released from cystic fibrosis (CF) and non-CF human epithelial monolayers in a reduced serum medium through catalysis of the luciferase-luciferin reaction, yielding a photon of light collected by a luminometer. This novel assay measures ATP released into the apical or basolateral medium surrounding epithelia. Of relevance to CF, CF epithelia fail to release ATP across the apical membrane under basal conditions. Moreover, hypotonicity is an extracellular signal that stimulates ATP release into both compartments of non-CF epithelia in a reversible manner; the response to hypotonicity is also lost in CF epithelia. The bioluminescence detection assay for ATP released from epithelia and other cells will be useful in the study of extracellular nucleotide signaling in physiological and pathophysiological paradigms. Taken together, these results suggest that extracellular ATP may be a constant regulator of epithelial cell function under basal conditions and an autocrine regulator of cell volume under hypotonic conditions, two functions that may be lost in CF and contribute to CF pathophysiology.

Lack of inducible nitric oxide synthase in bronchial epithelium: a possible mechanism of susceptibility to infection in cystic fibrosis

Cystic fibrosis (CF) is an inherited disorder associated with severe inflammation and repeated bacterial infection and colonization in the lung. Airway epithelium is involved in defence against bacteria, but this system may be defective in CF. Pro‐inflammatory cytokines can stimulate the expression of inducible nitric oxide synthase (iNOS), an enzyme generating nitric oxide, which functions as an important mediator in host defence mechanisms. To understand better the poor resistance to infections in the CF lung, the expression of the iNOS gene was investigated in explanted lungs from patients with cystic fibrosis (n‐13), bronchiectasis (n‐3), emphysema (n‐14), and in normal lungs (n‐8). In addition, bronchial epithelial cell lines were examined to study iNOS gene expression in vitro. Strong immunoreactivity for iNOS was seen in inflammatory cells and bronchial epithelium in all the diseased lungs, except for bronchial epithelium in CF. Quantitative analysis showed a significant reduction in the area of epithelium immunostained in CF [CF 6·8±1·6 (%±SEM); emphysema 18·2±2·8; normal 9·6±0·8, P<0·01], regardless of steroid treatment. These results were supported by in situ hybridization of iNOS mRNA, which showed a pattern of gene expression in CF, emphysema, and normal lung which paralleled that of protein immunoreactivity. Stimulation with cytokines (IL‐1β, TNF‐α, and IFN‐γ) increased the expression of iNOS mRNA detected by reverse transcriptase‐polymerase chain reaction (RT‐PCR) in cultures of normal (16HBE14o−), but not CF (CFBE41o−, with ΔF508 CFTR mutation) epithelial cells. Expression of iNOS in inflammatory cells suggests that the gene is normal in CF. Absence of iNOS from bronchial epithelium may be due to low expression of the gene resulting from abnormalities in the signalling system that normally causes induction, such as cytokine receptors, second messengers or transcription factors. The resulting deficiency of the nitric oxide defence system may be relevant to the susceptibility of CF patients to pulmonary bacterial colonization.

Long-term culture of normal and cystic fibrosis epithelial cells grown under serum-free conditions

SummaryThe understanding of pathways associated with differentiated function in human epithelial cells has been enhanced by the development of methods for the short-term culture of human epithelial cells. In general these methods involve the use of serum. The subculture and maintenance of epithelial cells in long-term culture has been more problematic. A serum-free medium developed for human bronchial epithelial cells was slightly modified and found to be useful for the subculture and long-term maintenance of not only bronchial epithelial cells, but also tracheal, nasal polyp, and sweat gland epithelial cells from either normal or cystic fibrosis individuals. The cells maintained epithelial-specific characteristics after multiple subcultures. Monolayers of epithelial cells showed junctional complex formation, the presence of keratin, and micro villi. Functional studies with Ussing chambers showed short circuit current (Isc) responses to isoproterenol, bradykinin, or calcium ionophore (A23187) in subcultured tracheal and bronchial cells.

A transformed human epithelial cell line that retains tight junctions post crisis

SummaryThe successful establishment of a postcrisis SV-40 T antigen transformed epithelial cell line, 1HAEo-, which retains tight junctions and vectorial ion transport, is described. Immunocytochemical analysis of 1HAEo- cells shows a defined pattern of cytokeratin staining and a characteristic pericellular localization of the adhesion molecule cellCAM 120/80, indicating the presence of junctional complexes. The presence of both tight junctions and desmosomes has been confirmed by electron microscopy. Cell monolayers have good transepithelial resistance measured in Ussing chambers. Cells increase chloride ion transport in response to addition of agents that raise either intracellular cAMP or calcium, measured either by36Cl− efflux or whole-cell patch clamp. An increase in short-circuit current, in response to these agents, can be measured in Ussing chambers. The presence of a depolarization-induced outwardly rectifying 45 pS chloride channel has been demonstrated in single cell detached membrane patches. In addition, the cells have been found to express mucin mRNA. These cells therefore demonstrate that it is possible to select transformed cell clones with particular morphologic characteristics, i.e. the presence of tight junctions and cell polarity, which also retain useful epithelial cell-specific functions, including vectorial ion transport. They also provide a major resource for the study of the structure and function of human epithelia.

Cholesterol enhances cationic liposome-mediated DNA transfection of human respiratory epithelial cells.

Cationic liposome transfection reagents are useful for transferring polynucleotides into cells, and have been proposed for human pulmonary gene therapy. The effect of adding cholesterol to cationic lipid preparations has been tested by first formulating the cationic lipid N-[1-(2,3-dioleoyloxy)propyl-N-[1-(2-hydroxy)ethyl]-N,N-dimethyl ammonium iodide (DORI) with varying amounts of dioleoylphos-phatidylethanolamine (DOPE) and cholesterol. Cholesterol was found to enhance lipid-mediated transfection in both the respiratory epithelial cells and mouse fibroblasts. These findings will facilitate nucleic acid transfection of many cell types including differentiated epithelial cell monolayers, and therefore may be useful for examining gene regulation in various cell types and for developing pulmonary gene therapy.

Cystic fibrosis transmembrane conductance regulator trafficking modulates the barrier function of airway epithelial cell monolayers

The cystic fibrosis transmembrane conductance regulator (CFTR) is an integral membrane glycoprotein which functions as an anion channel and influences diverse cellular processes. We studied its role in the development of epithelial tightness by expressing wild‐type (WT‐CFTR) or mutant (ΔF508‐CFTR) CFTR in human airway epithelial cell monolayers cultured at the air–liquid interface. Green fluorescent protein (GFP)‐tagged WT or ΔF508 constructs were expressed in the CF bronchial cell line CFBE41o− using adenoviruses, and the results were compared with those obtained using CFBE41o− lines stably complemented with wild‐type or mutant CFTR. As predicted, GFP‐WT‐CFTR reached the apical membrane whereas GFP‐ΔF508‐CFTR was only detected intracellularly. Although CFTR expression would be expected to reduce transepithelial resistance (TER), expressing GFP‐CFTR significantly increased the TER of CFBE41o− monolayers whilst GFP‐ΔF508‐CFTR had no effect. Similar results were obtained with cell lines stably overexpressing ΔF508‐CFTR or WT‐CFTR. Preincubating ΔF508‐CFTR monolayers at 29°C reduced mannitol permeability and restored TER, and the effect on TER was reversible during temperature oscillations. Expression of GFP‐ΔF508‐CFTR or GFP‐WT‐CFTR in a cell line already containing endogenous WT‐CFTR (Calu‐3) did not alter TER. The CFTR‐ and temperature‐dependence of TER were not affected by the CFTR inhibitor CFTRinh172 or low‐chloride medium; therefore the effect of CFTR on barrier function was unrelated to its ion channel activity. Modulation of TER was blunted but not eliminated by genistein, implying the involvement of tyrosine phosphorylation and other mechanisms. Modulation of CFTR trafficking was correlated with an increase in tight junction depth. The results suggest that CFTR trafficking is required for the normal organisation and function of tight junctions. A reduction in barrier function caused by endoplasmic reticulum retention of ΔF508‐CFTR may contribute to fluid hyperabsorption in CF airways.

Development and characterization of SV40 immortalized rat submandibular acinar cell lines

SummaryRat submandibular salivary gland acinar cells were transfected by CaPO4 precipitation using a plasmid containing a replication-defective simian virus (SV40) genome. Out of 27 clonal cell lines, two were shown to have moderate to high levels of cytodifferentiation and salivary gland acinar cell function. Functional studies with the two cell lines indicated that the β-adrenergic agonist, isoproterenol, vasoactive intestinal peptide, and prostaglandin E1 were effective activators of intracellular cyclic AMP production. Epinephrine, norepinephrine, phenylephrine, acetylcholine, and P2U-purinoceptor agonists were effective in increasing inositol phosphate production and intracellular free calcium levels, whereas substance P was without effect. Utilizing indirect immunofluorescence analysis, both cell lines were shown to express glutamine/glutamic acid-rich proteins, a submandibular acinar cell specific secretory protein family. Electron microscopic evaluation documented the maintenance of tripartite junctional complexes, cellular polarization, and the presence of moderate amounts of secretory granules and rough endoplasmic reticulum. The two cell lines had doubling times of 25 h.

Association of fibroblastoid features with the invasive phenotype in human bronchial cancer cell lines

The acquisition of a metastatic phenotype by epithelial cells implicates a series of changes altering their differentiation, their overall behavior and morphology. In the present study, we have examined the relationships between the cellular morphology, E-cadherin expression, matrix metalloproteinases expression and in vitro invasive properties in two human bronchial immortalized cell lines. The (16HBE14o-) cell line which did not show any invasive abilities in the Boyden chamber assay displayed a typical epithelial morphology in monolayer, expressed high levels of E-cadherin and synthesized neither MMP-2 and MT1-MMP nor vimentin. In contrast, the BZR cell line which was highly invasive displayed a more elongated phenotype in monolayer, did not produce E-cadherin but expressed vimentin, MMP-2 and MT1-MMP. Our data therefore suggest that the metastatic progression of broncho-pulmonary cancer cells results in a cellular dedifferentiation and the gain of some mesenchymal attributes (loss of E-cadherin and expression of vimentin) associated with enhanced degradative properties (expression of metalloproteinases).© Rapid Science 1998

Leukotriene A4 hydrolase activity of human airway epithelial cells

Human tracheal epithelial cells were incubated with LTA4 and metabolic products were identified in extracted supernatants by high pressure liquid chromatography, ultraviolet spectroscopy, and gas chromatography-mass spectrometry. In the presence of epithelial cells, LTA4 was converted to LTB4, but not to LTC4 or LTD4. Maximum LTB4 was released at an LTA4 concentration of 3 microM and had occurred by 30 min. LTB4 release was increased in the presence of albumin, but was not affected by extracellular calcium or A23187. This LTA4 hydrolase activity had a slower time course and could not be clearly inactivated by repeated exposure to substrate as is the case for previously described LTA4 hydrolase enzymes. This hydrolase appears to have novel biochemical characteristics.

Ionic selectivity of volume-sensitivity currents in human epithalial cells

The ion selectivity of swelling-activated Cl- currents has been investigated in three different human epithelial cell lines, two derived from the airway epithelium (9HTEo- and CFNPE9o-) and one from a colon carcinoma (T84). The relative permeability of volume-sensitive currents with respect to Cl- is: I- (1.19) greater than NO3- (1.07) approximately Br-(1.05) greater than Cl-(1.0) greater than F-(0.5) approximately HCO3-(0.48) greater than isethionate(0.28) greater than aspartate (0.14) approximately gluconate(0.13) approximately SO4(2-)(0.12). This type of ion selectivity is similar to that described for depolarization-activated outwardly rectifying Cl- channels found in epithelial cells.