IB3-1 Cells Research Articles

116. Functional Comparison of Four CFTR rAAV Vectors with Alternative Transcriptional Elements in Cell Lines and Polarized Human CF Airway Epithelia

The limiting packaging capacity (<5 kb) of recombinant adeno-associated virus (rAAV) has restricted the use of large promoters for the delivery of the cystic fibrosis transmembrane conductance (CFTR) cDNA in gene therapy of cystic fibrosis (CF). The relatively large size of the CFTR cDNA (4.5 kb) leaves little space for conventional, strong, promoters to enhance transcription. In clinical trials, the promoter activity of the ITR has been used to drive expression of CFTR. In the present study, we sought to compare different regulatory elements within rAAV2 vectors for their ability to express CFTR mRNA and functionally correct CFTR chloride channel defects. The vectors used in our study included: the current ITR promoter vector used in clinical trials (AVtgCF), a vector with a 83-bp synthetic promoter (AVCF83), a vector utilizing the ITR promoter and a 55-bp consensus sequence optimized intron derived from the rabbit Beta-globin gene (AV55globinCF), or a vector with a synthetic TATA box upstream of the 55-bp Beta-globin gene intron (AVmTATA55globinCF). These vectors were initially compared for their ability to express vector-derived CFTR mRNA following infection of HeLa and IB3 cells. Results from this analysis demonstrated significantly improved mRNA expression for most vectors as compared to the ITR-driven CFTR vector (AVtgCF). The approximate fold increase over that seen with AVtgCF was as follow: AVCF83: 1.1-fold in HeLa and 4.1-fold in IB3; AV55globinCF: 5.7-fold in HeLa and 42-fold in IB3; and AV-mTATA55globinCF: 4.7-fold in HeLa and 32-fold in IB3. These findings suggested that incorporation of the beta-globin intron might significantly improve CFTR correction in polarized human CF airway epithelia. Following apical infection of polarized CF airway epithelia, these regulatory elements showed improvements in the expression of CFTR mRNA as compared to AVtgCF (2.3-fold for AVCF83, 4.0-fold for AV55globinCF, and 3.3-fold for AVmTATA55globinCF). The functional correction of CFTR-mediated chloride transport was then assessed for each vector type as the cAMP-sensitive short-circuit current (Isc) in response to IBMX (100 M) and forskolin (10 M). The differences in the level of functional correction between the alternative promoter vectors and AVtgCF correlated with the increases in vector-derived CFTR mRNA. The delta-Isc in response to IBMX/forskolin for the AVCF83, AV55globinCF and AVmTATA55globinCF groups were 1.59-, 1.48-, and 1.83-fold higher than that observed in the AVtgCF group, respectively. Additionally we examined the kinetics of expression of AVtgCF and AV55globinCF following intranasal delivery to BALB/c mice. CFTR mRNA expression paralleled the in vitro data. AV55globinCF had higher levels of expression at all time points through 90 days ranging from 3-fold to greater than 10-fold. These studies provide further improvements in CFTR AAV vector design.

Down-regulation of IL-8 expression in human airway epithelial cells through helper-dependent adenoviral-mediated RNA interference

Interleukin (IL)-8 is a potent neutrophil chemotactic factor and a crucial mediator in neutrophil-dependent inflammation. Various cell types produce IL-8, either in response to external stimuli such as cytokines or bacterial infection, or after malignant transformation. Anti-IL-8 strategies have been considered for anti-inflammatory therapy. In this paper we demonstrate that the RNA interference technique can be used to efficiently down-regulate IL-8 protein expression in airway epithelial cells. We used a helper-dependent adenoviral vector to express a small hairpin (sh)RNA targeting human IL-8 in cultured airway epithelial cells (IB3-1, Cftr−/−; C38, Cftr-corrected) stimulated with TNF-α, IL-1β or heat-inactivated Burkholderia cenocepacia. Stimulated IL-8 expression in IB3-1 and C38 cells was significantly reduced by shRNA expression. The shRNA targeting IL-8 had no effect on the activation of NF-κB, or on the protein levels of IκB or IL-6, suggesting that this anti-IL-8 strategy was highly specific, and therefore may offer potential for the treatment of inflammatory diseases.Supplementary informationThe online version of this article (doi:10.1038/sj.cr.7290275) contains supplementary material, which is available to authorized users.

Modulation of deltaF508 cystic fibrosis transmembrane regulator trafficking and function with 4-phenylbutyrate and flavonoids.

Over 70% of patients with cystic fibrosis have the DeltaF508 mutation. This protein is a partially functional chloride (Cl-) channel that is prematurely degraded in the endoplasmic reticulum. Specific members of the flavonoid class of compounds have been shown to increase Cl- conductance of wild-type and DeltaF508 cystic fibrosis transmembrane regulator (CFTR). Although flavonoid effects on CFTR processing are unknown, evidence of effects on heat shock proteins, specifically those that have been shown to interact with CFTR, led us to believe that there would be an effect on CFTR processing through modulation of CFTR-chaperone interactions. We sought to determine (i) the effect of apigenin, genistein, kaempferol, and quercetin on CFTR processing in IB3-1 cells (F508/W1282X) and (ii) whether sequential treatment with 4-phenylbutyrate (4-PBA) to increase CFTR processing and flavonoid to directly stimulate CFTR would increase Cl- conductance. Our results show no significant effect on CFTR processing as measured by immunoblotting with 1 microM or 5 microM of apigenin, genistein, kaempferol, or quercetin. However, despite no effect on CFTR processing as determined by immunoblot, immunofluorescence demonstrated a favorable change in the intracellular distribution of CFTR with 24 h treatments of apigenin, kaempferol, and genistein. Furthermore, we observed an increase in Cl- conductance as measured by Cl- efflux in cells that were treated for 24 h with 4-PBA and then assayed with forskolin and 1 microM or 5 microM genistein, and also with cells treated for 24 h with either 4-PBA, 5 microM apigenin, or 1 microM quercetin. Thus, a combination of chronic treatment with 4-PBA or select flavonoids, followed by acute flavonoid exposure, may be beneficial in cystic fibrosis.

Purinergic signaling underlies CFTR control of human airway epithelial cell volume

Background: Loss of cystic fibrosis transmembrane conductance regulator (CFTR) function in cystic fibrosis (CF) causes dysregulation of multiple ion channels, water channels, and acid–base transporters in epithelia. As such, we hypothesized that dysregulation of many critical ion channels and transporters may cause defects in human airway epithelial cell volume regulation. Methods: Cell volume, regulatory volume decrease, and its regulation was assessed in real-time via Coulter Counter Multisizer III-driven electronic cell sizing in non-CF, CF, and CFTR-complemented CF human airway epithelial cells. SPQ halide fluorescence assay of hypotonicity-induced chloride efflux provided indirect validation of the cell volume assays. Results: CFTR, via autocrine ATP signaling, governs human airway epithelial cell volume regulation. Non-CF cells and wild-type (WT)-CFTR-transfected CF cells had normal regulatory volume decrease (RVD) responses that were attenuated by blockade of autocrine and paracrine purinergic signaling. In contrast, parental IB3-1 CF cells or IB3-1 cells expressing CFTR mutants (ΔF508, G551D, and S1455X) failed to RVD. CF cell RVD was rescued by agonists to P2Y G protein-coupled receptors and, more robustly, by agonists to P2X purinergic receptor channels. Conclusions: Loss of CFTR and CFTR-driven autocrine ATP signaling may underlie defective cell volume regulation and dysregulated ion, water, and acid–base transport in CF airway epithelia.

754. Intracellular Trafficking Patterns of rAAV-2 Demonstrate Significant Cell-Type Specificity

Serotype-dependent differences in recombinant AAV vector transduction have historically been attributed to differences in the distribution of serotype-specific receptors that affect viral binding and uptake by a target cell. Recently, this dogma has been challenged, as intracellular barriers responsible for limiting nuclear accumulation of rAAV have been uncovered. The efficiency of rAAV uptake by a cell is therefore no longer thought to always directly correlate with the efficiency of transgene expression in different target cell types. These intracellular barriers to transduction may also differ for various serotypes of rAAV that utilize distinct receptors' entry pathways. To further investigate the intracellular mechanisms of rAAV-2 transduction that might vary between cell types, we evaluated the subcellular localization of Cy3-rAAV-2 following transduction of HeLa and IB3 cells. Despite the fact that rAAV-2 enters these two cell types with similar efficiency, HeLa cells are much more transducible with rAAV-2 than with IB3 cells. However, tripeptidyl proteasome inhibitors can induce rAAV-2 transduction in IB3 cells (100-fold) with significantly greater efficiency than HeLa cells (10-fold). We hypothesized that these differences in transduction and responsiveness to proteasome inhibitors may be reflected by variations in the intracellular trafficking patterns of rAAV-2 between HeLa and IB3 cells. To test this hypothesis, we used fluorescent microscopy to evaluate the primary vesicular compartments in which Cy3-labeled rAAV-2 accumulate following infection of these two cell types. We have focused our analysis on three major endosomal compartments with different Rab small GTPase markers, including the peri-nuclear recycling endosome (Rab11), late endosome (Rab7), and late endosome to trans-golgi (Rab9). METHODS: Luciferase-expressing rAAV-2 was labeled with Cy3 and purified by column chromatography. EGFP N-terminus fusions with Rab11, Rab7, and Rab9 were generated in expression plasmids as markers for various intracellular compartments. IB3 and HeLa cells were transfected with various EGFP-Rab fusion constructs using lipofectamine for 48 hrs, followed by infection with Cy3-labeled rAAV-2 at 4°C for 30 minutes with an MOI of 10,000 DRP/cell. Cells were then washed and shifted to 37°C for 30 minutes to 2 hours, after which they were fixed and evaluated by fluorescent microscopy. RESULTS: A substantial degree of co-localization of Cy3-AAV-2 and EGFP-Rab11 was observed in HeLa cells from 30 min to 2 hrs postinfection. This pattern, however, was not observed in IB3 cells. In contrast, we found that the Cy3-labeled rAAV-2 was primarily co-localized with EGFP-Rab9 in IB3 cells. In HeLa cells, the degree of co-localization of Cy3-AAV and EGFP-Rab9 was not predominant. A significant amount of Cy3-labeled rAAV-2 was observed to be co-localized with EGFP-Rab7–tagged compartments in both HeLa and IB3 cells. These findings suggest that rAAV-2 traffics through a diversity of intracellular compartments in a cell-type specific manner. The effect of proteasome inhibitor treatment on the localization pattern of rAAV-2 in these two cell types is currently under investigation.

Activation of VPAC1 receptors by VIP and PACAP-27 in human bronchial epithelial cells induces CFTR-dependent chloride secretion.

1. In the human airway epithelium, VIP/PACAP receptors are distributed in nerve fibers and in epithelial cells but their role in transepithelial ion transport have not been reported. Here, we show that human bronchial epithelial Calu-3 cells expressed the VPAC(1) receptor subtype which shares similar high affinity for VIP and PACAP-27. 2. The stoichiometric binding parameters characterizing the (125)I-VIP and (125)I-PACAP-27 binding to these receptors were determined. 3. We found that VIP (EC(50) approximately 7.6 nM) and PACAP-27 (EC(50) approximately 10 nM) stimulated glibenclamide-sensitive and DIDS-insensitive iodide efflux in Calu-3 cells. 4. The protein kinase A (PKA) inhibitor, H-89 and the protein kinase C (PKC) inhibitor, chelerythrine chloride prevented activation by both peptides demonstrating that PKA and PKC are part of the signaling pathway. This profile corresponds to the pharmacological signature of CFTR. 5. In the cystic fibrosis airway epithelial IB3-1 cell lacking functional CFTR but expressing VPAC(1) receptors, neither VIP, PACAP-27 nor forskolin stimulated chloride transport. 6. Ussing chamber experiments demonstrated stimulation of CFTR-dependent short-circuit currents by VIP or PACAP-27 applied to the basolateral but not to the apical side of Calu-3 cells monolayers. 7. This study shows the stimulation in human bronchial epithelial cells of CFTR-dependent chloride secretion following activation by VIP and PACAP-27 of basolateral VPAC(1) receptors.

Gene expression profile analysis of 4-phenylbutyrate treatment of IB3-1 bronchial epithelial cell line demonstrates a major influence on heat-shock proteins.

Most individuals with cystic fibrosis (CF) carry one or two mutations that result in a maturation defect of the full-length CFTR protein. The DeltaF508 mutation results in a mutant protein that is degraded by the proteosome instead of progressing to the apical membrane where it functions as a cAMP-regulated chloride channel. 4-Phenylbutyrate (PBA) modulates heat-shock protein expression and promotes trafficking of DeltaF508, thus permitting maturation and membrane insertion. The goal of this study was to gain insight into the genetic mechanism of PBA action through a large-scale analysis of gene expression. The Affymetrix genome-spanning U133 microarray set was used to compare mRNA expression levels in untreated IB3-1 cell line cultures with cultures treated with 1 mM PBA for 12 and 24 h. The most notable changes in mRNA levels were transient elevations in heat-shock proteins. The majority of genes downregulated throughout the application period were functionally associated with control of gene expression. Another set of genes increased in expression starting at 24 h, suggesting these are downstream effects of altered gene expression initiated by PBA. More than one-third of the genes in this late expressing set were identified as having potential significance in understanding the pathology of CF. Our results demonstrate the usefulness of gene expression profile analysis in understanding the consequences of PBA treatment and provide insights in how this drug exerts its effect on the trafficking of CFTR.

Extracellular zinc and ATP restore chloride secretion across cystic fibrosis airway epithelia by triggering calcium entry.

Cystic fibrosis (CF) is caused by defective cyclic AMP-dependent cystic fibrosis transmembrane conductance regulator Cl(-) channels. Thus, CF epithelia fail to transport Cl(-) and water. A postulated therapeutic avenue in CF is activation of alternative Ca(2+)-dependent Cl(-) channels. We hypothesized that stimulation of Ca(2+) entry from the extracellular space could trigger a sustained Ca(2+) signal to activate Ca(2+)-dependent Cl(-) channels. Cytosolic [Ca(2+)](i) was measured in non-polarized human CF (IB3-1) and non-CF (16HBE14o(-)) airway epithelial cells. Primary human CF and non-CF airway epithelial monolayers as well as Calu-3 monolayers were used to assess anion secretion. In vivo nasal potential difference measurements were performed in non-CF and two different CF mouse (DeltaF508 homozygous and bitransgenic gut-corrected but lung-null) models. Zinc and ATP induced a sustained, reversible, and reproducible increase in cytosolic Ca(2+) in CF and non-CF cells with chemistry and pharmacology most consistent with activation of P2X purinergic receptor channels. P2X purinergic receptor channel-mediated Ca(2+) entry stimulated sustained Cl(-) and HCO(3)(-) secretion in CF and non-CF epithelial monolayers. In non-CF mice, zinc and ATP induced a significant Cl(-) secretory response similar to the effects of agonists that increase intracellular cAMP levels. More importantly, in both CF mouse models, Cl(-) permeability of nasal epithelia was restored in a sustained manner by zinc and ATP. These effects were reversible and reacquirable upon removal and readdition of agonists. Our data suggest that activation of P2X calcium entry channels may have profound therapeutic benefit for CF that is independent of cystic fibrosis transmembrane conductance regulator genotype.

Organic Solutes Rescue the Functional Defect in ΔF508 Cystic Fibrosis Transmembrane Conductance Regulator

The most common defect in cystic fibrosis, deletion of phenylalanine from position 508 of the cystic fibrosis transmembrane conductance regulator (Delta F508 CFTR), decreases the trafficking of this protein to the cell surface membrane. Previous studies have shown that low temperature and high concentrations of glycerol or trimethylamine N-oxide can partially counteract the processing defect of Delta F508 CFTR. The present study investigates whether physiologically relevant concentrations of organic solutes, accumulated by cotransporter proteins, can rescue the misprocessing of Delta F508 CFTR. Myoinositol alone or myoinositol, betaine, and taurine given sequentially increased the processing of core-glycosylated, endoplasmic reticulum-arrested Delta F508 CFTR into the fully glycosylated form of CFTR in IB3 cells or NIH 3T3 cells stably expressing Delta F508 CFTR. Pulse-chase experiments using transiently transfected COS7 cells demonstrated that organic solutes also increased the processing of the core-glycosylated form of green fluorescent protein-Delta F508 CFTR. Moreover, the prolonged half-life of the complex-glycosylated form of GFP-Delta F508 CFTR suggests that this treatment stabilized the mature form of the protein. In vitro studies of purified NBD1 stability and aggregation showed that myoinositol stabilized both the Delta F508 and wild type CFTR and inhibited Delta F508 misfolding. Most significantly, treatment of CF bronchial airway cells with these transportable organic solutes restores cAMP-stimulated single channel activity of both CFTR and outwardly rectifying chloride channel in the cell surface membrane and also restores a forskolin-stimulated macroscopic 36Cl- efflux. We conclude that organic solutes can repair CFTR functions by enhancing the processing of Delta F508 CFTR to the plasma membrane by stabilizing the complex-glycosylated form of Delta F508 CFTR.

Sustained Calcium Entry through P2X Nucleotide Receptor Channels in Human Airway Epithelial Cells

Purinergic receptor stimulation has potential therapeutic effects for cystic fibrosis (CF). Thus, we explored roles for P2Y and P2X receptors in stably increasing [Ca(2+)](i) in human CF (IB3-1) and non-CF (16HBE14o(-)) airway epithelial cells. Cytosolic Ca(2+) was measured by fluorospectrometry using the fluorescent dye Fura-2/AM. Expression of P2X receptor (P2XR) subtypes was assessed by immunoblotting and biotinylation. In IB3-1 cells, ATP and other P2Y agonists caused only a transient increase in [Ca(2+)](i) derived from intracellular stores in a Na(+)-rich environment. In contrast, ATP induced an increase in [Ca(2+)](i) that had transient and sustained components in a Na(+)-free medium; the sustained plateau was potentiated by zinc or increasing extracellular pH. Benzoyl-benzoyl-ATP, a P2XR-selective agonist, increased [Ca(2+)](i) only in Na(+)-free medium, suggesting competition between Na(+) and Ca(2+) through P2XRs. Biochemical evidence showed that the P2X(4) receptor is the major subtype shared by these airway epithelial cells. A role for store-operated Ca(2+) channels, voltage-dependent Ca(2+) channels, or Na(+)/Ca(2+) exchanger in the ATP-induced sustained Ca(2+) signal was ruled out. In conclusion, these data show that epithelial P2X(4) receptors serve as ATP-gated calcium entry channels that induce a sustained increase in [Ca(2+)](i). In airway epithelia, a P2XR-mediated Ca(2+) signal may have therapeutic benefit for CF.

Signaling intermediates required for NF-kappa B activation and IL-8 expression in CF bronchial epithelial cells.

Ligation of the asialoGM1 Pseudomonas aeruginosa pilin receptor has been demonstrated to induce IL-8 expression in airway epithelial cells via an NF-kappaB-dependent pathway. We examined the signaling pathways required for asialoGM1-mediated NF-kappaB activation in IB3 cells, a human bronchial epithelial cell line derived from a cystic fibrosis (CF) patient, and C-38 cells, the rescued cell line that expresses a functional CF transmembrane regulator. Ligation of the asialoGM1 receptor with specific antibody induced greater IL-8 expression in IB3 cells than C-38 cells, consistent with the greater density of asialoGM1 receptors in CF phenotype cells. AsialoGM1-mediated activation of NF-kappaB, IkappaB kinase (IKK), and ERK was also greater in IB3 cells. With the use of genetic inhibitors, we found that IKK-beta and NF-kappaB-inducing kinase are required for maximal NF-kappaB transactivation and transcription from the IL-8 promoter. Finally, although ERK activation was required for maximal asialoGM1-mediated IL-8 expression, inhibition of ERK signaling had no effect on IKK or NF-kappaB activation, suggesting that ERK regulates IL-8 expression in an NF-kappaB-independent manner.

Diprivan attenuates the cytotoxicity of nitric oxide in cultured human bronchial epithelial cells.

Excess nitric oxide (NO) and its reactive derivatives cause oxidative reactions that lead to cell death. Propofol, an intravenous anesthetic, exhibits antioxidant properties. Diprivan is a widely used commercial preparation of propofol that is emulsified in 10% intralipids. We sought to test the hypothesis that clinically encountered concentrations of Diprivan attenuate the toxicity of NO in a cell culture model. Prospective, randomized, controlled trial. University research laboratory. Cultured human bronchial epithelial (IB-3) cells. Human bronchial epithelial cell cultures were randomly assigned to one of the following six groups: no additives (negative control), NO alone (positive control), NO with either 1 micro M, 10 micro M or 100 micro M Diprivan, and 100 micro M Diprivan alone (Diprivan control). S-nitroso-N-acetylpenicillamine (SNAP) was used to generate NO. Hemacytometry with trypan blue staining was used to measure cell survival. To assess direct NO toxicity, immunoblot assays for nitrotyrosine-containing proteins in cell homogenates were performed. Exogenous NO significantly decreased live cell numbers and increased intracellular nitrotyrosine-containing protein concentrations (p<0.001). Diprivan significantly attenuated these changes in a concentration-independent manner (p<0.001). At concentrations as low as 1 micro M, Diprivan exhibited cytoprotective effects. Diprivan effectively attenuates the cytotoxicity of excessive NO exposure in IB-3 cells at concentrations that are clinically attainable.

Sodium 4-phenylbutyrate downregulates HSC70 expression by facilitating mRNA degradation.

Intracellular trafficking of the DeltaF508 cystic fibrosis transmembrane conductance regulator (CFTR) is repaired by sodium 4-phenylbutyrate (4PBA) by an undetermined mechanism. 4PBA downregulates protein and mRNA expression of the heat shock cognate protein HSC70 (the constitutively expressed member of the 70-kDa heat shock protein family) by approximately 40-50% and decreases formation of a HSC70-DeltaF508 CFTR complex that may be important in the intracellular degradation of DeltaF508 CFTR. We examined the potential mechanisms by which 4PBA decreases HSC70 mRNA and protein expression. In IB3-1 cells, 1 mM 4PBA did not alter the activity of the Chinese hamster ovary HSC70 promoter or of a human HSC70 promoter fragment in luciferase reporter assays nor did it alter HSC70 mRNA synthesis in nuclear runoff assays. In contrast, preincubation with 4PBA increased the rate of HSC70 mRNA degradation by approximately 40%. The initial rate of 35S-HSC70 protein synthesis in 4PBA-treated IB3-1 cells was reduced by approximately 40%, consistent with the steady-state mRNA level, whereas its rate of degradation was unaltered by 4PBA. 4PBA also reduced the steady-state accumulation of (35)S-HSC70 by approximately 40%. These data suggest that 4PBA decreases the expression of HSC70 mRNA and protein by inducing cellular adaptations that result in the decreased stability of HSC70 mRNA.

Induction of HSP70 promotes DeltaF508 CFTR trafficking.

The DeltaF508 cystic fibrosis transmembrane conductance regulator (CFTR) is a temperature-sensitive trafficking mutant that is detected as an immature 160-kDa form (band B) in gel electrophoresis. The goal of this study was to test the hypothesis that HSP70, a member of the 70-kDa heat shock protein family, promotes DeltaF508 CFTR processing to the mature 180-kDa form (band C). Both pharmacological and genetic techniques were used to induce HSP70. IB3-1 cells were treated with sodium 4-phenylbutyrate (4PBA) to promote maturation of DeltaF508 CFTR to band C. A dose-dependent increase in band C and total cellular HSP70 was observed. Under these conditions, HSP70-CFTR complexes were increased and 70-kDa heat shock cognate protein-CFTR complexes were decreased. Increased DeltaF508 CFTR maturation was also seen after transfection with an HSP70 expression plasmid and exposure to glutamine, an inducer of HSP70. With immunofluorescence techniques, the increased appearance of CFTR band C correlated with CFTR distribution beyond the perinuclear regions. These data suggest that induction of HSP70 promotes DeltaF508 CFTR maturation and trafficking.

Exaggerated activation of nuclear factor-kappaB and altered IkappaB-beta processing in cystic fibrosis bronchial epithelial cells.

In cystic fibrosis (CF), inflammatory mediator production by airway epithelial cells is a critical determinant of chronic airway inflammation. To determine whether altered signal transduction through the nuclear factor (NF)-kappaB pathway occurs in CF epithelial cells and results in excessive generation of inflammatory cytokines, we evaluated tumor necrosis factor (TNF)-alpha-induced production of the NF-kappaB-dependent cytokine interleukin (IL)-8 and activation of NF-kappaB in three different human bronchial epithelial cell lines: (1) BEAS cells that express wild-type CF transmembrane conductance regulator (CFTR), (2) IB3 cells with mutant CFTR, and (3) C38 cells, which are "corrected" IB3 cells complemented with wild-type CFTR. Treatment of cells with TNF-alpha (30 ng/ml) resulted in markedly elevated NF-kappaB activation and production of IL-8 by IB3 cells compared with BEAS and C38 cells. Despite the differences in NF- kappaB activation, no differences in basal levels of IkappaB-alpha or TNF-alpha- induced IkappaB-alpha processing and degradation were detected among the cell lines. In contrast, the basal level of IkappaB-beta was increased in the IB3 cells. Treatment with TNF-alpha resulted in increased formation of hypophosphorylated IkappaB-beta and increased nuclear localization of IkappaB-beta in IB3 cells compared with the other cell types. These findings provide additional evidence of a dysregulated inflammatory response in CF.

Cystic Fibrosis Mutations Lead to Carboxyl-terminal Fragments That Highlight an Early Biogenesis Step of the Cystic Fibrosis Transmembrane Conductance Regulator

Inefficient delivery of the cystic fibrosis transmembrane conductance regulator (CFTR) to the surface of cells contributes to disease in the majority of cystic fibrosis patients. Analysis of cystic fibrosis-associated missense mutations in the first nucleotide binding domain (NBD1), including A455E, S549R, Y563N, and P574H, revealed reduced levels of mature CFTR with elevated levels of carboxyl-terminal polypeptide fragments of 105 and 90 kDa. These fragments appear early in biogenesis and degrade rapidly in four distinct cell types tested including the bronchial epithelial IB3-1 cell line. They were detected at highest levels with CFTRA455E where the 105-kDa fragment accounted for 40% of newly synthesized polypeptide but for only 20 and 7% of nascent wild type and mutant DeltaF508 proteins, respectively. The bands represent core- and unglycosylated forms of the same CFTR fragment supporting that precursor forms are correctly inserted into the membrane of the endoplasmic reticulum. Proteolytic cleavage would be predicted to occur on the cytosolic face of the endoplasmic reticulum within the NBD1-R domain segment, but pharmacological testing did not support involvement of the 26 S proteasome. The examined missense mutations in NBD1 manifest differently than the major mutant, DeltaF508, and highlight a critical conformational aspect of biogenesis of CFTR.

Sodium 4-phenylbutyrate downregulates Hsc70: implications for intracellular trafficking of ΔF508-CFTR

The most common mutation of the cystic fibrosis transmembrane conductance regulator (CFTR), DeltaF508, is a trafficking mutant that has prolonged associations with molecular chaperones and is rapidly degraded, at least in part by the ubiquitin-proteasome system. Sodium 4-phenylbutyrate (4PBA) improves DeltaF508-CFTR trafficking and function in vitro in cystic fibrosis epithelial cells and in vivo. To further understand the mechanism of action of 4PBA, we tested the hypothesis that 4PBA modulates the targeting of DeltaF508-CFTR for ubiquitination and degradation by reducing the expression of Hsc70 in cystic fibrosis epithelial cells. IB3-1 cells (genotype DeltaF508/W1282X) that were treated with 0.05-5 mM 4PBA for 2 days in culture demonstrated a dose-dependent reduction in Hsc70 protein immunoreactivity and mRNA levels. Immunoprecipitation with Hsc70-specific antiserum demonstrated that Hsc70 and CFTR associated under control conditions and that treatment with 4PBA reduced these complexes. Levels of immunoreactive Hsp40, Hdj2, Hsp70, Hsp90, and calnexin were unaffected by 4PBA treatment. These data suggest that 4PBA may improve DeltaF508-CFTR trafficking by allowing a greater proportion of mutant CFTR to escape association with Hsc70.

The Second Half of the Cystic Fibrosis Transmembrane Conductance Regulator Forms a Functional Chloride Channel

The cystic fibrosis transmembrane conductance regulator (CFTR) consists of two transmembrane domains (TMDs), TMD1 and TMD2, two cytoplasmic nucleotide binding domains (NBDs), NBD1 and NBD2, and a regulatory domain. To elucidate the complex function of the CFTR, deletion constructs encompassing the second half of the CFTR distal to the first transmembrane domain were expressed in Xenopus oocytes and IB3 cells (a cystic fibrosis cell line). Constructs containing the regulatory domain, the second transmembrane domain, and the second nucleotide binding domain formed constitutively active channels, which were further stimulated upon the addition of cAMP. On the other hand, a construct encompassing the second transmembrane domain and the second nucleotide binding domain was stimulated to a small but noticeable extent upon the addition of cAMP. The selectivity of the second-half construct was the same for iodide and chloride, in contrast to the selectivity of wild-type CFTR, which is Cl- > I-. However, both constructs displayed single-channel conductances that were significantly smaller than those displayed by the first half of the CFTR. We conclude that regions of the second transmembrane domain may contribute to the overall channel of the pore, although the first half of the CFTR may confer its selectivity.

Activation of NF-kappaB by adherent Pseudomonas aeruginosa in normal and cystic fibrosis respiratory epithelial cells.

PMN-dominated airway inflammation is a major component of cystic fibrosis (CF) lung disease. Epithelial cells respond to organisms such as Pseudomonas aeruginosa, the major pathogen in CF, by expressing the leukocyte chemokine IL-8. Experiments were performed using several different types of respiratory epithelial cells that demonstrate that ligation of ceramide-associated receptors on epithelial surfaces by P. aeruginosa pili is a major stimulus for the translocation of transcription factor nuclear factor (NF)-kappaB and initiation of IL-8 expression by epithelial cells. Using electrophoretic mobility shift assays and Western hybridizations, nuclear NF-kappaB was found shortly after epithelial cells were stimulated by either whole organisms, isolated pili, or antibody to the pilin receptor asialoGM1. IB3 cells, which express mutations in cystic fibrosis transmembrane conductance regulator (CFTR) (DeltaF508/W1282X), were noted to have significantly greater amounts of endogenous nuclear NF-kappaB, but not the transcription factor C/EBP, than CF cells corrected by episomal copies of normal CFTR (C-38) or IB3 cells grown at a permissive temperature (25 degreesC). Activation of NF-kappaB and subsequent IL-8 expression in epithelial cells can result from activation of at least two pathways: an exogenous signaling cascade that is activated by ligation of ceramide-associated adhesins such as P. aeruginosa pilin, or endogenous stimulation, suggested to be a consequence of cell stress caused by the accumulation of mutant CFTR in the endoplasmic reticulum.

Analysis of ClC-2 channels as an alternative pathway for chloride conduction in cystic fibrosis airway cells.

Cystic fibrosis (CF) is a lethal inherited disease that results from abnormal chloride conduction in epithelial tissues. ClC-2 chloride channels are expressed in epithelia affected by CF and may provide a key "alternative" target for pharmacotherapy of this disease. To explore this possibility, the expression level of ClC-2 channels was genetically manipulated in airway epithelial cells derived from a cystic fibrosis patient (IB3-1). Whole-cell patch-clamp analysis of cells overexpressing ClC-2 identified hyperpolarization-activated Cl- currents (HACCs) that displayed time- and voltage-dependent activation, and an inwardly rectifying steady-state current-voltage relationship. Reduction of extracellular pH to 5.0 caused significant increases in HACCs in overexpressing cells, and the appearance of robust currents in parental IB3-1 cells. IB3-1 cells stably transfected with the antisense ClC-2 cDNA showed reduced expression of ClC-2 compared with parental cells by Western blotting, and a significant reduction in the magnitude of pH-dependent HACCs. To determine whether changes in extracellular pH alone could initiate chloride transport via ClC-2 channels, we performed 36Cl- efflux studies on overexpressing cells and cells with endogenous expression of ClC-2. Acidic extracellular pH increased 36Cl- efflux rates in both cell types, although the ClC-2 overexpressing cells had significantly greater chloride conduction and a longer duration of efflux than the parental cells. Compounds that exploit the pH mechanism of activating endogenous ClC-2 channels may provide a pharmacologic option for increasing chloride conductance in the airways of CF patients.