Epithelial sodium channel silencing as a strategy to correct the airway surface fluid deficit in cystic fibrosis

In the respiratory system, Na(+) absorption and Cl(-) secretion are balanced to maintain an appropriate airway surface fluid (ASF) volume and ensure efficient mucociliary clearance. In cystic fibrosis (CF), this equilibrium is disrupted by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, resulting in the absence of functional CFTR-dependent Cl(-) secretion. The consequences of defective Cl(-) transport are worsened by the persistence of Na(+) absorption, which contributes to airway surface dehydration. We asked whether normal ASF can be restored to an equal extent by recovering Cl(-) secretion from mutated CFTR or by reducing Na(+) absorption. This is highly relevant in the selection of the best strategy for the treatment of patients with CF. We analyzed the ASF thickness of primary cultured bronchial CF and non-CF epithelia after silencing the epithelial Na(+) channel (ENaC) with specific short, interfering RNAs (siRNAs) and after the pharmacological stimulation of CFTR. Our results indicate that (1) single siRNAs complementary to ENaC subunits are sufficient to reduce ENaC transcripts, Na(+) channel activity, and fluid transport, but only silencing both the α and β ENaC subunits at the same time leads to an increase of ASF (from nearly 7 µm to more than 9 µm); (2) the ASF thickness obtained in this way is about half that measured after maximal CFTR stimulation in non-CF epithelia (10-14 µm); and (3) the pharmacological rescue of mutant CFTR increases the ASF to the same extent as ENaC silencing. Our results indicate that CFTR rescue and ENaC silencing both produce a significant and long-lasting increase of airway hydration in vitro.

Non-canonical translation start sites in the TMEM16A chloride channel

TMEM16A is a plasma membrane protein with voltage- and calcium-dependent chloride channel activity. The role of the various TMEM16A domains in expression and function is poorly known. In a previous study, we found that replacing the first ATG of the TMEM16A coding sequence with a nonsense codon (M1X mutation), to force translation from the second ATG localized at position 117, only had minor functional consequences. Therefore, we concluded that this region is dispensable for TMEM16A processing and channel activity. We have now removed the first 116 codons from the TMEM16A coding sequence. Surprisingly, the expression of the resulting mutant, Δ(1–116), resulted in complete loss of activity. We hypothesized that, in the mutant M1X, translation may start at a position before the second ATG, using a non-canonical start codon. Therefore, we placed an HA-epitope at position 89 in the M1X mutant. We found, by western blot analysis, that the HA-epitope can be detected, thus demonstrating that translation starts from an upstream non-ATG codon. We truncated the N-terminus of TMEM16A at different sites while keeping the HA-epitope. We found that stepwise shortening of TMEM16A caused an in parallel stepwise decrease in TMEM16A expression and function. Our results indicate that indeed the N-terminus of TMEM16A is important for its activity. The use of an alternative start codon appears to occur in a naturally-occurring TMEM16A isoform that is particularly expressed in human testis. Future experiments will need to address the role of normal and alternative amino-terminus in TMEM16A structure and function.

•

TMEM16A is a membrane protein with chloride channel activity.

•

Two ATG codons are present at positions 1 and 117 of the TMEM16A coding sequence.

•

Deletion of the first ATG, in contrast to removal of the first 116 codons, does not abolish TMEM16A function.

•

Without the first ATG, TMEM16A translation begins from a non-canonical start codon.

A novel missense mutation in ANO5/TMEM16E is causative for gnathodiaphyseal dyplasia in a large Italian pedigree

Gnathodiaphyseal dysplasia (GDD) is an autosomal dominant syndrome characterized by frequent bone fractures at a young age, bowing of tubular bones and cemento-osseus lesions of the jawbones. Anoctamin 5 (ANO5) belongs to the anoctamin protein family that includes calcium-activated chloride channels. However, recent data together with our own experiments reported here add weight to the hypothesis that ANO5 may not function as calcium-activated chloride channel. By sequencing the entire ANO5 gene coding region and untranslated regions in a large Italian GDD family, we found a novel missense mutation causing the p.Thr513Ile substitution. The mutation segregates with the disease in the family and has never been described in any database as a polymorphism. To date, only two mutations on the same cysteine residue at position 356 of ANO5 amino-acid sequence have been described in GDD families. As ANO5 has also been found to be mutated in two different forms of muscular dystrophy, the finding of this third mutation in GDD adds clues to the role of ANO5 in these disorders.

Association of TMEM16A chloride channel overexpression with airway goblet cell metaplasia

The TMEM16A protein has a potential role as a Ca(2+)-activated Cl(-) channel (CaCC) in airway epithelia where it may be important in the homeostasis of the airway surface fluid. We investigated the function and expression of TMEM16A in primary human bronchial epithelial cells and in a bronchial cell line (CFBE41o-). Under resting conditions, TMEM16A protein expression was relatively low. However, TMEM16A silencing with short-interfering RNAs caused a marked inhibition of CaCC activity, thus demonstrating that a low TMEM16A expression is sufficient to support Ca(2+)-dependent Cl(-) transport. Following treatment for 24-72 h with interleukin-4 (IL-4), a cytokine that induces mucous cell metaplasia, TMEM16A protein expression was strongly increased in approximately 50% of primary bronchial epithelial cells, with a specific localization in the apical membrane. IL-4 treatment also increased the percentage of cells expressing MUC5AC, a marker of goblet cells. Interestingly, MUC5AC was detected specifically in cells expressing TMEM16A. In particular, MUC5AC was found in 15 and 60% of TMEM16A-positive cells when epithelia were treated with IL-4 for 24 or 72 h, respectively. In contrast, ciliated cells showed expression of the cystic fibrosis transmembrane conductance regulator Cl(-) channel but not of TMEM16A. Our results indicate that TMEM16A protein is responsible for CaCC activity in airway epithelial cells, particularly in cells treated with IL-4, and that TMEM16A upregulation by IL-4 appears as an early event of goblet cell differentiation. These findings suggest that TMEM16A expression is particularly required under conditions of mucus hypersecretion to ensure adequate secretion of electrolytes and water.

Cytokines induce tight junction disassembly in airway cells via an EGFR-dependent MAPK/ERK1/2-pathway

Epithelial barrier permeability is altered in inflammatory respiratory disorders by a variety of noxious agents through modifications of the epithelial cell structure that possibly involve tight junction (TJ) organization. To evaluate in vitro whether pro-inflammatory cytokines involved in the pathogenesis of respiratory disorders could alter TJ organization and epithelial barrier integrity, and to characterize the signal transduction pathway involved Calu-3 airway epithelial cells were exposed to TNF-a, IL-4 and IFN-g to assess changes in: (a) TJ assembly, that is, occludin and zonula occludens (ZO)-1 expression and localization, evaluated by confocal microscopy; (b) apoptotic activity, quantified using terminal transferase deoxyuridine triphosphate nick-end labeling staining; (c) epithelial barrier integrity, detected as transmembrane electrical resistance and expressed as G(T) values; (d) epidermal growth factor receptor (EGFR)-dependent mitogenactivated protein (MAP) kinase (MAPK)/extracellular signal-regulated kinases (ERK)1/2 phosphorylation, assessed by western blotting. Exposure to cytokines for 48 h induced a noticeable downregulation of the TJ transmembrane proteins. The degree ZO-1 and occludin colocalization was 62±2% in control cultures and significantly decreased in the presence of TNF-a (47±3%), IL-4 (43±1%) and INF-g (35±3%). Although no apoptosis induction was detected following exposure to cytokines, changes in the epithelial barrier integrity were observed, with a significant enhancement in paracellular conductance. G(T) values were, respectively, 1.030±0.0, 1.300±0.04, 1.260±0.020 and 2.220±0.015 (mS/cm²)1000 in control cultures and in those exposed to TNF-a, IFN-g and IL-4. The involvement of EGFR-dependent MAPK/ERK1/2 signaling pathway in cytokine-induced damage was demonstrated by a significant increase in threonine/tyrosine phosphorylation of ERK1/2, already detectable after 5 min incubation. All these cytokine-induced changes were markedly prevented when Calu-3 cells were cultured in the presence of an EGFR inhibitor (AG1478, 1 μM) or a MAP kinase inhibitor (U0126, 25 μM). In conclusion, cytokine-induced epithelial injury includes TJ disassembly and epithelial barrier permeability alteration and involves the EGFR-dependent MAPK/ERK1/2 signaling pathway.

Salbutamol: how does it enter smooth muscle cells?

Polyspecific organic cation transporters (OCTs) in human cell membranes are involved in the uptake, distribution and excretion of cationic compounds. Although their relevance to drug disposition in the liver, small intestine and kidney has been investigated previously, less is known about the influence of these transporters on the pharmacokinetics and pharmacodynamics of inhaled drugs. Drugs that are commonly administered by inhalation for the treatment of respiratory diseases, such as glucocorticoids and cationic β(2)-agonists, might interact with several of these transporters, which are strongly expressed on the surfaces of airway epithelial cells. We evaluated the expression of OCT3 and measured the in vitro uptake of the short-acting β(2)-agonist salbutamol (SALB), alone or in combination with corticosterone (CS) and beclomethasone dipropionate (BDP), by bronchial smooth muscle cells. Our results showed that these cells express the OCT3 transporter and that SALB enters the cell in a transporter-independent fashion. Moreover, CS and BDP have different activities on SALB transport inside the cell. CS increases SALB transport and BDP decreases SALB transport, although neither of these effects are statistically significant. A better understanding of these mechanisms might lead to the improved treatment of airway diseases.

Rescue of the mutant CFTR chloride channel by pharmacological correctors and low temperature analyzed by gene expression profiling

The F508del mutation, the most frequent in cystic fibrosis (CF), impairs the maturation of the CFTR chloride channel. The F508del defect can be partially overcome at low temperature (27°C) or with pharmacological correctors. However, the efficacy of correctors on the mutant protein appears to be dependent on the cell expression system. We have used a bronchial epithelial cell line, CFBE41o-, to determine the efficacy of various known treatments and to discover new correctors. Compared with other cell types, CFBE41o- shows the largest response to low temperature and the lowest one to correctors such as corr-4a and VRT-325. A screening of a small-molecule library identified 9-aminoacridine and ciclopirox, which were significantly more effective than corr-4a and VRT-325. Analysis with microarrays revealed that 9-aminoacridine, ciclopirox, and low temperature, in contrast to corr-4a, cause a profound change in cell transcriptome. These data suggest that 9-aminoacridine and ciclopirox act on F508del-CFTR maturation as proteostasis regulators, a mechanism already proposed for the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA). However, we found that 9-aminoacridine, ciclopirox, and SAHA, in contrast to corr-4a, VRT-325, and low temperature, do not increase chloride secretion in primary bronchial epithelial cells from CF patients. These conflicting data appeared to be correlated with different gene expression signatures generated by these treatments in the cell line and in primary bronchial epithelial cells. Our results suggest that F508del-CFTR correctors acting by altering the cell transcriptome may be particularly active in heterologous expression systems but markedly less effective in native epithelial cells.

A minimal isoform of the TMEM16A protein associated with chloride channel activity

TMEM16A protein, also known as anoctamin-1, has been recently identified as an essential component of Ca(2+)-activated Cl(-) channels. We previously reported the existence of different TMEM16A isoforms generated by alternative splicing. In the present study, we have determined the functional properties of a minimal TMEM16A protein. This isoform, called TMEM16A(0), has a significantly shortened amino-terminus and lacks three alternative segments localized in the intracellular regions of the protein (total length: 840 amino acids). TMEM16A(0) expression is associated with Ca(2+)-activated Cl(-) channel activity as measured by three different functional assays based on the halide-sensitive yellow fluorescent protein, short-circuit current recordings, and patch-clamp technique. However, compared to a longer isoform, TMEM16(abc) (total length: 982 amino acids), TMEM16A(0) completely lacks voltage-dependent activation. Furthermore, TMEM16A(0) and TMEM16A(abc) have similar but not identical responses to extracellular anion replacement, thus suggesting a difference in ion selectivity and conductance. Our results indicate that TMEM16A(0) has the basic domains required for anion transport and Ca(2+)-sensitivity. However, the absence of alternative segments, which are present in more complex isoforms of TMEM16A, modifies the channel gating and ion transport ability.

Dual activity of aminoarylthiazoles on the trafficking and gating defects of the cystic fibrosis transmembrane conductance regulator chloride channel caused by cystic fibrosis mutations

A large fraction of mutations causing cystic fibrosis impair the function of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel by causing reduced channel activity (gating defect) and/or impaired exit from the endoplasmic reticulum (trafficking defect). Such defects need to be treated with separate pharmacological compounds termed potentiators and correctors, respectively. Here, we report the characterization of aminoarylthiazoles (AATs) as compounds having dual activity. Cells expressing mutant CFTR were studied with functional assays (fluorescence-based halide transport and short circuit current measurements) to assess the effect of acute and chronic treatment with compounds. We found that AATs are effective on F508del, the most frequent cystic fibrosis mutation, which is associated with both a gating and a trafficking defect. AATs are also effective on mutations like G1349D and G551D, which cause only a gating defect. Evaluation of a panel of AAT analogs identified EN277I as the most effective compound. Incubation of cells expressing mutant CFTR with EN277I caused a strong stimulation of channel activity as demonstrated by single channel recordings. Compounds with dual activity such as AATs may be useful for the development of effective drugs for the treatment of cystic fibrosis.

IL-12 can target human lung adenocarcinoma cells and normal bronchial epithelial cells surrounding tumor lesions

Background

Non small cell lung cancer (NSCLC) is a leading cause of cancer death. We have shown previously that IL-12rb2 KO mice develop spontaneously lung adenocarcinomas or bronchioalveolar carcinomas.

Aim of the study was to investigate i) IL-12Rβ2 expression in human primary lung adenocarcinomas and in their counterparts, i.e. normal bronchial epithelial cells (NBEC), ii) the direct anti-tumor activity of IL-12 on lung adenocarcinoma cells in vitro and vivo, and the mechanisms involved, and iii) IL-12 activity on NBEC.

Methodology/Principal Findings

Stage I lung adenocarcinomas showed significantly (P = 0.012) higher frequency of IL-12Rβ2 expressing samples than stage II/III tumors. IL-12 treatment of IL-12R⁺ neoplastic cells isolated from primary adenocarcinoma (n = 6) inhibited angiogenesis in vitro through down-regulation of different pro-angiogenic genes (e.g. IL-6, VEGF-C, VEGF-D, and laminin-5), as assessed by chorioallantoic membrane (CAM) assay and PCR array. In order to perform in vivo studies, the Calu6 NSCLC cell line was transfected with the IL-12RB2 containing plasmid (Calu6/β2). Similar to that observed in primary tumors, IL-12 treatment of Calu6/β2⁺ cells inhibited angiogenesis in vitro. Tumors formed by Calu6/β2 cells in SCID/NOD mice, inoculated subcutaneously or orthotopically, were significantly smaller following IL-12 vs PBS treatment due to inhibition of angiogenesis, and of IL-6 and VEGF-C production. Explanted tumors were studied by histology, immuno-histochemistry and PCR array. NBEC cells were isolated and cultured from lung specimens of non neoplastic origin. NBEC expressed IL-12R and released constitutively tumor promoting cytokines (e.g. IL-6 and CCL2). Treatment of NBEC with IL-12 down-regulated production of these cytokines.

Conclusions

This study demonstrates that IL-12 inhibits directly the growth of human lung adenocarcinoma and targets the adjacent NBEC. These novel anti-tumor activities of IL-12 add to the well known immune-modulatory properties of the cytokine and may provide a rational basis for the development of a clinical trial.

Mutation-specific potency and efficacy of cystic fibrosis transmembrane conductance regulator chloride channel potentiators

Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel. The mutations G551D and G1349D, which affect the nucleotide-binding domains (NBDs) of CFTR protein, reduce channel activity. This defect can be corrected pharmacologically by small molecules called potentiators. CF mutations residing in the intracellular loops (ICLs), connecting the transmembrane segments of CFTR, may also reduce channel activity. We have investigated the extent of loss of function caused by ICL mutations and the sensitivity to pharmacological stimulation. We found that E193K and G970R (in ICL1 and ICL3, respectively) cause a severe loss of CFTR channel activity that can be rescued by the same potentiators that are effective on NBD mutations. We compared potency and efficacy of three different potentiators for E193K, G970R, and G551D. The 1,4-dihydropyridine felodipine and the phenylglycine PG-01 [2-[(2-1H-indol-3-yl-acetyl)-methylamino]-N-(4-isopropylphenyl)-2-phenylacetamide] were strongly effective on the three CFTR mutants. The efficacy of sulfonamide SF-01 [6-(ethylphenylsulfamoyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid cycloheptylamide], another CFTR potentiator, was instead significantly lower than felodipine and PG-01 for the E193K and G970R mutations, and almost abolished for G551D. Furthermore, SF-01 modified the response of G551D and G970R to the other two potentiators, an effect that may be explained by an allosteric antagonistic effect. Our results indicate that CFTR potentiators correct the basic defect caused by CF mutations residing in different CFTR domains. However, there are differences among potentiators, with felodipine and PG-01 having a wider pharmacological activity, and SF-01 being more mutation specific. Our observations are useful in the prioritization and development of drugs targeting the CF basic defect.

TMEM16A, a membrane protein associated with calcium-dependent chloride channel activity

Calcium-dependent chloride channels are required for normal electrolyte and fluid secretion, olfactory perception, and neuronal and smooth muscle excitability. The molecular identity of these membrane proteins is still unclear. Treatment of bronchial epithelial cells with interleukin-4 (IL-4) causes increased calcium-dependent chloride channel activity, presumably by regulating expression of the corresponding genes. We performed a global gene expression analysis to identify membrane proteins that are regulated by IL-4. Transfection of epithelial cells with specific small interfering RNA against each of these proteins shows that TMEM16A, a member of a family of putative plasma membrane proteins with unknown function, is associated with calcium-dependent chloride current, as measured with halide-sensitive fluorescent proteins, short-circuit current, and patch-clamp techniques. Our results indicate that TMEM16A is an intrinsic constituent of the calcium-dependent chloride channel. Identification of a previously unknown family of membrane proteins associated with chloride channel function will improve our understanding of chloride transport physiopathology and allow for the development of pharmacological tools useful for basic research and drug development.

Epithelial sodium channel inhibition in primary human bronchial epithelia by transfected siRNA

Na(+) absorption and Cl(-) secretion are in equilibrium to maintain an appropriate airway surface fluid volume and ensure appropriate mucociliary clearance. In cystic fibrosis, this equilibrium is disrupted by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene resulting in the absence of functional CFTR protein, which in turn results in deficient cAMP-dependent Cl(-) secretion and predominant Na(+) absorption. It has been suggested that down-regulation of the epithelial sodium channel, ENaC, might help to restore airway hydration and reverse the airway phenotype in patients with cystic fibrosis. We used an siRNA approach to analyze the possibility of down-regulating ENaC function in bronchial epithelia and examine the resulting effects on fluid transport. siRNA sequences complementary to each of the three ENaC subunits have been used to establish whether single subunit down-regulation is enough to reduce Na(+) absorption. Transfection was performed by exposure to siRNA for 24 hours at the time of cell seeding on permeable support. By using primary human bronchial epithelial cells we demonstrate that (1) siRNA sequences complementary to ENaC subunits are able to reduce ENaC transcripts and Na(+) channel activity by 50 to 70%, (2) transepithelial fluid absorption decreases, and (3) these functional effects last at least 8 days. A decrease in ENaC mRNA results in a significant reduction of ENaC protein function and fluid absorption through the bronchial epithelium, indicating that an RNA interference approach may improve the airway hydration status in patients with cystic fibrosis.

Thiocyanate transport in resting and IL-4-stimulated human bronchial epithelial cells: role of pendrin and anion channels

SCN(-) (thiocyanate) is an important physiological anion involved in innate defense of mucosal surfaces. SCN(-) is oxidized by H(2)O(2), a reaction catalyzed by lactoperoxidase, to produce OSCN(-) (hypothiocyanite), a molecule with antimicrobial activity. Given the importance of the availability of SCN(-) in the airway surface fluid, we studied transepithelial SCN(-) transport in the human bronchial epithelium. We found evidence for at least three mechanisms for basolateral to apical SCN(-) flux. cAMP and Ca(2+) regulatory pathways controlled SCN(-) transport through cystic fibrosis transmembrane conductance regulator and Ca(2+)-activated Cl(-) channels, respectively, the latter mechanism being significantly increased by treatment with IL-4. Stimulation with IL-4 also induced the strong up-regulation of an electroneutral SCN(-)/Cl(-) exchange. Global gene expression analysis with microarrays and functional studies indicated pendrin (SLC26A4) as the protein responsible for this SCN(-) transport. Measurements of H(2)O(2) production at the apical surface of bronchial cells indicated that the extent of SCN(-) transport is important to modulate the conversion of this oxidant molecule by the lactoperoxidase system. Our studies indicate that the human bronchial epithelium expresses various SCN(-) transport mechanisms under resting and stimulated conditions. Defects in SCN(-) transport in the airways may be responsible for susceptibility to infections and/or decreased ability to scavenge oxidants.

Block of CFTR-dependent chloride currents by inhibitors of multidrug resistance-associated proteins

The cystic fibrosis transmembrane conductance regulator (CFTR) is a membrane protein that belongs to the same family as multidrug resistance-associated proteins whose main function is to expel xenobiotics and physiological organic anions from the cell interior. Despite the overall structural similarity with these membrane proteins, CFTR is not an active transporter but is instead a Cl- channel. We have tested the ability of known inhibitors of multidrug resistance-associated proteins to affect CFTR Cl- currents. We have found that sulfinpyrazone, probenecid, and benzbromarone are also inhibitors of CFTR activity, with a mechanism involving blockage of the channel pore.

Effect of inflammatory stimuli on airway ion transport

The airway epithelium controls the chemical and physical properties of airway surface fluid and consequently mucociliary clearance. The treatment for 24-48 hours of human bronchial epithelial cells with interferon-gamma or interleukin-4 leads to marked changes in transepithelial ion transport properties. Both cytokines downregulate the activity of the epithelial Na+ channel and, at the same time, upregulate Ca2+-dependent Cl- secretion. Interleukin-4 also increases the expression and function of the cystic fibrosis transmembrane conductance regulator Cl- channel. These results suggest that some inflammatory stimuli may change the balance between fluid absorption and secretion to favor hydration of the airway surface and consequently mucus clearance.

Antihypertensive 1,4-Dihydropyridines as Correctors of the Cystic Fibrosis Transmembrane Conductance Regulator Channel Gating Defect Caused by Cystic Fibrosis Mutations

Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel gene. CF mutations like deltaF508 cause both a mistrafficking of the protein and a gating defect. Other mutations, like G551D, cause only a gating defect. Our aim was to find chemical compounds able to stimulate the activity of CFTR mutant proteins by screening a library containing approved drugs. Two thousand compounds were tested on Fischer rat thyroid cells coexpressing deltaF508-CFTR and a halide-sensitive yellow fluorescent protein (YFP) after correction of the trafficking defect by low-temperature incubation. The YFP-based screening allowed the identification of the antihypertensive 1,4-dihydropyridines (DHPs) nifedipine, nicardipine, nimodipine, isradipine, nitrendipine, felodipine, and niguldipine as compounds able to activate deltaF508-CFTR. This effect was not derived from the inhibition of voltage-dependent Ca2+ channels, the pharmacological target of antihypertensive DHPs. Indeed, methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-2(trifluoromethylphenyl)pyridine-5-carboxylate (BayK-8644), a DHP that is effective as an activator of such channels, also stimulated CFTR activity. DHPs were also effective on the G551D-CFTR mutant by inducing a 16- to 45-fold increase of the CFTR Cl- currents. DHP activity was confirmed in airway epithelial cells from patients with CF. DHPs may represent a novel class of therapeutic agents able to correct the defect caused by a set of CF mutations.

Small-molecule correctors of defective DeltaF508-CFTR cellular processing identified by high-throughput screening

The most common cause of cystic fibrosis (CF) is deletion of phenylalanine 508 (DeltaF508) in the CF transmembrane conductance regulator (CFTR) chloride channel. The DeltaF508 mutation produces defects in folding, stability, and channel gating. To identify small-molecule correctors of defective cellular processing, we assayed iodide flux in DeltaF508-CFTR-transfected epithelial cells using a fluorescent halide indicator. Screening of 150,000 chemically diverse compounds and more than 1,500 analogs of active compounds yielded several classes of DeltaF508-CFTR correctors (aminoarylthiazoles, quinazolinylaminopyrimidinones, and bisaminomethylbithiazoles) with micromolar potency that produced greater apical membrane chloride current than did low-temperature rescue. Correction was seen within 3-6 hours and persisted for more than 12 hours after washout. Functional correction was correlated with plasma membrane expression of complex-glycosylated DeltaF508-CFTR protein. Biochemical studies suggested a mechanism of action involving improved DeltaF508-CFTR folding at the ER and stability at the cell surface. The bisaminomethylbithiazoles corrected DeltaF508-CFTR in DeltaF508/DeltaF508 human bronchial epithelia but did not correct a different temperature-sensitive CFTR mutant (P574H-CFTR) or a dopamine receptor mutant. Small-molecule correctors may be useful in the treatment of CF caused by the DeltaF508 mutation.