Plasma membrane CFTR regulates RANTES expression via its C-terminal PDZ-interacting motif

Plasma levels of chemokines decrease during elexacaftor/tezacaftor/ivacaftor therapy in adults with cystic fibrosis

Background

Cystic fibrosis (CF) is associated with dysregulated immune responses, exaggerated inflammation and chronic infection. CF transmembrane conductance regulator (CFTR) modulator therapies directly target the underlying protein defects and resulted in significant clinical benefits for people with CF (pwCF). This study analysed the effects of triple CFTR modulator therapy elexacaftor/tezacaftor/ivacaftor (ETI) on CF-associated inflammation, especially systemic chemokines.

Methods

A bead-based immunoassay was used to quantify proinflammatory chemokines (IL-8, IP-10, Eotaxin, TARC, RANTES, MIP-1α, MIP-1β, MIP-3α, MIG, ENA-78, GROα, I-TAC) in plasma samples from pwCF collected before, at three, and at six months after starting ETI therapy.

Results

Fifty-one pwCF (47 % female; mean age 32 ± 10.4 years) were included. At baseline, 67 % were already receiving CFTR modulator therapy with tezacaftor/ivacaftor or lumacaftor/ivacaftor. After initiation of ETI therapy there was a significant improvement in percent predicted forced expiratory volume in 1 s (+12.7 points, p < 0.001) and a significant decrease in sweat chloride levels (-53.6 %, p < 0.001). After 6 months' treatment with ETI therapy there were significant decreases in plasma levels of MIP-3α (-68.2 %, p = 0.018), GROα (-17.7 %, p = 0.013), ENA-78 (-16.3 %, p = 0.034) and I-TAC (-3.4 %, p = 0.032). IL-8 exhibited a reduction that did not reach statistical significance (-17.8 %, p = 0.057); levels of other assessed cytokines did not change significantly from baseline.

Conclusions

ETI appears to affect a distinct group of chemokines that are predominately associated with neutrophilic inflammation, demonstrating the anti-inflammatory properties of ETI therapy.

Expression of CFTR, a hallmark gene of ionocytes, is downregulated in salivary glands of Sjögren's syndrome patients

INTRODUCTION

The autoimmune exocrinopathy, Sjögren's syndrome (SjS), is associated with secretory defects in salivary glands. The cystic fibrosis transmembrane conductance regulator (CFTR) of the chloride channel is a master regulator of fluid secretion, but its role in SjS has not been investigated. Our research found a link between CFTR and SjS at the genetic and protein levels, as well as through clinical data.

METHODS

We used single-cell RNA sequencing to identify the presence of CFTR in glandular epithelial cells of the human salivary gland (scRNA-seq) and confirmed the difference using immunofluorescence tests in labial glands and clinical data statistics from 44 non-SjS and 36 SjS patients.

RESULTS

The changes of CFTR expression in salivary glands of SjS patients was assessed at both mRNA and protein levels. According to the scRNA-seq analyses, CFTR was the hallmark gene of ionocytes. We firstly identified that SjS had a lower level of CFTR expression in the labial glands than non-SjS at mRNA level. Using immunofluorescence assays, we also found that CFTR expression was decreased in SjS patients compared to non-SjS. The results of the clinical statistics revealed that CFTR expression was adversely correlated with feelings of dry mouth, lymphocyte infiltration in the labial glands, and certain autoantibodies in serum (antinuclear antibody, anti-Ro/SSA, and anti-La/SSB antibodies).

CONCLUSION

Those findings above proved an obviously downregulated expression of CFTR in salivary glands of SjS patients and its clinical significance. Dysfunction in CFTR or ionocytes may contribute to SjS pathogenesis and represents a promising therapeutic target.

Guanylin ligand protects the intestinal immune barrier by activating the guanylate cyclase-C signaling pathway

Inflammatory bowel disease (IBD) impacts patient quality of life significantly. The dysfunction of intestinal immune barrier is closely associated with IBD. The guanylate cyclase-C (GC-C) signaling pathway activated by the guanylin (Gn) ligand is involved in the occurrence and development of IBD. However, how it regulates the intestinal immune barrier is still unclear. To investigate the effect of the GC-C pathway on intestinal mucosal immunity and provide experimental basis for seeking new therapeutic strategies for IBD, we focused on Caco-2 cells and intestinal intra-epithelial lymphocytes (IELs), which displayed inflammatory responses induced by lipopolysaccharide (LPS). GC-C activity was modulated by transfection with Gn overexpression or GC-C shRNA plasmid. Levels of Gn, GC-C, and CFTR; transepithelial electrical resistance (TER); paracellula r permeability; and levels of IL-2, IFN-γ, and secretory IgA (sIgA) were examined. The study found that after stimulation with LPS, Gn, GC-C, CFTR, TER, and sIgA levels were all significantly reduced, IL-2 and IFN-γ levels as well as paracellular permeability were significantly increased. These indicators changed inversely and significantly after transfection with the Gn overexpression vector. Compared to the vector controls, GC-C-silenced cells displayed significantly decreased levels of GC-C, CFTR, and TER and increased levels of IL-2, IFN-γ, and paracellular permeability stimulated by LPS. The results show that Gn ligand can protect the intestinal immune barrier by activating the GC-C signaling pathway, which may be helpful for the development of new treatments for IBD. DATA AVAILABILITY STATEMENT: The data used to support the findings of this study are available from the corresponding author upon request.

Bone Cells Differentiation: How CFTR Mutations May Rule the Game of Stem Cells Commitment?

Cystic fibrosis (CF)-related bone disease has emerged as a significant comorbidity of CF and is characterized by decreased bone formation and increased bone resorption. Both osteoblast and osteoclast differentiations are impacted by cystic fibrosis transmembrane conductance regulator (CFTR) mutations. The defect of CFTR chloride channel or the loss of CFTRs ability to interact with other proteins affect several signaling pathways involved in stem cell differentiation and the commitment of these cells toward bone lineages. Specifically, TGF-, nuclear factor-kappa B (NF-B), PI3K/AKT, and MAPK/ERK signaling are disturbed by CFTR mutations, thus perturbing stem cell differentiation. High inflammation in patients changes myeloid lineage secretion, affecting both myeloid and mesenchymal differentiation. In osteoblast, Wnt signaling is impacted, resulting in consequences for both bone formation and resorption. Finally, CFTR could also have a direct role in osteoclasts resorptive function. In this review, we summarize the existing literature on the role of CFTR mutations on the commitment of induced pluripotent stem cells to bone cells.

Dysregulated signalling pathways in innate immune cells with cystic fibrosis mutations

Cystic fibrosis (CF) is one of the most common life-limiting recessive genetic disorders in Caucasians, caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). CF is a multi-organ disease that involves the lungs, pancreas, sweat glands, digestive and reproductive systems and several other tissues. This debilitating condition is associated with recurrent lower respiratory tract bacterial and viral infections, as well as inflammatory complications that may eventually lead to pulmonary failure. Immune cells play a crucial role in protecting the organs against opportunistic infections and also in the regulation of tissue homeostasis. Innate immune cells are generally affected by CFTR mutations in patients with CF, leading to dysregulation of several cellular signalling pathways that are in continuous use by these cells to elicit a proper immune response. There is substantial evidence to show that airway epithelial cells, neutrophils, monocytes and macrophages all contribute to the pathogenesis of CF, underlying the importance of the CFTR in innate immune responses. The goal of this review is to put into context the important role of the CFTR in different innate immune cells and how CFTR dysfunction contributes to the pathogenesis of CF, highlighting several signalling pathways that may be dysregulated in cells with CFTR mutations.

Impairment of CFTR activity in cultured epithelial cells upregulates the expression and activity of LDH resulting in lactic acid hypersecretion

Mutations in the gene encoding the CFTR chloride channel produce cystic fibrosis (CF). CF patients are more susceptible to bacterial infections in lungs. The most accepted hypothesis sustains that a reduction in the airway surface liquid (ASL) volume favor infections. Alternatively, it was postulated that a reduced HCO3- transport through CFTR leads to a decreased ASL pH, favoring bacterial colonization. The issue is controversial, since recent data from cultured primary cells and CF children showed normal pH values in the ASL. We have reported previously a decreased mitochondrial Complex I (mCx-I) activity in cultured cells with impaired CFTR activity. Thus, we hypothesized that the reduced mCx-I activity could lead to increased lactic acid production (Warburg-like effect) and reduced extracellular pH (pHe). In agreement with this idea, we report here that cells with impaired CFTR function (intestinal Caco-2/pRS26, transfected with an shRNA-CFTR, and lung IB3-1 CF cells) have a decreased pHe. These cells showed increased lactate dehydrogenase (LDH) activity, LDH-A expression, and lactate secretion. Similar effects were reproduced in control cells stimulated with recombinant IL-1β. The c-Src and JNK inhibitors PP2 and SP600125 were able to increase the pHe, although the differences between control and CFTR-impaired cells were not fully compensated. Noteworthy, the LDH inhibitor oxamate completely restored the pHe of the intestinal Caco-2/pRS26 cells and have a significant effect in lung IB3-1 cells; therefore, an increased lactic acid secretion seems to be the key factor that determine a reduced pHe in these epithelial cells.

Cystic fibrosis transmembrane conductance regulator-emerging regulator of cancer

Mutations of cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis, the most common life-limiting recessive genetic disease among Caucasians. CFTR mutations have also been linked to increased risk of various cancers but remained controversial for a long time. Recent studies have begun to reveal that CFTR is not merely an ion channel but also an important regulator of cancer development and progression with multiple signaling pathways identified. In this review, we will first present clinical findings showing the correlation of genetic mutations or aberrant expression of CFTR with cancer incidence in multiple cancers. We will then focus on the roles of CFTR in fundamental cellular processes including transformation, survival, proliferation, migration, invasion and epithelial-mesenchymal transition in cancer cells, highlighting the signaling pathways involved. Finally, the association of CFTR expression levels with patient prognosis, and the potential of CFTR as a cancer prognosis indicator in human malignancies will be discussed.

CFTR mutation enhances Dishevelled degradation and results in impairment of Wnt-dependent hematopoiesis

Mutations of cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis (CF) with a multitude of clinical manifestations. Some CF patients develop clinically significant anemia, suggesting that CFTR may regulate hematopoiesis. Here, we report that cftr mutant zebrafish model exhibits primitive and definitive hematopoietic defects with impaired Wnt signaling. Cftr is found to interact, via its PDZ-binding domain (PDZBD), with Dishevelled (Dvl), a key component of Wnt signaling required for hematopoietic progenitor specification, thus protecting Dvl from Dapper1 (Dpr1)-induced lysosomal degradation. Defective hematopoiesis and impaired Wnt signaling in cftr mutant can be rescued by overexpression of wild-type or channel function-defective G551D mutant CFTR with an intact PDZBD, but not Cftr with mutations in the PDZBD. Analysis of human database (http://r2.amc.nl) shows that CFTR is positively correlated with DVL2 and Wnt-related hematopoietic factors in human blood system. The results reveal a previously unrecognized role of CFTR, which is independent of its channel function, in regulating DVL degradation and thus Wnt signaling required for hematopoiesis in both zebrafish and humans, providing an explanation for the anemic phenotype of CF patients.

Chemoattractants and cytokines in primary ciliary dyskinesia and cystic fibrosis: key players in chronic respiratory diseases

Patients with primary ciliary dyskinesia (PCD) and cystic fibrosis (CF), two inherited disorders, suffer from recurrent airway infections characterized by persistent bacterial colonization and uncontrollable inflammation. Although present in high counts, neutrophils fail to clear infection in the airways. High levels of C-X-C motif chemokine ligand 8/interleukin-8 (CXCL8/IL-8), the most potent chemokine to attract neutrophils to sites of infection, are detected in the sputum of both patient groups and might cause the high neutrophil influx in the airways. Furthermore, in CF, airway neutrophils are highly activated because of the genetic defect and the high levels of proinflammatory chemoattractants and cytokines (e.g., CXCL8/IL-8, tumor necrosis factor-α and IL-17). The overactive state of neutrophils leads to lung damage and fuels the vicious circle of infection, excessive inflammation and tissue damage. The inflammatory process in CF airways is well characterized, whereas the lung pathology in PCD is far less studied. The knowledge of CF lung pathology could be useful to guide molecular investigations of the inflammatory processes in PCD lungs. Current available therapies can not completely remedy the chronic airway infections in these diseases. This review gives an overview of the role that chemoattractants and cytokines play in these neutrophil-dominated lung pathologies. Finally, the most frequently applied treatments in CF and PCD and new experimental therapies to reduce neutrophil-dominated airway inflammation are described.

Ezrin-radixin-moesin-binding phosphoprotein 50 (EBP50) and nuclear factor-κB (NF-κB): a feed-forward loop for systemic and vascular inflammation

The interaction between vascular cells and macrophages is critical during vascular remodeling. Here we report that the scaffolding protein, ezrin-binding phosphoprotein 50 (EBP50), is a central regulator of macrophage and vascular smooth muscle cells (VSMC) function. EBP50 is up-regulated in intimal VSMC following endoluminal injury and promotes neointima formation. However, the mechanisms underlying these effects are not fully understood. Because of the fundamental role that inflammation plays in vascular diseases, we hypothesized that EBP50 mediates macrophage activation and the response of vessels to inflammation. Indeed, EBP50 expression increased in primary macrophages and VSMC, and in the aorta of mice, upon treatment with LPS or TNFα. This increase was nuclear factor-κB (NF-κB)-dependent. Conversely, activation of NF-κB was impaired in EBP50-null VSMC and macrophages. We found that inflammatory stimuli promote the formation of an EBP50-PKCζ complex at the cell membrane that induces NF-κB signaling. Macrophage activation and vascular inflammation after acute LPS treatment were reduced in EBP50-null cells and mice as compared with WT. Furthermore, macrophage recruitment to vascular lesions was significantly reduced in EBP50 knock-out mice. Thus, EBP50 and NF-κB participate in a feed-forward loop leading to increased macrophage activation and enhanced response of vascular cells to inflammation.

Tonic GABA inhibition in hippocampal dentate granule cells: its regulation and function in temporal lobe epilepsies

Both human and experimental evidence strongly supports the view of brain region- and cell-specific changes in tonic GABA inhibition in temporal lobe epilepsies (TLE). This 'tonic' form of signalling is not time-locked to presynaptic action potentials, which depends upon detection of ambient GABA by extrasynaptic GABAA receptors (GABAA Rs). Extrasynaptic GABAA Rs have distinct physiological and pharmacological features, including high GABA-binding affinity and low desensitization and a variety of the specific subunit combinations (α4δ-,α6δ-,α5γ-,ε-containing receptors). These features closely contribute to the function of tonic GABA current, which is preserved properly or increased in dentate gyrus in models of TLE, even in the face of a loss of synaptic inhibition and inhibitory interneurones. Markedly reduced tonic GABA inhibition may facilitate an episode of epilepsy, while persistent elevated tonic inhibition may contribute to the onset of spontaneous recurrent seizures. In dentate granule cells, tonic GABA inhibition is positively modulated by endogenous neurosteroids and other factors, which undergo changes related to hormonal status after TLE. Tonic inhibition regulates neuronal excitability through its effects on membrane potential by both offsetting the threshold and reducing the frequency of action potentials and input resistance. Therefore, extrasynaptic GABAA Rs are expected to be the most important pharmacological targets in TLE. It is likely that both elevate the ambient GABA concentration and potentiate the tonic currents, contributing to the antiepileptic effects.

Downregulation of CFTR promotes epithelial-to-mesenchymal transition and is associated with poor prognosis of breast cancer

The epithelial-to-mesenchymal transition (EMT), a process involving the breakdown of cell-cell junctions and loss of epithelial polarity, is closely related to cancer development and metastatic progression. While the cystic fibrosis transmembrane conductance regulator (CFTR), a Cl(-) and HCO3(-) conducting anion channel expressed in a wide variety of epithelial cells, has been implicated in the regulation of epithelial polarity, the exact role of CFTR in the pathogenesis of cancer and its possible involvement in EMT process have not been elucidated. Here we report that interfering with CFTR function either by its specific inhibitor or lentiviral miRNA-mediated knockdown mimics TGF-β1-induced EMT and enhances cell migration and invasion in MCF-7. Ectopic overexpression of CFTR in a highly metastatic MDA-231 breast cancer cell line downregulates EMT markers and suppresses cell invasion and migration in vitro, as well as metastasis in vivo. The EMT-suppressing effect of CFTR is found to be associated with its ability to inhibit NFκB targeting urokinase-type plasminogen activator (uPA), known to be involved in the regulation of EMT. More importantly, CFTR expression is found significantly downregulated in primary human breast cancer samples, and is closely associated with poor prognosis in different cohorts of breast cancer patients. Taken together, the present study has demonstrated a previously undefined role of CFTR as an EMT suppressor and its potential as a prognostic indicator in breast cancer.

CFTR activity and mitochondrial function

Cystic Fibrosis (CF) is a frequent and lethal autosomal recessive disease, caused by mutations in the gene encoding the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). Before the discovery of the CFTR gene, several hypotheses attempted to explain the etiology of this disease, including the possible role of a chloride channel, diverse alterations in mitochondrial functions, the overexpression of the lysosomal enzyme α-glucosidase and a deficiency in the cytosolic enzyme glucose 6-phosphate dehydrogenase. Because of the diverse mitochondrial changes found, some authors proposed that the affected gene should codify for a mitochondrial protein. Later, the CFTR cloning and the demonstration of its chloride channel activity turned the mitochondrial, lysosomal and cytosolic hypotheses obsolete. However, in recent years, using new approaches, several investigators reported similar or new alterations of mitochondrial functions in Cystic Fibrosis, thus rediscovering a possible role of mitochondria in this disease. Here, we review these CFTR-driven mitochondrial defects, including differential gene expression, alterations in oxidative phosphorylation, calcium homeostasis, oxidative stress, apoptosis and innate immune response, which might explain some characteristics of the complex CF phenotype and reveals potential new targets for therapy.

The mitochondrial complex I activity is reduced in cells with impaired cystic fibrosis transmembrane conductance regulator (CFTR) function

Cystic fibrosis (CF) is a frequent and lethal autosomal recessive disease. It results from different possible mutations in the CFTR gene, which encodes the CFTR chloride channel. We have previously studied the differential expression of genes in CF and CF corrected cell lines, and found a reduced expression of MTND4 in CF cells. MTND4 is a mitochondrial gene encoding the MTND4 subunit of the mitochondrial Complex I (mCx-I). Since this subunit is essential for the assembly and activity of mCx-I, we have now studied whether the activity of this complex was also affected in CF cells. By using Blue Native-PAGE, the in-gel activity (IGA) of the mCx-I was found reduced in CFDE and IB3-1 cells (CF cell lines) compared with CFDE/6RepCFTR and S9 cells, respectively (CFDE and IB3-1 cells ectopically expressing wild-type CFTR). Moreover, colon carcinoma T84 and Caco-2 cells, which express wt-CFTR, either treated with CFTR inhibitors (glibenclamide, CFTR(inh)-172 or GlyH101) or transfected with a CFTR-specific shRNAi, showed a significant reduction on the IGA of mCx-I. The reduction of the mCx-I activity caused by CFTR inhibition under physiological or pathological conditions may have a profound impact on mitochondrial functions of CF and non-CF cells.

Proinflammatory cytokine secretion is suppressed by TMEM16A or CFTR channel activity in human cystic fibrosis bronchial epithelia

Functional expression of either CFTR or the calcium-activated chloride channel TMEM16A attenuates expression and secretion of the proinflammatory cytokines IL-6, IL-8, and CXCL1/2 in respiratory epithelia. Thus augmented proinflammatory cytokine secretion caused by defective anion transport may contribute to lung inflammation in cystic fibrosis.

Cystic fibrosis (CF) is caused by the functional expression defect of the CF transmembrane conductance regulator (CFTR) chloride channel at the apical plasma membrane. Impaired bacterial clearance and hyperactive innate immune response are hallmarks of the CF lung disease, yet the existence of and mechanism accounting for the innate immune defect that occurs before infection remain controversial. Inducible expression of either CFTR or the calcium-activated chloride channel TMEM16A attenuated the proinflammatory cytokines interleukin-6 (IL-6), IL-8, and CXCL1/2 in two human respiratory epithelial models under air–liquid but not liquid–liquid interface culture. Expression of wild-type but not the inactive G551D-CFTR indicates that secretion of the chemoattractant IL-8 is inversely proportional to CFTR channel activity in cftr^{∆F508/∆F508} immortalized and primary human bronchial epithelia. Similarly, direct but not P2Y receptor–mediated activation of TMEM16A attenuates IL-8 secretion in respiratory epithelia. Thus augmented proinflammatory cytokine secretion caused by defective anion transport at the apical membrane may contribute to the excessive and persistent lung inflammation in CF and perhaps in other respiratory diseases associated with documented down-regulation of CFTR (e.g., chronic obstructive pulmonary disease). Direct pharmacological activation of TMEM16A offers a potential therapeutic strategy to reduce the inflammation of CF airway epithelia.

Innate immunity in cystic fibrosis lung disease

Chronic lung disease determines the morbidity and mortality of cystic fibrosis (CF) patients. The pulmonary immune response in CF is characterized by an early and non-resolving activation of the innate immune system, which is dysregulated at several levels. Here we provide a comprehensive overview of innate immunity in CF lung disease, involving (i) epithelial dysfunction, (ii) pathogen sensing, (iii) leukocyte recruitment, (iv) phagocyte impairment, (v) mechanisms linking innate and adaptive immunity and (iv) the potential clinical relevance. Dissecting the complex network of innate immune regulation and associated pro-inflammatory cascades in CF lung disease may pave the way for novel immune-targeted therapies in CF and other chronic infective lung diseases.

Hybrid organic-inorganic inhibitors of a PDZ interaction that regulates the endocytic fate of CFTR

Together strong: Cooperative binding of organic (see picture, red) and inorganic fragments provides a strategy for the potent inhibition of protein-protein interactions. By targeting specific Lewis basic side chains in peripheral regions of the binding site for coordination to a rhodium(II) center, the affinity of otherwise weak ligands is improved.

Induction of type I interferon signaling by Pseudomonas aeruginosa is diminished in cystic fibrosis epithelial cells

The clinical manifestations of infection in cystic fibrosis (CF) are restricted to the lung, and involve a limited number of pathogens, suggesting a specific defect in mucosal immunity. We postulated that cystic fibrosis transmembrane conductance regulator (CTFR) mutations could affect the activation of type I interferon signaling in airway epithelial cells, which function in immune surveillance and initiate the recruitment and activation of immune cells. In response to infection with Pseudomonas aeruginosa, Ifnb was induced more than 100-fold in the murine lung, and the phosphorylation of STAT1 was similarly induced by the expected TLR4/TRIF/MD2/TBK1 cascade. The stimulation by P. aeruginosa of CF (IB3) cells and control (C-38) human cell lines similarly resulted in the induction of IFN-β, but to a significantly lower extent in CF airway cells. The potential consequences of diminished type I IFN signaling were demonstrated in a murine model of P. aeruginosa pneumonia, pretreatment with polyinosinic:polycytidylic acid significantly enhanced bacterial clearance and correlated with increased numbers of mature CD11c(+)/CD86(+) dendritic cells (DCs) in the lung. Using culture supernatants from CF or control cell lines stimulated with P. aeruginosa, we similarly demonstrated the diminished activation of human monocyte-derived DCs by incubation with CF compared with normal epithelial cell culture supernatants, which was dependent on IFN-β. These observations suggest that dysfunction of the CFTR in airway epithelial cells may contribute to impaired immune surveillance in the CF airway and resultant colonization by P. aeruginosa.

CFTR negatively regulates cyclooxygenase-2-PGE(2) positive feedback loop in inflammation

Cystic fibrosis (CF) is an autosomal recessive disorder caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-dependent anion channel mostly expressed in epithelia. Accumulating evidence suggests that CF airway epithelia are overwhelmed by excessive inflammatory cytokines and prostaglandins (PGs), which eventually lead to the over-inflammatory condition observed in CF lung disease. However, the exact underlying mechanism remains elusive. In this study, we observed increased cyclooxygenase-2 (COX-2) expression and over-production of prostaglandin E(2) (PGE(2)) in human CF bronchial epithelia cell line (CFBE41o--) with elevated NF-κB activity compared to a wild-type airway epithelial cell line (16HBE14o--). Moreover, we demonstrated that CFTR knockout mice had inherently higher levels of COX-2 and NF-κB activity, supporting the notion that lack of CFTR results in hyper-inflammatory signaling. In addition, we identified a positive feedback loop for production of PGE(2) involving PKA and transcription factor, CREB. More importantly, overexpression of wild-type CFTR significantly suppressed COX-2 expression in CFBE41o- cells, and wild-type CFTR protein expression was significantly increased when 16HBE14o-- cells were challenged with LPS as well as PGE(2), indicating possible involvement of CFTR in negative regulation of COX-2/PGE(2). In conclusion, CFTR is a negative regulator of PGE(2)-mediated inflammatory response, defect of which may result in excessive activation of NF-κB, leading to over production of PGE(2) as seen in inflammatory CF tissues.

Cystic fibrosis: a mucosal immunodeficiency syndrome

Cystic fibrosis transmembrane conductance regulator (CFTR) functions as a channel that regulates the transport of ions and the movement of water across the epithelial barrier. Mutations in CFTR, which form the basis for the clinical manifestations of cystic fibrosis, affect the epithelial innate immune function in the lung, resulting in exaggerated and ineffective airway inflammation that fails to eradicate pulmonary pathogens. Compounding the effects of excessive neutrophil recruitment, the mutant CFTR channel does not transport antioxidants to counteract neutrophil-associated oxidative stress. Whereas mutant CFTR expression in leukocytes outside of the lung does not markedly impair their function, the expected regulation of inflammation in the airways is clearly deficient in cystic fibrosis. The resulting bacterial infections, which are caused by organisms that have substantial genetic and metabolic flexibility, can resist multiple classes of antibiotics and evade phagocytic clearance. The development of animal models that approximate the human pulmonary phenotypes-airway inflammation and spontaneous infection-may provide the much-needed tools to establish how CFTR regulates mucosal immunity and to test directly the effect of pharmacologic potentiation and correction of mutant CFTR function on bacterial clearance.

Domain location within the cystic fibrosis transmembrane conductance regulator protein investigated by electron microscopy and gold labelling

The domain organisation of the cystic fibrosis transmembrane conductance regulator (CFTR) protein was studied using electron microscopy of detergent-solubilised dimeric complexes. Ni-NTA nanogold labelling data suggest that in the nonphosphorylated, nucleotide-free state, the C-terminus is intimately associated with the cytoplasmic ATP-binding regions, whilst part of the regulatory domain occupies a position close to the cytoplasmic surface of the lipid membrane. Removal of the entire second nucleotide binding domain (NBD2) results in a deficit in the CFTR structure that is consistent with the size and shape of a single NBD. The data suggest that NBD2 lies closer to the C2 symmetry axis than the first nucleotide binding domain (NBD1) and that NBD2 from one CFTR monomer also contacts NBD1 from the opposing one. These data suggest that current homology models for CFTR based on other ATP-binding cassette proteins appear to be reasonable, at least to low resolution. We also find that Ni-NTA nanogold labelling of an internal hexa-Histidine sequence is a valuable approach to locate individual protein domains.

Syntaxin 6 and CAL mediate the degradation of the cystic fibrosis transmembrane conductance regulator

STX6 is a new component of the CAL complex that regulates the abundance and function of CFTR at the post-ER level. Our results suggest a therapeutic role of STX6 in enhancing rescued ΔF508-CFTR.

The PDZ domain–containing protein CAL mediates lysosomal trafficking and degradation of CFTR. Here we demonstrate the involvement of a CAL-binding SNARE protein syntaxin 6 (STX6) in this process. Overexpression of STX6, which colocalizes and coimmunoprecipitates with CAL, dramatically reduces the steady-state level and stability of CFTR. Conversely, overexpression of a STX6 dominant-negative mutant increases CFTR. Silencing endogenous STX6 increases CFTR but has no effect on ΔTRL-CFTR, which cannot bind to CAL. Silencing CAL eliminates the effect of STX6 on CFTR. Both results suggest a dependence of CAL on STX6 function. Consistent with its Golgi localization, STX6 does not bind to ER-localized ΔF508-CFTR. Silencing STX6 has no effect on ΔF508-CFTR expression. However, overexpression of STX6 coimmunoprecipitates with and reduces temperature-rescued ΔF508-CFTR that escapes ER degradation. Conversely, silencing STX6 enhances the effect of low temperature in rescuing ΔF508-CFTR. Finally, in human bronchial epithelial cells, silencing endogenous STX6 leads to increases in protein levels and Cl⁻ currents of both wild-type and temperature-rescued CFTR. We have identified STX6 as a new component of the CAL complex that regulates the abundance and function of CFTR at the post-ER level. Our results suggest a therapeutic role of STX6 in enhancing rescued ΔF508-CFTR.

CFTR in a lipid raft-TNFR1 complex modulates gap junctional intercellular communication and IL-8 secretion

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) cause a chronic inflammatory response in the lung of patients with Cystic Fibrosis (CF). We have showed that TNF-alpha signaling through the Src family tyrosine kinases (SFKs) was defective as determined by an inability of TNF-alpha to regulate gap junctional communication (GJIC) in CF cells. Here, we sought to elucidate the mechanisms linking TNF-alpha signaling to the functions of CFTR at the molecular level. In a MDCKI epithelial cell model expressing wild-type (WtCFTR) or mutant CFTR lacking its PDZ-interacting motif (CFTR-DeltaTRL), TNF-alpha increased the amount of WtCFTR but not CFTR-DeltaTRL in detergent-resistant membrane microdomains (DRMs). This recruitment was modulated by SFK activity and associated with DRM localization of TNFR1 and c-Src. Activation of TNFR1 signaling also decreased GJIC and markedly stimulated IL-8 production in WtCFTR cells. In contrast, the absence of CFTR in DRMs was associated with abnormal TNFR1 signaling as revealed by no recruitment of TNFR1 and c-Src to lipid rafts in CFTR-DeltaTRL cells and loss of regulation of GJIC and IL-8 secretion. These results suggest that localization of CFTR in lipid rafts in association with c-Src and TNFR1 provides a responsive signaling complex to regulate GJIC and cytokine signaling.

Hormonal control of the renal immune response and antibacterial host defense by arginine vasopressin

Ascending urinary tract infection (UTI) and pyelonephritis caused by uropathogenic Escherichia coli (UPEC) are very common infections that can cause severe kidney damage. Collecting duct cells, the site of hormonally regulated ion transport and water absorption controlled by vasopressin, are the preferential intrarenal site of bacterial adhesion and initiation of inflammatory response. We investigated the effect of the potent V2 receptor (V2R) agonist deamino-8-D-arginine vasopressin (dDAVP) on the activation of the innate immune response using established and primary cultured collecting duct cells and an experimental model of ascending UTI. dDAVP inhibited Toll-like receptor 4–mediated nuclear factor κB activation and chemokine secretion in a V2R-specific manner. The dDAVP-mediated suppression involved activation of protein phosphatase 2A and required an intact cystic fibrosis transmembrane conductance regulator Cl⁻ channel. In vivo infusion of dDAVP induced a marked fall in proinflammatory mediators and neutrophil recruitment, and a dramatic rise in the renal bacterial burden in mice inoculated with UPECs. Conversely, administration of the V2R antagonist SR121463B to UPEC-infected mice stimulated both the local innate response and the antibacterial host defense. These findings evidenced a novel hormonal regulation of innate immune cellular activation and demonstrate that dDAVP is a potent modulator of microbial-induced inflammation in the kidney.

Innate immune response in CF airway epithelia: hyperinflammatory?

The lack of functional cystic fibrosis (CF) transmembrane conductance regulator (CFTR) in the apical membranes of CF airway epithelial cells abolishes cAMP-stimulated anion transport, and bacteria, eventually including Pseudomonas aeruginosa, bind to and accumulate in the mucus. Flagellin released from P. aeruginosa triggers airway epithelial Toll-like receptor 5 and subsequent NF-kappaB signaling and production and release of proinflammatory cytokines that recruit neutrophils to the infected region. This response has been termed hyperinflammatory because so many neutrophils accumulate; a response that damages CF lung tissue. We first review the contradictory data both for and against the idea that epithelial cells exhibit larger-than-normal proinflammatory signaling in CF compared with non-CF cells and then review proposals that might explain how reduced CFTR function could activate such proinflammatory signaling. It is concluded that apparent exaggerated innate immune response of CF airway epithelial cells may have resulted not from direct effects of CFTR on cellular signaling or inflammatory mediator production but from indirect effects resulting from the absence of CFTRs apical membrane channel function. Thus, loss of Cl-, HCO3-, and glutathione secretion may lead to reduced volume and increased acidification and oxidation of the airway surface liquid. These changes concentrate proinflammatory mediators, reduce mucociliary clearance of bacteria and subsequently activate cellular signaling. Loss of apical CFTR will also hyperpolarize basolateral membrane potentials, potentially leading to increases in cytosolic [Ca2+], intracellular Ca2+, and NF-kappaB signaling. This hyperinflammatory effect of CF on intracellular Ca2+ and NF-kappaB signaling would be most prominently expressed during exposure to both P. aeruginosa and also endocrine, paracrine, or nervous agonists that activate Ca2+ signaling in the airway epithelia.

Cystic fibrosis enters the proteomics scene: New answers to old questions

The discovery in 1989 of the gene encoding for the cystic fibrosis transmembrane conductance regulator (CFTR) and its mutation as the primary cause of cystic fibrosis (CF), generated an optimistic reaction with respect to the development of potential therapies. This extraordinary milestone, however, represented only the initial key step in a long path. Many of the mechanisms that govern the pathogenesis of CF, the most commonly inherited lethal pulmonary disorder in Caucasians, remain even today unknown. As a continuation to genomic research, proteomics now offers the unique advantage to examine global alterations in the protein expression patterns of CF cells and tissues. The systematic use of this approach will probably provide new insights into the cellular mechanisms involved in CF dysfunctions, and should ultimately result in the finding of new prognostic markers, and in the generation of new therapies. In this article we review the current status of proteomic research applied to the study of CF, including CFTR-related interactomics, and evaluate the potential of these technologies for future investigations.

MUC4 expression is regulated by cystic fibrosis transmembrane conductance regulator in pancreatic adenocarcinoma cells via transcriptional and post-translational mechanisms

MUC4 mucin is a high molecular weight transmembrane glycoprotein that plays important roles in tumour biology. It is aberrantly expressed in pancreatic adenocarcinoma, while not being detectable in the normal pancreas. Previous studies have demonstrated that the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel that is defective in CF, is implicated in multiple cellular functions, including gene regulation. In the present study, using a CFTR-defective pancreatic cancer cell line and its derived subline expressing functional CFTR, we report that MUC4 expression is negatively regulated by CFTR. Short-interfering RNA (siRNA)-mediated silencing of CFTR also leads to an increased expression of MUC4. Additionally, our results suggest that CFTR-mediated regulation of MUC4 is cell density-dependent and is achieved by transcriptional and posttranslational mechanisms. Moreover, in a panel of pancreatic cancer cell lines and normal pancreas, we observed that CFTR was downregulated in pancreatic cancer cells and negatively correlated with MUC4 in most cases. An aberrant expression of MUC4 was also detected in the CF pancreas. Downregulation of CFTR in pancreatic adenocarcinoma and its inverse association with the tumour-linked mucin, MUC4, indicate novel function(s) of CFTR in pancreatic tumour biology and suggest the implication of new signalling pathway(s) in MUC4 regulation.

Changes in ion transport in inflammatory disease

Ion transport is essential for maintenance of transmembranous and transcellular electric potential, fluid transport and cellular volume. Disturbance of ion transport has been associated with cellular dysfunction, intra and extracellular edema and abnormalities of epithelial surface liquid volume. There is increasing evidence that conditions characterized by an intense local or systemic inflammatory response are associated with abnormal ion transport. This abnormal ion transport has been involved in the pathogenesis of conditions like hypovolemia due to fluid losses, hyponatremia and hypokalemia in diarrhoeal diseases, electrolyte abnormalities in pyelonephritis of early infancy, septicemia induced pulmonary edema, and in hypersecretion and edema induced by inflammatory reactions of the mucosa of the upper respiratory tract. Components of membranous ion transport systems, which have been shown to undergo a change in function during an inflammatory response include the sodium potassium ATPase, the epithelial sodium channel, the Cystic Fibrosis Transmembrane Conductance Regulator and calcium activated chloride channels and the sodium potassium chloride co-transporter. Inflammatory mediators, which influence ion transport are tumor necrosis factor, gamma interferon, interleukins, transforming growth factor, leukotrienes and bradykinin. They trigger the release of specific messengers like prostaglandins, nitric oxide and histamine which alter ion transport system function through specific receptors, intracellular second messengers and protein kinases. This review summarizes data on in vivo measurements of changes in ion transport in acute inflammatory conditions and in vitro studies, which have explored the underlying mechanisms. Potential interventions directed at a correction of the observed abnormalities are discussed.

Processing of CFTR: traversing the cellular maze--how much CFTR needs to go through to avoid cystic fibrosis?

Biosynthesis of the cystic fibrosis transmembrane conductance regulator (CFTR), like other proteins aimed at the cell surface, involves transport through a series of membranous compartments, the first of which is the endoplasmic reticulum (ER), where CFTR encounters the appropriate environment for folding, oligomerization, maturation, and export from the ER. After exiting the ER, CFTR has to traffic through complex pathways until it reaches the cell surface. Although not yet fully understood, the fine details of these pathways are starting to emerge, partially through identification of an increasing number of CFTR-interacting proteins (CIPs) and the clarification of their roles in CFTR trafficking and function. These aspects of CFTR biogenesis/degradation and by membrane traffic and CIPs are discussed in this review. Following this description of complex pathways and multiple checkpoints to which CFTR is subjected in the cell, the basic question remains of how much CFTR has to overcome these barriers and be functionally expressed at the plasma membrane to avoid CF. This question is also discussed here.

Global proteomic approach unmasks involvement of keratins 8 and 18 in the delivery of cystic fibrosis transmembrane conductance regulator (CFTR)/?F508-CFTR to the plasma membrane

Cystic fibrosis (CF) is a genetic disease caused by mutations in the CF gene (cftr). Physiologically, CF is characterized by an abnormal chloride secretion in epithelia due to a dysfunction of a mutated cystic fibrosis transmembrane conductance regulator (CFTR). CFTR is a cAMP-dependent chloride channel whose most frequent mutation, deltaF508, leads to an aberrantly folded protein which causes a dysfunction of the channel. However, a growing number of reports suggest that modifier genes and environmental factors are involved in the physiology of CF. To identify proteins whose expression depends on wild-type WT-CFTR or deltaF508-CFTR, we chose a global proteomic approach based on the use of two-dimensional gel electrophoresis (2-DE) and mass spectrometry. The experiments were carried out with HeLa cells stably transfected with WT-CFTR (pTCFWT) or deltaF508-CFTR (pTCFdeltaF508). These experiments unmasked keratin 8 (K8) and 18 (K18) which were differentially expressed in pTCFWT vs. pTCFdeltaF508. An immunoblot of K18 confirmed the 2-DE results. Intracellular localization experiments of WT-CFTR, deltaF508-CFTR, K8, and K18 suggest that the expression of these proteins are linked, and that the concentrations of K8 and K18 and/or their distribution may be involved in the traffic of WT-CFTR/deltaF508-CFTR. A functional assay for CFTR revealed that specifically lowering K18 expression or changing its distribution leads to the delivery of functional deltaF508-CFTR to the plasma membrane. This work suggests a novel function of K18 in CF.

Mechanistic Similarities between Cultured Cell Models of Cystic Fibrosis and Niemann-Pick Type C

Recent data demonstrate that inhibition of 3-hydroxy-3-methylglutaryl-CoA reductase restores normal signal transducer and activator of transcription-1 and inducible nitric oxide synthase expression regulation in cystic fibrosis (CF) cells through the modulation of RhoA function. These findings lead to the hypothesis that alterations in the cholesterol synthesis pathway may be an initiating factor in CF-related cell signaling regulation. A disease with a known lesion in the cholesterol synthesis pathway is Niemann-Pick type C (NPC). The hypothesis of this study is that CF cells and NPC fibroblasts share a common mechanistic lesion and should exhibit similar cell signaling alterations. NPC fibroblasts exhibit similar alterations in signal transducer and activator of transcription-1, RhoA, SMAD3, and nitric oxide synthase protein expression that characterize CF. Further comparison reveals NPC-like accumulation of free cholesterol in two cultured models of CF epithelial cells. These data identify novel signaling changes in NPC, demonstrate the cholesterol-synthesis pathway is a likely source of CF-related cell signaling changes, and that cultured CF cells exhibit impaired cholesterol processing.

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 (DeltaF508, 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.

Role of Cftr genotype in the response to chronic Pseudomonas aeruginosa lung infection in mice

Patients with cystic fibrosis have a lesion in the cystic fibrosis transmembrane conductance regulator gene (CFTR), which is associated with abnormal regulation of other ion channels, abnormal glycosylation of secreted and cell surface molecules, and vulnerability to bacterial infection and inflammation in the lung usually leading to the death of these patients. The exact mechanism(s) by which mutation in CFTR leads to lung infection and inflammation is not clear. Mice bearing different mutations in the murine homolog to CFTR (Cftr) (R117H, S489X, Y122X, and DeltaF508, all backcrossed to the C57BL/6J background) were compared with respect to growth and in their ability to respond to lung infection elicited with Pseudomonas aeruginosa-laden agarose beads. Body weights of mice bearing mutations in Cftr were significantly smaller than wild-type mice at most ages. The inflammatory responses to P. aeruginosa-laden agarose beads were comparable in mice of all four Cftr mutant genotypes with respect to absolute and relative cell counts in bronchoalveolar lavage fluid, and cytokine levels (TNF-alpha, IL-1beta, IL-6, macrophage inflammatory protein-2, and keratinocyte chemoattractant) and eicosanoid levels (PGE2 and LTB4) in epithelial lining fluid: the few small differences observed occurred only between cystic fibrosis mice bearing the S489X mutation and those bearing the knockout mutation Y122X. Thus we cannot implicate either misprocessing of CFTR or failure of CFTR to reach the plasma membrane in the genesis of the excess inflammatory response of CF mice. Therefore, it appears that any functional defect in CFTR produces comparable inflammatory responses to lung infections with P. aeruginosa.

A NHERF binding site links the betaPDGFR to the cytoskeleton and regulates cell spreading and migration

The Na(+)/H(+) exchanger regulatory factor, NHERF, is a multifunctional adapter protein involved in a wide range of physiological activities. NHERF associates with merlin and the ezrin/radixin/moesin (MERM) family of membrane-actin cytoskeletal linker proteins through its C-terminus and is capable of interacting via its PDZ1 domain to the betaPDGF receptor (betaPDGFR). Thus, NHERF, potentially links the betaPDGFR to the actin cytoskeleton through its interaction with MERM proteins. In the present study, we have examined whether abolishing the interaction of betaPDGFR with NHERF results in actin cytoskeletal rearrangements. We have stably expressed a wild-type betaPDGFR, a mutant betaPDGFR (L1106A) that is incapable of interacting with NHERF, as well as a kinase defective mutant receptor (K634R), in PDGFR-deficient mouse embryonic fibroblasts. Our observations indicate that cells expressing betaPDGFR (L1106A) were impaired in their ability to spread and migrate on fibronectin compared with wild-type and K634R cells. L1106A mutant cells also revealed an increased number of focal adhesions, a condensed F-actin ring at the cell periphery and a decrease in total focal adhesion kinase (FAK) tyrosine phosphorylation. Further, we show that NHERF and MERM proteins could act as intermediary bridging proteins between betaPDGFR and FAK. Thus, the interaction of betaPDGFR with NHERF may provide an essential link between the cell membrane and the cortical actin cytoskeleton independent of receptor activity.

Update on pathogenesis of cystic fibrosis lung disease

PURPOSE OF REVIEW

It has been an ongoing challenge to translate knowledge pertaining to the molecular basis of cystic fibrosis (CF) into a clear understanding of the development of CF lung disease. Various hypotheses have attempted to explain the apparent breach of innate defenses in CF, although a definitive explanation has been elusive.

RECENT FINDINGS

Recent data suggest that altered ion transport functions--namely sodium hyperabsorption and reduced chloride secretion--lead to a depletion of airway surface liquid. As a result, the overlying mucus layer may encroach upon cell surfaces and become adherent, thus interfering with cilia-dependent and cough clearance. These static, and ultimately anaerobic, niches provide a favorable environment for the development of bacterial biofilms and persistent infection with Pseudomonas aeruginosa.

SUMMARY

With a better understanding of pathogenic steps leading to CF lung disease, we may now be able to direct the development of therapies that will substantially improve disease outcomes.

Rescue of defective pancreatic secretion in cystic-fibrosis cells by suppression of a novel isoform of phospholipase C

BACKGROUND

Cystic fibrosis is caused by mutations in the gene encoding an ion-transport protein, the cystic-fibrosis transmembrane conductance regulator (CFTR). Defective secretion of anions is the primary cause of many of the clinical manifestations of cystic fibrosis, including pancreatic insufficiency. We aimed to identify a molecular mechanism from which a new method to circumvent defective pancreatic secretion could be derived.

METHODS

Multiple-human-tissue RT-PCR and semiquantitative RT-PCR analyses were used to examine gene expression. An antisense technique was used in conjunction with radioimmunoassay, Fura-2 spectrofluorometry, immunohistochemistry, and the short-circuit current technique (Ussing chamber) for elucidation of gene function and its application in rescuing defective pancreatic secretion.

FINDINGS

We cloned a newly identified gene, NYD-SP27, which has structural similarity to an isoform of phospholipase C. NYD-SP27 was expressed endogenously in human pancreatic-duct cells and upregulated in cystic fibrosis. Suppression of NYD-SP27, by transfection of its antisense into human cystic-fibrosis pancreatic-duct cells, resulted in augmentation of phospholipase-C-coupled calcium-ion release and protein kinase C activity, improvement in the amount of mutated CFTR reaching the plasma membrane, and restoration of cAMP-activated pancreatic anion secretion.

INTERPRETATION

NYD-SP27 exerts an inhibitory effect on phospholipase-C-coupled processes that depend on calcium ions and protein kinase C, including CFTR trafficking and function. Its upregulation in pancreatic-duct cells may reveal a previously unsuspected defect in cystic fibrosis contributing to pancreatic insufficiency, and thus represents a new target for pharmacological intervention in cystic fibrosis.

Localization of Cystic Fibrosis Transmembrane Conductance Regulator to Lipid Rafts of Epithelial Cells Is Required forPseudomonas aeruginosa-Induced Cellular Activation

The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) protein is an epithelial cell receptor for the outer core oligosaccharide of the Pseudomonas aeruginosa LPS. Bacterial binding leads to CFTR-dependent bacterial internalization, initiation of NF-kappaB nuclear translocation, cellular desquamation, and eventual apoptosis of the infected cells, all of which are critical for innate immune resistance to infection with this pathogen. Lack of this reaction in CF patients underlies their hypersusceptibility to chronic P. aeruginosa infection. In this study we tested whether these epithelial cell responses are dependent upon the localization of CFTR to lipid rafts. Confocal microscopy showed that green fluorescent protein-tagged CFTR (GFP-CFTR) and the lipid raft marker ganglioside GM1 colocalized at sites of P. aeruginosa contact and internalization. GFP-CFTR localized to low density Triton X-100-insoluble fractions in lysates of Madin-Darby canine kidney GFP-CFTR cells, and P. aeruginosa infection increased the levels of GFP-CFTR in these fractions as determined by Western blot. Cells expressing GFP-DeltaF508-CFTR did not have rafts with detectable CFTR protein. Extraction of cell surface cholesterol via cyclodextrin treatment of the cells inhibited CFTR entry into rafts. In addition, cyclodextrin treatment of both human and canine epithelial cells inhibited cellular ingestion of P. aeruginosa, NF-kappaB nuclear translocation, and apoptosis. These results indicate that lipid raft localization of CFTR is required for signaling in response to P. aeruginosa infection. Such signaling is needed for the coordination of innate immunity to P. aeruginosa lung infection, a process that is defective in CF.

Statin-mediated correction of STAT1 signaling and inducible nitric oxide synthase expression in cystic fibrosis epithelial cells

The expression of the inducible form of nitric oxide synthase (NOS2) is reduced in cystic fibrosis (CF) epithelium despite the presence of aggressive inflammation. A potential mechanism for reduced NOS2 expression in CF is diminished signal transducer and activator of transcription-1 (STAT1) activity, possibly due to an increase in expression of protein inhibitor of activated STAT1 (PIAS1). Previous evidence also suggests that NOS2 expression can be negatively regulated by increased activation of the GTPase RhoA, leading to the hypothesis that CF-related increases in PIAS1 expression and altered STAT1 signaling may be mediated by Rho GTPase function. Consistent with this hypothesis, data demonstrate increased expression of RhoA in two models of CF epithelium with a proportional increase in the active GTP-bound RhoA. Mouse embryonic fibroblasts null for p190B Rho GTPase-activating protein exhibit increased RhoA protein content and activation, similar to what is observed in CF models, and also exhibit CF-like alterations in STAT1 regulation, including decreased STAT1 activation, increased PIAS1 protein expression, and reduced NOS2 induction, implicating RhoA-mediated signaling in CF-related STAT1 alterations. Inhibition of the Rho GTPase pathway at the level of isoprenoid/cholesterol synthesis with mevastatin reduces PIAS1 expression, increases STAT1 activation, and restores NOS2 expression in models of CF epithelium, suggesting that pharmacological inhibition of the isoprenoid synthesis/Rho GTPase pathway may represent a potential avenue for therapeutic intervention for CF.