Defective phosphorylation of a calmodulin-binding protein in cystic-fibrosis submandibular glands

Defective formation of PKA/CnA-dependent annexin 2-S100A10/CFTR complex in DeltaF508 cystic fibrosis cells

Cystic fibrosis (CF) is characterised by impaired epithelial ion transport and is caused by mutations in the cystic fibrosis conductance regulator protein (CFTR), a cAMP/PKA and ATP-regulated chloride channel. We recently demonstrated a cAMP/PKA/calcineurin (CnA)-driven association between annexin 2 (anx 2), its cognate partner -S100A10 and cell surface CFTR. The complex is required for CFTR and outwardly rectifying chloride channel function in epithelia. Since the cAMP/PKA-induced Cl(-) current is absent in CF epithelia, we hypothesized that the anx 2-S100A10/CFTR complex may be defective in CFBE41o cells expressing the commonest F508del-CFTR (DeltaF-CFTR) mutation. Here, we demonstrate that, despite the presence of cell surface DeltaF-CFTR, cAMP/PKA fails to induce anx 2-S100A10/CFTR complex formation in CFBE41o- cells homozygous for F508del-CFTR. Mechanistically, PKA-dependent serine phosphorylation of CnA, CnA-anx 2 complex formation and CnA-dependent dephosphorylation of anx 2 are all defective in CFBE41o- cells. Immunohistochemical analysis confirms an abnormal cellular distribution of anx 2 in human and CF mouse epithelia. Thus, we demonstrate that cAMP/PKA/CnA signaling pathway is defective in CF cells and suggest that loss of anx 2-S100A10/CFTR complex formation may contribute to defective cAMP/PKA-dependent CFTR channel function.

Nasal and exhaled nitric oxide is reduced in adult patients with cystic fibrosis and does not correlate with cystic fibrosis genotype

STUDY OBJECTIVES

Inducible nitric oxide synthase (iNOS) is upregulated in a number of inflammatory lung conditions, and exhaled nitric oxide (NO) concentration is increased. However, previous studies in children with cystic fibrosis (CF) have shown that exhaled NO is reduced. The purpose of this investigation was to study exhaled NO concentration in adults with CF, and to investigate the effect of CF genotype and respiratory tract infection on this measurement.

DESIGN

Exhaled and nasal NO levels were measured in 54 adult CF subjects and 37 healthy nonsmoking age-matched subjects using a chemiluminesence analyzer. Spirometry (FEV(1) and FVC), CF genotype, and bacterial colonization were also recorded.

SETTING

This study was conducted at a national CF center.

RESULTS

The mean age of patients was 26.9 years, and the mean FEV(1) was 50.5% predicted (range, 17 to 104%). Nasal NO in the CF patients (mean, 520 parts per billion [ppb]; confidence interval [CI], 452 to 588) was significantly lower (p < 0.001) than in control subjects (987 ppb; CI, 959 to 1,015). Exhaled NO was significantly lower (p < 0. 001) in CF patients (5.0 ppb; CI, 4.1 to 6.1) than in control subjects (7.3 ppb; CI, 6.8 to 7.8). FEV(1) did not correlate with nasal or exhaled NO. No association was observed between genotype and NO values or colonization with Pseudomonas aeruginosa.

CONCLUSIONS

Despite the airway inflammation that is characteristic of CF, both nasal and exhaled NO were reduced. There was no association with genotype or infection status. As NO has bacteriostatic effects and may augment mucociliary clearance, this observation may be of clinical importance.

CPX, a selective A1-adenosine-receptor antagonist, regulates intracellular pH in cystic fibrosis cells

The selective A1-adenosine-receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (CPX), has been reported to activate Cl- efflux from cystic fibrosis cells, such as pancreatic CFPAC-1 and lung IB3 cells bearing the cystic fibrosis transmembrane regulator(delta F508) mutation, but has little effect on the same process in cells repaired by transfection with wild-type cystic fibrosis transmembrane regulator (O. Eidelman, C. Guay-Broder, P. J. M. van Galen, K. A. Jacobson, C. Fox, R. J. Turner, Z. I. Cabantchik, and H. B. Pollard. Proc. Natl. Acad. Sci. USA 89: 5562-5566, 1992). We report here that CPX downregulates Na+/H+ exchange activity in CFPAC-1 cells but has a much smaller effect on cells repaired with the wild-type gene. CPX also mildly decreases resting intracellular pH. In CFPAC-1 cells, this downregulation is dependent on the presence of adenosine, since pretreatment of the cells with adenosine deaminase blocks the CPX effect. We also show that, by contrast, CPX action on these cells does not lead to alterations in intracellular free Ca2+ concentration. We conclude that CPX affects pH regulation in CFPAC-1 cells, probably by antagonizing the tonic action of endogenous adenosine.

Immunoreactive calmodulin in cystic fibrosis kidneys

BACKGROUND

Microscopic nephrocalcinosis has been detected at autopsy in 35 of 38 (92%) cystic fibrosis (CF) patients. A primary defect of calcium metabolism in the kidney has been postulated. Intracellular calcium and calmodulin (a calcium binding protein) have been shown to be increased in CF tissues.

AIMS

To determine whether CF kidneys obtained at autopsy contain normal amounts of calmodulin and whether the presence of immunoreactive calmodulin correlates with nephrocalcinosis.

METHODS

An immunoperoxidase method was used to stain kidneys obtained from six CF individuals aged three to 27.5 years (mean 15.75 +/- 10.2 years) and five individuals who died of chronic debilitating disease aged eight to 17 years (mean 13.6 +/- 3.9 years). Calcium staining was undertaken using the von Kossa (silver precipitation) and Alizarin red methods.

RESULTS

No quantifiable difference in immunoreactive calmodulin staining was demonstrated in autopsy renal specimens between six CF patients and five chronically diseased controls. Three of six CF patients aged 22.8 +/- four years and two of five chronically diseased controls aged eight to 16 years respectively had detectable immunoreactive calmodulin staining. Within the CF group the presence of microscopic nephrocalcinosis did not correlate with immunoreactive calmodulin staining.

CONCLUSION

This study does not support the premise that a calmodulin-dependent defect of intracellular calcium handling contributes to the microscopic nephrocalcinosis seen in CF.

Impaired stimulus-evoked mucus secretion in cystic fibrosis bronchi

Baseline and agonist-stimulated secretion of fucose, hexose, and protein (markers of mucus secretion) was investigated in vitro in 45 bronchial segments from 14 patients with cystic fibrosis (CF) (three after heart-lung transplant, the remainder < 4.5 h after autopsy), in 51 segments from 26 patients with carcinoma (24 resection, 2 after autopsy), and in 4 segments from 3 patients with bronchiectasis (resection). Basal rates of secretion of each mucus marker by CF bronchi were not significantly different from those by carcinoma bronchi bronchiectatic bronchi. However, rates of secretion of each marker in response to the cholinomimetic methacholine (10 microM; n = 11-18, depending on marker) and the beta 2-adrenoceptor agonist terbutaline (10 microM; n = 9-11) were significantly (p < .05) increased in carcinoma bronchi (by 50-117% above basal), but not in CF airways (n = 11-14). The secretory response to the sensory neuropeptide substance P (1 nM to 10 microM; n = 5-7) was also reduced in CF compared with carcinoma bronchi. Physiological and morphological data indicated that the reduced response by CF tissue could not be accounted for by inclusion of autopsy tissue in the study. These data suggest a defect in autonomic control of bronchial secretion in CF, not in the basal rate of secretion, but in its response to receptor stimulation.

An antibody against a CFTR-derived synthetic peptide, incorporated into living submandibular cells, inhibits beta-adrenergic stimulation of mucin secretion

An antibody raised against a peptide in the first nucleotide-binding domain (NBD) of CFTR [1], incorporated into intact rat submandibular acini by hypotonic swelling, inhibited beta-adrenergic stimulated mucin secretion, without affecting cyclic AMP rise. The data are the first to show that a CFTR-antibody-containing cell results in defective stimulation of mucin secretion, as is seen in CF cells, and that this can be reversed by an excessive increase in cyclic AMP.