CFTR chloride channel activity modulates the mitochondrial morphology in cultured epithelial cells.

The impairment of the CFTR channel activity, a cAMP-activated chloride (Cl-) channel responsible for cystic fibrosis (CF), has been associated with a variety of mitochondrial alterations such as modified gene expression, impairment in oxidative phosphorylation, increased reactive oxygen species (ROS), and a disbalance in calcium homeostasis. The mechanisms by which these processes occur in CF are not fully understood. Previously, we demonstrated a reduced MTND4 expression and a failure in the mitochondrial complex I (mCx-I) activity in CF cells. Here we hypothesized that the activity of CFTR might modulate the mitochondrial fission/fusion balance, explaining the decreased mCx-I. The mitochondrial morphology and the levels of mitochondrial dynamic proteins MFN1 and DRP1 were analysed in IB3-1 CF cells, and S9 (IB3-1 expressing wt-CFTR), and C38 (IB3-1 expressing a truncated functional CFTR) cells. The mitochondrial morphology of IB3-1 cells compared to S9 and C38 cells showed that the impaired CFTR activity induced a fragmented mitochondrial network with increased rounded mitochondria and shorter branches. Similar results were obtained by using the CFTR pharmacological inhibitors CFTR(inh)-172 and GlyH101 on C38 cells. These morphological changes were accompanied by modifications in the levels of the mitochondrial dynamic proteins MFN1, DRP1, and p(616)-DRP1. IB3-1 CF cells treated with Mdivi-1, an inhibitor of mitochondrial fission, restored the mCx-I activity to values similar to those seen in S9 and C38 cells. These results suggest that the mitochondrial fission/fusion balance is regulated by the CFTR activity and might be a potential target to treat the impaired mCx-I activity in CF.

NLR family pyrin domain containing 3 (NLRP3) and caspase 1 (CASP1) modulation by intracellular Cl- concentration.

The impairment of the cystic fibrosis transmembrane conductance regulator (CFTR) activity induces intracellular chloride (Cl- ) accumulation. The anion Cl- , acting as a second messenger, stimulates the secretion of interleukin-1ß (IL-1ß), which starts an autocrine positive feedback loop. Here, we show that NLR family pyrin domain containing 3 (NLRP3) and caspase 1 (CASP1) are indirectly modulated by the intracellular Cl- concentration, showing maximal expression and activity at 75 mM Cl- , in the presence of the ionophores nigericin and tributyltin. The expression of PYD and CARD domain containing (PYCARD/ASC) remained constant from 0 to 125 mM Cl- . The CASP1 inhibitor VX-765 and the NLRP3 inflammasome inhibitor MCC950 completely blocked the Cl- -stimulated IL-1ß mRNA expression and partially the IL-1ß secretion. DCF fluorescence (cellular reactive oxygen species, cROS) and MitoSOX fluorescence (mitochondrial ROS, mtROS) also showed maximal ROS levels at 75 mM Cl- , a response strongly inhibited by the ROS scavenger N-acetyl-L-cysteine (NAC) or the NADPH oxidase (NOX) inhibitor GKT137831. These inhibitors also affected CASP1 and NLRP3 mRNA and protein expression. More importantly, the serum/glucocorticoid regulated kinase 1 (SGK1) inhibitor GSK650394, or its shRNAs, completely abrogated the IL-1ß mRNA response to Cl- and the IL-1ß secretion, interrupting the autocrine IL-1ß loop. The results suggest that Cl- effects are mediated by SGK1, in which under Cl- modulation stimulates the secretion of mature IL-1ß, in turn, responsible for the upregulation of ROS, CASP1, NLRP3 and IL-1ß itself, through autocrine signalling.

Identification and characterization of human PEIG-1/GPRC5A as a 12-O-tetradecanoyl phorbol-13-acetate (TPA) and PKC-induced gene.

Homo sapiens orphan G protein-coupling receptor PEIG-1 was first cloned and characterized by applying differential display to T84 colonic carcinoma cells incubated in the presence of phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) (GenBank AF506289.1). Later, Lotan's laboratory found the same gene product in response to retinoic acid analogues, naming it with the symbol RAIG1. Now the official HGNC symbol is GPRC5A. Here, we report the extension of its original cDNA fragment towards the 5' and 3' end. In addition, we show that TPA (100 ng/ml, 162 nM) strongly stimulated GPRC5A mRNA in T84 colonic carcinoma cells, with maximal expression at 4 h and 100 ng/ml (162 nM). Western blots showed several bands between 35 and 50 kDa, responding to TPA stimulation. Confocal microscopy confirmed its TPA upregulation and the location in the plasma membrane. The PKC inhibitor Gö 6983 (10 µM), and the Ca2+ chelator BAPTA-AM (150 µM), strongly inhibited its TPA induced upregulation. The PKA inhibitor H-89 (10 µM), and the MEK1/2 inhibitor U0126 (10 µM), also produced a significant reduction in the TPA response (~50%). The SGK1 inhibitor GSK650394 stimulated GPRC5A basal levels at low doses and inhibit its TPA-induced expression at concentrations ≥10 µM. The IL-1ß autocrine loop and downstream signalling did not affect its expression. In conclusion, RAIG1/RAI3/GPRC5A corresponds to the originally reported PEIG-1/TIG1; the inhibition observed in the presence of Gö 6983, BAPTA and U0126, suggests that its TPA-induced upregulation is mediated through a PKC/Ca2+ →MEK1/2 signalling axis. PKA and SGK1 kinases are also involved in its TPA-induced upregulation.

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-1ß. 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.

Intracellular Chloride Concentration Changes Modulate IL-1ß Expression and Secretion in Human Bronchial Epithelial Cultured Cells.

Cystic fibrosis (CF) is caused by mutations in the CFTR gene, which encodes a cAMP-regulated chloride channel. Several cellular functions are altered in CF cells. However, it is not clear how the CFTR failure induces those alterations. We have found previously several genes differentially expressed in CF cells, including c-Src, MUC1, MTND4, and CISD1 (CFTR-dependent genes). Recently, we also reported the existence of several chloride-dependent genes, among them GLRX5 and RPS27. Here, varying the intracellular chloride concentration [Cl- ]i of IB3-1 CF bronchial epithelial cells, we show that IL-1ß mRNA expression and secretion are also under Cl- modulation. The response to Cl- is biphasic, with maximal effects at 75 mM Cl- . The regulation of the IL-1ß mRNA expression involves an IL-1ß autocrine effect, since in the presence of the IL-1ß receptor antagonist IL1RN or anti-IL-1ß blocking antibody, the mRNA response to Cl- disappeared. Similar effects were obtained with the JNK inhibitor SP600125, the c-Src inhibitor PP2 and the IKK inhibitor III (BMS-345541). On the other hand, the IL-1ß secretion is still modulated by Cl- in the presence of IL-1RN, IL-1ß blocking antibody, or cycloheximide, suggesting that Cl- is affecting the IL-1ß maturation/secretion, which in turn starts an autocrine positive feedback loop. In conclusion, the Cl- anion acts as a second messenger for CFTR, modulating the IL-1ß maturation/secretion. The results also imply that, depending on its intracellular concentration, Cl- could be a pro-inflammatory mediator. J. Cell. Biochem. 118: 2131-2140, 2017. © 2016 Wiley Periodicals, Inc.

Disruption of interleukin-1ß autocrine signaling rescues complex I activity and improves ROS levels in immortalized epithelial cells with impaired cystic fibrosis transmembrane conductance regulator (CFTR) function.

Patients with cystic fibrosis (CF) have elevated concentration of cytokines in sputum and a general inflammatory condition. In addition, CF cells in culture produce diverse cytokines in excess, including IL-1ß. We have previously shown that IL-1ß, at low doses (∼30 pM), can stimulate the expression of CFTR in T84 colon carcinoma cells, through NF-κB signaling. However, at higher doses (>2.5 ng/ml, ∼150 pM), IL-1ß inhibit CFTR mRNA expression. On the other hand, by using differential display, we found two genes with reduced expression in CF cells, corresponding to the mitochondrial proteins CISD1 and MTND4. The last is a key subunit for the activity of mitochondrial Complex I (mCx-I); accordingly, we later found a reduced mCx-I activity in CF cells. Here we found that IB3-1 cells (CF cells), cultured in serum-free media, secrete 323±5 pg/ml of IL-1ß in 24 h vs 127±3 pg/ml for S9 cells (CFTR-corrected IB3-1 cells). Externally added IL-1ß (5 ng/ml) reduces the mCx-I activity and increases the mitochondrial (MitoSOX probe) and cellular (DCFH-DA probe) ROS levels of S9 (CFTR-corrected IB3-1 CF cells) or Caco-2/pRSctrl cells (shRNA control cells) to values comparable to those of IB3-1 or Caco-2/pRS26 cells (shRNA specific for CFTR). Treatments of IB3-1 or Caco-2/pRS26 cells with either IL-1ß blocking antibody, IL-1 receptor antagonist, IKK inhibitor III (NF-κB pathway) or SB203580 (p38 MAPK pathway), restored the mCx-I activity. In addition, in IB3-1 or Caco-2/pRS26 cells, IL-1ß blocking antibody, IKK inhibitor III or SB203580 reduced the mitochondrial ROS levels by ∼50% and the cellular ROS levels near to basal values. The AP-1 inhibitors U0126 (MEK1/2) or SP600125 (JNK1/2/3 inhibitor) had no effects. The results suggest that in these cells IL-1ß, through an autocrine effect, acts as a bridge connecting the CFTR with the mCx-I activity and the ROS levels.

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.