The CFTR chloride channel signaling

TOMÁS A. SANTA COLOMA; MARÍA M. MASSIP COPIZ; CHRISTIAN ASENSIO; MARIÁNGELES CLAUZURE; AGUSTINA VIDAL; IGNACIO VERGARA; ÁNGEL G. VALDIVIESO; CONSUELO MORI; VERÓNICA SOTOMAYOR

Rio de Janeiro

Congreso; IUPS 38th World Congress; 2017

INTERNATIONAL UNION OF PHYSIOLOGICAL SCIENCES ISPC and the Brazilian Society of Physiology,

The cystic fibrosis transmembrane conductance regulator (CFTR) is responsible for the cystic fibrosis (CF) disease. The channel activity is upregulated by cAMP, phosphorylation (PKA, PKC, cSrc) and ATP binding, and downregulated by WNK kinases. To explain the CF phenotype, after the CFTR cloning, initial studies focused in the nongenomic and extracellular effects of the CFTR failure. However, the phenotype was too complex to be explained only by the failure in the Cl-transport and the accompanying Na+ and water permeation. Thus, two decades ago, we hypothesized that the complex CF phenotype might be the result of the expression of a net of CFTR dependent genes, modulated by the activity of the CFTR channel (Cl-transport). Applying differential display to CF cells, we found several CFTR dependent genes, and characterized some of them, including c-Src, MUC1, MTND4 and CISD1. We then hypothesized that changes in the [Cl]i could be the first step in the CFTR ?signaling mechanism?, with a role for Cl- as a signaling effector or ?second messenger? in the modulation of CFTR and Cl- specific genes. To demonstrate this hypothesis, we used again differential display and analyzed the mRNA expression pattern of IB31 cells, an immortalized human tracheobronchial epithelial cell line derived from a CF patient. The cells were incubated at different Cl- concentrations, using nigericin and tributyltin to equilibrate the intracellular and extracellular Cl- concentrations ([Cl]i = [Cl]e). We found several differentially expressed mRNAs and characterized two of them, the ribosomal protein S27 (RPS27) and glutaredoxin 5 (GLRX5). RPS27 was further analyzed. It responded to increased concentrations of CFTR inhibitors, which also produced a progressive Cl- accumulation. In parallel, we also found that IL1β responded to changes in Cl. Thus, the hypothesis of Cl- acting as a second messenger for CFTR appear to be correct. We then identified additional steps in the CFTR signaling mechanisms that involve Cl, IL1β and cSrc that may explain the reduced mitochondrial Complex I activity and the increased reactive oxygen species (ROS) previously found in CF cells. In conclusion, the results suggest that Cl- may act as a second messenger for CFTR, and that Cl- constitutes a proinflammatory stimulus, inducing IL1β secretion and starting an autocrine, positive feedback loop, which in turn upregulates its own mRNA.