THE CFTR CHLORIDE CHANNEL SIGNALING

TOMÁS ANTONIO SANTA COLOMA; ANGEL GABRIEL VALDIVIESO; MARIANGELES CLAUZURE; MARIA MACARENA MASSIP COPIZ; IGNACIO VERGARA; VERONICA SOTOMAYOR ; CONSUELO MORI; CRISTIAN ASENSIO; AGUSTINA VIDAL

Río de Janeiro

Congreso; IUPS 38th World Congress; 2017

IUPS 38th World Congress

The cystic fibrosis transmembrane conductance regulator (CFTR) is responsible for the cystic fibrosis (CF) disease. The channelactivity is up­regulated by cAMP, phosphorylation (PKA, PKC, c­Src) and ATP binding, and downregulated by WNK kinases. Toexplain the CF phenotype, after the CFTR cloning, initial studies focused in the non­genomic and extracellular effects of the CFTRfailure. However, the phenotype was too complex to be explained only by the failure in the Cl­ transport and the accompanyingNa+ and water permeation. Thus, two decades ago, we hypothesized that the complex CF phenotype might be the result of theexpression of a net of CFTR­dependent genes, modulated by the activity of the CFTR channel (Cl­ transport). Applying differentialdisplay to CF cells, we found several CFTR­dependent genes, and characterized some of them, including c­Src, MUC1, MTND4and CISD1. We then hypothesized that changes in the [Cl­]i could be the first step in the CFTR ?signaling mechanism?, with a rolefor Cl­ as a signaling effector or ?second messenger? in the modulation of CFTR and Cl­ specific genes. To demonstrate thishypothesis, we used again differential display and analyzed the mRNA expression pattern of IB3­1 cells, an immortalized humantracheobronchial epithelial cell line derived from a CF patient. The cells were incubated at different Cl­ concentrations, usingnigericin and tributyltin to equilibrate the intracellular and extracellular Cl­ concentrations ([Cl­]i = [Cl­]e). We found severaldifferentially 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 Claccumulation.In parallel, we also found that IL­1β responded to changes in Cl­. Thus, the hypothesis of Cl­ acting as a secondmessenger 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 Clconstitutesa proinflammatory stimulus, inducing IL­1β secretion and starting an autocrine, positive feedback loop, which in turnupregulates its own mRNA.