Abstract
RationaleThe cystic fibrosis transmembrane conductance regulator (CFTR) and Calcium-activated Chloride Conductance (CaCC) each play critical roles in maintaining normal hydration of epithelial surfaces including the airways and colon. TGF-beta is a genetic modifier of cystic fibrosis (CF), but how it influences the CF phenotype is not understood.ObjectivesWe tested the hypothesis that TGF-beta potently downregulates chloride-channel function and expression in two CF-affected epithelia (T84 colonocytes and primary human airway epithelia) compared with proteins known to be regulated by TGF-beta.Measurements and Main ResultsTGF-beta reduced CaCC and CFTR-dependent chloride currents in both epithelia accompanied by reduced levels of TMEM16A and CFTR protein and transcripts. TGF-beta treatment disrupted normal regulation of airway-surface liquid volume in polarized primary human airway epithelia, and reversed F508del CFTR correction produced by VX-809. TGF-beta effects on the expression and activity of TMEM16A, wtCFTR and corrected F508del CFTR were seen at 10-fold lower concentrations relative to TGF-beta effects on e-cadherin (epithelial marker) and vimentin (mesenchymal marker) expression. TGF-beta downregulation of TMEM16A and CFTR expression were partially reversed by Smad3 and p38 MAPK inhibition, respectively.ConclusionsTGF-beta is sufficient to downregulate two critical chloride transporters in two CF-affected tissues that precedes expression changes of two distinct TGF-beta regulated proteins. Our results provide a plausible mechanism for CF-disease modification by TGF-beta through effects on CaCC.
Highlights
Our results provide a plausible mechanism for CFdisease modification by TGF-beta through effects on Calcium activated Chloride Conductance (CaCC)
Regulation of chloride transport is critical to the normal hydration and function of a variety of epithelia, including many of those affected in cystic fibrosis (CF) [1]
CFTR activity following TGF-beta treatment was reduced 93.2% and 98% in the two cell types
Summary
Regulation of chloride transport is critical to the normal hydration and function of a variety of epithelia, including many of those affected in cystic fibrosis (CF) [1]. Loss of cystic fibrosis transmembrane conductance regulator (CFTR) protein function disrupts chloride transport, with reduced or absent PKA-activated chloride conductance (through CFTR). This loss of CFTR function is frequently associated with an increase in chloride transport through the Calcium activated Chloride Conductance (CaCC) [2]. Downregulation of CaCC during respiratory viral infections may disrupt mucociliary clearance in the CF airway and contribute to pulmonary exacerbations [13,14]. These data support the notion that changes in CaCC activity are directly relevant to the CF phenotype
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