Increases in cytosolic Ca2+ induce dynamin- and calcineurin-dependent internalisation of CFTR

Abstract

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-regulated, apical anion channel that regulates ion and fluid transport in many epithelia including the airways. We have previously shown that cigarette smoke (CS) exposure to airway epithelia causes a reduction in plasma membrane CFTR expression which correlated with a decrease in airway surface hydration. The effect of CS on CFTR was dependent on an increase in cytosolic Ca 2+ . However, the underlying mechanism for this Ca 2+ -dependent, internalisation of CFTR is unknown. To gain a better understanding of the effect of Ca 2+ on CFTR, we performed whole cell current recordings to study the temporal effect of raising cytosolic Ca 2+ on CFTR function. We show that an increase in cytosolic Ca 2+ induced a time-dependent reduction in whole cell CFTR conductance, which was paralleled by a loss of cell surface CFTR expression, as measured by confocal and widefield fluorescence microscopy. The decrease in CFTR conductance and cell surface expression were both dynamin-dependent. Single channel reconstitution studies showed that raising cytosolic Ca 2+ per se had no direct effect on CFTR. In fact, the loss of CFTR plasma membrane activity correlated with activation of calcineurin, a Ca 2+ -dependent phosphatase, suggesting that dephosphorylation of CFTR was linked to the loss of surface expression. In support of this, the calcineurin inhibitor, cyclosporin A, prevented the Ca 2+ -induced decrease in cell surface CFTR. These results provide a hitherto unrecognised role for cytosolic Ca 2+ in modulating the residency of CFTR at the plasma membrane through a dynamin- and calcineurin-dependent mechanism. Electronic supplementary material The online version of this article (10.1007/s00018-018-2989-3) contains supplementary material, which is available to authorized users.

What are the respiratory effects of e-cigarettes?

“…Lack of functional CFTR causes cystic fibrosis lung disease. Acute and chronic cigarette smoke exposures rapidly inhibit CFTR function in smokers and in vitro 124125126. Similarly, e-cigarettes can also inhibit CFTR mediated Cl – secretion and induce airway dehydration in airway epithelia 113.…”

“…Acute and chronic cigarette smoke exposures rapidly inhibit CFTR function in smokers and in vitro. 124 125 126 Similarly, e-cigarettes can also inhibit CFTR mediated Cl – secretion and induce airway dehydration in airway epithelia. 113 Failure of ciliary beating induced by e-cigarette aerosol could conflate this, contributing to a retention of mucus and bacteria, increasing the chance of developing lung disease ( table 2 ).…”

CFTR Modulators: The Changing Face of Cystic Fibrosis in the Era of Precision Medicine

“…Low temperature incubation rescues CFTR in F508del-expressing cells (r.F508del) (Denning et al, 1992), but the protein still demonstrates reduced stability and is rapidly removed by peripheral quality control mechanisms (Okiyoneda et al, 2010). In fact, environmental stresses may also lead to destabilization and internalization of WT-CFTR (Bomberger et al, 2012;Patel et al, 2019). Stabilizers are agents that anchor CFTR at the PM, thus preventing its removal and degradation by lysosomes (Fukuda and Okiyoneda, 2018).…”

E‐cigarettes, nicotine, the lung and the brain: multi‐level cascading pathophysiology

“…1; Garcia -Arcos et al 2016;Chung et al 2019;Lin et al 2019). Whilst the mechanism of nicotine-dependent CFTR inhibition is not fully understood, we have previously found that CFTR is inhibited by elevations in cytoplasmic Ca 2+ (Rasmussen et al 2014;Patel et al 2019). This causes CFTR dephosphorylation (Marklew et al 2019), and we speculate that nicotine-dependent Ca 2+ influx through nAChRs likely inhibits CFTR through a similar process, indicating a mechanistic link between nicotine intake and epithelial ion channel dysfunction.…”