Abstract
Cystic fibrosis (CF) is a genetic disease caused by mutations in the gene encoding CF transmembrane conductance regulator (CFTR), a chloride channel normally expressed at the surface of epithelial cells. The most frequent mutation, resulting in Phe-508 deletion, causes CFTR misfolding and its premature degradation. Low temperature or pharmacological correctors can partly rescue the Phe508del-CFTR processing defect and enhance trafficking of this channel variant to the plasma membrane (PM). Nevertheless, the rescued channels have an increased endocytosis rate, being quickly removed from the PM by the peripheral protein quality-control pathway. We previously reported that rescued Phe508del-CFTR (rPhe508del) can be retained at the cell surface by stimulating signaling pathways that coax the adaptor molecule ezrin (EZR) to tether rPhe508del-Na+/H+-exchange regulatory factor-1 complexes to the actin cytoskeleton, thereby averting the rapid internalization of this channel variant. However, the molecular basis for why rPhe508del fails to recruit active EZR to the PM remains elusive. Here, using a proteomics approach, we characterized and compared the core components of wt-CFTR- or rPhe508del-containing macromolecular complexes at the surface of human bronchial epithelial cells. We identified calpain 1 (CAPN1) as an exclusive rPhe508del interactor that prevents active EZR recruitment, impairs rPhe508del anchoring to actin, and reduces its stability in the PM. We show that either CAPN1 down-regulation or its chemical inhibition dramatically improves the functional rescue of Phe508del-CFTR in airway cells. These observations suggest that CAPN1 constitutes an appealing target for pharmacological intervention, as part of CF combination therapies restoring Phe508del-CFTR function.
Highlights
Cystic fibrosis (CF) is a genetic disease caused by mutations in the gene encoding CF transmembrane conductance regulator (CFTR), a chloride channel normally expressed at the surface of epithelial cells
We first determined whether wt-CFTR and rPhe508delCFTR have different plasma membrane (PM) protein interactors that could contribute to their distinct cell surface stabilities
The present work is the first to globally characterize CFTR interactors occurring at the PM
Summary
Several studies have identified numerous CFTR interactor proteins with essential roles in the processing, localization, and function of the channel [32,33,34,35,36, 53, 54]. All the gathered evidence led us to propose the following model (Fig. 8): elevated Ca2ϩ intracellular levels coupled to the recruitment of CAPN1 to rPhe508del-CFTR–NHERF1 PM complexes lead to the hydrolysis and displacement of EZR from the complex, preventing its activation by endogenous signaling events (such as those mediated by RAC1 [28]) and avoiding NHERF1 opening and the anchoring of rPhe508del-CFTR to the actin cytoskeleton These events lead to the accelerated internalization and degradation of rescued channels, as described by us and others [19, 28, 29]. Further in vivo studies will be required to evaluate the therapeutic applicability of CAPN1 inhibition for the benefit of people with CF disease
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
