Role of Protein Kinase A-Mediated Phosphorylation in CFTR Channel Activity Regulation

Abstract

Cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel expressed on the apical membrane of epithelial cells, where it plays a pivotal role in chloride transport and overall tissue homeostasis. CFTR constitutes a unique member of the ATP-binding cassette transporter superfamily, due to its distinctive cytosolic regulatory (R) domain carrying multiple phosphorylation sites that allow the tight regulation of channel activity and gating. Mutations in the CFTR gene cause cystic fibrosis, the most common lethal autosomal genetic disease in the Caucasian population. In recent years, major efforts have led to the development of CFTR modulators, small molecules targeting the underlying genetic defect of CF and ultimately rescuing the function of the mutant channel. Recent evidence has highlighted that this class of drugs could also impact on the phosphorylation of the R domain of the channel by protein kinase A (PKA), a key regulatory mechanism that is altered in various CFTR mutants. Therefore, the aim of this review is to summarize the current knowledge on the regulation of the CFTR by PKA-mediated phosphorylation and to provide insights into the different factors that modulate this essential CFTR modification. Finally, the discussion will focus on the impact of CF mutations on PKA-mediated CFTR regulation, as well as on how small molecule CFTR regulators and PKA interact to rescue dysfunctional channels.

The burden of cystic fibrosis in North Africa

“…Consequently, ATP binds to the CFTR channel, leading to the opening of the channel pore and the secretion of chloride ions. ATP hydrolysis and CFTR dephosphorylation will allow the R domain to wedge between the NBDs and the channel to come back to its closed state ( Hegedus et al, 2009 ; Corradi et al, 2015 ; Liu et al, 2017 ; Della Sala et al, 2021 ) ( Figure 1B ). Like many other ion channels, CFTR channels are also able to aggregate in dimers and form a microdomain through connection with other interacting proteins such as synaptosome-associated protein, 23 kDa (SNAP23), AMP kinase (AMPK), protein phosphatase-2A (PP2A), syntaxin-1A (SYN1A), and Munc-18a which promote channel inactivation/closure or protein kinase C (PKC), Na+/H+ exchanger regulatory factor isoform-1 (NHERF1), ezrin and receptor for activated C-kinase-1 (RACK1) that in the opposite allow the efficient PKA-mediated phosphorylation of CFTR and ultimately its activation/opening ( Guggino and Stanton, 2006 ).…”

It Takes Two to Tango! Protein–Protein Interactions behind cAMP-Mediated CFTR Regulation

“…phosphorylation sites [32]. In this regard, the phosphorylation of different serine residues can be interdependent, as seen in S795 and S813.…”

A Mechanistic Model for Cell Cycle Control in Which CDKs Act as Switches of Disordered Protein Phase Separation

“…Another well-studied example is the intrinsically disordered regulatory (R) region of the cystic fibrosis transmembrane conductance regulator (CFTR). It is phosphorylated on over ten sites by different kinases (protein kinase A, protein kinase C, and 5 -AMP-activated protein kinase) and these modifications extensively alter the protein function and interactions [44,45]. In an unphosphorylated state, the R region interacts with nucleotide binding domains, NBD1 and NBD2, of CFTR, precluding opening of the ion channel [46].…”