BACKGROUND AND PURPOSE:Cystic fibrosis is an autosomal recessive disease caused by mutations in the CFTR gene, leading to progressive respiratory decline and reduced life expectancy. The most common mutation, CFTR-F508del, results in mislocalised and non-functional protein. Although triple therapy with elexacaftor/tezacaftor/ivacaftor (ETI) is prescribed for patients carrying this mutation, some biological defects remain unresolved. We previously identified COMMD1 as a potential therapeutic target, as its overexpression enhances CFTR-WT plasma membrane localisation. CIGB-552, a cell-penetrating peptide discovered in 2013, stabilises COMMD1. This study evaluates its therapeutic potential in cystic fibrosis. EXPERIMENTAL APPROACH:CIGB-552 was tested, with and without ETI, in CFBE and HEK cells stably expressing CFTR-WT or CFTR-F508del, and in primary human bronchial cells. CFTR function was assessed using YFP quenching and short-circuit current assays. Peptide uptake was evaluated using FITC-labelled CIGB-552 in submerged and air-liquid interface models. Plasma membrane density of CFTR was measured in CFBE CFTR-HA cells, and western blotting assessed CFTR maturation and COMMD1 expression. KEY RESULTS:CIGB-552 was non-toxic and preferentially entered CFBE CFTR-F508del cells rather than CFBE CFTR-WT cells, without altering COMMD1 expression or localisation. Although not a corrector or potentiator alone, CIGB-552 synergised with ETI, enhancing CFTR-F508del-mediated chloride efflux, confirmed in primary cells. CIGB-552 also increased YFP quenching of CFTR-WT and CFTR-G551D, in combination with ivacaftor. This effect required COMMD1. CONCLUSIONS AND IMPLICATIONS:COMMD1 expression was necessary for CIGB-552 to affect CFTR function positively. Its synergy with the triple therapy offers a promising strategy for improving CF treatment.

Human small heat shock proteins are molecular chaperones that regulate fundamental cellular processes in normal and pathological cells. Here, we have reviewed the role played by HspB1, HspB4 and HspB5 in the context of Cystic Fibrosis (CF), a severe monogenic autosomal recessive disease linked to mutations in Cystic Fibrosis Transmembrane conductance Regulator protein (CFTR) some of which trigger its misfolding and rapid degradation, particularly the most frequent one, F508del-CFTR. While HspB1 and HspB4 favor the degradation of CFTR mutants, HspB5 and particularly one of its phosphorylated forms positively enhance the transport at the plasma membrane, stability and function of the CFTR mutant. Moreover, HspB5 molecules stimulate the cellular efficiency of currently used CF therapeutic molecules. Different strategies are suggested to modulate the level of expression or the activity of these small heat shock proteins in view of potential in vivo therapeutic approaches. We then conclude with other small heat shock proteins that should be tested or further studied to improve our knowledge of CFTR processing.

Cystic Fibrosis is a lethal monogenic autosomal recessive disease linked to mutations in Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein. The most frequent mutation is the deletion of phenylalanine at position 508 of the protein. This F508del-CFTR mutation leads to misfolded protein that is detected by the quality control machinery within the endoplasmic reticulum and targeted for destruction by the proteasome. Modulating quality control proteins as molecular chaperones is a promising strategy for attenuating the degradation and stabilizing the mutant CFTR at the plasma membrane. Among the molecular chaperones, the small heat shock protein HspB1 and HspB4 were shown to promote degradation of F508del-CFTR. Here, we investigated the impact of HspB5 expression and phosphorylation on transport to the plasma membrane, function and stability of F508del-CFTR. We show that a phosphomimetic form of HspB5 increases the transport to the plasma membrane, function and stability of F508del-CFTR. These activities are further enhanced in presence of therapeutic drugs currently used for the treatment of cystic fibrosis (VX-770/Ivacaftor, VX-770+VX-809/Orkambi). Overall, this study highlights the beneficial effects of a phosphorylated form of HspB5 on F508del-CFTR rescue and its therapeutic potential in cystic fibrosis.