CFTR is subjected to various reversible chemical modifications whose regulation has been proposed as a possible therapeutic intervention. However, it has not yet been identified which modifications are actually important for the functional recovery of the mutated CFTR. Recently, it has been shown that the CFTR channel is subjected to methylation, a chemical modification characterized by the addition of methyl groups to specific amino acids. Methylation is an alternative modification to the ubiquitination, that is the addition of the ubiquitin protein which represents a sort of “label” that if attached to the protein leads to its degradation.
The researchers focused their studies on the regulation of methylation and ubiquitination and hypothesized that the regulation of methylation could be therapeutically important. In this project, the research team demonstrated how it is possible to increase the functional recovery of CFTR with the F508del mutation in the presence of correctors by blocking the action of two specific demethylases. The researchers also tried to directly block ubiquitination by inhibiting the UBA1 enzyme, which is responsible for binding ubiquitin to proteins. Using the molecule TAK-243, a new inhibitor of the enzyme UBA1, the researchers were able to block ubiquitination and prevent the degradation of the CFTR F508del protein both in a brochial epithelial cell line (CFBE) and in patient cells. Furthermore, from in vitro studies on bronchial and nasal epithelial cells obtained from people with cystic fibrosis, the researchers showed that TAK-243 is able to stabilize CFTR and make it available for the action of Kaftrio. Finally, it has been shown that a combined approach of TAK-243 and Kaftrio leads to an improvement in the functionality of mutated CFTR also on cells expressing other rare mutations, such as N1303K for which Kaftrio has not yet been approved.