Cystic fibrosis (CF) is a hereditary disorder affecting several exocrine glands including the pancreas, bronchi, and intestine. An exocrine gland secretes compounds such as digestive enzymes, into a duct as opposed to directly into the bloodstream (an endocrine gland). Normally, mucus-producing cells of the respiratory tract secrete thin and slippery mucus, digestive juices and sweat, substances that are constantly recycled and replenished. These fluids act as a protective barrier against infections. The low viscosity of these substances allows for quick and effective clearance of bacteria. A mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) protein results in abnormal ion balance/regulation. This mutation changes the composition of the mucus and impairs its clearance. Excessive mucus in the respiratory tract results in inflammation, lung infections and eventually, loss of lung function. Approximately 70% of CF cases are due to a deletion of phenylalanine 508 (an amino acid) in the CFTR protein (∆F508 CFTR), accelerating the degradation of the CFTR protein. Sandra Pankow and colleagues investigated the proteins interacting with ∆F508 CFTR. This has the potential to elucidate the molecular basis of CFTR protein function and CF pathogenesis.
Co-purifying protein identifying technology (CoPIT) and immunoprecipitation (IP) based proteomic profiling were used to identify the proteins that interact with non-mutated CFTR and ∆F508 CFTR. As expected, many of the proteins interacting with ∆F508 CFTR are responsible for CFTR degradation, however, proteins involved in transport, glycosylation and signaling were also identified. This suggests that multiple previously unknown protein pathways are affected by ∆F508 CFTR.
After the identification of the mutated CFTR proteome, Pankow and colleagues explored the effect of temperature on its morphology. Human bronchial epithelial cells are normally cultured at 37°C. When the authors decreased the temperature to 30°C, ∆F508 CFTR became heavily glycosylated (adding a carbohydrate to another molecule) and many of the proteins interacting with it were no longer present. Long-term incubation at 30°C removed 89% of the protein interactions with mutated CFTR. When the temperature was increased to 37°C, ∆F508 CFTR lost its glycosylation and regained its protein interaction partners.
Pankow and colleagues identified a comprehensive interactome of ∆F508 CFTR and wild type CFTR. Mutated CFTR results in a change in translation, associating protein partners and increased degradation. Many of the proteins binding to ∆F508 CFTR are also involved in protein-folding diseases, particularly neurodegenerative diseases. This implies that there may be an overlap between the molecular mechanisms of neurodegenerative diseases and cystic fibrosis. The research conducted by Pankow et al. may uncover therapeutic targets involved in CF as well as other diseases, lacking effective treatment options. The overarching question from this research is: Is body temperature regulation the Holy Grail for CF treatment?