BioID-Based Proximity Mapping of Transmembrane Proteins in Human Airway Cell Models

The cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel residing primarily at the apical membrane of epithelial cells, plays a major role in fluid secretion and the maintenance of epithelial surface hydration. Mutations in the CFTR gene lead to the fatal disease known as cystic fibrosis (CF). Drugs that improve mutant CFTR protein folding and channel function have dramatically improved CF patient outcomes. However, the current regimen only restores the function of the most common mutant, ΔF508, to ~62% of wildtype (WT). Notably, ~10% of patients harboring hundreds of less common CFTR mutations are not eligible or do not respond at all to treatment with current CFTR modulators. Better characterizing the WT and mutant CFTR protein interactomes could provide critical insight into how to treat patients with rarer mutations and thereby improve the druggability of this devastating disease. Here we describe how BioID (proximity-dependent biotin identification) can be used to map the CFTR interactome in a human airway model-bronchial epithelial cells grown at the air-liquid interface. Approximately 26% (>5500) of all human protein-coding genes are predicted to code for membrane proteins, which together account for ~30% of the druggable proteome. The methods described here could thus also be applied to improve our understanding of many additional respiratory, autoimmune, and metabolic diseases.