Ion the Prize: Defining the Complexities of Airway Epithelial Cell Ion Transport Functions

Interactions between ABCC4/MRP4 and ABCC7/CFTR in human airway epithelial cells in lung health and disease

ATP binding cassette (ABC) transporters are present in all three domains of life - Archaea, Bacteria, and Eukarya. The conserved nature is a testament to the importance of these transporters in regulating endogenous and exogenous substrates required for life to exist. In humans, 49 ABC transporters have been identified to date with broad expression in different lung cell types with multiple transporter family members contributing to lung health and disease. The ABC transporter most commonly known to be linked to lung pathology is ABCC7, also known as cystic fibrosis transmembrane conductance regulator - CFTR. Closely related to the CFTR genomic sequence is ABCC4/multi-drug resistance protein-4. Genomic proximity is shared with physical proximity, with ABCC4 and CFTR physically coupled in cell membrane microenvironments of epithelial cells to orchestrate functional consequences of cyclic-adenosine monophosphate (cAMP)-dependent second messenger signaling and extracellular transport of endogenous and exogenous substrates. The present concise review summarizes the emerging data defining a role of the (ABCC7/CFTR)-ABCC4 macromolecular complex in human airway epithelial cells as a physiologically important pathway capable of impacting endogenous and exogenous mediator transport and ion transport in both lung health and disease.