Deficiency of ubiquitin A20 promotes antigen transport across airway epithelial cells via a transcellular pathway.

The epithelial barrier dysfunction is associated with the pathogenesis of a number of diseases. Ubiquitin E3 ligase A20 (A20) plays a critical role in maintaining the homeostasis in the body. This study aimed to investigate the role of A20 in the degradation of endocytic antigens in airway epithelial cells. The expression of A20 in the human nasal epithelial cell line, RPMI 2650 cells (Rpcs), was evaluated. The role of A20 in maintaining the intracellular permeability in Rpc monolayers was assessed in Transwells. The endosome/lysosome fusion in epithelial cells was observed by immunocytochemistry. On the absorption of antigen, the expression of A20 was increased in Rpcs. The knockdown of the A20 gene in Rpcs increased the amounts of the endocytic antigens across the Rpc monolayers. A20 was required in the process of the endosome/lysosome fusion. The antigens transported to the basal compartment by A20-deficient Rpc monolayers still kept strong antigenicity. The nasal epithelial cell line, Rpcs, expresses A20 that facilitates the degradation of endocytic antigens in Rpcs by facilitating the endosome/lysosome fusion.