Ubiquitin E3 ligase TNFIAP3 mediates endosome/lysosome fusion in nasal epithelial cells.

The nasal epithelial barrier dysfunction is associated with the pathogenesis of nasal allergy; the causative factors are to be further elucidated. Ubiquitin E3 ligase TNFIAP3 (TNFIAP3, in short) plays a role in the maintenance of the homeostasis in the body. This study aims to elucidate the role of TNFIAP3 in the degradation of endocytic substances in nasal epithelial cells. The nasal epithelial cell line, RPMI 2650 cells (RPC), was cultured into monolayers in transwells. The endocytosis of staphylococcal enterotoxin B (SEB) by RPC monolayers was assessed by enzyme-linked immunoassay. The endocytosis of SEB-triggered endosome/lysosome fusion was observed by immunocytochemistry. The results showed that RPC monolayers expressed TNFIAP3 upon the endocytosis of SEB. Deficiency of TNFIAP3 resulted in abundant SEBs being transported to the basal chambers of transwells via the intracellular pathway. In the TNFIAP3-sufficient RPC, SEB-carrying endosomes fused with lysosomes were observed. The TNFIAP3-deficient RPC showed few SEB-carrying endosomes fused with lysosomes. In summary, TNFIAP3 plays an important role in tethering endosomes to lysosomes in RPC.