Effect of Uridine 5'-Triphosphate on Mucin and Lysozyme Expression in Human Middle Ear Epithelial Cells

Objective--Extracellular uridine 5′-triphosphate (UTP) regulates a variety of biological functions in the airway epithelium, including chloride and fluid transport, mucociliary clearance and mucin secretion via the P2Y purinergic receptors. This study was undertaken to investigate which P2Y purinergic receptors are expressed in normal human middle ear epithelial (NHMEE) cells. We also determined the levels of mucin and lysozyme secretion and their mRNA expressions following stimulation with UTP in passage-2 cultured NHMEE cells. Material and methods--An immunoblotting assay was performed for quantitation of mucin and lysozyme proteins and RT-PCR for their gene levels after treatment with UTP was done in normal human midle ear epithelial cells. Results--Middle ear epithelial cells expressed P2Y1, P2Y2, P2Y6, P2Y11 and P2Y12 receptors but not P2Y4 receptor. Apically applied UTP induced increased mucin and lysozyme secretion, as measured by dot blotting. In contrast, UTP did not enhance mucin and lysozyme mRNA expression until 72 h after treatment. Conclusion--This study suggests that UTP acts as a secretogogue on mucin and lysozyme secretion in NHMEE cells via the P2Y2 and/or P2Y6 receptor.