Maintenance of claudin-3 expression and the barrier functions of intercellular junctions in parotid acinar cells via the inhibition of Src signaling.

OBJECTIVES: Salivary acinar and duct cells show different expression patterns of claudins, which may reflect their different functions. To study the role of claudins in saliva secretion, we examined alterations in the expression patterns of cell adhesion molecules in parotid glands of γ-irradiated rats and analyzed the influence of those changes on intercellular barrier function using primary cultures of parotid acinar cells.

DESIGN: Rats were γ-irradiated with doses of 5, 15 or 20Gy, and expression levels of cell adhesion molecules were examined by immunoblotting analysis. Acinar cells were isolated from parotid glands and were cultured in the absence or presence of the Src kinase inhibitor PP1. Changes in protein and mRNA expression patterns were determined by immunoblotting and by RT-PCR analyses, respectively. Intercellular barrier function was examined by measuring transepithelial electrical resistance and the paracellular flux of FITC-dextran.

RESULTS: In irradiated parotid glands, the expression of claudin-4 was enhanced at 15Gy or higher, levels that induce the hyposecretion of saliva, although that increase was transient. At 30days after irradiation, expression levels of cell adhesion molecules were decreased. In primary cultures, the expression of claudin-4 was also increased transiently but the expression of claudin-3 and E-cadherin was decreased. The barrier function of tight junctions was disrupted although the localization of occludin was maintained. The Src kinase inhibitor PP1 suppressed those changes in gene expression and retained the intercellular barrier function.

CONCLUSIONS: These results suggest that the inhibition of Src signaling maintains the barrier functions of intercellular junctions in salivary glands, which can be lost due to tissue injury.