Exocyst Sec10 protects epithelial barrier integrity and enhances recovery following oxidative stress, by activation of the MAPK pathway.

Cell-cell contacts are essential for epithelial cell function, and disruption is associated with pathological conditions including ischemic kidney injury. We hypothesize that the exocyst, a highly-conserved eightprotein complex that targets secretory vesicles carrying membrane proteins, is involved in maintaining renal epithelial barrier integrity. Accordingly, increasing exocyst expression in renal tubule cells may protect barrier function from oxidative stress resulting from ischemia and reperfusion (IIR) injury. When cultured on plastic, Madin-Darby canine kidney (MDCK) cells overexpressing Sec 10, a central exocyst component, formed domes showing increased resistance to hydrogen peroxide (H₂O₂). Transepithelial electric resistance (TER) of Sec 10overexpressing MDCK cells grown on Transwell filters was higher than in control MDCK cells, and the rate of TER decrease following H₂O₂ treatment was less in Sec lO-overexpressing MDCK cells compared with control MDCK cells. After removal of H₂O₂, TER returned to normal more rapidly in Sec lO-overexpressing compared with control MDCK cells. In collagen culture MDCK cells form cysts, and H₂O₂ treatment damaged Sec lO-overexpressing MDCK cell cysts less than control MDCK cell cysts. The MAPK pathway has been shown to protect animals from hR injury. Levels of active ERK, the final MAPK pathway step, were higher in SeclO-overexpressing compared with control MDCK cells. U0126 inhibited ERK activation, exacerbated the H₂O₂-induced decrease in TER and cyst disruption, and delayed recovery of TER following H₂O₂ removal. Finally, in mice with renal LIR injury, exocyst expression decreased early and returned to normal concomitant with functional recovery, suggesting that the exocyst may be involved in the recovery following hR injury. [ABSTRACT FROM AUTHOR]