Modulation of renal epithelial barrier function by mitogen-activated protein kinases (MAPKs): Mechanism of cyclosporine A-induced increase in transepithelial resistance

Abstract

Background. Cyclosporine A (CsA) has been shown to increase transepithelial resistance in Madin-Darby canine kidney (MDCK) cells, and the mechanism may involve altered phosphorylation of junctional proteins. In this study, we examine the effect of the extracellular signal-regulated protein kinase (ERK) 1/2 and p38 mitogen-activated protein kinase (MAPK) pathways on the basal transepithelial resistance (TER) and on the CsA-induced increase in TER across MDCK monolayers. Here we present evidence that CsA may be mediating some of its effects through activation of the ERK 1/2 MAPK pathway. Methods. MDCK cells were treated with CsA (4.2 μmol/L) and paracellular permeability was assessed by measuring TER. The role of the ERK 1/2 and the p38 MAPK pathways in modulating TER was investigated using the inhibitors PD98059 and U0126 for ERK 1/2 and SB203580 for p38. ERK 1/2 and p38 phosphorylation/activation was also examined by Western blot analysis. Results. CsA (4.2 μmol/L) increased the TER of MDCK monolayers. The ERK 1/2 inhibitor PD98059 decreased basal TER and also ameliorated the CsA-induced increase in TER. Similar results were found with the U0126 inhibitor of ERK 1/2. The p38 inhibitor SB203580 had no effect on the basal TER of the monolayers, however, SB203580 significantly augmented the CsA-induced increase in TER. CsA was shown to significantly activate ERK 1/2 and this activation by CsA was prevented by PD98059. Inhibition of the p38 pathway by SB203580 also resulted in activation of ERK 1/2 and this activation of ERK 1/2 was further enhanced by CsA. No effect of CsA or the inhibitors PD98059 or SB203580 on p38 phosphorylation was detected. Conclusion. The results presented here suggest that activation of the ERK 1/2 MAPK cascade is important in the regulation of the paracellular permeability in MDCK cells. Activation of this pathway appears to be pivotal to the CsA-induced increase in TER.