MKP2 inhibits TGF-β1-induced epithelial-to-mesenchymal transition in renal tubular epithelial cells through a JNK-dependent pathway

Epithelial-to-mesenchymal transition (EMT) is a phenotypic conversion that plays a crucial role in renal fibrosis leading to chronic renal failure. Mitogen-activated protein kinase phosphatase 2 (MKP2) is a member of the dual-specificity MKPs that regulate the MAP kinase pathway involved in transforming growth factor-beta 1 (TGF-beta 1)-induced EMT. However, the function of MKP2 in the regulation of EMT and the underlying mechanisms are still largely unknown. In the present study, we detected the expression of MKP2 in an animal model of renal fibrosis and evaluated the potential role of MKP2 in tubular EMT induced by TGF-beta 1. We found that the expression of MKP2 was up-regulated in the tubular epithelial of unilateral ureter obstruction rats. Meanwhile, we also demonstrated that TGE-beta 1 up-regulated MKP2 expression in NRK-52E cells during their EMT phenotype acquisition. Importantly, overexpression of MKP2 inhibited c-Jun amino terminal kinase (JNK) signaling and partially reversed EMT induced by TGF-beta 1. Moreover, reducing MKP2 expression enhanced JNK phosphorylation, promoted the E-cadherin suppression and induced alpha-SMA expression and fibronectin secretion in response to TGF-beta 1, which could be rescued by a JNK inhibitor. These results provide the first evidence that MKP2 is a negative feedback molecule induced by TGF-beta 1, and MKP2 overexpression inhibits TGF-beta 1-induced EMT through the JNK signaling pathway. MKP2 could be a promising target to be used in gene therapy for renal fibrosis.