Expression of miR-106b-25 induced by salvianolic acid B inhibits epithelial-to-mesenchymal transition in HK-2 cells.

Epithelial-to-mesenchymal transition (EMT) is a highly conserved physiological program involved in renal fibrosis. Previous studies have shown that transforming growth factor (TGF)-β1 induces EMT in human kidney proximal tubular epithelial cells (HK-2 cells), whereas salvianolic acid B (Sal B) has a protective effect against EMT. The molecular pathogenesis of such processes is currently not well understood. In this study, a miRCURYTM LNA Array was used to screen HK-2 cells for expression changes of microRNAs (miRNAs) implicated in EMT. After validation by real-time PCR, all three members of the miR-106b-25 cluster (miR-106b, miR-93, and miR-25) were found to be markedly down-regulated during EMT in response to TGF-β1, whereas these miRNAs were up-regulated by Sal B treatment in a dose-dependent manner. Moreover, enhanced expression of miR-106b attenuated EMT by retaining the epithelial morphology of HK-2 cells, reducing the levels of α-smooth muscle actin (α-SMA), and increasing the levels of E-cadherin. To explore the molecular basis underlying the inhibitive effect of the miR-106b-25 cluster against EMT, bioinformatics analysis revealed that TGF-β type II receptor, a regulator of TGF-β signaling, might be a direct target of the miR-106b-25 cluster. In turn, low levels of TGF-β type II receptor in EMT of HK-2 cells were shown under the increase of miR-106b. In conclusion, our data suggest that the miR-106b-25 cluster may contribute to EMT in the kidney, and is involved in the protective effect of Sal B. Targeting of specific miRNAs may be a novel therapeutic approach to treat renal fibrosis.