Astragaloside IV downregulates the expression of MDR1 in Bel-7402/FU human hepatic cancer cells by inhibiting the JNK/c-Jun/AP-1 signaling pathway

Previous studies demonstrated that astragaloside IV (ASIV) is a potential P-glycoprotein (P-gp) -mediated multidrug resistance (MDR) reversal agent through mechanisms involving downregulation of the gene expression of mdr1. In order to investigate whether the c-Jun N-terminal kinase (JNK) signaling pathway is involved in the mechanism underlying ASIV-induced downregulated the expression of mdr1, the present study used 5-fluorouracil-resistant Bel-7402/FU human hepatic cancer cells as target cells. ASIV (0.1 mM) decreased the protein expression of phosphorylated (p)-JNK and p-c-Jun in the Bel-7402/FU cells, as determined using western blot analysis. Treatment with the JNK pathway inhibitor, SP600125, at a concentration of 11 mu M, decreased the mRNA expression levels of mdr1 and P-gp, as determined using reverse transcription-quantitative polymerase chain reaction and western blot analyses, and similar effects were observed following exposure to ASIV. Furthermore, electrophoretic mobility shift assays demonstrated that the DNA-binding activity of activator protein-1 (AP-1) was decreased by 0.1 mM ASIV or 11 mu M SP600125. Flow cytometric analysis revealed that 0.1 mM ASIV or 11 mu M SP600125 increased the intracellular accumulation of fluorescent P-gp substrates, including rhodamine 123. Taken together, these results indicated that ASIV reversed the drug resistance of Bel-7402/FU cells by downregulating the expression of mdr1 via inhibition of the JNK/c-Jun/AP-1 signaling pathway.