Abstract
Earlier studies have revealed one function of the inhibitory mechanism of curcumin. Activating PKCα induces WT1 gene expression via signalling through downstream JNK and c-JUN. In the present study, the effect of c-JUN/AP-1 binding and transcriptional regulation of the WT1 gene promoter was investigated in K562 leukaemic cells. The non-cytotoxic dose (IC20 values) of curcumin (WT1 and AP-1 inhibitors) was employed to examine its effect on WT1 gene-mediated WT1 and AP-1 protein expression. Non-cytotoxic doses of both tanshinone IIA (AP-1 DNA-binding inhibitor) and SP600125 (JNK inhibitor) were used to test the role of c-JUN/AP-1 in WT1 gene expression. Curcumin, tanshinone IIA, and SP600125 inhibited WT1 protein expression in a dose-dependent manner (5-15 μM) at 24 h as shown by immunoblotting. A ChIP assay showed that curcumin and tanshinone IIA inhibited AP-1 and WT1 binding to the proximal WT1 promoter (-301 bp), and a luciferase reporter assay showed that the WT1 luciferase gene reporter activity was decreased after curcumin, tanshinone IIA, and SP600126 treatments. Furthermore, depletion of c-JUN abrogated WT1 gene expression. In summary, AP-1 contributes to the WT1 autoregulation of WT1 gene expression in leukaemic K562 cells.