Co-activation of WT1 and AP-1 proteins on WT1 gene promoter to induce WT1 gene expression in K562 cells.

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.