Figure 6. Xanthine oxidase activation leads to increased oxidative stress and upregulation of the TGF-β/Smad3 pathway as well as galectin-9 expression. MCF-7 human breast cancer cells were exposed to ammonium molybdate for 24 h to induce xanthine oxidase activity in the absence or presence of the xanthine oxidase inhibitor allopurinol. Xanthine oxidase activity, TBRS levels, HIF-1α accumulation, secreted TGF-β (A), and cell-associated phospho-S423/S425-Smad3, Tim-3 and galectin-9 (B) were analysed as outlined in the Materials and Methods. Images are from one experiment representative of four which gave similar results. Data are shown as mean values ± SEM of four independent experiments. * - p < 0.05 and ** - p < 0.01 vs indicated events.