FIGURE 1 TA markedly suppresses the STAT3 signaling pathway. (a) Chemical structure of TA. (b) STAT3 luciferase assay in 293T cells. 293T cells with a transfected STAT3 luciferase reporter were stimulated with IL-6 (20 ng/mL) and different dose of TA (0, 0.1, and 1 μM) for 12 h. Normalized luminescence was plotted as STAT3 luciferase activity compared to control (%). Data are expressed as means ± SD (n = 5). *P < 0.05. (c) Modeling of TA binding with STAT3 (PDB: 1BG1). Left: TA binding with the STAT3β/DNA complex. Right: Ligand interaction diagram of the binding. The STAT3 structure was shown as ribbon representation and TA was shown as stick. (d) Interaction of TA with STAT3 in vitro . Surface plasmon resonance (SPR) assays of the immobilized STAT3 (127-722 AA) toward varied concentrations of TA (1.56-100 μM). (e) Left: Expression levels of STAT3 and p-STAT3 (Tyr705 and Ser727) in eight pancreatic cancer cell lines (PANC-1, CFPAC-1, AsPC-1, Capan-2, MIA PaCa-2, BxPC-3, HPAC and SW1990). GAPDH was used as a loading control. Right: Analysis of the results in (e). Protein levels were quantified by using ImageJ software. Data are expressed as means ± SD (n = 5). (f) Left: Effect of TA on the STAT3, p-STAT3 (Tyr705 and Ser727), and STAT3-regulated proteins in PANC-1 cells. The cells were treated with several concentrations of TA (0-0.8 μM) for 24 h. Whole cell lysates were subjected to western blotting for STAT3, p-STAT3 (Tyr705 and Ser727), c-Myc, Bcl-2, Cyclin D1, Survivin and ICAM-1. GAPDH was used here as a loading control. Right: Analysis of the results in (f). Protein levels were quantified by using ImageJ software. Data are expressed as means ± SD (n = 5). *P < 0.05.