3.3 TA induces cell-cycle arrest and suppresses the migration and invasion of PANC-1 cells
To evaluate the influence of TA on the cell-cycle progression, the cell cycle distribution of PANC-1 cells was measured using the flow cytometric assay. Compared with the control group, the percentage of cells in S phase was apparently increased in the TA-treated groups (Figure 3a), which was probably associated with the downregulation of cell cycle regulation proteins (e.g. Cyclin D1 and c-Myc) by TA. To evaluate the effect of TA on the apoptosis of PANC-1 cells, the apoptosis rates were analyzed using the Annexin V-FITC/PI double staining assay. As shown in Figure 3b, the percentage of apoptotic cells was not significantly increased in the TA-treated groups compared with the control group. Although the expression of apoptosis-related proteins Survivin and Bcl2, was downregulated by TA, TA might mainly arrest cell cycle instead of inducing apoptosis to inhibit the proliferation and growth of PANC-1 cells through blocking the STAT3 pathway.
To investigate the effect of TA on the mobility of PANC-1 cells, the transwell migration assay was performed. Compared with the control group, the migration of PANC-1 cells in the TA-treated groups was effectively suppressed in a concentration-dependent manner (Figure 3c). Next, the Matrigel invasion assay was performed to evaluate the effect of TA on the invasion of PANC-1 cells. As shown in Figure 3d, the invasive ability of PANC-1 cells in the TA-treated groups was dramatically reduced in a dose-dependent manner compared with the control group. Thus, TA suppressed the migration and invasion capacities of PANC-1 cells by inhibiting the STAT3 signaling pathway. Furthermore, we examined whether TA inhibited the migration and invasion of other pancreatic cancer cells. As expected, TA also observably inhibited the migration and invasion of other pancreatic cancer cells in a dose-dependent manner (Figures S4 and S5). In brief, all of these data indicated that TA inhibited the proliferation, growth, migration and invasion of pancreatic cancer cells by inhibiting the STAT3 pathway.