FIGURE 4.

TPA reduces the tyrosine phosphorylation and activity of STAT3 in melanoma cells. A, WM1205Lu cells were treated with either 0.1% DMSO (control) or 100 nm TPA. The phosphorylation level of pY-STAT3 as well as the expression of total STAT3 (t-STAT3) and actin were determined at the indicated time (top three panels). The results shown are representative of three independent experiments. The relative amount of pY-STAT3 to total STAT3 was calculated. The ratio of pY-STAT3 to total STAT3 at time 0 is represented as 1. Data are shown as mean ± S.D. (n = 4; *, p < 0.05; **, p < 0.01 versus time 0). B, WM1205Lu melanoma cells were treated with 100 nm TPA. DNA-binding activity of STAT3 in the cells at the indicated time was determined, and the results are shown as relative DNA-binding activity of STAT3. DNA-binding activity of STAT3 in the cells treated with 10 mg/ml IL-6 for 30 min was also determined. Data are shown as mean ± S.D. (n = 3). The results shown are representative of three independent experiments.