FIGURE 5.

TPA-induced decrease of phosphorylated STAT3 is due to dephosphorylation of STAT3 mediated through activation of a PTPase(s). A, WM1205Lu, WM239A, WM98-1, and WM35 cells cultured in EMEM containing 5% FCS were incubated without (vanadate (−)) or with 0.5 mm sodium orthovanadate (vanadate (+)) for 30 min and then stimulated with 100 nm TPA. The phosphorylation levels of pY-STAT3 as well as the expression of total STAT3 (t-STAT3) were determined at the indicated time point. B, WM1205Lu and WM35 cells were incubated with 0.5 mm sodium orthovanadate. The phosphorylation levels of pY-STAT3 as well as the expression of total STAT3 were determined at the indicated time point. The results shown are representative of three independent experiments.