Vitamin C suppresses GM-CSF–induced phosphorylation of Stat5.

(A) U937 cells incubated for 30 minutes with (+) or without (–) 500 μM DHA were treated with 1 nM GM-CSF for the periods shown. The phosphorylated Stat5 (p-Stat5) was visualized by immunoblotting with an antiphosphorylated Stat5 antibody (upper panel). Equal protein loading was demonstrated by immunoblotting the same membrane with anti-Stat5 (Stat5) antibody as shown in the lower panel. (B) Concentration dependence of the effect of vitamin C on the GM-CSF–induced phosphorylation of Stat5. U937 cells incubated for 30 minutes with different concentrations of DHA were treated with 1 nM GM-CSF for 3 minutes. The phosphorylated (p-Stat5) and nonphosphorylated Stat5 (Stat5) are shown at the upper and lower panels, respectively. (C) Cells were incubated with 500 μM DHA for the indicated time periods and treated with 1 nM GM-CSF for 3 minutes. The phosphorylated and nonphosphorylated Stat5 are shown at the upper and lower panels, respectively. Control (Ct) represents cells unexposed to GM-CSF or DHA.