Time-course and concentration dependence of vitamin C suppressing of GM-CSF–induced phosphorylation of MAP kinase.

(A) U937 cells incubated for 30 minutes with 500 μM DHA (+) or without DHA (–) were treated with 1 nM GM-CSF for the time periods shown. Phosphorylated MAP kinase (p-MAPK) was visualized by immunoblotting with an antiphospho-MAP kinase antibody (upper panel). Equal protein loading was demonstrated by immunoblotting the membrane with anti–MAP kinase antibody as shown in the lower panel (MAPK). (B) Concentration dependence of the effect of vitamin C on the GM-CSF–induced phosphorylation of MAP kinase. U937 cells preincubated for 30 minutes with different concentrations of DHA were treated with 1 nM GM-CSF for 3 minutes. (C) Time dependence of the effect of vitamin C on GM-CSF–induced phosphorylation of MAP kinase. Cells preincubated with 500 μM DHA for the time indicated were incubated with 1 nM GM-CSF for 3 minutes. Control (Ct) represents cells left untreated with either GM-CSF or DHA.