Vitamin C suppresses IL-3–induced phosphorylation of MAP kinase.

(A) HL-60 cells incubated for 30 minutes with 500 μM DHA (+) or without DHA (–) were treated with 1 nM GM-CSF for 10 minutes or incubated with 0.6 nM IL-3 for the period indicated. 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) U937 cells were incubated with DHA (+) or without DHA (–) and CK2 kinase activity was measured in cell lysates. One representative experiment is shown. C represents background activity in absence of lisate. Bars represent the average values of triplicate determinations ± SD.