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

293T cells cotransfected with plasmids containing the cDNAs for αGMR and βGMR were incubated for 30 minutes in the presence (+) or absence (–) of 500 μM DHA. 1 nM GM-CSF was added for the periods of time shown. βGMR was immunoprecipitated, subjected to SDS-PAGE, and the phosphorylated βGMR (p-βGMR) was visualized by immunoblotting with an antiphosphotyrosine antibody (arrow, upper panel). (B) Jak-2 phosphorylation is suppressed by vitamin C. βGMR was immunoprecipitated, subjected to SDS-PAGE, and the phosphorylated Jak-2 (p-Jak-2) was visualized by immunoblotting with antiphospho Jak-2 antibody (arrow, lower panel). Equal protein loading was demonstrated by immunoblotting the same membrane with an anti-βGMR antibody, as shown in the upper panel.