Type I IFN-dependent phosphorylation of the p70 S6 kinase in BCR-ABL-expressing cells. (A) KT-1 cells were treated with IFNα for different time points, as indicated. Equal amounts of total cell lysates were analyzed by SDS-PAGE and immunoblotted with an antibody against the phosphorylated/activated form of the p70 S6 kinase on threonine 421 and serine 424 (top panel). The same blot was then stripped and reprobed with an anti-p70 S6 kinase antibody, to control for protein loading (bottom panel). (B) Similar experiment to the one shown in panel A, except that IFNβ was used instead of IFNα. (C) Granulocytes isolated from the peripheral blood of a patient with CML were incubated with IFNα for 15 minutes. Top panel shows immunoblotting of total cell lysates with an anti-phospho-Thr421/Ser-424 p70 S6 kinase antibody. Bottom panel shows reprobing of the same blot with an anti-p70 S6K antibody, to control for protein loading.