(A) Kinase inhibition assays were performed using the kinase domain of JAK1 and JAK1GQM-DVP. JAK1GQM-DVP was not inhibited by SOCS3. Error bars represent +/− range from two experiments. Data were normalized to no-inhibitor controls.
(B) Wild-type and mutant (GQM-DVP) JAK1 constructs were transfected into JAK1−/− (U4A) cells. Cells were stimulated with IL-6 plus s-IL-6Rα for 15 min and then harvested at the indicated times. Lysates were analyzed by immunoblotting with antibodies specific for phosphorylated STAT3, total STAT3, SOCS3 and JAK1.