Time course and dose response of IL-6–induced Erk5 activation in myeloma cells. (A) Time course of the effect of IL-6 and IGF-1 on Erk1/2 activation and phosphorylation and Erk5 and Akt phosphorylation. MM1S cells were treated for the indicated times with the growth factors and cell extracts used for analyses of Erk1/2 activity using GST-Elk, Erk1/2, pErk1/2, or pAkt in Western blots of cell extracts. Erk5 was detected by Western blotting of anti-Erk5 immunoprecipitates. The panels show the results of an experiment that was repeated twice. (B) Dose effect of IL-6 on Erk5 phosphorylation. IL-6 was added for 15 minutes, and Erk5 was analyzed as in panel A.