IL-6 activates Erk5 in myeloma cells. MM1S (A) or MM144 (B) cells were incubated for 10 minutes with 10 nM EGF, IGF-1, IL-6, NRG, TNF-α, or SCF, and Erk5 expression was analyzed by Western blotting. The action of the polypeptide factors on Erk1/2 phosphorylation was detected by Western blotting with anti-pErk1/2 antibodies, and the total amount of Erk1/2 was analyzed on cell extracts with an anti-Erk1/2 antibody. (C) Effect of IL-6 on patient myeloma cells. Cells were treated with IL-6 as described in panel A and Erk5 analyzed by Western blotting from anti-Erk5 immunoprecipitates. (D) Cells were serum-starved for 18 hours and then treated with IGF-1 (10 nM) or IL-6 (5 nM) and Erk5 and pErk1/2 were analyzed by Western blotting.