Erk5 participates in MM proliferation. (A) Proliferation of MM1S (○) or MM1S cells expressing HA-Erk5^AEF (•). Cells were plated at identical densities and MTT uptake measured at the indicated times. Data correspond to the mean from quadruplicates ± SD of an experiment that was repeated 3 times. ^*P < .01. (B) Action of HA-Erk5^AEF on IL-6–induced MM1S proliferation. Cells were plated at identical densities and IL-6 (5 nM; ▪) was added or not (□) where indicated. One day or 3 days after the start of the experiment, MTT uptakes were measured. ^*P < .01. (C) Action of HA-Erk5^AEF on IL-6–induced BrdU uptake. Control or HA-Erk5^AEF–expressing MM1S cells were plated at 50 000 cells/well, and then IL-6 was (▪) added or not (□) for 3 days, where indicated. BrdU was added for the last 8 hours of the experiment, and then its uptake was measured as described in “Materials and methods.” Results are presented as the mean from quadruplicates ± SD.