FIG. 2.

Effect of MEKK2 and MEKK3 on ERK5 signaling. COS-7 cells were cotransfected with expression vectors encoding Flag-tagged MEK5α or MEK5β and HA-tagged MEKK2 or MEKK3 without (A) or with ERK5 (B). MEK5 and ERK5 activities were measured by protein kinase assays (KA) following immunoprecipitation using an anti-Flag (A) or an anti-ERK5 (B) antibody, respectively. The radioactivity incorporated into GST-MEF2C was quantitated after SDS-PAGE by phosphorimager analysis and expressed as a percentage of the maximum value (B). Data of three independent experiments are shown (means ± standard error of the means).