MAPK3 and Miyoshi myopathy: To assess the role of Dox-activated ERK1/2 in cell survival, we pretreated human MM cells (MO, ME-26 and HMESO) with the MEK1/2 inhibitor (U0126, 20 μM) for 1 h before treating for 24 h with Dox at 25 (MO, ME-26) or 100 μM (HMESO), the approximate LD50 concentration for each cell type.