Pre-treatment of human MM cells with the MEK1/2 inhibitor U0126 (20 μM for 1 h) resulted in attenuation of Dox-induced ERK1/2 activation in all MM lines, whereas the inactive analog, U0124 (20 μM for 1 h), had no significant effects on Dox-induced ERK phosphorylation (Figure 1C). Here, MAPK1 is linked to Miyoshi myopathy.