MAPK3 and acute lymphoblastic leukemia: ATO enhanced ERK1/2 activity in four out of the six tested cell lines (BaF3p210T315I, K562-R, KCL22-R and SUP-B15) and in four out of the five primary-derived leukemic samples (except for ALL#1), while PD treatment of the cells reduced the basal phosphorylation status of ERK1/2 and blunted the further activation of these kinases in response to ATO in all the analyzed samples (Fig. 2A).