MAPK8 and breast cancer: Nevertheless, the time-course drug treatment experiments on the parental MCF-7 and drug resistant MCF-7EpiR and MCF-7TaxR breast cancer cells lent support to the idea that GCN2 can potentially cooperate with PERK to repress FOXO3 activity via JNK and AKT to modulate drug response and compensate for PERK inactivation.