Regulation of eIF2α Phosphorylation by MAPKs Influences Polysome Stability and Protein Translation

Regulation of protein translation occurs primarily at the level of initiation and is mediated by multiple signaling pathways, majorly mechanistic target of rapamycin complex 1 (mTORC1), mitogen-activated protein kinases (MAPKs), and the eukaryotic translation initiation factor eIF2. While mTORC1 and eIF2α influence the polysome stability, MAPKs influence the phosphorylation of the cap-binding protein eIF4E and are known to influence translation of only a small set of mRNAs. Here, we demonstrate that p38 MAPK and ERK1/2 regulate translation through integrated stress response (ISR) pathways. Dual inhibition (dual-Mi) of p38 MAPK and ERK1/2 caused substantial phosphorylation of eIF2α in a synergistic manner, resulting in near-absolute collapse of polysomes. This regulation was independent of Mnk1/2, a well-studied mediator of translation regulation by the MAPKs. Dual-Mi-induced polysome dissociation was far more striking than that caused by sodium arsenite, a strong inducer of ISR. Interestingly, induction of ISR caused increased p38 phosphorylation, and its inhibition resulted in stronger polysome dissociation, indicating the importance of p38 in the translation activities. Thus, our studies demonstrate a major, unidentified role for ERK1/2 and more particularly p38 MAPK in the maintenance of homeostasis of polysome association and translation activities.