Phosphorylation of eIF4E Confers Resistance to Cellular Stress and DNA-Damaging Agents through an Interaction with 4E-T: A Rationale for Novel Therapeutic Approaches.

Alba Martínez,Javier Hernandez Losa,Marta Sesé,Trond Aasen,Nathaniel Robichaud,Nahum Sonenberg,Santiago Ramón y Cajal,David M Loeb

doi:10.1371/journal.pone.0123352

Abstract

Phosphorylation of the eukaryotic translation initiation factor eIF4E is associated with malignant progression and poor cancer prognosis. Accordingly, here we have analyzed the association between eIF4E phosphorylation and cellular resistance to oxidative stress, starvation, and DNA-damaging agents in vitro. Using immortalized and cancer cell lines, retroviral expression of a phosphomimetic (S209D) form of eIF4E, but not phospho-dead (S209A) eIF4E or GFP control, significantly increased cellular resistance to stress induced by DNA-damaging agents (cisplatin), starvation (glucose+glutamine withdrawal), and oxidative stress (arsenite). De novo accumulation of eIF4E-containing cytoplasmic bodies colocalizing with the eIF4E-binding protein 4E-T was observed after expression of phosphomimetic S209D, but not S209A or wild-type eIF4E. Increased resistance to cellular stress induced by eIF4E-S209D was lost upon knockdown of endogenous 4E-T or use of an eIF4E-W73A-S209D mutant unable to bind 4E-T. Cancer cells treated with the Mnk1/2 inhibitor CGP57380 to prevent eIF4E phosphorylation and mouse embryonic fibroblasts derived from Mnk1/2 knockout mice were also more sensitive to arsenite and cisplatin treatment. Polysome analysis revealed an 80S peak 2 hours after arsenite treatment in cells overexpressing phosphomimetic eIF4E, indicating translational stalling. Nonetheless, a selective increase was observed in the synthesis of some proteins (cyclin D1, HuR, and Mcl-1). We conclude that phosphorylation of eIF4E confers resistance to various cell stressors and that a direct interaction or regulation of 4E-T by eIF4E is required. Further delineation of this process may identify novel therapeutic avenues for cancer treatment, and these results support the use of modern Mnk1/2 inhibitors in conjunction with standard therapy.

Highlights

Regulation of protein synthesis has recently been linked to a central role in cancer development and malignant progression
Nuclear import of eIF4E is mediated by the transporter protein 4E-T. 4E-T binds to eIF4E through a conserved binding motif (YXXXXLF) that is found in eIF4G and in the family of translational suppressors known as eIF4E-binding proteins (4E-BPs) [5]
Control of protein synthesis has emerged as an important concept in the regulation of cancer development, cancer prognosis, and therapeutic response [18, 36,37,38,39,40]. eIF4E, a rate-limiting factor for mRNA translation and a potent oncoprotein, plays a central role in this process

Summary

Introduction

Regulation of protein synthesis has recently been linked to a central role in cancer development and malignant progression. EIF4E induces malignant transformation through the regulation of multiple cell features, such as by increasing cell proliferation, cell survival, and anchorage-independence [6, 9, 10]. This is at least partly due to eIF4E enhancing the translation of mRNAs with long and highly structured 5' untranslated regions (UTRs), such as C-MYC, BCL2, FGF2, and BIRC5 (survivin), referred to as eIF4E-sensitive mRNAs [11]. The exact molecular mechanisms of how eIF4E contributes to malignancy and, in particular, the role of eIF4E phosphorylation remain unclear

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Results

Conclusion