Abstract 4984: Phosporylation of eIF4E confer resistance to cellular stress

Abstract

Abstract Eukaryotic initiation factor (eIF) 4E mediates eIF4F association with the mRNA 5′ cap structure and is an essential factor for canonical protein translation. eIF4E can act as an oncogene when overexpressed in cell lines and high levels of eIF4E and phosporylated peIF4E have been described in a large number of human tumors. eIF4E has also been described as a component of cytoplasmic stress granules and processing bodies. Importantly, non-phosphorylated 4E-BP1 (often in response to stress) binds eIF4E to suppress protein translation. We demonstrated previously that high levels of peIF4E were associated with resistance to this suppressor effect in carcinoma cell lines. Because the role of peIF4E is not yet well established, we evaluated the role of eIF4E phosphorylation on in vitro stress resistance. Breast carcinoma cell lines (MDA-MB 231, MBA- MB 468 and HeLa cells) and an immortalized human keratinocyte cell line (HaCaT) were infected with retrovirus expressing wild type, hyperphosporylated (S209D) or hypophosporylated (S209D) mutants of eIF4E. Cells were subjected to different types of stress including oxidative (Arsenite), nutrient starving and cisplatin treatment. Immediate and long term response to stress was evaluated using colony formation, MTT cell proliferation assays, co-inmunoprecipitation and immunofluorescence microscopy. A significantly greater recovery after all forms of stress was observed in all the cell lines expressing hyperphosporylated eIF4E-S209D. After treatment with arsenite there was an increase of peIF4E, 4E-T and Hur and importantly higher increase of levels of Hur, CyclinD1, Mcl-1 and eIF4G in eIF4E-S209D expressing cells. Under normal condition we observed a unique colocalitzation of 4E-T and eIF4E-S209D in cytoplasmic bodies. This complex colocalize with Ago2 but not with markers of the stress granules (TIA-1) and processing bodies (DCP1A). By co-immunopreciptation, we observed that peIF4E binds to its carrier protein 4E-T, Ago2 and Hur. Conclusions: Phosphorylated eIF4E confer resistance to several stress conditions, including oxidative stress, DNA damage and nutrient deprivation. The fact that there was a relevant and significant increase of proteins such as Cyclin D1, Mcl-1 and Hur suggests that phosporylated eIF4E has an important role in selectively stimulating RNA translation under stress conditions, possibly via the formation of a unique type of 4E-T/peIF4E cytoplasmic bodies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4984. doi:1538-7445.AM2012-4984