1. ¹Department of Cell Biology, Harvard Medical School, Boston, MA, USA
2. ²Department of Pharmacology, UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ, USA
3. ³Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA, USA
4. ⁴State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai, China

Correspondence: J Yuan, Department of Cell Biology, Harvard Medical School, 240 Longwood Ave, Boston, MA, USA. Tel: +1 617 432 4170; Fax: +1 617 432 4177; E-mail: junying_yuan@hms.harvard.edu

⁵Current address: Department of Chemistry, University of California, Berkeley, CA 94720, USA

Received 25 June 2007; Revised 5 November 2007; Accepted 9 November 2007; Published online 11 January 2008.

Abstract

Apoptosis triggered by endoplasmic reticulum (ER) stress has been implicated in many diseases but its cellular regulation remains poorly understood. Previously, we identified salubrinal (sal), a small molecule that protects cells from ER stress-induced apoptosis by selectively activating a subset of endogenous ER stress-signaling events. Here, we use sal as a probe in a proteomic approach to discover new information about the endogenous cellular response to ER stress. We show that sal induces phosphorylation of the translation elongation factor eukaryotic translation elongation factor 2 (eEF-2), an event that depends on eEF-2 kinase (eEF-2K). ER stress itself also induces eEF-2K-dependent eEF-2 phosphorylation, and this pathway promotes translational arrest and cell death in this context, identifying eEF-2K as a hitherto unknown regulator of ER stress-induced apoptosis. Finally, we use both sal and ER stress models to show that eEF-2 phosphorylation can be activated by at least two signaling mechanisms. Our work identifies eEF-2K as a new component of the ER stress response and underlines the utility of novel small molecules in discovering new cell biology.