Ebp1 is a dsRNA-binding protein associated with ribosomes that modulates eIF2α phosphorylation

dsRNA-binding domains (dsRBDs) characterize an expanding family of proteins involved in different cellular processes, ranging from RNA editing and processing to translational control. Here we present evidence that Ebp1, a cell growth regulating protein that is part of ribonucleoprotein (RNP) complexes, contains a dsRBD and that this domain mediates its interaction with dsRNA. Deletion of Ebp1's dsRBD impairs its localization to the nucleolus and its ability to form RNP complexes. We show that in the cytoplasm, Ebp1 is associated with mature ribosomes and that it is able to inhibit the phosphorylation of serine 51 in the eukaryotic initiation factor 2 alpha (eIF2 alpha). In response to various cellular stress, eIF2a is phosphorylated by distinct protein kinases (PKR, PERK, GCN2. and HRI), and this event results in protein translation shut-down. Ebp1 overexpression in HeLa cells is able to protect eIF2 alpha from phosphorylation at steady state and also in response to various treatments. We demonstrate that Ebp1 interacts with and is phosphorylated by the PKR protein kinase. Our results demonstrate that Ebp1 is a new dsRNA-binding protein that acts as a cellular inhibitor of eIF2 alpha phosphorylation suggesting that it could be involved in protein translation control. (c) 2006 Elsevier Inc. All rights reserved.