Elongation Factor 2 Kinase Is Regulated by Proline Hydroxylation and Protects Cells during Hypoxia

Protein synthesis, especially translation elongation, requires large amounts of energy, which is often generated by oxidative me-tabolism. Elongation is controlled by phosphorylation of eukaryotic elongation factor 2 (eEF2), which inhibits its activity and is catalyzed by eEF2 kinase (eEF2K), a calcium/calmodulin-dependent -kinase. Hypoxia causes the activation of eEF2K and in-duces eEF2 phosphorylation independently of previously known inputs into eEF2K. Here, we show that eEF2K is subject to hy-droxylation on proline-98. Proline hydroxylation is catalyzed by proline hydroxylases, oxygen-dependent enzymes which are inactivated during hypoxia. Pharmacological inhibition of proline hydroxylases also stimulates eEF2 phosphorylation. Pro98 lies in a universally conserved linker between the calmodulin-binding and catalytic domains of eEF2K. Its hydroxylation par-tially impairs the binding of calmodulin to eEF2K andmarkedly limits the calmodulin-stimulated activity of eEF2K. Neuronal cells depend on oxygen, and eEF2K helps to protect them from hypoxia. eEF2K is the first example of a protein directly involved in a major energy-consuming process to be regulated by proline hydroxylation. Since eEF2K is cytoprotective during hypoxia and other conditions of nutrient insufficiency, it may be a valuable target for therapy of poorly vascularized solid tumors. Many cells require aerobic metabolism to generate energy, ne-cessitating an adequate supply of oxygen. Protein synthesis, especially translation elongation, is a major energy-consuming process, and translation elongation uses both ATP (for amino-acyl-tRNA charging) and GTP (at least two GTP equivalents ar