Phosphorylation of Eukaryotic Initiation Factor (eIF) 4E Is Not Required for de Novo Protein Synthesis following Recovery from Hypertonic Stress in Human Kidney Cells

• Published in: The Journal of biological chemistry Vol. 277; no. 36; pp. 32855 - 32859
• Main Authors: Morley, Simon J., Naegele, Susanne
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 06.09.2002; American Society for Biochemistry and Molecular Biology
• Subjects: Aniline Compounds - pharmacology; Cell Line; Dose-Response Relationship, Drug; Electrophoresis, Polyacrylamide Gel; Enzyme Inhibitors - pharmacology; Eukaryotic Initiation Factor-4E; Guanosine Triphosphate - metabolism; Humans; Hypertonic Solutions - pharmacology; Immunoblotting; Isoelectric Focusing; Kidney - cytology; Kidney - drug effects; Kidney - metabolism; Peptide Initiation Factors - chemistry; Peptide Initiation Factors - metabolism; Phosphorylation; Protein Binding; Protein Biosynthesis; Protein Structure, Tertiary; Purines - pharmacology; Ribosomal Protein S6; Ribosomal Proteins - metabolism; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.C200376200

Previous work has suggested that increased phosphorylation of eukaryotic initiation factor (eIF) 4E at Ser-209 in the C-terminal loop of the protein often correlates with increased translation rates. However, the functional consequences of phosphorylation have remained contentious with our understanding of the role of eIF4E phosphorylation in translational control far from complete. To investigate the role for eIF4E phosphorylation in de novo translation, we studied the recovery of human kidney cells from hypertonic stress. Results show that hypertonic shock caused a rapid inhibition of protein synthesis and the disaggregation of polysomes. These changes were associated with the dephosphorylation of eIF4G, eIF4E, 4E-binding protein 1 (4E-BP1), and ribosomal protein S6. In addition, decreased levels of the eIF4F complex and increased association of 4E-BP1 with eIF4E were observed over a similar time course. The return of cells to isotonic medium rapidly promoted the phosphorylation of these initiation factors, increased levels of eIF4F complexes, promoted polysome assembly, and increased rates of translation. However, by using a cell-permeable, specific inhibitor of eIF4E kinase, Mnk1 (CGP57380), we show that de novoinitiation of translation and eIF4F complex assembly during this recovery phase did not require eIF4E phosphorylation.