Caspase cleavage of initiation factor 4E-binding protein 1 yields a dominant inhibitor of cap-dependent translation and reveals a novel regulatory motif.
Eukaryotic initiation factor 4E (eIF4E) binding proteins (4E-BPs) regulate the assembly of initiation complexes required for cap-dependent mRNA translation. 4E-BP1 undergoes insulin-stimulated phosphorylation, resulting in its release from eIF4E, allowing initiation complex assembly. 4E-BP1 undergoes caspase-dependent cleavage in cells undergoing apoptosis. Here we show that cleavage occurs after Asp24, giving rise to the N-terminally truncated polypeptide Delta4E-BP1, which possesses the eIF4E-binding site and all the known phosphorylation sites. Delta4E-BP1 binds to eIF4E and fails to become sufficiently phosphorylated upon insulin stimulation to bring about its release from eIF4E. Therefore, Delta4E-BP1 acts as a potent inhibitor of cap-dependent translation. Using a mutagenesis approach, we identify a novel regulatory motif of four amino acids (RAIP) which lies within the first 24 residues of 4E-BP1 and which is necessary for efficient phosphorylation of 4E-BP1. This motif is conserved among sequences of 4E-BP1 and 4E-BP2 but is absent from 4E-BP3. Insulin increased the phosphorylation of 4E-BP3 but not sufficiently to cause its release from eIF4E. However, a chimeric protein that was generated by replacing the N terminus of 4E-BP3 with the N-terminal sequence of 4E-BP1 (containing this RAIP motif) underwent a higher degree of phosphorylation and was released from eIF4E. This suggests that the N-terminal sequence of 4E-BP1 is required for optimal regulation of 4E-BPs by insulin.
Tee
Andrew R
AR
Division of Molecular Physiology, School of Life Sciences, Medical Sciences Institute, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland, United Kingdom.
Proud
Christopher G
CG
D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D020816:Amino Acid Motifs / Q000502:physiology; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism*; D018797:Cell Cycle Proteins; D017124:Conserved Sequence; D039562:Eukaryotic Initiation Factor-4F; D039642:Eukaryotic Initiation Factors; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D051379:Mice; D010446:Peptide Fragments / Q000096:biosynthesis / Q000494:pharmacology; D010448:Peptide Initiation Factors / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D010766:Phosphorylation; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D014176:Protein Biosynthesis / Q000187:drug effects / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D012097:Repressor Proteins / Q000096:biosynthesis* / Q000494:pharmacology; D017384:Sequence Deletion
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; C104151:EIF4EBP2 protein, human; C499527:Eif4ebp1 protein, mouse; C499526:Eif4ebp1 protein, rat; C491255:Eif4ebp2 protein, mouse; D039562:Eukaryotic Initiation Factor-4F; D039642:Eukaryotic Initiation Factors; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D010446:Peptide Fragments; D010448:Peptide Initiation Factors; D010750:Phosphoproteins; D012333:RNA, Messenger; D012097:Repressor Proteins; D020169:Caspases