Changes in integrity and association of eukaryotic protein synthesis initiation factors during apoptosis.
Induction of apoptosis results in inhibition of the rate of overall protein synthesis in a variety of cell types. We have shown previously that polypeptide chain initiation factor eIF4GI is rapidly cleaved by caspase-3, whereas other components of the eIF4F complex are much more stable during apoptosis in BJAB and Jurkat cells. We have now extended our analysis to other factors involved in the initiation of protein synthesis and we report here that eIF4B, the p35 subunit of eIF3, and minor proportions of the alpha subunit of eIF2 and the eIF4E-binding protein 4E-BP1 are also cleaved to give rise to discrete fragments. These cleavages occur with delayed kinetics relative to that seen for eIF4GI, and eIF2beta and eIF2gamma levels also decrease at a relatively late stage of apoptosis. In contrast, the second form of eIF4G described recently, eIF4GII, is cleaved as rapidly as eIF4GI under the same conditions. Purified recombinant caspase-3 is able to degrade eIF4B and eIF3(p35) in vitro, producing fragments of the same sizes as those seen in intact cells. Induction of apoptosis also results in a biphasic change in the association of 4E-BP1 with eIF4E. Thus the progress of apoptosis is characterized by a complex programme of changes in several initiation factors, including the specific fragmentation or complete degradation of some and alterations in the association status of others. These events are likely to contribute to the inhibition of protein synthesis seen under these conditions.
Bushell
M
M
Biochemistry Group, School of Biological Sciences, University of Sussex, Brighton, UK.
Wood
W
W
Clemens
M J
MJ
Morley
S J
SJ
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D017209:Apoptosis / Q000187:drug effects; D002352:Carrier Proteins; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D018797:Cell Cycle Proteins; D003513:Cycloheximide / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D039621:Eukaryotic Initiation Factor-3; D039561:Eukaryotic Initiation Factor-4E; D039562:Eukaryotic Initiation Factor-4F; D039603:Eukaryotic Initiation Factor-4G; D039642:Eukaryotic Initiation Factors; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010448:Peptide Initiation Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000502:physiology
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D061945:Caspase Inhibitors; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; C113920:EIF4G1 protein, human; C491300:EIF4G2 protein, human; D015852:Eukaryotic Initiation Factor-2; D039621:Eukaryotic Initiation Factor-3; D039561:Eukaryotic Initiation Factor-4E; D039562:Eukaryotic Initiation Factor-4F; D039603:Eukaryotic Initiation Factor-4G; D039642:Eukaryotic Initiation Factors; D010446:Peptide Fragments; D010448:Peptide Initiation Factors; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; C031799:eIF-4B; D019014:fas Receptor; D003513:Cycloheximide; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases