Cap-independent translation promotes C. elegans germ cell apoptosis through Apaf-1/CED-4 in a caspase-dependent mechanism

• Published in: PloS one Vol. 6; no. 9; p. e24444
• Main Authors: Contreras, Vince, Friday, Andrew J, Morrison, J Kaitlin, Hao, Enhui, Keiper, Brett D
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01-09-2011; Public Library of Science (PLoS)
• Subjects: Amino acids; Animals; Apaf-1 protein; Apoptosis; Apoptosomes - metabolism; Apoptotic Protease-Activating Factor 1 - metabolism; Aspartic Acid - metabolism; Base Sequence; Bcl-2 protein; Binding Sites; Biocatalysis; Biochemistry; Biology; Caenorhabditis elegans; Caenorhabditis elegans - cytology; Caenorhabditis elegans - metabolism; Caenorhabditis elegans Proteins - metabolism; Calcium-Binding Proteins - metabolism; Caspase; Caspase 3 - metabolism; Caspase-3; Caspases - metabolism; Cell cycle; Cell death; Disruption; Drosophila; Eukaryotic Initiation Factor-4G - metabolism; Germ Cells - cytology; Germ Cells - metabolism; Homology; Humans; Initiation factor eIF-4G; Insects; Isoforms; Kinases; Machinery; Machinery and equipment; Medicine; Molecular biology; Molecular Sequence Data; mRNA; Mutagenesis; Nematodes; Oocytes; Physiological aspects; Protein Biosynthesis; Protein Isoforms - metabolism; Protein synthesis; Proteins; Proto-Oncogene Proteins c-bcl-2 - metabolism; Recombinant Proteins - metabolism; Ribonucleic acid; RNA; RNA Caps - metabolism; RNA-mediated interference; Site-directed mutagenesis; Sperm; Substrate Specificity; Translation; Translation (Genetics); Worms; North Carolina; United States > US
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0024444

Apoptosis is a natural process during animal development for the programmed removal of superfluous cells. During apoptosis general protein synthesis is reduced, but the synthesis of cell death proteins is enhanced. Selective translation has been attributed to modification of the protein synthesis machinery to disrupt cap-dependent mRNA translation and induce a cap-independent mechanism. We have previously shown that disruption of the balance between cap-dependent and cap-independent C. elegans eIF4G isoforms (IFG-1 p170 and p130) by RNA interference promotes apoptosis in developing oocytes. Germ cell apoptosis was accompanied by the appearance of the Apaf-1 homolog, CED-4. Here we show that IFG-1 p170 is a native substrate of the worm executioner caspase, CED-3, just as mammalian eIF4GI is cleaved by caspase-3. Loss of Bcl-2 function (ced-9ts) in worms induced p170 cleavage in vivo, coincident with extensive germ cell apoptosis. Truncation of IFG-1 occurred at a single site that separates the cap-binding and ribosome-associated domains. Site-directed mutagenesis indicated that CED-3 processes IFG-1 at a non-canonical motif, TTTD(456). Coincidentally, the recognition site was located 65 amino acids downstream of the newly mapped IFG-1 p130 start site suggesting that both forms support cap-independent initiation. Genetic evidence confirmed that apoptosis induced by loss of ifg-1 p170 mRNA was caspase (ced-3) and apoptosome (ced-4/Apaf-1) dependent. These findings support a new paradigm in which modal changes in protein synthesis act as a physiological signal to initiate cell death, rather than occur merely as downstream consequences of the apoptotic event.