title: Cap-independent translation promotes C. elegans germ cell apoptosis through Apaf-1/CED-4 in a caspase-dependent mechanism.
abstract: 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.
authors: Department of Biochemistry and Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina, United States of America.
authors: Vince
authors: V
authors: Contreras
authors: Andrew J
authors: AJ
authors: Friday
authors: J Kaitlin
authors: JK
authors: Morrison
authors: Enhui
authors: E
authors: Hao
authors: Brett D
authors: BD
authors: Keiper
mesh_terms: D000818:Animals; D017209:Apoptosis; D053478:Apoptosomes / Q000378:metabolism; D053477:Apoptotic Protease-Activating Factor 1 / Q000378:metabolism; D001224:Aspartic Acid / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D055162:Biocatalysis; D017173:Caenorhabditis elegans / Q000166:cytology* / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D053148:Caspase 3 / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism; D005854:Germ Cells / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D020033:Protein Isoforms / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D012315:RNA Caps / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D053478:Apoptosomes; D053477:Apoptotic Protease-Activating Factor 1; D029742:Caenorhabditis elegans Proteins; D002135:Calcium-Binding Proteins; C089224:Ced-4 protein, C elegans; C087233:Ced-9 protein, C elegans; D039603:Eukaryotic Initiation Factor-4G; D020033:Protein Isoforms; D019253:Proto-Oncogene Proteins c-bcl-2; D012315:RNA Caps; D011994:Recombinant Proteins; D001224:Aspartic Acid; D053148:Caspase 3; D020169:Caspases; C089223:ced-3 protein, C elegans