RESUMO
Drosophila provides a powerful genetic model for studying the in vivo regulation of cell death. In our large-scale gain-of-function screen, we identified Eiger, the first invertebrate tumor necrosis factor (TNF) superfamily ligand that can induce cell death. Eiger is a type II transmembrane protein with a C-terminal TNF homology domain. It is predominantly expressed in the nervous system. Genetic evidence shows that Eiger induces cell death by activating the Drosophila JNK pathway. Although this cell death process is blocked by Drosophila inhibitor-of-apoptosis protein 1 (DIAP1), it does not require caspase activity. We also show genetically that Eiger is a physiological ligand for the Drosophila JNK pathway. Our findings demonstrate that Eiger can initiate cell death through an IAP-sensitive cell death pathway via JNK signaling.
Assuntos
Proteínas de Drosophila/metabolismo , Drosophila melanogaster/fisiologia , Sistema de Sinalização das MAP Quinases/fisiologia , Proteínas de Membrana/metabolismo , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Proteínas , Fator de Necrose Tumoral alfa/metabolismo , Sequência de Aminoácidos , Animais , Apoptose/fisiologia , Proteínas de Drosophila/química , Proteínas de Drosophila/genética , Drosophila melanogaster/anatomia & histologia , Drosophila melanogaster/genética , Drosophila melanogaster/crescimento & desenvolvimento , Embrião não Mamífero/anatomia & histologia , Embrião não Mamífero/fisiologia , Genes de Insetos , Hibridização In Situ , Proteínas Inibidoras de Apoptose , Proteínas de Insetos/fisiologia , Proteínas Quinases JNK Ativadas por Mitógeno , Ligantes , Proteínas de Membrana/química , Proteínas de Membrana/genética , Dados de Sequência Molecular , Família Multigênica , Peptídeos/genética , Peptídeos/metabolismo , Fenótipo , Células Fotorreceptoras de Invertebrados/crescimento & desenvolvimento , Alinhamento de Sequência , Fator de Necrose Tumoral alfa/genéticaRESUMO
Members of the inhibitor of apoptosis protein (IAP) family can inhibit caspases and cell death in a variety of insect and vertebrate systems. Drosophila IAP1 (DIAP1) inhibits cell death to facilitate normal embryonic development. Here, using RNA interference, we showed that down-regulation of DIAP1 is sufficient to induce cell death in Drosophila S2 cells. Although this cell death process was accompanied by elevated caspase activity, this activation was not essential for cell death. We found that DIAP1 depletion-induced cell death was strongly suppressed by a reduction in the Drosophila caspase DRONC or the Drosophila apoptotic protease-activating factor-1 (Apaf-1) homolog, Dark. RNA interference studies in Drosophila embryos also demonstrated that the action of Dark is epistatic to that of DIAP1 in this cell death pathway. The cell death caused by down-regulation of DIAP1 was accelerated by overexpression of DRONC and Dark, and a caspase-inactive mutant form of DRONC could functionally substitute the wild-type DRONC in accelerating cell death. These results suggest the existence of a novel mechanism for cell death signaling in Drosophila that is mediated by DRONC and Dark.
