Dataset Information

Inhibition of CED-3 zymogen activation and apoptosis in Caenorhabditis elegans by caspase homolog CSP-3.

ABSTRACT: Inhibitor of apoptosis (IAP) proteins have a crucial role in apoptosis, through negative regulation of caspases in species from fruitflies to mammals. In Caenorhabditis elegans, however, no IAP homolog or caspase inhibitor has been identified, calling into question how the cell-killing caspase CED-3 can be negatively regulated. Here we show that inactivation of the C. elegans csp-3 gene, which encodes a protein similar to the small subunit of the CED-3 caspase, causes cells that normally live to undergo apoptosis in a CED-3-dependent manner. Biochemical analysis reveals that CSP-3 associates with the large subunit of the CED-3 zymogen and inhibits zymogen autoactivation. However, CSP-3 does not block CED-3 activation induced by CED-4, nor does it inhibit the activity of the activated CED-3 protease. Therefore CSP-3 uses a previously unreported mechanism to protect cells from apoptosis.

SUBMITTER: Geng X

PROVIDER: S-EPMC2574878 | biostudies-literature | 2008 Oct

REPOSITORIES: biostudies-literature

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Inhibition of CED-3 zymogen activation and apoptosis in Caenorhabditis elegans by caspase homolog CSP-3.

Geng Xin X Shi Yong Y Nakagawa Akihisa A Yoshina Sawako S Mitani Shohei S Shi Yigong Y Xue Ding D

Nature structural & molecular biology 20080907 10

Inhibitor of apoptosis (IAP) proteins have a crucial role in apoptosis, through negative regulation of caspases in species from fruitflies to mammals. In Caenorhabditis elegans, however, no IAP homolog or caspase inhibitor has been identified, calling into question how the cell-killing caspase CED-3 can be negatively regulated. Here we show that inactivation of the C. elegans csp-3 gene, which encodes a protein similar to the small subunit of the CED-3 caspase, causes cells that normally live to ...[more]

PMID: 18776901

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Project description:Caspases are cysteine proteases that can drive apoptosis in metazoans and have critical functions in the elimination of cells during development, the maintenance of tissue homeostasis, and responses to cellular damage. Although a growing body of research suggests that programmed cell death can occur in the absence of caspases, mammalian studies of caspase-independent apoptosis are confounded by the existence of at least seven caspase homologs that can function redundantly to promote cell death. Caspase-independent programmed cell death is also thought to occur in the invertebrate nematode Caenorhabditis elegans. The C. elegans genome contains four caspase genes (ced-3, csp-1, csp-2, and csp-3), of which only ced-3 has been demonstrated to promote apoptosis. Here, we show that CSP-1 is a pro-apoptotic caspase that promotes programmed cell death in a subset of cells fated to die during C. elegans embryogenesis. csp-1 is expressed robustly in late pachytene nuclei of the germline and is required maternally for its role in embryonic programmed cell deaths. Unlike CED-3, CSP-1 is not regulated by the APAF-1 homolog CED-4 or the BCL-2 homolog CED-9, revealing that csp-1 functions independently of the canonical genetic pathway for apoptosis. Previously we demonstrated that embryos lacking all four caspases can eliminate cells through an extrusion mechanism and that these cells are apoptotic. Extruded cells differ from cells that normally undergo programmed cell death not only by being extruded but also by not being engulfed by neighboring cells. In this study, we identify in csp-3; csp-1; csp-2 ced-3 quadruple mutants apoptotic cell corpses that fully resemble wild-type cell corpses: these caspase-deficient cell corpses are morphologically apoptotic, are not extruded, and are internalized by engulfing cells. We conclude that both caspase-dependent and caspase-independent pathways promote apoptotic programmed cell death and the phagocytosis of cell corpses in parallel to the canonical apoptosis pathway involving CED-3 activation.

Project description:A critical accomplishment in the rapidly developing field of regenerative medicine will be the ability to foster repair of neurons severed by injury, disease, or microsurgery. In C. elegans, individual visualized axons can be laser-cut in vivo and neuronal responses to damage can be monitored to decipher genetic requirements for regeneration. With an initial interest in how local environments manage cellular debris, we performed femtosecond laser axotomies in genetic backgrounds lacking cell death gene activities. Unexpectedly, we found that the CED-3 caspase, well known as the core apoptotic cell death executioner, acts in early responses to neuronal injury to promote rapid regeneration of dissociated axons. In ced-3 mutants, initial regenerative outgrowth dynamics are impaired and axon repair through reconnection of the two dissociated ends is delayed. The CED-3 activator, CED-4/Apaf-1, similarly promotes regeneration, but the upstream regulators of apoptosis CED-9/Bcl2 and BH3-domain proteins EGL-1 and CED-13 are not essential. Thus, a novel regulatory mechanism must be utilized to activate core apoptotic proteins for neuronal repair. Since calcium plays a conserved modulatory role in regeneration, we hypothesized calcium might play a critical regulatory role in the CED-3/CED-4 repair pathway. We used the calcium reporter cameleon to track in vivo calcium fluxes in the axotomized neuron. We show that when the endoplasmic reticulum calcium-storing chaperone calreticulin, CRT-1, is deleted, both calcium dynamics and initial regenerative outgrowth are impaired. Genetic data suggest that CED-3, CED-4, and CRT-1 act in the same pathway to promote early events in regeneration and that CED-3 might act downstream of CRT-1, but upstream of the conserved DLK-1 kinase implicated in regeneration across species. This study documents reconstructive roles for proteins known to orchestrate apoptotic death and links previously unconnected observations in the vertebrate literature to suggest a similar pathway may be conserved in higher organisms.

Dataset Information

Inhibition of CED-3 zymogen activation and apoptosis in Caenorhabditis elegans by caspase homolog CSP-3.

Publications

Inhibition of CED-3 zymogen activation and apoptosis in Caenorhabditis elegans by caspase homolog CSP-3.

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