The Effector Phase of Physiological Cell Death Relies Exclusively on the Posttranslational Activation of Resident Components

We examined cell death in developing retinal tissue, following inhibition of protein synthesis, which kills undifferentiated post-mitotic cells. Ultrastructural features were found of both apoptosis and autophagy. Only approximately half of the degenerating cells were either terminal dUTP nick-end labeling (TUNEL)-positive or reacted with antibodies specific for activated caspases-3 or -9. Bongkrekic acid completely inhibited any appearance of cell death, whereas inhibitors of autophagy, caspases-9 or -3, prevented only TUNEL-positive cell death. Interestingly, inhibition of caspase-6 blocked TUNEL-negative cell death. Simultaneous inhibition of caspases-9 and -6 prevented cell death almost completely, but degeneration dependent on autophagy/ caspase-9 still occurred under inhibition of both caspases-3 and -6. Thus, inhibition of protein synthesis induces in the developing retina various post-translational, mitochondria-dependent pathways of cell death. Autophagy precedes sequential activation of caspases-9 and -3, and DNA fragmentation, whereas, in parallel, caspase-6 leads to a TUNEL-negative form of cell death.

Section: Caspase-9 Induces An Alternative Pathway Of Cell Death Inmentioning

confidence: 91%

mentioning

confidence: 99%

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Alternative Programs of Cell Death in Developing Retinal Tissue

Guimarães

Benchimol

Amarante-Mendes

et al. 2003

“…HeLa human cervical carcinoma cells and B2 cells, a transfectant reporter clone of 293T human transformed kidney epithelial cells (13), were grown in DMEM with 4.5 g/liter glucose (Mediatech) supplemented with 10% (v/v) FBS and 2 mM L-glutamine. Physiological cell death (apoptosis) was induced by treatment of cells with the macromolecular synthesis inhibitor actinomycin D (200 ng/ml, 12 h) (28), by irradiation (20 mJ/cm 2 ) with UVC (254 nm) light, or with staurosporine (1 M in serum-free medium for 3 h). Autophagy was induced by serum starvation with L-canavanine (1 mM) in the presence of the pan-caspase inhibitor quinolylvalyl-aspartyl-difluorophenoxy methyl ketone (10 M; R&D Systems, Minneapolis, MN) and was confirmed by the development of LC3-GFP puncta in transfected cells (29).…”

Section: Methodsmentioning

confidence: 99%

Externalized Glycolytic Enzymes Are Novel, Conserved, and Early Biomarkers of Apoptosis

Ucker

Jain

Pattabiraman

et al. 2012

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Background: Apoptotic cell recognition triggers profound immunosuppressive responses; relevant recognition determinants are uncharacterized. Results: Surface exposure of glycolytic enzymes is a common early apoptotic event. Conclusion: Externalized glycolytic enzyme molecules are novel apoptotic biomarkers and candidate immunomodulatory/ recognition determinants. Significance: Apoptotic glycolytic enzyme externalization explicates plasminogen binding to mammalian cells and potential mechanisms of immune privilege by commensal bacteria and pathogens.

“…6 Reassessing the Role of PS in Apoptotic Cell Clearance-We have argued that PS, which is taken to be the archetypal recognition molecule, is externalized on both apoptotic and necrotic cells and is not a specific ligand for the recognition of either one (1). 5 The appearance of determinants for recognition and inhibition of inflammation represents a post-translational gain-of-function, the revelation of cryptic activity during the process of physiological cell death specifically (1,18).…”

Section: Psr Is Dispensable For the Specific Anti-inflammatory Recognmentioning

confidence: 99%

The Presumptive Phosphatidylserine Receptor Is Dispensable for Innate Anti-inflammatory Recognition and Clearance of Apoptotic Cells

Mitchell

Cvetanović

Tibrewal

et al. 2006

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The role of the presumptive phosphatidylserine receptor (PSR) in the recognition and engulfment of apoptotic cells, and the antiinflammatory response they exert, has been of great interest. Genetic deficiency of PSR in the mouse is lethal perinatally, and results to date have been ambiguous with regard to the phagocytic and inflammatory phenotypes associated with that deficiency. Recently, we found that the specific functional recognition of apoptotic cells is a ubiquitous property of virtually all cell types, including mouse embryo fibroblasts, and reflects an innate immunity that discriminates live from effete cells. Physiological cell death is a process whose purpose is the elimination of functionally inappropriate cells in a manner that does not elicit inflammation. The ability of apoptotic corpses to be cleared in a noninflammatory manner by phagocytes is a consequence of their specific expression of determinants for recognition and modulation of pro-inflammatory responses. The acquisition of these apoptotic determinants is a gain-of-function common to all physiological cell deaths, without regard to suicidal stimulus, and conserved widely across species (1, 2).Numerous cellular alterations associated with apoptotic cell death have been described, including plasma membrane reorganization associated with blebbing (3), shrinkage, and the loss of membrane phospholipid asymmetry (4, 5). In particular, phosphatidylserine (PS), 4 an anionic phospholipid normally cloistered in the inner leaflet of the plasma membrane, is externalized during physiological cell death (5). It still remains to be determined what specific molecular events are responsible for the recognition of the effete cell.The view that externalized PS serves as a ligand for macrophage recognition of apoptotic cells followed from studies demonstrating that similar changes target aged erythrocytes for clearance (6, 7) and gained support from observations that phospho-L-serine and PS vesicles could inhibit partially the interaction of dying nucleated cells with macrophages (5,8,9).A presumptive cell surface PS-specific receptor (PSR) was identified molecularly following a screen for monoclonal antibodies whose binding to human macrophages was inhibited by PS-containing liposomes (10). The product of that screen, mAb 217, bound to cell surface determinants on macrophages and other cell types, notably excluding lymphoid cells. Significantly, mAb 217 triggered macrophages to release the anti-inflammatory cytokine TGF␤, further suggesting that mAb 217 engaged an apoptotic-like recognition mechanism (10).Controversy regarding this presumptive receptor arose, however, when PSR was observed to localize to the nucleus in mammalian cells (11) as well as in Hydra (12). The role of PSR has been further clouded by the disparate results of three groups of investigators who independently generated mice with targeted disruptions of the PSR locus (13-15). While homozygous PSR disruptions result in perinatal lethality in each case, different effects on the phagocytosi...