title: Caspase activity is not sufficient to execute cell death.
abstract: Molecular studies of the physiological cell death process have focused attention on the role of effector caspases as critical common elements of the lethal mechanism. Diverse death signals act afferently via distinct signaling pathways to activate these resident proenzyme molecules post-translationally. Whether this molecular convergence represents the mechanistic point of irreversible commitment to cell death has not been established. That a number of caspase substrates are proteins that serve important roles in cellular homeostasis has led to the view that the acquisition of this activity must be the determinative step in cell death. Observations that caspases serve in a regulatory role to catalyze the appearance of new activities involved in orderly cellular dissolution challenge this model of death as a simple process of proteolytic destruction. We found previously that caspase-dependent nuclear cyclin dependent kinase 2 (Cdk2) activity appears to be necessary for cell death. Employing direct cytofluorimetric analyses of intracellular caspase activity and colony forming assays, we now show that transient blockade of caspase-dependent Cdk2 activity confers long-lived sparing from death on cells otherwise triggered to die and fully replete with caspase activity. These data demonstrate that caspases, while necessary for apoptosis, are not sufficient to exert lethality. Caspase activation per se does not represent an irreversible point of commitment to physiological cell death.
mesh_terms: D042846:CDC2-CDC28 Kinases; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects / Q000502:physiology*; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D006367:HeLa Cells; D006801:Humans; D010447:Peptide Hydrolases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins; D015843:Serpins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D019311:Staurosporine / Q000494:pharmacology; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014764:Viral Proteins
chemical_list: D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D011993:Recombinant Fusion Proteins; D015843:Serpins; D014409:Tumor Necrosis Factor-alpha; D014764:Viral Proteins; C074641:interleukin-1beta-converting enzyme inhibitor; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D010447:Peptide Hydrolases; D020169:Caspases; C108711:DEVDase; D019311:Staurosporine