Calpain activation in apoptosis.
Programmed cell death is an active process wherein the cell initiates a sequence of events culminating in the fragmentation of its DNA, nuclear collapse, and disintegration of the cell into small, membrane-bound apoptotic bodies. Examination of the death program in various models has shown common themes, including a rise in cytoplasmic calcium, cytoskeletal changes, and redistribution of membrane lipids. The calcium-dependent neutral protease calpain has putative roles in cytoskeletal and membrane changes in other cellular processes; this fact led us to test the role of calpain in a well-known model of apoptotic cell death, that of thymocytes after treatment with dexamethasone. Assays for calcium-dependent proteolysis in thymocyte extracts reveal a rise in activity with a peak at about 1 hr of incubation with dexamethasone, falling to background at approximately 2 hr. Western blots indicate autolytic cleavage of the proenzyme precursor to the calpain I isozyme, providing additional evidence for calpain activation. We have also found that apoptosis in thymocytes, whether induced by dexamethasone or by low-level irradiation, is blocked by specific inhibitors of calpain. Apoptosis of metamyelocytes incubated with cycloheximide is also blocked by calpain inhibitors. These studies suggest a required role for calpain in both "induction" and "release" models of apoptotic cell death.
Squìer
M K
MK
Department of Immunology, University of Colorado Health Sciences Center, Denver 80262.
Miller
A C
AC
Malkinson
A M
AM
Cohen
J J
JJ
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001853:Bone Marrow / Q000187:drug effects; D001854:Bone Marrow Cells; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism; D005260:Female; D005720:Gamma Rays; D051379:Mice; D008807:Mice, Inbred BALB C; D013950:Thymus Gland / Q000166:cytology / Q000201:enzymology / Q000528:radiation effects
D004792:Enzyme Precursors; D003907:Dexamethasone; D003513:Cycloheximide; D002154:Calpain; C047018:procalpain