Apoptosis in motion. An apical, P35-insensitive caspase mediates programmed cell death in insect cells.
Activation of caspases by proteolytic processing is a critical step during apoptosis in metazoans. Here we use high resolution time lapse microscopy to show a tight link between caspase activation and the morphological events delineating apoptosis in cultured SF21 cells from the moth Spodoptera frugiperda, a model insect system. The principal effector caspase, Sf-caspase-1, is proteolytically activated during SF21 apoptosis. To define the potential role of initiator caspases in vivo, we tested the effect of cell-permeable peptide inhibitors on pro-Sf-caspase-1 processing. Anti-caspase peptide analogues prevented apoptosis induced by diverse signals, including UV radiation and baculovirus infection. IETD-fmk potently inhibited the initial processing of pro-Sf-caspase-1 at the junction (TETD-G) of the large and small subunit, a cleavage that is blocked by inhibitor of apoptosis Op-IAP but not pancaspase inhibitor P35. Because Sf-caspase-1 was inhibited poorly by IETD-CHO, our data indicated that the protease responsible for the first step in pro-Sf-caspase-1 activation is a distinct apical caspase. Thus, Sf-caspase-1 activation is mediated by a novel, P35-resistant caspase. These findings support the hypothesis that apoptosis in insects, like that in mammals, involves a cascade of caspase activations.
Institute for Molecular Virology, and Department of Biochemistry, Graduate School and College of Agricultural and Life Sciences, University of Wisconsin, Madison, Wisconsin 53706, USA.
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Manji
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Friesen
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D001426:Bacterial Proteins / Q000378:metabolism; D016367:Baculoviridae; D020170:Caspase 1 / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D004792:Enzyme Precursors / Q000737:chemistry / Q000378:metabolism; D051034:Inhibitor of Apoptosis Proteins; D019476:Insect Proteins; D009036:Moths; D009842:Oligopeptides / Q000494:pharmacology*; D021122:Protein Subunits; D011506:Proteins; D018411:Spodoptera; D014162:Transfection; D014466:Ultraviolet Rays; D014764:Viral Proteins / Q000378:metabolism*
D001426:Bacterial Proteins; D015853:Cysteine Proteinase Inhibitors; D004792:Enzyme Precursors; D051034:Inhibitor of Apoptosis Proteins; D019476:Insect Proteins; D009842:Oligopeptides; D021122:Protein Subunits; D011506:Proteins; D014764:Viral Proteins; C086430:inhibitor of apoptosis, Nucleopolyhedrovirus; C425644:isoleucyl-glutamyl-threonyl-aspartic acid fluoromethyl ketone; D020170:Caspase 1