Simultaneous degradation of alphaII- and betaII-spectrin by caspase 3 (CPP32) in apoptotic cells.
The degradation of alphaII- and betaII-spectrin during apoptosis in cultured human neuroblastoma SH-SY5Y cells was investigated. Immunofluorescent staining showed that the collapse of the cortical spectrin cytoskeleton is an early event following staurosporine challenge. This collapse correlated with the generation of a series of prominent spectrin breakdown products (BDPs) derived from both alphaII- and betaII-subunits. Major C-terminal alphaII-spectrin BDPs were detected at approximately 150, 145, and 120 kDa (alphaII-BDP150, alphaII-BDP145, and alphaII-BDP120, respectively); major C-terminal betaII-spectrin BDPs were at approximately 110 and 85 kDa (betaII-BDP110 and betaII-BDP85, respectively). N-terminal sequencing of the major fragments produced in vitro by caspase 3 revealed that alphaII-BDP150 and alphaII-BDP120 were generated by cleavages at DETD1185*S1186 and DSLD1478*S1479, respectively. For betaII-spectrin, a major caspase site was detected at DEVD1457*S1458, and both betaII-BDP110 and betaII-BDP85 shared a common N-terminal sequence starting with Ser1458. An additional cleavage site near the C terminus, at ETVD2146*S2147, was found to account for betaII-BDP85. Studies using specific caspase or calpain inhibitors indicate that the pattern of spectrin breakdown during apoptosis differs from that during non-apoptotic cell death. We postulate that in concert with calpain, caspase rapidly targets critical sites in both alphaII- and betaII-spectrin and thereby initiates a rapid dissolution of the spectrin-actin cortical cytoskeleton with apoptosis.
Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan 48106, USA. Wang@WL.com
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Wang
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Posmantur
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Nath
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McGinnis
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Whitton
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Talanian
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Glantz
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Morrow
D000595:Amino Acid Sequence; D017209:Apoptosis; D053148:Caspase 3; D020169:Caspases; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D013049:Spectrin / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured
D013049:Spectrin; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D003546:Cysteine Endopeptidases