Transforming growth factor beta induces caspase 3-independent cleavage of alphaII-spectrin (alpha-fodrin) coincident with apoptosis.
Transforming growth factor beta (TGF-beta) is a potent growth inhibitor and inducer of cell death in B-lymphocytes and is essential for immune regulation and maintenance of self-tolerance. In this report the mouse immature B cell line, WEHI 231, was used to examine the mechanisms involved in TGF-beta-mediated apoptosis. Induction of apoptosis is detected as early as 8 h after TGF-beta administration. Coincident with the onset of apoptosis, the cytoskeletal actin-binding protein, alphaII-spectrin (alpha-fodrin) is cleaved into 150-, 115-, and 110-kDa fragments. The broad spectrum caspase inhibitor (Boc-D-fmk (BD-fmk)) completely abolished TGF-beta-induced apoptosis and alphaII-spectrin cleavage. Caspase 3, although present in WEH1 231 cells, was not activated by TGF-beta, nor was its substrate, poly(ADP-ribose) polymerase. These results identify alphaII-spectrin as a novel substrate that is cleaved during TGF-beta-induced apoptosis. Our data provide the first evidence of calpain and caspase 3-independent cleavage of alphaII-spectrin during apoptosis and suggests that TGF-beta induces apoptosis and alphaII-spectrin cleavage via a potentially novel caspase. This report also provides the first direct evidence of caspase 3 activation in WEH1 231 cells and indicates that at least two distinct apoptotic pathways exist.
Brown
T L
TL
Department of Cell Biology, The Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
Patil
S
S
Cianci
C D
CD
Morrow
J S
JS
Howe
P H
PH
D000818:Animals; D017209:Apoptosis; D002352:Carrier Proteins / Q000378:metabolism*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D006868:Hydrolysis; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D013049:Spectrin
D002352:Carrier Proteins; D053148:Caspase 3; D020169:Caspases; D008840:Microfilament Proteins; D016212:Transforming Growth Factor beta; D013049:Spectrin; C505409:Casp3 protein, mouse