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Caspase activation by BCR cross‐linking in immature B cells: differential effects on growth arrest and apoptosis
Author(s) -
Brás Alexandra,
Ruiz-Vela Antonio,
Buitrago Gonzalo González,
Martínez-A Carlos
Publication year - 1999
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.13.8.931
Subject(s) - proteolysis , caspase , apoptosis , microbiology and biotechnology , programmed cell death , biology , caspase 3 , chemistry , biochemistry , enzyme
The B cell lymphoma WEHI‐231 has been used as a model to study immature B cell tolerance, based on its capacity to undergo growth arrest and programmed cell death on B cell receptor (BCR) cross‐linking. Using this model to identify the molecular mechanisms underlying these processes, we found that BCR cross‐linking results in the selective activation of caspase 7/Mch3, but not of the other two members of the CPP32 family, caspase 2/Nedd2 and caspase 3/CPP32. This was evidenced by the induction of proteolytic activity against the substrate for the CPP32 subfamily of caspases (z‐DVED‐AMC) in vitro , as well as PARP proteolysis in vivo and by the processing of the 35 kDa Mch3 into a 32 kDa species, which was later further proteolyzed. The general caspase inhibitor z‐VAD‐fmk, but not the CPP32 family inhibitor Ac‐DEVD‐CHO, blocked anti‐μ‐induced apoptosis, indicating that a caspase not belonging to the CPP32‐like family is also implicated in anti‐μ‐triggered apoptosis. In contrast, z‐VAD‐fmk was not able to counteract growth arrest induced by anti‐μ, treatment, suggesting that caspase activation is not necessary for induction of growth arrest. Neither of the inhibitors prevented Mch3 processing; however, z‐VAD‐fmk prevented proteolysis of the p32 subunit, suggesting that further processing of this subunit is associated with apoptosis. Bcl‐2 overexpression prevented anti‐μ. induction of CPP32‐like activity and apoptosis, and blocked further processing of the Mch3 p32 subunit. In contrast, CD40 stimulation completely blocked the appearance of the p32 subunit in addition to blocking CPP32‐like activity and apoptosis induced by BCR cross‐linking. Moreover, only CD40 stimulation was able to prevent anti‐μ‐induced growth arrest, which was correlated with inhibition of retino‐blastoma and of cyclin A down‐regulation. In splenic B cells, Mch3 is also specifically proteolyzed ex vivo after induction of apoptosis by BCR cross‐linking, demonstrating the specific involvement of caspase 7/Mch3 in apoptosis induced in B cell tolerance.—Brás, A., Ruiz‐Vela, A., González de Buitrago, G., Martínez‐A., C. Caspase activation by BCR cross‐linking in immature B cells: differential effects on growth arrest and apoptosis. FASEB J. 13, 931–944 (1999)